PBEDICrING DRYING TIUES O? SJME BU&MESE WOODS F::>i?. :I'vlO TYP.E:S 01-' SOI.Ah K:ILNS
by
Win Kyi
Thesis suhmit·t~:l to the Fa::ulty of t..he
Virqinia Polytechnic Institute and State University
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
in
Forest Products
Al?PlWVrm:
----;;,-E .. -N .. -'!Jengelt, ______ _
July., 1983 Blacksburg, Viryinia
Lamb
ACK.Now· LEDG.EMEN1'S
This thesis has benefited first and foremost from the
technical. guidance and encourage.ment of my major aa.viser Dr.
Christen Skaar. Second from Dr. Eugene Wengert who provided
technical. advice particularly in the area of l.lllllbe:c-d:cying.
Also, from Dr. Fred Lamb, a mem.ber of m:z committee and all
other facu.lty of the Department of .Forest Products who wi.1-
_ingly sh a.red their time, especially Dr. Geza If ju.
Special thanks to Dr. W. T. Simpson an.d Dr. J. .i..
Tschernitz from the Improvement in Drying Technology Sec-
tion., u.s.Department of Agriculture, Forest Prcduc-t.s r.abora.-
tory, Madison, Wisconsin, who generously made ava.ilaole t.he
use-of their facilities. Likewise, to Ted liianowsxi and all
other staff who hel.ped me during my ten-week. study at t.neir
laboratory.
TO Dr. G. Armstrong, former chief technical adviser a!!.a
Dr. A. Wtl.ie chief technical. adviser of Forest hesea.rch In-
stitute, Yezin, Burma; To Dr. c. de zeeuw and Dr. ft .. w .. :Ja.-
vidson visiting consultants from State University of N~w
York, Co11ege of Environmental. Science and Forestry who made
the necessary arrangements for my studies at Virgi.ni.a Poly-
technic Institute and state University.
il
To .F .. A.O •. for providing tite fu.nds .for my stud.ies... To
Dr .• J ... Hoffman, development training specialist.,
u.~.Oepartment of Agricultnre# Office of the International
Cooperation and Development, wasld~gtot\, D"'C .. and sta.ff of
F.~1.0... offic.es i:n Bu-.crea, Rome and the United s.tates who ef-
ficiently took care of administrat.ive .arrangements. ..
To U Sein Na ung Mint, Director Gene.ra.1 of • the .;forest
Department, form-er director o.f t.he l:'orest Re.search Institute
and a.11 my colleagues f.rom the .t"ore:s·t Research Institute who
attended to the work I left behind •.
To ·the .Bur:.mese gove:rnme.nt fo.r kindly permit·titHJ me to
undei:tak.e studies a:broad,.
Last but. not the least, to .my pa.r<c1nts .for raising .me up
to appreciate the value of educati.on and my teachers f qr
providing me with U1e ha.sic skills to pursue higher educa-
tion .•
iii
TABLE OF CONTENTS
ACKNOwLEDGEI-nrnTs . -• • ii
L.
II.
III.
IV.
v .•
INTRODUCTION 1
REVIEW OF LITEBATURE 5
Background R<~vielii' o·_f Solar .Lumber Kilns Energy Studies on .Solar .I.umber Kilns ••
... ... .. ,. 5 6
OBJECTIV.ES AND .APPROACH .• .,. -• ·• '.. . 8
obj ect.i·v<~!., ... .• .• • ,. °' .• ... .. _,. i• .. ,. •• _ • _ .. . • ., .• • 8 Approach .• ,. • .. • • ,. ,. • .• ,. .. • • _. .• • • • .. 8
Energy Balance Conce_pt .... - ..... _. • .. _... .. 9 Total Energy Input to the System ••••• 9 Tota.l Energy output ............ _. .• • .• • 13 Energy Balances ........... •• 22
Efficiency • • .. .• _ ,. .. • ,. .. .• .. • .• .• .,, . • • 2:2 Empi1:ica1 Eguation for Es-ti.mating D:aily
Moisture Content Loss ...... ,. ••• 24
MATERIALS AND NETHODS •• ... ,. ... External Collector So.laL" Kiln
Descriptio:11 o.f the Kiln • Solar Collector .. • •
. .. ·• ·• 26
.. 26
.. 2£ 28
Drying Chamber • • • .• .• • .• • .• . .• • • ,. -• .28 .First Run ,. .. .. "' "' _ ,. .. . ... .. .. ,. • • , • _,. .. .. '"' 29
Materials ••••••••••••••• 29 Experimental Procedure ,. .. .. • .. .. • • .. • .30. Analytical Procedure.,. ••••••••• 35
Second Run .. _. ... .. .. .. ,. • .• • • " _ • .. . .• .. .. .. 45 Semi-Greenhouse Kiln .. - •• <a .... _ •• .. • • • -• .. • 45
Description of the Kiln ............. ~5 Materials ••••••• - ........... 48 Ex_p-erime:utal Procerlure • _.. ,. .. .., • , .. ,. • ,. • 4 8 Analytical .l?rocea. ure .. • • • • • • ,. .. • ,. • 50,
RESULTS AND DISCUSSIONS.
External Colllector Kiln~ • First Run ••••••••
Gen-er-al observations ,.
iv
. .. .... ·•
. .. ·•
, -• ~- . .. . .. ... .. ·53 ..... ,. .... 53 .. • _ • • . ... • 53
VI.
VIL.
Energy Input~-- •••.•• - ••• _ •••• 57 Energy Output •••••••••• , ....... 64 Ene.rgy Balance ..... _ .......... ,. ,. ,. ,. .... ·69 Efficiency~ ••••••••• -........ 70 Emp.ir:ical r1odel .for Effic.ie~cy • . .. . • . .. . .. • 70_
Second Bun .................. _ •••• 74 General Observations.,., ..... ••.•• 74 Com_parison o.f Actual and Pr~dicted D:cying
'1.'i-nt;es .. .• • .. .. • • .• _ .• .. . ,. _.- .... i •. • •• ,. 75 Improvement of Kiln Efficiency • • • .. • . .. .. .. 77
.Increasing Solar E:ne.rgy Input ........ ,. .• • 77 Reducing Heat Losses ..... ,. .......... 78
Semi-Greenhouse Kiln ••• • _. 0 • •••• • ••• 82 General Obse.rvations • • .·.. . .• • .·,. • .• • .. . .• .. 83 Efficiency •.••• _ ........ ff ., ••••••• 85 Empirical .Model :for the Eff.icie4cy of U1e
Kiln ..... , .,. ... _ . ., -• • _., • .,, _ • .-.·• !•, ..... ,,... ,. _. 86
APPLICATION IN BURMA
SU.rl.NllRY l\.ND CONCLUSIONS
• 89
97
LITERATURE CITED 103
!_ppendix
It.
B •.
c.
FOREST ARE.A AND FORES'T INDUS''I\lUE.S O.F BU.R11A., MALAYSIA, AND PHILIPPINES•.• .....
Tii'H3.ER ,EXPORT -OP BUR.i'1A FOR .FISCAL Y.EAR 1977-78
BEVIEH OF SOLAR LUMBER KILNS
••
United States of Am,e.cica .. .. • .•. , ..... , .. . • . • • • Dodgeville, '11isco~sin • .. . - ... ·,. .. • . .• .• • .. r:iadison_, Wis cousin • ,. • • . .. .. .. . •. · ......... , ,.. Sauk City, -Wisconsin • • . .. • • • • . • . • • .• Fort Col.lins., Colorado .. , ................. ; • Blacksburg, Vir9inia, Semi'"".,g,.:ceenhouse Type Badison, Wisconsin • •:• .• .• ••••.• "~· Madison, Wisconsin, Bxternal-collector Type Baton Rouge, Louisiana~ ......... -.~. Carbondale, Illinois •••• _.,.. ,. , ,., ..... Some Commercial Kilns~ ••.•. •~.• •.• •.•.
Somerset, Oh.io • ,. .• .• .. • , •.•.•• , .... . Afton flou:ntain Region, Virginia. • __ ,. .... .
India Dehra Dun .•.• . , ,. ' .
V
111
112
113
113 113 114 114 115 115 117 117 118 119 120 120 120 121 121
Ut ta Pradesh commercial Kilns .. Puerto Rico
Japan .•.•••• Taiwan ... ·• Uganda • • • • '"' ·ranzania •.•
.. Rep ub lie of the Philippines Ghana • '" .. .. Madagascar ••• Australia ....... Brazil .. • • United Kingdom .. Indonesia .. ,. • Fiji .. -~ . .. ,. Federal Repub l.ic Canada ....... ,.
of GH.cmany
Ivory Coast P..f:?pub lie o.f
..... ·.. ·• .. China • Sri Lanka Pakistan ,. Bangladesh .• Burma • • ,.
South Africa ·• ·Q ......
·•
.. ,. .. . . . • . .. .. ..
,_ ft . IN
D. LIST OP PUBLISHED OR UNPUBLISHED TNP0B.£1.lt'l'I0N OM SOL.A.R-LUf'iBER KILNS
LOCATIONS OF 24 THERMOCOUPLES. •
VTTA 149
vi
122 123 123 124 125 126 127 127 128 129 130 131 132 133 133 134 135 136 137 137 138 139 139 140
141
147
1.
l.
2 ..
LIST OF 'l~ABL.ES
Var.:-i.ables and Coefficients tor the External Collector Ki.ln • • • • . •· •·
I-tun of • • • •
(continued} . •· . . . •. .. . - . . . . . . . . . •• 58
Dai.i.y Total Energy In.put • • . . • • . . .. . . .. . • 60
components of Total Energy Input . . . . . . • • •• 61
4. DaiJ_y Tota.l Energy Potentiall.y Availabl.e to S:ystem • 62
5. Components of Total Energy PotentiallJ A vaila.ol.e • • o.3
6.
7.
8 ..
9.
10.
1 1 ..
12.
Daily Total Heat Losses from the Collector • • •
Daily Conduction. Losses f:com the Drying Chawber
. . .. .
65
66
Dctlly Total Energy output - . . . . • • • • . .. •• o7
components of Total Energy output . . . . . •••• 68
Daily Energy Bala.nee . . . . . ., . • • • • . . .. Dail:,r .B£ficienc1 of External. Collect.or Kiln • • • • 12
EfficieucJ ot Semi-Greenhouse Kiln •• • • • . . . • &7
13. Predicting DrJing Ti.i11es for some Commercial Burlilese Woods using External Collector Kiln ••••••• 90
14. Predicting Drying Times for Some commercial Burmese woods using semi-greenhouse Kiln • • • • • • .. • 91
vii
LIST OP ?IGilH.ES
Ex -cer :ual Col l\1ctor Kiln,. Maui.son. • • • • • 27
2. S€,mi-Gref:L.b.OUS'? Kiln, '>/PI & so, Blacksburg. . . / . . • 46
3. Drying curves of sugar maple. First Run, Exte:cnc'..l Collector Kiln •••••••••••••••••• 55
4.. Actual a.nu Preaicting Dryiug Cur-ves o:t Sugar maple, Second Run, External. collector Kiln •••••••• 7b
Solar ~nd Air-drying curves of yellow pcpla,r, Greenhouse KiLn ••••••••••••••
!::iemi-• b4
INTRODUC'rION
The forest area of Burma constitutes more than half the
country's total area, and supplies about 25 percent of its
foreign exchange earnings.
How.ever, in terms 0£ thr:? level of timber pt:oduction re-
la ti va to the forest a.rea, Burma is below trre levels of pro-
duction in Malaysia and Philippines (Appendix-A). D11e \vay
to increase national income is to search for ways to improve
timber production.
Data in Appendix-B indicate somewhat higher figures for
teak log export corn pa red to teak con versi::>n into man ufac-
tured pcodu::::ts~ '.l'hey also show that e,x:p9rts of hardwoods
other than teak are extremely low compared with ti.?.alL, Df I
particular c~ncern is the fact that export of hardwood con-
version products was such a. small :fraction (less than two
percent) of that of hardi:rnod logs other tha.n teak. The table
also indicates that production of plywood, veneer, mosaic,
parquet and other finished products are very low~.
export of hardwoods other than teak and the domestic pro-
cessing- of logs (both t.ea k a.nu hard ,wads other than teak)
into lumber, veneer or finished products can be increased,
the nation ~ill gain in several ways.
1
2
Economic losses ace heavy in the timber industry of
Burma dne to the inadequate hand.ling, processing and utili-
zation of wood. J. laC"ge part o~f these losses can be pre-
vented hy using appropriate. methods of drying ·to r: educe dry-
ing defects associated with shrinkage, and to eliminate or
to celuce tile risk o.f occurrence 0£ mold, stain, decay and
insect attack,.
Higher yield and better quality lumber, veneer and oth-
er finished prod uct.s depend on application <>f the best tech-
nology in processing, especially in drying and application
of preservative tcea tments to lumber, ve11eer, poles, rail-
roai sleepe~s and other products for cqostruction. In the
United states of America 60, to 70 percent of the energy used
in lumber pcoce:ssing was COllSUHed in lumber drying
(Skaar,1977). Wengert (1974) had calculated that the energy
raguired foe kiln drying
about 75 trillion Btu {22
ma tely equivalent to O. 1
lumber in the United States was
bill~on KWhr) in 1972, approxi-
perGen·t of ·the total energy con-
sumed annually in the United States •.
At present, the bulk of hardwood timber in Burma is
still · used without adequate seasoning, and losses thro11gl1
drying def ect.s that develop in subseg:ue.n·t service are ex-
tremely high •.
3
In Burma, there are only twenty coµventional Kilns with
a total c~ipa.city of about 130 NB.Pl (10,800 cubic feet) lo-
cated at the Furniture Industry Depactment, State Timber
Corporation, Rangoon. These kilns are used for drying lum-
bsr of valuable pcimary species only for furniture-making
and mosaic ard pan1uet flooring •. This small capacity,
{about 5 percent of total lumber production in 197-0J, ~s due
maialy to the high initial investment and high operating
cost for a kiln, as well as to lack of knouledge of drying
technology ... On the other hand, air-drying requires a long
period of time resQlting in high inventory costs and in unc-
ertain del~very peciods due to dependence on weather condi-
tions. Compared to kiln drying, air drying results in more
dryirtrJ d efocts, slower rates of drying and higher final
moisture contents.
The mission, therefore, is to investigate a low-cost
and low-enecgy procedure which will dry lumber faster and to
a lover final moisture content than does air-drying, and
with a minimum of drying defects. The hypothesis is that so-
lar drying is the best drying system to accomplish this mis-
sion"'
1 1000 board feet= 2.9 cubic meter
4
Tt had been known that tr:-opic:al a.reas between la·titude
35° North and south and receiving 2000 hours of bright
sunshine in the year are ideal for collecting a.nd utilizing
solar heat •. Conditions in a.lmost a.ll parts of B·urma, which
is located bet~een latitude 10"' and 28°. North, appear to be
quite favorable far this purpose during e~ght to ten months
of the year.
A prototype solar kiln of 1000 board feet capacity was
recently built at Yezin, Burma, at the Forest Besearch In-
stitute where the author is employed. The author is to have
direct supervision 0£ this kiln when he returns to his co1111-
try after complc~ting his studies in the United states o.f 1\m-
e;cica,. Tl1e ki.ln is o.f the sane design ana. size as the Nadi-
son (Forest Product~ Laboratory) prototype except that the
collector is 140 pe.rcrrn.t la..i:.-ger than that of the !'ladison
kiln,. . It is identical to a kiln which Nas built in Sri
Lanka in February., 1981., by w ... T • .Simpson and J. I.,. Tscher-
nitz of the u.s. Forest Products Laboratory, Madison~ Wis-
consin.
Cli.a. pte:r: II
REVIEW OF LITERATURE
This chapter is di viderl into two sections. The first
section vill give a brief background review 0£ the solar
drying of lumber and the second section will describe energy
studies on the solar lumber kilns.
2;. J BACKGROUND REVIEW OF SOLAR I.UFlBP.R: KILNS
several s-tudies of solar drying of lumber began at
about the same time, Jo.hns:011 (1961) .in ·the United States and
Rehman and Chawla (1961) in India. Thece are now a,t least
250 solar lufilber kilns -throughout. the -world •. Gt these.,
about 40 are experimental kilns built at univ0rsities or go-
vernment resea.rch laboratories, whereas the others are com.-
mercial kilns .• , A list o.f countries in which so.lar dry.in-g of
.lumber have ber~n conducted, given .i.n chronological ol.:·der
are, United States of America, India, Puerto Rico, Japan,
Taiwan, Uganda, Tanzania 11 Philippines, Ghana., Madagascar.,
Australia~ Rcazil, United Kingdom, Indonesia, Fiji, Best
Germany, Canada, Ivo.ry coast, South_ Africa,, Cliina, Sri
Lanka, Pakistan, Bangladesh and Burma~
these studies i:n ,~ach of these countries,
A brie£ .rev.iew of
·together with a
list of some :>:f the solar kilns which are knmrn to the au-
thor, are given in Appendices C and D.
5
2.2 ENERGY STUDIES OH SOLAE LUtlBEB KILNS
There were several studies on energy ga~n and loss and
efficiency on -the solar lumber ! :' ·1 ,c1...,_ns .. O.f these studies,
only two which arz"' believed to be important to this study
will be described.
Host of the solar lumber kilns used in the 1960 1s were
of the greenh3use type, constructed with a wood frame and
cover~d with a tra.nspar:ent or a tranlucent lll.aterial such as
glass, plastic or fiberglass.
Io 1967, Hengert (1967) studied the euergy losses from
a greenhouse solar lumber kiln at C3lorado State University.
{The description of this :!ciln is given in Appendix C..)
In order to calculate the energy gain and losses from
the kiln, Wengert had collected the data during the morning
hours 0£ clear days during the summer of 1967. He indicated
tbat,"there were five energy losses account for about 84
percent of the incoming solar energy: losses by convection
(sensible heat loss), 29 percent; outgoi119 solar energy, 17
percent; ventilation, 14 per.cent; net longwave radiation, 13
percent; a.na. conduction throug.h thf:! floor, 11 percent. The
remaining 16 percent of solar energy was utilized for drying
the wood and for minor losses."
Based ~n his results., he gave several suggesstions to
reduce the energy losses from the solar kiln (Wengert.,
7
1971) .. Laber on., he modified the design of the grf.,enhouse
solar lumber kilns by using well insulated walls (Wengert,
1.980). This design is known as the .semi-9rEienhouse kiln •. ·
Rosen and Chen {1980) studied the efficiency of an ex-
ternal collector solar lumber kiln at the North Central For-
est Experiment Station, USDA .Foreist Service, Carbondale, I 1-
linois. {Description of this kiln was given in Appendix C)
Yi ve chacges of oni~-inch thick gree11 yellow poplar lum-
ber were dried tkrou,:;l1 the sum.mer of 1978 to the sprir19 of
1979,
cant ..
in each case to a final moisture cm1tent of 15 per-
Duri.ng these tests, they collected the data. reguir:ed
to ca1cula te the efficiency 0£ the collector and 0£ the dry-
ing chamber for each run. According to their report, the
collector efficiency, ba SF.~d o.n da ytir1e ca1c ula tio.ns only,
ranged between ~1 and 66 percent, whereas the drying chamber
.:.=:fficiency, ranged b,2tw,~en 29 and 90 percent. They conclud-
ed that solar kiln di:ying was most eff~ctive in the surumer
and early fall, when drying chamber efficiencies were 90 and
67 percent, respectively.
3. 1 OB,JECT IV ES
Chapter III
OBJECTIVES AND APPROACH
The principal objective of this study is:
To develop an empirical model for estimating the drying
times for diffe;cent lumber species in Burma and at other 1o-
ca.tions for each of the two types of :so.lar kiln.
And the secondary objectives are:
1. To describe the principles and practices of lumber
drying using solar energy.
2. ·ro become familiar with the t1adison prototype exter-
nal collector solar kiln and the VPI i.r SU semi-green-
house type of solar kiln.
J. 2 1Ht.£E.Q.!£l!
In order to satisfy th,2 pr i.n.cipal objective described
above it is necessary to formulate an experiment from which
a suitable .rilodr:l and. associated para meters for predicting
drying time foe di£fecent species at different locations
could. be derived. This was accomplished by first applying
the energy balance concept to the drying process followed by
calculation of the kiln efficiency and finally der~ving an
8
empirical eguati~n for estimating daily moisture content
loss.
3,. 2. 1 .E.nerg_y Balance Co11 ce:p:t
In order to obtain the energy balances during the dry-
ing process, the magnitude of the various energy input and
various E'HH?..cg-y output of the solar kiln for each day have to
b2. determined.. The following ge.r.u?.ral equation describes the
energy balance for each day t.hronghout. the drying period;
Total Energy Input -, J
to the System
Total Energy output - {
from the System
.Each of the total Eni.ergy input to the system and the
total energy output from the system uill consider:- seperate-
ly.
3. 2. 1. 1 Total Energy Input to the System
'I'he impor:ta.nt sources of energy input to the solar kiln
considered here will include: solar energy# electrical ener-
gy, sensible beat obtained from thermal conduction and sen-
sible heat released. from cooling of moist lumber,.
Solar Energy Input to Collector: For a flatplate horizontal
collector total solar energy {SETR) transmitted through the
cover for any day can be calculated by;
10
Transmitted Solar Ewergy -= (Tran:smissio1t E£ficiency
of the Cover) * { Daily Solar
Insolation) ;'< (Area o.f the Cove:::J
or in symbolic form,
SETR = RCV*SI*ACV (].., 1)
where,
RCV = transmission efficiency of the. cover
SI = daily solar insolation in Btu/ft2
on a horizontal surface
llCV = area of the covf:r in £t2 Electrical Ene.r-gy Input :
Electrical energy input to the system is supplied by the
fans and blower in the external collector kiln and by the
fan in the semi-greenhouse Kno~iog the power and to-
tal running time of each fan or motor blower, the t.otal
electrical energy input for each day for each of the kiln
can be calculated.
Energy Gain by conduction from Drying Cham.ber ; The ex-
terior walls and the roof of the drying chamber will usually
be hot during .,_ Al
Llffie, ,especially on
Therefore temperatures of the exterior walls and the roof
will be higher tha:n that of the interior walls and the c0il""'."
ing during that time, and some energy ujll be gained by con-
duction. This amount 0£ energy galn can be calculated by,
Total Conduction Gain= ~um of Condaction Gain from each
Wall)+ (Conduct.ion Gain from the Hoof}
11
or in symbols,
whece,
CDG = total conduction gain in Btu
aw = effective overall neat transfer coefficient
of the walls in Btu/lu::-ft:.2- 0 p
AWi = area of each wall in ft 2
(3. 2}
DTEi - average temperature difference between the e.xte.cior
and intecior for each wall in °F
twi = total time during which the temperature of the
extrerior wall is higher than that of
the interior wall
URP = effective overall heat transfer coefficient of
the roof in Btu/hr-ftz- 0 p
ARP = area of the coof in ft 2
DTRF -= temperature difference between the outside
and the inside 0£ the roof in °F
trf = total time during which the temperature of the
outside roof is higher than that of
the inside roof
12
Energy Gain from the Load .: Daily so.la.r iI1sola.tion iiiill .not
be uniform throughout the drying process~ Since it ,1ill
vary from day to day# the initial a.ad .f.inal tempera·ture in-
side the ch.amber 1'i11 also vary over -the 24·""'.hour -time per-
. -~ J.OCl. For example if it is cloudy or rainy o~ a particular
day and if the pre.:1rio-us day haa. been snnn y # the initial
temperature inside the chamber: wi.Ll be 1:dgh,e.c than the final
temparature inside the chamber over the 24~hour period.
:I'hus, for- tl:ta-t day the syst,em will gain some stored en,e:cgy
from the wood sub-ta.nee a:nd. ·the residual water in the wood as
they coo.h:.d.
late.:! l1y,
'rite amount of this energy gain can be calcu-
Energy Gain from the Load= (Energy Loss from the Hater)
+ {Energy Loss from the Wood)
+ (Energy Loss f_rom the Other
~la te:c.ials}
or in symbols,
(3. 3)
BGL = energy gain from the load in Btu
wt - total ove.n-dr:ied weight of l,/OOd in lb
including stickers and plywood
Ho = oven-dried weight o_f sugar map.le or lumbeI:' in 1.b
WX - total ·we.ight of other materials in lb
CPWo = specific heat o··F oven-dried wood in Btu/lh-°F
CPH = specific heat of water in Btu/lb-°F
CPX = specific heat of other rnaterials in Btu/lb- 0 :F'
AVNC = a·v-erage miosture conten·t ou that day in percent
D'I'L = differencH in ini·tial and fi.na.l temperatures
inside the c:hamber for:: a 2-4-hour pe.r::.iod
3 .. 2.1,.2 Total Energy Output
For the external collector kiln,there are two primacy
sources of energy loss from -the system, those .from, the. col·-
.lector and those frm1 the drying cha.mh-er. .Energy losses
fro.m the collector include top loss, bottom loss and edge
loss. Those fco.m the drying chamber a.re, evaporation loss,
hy9roscopic .loss, ventilation loss# conduction loss and en-
ergy required to heat the wood subtance and the residual wa-
ter ..
Heat Losses from the Collector: The three main losses from
the collector are top loss, bottom Loss, and edge loss,.
Kach of thest~ losses will be considered separately .•
IQE ~OS§.: :T:o calculate ·the heat losses from the ·top of the
collector, the procedu:r.·f)S o'.E Duffie a.nd Beckman { 1974}
be . followed .. For a :single cover ·th.aJ: is partially t.1:·anspa-
14
rent to infrared radiation, the top loss coeffic~ent (UT) is
given hy,
+ [ {1/(hpc+hrpc)} +{1/{luHhrcs}} ]-1
where,
T = transmittance of the cover for radiation
from plate to sky
EP = emittance of plate
SB - Stefan-Boltzmann constant
TAV= average temperature between plate and cover in °K
= {TP+TC)/2
TP = plate temperature in
TS= sky temperature in °K
TA= ambient temperature in °K
hpc= convection coefficient or heat transfer coe£:ficient
between plate and cover in W/:ra2 - 0 c
hrpc= radiation coefficient from plate to cover
11w =convection heat transf,~r coefficient for wind
blowing over the cover or wind coefficient
15
hrcs=cadiation coefficient from cover to SKY
Four of these coefficients are calculated fr:om the fol-
l:>wing for;nulae,
.• 281 hpc = 1.613*( DT }*11-0.0018{TAV-10)]
.157 '" 1
' hrpc = [ (TP2+TC2)*(TP+TC} ]/[ {1/EP)+(1/EC)-1J
hw = 5.7 + 3.8 V
hrcs = EC*SB*(TC2+TS2)*{TC+TS)
lilhere,
DT = temperature difference between plate
and covec in °K
1 = space between plate and cover in cm.
EC= emittance of cover
TC= cover temperature in °K
V = wind speed in m/sec
( 3. 5)
(J. 6)
(3. 7)
(3 .. S)
Knowing the value of top loss coefficient (Uf}, the top
loss from the collector for each day can be calculated by,
Top Loss= {Top Loss Coefficient) * (Area of the Cover} *
{Average Temperature diffec.ence between Plate
and Ambient) * {Total TiDe during which the
Collector Tempecat•Jre is higher than th.at
of Ambient Air)
16
ot· i.n symbols,
(3 .. 9)
where,
TOPL - total top loss in Btu
UT - top loss coeffient in Btu/f t2-°F-hr
ACV = area of the cover in ft 2
D'J~C - average of hourly tempe r:a ture tli.f ference bet.H?en
the collector and ambient .air in °7
ttc = total time during which the collector teraper:ature
was higher than that of ambient air in hr
Botto.m Loss :: The temperature of the plate will be usually
higher than that of th1cJ groutH1 1 resul.ti:ng in some co11ductio.t1
:heat 1os·t to the ground.. Knowing the eff~ctive conduction
coeftici.ent {UB) for ttH= plate, this heat .loss (B'TL) for
each day can be calculated by,
Bottoru Loss = (Conducti:>n Coefficient of the Plate} * (Area of the Plate) * {Av~rage Terape.rature
difference between Plate and Ground) * {Total Time during ~hich the Tempe.cature of
the Plate is higlrn.c than that of the Gr:ound)
or in sym.bols,
BTL (]. 10)
17
where,.
BTL = total bottom loss in Btu
UR = conduction coeffici,~nt in Btu/ft2 - 0 .F-hr
APL = acea of the _plate in ft2
DTB - ,average temperature difference · bet:s1een
plate and gcound in op
t.b = total time during ~,hich the temp.e.cature of the
plate is higher than that of the ground in hr
Edge Loss : The edge loss could he calculated us.ing the sa.me
procedure as for the bottom loss.
Energy Loss from the ll~!i!!.9:. Cham.be:r : There are five rnain
losses from the drying chamber, namely; eva_po:cation loss,
hygroscopic loss,. conduction loss, energy given to the load
and ventilation loss.
Evaporation Loss : This is the ene1:gy requ.Lred to evaporate
the wa·ter from the wood.. The evaporation loss .fo.r each day
can be calculated by,
Evaporation Loss - {1Weig±d: of Water Evap.orated} * {Energy
required to Evapor.ate One Unit tfass
of .water)
or in symbols,
EVP = iv*[ {CPW*(212-Ti}
where,
18
-t CP V* ('.r .i-212}} + L V: ]
Ww = weight of water removed or evapqrated in lb.
CPW= specific heat of water in .Btu/lb-°F
CPV= specific heat of vapor in Btu/lh-°F
Ti = average initial temperature inside the chamber
LV = latent heat of vaporization of water
- 972 Btu/1b-°F
{3 .. 1 1)
The weight of ,water evapo.,rated can be estimated from
the average moisture content loss per day of the samples and
total overn-dried weight of the lumber which is equal to
62. IJ*V*SG, where V is the green volume o.1E the lumber in cu.-
bic feet an:i SG is the g.cee.n specific gravity of the lumber ..
Since specific .hea·ts of wa·ter {C'l?W} and vapor (CPY} are 1. 0
and o. 47 Btu/lh-°F respt-3<::tively I equation p .. 11) can he s:im-
pli.fied to,
EVP = (62.4*V*SG)*(HCL/100)*[0.53{212-Ti)+972] (.3. 12)
where 1
MCL = da.ily mois,tu.re content lo.ss in percen·t
Hygroscopic Loss: In re.moving water from !wood belqw the
.fiber saturation point, some additional ene.rgy is required
to oveccome hygroscopic forces. 'J:'his energy .becomes higher
as ·the moisture content approaches ·to zero .. The ene1:gy re-
19
g:uired to overcome hygroscopic .f orc-es £or each day can be
Galculated by,
(3,.13)
1o1here,
HYG = energ-y regui:r:~d to overcome hygroscopic forces in
Bt.u
Wo - oven-dried weight of lnmher
Mi - aveca9e initial moisture co.ntelit of the lumber:
in percent
Nf - average fi:nal moisture contf:HJ.t o.f the .lumber
in pe:rce.nt
The above equation is the i.ntt~gral heat of wetting over
_the temperature range of 60°F and 120°p for different mois-
ture content below the fiber saturation point which was here
assumed as 30 percent moisture con.:tent. This eguatio:n was
derived from the equation for the dif·ferential heat of sorp-
tion given by Skaar (1972).
C::>ntluctio:n Loss : Since the tempera-ture inside the chamber
will be higher than ambient. most of th~ ti11le, some energy
!fAill be lost by conduction through the i?alls, the roof a.nd
the floor,. 'l'he expression for th.is total enez:-gy loss is
identical to that for to-tal entH:gy gained by conduction with
the addition. of a teem for the .floor losses ..
20
Total Conduction Loss = (Conduction, Losses from the .walls)
+ {Conduction Loss from the Roof)
+ · (Con.d uc rion Loss to the Floor)
or in symbols,
4 CDL = l: UW*AWi *DTWi *twi + URF*A.RF*D'l'RF*trf i=l
+ DFL*AFL*DTPL*tfl
where,
DPL = effective overall heat transfer-coeffient
of the floor in Btujlu:-ft 2-°F
AFL = area of tne floor in ft2
(3. 14)
DTFL= di·f~erence in average temperatures of the .flooc
and the ground in op
tfl = total time d urin<J which the f looc telilperat ure wai:i
higher than that of the ground in hour
Energy Given to the Load : The same equation used to calcu~
late the heat gained when the lumber is cooled over a
24-hour period inside the drying chamber. can be used to cal-
culate the energy re':luired to heat the lumbe.r {EOL} when its
temperature increases over 24-hours. This will occurr when
a particular day is sunny following a cloudy or rainy day.
The expression to be used to caiculate this energy is there-
fore
EOL = Wt*CPW-* TL + Wo* {AVIiC/100) *CPWT* TL + W.X*CPwX* T.L
- - {3 .. 15)
21
Ventilation Loss ! 'l'he total ventilation loss can be calcu-
la ts::>11 h y,
Ventilat.ion I.oss=Mass of outlet Air*[ Heat Added-Work Done]
or,
Ventilation Loss = tlass of o ut.J.,at Ai e * [ (Specific Heat
of Air* Tem,per:ature Diff,.:,rence) - (Gas
Constant ~): Temp,2ra ture Difference} J
or in symbolic form,
or it can be written as,
VTL = {rvt>l<rho*tvt) ;or- {CPA-B.) ;'<DI'J\.
where,
VTL = ventilation loss in Btu
rvt = volume ra.:te of flow of outlet air in ft 3 /m.in
rho= density of air in lb/ft 3
tvt - time in minute
CPA = specific heat of air at constant pressure
in Btu/lb- op
B = Universal gas constant in Btu/lb-°F
DTA = average difference between outlet
and inlet air temperatures in °F
{3.16)
22
3. 2 .. 1. 3 Ene:r.gy Balances
Using the data obtained for the various energy .input
and the various energy outpu:t for each day, the energy ba-
lance relationships for the kiln can be calculated £or each
day using the follo•ing expressions,
TEI= SETR +ELI+ CDG + EGL
TEO = (TOPL + BOTL) t (F;VA+HYG+]~O.L+CDLf-VTL)
(3. J7)
{ 3,. 1 8)
where, TEI is the total energy input and TEO the total ener-
gy output for a given day, the other ter.l!is are the safile from
equations (3.1) through (3.16).
The energy balance for each day was calculated by,
TET =TEO+ E {3, .. 19)
where,
TEI - total energy input to the syste1n .i;n Btu
TEO = total energy out.put .f-r.-0111 th:e system in B-tu.
E = error
3.2.i Efficiency
The efficiencies o-f the collector (EFFCL) and the ilry-
ing chamber {r;FFDC) can he calc u1ated for each day as fol-
.Efficiency o.f the Collector = (Solar Energy Input to the
Drying Ch,a.mber_} / (Solar Energy
Incident :> n the Collector)
23
Efficiency of the Drying Chamber ·= (E vaporatio.Q. Loss
+ Hygroscopic Loss)/ (':r.otal
oc i:n symbolic forms,
EF.r.'CL = SEIDC/SEIC
.Energy
Drying-
E.FFDC = {EVP+H.YG) / {SEIDC+ELii-CDG+EGL)
wttere,
Iqput to
Cham.ber)
the
(.3. 20}
(3 .. 21)
· SEIC - total solar energy incident on the collector-cover
on each d-a.y
SEIDC - total solar energy input to t.he drying cha-m.ber
on each day
= SETR- {TOP.L+BO'J'.L)
and the other terms are as defined in equations (3 .. J)
through {-3 .. 19),. _.
The overall e:fficiency (EFF) o:f the kiln ·for each day
can be calculated from the equation#
Ovecall Efficiency - (Evaporation Loss + Hyg-roscqpic Loss)/
rrotal Energy .Available tC> the Sy.stem)
or in symbols,
EFF· = (F.VP+HYG} / {TE.A)
or,
EPP= (EVP+HYG}/~EIC+ELI+CDG+EGL)
24
where,
TEA= SEIC+ELI+CDG+EGL { 3 .. 23)
= total energy available to the system
3"' :2. 3 Empirical Egua tio n fQ£ Estimating D.aily Noisture Content Loss
An empirical equation for the overall efficiency of the
kiln can be found a11d t.oget her with etJUa tions for e 1rapora-
tion loss (egu.3.12) and overall efficiency of the kiln
{egu.3.22), daily moisture content loss in percent {HCL) can
be estimated by the follo•ing equation.
In the above equation, the energy required to overcome
hygroscopic forces which are only effective below the fiber
saturation point and are also very small compared to the
evaporation loss, are neglected for simplicity.
Knowing the total solar energy incident on the collec-
tor-cover1 the total energy available to the system (TEA)
can be estimated by,
TEA.= SEIC/R (3 .• 25)
where,
SEIC = total solar energy incident on the co11ector~cover
in Btu
= SI*.ACV
Chapter IV
MATERIALS ARD METHODS
Two types of so.lar kilns were studied .• The main par--
tion of this study was conducted on a prototype external-
co.llector .kiln a.t the u • .s. Forest Products Laboratory, f'ladi-
son, Wisconsin .• For pucpose of coll1pacison, a solar kiln of
.semi-greenhouse type loca tell at Virginia Po.lytechnic Insti-
tute and State University.., Blacks.burg, V.icg.inia was also
studied ..
4. J E.XTERlO\L COLLE£.:!:_OH SOLAR !£.I.1.[
Two loais of green sugar maple lumber were dried during
the summec of 1982~ Thes-e two r:un.s will be discussed sepa-
ratelr, following a .b.:cief description of the kiln itself.
Description of the Kiln
The prototype external-collector solar lumber kiln used
in this study .is located at the u • .s • .p .• A. :Forest P:cod ucts La-
bora-tory, adjacent to the cam,pu.s o.f. the University o.f Wis-
It mainly consists of two
parts, the solar collector and the drying chamber, as shown
·• '!7- .• 1 1.n "' 19 :ure · ...
26
Legend
A - Drying Chamber 8 - Collector C - Blower D - Air Duct E - Circulating Fans Fl,F2 - Humidistats H - Damper Motor J - Fresh Air Duct K - Exhaust Fan L - Thermostat
..... MIS2091 Figure 1:
I IOFT
K 11 Al
~H t.JO
External Collector Kiln, Madison. (Courtesy USDA Forest Products Lahoratory)
N -..J
2H
Solar Collector
''.!'.'he collector is external to the dr.ying cham.ber ... It is
horizon ta 1 and bui l.t into the ground. It is 8 feet wide and.
25 feet long, 1dth a cov~r-abso.rbe.:c spacing of 6 inches.
A layer of granulated charcoal about l/2 inch thick was
usHrl as a heat-ahsorbi:ng surface and hea :t transfer medium.
The collector cover material is a si.q.gle laye.r of fiber-
glass-reinforced polyest.er o. J cm thick.
'I'h.e path of air circulation hetwecen the· collector and
the dryer is indicated by arrows in Pig.1 •. Air is draao
from one side of the dryer, t.ravel.s down the ~est s.ide o.f
the collector, then across the ,e11d and down the east side of
the collector and back .into the dryer. A .blower of about
1/2 HP just inside the drying chambE;!r induces air flow
through the collector.
4.1.1.2 Drying Chamber
The drying chamb~r is approximately 9 feet square by 10
feet high with a capacity of about 1000 btiard feet of one
inch lumber. The walls £ramed with 2x4 co.nstruction
lumber.. The inside and outside are cove.cad with 1/2 and 5/8
inch exterior~grade plywood, respectively. The 3.5 inch
space between inside and outside p.1ywoqd sheathing, is insu-
lated witr1 o.ne 2. 5 inch thick fiberglass .insula tiou .batts
and one one-inch thick polystyrene sheet.
29
a polyethylene vapor barrier .is ·placed be.hind the
interior plywood sheet. 'l'he roof is of similar except that
the r:-aftecs ,:u:e 7 inches wide instead of 3 .. 5 inches,. 'fhe
rafter space is filled with loose fiberglass insulation, and
roof lng paper is used on the outside.. The floor .is :filled
with gravel up to 4 inches, with a s.heet of pqlyethy.lene
placed below t.he gra ve.l.
Two 2-speed overhead fans, each of about 1/2 HP, are
nsed to circulate the air th.cough ·the lumber pile. itn ex-
haust fan of about 1/3 HP, located at the bottom of the east
wall, is used for venting.
The first drying test was
third week of June, 1982 and
carried out beginning at the
ending at the third •eek of
,July, 1982. The purpose of this run was to co.i.lect the data
which were used to calculate the energy balances and then to
pr(~dict an empirical model foe the ef-f.iciency of the kil:n
with respect to the several variables ..
4. 1. 2 .• 1 Materials
Five-quarter inc.h green sugar maple ( !£g~ §.a££hat:!!.i.!!
tiarsh •. ·) lumber was solar-d.ritad in this study.
was cut i.n the Forest Products Laboratory saw mill f.rom 12
8-foot logs whose diameters ranged from 12 to 20 inches.
30
4. l.2 .• 2 Experimental Procedure
Each board was marked according to the log number im-
mediately after cutting. There were a total of 181 boards.
The width of each board was measured, and ranged from ~20
The length and average thickness of the
boart1s were 8 feet. and 1 .. 25 inches1 .respectiv,ely.
Since it was sawn 4 days before drying, the lumbec was
hulk-piled and the whole pile wrapped with polethylene and
stored in a cold room at 35°F until needed.
1'he lumber was stacked in tiu~ dryd.ng en.amber on June
15, 1982 .. The total load of the pile was 1040 board feet in-
eluding sample hoards. Just b~fore stac.kin9, 9 boards iihich
were from diffecent logs and of different widths were se-
lected to provide kiln saThples. Two matched kiin sa~ples,
each 26 inches long were cut from each hoard, after discard-
ing a filinimu.m of 12 inch;es trim from both ends ot the
boar:'ls. Care l.-ias also taken to eIJ.SUD'! that the sample
boar as contained a minimum a ru.ount. of natural d.e.fects such as
knots# bark, and decay.
one-inch moisture content sections were cut from both
ends of each sample board. Then each sample and each mois-
tnre content section was weighed. The sample boards were
end coated with a commercial end sealer and weighed again to
estimate the we~ght of end-coating material. T.he moisture
31
conte.nt sections were then ovendried at 219°F (104°C) for .36
hou.rs 1 and weighed again in (lrder to calculate the average
green moisture content. which was used; in tu:r.:-n to estimate
the oven-dried Yeight 0£ each sample board,,. Befor·e ove11-
drying1 the green volume of each moisture content section
was :also measu:i:ed by water displacement in order to de:t;:Jr-
min,? the average green volume specific gra vi·ty.
Tk.e width of the pile was 4 feet and t.here :were 29 lay-
ers making the pile about 5 feet high. The st~ckers were
D.75 inch thick by 1.25 inch wide by 4 feet long, and were
of mixed white and red oaks 1 spaced 2 feet apart •. A sheet
of plywood vas laid on top of the pile and top loa.ded with
10 concrete blocks for .a total load o:f a.bout 1:90 pounds.
sample boards were placed at 16 dif . .ferent positions, 9
on one side and 9 on the othe:c side of the pile ... To get a
comparison 0£ moisture co:ntent loss for each day between th.e
air ent(~ring side and lea vi.ng sides or the pile., one board
of each of the nine matched sample pairs was placed at cor-
responding positions on o_pposite side of the p:ile.
The data required £or calculatin~ the energy balance
for each day were obtained using the following procedures~
The temperatures at diff~cent positions in the system
were obtained by means of 24 thennoco.uples of iihich seve.n
were :located in.side and three outside the co.llector, as well
32
as six inside and eight outsid,e the dryi.ng ch.amber.. The ex--
act location of each thermocouple is given in ,llppeudix E.
The temperatures of these thermocouples were recorded at
half-hour intervals on a Honeywell strip-chart recqrder .•
The tlaily solar inso.l:i1t.i0Il. :was obta.iued by mean.s of an
Eppley b.lack and 'finite pyra.nome·ter set up 911 the :coof 9f the
chamber.
Two hygrothermographs one located inside and the othe:.i:
outside the chamber, cecorded the relative humidities inside
the chamber and of the ambient a·tmosphe.re .•.
A timer was set up to control the .fans, b.lower and ex-
haust •. · Two huroidistats, a thermostat and a differe:ntia.l
temperature control were al:so set up in or-d,i2r to co.ntrol
each of these independently.
The humidistat switch RH1 (F1 in Fig.1) coµt.ro.lled th.e
venting. It was used to est.ah lisn tbe mini11lU'fil re la ti ve hum·-
idity in the chamber below which the exhaust fan vould not
operate .•
A second humid:i.stat switch RH2 {F2 in Fig .. 1) was a.lso
used to es·tahlish. the maximum relati va h.umidi ty abovH w;hicli
the dryer would not operate, specially for long periods o.f
loiJ sola:c input and higl1 humidities:, ie. •.. rainy periods ..
The ·fa11. thernost.at was used to establish a mininrnm
temperature above which the :Eans woula ope.rate even after
the timer was off, especially for the typical sanny days.
33
The differential temperature contro.1 was used in. order
to turn the blower on whenever the temperature in the col-
lector was higher than that in the dryi~g chamber.
Three counters moni to.red the running times .for eac1, of
the blower, the exhaust fan and circulating fans. I
Solar drying was started on June 16 1 198 2. •. The timer
was set to be active between 8:10 am and 10 pm, and the
thermostat was set up at 90°w.
All sample boards were VBighed every morning before
8 am, unless it had rained. The moisture conu:mt of each
sample board was ca le ula ted. immediately ~1fter weighing and
then the two humidistats were changed if necessary, accocd-
ing to the aYerage moisture corrtent of these samples.
Daily solar insolation and total running times for the
circulating fans, blower and exhaust fan were recorded every
morning before B am. A tru;~rmocouple recorder arrd two hy-
grotherrnographs were also checked at the same time. The
cover of the collector was cleaned in the early morning at
least two to three times every week to r:emove the accularoa t-
ed dust, and thus maintain the transmission e£ficiency o.f
the cover ..
The fans were run at high speed at the beginning of the
test and it was chan9ed to th,e low speE~d whePo the average
moisture content of the samples decreased to 28.5 percent on
day 1 O .•
34
l e .... 1.I:.::,. ...lu mh cf=" ~ct {+'r.:r1} aurl -the second humidistat {RH2} were
set initially at 70 and 100 p12rcent h.u.miitity, a:espective1y.
They were re.set to 50 and :90 pe.r:cen t 0I1 day 10. They were
again reset to 40 and 70 percent on day 20 when the average
moisture content was 13.8 percent. Finally on day 22 they
were reset UP at . .30 and 6,0, perce.1d: when -the a'verage moisture
content of the samp.les was ·12 • .3 pet:ce.nt ..
'Tlte solar dr_ying was termina·ted 011 July 15, 1982 after
29 days of drying,. _ The pile was unstacked and each .boar:-d
was l-Jeighed to det.e.a:mine the tot.al final weight of the lum:-
her ..
To estimate the actual po¥er c<:n1sum,1_:,-tion of the ciccu-
lating £a:n.s, blower and exhaus,t fan, e,ach vas run separately
for 24 hours,. The power consumption o.f each fan or blower:
was measured by means of a po11er-meter •. ·-
The bread -t:h and the leng·th o,f the cq,1:lector and the
leng-th of each ra.fter used in constr.uct:ion of t.he collector
cover were measured in order to ca:lcula te the actual area o.f
the cover:.
The average -t:r-ansmissio:n efficiency of t.he collector
cover was estimated based on au experiment using a sheet of
one-square feet fiberglass- reinforced polyes·te.c whJ.ch :was
of the same material and the same expo,sure history as the
cover,. Solar insola tion with and 'Without this sheet iias
35
measured hourly by a pyranometer rf.:>corcler on day 23 and day
27.. The total solar i11solation on these ilay.s were 2507 ari.d
2295 Btu per square feet" respectively ..
4. 1. 2 .. 3 Analytical Procedure
As described in the precedin9 chapter, to get the ener-
gy balances during the JryI. ng process, the various energy
input and the various ener9y output from. the system .for ea.ch
nay were calculated sepa.ra te1y as follows.
Solar Energy Input to Collector The total solar energy
transrt,itted through the cover (SETR) for Eiach day was calcu-
lated from eguation (3.1) 1
SETR: RCV*SI*ACV
In this study daily solar insolation (SI) was obtained
from recording the pyranometer, transmission ef.f.iciency of
the cover {RCV'} was estimated to be 0,. HO .from a separate ex-
periment, and area of the cover (ACV) was measured to be 167
square feet.;
Electrical Energy Input : The eli:~ctrical energy input to the
system (EI.I} for each day was calculated from the total pow-
er consumption of two fans ,:111a. moto,r blowe.c. The power con-
sumption of each fan or motor blower for .,2ach day was oh-
t ained by the product of th.e power .a.nd the
time of each fan or blower.
total runnin9
36
In this kiln, the power of each fan vas 0.715 HP (30.28
Btu/min) at high speed, 0.211 HP (8~97 Btu/min) at the low
speed. That of the blower was 0.746 H.P { 3l.63 Btu/min).
Total running time of each fan or blower for each day was
obtained from the two counters.
Energy Gain by Conduction from Drying Chamber: This energy
gain for each day was calculated from e~uation (3.2),
4 CDG =~ Ui*Aw1 *twrDTW1 + lJ"RF*A.R.F*DTRf'*trf
i=l In this study, The effective overall heat transfec
coefficients of the walls (OW) and of the roof {URF) ~ere
estimated (Tscherni tz and Simpson_, 1979) as o. 0611 Btu/h.r-
ft'2-0F and o. 0.365 Btu/hr-ftz- 0 p respectively.
The outside temperatures of the east, south, west and
north walls and of the roof were determined by the thermo-
couple nura.bers (7),(8} 6 {9) 1 (10} and (6), respectively. The
inside temperatures of the west and the ea.st walls were mea-
sured by the thermocouple numbers U} and (4). Those of the
south and the north. walls were estimated fro 111 the average of
thermocouple numbers (J) and {4}.
was given by thermocouple number {~.
The ceiling temperature
gnergy Gain from the Load: It was calculated from equation
(3. 3} ,
EGL = Wt*CPiO*DTL + [ ( Wo*AVMC) /100 ]*CPW.*DTL+aX *C?X*D.TL
37
In this case, oven-dried weight of the lumber (Wo} was
estimated. fro.m the tota 1 g r-ee n volume and the green volume
specific gra_vity of the lumber 0J;tai1H2d by the watHr dis-
placement method. The total oven-dried weight of the stick-
ers and the plywood was estimated as 215 pounds. based on
their dimensions and specific gravity.. 'fh.e total weight of
other materials (iX) was taken from the total weight of con-
crete blocks which was about 190 pounds and the specific
heat of concrete was taken as 0.2 Btu/lb oy {Luikov,1966).
Specific heat CPio of dry wood was calculated by Dun-
lap1s equation as given by Skaar {1972),
CPWo = o,.266 + o,.00116 *'I'
where,
T = wood temperature in °c
or.,
CPNo = 0.266 + 0.00064 {Tav-32)
CP~Jo= specific heat of dry wood in Btu/lb- 0 .F
':rav = average wood terupe1:ature, t.aken to be that
of the chamber
{ 4. 1)
{ 4 .. 2)
In this ca.se the average tempe:ra·tu.:ce {'I'av) was estimat-
ed. from the a ver3.9e hour J.y temperature throughout the day
from thermocouple numbers {3) , {4) a:nd {5}.
38
The average moisture content of the wood was taken to
be the mean of the initialand final illOisture contents of the
sample boards for a 24-hour period.
water was takeu as 1 Btu/lb-°F.
The specific heat of
Heat Losses fron1 the Collector : The three main losses
from the collector were calc u.la ted .separately, as follows.
Top Loss : Top loss from the collector {"rO.PI.) for each day
was calculated by using equations (3. 5), (3.6),
(3. 8) , {J. 4) and {3. 9) •
• 281 hpc = 1.613* { D:-r ) *[ 1 - 0.001B(TAV-10)]
1.157
hrpc = [ ( TP 2+ TC2) * (TP+TC} ]/[ ( 1/E2) -J- { 1/EC) -1 ]
h w = 5. 7 + 3. a* V
hrcs = EC*SB*(TC2+TS2)*(TC+TS}
OT= 4T*EP*SB*{TAV) 3 *{TP-TS)/(TP-TA)
+ [ [1/ (hpc+hrpc)} + (1/(hw+hrcs} J J-1
TOPL = ·OT*ACV*TC>o'cttc
(3.7),
(3.5)
{3. 6)
(3 .. 7)
( 3. B)
(3. 4)
(.3 .. 9)
In this study, the transmittance of the cove~ £or radi-
ation ft"O!!I plate to sky (T} and emm.ittance of the cover- (EC)
for the fibecglass-reinfocced polJt::.Ster were assumed to be
0.2 and 0.8, Cf~specti vely. The plate e:ni ttance {EP) of
granulated charcoal, was estimated to he 0.95.
39
The plate temperature {'l~P) was obtained from thea:-mocou-
ple .number { 13) and tiH~ cover temperature (TC} from the av-
erage of therm:>couple .numbers {11), (12),(14),{15),a.nd (16).
Th,;:~ ambient temperature was obtainea. frorii thermocoupl,e num-
bar (20) ~nd the sky temperature {TS) calculated fcom the
a.mbient te.mpera t.ure (TA.) by use of the formula,
J;verage wind speed. for each day w-as obtained from the
local cl imatoloqical data ohtained from the National Wea the~
Service at DanB County .Regional Airport, about 5 miles far
from the solar kiln.
Bottom Loss : 'I'he concl.uction coefficient (UB) of granulated
cha.rcoal was assumed as o ... 432 9 from
ieast(1967) •. The surfa:e area (APL) of the plate (the char-
coal) was estimated to be 170 .s1;1uare :feet .. The averaqe
temperature difference between plate and ground :was
estimated from the readings of thermocouple numbers (13)
and (24), respectively.
.Edge Loss '1.'he edge loss was ca.le ula tea. using the same
procedure a.s for the bot tom loss ... How~ver, since the total
area. of plate in cont.act with the ed.ge of the collector is
very small, about 2.5 square feet, the total edge loss was
presumed to be negligible.
40
Enerqy Loss from the Drying- Ch.amber The five main losses
from the drying chamber were calculated as follows.
Evaporation Loss: This was calculated from equation (3.12),
EVP = {62.4*V*SG}*(MCL/100)*[0.53{212-Ti)+972]
In this study the green volume of the lumber (V) was
estimated from the dimensions of the boards and the green
specific gravity (SG) was estimated from the moisture con-
tent sections of the 18 sample boards by water displacem~nt
method .. Daily moisture content loss in percent (BCL) was
estimated from the average moisture content of the sample
hoards .. The average ini tia1 te.mpe rature inside the dryer-
was taken from the average values of thermocouple numbers
(3), (4) and {5) recorded at a am.
Hygroscopic Loss· It was calculated from equation (3. 13),
The oven dried weight of the lumber {Wo) was estimated.
from thfo total green volume and green volume s1Jecific gravi-
ty of the lumber. Daily average ini t±a.l moisture cn.ntent
and average final moisture content (Mi and Nf) were estimat-
ed from the daily average i.ni tial moisture content and final
moisture content of tht, .sample boards. It was realized. that
41
the surface moistu.re content is lower than the average mois-
ture con tent.. This causes some er:co.r in the calcula tioas of
hygroscopic los~ However, the surface moisture content ~as
unknown and this factor was neglected in the calculations
based on equation (3.13).
Condu~tion Loss: Co~duction loss from the drying chamber
was calculated from equation {3.14),
4 CDL =I UY *AWi *DTWi *twi + URF*ARF*DTRF*trf
i=l + UFL*AFL*DTFL*tfl
In this case calculation for the conductior;i. losses from the
walls and the roof were similar to that of the conductio.n
gain as mentioned before. In calculating the conduction
loss to the floor, the ovecall heat trans£er coeffient of
the floor which consists 0£ a 4-inch th,ick layer of gravel
was assumed as O.S208 Btu/hr-ft2-°F {Wood Handbook, 1974}.
The average temperature o~ the floor was taken from the av-
erage values o.f thermocouple numbers (3.) _and (4} and the av-
erage temperature of the ground was taken from thermocouple
number ( 17) respectively •.
Energy Given to the Load: Similar calculation as that of
the energy gain from the load as mention;ed before.
Ventilation Loss: It vas calculated from equation (3.16),
42
VTL - {rvt*ch.o*tvt) * (C.P.A - R) *D'T.A
.For this solar kiln, in calculating the total ventilation
loss :for each day, four cases were considered;
1. any the exhaust was on
2,. . The exhaust was off but · tl,e circulati,ng fans and
:blmi1er were on
3,. The exhaust and blower :\we:ce off but the fans were on
4. The exhaust, .fans and blower "Mer~ off
The volume~ rate .of .flow of outlet air (rvt) .for each
case was taken to be,
case {1) 600 ft3/min
case {2) 300 ft3/min
case (3) 250 £t 3 /min
case (4) mo ft 3 /min
The density (rho) an:1 specific he.at of air (CPA) were
calculated at 85 .. 5op and 52 %RH which were the average temp-
erature and relative humidity inside the ch.am.her for tile
~hole d.rying process.. They were t,clke:n as 0,. 7113 ll'.1/cu£t and
Uni -versa.1 gas constant H
was taken as 0 .• 0685 Btu/lb°F .from publislted values.
The total running time (tvt}
from the counters ..
.for each case :was taken
43
The outlet and inlet ai.c tempera·ture.s were taken from
the~ruocouple numbers {4) and (20) respectively.
Calculation of Ene.cgy Balances : The energy balan,ce rela-
tionships for. the lciln were calculated fm: each day u.si:ng
equations (3.17) and (3.JB),
TEl =SETH+ ELI+ CDG • EGL
~rEC = {TOPL + BOTL) + (EV A+HYG+EOL+CDI. +VTL)
and then, the energy balance for each day was calculated b~,
TEI - TEO+ E
Calculation of Efficie11cies : Th.e e.fficiepcies of the co.1-
lec·tor (EFFCL) and thi:-; d.r_yinq- chamber (EFFDC) were calculat-
ed for each day {24 hour period), using e;1uatious (3.20) and
(3. 21), ~1hereas overall efficie.ncy 0£ th.e kiln was calculat-
ed by eguation (3.22).
Empii:ical Modf.ds fo.r: Efficienci-e.s A statistical analysis
system (SAS) was used to indicate which fac·tors explain the
variation in efficienci-es during the drying period of the
collecto.c (El''FCI.) and drying chambe_r (EFFDC), as well as the
overall efficiency (EPF).
linear regression was,
The model used i.n the multiple
EPFICTENCY = f (IMC.,S.I 11 TA,.S\TP.H,VW)
where,
.IdC = daily average initial moisture content
of the samples in percent
SI = daily solar insolationin Bi.:u/ft2
TA = daily average ambient temperature in op
SVPR·= daily a vera91~ sa tun. ted vapor pressure in mm
VW = daily average wind speed in ~ph
N ul tiph:,, linear regression tests using a stepwise
procedure were executed for e.acb. of the three efficiencies,.
Js'or the collect.or effici:ency {Et'FCL} the daily solar
insolation was the significant factor. Therefore a polyno-
mia1 regression test with stepwise riroced ur:~ as well as sev-
Bral exponential .models of collector t::£f.icie.ncy against dai-
ly solar insola tion were tes·ted,.
.For th.e drying chamber efficiency {EFFDC) and the ove-
rall efficiency (EFF) the averag,2 ini t.ial moisture conte.nt
was the significant factor. a. polynomial
regression test with stepwise procedure as well as several
exponential models of arying chamber efficiency {.E.FFDC)
against average initial moisture content (INC) and overall
efficiency (Ki.'~P)
(IaC) were testeda
against average initial moisture content
45
Second £!:}!!1
·rollowing the same procedure as in the .first run,. a
second load of the same thickness and the sa.me length was
solar d.ried again beginning ,July 20_,. 1982~ This test termi-
nated o.n August 15, 1982 after 26 days of drying ..
The purpose of t.liis nm was to test the empirical egua-
tion dcrneloped in t11e first nm for predicting daily mois-
ture con tent loss a_;gains t actual data,.
4,.2 SENI-GREENHOITSE !!bl
For purpose of c o.mpa:cisma with -the pr,evious study of
the external collector solar kiln, a semi-greenhouse type
solar kiln was also studied during the Fall of 1982 •.
4.2.J Description of the Kiln
The semi-greenhouse solar lumber kiln used in this .stu-
cly is .located at Virginia Poly b?,!chnic Institute a:nd State
University, on the campus of the Thomas l'l"'Brooks Forest Pro-
duc·ts Center, Blacksburg-, Vir:g.inia {35°,9'N,8l0 W). :rhe kiln
is 4 feet square by 8 feet high at the north and 4 feet high
at the :sou·th, as shown in Figure 2 •.. ·
It has a capacity of 150 to 200 board feet, with a max-
imum board length of 4 feet. '£ he insidEi and outside Tiilal1.s
are sheathed with. 1 /i~ inch ply:wood and are insulated with
8 FT.
ACC 00
46
~------ 4 FT.-----l' ... 1
7
4FT.
Figure 2: Semi-Greenhouse Kiln, VPI & SU, Blacksburg.
47
4-inch thick fiher glass insulation, including a vapor bar-
rier on the inside face~ The floor is of similar construe-
tion to the walls except that the upper surface is seathed
with 3/4 inch plywood.. The roof is tilt<.-'!d at a 45° angle to
the south.. I-t is covered lvi th two layers of t:canlucent.
'Weather resistant polyester fi:lm spaced two inches apart.
The kiln has one access door on the east ,~all ·to permit
periodic examination of the lumb;er and. measurement of mois--
ture content .. The roof and the south wall are also hinged
to the north wall and to the floor, for loading and unload-
ing ..
The overall heat trans£er coeff~ents £or the Malls1
floor and roof are about 0,. 071 ,and. 0. 51 Btu/
ft2-hr~°F 1 respectively (Oliveira et _g,_,b, 1978) ..
two adjustable vents of about 48 square inches near the top
and bottom of the north wall,.
A one-speed window fan of a.tout O.l HP is also provided
for the circulation of air.
Zill the interior walls as well as ·the fan support plat-
form are painted flat black to maximize the .absorption of
solar radiation ..
48
4.2.2 Ha teria.ls
Green yellow poplar- { Liriodendron tu.J..i.Qif~£i! -1 ... ) ~lum-
ber of a vera.ge thickn,ess 1 125 inc hes was solar dried in
th.is study,. A total of 34 boards were cut in the Forest
Products Center- sawmill from two 8-foot logs and two l0-£oot
logs whose diameters ranged froM 11 to 16 inches.
4.2.3 Exee:rimenta1 Procedure
Each board was marked according to the log number, im-
mediately after cutting. One 1-inch section was cut from
the center of each board in order to estimate its average
initial moisture content and speclfic gravity. 'I'b.e width
and the thickness of each moisture content section were also
measured in order to estimate the tot.a.l green volllille of each
board.
A total of 34 4-foot length boards of different widths
'were stacked in Uu~ kiln, one · from Gach of the original .34
full length boards. 'I'.he width of the pile was only 2 feet
and there were total of 17 layers rna.kiri.g the pi.le a.bout 2 .• 5
feet. hig.h. A sht~et of black-painted plywood was laid on top
of pi.le as a.n absorber. Just before stacking, fou:r. boards,
each from a different l::,gs and of different widths were se-
lected and used as sarnp1e .boards.
49
To get :a comparison, the remaining 34 hoards which were
also 4 feet long and from the opposite ends of the 8-foot
length hoards were also stacked for air drying close to the
solar kiln. Four boards which =ere end matched with the
sample boards in the solar kiln were a.lso used as sample
boards in the air-dried pile.
Bacause of instrument limitations the data collected
for the energy balance calculations wer-€ not extensive as
those for the external collector kila.
Seven -ther: mistors were s12t U? to measure the tempera-
tures at different locations in the kiln. There were two on
the air entering and t;,vo on the air leaving side of the
pile, one just below the inner layer of tl,e pqly2ster, o:rnS!
at the center of the outside-south wall# and one just out-
side the kiln near the top of the north ~all. The tempera-
tures of these thermistors were recordEJd every hour by a Ho-
n,,~ywell strip-chart recorder.
A hygrothermograph was placed inside th,e kiln. to esti-
ma.te Ute relative humidity insicle !:hE~ kiln~ The circulation
fan Mas activated by an electrical timer for the six hours
between 10 am and 4 pm each day.
Both solar drying anc1 air dr:ying wen:~ started on Octo-
ber 6, 1982. A.11 sampL2 boarc1s from both piles wzre weighed
every morning before 9 am, unless it had rained.
50
ture content of each sample then calculated based on
the prev.iously estima·te oven-dried s-eight of each sam;ple
board, in ocder to estimate the average moisture content of
the lumber.
The solac drying was terminated on November 3, 1982
after 28 days of drying.. The pile was unstacked and each
board :was weighed to measure the tota.l .final weight of the
lumber ... · A 1-inch section was cut f.roru tlu?. center of each
sample board to calculate ·the actuc.l final Inoisture content.
The air drying was te.i::minated. on, Novemb,:er 10., 1982,
after 34 days of dry.in9.
4. 2. 4 £.!!~lytical Procedure
Total green volume of the solar-dnied lumber :ilas esti-
matea. from the average thickness,
the boards. Based on the total
l ume specfic gcavit.y obtained
width and the length of
green volu:me and green vo~
by the ~ater displacemeRt
method, the tota.l oven-dried weigb;t of the lumber vas esti-
mated ..
The oven-dried ~eight of each sample board from hot.b.
piles was recalculated based on their actual final moisture
cont.ent obtained from the moisture section cut at the end of
the run~. The average initial and da.il.y .moisture co,nte.nts of
the sample boards from ea.ch o:ile were recalculated based 011 L .
their recalculated oven-dried weights.
51
Daily solar insolation data measQced at a 45° tilt
angle were obtained from the Department of Mechanical Engi-
neering at Virqinia Polytechnic Institute and State Univer-
sity3 Blacksburg, Virginia.
The data obtained in this study were not sufficient to
calculate tte energy balances during the drying period.
Daily solar insolatio-n ~as o.:btaii1ed on,ly for 15 out of the
28 days and the temperatures obtained from some thermistors
were also not correct at some times. For this reason only
thfJ overall daily efficiency o:f the kiln {RFI·") could be cal-
culated ana this only for the 15 days that solar insola tion
data were available. The following equation,
EFF = (EVP+RYGJ/(SEIC+ELI) (3. 27)
§there, thB ,avapor-a tion loss (EVP} a.nd hygroscopic losses
(HYG) were calculated from equations {3.12) and (3.-13); to-
tal solar ener-qy incident on the cover (SKIC) was calculated
by the product of thr~ collector area (22 sguare feet) and
the daily solar insolation in Btu per square feet; total
electrical energy input to the system (ELI) by the circulat-
ing fan was calculated £rom th,?. power con:suIDed by the fan
100 watts (5.69 Btu/:m.in} and total running time 011 each day
(6 hours),.
52
In ca.le ulating the total energy input to the system,
energy gain :by conduction ana. energy gac.in f.com tl1e load Were
neglected in the above equatio~.
Chapter V
RESULTS AND DISCOSSIQNS
The results o.bta.ined on each of the two types of kiln
will be discussed sepa.ra t.ely,.
5 .. J !!T.E!iJi!"!!. C0LI.LECT0R [ill
'the discussion of the external col.lector ki.ln cesults
is divided into th.rea sections. The first sect.ion wil.l dis-
cuss -t:he results of t..h.e ·.first run on sugar ll1aple .. The sec-
onJ section concerns the seco~1d run o~ suga:;c Eaple. 'l'hi3
third .section 1iil1 discuss possible methods to improve the
kilo ef.ficieny.
This section :will include general Qhservations, energy
input., energy output, energy ba1a.nce, ~fficiency, and empia:-
ica1 mode.l £or ef-ficiency for the first run from 16 ~June,
1982 through 14 July, 1982.
5. J .. 1 .. J General Observations
The total green voluBe of the lumber used in this study
was 1040 board feet of sugar maple of 0.58 green sp~c:ific
gravity. Based on the total green volume and t.he grRen Sfn~-
53
54
cific qravity, the total ovend ry weight of the lumber ~as
estimated to be 3137 pounds.
The average initial and final moisture contents of the
18 sample boards were 6Q.4 and 8.0 percent, respectively.
The total drying time was 29 days and the average daily
moisture content loss was therefore 1.94 percent~
ing curves based on the average for 18 sample boards togeth-
er llli th those for the 9 sample boards each on the air enter~
ing and leaving sia.es ot ·tht: pile are s:hown in Figure 3 ..
Daily average initial and final moisture contents of 181
boards in the load were estimated using the average of the
18 sample boards. There was some variation o.f the moisture
content among the sample boards especially at the beginning
of the run .•
Average £inal moisture content obtained from 9 boards
taken from different positions in the pile at the end of the
run vas 9.7 percent with inaividual values rang~ng from 8.9
to 10.3 percent. The average final moisture content was 8.Q
perce'fft which was based on the 18 sample boards ..
:rh0 i1istribution of moisture cont!:~nt in the load can
also be estimated from the two drying curves .based nn the
sample boards on the a.ir entering a .nd leaving sides of the
pile ( Fig.J ) •. • At tln::; .'hegj_nn.ing of the run, the average
drying rate of the :samples on the ai.r-en ter ing sid{~ was
85
60
55
so
us
uo
ss ti
C 30
X
2S
20
15
10
5-
0
side
erage
Entering air side
11. I •• I. 'I I I I' I I •• ii I. I •'l""J'"""W'T~-r- ••• I • i ~. • I ii I. I .... J'T""'T'....,.__., I I" .. I" •• I ii I'." I I.' I I.. 'I. I.. i' I I I I" 'I .. I I I I I" I
0 2 S U 5 6 7 8 10 II 12 13 1q 15 16 17 18 19 20 21 22 23 2ij 25 26 27 28 29 OATS
Figure 3 Dryirig Curves of Sugar maple, First Run .•
l11 IJ1
56
higher than that of the samples on air~ leaving side.. Howe v-
er, afte.r 7 days the average drying rate of the samples on
the air:~leaving side became faster than Uiat of the samples
on the air-en:tering side,. At the end of run, -t.h.e average
moisture content of the sample boards on hotil sides oft.he
pile was within o .. 4 percent moi.sture co.,ntent.
As m~ntioned earlier, the total ove.:wlry weight of the
lumbe.r 'i,l,as estimated initially from th.e total greeu volume
of the lumber aud the average green speci.fic gravity of the
sample boards.. This calculatio.n is subjected to err:o.r,
since the tot.a.l green volume was calculated from the dimen-
sions of each hoard. As a check~ the total ovendry weight
of the 1 umber cal.culated from the a v,arag~ ·.final moisture
content ( 9. 7 Yi } obtain.ad f r-o:m the 9-boa.rds and the total
final w1:.1ight o;f 181- !wards which Ji1as 3·45.3 pounds, :was .3148
pounds,.. This is within 0 .. .33 percent of ·the tota.l ovendry
weig~t 3137 pounds which had been estimated based on the
specific gravity and green volume measurements. The best
method to es·timate this weight would be to devise a system
to measure the total weight of the whole pile at any time,.
The average daily solar insqlati.on du.ring the dryi:i1g
period was 1906 Btu/ft 2 ., and ranged from 5·12 to 2736 Btu/ft2 •
There were total 0£ 11 :rainy days resulting ill. a total pre-
cipitation of 2. 42 ir1ches.. '.fh.e avera.g,e amhient tcrnrperature
57
during the arying period was 67.5°F and ranged from 46.0 to
Other climatological sta ti sties which are be.lieved
to be import.ant are given in Table 1 ..
'Jl:he average temperature and. relative humidity inside
the drying c.hamher during the drying period was 85,. 5°.F and
.52 percent, and ranged from 60.0 to 117.0°P and 26 to 90
percent, respectively.
The average temperature o~ the air inside the collector
was 78.6°F with lower and upper limits of 46.0 arid 119.5°P~
That of the plate was 82 .• 8°:F and ran9ed from 46 .• 5 to
138 .• 5°.?;e.
The average daily total po,wer consumption by the circu-
lating fan, blower and exhaust fan was 13.7 Kihr1 ranging
from 7.0 to 22.5 Killhr.
5.1.1 .. 2 Energy Input
The total energy input for each day, calcu.la ted from
the total ener9y transmitted through th,e collector-cover is
given in Table 2. The total errnrgy input component.s for
the whoLe drying process are also shown in Table 3
Table 4 indicates the total da~ly energy potentially
available to the system iricJ.uding tln::.? total solar energy in-
cident on the collector cov(~r.. Tabh, 5 sho~rs the components
of the ener:gy potentially available £o_r the whole drying
period,.
58
TZI.BI.B 1
Variables and CoBfficie.nts for the First H u.n of External Collector Kiln
r·------------.---------------1 Varia.b1es or J Coefficients J-I
Unit
I
I i1ean l . ' I
l riinim.umJ Naximumj j J l
}Daily Solar Insola- I Btu/ft.2 l l :1 j
,j 1906j
I 6,.. o I
I 5121
j 1,. 61
I 46. 01
7,. BI I l
26,. Ol j
D,. 31 I
I 27361
1 tion l n J J A mhient Tempera tun=: ! u n
I I Ambient JRelative Humidity j JAmbient Saturated )Vapor Pressure I n u ,.
I !Pr,ecipitation I H
'l jWind Speed I ;f H
f )Chamber Temperature
j l I j l I I ij I i l j l I l l i J l l
j n n j 1 l JBelative Humidity i I {inside the Chamber) j J i JCollector Temperaturej
·n n j
!Absorber Temperatuce l 11 u l !Solar Energy Input 1 " " " j
I I l j J i !
jElect:cical I n
.Bnergy I11pJ H ff j
# KBtu = 1000 Btu
KW-.hr/m2
mm-Hg
J I j l j i I j l i
j_nch.es/day j mm/day I
mph Km/hr
l I J J I 1 J I j I l i
' I 1 i
KBtu/day f, I KW-hr/day j
KBtu/day KW-hr/day
l I I
I 67,.51 19. 7J
.j I
62.0j I
O, 611 l
Hi. 96J I
0.221 5.59j
I 8.62j 3 .. t35j
j 85.Sj 29 .. 7j
.i 52,.0j
j l
7 8 .. t:> I 25 .. 91
j 82. 81 28 .. ?1
I 254.,.61
74. 61 I
40,.0j l1. 7 j
1 7.971
I o,.03l 0,.76)
J 4.201 l.88l
i 60 .. 01 15 ... 6 l
I 26. OJ
l j
46. Gj 7 .. 8 I
j 46,. 5 l
B .. 1 i l
68 .. 41 20,.01
l 15,. 6 j
4 .. 6 J
i B. 6J
,I 87,.0} 30. 6 i
a l
92,. OJ i
1.26j I
32 .. JO J j
o .. 42 i rn. 6 7 l
I 15. 10 I
6.,751 I
117.0j 47 .. 2l
j 90 .. D j
j i
119, .. :3] 48 .• 6 j
j 138,. 5 j 59. 21
j 365 .. 61 107.0j
j 6fJ. Ji .20. o l
Variables or Coefficients
} JTotal JPower I H
EL.?.ctrical Consumption
u
l I Total I u
Energy Input n ,n
,J )Total Ener:gy Output. I H H 0
J }Difference in Total JEnergy Input&Output I u " « ! ]Heat Transfer Coeff: I bet: Pla be> t; cover .) 0 H n u
l JRadiation Coeff:from !Plate to Cover j n u a o n u j jRadiation Coe:ff: from j Cover to Sky l n n n u
I JWi11d Coeff: j n n
l )Top Loss Coeff.: I u 11 u
i L
n
# KBtu = 1000 Btu
l j j I j j I I l I j
l 1 J j
l j I j l I J l J J l I J J I ! I I
59
TABLE 1
{continued)
Unit
KBt11/day :/j:
KW-hr/day
rrntu/cl.ay KN-hr/day
KBtu/day K~v-hr/day
Btu/d.ay
KW-hr/day
Btu/ft-= o·"' ;{'
J.;Jjm2 oc
Btu/ft:2 op
W/m2 oc
Btu/ft2 o:~
W/m 2 0"' ....
Btn/ft 2 Op W/m~ oc
Btu/ft2 oy W/m 2 oc
l I l I I i I I I j j l I
' 1 l I 1 I f I i I l j 1 i ! I i 1
Hean 1 rlinim um l l"la ximum] l I I I i f i I J
46 .. 91 23.8J 76 .• 9j 1 I J
13.7) 7.0J 22.51 I J l
300.01 120.0J 433.6J 87.91 35.2] 127.0j
I I l 299 .. SJ 172.QJ 429.0J 88.lJ 49.61 126.11
i j j 580j 30001 89,000,j
l I l 0.221 0.021 2.61j
l J J 0.221 0.19j 0.27j
J j j L27J 1 .. Q.81 1.54j
I J J 0.831 0.741 0.91J
I I J q.114 4.191 5.14j
I l I 0.761 O.ij81 Ob84j
i J I 4.33) J.84J 4.751
I I J o.681 o .. 33J 1 .. JJJJ 3~85j 1,.88) 6.75j
1 I I B.521 7.61,) 9 .• 90! l.'.;>Oj 1..341 1 .. 751
I I I
TABLE 2
Daily Tota.l Ene:cgy Input
r--T :l D l Daily i 'fotal I Total I E.n.ergy I Energy I Total J I I Sola.r 1 Solar 1 :i~lec- fGain bYI Gain from ,j ,I ) .A Un.sola-1 Energy I trical I Con.due-) t:11e Load j Ene;cgy i I · I tion JTrans- j .Ene:rgy .j tiop. ;I j 4 I 'l I lmitted I Input j ) :I Input J l J Btu/ft2 i {KBtu) J (KBtu) j {K.Btu) j (KBtu) ;f1: I (KB tu) j :r--· j J I J i I i ) 1 J 2736 I 366 I 64 I 3 j j 4.33 .
. I t '"I
.;f. j 1224 J 163 I 64 I 1 I t 228 J l 3 I 1095 I 146 I 50. i 0 J 24 j 221 J I 4 I 2415 I 323 l 68 l 3 j J 393 l I 5 j 2182 J 292 I 67 J 1 l 1 .]60 I j 6 J 2223 I 297 j 67 j 1 J J 365 I I 7 .I 2534 I 339 I 68 j 3 J j 409 j I 8 J 2232 j 298 l 68 l 2 i j 368 I l 9 J 2316 I 309 j 66 I 1 l i 377 I J10 l 512 l 68 l 18 I 0 ff 36 I 122 l J 1 1 J 2-009 I 268 l 32 I 2 J I 30,2 j 112 I 1391 j 186 I 29 l 3 J j 217 j. ]13 J 1894 l 253 J 33 l 3 I j 289 j I 14 I 817 I 109 I 18 I 0 . 23 l 150 j J 115 t 2538 t 339 i 32 j 2 1 j 37:) I !16 I 2443 I 326 J 36 J 1 I I 364 I J17 I 1354 I 182 J 26 ,t 0 l 3 ) 211 .i 118 1 1304 I 174 I 28 J 1 l I 203 i I 19 1 2597 I 347 J 43 I 2 i ! 393 j J20 l 233.2 J 312 I 38 j 1 i 7 t 357 I j21 t 761 J 102 j 19 I 0 J 16 1 137 l 122 ! 2607 I 348 I 30 I 1 l I 379 l 123 l 2507 l 335 l 33 t 2 I J 370 j 124 .J 1765 I 236 J 26 j 0 1 4 cl .266 I J25 I 983 J 131 .. J 16 I 0 I 7 j 154 j j26 1 2116 j 28.3 I 25 j 0 j .I 308 1 127 j 2285 I 305 I 32 J 1 l j 339 i J28 I 1980 i 265 J 31 j 1 I J 291 I )29 I 21'15 J 283. j 33 I 1 I 2 l 319 I I J J I j I l j L- J
# KBtu = 1000 Btu;
61
ComponHrd:.s of Total .Energy Input
r------------------------------..------'.} I ) j f-l
Source
] Solar Energy Transmitted through J I the Cover J J Electrical Energy Input by the Fans 1
j a I ,j
j j l
J Electrical Energy Input by the Blower) I I Energy Gain from the Load+ J I Energy Gain :by Conduction f-1 I Total Energy Input a # KBtu = 1000 Btu
a I
l I J
Energy I Input jPercent j (KBtu) # .I 1
71384
775
386
122
35
B,702
-f l i I 8 1L,9 I J l I i i l 1 8. 9 l j J l 4. 4 i I l I 1. 4 I I l j 0,. 4 j
1 J l i 100.0 l I .t
+ solar and electrical energy stored in the load
62
'TAB.LE 4
D:ai.ly Total Energy Potentially A vai.lable to system
T 1 J DJ Daily I Total j Total I Energy A Energy I Total j
I I Solar I Solar i ,Electr i- JGain by·t Gain from l Energy 1 j AJ Insola-1 Ene:rgy jcal Energy l Co nduc-,jthe load j Avail- j J J tion I Incide.ntj Inpu-t I tion j I a.ble j j YI Btu/:ft2 I (KBtu) I {KB:tu) J (KBtu} j {KBtu) i j {KBtu) J f--I j 1 I J j J J I 1 I 2736 j .f.1.57 I 64 j 3 i j 524 I J 2J 1224 j 204 ,J 64 J 1 J. I 269 j J 3) 1095 .I 183 I 50 j 0 j .24 t 257 I j 4J 2415 J 403 ) -68 t 3 l· I 474 J I 5j 2182 I 364 J 67 .I 1 J ,I 43.2 .I l 6J 2223 I 371 I 67 I 1 l J 439 l 1 71 2534 J 423 j 68 I 3 j j 493 J J 8] 2232 j 373 J 68 I 2 l J 44.2 j I 9J 2316 I 387 I 66 j 1 I l 454 J I 1 OJ 51.2 I 85 I 18 J 0 I 36 J 139 j .J 11 J 2009 j 33.5 I 32 J 2 I j 369 I j 12 j 1391 J 232 j 29 .I 3 I l 264 J j13] 1894 J 316 I 3.3 ,j 3 I I 352 I J 14 J 817 I 136 I 18 I (l .I 23 J 1TJ -1 1151 2538 J 421-1, J 32 I 2 J l 4.58 j
'.1 16 I 2443 ) 408 j 36 I 1 -i J IJ46 j J 17I 1364 J 228 I 26 I 0 1 3 l 257 j J 18 I 1304 I 218 J 28 i 1 l 1 246 J J 191 2597 I 434 I 43 ' 2 I J 479 J 1201 .2332 j 389 j 38 j 1 j, 7 ,I 435 J J 21 t 761 I 127 j 19 I 0 J 16 I 162 j j22J 2607 j 4.35 J 30 j 1 I l 467 I J2Jf 2507 I 419 J 3.3 J 2 I i 453 1 I 241 1765 J 295 l 26 I 0 d 4, J 325 .i J25j 983 J 164 l 16 t 0 l 7 j 187 I 1261 2116 j 353 l 25 l 0 l a 378 I )271 .2285 J 382 I 32 J 1 j 1 415 j 1281 1980 j 331 I 31 J 1 l 1 363 I ]291 2115 j 353 j 33 I 1 I 2 I 390 j g I j j J j I I :L y
# KBtu = 1000 Btu;
63
Components of 'Iotal E.nergy Potentially Available
J I I t J
Source j
I j
j Solar Energy Incident on the Cover I I I 1 I i j j
i
Electrical Energy Input by the
Electrical Energy Input by the
Energy Gain from the Load•
Energy Gain by Conduction
Fans
B.lower i j j l I
J Total Energy Potentially Available j L
# KBtu = 1000 Btu
Energy Input {KBtu) #
91231
775,
386
122
35
10,549
+ solar and electrical energy stored in load
jPe.rcent I
l I 87 .• 5 l I T.3 j J 3.7 j I l. 2 l I o .• J
100.0
l J j
·1 j i J j I I I I i I l .I i I
64.
It can be seen that the t.o·tal incident solar energy -was
87 .• 5, percent of the tota.l energy supplied, whe·reas the total
electrical energy consumed :was only 7 •. :3 per:cent of the to-
tal.
5 .. J. J .. 3 Energy Ou-tput
Total daily l1eat losses :from the collec·tqr and ce>nduc-
tion losses from the drying cha.l!lber are given in Tables 6
and 7 • The values of heat transfer coe:f.ficient between
plate and cover, radiation coefficient from _plate to cover, -
radiation coe£ficient 'from cover to sky and w.ind coefficient
are also given in Table 1. Tah:le 8 indicates the total en-
ergy output .from the system for each day w.hereas Tahle 9
shows the total energy output components for the whole d.cy-
ing process. __
Prom Tab.le 8, it can he seen that the veQ.tila-tioJ1 loss
was highest on rainy days, a:nd also Oil days towa.cd the end
of the run,. It was the largest of component of loss, av·er-
agin.iJ 36 percent of the total energy output {Tab.le 9) ..
According :to Table 9, the total energ_y used .in the sys-
tem for the ,entire drying proct0:ss was about 8 .. 7 millio.n Btu.
The tot.a.1 amount o-f: water evapo.rab?.d during t.he drying per-
iod was about 1770 pounds.
the system were requ.irecl
from the wood.
Thus, about 4900 Btu input to
to evaporate one pgund of water
65
TllBL.E 6
Daily :rota.1 Heat LOSSBS f r:om the Collector
r l D J Conduct.ion Loss J Top Total Heat LOSSBS j l A t to ·the Ground I Lo.s:;5_ 1 f.rom the Collector I J y I {KBt. u) j {K.Bt U) ! (KBtu) it j f-J I l j l I 1 t 26 i 1 1B I 147 I I 2 l 9 l 66 I 76 i l 3 l 2 j 60 j 61 j J 4 i 26 l 105 I 131 j j 5 l 24 j 96 I 120 J l 6 l 23 i 94 I 1 17 j I 7 .I 30 l 108 l 138 l j s I 24 j 71 t 95 i J 9 l 30 I 81 ' 112 l a 10 1 5 I 59 l 64 j I 11 l 19 I SJ l 10.2 j I 12 l 22 I 54 j 76 l l 13 I 33 I 68 1 101 l 14 l -6 I 48 I 54 1 j 15 I 29 I 100 ! 129 I I 16 I 29 j 96 l 124 I I 17 l 20 ! 72 l 9.2 J I Hl J 20 I 65 l 85 j I 19 l 41 j 98 I 139 I l 20 l 32 I 85 I 118 I 1 2 :1 i ·12 I 58 I 70 I ) 22 J 30 l 104 .J 134 j J 23 j 32 I 109 I 141 J j 21.i I 26 I 74 'JOO j I 25 J 15 1 60. I 74 l I 26 t 25 l 85 i 110 J I 27 j 33 l 90 l 123 ! J 28 2 29 l 70 j 99 J I 29 j 28 1 84 112 i 1-1 l I j I l ~cot- I 679 ' 2,360 i -3,039 j
a al J I l i
# KRtu,=1000 Btu
66
TABLE 7
Daily Conduction Losses from the Drying Chamber
.--,---------...-----.-·-----------...----,.-----. I D J East I A J Wa.ll I J Y J(KBtu)j J---· i 1 I J 2 l 1 3 J I 41 I 5 J I 6 J J 71 l BI .J 9 l I 10J I 11 I J 12 ,i ·1 13 l f 1 4 i l 15 I I 16] i 171 l 18 J J 19 J I 20 i J 21 J J 22j J 231 i 24J J 25) l 261 1 27 I ,t 28 I J 291 i-i j I TOT I I AI.j j 1
1 .. {) J o. 6J 1. 3 j o. 8j l. Jj 1. 5 J l. 6 i 1. 31 l. 21 1. 5 I 1. OJ o. 81 o,.s1 1"' 6 J 2 .. 1.f J 2 .. 9j 2 .. Ji 2 .. Oj 2 .. :5 j 1. 5J 1,. 71 2. :2 l 2.HJ 2. 2j 2 .. 01 2. 71 2. 71 2. 1 i 2 .. ;ij
Southl iest j North i Roof !Floor j Total Wall j Wall i Wall i I I
{I{Btu) I (KBtu) i (KBtu} J (KBtu) #i {KBtu) j
o .. 9 J o .• $ l 1.21 1. o I 1.01 1. 2 I 1 • .iq l,. lH 1 .• 3 I 1,. 4 l t. 2 I 1. o I Oco 9 I 1.,51 2.21 2. iq 2"' o I 1. 71 2. 1 J L. 9) 1,. <3 I 2 .• 0 J .2 • .31 l. 6) L9j 2. 1 j .2. O I 1. HI 2 • .2 J
I 46. JI
I
0~ BJ L.,01 l. 3 j 1 .• 01 l .. :2J 1.-6 J l .. 8J 1,.,5 I 1 .. 8 J L,61 1.01 0.9j o. I 1 ... 71 2. 3t 2 .. 8 I .2 • ...3J 1 .. 91 2 .. Jj 2.21 2.0j 2 .. 1 I 2 .• 5 i 2 .. 3 I 2 .. o l 2.21 2 .• 71 2 .• 1 j 2., 61
I 52. 3 i
J
1. l J o. 7 i 1.3 j 1,. 01 1. 3 l 1. 8j l .. 91 1 .. SJ 1,. /¾.J l. 6J 1 .. 0 J 0.9 j o .. ~) 1 .. 6j .2. 7J 2. $.i 2. lJ 2 .. UI 2 .. Hj 2. 51 1 .. 7 J 2 .. q. l 3. 1 J 2.11 1.9j 2. 8j 2. 8J 2.21 2,. 6 i
J 54 .. 6j
I
O.oj -.0, .• 5 j 0.6J {),. 5 J O .. BJ o. 9 j 1 .. 0 i o. 9 J o .. 71 o,. 81 o. 6 j o .. 51 0.6j o,. 9 l 1 .• 3 I 1 .. 5J 1,. H 1. Oj 1,. 2J 1 .. 11 0'9 9 I 1. 1 J 1 .• 2J 1. OJ 1 .. 0 J 1. 3 I 1 .. J j 1,. 1 j 1 .. 2 I
7 .. 9 I 4 .. 51 O .. -5 I 4 .. 71 4 .. 0.1 4,. 1 J 5 .. 8 I 7.BJ
10,. 8J 1. 2 J s .. 91 B,. .t3 J
11. 31 3. 31
·12 .. J+j 15,. 7 j to .. 21 10,.. 6 J 18.81 H:i,.21 4. ?J
11. 4 f 14 .. 9 j 13. 4J 6 .• 71
10. H 12.6,j 12,. ·-4 j 13,. 91
I J 27. 5 l 263 .. ~l
I I
(KBtu) j -i
12 .• 1 .J 8 .• 2 .J 6 .. 2 I 9. 0 j 9 .. 4 j
11 .. 0 i 13.4 I 11.J .. 2 I 17.2 1
8 .. 0 I 10. J 13.0 l 15.5 J lO. 7 J 23.3 I 28. 1 j 19. 8 j 19. 2 j 29 .. 7 J 25.4 i 12 .. 6 1 21. 2 j 26 .. 9 l 22 .. 6 I 15 .. 4 i 2 L, 2 i 24 .• 1 I 21,.5 i 25 .. 1 l
l 494 .. 7 l
i
# KBtu=1000 Btu
67
'1:llBLE 8
Daily Total Ewergy Output
r--., ---ID I Evapo- !Hyg·rosco- j Venti-}Cond uc- JGi ven JCoLl.ector l '.I'otal l JA Ira tion j pie jlationl tion j to J Losses I Energy j aY I Losses I Losses j Losses j Losses I load I J cutputJ I j (KBt u) l {KBtu) l (KB tu) I {KBtu} l (KB tu} { KBtu) # j (KBbl) I 1 j j l I I j I I i I j 11 185 j j 73 I 12 l 16 j 144 I 429 I l 2j 128 3 I 45 j 8 j 3 I 75 j 260 I I .3 J 92 i I 83 j 6 j - i 61 J 242 J J 4j 1.25 1 I 56 I 9 j 16 1 131 I 337 I j 5 .I 135 t J 79 I 9 j 4 I 120 j 347 j 1 6j 125 I j 73 I 11 j 7 j 117 j 333 j
l 71 131 I j 86 J 13 I 4 I 138 j 372 l I BJ 112 I l 48 J 14 I 9 J 95 J 278 I J 9 I 112 I l 5.2 l 17 l 11 j 112 j 304. l I 10 ! 23 I I 101 ) 8 I - j 64 J 197 j l 111 89 ] 1 i 65 I 1 1 I 19 I 102 j 287 l I 12J 56 1 1 I 71 I 13 ,, ll I 76 l 227 j 1 j 13 .I 56 j 1 l 46 I 16 l 5 l 101 j 224 l I 14 ! 33 1 1 l 107 I 11 J - 1 54 I 204 i I 151 72 I 1 J 102 i 23 1 25 I 129 I 352 j 1 16 ! 68 I 2 I 129 l 2fl I 2 ! 124 j 354 I j 17 I 29 I 1 I 72 I 20 i - I 92 I 214 j j 18] 29 i 1 I 77 j 19 I 4 I 85 l 215 j I 19) 62 l 3 i 167 l 30 l 12 I 139 I 412 j 1201 39 I 2 I 149 J 25 I ,_ j 118 j 334 l J 2 1.i 10 I 1 I 119 l 13 1 ·- I 70 I 212 i I 221 29 1 2 J 151 I 21 1 11 i 134 I 348 1 ., 23 J 33 I 3 I 203 I 27 I 4 J 141 I 410 j i 24 j 16 l 2 j 151 j 23 l - j 100 .i 291 J 1251 7 I 1 l 76 l 15 l - I 74 j 172 j l 26J 13 J 1 .i 149 j 21 l 7 I 1 10 I 303 j i27J 20 J 2 l 184 i 24 i 2 I 123 j 355 j J28f 13 j 2 l 191 j 22 l 2 l 99 a 328 I J29t 10 I 1 I 196 l 25 t - l 112 j 344 j ;j I I I i i J I j
# KBtu = 1000 Btu;
68
TABLE 9
Compone11ts of Total .Energy out.put
l I .Energy J Delivered I Total J Sou.rce I Re~1 uiremen t 1 to, the Ki.ln I system j J i {KBtu} if j (Percent) I (Percent) t l I j J 1 .l .I Evaporation Loss I 1,851 I 32.. 8 l 2 1 • .3 j a J a I J .I Hygroscopic Loss i 28 I o.s j o .• 3 j I j j J j I Energy Given to J l7tl J 3. 1 j .2,. 0 l l the Load I l J I J J l J ' I Ventilation Loss j 3,099 j 54 .• 8 j 35 .. 7 j J i j J I 1 Conduction Loss J ;4:95 ij 8.~l l 5 .. 7 I j {Chamber-} j j j j I j J I I l Conduction Loss j 679 j J 7,.B I I (Coll,ector) J I l I I f I 1 J I Top Loss I 2,360 .l I 27,.2 ,I I (Collector) I j .J I f---I J j I .I j Total Energy output j 8168-6 j 100. 0 I 100,. 0 I I l J j l L
·J KBtu - 1000 .Btu
69
Based on the total energy consumed ~n the drying ··-
ch amber (not including collector losses) about 3190 Btu {Ta-
hle 9) were .reguiH3d to evapo,,rab:j one. pound of 'il!ater from
the wood. Accocding to Taylor (1982) the energy reguired in
a 12{l0-bd.f t capacity e.xper.i mental steam-heated kiln rangt":!d
from 2259 to 2590 Btu to evapqrate one pound of water from
the southern pine dimension lumber. He indicated that the
energy required decreased slightly with kiln tempt3i·ature
ovec the range from 175 to 240°F. Co.mpar2d to that co.nven-
tional kiln 1 the drying chamber used in this study was about
81.50 percent as e£ficient as the conventional kiln.
Energy Balance
The energy balance for each· clay, based ori the data oh-
tained for total energy input and total energy output for
each <lay (Tables 2 & 8), is given in Table 10. The differ-
enca in total energy input and total energy output per day
for the whole drying period ranged from -7.5,00D to +89.,000
Btu. A negative sign indicates tha.t tlH? calculated dai.ly
total energy input was lower than the output £or a g~ven
day,. These daily differencfaS ar·e caus<?d by errors i:n calcu,-
latin9 ventilation losses (ee.111. 3 .• 16) ar1d rounding errors in
measuring teraperat uces and d.aily solar insolation as well as
daily moisture content losses.
70
It can also be seen from Tables 3 and 9th.at difference
between the total energy :input and out.put for tue system :was
only 16#000 Btu~ Thus. the average difference £or O¥e day
was only about 580 Btu, only about 0 .. 2 percent of the daily
energy ~nput or output, indicating that the daily errors es-
sentially cancel out.
s .. 1.1.s J~f:fi ciency
The efficiency of the collector and of the drying cham-
ber, and the overall efficiency of the kiln, together with
daily solar insola tion, average initial moisture content,
daily average ambient temper at ur:-e, daily a verag£~ .saturated
vapor pressure and the average wind .speed are given i11 Table
11 •
Th,~ average efficiency of the collector was 4LJ.., 8 per-
cent ranging from 4.6 to 54.4 percent~ That of the drying
chamber was 3.2. 0 p,.?rcent and ranged from 5.3 to .83. 7 per-
cent. The average overall efficiencs of the kiln :was 17.4
percent with a range of 2.0 to 47.7 percent.
Empirical Model for Efficiency
i:1ul ti ple linear re9ression tests indicate that the ef-
ficiency of the collector (KFFCL) was significant.ly related
71
TABLE 10
Daily Enecgy Balance
DjDa:ily I Ini- lFinal I l"IC J To·ta1 J 'rotal JDif.ference i.r;q )Solar Jtial.l I I Energy !Energy J Total Energy I
Atinso- ! MC I MC iLosst Input I :outputjinput £. '.l'otal I tlation t l J J I l Energy outputJ
Yj {Btu/f t 2 } I {)'t) 2 (%) J ( %) j (K.Btu} I (KBtu} 1 ('.KBtuJ # i ·1--· I j l j J 1 I I j I 1 J 2736 j64 .. 4!58 .• 8 j5.6 I 433 j 429 j 4 I
:1 21 1224 . l 5 8 • G I 5·4. J] .• 9 I 228 I 26,0 ! -32 .... I . .,. I 3} 1095 I 54,. 9J 52 .. 1 j.2,.8 j 221 j 242 j -.22 i ,J 41 2415 J 52,. 1148 .. 1 14,. 0 I .393 . l 331 ,1 56 l I 5j 2182 J 48 ... 1 I 44,. 2 f3.9 f 360 I 347 l 13 l I 6j .2223 1144,. 2 i 40,. !¾ j 3 .. $ a 365 j 3.33 J 33 J l 71 2534 140.4J36.4 I 4,. 0 l 41).9 I 372 j 36 I j 8 I 2232 I 36.4 J.33 .. o J 3 .. 4 I 368 I .278 J 89 a I 91 2316 I 3.3. 0 J 2 9 .. 6 I 3,.4 I 377 I 304 I 7.3 I 11 O I 512 I 29,. 9 J.28. 10.7 j 122 l 197 I -75 .J f 11 l 2009 j28.9J.26.2 J 2, • .3 I 302 I 287 i 16 j 1121 · 1391 126.2)24.5 J 1,. 7 a 217 I .227 J -.9 j
• 13,1 1894 I 2lt,. 5 J 2.2,. ? J ·1. 7 ) 289 i 224 a 65 1 I 141 817 122.0121. ,I 1.. {) j 150 I 204 J -55 I PSJ 2538 121.8119.6 ]2.2 I .373 J 352 I 21 J I 161 2443 j19,.6,J17..5 i 2 ... J j 364 I 354 I 1 Q. j I 17J 1.364 117 .• 5116. 6 I 0.9 i 211 j 214 J 3 J I 181 1304 J 16 .. 6 115 .. 7 Jo .. I 203 J 215 j --12 J ,I 19j 2597 l 15. 7 i l],. 8 11,.9 I 393 l 412 I -20 I ,J 20 1 2332 i 13 .. 112 .• J 1. 2 J 357 I 3.34 I 24 1 J 211 761 I 12 .. 6 J 12,. 3 I 0 .• 3 cf 1.37 ,i 212 .I -75 j j.221 2607 112.3111.9- JO,. 9 J 379 j 34-8 J 31 j j23i 2507 I 11 .. 4110.iJ, I 1 .. 0 I 37:0 1 410 j -4-0 J )241 1765 J 10,.lH 9. '9 I 0.-'5 I 266 I 291 l ·-26 j 1.2s 1 983 I 9 .. 9 J :9 .• 7 .) o. 2 J 154 j 172 t -18 1 J 26 I 2116 I 9. 7 I 9.3 ) o. 14 j 30!3 I 303 a 5 I 1211 2285 I 9.31 8.7 J 0 ... 6 I 339 j 355 j -17 I I 28J 1980 l a .. 7 .I 8,. 3 Jo. 4 I 297 I 328 j -31 1 )291 2115 J 8.-;jJ 8. 0 I 0 ... 3 i 319 J 344 I -:25 J j 1 I I 1 ,1 j J J t.
* negative sign indicates that ene,cgy inpu:t is lower than energy ou-tpu·t; if KBtu - 1000 Btu
TABLE 11 Daily Efficiency of External Collector Kiln
D Daily Initial Average Average Average Collector Chamber Overall Solar Moisture· Ambient Sat, Wind. Effi- Effi- Effi-
A Ineo-· Con tent Temp: Vap, Speed. ciency ciency ciency lation2 Pr,
y Btu/ft (%) ("F) (mm-Ilg) (mph) (%) (%) (%)
1. 2736 64,4 59,6 12,9 8,3 48,S 63,8 35,2 2. 1224 58.8 64,1 15,1 9,4 43,J 83,7 47.7 3 1095 54,9 52,S 10.1 10,4 46,4 57,8 35,8 4 2415 52,1 60°, 7 13.4 7,9 47,6 47.7 26,5 5+ 2182 48,1 60,9 13,5 12.9 47,2 56, 2 31,2 6 2223 44.2 60,2 13.2 9.4 48,6 50,3 28,4 7 2534 40.4 60,1 13.2 5,0 47.3 48,5 26,6 ...... 8 2232 36. ,, 66,4 16.J 5,3 54.4 40,9 25,2 N 9 2316 33.0 71.0 19.1 12,2 51.2 42.0 24,S
10* 512 29.6 58,3 12.4 10.2 4.6 40,0 16,5 11+ 2009 28,9 62,6 14.3 8.1 49,5 44,8 24,3 12 1391 26.2 69,4 18,1 6,3 47.1 39,9 21.3 n. 1894 24.5 75.3 22,0 4,2 48,0 30,0 16,0 14 817 22,8 60,5 lJ,4 8,8 40.6 34,5 18,7 15· 2538 21.8 63,1 14.6 7,5 49,6 30,1 16,1 16. 2443 19,6 65,2 15.7 4,2 49,5 29.3 15,8 11. 13S4 17,5 69,5 18,2 9,1 39,6 25,5 11, 8 18 1304 16,6 71.J 19,J 6,8 41,2 25,8 12,4 19 2597 15,7 78,6 24,5 4.9 48,0 25,6 1),6
. 20. 2332 13,8 79,8 25.5 15,1 49,8 17 .2 9.5 21 761 12,6 70.8 18.9 14.8 24,9 15,7 6,4 22 2607 12,3 70,9 19,0 13,5 49,J 12,9 6.8 2) 2507 11.4 69.9 18.4 6.9 46.4 15.5 7,0 24* 1765 10,4 74.6 21.5 8.5 46,1 10,8 5,5 25+ 983 9.9 71,0 19,6 9.4 34,9 9,0 ),9 26 2116 9,7 67,9 17 .2 12.5 48,8 7,4 J,8 27 2285 9,J 72, 1 19,8 5,6 47.7 10.2 5,3 28 1960 8,7 75,0 21.8 4,9 50,l 7,4 4,1 29 2115 8,J 74,9 21.7 7,6 48,4 5,J 2,8
* rained during day time; + rained during niRht time
73
only by the daily solar insolation (SI) (at alpha;;:: .• 0001 lev-
el) uith an R-square value of o. 54 • However, the e.f:ficien-
cy of the drying cha:mber {EFFDC) and the overall ef.ficiency
0£ the kiln {KFP) were significantly related by the average
initial moisture con tent {I~lC) {at alpha=. DO 1 level} 1 wit.h
R-squa.re values of 0.90 and 0,.91 11 respectively ...
Using p olynornia.1 regression tests and several exponeri.-
tial moa.els (by SAS), the best IDO;d<.=ds .for thE! ef.ficiencie.s
of the collector {KFFCL) and drying chamber {.EFi'DC) and ·the
overall efficiency of the kiln {EFP} ~~re,
EFFCL=1 .• J7 - 4.{)9*log SI + 1 .• 70*{1og SI)2
- 0.0500*{log SI) 4
R-square= .. ?9 .; alpha-level= .. Qt)O 1
EFFDC= - .Q621 + .0189*{IHC) - .QD0118*{IBC)2
R-sguare 0=,. 93; alpha-lev,el= .. 001
EF.F - -. 9413 + .• () 102* {IMC) - .. 0000562* (.IHC) 2
.R-sguare=. 93; alp.ha-level=.001
{5 .. 2)
(5. 3)
During the 29 days drying period, there vere 8 days
during w.hich it had rained during the daytime {Ta.ble 10).
For the purpose of a.pplicatio~ to Burma co.ndit.ions for the
summer t,ime, an empirical equation tor the ove.cal.l e£ficien-
cy of tlie kiln (EF.FS) .only for the 21..,.sunuy days was also
74
developed, following the same proced u.i:e used above. The
best empirical equation was found to be,
EFFS - -.0794 + .0206*(IBC) - .000159*(IMC) 2
R-sguare= .. 96; alpha·-level= .• 000,1
Second .n}l!!.
(5. 4}
Th.is section will include general obs~~.rvations and com-
parison of actual and predicted drying times for the second
run conducted from 20 July, 1982 thr:-ouyh 15 August, 1982 ...
General Observations
The average initial moisture co.n-tent a.nd green specific
gravity of t.he sample .boards wece 54 .• 6 percent and o •. 63 re-
spectively. The ma ·teria1 of this ruq was be:tter guality,
highEir specific gravity aI1.d lo:wer- initial moisture co.nte:nt
than tile material used. in the fir.st ru:n. Th.e ·total green
volume of the :lumbe.r was 940 bo.ard .feet (78 .• 4 cu.ft .. ). Tile
average daily sola.r insolatio:Q. ducing that pe:riod was 183.J
Btu/ft.2 and average initial telliperature i;r1side the drying
chamber was 87 .. 3°F.. After 26 days of drying, ·the a~1erage
final moisture content attained was 8.2 percent •.
75
Comparison of Actual and Predicted Drying Times
The predicted dryiug -ti:me for this run was obtained :by
substituting appropriate data .into the prediction equation
{equ. 5 .. J) obtained from the .first run. ·rh,is :was accom-
plished by substituting the va.lu,es of average initial mois-
ture content {I1'1C) , total green volume. of the lumber {V) ,
average green s:pecific gravity of ·the sample hoards (S) _., av-
er.age daily solar insolation (SI), togethe1: with the ratio
of total solar energy incide.nt on the cover iQ. the tot.al en-
ergy a va.ilable {a taken as O. 87) , in ,equations (5 .• 3) ar.td
(3.26} the predicted dcying time thus obtained was 26 days
to reach final moisture content of 8.0 percent.
Co.w.parison of the daily actual and predicted drying
curves are shown in Figure 4 • The pi:edictad curve is
smoother than the actual curv,e because a constant da:il.Y so-
lar i.nsolation {taken to be the average for t.he en-tir.e dry-
ing period) as well as a constant B value of O.ij7 were used
throughout. . 'l'he lower slope of the predicted dryiug curv,e
during the first few days of dcying ls caused by the fact
that the H value (<~. g.. . the average R valu('1 for the first 9
days, t1ilhen t.:he fan speeds were. high, was about o. 83) du:cip.g
this period was lower than the avrc}rage R va:lue {0.87.) used
in the prediction egua tion ..
55
50
"5
"o
35
30 H
: 2J ~. j Predicted
15
Actual ..
...... , .... , ............. ,. , ........................ ,, ........ , , .... ,., , .... , 0 I 2 J S 6 7 8 9 10 II 12 IJ 1q IS 16 17 18 19 20 21 22 23 2ij 25 26
OATS Pigure 4!' Actual and Predicting Drying Curves of Sugar maple,
Second Run.
"'-.I Q\
77
.Although the actual drying was more rap.id than that
pr·edicted during most of tlie drying pe.a:iod they coiricided
toward the end, and the final predicted dryi.ng time was ver:y
close to the ac-tua 1 tota.l drying time ...
5 .. 1. 3
'.I'here are two approaches to im.prove the efficiency of
the kiln, one or both of
ace to increase tiH:! solar
the he:at losses •..
which may be im_plemented. :rhese
energy input and/or to decrease
5. l • .;3 .. 1 Increasing Solar Energy Input
The transmission efficie.ncy o:f the collector-cover ma-
terial used in this study :was only about 0.80 .• Th.is .means
that about 20 pe.r-cen t of the total sola.r energy incident on
the cove.r did not reach the a.bsorlH~.r.. If thi.s cover ma te:ci-
al is replaced ~ith a mo.re effective transmission material
such as glass, which h.as a transfilission efficie.ncy of up to
O. 95, only 5 pe:rcent of the tota.l incide.:nt solar energy will
be lost., That will increase the present solar energy input
by about 19 percent.. Furthe.r:more th~ tran.smis.sion of 1o{tg
wave ene.rgy from the a.bsorber through. the co11-e·c :will he re-
duced because of the low t.ransmi ttance value for loug_--wave
raaiation through glass.
78
Reducing Heat Losses
Only about 21 pe.r:cent of the total energy input to the
system had been used to remove , the water f·rom the :wood ('.ra-
ble 9). The :cemaining 79 percent of the total energy output
consisted of collector losses {JS pe.rce1~t) , venti.latiou loss
(36 percent), conduction loss (6 perce1rt), and load heating
loss (.2 percent). It is appa.rent that losses front the col-
lector aad through venti.lation are the ma_jqr ones that
should be reduced to improve the eff1ciency or the kiln .•
I'ieans of reducing losses from these two sources a:re consid-
ered separately~
Heat Losses from the Collector : o·f the .35 percent heat loss
from the collectm:-, abot1t .27 _perceQ.t was due to top loss and
the remaining 8 percent to bottom loss or conduct.ion lo,ss to
the grou.nd {'l'a:ble 9}.
According to theory and egua tion (3. 9) , top loss was
mainly affected .by the tem.peratur-e difference between the
collector and t11e ambient air. '£his loss increased as th.e
tempera.tu.rE~ 0£ the collector became hig:.her. This tempe.ra-
t.ure differences can be reduce,d by lo.wering the collecto.r
temperature which can be effected most easily by improvip.g
the air circulation system through the col.l,ector, and/·or by
increasing the blower .l:'nnning time, especially on sunny
days,..· The t:e1upe.catu.i:e o.f the col1ecte>r can be d-ecreased by
79
reducing the length of the air circuliition path or the total
.length o-f the collect.or .since the temperature in.side the
collector was increased with the length of the air-path.
The running time of the blower would be increased if the
temperature inside the drying chamber was lower. There will
he an optimum condition which depends on the daily sola.L' in-
solation, ambient temperature, the avecage initial moisture
content and volume of the lumher. The volume of the lumber
can be increased if the initial moisture content is low.
The maximum plate temp1~rature attained during the first
drying test was 138.5°F. Since this temperature is consid-
erably lo1<rer than the n1a.ximu.lll temJ.x~ratm:.:e o,f the roof
{157 .. 5°F) 1 the air-circulating system through the collector
was e:E.ficient.
According to the multiple linear regression test for
the ef:ficiency of thH collector taking sunny days only, it
was found that efficiency of the collector was not signifi-
cantly related to the daily solar i.nsolation,. It shows that
if there was no cain collector efficiency was :neither cle-
creased nor increased when the .solar insolatiou was changed.
It can also be seen from table 11 that for the sunny days#
the collector ef£ic.iency ranged only .bHtween 46.,. 4 and 54 .. 4 .•
:rhis also indicates that thE~ air-circulating syste.m throug.h
the collector was efficient ..
80
However, .further .research is nece.ssar_y to find a be·tte1:
system foe differeut weathe.r conditions a11d at di.fferent lo-
cations •
.In this study, the overall heat t-rans:t:er coe£fic.ient of
the plate which consisted of a 1/2 inch thick layer of gra1,1·-
ula ted charcoal# was taken as O ... ll32,9 .Btu/hr-:ft2- 0 ? and total
conduction loss to the grqund was a.bout 679"000 Btu {Table
9) .• . If the thickuess of the charcoal layer is increased to
3 inches the overall b.ea t transfer coefficient will be only
about O .. JOB Btu/iu:-...,..ft2 ·-°F.. :J?he11 the total conduction loss
to the ground will become about 169,00Q Btu, sav~ng about 75
percent of the initial loss. This coqduction loss will .be-
come only about 2 percent of the total energy output instead
of the present 8 pe.cce.nt ..
According to Ta.ble 1 O, the e:fficiency of th-e collector
was ve.ry lo"N on those days dur.ing which it had rained du:cing
the day time.. It 1was a minimum on di1J 10 (4 .. 6%_) during
which 0 .. 35 inch of rain ·fell bet·ween 12 am and 8 pm,. Thus,
solar drying would not be ve.r.y effective d ucing rai.ny .season
at locations *hich have heavy rains during the rai.ny seasoµ,
because of low so.lar insolation a:nd high losses fr:om the
collector.
The tempera. ture inside the co11ec to.r was a maxim um d1,11.·-
ing the day time and a minimum during the night. The di£~
81
fe.rence between the maximum and minimun1 temperatures was up
·to 70° F.. If the· collecto.r tempera tu:c~ can mairrtaiu a·t hig.h
temperature after the sunset, blower can run more thus in-
creasing the solar energy input~ The simplest method to
maintain th.is col.lector temperature would .be to cov~r the
collector-cover with an opaque ma't-Q:i:ia.l such as a plywood or
a tarpaulin •. This will also reduce the transmission of
lo.ngwa·ve radiation through. the cove.r .• Thi.s is qui·te pos.si-
ble in the developing countries where labor cos·ts are low.
Heat Losses from the Drying Chamber : From Table 8, it can
he seen that ventilation .losses were very high on rainy
days. This happened because of long periods of lov solar
input and high humidities of ·the amh:ien.t op. these days,
causin9 a high humidity inside the cham.he1: .... T,hus, the hum-
idi.ty inside the chamber -was higher t.ha11 the set-point va-
lue of (RH1) which controlled the exhaust fan, resu.lti:ng the
operation o:f the exhaust fan almost th.e -whole day. T.he .best
wa_y to minimize this loss is to shut down the :kiln on :rainy
days.
The vent should be also closed Yith a lid to prevent
the out.let o:f hot air from the chamber :When the .blo~er is
o.ff. It should also be c:losed either automa t.ically or manu-
ally after the timer is turned of£. If, ·there is no leakage
of hot air during the night the to.tal vent.i1atioI,.l loss may
-82
be reduced by 16.3 percent. :This is e,;1ui vale:11t to 5 ... 8 per-
cent. of the total energy output. (Some ventilation may be
req_uir-ed if relativ1::, humidity inside the kiln .~.xceeds 92
percent in order to prevent mold, stain, etc.)
Comparing the conduction losses from the walls, roof
and floor, the condi.1ction loss to t.he floor was the greatest
(Table 7) ; about 53 percent oF th,2 total conduction loss
from the chamber or about J percent of the total energy out-
put. .If the presfrnt gravel-flooi: (overall heat transfer
coefficient of a..bont 0.52 Btu/hr-ft2-°F) is replaced by a 4
inch-thick layer of sawdust (overall heat transLer coeffi-
cient of about 0 .. 1 Btu/hr-ft 2 -°F, according to the Heating,
Ve11tilati119 and Air Conditioning Guide, 1958) , conduction
losses from the chamber would be reduced to about 18.6 per-
cent of the total conduction loss from the chamber. This is
about O. 6 percent of the total energy output ..
5. 2 ,2:!;;tH-GI.tEEN HOUSE Klb_!
The following discussiJn of the semi-greenhouse kiln is
diveded into three sections.
observations of the results,
TIH::; ficst consists 0£ general
the second discusses the ef.fi-
ci1:mcy o:f th~ kiln, ar1d the third is concerned with develop-
ing an empirical model for the efficiency of the kiln.
83
5. 2. 1 Genera.l Observations
The total green volume of Yellow poplar { _L;ir-iodendron
tul:iQifera L,.) used in this st.udy was 96 board feet.
average gr:een volume speci.fic gravity was 0,. 43 and the total
ove:ndry :weight o.f the luruber calculated from the total gree:n
volullle and average green s_;pecif.ic g.ra vi-ty was 214 pounds .•
This is close to the value o.f 211 pounds calculated from t.he
tota.1 :final weight (230 pounds) 0£ the dried lumber and t~e
average :final moisture content of the four sample .boards
The average i11itial moist,ure conteµt o.f the £our sample
boards ~as 50. 4 percent. The average final mo.istu;ce content
attained after 28 days of drying was 8.8 perce~t •. Thus, the
average daily moisture co.ntent loss was about 1. 5 percent ..
The average initial and final moistuce contents of ·the
air-dried sa.mp.les were 15,.9 and :5 l .. 8 percent .respectively .•
The total drying time was 34 days and the average daily
mois·ture conten·t loss was therefore 1 .. U percent., about 2/3
that for solar drying.
The drying cu.rve based on the a ve:cage moisture contents
of the four-solar-dried samiple boards .is shown in Figu.ce 5 •
Also shown is a similar curve fo,r the air-,.dried lumber,
based on the average of four sam:p.le, boards ..
50
"5
"o
C
15
10
5
/Air Drying
Solar Drying
.......... , ......... ,... .,... '' .. , ......... . '""*"' , .... , ''""' O I 2 3 q 5 6 7 8 9 ID 11 12 13 1q 15 16 17 18 19 20 21 22 23 2q 25 28 27 28
DRYS
Figure 5: Solar and Air-drying Curves of yellow poplar, Semi-Greenhouse Kiln.
lio .i::-
Ba.sed on these results, it ca.n be seen that lumber can
be solar dried during the fall in Blacksburg (35°9'N,81°~
to a final moistm:e content beloN 10 p,ercent while w-it.h
ai:c-,dr: yin9 it was impossible to attain a fina.l mo.is-ture con-
tent much belov 15 percent.
i'he average daily solar i:nsola tion (9nl_y for 15 days
for which data was available) measured at a 45° tilt angle
to the south :was 1B16 Btu/ft 2 and :r-a.n,gt.~d from 512 ·to 2736
Btu/ft2. _
'1'.he maximum temperature attained in the kiln was a.bout
112.5°P, while the minimum relative hum~dity was about 22
percent. The minimum and maximum tem_:perature of the ambie:n-t
during the who:le drying period was 19°F and 82°£ respective-
ly ..
The average dai:ly power consumption by the c.irculation
fan was 0.6 KWhr, cor:-cesponding to 2048 Btu per day.
s.2.~ Efficiency
Table 12 indicates the dai.ly overall efficiency of the
kiln .for 15 out of the 28 days of dry.ing., together cwit.h 0th-
er statistics. The average ove:call efficieucy 0£ the kiln
was ca.lacula ted to be 8 •. 3 percent.. However., this value is
not a good indicator- since the calculations :f,or the e.f·fi-
cienc_y was only started f :com. day 9 when ·the averag~ moisture
86
content of the lumber was 32.5 percent {Table 12),. If t.he
calculations include th:e whole drying per-iod,
efficiency would undoubtedly b~ higher.
the average
5. 2 .. 3 ~m 2iri@!. l'1 ode l fQ!: the E f.:fici en:£!. Q.f th~ K~l!l
"J?ollowing the same procedu.ce as was u:sed for external
collector :k.iln, an empirical model for the overall efficien-
cy { EF-P) o.f the semi-greenhouse kiln -was obtained~ It is,
BPF = -~-0381 + ,00982*IMC - .0000207*SI
:a-sgua.re= .• 99; alpha-level= .. 000,1
where,
IMC= average daily initial moisture conteut in perce.nt
SI -= daily solar inso1a tion in Btu/£ tz·
However, ·for purpose of simplification, the empirical
model with only one .independent variable, the initial mois-
ture content {IMC) was testea. again and it was found to be,
EFF = -.Q167 + .00988*IMC
R-sguare-= .. ~8; alpha le ve.1=. 00 1
This is not as good a .rnode.1 a..s given by e!"1ua t:iou (5 .. 5), but
it is more pcactical and easier to app.ly.
87
1' AB.L.f: 12
Efficiency of Se rui-G:ree Ilh o use Kiln
i j
jObser-tDayjAveragej Daily JAverageJAverage i Oveca.l.l ! jvationJ jinitialj Solar j Ambien-t jSa t. Vap. J E.ffi ciency.J l I I ~l C IInsolationj Temp: J Pressm:eJ ] l i I (f:') ..-t l Btu/:ft2 1 {o E} I mm-Hg l ( %) j
j 1 I 91 32.5 l 1273 I 54::. :;i "
10 ... 8 l 27 .. 1 i I 2 ,1 1 O I 28.~ l 2145 I 54,.:2 I 10.7 j 19.4 j
I ] l 11 J 24.7 I 1912 i 46.2 .j <l.O I 15 .. 6 j :I 4 I 121 21 .• 7 I 2251 j 47. Lt l 8, .. 4 i 12. 5 I I 5 I 131 18 .• 9 I 1298 j LU) .. 9 ] 6,.6 j 11. 4 } a 6 I 141 17.4 l 2115 J 55':.)f J ·11,..2 j 9 .• 1 l J 7 I 'J 7] 14.0 I 1381 j 41.9 i 6 .. t 6.2 I t 8 l 21 i 13 .. 0 i 1776 j 42. 4 I 7 .. Q 1 5,.3 A J 9 I 22) 12.1 j 20.98 1 41 .• 6 t 6.$ I 4. l j j 10 I 231 11. J j 2082 A /.J.2. 0 I 6,.9 I 4 .. 1 l J 11 I 241 10 .. 5 I 2032 J 45 .. 5 j 7 .• H I 2 .• 1 j I 12 .i 251 10,. 1 i 1681 1 J.J.8.5 J 8.7 l 3 ... 2 l I 13 I 26.1 9. 6 I 1951 j 61.0 j 13.6 I 2 .. 2 l .I ·14 j 271 9 .• 2 I 1528 I 53.'f ,I 10 .. 6 j 1 .. ·4 t l 15 I 281 9aa0 I 1722 l 53 .• 8 l 10,.6 I 1.3 I
.J
88
E!J:Uation (5. 5) indicates that efficiency of the kiln is
high when the initial moistuce content (IMC) is hig.h a.nd it
is low when the solar insola tion {SI) Ls high .• :I'his indi-
cates that when the solar insolation becomes higher the kiln
becomes less efficient. 'l'his is believed to be related to
the increase in top-loss from the cov,ff£ due to the 11igh,er
absorber temperature.
As metioned in the precet1ditHJ chapter, the data ob-
taiued in this study was not sufficient to calculate the
sources of energy input or output,. Therefore ~t &as not
possiblE.\ to ana1y:ze the energy .balance relations in the
semi-greenhouse kiln in the same manner as was done in tne
external collector kiln.
Chapter VI
APPLICilTION. IN BURMA
Apply.ing ·the empirical .models (e;3:u.atio11s 5-.3 and 5-4)
obtained .for the external collector ,Jdln together with equa-
tion (3.-26}, the so.lar dryiug ti.mes of so:me commercially im-
portant Burmese species of dif,ferent .speciof:ic gravity were
predicted. These predicted drying times for both the normal
and summe.r climatE~ conditions are given in Table 13 • The
thickness and volume of the luaber (V) to be solar dried
were one inch and 83 cubic feet {1000 bd£t) .respectiv,2ly.
The averagt.~ daily solar insolation (SI) a~d average initial
temper:at m:e inside the drying chamber {T) were taken as 2500
Btuj.ft2 and 100°F respectively,.
Si11.lilarly, pr-edicted drying times 0£ the same .species
and of t"he same thickness obtained fo:c: the semi-g.reenhouse
are given i:n Tabli;:~ 14 .•. · The volurie of the lumbe.r (V) to :be
solar-dried lilas 8 cubic-feet {about HW bdft},. To get a
comparison. the values of the variables, average daily solar
insolation (SI) and average .ini.tial ·temperature inside the
kiln {T) were taken to be same as thos~ used in the external
col.lector kiln,.
However, since the em:p.irical model for the kiln eff i-
ciency obtained for this kiln was limit.ad to data o.btained
89
90
TABLE 13
Pr:e11ictiri.g Drying Times for so.me Commercial Burmese \~oods using External Collector Kiln
Initial [1oisture Content 20-50 percent Final Moisture Content 8 percent
r I Sr. J Trade J B otanica.1 JNo.JName j Name J l i 1----· l I J J 1 jTeak }Tectona I j J gr an dis J 2 j2yinkadoJXylia I l j dola:i:hri for.mis I 3 ! Pauda uk j Pteroca rpus l J j macr-ocarpus j 4 I Thi tya j Shorea J l Aoblongifolia ! 5 J Ingyin fPa.ntacme I J tsiamens~s J 6 )In )Dipterocarpus J J JtuberculatQs J 7 ]Kanyin- JDipterocarpus ,) Jbyu Jalatus l 8 J Ka11yin- ,l Dipterocarpus 1 J ni l t.urbinatus J 9 jYernane ]Gmelina arborea J 10 J Sagawa i 3iche1ia cha-m,paca .111 i Hnaw 1 Adina cord if olia 112 i Binga J Hitrag-yna I j Jrotundifolia J 13 l'Thinga.n J .Hopea odorata 114 I Pyinma ! Largerstroe:mia j I J speciosa 115 ! Yon J Anogei.ssus ] J i accumina ta J16 jTaukkyanJTerminalia tomentosa 117 I Thinwin j Millettia _pend ula J18 JTaong- JSwintonia I ,tthayet .lfloribu.nda J 19 jTha.di jProtium seeratum J20 JThitkadoJCedrela toona
j G.:reen j I j j J j I I i I I I l l I j I j 1 I I I ] I J l i ! J I I I a 1 1 i
Sp.G£
0.:59
0,. 75
0 .. 86
0.78
o. 7 3
0.57
Q_,. L~2 0 .. 43 0.58 0,. 5.5
0,.64 0 .. 52
0.74
o .• 71 0,. 85
o .• 71 .o. 4-,
I Time I Time I I NormalJSummerj i (day} I (day) A j i I I l 5 j I i l I j J I .I 3 I l j j I ,I J I I J I I 1 I I i I I
1 I
10-181 :I
12-241 1
12-221 J
14-26 t I
12-24.1 J
11-22j I
10-18 i I
10-18 .I j
6-121 6-12j
10-181 8-16 j
a 11-20 J
8-161 j
12-221 I
1 l-22j 14-26 i 8-16}
I 11-22)
7-1:41
f j
5- 9j I
6-11 J I
6-1 OJ j
8--121 i
6-11,j l
5-10 J j
5- 9 J I
5- .9j j
J- 61 3- 61 5- 91 4- 8J
I 5- 9) 4·- 84
,i 6-101
I 5-101 8·-14j 4- 8 j
j 5-10J 4- 71
91
TllBLE 14
Predicting Drying Times £or Some Commercial Burmese Woods using Semi-greenhouse Kiln
Initial !oisture Content 20-30 perceQt Final Moisture Content 10 perceu-t
r , J Sr .• I Trade I Botanica.l I Gre:eu j Time I )No .. JName I Name t Sp.G.c.j Hormal J I i l I (day) I (day) J }---~-----+-----------,---+------+-----f i l I 1 I l :I 1 )Teak J T,ectona i 0.59 ;I 11-14 t I I I grand:is 1 ,I l l 2 tPyinkado I Xylia t 0,.7.8 :I 16-19 J I l I dolarbr:if or mis I I j I .3 JPaudauk I Pterocarpus .t O. 75 j 15-18 1 J l I macrocarpus I l J l 4 ,JThitya J Shorea l 0 .• 86 I 17-21 i 1 :J I oJ:JJ.ongifolia i I J I 5 Jingyin J Pantacrue I 0~78 1 16-19 J 1 I I sia.mensis I 1 l J 6 I In I Dipt.e.rocarpus I D .. 13 t 14-17 J ) J J tuberculatus J J l J 7 JKa.nyinbyu 1 Dipterocarpus j 0 .• 57 I '11-14 I t I ,I a.lat us I I J J 8 I Kanyi:n- I Dipterocarpus I O .• 60 1 11-1 ti i 1 Jni J turhinatus I i I l 9 I Ye1uane J G.melina ac borea ,} 0 .. 2 1 7- 'J J J 10 JSagawa j I'lichelia champaca I 0 .. 43 j 7- 9 j l 11 I Hnaw i Adina coardifolia 1 0,. 58 I 1 l-14 I J12 JBinga j Nitragyna I 0.55 j 11-13 I ,i J J rotund.ifoli.a l 1 j J 13 JThi.ngan I Hopea odora·ta j 0.64 j l.2-15 j 114 I Pyi nma I Largerstroemia. speciosa J D. 52 l 10-12 j )15 }Yon j Anoge.issus accum.iI1ata j 0,.74 I 15-18 I 116 jTaukkyan I Ter.minalia tom.entosa i 0,. 71 :1 33-16 I 117 IThinwin 1 r1illettia pendula 1 0.85 I 17-21 ,I 118 l'I'aung- I Swintonia flo-ri.buna.a I D.55 J 10-13 I J jthayet I 1 j J 119 jThadi l Prot..ium seeratum J 0.71 ) 13-16 j J20 1Thitka.do J Cedrela toona t o.rn J 9-11 J L---.l.
92
between 32.5 percent, initial moisture content and B.8 per-
cent final mois·ture content, the drying times g.i ven -were
predicted only b,etween 30 percent ini tia.1 d.nd 9 percent f i-
nal moisture content.
'fhe prt:H'l.icted drying times obtaiJ1,ed for hot.h ·types of
kilns indica,te th.at. the lumber with about 50 per-cent m.ois-
ture content can be dried within 6 to 26 days (table 13) ,
whereas the lumber initially at about 20 percent moisture
content can be dried below 10 percent moisture content with-
in 3 to 18 days (table 13 & 14).
Other wor.K in Bucma has shown that green .lumber two-
inch thickness and a.bout O .• 6 O green speci fie gravity can he
air-dried (under an open-shed}
tent within 7 veeks (Kyi,1981).
to 21 percent moisture con-
Therefo:r:e, solar drying
preceeded by air drying is ,Jui te favorable to dry the lnmher
bEi.lo:w 10 percent moisture content within one ~eek to three
For some locations which have heavy rain during the
four-,-mo.nth-rainy season ( .-p ,g . ·--• .... Rangoon) 1 solar drying can he ' used for eight months. Thus, for these places, air dryi.ng
under a shed can be started during the rainy season, espe-
cially for the re.fractory species,.
93
Estim.atinq Solar Drying_ &Q§.t iJ.! 12..i!:£!\El
Ba.sea on the designs of these ·two types of solar kiln,
the author estimated that he could build a solar kiln o.f ca-
p:aci ty two· tons2 at a cost of 2-0,000 Kyats3 including stick-
ers1 etc. According to the _predicted drying times ohtai.ned
three charges of air-dried lumber could be dried per 111011th
for at .least eight months per _yea:c. Th.erefo.r:e there will be
total of 24 chacges or 46 :tons _per y.ear.
Assu:rning that the capital investment for buildi.ng the
kiln will he borrowed from ·the World :Bank or Asian Develop-
ment Bank wiU1 a payback over 1 O yea rs :in 10_ annual payments
at one percent interest~ It is a.ssu JRt~d that tfoe kiln wi.11
be totally depreciated and has no salvage value,.
The annual loan payment will be K 2111.60 ($281.50)
equivalent to K 2111 .. 60/48 = K 44.00 {$5 .. 86). p.er ton.. As-
suJUing maintaina.nce cost for the kil.n as K 500 {$66 ... 67) per
year there will be added about K10 ($1.33) per ton for main-
taina.nce .•.
It is assumed that, an operator at a salary of K 500
per month could control four kilns. Thust with 12 charges
or 24 tons of lnmber per month operato,.r cost wi.11 be K 21
2 unit for measurement of lumber in Burma; 1 .ton = 50 cubic fee·t = 1. .. 4 cu.bic .meter
3 Burmese Currency; 1 $ = 7.5 Kyats
94
For loading and unloading the lum.ber, labor cost. is es-
timated to be K 10 ($1.33) per ton.
Electric power consumption :fo:c the .kiln will be at most
15 KWh r per day. The electric power rate in Burma is a.bout
K 0 .. 25 pee KW hr. Assuming an average dryi.i,1g time per charge
as 7 days, the po"Wer cost per- ton wil.l be 1/2 .x
{15x7) x0 .. 25=K13 {$1. 75). _
.Finally, the tota 1 cos·t to sqlar""'.".d.r_y one to.n o .f air--
dried lumber is:
1. Annual payment on loa.n K 44 ($5 .. 87)
2,. I•l aintainance cost K 10 ($ l. 33)
3. Wages for operator K 21 {$ 2. !;30)
4;. Labor cost K 10 ($1..33}
5,. Elec·tric powe.r cost K 13 {$l. 7J) ________ . __ , _______
Total Cost K 98 ($13,. 07}
This cost excludes air--dry ing cost an.d following the
same procedure, the cost for air cirying of green lumber can
be estimated as follows.
It is estimated that an air-drying she-d o:f capacity .1 O
t::>ns (6,000 bdft) wi.11 be required to supply the solar kilu ..
This will cost abou·t K 5,000 ($666,.67). including stickers,
etc. It is assumed that there will be five charges per year
and thus 50 tons of lumber can be dried per year. FolloYing
95
the same assumptions which were made fqr the solar kiln# an-
nual. loan payment per ton of green lumhe£· will be K 10. 56
($1,.41) .• Assuming Hie maintainamce cost for the shed as K
200 ($26.67) per year, this will cost about K 4 ($0.53) per
ton of green luml>er,.
It is assumed that the sam:e Of)_era.tor of the solar kilns
can also handle the air drying operatio~~
additional cost for the operator.
Tims the.[>e is .no
Labor costs for loading and unloadin9 ace 'the same as
for solar drying, K 10 ($1.33) per ton.
Inventory cost for air-drying one ton 0£ green lumber
.for two months, taking the cost of onE· to.r1 of lumber (Group
One) as K 1#600 ($.213.~3), and with an interest ra·te of 8
percent, will be 1600x.08x(2/12) = K 21~33 ($2.$4) • Thus
the total air~drying cost for one ton of green lamber is:
1. Annual payments on loan K 10.56 ($1 .. 41)
2. Maintainance cost K 4.00 ($0 .• 53J
3. Labor cost K 1 o. 0.0 ($1..,33)
4. Inventory cost K 2 ·1 .• 3.3 {$ 2 .. 84):
Total Cost K 45 .. f39 ($6 .• 12)
'N:ierefore, Lt will cost about 98+4'6=K 141+ ($19. 20) to
dry one ton of green lumber using solar drying preceded by
air a.rying. Compare to the p1:-ice of group one Burmese spe-
96
cies (about K1500 per ton) r total d..r:ying cost is abut 9 per-
cent o-f the lumber cost. In the United states solar drying
preceded by air drying 1 was e.stima t~cl to cost $21.. 27 per
thousand board fe-et of y,el.low pop.lac {Weik, 198..3).. '.rhi.s is
about 10.5 pe.r:cent of the total lumber cost, since the price
of 1000 board £eet of yellow PQ.p.la:c is about $ 200 .•
It is not necHssary to ai.r dry teak { '.Fectona g_raW,iis }
which has been girdled, since the moisture content of the
log is about 25 to 30 percent.. Th us ·the cost for sola.c dry-
ing of one t<>n of girdled.-t,eak .lumber will be a.bout K 98 ...
The estimated costs given here ar~ mostly overestimated
and are also based on a small scale operation. Thus costs
will be reduced, in a large scale opera·tion.
Chapter VTI
SUMMARY AND CONCLUSIONS
ExpE1r imenta.l drying studies were made on two types of
solar lumber kilns, a.n external collector ·type and a semi-
greenhouse type of kilns •.
Tim cha:rges 0£ five gua.rter inch green suga.r maple lum-
ber were dried in an external collecto:c prototype solar kiln
at the u.s.. Forest Products Laboratory, i:1adison, Hisconsin,
during ·the sum.mer o:f 198.2.. The kiln, was instrumented to
collect the regu.ired data for calculating the energy bala.uc·-
es ...
In the fir.st run, the energy .balance for each day for
the whole drying _period was calculated .... from these results,,
the daily efficiencies of the collec·tor and dr.yi.ng ch.amber,
as well as the overall effici~ncy of kiln •e:ce calculated.
A sta-tistical analysis syste.m (S.l\S) ·was used to obtain
empirical .models for the efof:iciencies o_:f the collectqr and
drying cha mher" and for the overall e:fficiency of the kiln .•
Using the model obtained for the overall efficiency, an em·-
pirical equation for _predicting th,e average da:ily moistu.n::
loss was developed.
Following the same procedure as in the firs·t run, t.he
cequired data were co1lect?.d fro.m the second run to use in
97
9B,
the predicti v1:1 eg:uatio:n developed from the .f i.rs-t run. . Com-
parison \'las then ma.de o:!E the predicted and actual d:r:ying
curves obtained in the second run.
A single cha:r:ge of 9/8 inch g-reen yellow pqpla.r lumber-
was dried. in a semi-greenhouse kiln at Vi.rginia Polyt~chnic
Institute and Stab~ University, Blacksburg, Virg"inia, during
the fall of 19 82 •.. · f'or purpose cf compai:ison, a matched ,pi.1,e
of the same thic.kness and same species was also ai.r-d:cied at
the same time.
Based on data collected from the solar-drying experi-
ment, an empiprical model for the overall efficiency of the
k:iln :was obtained. Using this model an e,iuation f m: p·ced-
icting daily moisture loss was developed., similar to that o.f
the external collector :kiln.
The conclusions drawn from the external collector kiln
experiments are::
1 .. , Five-quarter green sugar maple lumber ( 54 - 64% t1C )
can be solar dried in an external collector sola:r ki,ln to a
moisture content below 9 percent i.tl less than one month dur-
ing the summec., at L'iadison (43°5 1 N.,.89°23 1 W), Wisconsin ..
2 •. ·· The available inchl;ent solar energy was about 88 pee-
cent and the total electrical energy consumed was about 11
99
percent of the tota.l energy pot.entially available ·to the
system.
3. The total energy ontput for the entire drying process
fincluding collector losses) was about 8.7 million Btu# 0£
which 5 .. 6 million Btu ;.,1as input tiH,i drying chambea::-. The to-
tal amount of water evaporated was about 1770 pounds.
4. The major losses from the kiln were collector losses
(355S} 1 ventilation loses {365i) a:nd conduction losses from
drying chamber (6%). The remaining 23 percent of total en-
ergy input was utilized for removing water from the wood and
for minor losses.
5. The average efficiency of the collector was 44.8 par-
cent, ranging from 4.6 to 54.4 percent. The efficiency 0£
the collector (EFFCL) for the whole drying period (29 days)
was significantly related to the daily sola.r insola tion
(SI)... The empicical .morli~l for. the efficiency o_f the collec-
tor is given by,
EFFCL - 1.37 - 4.09*log SI+ 1.70*(log SI} 2
- .. 0500*{109 S.I)4
.a-square= .. 89; alpha-level=.0001;
100
Howevec, the efficiency o.f the c9llector only fo.c th.e
2·1 sunny days (excluding 8 rainy days} @as not sigui.fica.ntly
rela tea. to the dai.ly solar insolat in ..
6 •. _ The average e.fficiency o:f th:e drying chamber :was 32 .. 0
percent and ranged from 5.3 to 83 .• 7 pei:cent. The efficiency
of the drying chamber (EFFDq for tile whqle drying period
was sign.ificantl_y :c,ela ted ·to
content of ·the lumber (IMC).
the a v-erage in.i·tial moisture
T.he empirical model for ·the
efficiency of the drying chamber was,
BPPDC = .Q627 + .01B9*(INC) - .000118*(IHC)2
alpha-level.=.,.001;
7.. The average overa.J.l ef.ficiency of the kiln was 17 .. 4
percent, ranging from 2 .. 8 to 4 7. 7 percent., The overall ef·-
ficiency of the kiln (E.Fr') for the whq_le drying period {29
days) was significantly related to the average initial mois-
ture con.tent of the lunibei: {IMC). The empi.:cical model f<>.r
the overall efficiency 0£ the J;:iln {EFFJ, was,
EFF -- -.()413 + .()102*(IMC} - .. 00005;62*(.I11C) 2
R-sy uare= .. 93; alpha-level=.001;
The e mpirica.l model .for the overall e:fficiency of the
Iciln for the 21-sunny days only (EFFS) was,
EFPS = -~0794 + ~0206*µMC) -.Q00159*(IBC) 2
R-s~1uare= .. Q-6; alpha-Level=. {WO 1,;
101
Based on the results obtained for the semi-greenhouse
kil.n, it can be coricludad th.at;.
9/8 green yellow poplar lumbe.r can be so.lar
dried by a semi-greenhouse kiln to a moisture content belo\t
9 percent in less thau one month during the fall at
Bl~ ·, b · · ( 3· 5 09 I" o 1 0 P) ~r • -· ·· a.cKs urg., . N., o ,.,, , vi rg.1n.1.a .• With air drying it ~as
impossible to attain a final moisture content much belo14 15
percent.
2. _ The aver:-agf., overall efficiency o.f the kiln for 15 out
of 28 days of dr_y:ing f o.r which were o.bta.ined {a:ve.r-a~ge ,.in.i-
t.ial r,c, 32. 5-9 %} was 8 .• 3 per-cerlt .• The overall e:fficiency
of the kiln {E:PF) ~as significa:nt.ly related to the averag:e
initial moisture content of the lumber and daily solar iu.so-
lation. A practical empirical mod-Hl for the overall ·effi-
ciency was,
EFF = -.0767 + .Q0988*IBC
R-squa.re=. 98; alpha-leve.l=.tl01;
Final conclusions reached from: thi.s study are,
1. Solar d:cying times of difterent .lumber :species at
different locations .for both solar 'k.ilns can be predic·ted by
the following empirical equation.
102
where,
MCL= daily moisture content loss .in percent
EFP= tlie value obtained from the efficiency model
SI= daily solar insolation in Btu/ft2
ACY= .area of the collector-cm1er in f t 2
:R = ratio of total solar energy incident on the collec-
tor cover to the to·tal energy available to the syste.m
V = green volume of lumber in £t3
SG - green specific gravity
:i'i - average Lnitia.l temperat-u:cr~ insid.e the drying ch.amber
in °F
2. _. A comparison of the actual drying curve observed. i:n the
second run of the external collector kiln showed good agree·-
ment with the predicted drying curv,e obtained from the empi-
raica1 equ.at.ion.
J.. Based on this study it is believed that. solar tlr_ying of
lumher preceded by air d.ryin.g will .be su.ita.bl-e for condi-
tions in Burma, in order to attaln a £inal moisture content
be.low 10 peccent vithin one to thrf'..!e weeks ..
LITERATU.RE CITED
American Society of Heating and Air-conditioning Engineers. 1958. Beating 1 Ventilating and Air Conditioning Guide. 36th Edition. American Society of Heating and Ai.r Conditioning Guide, Inc •. 62 ~orth st. New York 13* NY. 503 pp ..
Anonymous, 1980 •. One ray of sunshine~- the energy crisis. lJo.rthe.rn Logger and Timber Processo,r,, March,, 198:0 •. pp 24-25 ...
Banks, c •. H. . 1969.. . Solar dr_ying of tim;ber - a development study. CSIH Sub·ject. SRcvey O/Hou t l0., i?.:cetoria, .South A .. frica, June, 1969.. 27 pp. (Un_publishedJ ..
Bob, I.. 1981,. Solar~heated .dry kilns,. A.merican Pulpwood Association, Forest Prod .. 5 .. 43, 10 July, 19.81.. 5 pp .•
Bois, P.J. 1977. Constructing and op~:c:ating a smal.l solar-heated 1.umber dcyer. u. $ .. _p .• .lL, Fore.s:t Service, Forest Products Ut.iliza tion Technical He port No .. 7... January, 1977. . 4 pp ...
.Brace Research Institute. 1975 •. · A surv,ey of so.la.r ag:cicul ture dryers, •. · Technical Report T99.. Decem.be.r,, 1975. r1cG.i11 University .Fae ulty o.f Engineeri11g.. Brace Besea.cch InstitutH, 1'1ontr-ealJ Quebec, Canada ..
Casin., R • .F. 11 E. B .. Ordinario, a.nd K. Tamayo. 1969 ... · S9lar drying of apitong. 11arra, .red .lauan, and tangi.le. The Philippine Lumberma.n 15(4) :23-JO...
Casin, R._F., P .• __ .v .. Bawagan .. 1978,.. Solar drying -of .lumber in the Philippines •. _ Proceedings o.f the solar d.rying workshop.. . !'la.nila, Philippines.. October 18-2·1, 1978,. Organized .by ·the ministry 0£ energy ..
Choong, E. _T., and D ... M. Wetzel. 1981.. Feasibility of utilizing solar and forest biomass energy .for dry.ing Mood in Louisiana. .Re.search proposal submit·ted to Division o:f Research and Develop.me.nt, D~partment of Natural Resources, state of Louisiana. f'ehruary;, 1981.. 10 pp. (Unpublished)
103
104
--------------. 19Kl. Feasibility of u·tili:zing solar and forest. biomass energy for: drying wood, in Louisiana .. Prepared for Department of Nat.u.ral Hesom:ces 1 state of Louisiana. January, 1983.. 87 pp.. (Unpublished)
Chu.ndo.ff, M., E. D .. Maldonado, and .E •. Goytia. 1966 •. , Solar drying of tropical hardwoods,. .For. Se.rvice .Research Paper ITF-2.. April,, 1966. 26 pp.
Cooper, G .. A. 1966 •. Utilizing of solar- energy for drying of wood.. North Central Fo:rest E:xperiment Station, Ca.rbondale, Illinois,. June, 1966,. _ 8 pp... (U}i.puhlished) ..
Davidson, R. w.. 1980 .•. Se.rvice Re.l_:)Ort :for esta.blislun.ent of the Forest Research Institute at Burma.. JS pp. (Unpublished) •. ·
Denig •. J, and E~ M. Wengert. 1982. Estimating air-drying moisture co.ntent losses for red oak and yellow pop.lar lumber. Por. Prod. J. 32{2):26-31.
Dohn, G,. . D. .. 1963,. . D,egrade in so.lctr ilcying o.f mahogany (Sweetenia marcophyl1a, King).. Repo.:rt submitted in partial fullfilment of the .requireme~ts fo.r credict in Ge.nera.l .Forestry 191, Problems in wo:i:Ld .Forestcy, Rio Piedras, Puerto Rico. August, 1963. 21 pp. { Unpublished) ..
Duffie., J.,. A • ., and w. A •.. Heckman... 1974.. Solar energy thermal processes. A r«iley-Inte;1::scie:nce publication. John Wiley & Sous, New York., N. Y.. 386' pp ....
Duffie, N. A., and D. J. Close.. 1978. The optimisation of a solar . timber drier using an adsm:hent energy store. Solar Energy, Vol. 20: 405-411
Forest Dept., Burma.. 1979,. .· Report submited to the .Hinistry of Agriculture &, Forests. 211 pp.
Garg, a. !?. , 1974 .. , :E.f.fect of dirt on transpare.n·t covers in flat-plate solar energy col.lec·tors. Solar E:~ergy, Vol .. 15:299-302 •.
Gough, D. , K .. " 1977.,. The design and ope;ration <>.f a so.la:c timber kiln,. Dist..rihuted by the .D~p.artm,ent of Fo:xestry, Suva. No. ,67" 1977. pp 17.
105
Guo, X. z., 1981. Drying lumber with sola.r energy .. Industry o-f Forest:cy .Products (Linch.an Go.ngye)'". No,. l, 7-8 (Ch,,:q Timber Company of Fuyang Prefecture, Anhui, China. (Cited in Po.rest. Products Abstract No. 1230, June, 1983 •.
I:z;la:c, B. 1981.. Solar~ heated dry kilns. Technical release 81-R-36, July, 1981.. American Pulp-wood Ass9cia-tion ... 1619 Massachusetts Ave •. , N.w., ·washi11gton, n.c. 20036,.
Johnson, c.. I..... 1961.. . Wind-pow:er:ed solirr-heated. lulitbeu dryer. so. Lumber, 203(2,532):41-42, 44.
Kumar, s .... 1981 .... · Utilization of solar en,ergy in India. For. Prod. J. 31 (9): 10-12.
Kyi, w,. 198 l. Preliminary Studies: on the ai:c-seaso.uing behaviour o.f leza { Laqe:i;:stro-em;i&!: tontentosa ) .. F'c • .R. I .. Leaflet No. 6, Forest .ResHarch. Institute, .Yezin, Burma .. February, 1981. pp 7~
------... 198 l. . Investigation ~n the physical and mechanical properties 0£ thadi and tinyu,. . if.; R. L. Leafl.et Mo,. 10, Forest Research Institute, Yeziµ, Burma~ February, 1981. pp 10. .
Lee, J. F,. , and F .. w. S,ears. , 196,3. Thermodynam·ics, Seco.nd Ed .... Addison - Wesley Publ .• Co,., .Palo .Alto.
Luik.ov, 11 ... v. 1966,. .. Heat and r1ass Tra1is.f,er in Capillary-porous Bodies.. PHrgamon Press, Ne'W Y,ork ...
Lumley, T ... G., and E,. , T .. Choong. 1978 •.. use of sola.r e.nergy to dry southern bottom.land ha:rdwoods. Paper presented at Session 33,, drying and storage, 0£ the 3.2:nd Annual i1eeting of the Forest Products Research soc.ie·ty • June 29, 1978, Atlanta, Georgia.. 10 pp •.
Maldonado, E., and E. Peck. radiation in Puerto Rico.
1962. Drying by solar For. Prod •. J._ 12(10):487-488.
Nartawijaya, A,., K,. Kadir, and K. Sali)d. 1976 ... Solar drying o.f jeungjig { Alhi,sia, !a.lcat$ Back,.) and rubber wood { ,!!~Ye!! brasilie.nsis Muell ... Arg,.) .. Forest Products Research .Institute, Bogor-Indone.sia, .January, 1976.. 11 pp ..
Martinka, E. 1969.. Predrying of some ,G.hanain timhe.rs. Forest .Products Research I:nst:itn,te (Kumasi, Ghana). Technical Note No,. 1 L •. September, 1969.. 8 pp ..
106
L'.Ic,. Comick, P ... o .. , 1980.. Sol.ar heating system for kiln drying lumber •.. su:nworld., 4 (6) ., 198{'1: 204-20 . .6.
:Na th,, P .. , a:ud B •. L. Bali •. ·· 19 ., A process for the small sawmiller and timber-based industry.. Wood Seas01ling B~anch, P •. R. I., Dehra Dun, India. 10 pp ...
Oliveira, .r .... c •. s •. 1978,. . Solar drying of green oak {Quercus spp.) lumber.,.. Unpublished M.$ .. thesis •.. · VPI &. SU, Blacks.burg, Virginia .•. · 61 pp .•.
Oliveira, L •. · c., s .. , c •. Skaar, and .E •.. fi .... Weng,ert. 1982. Solar and air lumbe:r drying during -winter il\: Virginia .. For. Prod. J. 32(1):37-44.
Panshin. lt,.. J •. and c •. deZeeuw. 1970 ... Technology., McGcaw-Hill, New York ..
Textbook of :wood 705' pp,.
Peck., E. c.. 1962 a. Drying 4/4 red oak by so.lar h.ea·t. For. Prod. J .•. 12 (3): 103-107 ..
• .. 1962 b ... Drying lumber by solar ene,rgy .. Third Quarter., 1962,.
Sun at
~Plumtre, R •. A ... · 1967. The design and operatio:g. 0£ a sma.11 solar seasoning };:iln on the equator in Uganda ... · Co:ramonw,. For. Rev., 46(4):298-309.
-------------.. 1973,. . Solar kilns: Their suitability .for developing countries._ ON Ind. Dev •. Organ., ID/WG •. 151/4 •. 38 PP•
.. . 1979. Sim.ple so.lar heated timber drye.rs:: Design, performance and comm.ercial viabili·t:y.. Comm9nw .. Por. Rev •. •· 58 (4) :243-250 •..
Ramos,, J,. B. F,., et §..1 1981. study on methods of drying the .a.mozonian timbers.. Center of wood Tech.nology, .Bel-e,m/PA-Brazil, 1981 •. 5pp.
Read, w. B., A •. Choda, and P,. I,. Cooper. 1974. A solar lu.mhec kiln. . Sol .•. Energy, 15 ( 4).: 309·-316.
Rehman, M. A. and o .. .P .•. Chawla. . 196 l. Seasoning of timber using solar energy:.. . Indian .Forestry Bullen.tin No .. 229 {New Series).. 13 pp ..
Rodger, .A.. . 196.3.. A Handbook of the .For,est Products of Bu.rma.. Superintendent, Government Printing & Stationary, Rangoon •. 149 pp.
107
Rosen1 H. N., and P •. Y. s. Chen. 1980. Drying lumber in a kiln.with ·external solar collectocs. American .Instituta of Chemical Engineers. No ... 200, Vol .. 76:82'.-'89,.
Ryley, T.. 1980 •.. Solar timber kilri. .Australian For. Indus. J. ~1980. pp 25-26.
Schneidec, A., F .•. Engelhardt, and L •. Hange;c. · 1979,. Vergleichende untersuchungen ube.r di~ freilufttrocknung und solartrocknung von schnittholz lll\ter mitteleuropaischen wetterverhaltnissen. Ho.lz/als Roh und Werkstoff 37(1979):427-433 •.
Sha:cma, S. N .. , .P .. Nath, and B. L. Bali... 1972.. A solar timber seasoning kiln .... · J ... Timber Devel. Ass.oc ... Lndia. 18 { 2) : 2 8- 3 L,
Sharma, s,.. M.,.. P .. Nanth, and s .. P ... Bandoni. 1979 .. Commercial T:cials on a 7 .. 1 cu. M,. solar kiln. India:i;i For, • .Bull, •. No •. 274 1 Forest Research Institute and Colleges, Dehra Dun, India.
Sharma, s. N. . 19 80. . Feasibility o:f solar tLmber drying in tropical locations.. Paper presented at the IU.F:RO Division V Conference ... Oxford, England, April, 1980.
Shelton, J. . 1975. .. Underground .sto,:cage of hea·t in solar heating systems .•. Sol,. Energy Vol. 17, pp 137-1'.43 ••. ·
Slterwood, G .• E. 1979.. Perfo:r:mance of wood in a do-it-yourself solar collector.. For. Prod ... Lab •. , Res •. Note FPL-0204, 1979.
Shottafer, J ... E., and c. E .. Shuler ... 1974. Estimating heat consumption .in kiln drying lumber •. Life science and Agriculture Experiment Station .•. 'l'ecb.nical .Bull .. 73, Sep·tember, 197f.J,. .· 25 pp .•
Siau, J .. , F. 1971.. Flow in Wood. ... Syracus,e University Press •. Syracuse, N •. Y. 131 pp.
Simpson., w. T. 1977... Solar lu.mber designs for devel:oping countries,. Proc. Practical Application of Solar .EuergJ to Wood ProcE~ss.ing ... Blacksburg, VA,. January 6-7, 197'7. Published by For.. Prod ... Res,. Society., .Madison, llL. PP• . 56-61.
-------------•. 1981.. Tcip :cepq,rt travel ·to Sri Lanka :from February 1, 1981 to February 14, 1981. 3 pp. (Unpublished) .•
108
Simpson~ w. T • ., and J •. L. Tschernitz. dry kilo gets trial in Sri Lanka. February.,, 1982. pp ... 13 .•
198 2. Low---cost solar World Woqd .J,,.
Simpson, !& .. T. 198.2. Trip report on FPI. sola:c kiln activities in Sri Lanka and Burma ... October,. 1982 •. 1 pp ... ( Unpublished} •
-------------.. 1982.. Insta.latiou of solar .kiln at the Forest Research Institu,te at Ye.zin., Burma,. . .Service Report. . 97 pp.. (Unpublisltecl) ..
Singh., Y •. 1976.. .s·tudies on a .solar timber seasoning kiln .. '!PI.RI Journal, 6 (1}" 1976. pp i.n-4.4 •.
Singh, Y ... , and A •. Chandra... 1978. Design of a so.lar timber seasoning kiln. Paper presented at :1n·te.rnational Solar Energy Cougress., Jan. 16-21, 1978., New Dehli, India .•
Skaar,, c,. . 1972,. . Syracuse N. Y .•
water in Wood,. 218 pp._
Syracuse Uni ver.s.ity Press .•
--------- .. J977 •. Energy requirements fo:c drying .luilber,. Proc •. · Practical Application. of So.lar Ene.rgy to Wood Processing. Blactsburg 1 VA •. January 6-7, 1977. Published by ·For .. Prod.. Res. so.ciet:y, Madison, WI. pp .•. 29-32 ..
Stein.mann, D. E • ., H .. p. Vermaas,., and J .. B •. For.rec,. . 198D,.. So lac timber drying Jt.ilns: Part 1: Review 0£ previou,s systems a.nd control rneasui::es a1td descriptio,!l of an automated solar kiln.~ J •. Inst. Wood Scienc~. 48. pp. 254-257 ..
------------ --. 1981. Solar timber drying kilns:Part 2: iv! icroproces.ser control of a solar .k i:Ln .•. · .a,. Inst. :woo a Science.. 49. pp ... · 27-31,.
Tao, Y .. , a.nd c. Hsiao.. 1964.. Lumber solar drying at Taichung-.. Bull, •. No,. 63-N-490/C, Natl .... · Chung Hsiug Univ .• , Taichung, Taiwan.
Taylor, .P ... w.. 198 2.. A compa;c:ison of enecgy .ro1a,;ruirements for kiln-drying southern pLne at different drying temperatures. Wood and Fiber.Sc., 14(4). 1982. pp 246-253 ..
Terazaw-a,. s.. .. 1963"' . .Predryiug equipmen,t of lulllber .. , J.. Woo.d Processing Ind. {Japan) 7 (10): 28-3 l ..
Troxell, H. E., and L. A. Muller •. 1968. Solar lumber drying in the central Rocky Mountai~ region .... For .. .P.rod. J.. 18 { 1) : 19-2 4 ,.
Tscherni·tz, J. L., and w •. T .. Silllpson. 1977. Feasihility of utilizing sqlar energy .for in developing countries,. u.s .. D .. {\ .. Fo_rest Prod •. Lab .. , Madisop, HI~ January, 1g11.
Solar kilns: drying lu:iabe.c Service, :For ..
63 pp.
--------------... 1979,.. Solac-heat.ed., forced-air, lumber drye:r fo.r tropical latitudes •. · Sol. Energy YoL •. 22, pp. 563-566 ..
Tschernitz, J,. L.. 1981. Ins·tructions for o,peration of FPL solar kiln,/Sri .La.nka (Horana) •. U .. $ .. D..:A. Forest Service, Por. Prod._Lab., Madison, WI. February, 1981. 10 pp.
----------------. 1982.. .. Operation of FPL £orced air solar dryer, Forest Research Institute, Yezin, Burma.. u.s .. p • .1t. • . Forest Service, Poe. Prod. Lab .. , Had.iso11, PU. Aug·u.st, 198.2,.
USDA Forest Service. 1974,. iood hand.hook--wood as an engineering Jnateria.L, . US.DA Agric .• Ha.ndbk •.. No .•. 72 •. · u. s •. · Govt •. Print .•. O:f:f., WAshington, DC.
Vick, c.., B. 1977.. A solar air-heater as a supp.lemental heat source in lumber force!l-a.i.c dryer. 4710 • .FS-SE-3501-6 (6.5) .•.. Final study repqrt •.. Athens,. Gt:orgia. November, 1977,. . (Unpublished) •. ·
Vital, B .. .. R.. 1976 •. · Uti.lization of solar en,e~rgy for: seasoning wood. Re vista Ceres 23 {l.25): 1-10, l976.. 10 pp.
ffeast, R •.. c.. 1967.. Handbook of Chemistry and .Physics. 48th edition, 1967-68.. The chemical rubber co ... , 18901 cramrnod .Parkway, c leveland, Ohio, 44128,.
Weik, B,. .· R,. Practical drying techni;1ues for yellqw:-poplar S-D-R flitches .•. 1982. Unpublished rl.S. Thesis .• Virginia Polytechnic Institute & State Univec.sity, Blacksburg, VJL. 63 pp .•
Wengert, E. M •. · 1967.. Ene:r-gy losses fro •. m a solar dryer,. Unpublished M. s .. thesis.. Colorado State University 1 .Fort Collins, CO. 6Q pp.
110
-------------. 197 l. Improvements in soJ.ar dry kiln cles.ig.q,. . u. s .. D .. A .• Forest Ser.vice, .For.. Prod •. La.b.., Madison, WI. Research Note FPi.-0212,, 1971... 10 pp .•
------------- .•. 1974,. How to reduce energy consumptim,1 :i,,n kiln-drying lmnber. u.:s.D.l,l,. ~'orest Servic~, For'9 Prod. Lab., L'ladiso.n, WI.. Resea:rc;h .Note FPL-0228, 1974.. 4 pp.
·-------------, •.. · 1960. Solar heated. lumber dryer for the small business. Virginia Coopei:-a ti ve Extension Service. VPI & SU, .Blacksburg, VA,.., April, 1980. 16 pp ..
Whaley, s. n~ 1981 .. Solar kiln drying .. ----------------·------- ·--· . - pp.. 28' · .29.
Yang, K. c. 1980.. Solar k.iln performa:rice at high latitude, t+8°N.,. . For ... ]?rod. J •. 30 (3) ::pp,. 37-40
Youngs, R. L... 1959.... Recomme11da tiq.ns of. the Madison confE?rence 011 fundamental res•earch in wood drying·.. For •. · Prod. J. 9{~ :121-124.
Zimmerman, o~ T.# and I. Lavine. 1945. Industrial Reseacch Se.rvice•s Psychrometic Table,s and Charts ... · Dover, N ... H., Industrial research service, 1945 •. · 162 .P.P•
Append..i:x A
·poffEST A.REA AWD .FOREST INDJJSTftIES OF HIJRH.A, MALAY SI.A, .AHD PHILIPP TN.ES
Item Burma EiaLaysia
I ] J jForest Acea (acres) j96,000,000f 20,0.00,001) J I l J Reserve Forest (acres) j 24,000,000 j 14,000 ,00,0 i I J jLog Production 1 5,600,-000j.231.,IWO,OOO ! (cubic .ft) (1970) I j J I J )Lumber P:roduction ]21.,tHHl,OOOj 82,0,,00,000 I (cubic :ft) ( 1970) I .I I I i JPlywood Production l 380,0901 8.,000~00-0 l (cubic ft,) ( 1970) I I I I I
I Phili.ppi:nes I
l :1 31,00:0,000 l j 23,500,000 ,t j388,000,000 i j I IJ7., 700,000 j ,I I 20 ,.000,000 J ]
] J j I j I j j I i j I I
J No. of Saw.mills J 207 (1979) I J J l j No'"' of Plywood I1il1s I 3 ( 19.7:9} 1
650(1979) J 1
37(1979) I
1 325(1976) J
J 33{1976) l
j 100 {1.976) I
I 15 { 1976) J
j j
1 i l J No. of :pry Kilns i 20,{ 1979) I 1 J J I No. of P rese.rvation I 1 { 1979) I J Plants l J J l l
sl 82(1979) j
I I I I ___________ __.. _____ ;;,__. ______ -'-----~
Adopted from Davidson (1980).
]l 1
Appenclix B
Tnrn1rn EXPOH'r OF BU.Ht!IA .FO.R ~"'ISCAL YEA.R 1977-78,
i j HOPJ?US ton) Cubic Meter j Value I Source I /ton * 4 I (.Kyats i.p l j 1 j l T housaitds) j
J 1 j t t l j I jTeak log I 45,266 ) ·s 1,479 :I 233,722 I J j l JHardwood log j 9,630 .I 17, .J3lJ J 7,272 I l J j jTeak Conv,ersio.n j 38,653 1 5'.c4, 114 I 160,918 J J l i i:Hardwood Conversion 1 171 I 239 ,I 205 3 1 ! J JPlywood, Veneec., I j j j I i i J ?losaic, Par,{ue·t & etc I j 1 7.95 J I I J JTotal J 93,720, I 153~ l66 ;) 402,912
* Hoppus ton - unit for measurement of log in Burma = 63. 7 cubic feset : 1. 8 cubic meter
ton - unit for measurement of convta:rsion - 50 cubic feet = t. 4 cubic meter
+ Kya t - Burm,ese Currency; 1 :ji = 7 .. 5 Kyats
Adopted from the Repor·t {1980} o.:f forest Department to
the Mlnistcy of Agricultui:e and Forest, Burma.
112
., a I ,j J I I J I I j I j j I 1
REVIEW OP SOLAR LUMBER KILNS
C. 1 !J.li.l::£.ED STATES Qf AfilERICA
C.-.. 1.1 Dofulg!il!g, Wisconsin
One of the earliest studies on the solar: drying o-f lum-
ber in the United States w.as carried out by Johnson (1961}
at Dodgeville, Wisconsin {42°5B'N,90°7',W). A solar .lumber
dryer with a capacity o.f 400 board feet4 was built in Octo-
her- 1959,. The south wall, containing :four windoMs of si.n-
gle-streng-!::h glass, was sloped at an angLe of 67. 5° with the
horizontal. The total area of the glass W<i.s .37 sguar,e f-eet.
Air circula.tion was prqvided by a fan W;hicll ~as driven by a
wind mill, and vents were also prov:i.d?d fol:" dehmuidify ing.
Two tests were car-ried out duri.ng the smu.me.r a:ud it was re-
ported that one inch cherry lumber dried from 15.5 to 8 per-
cent in 52 days and the same thickness of white oak: lumber
dried from 60 to 6 ... 5 percent in the same period .• 'l'he other
test was begun during the fall and it was noted that one
inch black cherry lmrtber of in.itial moisture content 50 per-
cent was dried to 8.5 percent after 220 day.s.
4 unit for measurement of lumber ln the United States 1 board foot= 1 inch x 1 foot x 1 foot 1000 board feet= 83 cubic feet= 2.~ cubic meter
113
114
Madison. Wisconsin
In 1961, Peck ( 196 2 a,) d;esigne<l and tested a solar
dryer at Hadison, Wisconsin {4.J/.>5-'N, 890.23 1 W). _ The r:oof and
all Ji.falls except thu north wall, which was sheathed :with
plywood, we;r:-e coverf:1d with. two layers of tra:nsparent plas-
tic._ The size of the dryer .was 7 .• 5x l2. 7x8 fe.et with a ca-
pacity of 425 hoard feet. :rlu:ee charges o.f green ope-inch
red oak lumber were dried to 20 percent moisture content ..
He reported that this required 33 days during Hay and June,
23 days during Augus-t. and September, and 105 days :fcoiil No-
vember through Harch. Peck also noted that the temperature
inside the d.ryer was a.l;;.ra ys higher, and the relative humidi-
ty inside the dryer was genera.lly lower than -ambient condi-/
tions. He concluded that the so.la.r drying time to a mois-
ture content 20 percent can be ceduced to about one-hal.f
that req:uired ·to ai:r d.i:-y the same lumber.
c .• l.3 Sauk £itY., Wisconsin
'.l'wo other solar gr2enhouse type dry-fH,s, designed by
Peck ( 1962 b) , were cons·t.ructed at a small sawmill in Sauk
Wisconsin. 'IU1e capacity o.f each
dryec was about 2,500 .board feet and ain circulation in each
kiln was provided by two 18-inch £aas •. The dcyers were
identical except that th.e fan.s in one dryer were powered b_y
115
1/3 HP electric motors ~,herea.s in the other they were driven
by a wind mill.
Fort Collins Colorado , --- __ , _____ I --------
In 1962, a greenhouse solar drye.r with a capacity of
1500 board £eet was co:nstrur;ted at the Colorado state Univ-
ersity, Fort Collins, (40°36'N .. 105°4 1 W) .. The dryer wa.s 18
:feet long froill east to west, and 10 fe;et Yide fr:om north. to
south .• , A.11 walls except the north wall were covered with
translucent fi.bf:~rglass (li!here:as the r:oof :and the no.cth wall
were covered with fiberglass~ The roof was tilted at an an-
gle of 17° to the horizontal, facing south. Troxell and
Mueller ( 1968} tested seven charges of one-inch Engelmann
.spruce and lodgepole pine lumber at diffen:'!nt seasons. .Each
charge consisted of an e gua.l mixture of both species
,. According to tht..~ir report 1 it rf,iguired only 5 to 13 days to
dry the lumber to 1.2 percent moisture conten-t du.cing summer
and fall 1 and 13 to 25 days during the winter~
c.1.s In 1977, Wengert designed a.nd constructed two semi-
greenhouse type solar kilns at Virgi,nia Polytechnic Insti-
tute and State University, Blackshurg(35°9'N• 81°0 1 W). The
first ki.ln had a capacity o.f 150 to 200 board feet with a
116
maximum board length of 4 feet •. The flo.or: and the wall.s ex-
cept the south :wa.11 were well insulated... The roof Yhich :was
tilted at 45° '.to the horizontal , and the south £acing wall,
'ffere covered with two layers of t:cauluc~ut weather re.sista:q.t
polyester film two inches apart.
Oliveira, Skaar and Ren.gert (1982) tested a mixture of
one .inch thick red oak and white oak lumber during the win-
ter o.f 1978 .. They found t.hat th,e lumber reached 20 a:nd 6
_percen-t: Rloisture co:nteut in 80 days a:nd 125 days respectiv·e-
ly.. The average They also air dried a pile o.f end-matched
samples during the same timB :p.eriod,. This lumber reached 20,.
percent mois·ture con tent in 105 days a~ii 14 ;percent in 162
days.
A description of tile qt.her k:iln which was conducted in
this study is given later u.nd.e:r pro,ced ure.
The third solar .kiln d,e.signed and co11structed at
B.ladcsbm:g in 1979 had a capac.i ty of 1500 boa:c-d :feet,. The
roof consistail of a double lay~r
ped at a 45° angle facing sout4.
of cl,ear .Plastic and slop-
It ·w1as 17. 6 fee·t long £rom
east to west, 6,. 2 feet wide from south to n9rth .. The south
:wall was 3.1} f ee·t high a 11d the no:rth wall was 9. 5 feet high
The walls and floor ·wece insula:ted with 4-inch-thick fi-. '
berglass faced with 1/4 inch plywood inside and out.
117
One inch thict black walnut 1uIDber were dried during
the period from t'e.brua.ry, 19 80 th i:-ou.gh April,, 1981 •. · Afb~r
69 days of clryi.ng, it reached 8 perce11t moisture coutent ..
The. initial moistuce content was repq.r:t.ed to be 71 .. l;i per-
cent.
c. 1.(:i
A small sola".1: heated lumber drye;r 1dlich was .basically
th.a same design as the dryer of Joh.n.so:a (1961) was described
by Bois (1979).. Johnso.n constructed and tested this dryer
with greater holding capacity of 750 board .feet and oth~.r
i.mprovements •. The south wall which was ti.lted at 50° to the
horizontal consisted of four storm glass windows .with a to-
tai g.lass area o:f a.bout 47 sguare f,e-et.·
c. J. 7 Magj._:~Q!!, Wisconsin , .E.xternaJ:-c:ol.lec-tor IX.Bti
Tschernitz and Simpson ( 1977) p:ropo,sed two.. types o.f .so-
lar .lumber dry .kilns, one a greenho,use type and the other- an
external-co.llectoc type They teste.d the feasibility of
using solar energy to j_mprove lumber drying by small-to-med-
ium-scale operators in developing countries ...
.Based on the .feasibilit..y study, tb;e.y designed and ·test-
ed a prototype solar dryer of l, 000, board feet caf?acity, at
the Forest. 21.·oducts Laboratory, in Madi.son i:n 1978. The
118
collector :was e.xterna 1 to the drying chamber and ·was hori-
zon taL. . It was designed to be locat~d at t.he Republic of
the Philippines, located at 14°N latj_tude. Thus horizontal
orientation was considered to be satisfactory in order to.
take advantage of the low expense of building t.he collector
in the ground,. ..
The description of this sola.r kiln., which was used in
the main portion of this stud.Y# is given in the pro,cedure.
Ba ton .Rouge , Louisiana
Lume:1.y and Choong (1978) designed a.nd tested an experi-
mental solar kiln of 360 board feet capac:i ty at the Louisia-
na State University, Baton Rouge (30°281 N# .9l 0 l0 1 W}., in 19T7
• The kiln was first designed and operarted with a horizoQ.-
tal fl.at·-plate collector but was later, modified by r~plac-
ing the flat-plate collector with a tb,ree d:imensional box-
·type collector,. The collector area was 26 .. 25 squa.re .feet
inclined at a 49° pitch to the south.. six bottom.land hard-
wood species ·were tested, :starting frQm April, 1977 and it
was re.ported tltat elm, sweetgum, hackbe.r.ry and sycamore
which were dried during the sutllmer to a final mois·ture cou-
tent of 15 peccent in 10 to 17 days, wl~ereas ash, hackberrJ
and .. red oak which were dried a. uring t}i,e spriilg required 18
to 27 days to reach 15 p,ercent moisture. content .. They al.so
119
· concluded that solar-dr_yi.ng rates :were two to three times
faster than ai.r-drying,.
C .. l. 9 Carbondale, Illinois
.An experimental-scale exterr,tal collector type solar
kiln of capacity 500 boardf'-eet :was designed aud tested by
Rosen and C.hen { 198()) a-t; the North Central .Forest .Experimen-
tal Stat.ion, USDA Po.rest Service, Carbondale {37°4.2 1 1'1,
89°12 1 W), Illinois.
Tile co.llector was t.il ted at 37. 5° to the a!1orizonta.l and
the collector plate was built from the aluminium beer cans.
The d:rying chamber was about 8x8x6 .• 5 :f~:et in dime.nsions, and
the walls, ceiling and floor were well insulatedv
.Five char9es 0£ one-inch thiCk 9.re.en yellow po,plar luni,-
ber were solar dried th.roug.h thB su:mmer of 1978 to the
:spring of 1979 to a final moistu:ce content o:f 1.5 percent ..
Each run was mar1e on a load o.f about 500, board feet.. Simi-
lar loads lie.re air dried at the sam.e time.. Solar d.c.:ying
times ranged f1:.-om B to 5.3 days depending on the sea.son o_f
the year. The authors co.nc.lu.ded that solar _drying was 2 to
3-1/2 times fast.er ·than the air drying .. ,
120
C. 1. 10 §.Qg2 Commerci;al !iil.rill
c.1.10.1 Somerset, Ohio
Deco Materials Service of Somerset (Anonymous, 1980)
had developed a kiln and d.rying methoc1, using. solar :heated
air, .. The capacity of the kiln was about 190 MBF {NBF=1000
board feet). 'l'he 5.,000 square foot shea. was painted with
sor.1e specially absorbent coating. 1\ ti1,o-inch air cavity was
created on the outside of the building, by applying translu-
cent. plastic film over furring .strips to the .sides and :r:oof .•
ltnother- wir1e air cavity was created 011 the inside, using the
same materials. The earth floor was also covered with
crushed rock for heat storage.
This kiln is now drying 8/4 and 10/4 red oak for three
major companies from Ala~ka, Oregon and Idaho. It was also
metioned that this company was managing to build several si-
milar solar kilns in three states ..
c .. , .. 10~.2 ll..fton t1ountain Region, Virginia
A semi- gr>eE~n house solar kiln which 'Was the sa.me design
as that of Virginia Polytechnic Ir\stitute 1 was built and
operated by Heartwood Designs at .Afton Momitain l{egion {t:lha-
ley, 1982),. The kiln was capable of drying 25 to 30 £'.iBF
(t'lBF= 1000 board feet} of 1umhe,c per year. about 5 I1BF o.f
oaks ana. poplar are dried. for tiu~ir business and the rest
are sold to the private woodworkers.
121
It was noted th.at the kiln ~as reduced controlled
expenses thr:oug.h its f unctio.nal, reliable design and its use
of a. free solar energy .•
a.,cy thei:c own .lumber.
C • 2 !!!Q.1!
It also permitted small firms to
Re.hman and Chawla ( 1961) designed and tested a lan-sca-
le solar dryer at Dehra Dun, Tndia (30°9 1 N , 78°7'E) • Tll-e_y
tested eight different kiln desig.ns. Some designs had ex-
te.::-:nal collector connected to the drying chamber: on top of a
simple metal box co.l.lector.. Most of the dc~signs used natuc-
al cii:cula tion by various arrangements o:t chimneys.
They dried nine tropical hard:Woods and one tropical
pine.. They reported that the final moisture co_ntent o.b-
tained wece 8.J to 15 percent with drying tim~s from 11 to
74 days depending o.n the season, species, thickness a.nd ini-
tial moisture content .. A 25 to 71 ,percent reduction iu
drying ·time compared to air-drying was noted,. ,
c. 2. 1 Debra Dun
Based on the tests o.f Rehman and Chaw.la and othe:r solar
dryers, Sharma, Nath and Bali {1971} designecl and tested a
so.lar lumber dryer at the Forest Resea.rch Institute, Debra
Dun in 1969 • The capacity o.f the kilp. was 1.500 board feet.
123
c. 4,. 3 Commercial Iii!.!!§.
Based on the Forest Research Ins·titute design, eight
commercial solar dryers had beeu constructed and are in use
in different parts of the country {S,.Kumar, ·1981) ... The ca-
pacity of ·the dryers a.re 2,400 to 3 1 000 board feet.. 1.'hes.e
dryers are drying different hardwood sp:ecies for furnitur~,
doors, ~indows, doors and windows frame* joinery, carving
and ammu.ni tiou .boxes.. s i11ce the drying costs a,re 01l..ly a.oout
40 percent o.f those involved i11: s-team drying, it :was report-
ed ·that several mo:ce solar dryers. uer-e likely to hH in-
stalled in India.
Maldonedo and Peck (1962), designed and constructed a
pilot .solar dryer in late 1961 , at Rio P.iedras {18°H, 1 N,
66050, rr) - .. . ll. . .,. The dryer was of th,e greenhouse type wi tit a cap-
city of 2,000 board feet. The roof 0!tlas tilted toward the
south at an angle of 16° ,to the horizontal. Two test-runs
vere conducted one with 1,000 board fe~t of 5/~ mahogany and
the other with 2,000 board feet of 4/4 mahogany._ The 5/4
mahogany dried from 50 to 8 .. 5 percent moisture content in 29
days, and the 4/4 material dried from 32 to 12 percent in 13
days... The first drying test was car:ried out during oc.tobec
a.ud November Whereas the second. was cari:i~d out du.ring De·-
cember and January.
1.24
One year later the kiln was reconstructed and the
capa.ci ty enlarged about 3 1 000 boa.rd fi~et by extending the
length to 20 £eet. nfte.r two years of si:n:v.ice, the plastic
film of the roof was also removed and replaced by the single
layer of double strength window glass. Seven charges of
Hondurus mahogany of different thicknesses, and one mixed
charge of eleven hardwood species were tested by Cbudnoff,
Maldonado and Goytia (1966). They found that 1-inch mahoga-
ny can be dried to 12 percent moistu.n.~ content in 18 days
and 2-inch stock in 41 days, each from average initial mois-
ture content of 50 percent. They also reported that mixed
hardwoods of speci:fic gravity ranging from O. 48 to O. 82, re-
guired 43 days to dcy from an average ini ti.al moisture con-
tent of 60 percent to a final moisture content of 12 per-
cent.
Terazawa ( 197 5) designed and tested a greenhouse type
solar lumber kiln at Tokyo (35037 1 N., 139042 • E), in 1962 "'
The kiln was supplemented with an automatic steam heating
system which was used durin9 rainy o.r cloudy hours of the
day and during the nlght. The d~mensions of the kiln were
6. 5 feet long, 6.5 feet wide Tlw flat
roof and the walls were covered with transparent v iny.l
sheets and there was no insulation.
125
:r·t required 15 and 20 days respectively in Augu.st and
No·vember to dry 1.;) inch red lauan { .I?ipterocr.u:v2:.£fil.!!g ) from
90 to .20 percent moi.stu.re content .. The authoc also reported
that solar drying was .not econq_mica1ly feasible in Japan .be-
cause 0£ the. few sunsh.iue hours and fre'",lue.nt rainy days ..
C.5 TAIMAN
Ia late 1963, a solar lumber kiln with a capacity of
.2 ,500 board feeot was designed and tested in Taichung (24° 1 O 1 N
120°42'.E) by T'ao a:nd Hsiao {1964) •. · The kiln of tl1e g-reen·-
house type with the roof tilted south at an ang.le of 24° to
the horizontal •. '1'11e roof and tne walls ,except the north
wall were sheathed '~ith doub.le layers of transparent plas-
tics. The dimensions of the dryer were 14.7 feet long from
east to ~est, 10 feet wide from south to nqrth and 9.75 feet
and 13.3 feet high at the south and north sides, r·espBct.ive-
ly.
Two test trials were conducted ~ith two speci,es, :2£h.i.~
superba and Chinese hemlock. They reported that 1840 board
feet. of 1-inch schima lumber dri.ed f·rom 44 .• 1 to 12 percent
moisture content iu 4 8 days during ·th,e w:inter.. The Sall}e
thickness of hemlock dried from 200. to 12 percent in 64 days
during the spring.
126
C • 6 QQ!!IJ2.!
A greenhouse type solar kiln of capacity 1400 board
·feet was designed and operated by :P lumptre { 1967; 1.973) in
Kampala (G 0 19 1 N, 32°25 'E).. All of the walls :were covered ;by
two layers ( 1 to 3/4 inch apart ) of a polyester film.. 'l'h.e
kiln -was 15 feet long, 6 feet wide and 4 feet high.. Alt--
hough two side alumi-nimn-ref lectors were provided, there 'was
no collector plate. Ninf>. s_pecies of b~th. one-inch and two-
inch lumber wei:e tested from early 196:4 to late 1965. It
was reported tha-t the solar kil.n could dry lumber to as low
as 6 to 7 percent i:wisture content.
Based on the experience of the first kii.n, the same de-
signer coust.ructed a second solar kiln in 1968, essentially
the same as the first. kiln... It ~as also built at the same
location as the .first kiln but its capacity was increased t.o
about 5,700 board feet.
A third kiln wi·th a capacity of over 10,000 board feet
was const:r ucted in early 1971 by the same designer, Plumptce
(1973}:, and at the same .locatio.n. U-nfortunate]"y, no data on
drying tests were published for th.e second and thi.rd kilns .•
127
C. 7 Tl\ NZ ANIA
A solar kiln with a capacity of 2,5.00 hoard feet was
is available on its performance.
(1973), the designer was P.J.Wood.
No i.nf or-ma ti on
According to Plumptre
'I'he kiln was of the
greenhouse type with a flat roof. A single layer 0£ glass
covered the roof whereas the fom:: walls were sheativ,~d. with
polyethylene ..
c.a REPUBLIC OF THE PHILIPPINES
Casin~ Ordinario and Tamayo (1969) of Forest Products
Research Institute, designed and tested a portable, demou.n-
table-·type solar dryer of 480 board feet capacity. The
dryer was 7 feet with=! by 5.5 feet long by 7.5 feet high ..
The roof and two side walls were sheathed with transparent
plastic sheet whereas the front and back lialls were covered
with plywood .. The firs-t test was conducted at Que-
zon { 14 °4 0 'N, 121 °2 • E) with 2-inch thick red. lauan ( Jh.Q£§hl
neg:rose.nsis ) and tangile ( Sh.orea 120Tv2Qecma ) .in Hay 1965.
After 58 days of drying 1 the moisture contents obtained were
reported to be 19.3 and 18.1 percent respectively.
In April, 1966, a second test was carried out with
three hard wood sp ... 1cies namely, apitong { Diote rocil2Y& 9.£ftQ-
diflorus ) ., nar:ra ( Ptf~rocarpus indi,£~§. ) and tangile. They
128
reported that it took 48 and 52 days for 1-inch and 2-inc.h
apitong to reach 10.4 and 18.6 peccent moisture content ;37
and 5.2 days fo:r 1- inch and 2-incb. narra to reach 9 and 12,.. 9
percent moisture content ;and 38 and .52 days for 1-inch. and
2-inch tangile to reach 9 .• and 15~ 7 percent moistur-e con-
tent, respectively.
A third test was performed at L -(P••0_2'''N·, agu.na ""' ,,.
1968. This was also on 1-inch and
2-inch apitong and it was noted that the lumber were i.h:ied
to 7.$ and 14 percent moisture content wjthin 55 and 79 days
respectively._ It was concluded ·that "in areas 'riith pro-
longed dry season, solar drying lumb-er: to a moisture content
not attainable by ordinary air drying is pqssi.ble at a much
short.er period,. u
C .. 9 GI-I.ANA
Iiartink.a (1969), tested seven G.hanain species to co.m-I
pare predr_ying with solar dryi!\g and air drying .. The tests
were carried out at Kumasi {6°41'N• 0°.35 1 11). The solar dry-
ing was performed in an :improvised solar kiln ~hich ·was a
greenhousa of .size 8-by 10-by 7-:foot, capable of holding
about ·1, 700 board feet of lumbe:c... .A hl-ack painted aluminium
sheet was used as the collector anc1 a :fan was provided to
circulate the air. Drying tests we re. tiutd.e on seven species
129
from green to 20 percen·t moisture content.. Lt was r:epo:cted
·that air drying was 1. 5 to 3. 9 times long-er tha.n solar dry-
ing, however so;tar drying w-as 1.2 t.O 2 times .lqnger th.an was
reguir-ed .for predrying.
c.10 .MAD AG AS CAR
f1 so.lar lumbe.r: drye.r of cal:)acity ilbou.t 1,500 board faeet
was constructed and tested by Bedal and Gueneau {1970) at
Tannanarive {10°55' S, 47°32'E}, .in 1970 .. The design was
the same as that of the dryer from the Colorado sta·te Univ·-
ersity, u,..s .• A.. The diuH~nsioTls of tl1e dryer were 16 .• 4 f•eet
long~ 10 feet wide, 8.2 feet h~gh at t4e north side and 10.S
·feet high at tl1e south side respectively. The roof was
tilted a-t 23° to the horizontal .facing nocth. Pine boards
of thickness 4. 75 inches were tested and i·t reqai.ced 67 to
129 days to reach 15 percent moisture content ,. They also
men-tioned that it was possible to dry wood to a moistu.re
content as low as 7 to 8 per-cent in the solar kiln, which
was impossible in the natu.ra.l ai.r-d.cying pri?.cess ..
130
c. J 1
The first solar lumbe.r kiln in Australia was designed
and tested by Read, Choda and Copper in 1973,. at Gri£fith
(34°16'S, 146°10'E). •rhis kiln was also the first exte.·cnal
collector type solar kiln. A cock pile was also co.nstr:ucted
below the drying chamber .for t.herrna 1 storage. :rJ1e area o:t
the solar collector was 60.2 .. 5 square· feet a..nd it was faced
a.ue north , inclined at an angle of 38° to the hor.izonta.L.
The capacity of the chamber was 2,750 board feet.. It was
reported that one inch thick green alpine ash { ~:Y.£.a!Y..Et.!ll?.
d.elegatensis ) dried from 95 to 16 peccent mois:ture :eqntent
within 20 days.
The other solar Kiln, of the gr~~nhouse-type was de-
signed and tested by ay.ley in early 1979 .. '.I'ite kiln which ilad
a capacity 0£ 6,.350 board fee-t ·was built at .Rockland
(36°55 'S, 142°2(P E},. Two charges werE! t·ested J#'ith narrow-
leaf i.ronbark and hoop pine,. .I'l took 32 days for irqnbark
to dry from 33 to 12.5 percent moisture content and 24 days
for hoop pine to dry from 3.2 .. '.;) .. to 8 .. 5 percent moisture con-
tent • These teS'ts were car.ried out during Ma:rch through
.May.
131
c. 12
Vital (1976) d"~signed and tested a solar lumber dry,er
at Vicosa (23°46'S, 42°51'W) .. The capacity of the dryer was
about 850 hoa.cd feet and it was 9 .• 8 :fe.et l01l(;J by 6. 6 feet
wide and 6 .. 6 feet high at the north and 7 feet hi91'1 at the
south side respectively. The roo£ was tilted at 23° £acing
north and iiia.s covered with 5 mm thick glass,. 'fhe east, the
.. est and the north wa.1.ls were shBathed :with two lay1.~.c.s of
plastic whereas th.~ south wall was cov<-n~ed with fiberboard .• _
Two tests were conducted with .EucalY2.!-J!e. salig_na and Virola
species. The drying time £or: the f ocmer species, ~ilich had
55.6 percent initial moisture content, was 21 days to reach
16 percent moisture content. That of the latter species,
which had 42.3 percent initial moisture content, was 65 days
to reach 16 percent.
The other solar kiln which was desig·ned and t<.~sted at
the Center of wood I'ec hnology, S.antareru
{202s•s,s4°J7 1 W) wa.s also of the gree.qhouse type {:Ra:s1os g_t_
~! 1981). The dimensions of the kiln were 19.7x8.4x7.2
.feet, with a capacity of ah out 1,850 board feet ..
and the walls were all .sheathed by clear plastic.
The roof
Eight
Brazalian hardwoods were tested during December to May when
the relative humidity was very high, ranging :from .6 0 to .95
peccent. It was reported that, after 110 days of solar dry-
132
in.g the final moisture content of the tested lulilber ranged
.from fl. 5 to 25. 4 _pe.rcent, w-.hill';} that o·f the air-dcied lumbe:c
:Was considei:.-.ably higher, ranging from 15.6 to 31.3 percent,
even after 147 days of drying'- 'fhe, initial moisture cqnten-t
of the tes·teii species varied bet ween 3 9. 7 and 11 O. 4 percent ..
c.J3 UNIT.ED K.INGDOI1
Several solar kilns w.hicl1 we:re easy to erect., disas-
sembl and move were operated ( .Plumptre,. 1976 ;Izler, 1981}
at Magdala College of the Un~versity of oxford (51°43 1 N,
Each kiln was co-nstruc·ted o.f t~o sections which
were bolted together. The smaller kilns :were 21 feet long,
16 feet wide and 11 feet hig.b. a.long- the ·ridge line where the
two halves were joined. The 'whole fram•e was covered 111:ith
po1yuretheme Myler plastic and blac.:k painted
corrugated tin was used as the collector,.
Another kiln which was much large.r ·than those described
above was operated at the Eynshan Park. Estate sawmill,. The
capacity of this kiln was 9,00U board f~et , and the dim.e:n-
sions vere 32.5 feet long, JO feet wide and 12 feet high.
The frame was made of galvanized st.ee.l tubing ~ith. l. 5 to
2. 25 inches in diameter ana. :was co.ve:ced. ~i th yellow ultra.-
violet-resistant horticultural plastic.. ICI b.la.c.k polycac-
bonate was used as the collecte>.c ..
times
It was reported that
as dry
13.3
solar--d.rying kilns reJuir-ed three
lumber as did co~veijtional k~lns long to
they were inexpe.nsi ,,e, required low-le.vel opera t-
iug skills and obtained .high g:uality dried--lumber,.
All these kilns were designed and tested by Plumptre
who started the solar lumber drying in Uganda.
INDONESI.A
f'lartaidjaya g_:t, al (1976) designed and tested a green-
house type solar .lumber dryer at Bogar {6°45 1 s, 106°45 1 l•
The roo£ and the -wal.ls -were covered iWLth. transparent plastic
sheet.. The dimensions of the dryer were .6.9 .feet long, 5.4
feet wide and 6,. 4 feet hi9h. _. Jeungj iri,g species ( AJ.hi.1:ia
@J&s!.1~ } of 1-inch thickness .and l,. 5 inch thick rubbe.c wood
{ Jig_yg2;_ hca.siliensis ) were dried .. It was concluded that
solar drying was always faster than th,e air dr1•ing foJ:: .both
S,Pecies.
c ... J5 f..LLI A solar dryer ·with a capacity of 2,100 board feet was
constructed and operated in P:iji (18'l50 1.,S, 175.0.E} by Gough
(1977}. Several .Fiji timhec species we.i:e tested and the re-
sults obtained we:re considered to be satisfactory,. r·t was
·noted that 1-inch kavuea { .Endos11ermu.m ~'a.£:£QEl!Ji.:llJ!.!!1 ) , which.
134
was taken directly from pressure t.reat-me1lt with water-borne
pr.-eser va ti ve salts, dried frmn 115 to 16 _percent moisture
content in 30 days. The te,st. was carried out d1.1.1:ing April
which is a very we,t month for the location,. Another ·test on
t.he same thickness and the same species was also co.nducte.d
during March requ.ired 31 days to dry the lu-mber .from. 85 to
14.7 percent moisture content.
was dried, during October and November, and the lumber were
dried -to 15 .. 5 moistu.re content in 2:3 days from an average
initial moisture con'tent of 47 .. 5 perce:n_t. Drying1 during
hot dry veath.er in February, with 1-inc.h ai.c-dried .mahogany
( 2.Rietenia macr:oph.ylla } from an initial mois·ture co.utent
39 percent,
days.
to 17. 3 ;percent moisture content took only 7
This kiln -was of the greenhouse ·type with a capacity of
2~100 board feet.
c .. 16
Schneider gJ;;. al ( 1979) designed and. te.s:ted a g:ceenhou.se
.28 miles
from riuuich,. .· The dryer had a capacity of a:bout 3,500 board
.feet and it was 16. 4 feet. 1o ng from east to west, 8 .. 2 feet
wide from south to north, 8 .. 2 fee.thigh at the south side
and 12. J feet high at the north side re.s,pecti vely,. The roof
135
was tilted at. 25° to the horizontal, facin.g so:u:th a;ld :was
sheathed with 1 mm th:ick transpar,ent .PVC. All walls except
the north wa.11 which 1.;as constructed t:ith 1/2 inch particle-
board. were sheathed with two layers of transparent. PVC an,d
polyester, •. The outside layer was l Iil!!l thick transpare1.1t PVC
while the ~nside was 0.2 mm thick polyester. The air space
between these layers aas 2.4 iqches~
Four test runs were conducted durin,g the years 1978 and
1979 ,. , The tested lumber: was spruce, beam of size l. 6nby
J.5nhy 13 1 and ·they repo:r-ted that the first :can too.k 39 days
(5.11.18 to 6 .• 20.78) to reach 8.3 percent; the second run
took. 46 days (7 • .5 .• 78 to 8.41..78) to reach 8 .. 2 perce+it;th,e
third run took 46 days (8. 31. 78 to 10 .16. 78) to r,each Y. 5
percent, and the fourth run took aa days (11.15.78 to
1. 12.19) to reach 17 .. 9 pe.ccent • Ai:r drying tests we;ce also
cond.ucted at the same time aud it was found that the .final
moisture content obtained were only 15..9, 16~7, 19.4 and
25.2 ,:percent, respectively, for the co.rrespo,nd.ing ma·tecials ..
c. 17
In 1977, K.C.Yang {1980) designed and tested a small
·solar kiln on the La.kehead University campus., Tl1underbay
(48028 1 .N, 89°12 1 ¥1),. The main objective of his work ~1as :to
exawine the po:.:;s:ibility o.f using solar energy for .lumber
1]6
drying at higher latitudes. The roof, which was tilted at
an angle of 30° to the horizoQtal, and the s~uth wall ~ere
covered with a double layer of glass. The east, the west
and the north walls were covered with _plywood and ~el:'e all
·well insulated .• A rock pile 1rns also built u.nder the lciln
fo.c the heat storage. 'f.h.e capacity of the kiln was re;pocted
to be 760 boa.rd £eet.
Green jack pine studs of siz·e 2'" by 41Jby 41 were testH.d
and it reguired 30 ar.a. 140 days ·to dry them 10 pe·rcent mois-
ture con tent, in the smnmer and in the w,inter, res-pecti vely,.
Based on the two years of test data,
that sola.r drying :was superior to air-drying in lumber dry--
ing r-ate., quality, and in 1.owe.c final moisture contents. HB
also noted that the lmiber dried by a sola.r kiln in the win-
te:c period had ffrne:r: dr:ying d~-fects ·th-an that d.c.ied in the
summe.r season ..
A solar kiln with a capacity of about 420 board feet
{ 1 cubic meter)
1979-80. No info.rmation is available on its performance ..
According to "J?. Y. .Du.cand5 (personal commmunication), the
5 P.. Y-. Avenue 94130.
Durand, Centre Tecllnigul'?. .:for·e-stier Trqpical, 45 bis de. Pa Belle Gabrielle, Noge.nt s/Marne,; France
137
roof consistad of a black painted metal sheet /jJh.ich acted .as
a collector. The lumber pi.le can be. isolatf}d from the col·-
lector if necessary •. • There were three fans to circulate the
air and vents :we.re also provided to control the humidity in-
side the kiln.
RE.PUBLif :Qf SOQ!fi AF.RICA
A microprocessor controlled solar kiln was designed and
tested by Stein1nann et !!.l (1980.)&{1981) at the UuLversity of
Stellenbosch {28°s, 24°SO•E). The kilq was 0£ the external
collector type with ai:c as the drying medium,. The collecto.c
was .faced due north and was tilted at an angle of 4.5 ° to t.he
horizontal. fi:!l!!§. radiata (about 186 board feet) was dried
daring winter. They reported that after 16 days of drying~
the solar-dried lumber reached 12 pei::cent, Ir.bile the air-
dried material· reached only 23 per:cent moisture content .both
from an average initial moisture content of 93 percent.
c.20 CELINA
In 1980 1 a solar lumber kiln with a capacity of about
6,000 to 8,000 board feet (15-20 cubic meter) was built and
tested in Tai'he County, Itnhui (31°30 1 N1 H7°15'1 E)., China
(Guo~ 1981)~ The roof and upper parts of east1 ~est and
south walls were cove:i::ed lili th 2 and 3 layEtcs o,f glass, re-
138
spective1y ... The north wall and lower: pacts of the other
wa.1ls were constructed. wit:i1 bricks and sawdust filler and
the interior of brick walls were painted black. An under-
ground sawdust combustion chamber was also provided as ace-
serve heat source. It was .reported that a batch of lumbif!.C,
mainly consisted of thin l)oa.n1s and small :sguares, with an
initial moisi::ur·e ,content of 30 percent :was dr.ieci to 15-18
percent moisture content with~n 6-7 days.
c .. 21
A lumber solar dryer was d,esig-ned and constructed by
Tschernitz and Simpson at Borwood Ltd. in Horana (6°581ii,
79°52'~, near Colombo in February, 1981. It was a dupli-
cate of the r-Iadison prototype exce1,Jt that the collector area
was 40 percent larger. Before instal.ling this kiln, Bor:wood
had only an air-drying shed. to dry rubber wood for Low·-cost
furniture making. In the air-drying it required about three
months to r:each 15 percent moisture content .. The solar
kiln had been operated continuously for 18 months and it was
reported that 1-inch green rubber wood of moisture content
about 60 percent could be dried to 15 percent moisture con-
tent within two weeks.
139
c.22 PAKISTAN
A solar lumber dryer ¥as designed and tested at the
Pakistan Forest Institute1 Peshawar (34°01'N.71°34'E), in
1981-82. Unfortunately, :no information is available on its
performance. .However, according to w ... Killmann 5 {persona.1
communication), lt was of an cexternal coll,ector type with a
capacity of about 1200 board feet (3 cubic meter) and the
collector was built. on the roof of the ki1.n .•
c .. 23
A solar k:iln with a capacity of about 600 board feet
was designed and tested at tli.e Forest Research Institute,
According to R.
A •. Pl umtre 7 {personal comm u:nica tio11) , it 1.as of a greenhouse
type sheathed with polythene and air was circulated by a
24-inch diameter fan~ No other information is available on
its performance ..
6 H. Killmann, Timber Technologist, Forest Engineering and Forest Products, Pakistan Forest InstitutB.; Peshawar, Pak-istan .•
7 R. lt. Plumtre, Commonwealth For,estry Institutt?, South Par:k. Road; Oxford, United Kingdom OX1 3BD.
140
c,. 24 12.!!ftl'li\
The first solar dryer in Burma was d.~signed and con-
structed by Tschernitz and Sirnpso.l! at the Forest Research
Institute, Yezin (19°47 1 N, 96°15 1 E), in September, 3982
It was a replicate of the Porest Pcoducts Laboratory, Badi-
so.n prototype except th,tt the collector is, 40 teet long in-
stead of 25 £eet. Since it Mas r~cently bu~lt, no informa-
tion on its performance is available .. ·
r---.--
Appendix D
LIST OP PUBLISH.ED OR IJNPU.BLISHl-:D .IN.FOfi'.i1A:IION OJI SOLAR-LUMBER KILNS
JSr.JDesig.ner/ !Location !Da.te I .Luuiher jLumber !Type 1 I I 1 I I Capacity.:: l I No. ! Res ea re her I JRepor~JCapacityJCollectorl ,i i ) 1 ted 1 j Area ~- I -'!f"
l j l I I { bdft) J {hdft/ft2) l--, ;1 11 Johnson JEdmond, i 1961 I l lJ.3 .! GH if
I I I Wisconson, j I l j
l I JU .• 53.A. l ' a I ] l I (42°58'N, I ,i l I j J 90°7• W) f I I I j j i l I i 2 JP eek j I•!adison, I '1962 i 425 I 3 .. 1 ;i GH I j J Wisconsin .. t l l I ,1 j j (43°5•N, j I J 1 I I l 87°23 'W) I j I l j I j J j J I I 3jPeck j Sauk City I i 196 2 I 2500 A }GH I J !Wisconsin .. l i j t l I J (43°16 1 N, J I I j l j I 89°45 'W) I j 1 i I l I I ! I i I 4 JPeck I n If I 1962 I 2500 1 IGH I j J l i j 1 .I 5 ,l Troxell f; t:Port Collins l 1968 l 1 ,200 .I 5 ... 5 jGR ) l r1axwell jColor-ado t I l 1 I I I (4D 0 36 1 N j I I I I l I 1os0 4'W) t i I I 1 J I I i l j j 6jTschernitzJMadison1 j 1977 i 1,000 j 6.8 jEC+ 1 .~ & Simpsonj~isconsin. 1 i l J I I I l i I ,j
I i i i I I I l j j j i J l l l l i j I I j I I i l
l 7JJollnson J l"ladison 1 I 1977 1 750 I 16.0 )SGH++i I J !Wisconsin. I 1 i J I L _J
* Collector area is based on the equivalent area perpendicu-lar to the· sun at solar .noon on the ,2,1uinoxes (v,~rnal and auturnna.1). ,Jt- GH - 9reenhousf~; + EC external collector ++ SGH - St:Iil.i-gree:nhouse;
141
142
r I BlWen9ert j l3la.cks1rnrg, I 1977 I 200 I H;.Q ISGH j I I ! Virginia t j J j I I i I p5091 N, j l J ' I I J 1 8 1°30 '}i) I l I J I 1 I I I I l j t I 9JWengert j u n I 1977 j 200 I 9 .. 0 iSGH I I l j j "1 I I I I 10)1.umely & jBa ton ROU•Je j 197,8 I 360 l 14.5 ISGH j I JChoong I Louisiana ) I j j I I I j (30°28 •N, 1 j j I I 1 l t 91o10' W) i l I I i l l j j j l l I I 11JHengert )Blacksburg, I 1980 l 1 #500 I 10.0 15GB j J I )Virginia"- j I J .I I l I J j I j I I a 12jB.osen .& JCar.bondale, I 1980 i 500 J 4 .. 3 j EC I 1 IChen j .Illinois .• j I J j l J j l (3J<>lU 1 N, l I I l l I I I 89°12•w) 1 i .J I I I I l ,l I j J l I 13 j Decor I Sot\l.erset, I 19HG j 190,000 I 36.0 jCom- ! ) j!1aterial )Ohio I I i I iller- l l J Service l {40°30 1 N, I I l jcial 1 l I 1 83°15 1 W) I 1 J cl I I il l I l j l j I 14 J Heartwood JAfton I 1981 1 j jSGB 1 l jDesign I I1ounta in 1 J j I jCom- al I j 1 Vi.cg in ia I I jmer:- j j 1 I {37° N, I l j jcial j I I i 80°45 1 W) I 1 i l j I l j J t I I I l 15 f Weng·ert,. .) Various u • .s. j l l jSGH l j I tabout 200 l i l jCom- j I i i l j 1 1mer- J j I l 1 I I jcial I I I l j j j I I l 16JRehman J De.hra Dun j 196 1 I Lab- l !Box- .j l l D jTndia i I scale j )type I J IC.hawla. i (30°9' N, I l j l I ] I 78°7'E) I I l I t J
14.3
... ---. I 17 j Shanaa JDehra Dun j 1971 1 1~500 l .JGH I I Jet al !India j j I I J I l I J l I I j. J 18JSingh jRoorkee 11974 l Lab- l IEC I I j j Utta I j scale I j I i i t Pradesh,, a J 1 l I ] I IIndia I J J I I I I I (27°N, I l i l 1 I I j 80°E) I :i I j I j I I l J j l I I 19)1"1U; JBallarsh J19BO I 3 ,.ooo I 9 .• ? .iCom- I I JDehra I Haha.rasl1- I I I jmer:- j
J JDun I tra1 Ind,ia j j 1 tcial J 1 • ;J {19°6 1 N, .I I i I j l j J 79°E) I I 1 I I 1 ,) I I I j I J j 20J 11 u j 11a·jahmi.m- 11980 I 2140.0J P' .I a I I dry, And- ) I j j I I J Jhra Pra- I j I j j I I jdesh(17° I t i l j I l 13'N,82°E) l I I 1 I I ' 1 ! I J J i J 211 n H I Vansda, )1981 a 3,:000 j J Jl ' I 1 .I Gujarat I J I I I i l j (22°54 1 N, I j l j I l J I 79°E) I I 1 I I 1 I J j j I I I 1 22111 u 1 Nagpur, 11981 i 3:,000 1 I u j I I l Ma.hara- J J .1 I j I I Jshata I l l j j
I l l (19°6•N., I j I I I 1 I j 79°E) .I I I j i J I I J I j J 1 I 2Jjll n t Hoshiar- j 1981 I small-I I 1, j j I Jpur, Punjab l J sca.lt:! J I I I 1 j (31°N, 1 I 1 I j
J I j 75° 30' E) I J I I l I 24j 11 n I H H j 1981 J J,,ooo. 1 I n j ) 1 ) j I J I 1 1 251" " I Kashipur, I 1981 ,I 3,000 J I ti I J I Jutta j j 1 ,1 i I J )Pradesh. 1 J j l J ! I I (27°N, j t j J I j j j 8iJ 0 E) 1 l I I l 1 ! 1 I I I t J 1 26JU n I Luc.know., ,j 1981 l 3;000 J I n I ) J IUtta j 4 I I j I J I Pradesh J l ) I i L
144
r--r--j 27 P,l aldo:nado JPuer-to i1962 i 2,, 000. I lJ .. J .iGH I J jnado )Rico j j I J l l j i ( 18° 16 'N, :I 1 I l I 1 1 I 66'0 50'W) J j I j .I a I I J l J I I ,) 28.1 Cb.udnof f I u II i 1966 ,j 3 ,:000 j 14 .. 4 iGH J J Jet al i J .1 -~ 1 J J J I J I J I I J 29JTerazawa tTokyo, 11962 I I jG.H j j !Japan I ! I I l 1 1 l (35°37 1 N, I l 1 J j I J I 139°42 1 :E) ;I j J l ·}
1 1 J i j j I I l 30iTao & J Taichnng, 11964 l 2,,.soo I 11.4 IGH I I )Hsiao !Taiwan l j j a I I a I {24°10'N, t I 1 j i I j l 120°421 .E} l 1 I I I I 1 I J .I I l l al 31 I Plumptre J Kampala, 11967 l 1,400 1 15.6 JGH 1 J j 1 Uganda l I j I J a I I (0° 19 1 N, j ) I j I I l I 32°25 1:E) j I I j J l I J l 1 l I i l 3 2 J .P.lumptre I H u 11973 :I S,700 j JGH j I t I J j I J l J 33 i Plump tre ! H fl f 1973 1 10,000 j jGH 1 l I 1 i 1 J I l I 31.q wood tMoshi, 11 11973 J j jGH I 1 i .I Ta,nza.nia I J l I j J l J (3°21 1 S, I I I j J I I I 37° 20 'E) 1 I
J J I i .I ) I I 1 J J J I 35JCasin I Philippines 11969 ! 480 I 9.6 jGH l I ;et al I i ,I i ,jpqrt-l j a I j I J jahle 1 j j I I I I I I 1 36 J Martillka JKumasi, }1969 l l,700 ) JGH I I ) jGhana l i j J j J j 1 (6°4·1•w, j j I I i I i I 1°.35'W) 1 l J 1 I I I I J i J .1 I I 37)Bedal & I Tann.ana- J 1970 j 11500 J 7.0 I Gii l J JGueneau t r:i11e, j i I .I J i I IBadagscar l I j I I J i I (10°55'5, J j I j I j I I 47°32 1 E) J j j l I L----L . ·t
145
,r j 38j11ead ,I Griffith, ]1974 j • .2,750 I !+ .. 6 .IEC I 1 jet a.l 1 Austra.lia I l I I j I l l (34°16'S, I l l I I i I I 146°10'£) J l ,1 J l l l l & j I I I J 39 jRyley J Rock.land., l 1979 1 6,350 ! 11 .. 6 jGH I J I l Australia I I i j l l I j (36°55 1 5., j I l i j I I I 142°20'E.) I J J I I I i ) I 1 I j I 40)Vita1 JVicosa, J1976 j 850 J 12 .. 1 IGH j J J I Brazil ' } l i i J ] J {23°46'S, 1 j I I 1 J 1 I 42°51'W} I I 1 I l I I I a i t I j l 41j 1 San:tar:em, 11981 j 1,850 :! 1 h 1 IGH l I 3 I Brazil J i j .i l I l l (2°2H' s, i j I J J 1 I i 54°37'W) J j I l i I j j J l I t I j 42 I Plumptr:e JOxford, 11976 J.,ooo I jGH I j J JU .. K. 1 j I lpor- 1 I j I (51° 4 3 '1 N, J l ) I table} I I I 1°16 1 W) I I a l (sev-J J ,I I J l j teral)l I I I J I I I i I 431 Plurupt:ce I n u j1976 i 9,, 000 j jU I t 1 I I j J j I I 44J Martawi- JBogor, j 1976 l,400 J JGH I l Jjaya 1 Lndon,esia 1 l I I I i
ii I e·t a1 l {6°45 1 3 1 .I ·l A I j I I I j 106°45 1 £) I l .I l j I I j I >! l I I l 45)Gough JPiji 11977 i 2,HW 1 jGH I I j I ( 10°so 1 s, I i .I I i ;l ii l I 175°E} I I l j ' I I I i I I I I J 46JSchneider J Weilhe:im, J 1919 j 3,500 I 25.6 JGH .i I Jet al J w .• Germany j l :l I j
I I J (47°50 1 N, I I J I j a j I 11°6'E} l J ' 1 I j J l j j I I J J 47.f Yang l Thunderbay,, )1980 i 760 I 8 .. 4 .JSGH l I J 1ca.nada I I j 1 I J 1 1 {48°28 IN. J il 1 I I I I I 89°1.2'{,f) J I J J J L
146
r---T , 1 48 J ,:l.nonymo us jAbidjan, I 1980 ) 420 J JSGH I I l )Ivory Coast I I l I I I I I (5°09 1 N, i l j I 1 I j l 4°02 1 W) I I j I ) I 49JStei.n.mann j Republic of ! 1980 I 185 j 4M4 J E;C I j J.:et al JSouth .Africa l l j 1 j
I l I {28° s, I ,l I I j l j j 24°5v 1 E) l I I i I I l i l i j I 1 50JGuo !Anhui, I 1980 I 6,000j lSGH j J I I China I J I j l J j l {.31°.3tP N4 j 1 I j I J ! I 1 17°15 1 E) j i j l I l l I i I j i j
I 51JTschernitzlBorana, l 1981 I 1,000 l 3 .. 6 I EC l l J& Sirrq_:>s~n 1.s1:i Lanka i } I j J I I {6°58 • N, l I l I J j j 79°52'E) I I j j I l l J l j i J 52jAnonymous 1 Peslta i,rnr , I 1981 I 1,200. I IEC l j i J Pakistan l .j i l l I 1 I {34°01 'N, l i I I l 1 1 I 71° 314 'E) J j I a j .l I l j I l l I t 53 ,1 Anonymous I Cl1ittagong,,. l l.98 ·1 I 60-0 l iGH I I l I Bangladesh I 1 i I l I l 1 (22°26 'N # i j I I 3 I i l 90°51 'E) I j 1 I I t j l I I I I I I 54JTschernitzfYezin, ! 1982 l 1,000 3 .3.6 j EC j J j& Simpson JBurma J i I l j I I l {19°47 1 N, i i t I I a I l 96°15 1 K) j I l I ' J j l l I j l I J :L
Append.ix E
LOCATIOUS OF 24 THERuOCOOPLES
1. Outlet o:f drying chambe :.c (base da.m,pered duct)
2. Inlet to drying cha.mber f:com co.llector before b.lower
3. rl iddle of the .1est end side of th,e load
4., Riddle of the east end side of the load
5. Middle of the ceiling (inside of the roof)
6... f{iddle of tile roof (outside)
7,. . Middle of the exterior of tile east wall
8. Midd.le of the exter.ior of the south wa.11
9,. Middle of the e.x·te.rior of the west wall
10. Middle of the exterior of the north wall
l l. 6. 2 feet from the outlet of the drying chamber (in-
side the collector)
12. 13 .. 5 feet from the outlet of the drying ch.amber (in-
side the collector)
1.3 • .20. 4 feet from the outlet o.f the d:cying chamber
(charcoal surf ac,e)
14. 27.6 .feet from the outlet (?.f t.he .drying c.hamber (i11-
side the collector)
15. 34. 3 feet from the outlet of the drying chamber (in-
side the collector)
147
148
16 •. 1-4, 1. 0 feet from the outlet of the drying chamber (in-
side the collector}
17. Center load, 4 inches into qcavel (at plastic)
18 •. Charcoal/sand interface (insidH t.he collect9r)
19. 3 inches into clay - 6 .inches outside the collector,
Sil corner
20. N octh side o.f the j_ nstrumen t s4ed {amhien-t tem:pera-
t11r•21}
21. R H.2 sensor
22. Inlet air duct
23 •. Hygrothermograph box (on the south wall)
2-ll. 3 inches into clay at plastic opposite No. 16
The vita has been removed from the scanned document
PREDICTING DRYING TIMES OE' SOME BURMESE WOODS
E'OR TWO TYPES OE' SOLAR KILNS
by
Win Kyi
(Abstract)
Experimental drying studies were made on two types of
solar lumber kilns, one an external collector type and the
other a semi-greenhouse type.
Two charges of green sugar maple lumber ( 5/4 inches·
thick) were tested in an external collector solar kiln· at
the U.S. Forest Products Laboratory, Madison (43°S'N,
89°23 1 W), Wisconsin, during the summer of 1982.
In the first run detailed drying data were obtained and
the energy balance was calculated for each day during the
entire drying period. Based on these results, the following
empirical model for the overall efficiency of the kiln was
obtained:
EFE' = - .0413 + .0102*(IMC-) - .0000562*(IMC) 2
where,
EFF = overall efficiency of the kiln
IMC= average initial moisture content of the lumber
in percent
Using· this model, the average daily moisture content
loss in percent (MCL) can be calculated as follows:
MCL = (100*EFF*SI*ACV)/[R*(62.4*V*SG)*{0.53*(212-Ti)+972l]
where,
EFF = the value obtained from the first equation
ACV = area of the collector in ft 2
SI = average daily solar insolation in Btu/ft 2
R = ratio of total solar energy incident on the collec-
tor cover to total energy available to the system
V = green volume of lumber in ft 3
SG = green specific gravity of lumber
Ti = average initial temperature inside the kiln in °F
A comparison of the actual drying time observed in the
second run showed good agreement with the predicted drying
time obtained from the above equations.
A single charge of 9/8 inches green yellow poplar was
dried in a semi-greenhouse kiln at Virginia Polytechnic In-
stitute and State University, Blacksburg (35°09'N, 81°30'W),
Virginia, during the fall of 1982. Following the same
procedure as for the external collector kiln, an empirical
model for the overall efficiency (EFF) of the kiln was ob-
tained as a function of initial moisture content (IMC),
EFF = - .0767 + .00988*IMC
'\
Using this model, the average daily moisture content
loss can be calculated, in the same way as for external col-
lector kiln.
These prediction equations have been used to estimate
drying times for some commercially important woods of Burma
for both types of ki.lns.
