US2759708A

US2759708A - Air to air heat pump apparatus

Info

Publication number: US2759708A
Application number: US389640A
Authority: US
Inventors: Russell H Burgess
Original assignee: Drying Systems Inc
Current assignee: Drying Systems Inc
Priority date: 1953-11-02
Filing date: 1953-11-02
Publication date: 1956-08-21
Anticipated expiration: 1973-08-21

Description

Aug. 21, 1956 R. H. BURGESS 2,75

AIR TO AIR HEAT PUMP APPARATUS File'd.Nov. 2, 1955 7 Sheets-Sheet 1 FIE. 1

Aug. 21, 1956 R. H. BURGESS ,7 9,

AIR TO AIR HEAT PUMP APPARATUS Filed Nov. 2'. 1953 I 7 Sheets-Sheet 2 ZS V Z8-Z /00 7 Aug. 21, 1956 R. H. BURGESS 2,759,708

AIR TO AIR HEAT PUMP APPARATUS Filed Nov. 2. 1953 I '7 Sheets-Sheet 5 FIE. 31

Z Z-Z 25-2 296/ 8 Z0 235,) /00 280 25 L Z5 96 [72 (/672 250/" izzas eZZ 473129655 Aug. 21, 1956 R. H. BURGESS 2,759,703

AIR TO AIR HEAT PUMP APPARATUS Filed Nov. 2, 1953 v Sheets-Sheet 4 F1E. E

fizfvzzor' r $11556 (Z 17 3125 71255 Aug. 21, 1956 R. H. BURGESS 2,759,703

AIR TO AIR HEAT PUMP APPARATUS Filed Nov. 2, 1955 'r Sheet s-Sheet Z FIE] 2/ z Aug. 21, 1956 R. H. BURGESS AIR TO AIR HEAT PUMP APPARATUS 7 Sheeiis-Sheet 6 Filed NOV. 2, 1953 United States Patent AIR TO AIR HEAT PUMP APPARATUS Russell H. Burgess, Chicago, Ill., assignor to Drying Sys tems, Inc, Chicago, 111., a corporation of Illinois Application November 2, 1953, Serial No. 389,640

12 Claims. (Cl. 2573) This invention relates to air to air heat pump apparatus and particularly to the control means for such apparatus.

In the use of air to air heat pump apparatus for conditioning air within a building, the wide range of heating and cooling requirements has introduced design and control problems which have in many instances resulted in undue cost of manufacture or operation, or which have resulted in unsatisfactory operation in other instances, and it is the primary object of the present invention to improve the control means for such apparatus in such a way as to obviate the major diificu'lties and objections heretofore encountered.

Thus in respect to the compressor capacity afforded in prior apparatus, it is well known that such capacity has been afforded by a single compressor of a size large enough to meet the maximum demands of the system. This of course puts a large star-ting load on the electric power lines, and also results in short and frequent operating cycles of the apparatus with high starting loads imposed at frequent intervals on the power lines. It is therefore a more specific object of the invention to enable smaller compressors to be used in multiple in such heat pump apparatus, thereby to reduce the starting loads on the power lines and cause longer and less frequent operating cycles so as to correspondingly reduce the number of starting loads placed on the power lines.

Another object of the present invention is to afford a normally inactive booster heater in an air to air heat pump apparatus and to control the same in such a way as to afford additional heating capacity when this is required and to supply heat in the inside air circuit during defrosting of the heat exchangers in the outside air circuit. An object related to the foregoing is to provide for thermostatic control of such a booster heater through the use of a subthermostat that senses the need for heat beyond the capacity of the heat pump.

In an air to air heat pump apparatus one of the most troublesome problems has been the attainment of a satisfactory automatic defrosting cycle in respect to the outside heat exchangers, and in the past, various control expedients have been proposed and used. Thus such defrosting has been initiated by time controlled means which perform the defrosting at predetermined intervals and in defrosting periods of predetermined length, re gardless of the need for such operations. In other instances, air flow or air pressure in the outside air circuit has been sensed to determine the need for defrosting, but such systems have also been found to be unsatisfactory in many instances. It is therefore a further object of the present invention to improve the automatic defrosting control in such heat pump apparatus, and related objects are to enable varying pressure conditions in the outside heat exchangers to control the initiation and duration of the automatic defrosting operations, to control the other elements of the heat pump apparatus to minimize the length of the defrosting periods, to control the booster heater by the same means so as to prevent temperature drop in the inside air circuit, and to Patented Aug. 21, 1956 ice 2 enable such defrosting operations to be accomplished at the minimum cost.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show a preferred embodiment of the present invention and the principles thereof and what I now consider to be the best mode in which I have contemplated applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

Fig. 1 is a side elevational view taken partially in vertical section and illustrating a heat pump apparatus embodying the features of the invention;

Fig. 2 is a view taken from the left in Fig. 1 and showing details of internal construction of the apparatus;

Fig. 3 is a view similar to Fig. 2 and showing additional details;

Fig. 4 is a fragmentary perspective view showing the sump and related parts of the base;

Fig. 5 is a sectional view taken substantially along the line 5- 5 of Fig. 4;

Fig. -6 is a sectional view taken substantially along the line 66 of Fig. 4;

Fig. 7 is a schematic view illustrating the refrigerant circuit;

Fig. 8 is a perspective View illustrating further details of the refrigerant circuit; and

Fig. 9 is a wiring diagram illustrating the electrical control circuit of the invention.

GENERAL ORGANIZATION For purposes of disclosure, the invention is herein illustrated as embodied in an air-to-air heat pump apparatus 20 that is sectionalized in its physical structure so as to facilitate transportation and installation. Thus, the heat pump 20 comprises a relatively flat base unit 21, a blower unit 22 that rests on and completely covers the base unit 21, a compressor and heat exchange unit 23 that rests on and completely covers the unit 22, and an upper duct unit 2 4 that rests upon the unit 23, and these sections or units may be secured in such relation by conventional fastening means such as screws, bolts or the like. The

units

21, 22, 23 and 2-4 are so formed and related, as will be described in detail hereinafter, that a generally U- shaped inside air passage 25 is provided including

heat exchangers

26 and 27, and a generally U-shaped outside air passage 28 including

heat exchangers

29 and 30 is provided. As will be hereinafter explained, the present apparatus may be set selectively for winter operation or summer operation, and in the winter setting of the apparatus the heat exchangers 27 and 2'6 act as a common condenser in the refrigerant circuit, while the

heat exchangers

30 and 29 in the outside air circuit act .as a common evaporator. Conversely, in the summer setting of the apparatus, the

heat exchangers

27 and 26 in the inside air circuit act as evaporators so as to cool the air in the inside air circuit, while the

heat exchangers

30 and 29 in the outside air circuit serve as a common condenser to dissipate heat to the air flowing in the outside air circuit.

THE INDIVIDUAL SECTIONS OR UNITS The base 21 is formed primarily by two end. channels 31 and two side channels 32 secured together so that they rest on edge and define a rectangle. Midway between the side channels 32 and parallel thereto, an elongated pan or sump 33 is mounted in fixed relation to the end channels 31, and throughout a substantial portion of its length the pan 33 is of the same depth as the base, as shown in Fig. 1, while throughout the balance of its length the bottom of the pan slopes upwardly so that it will drain toward the deep end. Within the sloping end portion of the pan 33 a central division wall is formed by an inverted U-shaped member 33F that has its lower edges fixed to the bottom wall of the pan and which has its closed upper end disposed in the plane of the upper edges of the

channels

31 and 32. At the left hand end of the member 33F, Fig. 4, a cross plate 33E is extended across the pan 33 with its upper edge in the plane of the upper edges of the

channels

31 and 32, and its lower edge spaced from the bottom of the pan 33 below the normal level of water that is maintained in the sump or pan 33, as will be explained hereinafter.

The unit 22 is afforded by a plurality of square tubular frame members 39 on which parallel end walls 41) and 41 and an intermediate wall 42 are supported, the intermediate wall 42 being spaced from the end wall 49 so that the intermediate wall 42 will be disposed directly over and will engage the upper edge of the cross plate 33E, and on opposite sides of the pan 33, this wall 42 rests on channels 44 which extend from the side channels 32 to the opposite sides of the pan. The unit 22 also has

side walls

45 and 46 and between the end wall 41 and the intermediate wall 42, a heavy insulated vertical wall 47 is provided which rests at its lower edge on the division wall 331 of the pan or sump 33. In the present instance the wall 40 is afforded by doors which extend the full height of the

sections

22, 23 and 24 so that these doors or walls 40 form the front or left-hand wall in Fig. 1, for all of the units. The unit 22 is thus divided into a pump chamber 48 defined by the walls 40, 42 and 46, an inside fan chamber 49 defined by the

Walls

41, 42, 46 and 47, and an outside fan chamber 50 defined by the

walls

41, 42, 47 and 45.

Within the pump chamber 48 a water pump 51 is supported with an intake pipe 51F projecting downwardly into the sump 33. This pump 31 is driven by a motor 51M, and its discharge passes through a pipe 51D to its point of use, as will be described hereinafter.

Within the inside fan chamber 49, an inside blower or fan 52 is mounted on support bars 52B, so that the discharge 52D of the fan opens upwardly adjacent to the wall 47 Similarly, an outside blower or fan 53 is mounted on supports 53B in the chamber 50 so that the discharge 53D is directed upwardly adjacent to the other side of the wall 47. The

fans

52 and 53 are driven by belt connections from drive motors 52M and 53 that are supported from

cross bars

52B and 53B in the

chambers

49 and 50 of the unit 22. The

chambers

49 and 50 constitute portions of the respective inside and

outside air passages

25 and 28 and cooperating portions of these passages are formed in part in the unit 23 and in part in the unit 24, as will now be described.

The unit 23 also has a framework formed from square tubular members 59 closed at its forward end by the wall afforded by the doors 40 and on which an end wall 61 and an intermediate wall 62 are mounted in parallel relation, so that the intermediate wall 62 is substantially above the wall 42. The unit 23 has

side walls

65 and 66, and between the wall 62 and the end wall 61, a thick insulating wall 67 is mounted so as to rest on and form an upward continuation of the wall 47. Midway between the walls 66 and 67 a vertical division wall 68 is extended parallel to the

walls

66 and 67 thus to afford a downward passage 25D between the

walls

66 and 68, and an upward passage 25U between the

walls

68 and 67. Similarly, a wall 69 is mounted midway between and parallel to the

walls

65 and 67 to define a downward passage 28D between the

walls

65 and 69 and an upward passage 28U between the

walls

67 and 69. In the lower end portion of the passage 28D, the heat exchanger 29 is mounted; in the upper end of the passage 28U the heat exchanger 30 is mounted; in the lower end of the passage 25D, the heat exchanger 26 is mounted; while in the upper end portion of the passage 25D, the heat exchanger 27 is mounted; and these heat exchangers function in the operation of the heat pump system, as will be hereinafter described. Above the heat exchanger 29 and in the passage 28D, a spray nozzle 75 is mounted and is connected to the discharge 51B of the water pump 51 so that the heat exchanger 29 may be caused to function as an evaporative condenser, as will be described.

The passages 25U and 28H have their lower ends partially closed by cross walls 63W and 69W, each of which has a relatively large opening therein, these openings being connected to the respective discharge ends of the

fans

52 and 53 by

flexible sleeves

52F and 53F.

The space defined by the

walls

49, 62, 65 and 66 constitutes a compressor chamber and has bottom and top walls 81 and 82 so as to constitute a closed chamber, and since the doors 40 may be opened at will, an inside stationary wall 60 is provided just inside the doors 40. The wall 60, as well as all of the other walls defining the compressor chamber 80, are lined with sound absorbent material so as to eliminate objectionable noise transmission. Within the compressor chamber 2'0, first and second motor driven compressors C1 and C2 are mounted, along with a considerable portion of the refrigerant piping and control means including a four-way control valve 84 and a suction gas superheater afforded by a heat exchanger 85 suspended above the coinpressors C-1 and C-2 and functioning as will be described hereinafter to dissipate and effectually utilize the heat of the compressors.

The upper unit 24 of the structure is afforded by a framework made from square tubular members 89 having its forward end closed by the walls or doors 40 and having an end wall 91 and an intermediate wall 92 which falls substantially in the plane of the wall 62.

Side walls

95 and 96 are also provided and between these side walls a heavy insulated division wall 97 is provided which rests on and forms an upward continuation of the wall 67. Between the Walls 96 and 97 a division wall 98 is afforded which rests on the wall 68 and forms an upward continuation thereof; and similarly, a wall 99 is afforded so as to rest on and form an upward continuation thereof. The side wall 95 is arranged in the present instance to afford an intake passage or opening 95A through which outside air may enter to pass downwardly through the passage 28D, and the top of the unit 24- between the

walls

95 and 96 is in this instance closed by a top wall 100. Between the

walls

97 and 99 the top wall 100 has a discharge opening 28-2 from which such outside air may be discharged after use. Similarly, the top wall 169 closes the upper side of the unit 24 between the

walls

96 and 98, while a discharge opening 25-2 for the inside air circuit is afforded in the wall 100 between the

walls

97 and 98. The side wall 96, in the form shown, has an intake opening 96A formed herein to which the return pipe of the ductwork may be connected. Within the passage 25D and in the space between the

walls

96 and 98, an air filter 101 is preferably positioned to filter the air passing through the inside air system. The inlet openings for the inside and outside air intake passages may, if desired, be provided in the top wall 100, as indicated in dotted outline at 295A and 296A in Fig. 3, and in such an instance the

corresponding intake opening

95A or 96A,

or both, would be eliminated through the provision of

imperforate side walls

95 and 96.

Within the inside air passage 25U and disposed above the heat exchanger 27, an electric booster heater 105 is mounted so that this heater may be rendered operative when additional heat beyond the normal capacity of the system is required, or during the defrosting cycle that will be described hereinafter.

The water level in the sump 33 is maintained at a constant level through the provision of a water supply line 107 and a float control valve 108 which, with its controlling float 108F, is mounted on the lower surface of the pump support platform. The sump 33 is also provided with an overflow 169.

The sump 33 is arranged to receive and collect condensate that may be formed on any one of the heat exchangers 26 to 30, and for this reason a drip pan 110 is mounted in the outside fan chamber 49 beneath the support 53B, while a similar drip pan 111 is mounted in the inside fan chamber 50 beneath the supports 523. These drip pans slope toward the sump 33 and are arranged to discharge the collected water into the sump.

Within the inside air passage 25, and associated with the sump 33, is an upstanding humidifier plate 115 of an absorbent material, having a wick-like action, and this plate is mounted so that its lower edge is disposed in the sloping portion of the sump 33 below the normal water line that is maintained therein. The humidifier plate 115 extends upwardly for a substantial distance into the chamber 51 so as to be subjected to air flow, and is notched at 115N along its lower edge to afford clearance for the fan supporting bars 528. The humidifier plate 115 attains its humidifying action in such a Way as to afford the desired humidity in the inside air circuit within a range variation that is satisfactory in many instances. Under other instances, however, it may be desirable to attain a more accurate regulation of humidity, and in such an instance, the wall sections 68W in the inside air circuit are constituted in the form of pans to which a constant but relatively small supply of water is supplied, and the control of humidity is attained through the association of an intermittently operable electric heater 1151-1 with each of the pans 68W. The manner of control of the heaters 115H will be described in some detail hereinafter. It should be pointed out that any excess water that may be supplied to the pans 68W merely overflows onto the drain pan 111 so as to be discharged into the sump 33.

THE ENCLOSED COMPRESSOR MEANS inside air system and, as will be further explained, the

heat exchanger 85 in this arrangement serves as a super heater for the return refrigerant as it approaches the compressor.

THE REFRIGERANT CIRCUITS The 4-way valve 84 is of a well known type, and serves as the primary governing means for determining the flow path of the refrigerant in the present system. This 4-way valve is actuated between its two positions by means of a pilot valve 841, which is shifted between its two effective positions by means of a solenoid 84S, and the way in which this solenoid is controlled will be described hereinafter (see Fig. 7).

The refrigerant that is being returned to the compressors C-1 or (3-2 flows from the 4-way valve 84 through a line 118 to one end of the super-heater 85, and any liquid components of the refrigerant that are thus fed to the super-heater 85 are evaporated within the superheater and pass to a suction line 119 that has branches 119-1 and 1119-2, which convey the low pressure gaseous refrigerant to the respective compressors C-1 and C-2. The refrigerant gas is compressed within one or the other, or both, of the compressors, the suction pressures of which are equalized by an equalizing line 120. Compressor discharge is fed through high pressure lines 121-1 and 121-2 to a common hot gas line 121 that extends to the 4-way control valve 84. In one setting of the 4-way valve 84, this hot gas is fed through a line 122 to the upper or intake header 30-1 of the heat exchanger 30 (see Fig. 8).

As it passes through the heat exchanger 30, the gas is subjected to a condensing action, and passes to a common header 29-30H which constitutes the lower header for the heat exchanger 30 and the upper header for the heat exchanger 29. The gaseous and condensed portions of the refrigerant then flow to a lower header 29-2 of the heat exchange unit 29, and pass through a pipe 124 to a 3-way hand valve 123 and to a line 125. This line includes a check valve 130, a filter-dryer unit 131 and an expansion valve 132, from which the expanded gas flows to a 3-Way hand valve 133 and through a pipe 134 to the lower header 26-2 of the heat exchange unit 26. The expansion valve 132 is controlled in a conventional manner by a control element 132C that is associated with the return or suction line 118 (see Fig. 7). The refrigerant that is thus supplied to the heat exchanger 26 passes through this heat exchanger and a common header 26-2711 to the lower end of the heat exchange unit 27, and in passing through the unit 27, the evaporation is substantially completed and the gaseous refrigerant and the remaining unevaporated portions thereof pass into an upper header 27-1 of the unit 27 and through a return pipe 135 to the 4-way valve 84. The action of the system in the summer setting thereof is therefore to cool the air passing through the inside air passage 25.

In the winter setting of the 4-way valve 84, the hot gases under pressure from the compressors pass through the line 135 and through the

heat exchange units

27 and 26 in succession, so that the hot gas is condensed, and since this condensing action is obtained by air flow through the inside air passage 25, this serves to heat the air in the inside air system. The condensed refrigerant then passes through the line 134 and the hand valve 133, but since it cannot flow through the check valve 130, this condensedor liquid refrigerant is transmitted through a line 136, a check valve 137, a filter-dryer unit 138, an expansion valve 139 and a pipe 140 to the 3-way valve 123 from which it passes through the line 124 to the lower header 29-2 of the heat exchange unit 29. This refrigerant then passes through the

heat exchange units

29 and 30, and since for winter operation the system is set, as will hereinafter be described, so as to supply such liquid refrigerant to the heat exchangers 29 and 3d at a temperature which is fifteen to twenty degrees below the minimum outside air temperature, the refrigerant will absorb heat from the air flowing through the outside air system of the apparatus. This is effective to evaporate a large proportion of the refrigerant, and this evaporated refrigerant, along with the entrained unevaporated portions thereof, will pass through the line 122 to the 4-way control valve 84 which in this winter setting transmits the refrigerant to the suction line 118 and the superheater so that after superheating, the gaseous refrigerant is returned to the intake of the compressor through the line 119. The expansion valve 139 is governed in a conventional manner by a control unit 1390 that is associated with the suction line 118 adjacent to the control unit 132C.

The pilot valve 84F has a control connection 84-1 to the main valve 84, and pressure connections for the pilot valve 84F are afforded by pipes 84-2 and 84-3 extended respectively to the return line 118 and the high pressure line 121-1.

THE PRESSURE OPERATED CONTROLS For control purposes that will be described in further detail hereinafter, a high pressure control line 142 is extended from the high pressure line 121-1, and has a pressure operated high limit switch 143 associated therewith. The line 142 also has a pressure operated switch 144 connected thereto for the purpose of controlling the inside fan 52, as will be described. A pressure operated switch 145 is also associated with the high pressure line 142 for the purpose of controlling the pump 51 that supplies water to the evaporative condenser, and this action will be described hereinafter.

A low pressure control line 146 is connected to the intake of the compressor C-2 so as to be thereby associated with the suction line 119, and this low pressure line 146 has a pressure switch 147 associated therewith that is effective to control the operation of the secondary compressor C-2 so as to start the compressor C-2 when the return line pressure is reduced to such a level as to indicate the need for added compressor capacity in the systerm.

A third control pressure line 148 is connected to the gas line 122 and this line is utilized to govern the operation of a pressure switch 149 which, in turn, serves as a primary control for governing the automatic defrosting operation of the system. The pressure switch 149 is of the snap acting type arranged at an adjustably set low pressure to snap to its low pressure position, and at an adjustably set high pressure position to snap to its high pressure position. The pressure switch 149 is connected to the line 148 through a check valve 150 and a spring biased relief valve 151 connected in parallel, the check valve 150 being arranged to permit flow of gas from the pressure switch 149 to the line 148, while the relief valve 151 is an adjustable spring-loaded valve arranged to prevent flow of gas from the pressure switch 149, and to allow flow of gas to the pressure switch 149 when the pressure of such gas in line 148 reaches a predetermined value, and the relationship of the snap acting pressure switch 149, the check valve 150 and the relief valve 151 is utilized to govern the starting time and length of the defrosting cycle and the pressure settings of the switch 149 and the relief valve 151 will be described hereinafter as they are related to each other and to the refrigerant circuits attaining this result.

The pressure switches just described are included in the main electrical control circuit of the system, as will now be described.

THE ELECTRICAL CONTROL CIRCUITS The electrical power for operating and controlling the present system is illustrated in Fig. 9 as being afforded by a 220 volt cycle l-phase circuit having a common wire 160 and two

other wires

161 and 162. The compressor C1 is arranged to be energized through a magnetic contactor C-1S, while the compressor C-2 is arranged to be controlled by a magnetic contactor G28, and these two contactors are connected to the 220 volt l-phase circuit in a conventional manner, as illustrated in Fig. 9. Similarly,

the motor for the outside air fan 53 is controlled by a magnetic contactor 538, while the motor for the inside fan 52 is governed by a magnetic contactor 52S, and these contactors are connected to the 220 volt l-phase circuit in the conventional manner. also afforded for controlling the inside air heater 105, and this contactor is also connected in a conventional manner.

The magnetic contactors and the heater H constitute the primary elements that must be governed and controlled in the automatic operation of the present system, and such control is attained through a low voltage control circuit that obtains its low voltage from a transformer 165, the primary of which is connected between the wires and 161. The secondary of the transformer is connected to leads 164 and 165 between which the various control circuits are disposed.

The primary setting control for the present system is afforded by a 4-position rotary switch 166 that has its common contact connected to the wire 164 by a wire 167. The settable contact for the switch 166 is afforded by a cross bar 166M that may be set in any one of four positions. In addition to the off position, the switch has an on position, a winter position indicated by the letter W and a summer position indicated by the letter S. In the winter position, the moveable contact 166M Another contactor 1058 is extends circuit from the wire 167 to two opposite W" contacts, and from the upper one of these

W contact wires

168 and 169 extend in series to one end of a relay coil 170C, the other end of which is connected by a wire 171 to the wire 165.

Wires

172 and 173 extend from the wire 169 respectively to the on position and the summer position so that when the cross bar 166M is in either the on position, the winter position or the summer position, the coil 170C will be energized. The other stationary W contact of the switch 166 is connected by a wire 174 to a terminal 175, and between this terminal 175 and the wire 165, a relay coil 176C is connected. Similarly, a relay coil 177C and a relay coil 178C are connected in parallel between the terminal 175 and the wire 165. Thus, in the winter position of the switch 166, the

coils

176C, 177C and 178C will be energized, and this is in addition to the energization of the coil 170C.

Also connected in the low voltage circuit are the main sensing controls that sense conditions in the conditioned space for governing the operation of the system. Thus, a main thermostat 180 is connected between the wire 164 and a terminal 181, and relay coils 182C, 183C and 134C are connected in parallel between the terminal 131 and the wire 165. Thus, upon closure of the main thermostat 180, these three relay coils will be energized. A humidistat 185 is also connected at one of its terminals to the wire 164, and between the other terminal of the humidistat the wire 165, a relay coil 136C is connected so that this coil will be energized when sensing of the need for humidification causes the humidistat 185 to close. A secondary or sub-thermostat 188 is connected at one of its terminals to the wire 164 and from the other terminal of the secondary thermostat 188, a relay coil 1870 is connected to the wire 165. The

thermostats

180 and 188 are of the type which close their contacts upon a drop in temperature to a predetermined level, and such thermostats may be of any conventional type arranged to afford a working differential whereby the thermostat opens circuit at a slightly higher temperature level. The thermostat 180 is mounted in the usual position on an inside wall of the building that is being conditioned, while the sub-thermostat 188 is mounted on the inside surface of an outside wall and near the floor of a room. The location of the sub-thermostat 188 is preferably on the outside where the greatest heat loss may be expected, and the thermostat 188 is set about 5 degrees below the setting of the thermostat 180 so as to attain a highly advantageous heat control in winter, as will be explained.

The relay coils that have thus been described serve to control correspondingly numbered relays shown in Fig. 9 which, in turn, govern the energizing coils of the different magnetic contactors.

Conditioning relays 170, 176, 177 and 178 are provided which are under control respectively of the relay coils 170C, 176C, 177C and 178C, and all four of these relays are of the single pole double throw type, and are arranged so that the contact bars thereof are disposed normally in the lower position shown in Fig. 9 and are actuated to their upper position when their respective coils are energized. A wire 190 extends from the wire 162 to one of the upper contacts of the relay 170, while a wire 191 extends from the other upper contact of the relay 170, and has branch leads extended therefrom to one upper and one lower contact of each of the

relays

176 and 177. The other lower contact of the relay 177 is connected by a wire 193 to one end of the operating coil 52C of the magnetic contactor 528 of the inside fan 52. Thus, when the relay 170 is energized and the relay 177 is de-energized, the inside fan 52 will be operated, and this condition prevails when the main control switch 166 is in its on position.

The other upper contact of the relay 177 is connected by a Wire 194 to one contact of the pressure operated switch 144, the other contact of which is connected by a wire 194E to the wire 193. Thus, when the relay 177 is in its upper or winter position, and the conditioning relay 170 is in its upper or winter position, the inside fan is placed under control of the pressure switch 144. With this arrangement, the inside fan remains inoperative until pressure in the compressor output line 121-1 reaches a predetermined operative level so as to close the pressure switch 144.

The other conditioning relay 178 is connected by a wire 195 to the line wire 162, and this wire 195 has branches extending to one bottom contact of the relay 178. The other bottom contact of the relay 178 is connected by a wire 196 to one contact of the pressure switch 145, and the wire 197 extends from the other contact of the switch 145 to one terminal of the motor 51M, the other terminal of this motor being connected to the common line wire 160. The actuation of the relay 178 to its upper or winter position renders the circuit to the motor 51M ineifeetive, but when the relay 178 is de-energized and its common contact is in its lower position, the pump circuit is conditioned for operation under control of the pressure switch 145. This pressure switch is arranged to close when pressure in the output line 121-1 of the refrigerant circuit becomes too high, and this causes the pump 51M to pump water through thespray, thus to cause the condenser 29 to operate as an evaporative condenser.

Control relays 182 and 184 are also provided in the control circuit, and these relays are of the single pole double throw type, and are controlled respectively by the relay coils 182C and 184C. One upper contact of the relay 182 is connected by a wire 198 and a wire 199 to the other upper contact of the conditioning relay 176, and the wire 199 has an extension 199E that extends to the common contact of the pressure switch 149. The other upper contact of the relay 182 and the corresponding lower contact thereof are connected by

Wires

200 and 201 in series to one contact of the normally closed safety or overload pressure switch 143, the other contact of which is connected by wire 202 to a terminal 203. From this terminal, a Wire 204 extends to one contact of a normally closed thermostatic overload switch 205 that is located in the compressor C1, and the other contact of this switch is connected by a contact 206 to one terminal of an operating coil C1SC that constitutes the operating coil of the magnetic contactor C1S that governs the compressor -1. The other terminal of this coil is connected to the common line wire 160.

From the terminal 203, a wire 207 is connected to corresponding upper and lower contacts of a conditioning relay 183 that is governed by the relay coil 103C. The other upper contact of the relay 183 is connected by a wire 208 to the low pressure contact of the pressure switch 147, and a wire 209 extends from the common contact of the switch 147 to one stationary contact of a time delay relay 210. The other stationary contact of this relay is connected by a wire 211 to a thermostatically operated normally closed safety switch 212 that is included in the compressor C2 and the wire 213 extends from the other contact of this safety switch to an operating coil C2SC that serves as the operating coil for the magnetic contactor C2S. The other terminal of this operating coil is connected to the common line wire 160. The time delay relay 210 has an operating coil 210C connected across the two stationary contacts of this relay, and the operation is such that the relay 210 is closed only after a predetermined period, thus to avoid concurrent starting of the two compressors.

The other stationary contact of the pressure operated switch 147 is connected by a wire 214 to the other lower contact of the relay 183, and thus the switch 147 causes operation of the second compressor in response to low pressure in the suction line 119 during the winter operation of the system, and in response to high pressure in the line 119 during summer operation of the system.

The other lower contact of the control relay 182 is connected by

wires

220 and 221 to the other lower contact of the conditioning relay 176, and a branch lead 222 extends from the wire 221 to one lower contact of the control relay 184. The other lower contact of the relay 184 and the corresponding upper contact thereof are connected by a wire 223 to one terminal of the operating coil 53SC, which serves to operate the magnetic contactor 538 that controls the outside fan 53. The other terminal of the coil 538C is connected to the line wire 160. The other upper contact of the relay 184 is connected by a wire 224 to the high pressure stationary contact of the pressure operated switch 149, and a wire 225 connects this same contact to one terminal of the operating coil 848 of the magnetic pilot valve 84, the other terminal of this operating coil being connected to the wire 160. The other or low pressure stationary contact of the switch 149 is connected by a wire 227 to a terminal 228, and this terminal 228 is aiforded in the control circuit for the inside air heater 105. This inside air heater circuit may be completed by movement of the pressure switch 149 to its low pressure position, or through closure of the secondary of sub-thermostat 188, and for obtaining control in response to the operation of such thermostat, a relay 187 which is controlled by the coil 1870. Thus, a wire 230 extends from the wire 199E to one stationary contact of the relay 187, and a wire 231 extends from the other contact of this relay to the terminal 228. From the terminal 228, a wire 232 extends to one stationary contact of a normally open holding switch 233 that is arranged to be moved to its closed position as an incident to the operation of the magnetic contactor C-lS. A wire 234 extends from the other stationary contact of the switch 233 to one contact of a flow switch 235 that is normally open and is arranged to be closed by air flow in the inside an passage 25. A wire 236 extends from the other contact of the flow switch 235 to one terminal of an operating coil SC of the magnetic contactor 1058, the other terminal of this coil being connected to the wire 160. Thus, when the circuit is closed by the switch 149 or by the relay 187, the inside air heater 105 will be eifective, it being understood, of course, that such operation can take place only when the conditioning relay 176 is in its upper or winter position.

The heater H that is included in the humidifier has one terminal connected by a wire 240 to the line wire and the other terminal of the heater is connected to one stationary contact of a normally open relay 186 that is arranged to be closed by operation of the operating coil 186C. The other stationary contact of the relay 186 is connected by a wire 241 to one stationary contact of a holding switch 242 that is normally open and which is arranged to he closed as an incident to the operation of the magnetic contactor 528. A wire 243 extends from the other contact of the switch 242 to the line wire 162. Conventional circuit breakers, as shown, are used in the usual manner to protect all motors and branch lines.

OPERATION Use and operation as air circulating and filtering means During those periods when the heat pump apparatus is not required for either heating or cooling purposes, it may nevertheless be used for circulating and filtering the air in the building, and this is accomplished by setting the main switch 166 to its on position. This causes conditioning relay 170 to be operated so as to extend circuit through the wire 191, the lower contacts of the relay 177 and the wire 193 through the coil 52C of the contactor 52S, and this closes the contactor and causes operation of the inside air circulating fan 52.

Use and operation as a heating means in winter When the heat pump is to operate as a heating and air conditioning means, the main control switch 166 is set to its W or winter position. This causes simultaneous operation of the conditioning relays 170, 176, 177 and 178 so as to locate their contact bars in their upper positions of Fig. 9, and circuit is extended from the upper contacts of the relay 176 through the wire 199 to one upper contact of the relay 182 so as to condition this relay 182 for thermostatically governed controlling action of the compressor C1, and circuit is also extended through the switch 149, which is then in its left-hand or high-pressure position, and through the wire 225 to the control coil 848 of the 4-way valve 84, thus to actuate this valve to its normal winter setting in which the hot compressed gaseous refrigerant from the compressors will be fed to the heat exchangers 26-27 in the inside air passage 25.

Operation of the conditioning relay 176 also extends circuit through the wire 224 to the upper contacts of the relay 184 so as to condition this relay for governing the outside fan 53. The relay 177, when thus operated to its winter position, extends circuit to the pressure switch 144, and this switch is arranged upon the operation of the compressor means, to be closed by the resulting high pressure in the compressor output line 121-1, thus to energize the coil 52C and initiate operation of the inside air circulating fan 52.

Operation of the conditioning relay 178 merely serves to disable the pump 51 by breaking circuit to the pump motor 51M, and this insures that the pump 51 will not operate even though the pressure switch 145 may close.

Thus, the setting of the main switch 156 to its winter or 'v position initially results in setting of the 4-way valve 34 to its winter position wherein the flow of hot gaseous refrigerant is normally directed to the heat exchangers 2627 in the inside air circuit so that the heat exchangers 2627 act as condensers and serve to heat the air in the inside circuit, and the condensed refrigerant is thereafter directed through the expansion valve 139 into the heat exchangers 2930 which act as evaporators so as to cause the refrigerant to absorb heat from the outside air, and then through the 4-way valve 84- and the superheater 85 where further heat is absorbed from the compressor compartment 80, after which the hot gaseous refrigerant is returned to the compressor intake or suction line 119.

The main thermostat 180 along with the humidistat 185 are mounted in the usual location on an inside wall of the space that is to be conditioned, and the secondary thermostat 138 is mounted on the inside face of an outside wall of such space and near the floor level. The secondary thermostat 188 is thus in a position to sense those conditions which result in extremely rapid heat transfer through such outside wall. would be brought about by a high wind, or an unusual drop in the outside air temperature, and in the present system it has been found desirable to set the secondary thermostat 188 from three to five degrees below the setting of the main thermostat 180.

When the system has thus been conditionsd for winter operation under automatic control by the thermostats 130 and 133 and the humidistat 185, a drop in the temperature in the inside space below the desired level will cause closure of the main thermostat 189. This serves to operate the rela s 182, 183 and 184. The operation of the relay 184 extends circuit to the operating coil 538C thus to operate the magnetic contactor 53S and start the outside fan 53.

Operation of the relay 182 in response to the closure of the thermostat 180 extends circuit to the coil CISC, thus to operate the magnetic contactor CIS so as to start the compressor Cl. Operation of this compressor builds up pressure in the output line 121 and serves to close the pressure switch 144, and this energizes the coil 52C so as to operate the contactor 52S and thus start the inside fan 52.

Operation of the relay 183 in response to closure of the main thermostat 180 serves to condition the control circuit for the second compressor C2, but this second com- Such circumstances pressor remains inactive since the pressure switch 147 is located in its high pressure or right-hand position as viewed in Fig. 9.

Such operation of the compressor C1 serves to initiate the heating action in the inside air circuit through the feeding of the hot compressed gaseous refrigerant to the

heat exchangers

26 and 27 in the inside air circuit, and in the event that the capacity of the compressor 0-1 is insufiicient to accomplish the desired degree of heating, this fact is reflected by a drop in the suction line pressure in the line 119. This causes the pressure switch 147 to be shifted with a snap action to its low pressure or lefthand position as viewed in Fig. 9, and this completes circuit to the coil C2SC which serves to operate the magnetic contactor C2S. This results in starting of the compressor C-2, and hence the heating capacity of the system is increased. This increased heating capacity is maintained until thermostat 130 is satisfied and breaks the circuit to relay holding coils 182C183C and 184C. It will be recognized that the switch 147 may be of the adjustable type so that the pressure differential required to cause a return movement of the switch 147 may be adjusted to meet conditions that may be encountered in use.

If the heat losses from the space that is being conditioned are exceptionally high, due for example to high wind conditions or extremely low outside temperatures, the secondary thermostat 138 will close, and this causes operation of the relay 187. The relay 187, when thus actuated, extends circuit to the coil ZUSSC so as to operate the magnetic contactor 1058, and when this contactor is thus operated, the booster heater is rendered operative so as to increase the overall heat output that is transmitted to the inside air circuit. When the need for such additional heat has been satisfied, the secondary thermostat 183 will, of course, open and the booster heater will be tie-energized.

When outside air conditions are such that there is no appreciable tendency to form frost on the

outside heat exchangers

29 and 30, the pressure in the return line 122 maintains a relatively constant value, as for example about 30 pounds per square inch, but when frost forms the

heat exchangers

29 and 39, this pressure in the return line 122 may reduce to a value of five pounds per square inch or even less, and such a low pressure in the return line 12 2 clearly indicates that a defrosting operation is needed. The setting of the snap acting pressure switch 149 is coordinated with the normal and abnormal pressure levels that are experienced in the suction line 122, such for example as the values hereinabove mentioned, and thus when the pressure in the line 122 drops to a value of five pounds per square inch, the pressure switch 149 will shift with a snap action from its normal high-pressure or left-hand position of Fig. 9 to its lowpressure or defrost position which is the right-hand position of Fig. 9. This shifting of the pressure switch 149 initiates the defrosting action and the related functions in the apparatus. One of these related functions is the stopping of the outside fan 53 so as to avoid dissipation of the defrosting heat that is to be applied to the

heat exchangers

29 and 30. This stopping of the outside fan is caused by breaking of the circuit from the line 19913 to the upper contacts of the relay 184-. Another of the related functions is the stopping of the second compressor C2 if this compressor happens to be in operation at this time, and this is accomplished by the pressure switch 147. In this respect, it should be pointed out that the reversal of the refrigerant flow, as will hereinafter be described, causes a marked increase in the pressure at the return line 119, and it is this increase in pressure that causes the switch 14-7 to shift from its low pressure position to its high pressure position at this time.

When the switch 1 .9 shifts to its low pressure or right hand position, as viewed in Fig. 9, so as to institute the defrosting operation, it breaks circuit to the wire 225 and the coil 848 of the 4-way valve 84, and this causes the valve 84 to return to its summer setting wherein the hot compressed gaseous refrigerant is fed through the line 122 and directly to the

outside heat exchangers

29 and 30. This hot gas serves, of course, to accomplish the desired defrosting action, and the melted frost is drained downwardly onto the drip pan 110 so that it flows into the sump 33, and any excess water collected in the sump will of course be discharged through the drain 1%.

It should be observed that when the hot gaseous refrigerant is fed into the line 122, there is an immediate increase in pressure in this line, and this immediate increase in pressure may reach a level of 100 pounds per square inch, or even more. It will be realized, of course, that such a pressure would be sufficient to return the pressure switch 14-9 to its high pres-sure or normal position since the switch 149 is set for operation at about 30 pounds, and to prevent such immediate return of the switch 1&9 to its high pressure position, the relief valve 151 is set to a value substantially higher than the value of 100 pounds per square inch that has been assumed hereinabove. The differential above such a value is selected at a fairly high value that is somewhat below the value or pressure that will be reached in the line 122 when the defrosting operation is completed. Thus, the pressure in the line 122 will remain at about 100 pounds per square inch until such time as the frost has been completely melted from the

heat exchangers

29 and 30, and at this time the pressure in the line 122 will increase to about 200 pounds per square inch, or even higher. Thus, the relief valve 151 may be set so as to open at a pressure of about 175 pounds per square inch, and when defrosting has been completed, the resulting increase in pressure in the line 122 will open the relief valve 151 and cause the pressure switch 149 to be snapped back to its high pressure position. This will again set the 4-way valve 84 to its winter position, and when the pressure in the line 119 has been changed to its normal value, the pressure switch 147 will return to its low pressure position so as to cause the second compressor C2 to resume operation. Also, the outside fan 53 will again be started.

In the course of a defrosting operation, the

inside heat exchangers

26 and 27 will no longer be supplied with hot gaseous refrigerant and, as a matter of fact, will be serving as evaporators. Hence at this time there is a need for additional heat in the inside air circuit, and such heat is supplied by the booster heater 105, which is caused to operate so long as the switch 149 remains in its low pressure or right-hand position as viewed in Fig. 9. The circuit at this time is extended through the wire 227 to the coil 1058C so that the magnetic contactor 1058 is operated and the heater 105 is energized. Hence, when the switch 149 returns to its high-pressure position to terminate the defrosting operation, the circuit to the wire 227 is broken and the booster heater 105 is deenergized and the system returns to its normal heating operation.

In winter use of the present apparatus, the humidistat 185 may, of course, detect a need for humidification, and this closes circuit to the coil 186C so as to cause operation of the relay 186. The relay 186 thus completes circuit to the heater 115E of the humidifier so as to raise the temperature of the water in the humidifying pans and thus supply the needed humidification to the air flowing in the inside air circuit.

Use and operation as a cooling means in summer When the heat pump is to operate as a cooling and air conditioning means in the summer, the main control switch 166 is set to its S or summer position. This causes operation of the main conditioning relay 170, but it will be observed that the

relays

176, 177 and 178 remain in their lower or summer positions. The 4-way valve 84 therefore remains in its normal or summer position wherein the hot compressed refrigerant gases are 14 first fed to the

outside heat exchangers

29 and 30 which act as condensers and are subsequently fed through the expansion valve 32 and throu 1;h the

inside heat exchangers

26 and 27, which act as evaporators so as to cool the air flowing in the inside air circuit.

When the circuit is extended through the relay to the relay 177, circuit is extended through the lower contacts of this relay to the coil 52C, which operates the magnetic contactor 528, thus to start the inside fan 52. This inside fan runs constantly so long as the main switch 166 is in its summer setting.

The relay 176 extends circuit to the bottom contactors of the two

relays

182 and 184, and it will be observed that these two

relays

182 and 184 remain in their lower or unactuated positions, as shown in Fig. 9, so long as the temperature in the inside air space remains above the value that has been set on the main thermostat 180. Hence, under such conditions, circuit is extended from the relay 182 to the coil C-TLSC so that the magnetic contactor C18 is operated so as to cause operation of the compressor C-l. Circuit is extended from the lower contacts of the relay 184 to the coil 538C so that the contactor 538 is operated so as to cause operation of the outside fan 53. This will cause normal operation of the system as a cooling means, and it might be pointed out that if the cooling load on the system is excessive, the pressure switch 147 may operate in the manner hereinabove described so as to bring about operation of the second compressor C-2. Any condensate resulting from such cooling is of course collected in the sump 33. In the event that the condensers action of the

outside heat exchangers

29 and 30 is insufficient, this may result in an excessively high pressure in the output or high pressure line 121, and in such an event, the pressure switch 145 will be closed so as to energize the pump motor 51M, it being noted that this is possible during summer operation because of the fact that the relay 178 is in its lower or unactuated position. Operation of the pump 51 serves to pump water from the sump 33 and to spray this water over the heat exchanger 29, which thus serves as an evaporative condenser and operates at increased efl'iciency.

When the inside air has been cooled to a sufficient extent, the inside thermostat 180 will close, and this serves to energize and operate the

relays

182, 183 and 1845. The operation of the relay 182 stops the compressor operation, while the operation of the relay 184 stops the outside fan 53, and operation of the relay 183 stops operation of the second compressor C-Z in the event that this compressor has been in operation.

CONCLUSION From the foregoing description, it will be apparent that the present invention affords improved control means for heat pump apparatus, and that such improved control means eliminate the major difficulties and objections heretofore encountered with apparatus of this character. It will also be evident that the present invention enables a heat pump system to be operated with relatively small compressors utilized in multiple so that the power demands in starting of the compressors are relatively small, thereby to adapt the apparatus for use in homes where high electrical starting loads are undesirable. It will also be evident that through the use of multiple compressors, the invention has enabled more eflicient operation of heat pump systems to be obtained, and specifically it will be evident that through the attainment of longer and less frequent operating cycles, the maintenance of the apparatus is materially reduced.

It will also be evident that the present invention attains a novel and effective use of a booster heater in a heat pump system whereby this heater acts to supplement the normal capacity of the system, and also serves to maintain the desired inside air temperature during defrosting operations.

It will also be apparent from the foregoing description that the present invention enables an unusually efiective 15 and efficient defrosting action which is automatic in character and which maintains the defrosting time at the minimum, thus to nsure economy of operation of the system as well as satisfactory performance.

Thus, while I have illustrated and described the preferred embodiment of my invention, it is to be understood that this is capable of variation and modification, and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, a main control valve in said refrigerating system having summer and winter settings for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, control means having a normal position and a defrost position, means governed by said control means when said control means is in its defrost position to shift said valve from its winter setting to its summer setting and to return said valve to its winter setting upon return of said control means to its normal position, pressure operated means subjected to the pressure of the suction gas outlet portion of said outside heat exchanger and operable upon said control means to shift the same to said defrost position when the pressure in said outlet portion falls to a predetermined minimum level indicative of a frosted condition, and to return said control means to said normal position when the pressure in said portion rises to a predetermined high level indicative of completion of the defrosting action, an air circulating fan in said outside air passage, and governing means for said fan including means operable to stop said fan when said control means are in said defrost position.

2. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, inside and outside air circulating fans in said inside and outside air passages, fan governing means normally effective to cause operation of said fans during operation of said refrigerating system, a main control valve in said refrigerating system having summer and winter settings for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, control means having a normal position and a defrost position, means governed by said control means when said control means is in its defrost position to shift said valve from its winter setting to its summer setting and to return said valve to its winter setting upon return of said control means to its normal position, pressure operated means subjected to the pressure of the suction gas outlet portion of said outside heat exchanger and operable upon said control means to shift the same to said defrost position when the pressure in said portion falls to a predetermined minimum level indicative of a frosted condition, and to return said control means to said normal position when the pressure in said portion rises to a predetermined high level indicative of completion of the defrosting action, said control means being associated with said fan governing means and being effective to stop said outside fan when said control means are in said defrost position, and a booster heater in said inside air passage rendered effective by said control means when such control means are in said defrost position.

3. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, a main control valve in said refrigerating system having summer and winter settings for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, control means having a normal position and a defrost position, means governed by said control means when said control means is in its defrost position to shift said valve from its winter setting to its summer setting and to return said valve to its winter setting upon return of said control means to its normal position, and pressure operated means subjected to the pressure of the suction gas outlet portion of said outside heat exchanger including a check valve through which gas may flow to said outlet portion and operable upon said control means to shift the same to said defrost position when the pressure in said portion falls to a predetermined minimum level indicative of a frosted condition, and a pressure threshold device comprising a relief valve through which gas may flow from said portion to said control means to return said control means to normal position only when the pressure in said inlet portion rises to a predetermined high level indicative of completion of the defrosting action.

4. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, a magnetically controlled valve in said refrigerating system for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, a supplemental heater in said inside air passage, a main settable control switch governing said valve, a main thermostat and a supplemental thermostat, a pressure operated single-pole double-throw snap switch subjected to the refrigerant pressure in the hot gas inlet portion of said outside heat exchanger and having dominating control of said valve to set said valve in its cooling position and to concurrently render said auxiliary heater effective upon predetermined reduction of the pressure exerted on said switch, means controlled by said main thermostat for rendering said system effective and ineffective, and means governed by said secondary thermostat for rendering said auxiliary heater effective independently of said pressure switch.

5. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, a main valve in said refrigerating system having a summer setting and a winter setting for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, a supplemental heater in said inside air passage, a main settable control for governing the setting of said valve, a main thermostat and a supplemental thermostat, a first pressure operated means and operable thereby to a high pressure position or a low pressure position, a pressure supply connection from the hot gas inlet portion of said outside heat exchanger to said first pressure operated means and including a pressure operated relief valve operable to prevent transmission of pressure to said first means until such pressure reaches a pressure several times the value of the high pressure value required to operate said first pressure operated means to its high pressure position, a checked valved pressure return line connected in parallel around said relief valve for allowing release of pressure from said first means, means operated by said first pressure means to shift said valve to its summer setting when said pressure means is operated to its low pressure position and to concurrently render said auxiliary heater effective upon predetermined reduction of the normal pressure exerted thereon, means controlled by said main thermostat for rendering said system effective and ineffective, and means governed by said secondary thermostat for rendering said auxiliary heater efiective independently of said first pressure operated means.

6. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, a main valve in said refrigerating system having a summer setting and a winter setting for changing said system from a cooling cycle to a heat 17 ing cycle with respect to said inside air passage, a supplemental heater in said inside air passage, a main settable control for governing the setting of said valve, a main thermostat, a first pressure operated means and operable thereby to a high pressure position or a low pressure position, a pressure supply connection from the 'hot gas inlet portion of said outside heat exchanger to said first pressure operated means and including a pressure operated relief valve operable to prevent transmission of pressure to said first means until such pressure reaches a pressure several times the value of the high pressure value required to operate said first pressure operated means to its high pressure position, a checked valved pressure return line connected in parallel around said relief valve for allowing release of pressure from said first means, means operated by said first pressure means to shift said valve to its summer setting when said pressure means is operated to its low pressure position and to concurrently render said auxiliary heater effective upon predetermined reduction of the normal pressure exerted thereon, and means controlled by said main thermostat for rendering said system effective and ineffective.

7. in an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, a main valve in said refrigerating system having a summer setting and a Winter setting for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, a supplemental heater in said inside air passage, a main settable control for governing the setting of said valve, a main thermostat, a first pressure operated means and operable thereby to a high pressure position or a low pressure position, a pressure supply connection from the hot gas inlet portion of said outside heat exchanger to said first pressure operated means and including a pressure operated relief valve operable to prevent transmission of pressure to said first means until such pressure reaches a pressure several times the value of the high pressure value required to operate said first pressure operated means to its high pressure position, a checked valved pressure return line connected in parallel around said relief valve for allowing release of pressure from said first means, means operated by said first pressure means to shift said valve to its summer setting when said pressure means is operated to its low pressure position and to concurrently render said auxiliary heater effective upon predetermined reduction of the normal pressure exerted thereon, means controlled by said main thermostat for rendering said system effective and ineffective, and means governed by said main settable control for reversing the controlling action of said thermostat concurrently with the shifting of said main valve.

8. in an air to air heat pump apparatus having inside and outside air-circulating passages and refrigerating system with heat exchangers in said outside and inside air-circulating passages, a main control valve in said refrigerating system having summer and Winter settings for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, control means having a normal position and a defrost position, means governed by said control means When said control means is in its defrost position to shift said valve from its winter setting to its summer setting and to return said valve to its winter setting upon return of said control means to its normal position, a first sensing means operaulc to sense the presence of objectionable frost on said outside heat exchanger and operable upon said control means to shift the same to said defrost position when such objectionable frost is sensed, a second sensing means responsive to return line pressure to sense completion of a defrosting operation and operable to return said control means to said normal position when completion of the defrosting action is thus sensed, and

:18 a booster heater in said inside air passage controlled by said control means and rendered effective during each such defrosting operation.

9. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, a main control valve in said refrigerating system having summer and winter settings for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, control means having a normal position and a defrost position, means governed by said control means when said control means is in its defrost position to shift said valve from its winter setting to its summer setting and to return said valve to 'its Winter setting upon return of said control means to its normal position, a first sensing means operable to sense the presence of objectionable frost on said outside heat exchanger and operable upon said control means to shift the same to said defrost position when such objectionable frost is sensed, a second sensing means responsive to return line pressure to sense completion of a defrosting operation and operable to return said control means to said normal position when completion of the defrosting action is thus sensed, a booster heater in said inside air passage controlled by said control means and rendered effective during each such defrosting operation, a main thermostatic means for controlling operation of said refrigerating system, and a secondary thermostat operable to control said booster heater independently of said control means.

l6. in an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, said system including two compressors connected in parallel in the system, means for controlling said system including thermostatic means for starting and stopping a first one of said compressors, and means for starting and stopping the second one of said compressors including pressure responsive means responsive to the suction pressure at the intake of said first compressor, a main control valve in said refrigerating system having summer and winter settings for changing said system from a cooling cycle to a heating cycle with respect to said inside air passage, control means having a normal position and a defrost position, means controlled by said control. means for de-energizing said second compressor whenever said control means is actuated to its defrost position, means governed by said control means when said control means is in its defrost position to shift said valve from its winter setting to its summer setting and to return said valve to its winter setting upon return of said control means to its normal position, a first sensing means operable to sense the presence of objectionable frost on said outside heat exchanger and operable upon said control means to shift the same to said defrost position when such objectionable frost is sensed, and a second sensing means responsive to return line pressure to sense completion of a defrosting operation and operable to return said control means to said normal position when completion of the defrosting action is thus sensed.

ll. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system With heat exchangers in said outside and inside air-circulating passages, said system including two compressors connected in parallel in the system, means for controlling said system including thermostatic means for starting and stopping a first one of said compressors, automatically operable defrosting means for the outside heat exchangers, and means controlled by said defrosting means operable to stop said second compressor during defrosting operations.

12. In an air to air heat pump apparatus having inside and outside air-circulating passages and a refrigerating system with heat exchangers in said outside and inside air-circulating passages, said system including two compressors connected in parallel in the system, means for controlling said system including thermostatic means for starting and stopping a first one of said compressors, defrosting means for said outside heat exchangers, defrosting control means for initiating and terminating defrosting operations in respect to said outside heat exchanger, and means controlled by said defrosting control means operable to stop said second compressor during defrosting operations.

References Cited in the file of this patent UNITED STATES PATENTS 2,049,625 Ruppn'cht Aug. 4, 1936 Crago Aug 1, Lodwig May 4, Graham June 4, Lund Oct. 19, Cody Apr. 5, Backstrom Ian. 31, Clancy 90v. 21, Vargo May 12, Ditzler et al Mar. 23, Telkes May 4,