US3171263A

US3171263A - Heat pumps

Info

Publication number: US3171263A
Application number: US309681A
Authority: US
Inventors: James R Harnish
Original assignee: Westinghouse Electric Corp
Current assignee: McQuay Perfex Inc
Priority date: 1963-09-18
Filing date: 1963-09-18
Publication date: 1965-03-02
Anticipated expiration: 1982-03-02

Description

J. R. HARNISH HEAT PUMPS Filed Sept. 18, 1963 1- 1a REVERSAL p VALVE 1a I fi SURGE DRUM -r/7 48 Tg, 38 as A I E[ I INDOOR HEAT g. EXCHANGER 420 k v E35 a4 f: 25

nsamsnc COMPRESSOR 6 5 /a I 19 TH, SURGE DRUM 1.5 38 59 66 l L I i #1 mooon HEAT EXCHANGER 54 a5 a4 I a! 1 /6 2 Sheets-Sheet 1 HERMETIO COMPRESSOR OUTDOOR HEAT EXOHANGER March 2, 1965 J. R. HARNISH HEAT PUMPS Filed Sept. 18, 1963 2 Sheets-Sheet 2 DOOR HEAT EXCHANGER REVERSA VALVE LI LE.

INDOOR HEAT EXGHANGER HERMETIC COMPRESSOR 3/ Inventor.- Jaraaea R.IIa3 naJs by W fltfom'aey United States Patent 3,171,263 HEAT PUMPS James R. Hamish, Staunton, Va., assiguor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 18, 1963, Ser. No. 309,681 8 Claims. (Cl. 62204) This invention relates to heat pumps using auxiliary liquid pumping means in addition to the usual refrigerant compressors, and using surge drums.

In large heat pumps used for cooling or heating indoor air, particularly those heat pumps in which the compressors are unloaded at reduced loads, it is known that auxiliary liquid pumping means are desirable for keeping multi-circuit coils when used as evaporators, filled with liquid, and for lifting liquid to the outdoor coils which usually are located above the remainder of the components, and that surge drums, also known as accumulators, are desirable for separating gas from liquid, for storing liquid, and for preventing liquid from flowing to the compressors.

This invention is such a large heat pump that requires fewer valves, less and smaller piping, less insulation, and a smaller refrigerant charge than prior large heat pumps. It has the additional advantage that it can use a conventional four-Way reversal valve.

An object of this invention is to simplify large heat pumps.

Another object of this invention is to improve the reliability of large heat pumps.

Other objects of this invention are to reduce the capital and operating costs of large heat pumps.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a diagrammatic view of a heat pump embodying this invention, in which a liquid pump is used to pump all of the liquid used;

FIG. 2 is a diagrammatic view of another embodiment of this invention in which a liquid pump is used to pump excess liquid only;

FIG. 3 is a diagrammatic view of another embodiment of this invention in which liquid is pumped by a pumping receiver, and

FIG. 4 is an enlarged cross-section of the expansion valve used in the heat pumps of FIGS. 13.

The drawings show approximately the elevations of the components of the heat pumps. The solid-line arrows alongside the flow lines show the direction of refrigerant flow during cooling operation, and the dashed-line arrows alongside the flow lines show the direction of refrigerant flow during heating operation.

Description of FIG. 1

The discharge side of a refrigerant compressor is connected by discharge line 11 to a conventional fourway reversal valve 12. The valve 12 is connected by line 13 to one side of outdoor heat exchanger 14, and is connected by line 15 to one side of indoor heat exchanger 16. The valve 12 is also connected by line 19 to the top of surge drum 17. The top of the surge drum 17 is also connected by suction line 18 to the suction side of the compressor 10.

The bottom of the surge drum 17 is connected by line 20 to an expansion valve 21 which is connected by line 22 to outlets of

checlg valves

24 and 25. The inlet of the valve 24 is connected by

lines

26 and 27 to the other side of the outdoor heat exchanger 14, and to the outlet of a check valve 30. The inlet of the valve is connected to the other side of the indoor heat exchanger 16, and by line 31 to the outlet of a check valve 32, the inlet of which is connected to the inlet of the valve 30.

3,171,253 Patented Mar. 2, 1965 The bottom of the surge drum 17 is also connected by line 34 to the inlet of liquid pump 36, the outlet of which is connected to the inlets of the

check valves

30 and 32.

The expansion valve 21, shown in detail by FIG. 4, responds to the amount of liquid subcooling. It has a control bulb 23 responsive to the temperature of the refrigerant in the line 22 from the heat exchanger which is operating as a condenser. It has an upper, generally eliptical shaped casing 25 around a diaphragm chamber 26. The chamber 26 has a diaphragm 27 extending horizontally across its center. The control bulb 23 contains the same refrigerant that is used in the heat pump, and is connected by a capillary tube 28 to the space within the chamber 26 above the diaphragm 27. The diaphragm 27 is connected at its center to a piston rod 28 which extends vertically through the center or" the bottom of the casing 25. The valve 21 has a liquid inlet 60, a liquid outlet 61, and a partition 42 extending across the space between the inlet 60 and the outlet 61, the partition 42 having an opening 43 aligned with the rod 28. The rod 28 has a piston 44 attached to its bottom above the opening 43. The piston 44 is biased towards the opening 43 by a coiled spring 45 extending around the rod 28 between the top of the piston 44 and the bottom of the casing 25. The space within the chamber 26 below the diaphragm 27 is at condenser pressure through being connected by an equalizing capillary tube 46 to the interior of the tube 22.

The spring 45 is adjusted to provide the amount of liquid subcooling that is desired, which may be 10 F. at a condensing temperature of 100 F., with the valve 21 wide open. At such time, the temperature at the bulb 23 may be F.: the pressure at the top of the diaphragm 27 may be 170.1 p.s.i., and the pressure at the botom of the diaphragm 27 may be 197.9 p.s.i. If the subcooling decreases to 8 F., the temperature at the bulb 23 will be 92 F.; the pressure at the top of the diaphragm 27 will be 175.4 p.s.i.; the pressure at the bottom of the diaphragm 27 will be 197.9 p.s.i., and the valve 21 will be half closed. If the subcooling decreases to 6 F., the temperature at the bulb 23 will be 94 F., the pressure at the top of the diaphragm 27 will be 180.9 p.s.i.; the pressure at the bottom of the diaphragm 27 will be 197.9 p.s.i., and the valve 21 will be closed.

The pump 36 is driven by an electric motor 37. A fan 40 driven by an electric motor 41 moves outdoor air over the outdoor heat exchanger 14. The indoor heat exchanger 16 is of the shell-and-tube type having multiple refrigerant circuits which are not shown, and has an inlet 38 and an outlet 39 for water to be cooled or heated, and which may be supplied to local heat exchangers which are not shown.

Cooling operation of FIG. 1

The compressor 10, the pump motor 37 and the fan motor 41 are started. The compressor 10 supplies discharge gas through the discharge line 11 to the reversal valve 12 which is adjusted to route the discharge gas through the line 13 into the outdoor heat exchanger 14 operating as a condenser. Liquid from the heat exchanger 14 flows through the

lines

27 and 26, the check valve 24 and the line 22 to the expansion valve 21 which meters liquid which is supplied through the line 20 into the surge drum 17. Liquid flows from the surge drum 17 through the line 34 to the pump 36 which pumps the liquid through the check valve 32 and the line 31 into the indoor heat exchanger 16 operating as an evaporator. The gas and any unevaporated liquid leaving the heat exchanger 16 flows through the line 15, the reversal valve 12 and the line 19 into the top of the surge drum 17. Gas separated from the liquid in the surge drum 17 flows through the suction line 18 to the suction side of the compressor 10.

3. Heating operation of FIG. I

The compressor 11), the pump motor 37 and the fan motor 41 are started. The compressor supplies discharge gas through the discharge line 11 to the reversal valve 12 which is adjusted'to route the discharge gas through the line 15 into the indoor heat exchanger 16 operating as a condenser. Liquid from the heat exchanger 16 flows through the check valve to the expansion valve 21 which meters'the liquid supplied through the line 20 into the surge drum 17. Liquid flows from the surge drum 17 through the line 34 to the pump 36 which pumps this liquid through the check valve and the line 27 into the outdoor heat exchanger 14 operating as an evaporator. The gas and any unevaporated liquid leaving the heat exchanger 14 flows through the line 13, the reversal valve 12 and the line 19 into the top of the surge drum 17. Gas separated from the liquid within the surge drum 17 flows through the suction line 18 to the suction side of the compressor 10. 7

During both the cooling and heating operations, any excess liquid that is not evaporated flows from the heat exchanger that is operating as an evaporator, through the reversal valve into the surge drum. The liquid from the heat exchanger that is operating as a condenser flows through the expansion valve into the surge drum. The liquid pump pumps liquid from the surge drum to the heat exchanger that is operating as an evaporator through a line that is alternately used to supply liquid from the same heat exchanger to the surge drum when the same heat exchanger is operating as a condenser. A line that is used to supply discharge gas to a heat exchanger when that heat exchanger is operating as a condenser, is used alternately to flow suction gas plus any unevaporated liquid from the same heat exchanger when the latter is operating as an evaporator.

In the heat pump of FIG; 1, the expansion valve meters liquid from the heat exchanger that is operating as a condenser into the surge drum, and the liquid pump pumps all of the liquid to the other heat exchanger that is operat-' ing as an evaporator.

Description of FIG. 2 V

In the heat pump of FIG. 2, the liquid from the heat exchanger that is operating as a condenser is supplied through the expansion valve to the other heat exchanger that is operating as an evaporator. For changing load conditions, excess refrigerant from the heat exchanger that is operating as an evaporator spills over into the surge drum. The liquid pump pumps this excess liquid into the heat exchanger that is operating as an evaporator to pre'vent that heat exchanger from becoming starved. Otherwise, the components of FIG. 2 are similar to corresponding components of FIG. 1, and are given the same reference characters.

Referring now to FIG. 2, the expansion valve 21 instead of being connected to the surge drum 17, is connected by a line 50 to the inlets of check valves '30 and 32. A superheat control bulb 55 responsive to the temperature of the vapor in the line 19, has a switch 56 in series with electric supply lines L1 and L2 and the pump motor 37.

Otherwise, the heat pump of FIG. 2 is similar to that of FIG. 1. r

Cooling operations of FIG. 2

The compressor 10 and the fan motor 41 are started. The compressor supplies discharge gas through the discharge line 11 to the reversal valve 12 which is adjusted nected by line 81 to the discharge line 11.

through the line 15, the reversal valve 12 and the line 19 into the surge drum 17. Gas separated from the liquid within the surge drum flows through the suction line 18 to the suction side of the compressor.

When the indoor heat exchanger 16 is about to become starved, the bulb 55 closes its switch 56, starting the pump motor 37, following which the pump 36 pumps liquid from the surge drum 17 through the

lines

50 and 31 into the heat exchanger 16.

Heating operation of FIG. 2

The compressor 10 and the fan motor 41 are started. The compressor supplies discharge gas through the discharge line 11 to the reversal valve 12 which is adjusted to route the discharge gas through the line 1 5 into the indoor heat exchanger 16 operating as a condenser. Liquid from the heat exchanger 16 flows through the check valve 25 and the line 22 to the expansion valve 21 which meters liquid supplied through the line 50, the check valve 30 and the

lines

26 and 27 into the outdoor heat exchanger 14 operatirn as an evaporator. The gas and any unevaporated liquid leaving the heatexchanger 14 flows through the line 13, the reversal valve 12 and the line 19 into the surge drum 17. Gas separated from the liquid within the surge drum flows through the suction line 18 to the suction side of the compressor.

When the outdoor heat exchanger 14 is about to become starved, the bulb 55 closes its switch 56, starting the pump motor 37, following which the pump 36 pumps liquid from the surge drum 17 through the

lines

50, 26 and 27 into the heat exchanger 14. I

Advantages of the heat pump of FIG. 2 over that of FIG. 1 are that by using the pump to pump excess liquid only, the size, cost and operating expense of the pump are reduced; operating the pump intermittently reduces pump cavitation problems, and the flash gas introduced directly into the heat exchanger which is operating as an evapo rator, increases heat transfer.

Description of FIG. 3

The heat pump of FIG. 3 is similar to that of FIG. 2 except that a small pumping receiver is substituted for the motor driven pump of FIG. 2, for pumping excess liquid in the surge drum to that heat exchanger that is operating .as an evaporator. Similar components of FIGS. 2 and 3 are given the same reference characters.

Referring now to FIG. 3, the compressor 10 is con nected to the reversal valve 12 and to the surge drum 17 by discharge line 11 and suction line 18 respectively. The valve 12 is connected to the outdoor heat exchanger 14 by line 13, and to the indoor heat exchanger 16 by line 15. The valve 12 is connected by line 19 to the surge drum 17. The bottom of the surge drum 17 is connected to the inlet of check valve 82, the outlet of which is core nected to the top of pumping receiver 80. The receiver is gas vented to the surge drum 17 through line 87, three-way valve 88 and line 89. The valve 88 is con of the receiver 84) is connected to the inlet of check valve 84-, the outlet of which is connected to adjustable valve 85 and through the latter, line 86, check valve 32 and line 31 to the indoor heat exchanger 16; The line 31 is also connected to the inlet of check valve 25, the outlet of which is connected to the outlet of check valve 24, the inlet of which is connected through the line 27 to the outdoor heat exchange 14. The inlets of the

valves

24 and 25 are connected through the expansion valve 21 to the line 86.

The pumping receiver 81) has afloat operated switch 91 which is connected in series with solenoid which adjusts the three-way valve 88, and with the electric. supply lines L1 and L2.

Cooling operation of FIG. 3

The compressor 10 and the fan motor 41 are started.

The bottom 7 The compressor supplies discharge gas through the discharge line 11 and the reversal valve 12 into the line 13 and through the latter into the outdoor heat exchanger 14 operating as a condenser. Liquid leaving the heat exchanger 14 flows through the line 27, the check valve 24, the expansion valve 21, the check valve 32 and the line 31 into the indoor heat exchanger 16 operating as an evaporator. High pressure discharge gas supplied through the line 81, the valve 88 and the line 87 into the liquid receiver 80 increases the pressure within the latter, closing the check valve 82 in the drain line from the surge drum 17 to the receiver 80, and pumping liquid previously drained from the surge drum 17 into the receiver 80, from the latter through the line 83, the check valve 84, the adjustable valve 85, the line 86, the check valve 32 and the line 31 into the indoor heat exchanger 16 for preventing it from becoming starved. The switch 91 opens when the receiver 86 is nearly empty, and deenergizes the normally energized solenoid 99 which adjusts the valve 88 to shut off the supply of discharge gas through the line 81 into the receiver 80, and to vent gas from the receiver through the line 89 into the surge drum 17. Liquid then flows from the surge drum through the check valve 82 to refill the receiver. Gas and any unevaporated liquid from the indoor heat exchanger 16 flows through the line 15, the reversal valve 12 and the line 19 into the surge drum 17, and gas separated from the liquid within the surge drum flows through the suction line 18 to the suction side of the compressor 10.

Heating operation of FIG. 3

The compressor supplies discharge gas through the discharge line 11, the reversal valve 12 and the line into the indoor heat exchanger 16 operating as a condenser. Liquid from the heat exchanger 16 flows through the check valve 25, the expansion valve 21, the check valve 39 and the line 27 into the outdoor heat exchanger 14 operating as an evaporator. Discharge gas supplied through the line 81, the valve 88 and the line 87 into the receiver 8%, increases the pressure within the latter, closing the check valve 82 in the drain line from the surge drum 17 into the receiver, and pumping liquid previously drained from the surge drum into the receiver, through the line 83, the check valve 84, the valve 85, the line 86, the check valve 30 and the line 27 into the outdoor heat exchanger 14, preventing the latter from becoming starved. The swtch 91 opens when the receiver 80 is nearly empty, and deenergizes the normally energized solenoid 90 which adjusts the Valve 88 to shut off the supply of discharge gas from the line 81 into the receiver, and to vent gas from the receiver through the line 89 into the surge drum. Liquid then flows from the surge drum through the check valve 82 to refill the receiver. The switch 91 again closes and again energizes the solenoid 90 which adjusts the valve 83 to admit discharge gas into the receiver, and to prevent gas from the receiver from being vented into the surge drum. Gas and any unevaporated liquid leaving the heat exchanger 14 flows through the line 13, the reversal valve 12 and the line 19 into the surge drum, and gas separated from the liquid within the surge drum flows through the suction line 18 to the suction side of the compressor 10.

While the invention has been described in connection with air-to-water systems, it could be used with air-to-air systems.

Other forms of one-way valves, such as solenoid adjusted ones, could be used instead of the automatically adjusted check valves which are shown by the drawings, and the term check valve is to be construed as applying to any form of one-way valve.

What is claimed is:

1. A heat pump comprising a refrigerant compressor, an indoor heat exchanger, an outdoor heat exchanger, reversal valve means, a surge drum, a discharge line connecting said compressor to said valve means, a suction line connecting said drum to said compressor, a third line connecting said valve means to said outdoor exchanger, a fourth line connecting said valve means to said indoor exchanger, a fifth line connecting said valve means to said drum, liquid pumping means having its inlet connected to said drum, a sixth line connecting the outlet of said pumping means to said indoor exchanger, a seventh line connecting said pumping means to said outdoor exchanger, said valve means in cooling position routing discharge gas from said discharge line through said third line into said outdoor exchanger operating as a condenser, and routing gas and unevaporated liquid from said indoor exchanger operating as an evaporator through said fourth and fifth lines into said drum, said valve means in heating position routing discharge gas from said discharge line into said indoor exchanger operating as a condenser, and routing gas and unevaporated liquid from said outdoor exchanger operating as an evaporator through said third and fifth lines into said surge drum, a first check valve in said sixth line for preventing liquid from said indoor exchanger when the latter is operating as a condenser from flowing into said pumping means, a second check valve in said seventh line for preventing liquid from said outdoor exchanger when the latter is operating as a condenser from flowing into said pumping means, a third check valve having its inlet connected to said sixth line between said indoor exchanger and said first check valve, a fourth check valve having its inlet connected to said seventh line between said outdoor exchanger and said second check valve, and an expansion valve having its inlet connected to the outlets of said third and fourth check valves and its outlet connected to said outlet of said pumping means.

2. A heat pump as claimed in claim 1 in which said pumping means is a motor driven pump, and in which a control responsive to the temperature of the refrigerant flowing through said fifth line into said drum, is provided for starting the motor of said pump when the one of said exchangers operating as an evaporator is about to become starved.

3. A heat pump as claimed in claim 2 in which control means responsive to the temperature and pressure of the refrigerant flowing from said third or fourth valves into said expansion valve is provided for opening and closing said expansion valve to maintain a predetermined amount of subcooling.

4. A heat pump as claimed in claim 1 in which said pumping means is a pumping receiver connected to said discharge line, and in which there is a fifth check valve connected between said drum and said receiver for preventing gas from said receiver from flowing into said surge drum.

5. A heat pump as claimed in claim 4 in which there is provided a three-way valve connected between said discharge line and said receiver and connected to said drum, in which a solenoid is provided to adjust said three-way valve, and in which said receiver is provided with a liquid level operated switch connected to said solenoid for connecting said solenoid to electric supply connections for causing said solenoid to adjust said three-way valve to admit discharge gas from said discharge line into said receiver, or to vent gas from said receiver into said drum.

6. A heat pump comprising a refrigerant compressor, an indoor heat exchanger, an outdoor heat exchanger, reversal valve means, a surge drum, a discharge line connecting said compressor to said valve means, a suction line connecting said surge drum to said compressor, a third line connecting said valve means to said outdoor exchanger, a fourth line connecting said valve means to said indoor exchanger, a fifth line connecting said valve means to said drum, said valve means in cooling position routing discharge gas from said discharge line through said third line into said outdoor exchanger operating as a condenser, and routing gas and unevaporated liquid from said indoor exchanger operating as an evaporator 7 through said fourth and fifth lines into said drum, said valvemeans in heating position routing discharge gasfrom said discharge line through said fourth line into said indoor heat exchanger operating as a condenser, and font- 7 said expansion means from the oneof said heat exchangers that is operating as a condenser for opening and closing said expansion means to maintain a predetermined amount of suhcooling.

' 7. A heat pump as claimed in claim 1 in which an expansion valve is provided with its inlet connected to the outlets of said third and fourth valves and its outlet connected to the outlet of said pumping means, and in which control means responsive to the temperature and pressure of the refrigerant flowing from said third or fourth valve into said expansion valve is provided for opening and closing said expansion valve to maintain a predetermined amount of subcooling.

8. A heat pump comprising a refrigerant compressor, an indoor heat exchanger, an outdoor heat exchanger, reversal valve means, a surge drum, a discharge line connecting said compressor to said valve means, a suction line connecting said drum to said compressor, a third line connecting said valve means to said outdoor exchanger, a fourth line connecting said valve means to said indoor exchanger, a fifth line connecting said valve means to said drum, liquid pumping means having its inlet connected to said drum, a sixth line connecting the outlet or said pumping means to said indoor exchanger, a seventh line connecting said outlet of said pumping means to said outdoorexchanger, said valve means in cooling position routing discharge gas from said discharge line into said outdoor exchanger operating as a condenser, and routing gas and unevaporated liquid from said indoor exchanger operating as an evaporator through said fourth and fifth lines into said drum, said valve means in heating position routing discharge gas from said discharge line into said indoor exchanger operating as a condenser, and routing gas and unevaporated liquid from said outdoor exchanger operating as an evaporator through said third and fifth lines into said drum, a first check valve in said sixth line for preventing liquid from said indoor when the latter is operating as a condenser from fiowing into said pumping means, a second check valve in said seventh line for preventing liquid from said outdoor when the latter is operating as a condenser from flowing into said pumping means, a third check valve having its inlet connected to saidsixth .line between said indoor exchanger and said first check References Cited by the Examiner UNITED STATES PATENTS 2,716,868 9/55 Biehn 62l60 3,077,086 2/63 Japhet 62-324 3,077,087 2/63 Japhet 62-324 ROBERT A. OLEARY, Primary Examiner.

WILLIAM J. WYE, Examiner.

a "an

Claims

1. A HEAT PUMP COMPRISING A REFRIGERANT COMPRESSOR, AN INDOOR HEAT EXCHANGER, AND OUTDOOR HEAT EXCHANGER, REVERSAL VALVE MEANS, A SURGE DRUM, A DISCHARGE LINE CONNECTING SAID COMPRESSOR TO SAID VALVE MEANS, A SUCTION LINE CONNECTING SAID DRUM TO SAID COMPRESSOR, A THIRD LINE CONNECTING SAID VALVE MEANS TO SAID OUTDOOR EXCHANGER, A FOURTH LINE CONNECTING SAID VALVE MEANS TO SAID INDOOR EXCHANGER, A FIFTH LINE CONNECTING SAID VALVE MEANS TO SAID DRUM, LIQUID PUMPING MEANS HAVING ITS INLET CONNECTED TO SAID DRUM, A SIXTH LINE CONNECTING THE OUTLET OF SAID PUMPING MEANS TO SAID INDOOR EXCHANGER, A SEVENTH LINE CONNECTING SAID PUMPING MEANS TO SAID OUTDOOR EXCHANGER, SAID VALVE MEANS IN COOLING POSITION ROUTING DISCHARGE GAS FROM SAID DISCHARGE LINE THROUGH SAID THIRD LINE INTO SAID OUTDOOR EXCHANGER OPERATING AS A CONDENSER, AND ROUTING GAS AN UNEVAPORATED LIQUID FROM SAID INDOOR EXCHANGER OPERATING AS AN EVAPORATED LIQUID FROM SAID FOURTH AND FIFTH LINES INTO SAID DRUM, SAID VALVE MEANS IN HEATING POSITION ROUTING DISCHARGE GAS FROM SAID DISCHARGE LINE INTO SAID INDOOR EXCHANGER OPERATING AS A CONDENSER, AND ROUTING GAS AND UNEVAPORATED LIQUID FROM SAID OUTDOOR EXCHANGER OPERATING AS AN EVAPORATOR THROUGH SAID THIRD AND FIFTH LINES INTO SAID SURGE DRUM, A FIRST CHECK VALVE IN SAID SIXTH LINE FOR PREVENTING LIQUID FROM SAID INDOOR EXCHANGER WHEN THE LATTER IS OPERATING AS A CONDENSER FROM FLOWING INTO SAID PUMPING MEANS, A SECOND CHECK VALVE IN SAID SEVENTH LINE FOR PREVENTING LIQUID FROM SAID OUTDOOR EXCHANGER WHEN THE LATTER IS OPERATING AS A CONDENSER FROM FLOWING INTO SAID PUMPING MEANS, A THIRD CHECK VALVE HAVING ITS INLET CONNECTED TO SAID SIXTH LINE BETWEEN SAID INDOOR EXCHANGER AND SAID FIRST CHECK VALVE, A FOURTH CHECK VALVE HAVING ITS INLET CONNECTED TO SAID SEVENTH LINE BETWEEN SAID OUTDOOR EXCHANGER AND SAID SECOND CHECK VALVE, AND AN EXPANSION VALVE HAVING ITS INLET CONNECTED TO THE OUTLETS OF SAID THIRD AND FOURTH CHECK VALVES AND ITS OUTLET CONNECTED TO SAID OUTLET OF SAID PUMPING MEANS.