Heating by Reversed RefrigerationREG I S D. H E I T C HUE

The elements of reversed refrigeration, amethod by which heating may be accom­plished, are to be found in all refrigerating andair-conditioning systems. In reversed refrig­eration the heat derived from the motor andthe compressor and from the substance cooled-air or water-is utilized, The method isparticularly applicable in industrial plantsrequiring refrigeration throughout the year,where the relatively hot condenser-coolingwater now being wasted might be salvagedfor heating purposes. Two industrial re­versed-refrigeration plants now in successful

operation are described here.

GIVEN a source of heat which results in a reasonablecoefficient of performance, the practicability of a

reversed-refrigeration plant will depend upon the costof electricity relative to coal, gas, or oil, and the initialcost, which in turn will depend upon the ratio of heatingto cooling loads. Obviously a detailed survey by a com­petent air-conditioning engineer would be required todetermine whether or not a contemplated installationmeets the technical requirements.

Because of the growing popularity of refrigerationequipment for both comfort and process cooling, itreasonably can be expected that the use of reversedrefrigeration for heating will increase when it becomespossible to resume the manufacture of the requiredequipment. In industrial plants requiring refrigerationthroughout the year, therelatively hot condenser­cooling water now beingwasted might be used togood advantage.

WHAT REVERSEDREFRIGERATION IS

One need look no furtherthan one's own kitchen tosee the workings of reversedrefrigeration. The electricrefrigerator has all the ele­ments of this fascinatingheating scheme. Supposethe ice trays are filled withcold tap water. Soon thiswater becomes ice. In theprocess, the kitchen is heated by an amount equal to theelectric energy used by the motor plus the amount ofheat taken from the tap water in the trays.

Every refrigerator, air conditioner, or reversed­refrigeration heating system works exactly this same way;in fact the name reversed refrigeration is a misnomer.Heat is extracted from air or water, is combined with theheat developed by the motor and compressor, and addedto other air or water. If the cooled air or water is sentto the living or working areas, the conventional air­conditioning system is the result. If, instead, the heatedwa ter or air is circulated, a reversed-cycle refrigerationplant is the result. The heat comes from two sources:the electric energy converted to heat by the motor andEssential substance of a paper presented at a meeting of the AlEE Springfield(Mass.) Section, September 8, 1941; subsequently expanded to include operating­results data.

Regis D. Heitchue is an air-conditioning engineer in the merchandise engineeringdepartment of the Westinghouse Electric and Manufacturing Company, EastSpringfield, Mass.

compressor, paid for as kilowatt-hours; and the sub­stance cooled. It is because this second quantity of heatcan be taken from the free air or from low-cost waterthat the system has the appearance of giving more thanis paid for. Heat is simply extracted from an additionalsource, which, although of lower temperature than theroom being heated, still contains a large quantity ofheat that can be made available.

TECHNICAL REQUIREMENTS OF A REVERSED.REFRIGERATION PLANT

Source of Heat. Essential to the operation of a reversed­refrigeration heating plant is a suitable source of heat.Not only must the heat source be available in amplequantity, but it must also exceed certain minimum tem-

perature limits, if the gain inheat is to be worth-while.

There are two naturalsources of heat: outdoor airand water. In cool climateswhere freezing tempera­tures are often encountered,water is the only satisfactorysource of heat. In the caseof the household refrigera­tor, the tap water, plus theheat removed from the foodis the source. In a largeplant requiring considerableheat, the cost of using citywater would probably be toogreat or there might be re-strictions on its use for such

purposes. Also, in the colder climates, the temperatureof the city water, rivers, or lakes would, in all probability,for reasons to be pointed out later, be too low. The drill­ing of private wells, then, appears to be the only way ofaffording a source of heat in the colder climates. Wherewell water is not available or it is not feasible to drillwells, the use of the reversed-refrigeration heating plantis obviously not practical.

Where the outdoor temperature seldom falls to freez­ing, air may be employed as the source of heat. A dis..advantage of air as a source of heat however, is that itstemperature is lowest when the need for heat is greatest.Since the efficiency of a reversed-refrigeration plant isgreatly affected by the temperature of the source, the useof air might necessitate a larger plant than would be re­quired if water were used.

The quantity of heat to be removed from the sourcewould obviously depend upon the size of the intended

556 Heitchue-i-Reoersed Refrigeration ELECTRICAL ENGINEERING

installation. The temperature of the heat source, how­ever, has fairly strict economic limits. In the householdrefrigerator, heat is removed from the water and givenup to the room even during the freezing process. Whileit would be possible to utilize the heat thus liberated, itwould not, in most cases, be economically practical.The minimum temperature limits are 45 degrees Fahren­heit for air and 40 degrees for water. Of course, theselimits may be modified somewhat, but as will be shownlater, the coefficient of performance or efficiency falls offappreciably with a decrease in the temperature of theheat source.

Coeficien: of Performance. The efficiency of a refrigerat­ing machine is defined as the coefficient of performance(COP), and is simply the ratio of output to input. In areversed-refrigeration machine, the output is measuredat the condenser, and, disregarding losses, is equal to theheat represented by the motor watts plus the heat re­moved from the source, or the refrigeration effect. Theinput is the heat equivalent of the motor watts. Theexpression then for the efficiency is:

heat from electricity-l-heat from sourceCOPheat from electricity

It was said that the coefficient of performance isgreatly affected by the temperature of the heat source.It is also true that the coefficient of performance is verymuch dependent upon the condensing temperature,which in turn is dependent upon the medium employedto transfer the heat from the refrigerating machine to thebuilding. In the household refrigerator, the room air iscirculated over the air-cooled condenser, absorbingheat directly from the refrigerant through the metal ofthe condenser. Although this method is practical forsmallinstallations, it is not for large ones. Instead, water­cooled condensers are employed. The heat from therefrigerant is first transferred to water and then by means

Table I. Effect of Evaporating and Condensing Temperatureson the Coefficient of Performance

1()()- Ton Condensing Unit

, fIl

(I,.........

~fIl ~ '8

bi: bi. ~;~

Q> Q> ...Q Q e $ to; -~

at')Q> Q ... ... fIl e Cl'" ... e

= s Cl ...Z :I ~ ~ e

~Q.,

fIl Q., o eft "e..c:- ='~ t'd~.~ gE-4 ~'" ... > '2 ~ '0Q> ~ ~ ~ c:: Ua. c. ~ eft o~~ u.; ee e ~ ... +

1t; =' -=0;; ........ ='Q> ~ 0 ~'E'O <.0~ ~ ! .!e~ d

-e~t~ =ubI) bI) ~tx .... + e.5 .5 o~..c: ~ .... ..c:~ ~Z"Cl') ='

f =] bIlE-4 $ ;'E-4 c:: 'Q)'I ~ Cl §

0 ~ ~~3 ... ~..c: e =: '= ea. -e 0

~:€ .a .... ~ ='~~ I: ~ (').~ e ~ bIl8:. e =£= ~ ~"'u 0

~ U ==- =.5- o

SO 96 1,430,000 87,000 297,000 1,727,000 5.8040. . . . .. 96 1,185,000.... 83,300 285,000 1,470,000 5.1534....•. 96 1,040,000.••• 80,500 275,000 ..•. 1,315,000 .4.78SO 117 1,290,000...• 100,000 341,500 1,631,500 .4.7740 117 .•... 1,055,000. . .. 94,500 323,000 1,378,000 4.2634 117. . . .. 920,000 .... 90,400 309,000 1,229,000 3.97

of additional heating coils, the heat is transferred fromthe water to the room air. The lower the temperature ofthe water, the higher will be the coefficient of perform­ance. Offsetting this advantage, however, is the dis­advantage that as the temperature of the water is de­creased, the size of the heating coils must be increased,requiring a greater investment in equipment. In prac­tice, it would be necessary to strike a balance betweenoperating cost as determined by the coefficient of per­formance and amortization and interest charges. Thecoefficient of performance for an actual machine, alOO-horsepower condensing unit operating at severalevaporating and condensing temperatures is shown inTable I.

Operating Costs. The installation and operation of areversed-cycle heating plant is economically practicalonly when the total cost of operation is equal to or lessthan the cost of heating by other methods-coal, gas,or oil. The operating cost is made up of the following:

1. Interest on the capital investment.2. Amortization of capital investment.3. Maintenance charges.4. Electricity.

When the refrigeration and air-conditioning equipmentis necessary during the summer months to provide cool­ing, and the heating load is not much greater than thecooling load, the capital investment and interest chargesare not of major consideration. It can be argued justlythat only the depreciation and maintenance expenseshould be charged against winter operation. In suchcases, the cost of electricity would be the determiningfactor. If the cost is high compared with coal, gas, oroil, it might be cheaper to install a separate heatingplant. On the other hand, if electricity is cheap, theinstallation of a separate heating plant might not bewarranted. If there were a considerable disparity be­tween the heating and, cooling loads and if cooling werea summer-time requirement, then winter operationshould be charged with only the additional equipmentemployed and, of course, depreciation charges on thewhole plant. If the cost of operation thus computedwere less than that of other methods in which interestand amortization charges were also included, the re­versed-refrigeration plant would be economically justi­fied.

PRACTICAL APPLICATIONS

The reversed-refrigeration plants chosen for discussionwere selected because of their sizes, locations, sources ofheat, and methods of changing from heating to cooling.The plant on which the operating data is presented isprobably the largest reverse-refrigeration heating instal­lation in existence.

Reversed-Refrigeration Plant in California. As might besupposed, air is the source of heat of the plant whichserves the Westinghouse Electric and Manufacturing

NOVEMBER 1942 Heitchue-i-Reoersed Refrigeration 557

Figure 1. Heating cycle

Company district office building in Emreyville, Calif.The heating equipment consists of two 71/ 2-horsepower

compressors, extended-surface evaporators of the typecommonly used in air-conditioning work, and air­cooled, extended-surface condensers, a conditioned-airfan, and an exhaust-air fan (Figures 1 and 2).

Winter operation (Figure 1) is as follows. Air drawnin from outdoors and air returned from the air-condi­tioned space mix in the mixing chamber in about equalproportions and divide into two streams. One of thesestreams flows through a set of filters, then over theevaporator where the air gives up heat to the refrigerantin the evaporator. The air then passes through the opendampers into the exhaust-air fan which discharges theair to the outdoors. The other stream flows over theother set of filters, then over the condenser, which heatsthe air, after which it passes through the open dampersto the conditioned-air fan which delivers the air to theducts leading to the air-conditioned space. When theoutdoor temperature falls below 35 degrees Fahrenheita thermostatically controlled valve admits city water tothe preheating coil. The city water being at a tempera­ture of around 60 degrees Fahrenheit adds sufficientheat to the incoming outdoor air to prevent the formationof frost at the evaporator. With an outdoor temperatureof 35 degrees Fahrenheit, the air delivered to the air­conditioned space leaves the condenser at 90 degreesFahrenheit, and the coefficient of. performance is ap­proximately 5.

There may be some doubt as to how it is possible toobtain such a high coefficient of performance in view ofwhat was said previously concerning the outdoor tem­perature. The answer is the mixing chamber. Thetemperature of the air in this chamber is higher thanthat of the outdoor air and yet lower than that of the air

CONDITIONED-AIR FAN

COM­PRESSOR~L...-... ----I

Figure 2. Cooling cycle

EXHAUST-AIR FAN

returned from the air-conditioned space. The result isthat the evaporating temperature is higher than wouldbe the case if only outdoor air were circulated over it,and the condensing temperature is lower than it would beif only indoor air were circulated over it. By thus intro­ducing and discarding the air needed for ventilation(It is made to pass first over the condenser and then,when it is discharged, over the evaporator.) most of theheat is regained at the evaporator that was given up tothe ventilation air at the condenser.

When weather conditions are such as to require cool­ing, a thermostat located within the building changes thepositions of the two sets of dampers, closing the one andopening the other. Figure 2 shows the dampers thusmanipulated. In this cycle, the cooled air from theevaporators is delivered to the air-conditioned space bythe conditioned-air fan, and the air from the condensersis discharged to the outdoors by the exhaust-air fan.

An effort was made to obtain operating data on thisplant, but inasmuch as the equipment very often iscalled upon to furnish heat in the morning and coolingin the afternoon of the same day, the watt-hour meterreadings do not reveal the energy consumed for heatingalone. For the purpose of determining costs, it mightprove worth while to install two watt-hour meters, onefor the heating cycle, and the other for the cooling.Switching from one meter to the other could be ac­complished by a suitable device attached to the damper­operating motor.

Reversed-Refrigeration Plant in Connecticut. Anyonehav­ing only a meager knowledge of reversed refrigerationwould readily agree that the last place he would lookfor a reversed-refrigeration plant would be in NewEngland. Yet, what is probably the largest such heatingplant in the world is installed in the new administrationbuilding of the United Illuminating Company, New

COM­PRESSOR

-~

CONDITIONED-AIR FAN

PREHEATING COIL

EXHAUST-AIR FAN

558 Heitchue-Reversed Refrigeration ELECTRICAL ENGINEERING

TO SEWER

SAND­SETTLING

TAN K

CONDENSERS

Figure 4. Heat flow in the United lliuminating Companyplant

water continues to flow through the condenser withoutany added heat, but th e flow of water through the cooleris stopped.

When cooling is required, the eq uipme nt operates asa conventional summer air-conditioning plant, the cooledwater from the evaporators bein g delivered to the air­conditioning units, and th e conde nse r water discarded.

Summary of Operating Data. The data on the reverse­refr igeration plant of the United Illuminating Companyhere presented are for the heatin g season of from Decem­ber 1, 1940, through March 31, 1941 . The month ofNovember 1940, is excluded becau se data are not avail­able for the whole month.

T able II shows the hours of opera tion of the compres-

Refrigeration equipment in the plant of the United Illuminating Company, NewHaven, Conn.

Figure 3.

Haven, Conn. This is madepossible because of a largeunderground body of freshwater, having a temperaturewhich deviates very littl efrom 58 degrees Fahrenheitthroughout the year. Figure3 shows the refrigerationequipment of this plant.

Six well pumps having acombined capacity of 600gallons per minute drawwater from underground anddeliver it to a large sand-set­tling tank (Figure 4). Fromhere the water flows over aweir, to which is connectedan integrating meter, to asecond tank. Another pumptakes water from this tankand delivers it to one or moreof eight water coolers, whichare the evaporators of therefrigerating system. Inthese coolers, the water is re-duced in temperature and is th en discharged to th esewer . The heat removed from the water is raised intemperature and transferred to a closed hot-water-heat­ing system by one or mo re of eigh t 40.horsepower,hermetically sealed, water-cooled condensing units. Apump in this water circuit circulates the water throughthe eight condensers in series and delivers the water tothe air-conditioning units located throughout the build­ing. After passing through all of th e air-conditioningunits , the water is returned to the first condenser.

It was stated that the condensers are connected inseries. This was done to increase the coefficien t of per­formance. With this arrangement, eac h condenser rais esthe water temperature several de grees, a nd only the endcondenser is operated at the final condensing temperatureand pressure. If the condensers were connected inparallel, each condenser would have to operate at afinal condensing temperature such as to give the desiredheating-water temperature.

The heating system was designed on th e basis of de­livering water 124 degrees Fahrenheit to th e heatingunits when the outdoor temperature is 20 degrees. Fo routdoor temperatures below this va lue, the temperatureof the heating water is increased, and reaches a maximumof 135 de grees when the outdoor temperature is zero.For temperatures above 20 degrees, the heating-watertemperature is lower than 124 de grees.

Control of the condensing units is obtained 'through anoutdoor compensated type of thermostat located in theheating-water circuit. This thermostat, through a stepcontroller, turns on or off the condensing units as re­quired. When a condensing unit is shut down, the

NOVEMBER 1942 Heitchue-i-Reoersed Refrigeration 559

Table III. Coefficient of Performance for Heating Season

) ,

Table II. Compressor-Hours Operation and Per Cent ofAvailable Hours Versus Degree-Days

Degree-DaysPer Cent of

Compressor..Hours Available Hours

..... ..".. ..~~

1<"d ~

da :;S ~SIol~

e "';J.. 0 ~!-' e ~!-' .5 !-'.. = E s= .. olol= 1<=~ .... '" e 00 ... "0

"0 it ..... 0=0... ~o .. rz. '=: 'Eg..il ~.;,

rz. o ~ 3~:;g ~ . llo.. 0 .. "'00 .. .. "0 'i:=~g

00 0::e ~e !-'~ =c Z !-'~ c

Month

reversed-cycle heating plant, including well-pumpmotors, condenser-water-pump motors, and booster­pump motors. Power required by the ventilation fan ismetered separately and is not included.

Calculation of the coefficient of performance is:

(Heat from well water) = (Gallons of well water) (temperature dif­ference) 8.33

(Heat from electric energy) = (kwhrs) 3,415COP (Heat from well water)+(Heat from electrical energy)

(Heat from electrical energy)

The average coefficient of performance for the entireseason is 2.98 . This means that almost three times asmuch heat is obtained from this plant as would be ob­tained from direct resistance heating.

Residence Application. For residences and small officesa self-contained, portable heating and cooling unitknown as the Mobilaire (Figure 5) has been made avail­able. It can be installed in any standard window, re­quires neither water nor drain connections, and plugs intoan appliance outlet . It has sufficient capacity to heat asingle room with an outdoor temperature above 40 de­grees Fahrenheit. Heating or cooling is selected simplyby operating a special four-way valve. This new type ofunitismounted in the window so that one coil is outdoorsand the other coil is indoors.

The heating capacity of this unit is 6,600 Btu perhour when the outdoor temperature is 60 degrees Fahr­enheit and the indoor temperature is 75. The compres­sor motor draws 850 watts under these conditions, re­sulting in a coefficient of performance of 2.28. Whenused for cooling, this unit can cool at the rate of 6,000Btu per hour with an outdoor temperature of 95 andan indoor temperature of 80.

December 1940 1,470 24.7 912January 1941. 1,577 26 .5 1,184February 1941 1,282 23 .8 . ... . . . . . 985March 1941 . . . . .. . .. . . • . . . 1,456 . . . • . . . . • • • • . . 24.5 956

December 1940 10,380 6.5 5,620 81,915 2,800 8,420 3 .00January 1941 11,480 6 .5 6,230 86,615 2,960 9,190 3 .10February 1941 9,460 6 .5 5,120 77,780 2,660 7,780 2 .92March 1941. 9,750 6 .5 5,275 81,215 2,780 8,055 2 .90

Figure 5. The Mobilaire

sors and the per cent of available compressor-hoursversus degree-days. This table was compiled from thedaily readings of hour meters. Provision is made wherebythe sequence of operation of the compressors can bechanged so that the hours of operation will be about thesame for each compressor. The degree-days were ob­tained from the local weather bureau.

It might be inferred from Table II that the plant isoversized. This is not the case, however, because thefull load is not imposed upon the plant 24 hours a day.Quite often the ventilation fan is in operation only dur­ing the day. This fan draws in a large volume of out­side air representing a considerable portion of the heatingload. Also, an additional heavy load is imposed upon theplant from the garage area when the doors are opened toallow the trucks and cars to depart and return. Thistraffic is heaviest during the morning and evening, al­though a considerable number of vehicles go in and outduring the noon hour. This load is of such short dura­tion, however, that it has little effect on the total hoursof operation of the plant. For the heating season inquestion, the records show that the maximum numberof compressors in operation at anyone time was five.

In Table III are shown the gallons of water used,kilowatt-hours consumed, and the coefficient of per­formance for each month of the heating season. Theamount of water used was obtained from daily readingsof an integrating flow meter. The figures in the "tem­perature-difference" column were obtained from record­ing thermometer charts covering a two-month period.The temperature of the well water was found to be prac­tically constant at 571/ 2 degrees Fahrenheit. The aver­age temperature of the outlet water was found to beapproximately 51 degrees, making a difference of 6.5degrees.

Allowance is made for the kilowatt-hours consumedby certain auxiliary motors which would be necessaryin a conventional heating plant. The figures in the"net" column of Table III, therefore, show the totalpower consumed by all of the apparatus required by the

560 Heitchue-Reversed Refrigeration ELECTRICAL ENGINEERING