US2498861A

US2498861A - Reverse cycle refrigerating system

Info

Publication number: US2498861A
Application number: US10793A
Authority: US
Inventors: Alwin B Newton
Original assignee: Chrysler Corp
Current assignee: Old Carco LLC
Priority date: 1948-02-25
Filing date: 1948-02-25
Publication date: 1950-02-28
Anticipated expiration: 1967-02-28

Description

A. B. NEwroN 2,498,861

REVERSE CYCLE REFRIGERATING sYs'rEu 3 Sheets-Sheet 1 Feb. 28, 1950 Filed Feb. 25, 1948 Feb. 2s, 195o 3 Sheets-Sheet 2 Filed Feb. 25, 1948 Feb. 28, 1950 A. a. NEWTON 2,498,861

Rnvmsm wcm REFRIGERATING isv'sm Filed Feb. 25, 1948 3 Sheets-Sheet 3 llraolufr Weasur Condenser is Ils. P

z'vere idr m 72911;.

Room

rauf! Temp H- 5- XW WQ HM Patented Feb. 28, 1950 REVERSE CYCLE REFRIGERATIN G YSTE Alwin B. Newton, Dayton, Ohio, assignor to Chrysler Corporation, Highland Park, Mich., a

corporation of Delaware Application February 25, 1948, Serial No. 10,793

19 Claims.

'system a refrigeration system is employed to do the heating. The difference between a reverse cycle system and an ordinary refrigeration system for cooling is that in a reverse cycle system the heat dissipated by the condenser is used for a useful purpose such as heating a room or heating water. In the ordinary refrigeration system it is the ability of the evaporator to extract heat from surrounding objects that is used ffor cooling some object. The evaporator of a reverse cycle system is exposed to some source of heat such as the outside air or ground or an outside source of water and the heat picked up in the refrigeration system from the outside source is discharged from the condenser Iand serves to heat the building or water. The discussion herein will be devoted to the appli-cationl of a reverse cycle system to the heating of a building such as a home although it is to be understood that the heat made available by the reverse cycle system may be used for any desired purpose.

If a reverse cycle system is designed to heat a particular residence that'system must have a. capacity suilicient to heat the residence on the coldest days. It has been found that the average seasonal requirement is about 40% of the maximum requirement in a typical locality due to the fact that the most extreme heating requirements do not exist on the milder days. Heretofore, systems of xed compressor displacement capacity have been used to heat residences throughout the season in which climatic changes produce diierent demands for heat. Controls have been used to regulate the time of operation of these systems but the compressor displacement capacity has remained constant. It is a principal object of this invention to provide a means for more than doubling the efciency of such a system by unloading individual compressor cylinders to adapt the system to the heating requirements instead of running the system at full compressor displacement capacity for short intervals. This increase in eiliciency is obtained by providing an automatic control of the compressor compression ratio so that the mean temperature differences between the refrigerant and the heat source and the refrigerant and the substances to be heated are always at a minimum. Appreciable reductions in compression ratio are obtained thereby which greatly improve the overall eiiiciency during light load periods. 1

Some suggestions to overcome the problem presented by systems of xed compressor displacement capacity have contemplated the use of systems of small capacity and the heating of water in a water tank during mild weather and using this stored heat to heat the house during the periods when the refrigeration system lacks sufficient capacity. This system is impractical for tremendous quantities of water are involved. It is much more desirable to provide a system of suiiicient -capacity and to unload a portion of the system when all of the capacity is not required.

One type of reverse cycle system or heat pump has the evaporator exposed to the atmosphere to extract heat therefrom. This type of system has Icertain inherent advantages relating to its installation. However, it also presents additional diiculties. In view of the fact that the function of the evaporator is to extract heat from the atmosphere it is evident that when the outside temperature increases the system has its greatest heat extracting capacity. Unfortunately this is just the reverse of what is desired, for the greatest demand for heat exists when the outside temperature is low and at this time with present systems of this type the capacity of the system to obtain heat is lowest. It is an object of this invention to provide means for adjusting the capacity of a reverse cycle system and to provide in this means a recognition of the changes in its capacity.

The volume of air delivered by either system is determined by the requirement for 'air at the established delivered air temperature under extreme conditions. The temperature of the delivered air in the conventional system increases as the load decreases or outside temperature increases. Since the system operates under what may be termed a partial load for the major portion of the season the delivered air temperature of a conventional system is greater than necessary most ofthe time and itis axiomatic that/"as the delivered air temperature increases the eiiiciency of the system decreases. In contrast to this in a system operating in accordance with my invention the delivered air temperature may be decreased as the load on the system decreases (i. e. outside temperature increases). Throughout the major portion of the season when partial load conditions prevail the temperature of delivered air is therefore less with my invention than in a conventional system and therefore the season average of the eiiiciency is greater. 'I'he volume of air delivered per unit of time by either system is constant for that system throughout the season but this volume may be established at a lower value in a system incorporatlngmy invention for a higher delivered air temperature may be used under extreme load conditions without significantly penalizing the efficiency of the system under the more frequent partial load -conditions.

In addition, discussions heretofore made involving heat pumps and reverse cycle systems have considered the advisability of using the system for heating during winter months and cooling during summer months. This produces an additional problem in view of the fact that the system and particularly the compressor of the system will have altogether too much cooling capacity compared to the heating capacity required to handle a given installation. For example, a 5 H. P. compressor might be required to provide the necessary B. t. u. output for heating a particular residence whereas only a2 H. P. compressor would be required to cool the same residence. It is an additional object of this invention to provide a means for varying the capacity of the system between summer and winter requirements.

It is a further object of this invention to provide a reverse cycle system or heat pumpwith a compressor unloading means therein and to provide means for utilizing the refrigerant pressure within the system to operate the unloading means.

It is van additional object of the invention to provide a heat pump or reverse cycle system having a variable capacity compressor therein and control means to vary the capacity of the compressor in response to outside temperature and delivered air temperature conditions. If desired, a supplemental control mas7 be associated with the system to initiate the operation of the system in response to a room temperature thermostat.

It is a further object of the invention to improve the electrical load characteristics of a reverse cycle heating system. It is.recognized that an electrical power supply company nds a reduced load operating for a relatively long length of time to be more acceptable than a relatively high load imposed for short intervals. Varying the capacity of the compressor rather than varying the time of operation of a compressor of xed capacity accomplishes this.

These and other objects of my invention will become apparent from the following description taken in conjunction with the accompanying drawings in which:

Fig. l is a diagrammatic showing of a heating system for a residence incorporating my invention;

Fig. 2 is an elevation, partly in section of a compressor having an unloader means incorporated therein;

Fig. 3 is an enlarged fragmentary section of a portion of the Fig. 2 compressor unloader means;

Fig. 4 is a vertical sectional view of a control ""f'adapted-to beincorporated in the rev@rse Cycle Fig. 6 comprises 3 charts from which computations showing the relative eiciency of a conventional system and a system incorporating my invention will be made where these systems utilize an evaporator coil exposed to the atmosphere.

In Fig. l a residence I0 is illustrated as having a room I2 therein which is to be heated by a reverse cycle refrigerating system. A hot air discharge grille I4 and a cold air return grille I6 are illustrated as being connected by a duct I8. A fan 2D is positioned in the duct to induce the circulation of air therein. The condenser 22 of a reverse cycle refrigeration system is also located in the duct I8 so that air circulating therein is heated by passing through the condenser 22. The air from room I2 is thus recirculated and heated by the condenser 22.

The reverse cycle refrigerating system which provides heat to the condenser 22 comprises a compressor 2li having unloading means 26 associated therewith, an expansion valve 28 and an evaporator coil 3B. The evaporator coil 30 may either be located in the air outside of the building I or be buried in the ground adjacent the building Ill. Refrigerant is conveyed from the evaporator 36 to compressor 2li by line 32. The compressed refrigerant is delivered from compressor 24 to condenser` 22 by lines 34 and 35 and conveyed from condenser 22 to the expansion valve 28 by a line 38. The unloading means 25 to be described herein receives compressed refrigerant from compressor 24 through lines 36, dil, and 4I. The passage of refrigerant to unloading means 26 through lines 3G and li is regulated by a control means generally designated by the numeral @2. The control 'means 52 operates in response to a temperature bulb 236 located in the duct l@ and temperature bulb LIS located outside the building Ill and throttles the supply of refrigerant to unloading means 2t in response to conditions measured by the bulbs lli and 65. A line i3 having a restriction I5 therein is provided to bleed refrigerant from unloading means 2t to suction line 32.

If desired a supplemental control may be provided to initiate and terminate the operation of the compressor 24 in response to room temperature conditions. Electric energy to operate the compressor 24 is provided by an electrical line 48 and an electrical line 50. The electrical line 5G contains a switch 52 which is opened by a spring 54 and closed by a solenoid 5B. The solenoid 56 is wired in series with a source 58 of low voltage electric energy and a room temperature responsive thermostat switch 60. When the room temperature responsive thermostat 60 demands heat the switch (not shown) therein is closed and the electrical circuit between source 58 and solenoid 56 is closed. Energization of solenoid 56 closes switch 52 which completes the electrical circuit to compressor 24. Although means will be described herein for controlling the delivery of heat by the system in response to outside temperature conditions the supplemental room thermostat control is desirable for it is able to compensate for conditions such as whether the day is sunny or cloudy or whether a high wind is blowing. In other words, control 42 determines the capacity of the system during each operating period, bul the duration of the operating period is determined by thermostat 60.

Referring to Figs. 2 and 3 the construction 'o1 the compressor 24 and the unloading means 2E may be seen in greater detail. The compresso] 75 unloading means illustrated herein is describe:

in greater detail in my application, Serial No. 792,277, tiled December 17, 1947, as a continuation in part of application, Serial No. 825,864, filed October 31, 1945, now abandoned. Compressor 24 comprises an electric motor 82 which drives a compressor crankshaft 64 to which are connected a plurality of connecting rods 66 each operating a piston 68 in a cylinder 10. A suction manifold 12 in the compressor is connected to the line 32 by an orifice (not shown). Re-

frigerant passes into the interior of each of the.

cylinders through a suction valve 14 and is ejectedthrough a discharge valve 16 into a discharge passage 18 operatively connected to the line 34 by an orifice. Details of the valve and piston construction may be ascertained from the Patent No. 2,137,965, which issued on November 22, 1938, and the Patent No. 2,185,473 which issued on January 2, 1940, to Charles R. Neeson.

The suction manifold 12 is connected through` ports 80 with the interior space 82 of the compressor crankcase containing a flexible metallic bellows 84. Bellows 84 is thus subjected to the pressure of expanded refrigerant vreturned from the evaporator 30. Movement of the Abellows 84 which has an end piece 86 welded to a link rod 88 causes reciprocation of the link rod 88 which is connected by rocking levers 90 to a master valve member 92 contained in a master valve 93. The master valve member 92 is provided with a plurality of notches 94 so that aspring pressed ball 96 engaging in the notches permits step by step movement of the master valve member. Each step causes one of a plurality of slots 98 to be connected to or disconnected from a source of oil pressure in an oil pressure tube |00. Each of the slots 98 is connected to a short tube |02 leading to a cylinder |04 (Fig. 2) in which is mounted a spring loaded `unloader piston |06 connected to an unloading mechanism including a yoke |08 adapted to ride on a ramp ||0 and to be moved axially of piston 68 as the piston |06 moves the yoke |08 longitudinally. The yoke causes axial movement of a collar ||2 having unloader pins ||4 mounted thereon which when moved axially causes the suction valve 14 to be held open continuously whereby the cylinder is unloaded. The position of the movable valve part 92 therefore controls the number of unloader pistons i06 to which oil pressure is applied and hence controls the number of cylinders in operation. When -as disclosed in Fig. 2 all but one of slots 98 are connected to tube |00 through the annular space surrounding a reduced portion of valve member 92 all but one of the individual cylinders will be loaded or operating. When valve member 92 is moved to the left by the length of another notch 94 two cylinders will be unloaded since another one of the unloader cylinders |04 will be disconnected from the source of oil pressure.

Oil pressure is applied to the unloader mechanism through the master valve from Aa pressure lubrication pump (not shown) details of which may be ascertained from the aforesaid Patent No. 2,185.473. The oil pressure pump operates coextensively with the operation of motor 62 so that no oil pressure will be supplied to the master .valve unless the motor is operating and since it takes a short while for the pressure to be built up by the oil pump it is apparent that all cylinders will be unloaded during starting thereby preventing large starting current demand. It is also apparent that after oil pressure is available a number of cylinders may be unloaded depending upon the position of the link rod 38.

The position of link rod 88 may be controlled by the degree of compression of the flexible metallic bellows 84 which compression is effected by the pressure of the refrigerant in the space 82 connected to the suction side of the refrigerating system through the port 80. The pressure of the gas against bellows 84 operates against a compression spring ||8 positioned between the end of the bellows and a disc Ill. The disc has wings |20 at opposite sides projecting through a slot in a threaded sleeve |22. The sleeve is secured as by welding to an apertured member |24 to which the bellows 84 is secured. A nut |28 threaded on the sleeve |22 determines the position of the disc ||8 and consequently the compression of the spring H6. The link rod 88 has a reduced outer end on which is threaded a nut |28 serving to guide the rod in sleeve |22. A lock nut |30 retains the nut |28 in position. An additional light spring may be provided to react between nut |26 and nut |28. 'I'his facilitates an adjustment of the spring pressure opposing compression of bellows 84 since springs ||8 and |3| oppose each other. The resultant spring force controls the unloading pressure of the master valve 93 so that the suction pressure of the refrigerating system may be controlled within reasonable limits.

In addition to the use of suction pressure to determinev the compressor unloading additional V means for unloading the compressor in response to temperature of the heated delivered air and the outside temperature are provided. A housing. |32 is secured in fluidtight relationship to apertured member |24. A collar |34 is threaded on housing |32 and a dome |36 is secured as by welding to the collar |34. An orifice |38 is provided in housing |32 and has connected thereto the line 4| adapted to conduct refrigerant to the interior of the housing |32 and dome |36 so that the pressure Voi' this refrigerant may act upon the interiorof the bellows 84. Thus on the exterior'of the bellows 84 the suction pressure tends to compress the bellows. From the interior of the bellows 84 the spring ||6 and the pressure of refrigerant supplied by line 4| are tending to expand the bellows 84. The resultant of these forces acting on the bellows 84 will determine the degree of compression thereof and thereby determine the position of the link rod 88 and the master valve member 92 which in turn determines the number of cylinders of compressor 24 which are loaded. The refrigerant permitted to enter unloading means 26 from line 4| is controlled by a control 42. The line 43 bleeds refrigerant from dome |36 and thereby permits the pressure within dome |36 to decrease when the supply from line 4| is restricted. The line 43 is provided with a restriction and the capacity of this bleed line 43 is less than the capacity of line 4| so that pressure may be built up in dome |36 when the line 4| is not restricted by control 42.

The control 42 is adapted to throttle the supply of refrigerant from line 34 of the compressor 24 through the

lines

40 and 4| to the unloading means 26. A control means similar to the lcontrol 42 used for a different application is illustrated in my copending application, Serial No. 763,596, filed July 25, 1947. The

lines

40 and 4| conducting refrigerant from compressor 24 to compressor unloading means 28 have the control 42 positioned between them. The control 42 serves as a valve governing the passage of.

refrigerant from line`40 to line 4|.

The control 42 is mounted in a housing |66 having openings in which the

lines

40 and 4| are received. A dome |18 is secured to a side wall of the housing |68 over an opening |1| therein. A pressure responsive bellows |12 is positioned within the dome and cooperates therewith to form a liquidtight compartment |14. The bulb 46 previously referred to is connected to compartment |14 and the compartment |14 and bulb 46 are lled with an expansible medium such as one of the liquids commonly employed for this purpose. Temperature changes will cause the medium in the bulb 46 to expand and activate the bellows |12. The bulb 46 is positioned outside the building |0 as illustrated in Fig. 1 and exposed to the atmosphere. A rod |16 is adjustably secured to the bellows. An L-shaped lever |18 is pivoted at |80 and has one leg thereof adapted to be engaged by the rod |18. Movement of the rod |16 rotates the lever |18 about the pivot |80 against the spring 8| to be described. The other leg of the lever |18 has a valve element |82 in theform of a pad secured to the end thereof. `Valve element |82 is positioned in a predetermined position for each outside temperature bythe apparatus described.

A similar Amechanism is'provided to control the position of a second valve element |84. A dome |86 is associated with the housing |68 and contains a bellows element |88 which cooperates with the dome |86 to provide a liquidtight compartment |90. The compartment |90 is connected to the bulb 44 which was previously referred to and the bellows |88 is activated by expansion and' contraction of a medium provided in the compartment |90 and bulb 44. Bulb 44 is positioned in the heated air delivery duct I8 as shown in Fig. l. A lever |92 carrying valve element |84 is pivoted on the housing |68 at |94. The spring |8| tends to separate levers |18 and |92 While movements of the bellows elements tend to move the levers toward each other. A lever |96 is pivoted on the housing |68 at |98. A plate member 200 is also pivoted `at |98. A threaded ele-= ment 204 is positioned between levers |92 and |96 and in engagement with these levers. The threaded element 204 is threaded upon an adjusting rod 208 carried by the plate member 200. A knob 208 is provided on rod 206 for manual adjustment thereof. A rod 2 0 is operatively connected to the bellows |88 and adapted to engage the lever |96 in response to contraction and expansion of the bellows |88. Means are thus pro-v vided to position the valve element |84 in a predetermined position for each temperature in the duct |8. The'valve element |84 is connected by a flexible tube 2|2 to the line 40. It will thus be seen that the valve element |82 when properly. positioned can close the tube 2|2 so that refrigerant cannot be emitted therefrom. When valve |82 is positioned away from valve element |84 so that refrigerant may escape from line 40 and tube 2|2 the housing |68 is filled with refrigerant which entersline 4| and is transmitted thereby to unloading means 26. A modulating control is thus provided. The supply of refrigerant to the unloader control means 26 is thus dependent upon both outside temperature conditions and the temperature of the air, in the duct I8 which are measured by the bulbs 46 and 44 respectively. Although refrigerant has been described as the medium delivered by pipe 4| to control the unloading of the compressor cylin;

8. ders it ls to be understood that a source of compressed air could be substituted so that the air supply to the unloading means 26 would be modulated by control means 42. A system using an air supply to operate the unloader means is illustrated in my copending application Serial No. 792,277 referred to above.

As previously explained in setting forth the objects of my invention the outside temperature dictates the requirement for heat and when an evaporator exposed to the atmosphere is used the capacity of the system to absorb heat is also a function of the outside temperature. Both of these factors are therefore important in selecting the optimum capacity of the compressor which is accomplished by unloading means 28. In addition, the temperature of air in duct I8 is directly related to the ability of this 'air to heat the room I2 and therefore the capacity of compressor 24 has been controlled so that its capacity is suiiicient at all times to provide a satisfactory temperature of heated air in duct I8.

Changes in the condition of the heat source are automatically-compensated for by the apparatus described herein. For example, where an evaporator exposed to the atmosphere accumulates frost or Where long continuous operation of a ground coil lowers the temperature of the ground in the vicinity of the coil the ability of a conventional reverse cycle system to deliver heat is impaired. In contrast to this the controls described herein automatically adjust the system to compensate for this change in the condition of the heat source. This change induces a drop in compressor suction pressure which is followed by a drop in compressor discharge pressure and temperature which in turn drops the delivered air temperature which activates bulb 44 which automatically loads the compressor to compensate for this. The compressor loading as described herein is therefore controlled in response to four conditions which include the outside air temperature, the delivered air temperature, the condition of the heat source as explained above, and the room temperature by the thermostat 68.

In Fig. 5 charts have been illustrated which facilitate a comparison of the efoiency of a reverse cycle heating system controlled by an onoff thermostat and a system incorporating my invention in which the compressor displacement capacity may be varied. Both of these systems have the evaporator buried in the ground. The chart on the left labelled conventional system shows the ground at a temperature of F. as the heat source. Under heavy load conditions a reasonable evaporator temperature would be approximately 20 F. which corresponds to 37 pounds absolute pressure. To produce a room temperature under extremely cold conditions the delivered air temperature would be about F. and this would require a condenser temperature of about F. which corresponds to 194 pounds absolute pressure. The efficiency or power requirements of the system are related to the absolute pressures of the refrigerant in the system Vbecause the density of the ,refrigerant increases as its absolute pressure increases and therefore, a greater weight of refrigerant will be compressed as the density increases. By consulting tables familiar to those skilled in the art it may be seen that .124 H. P. per thousand B. t. u.s per hour of operation of the heating A apparatus would be required for this conventional It is estimated for a typical locality that the average of the heating requirements over the period of a season approximate 40% of the maximum requirements under extreme conditions. By varying the capacity of the system advantage may be taken of this fact. Referring to the chart in Fig. 5 labelled Variable capacity system" the system has been illustrated as operating at its usual or average load which is only 40 per cent of its potential capacity. The average delivered air temperature is considerably lower and the average condenser temperature and pressure are lower while the average evaporator temperature is higher than in the conventional system chart. Note that the disadvantage in the conventional system was that its time of operation could be controlled but its capacity was always that required for extreme conditions. Reference to the tables previously referred to disclosed that the average horsepower requirement for the season for the variable capacity system is .054 H. P. per thousand B.'t. u.s per hour of operation. Therefore, over the period of a season the variable capacity system requires only about forty-three per cent of the power or electrical energy that the conventional system requires.

In Fig. 6 a similar set of charts have been illustrated for systems using evaporators exposed to the atmosphere. In view of the fact that changes in outside temperature affect the eiliciency of the conventional system of this type, this system has been shown with anoutside temperature of F. and an outside temperature of 40 F. 'I'he outside temperature of 40 F. has been used as illustrative of the average of temperature conditions which might be obtained in certain localities over the period of a season while the 0 F. has been used as illustrative of extreme conditions for which the apparatus must be designed. By computations similar to that explained with reference to Fig. it is seen that the horsepower requirements vary between .18 H. P. per thousand B. t. u.s per hour for operation at 0 F. and .218 H. P. per thousand B. t. u.s per hour for operation at 40 F. In the latter case the absolute pressures are greater and the capacity of the system cannot be varied and therefore the efdciency of the system is lower. By contrast to this the Variable capacity system operating at its seasonal average of 40% of its capacity or 40 F. uses .057 H. P. per thousand B. t. u.s per hour. The savings in energy consumption produced by varying the capacity of the system are thus of major proportions and constitute an unanticipated result obtained by the modiiication of the reverse cycle system as described herein.

The charts of Figs. 5 and 6 illustrate the fact that with my improved control the temperature difference between the refrigerant in the evaporator and the heat source and the temperature difference between the refrigerant in the condenser and the substance to be heated are simultaneously controlled so that each of these temperature differences are maintained at the minimum value compatible with the requirement for heat.

I claim:

1. In a reverse cycle refrigeration system having an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated and a compressor, unloader means to vary the capacity of said compressor and control apparatus responsive to conditions indicating the available heat in said source and the demand for heat by said substance to control said unloader means and thereby adjust the capacity of said system so that it operates at its optimum efliciency for said conditions.

2. In a reverse cycle refrigeration system having an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated and a compressor, unloader means to vary the capacity of said compressor and control apparatus responsive to the temperature of said source and the temperature of said substance to control said unloader means to determine the number of operating cylinders in said compressor to thereby adjust the capacity of said system so that it operates at its optimum efficiency.

3. In a reverse cycle refrigeration system adapted to heat a space in a, building by extracting heat from a natural source outside of said building, a compressor, a cylinder unloading mechanism associated with said compressor and adapted to vary the capacity thereof by determining the number of loaded cylinders in said compressor and control mechanism responsive to temperature changes outside of said building to control the operation of said unloading mechanism whereby the capacity of said compressor is at all times a function of the temperature outside of said building.

4. In a building having a space to be heated and a, duct for heated air to heat said space, a reverse cycle refrigeration system to heat air in said duct comprising a condenser located in heat transfer relationship with said air, an evaporator adapted to assimilate heat from a source outside of said building, a refrigerant compressor, a cylinder unloading mechanism associated with said compressor and adapted to reduce the capacity of said compressor by unloading individual cylinders thereof and control means responsive to the temperature outside of said building tocontrol the operation of said unloading mechanism so that the capacityof said compressor is at all times a function of the temperature outside of said building.

5. In a building having a space to be heated and a duct for heated air to heat said space, a reverse cycle refrigeration system to heat air in said duct comprising a condenser located in heat transfer relationship with said air, an evaporator adapted to assimilate heat from a source outside of said building, a refrigerant compressor, a Lcylinder unloading mechanism associated with said compressor and adapted to reduce the capacity of said compressor thereof, control means responsive to the temperature outside of said building and to the temperature of heated air in said duct to control the operation of said unloading mechanism so that the capacity of said compressor is at all times a function of said temperatures.

6. In a refrigeration system, means forming a circuit for refrigerant in said system, a multi-cylinder compressor interposed in said circuit, unloader mechanism associated with said compressor and adapted to unload individual cylinders of said compressor and control means for said unloader mechanism including a path for said refrigerant forming a portion of said circuit, said control means being adapted to regulate the ow of refrigerant in said path and to deliver said regulated flow of refrigerant to said unloader mechanism to control the latter.

7. In a reverse cycle refrigeration system having an evaporator located in heat transfer relation with a source of heat. a condenser located in heat transfer relation with a substance to be heated, a compressor and means forminga circuit for refrigerant through said evaporator, said compressor and said condenser, unloader means interposed in said circuit to vary the capacity of said compressor in response to the pressure of refrigerant supplied to said unloader means and control means adapted to throttle the supply of refrigerant to Said unloader means in response to outside atmosphere temperature and in response to temperature of the substance to be heated.

8. In a reverse cycle refrigeration system hav- :lng an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated and a compressor, unloader means to vary y the compression ratio of said compressor and control apparatus responsive to outside temperature and to the demand for heat to control said unloader means and thereby adjust the compression ratio of said compressor.

9. In a reverse cycle refrigeration system adapted to heat a space in a building by extracting heat from the outside atmosphere, an evaporator exposed to said atmosphere, a condenser located in heat transfer relation with respect to said space, a compressor, unloader means to vary the capacity of said compressor and control apparatus associated with said unloader means and adapted to operate said unloader means in response to changes in the capacity of said system to absorb heat from the atmosphere. v

10. In a reverse cycle refrigeration system having an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated, a compressor and means forming a circuit for refrigerant through said evaporator, condenser and compressor, unloader means to vary the capacity of said compressor and ,control apparatus adapted to maintain the mean temperature dierential between said refrigerant and said source and said refrigerant and said substance at a predetermined minimum.

i1. In -a reverse cycle refrigeration system adapted to heat a space and having an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated and a compressor, unloader means to vary the capacity of said "compressor, control apparatus responsive to conditions indicating the available heat in said source and the demand for heat by said substance to control said unloader means and thereby adjust the capacity of said system and supplemental space temperature responsive ,control means adapted to initiate and terminate operation of said compressor in response to space temperature conditions whereby the capacity of said system during each operating period is established by said control apparatus and the duration and frequency of the operating periods are vdetermine by said supplemental control means. f

12'. In a reverse cycle refrigeration system adapted to heat a space and having an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated and a compressor, space temperature responsive control means to initiate and Vterminate operation of said compressor and control apparatus responsive to the temperature of air delivered to said space to control the capacity of said system during each operating period of said compressor so that the heat supplied by delivered air during each operating period will equal or exceed the demands of the space.

13. In a reverse cycle refrigeration system adapted to heat a space and having an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated and a compressor, space temperature responsive control means to initiate and terminate operation of said compressor and control apparatus responsive t0 the outside temperature to control the capacity of said system during each operating period of said compressor so that the heat supplied by said system to said space during each operating period will equal or exceed the demands of the space for the existing outside temperature conditions.

14. In a reverse cycle refrigeration system adapted to heat a space and having an evaporator located in heat transfer relation with a source of heat, a condenser located in heat transfer relation with a substance to be heated and a compressor, unloader means to vary the capacity of said compressor and control apparatus adapted to control said unloader mechanism so that the heat discharged by said system to said space is substantially constant when the ability of said evaporator to obtain heat decreases, said control apparatus being adapted to cause said unloader means to increase the loading of said compressor to maintain the discharge of heat by said system at a constant value during a uniform weather condition.

15. In a space heating apparatus utilizing a reverse cycle refrigeration system to obtain heat outside said space and to deliver said heat to said space a refrigerant compressor, cylinder unloading mechanism associated with said compressor and control apparatus to control said unloading mechanism, said control apparatus including means to control said unloading mechanism in response to changes in the temperature 0f air dey livered to said space to compensate for changes in the ability of said system to absorb heat from the outside, means to control said unloading mechanism in response to changes in temperature outside of said space, and supplemental space temperature responsive control means to initiate and terminate the operation of said compressor in response to changes in the temperature of said space.

16. In a reverse cycle refrigeration system adapted to heat a space in a building by extracting heat from a natural source outside of said building and vheating air from said space, a compressor, a cylinder unloading mechanism associated with said compressor and adapted to vary the capacity thereof by determining the number of loaded cylinders in said compressor and control mechanism responsive to the temperature of said heated air to control the operation of said unloading mechanism.

1'7. In a building having a space to be heated and a duct for heated air to heat said space, a reverse cycle refrigeration system to heat air in said duct comprising a condenser located in heat transfer relationship with said air, an evaporator `adapted to -assimilate heat from a source outside of said building, a refrigerant compressor, a cylinder unloading mechanism associated with said compressor and adapted to reduce the capacity of said compressor by unloading individual cylinders thereof, and control means responsive to the temperature of air in said duct to control the operations of said unloading mechanism so y.that the capacity of said compressor isat all times aiunction-of the temperature of air in said duct whereby the effect of outside conditions` on-said system is automatically compensated for by adjusting the capacity of the system to produce an optimum delivered air temperature.

18. In a reverse cycle refrigeration system including an evaporator for refrigerant located in heat transfer relation with a source of heat and adapted to receive heat by virtue of a first temperature differential between said refrigerant and said source, a condenser for refrigerant located in heat transfer relationship with asubstance to be heated and adapted to deliver heat 'to said substance by virtue of a second temperature differential between said refrigerant and said substance, a compressor to pump heat and refrigerant from said evaporator to said condenser, cylinder, unloading mechanism associated with said compressor and control mechanism to control said unloading mechanism so that the, said ilrst and second temperature diierentials are maintained at the minimum values capable of delivering the required heat to said substance.

19. In a building 4having aspace to be heated and a duct for heated air to heat said space, a reverse cycle refrigeration system to heat air in said duct comprising a condenser located in heat REFERENCES C ITED The following references are of record in the file of this patent:

UNITED STATES PATENTS v Number Name Date 1,969,076 Hirsch Aug. 7, 1934 2,122,012 Smith June 28, 1938 2,185,473 Neeson Jan. 2, 1940 2,296,304 Wolfert Sept. 22, 1942 2,296,822 Wolfert Sept. 22, 1942 2,313,390 Newton Mar. 9, 1943 FOREIGN PATENTS Number Country Date 173,493 Switzerland Nov. 30, 1934