SWA Report on WWSV Heating Systems

8/14/2019 SWA Report on WWSV Heating Systems

1/23

BuildingAmericaSystemsEvaluation

Simple,Non

Distributed

Heating

Systems

inColdClimateHomes

PREPAREDFOR:

NATIONALENERGYTECHNOLOGYLABORATORY

3610COLLINSFERRYROAD

MORGANTOWN,WV

265070880

&

MIDWESTRESEARCHINSTITUTE,

NATIONALRENEWABLEENERGYLABORATORYDIVISION,

1617COLEBOULEVARD,

GOLDEN,CO

804013393

PREPAREDBYSTEVENWINTERASSOCIATES,INC.

FORTHE

CONSORTIUMFORADVANCEDRESIDENTIALBUILDINGS(CARB)

STEVENWINTERASSOCIATES,INC.

50WASHINGTONSTREET

NORWALK,CT06854

TEL:(203)8570200/FAX:(203)8520741

CONTACT: ROBBALDRICH


2/23

Table of Contents1.

EXECUTIVE SUMMARY .................................................................................................... 3

1.1. Overview ........................................................................................................................ 3

1.2. Key Results ................................................................................................................... 3

1.1. Gate Status .................................................................................................................... 3

2. PROJECT OVERVIEW RDI WISDOM WAY SOLAR VILLAGE ..................................... 4

2.1. Plans .............................................................................................................................. 4

2.2.

Basement ...................................................................................................................... 4

2.3. Above-Grade Walls ....................................................................................................... 4

2.4. Attic ................................................................................................................................ 5

2.5. Windows ........................................................................................................................ 5

2.6. Heating Systems ........................................................................................................... 6

2.7. Ventilation Systems ..................................................................................................... 6

2.8.

Water Heating ............................................................................................................... 7

2.9. Solar Electric Systems ................................................................................................. 7

3. SHORT-TERM TESTING .................................................................................................... 7

3.1. Research Questions ..................................................................................................... 7

3.2. Blower Door, Airflow, and Power Measurements ...................................................... 8

3.3. Tracer Gas and Temperature Distribution Testing Procedure ................................. 9

3.4. Air Distribution Results ............................................................................................... 9

3.5. Thermal Comfort Analysis and Results ................................................................... 113.5.1. Thermal Design Considerations ............................................................................................................. 113.5.2. Thermal Comfort Test Results ............................................................................................................... 12

3.6. Recommendations to Residents ............................................................................... 17

4. LONG-TERM MONITORING AND EVALUATION ........................................................... 17

5.

GATE CRITERIA .............................................................................................................. 17

5.1. Must Meet Criteria ................................................................................................... 175.1.1. Source Energy Savings and Whole Building Benefits ............................................................................ 175.1.2. Performance-Based Code Approval ....................................................................................................... 18

5.2. Should Meet Criteria ............................................................................................... 185.2.1. Prescriptive Code Approval .................................................................................................................... 185 2 2 Cost Ad antage 18


3/23

Building America System Evaluation

NON-DISTRIBUTED HEATING SYSTEMS IN 50% COLD-CLIMATE HOMES

1. Executive Summary

1.1. Overview

Asenvelopeperformancedramaticallyincreasesincoldclimatehomes,designheatingloads

becomeverysmall. BuildingAmericateamshavestruggledtofindsystemssmallenoughto

meettheseloadsefficiently,comfortably,andcosteffectively. AtWisdomWaySolarVillagein

Greenfield,MA,RuralDevelopmentInc.(RDI)isbuildinghomeswithexceptionalthermal

envelopes. Toheateachhome,asingle,gasfired,sealedcombustionroomheaterislocatedinthecentrallivingspaceofeachhome. Thereisnoheatprovideddirectlytobedrooms,thougha

simpleventilationsystemprovidessomethermalequalization. CARBhasperformedshortterm

testinginconjunctionwithNRELinFebruary2009,andlongtermmonitoringisunderwayfor

thewinterof20092010.

1.2. Key Results

ShorttermtestresultsfromFebruary2009indicatedthattemperaturedistributionthroughout

thetested

home

would

be

acceptable

under

nearly

all

conditions.

At

outdoor

temperatures

above1015F,testsshowedthatmodestinternalgains(125W)willkeepbedroomswithin34F

ofthetemperatureofthecentrallivingspace. Atlowertemperatures,nearthedesign

temperatureof2F,ifroomshaveverymodestinternalgains,occupantsmaywanttoleave

bedroomdoorsopenoruseportableelectricheaters(verysparingly)tokeepupstairsbedroom

temperatureshigher.

Thespaceheatingsystemwillrequireadifferentlevelofresidentawareness. CARBhas

presentedinformation

to

residents

about

recommended

practices

(such

as

keeping

bedroom

doorsopenwhenunoccupied,avoidingextremedaytimetemperaturesetbacks,etc.). Onlyone

homewasoccupiedduringthewinterof20082009,andCARBwasnotabletomonitor

temperaturesthroughoutthishome. Forthewinterof20092010,fourhomeownershave

agreedtoletCARBmonitortemperaturesandinterviewthemaboutcomfortandenergyissues.

OnekeyresultinthecosteffectivenessofthesystemisthatRDIsavedapproximately$4,500on

mechanicalsystemsforeachhomewhencomparedtoaconventionalhomewithaboilerand

hydronicbaseboard

convectors.

Todate,resultshaveshownthatsimpleheatingsystemswithminimalornodistributioncan

effectivelyprovidecomfortinsomesuperinsulated,coldclimatehomes.

1.3. Gate Status


4/23

Table1. Stage1BGateCriteriaforNonDistributedHeatingSystemEvaluation.

2. Project Overview RDI Wisdom Way Solar Village

RDIsWisdomWaySolarVillageisdescribedinmoredetailinthecasestudyBuildingAmerica40+%

ColdInitialCommunityScale: RDIsWisdomWaySolarVillageupdatedinDecember2010. Thekey

featuresof

the

home

energy

systems

are

also

listed

here.

2.1. Plans

Thecommunityconsistsoftwentyhomesintenduplexesasoutlinedbelow:

Four2bedroom,onestoryhomes(1,137grossft2;twoofthesearefullyaccessible)

Four2bedroom,twostoryhomes(1,140grossft2)

Nine3bedroom,twostoryhomes(1,390grossft2)

Three4bedroom,twostoryhomes(1,773grossft2)

Thecommunitywasdesignedsothatallhomeshaveexcellentsolaraccessforbothpassiveand

activecollection. Plansforthethreebedroomhomeusedforshorttermtestingareincludedin

theAppendix.

2.2. Basement

"Must Meet" Gate Criteria No Go Recycle Go

1. Source Energy Savings and Whole Building BenefitsNew whole house system solutions must provide demonstrated source energy and

whole building performance benefits, including labor and material cost tradeoffs,

comfort, durability, reliability, health, ..., relative to current sys tem solutions based on

BA test and analysis results.

X

2. Performance-Based Code Approval

Must meet performance-based safety, health, and building code requirements for use in

new homes.

X

"Should Meet" Gate Criteria

1. Prescriptive-Based Code Approval

Should meet prescriptive safety, health, and building code requirements for use in newhomes.

X

2. Cost Advantage

Should provide strong potential for cost benefits relative to current systems within a

whole building context.

X

3. Reliability Advantage

Should meet reliability, durability, ease of operation, and net added value requirements

for use in new homes.

X

3. Manufacturer/Supplier/Builder Commitment

Should have sufficient logistical support (warranty, supply, installation, maintenance

support) to be used in prototype homes.

X

5. Gaps Analysis

Should include system's gaps analysis, lessons learned, and evaluation of major

technical and market barriers to achieving the targeted performance level.

X


5/23

wallfiveinchesinsideoftheloadbearing,exteriorwall. Fiberreinforcedpolyethylene(inthe

firsttwohomes)orinsulationnetting(inthelaterhomes)isstapledtotheinnerstuds,andthe

entire12

wall

cavity

is

filled

with

dry

blown

cellulose

insulation

at

densities

of

approximately

3.4lbm/ft3. WholewallRvalueisapproximately42ft2hrF/Btu.

Figure1. TypicalwallsectionfromAustinDesign,Inc.

2.4. Attic

Roofsofthehomeareconstructedwithmanufactured,raisedheeltrusses. Ventedattics

incorporatefullsoffitandridgeventsandfullinsulationbafflesateverytrussbay. Homesare

insulatedwith14oflooseblowncelluloseforanRvalueofapproximately50ft2hrF/Btu.

2.5. Windows

Onnorth,east,andwestfacades,RDIinstalledtriplepanewindows. Onthesouthernfacades,

highersolargaindoublepanewindowswereused. WindowpropertiesareshowninTable2.

Table2. WindowpropertiesattheWisdomWayVillage.U-value

2


6/23

2.6. Heating Systems

Thedesignheatloadsofthehomesareverysmalllessthan12,000Btu/hr. Withthevery

smallloads,

RDI

selected

avery

small,

simple

heating

system:

asealed

combustion,

natural

gas

firedroomheaterlocatedinthecentralareaonthefirstfloorofeveryunit. Theunitisa

MonitorProductsmodelGF1800;capacityis10,200Btu/hatlowfire,16,000Btu/honhighfire,

andtheAFUEis83%.

Figure2. Gasroomheaterinthelivingroomofthe3bedroomhometested.

Toalleviate

concerns

about

temperature

differentials

and

to

improve

ventilation

performance

CARBworkedwithRDItodesignaverysimpleairdistributionsystem. Thisisdescribedmore

intheVentilationSystemssectionbelow. Toassurecomfortinbathrooms,eachupstairs

bathroomcontainsasmall,500Wattelectricresistanceheater. Theelectricheatersarewired

toacranktimersotheycannotbeleftONforlongperiodsoftime.

2.7. Ventilation Systems

AswithmostofRDIshomes,theWisdomWaydwellingswilluseanexhaustonlyventilation

strategy.In

the

primary

bathroom

of

each

home,

aPanasonic

Whisper

Green

exhaust

fan

(modelno.FV08VKSL1)isinstalledandprogrammedtoruncontinuouslytomeetthewhole

buildingventilationrequirementsofASHRAEstandard62.22007(3060CFM,dependingonthe

unit). Thefanisalsoequippedtoboosttohighspeed(80CFM)foranadjustableamountof

timewhenthebathroomisinuse.


7/23

Figure3. Theexhaustfanandsimpleductdistributionsysteminstalledbetweenthefirstand

secondfloors.

2.8. Water Heating

Mostoftheenergyneedsfordomesticwaterheatinginthehomeswillbeprovidedbysolar

thermalsystems. Flatplatesolarcollectorsaremountedonthesouthernroofofeachhome,

andapropyleneglycolantifreezesolutioniscirculatedbetweenthecollectorsandaheat

exchangerlocated

in

astorage

tank

in

the

basement.

A

direct

current

pump

circulates

the

glycol;thepumpispoweredbyadedicatedPVmodule. Auxiliarywaterheatingineachhomeis

providedbyasealedcombustion,naturalgasfired,tanklesswaterheaterinstalledinthe

basementnearthesolartank.

2.9. Solar Electric Systems

Three andfourbedroomhomeshave3,420WattPVsystems,and2bedroomhomeshave

2,850Wattsystems. Overthecourseofayear,thelargersystemswillgenerateapproximately

3,750kWh;

the

smaller

systems

will

generate

3,125

kWh.

Benchmark

analyses

show

that

in

a3

bedroomunit,the3.4kWPVsystemwillprovide77%ofthehomeselectricalneeds.

3. Short-Term Testing

CARBworkedwithresearchersfromtheNationalRenewableEnergyLaboratory(NREL)toassessthe

performanceofatypicalthreebedroomhomeoneofthefirstthehomescompleted. Testingwas

performedduringoneweekinFebruary2009beforethehomewasoccupied.

3.1. Research Questions

ThefollowingresearchquestionsandgoalswereidentifiedbyCARBandNRELbeforethetesting

wasperformed.

1. Whatistheeffectiveleakageareaoftheunitasmeasuredwithablowerdoor? How

doestheleakageareachangewhentheadjacentunitisalsopressurized(guarded)? Do


8/23

ratesofthedistributionsystem? Whatarethepowerdrawsoftheventilationandair

distributionfansineachoperatingstate? Doallofthesequantitiesmeetthedesign

targets?

3. Whatarethetemperaturesinvariousroomsthroughouttheduplexoverconsecutive

24hourperiodswitheachoftheconditionsshowninTable3? Doesacentralpointin

eachroommeettheASHRAEStandard55comfortrecommendationsatvarioustimes

duringeachtest? DotemperaturedifferentialsbetweenroomsmeetACCAManualRS

guidelines(4Fmaximum)? Arethereanynoticeablehotorcoldspotsoninterior

surfacesasmeasuredusinganIRcamera?

Table3. Testmatrixformeasuringuniformityofheatingandoutsideairdistribution.

4. Usingoneunitoftheduplexasthetestspace,whatarethedifferencesinoutsideair

distribution(i.e.RAoA)throughouttheduplex,usingtheoperatingconditionsshownin

Table3?

3.2. Blower Door, Airflow, and Power Measurements

Totestenvelopeairleakage,CARBperformedblowerdoortestingoneachhalfoftheduplex

separatelyandcoincidentallytoassessleakagethroughthepartywall. Thethreebedroomunit

wheretheshorttermtestingwasperformedhadtotalenvelopeleakageof273CFMwhenthe

homewasdepressurizedto50Pa. Afivepointblowerdoorregressionshowedtotaleffective

leakagearea(ELA)of11.2in2. Whentheneighboringunitwasdepressurizedcoincidentally,

leakagedropped

by

40

CFM50

and

0.2

in

2

.With

such

low

party

wall

leakage,

researchers

concludedthattracergastestingandRAoAcalculationscouldbedoneeffectivelyinonlyone

halfoftheduplex. Significanttestingintheotherhalfwasnotpossibleasitwasalready

occupied.

TheHVAClayoutforthehometestedisincludedintheappendix. CARBmeasuredairflowand

Test

Case Doors

Ventilation

Fan

Distribution

Fan Notes

0 Closed Off Off Basecase;noventilation

1 Closed On On

2 Closed On Off

3 Closed On Off 1in2

openingineachbedroom

4 Open On On

5 Closed On On60Wlampineachbedroom. Notracer

gastests;tempmeasurementsonly.


9/23

3.3. Tracer Gas and Temperature Distribution Testing Procedure

Atsixpointsthroughoutthehome,NRELresearchersinstalledthermocoupleswithinradiation

shieldsat

4

above

the

floor.

A

simple

weather

station

also

measured

outdoor

air

temperature

andwindspeed. ThermocouplesandothersensorswerewiredtoaCampbellScientificCR10

datalogger,andconditionswererecordedat5minuteintervals.

Atthesamelocationofeachofthesixinteriorthermocouples(seeFigure4),NRELalsoinstalled

2.5mm(ID)polyethylenetubingthroughwhichairsamplesweredrawnevery12minutes. Air

sampleswererunthroughaBruelandKjaermodel1303multipointsamplerandmodel1302

multigasmonitor. Atthebeginningofeachtest,researchersintroducedasmallamountof

sulfurhexafluoride

(SF6)

into

the

home

and

distributed

it

evenly

through

all

spaces.

By

analyzing

theratesofdecayinSF6concentration,researcherswereabletocalculateeffectiveairchanges

ineachspace;moreaccurately,researcherscouldcalculatereciprocalageofair(RAoA,hr1)in

eachspace. Formoredetailsonthistestprocedure,seeNRELdocumentNREL/TP55031548,

ATestProtocolforRoomtoRoomDistributionofOutsideAirbyResidentialVentilation

Systems. Eachtestbeganatapproximately8:00AMandranforapproximately23hours.

Figure4. Sensorstandinonebedroomcontainingtracergassamplingpointandshielded

thermocouple. PhotofromNREL.

3.4. Air Distribution Results

Tracer gas tests performed ith all doors closed and the distrib tion fan t rned off (test case 2)


10/23

closed. Whendoorsareopen,thereisvirtuallynodifferenceinairchangerates. Inthistested

RDIhome,whenthedistributionfanwasturnedON(Case1),thevariationsinairchangerates

are

dramatically

reduced.

The

lowest

RAoA

is

again

in

the

northeast

bedroom

at

0.27

hr

1

,

but

thehighestvaluesinthekitchenandlivingroomisonly0.32hr1.

Basedontheseresults,CARBhasconcludedthatthissimpledistributionsystemmoving2530

CFMfromthecentralspacetoeachbedroomdoesindeedaddressconcernsaboutunequalair

changeratesindifferentpartsofthesehomes.

Whatremainsuncleariswhatrealimplicationsthatsuchvariationsinairchangerateshave.

Builders

like

RDI

have

used

exhaust

only

ventilation

in

hundreds

of

relatively

small,

efficient

homeswithnoapparentperformance,health,ordurabilityproblems. Ontheotherhand,when

bedroomsareoccupieddoorsareoftenclosed;receivinghalftheairchangesunderthese

circumstancesdoesnotseemideal. Itseemsthatthesimpledistributionsysteminthesehomes

seemstoaddressthisproblemquiteeffectively. CARBhopesthisresearchwillleadtogreater

understandingofthesesystems,butCARBbelievesmoreinvestigationisneededof

performanceissuesandIEQimplicationsofvariousventilationsystems. CARBalsohopesthat

theseinvestigationswilldrivedevelopmentofmoresmall,simple,lowcostmechanicalsystems

for

high

performance

homes.

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Case 1 Case 2 Case 3 Case 4

RAOA,

hr

1

AirChangeComparisons

LivingRoomKitchen

SWBRSEBRNEBRBath


11/23

3.5. Thermal Comfort Analysis and Results

3.5.1. Thermal Design Considerations

Thekeythermalcomfortconcerninthehomesiswintertemperaturesinupstairsbedrooms

thatarenotdirectlyheated. Whileloadsvaryfromroomtoroom,theaveragedesignloadofa

bedroomisapproximately1,500Btu/h(440W)withoutdoortemperaturesof2F. Asdesign

loadsgenerallyoccurduringthenight,solargainswerenotconsideredinthisanalysis.

Thesimpleheatingsystemreliesonmeetingthisloadinfourbasicways:

Internalgains(people,lights,electronics,etc.inbedrooms);

Natural

convection

air

moving

upstairs

from

a

warmer

downstairs;

Conductionthroughthefloorfromtheheatedspacesbelow;

Forcedconvectionfromthesmalldistributionsystem.

Internalgainswillvarytremendously. Asleepingpersonmaygiveoffapproximately60W,while

anawakepersonnotperformingrigorousexercisemaygenerate80100Watts. Avery

conservativeestimateforlightsandotherelectronics(TV,computer,alarmclock,stereo,

chargers,etc.)is45Wattswhileabedroomisoccupiedbyanawakeperson. Asanexample,a

bedroom

occupied

by

a

single,

awake

person

reading,

studying,

or

watching

TV

might

have

internalgainsof125W. Thisvalueisapproximately30%ofthedesignloadofthebedroom.

CARBbegancomputationalfluiddynamicsanalysis(CFD)toattempttoquantifyenergytransfer

fromnaturalconvectionwithinthehome. However,itsoonbecameapparentthatthe

quantitiesofheattransferredweresosmallandimpactoffactorssuchasresidenthabitswere

solargethathighuncertaintiesintheanalyseswouldmaketheresultsnexttomeaningless.

However,itispossibletoperformsimpleUAcalculationsonthefloorassemblybetweena

downstairs

space

(heated

directly)

and

an

upstairs

bedroom.

With

a

floor

area

of

160

ft

2

,

an

effectivefloorassemblyRvalueof3ft2hrF/Btu,andatemperaturedifferentialof7F,heat

conductionthroughthefloorassemblyisapproximately340Btu/hor100Watts. This

represents2025%ofthetypicaldesign load.

Notethatthetemperaturedifferentialinthiscalculationhastwoelements:

Upstairsbedroomairtemperatures(at4abovethefloor)of23Fcoolerthan

downstairsairtemperatureat4abovethefloor;

Airtemperatures

at

the

ceiling

of

the

first

floor

from

where

the

exhaust

fan

exhausts

of45Fhigherthanroomairtemperaturesat4feetfromthefloor. Duringthe

testing,CARBverifiedthatairattheceilingwasindeed45Fwarmer.

Thefinalheattransferelementisheatfromthesmalldistributionsystem. Usingthesame

temperaturedifferentialfromabove(7Ffromtheceilingofthefirstfloortotheaverage


12/23

Naturalconvection i.e.warmairrisingfromdownstairstoupstairswillprovide

significantheattobedrooms,especiallywhenbedroomdoorsareleftopen. Thiswas

not

quantified

during

design

stages;

Whenusedforsleeping,bedroomtemperaturesoflessthan6870Fareoftendesired

orconsideredacceptable;

Ifnotusedforsleeping,e.g.ifabedroomisusedasanofficeorstudy,internalgains

substantiallyhigherthanthe125Wattsusedintheexampleabovearelikely. Also,

designtemperaturesoccurinthenightorveryearlymorningnotwhenactivityinsuch

roomsishighest;

Finally,somesparinguseofportableelectricheatersmaybeusedunderextreme

conditions.

3.5.2. Thermal Comfort Test Results

TheweekoftestinginFebruary2009hadconsistentwinterweather: amixofcloudsandsun,

hightemperaturesinthe30sor40s,lowtemperaturesintheteensortwenties(F). When

CARBandNRELarrivedatthehome,theheaterthermostatwassettoapproximately50F;

researcherssetthetemperatureupto68F,butitrequiredalmost1012hoursbeforeupstairs

bedroomswerewithin4Fofdownstairstemperatures.

Plotsshowingtheresultsofthefourrelevanttestcasespertainingtotemperaturedistribution

areshownbelowinFigure6throughFigure9. Table4showsasummaryofthefinal

temperaturemeasurements. Thetableshowsairtemperaturesmeasuredat4:00AMduring

eachtest. Astestsbeganatapproximately8:00AMeachday,at4:00AMtestshadrun

approximately20hours,andoutdoortemperatureswereusuallynearthecoldestofeach24

hourperiod;CARBbelievesthesevaluesareasclosetosteadystateconditionsaspossible

duringthesetests.

Table4.

Summary

of

temperature

distribution

test

results.

Final

temperatures

were

recorded

at4:00AMofthedayofthetest,whenthetesthadbeenrunningapproximately20hoursand

outdoortemperatureswereneartheircoldest.

Test

Case Doors

Dist.

Fan Notes

Out

doors

Living&

Kitchen SEBR NEBR SWBR Bath

1 Closed On 17.3 68.9 65.4 63.1 66.4 64.1

2 Closed Off 34.8 70.6 61.8 60.6 62.7 63.7

4 Open On 23.7 69.1 65.9 65.9 66.6 65.7

5 Closed On60Wlampin

eachbedroom.26.6 68.1 66.3 65.0 67.4 64.6

"Final"Temperatures


13/23

Figure6. Plotshowingtemperaturesduringtestcase1. Alldoorsinthehomewereclosed,the

distributionfanwasrunning,andthesetpointoftheheaterinthelivingroomwas70F.

10

15

20

25

30

35

40

45

50

55

57

59

61

63

65

67

69

71

73

75

1

200

1

400

1

600

1

800

2

000

2

200

2

400

200

400

600

OutdoorT

emperature,

F

RoomT

em

perature,

F

Hour

RDI Room TemperaturesCase 1: Doors Closed, Distribution Fan On

Living

Kitchen

SE BR

NE BR

Bath

SW BR

Outside

10

15

20

25

30

35

40

45

50

55

57

59

61

63

65

67

69

71

73

75

OutdoorT

emperature,

F

RoomT

emperature,

F

RDI Room TemperaturesCase 2: Doors Closed, Distribution Fan Off

Living

Kitchen

SW BR

SE BRNE BR

Bath

Outside


14/23

Figure8. Plotshowingtemperaturesduringtestcase4. Alldoorsinthehomewereopen,the

distributionfanwasrunning,andthesetpointoftheheaterinthelivingroomwas70F.

10

15

20

25

30

35

40

45

50

55

57

59

61

63

65

67

69

71

73

75

800

1000

1200

1400

1600

1800

2000

2200

2400

200

400

600

Outdoor

Temperature,

F

RoomT

emperature,

F

Hour

RDI Room TemperatureCase 4: Doors Open, Distribution Fan On

Living

Kitchen

SW BR

SE BR

NE BR

Bath

Outside

10

15

20

25

30

35

40

45

50

55

57

59

61

63

65

67

69

71

73

75

Outdoo

rTemperature,

F

Room

Temperature,

F

RDI Room TemperaturesCase 5: Doors Closed, Distribution Fan On, 60W lights On

Living

Kitchen

SW BR

SE BR

NE BR

Bath

Outside


15/23

Whilethechartsoftemperatureresultsareinformativeinthemselves,CARBusedthetest

resultstocreateasimple,steadystateheattransfermodeltopredicttemperaturesin

bedrooms

under

varying

conditions.

The

variable

inputs

to

this

model

are

outdoor

temperature,

livingroomtemperature,internalgainsineachbedroom,andconditionofthebedroomdoors

(openorclosed). ThismodelwasbasedoncalculationssimilartothosedescribedinThermal

DesignConsiderationsabove,buttheassumptionswererefinedbasedonmeasurementsand

testresults. Thetestsalsoallowedapproximationsfornaturalconvectiveheattransferfrom

downstairstoupstairsbedrooms(whichvariedtremendouslywhendoorswereopenorclosed).

Whilethemodelisverysimple,ithashelpedCARBpredictthermalcomfortundervarious

conditionsanddeveloprecommendationsforRDIandhomeresidents.

Severalexampleresultsofthesteadystatemodelareshownbelow. Thefirst,inTable5,shows

conditionssimilartotestconditions1and4(seeTable4). Inthisscenario,theunoccupied

northeastandsoutheastbedroomswithdoorsclosedwouldbemorethan4Fcoolerthan

thedownstairsspace(this4FtoleranceisusedincomfortstandardssuchasACCAManualRS).

Table5. OutputofCARBssteadystateheattransfermodelpredictingbedroomtemperatures.

Theexample

shown

in

Table

6parallels

test

case

5,

where

a60

Watt

lamp

was

lit

in

each

bedroomtosimulateasingle,sleepingperson. Theeffectsofsuchasmallloadarenoticeable

(seeFigure9aswell),butthetemperatureinthenortheastbedroom(withdoorsclosed)isstill

morethan4Flowerthanthecentralspacedownstairs.


Downstairs Temp: 70 F

Outdoor Temp: 20 FInternal Gains: 0 Watts

SW BR SE BR NE BR

Doors Closed 67F 65F 63F

Doors Open 68F 67F 66F



SW BR SE BR NE BR


D O 70F 69F 68F


16/23


Ofcourse,20FisnotthedesigntemperatureinGreenfield,MA;the99%designtemperatureis

2F. Undertheinteriorloadconditionswith2Foutdoortemperature,Table8showsthatair

temperatureinthenortheastbedroomwithdoorsclosedisagainpredictedtobemorethan

4Fbelowtheairtemperaturedownstairs.


Underdesign

conditions,

the

model

shows

that

with

internal

gains

of

only

200

Watts

the

bedroomtemperaturesarenotmorethan2Fbelowthedownstairsairtemperature(seeTable

9). Suchgainsarenotatalluncommoninoccupiedroomswherecomputerequipment,audio

equipment,ortelevisionsarebeingused. Insomecaseswhenoutdoortemperaturesarevery

lowandinternalgainsaremodest,residentsmayusesmallelectricresistanceheatersforshort

periodsoftimetomakeupthisdifference.



Outdoor Temp: 20 F

Internal Gains: 120 Watts

SW BR SE BR NE BR





SW BR SE BR NE BR




Outdoor Temp: 2 F

Internal Gains: 200 Watts

SW BR SE BR NE BR


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3.6. Recommendations to Residents

SWAhaspresentedasummaryofthesetestresultstohomebuyersandfoundthemquite

interestedand

receptive

though

they

were

certainly

most

excited

about

the

extremely

low

energycostsexpected. SWAhasalsoprovidedmaterialtoRDIforthehomeownersmanualson

recommendationsforoperatingandstayingcomfortableinthesehomes. Briefly,the

recommendationsinclude:

Comfortispersonal;neighborsmaybecomfortableunderverydifferentconditions.

Onceroomsarewarm,theytendtostaywarm. However,coldbedroomsmaytake

severalhourstofullyheatup.

Werecommendagainstextremedaytimethermostatsetback. Recoverymaybeslow,

andenergy

savings

are

minimal

for

two

reasons:

o Verylowenvelopeheatloss.

o Duringsunnydays,theheaterdoesnotneedtorun.

Ifyoudousedaytimesetback,makesetbackssmallandstartincreasingtemperatures

early.

Itisworthsettingthetemperaturedownifleavingforseveraldays.

Youmayalsowanttolowertemperaturesslightlyatnightforsleeping.

Keepbedroomdoorsopenwhennotoccupied.

Itspossible

that

sparing

use

of

small,

inexpensive

electric

heaters

may

be

desirable.

Oncearoomiswarm,heatersshouldntbeneededexceptunderextremelycold

conditions.

Duringcoldestweather,keepingdownstairsattheupperendofcomfortrange(7072F,

ratherthan6668F)willkeepbedroomswarmer.

Learnwhatworksbestforyou.

4. Long-Term Monitoring and Evaluation

Duringthe

winter

of

2009

2010,

CARB

has

made

agreements

with

residents

of

four

homes

to

record

temperatureandhumidityconditionsatseverallocationsineachhome. Temperaturesineach

bedroom,thecentrallivingspaces,andoutdoorsarebeingrecordedat10minuteintervalsthroughout

thewinter. Inthespring,CARBwillalsointerviewresidentstodetermine:

Howtheygenerallyusedeachspace;

Theirimpressionsofcomfortconditionsinvariousspaces;

Whatpracticestheyusedtostaycomfortable(opendoors,thermostatsetbacks,spaceheaters,

etc.);

OtherfeedbackorerecommendationsrelatedtotheperformanceoftheHVACsystems.

CARBfeelsthatlongtermmonitoringofoccupiedhomesalongwithfeedbackfromresidentsis

criticaltoaccurateassessmentofthisHVACstrategy.

5. Gate Criteria


18/23

equipment. CondensinggasroomheatersareavailableinEurope;theymaybecomemore

availableintheUSsoon.

5.1.2. Performance-Based Code Approval

Therewerenocodeissueseitherperformanceorprescriptiveencounteredrelatedtothe

mechanicalsystemsinthesehomes.

5.2. Should Meet Criteria

5.2.1. Prescriptive Code Approval

Therewerenocodeissueseitherperformanceorprescriptiveencounteredrelatedtothe

mechanical

systems

in

the

homes.

5.2.2. Cost Advantage

Thecostsavingsistheprimarybenefitofthistypeofsimplemechanicalsystem. Inthese

homes,thesimpleheatingsystemsavedRDIapproximately$4,500(whencomparedtotheir

standardsystemofaboilerwithbaseboardconvectors). Thissubstantialsavingswentalong

waytooffsettheadditional$6,050spentinthermalenvelopeimprovementsineachhome.

5.2.3. Reliability Advantage

Theoperation

and

maintenance

of

sealed

combustion,

gas

fired

room

heaters

is

generally

simplerthanmaintenancerequiredoncentralfurnaces. Thesedeviceshavebeenavailableand

inusefordecades;theysimplyhavenotoftenbeentheprimaryheatsourceforanentirehome.

CARBfeelsthatthisreliabilitycriterionhasnotyetbeenfullyaddressedbecauseofthelackof

documentationofcomfortconditionsinoccupiedhomes. Afterthewinterof20092010,CARB

hopestohavedatatomorefullyaddressthiscriterion.

5.2.4. Manufacturer/Supplier/Builder CommitmentTherearenomanufacturerorsupplierissuesrelatedtothistechnology. Theseroomheaters

arereadilyavailablefromseveraldifferentmanufacturers. CARBhasalsoheardreportsofmore

modelsandmoreefficientmodelsbecomingavailable.

Regardingbuildercommitment,aslongascomfortandreliabilityisaddressed,RDIiscertainly

opentousingsimilarsystemsinfutureprojects. Withthesignificantpublicitythatthisproject

hasachieved,therehavebeenseveralotherbuildersanddeveloperswhohaveexpressed

interestin

such

simple

mechanical

systems.

5.2.5. Gaps Analysis

5.2.5.1 Comfort

Asdescribedabove,comfortinbedrooms(withoutdirectheat)isoneofthelargestconcerns

i h hi B d d li d h i CARB b li h f ill b


19/23

threesmall,pointsourceheaters(gasroomheaters,minisplitheatpumps,etc.)ratherthana

conventionaldistributedHVACsystem. Implicationsforlargerhomesneedtobeinvestigated

further.

5.2.5.3 VentilationAirDistribution

Thesmall,simpledistributionsysteminstalledinthesehomescombinedwiththeexhaustonly

ventilationsystemappearedtoaddressvariationsinairchangeratesinallspaceswhendoors

areclosed. However,thereisstillaquestionaboutperformanceofexhaustonlyventilation

withoutsuchadistributionsystem.

Inaddition,thedistributionsystemusesanexhaustfan. CARBhastalkedtoseveralHVAC

equipmentmanufacturers

about

adistribution

fan

of

similar

size

and

power

consumption

but

withpotentialforairfiltrationandpossiblyevenauxiliaryresistanceheat. Forlargerhomes,

slightlylargerfansmaybeappropriate. Asthisisrelativelynewterritory,CARBbelievesagreat

dealmoreinvestigationisneededintoappropriateapplicationsandequipmentforsuchsmall,

simpleairsystems.

6. Discussion and Conclusions to Date

HomeslikethesethatarereallyapproachingzeroenergyareforcingaparadigmshiftinHVAC

systems.There

are

simply

no

conventional

heating

systems

sized

to

meet

these

small

loads.

Also,

as

shownabove,typicalinternalgainsinbedroomsareonthesameorderofmagnitudeasheatlost

throughtheenvelope. Notonlywouldanyconventionalfurnaceorboilercapacitybethreetimesthe

sizeofthedesignloadofthesehomes,unlesseachbedroomwasaseparatezone,aconventional

systemwouldalsonotaccountforvaryinginternalgainsinbedrooms;thiscouldfrequentlyresultin

overheatingofspaceswithoutathermostat.

Withtheinvestigationsdonetodate,SWAbelievesthissimple,efficient,lowcost,lowmaintenance

HVACsystem

will

provide

comfort

as

good

if

not

better

than

aconventional

system

(such

as

acentral

gasfurnace). Theonehomeownerwhooccupiedahomeduringthewinterof20082009saidtherewas

noneedforauxiliaryheatinbedrooms;theystayedcomfortable. Monitoringandinterviewsfromthe

winterof20092010willshedmorelightoncomfortandperformanceissuesinthehomes.

Ifperformanceresultscontinuetobepositive,CARBbelievesthatsmall,simpleHVACsystemscanoffer

tremendouscostsavingsinhighperformancehomesatleastpartiallyoffsettingthecostofsuper

insulatedenvelopes. IntheseRDIhomes,theaddedthermalenvelopefeaturescostRDIapproximately

$6,050(when

compared

to

their

standard

construction:

2x6

walls

with

blown

cellulose,

double

pane

windows,R38attics). Withthesimplemechanicalsystems,RDIsavedapproximately$4,500when

comparedtotheirconventionalheatingsystem(boilerwithhydronicbaseboardconvectors). Such

savingscanbetremendouslyhelpfulinachievingBuildingAmericaperformancegoalscosteffectively.


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SWA Report on WWSV Heating Systems

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