Unit a (Alternative Heating)

8/2/2019 Unit a (Alternative Heating)

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Codes, regulations, and laws regarding wood-heating,

gas appliances, and components change frequently. It is

essential that you be familiar with the appropriate cur-

rent National Fire Protection Association (NFPA) infor-

mation and other codes, regulations, and laws.

OBJECTIVES

After studying this unit, you should be able to

list reasons for the formation of creosote.

describe methods to help prevent the formation of

creosote.

explain how stovepipe should be assembled andinstalled.

list safety hazards that may be encountered with wood

stoves.

describe the three types of venting for gas stoves.

explain how a fireplace insert can improve on the

heating efficiency of a fireplace.

describe the difference between passive and active

solar systems.

describe the declination angle and the effect it has on

the suns radiation during winter and summer.

list the typical components in a liquid-based solar

system and describe the function of each.

describe the operation of a solar domestic hot watersystem.

describe a swimming pool solar-heating system.

SAFETY CHECKLIST

Many safety practices must be adhered to when

installing or using a wood-burning appliance. Many of

these safety practices are stated within this unit, printed

in red. Many other safety practices must be adhered to

including those provided by manufacturers and local,

regional, and state codes. It is also necessary to use good

judgment and common sense at all times.

If an antifreeze solution is used in a solar domestic hot

water system, a double-walled heat exchanger must be

used.

A.1 WOOD-BURNING STOVES

Stoves are used as an alternative heating appliance in many

homes. Some homes use stoves as a primary heat source, and

others use them to supplement primary heat sources. Both

wood- and gas-burning stoves are used. Wood must be read-

ily available to make the use of wood-burning stoves prac

cal. However, pellet stoves, which burn small compresse

wood by-products, may be used in many locations where pe

lets are available.

A.2 ORGANIC MAKEUP ANDCHARACTERISTICS OF WOOD

Wood plants manufacture glucose. Some of this glucose,

sugar, turns into cellulose. Approximately 88% of wood

composed of cellulose and lignin in equal parts. Cellulose

an inert substance and forms the solid part of wood plants.

forms the main or supporting structure of each cell in a treLignin is a fibrous material, a polymer, which binds to cell

lose fibers and hardens and strengthens the cell walls

trees. The remaining 12% of the wood is composed of resin

gums, and a small quantity of other organic material.

Water in green or freshly cut wood constitutes from o

third to two thirds of its weight. Thoroughly air-dried woo

may have as little as 15% moisture content by weight.

Wood is classified as hardwood or softwood. Hickor

oak, maple, and ash are examples of hardwood. Pine an

cedar are examples of softwood. Figure A1 lists some common types of wood and the heat value in each type in m

lions of Btu/cord. A cord of wood can be split, unsplit,

mixed. It is important to know whether the wood is split, bcause there is more wood in a stack that is split. Wood is so

Alternative Heating (Stoves,Fireplace Inserts, Solar)A

UNITUNIT

A

Figure A1 The table indicates the weight per cord, the Btu percord of air-dried wood, and the equivalent value of No. 2 fuel oil in

gallons. Courtesy Yukon Energy Corporation


2/16

by the cord, which is a stack 4 ft 4 ft 8 ft or 128 ft3. Be-

cause wood is sold by volume and not by weight, wood that

is split has less air space between the individual pieces. This

will give the cord of wood a higher density, meaning more

wood per cord.

Wood should be dry before burning. Approximately 20%

more heat is available in dry wood than in green wood. Wood

should be stacked off the ground on runners and should be

well ventilated, Figure A2. When possible, the wood shouldbe covered, but air should be allowed to circulate through it.

Wood splits more easily when it is green or freshly cut and

dries better when it has been split. When green wood is

burned, combustion will be incomplete, resulting in un-

burned carbon, oils, and resins, which leave the fire as

smoke.

During oxidation or burning, oxygen is added to the

chemical process. This actually turns wood back into prod-

ucts that helped it grow as a plant: primarily carbon dioxide

(CO2), water (H

2O), and other miscellaneous materials. Heat

also is produced. Some woods produce more heat than oth-

ers per cord, Figure A1. Generally, dry hardwoods are themost efficient.

A.3 ENVIRONMENTAL PROTECTIONAGENCY (EPA) REGULATIONS

On July 1, 1988, the Environmental Protection Agencys first

national woodstove emissions standards went into effect.Emissions from wood-burning appliances were adding to the

pollutants in the air along with all the other sources of air pol-

lutants. C Wood smoke contains both polycyclic organicmatter (POM) and nonpolycyclic organic matter, which are

considered to be health hazards and are of concern to many

people.CAll wood-burning stoves manufactured after July1, 1989, must be EPA certified. Two EPA standards exist

one for catalytic stoves and one for noncatalytic stoves. Cat-

alytic stoves contain a catalytic combustor and may not emit

more than 5.5 g/h of particulates for those stoves manufac-

tured between July 1, 1989, and June 30, 1990. The noncat-

alytic stoves manufactured between these dates may not emit

more than 8.5 g/h. These limits are reduced further for those

stoves manufactured after July 1, 1990, to 4.1 g/h for the cat-

alytic models and 7.5 for the noncatalytics. As new stoves are

purchased and installed, replacing older stoves, the air pollu-

tants from wood-burning stoves will be reduced drastically,

because the particulate emission of the catalytic stove is ap-

proximately 10% of the emissions of the older stoves.

A.4 CREOSOTE

Creosote is a mixture of unburned organic material. When it

is hot, it is a thick dark-brown liquid. When it cools, it forms

into a residue like tar. It then often turns into a black, flaky

substance that adheres to the inside of the chimney or stove-

pipe. The formation of creosote is particularly a problem

with the uncertified stoves manufactured before July 1,

1989. Some of the primary causes of excessive creosote are:

smoldering low-heat fires.

smoke in contact with cool surfaces in the stovepipe or

chimney.

burning green wood. burning softwood.

SAFETY PRECAUTION: Creosote buildup in the stovepipe and

chimney is dangerous. It can ignite and burn with enough

force to cause a fire in the building. Stovepipes have been

known to be blown apart, and chimney fires are common

with this excessive buildup.

To help prevent the formation of creosote, burn dry hard-

wood. Fires should burn with some intensity. When the

stovepipe or chimney flue temperature drops below 250F,

creosote will condense on the surfaces. Use as little run of

stovepipe as possible. The minimum rise should be 1/4 in. per

ft of horizontal run. A rise of 30 is recommended, FigureA3. Anything that slows the movement of the gases allows

2 Refrigeration and Air Conditioning Technology

1 CORD OF WOOD

8 ft

4 ft

4 ft

Figure A2 Wood should be stacked on runners so that air cancirculate through it.

FLUSH WITHINSIDE OFFLUE LINER.

STOVEPIPE SHOULDRISE FROM STOVE

TO CHIMNEY (1/4" RISEPER FOOT IS THE MINIMUM

RECOMMENDED).

KEEP RUN ASSHORT ASPOSSIBLE.

CHIMNEY FLUE

Figure A3 The stovepipe should rise from stove to chimney.


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them to cool, which will cause more creosote condensation.Stovepipes and chimneys should be cleaned regularly.

Assemble the stovepipe with the crimped end down,

Figure A4. This will keep the creosote inside the pipe.

A.5 DESIGN CHARACTERISTICS OFWOOD-BURNING STOVES

As mentioned earlier, all wood-burning stoves manufactured

since July 1, 1989, must be EPA certified. These may be cer-

tified as noncatalytic or catalytic combustor stoves.

Noncatalytic Certified StovesThese stoves force the unburned gases to pass through a sec-

ondary combustion chamber. Temperatures higher than

1000F are maintained in this chamber, burning the gases.

This burns the pollutants, including most of the creosote, and

produces more heat, providing a better stove operating effi-

ciency. Figure A5 is an example of one design of this typeof stove.

Catalytic Combustor Certified Stoves

The catalytic combustor is a form of afterburner that in-

creases the burning of wood by-products. These combustorsuse a catalyst to cause combustion by producing a chemical

reaction, which burns the flue gases at about 500F rather

than the 1000F otherwise required.

Most combustors are a cell-like structure, Figure A6, andconsist of a substrate, washcoat, and catalyst. The substrate

is a ceramic material formed into a honeycomb shape. Ce-

ramic material is used because of its stability in extremely

cold and hot conditions. The washcoat, usually made of an

aluminum-based substance called alumina, covers the ce-

ramic material and helps disperse the catalyst across the com-

bustor surface. The catalystis made of a noble metal, usually

platinum, palladium, or rhodium, which is chemically stab

in extreme temperatures. Figure A7 is an illustration ofwoodstove with a catalytic combustor. A disadvantage of th

combustor is that it must be replaced every few years.

Radiation and Convection Characteristics

Wood-burning stoves heat by both radiation and convectio

Radiation is heat that comes from the stove in waves an

heats objects in its path, such as the walls, floor, and furn

ture. The stove also heats the air around it. This is called co

vective heat. As the air is heated, it rises, and cooler a

comes in to take its place, and it is heated. The cycle conti

ues, and the currents are referred to as convection curren

Some stoves are designed to utilize the convective heating

a greater extent than others. These stoves may have a blow

Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)

CRIMPEDEND DOWN

CREOSOTE WILLRUN DOWNSTOVEPIPETO STOVE.

CREOSOTE WILLLEAK OUTAROUND JOINT.

CRIMPEDEND UP

WRONGRIGHT

Figure A4 The stovepipe should be assembled with the crimpedend down so that creosote will not leak out of the joint.

Figure A5 A noncatalytic wood-burning stove. CourtesyHearthStone NHC, Inc.

CATALYST

WASHCOAT

SUBSTRATE

MAGNIFIED SECTION

LENGTH

DIAMETER

CELL DENSITY(NUMBER OF COPENINGS PERSQUARE INCH)

Figure A6 A catalytic combustor element. Courtesy of CorningInc.


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system to spread the heat out further and to make the con-

vection process more efficient.

Pellet Stoves

Pellet stoves are a more recent design, are energy efficient,

and use a renewable energy source, Figure A8. The fuel con-sists of small compressed pellets made from waste wood, pri-

marily sawdust from lumber sawmills. However, the pellets

may be made from waste cardboard or even agricultural

wastes such as sunflower and cherry seed hulls. Stove own-ers should be sure that only the type of pellets recommended

by the manufacturer are used. They are normally provided in

40- or 50-lb bags.

Most pellet stoves are designed with a hopper at the back

or top. The pellets are fed to the combustion chamber with an

auger powered by an electric motor, which is often con-

trolled with a thermostat. The room air is generally circulated

through the heat exchanger and into the conditioned space by

a multispeed blower.

Very little air pollution is produced with as little as 1%

of the pellet material remaining as ash. Most stoves do not

require a chimney because exhaust gases are forced outsidethrough a vent pipe by a combustion fan. Combustion air

may be drawn in from outdoors so that heated room air is

not used for combustion. This provides additional effi-

ciency by not creating a negative pressure in the room thus

decreasing the cold air that will infiltrate through cracks in

doors and windows. Venting of exhaust gases may be

through a horizontally positioned vent pipe with an end cap

to prevent wind from blowing air and the exhaust gases into

the stove, Figure A9. This horizontal vent pipe must beconstructed of PL vent pipe tested to UL 641 standards. It

is a double-walled pipe with an air space between the walls.

All joints must be sealed with an approved sealer. This is

important because this venting system has an electrically

operated exhaust combustion fan; if there should be a

power failure, the combustion fumes could enter the condi-

tioned space.

A lined masonry chimney that meets all appropriate codes

may be used. However, many masonry chimneys will be

large enough to affect the operation of pellet stoves ad-

versely. These chimneys may be relined with a stainless steel

liner, Figure A10. Consult the stove manufacturers litera-ture for the recommended diameter for these liners.


WOOD

THERMALINSULATION

FLUE

SECONDARY AIRDISTRIBUTOR

ADJUSTABLEPRIMARYAIR SUPPLY

Figure A7 An illustration of a woodstove with a catalyticcombustor. Courtesy of Corning Inc.

Figure A8 A pellet stove. Courtesy Vermont Castings

Figure A9 A horizontal vent pipe must have an end cap to preventair or exhaust gases from being blown into the stove. A vent pipe may

be extended vertically above the eaves. Courtesy Vermont Castings


5/16

Stove Construction

Stoves may be constructed of steel, cast iron, soapstone, or a

combination of these materials. Stoves made of steel are nor-

mally the least expensive. They are made of sheet steel

welded together normally with a firebox of refractory bricks.

These stoves give off heat almost immediately after the fire

is started. With a large, hot fire, they will quickly give off a

considerable amount of heat. However, when the fire dies,the heat from the stove will also quickly cool.

Many stoves are manufactured of cast iron. These stoves

can be much more decorative, because the casting process

provides an opportunity for intricate detail particularly on

the sides and legs, Figure A11. Cast iron is more durablethan steel, and the heat is more even and less intense than that

of a sheet-steel stove. These stoves also cool down more

slowly after the fire dies down or goes out.

Soapstone may be used, particularly in combination with

cast iron, as a material in the manufacture of wood-burning

stoves, Figure A12. Soapstone can withstand the changes intemperature such as from room temperature to very intense

heat. It may be used not only on the exterior of stoves, butalso may be used for the firebox, because it can withstand ex-

posure to direct flames. This material provides a gentle heat

and can hold and radiate heat for longer periods than the

other materials.

Makeup Air

Air used in combustion must be made up or resupplied from

the outside, for example, with an inlet from outside directly

to the stove, Figure A13. Often an older home has many airleaks. The hot air may leak out near the ceiling or through the


Figure A10 Pellet stoves may operate more efficiently if masonrychimneys are relined with a stainless steel liner. Courtesy Vermont

Castings

Figure A11 A wood-burning stove made from cast iron. CourtesMajestic Products Co., Huntington, IN

Figure A12 A wood-burning stove made with soapstone.Courtesy HearthStone NHC, Inc

DAMPER

FRESH AIR INLETFROM OUTSIDE

Figure A13 A stove with a fresh air tube entering it from outside


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attic. Cool air can leak in through cracks around windows,

under doors, and elsewhere. Although this may disturb the

normal heating cycle, it does help to make up air for that air

leaving the chimney as a result of the combustion and vent-

ing. SAFETY PRECAUTION: In modern homes that are sealed

and insulated well, some provision may have to be made to

supply the makeup air. A door may have to be opened a crack

to provide a proper draft. A stove could actually burn enough

oxygen in a small home to make it difficult to get enough oxy-gen to breathe. Always make sure that there is enough

makeup air.

Safety Hazards

SAFETY PRECAUTION: Live coals in the stove in the living

area of a house, along with creosote in stovepipes and

chimneys, make it absolutely necessary to install, main-

tain, and operate stoves safely. This cannot be empha-

sized enough.

Following are some of the safety hazards that may be en-

countered:

A hot fire can ignite a buildup of creosote, resulting in a

stovepipe or chimney fire.

Radiation from the stove or stovepipe may overheat

walls, ceilings, or other combustible materials in the

house and start a fire.

Sparks may get out of the stove, land on combustible

materials, and ignite them. This could happen through a

defect in the stove, while the door is left ajar, while the

firebox is being filled, or while ashes are removed.

Flames could leak out through faulty chimneys, or heat

could be conducted through cracks to a combustible

material.

Burning materials coming out of the top of the chimneycan also start a fire at the outside of the house. These sparks

or glowing materials can ignite roofing materials, leaves,

brush, or other matter outside the house.

A.6 INSTALLATION PROCEDURES

A national testing laboratory should approve a wood-burning

stove or appliance. Before installing a stove, stovepipe, or

prefabricated chimney, be sure that all building and fire mar-

shals codes are followed, as well as the instructions of the

testing laboratory and manufacturer. If one code or set of in-

structions is more restrictive than another, follow the most

restrictive instructions.These instructions should include the distance the stove

should be located from any combustible material, such as a

wall or the floor. They should indicate the minimum required

protective material between the stove and the wall and be-

tween the stove and the floor. Excessive heat from the stove

can heat the walls or floor to the point where a fire can be

started.

The stove must be connected to the chimney with an ap-

proved stovepipe, often called a connectorpipe. Codes and

instructions must be followed.

A stove collar adapter often supplied by the manufac-

turer should be used to install the stovepipe to the stove,

Figure A14. The manufacturer may provide a special pro-vision for this.

Figure A15 shows three different types of installations.The stovepipe must not run through any combustible mater-

ial, such as a ceiling or wall. Approved chimney sections

with necessary fittings should be used. Figure A16 illus-

trates details for adapting the stovepipe to the through-the-wall chimney fittings. Remember to keep horizontal

stovepipe runs to a minimum. A rise of 1/4 in. per ft should

be considered a minimum, Figure A3. Local codes or man-ufacturers may require a greater rise. Be sure that approved

thimbles, joist shields, insulation shields, and other neces-

sary fittings are used where required. Ensure that a recog-

nized national testing laboratory approves all materials and

that all codes are met.

Only one stove can be connected to a chimney. For ma-

sonry chimneys with more than one flue, no more than one

stove can be connected to each flue. A factory-built chimney

used for woodstoves should be rated as a residential and

building heating appliance chimney. Check all codes.

SAFETY PRECAUTION: Many stoves are vented through ma-

sonry chimneys. If a new chimney is being used, it should

have been constructed according to applicable building

codes and carefully inspected. If an old chimney is being

used, an experienced person should inspect it to ensure that

it is safe to use. The mortar in the joints may be deteriorated

and loose, or a serious chimney fire may have cracked the

chimney. All necessary repairs should be made to the chim-

ney by a competent mason before connecting the stove to it.

Manufacturers or their suppliers may recommend that chim-

neys be lined, Figure A10. This may be recommended for a

better draft and/or safety.


USE ALL THREESPECIAL SCREWS.

Figure A14 A stove collar adapter for double-wall stovepipe.


7/16

A.7 SMOKE DETECTORS

SAFETY PRECAUTION: Smoke detectors should be used in

homes regardless of the type of heating appliance used. It

even more important to install smoke detectors when bur

ing wood fuel. Many types of detectors are available. Thes

may be AC-powered photoelectric type or an AC- or batter

powered ionization chamber type.

A.8 GAS STOVES

Gas stoves are becoming popular as a heating appliance. Th

American National Standards Institute (ANSI) may certi

these as a decorative appliance or as a room heater. De

orative appliances are attractive but not designed for larg

space heating. Room heaters are, as the name implies, hea

ing appliances and will have efficiency ratings. These stov

may be manufactured of materials similar to woodstoves an

are available in many attractive colors, Figure A17.


ROUND CAP

PIPE

STOVEPIPE

STOVEPIPE

STOVEPIPE

WALLTHIMBLE

ROUNDSTORM

COLLAR

ROUND

FLASHING

PIPE

WALL SUPPORTWITH CLEAN OUT

NOTE: OUTSIDE CHIMNEYS ARE NOT ASDESIRABLE, SINCE THEY ARE MORESUBJECT TO DOWNDRAFTS AND

CREOSOTE BUILDUP.

CHIMNEY MUST BE ENCLOSED WHERE IT PASSES THROUGH

OCCUPIED SPACES TO MAINTAIN REQUIRED CLEARANCES

TO COMBUSTIBLES AND TO PROTECT AGAINST DAMAGE.

TEEASSEMBLY

ROUND CAP

OPEN BEAM CEILINGINSTALLATION USING

ROOF SUPPORT

EXTERIOR WALL INSTALLATIONUSING WALL SUPPORT, BRACKETS,

AND THROUGH-THE-WALL TEE

STANDARD INSTALLATIONUSING CEILING SUPPORT

PIPE

ROUND CAP

ROUNDSTORM COLLAR

ROUNDSTORM COLLAR

ROUND

FLASHING

ROUND

FLASHING

ATTICINSULATIONSHIELD

FIRESTOP ASSEMBLY

CEILING SUPPORTASSEMBLY

ROOFSUPPORT

ASSEMBLY SUPPORTBRACKETASSEMBLY

Figure A15 Three different types of stove installations.

CHIMNEY TEE BRANCH EXTENSION

CHIMNEY TEE PIPE END PLATE

CHIMNEYCONNECTOR RING

18-INCHDOUBLE-WALL

BLACK STOVEPIPEADJUSTABLE LENGTH

24-INCHDOUBLE-WALL

BLACK STOVEPIPEPIPE SECTION

STOVE COLLARADAPTER

CHIMNEYPIPESECTIONCHIMNEYTEE

CHIMNEY

TEE WALLSUPPORT

TYPICALINSTALLATION

USING90 ELBOW

WITHTHROUGH-THE-WALL

CHIMNEY TEE

WALLTHIMBLE

90 ELBOW

Figure A16 Details of a through-the-wall installation.


8/16

These stoves may be designed to burn natural or propane

gas. Many are designed so the orifice can be adjusted or

changed to switch from burning one gas to the other. Most

utilize a standing pilot for ignition and have controls to shut

off the gas should the pilot be out. Many of these stoves op-

erate without electricity and can be used for heating during a

power outage. Some have variable-speed convection blow-

ers to help circulate the heated air.

VentingThese gas stoves may be designed asB-vent, direct-vent, or

vent-free stoves.

B-VENT. Stoves requiring a B-vent must be vented throughthe roof or into an existing chimney. Aflue liner may be sug-

gested or required if venting into an existing chimney. The

liner will reduce the size of the flue so that the stove will draft

properly.

DIRECT-VENT. Stoves utilizing a direct-vent system use adouble-wall pipe to pull outside air in for combustion and to

vent flue gases to the outside. Direct-vent options mayinclude:

venting straight back from the stove and through the

wall.

venting up from the stove and then through the wall.

venting up through the roof.

in some cases venting into a lined fireplace flue.

VENT-FREE. Vent-free stoves, as the name implies, requireno venting. Some people are concerned about gas combus-

tion in the living area and not venting the flue gases. These

stoves do have a good safety record but are not approved at

this writing in all states. They have an oxygen depletion

sensor (ODS), which turns off the pilot light and gas supply

when the oxygen level in the area of the stove is depleted to

a certain level.

Gas appliances should be installed by certified personnel

or by those approved in that region to do so.

A.9 FIREPLACE INSERTSFireplace inserts can convert a fireplace from a very inefficientheat source to one that is more efficient. Very little heat can be

obtained from a fireplace without some device to help contain

the heat and to move heat from the fireplace into the room. The

fireplace insert provides a way to retain the heat and blow it

into the room. Figure A18 is a photo of a fireplace insert.

Wood-Burning Inserts

Awood-burning insert is basically a woodstove that is designed

to be placed into an existing fireplace. Fireplace inserts can be

either wood- or gas-burning. New wood-burning inserts must

be certified by the EPA as woodstoves are. This makes them

more clean burning and more efficient. For a wood-burning in-

sert to be used, the fireplace and chimney must generally be of

masonry construction. Local building codes and the manufac-

turers specifications for the particular insert should be con-

sulted to ensure that the size and construction of the fireplace

would accommodate the insert. All installations should meet

the NFPA and other appropriate codes. Many factory-built or

prefabricated fireplaces are not approved for inserts.

Inserts are usually made from plate steel, cast iron, or a

combination of these materials. They may fit into the fire-

place opening so that they are basically flush with the front,

or they may protrude to some degree onto the hearth. Thosethat protrude are usually more efficient as this part of the in-

sert will provide more radiant heat. Inserts normally have

blowers that may be controlled manually or with a thermo-

stat and which improve the efficiency.

Codes now in many areas for new insert installations re-

quire that the insert be installed with a positive connection to

the chimney flue, which prevents creosote from running down


Figure A17 A gas stove. Courtesy of Majestic Products Co.,Huntington, IN

Figure A18 A wood-burning fireplace insert. Courtesy of MajesticProducts Co., Huntington, IN


9/16

into the fireplace, causing a fire hazard. Smoke and gases then

exit the fireplace more directly into and out of the chimney.

Before an insert is installed, a professional should inspect

the chimney. If there is creosote buildup, the chimney must

be cleaned. The chimney and fireplace should be checked for

cracks or flaws that could be a fire hazard. Inserts should

never be used in a chimney flue used for another purpose.

Many inserts make it more difficult to clean the chimney,

as they must be removed from the fireplace. Some insertshave a special collar and direct flue liner to the top of the

chimney, and these may be left in place for cleaning. Pro-

fessional chimney sweeps should be employed to clean

chimneys.

Gas Fireplace Inserts

These inserts may be used to convert an existing wood-

burning fireplace to a gas appliance. Many of these may be in-

stalled in prefabricated fireplaces where wood-burning units

may not. They may be designed to burn either natural gas or

propane but usually need to be adjusted for one or the other.

Before installing any insert, ensure that the existing fireplace

and chimney are approved for the insert chosen to be installed.

Many of these units and/or installations require that the

chimney flue be lined with a metal liner and connected to the

insert. This produces a better draft and more efficiency.

These inserts are usually sealed with glass doors and have

blowers that help to make them more efficient. The doors

prevent excess indoor air from being used for combustion.

Just the right amount of combustion air is usually introduced

through adjustable air shutters. Blowers simply make the

convective heat transfer more efficiently. NFPA and other

codes should be consulted regarding these liners.

Some newer gas inserts are designed so that they do notneed a chimney liner. They are less efficient and allow more

heat up the chimney, which heats the existing chimney flue

liner and increases the draft.

All gas appliances, stoves, or inserts must be connected to

the gas source. Piping needs to be routed and installed. This

usually means cutting, threading, and sealing pipe and should

be done by a professional trained and approved to do this work.

A.10 SOLAR HEATING

The sun furnishes the earth with tremendous amounts of di-

rect energy each day. It is estimated that 2 weeks of the suns

energy reaching the earth is equal to all of the known de-posits of coal, gas, and oil. The challenge facing scientists,

engineers, and technicians is to better harness and use this

energy. We know that the sun heats the earth, which heats the

air immediately above the earth. One of the challenges is to

learn how to collect, store, and distribute this heat to provide

heat and hot water for homes and businesses. Many advances

have been made, but the design and installation of solar sys-

tems has progressed very slowly. It is assumed, however, that

as the resources are further depleted and as economics or po-

litical actions cause energy crises, it will be only a matter of

time before direct energy of the sun is used extensively.

A.11 PASSIVE SOLAR DESIGN

Many structures being built presently are usingpassive sol

designs. These designs use nonmoving parts of a building

structure to help provide heat or cooling, or they elimina

certain parts of a building that help cause inefficient heati

or cooling. Some examples follow:

In areas where there are harsh winters, more windows

can be placed on the east, south, or west sides ofhomes and fewer on the north side. This allows

warming from the morning sun in the east and from th

sun throughout the rest of the day from the south and

west. By eliminating windows on the north side, this

coldest side of the house can be better insulated.

Place greenhouses, usually on the south side, to collec

heat from the sun to help heat the house, Figure A19 Design roof overhangs to shade windows from the su

in the summer but to allow sun to shine through the

windows in the winter, Figure A20.


Figure A19 A greenhouse will allow the sun to shine into thehouse. It may also have a masonry floor, or barrels of water may be

located in the greenhouse to help store the heat until evening whenthe sun goes down. This heat then may be circulated throughout the

house.

WINTER SUN

SUMMER SUN

Figure A20 An overhang may be constructed to allow the sun toshine into the house in the winter when it is lower in the sky and ye

shade the window in the summer.


10/16

Provide a large mass such as a concrete or brick wall to

absorb heat from the sun and temper the inside

environment naturally.

Place latent-heat storage tubes containing phase-

change materials where they can collect heat to be

released at a later time, Figure A21.The remainder of this unit is limited to a discussion ofac-

tive solar systems. These systems use electrical or mechani-

cal devices to help collect, store, and distribute the suns

energy. The distribution of this heat to the conditioned spaceis by means of the same type of equipment used in fossil-fuel

furnaces.

A.12 DIRECT AND DIFFUSE RADIATION

The sun is a star often called the daystar. A very small

amount of the suns energy reaches the earth. Much of the en-

ergy that does reach the earths atmosphere is reflected into

space or absorbed by moisture and pollutants before reach-

ing the earth. The energy reaching the earth directly is direct

radiation. The reflected or scattered energy is diffuse radia-

tion, Figure A22.

A.13 SOLAR CONSTANT ANDDECLINATION ANGLE

The rate of solar energy reaching the outer limits of theearths atmosphere is the same at all times. It has been de-

termined that the radiation from the sun at these outer lim-

its produces 429 Btu/ft2/h on a surface perpendicular (90)

to the direction of the suns rays. This is known as the

solar constant. The energy from the sun is often called

insolation.

The earth revolves once each day around an axis that

passes through the north and south poles. This axis is tilted

23.5, so the intensity of the suns energy reaching the north-

ern and southern atmospheres varies as the earth orbits

around the sun. This tilt or angle is called the declination an-

gle and is responsible for differences during the year in the

distribution of the intensity of the solar radiation, FigureA23.


Figure A21 Latent-heat storage tubes may be placed in windows

where heat is stored when the sun is shining. Courtesy of CalorthermAssociates

CLOUDS(SCATTERING ANDABSORPTION)

ATMOSPHERE(ABSORPTION)

DIRECTRADIATION

UPPER ATMOSPHERE

EARTH

DUST(SCATTERING)

Figure A22 Radiation striking the earth directly from the sun is considered direct radiation. If it reaches the earth after it has been deflected byclouds or dust particles, it is called diffuse radiation.

DECLINATIONANGLE

EARTH

WINTER

WINTER

SUMMER

+23.5

23.5

SUMMER

DECLINATIONANGLE

SUN

Figure A23 The angle of declination (23.5) tilts the earth so thatthe angle from the sun north of the equator is greater in the winter.

The suns rays are not as direct, and the normal temperatures are

colder than during the summer.


11/16

The amount of radiation reaching the earth also varies ac-

cording to the distance it travels through the atmosphere. The

shortest distance is when the sun is perpendicular (90) to a

particular surface. This is when the greatest energy reaches

that section of the earth, Figure A24. The angle of the sunsrays with regard to a particular place on the earth plays an

important part in the collection of the suns energy.

A.14 ACTIVE SOLAR DESIGN

The systems discussed and illustrated in this unit are basic

systems with a minimum of controls, check valves, pressure

relief valves, and other safety protection included. Manufac-

turers instructions and local and state codes must be fol-

lowed when installing equipment.

Active solar design utilizes collectors, storage systems,

distribution devices such as pumps and fans, and control sys-

tems. These solar systems are used primarily for space heat-

ing, domestic hot water, and swimming pool heating.

Liquid Solar Forced AirSpace-Heating Systems

Figure A25 illustrates a basic water drain-down liquspace-heating system, which also includes a domestic h

water tank. Drain-down systems are one type of system us

in areas where water to and from and in the collectors wou

freeze if left in the system. When collectors are producin

heat at a higher temperature than the storage water, circultor pump A moves water from the storage to be heated a

from the collectors back to storage. When the house therm

stat calls for heat, circulator pump B moves water from sto

age to the heat exchanger in the furnace duct. The furnace fa

blows air across the heat exchanger, warming the air, and di

tributes it to the house. Also shown is a domestic hot wat

tank heated through a heat exchanger in the water storag

When circulator pump A shuts down, the collector water w

all drain to a heated area to keep the water from freezing

cold weather. Note that the pipe from the collector into th

storage tank does not extend into the water. This provid

venting and allows the collectors and piping to drain. If th

space is not provided, other venting in the collector system

necessary.

An alternative design that is often preferred, particular

in colder climates, requires a closed-collector piping syste

using an antifreeze solution instead of water, Figure A2This figure illustrates a closed liquid collection to a wat

storage system with air distribution to the house. The liqu

in the collector system is an antifreeze and water solution.

is heated at the collectors and pumped through the coil at th

heat exchanger and back to the collectors. This continues

long as the collectors are absorbing heat at a predetermine

temperature.

When the room thermostat is calling for heat, thre

way valve 1 allows the water to be circulated by pump

through the liquid-to-air heat exchanger and back to th


EARTH'S SURFACE

ATMOSPHERE90

POINT 1

POINT 2

POINT 3

Figure A24 Radiation from the sun will be warmer at point 1 as ittravels the shortest distance through the atmosphere.

COLLECTOR PANELS

ROOMTHERMOSTAT

HOTWATER

TANK

LIQUID-TO-AIRHEAT EXCHANGER

HEATEXCHANGER

STORAGE TANKCIRCULATOR PUMP

PUMP

CONTROLLER

PUMP

AIR INTAKE

BA

Figure A25 Collectors use water as the liquid. This is a drain-down system because the water in the collectors would freeze on cold nights.


12/16

liquid-to-liquid heat exchanger, where it absorbs more heat.

If the room thermostat is not calling for heat, three-way valve

1 diverts the water to storage. If the storage temperature has

reached a predetermined temperature, the collector solution

is circulated through the purge coil. The solution is diverted

to this purge coil through three-way valve 2. (The heat is dis-

sipated into the air outside through this coil.) This is a nec-

essary safety precaution because it is possible for the

collector system to overheat and damage the equipment.

Note that a liquid-to-liquid heat exchanger is used to heat

the storage water. The collector antifreeze fluid must be kept

separated from the storage water. This system is less efficient

than the drain-down system, which does not require the ex-

tra heat exchanger.

In most areas an auxiliary heating system is required to

provide comfort heating at all times. A conventional hot airheating system can be used in the same duct used for the so-

lar system. Room thermostats in each system may be used to

provide steady comfortable heat.

Liquid Collection/Water Storage/AuxiliaryConventional Hot Water Boiler

A liquid-based solar collector system may be paired with a

hot water finned-tube convector heating furnace. The col-

lector system can be of the same design as an air distribu-

tion system. It can be a drain-down water design or one that

uses antifreeze in the collectors with a heat exchanger in the

storage unit. Solar collector and storage temperatures maybe lower than those produced by a hot water boiler. This can

be compensated forto some extentby using more fin

tubing than would be used with a conventional hot water

system.

Figure A27(A) illustrates a design using a liquid-basedsolar collector with a hot water boiler system. This design

uses the auxiliary boiler when the storage water is not hot

enough. If the solar storage is hot enough, the boiler does

not operate. Water is pumped from the storage tank and by-

passes the boiler. It goes directly to the baseboard fin tubing.

The three-way diverting valve automatically causes this

boiler bypass. When auxiliary heat is called for, the 2 three-

way diverting valves cause the water to bypass the storage.

It would be very inefficient to pump heated water through

the storage tank.

A system can be designed as two separate systems in par-

allel as in Figure A27(B). These separate systems can bothbe operated at the same time. With this design, the solar sys-

tem can help the auxiliary system when the temperature of

the storage water is below that which would be satisfactory

for it to operate alone. Sensors are used in either system to

tell the controller when to start and stop the pumps and when

to control the diverting valves.

A.15 SOLAR RADIANT HEAT

Figure A28 illustrates a water storage, radiant heating sys-tem with an auxiliary hot water boiler. Either water or an an-tifreeze solution is piped through a collector system and in

the case of an antifreeze solution, through a heat exchanger

in the water storage. The heating coils may be imbedded in

concrete in the floor or in plaster in ceilings or walls. The

normal surface temperature for floor heating is 85F, and for

wall or ceiling panels, 120F.

Floor installations are most common. The coils are

imbedded in concrete approximately 1 in. below the surface.

If this is a concrete slab on grade, it should be insulated un-

derneath. In ceiling and wall applications there should be

coils for each room to be heated. When installations are on

outside walls, they should be insulated very well between thecoils and outside surfaces to prevent extreme heat loss.

Radiant heating installed in the floor is very comfortable

with little temperature variation from room to room. FigureA29 illustrates a polybutylene pipe being installed in a floor.The pipe is tied to a wire mesh and propped on blocks to keep

it near the top of the concrete slab, and the concrete is poured

around it, covering it by approximately 1 in. There should be

no joints in this pipe in the floor. Polybutylene pipe is popu-

lar for this installation. Any joints necessary should be man-

ifolded outside the slab. Almost any type of flooring material

may be used over the slab. Common materials are tile, wood,


LIQUID-TO-LIQUIDHEAT EXCHANGER

SENSOR

SENSOR

SENSOR

3-WAY VALVE 1

3-WAY VALVE 2

RETURN

COLLECTOR

ANTIFREEZE

PURGECOIL

LIQUID-TO-AIRHEAT EXCHANGER

ROOMTHERMOSTAT

ROOM

COIL

CONTROLLER

FURNACE SUPPLY

STORAGE

PUMP PUMP

A B

C

PUMP

Figure A26 A closed liquid collection, water storage system with air distribution to the house.


13/16


COLLECTOR ARRAYCONVECTION HEATDISTRIBUTION COIL

AUXILIARYBOILER

AUXILIARYBOILER

AUXILIARYFIN TUBES

SOLAR FIN TUBES

2-POSITION, 3-WAYAUTOMATICDIVERTING VALVE

GATE VALVEGATE VALVE

PUMP

PUMPVENT

RETURNTOSTORAGE

RETURN TOBOILER

RETURN TOBOILER

RETURN TOSTORAGE

3-WAYAUTOMATICDIVERTINGVALVE

SUPPLYFROM

STORAGE

STORAGE TANK

(A)

(B)

STRAINER

Figure A27 (A) A liquid-to-liquid solar space-heating system. (B) Both solar and auxiliary heat can be used at the same time.

AUXILIARYBOILER

3-WAY AUTOMATICDIVERTING VALVE

3-WAY AUTOMATICDIVERTING VALVE

GATE VALVE

GATE VALVE

PUMPSTRAINER

SOLARSTORAGE

Figure A28 A solar space-heating radiant system. The radiant heating coils are normally embedded in a concrete floor.


14/16


15/16

These collectors may use one or two panels of glass. This

glass may vary in quality and design, but a low-iron tem-

pered glass is often used. The absorber plate is usually made

of copper and formed tightly around the copper tubing and/or

may consist of fins welded to the tubing. These assemblies

are painted black, using a paint designed for this purpose, to

absorb the maximum heat from the sun.

A.17 SOLAR POOL HEATING

Many solar pool heating systems simply use the pump th

circulates the pool water through the filter for this system

The pool water is pumped through the filtering device(

and then is diverted to the solar collectors where it

heated. The water then flows back to the pool, Figure A3

This continuous flow of water through the collectors anback to the pool gradually heats the water. When the po

has reached the desired temperature level, the water b

passes the collectors and is returned directly to the po

from the filters.

Collectors for pool systems are often made of extrud

plastic, Figure A35. A cross section of a collector producby one manufacturer is shown in Figure A36. As shown bthis illustration, the collector receives diffuse radiation an

direct radiation for optimum heating of the water passin

through.


Figure A31 The heat exchanger piping has a double wall when an antifreeze solution is used in the collectors in a domestic hot water system

COLD WATER SUPPLYTO COLLECTORCIRCULATION PUMP

HOT WATER RETURNFROM COLLECTOR

TEMPERATUREMODULATING VALVE

TEMPERATURE-PRESSURE RELIEF VALVE

HOT WATER SUPPLY

CONVENTIONAL DOMESTICHOT WATER TANK

HOT WATER TRANSFERLINE TO WATER HEATER

COLD WATER SUPPLY FORTEMPERING HOT WATER SUPPLY

COLD WATER MAKE-UP

SOLARPREHEAT

TANK

Figure A32 A solar preheat tank provides additional storage for a domestic hot water system.

Figure A33 A solar collector. Courtesy AET


16/16

SUMMARY

Approximately 20% more heat is available in dry wood than

in green wood.

Wood smoke contains both polycyclic organic matter (POM)

and nonpolycyclic organic matter, which are considered to

be health hazards. EPA standards exist for both catalytic and noncatalytic

stoves.

Creosote, when hot, is a thick dark-brown liquid that forms

into a residue like tar when it cools and often turns into a

black, flaky substance inside the chimney or stovepipe.

Stoves heat by both radiation and convection.

Pellet stoves burn small, compressed pellets made from

waste-wood products or agricultural waste products.

Makeup air must be provided to replace air used in the com-

bustion process.

Gas stoves may be certified by ANSI as a decorative appli-

ance or as a room heater.

Gas stoves may be designed to use a B-vent or a direct-vent,

or they may be vent-free.

Fireplace inserts convert a fireplace into a more efficient heat

source.

Both wood-burning and gas-burning fireplace inserts are

available.

Liquid solar forced air space-heating systems may be the

drain-down or closed-collector piping system type.

Liquid solar space-heating systems may be combined with

many types of conventional heating systems.

Solar heating may be used to heat domestic hot water.

Swimming pools may be heated with solar heating systems.


Figure A35 The solar collector for a swimming pool solar heatingsystem. Courtesy Aquatherm Industries/Solar Industries

Figure A36 A cross-sectional view of a swimming pool solarcollector. Courtesy Aquatherm Industries/Solar Industries

THERMOMETER

(OPTIONAL)

INLET LINE

TO SOLAR

COLLECTOR

FLOW

METER

VALVE

CONTROL

LINE

SP SOLAR

COLLECTORS

THERMOMETER

(OPTIONAL)

ISOLATION CHECK VALVE

(OPTIONAL)

OUTLET TEE

HEATER BY-PASS

BALL VALVE

(OPTIONAL)

HEATER

(OPTIONAL) HEATED WATER

TO POOL

CHECK

VALVE

ISOLATION

BALL VALVE

(OPTIONAL)

POOL WATER

SENSOR

POOL

FILTER

120/240 V LINE

ELECTRONIC CONTROL

PUMP

COOL WATER

TO SOLAR

HEATER

VACUUM RELIEF VALVE

(OPTIONAL LOCATION)

VACUUM RELIEF VALVE

SOLAR SENSOR

END CAP

OUTLET LINE

Figure A34 A swimming pool solar heating system. Courtesy Aquatherm Industries/Solar Industries

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Unit a (Alternative Heating)

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