chapter xll heating and cooling equipment

Chapter Xll

HEATING AND COOLING EQUIPMENT

Chapter Xll.— HEATING AND COOLING EQUIPMENT

PageIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507Electric Air-Conditioners and Heat Pumps.... 507

System Performance. . ..................510Potential for Improving Performance .. ..511

Direct Fossil-Fired Heating and Air-Condi-tioning Equipment . . . . . . . . . . . . . . . . . . . . 514

Heating Equipment. . . . . . . . . . . . . . . . . . . . . 514Potential for Improving Performance .. ..517

Absorption Air-Conditioning ... ............519System Performance. . ..................520

Conventional Gas and Electric Water Heaters. 522Operating Costs. . . . . . . . . . . . . . . . . . . . . . . . . .522Adaptation of Conventional Equipment to

Solar Power . . . . . . . . . . . . . . . . . . . . . . . ..523Solar Heat Engines. . ...................524Solar Absorption Equipment . . . . . . . ......524

The Adsorption Cycle System . .........524

LIST OF TABLES

Table No. Pagel. Cooling Coefficients of Performance for

Systems Smaller Than 65,000 Btu/Hour. ...5lO2. California Standards for Cooling Equipment 5113. Average Cost of Maintenance Contracts for

Residential Heating and Cooling Equipment 522

Table No. Page4. Cost of Maintaining Commercial Heating

and Cooling Equipment . ................523

LIST OF FIGURES

Figure No. Pagel. A Typical ’’Split System” Heat-Pump

Instal lat ion. . . . . . . . . . . . . . . . . . . . . . . . . . .5082. A Typical Packaged Outdoor Chiiler .. ....5093. 1976 Air-Conditioning Performance of

4.

5.

6.

7.

8.9.

10.

Units Smaller Than 65,000 Btu/Hour .. ....510Performance of the Carrier Split-SystemHeat Pump . . . . . . . ....................512The Seasonal Performance of Heat-PumpUnits as a Function of Local Climate .. ...513Estimated Cost of lncreasing thePerformance of Air-Conditioners Fromthe lndustry Average COP of 2.0 to thePerformance Levels Indicated . ..........513Some Examples of Proposed AdvancedHeat-Pump Cycles. . ...................515Residential Heating Systems. . ..........516Efficiency of Gas Furnaces . ............516A Fossil-Fired Heat-Pump System . ......517

11. Basic Single-Effect Absorption Refrig-e ra t ion Cyc le . . . . . . . . . . . . . . . . . . . . . . . . . 519

12. Estimated Refrigeration Unit Cost Per Ton 52013. Coefficient of Performance Versus

Supply Water Temperature. . ............52114. An Adsorption Chiller. . ................525

Chapter XII

Heating and Cooling Equipment

INTRODUCTION

This chapter has two major objectives: to estimate the cost of providingspace conditioning from conventional electric equipment as well as from oil-and gas-fired devices, and to analyze the performance of systems which canbe coupled with solar devices. Technologies examined include electric andabsorption air-conditioners, heat pumps, and conventional gas- and oil-firedboilers. Systems examined are compatible with loads varying from that of asingle family residence to the requirements of a district heating system.

Much of the data needed to perform a careful study of the cost of providingheat ing and cool ing from convent ional equipment is not easi ly avai lable.Some of the relevant data remains proprietary and, in a number of cases, ade-quate measurements of performance in real ist ic operat ing environmentshave never been taken. A detailed study of the performance of many heatingand cooling devices is now underway at the Building Environment Division ofthe National Bureau of Standards. A more accurate comparison of systemswilI be possible when that study is completed.

Given the uneven quality of the information utilized, no attempt should bemade to use the results to judge the relative merits of different conventionalapproaches to space-conditioning. The object of the cost computations issimply to provide a reasonable background against which to test theeconomic merits of solar equipment. These computations are based on themost reliable information now avaiIable to OTA, but the lack of precision isf reel y acknowledged.

ELECTRIC AIR-CONDITIONERS AND HEAT PUMPS

A typical residential air-conditioner/heat-pump installation is iIlustrated in figureXl 1-1, and a large central chiller is shown infigure Xl 1-2. Both units employ the samebasic ref r igerat ion cycle, a l though thesmaller units usually cool and dehumidifyroom air directly while the larger systemstypically produce chil led water which ispiped to fan-coil units in various parts of thebuilding. The cooling systems have threebasic components: 1 ) a unit which permits arefrigerant to expand, vaporize, and absorbheat from the room air (or water system); 2) acompressor which compresses the heatedvapor (increasing its temperature); and 3) acondenser located outside the bui ldingwhich rejects the heat absorbed from theroom air into the atmosphere (condensingthe compressed vapor to a Iiquid). I n‘‘s i ng I e-pa c k age’ units, alI three functions

are provided i n the same unit and can b econnected direct ly to the ductwork (orchilled water system) of the building. I n“split-system ” devices, refrigerant is sent toan air-handIing unit inside the building. (Thissystem is illustrated in figure Xl l-l. ) Anotherdistinction which is frequently made i n -volves the technique used to compress therefrigerant vapor. Smaller units typically usea simple piston system for compression andare called “reciprocating” units. Larger u nitsmay use centrifugal pumps or screw com-pressors for this purpose.

Heat pumps use the same three basiccomponents as the air-conditioners de-scribed above, but the cycle is reversed. I nthe heating cycle, the indoor air absorbsheat from the refrigerant and heat is ac-quired by the refrigerant from the outdoor

507

508 Solar Technology to Today’s Energy Needs

Figure XI I-I .—A Typical “Split System” Heat-Pump Installation

SOURCE. Carrier CorDoratlon

fan unit (the “condenser” in the coolingmodel).

Heat pumps which can extract usefulenergy from outdoor air temperatures aslow as 00 F are now on the market, althoughsystem performance is seriously degraded atlow temperatures. The electricity used bythe system can be considerably reduced if asource of heat with a temperature higherthan that of the outside air can be found.Lakes or ground water, for example, areusualIy above ambient air temperatures dur-ing the winter and can be used to provide asource of input heat if they are available.Many buildings have sources of heat (suchas Iighting, mechanical equipment, roomswith large southern exposures, etc. ) whichcan be recovered and used to heat a storagereservoir. A number of small heat pumpscan be located throughout a building. Someof these pump heat from warm areas into

the water reservoir, while others recoverthis energy and pump it into rooms requiringheating. Solar energy can also be used toprovide a source of heated water. Systemswhich extract heat from water are called“water-te-air” heat-pump systems, whileunits extracting energy from the air arecalled “air-to-air” systems.

While less than half of the residentialunits in the United States were equippedwith air-conditioners in 1974, the demandfor air-conditioners is growing. 1 in 1974,about 45 percent of all single family h o m e sand 34 percent of all multifamily dwellingunits were equipped with some type of air-conditioner. 2 A DOE forecast estimated that

IGordian Associates, Inc , Evacuation of the A;r-tGAir Heat Pump for Residential Space Conditioning,prepared for the Federal Energy Administration, Apr23,1976, p. 114

‘Ibid , p 115

Ch. XII Heating and Cooling Equipment 509

ROOMTHERMOSTAT INCONDITIONEDSPACE

Figure Xll-2.– A Typical Packaged Outdoor Chiller

,,

SOURCE Carr ier Packaged Outdoor Air-Cooled Llquld Chillers Carrier Co rpo ra t i on

by 1985, air-conditioning will be installed in75 percent of all residential and commercialbuildings and will require about as much en-ergy as electric heating. 3

Heat pumps are l ikely to have a farsmalIer impact on overall U.S. energy con-sumption unless some dramatic change oc-curs in public acceptance of the units. Lessthan 1 percent of U.S. homes currently haveheat pumps, and only about 7 to 8 percentof the new housing starts in 197.5 used the

‘Nationa/ P/an for Energy Research Developmentand Demonstration, Vo/ume /, ERDA-48, p B 10

a *

ST - STARTER

FD - FUSEO DISCONNECT

1974, Form 30GA-5P

system. 4 The growth of the market has beenslowed by the sensitivity of buyers andbuilders to the initial cost of the equipment(which is higher than conventional electric-resistance heat) , and by the fact thatregulated gas prices and promotional elec-tric prices have made the cost of operating

competitive heating systems artificially IO W

Concerns about reliability have also been aproblem. Some of the heat pumps marketedin the early 1960’s were extremely unreli-able, and sales of the units fell steadily be-

‘Gordlan Associates Inc , op clt , p v

510 ● Solar Technology to Today’s Energy Needs

tween 1965 and 1970. While most of the reli-ability problems have been resolved, a re-cent study showed that the problem has notvanished. The compressors examined in thestudy failed at a rate which varied from 3.6percent to an astonishing 23.3 percent peryears A 5-percent annual failure rate is con-sidered tolerable for this kind of space-condit ioning equipment, and apparent lyvery few manufacturers were able to meetthis standard.

In spite of their relatively small share ofthe U.S. space-condit ionin g market , heatpumps are likely to be in direct competitionwith solar equipment during the next fewdecades. They would tend to appeal to thesame category of buyers, those willing toconsider Iife-cycle costing, and are Iikely tooffer the lowest Iife-cycle cost of any non-solar space-conditioning system if the priceof heating oil and natural gas increasessignificantly.

SYSTEM PERFORMANCE

The performance of heat pumps and air-conditioners now on the market varies great-ly. Figure Xl I-3 indicates the performance ofair-conditioners smaIIer than 5½ tons now

on the market. The difference in perform-ance reflects both the quality of design andthe cost of the unit. High-performance unitsmay also result from a fortuitous combina-tion of components. Manufacturers cannotafford to design condensers optimalIy suitedfor all compressors to which they may be at-tached, and some combinations of theseunits (in the absence of information of com-parable quality about the variety of systemsexamined here) may therefore result in ahigh-efficiency system. As a result, whilethere are a few units on the market with veryhigh efficiencies (figure XII-3, for example,indicated that 10 percent of the units on themarket have a coefficient of performance(COP) greater than 2.5), this performance isnot avaiIable in alI size ranges.

51 bld

Figure Xll-3.— 1976 Air-Conditioning Performanceof Units Smaller Than 65,000 Btu/Hour

.“

1 00%

1976 Industry Average 2.00

50% -

I I I I I1.5 2.0 2.5

Tables Xl l-l and Xl I-2 give some indica-tion of the performance which can be ex-pected from different cooling devices, T h e1976 industry average COP was 2.00.

Heat pumps were about 5 percent less ef-ficient than the average air-conditioner,There are a variety of reasons for this. Heatpumps cannot be optimized for maximumcooling performance as somewhat morecomplexity is required in the coolant piping,and the valve which switches the directionof the refr igerant when the system ischanged from heating to cooling introducessome inefficiencies.

Under some circumstances, small windowunits are capable of better performancethan central air-conditioners; central units

Table XII-1 .—Cooling Coefficients ofPerformance for Systems Smaller Than

65,000 Btu/Hour (1976 industry averages)

Average COP

All ARI listings 2.00

Split-system cooling 2.00Single-package cooling 1.90Single-package heat pumps 1.94

Split-system heat pumps 1.90— ——— .—SOURCE George D Hudelson (V ice PresldentEnglneerlng, Ca r r i e r

Corporation), testimony before the Caltfornla State EnergyResources Conservation and Development Commlsslon, Aug10, 1976 (Docket No 75, CON3)

Ch. XlI Heating and Cooling Equipment ● 511

Central Air-Conditioners

Heat pumps (cooling mode)Air-conditioners

Room Air-Conditioners

All systems with capacity greaterthan 20,000 Btu’s

Other heat pumpsOther air-conditionersAll systems using voltages

greater than 200 v.Other heat-pump systemsOther air-conditioners

1.96 2.22.05 2.34

2.05 —2.08 —2.20 —

— 2.40— 2.43— 2.55

.—“No system m~y be sold n fhe State atter this date with a COP below the standard

must pump chilled air or refrigerant oversignificant distances, and require moreenergy to operate the pumps and fans need-ed to transport chilled air or liquids to andfrom the space to be cooled. The perform-ance of large, central chilling units them-selves (such as the one shown in figure Xl 1-2)is better than window units, however. Thelarger units typically employ more efficientmotors and more sophisticated designs;many units are able to achieve better per-formance at part loads by adjusting the flowof refrigerant (Many of these improvementscouId, of course, be incorporated in asmaller unit at some increase in the initialcost. ) The advantages of larger systems areoffset, however, by losses incurred in otherparts of of the system.

A large number of designs are employed,and overall performance varies greatly fromone installation to another. Some systemsmay require significant amounts of pumpingenergy to either move chIIled Iiquids or airto different parts of a buiIdIng or to operatea cooling tower which may be located onthe roof

The performance of electric-cooling andheat-pump systems also varies as a functionof the temperature and humidity of both the

inside and outside air. This is due both to thefact that the theoretical capacity of a unitvaries as a function of these parameters, andbecause most units must either be fully onor fully off. The load control achieved by“cycling” the system from full capacity tozero output requires heating or coolinglarge parts of the system before useful spaceconditioning c a n b e p e r f o r m e d . U s i n genergy to heat or cool the units decreasesthe system’s efficiency. The dependence ofa typical residential heat-pump unit COP onthe outdoor temperature is shown in figureXl 1-4. The fact that the heat pump’s capacityto produce heat decreases as the outsidetemperature decreases results in a highlytemperature-dependent heating mode, Asystem large enough to provide 100 percentof the heating load at the lowest anticipatedtemperature would be prohibitively expen-sive in most locations, and a most commoncompromise is to assist the heat pump withelectric-resistance heat whenever its capaci-ty falls below the heating demand. Theaverage COP of a heat-pump system duringthe winter season is called the seasonalperformance factor (SPF). This parameter isshown in figure Xl I-5 as a function of localclimate. As expected, the average COP ofheat pumps is lower in northern parts of thecount ry.

The performance of water-to-air heat-pump systems can be significantly higherthan air-to-air systems if heated water i savailable. When 600 F water is available,most commercial units have COPS in therange of 2.5 to 3.5,6 but units with COPS aslow as 2.0 and as high as 3.7 are on themarket.

Potential for Improving Performance

Research which could significantly im-prove the performance of these devices i scurrently underway in the laboratories of anumber of heat-pump and air-conditionermanufacturers. Figure Xl I-6 summarizes a re-

‘)LIIreC ~or} of Cert/f/ed UnJtJry A )r-( ond~t)oners,Unitar} He<?t Pumps, Sound-Rdtcd ~~ljtdoor un~tar]’

Lqu Iprncn(, Cerrtra / $} stem }fLIm Idit Iers, AI r-Condl-t IcjrI I ng d n~ Refrlgerat Ion [ nst It u t(>, 1‘j76


Figure Xll-4.– Performance of the Carrier Split-System Heat Pump

I I I I I 1 I I 1 I 1 I II o 10 20 30 40 50 60 70 80 90 100 110 120

Ambient Temperature

Model 38CQ020 ARI ratings:

Assumptions used in computingsystem performance:

Heating mode nominal capacity21,000 Btu/hour. COP at high tem-perature is 2.9, COP at low temper-ature is 1.7.

Cooling mode nominal capacity is19,000 Btu/hour. COP is 2.1.

Heating mode entering indoor airis 70- F (db) heating demand in-cludes energy used for defrostbalance point at 30’ F.Cooling mode entering indoor airis 80 F (db) and 67 F (wb). Fanpower is 0.2 kW.

Energy use includes: compressor motor demands; resistance heat;the demands of indoor and outdoor fans; and the energy used indefrost cycles. The air-flow was assumed to be 700 cfm. Assumptionsmade about decrease in efficiency due to part load conditions werenot explained in the literature.SOURCE Carrier Spilt-System Heat Pump Outdoor SectIons Carrier Corporation 1976, Form 38CQ-l P


Figure XII-5.– The Seasonal Performance of Heat-Pump Units

SOURCE What IS a S/rig/e Packaged l-leaf Pump and How Can It Save You Money?, Carrier Corporation, Catalog No 650.069

Figure Xll-6.— Estimated Cost of Increasing the Performance of Air-ConditionersFrom the Industry Average COP of 2.0 to the Performance Levels Indicated

(estimates assume production rates equivalent to current production rates)

2-piece cooling

/

20 21 22 23 24 25 26System Coefflclent of Performance

SOURCE George D Hud~lson (Vice Prewdent - Englneerlng Carrier Corp } Presenlatlon to the solar Emmy Resources Conservation and Development Commlsslon of Call forma Aug 10 1976 Docket No 75 CON 3


cent series of estimates of the increase inair-conditioning COP achievable withoutchanging the basic design of the air-condi-tioning system and using a compressor unitwhich is currently available, and the cost ofproducing these new designs. Equipment in-corporating these new designs could bemade in the next few years. The re-quirements which will be imposed on air-conditioners and heat pumps sold in theState of California during the next 5 yearsare shown in table Xl 1-2.

Looking further into the future, a numberof systems have been proposed which couldincrease the COP o f a i r - cond i t ion ingsystems and heat pumps by as much as so

percent. A series of designs being con-sidered by the General EIectric Corporationis indicated in figure Xl 1-7. Researchers atG.E. believe that it would be possible toachieve an approximate 50-percent increasein the average COP of both heating andcooling for an increase in the initial cost ofthe unit of about 20 to 30 percent 7 It shouldbe noted that performance can be improvedby increasing low-temperature performance,high-temperature performance, or both, Thespeed with which these new units appear onthe market will depend strongly on the com-pany’s perception of whether the public iswilling to invest in equipment which canreduce their annual operating expenses overthe long term. These attitudes, of course,may be infIuenced by legislative initiatives.

DIRECT FOSSIL-FIRED HEATING ANDAIR-CONDITIONING EQUIPMENT

HEATING EQUIPMENT

The majority of residential and commer-cial b u i l d i n g s in the United States areheated with direct-fired oil and gas furnacesand boiIers. There is considerable controver-sy about the typical operating efficienciesof these systems. One reason is that remark-ably Iittle is known about the performancecapabilities of these systems in actual oper-ating environments, and the literature in thearea is filled with inconsistent information.Some indication of the difficulty can beseen by examining figure Xl 1-8, which in-dicates the performance estimates made bya variety of different organizations. Per-formance undoubtedly varies with the ageof the unit, its installation, its position in thebuilding, and a variety of other variableswh ich a re d i f f i cu l t to ho ld cons tan t .Another reason for the controversy is theinconsistency in the definition of efficiency.Unti l recently, the most common valuequoted was the steady-state or full-loadcombustion efficiency, which is defined asthe ratio of useful heat delivered to the fur-

nace bonnet divided by the heating value ofthe fuel.8 Typical values for direct-combus-tion furnaces are 70 to 75 percent; heat lossprincipally results from heated stack-gasseslost during combustion, This definition doesnot give a complete measure of the fuel re-quired to heat a living space over the heat-ing season. A more useful definition whichaccounts for this, and which is increasinglybeing used, is the seasonal performance fac-tor or seasonal efficiency. This measurecompares performances of various space-heating systems. It is defined as the ratio ofthe amount of useful heat delivered to thehome to the heating content of the fuel thefurnace used over the entire heating season.Typical gas furnaces have seasonal efficien-cies in the range of 45 to 65 percent (figureXl 1-8). Seasonal efficiency accounts for allfactors affecting the heating system’s per-formance in its actual operating environ-

7Conley, General Electrmunicatlon, 1977

‘Hlse and Holman, op clt

c Corp , p r iva te com-

Ch. XII Heating and Cooling Equipment ● 515

I

cd oJ -

1-

1-

01

7


Figure XII-8. – Residential Heating Systems

OILSteady-State Efficiency

(3) Columbus, Ohio(1) New England(2) New York(4) Washington, D.C.(8) U.S.

Seasonal Efficiency

(4) Washington, D. C.(4) Maryland

(5) New York

(6) U.S.(7) Us.(8) Us.

(9) Us.(10) Philadelphia

GAS

Steady-State Efficiency(3) Long Island

Seasonal Efficiency(14) Baltimore

(12) Canton, Ohio

(10) Philadelphia(13) Philadelphia

(4) Washington., D.C.

(429—well maintaine(72—as found)

mversion)

v

o 20% 40% 60% 80% 100%

SOURCE: J. H. Leggoa, “Seasonal Efflclency of Home Fuel 011 Furnaces”Phdadeiphla Electric Company PapeC Aug. 26, 1976.

ment. In addition to stack gas losses (thelargest contributor) these factors includeloss of heated room air through the chimneywhile the furnace is off, cycling losses, pilotlight (gas furnaces only), and heat lossesthrough the air distribution ducts when inunheated spaces.9 Cycling losses are a resultof operation at part loads, which causesheat to be lost in raising the temperature ofthe furnace before useful heat can bedel ivered to the l iv ing space. A recentmeasurement of this part-load performance

‘G Samuels, et al , MIUS Systems Ana/ysis– /rtitia/Comparisons of Modular-Sized Integrated Utility Sys-tems and Convention/ Systems, ORNL/H UD/Ml US-6,June 1976, p 24.

is indicated in figure Xl 1-9. The seasonal effi-ciency of many installations is reduced

Figure Xll-9.— Efficiency of Gas Furnaces

80

60

40

20

Oak Rtdge’

t

20 40 60 80 100

by


installing units which are larger than neces-sary, meaning that the systems are alwaysoperating at relatively inefficient part-loadconditions. 10

In addition to the fossil fuel required forthe burner, gas and oil furnaces and boilersrequire electric energy to operate fans andpumps. A typical small gas furnace will re-quire about 13 watts per 1,000 Btu/hourcapacity, 11 A large central boiler and hot-water distribution system wiII also requireabout 13 watts per 1,000 Btu/hour of heatingcapacity to pump heated water. 2

Potential for Improving Performance

The performance of gas furnaces can beincreased by improving fan controls, usingsystems which preheat the air entering thefurnace with the heat in the chimney, install-ing an electric ignition system to replace thepilot, and a variety of other rather straight-forward changes in design, A recent studyconducted by the Oak Ridge National Lab-oratory estimated that fuIl-load combustionefficiencies of gas furnaces could be in-creased from 75 to 82 percent if thesechanges were implemented.13 The combus-tion efficiency of oil-burning furnaces canalso be improved by using improved burnerheads and by ensuring that the burners arewelI maintained

An entirely di f ferent approach to theproblem, using fossil fuels to operate a heatpump, has been under investigation forsome time under the sponsorship of theAmerican Gas Association. These designsburn fuel to operate a small onsite heatengine, which in turn drives the heat-pumpcompressor.

An advanced fossil fuel heating conceptinvolves using the fuel to power a small heatengine directly coupled to the compressor

‘“H Ise and Hol man, op clt

‘ ‘Sears Fall-W Inter Catalog, 1976, p 955‘‘1 bld

‘ ‘Hlse and Holman, op cit , p 3

or a heat pump (figure Xl l-l O). The heat re-jected by this engine can be used to main-tain a source of heated water, which canthen provide the heat pump with a source ofthermal energy at a temperature higher thanthe ambient air. Studies of this approach

Figure XII-10.—A Fossil-Fired Heat-Pump System

Hot AlrT O Builldlnq

rHeat Pump

Outdoor

CompressorHeat

Exchanger

1 %

II

I

Heat

Engine

S O U R C E O T A

have been underway for some time in in-dustrial laboratories and a number of proj-ects in this area have been supported by theAmerican Gas Association.

A variety of different heat-engine designshave been considered. Designs employingStirling and Ericsson cycles are being exam-ined by RCA, the N.V. Philips Corporation,Sun Power, Inc., Energy Research and Gen-erat ion, Inc. , and by the Universi ty ofW a s h i n g t o n . 14 15 16 A number of workin g

systems have been designed and tested.

“W Beale (Sun Power, Inc.), private communica-tion, June 1976

“G Benson (Energy Research and Generation, Inc ),Therrna/ Osci//ations, presented at 8th I ECEC meeting,

Aug 14 , 1973

‘‘W R Martlnl, Developments in St i r l ing Engines,presented to the Annual Winter Meeting of the Ameri-can Society of Mechanical E nglneers, New York, N.Y ,Nov 26-30, 1972


A number of advanced, gas-fired, heat-pump systems are being examined by the in-dustry, with the support of DOE and theAmerican Gas Association:* **

●

●

●

●

Thethe

An absorption system capable of pro-ducing both heating and cooling isbeing developed by the Allied ChemicalCorporation and the Phillips Engineer-ing Co.

A concept which uses a subatmosphericgas turbine is being developed by theGarrett Air Research Corporation.

A free-piston Stirling engine is beingdeveloped by the General Electric Cor-poration (the project received about $1miIIion from the American Gas Associa-tion and about $2 million from DOE in1 977).

Systems based on diesel engines andRankine-cycle devices are also being ex-amined.

technology of the engines used to drivecompressors was discussed in greater

detail in the previous chapter. An interestingfeature of the heat-fired, heat-pump systemsis that their performance does not decreasewith temperature as fast as the performanceof conventional heat pumps.

While working systems have been de-signed, commercial production is unlikely tobegin for the next 5 to 10 years.

The performance of the engines beingconsidered for use with fossil-fired heatpumps is discussed in greater detail in thesection on Solar Heat Engines in this chapter.

Stirling and Ericsson cycle, free-pistondevices may be able to achieve efficienciesin the order of 60 to 90 percent of ideal Car-not efficiency. 17 An engine operating be-

*“Advanced Gas-Fired Heat Pumps Seen CuttingHeating E3111s in Half, ” Energy Users Report #188, Mar17, 1977, p 25

* * Paul F Swenson, “Competltlon Coming In HeatPumps Gas-Fired May Be Best In Cold Climate, ”Energy Research Reports, Vol 3, No 5, Mar 7, 1977,p 2

‘ ‘Benson, 011 clt

tween 1,4000 and 1000 F could thereforeachieve a cycle efficiency of 40 to 63 per-cent. (ERG has reported a measured in-dicated efficiency which represents 90 per-cent of Carnot in a free-piston deviceoperating i n roughly this temperature re-gion. )18 The Gar re t t Corporation hasreportedly achieved a cycle efficiency of 38percent, using a small regenerated gas tur-b i n e .

If it is assumed that seasonal performancefactors for heat pumps can be in the rangeof 2.5 to 3.0, the overalI system COP (or ratioof heat energy delivered to the Iiving spaceto the heating value of the fuel consumed)of a heat pump combined with a heat enginewhich is 38 to 60 percent efficient can be inthe range of 0.95 to 1.8, If waste heat fromthe engine is used, the effective COP can beas high as 2.2.

A 38- to 60-percent efficient engine com-bined with an air-conditioning cycle with aCOP of 2.5 could achieve system COPS of0.95 to 1.5. These coefficients cannot becompared directly with COPS of electricheat pumps. In order to obtain comparable“system efficiency” for an electric system,the electric COPS must be reduced by the ef-ficiency of converting primary fuels to elec-tricity and transmitting this energy to a heat-pump system. The average generating effi-ciency in U.S. utilities is approximately 29percent, the average transmission losses, ap-proximately 9 percent. Under these assump-tions, an electric heat pump with a heatingCOP of 3.0 and a cooling COP of 2.5 wouldhave an effective “system” COP of 0.79 forheating and 0.66 for cooling. There are anumber of questions about the system’sperformance as an integrated unit , i tsreliability, safety, noise, ease of mainte-nance, etc., which can only be resolved aftermuch more experience has been obtained.

“lbld

“Patr ick G Stone (Garrett Corporation), privatecommunication, December 1976.


The devices do offer the prospect of a muchmore efficient approach to converting fossiIfuels to useful space-conditioning,

A major question concerning any onsitesystem requiring oil or gas is whether thesefuels will continue to be available at accept-able prices, or whether they wilI be available

at al 1. The heat-engine devices just discussedcould, at least in principle, be used in con-nection with a coal-burning, fluidized-bedboiler or other system, and thus might pre-sent a promising long-term alternative. Oneadvantage of electric systems is that theymay be able to use a greater variety ofprimary fuels than onsite systems.

ABSORPTION AIR= CONDITIONING

An “absorption-cycle” device for usingdirect thermal energy to operate air-con-ditioning systems has been available f o rsome time. A standard cycle is illustrated infigure Xl 1-11. The refrigeration cycle is verysimilar to cycles used in other types of air-conditioning systems (vapor-compression). Achilled liquid (usually water instead of arefrigerant) is permitted to expand and coolair. This water is then recompressed and the

Figure XII-11 .—Basic Single-Effect AbsorptionRefrigeration Cycle -

1

Refrigerant(Liquid) I

Heat I I Heat InputReject!on (Coollng Load)

SOURCE: National Science Foundation.

absorbed heat rejected into the atmosphere(this cycle is on the right side of figureXl 1-11). The absorption cycle accomplishesthis recompression by absorbing the low-pressure water vapor in a concentrated saltsolution. This concentrated solution is con-tinuously produced in a distilling unit whichis driven by the heat from the fuel.

The cooling performed by the absorptionsystem can be separated into two distinctphases, and it would therefore be possible tostore the concentrated salt solution for usewhen required by the cooling load. This con-cept is discussed further in chapter Xl,Energy Storage. The major limitation to sucha procedure at present is the cost of theworking fIuids,

An enormous amount of time and moneyhas been invested in the search for betterworking fluids. Lithium bromide/water solu-tions are used most frequently at present.Ammonia/water solutions are also used.

Absorption units are inherently more ex-pensive than electric systems 1 ) because ofthe larger number of heat exchangers re-quired, and 2) because the unit’s coolingtowers must be large enough to reject bothheat from the combustion process and heatremoved from the space which was cooled.(In electric systems, the heat from genera-tion is rejected at the electric generatorsite )

Double-effect units are also more expen-sive than single-effect devices because evensmaIIer numbers are produced An anaIysis


of the components required indicates thatdouble-effect machines could cost about 20percent more than single-effect units in thesame capacity range. The prices shown inf igure X I I-1 2 indicate that double-ef fectunits operating at 3050 F instead of 3600 Fwould cost nearly twice as much becausecapacity would be decreased. Little workhas been done to produce an optimum de-sign for low-temperature systems, and D O Eis currently funding several projects in thisarea.

The only small absorption units now onthe market are the Arkla single-effect de-vices, manufactured in 3- and 25-ton sizes.There are currently no small double-effectmachines on the market. In the early 1960’s,the Iron Fireman Webster Division of theElectronic Specialties Corporation briefly

700

600

500

400

$/Ton

300

200

100

marketed a small (1 5-ton) Iithium bromide,double-effect, absorption machine. The de-sign was taken from work supported in partby the American Gas Association, and wasapparently capable of achieving very highefficiencies. I t w a s r e m o v e d f r o m t h emarket after only a few hundred were sold,apparently because the company felt that itcould not overcome problems with the sys-tem’s reliability at a reasonable cost. Theunit was sufficiently different from single-effect units that gas company maintenancepersonnel had difficulty repairing the de-vices. The unit at least demonstrated thefeasibility of small double-effect units.

System Performance

The coefficient of performance (COP) ofcontemporary absorption air-conditioners is

Figure Xll-12.— Estimated Refrigeration Unit Cost Per Ton, 12,000 Btu/hr(contractor’s cost)*

I I I I I 1 I I I

1. Single Effect Absorption, 195° F Supply Water2. Single Effect Absorption, 250° F Supply Water3. Double Effect Absorption, 305° F Supply Water4. Double Effect Absorption, 360° F Supply Water5. Electro-Mechanical Vapor Compression–Reciprocating6. Electro-Mechanical Vapor Compression-Centrifugal

L

o 40 80 120 160 200 240 280 320 380 400Unit Size in Tons

.Industry Average- 1976 Costs

NOTE Prices do not Include Inslallat!on or subcontractor O&P costs

SOURCE prepared for OTA by H CorbY r) Rooks April 1976


shown in figure Xl 1-13. A typical single-effect device has a COP of 0.65 and double-effect units can have COPS of 1.1. TheseCOPS must, however, be carefully qualified.(As in the case of fossil-fired heat pumps,these COPS should be compared with the“system” COPs of electric system s.)

The COPS shown in figure Xl 1-13 includeneither the electric energy required to oper-ate pumps which move chilled water to thebuilding loads and cooling water to andfrom the cooling tower, nor the electricityrequired to operate the fan in the coolingtower. These ancillary units require about0.14 kW per ton of cooling in a typical in-stalIation. 20

20 Samuels, et al , op cit , p 20

1.2

1.1

1.0

.9

.8

.7

COP.6

.5

.4

.3

.2

.1

0

With-850 Cooling Tower Water to Unit44° Chilled Water Temp. From Unit

The COPS also do not include the ineffi-ciency of the boiler which must be usedwhen the absorption units are used withfossil fuels. Typical boilers used in such ap-plications lose about 20 to 22 percent of theheating value of the fuel burned in hotgasses escaping up the chimney. The COPSshown in the figure would apply to unitsoperated from solar-heated fluids or bysteam generated by a waste-heat boiler -con-nected to a direct or other heat engine. Theymust be reduced by 20 to 22 percent whenused to represent the performance of direct-fired devices.

It is reasonable to expect that improve-ments in current designs could lead to sig-nificant improvements in performance. Anew series of absorption units, soon to bemarketed by Arkla, will probably achieve aCOP greater than 0.7 for a single-effect de-

I I100 140

I I I I /

.

‘.

I I I 1 I I I I I A180 220 260 300 340 380 420 440

Temperature of the Supply Water (“F)SOURCE Prepared for OTA by H Corbyn Rooks, April 1976


vice with no substantial increase in price. Anexperimental machine, which was a modi-fied version of the single-effect Arkla de-vice, has been tested with a COP greaterthan 0.8. 21

The Iron-Firemen double-effect devicediscussed previously was able to achieve aCOP of 1.2 (not including boiler losses andelectric energy requirements) .22 Some engi-neers believe that it would be possible to

CONVENTIONALWATER

Residential hot water heaters are very in-efficient. z’ A gas water heater has a COP ofabout 0.50, and an electric water heater aCOP of about 0.75. 25 2 ’ 27 Better insulat ionand other improvements could increase the

COPS of future electric units to 0.85 and the

construct double-effect absorption deviceswith COPS in the range of 1.35.23

Absorption units have good performanceat part ia l loads because their ef fect ivecapacity can be varied by simply changingthe rate at which the salt solutions arepumped through the systems. This type ofcontrol works until the load falIs to about 35percent of the peak load, at which pointsubstantial inefficiencies are experienced.

GAS AND ELECTRICHEATERS

COPS of gas units to 0.80.

The efficiency of water heaters variessomewhat as a function of loads, but forsimplicity it is assumed that water heatershave a constant “average” efficiency.

OPERATING COSTS

The costs of operating conventional heat-ing and cooling equipment (exclusive of fuelcosts) are not well documented, and no ex-tensive study has been conducted on thesubject. The estimates used in later analysesare shown in tables Xl I-3 and Xl 1-4. The costsused in this study were taken from the costsof purchasing a service and maintenancecontract for equipment instal led in theWashington, D. C., area. The actual costs willvary as a function of geographic location,quality of the equipment, location of theequipment in the building, design of thesystems, etc. The costs must be consideredconservative since the selIers of mainte-

2’joseph Murray, Chief Engineer of Applied Sys-tems, Airtemp Corporation, private communication,Sept 23,1976

‘Z)oseph Murray, private communication, 1977

2’G.C Vllet, et al , A Thermodynamic Approach tothe Developments of a More Efficient Absorption Air-Conditioning System, University of Texas at Austin –Center for Energy Studies

nance contracts must increase the actualmaintenance costs by a margin sufficient tocover overhead and profit requirements.

Table XII-3. — Average Cost of MaintenanceContracts for Residential Heating

and Cooling Equipment——. . . —

Annualcost

Gas furnace and eleotric air-conditioning $60Air-to-air heat pump $50

Baseboard electric heat and windowair-oonditioners $30

—— — — — — . . . . . —SOURCE Gordlan Associates, Inc Evaluation of the Air-to-Air Heat Pump for

Resldentlal Space-Condltlonmg. April 1976

2 4 CiIlman, o p clt

2’APS, Efficient Use of Energy, p 83.

“J J. Mutch, Residential Water Heating, Fue/ Con-servation Economics and Public Policy, pp. 8 and 55

27 Arthur D Little Co,, Study of Energy-Savings Op-tions for Refrigerators and Water Heaters, draft, ppS-12,1 3,14

Ch. XII Heating and Cooling Equipment ● 5 2 3

Table XII-4. —Cost of Maintaining CommercialHeating and Cooling Equipment*

(Parts and Labor)

Low Rise

Heating (106 Btu/hour)Gas . . . . . . . . . . . . . . . . . . . . . . $1,000 $1,000Oil . . . . . . . . . . . . . . . . . . . . ..... 1,250 1,250Electric . . . . . . . . . . . . . . . . . . . . .1,000 1,000

Cooing (50 tons)Gas. ... ... ..... .... ........ 3,8OO-4,5OO 6,300-7,500Electric ..... .... ........ ....3,000-3,6OO 5,000-6,000

High Rise

Heating (2 units@ 2x106

Btu/hour)Gas . . . . . . . . . . . . . . . . . . . . . . . . 2,000oil . . . . . . . . . . . . . . . . . . . . . . . . . 2,500 625Elec t r ic . . . . . . . . . . . . . . . . . . . . .2 ,000

Cooling(200tons)G a s . . . . . . . . . . . . . . . . . . . . . . . .5,000-6,000 2,000-2,500Electric...............................4,000-5,000 1,700-2,000

Shopping Center

Heating (2 units@ 8x106

Btu/hour)Gas . . . . . . . . . . . . . . . . . . . . . . . .2 ,500 150Oil . . . . . . . . . . . . . . . . . . . . . ... .3,000 190Electric . ....................2,500 150

Cooling(2000tons)Gas. . . . . . . . . . . . . .........19,000 800Electr ic . . . . . . . . . . . . . . . . . .15 ,000 600

‘Actual costs wIfl vary greatly as a function of equipment quality, ln-stallatron, bulldlng fea tu res , e t c C o s t s b a s e d o n “very rough’estimates of Robert NoYes of R E Donovan Co, Inc a service corn.pany[nthe Wasthlngton DC area Sept 23 1976

ADAPTATION OF CONVENTIONALTO SOLAR POWER

Conventional heating and cooling equip-ment can be integrated with solar energy intwo basic ways: 1 ) electricity or mechanicalenergy generated by solar energy devicescan be used to supplement electricity pur-chased from a utility, and 2) direct use ofthermal energy generated by solar devices

can provide a

EQUIPMENT

source of thermal energy forliquid and air-heat pumps, for absorptionair-conditioning, forced-air heating, and toheat domestic hot water.

The direct use of solar-heated fluids forspace heating or for the heating of hot water


requires no sophisticated equipment, andthe problems of designing these systems arediscussed elsewhere.

SOLAR HEAT ENGINES

Direct use of solar-heated fIuids can oper-ate heat engines such as Rankine cycle tur-bines or Stirling engine devices which arecoupled mechanically to heat pumps andair-conditioners. The direct-drive systemshave a substantial theoretical advantageover systems operating from solar-generatedelectricity in that the losses associated witha motor and generator can be avoided. Thiscan be a substantial gain, since typical effi-ciencies of small motors and generators arein the range of 80 to 90 percent and com-bined losses can amount to 30 percent.Total energy systems, which use the solar-powered engine to drive both a generatorand a heat pump, could be driven directlyfrom utility electricity when solar energy isnot available by using the electric generatoras a motor to drive the compressor. Direct-drive systems have a potential disadvantageif they cannot be designed as a single-sealedunit, since seals on rotating shafts couldreduce overall system reliability. It may bepossible to develop completely sealed en-gine-compressor units, but this wilI require alengthy development program,

All of the heat engine alternatives are dis-cussed in detail in the chapter discussing theconversion of solar energy into electricity.The operating characteristics of conven-tional heat pumps and air-conditioners in-tegrated into solar energy designs usingdirect-drive connections will need adjust-ment to eliminate the inefficiency of themotors used in conventional systems. F o r

t h e p u r p o s e s o f t h e c a l c u l a t i o n s w h i c hfollow, it is assumed that the motors used onconventional systems are 80 percent effi-cient. Systems connected electrically areassumed to be identical to conventionalequipment, and conventional performancecharacteristics are assumed.

SOLAR ABSORPTION EQUIPMENT

Absorption cooling equipment can beeasily converted for use with solar-heatedfluids, and the modifications being sug-gested for high-performance solar applica-t ions should not require major designchanges. As a result, absorption equipmentwill probably represent the majority of unitsused in solar air-conditioning systems in thenear future. The water sent to the absorp-tion generator can be heated either from aconventional boiler or from a solar collec-tor. The coefficients of performance usedfor solar absorption equipment will be thesame as those used for the steam-driven ab-sorption equipment, since no boiler lossesare involved.

The Adsorption Cycle System

The adsorpt ion cycle was or iginal lydeveloped by Carl Munters of Stockholm,and is often known as the Munters system.The system is basically a desiccant system,drying the air with various kinds of saltcrystals, silica gels, or zeolite. Heat andmoisture are typically exchanged betweenan exhaust airstream and a supply airstreamusing a heat exchange wheel and a dryingwheel as shown in figure Xl 1-14. The air istaken from the room and passed over thedrying wheel which contains the desiccant.In passing through this wheel, the air is driedand heated to about 180oF. It then passesthrough the heat exchange wheel, where itcools to near room temperature. The air isfinally passed through a humidifier, where itpicks up moisture and cools to 550 to 600 F.The exhaust airstream takes ambient air andhumidifies and cools it slightly to keep theheat exchange wheel as cool as possible.After passing through the heat exchangewheel, the air is still not hot enough to drivethe moisture out of the drying wheel, so ad-ditional heat from a solar or gas source isadded. This hot air then passes through thedrying wheel, where it evaporates moisturefrom the desiccant, and the moist, heatedair is exhausted to the atmosphere,

Ch. XII Heating and Cooling Equipment ● 525

Its advantage is that it takes no refrigera-tion unit, but the wheels are large and re-quire power to drive. After years of develop-ment, problems still exist with desiccantsystems, including the desiccant, the sealsbetween the supply and discharge airstream

Ambient

Humidifiers\ \

on the rotating wheels, and the wet pads.Variations of this adsorbent system are be-ing properly supported by DOE. It has ad-vantages, but still requires developmentprior to demonstration.

Figure XII-14. —An Adsorption Chiller

Heat Gas BurnerExchange or Solar Heat

Wheel I

56.5o/53o

SOURCE Based on a drawtng by W F Rush, statement relative to H R 10952(Institute of Gas Technology, Illlnols Institute of Technology, Chicago, Ill ) Nov 14, 1973

chapter xll heating and cooling equipment

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