US2938361A

US2938361A - Reversible refrigerating system

Info

Publication number: US2938361A
Application number: US683876A
Authority: US
Inventors: Ralph D Mcnatt
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1957-09-13
Filing date: 1957-09-13
Publication date: 1960-05-31
Anticipated expiration: 1977-05-31

Description

May 31, 1960 R. D. MCNATT 2,938,361

REVERSIBLE REFRIGERATING SYSTEM Filed Sept. 15, 1957 2 Sheets-Sheet 1 OUTDOOR IN VEN TOR.

44m D. Mc/Vnrr Warner Corporation, Chicago, Illinois assignor to Borg- III., a corporation of Filed Sept. 13, 1957, Ser. No. 683,876

8 Claims. (Cl. 62-117) This invention relates to reversible refrigerating apparatus more commonly known as heat pumps.

It is well known, of course, that refrigerating apparatus can be reversed and utilized for heating an enclosure rather than for cooling an enclosure. Operated in this manner, heat is picked up from outside air or water by evaporating low temperature refrigerant which is then compressed to a sufiiciently high pressure and correspondlng temperature by the refrigerating compressor to give up its heat to the air Within the enclosure, the refrigerant becoming condensed thereby. Since in the great majority of instances there is not sufiicient amounts of water practically available, outside air must be utilized as the heat source.

There are many factors limiting the use of outside air as a heat source, however. The primary one is the fact that as the outside air temperature drops, the capacity of the apparatus drops at the very time when heating requirements are increasing. This drop is caused by two factors: one, as the outside air temperature drops, the temperature and corresponding pressure differentials at which the compressor must operate correspondingly increase, since the upper or condensing temperature and corresponding pressure must remain fairly constant and at an elevated point. The volumetric efiiciency of the compressor thereby decreases, since it is a well established fact that the efficiency of a compressor varies inversely as the pressure differential at which it must operate increases. Two, as the outside air temperature drops, the evaporator of the refrigerating apparatus must operate at a correspondingly lower temperature and corresponding pressure to remove heat from the outside air, thereby decreasing the density of the refrigerant gas circulated. It will be appreciated, of course, that with a compressor of fixed volumetric displacement, as the density of the refrigerant decreases, the total weight of refrigerant circulated decreases with a corresponding decrease in capacity. The capacity, of course, is directly dependent on the pounds of refrigerant circulated through the apparatus.

For the above reasons, heat pumps, although performing satisfactorily in moderate climates, are not in general use in those climates having sustained cold periods below 30 F. unless, as pointed out above, there is sufficient water available as a heat source.

It will be appreciated that a considerably expanded use of refrigerating apparatus could be had it the same apparatus that cooled the enclosure could be efficiently utilized for heating the same. In application No. 517,971, now Patent No. 2,869,335, owned by the assignee of my invention, there is disclosed a heat pump system wherein means are provided for operating the customary compression means on simple compression when cooling and on compound compression when heating. As pointed out in said application, heat pump operation with satisfactory performance was obtained in climates where the temperature dropped to F. and lower, thereby considt$ atgnt 2,938,361 Patented May 31, 1960 erably extending the range of heat pumps. By utilizing such a compound compression system for heating, it was found that the evaporator temperature could be maintained at a low enough level to extract heat from 0 F. air or lower and still efiiciently pump heat up to a high enough pressure and temperature to supply sufiicient heat for the enclosure to be heated.

As disclosed in said application No. 517,971, at least two compressors were provided connected in series flow relationship and means were provided for bypassing one of said compressors. It will be apparent that when both compressors operated, compound compression was effected and when one of said compressors was bypassed, simple compression was effected. It will also be apparent that when operating on simple compression, no utilization was had of the bypassed compressor.

I now propose a heat pump system utilizing the concept of simple and compound compression but wherein full utilization of various compression equipment is had. In my system, I utilize at least two compressors and provide refrigerant flow directing means such that the two compressors operate in parallel when desired (simple compression), or in series when so desired (compound compression).

It is an object of this invention, therefore, to provide a reversible refrigerating system wherein at least two compressors are utilized and means are provided for operating said compressors most efficiently over their entire range of operation.

It is a further object of the invention to provide a reversible refrigerating system wherein at least two compressors are utilized and means are provided for operating said compressors in parallel or in series flow relationship.

It is yet another object of the invention to provide a reversible refrigerating system wherein at least two refrigerating compressors are utilized and means are provided for operating said compressors on simple compression and for automatically operating said compressors compounded at that temperature wherein compound operation becomes most efiicient.

The invention consists of the novel constructions, arrangements and devices to be hereinafter described and claimed for carrying out the above-stated objects and such other objects as will appear from the following description of a preferred embodiment of the invention described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of an air conditioning system embodying the invention showing refrigerant flow when operating on simple compression and on the cooling cycle;

Fig. 2 is a schematic representation of the air conditioning system of Fig. 1 showing refrigerant flow when on compound compression and on the heating cycle; and

Fig. 3 is a graph of capacity vs. temperature and showing the effect of decreasing temperatures on a typical simple compression refrigerating system and on a typical compound compression refrigerating system.

Turning now to the drawings, the system comprises a first compressor 10 driven by an electric motor 11 deriving its power from any suitable source. A second compressor 12 is also provided driven by an electric motor 13. It will be appreciated that at least two compressors must be provided in the simplest form of the invention. However, these need not be separate machines but instead may form a single machine, such as a two-cylinder compressor, wherein each cylinder and its associated piston comprises a compressor.

An outdoor heat-exchanger 14 including a heat-exchange coil 14a and an indoor heat exchanger 15 including heat-exchange coils 15a are provided. For purposes of clarification, the outdoor heat-exchanger is in heatexchange relation with outside air. The indoor heat-exchanger is in heat-exchange relation with the medium to be conditioned. It will be appreciated, therefore, that the terms outdoor and indoor refer to function rather than location.

A conventional reversible four-way valve 16, including

junctions

16a, 16b, 16c and 16d, is utilized for directing the refrigerant flow first to either of heat-

exchangers

14 and 15. In addition, a four-way valve 17, including

junctions

17a, 17b, 17c and 17d, serves to direct the refrigerant flow such that

compressors

10 and 12 operate in parallel or in series, as desired. Control of valve 17 is elfected by way of a thermostatic control device comprising a bellows 18 connected'tovalve 17 through a linkage 19 including a central link 20 pivoted as at 21 to provide the desired action. placed such that it is subject to the outside air temperature and is connected to bellows 18 by way of a capillary 23. Bulb 22 contains a volatile fluid, so chosen that it will develop a suitable pressure at the desired outside air temperature. The pressure thus developedin the bulb 22 is transmitted through capillary 23 to the bellows 18 which is connected to actuate valve 17 through linkage .19. I

Compressors

10 and 12, heat-

exchangers

14 and 15, and valves 16 and 17 are all connected in a closed refrigerating circuit'as follows: a line 24 connects the dis charge of compressor 12 to junction 16a of four-way valve 16. Junction 16b of valve 16 is connected to outdoor heat-exchange coil 14a by way of a line 25. Line A thermostatic bulb 22 is into line 25 whence it flows to outdoor heat-exchanger 14. Outdoor heat-exchanger 14, on cooling duty, functions as a refrigerant condenser and the refrigerant flowing through coil 14a gives up its heat to the outdoor air passing thereover, becoming condensed. The now condensed refrigerant exits outdoor heat-exchanger 14 and flows via line 28 to indoor heat-exchanger 15 functioning as a refrigerant evaporator. In flowing through capillary 29, its pressure and corresponding temperature 1s reduced; The cold liquid refrigerant within indoor heatexchange coil 15a absorbs heat from'the medium to be conditioned flowing thereover and becomes evaporated. The evaporated refrigerant exits indoor heat-exchanger 15 by way of line 26 and flows to four-way valve 16. From valve 16 the refrigerant flows into line 27 and thence flows, part back to the inlet of compressor 10 and part through line 33, valve 17 and line 30 to the inlet of compressor 12 to complete the cycle; I

When heating of the medium to be conditioned is de sired, valve 16 is rotated 90.from its position shown in Fig. 1 to reverse the flow of refrigerant. Assuming that 26 connects one side of indoorheat-exchange coil 15a to junction 16d of valve 16. Junction 160 of valve 16 .is connected by way of a line 27 to the inlet side of compressor 10. A line 28, including a restrictor or capillary tube 29, connects the free ends of heat-exchange coils 14a and 15a. It will be appreciated that any re- .frigerant expansion means may be utilized in place of restrictor 29. Junction 17a of four-way valve 17 is connected to the inlet of compressor 12 by way of a line 30. A line 31 connects the discharge of'compressor 10 to junction 17b of valve 17. A line 32 interconnects junction 170 of valve 17 and .line 24. Junction 17d of valve 17 isv connected to line 27 by way of a line 33.

'Turning now to Fig. 3, it will be apparent that for most efiicient operation the compressors should be operated in simple compression for a portion of the normal operating temperature range and compounded for the remainder of said range. As seen in Fig. 3, locus AB represents the combined capacity of

compressors

10 and 12 operated in parallel and as the outside temperature drops. Locus CD represents the combined capacity of

compressors

10 and 12 operated in series and as the outside temperature drops. The point at which the two lines cross has been indicated at E. -It will be appreciated that for most efiicient operation, i.e. greatest capacity,

compressors

10 and 12 should be operated in parallel (simple compression) from A to E and in series (compound compression) from E to D. 'The thermostatic control should be so selected that it will throw valve 17 at the changeover temperature corresponding to point E in Fig. 3.

In operation during such times of the year as the temperature is above the changeover temperature, valve 17 is in the position shown in Fig. 1 due to the expansion of bellows 18 under the influence of the fluid in bulb .22. Assuming that the system is operating on typical cooling duty, then four-way valve 16 is set as shown in Fig. 1. Refrigerant compressed in compressor 12 then flows via line 24 to four-way valve 16. Refrigerant compressed in compressor 10 flows via line 31 to valve 17 and thence, as indicated by the arrows, is directed through line 32 to line 24 joining the flow from compressor 12. The combined refrigerant is then directed by valve 16 the system is still operating on simple compression,-then theposition of valve 17 remains as shown in 'Fig. 1. Refrigerant compressed in compressor 12 then flows via line 24 to four-way valve 16. Refrigerant compressed in compressor 10 flows via line 31 to valve 17 and is .then directed to line 32 through whichit flows to line 24 joining the flow from compressor 12. The combined refrigerant then flows throughvalve 16' and into line 26 whence it flows to indoor heat-exchanger 15. heat-exchanger 15, on heating duty, functions as a refrigerant condenser and the refrigerant flowing through coil 15a gives up its heat to the medium to be conditioned flowing thereover, becoming condensed. The now condensed refrigerant exits indoor heat-exchanger 15 and flows via line 28 to outdoor heat-exchanger 14 functioning as a refrigerant evaporator. In flowing through capillary 29 the pressure and corresponding temperature of the refrigerant is reduced. The cold liquid refrigerant within outdoor heat-exchange coil 14a absorbs heat from the outside air passing thereover and becomes evaporated. The evaporated refrigerant exits outdoor heat-exchanger .14 by way of line 25 and flows to four-way valve 16.

From valve 16 the refrigerant flows into line 27 and then flows, part back to the inlet of compressor 10 and part through line 33, valve 17 and line30 to the inlet of compressor 12 to complete the cycle. 1 1

Turning now to Fig. 2, the cycle will be traced wherein valve 16 is set for heating and thereby rotated 90 to the position shown in Fig. 2. Assuming a temperature such that" compound compression is indicated, i.e. the changeover temperature indicated at point B in Fig. 3 has been reached, then bellows 18 of the thermostatic con trol device contracts sufficiently to actuate valve 17 to its position as shown wherein series flow operation is effected. Refrigerant vapor compressed in compressor 10 then flows via line 31 to valve 17 whence it is directed into line 30, as shown by the arrows. The refrigerant then flows via line 30 to the inlet of compressor 12 wherein it is further compressed, constituting compound The refrigerant then exits compressor 12 by way of line 24 flowing to four-way valve 16. Flow through line 32 will be closed by valve 17 and all the refrigerant will then be directed by valve 16 into line 26 and thence to indoor heat-exchanger 15, which is now functioning as a refrigerant condenser. The refrigerant gives up its heat to the medium to be conditioned, which medium flows through the indoor heat-exchanger and over coil 15a, the refrigerant becoming condensed thereby. The condensed refrigerant liquid flows through line 28 and has its pressure and corresponding temperature reduced by capillary 29 and flows thence into the outdoor heat-exchanger 14 now functioning as a refrigerant evaporator. The low pressure cold liquid refrigerant absorbs heat from the outside air flowing through heat- Indoor exchanger 14 and o er coil 14a becoming vaporized. The refrigerant vapor leaves heat-exchanger 14 by way of line 25 and is directed by four-way valve 16 into line 27 and thence back to the inlet of compressor to complete the cycle. No flow through line 33 is permitted by valve 45.

It will be apparent that I have provided for the utilization of the maximum capacity in a refrigerating system operating over a wide range of temperatures. It is only necessary that at least two compression means be provided in order to practice the herein-disclosed invention.

I wish it to be understood that my invention is not to be limited to the specific constructions and arrangements shown and described, except only insofar as the claims may be so limited, as it will be apparent to those skilled in the art that changes may be made without departing from the principles of the invention.

What is claimed is:

l. A reversible refrigerating system for cooling or heating a conditioning medium comprising an outdoor heat-exchanger in heat-exchange relation with outside air, an indoor heat-exchanger in heat-exchange relation with said conditioning medium, and a plurality of refrigerant compression means, said compression means and heatexchangers being connected in a closed refrigerant circuit; first refrigerant flow directing means for routing refrigerant from said compression means first to said outdoor heat-exchanger when cooling of said conditioning medium is desired, or first to said indoor heat-exchanger when heating of said conditioning medium is desired; and

second refrigerant flow directing means for routing refrig erant through said compression means in parallel flow when cooling said conditioning medium and in series flow in heating said conditioning medium.

2. The system of claim 1 including means responsive to a predetermined outside temperature for automatically controlling said second refrigerant flow directing means.

3. A reversible refrigerating system for cooling or heating a conditioning medium comprising an outdoor heatexchanger in heat-exchange relation with outside air, an indoor heat-exchanger in heat-exchange relation with said conditioning medium, and a plurality of refrigerant compression means, said compression means and heatexchangers being connected in a closed refrigerant circuit; reversing valve means for directing refrigerant from said compression means through said circuit to said outdoor heat-exchanger and thence to said indoor heat-exchanger when cooling of said conditioning medium is desired, or for reversing said flow when heating of said conditioning medium is desired; and means for operating said compression means in parallel relationship when cooling said conditioning medium and in series relationship in heating said conditioning medium.

4. The system of claim 3 including means responsive to a predetermined low outside temperature for automatically controlling said last-mentioned means.

5. In a reversible refrigerating system of the type wherein a compression means delivers refrigerant first erating said compressors in parallel when cooling and in series when heating; and means responsive to a predetermined condition for automatically controlling said last mentioned means.

6. A reversible refrigerating system for cooling or heating a conditioning medium comprising an outdoor heatexchanger in heat-exchange relation with outside air, an indoor heat-exchanger in heat-exchange relation with said conditioning medium, and a plurality of refrigerant compression means, said compression means and heatexchangers being connected in a closed refrigerant circuit; first valve means for directing refrigerant from said compression means through said circuit to said outdoor heat-exchanger and thence to said indoor heat-exchanger when cooling of said conditioning medium is desired, or for directing refrigerant from said compression means through said circuit to said indoor heat-exchanger and thence to said outdoor heat-exchanger when heating of said conditioning medium is desired; and second valve means for directing said refrigerant through said compression means in parallel flow when heating said conditioning medium and in series flow in heating said conditioning medium.

7. The system of claim 6, including means responsive to a predetermined outside temperature for automatically controlling said second valve means.

8. A method of operating a reversible refrigerating system for supplying a cooled or heating conditioning medium, said system being of the type comprising a first heat-exchanger in heat-exchange relation with outside air, a second heat-exchanger in heat-exchange relation with the medium to be cooled or heated, and a plurality of refrigerant compression means, comprising the steps of directing refrigerant through said compression means in parallel flow and thence through said first and second heat-exchangers respectively when cooling of said conditioning medium is desired and directing refrigerant through said compression means in series flow and thence through said second and first heat-exchangers respectively in the period of heating said conditioning medium and at a predetermined outside temperature such that said series fiow produces optimum efliciency of operation.

References Cited in the file of this patent UNITED STATES PATENTS 2,318,318 Lodwig May 4, 1943 2,619,326 McLenegan Nov. 25, 1952 2,693,092 Laballe Nov. 2, 1954 OTHER REFERENCES published May 8, 1951, 646 0.6. 669 (1 sheet 0f draw-- ing-8 pages spec.).