US3365902A

US3365902A - Reverse cycle refrigeration system

Info

Publication number: US3365902A
Application number: US589906A
Authority: US
Inventors: Otto J Nussbaum
Original assignee: Larkin Coils Inc
Current assignee: Larkin Coils Inc
Priority date: 1966-10-27
Filing date: 1966-10-27
Publication date: 1968-01-30
Anticipated expiration: 1985-01-30

Description

Jan.'30, 1968 o. .J. NUSSBAUM 3,365,902

' REVERSE CYCLE REFRIGERATIONSYSTEM Filed Oct. 27, 1966 s Sheets-Sheet 1 CONOE/VSEZ OTTO I. Nuggg u ATTORNEYS Jan. 30, 1968 o. J. NussBAuM 3,365,902

REVERSE cxrcnnnsmieanmzon SYSTEM H I 3 Sheets-Sheet 3 Filed Oct. 2'7, 1966 V 7.7. S 2 23 l I INVENTOR 01 110 J-Nusssaum.

ATTORNEYS United States ra Q 3,365,902 REVERSE CYCLE REFRIGERATION SYSTEM Otto J. Nussbaum, Atlanta, Ga., assignor to Larkin Coils,

Inc, Atlanta, (2a., a corporation of Georgia Filed Oct. 27, 1966. Ser. No. 589,906

23 Claims. (Cl. 62-155) The present invention relates in general to refrigeration systems, and more particularly to reverse cycle refrigeration systems for use as a heat pump system or as a system having a normal refrigeration phase and a hot gas defrost phase. i

Reverse cycle heat pump systems for winter heating have been widely use-l in the past, but with questionable success. Such heat pump systems customarily employ a motor-driven compressor, an indoor coil and-an outdoor coiltogether with suitable conduits and valves for connecting the compressor discharge or high-pressure outlet to the outdoor coil and the compressor suction intake to the indoor coil for cooling operation, and for connecting the compressor discharge to the indoor coil and the coinpressor suction intake to the outdoor :oil for heating operation. The primary common shortcoming of such reverse cycle heat pump systems as heretofore customarily produced was the fact that upon reversal of the cycle from cooling to heating, the substantial liquid refrigerant I conditioning level, at relatively low evaporating tempera tures during the heating cycle. Since a suction gas cooled motor-compressor depends on cooling of its motor windings by a refrigerant and the refrigerant flow rate during the heating cycle is radically reduced, overheating of the motor and consequential burnout was one of the causes of failure of such heat pump systems. Later equipment now on the market have dealt with this problem by installing a trap or accumulator in the suction line immediately up- 1 stream from the compressor intake so as to intercept large slugs of liquid and to feed a homogenized vapor-liquid mixture to the compressor suction intake which it is better equipped to handle than intermittent slugs. Compressor manufacturers also offer compressors with enlarged crankcase volumes and with built-in slinger devices which are intended to perform the same homogenizing effect as the accumulator does. None'of these systems attack the problem as such; they simply propose to deal with it in a way which reduces the hazard to the compressor, but does not eliminate it. A further shortcoming of the currently used reverse cycle heat pump refrigeration system is a need to resort to a four-way reversing valve which is costly, cumbersome and causes less of capacity due to leakage and heat transfer between the discharge gas and the suction gas stream leaving and entering the compressor respectively.

Also, reverse cycle refrigeration systems having hotgas defrost feature have been widely used, wherein a valved hot-gas line extends from the compressor discharge outlet to the evaporator, which is opened during the de frost cycle to admit hot. gaseous refrigerant directly to the evaporator for defrosting. A practical disadvantage in such hot-gas defrost systems is the fact that in addition to the conventional liquid line and suction line of the refrigeration system, athird line, the hot gas defrost line needs to be installed. This adds to the cost of the hot gas defrost system and very often prompts the decision to go to a less reliable system which has a lower initial cost 3,365,902 Patented Jan. 30, 1958 but a higher operating cost. Another shortcoming of oertain hot gas defrost systems is that they depend on an artificial source of heat to generate refrigerant vapor to enable the compressor to supply compressed hot gas" to the evaporator for defrosting. Other types of systems depend upon the vaporization of liquid refrigerant in the receiver and condenser when their pressure is reduced upon connection to the compressor suction intake during the defrost cycle for the supply of refrigerant vapor to the compressor, the condenser and receive: exposed to ambient air serving'as the heat source. Supply of vapor to the compressor during the defrost cycle is erratic either because the artificial heat source runs out of bee f in which case liquid refrigerant returns to the compressor which the compressor is not equipped to handle; or there is not sufficient liquid condensed in the evaporator to vaporize in the heat source at the rate which the compres sor demands. In the latter instance, the compressor evacuates the heat source which results in a very low suction pressure so that the pressure of the discharged fhot gas is not high enough to perform defrosting of the evaporator.

Further, some progress has been made to ensure adequate supply of refrigerant vapor to the compressor during the hot gas defrost cycle by directing refrigerant which is exposed to the, suction intake pressure of the compressor during the defrost cycle through a system of coils immersed in a tank of heated fluid, but such a system obviously involves the additional expensev of providing a third coil system independent of the evaporator and condenser coil systems, together with tank housing and support structure for the separate coil systemand sometimes energy consuming means for heating the fluid within the tank and surrounding the separate: coil system.

I have discovered that an adequate source of heat to supply the compressor with refrigerant vapor, either during the heating cycle of a reversible heat pump system or during the hot gas defrost cycle of a refrigeration system having hot gas defrost, can be provided by a set of heat source coils forming a distinct refrigerant circuit from the condenser coils but being contained in a common fin bundle with the condenser coils, whereby this composite coil system sharing the same fins and exposed to ambient temperatures in a manner similar to conventional air cooled condenser systems will provide the necessary heat exchange surface for the heat source.

An object of the present invention therefore, is the provision of a reverse cycle heat pump system or hot gas defrost refrigeration system with a heat source which which eliminates hazardous liquid fioodback to the compressor upon reversing of the cycle and ensures adequate supply of heat for the heating or defrosting cycles.

Another object of the present invention is the provision of a novel reverse cycle heat pump system or hot gas defrost refrigeration system which eliminates the need for a separate hot gas line for defrosting.

Another object of the present invention is the provision of a novel reverse cycle heat pump system or hot gas defrost refrigeration system which uses a single heat transfer device to perform the function of a condenser during the. normal cooling or refrigeration cycle and which performs the function of a heat source for the 1 heating or defrosting cycle.

Another object of the present invention is the provision of a novel reverse cycle heat pump system or hot gas defrost refrigeration system as described in the im-- mediately preceding paragraph, wherein the single heat transfer device is a combination condenser and heat source having a condenser circuit and a heat source circuit separatesfrom the condenser circuit, both of which share a common fin bundle used alternately as extended surface either for the condenser or for the heat source functions.

Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings illustrating the preferred embodiments of the invention.

In the drawings:

FIGURE 1 is a schematic view of a refrigeration and hot gas defrosting system, or a heat pump system, embodying; the present invention;

FIGURE 2 is a transverse section view of the combination condenser and heat source unit illustratirg an 1 example of an arrangement of condenser coils and heat source coils sharing a common fin bundle, usable in the systems of the present invention.

FIGURE 3 is a schematic wiring diagram of an electrical control circuit which may be used with the systems of FIGURE 1; and,

FIGURES 4 and 5 are schematic diagrams of other modifications of refrigeration and hot gas defrosting systems or heat pump system embodying the present invention.

Referring to the drawings, wherein like reference characters designate corresponding components in figures which depict the same embodiment of the invention, and particularly to FIGURES 1 and 2 there is schematically shown a refrigeration circuit embodying the present invention usable as either a refrigeration system having hot gas defrosting features or as a reversible cycle heat pump.

This refrigeration system comprises a compressor of conventional construction, having a suction intake or low side 11 and a discharge or high side 12. The condenser discharge is connected through conduit 13 to a threeway valve 14 having a connection with conduit 15 for discharging compressed refrigerant vapor to the inlet of the condenser circuit coils 16. The condenser circuit outlet is connected through check valve 17 and line 18 to a receiver inlet branch line or dip tube 19 extending into the receiver 20 to a point below the liquid level therein. Conduit 18 extends from its junction with the receiver inlet branch line 19 through a manual valve 21,

a liquid solenoid valve 22 and an expansion device 23 to the inlet of evaporator 24 of conventional construction located in the space to be cooled, which serves asv the inside coil in a heat pump system, the outlet of which is connected by suction line 25 and pressure operated shut-off valve 26 to the suction inlet 11 of the compressor 10. The expansion device 23, may, of course, be any known refrigerant control device such as, for example, a thermostatic or constant pressure expansion valve, a float valve, a capillary tube, and the like.

A reversing conduit 27 having a check valve 28 therein is connected to the liquid line 18 across the expansion device 23, for flow of refrigerant from the evaporator 24 toward the condenser 16 when the system is in the heating mode or the hot gas defrosting mode. A drain pan heating coil 29 may also be employed, if desired, in thermal communication with the conventional evaporator drain pan, the drain pan heating coil 29 communicating with the suction line 25 and through line 30 and check valve 31 with the liquid line 18, for example, between the expanson device 23 and receiver inlet branch line 19. The purpose of check valve 31 is to prevent flow of refrigerant through the drain pan heating coil 29 at times other than defrost, since obviously flow of refrigerant through the drain pan heating coil during refrigeration would cause either heating or frost formation in the drain pan which is highly undesirable.

In order to provide an adequate heat source to supply the compressor 10 with refrigerant vapor during the hot gas defrost or heating cycle, I propose to combine with the condenser circuit 16, a separate and distinct heat source circuit 32 in the form of a conduit coil similar to that forming the condenser circuit 16 which is separate and distinct from the condenser circuit 16 but is contained physically with the latter in a common fin bundle sharing the same fins which form the necessary extended surface for the condenser coil. One means of incorporating both the condenser circuit conduit coil and the heat source circuit conduit coil in a common fin bundle structure is illustrated in FIGURE 2, one of the fins being indicated by the reference character 33, the conduit sections for the condenser circuit conduit coil 16 being shown in heavy lines and the conduit sections forming the heat source conduit coil being shown in lighter lines to visually distinguish them.

Condenser inlet and outlet headers have been indicated diagrammatically at 3 8, and 35, respectively, and the heat source suction header being indicated diagrammatically at 36. It will be understood that a conventional refrigerant distributor, indicated diagrammatically at 37 may be provided to distribute the refrigerant to the heat source circuit coil sections 32. The inlet end of the heat source circuit 32 is connected by line 38 through a defrost pressure control valve 39 and a defrost solenoid valve 40 to the liquid line 18, for example, between expansion device 23 and the solenoid valve 22. The outlet end of the heat source circuit 32 is connected by defrost suction line 41 to the suction intake 11 of the compressor 10. A vent line 42 having a check valve 43 therein is connected between the receiver 20 and the conduit 13 connected to the compressor discharge 12 for venting the gas space in the receiver 20 to the discharge line 13 during defrost or heating. A line 44 extends from a second outlet of the three-way valve 14 to the suction line 25 between the pressure-operated shut-01f valve 26 and the evaporator 24 to directly communicate the evaporator with the compressor discharge 12 when the three-way valve 14 is positioned to establish the hot gas defrost or heating mode.

In normal operation for refrigerating or cooling, the compressor 10 discharges through the three-way valve 14 and line 15 to the condenser circuit 16, condensing the refrigerant and delivering liquid refrigerant through the check valve 17 and di tube 19 to the receiver 20. From the receiver 20, the liquid refrigerant enters the evaporator 24 through the

conduits

18 and 19, liquid solenoid valve 22 which is now open, and the expansion device 23. vaporized refrigerant from the evaporator 24 returns tothe compressor 10 through the suction line 25 and pres sure operated shut-off valve 26. The pressure operated shut-off valve 26 is completely divorced from the thrceway valve 14 so as to eliminate undesirable leakage or heat transfer between hot discharge gas and suction gas. The valve 26 is actuated by discharge gas pressure which serves to close the valve. Valves of this type are commercially available and need no detailed description. When the discharge gas pressure is removed at the end of the defrost cycle, the valve 26 returns to its fully open position either by gravity or by force of a spring. Of course, a solenoid valve or a pneumatically operated valve may be used instead of the valve 26. i

To initiate either defrost operation in a refrigeration and. hot gas system, or heating operation in the heat pump system, the three-way valve 14 is simply moved to connect the discharge line 13 with the conduit 44 and disconnect the same from the condenser inlet line 15. The compressor '10 then discharges through the three-way valve 14 to the suction line 25 and the evaporator 24, causing hot gaseous refrigerant to be supplied to the evaporator 24 and flow through the evaporator in a direction opposite to that of the normal refrigeration cycle. The evaporator 24 now functions as a condenser and the condcnscd liquid refrigerant flows from the evaporator 24 through the line 27 and check valve 28 toward the Ic cciver 20, and defrost solenoid valve 40 which is opened concurrently with reversal of the three-way valve 14.

Liquid flows to the heat source circuit 32 through the now opened solenoid valve 40 and defrost pressure control valve 39, Wl1lCh may be a pressure limiting thermostatic expansion valve, or similar refrigerant control device. Condensed liquid coming from coil 24 and/or liquid from the receiver 20 is evaporated in the heat source circuit 32 by heat abstracted from the ambient air moved by the condenser fan, the evaporating temperature being adjusted automatically by thevalve 29 so as to be always below the temperature of the ambient air, and vapor enters the compressor-.10 through the defrost suction line at. The check valve 17 between the condenser outlet and the inlet 19 of the receiver 2t serves to prevent loss of refrigerant from the receiver 20 to the condenser 16 dur ing reversal of the cycle, particularly when air is moving through the condenser during defrost andthe temperature of the air is relatively low.

The check valve 43 functions only during reversal of the cycle when the receiver pressure isililtely to be higher than the pressure at the compressor discharge 13 which at that time communicates with the evaporator 24. For

thisieason, it is highly desirable to reduce the receiver pressure at the start ofdefrost; otherwise check

valves

31 and 28 will not open and the refrigerant condensed in the evaporator for defrosting will be trapped. Thus, the vent valve 43 assists in raising the defrosting pressure rapidly at the onset of defrost, and reduces receiver pressure so as to permit liquid refrigerant flow from the evaporator 24 toward the receiver 20 and heat source 32 immcdiately.

it will be noted that in the above described arrangement, the heat source circuit 32 is always open through the line ll to the suction intake 11. The importance of this is that if the heat source circuit 32 is isolated from the suction intake Ill, during the refrigeration or'cooling cycle, it would fill with high pressure refrigerant from the receiver 20 while it is not in use, and upon shifting of the three-way valve 14 to initiate the defrost or heating cycle, a heavy load of high-pressure liquid refrigerant would be: imposed upon the compressor it) which would soon lead to its failure, particularly, if the heat source circuit is exposed to a high ambientor a high temperature heat source.

At the end of the defrost cycle, the circuit is shifted to a post-defrost condition for a short time interval immediately following defrost. During the post-defrost cycle, the defrost solenoid valve 49 is open and the liquid solenoid valve 22 is closed, while the reversing three-way valve 14 is in the refrigeration position and shut-off valve 26 remains closed. The evaporator fan also remains stopped during this post-defrost cycle. The effect of this is to rapidly evacuate liquid remaining in the heat source circuit 32 as well as in the evaporator 24, rapidly reducing the pressure in the evaporator to vaporize any liquid that may remain therein so as to prevent overloading of the compressor motor upon resumption of normal refrigeration. At the end of post-defrost, when the pressure in

lines

44 and 25 has been reduced to that existing in line 11, shutoff valve 26 will be automatically returned to its open position by its opening spring force. The duration of post-defrost, depending on the length of lines 18 and 2.55, may be from one to two minutes. At the termination of post-defrost, solenoid valve 40 is closed while solenoid valve 22 opens; this may, for instance, be accomplished by pressure switch PS (shown in FIGURE 3) connected to line 25. This switch may, also, operate a pilot solenoid valve 26A which closes when valve 22 opens; in which case valve 26 will open at a predetermined safe pressure in line 25 sciised by switch PS.

FIGURE 3 is a schematic wiring diagram of a typical control circuit which may be used to control the system of FIGURE 1, from which an adequate understanding will be had to provide control circuits for the other embodiments herein described. As shown in FIGURE 3, the compressor starter indicated at 10a is connected in series with the usual overload protectors, oil pressure safety switch, low pressure and high pressure cutout switches, collectively indicated at 55. Thetimer motor 56 is connected in series with the contacts of the thermostat T1, which is the thermostat monitoring the space to be conditioned by the system, so that the timer motor 56 operates only when the thermostat Tl calls for cooling. This prevents a defrost operation from being initiated when the compressor 10 is not running and at the same time adjusts the interval between defrost operation to actual compressor running time. At the start of defrost the timer 56 closes single throw switch 56A which opens theheat source solenoid valve as and energizes pilot valve 26A to close 'valve 26 while double throw switch 56B opens the three-way solenoid valve 14 to the evaporator, and stops flow to the condenser. The timer switch 56B also stops operation of the evaporator fan during defrost. The solenoid valve as at the inlet of the heat source coil and the pilot solenoid 26A of the suction shut-off valve is are each wired in series with a pressure switch, designated PS, which senses suction pressure and is set to close a selected higher pressure-condition exist ing at the onset of defrost and to open at a selected low level when the suction pressure has been reduced to a point corresponding to approximately minus l0- evaporating temperature, de-energizing and closing valve 4-0 and pilot valve 26A and permitting valve 26 to open to its normal position.

A release solenoid 51 is mechanically coupled to the timer switches 56A and 5613 to return these switches to the position they occupy before defrost, and is connected electrically to a "hot contact of a defrost terminating thermostat 58 having its remote bulb attached to the coldest point of the evaporator 24. During, the refrigeration cycle, the thermostat switch 58 is in a position indicated as cold maintaining thefan of evaporator 24 running. During defrost, the temperature sensed. by the feeler element of thermostatic switch 582 gradually rises until it reaches the'level to cause the switch to shift to the position indicated as hot whereupon the switch 58 energizes the release solenoid 57 which returns the timer switches A and B to their refrigeration position, and closes liquid solenoid valveZZ. Howevenrthe heat source valve 40 remains open and the suction shut-olf valve 26 remains closed due to the closed state of pressure switch PS, which breaks contact only after the evaporator and heat source have been evacuated and the suction pressure has been reduced to the selected point corresponding approximately to minus 10 evaporating temperature. The shut-off valve 26 is then opened and normal flow resumes when switch PS breaks contact. The evaporator temperature is then gradually reduced and the defrost termination thermostat 58 returns to the cold position restarting the evaporator fan 24A and also reopening liquid solenoid valve 22. This prevents undesirable heating of the refrigerated space after the defrost operation, and also provides a time interval for draining of residual water from the surfaces of the evaporator coil 24 before refrigeration is resumed.

The above-described systems also provide a means for effecting partial load compensation where it is desired to maintain the compressor in continuous operation with heavily fluctuating loads. In systems with heavily fluctuating loads, the heat source circuit may be used during normal refrigeration when the load at the evaporator is relatively low, where the compressor must remain inoperation. Under conditions of heavily fluctuating loads, considerable imbalance between the evaporator and the compressor occurs in conventional systems and it is usually considered preferable to stop the compressor or run it intermittently. This, in turn, results in greatly fluctuating temperature and humidity conditions in the space served by the evaporator. With the systems hereinbefore shown having the heat source circuit 32 incorporated therein, the heat source circuit 32 may be opened during conditions of light evaporator load by opening the solenoid valve 40 7 at the inlet to the heat source circuit, in the systems of FIGURE 1, so that the load lacking at the evaporator 24- is supplied to the compressor it by the heat source circuit 32. This establishes a good balance between the low side and the compressor 10 which makes it possible to operate the compressor continuously and to maintain completely stable temperature and humidity conditions in the space served by the evaporator.

The combination condenser and heat source coil system incorporated in the single coil and fin structure wherein the coil tubes for the two circuits share the same common fin bundle may also be employed in a system wherein the heat source circuit is utilized not only during defrost, but also serves as the subcooling circuit or as a supplementary condenser, during normal refrigeration. Such a system may be used either with or without a liquid receiver without requiring any vent line such as was employed in the previously described embodiment wherein the vent line was provided to rapidly reduce receiver pressure at the beginning of the defrost cycle. The receiverless system employing the heat source circuit as the sub-cooling circuit of the condenser is illustrated in FIGURE 4, wherein the components corresponding to the refrigeration system components of the previously described embodiment are indicated by the same reference characters. In the system of "FIGURE 4, the three-way reversal valve 14 in the compressor discharge line in the previously described embodiment is dispensed with and a valve 60 is provided in the condenser inlet line 15, the valve 69 being a commercially available pressure regulating valve opening on high inlet pressure and closing on low inlet pressure. Communication between the condenser 16 and the compressor discharge 13 for venting purposes is directly through the discharge line 13 by way of the pressure regulating valve 69, this valve being open as long as the condenser pressure is equal to or higher than the compressor discharge pressure. The defrost solenoid valve 40 of this embodiment is connected directly to the heat source circuit inlet, and a line 61 having a check valve 62 therein similar to the line 27 and check valve 23 in the previous embodiment connects the evaporator to the heat source 32 by way of pressure control valve 39. The outlet end of the heat source or sub-cooler circuit 32 is connected by line 63 to a threeway valve 64 provided in the suction line between the evaporator. 24 and the compressor intake 11. A line 65 controlled by a hot gas solenoid valve 66 provides a conncction during the defrost cycle between the compressor discharge 13 and the suction line 25 between the threeway valve 64 and the evaporator outlet.

In the operation of this system during refrigeration,

the three-way valve 64 connects the suction line 25 to the compressor suction intake 11 and closes the heat source outlet line 63. Gas from the compressor 10 is discharged through the valve 66 to the condenser 16, the condensed liquid refrigerant then passing through check valve 17 and open solenoid valve 40, into the combination coil section formingthe sub-cooler or heat source 32. The refrigerant then passes through the open liquid solenoid valve 22 and thermostatic expansion \a'lve 23 to the evaporator 24, the refrigerant vapor 'being returned through the suction line 25 and three-way valve 64, open to the compressor intake 11 but closed both to the hot gas line 65 and the sub-cooler line 63.

Immediately prior to establishing the defrost cycle, the system is set in a prc-defrost mode to evacuate the heat source 32 and bring its pressure down to suction pressure. For this purpose, the solenoid valve 40 between the condenser outlet and the inlet of the sub-cooler 32 is closed. Flow is otherwise identical to that just described for the refrigeration cycle. With the solenoid valve 40 at the subcooler inlet closed and no flow restricted through the solenoid valve 22 and expansion valve 23, the residual liquid refrigerant in the sub-cooler 32 will be quickly exhausted as the result of which the suction pressure in the low side of the system will drop rapidly, thus initiating the next stage of defrost by way of a pressure switch sensing the low side system pressure as described in connection with the embodiment of FIGURE 1. y

In the defrost cycle, the hot gas solenoid valve 66 opens, permitting flow from the compressor discharge 13 through valve 66 and hot gas line to the su lion line 25 through the evaporator 24 in a direction op; ssite the normal flow direction through the evaporator., The re frigerant condenses in the evaporator 24, rejecting heat to the frost on. the evaporator coils to melt the same, and passes through check valve 62, line 61 and pressure regulating valve 3?) into the inlet of the sub-cooler 32, bypassing the expansion valve 23 and liquid solenoid valve 22. The sub-cooler 32 now functions as a heat source by way of pressure regulating valve 39, the refrigerant vaporizing in the coils 32 and returning to the suction intake ll of the compressor 10 by way of the line 63 and threeway valve on, which is now positioned to connect the subcooler or heat source outlet line 63 with the com-pressor intake 11 and isolate the evaporator 24 from the compressor suction. At the same time, the pressure in the high side is vented from the condenser 16 to the compressor discharge 13 as long as the condenser pressure exceeds the compressor discharge pressure, due to operation of the pressure regulating valve.6 0l During the initial stages of defrost, the condenser pressure may exceed the compressor discharge pressure and therefore pressure in the high side would be vented from the condenser to the compressor discharge. Eventually, as defrost progresses, the condenser pressure will drop in which case the pressure regulating valve 60 closes.

. Immediately following completion of the defrost cycle, the system enters a postdefrost cycle, to reduce the evaporator pressure rapidly before normal refrigeration operation is resumed. During this post defrost cycle the liquid solenoid valve 22 at the inlet to the evaporator 24 is closed, the hot gas valve 66 is closed, the solenoid valve 40 at the inlet to the sub-cooler is closed, and the three-way valve 64 is positioned to connect the sub-cooler outlet line 63 to the compressor intake 11. The evaporator fans are turned oif. The compressor therefore rapidly reduces the evaporator pressure, by way of check valve 62, line 611, regulation valve 39 and sub-cooler 32; termination of the post'defrost cycle is signaled by a drop in evaporator pressure as described in connection with the embodiment of FIGURE 1.

The general scheme illustrated in PIGU RE 4 may optionally include a liquid receiver, in which case the system should be arranged as illustrated in FIGURES. The system of FIGURE 5 corresponds to that of FIGURE 4,

except that the receiver 20 is connected by a line to the downstream end of the check valve 17 at the outlet of the condenser 16, the liquid line 18 conveying liquid refrigerant from the receiver 20 to the inlet of the subcooler or heat source 32. This system also includes means for controlling head pressure by means of a by-pass line 70 from the compressor discharge 13 to the inlet of the sub-cooler or heat source coil 32, a solenoid valve 71 being provided in the by-pass line 70 actuated by condensing pressure and so wired that it is closed during the defrost operation. In cold weather, when the pressure regulating valve 60 closes, the condenser 16 would be lay-passed by passage of liquid through the by-pass line 70 and valve 71 to the sub-cooler coils 32. The sub-cooler 32 which has a relatively small condensing surface compared to that of the main condenser 16 would become the sole condenser of the system. Because of the modulating action of the pressure regulating valve 60, the flow rates through the condenser 16 and the sub-cooler 32 with such a system would be proportioned until the regulating valve 60 closes completely.

While several preferred embodiments of the present invention have been particularly shown and described, it is apparent that various modifications may be made therein within the spirit and scope of the invention, and

asssscz' it is desired, therefore, that only such limitations be placed on the invention as are imposed by the prior art and set forth in the appended claims.

What is claimed is:

1. A reversible refrigeration system having a cooling cycle and a heating cycle, comprising a compressor having discharge and suction sides, an evaporator located in a space to be conditioned having an outlet selectively connectible to the compressor suction side during the cooling cycle and to the compressor discharge side during the heating cycle, a single heat transfer device of the fin and tube type exposed to ambient temperatures in a zone outside said space having first and second independent sets of cc nduit coils and plural heat transfer fins defining a fin bundle for said device with the fins disposed in highly thermally conductive physical contact with the coils of both said sets forming the extended surfaces thereof whereby said fin bundle is shared by both said sets of coils, said first set of coils forming condensing coils during the cooling cycle for condensing compressed refrigerant vapor supplied thereto and said second set of coils forming heat source coils during the heating cycle for vaporizing liquid refrigerant supplied thereto by extracting heat from said zone, a first refrigerant flow circuit including said first set of coils selectively interconnected between the compressor discharge side and the inlet of the evaporator during only the cooling cycle, a second refrigerant flow circuit including said second set of coils selectively connected between the inlet of the evaporator and the compressor suction side during the heating cycle to vaporize any liquid refrigerant returning from the evaporator to the compressor, and means for disconnecting the inlet of the condenser. from the compressor discharge side during the heating cycle.

2. A reversible refrigeration system as defined in claim 1, including a movable reversing valve having first and second positions, said reversing valve communicating with said compressor discharge side in both said positions and having communication with the inlet of said first set of coils in said first position and with the outlet of said evaporator in said second position for connecting the first set of coils with-said compressor discharge side during the cooling cycle and for connecting the evaporator outlet with the compressor discharge side during the heating cycle.

3. A reversible refrigeration system as defined in claim 2, including a suction conduit connected between the outlot of said evaporator and the suction side of said compressor having a pressure operated shut-off valve therein,

and a by-pass conduit connecting said reversing valve in said second position with said suction conduit in bypassing relation to said pressure operated shut-oil valve, said reversing valve in said first position cornmuncating said condensing coils with the compressor discharge side for cooling cycle operation and closing said by-pass conduitand in said second position opening said by-pass conduit to said compressor discharge side and disconnecting the inlet of said condensing coils from said com-, pressor discharge side, and means responding to compressor discharge side pressure in said bypass conduit when said reversing valve assumes said second position to close said shut-oil valve.

4. A reversible refrigeration system as defined in claim 1, wherein said second fiow circuit includes a continuously open conduit connecting the outlet of said heat source coils to the suction side of said compressor and conduitportions including control valve means connecting the inlet of said heat source coils with the evaporator, said control valve means being closed during said cooling cycle and open during the heating cycle.

5. A reversible refrigeration system as defined in claim 1, including a receiver, a first conduit connecting the outlet of said condensing coils with said receiver having check valve means therein permitting flow from said condensing coils to said receiver and preventing fiow from ill the receiver to the condensing coils, said first conduit means comprising a second conduit connecting said re ceiver with the inlet of said evaporator having a first expansion device therein and including a control valve therein, a lay-pass conduit coupled to said second conduit in by-passing relation to said first expansion device having valve means therein closing said by-pass conduit during said cooling cycle and opening said by-pass conduit during said heating cycle, conduit means connecting the inlet of said heat source coils to said second conduit between said first expansion device and said control valve having a second control valve therein open during the heating cycle for passing refrigerant to said heat source coils, and means for controlling said first and second control valves to maintain the first and second valves respectively closed and open during a selected short period at the onset of the conduit means connecting the inlet of said heat source coils to said last mentioned conduit means between said receiver and evaporator to admit refrigerant from said evaporator to said heat source coils during the heating cycle, conduit means continuously connecting the outlet of said heat source coils to the suction sideo' said compressor, and vent conduit means connecting Sold receiver to the discharge side of said compressor having check,

valve means therein opening only when receiver pressure is higher than compressor discharge side pressure to promptly reduce receiver pressure at the onset of the heating cycle.

7. A reversible refrigeration system as defined in claim 1 wherein said heat source coils have an outlet conduit extending from the outlet of said heat source coils, the system including a suction conduit connected between the outlet of the evaporator and the compressor suction side, a three way valve in said suction conduit concurrently communicating the evaporator outlet with the compressor suction side and disconnecting the said outlet conduit therefrom during the cooling cycle and disconnnecting the evaporator outlet from the compressor suction side and connecting the outlet conduit therewith during the heating cycle. 7

8. A reversible refrigeration system as defined in claim 1, including conduit means including a first valved conduit connecting the outlet of said condensing coils with an inlet of the heat source coils and a second valved conduit connecting the outlet of the heat source coils to the inlet of the evaporator for intercoupling the heat source coils in a refrigerant flow circuit between the condenser and evaporator during the cooling cycle to provide subcooling or supplementary condensing of refrigerant, means for admitting refrigerant from the evaporator inlet to the inlet of the heat source coils during the heating cycle in lay-passing relation to said second valved conduit, and means for connecting the outlet of the heat source coils to said compressor suction side during the heating cycle.

9.A reversible refrigeration system as defined in claim 8 wherein said heat source coils have an outlet conduit extending from the outlet of said heat source coils, the system including a suction conduit connected between the outlet of the evaporator and the compressor suction side. a three-way valve in said suction conduit concurrently communicating the evaporator outlet with the compressor suction side and disconnecting the said outlet conduit therefrom during the cooling cycle and disconnecting the evaporator outlet from the compressor suction side and connecting the outlet conduit therewith during the heating cycle.

ll ll 10. A reversible refrigeration system as defined in claim 7, including a by-pass conduit connecting the compressor discharge side with said suction conduit between said three-way valve and said evaporator, said by-pass conduit having a valve therein closing the same during the cooling cycle and opening the same during the heating cycle.

11. A reversible refrigeration system as defined in claim 14), wherein 'said'cooling cycle circuit includes a condenser inlet conduit connected to the compressor discharge. side having a pressure responsive valve therein responsive to pressure differentials across the same set to open throughout said cooling cycle and during such portions of the heating cycle when condensing coil pressure exceeds compressor discharge pressure and to close during the remainder of the heating cycle.

12. A reversible refrigeration system as defined in claim 7, wherein said cooling cycle circuit includes a condenser inlct conduit connected to the compressor discharge side having a pressure responsive valve therein responsive to pressure diilerentials across the same set to open throughout said cooling cycle and during such portions of the heating cycle when condensing coil pressure exceeds compressor discharge pressure and to close during the remainder of the heating cycle.

13. A reversible refrigeration system having a cooling cycle and a heating cycle, comprising a compressor having discharge and suction sides, an evaporator located in a space to be conditioned having an outlet selectively connectible to the compressor suction side during the cool. ing cycle and to the compressor discharge side during the heating cycle, condensing coils exposed to ambient temperatures in a zone outside said space for condensing compressed refrigerant vapor supplied thereto, heat source coils exposed to ambient temperatures in said zone for vaporizing liquid refrigerant supplied thereto by extracting heat from said zone, conduit means interconnecting said condensing coils and heat source coils in plural refrigerant flow circuits between said compressor and evaporator including a cooling cycle circuit coursing refrigerant from said compressor discharge side through said condensing coils and evaporator in a first direction to the compressor auction side and a heating cycle circuit coursing refrigerant from said compressor discharge side through said evaporator in an opposite direction and through said heat source coils to said compressor suction side in by-passing relation to said condenser, and means controlling said conduit means to selectively direct, refrigerant flow through only said cooling cycle circuit and through only said heating cycle circuit during the major portions of said cooling and heating cycles respectively, and means for concurrently coupling said heat source coils and evaporator to the compressor section side and isolating the same from saidcondensing coils and compressor discharge side for a selected period at transitions between said cycles to evacuate any residual liquid refrigerant therefrom.

14. A reversible refrigeration system as defined in claim 13, wherein said cooling cycle circuit includes means connecting said heating coils between the outlet of said condensing coils and the inlet of said evaporator during said cooling cycle to sub-cool refrigerant coursing from the condenser to the evaporator.

15. A reversible refrigeration system as claimed in clai 14 wherein such heat source coils have an outlet conduit extending from the outlet of said heat source coils, the system including a suction conduit connected between the outlet ofthe evaporator and the compressor suction side, a three-way valve in said suction conduit concurrently communicating the evaporator outlet with the compressor suction side and disconnecting the said outlet conduit therefrom during the cooling cycle and disconnecting the evaporator outlet from the compressor suction side and connecting the outlet conduit therewith during the heating cycle.

16. A reversible refrigeration system as claimed in claim 15, wherein a condenser inlet conduit having an expansion device connects said outlet conduit of the heat source coils to the evaporator inlet, said inlet conduit including valve means opening the same during the cooling cycle, and closing the same during the heating cycle, and conduit means having a unidirectional flow control valve therein between the inlet of the evaporator and the inlet of said heat source, coils to convey refrigerant from said evaporator to said heat source coils in by-passing relation to said inlet conduit during the heating cycle and during said selected period. 17. A reversible refrigeration system as defined in claim 14, including a by-pass conduit connecting the compressor discharge side with said suction conduit between said three-way valve and said evaporator, said by-pass conduit having a valve therein closing the same during the cooling cycle and opening the same during the heating cycle.

18; A reversible refrigeration system as defined in claim 17, wherein said cooling cycle circuit includes a condenser inlet conduit connected to the compressor discharge side having a pressure responsive valve therein responsive to pressure differentials across the same set to open throughout said cooling cycle and during such portions of the heating cycle when condensing coil pressure exceeds compressor discharge pressure and to close during the remainder of the heating cycle.

19. A reversible refrigeration system as defined in claim 13, including a receiver, said conduit means including a first conduit connecting the outlet of said condenser with said receiver having check valve means therein permitting flow from saidcondenser to said receiver and preventing flow from the receiver to the condenser, a second conduit connecting said receiver with the inlet of said evaporator having said pressure reducing means thereinv and including a first control valve therein which is open during said cooling cycle and is closed during said heating cycle, a by-pass conduit coupled to said second conduit in bypassing relation to said pressure reducing means having valve means therein closing said by-p: ;s conduit during said cooling cycle and opening said by-pass conduit during said heating cycle, a third conduit connecting the inletof said heat source coils to said second conduit between said first control valve and said pressure reducing means having a second control valve therein for passing refrigerant to said heat source circuit coils only during the heating cycle and a pressure regulating valve therein, a continuously open conduit connecting the outlet of said heat source coils to the suction side of said compressor, and vent conduit means connecting said receiver to the discharge side of said compressor having check valve means therein opening only when receiver pressure is higher than compressor discharge pressure to promptly reduce receiver pressure at the onset of the heating cycle.

20. In a reversible refrigeration system as claimed in claim 13, said conduit means including a first conduit connecting the compressor discharge side to the inlet of said condensing coils having a pressure responsive valve therein responsive to pressure differentials across the same to open when condensing coil pressure exceeds comprcssor discharge pressure, a second conduit connecting the outlet of the condensing coils to the inlet of said heat source coils having a first control valve therein which is open during the cooling cycle and closed during the heating cycle, a third conduit connecting the outlet of said heat source coils to the inlet of the evaporator having pressure reducing means and a second control valve therein which is open during said cooling cycle and closed during the heating cycle, a fourth conduit connecting the inlet of said evaporator with the inlet of said heat source coils between the latter and said first control valve having a pressure regulating valve therein and a third valve which closes the fourth conduit to refrigerant llow during the coolingcycle and opens the fourth conduit to flow from the evaporator to the heat source coils during the heating cycle, a fifth conduit extending from the outlet of said heat source coil, and valve means for connecting said outlet conduit directly to said compressor suction side during the heating cycle.

21. A reversible refrigeration system as defined in claim 20, including a conduit connecting the inlet of said heat source coils directly with said compressor discharge side having a valve therein controlled responsive to condens ing pressure and closed during said heating cycle to admit refrigerant from the compressor discharge side to the heat source coils in lay-passing relation to the condensing coils when said pressure responsive valve in said first conduit closes whereby the heat source coils operate as the sole condensing component of the system.

iside having a valve therein controlled responsive to condensing pressure and closed during said heating cycle to selectively admit refrigerant from the compressor discharge side to said second set of coils in lay-passing relacircuit coursing refrigerant from said compressor disa lowside portion wherein lower pressures prevail, said first system portion having an indoor coil employed as a condenser during said heating cycle and as an evaporator during said cooling cycle, said second system portion having outdoor coil means for evaporating refrigerant during the heating cycle and for condensing refrigerant during the cooling cycle, fluid circuit means including connecting conduits and valves for interconnecting said indoor and outdoor coils with said compressor in plural refrigerant flow circuits including a cooling cycle circuit connecting the outlet of said indoor coil to said compressor suction side and coursing reirigexant from said compressor discharge side through said second system portion and said indoor coil in a first direction to the compressor suction side during said cooling cycle and a heating cycle charge side through said indoor coilin an opposite direction and through .said second system portion to said compressor suction side during said heating cycle, and control means conditioning said fluid circuit means to reduce pressure in said highside portion to a level rapidly evaporating all residual liquid refrigerant therein immediately before each reversal of said system from the heating cycle to the cooling cycle for evacuating said highside portion before connecting said indoor coil outlet to said compressor suction side.

tion to said first set of coils whereby the second set of coils operates as the sole condensing component of the system. l

23. A reversible refrigeration system having a cooling cycle and a heating cycle, comprising a compressor having discharge and suction sides, said system including a first system portion forming during said heating cycle a highside portion wherein higher pressures prevail, and a second system portion forming during saidheating cycle References Cited Redfern 62-160 WILLIAM J. WYE, Primary Examiner.-

Claims

1. A REVERSIBLE REFRIGERATION SYSTEM HAVING A COOLING CYCLE AND A HEATING CYCLE, COMPRISING A COMPRESSOR HAVING DISCHARGE AND SUCTION SIDES, AN EVAPORATOR LOCATED IN A SPACED TO BE CONDITIONED HAVING AN OUTLET SELECTIVELY CONNECTIBLE TO THE COMPRESSOR SUCTION SIDE DURING THE COOLING CYCLE AND TO THE COMPRESSOR DISCHARGE SIDE DURING THE HEATING CYCLE, A SINGLE HEAT TRANSFER DEVICE OF THE FIN AND TUBE TYPE EXPOSED TO AMBIENT TEMPERATURES IN A ZONE OUTSIDE SAID SPACE HAVING FIRST AND SECOND INDEPENDENT SETS OF CONDUIT COILS AND PLURAL HEAT TRANSFER FINS DEFINING A FIN BUNDLE FOR SAID DEVICE WITH THE FINS DISPOSED IN HIGHLY THERMALLY CONDUCTIVE PHYSICAL CONTACT WITH THE COILS OF BOTH SAID SETS FORMING THE EXTENDED SURFACES THEREOF WHEREBY SAID FIN BUNDLE IS SHARED BY BOTH SAID SETS OF COILS, SAID FIRST SET OF COILS FORMING CONDENSING COILS DURING THE COOLING CYCLE FOR CONDENSING COMPRESSED REFRIGERANT VAPOR SUPPLIED THERETO AND SAID SECOND SET OF COILS FORMING HEAT SOURCE COILS DURING THE HEATING CYCLE FOR VAPORIZING LIQUID REFRIGERANT SUPPLIED THERETO BY EXTRACTING HEAT FROM SAID ZONE, A FIRST REFRIGERANT FLOW CIRCUIT INCLUDING SAID FIRST SET OF COILS SELECTIVELY INTERCONNECTED BETWEEN THE COMPRESSOR DISCHARGE SIDE AND THE INLET OF THE EVAPORATOR DURING ONLY THE COOLING CYCLE, A SECOND REFRIGERANT FLOW CIRCUIT INCLUDING SAID SECOND SET OF COILS SELECTIVELY CONNECTED BETWEEN THE INLET OF THE EVAPORATOR AND THE COMPRESSOR SUCTION SIDE DURING THE HEATING CYCLE TO VAPORIZE ANY LIQUID REFRIGERANT RETURNING FROM THE EVAPORATOR TO THE COMPRESSOR, AND MEANS FOR DISCONNECTING THE INLET OF THE CONDENSER FROM THE COMPRESSOR DISCHARGE SIDE DURING THE HEATING CYCLE.