WO1997041398A1

WO1997041398A1 - Defrost operation for heat pump and refrigeration systems

Info

Publication number: WO1997041398A1
Application number: PCT/US1997/007384
Authority: WO
Inventors: Alexander P. Rafalovich; Oleg Mankovskiy
Original assignee: Store Heat And Produce Energy, Inc.
Priority date: 1996-05-02
Filing date: 1997-05-02
Publication date: 1997-11-06
Also published as: AU3056997A

Abstract

Described are preferred space conditioning systems such as heat pump (10) or refrigeration systems (50), which control the operation of components thereof as condensers (5)/subcoolers (9) or evaporators (8) to achieve advantageous defrost cycles.

Description

DEFROST OPERATION FOR HEAT PUMP AND REFRIGERATION

SYSTEMS

BACKGROUND

The present invention relates in general to space conditioning systems, including for instance heat pump systems. More particularly, the invention relates to space conditioning systems which include defrost operations such as those used in air source heat pump systems or refrigeration systems.

As further background, air source heat pumps, including central systems, packaged terminal heat pumps, room split heat pumps and window heat pumps, extract heat from outdoor air and deliver it to an indoor space to be heated, or they cool the indoor space by extracting indoor heat and delivering it outdoors. It is widely recognized that when the surface temperature of an outdoor heat exchanger coil falls below about 32°F (0°C) and the relative humidity of the outdoor air is above some certain level, water vapor from the air condenses on the coil as ice (frost) . In turn, frost reduces the heat transfer rate and blocks the airflow through the outdoor heat exchanger. Hence ice on an outside coil must periodically be removed in a defrost operation, and in the case of window heat pumps they are generally not operable at temperatures below about 35°F. The most widely used method for defrosting the coil in air source heat pumps is known as a "hot gas defrost" operation, and involves reversing the heat pump cycle to direct hot gaseous refrigerant exiting the compressor to the outdoor coil which in the normal heat pump operation is an evaporator. The method itself is very simple. However, there are several disadvantages. First, the method can be complicated to control, requiring the use of a timer, a refrigerant temperature sensor, a low pressure sensor, etc. Second, the method leads to a reduction of the overall heating capacity of heat pumps by 5-10%. Third, for comfortable conditions it is necessary to run a supplemental heater to offset conditioning of the indoor space with cold air which occurs during the reverse cycle. Fourth, the method places additional strain on the compressor and motor due the frequent reversing of the refrigeration cycle. Fifth, the method can lead to reduction in the reliability of heat exchangers in the system due the sharp temperature fluctuations which occur upon repeated reversal of the cycle. Sixth, it is often impossible to run simultaneously both an auxiliary heater and ref^rigeration compressor, especially in room heat pumps. Resistive .'.eat has also been used to defrost heat exchangers in such systems. However, the use of an electrical heater to defrost outdoor heat exchanger is very difficult with finned coils. Hence capital expenses are increased on a heat pump with an electrical heater while reliability is compromised. In addition, the capacity of a heat pump is still reduced considerably.

Evaporators of conventional refrigeration systems likewise must periodically defrosted. Again, hot gas defrost methods or resistive heat are the most commonly used means for these defrost cycles, and present similar problems in conventional refrigeration systems.

In light of this background, there is a need for improved defrost operations which avoid some or all of the disadvantages of prior systems. The present invention addresses this need.

SUMMARY OF THE INVENTION

Accordingly, one preferred embodiment of the present invention provides a space conditioning system operable in a primary space conditioning cycle and a subcooling defrost cycle. The system includes a compressor, a condenser which condenses compressed refrigerant from the compressor, and a heat exchanger which evaporates refrigerant exiting the condenser during the primary space conditioning cycle, and which subcools (and optionally at least partially condenses) refrigerant exiting the condenser during the subcooling defrost cycle. The system also includes an evaporation device which evaporates subcooled refrigerant exiting the heat exchanger during the subcooling defrost cycle, a first fluid path which returns refrigerant exiting the heat exchanger to the compressor during the primary space conditioning cycle, and a second fluid path which returns refrigerant exiting said evaporation device to the compressor during the subcooling defrost cycle. Such systems can be, for example, heat pump or refrigeration systems, and the evaporation device can be either a thermal storage device or a third heat exchanger.

In one preferred aspect, the invention provides a heat pump system operable in at least one of a heating and a cooling mode. In accordance with the invention, the heat pump system includes a primary refrigerant circuit including a compressor, a first four-way reversing valve, and in serial connection, a first heat exchanger, a first metering device, and a second heat exchanger. The system also includes a first bypass circuit including a second four-way reversing valve, a thermal storage device with a thermal storage medium, and a second metering device. Means are also provided for controlling operation of the first four-way reversing valve to operate the first heat exchanger either as a condenser in a heating mode to supply positive thermal potential to a conditioned space, or as an evaporator in a cooling mode to supply negative thermal potential to the conditioned space. Control means of the system control the operation of the second four-way reversing valve to manage the thermal storage device to operate either as a subcooler (and optionally also at least partially a condenser) or an evaporator. In the preferred embodiment, the second reversing valve is operable in a defrost cycle to cause condensed refrigerant exiting the first heat exchanger to pass to the second heat exchanger and there subcool (operating to defrost the second heat exchanger) . Thereafter, the subcooled refrigerant is expanded in the second metering device, evaporated in the thermal storage device, and passes back to the compressor. During the heating cycle (and not during defrost) , the second reversible valve is operable to cause condensed refrigerant from the first heat exchanger to pass to the thermal storage device, where it is subcooled (and optionally at least partially condensed) when the thermal storage device carries negative thermal potential, thereby rejecting heat to the thermal storage device which can later be used in a defrost cycle. After exiting the thermal storage device, the refrigerant is expanded in the second metering device, evaporated in the second heat exchanger, and returns thereafter to the compressor.

Another preferred embodiment of the invention provides a heat pump system operable in at least one of a heating and a cooling mode, which includes a refrigerant circuit including a compressor, a first four-way reversing valve, and in serial connection, a first heat exchanger, a first metering device, and a second heat exchanger. A first bypass circuit is also provided, including a second four-way reversing valve, a third heat exchanger, and a second metering device. The system includes means for controlling operation of the first four-way reversing valve to operate the first heat exchanger either as a condenser in heating mode to supply positive thermal potential to a conditioned space or as an evaporator to supply negative thermal potential to a conditioned space; and means for controlling operation of the second four-way reversing valve in the heating mode to operate either the second heat exchanger as a subcooler (and optionally also at least partially as a condenser) and the third heat exchanger as an evaporator, or the third heat exchanger as a subcooler (optionally at least partially a condenser) and the second heat exchanger as an evaporator. In a preferred embodiment, the second reversing valve is operable in a defrost cycle to cause condensed refrigerant exiting the first heat exchanger to pass to the second heat exchanger and there subcool (operating to defrost the second heat exchanger) . Thereafter, the subcooled refrigerant is expanded in the second metering device, evaporated in the third evaporator, and passes back to the compressor. A similar operation can then be used to defrost the third heat exchanger by reversing the flow of refrigerant after the condenser (i.e. to operate the third heat exchanger as a subcooler, optionally also at least partially as a condenser, and the second heat exchanger as an evaporator) .

Another preferred embodiment of the invention provides a method for heating a space using a heat pump system having a thermal storage device. In the invention, the method includes the steps of (i) charging the thermal storage device with positive thermal potential during operation of the thermal storage device as a subcooler (optionally also at least partially as a condenser) in the system; (ii) discharging the charged positive thermal potential from the thermal storage device during operation of the thermal storage device as an evaporator and an outside evaporator as a subcooler (optionally also at least partially a condenser) , whereby the outside evaporator is defrosted during said discharging step.

Still another preferred embodiment of the invention provides a method for defrosting a frosted evaporator in a refrigeration system, which includes the step of passing warm condensed (liquefied) refrigerant through the evaporator so as to cause the frosted evaporator to subcool the refrigerant, the refrigerant thereby rejecting heat to and defrosting the evaporator. The systems and methods of the invention provide space conditioning systems, such as heat pump, refrigeration and air conditioning systems, which incorporate advantageous defrost operations which increase system capacity while also avoiding imparting large thermal fluctuations to system components such as heat exchangers. Additional features, advantages and embodiments of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram which illustrates one embodiment of the present invention employing a thermal storage device for defrost of an outdoor heat exchanger of a heat pump.

Fig. la is a diagram which illustrates another embodiment of the present invention employing a thermal storage device for both defrost of an outdoor heat exchanger of a heat pump in a heating mode and subcooling in a cooling mode.

Fig. lb is a diagram which illustrates another embodiment of the present invention employing a thermal storage device for defrost of an outdoor heat exchanger of a heat pump. Fig. 2 is a diagram illustrating another embodiment of the invention using an additional outdoor heat exchanger in a defrost operation for a heat pump.

Fig. 3 is a diagram which illustrates another embodiment of the invention wherein a thermal storage device is used for defrost of an evaporator of a refrigeration system.

Fig. 4 is a diagram which illustrates another embodiment of the invention wherein a refrigeration system employs an additional heat exchanger for a defrost operation.

Fig. 5 is a diagram illustrating another embodiment of the invention wherein some of a plurality of evaporators of a refrigeration system are defrosted during operation as subcoolers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to certain preferred embodiments thereof and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations, modifications, and further applications of the principles of the invention being contemplated as would normally occur to one skilled in the art to which the invention pertains.

One preferred arrangement for a heat pump with a defrost system is shown in Fig. 1. A heat pump system 10 includes a compressor 1 discharging compressed refrigerant through a conduit 21 to a first four-way reversing valve 3. The first reversing valve 3 communicates compressed refrigerant to either conduit 23 when the heat pump is operating in a heating mode or to conduit 25 when the heat pump is operating in a cooling mode. In the heating mode, after passage through conduit 23, hot compressed refrigerant flows to a first heat exchanger 5 where it rejects heat to a space and condenses. Still warm liquid refrigerant then passes through conduit 29. A first metering device 51, which may be a thermostatic expansion valve expanding refrigerant in the direction of first heat exchanger 5 or a check valve with a capillary tube or orifice, prevents refrigerant from flowing into conduit 27. In conduit 29 refrigerant passes through an optional check valve 48 and an optional pressure reducing device 17, e.g., an orifice, and then flows to second four-way reversing valve 7. During a thermal storage charging cycle, four-way valve 7 connects conduit 29 and conduit 35 such that liquid refrigerant flows to a thermal storage device 9 containing a thermal storage medium, e.g., phase change material, as, for example, water. In the thermal storage device 9, refrigerant subcools and conveys heat to the thermal storage medium, e.g., heat from the refrigerant melts ice when water is used as a thermal storage medium. Subcooled liquid refrigerant exiting thermal storage device 9 passes through a second metering device 13 which can for example include a capillary tube, an orifice, or two thermostatic expansion valves with check valves, or a check-flo-rater 14 and a check-flo- rater 15. In second metering device 13, liquid refrigerant expands and then is evaporated in second heat exchanger 8, after which it passes through conduit 31, second four-way valve 7, conduit 25, first four-way valve 3, and conduit 33 to compressor 1. The above- described cycle can then be repeated.

If the thermal storage medium in thermal storage device 9 does not have negative thermal potential, e.g., there is no ice left (only warm water), it will not subcool the refrigerant in the thermal storage device 9 and thus refrigerant flows in a conventional heat pump cycle. If the evaporating temperature in second heat exchanger 8 is below about 32°F (0°C) , ice may start to form on the outside surface of a coil of heat exchanger 8.

If the thermal storage medium is charged by positive thermal potential, such may be used to defrost heat exchanger 8 and to increase the heating capacity of the heat pump. In such an operation, second four- way valve 7 connects conduit 29 with conduit 31 and conduit 35 with conduit 25. Liquid refrigerant after condensing in first heat exchanger 5 flows to second heat exchanger 8, where the refrigerant subcools, thereby defrosting second heat exchanger 8 by rejecting heat. To reduce heat flux to cold air, a fan 65 for moving air through heat exchanger 8 during other conventional operations of system 10 may be off. After second heat exchanger 8, refrigerant flows through second metering device 13 to thermal storage 9 which now acts as an evaporator. Refrigerant evaporates in thermal storage device 9, thereby cooling down the thermal storage medium, e.g. freezing water. Refrigerant thereafter flows through conduits 35, 25 and 33 and returns to compressor 1. An optional heater 41 with an external source of heating energy (e.g. an electrical heater or gas heater, etc.) can be provided, which can be operated if the positive thermal energy saved during the charging cycle in the thermal storage device 9 is not sufficient to complete the defrost operation. Another way to increase energy flow and the rate of energy saving in thermal storage device 9 during a thermal storage charge period, and/or to increase the defrost rate in second heat exchanger 8 during a thermal storage discharge, is to use thermal storage device 9 and/or second heat exchanger 8 partly as a condenser in addition to subcooling. In this case, a portion of the gaseous refrigerant is caused to condense after the first heat exchanger 5 in thermal storage device 9 or in the second heat exchanger 8. For this operation there is no pressure reducing device 17, or the extent of the pressure drop provided by this device 17 is reduced. Another method to increase the amount of thermal energy stored in thermal storage device 9 when partly charging thermal storage device 9 by its use as a condenser involves the use of an optional by-pass line 37 with a solenoid valve 43. Solenoid valve 43 can be positioned to allow at least part of the hot gaseous refrigerant after compressor 1 to go through conduit 37 to thermal storage device 9, condensing there and rejecting additional heat energy to the thermal storage medium. This same procedure can also be used to push liquid refrigerant out of the thermal storage device 9 before reversing the flow of liquid refrigerant to heat exchanger 8 using second reversing valve 1 , or to push liquid refrigerant from heat exchanger 8 before reversing refrigerant flow to thermal storage device 9. In addition, this same by-pass line 37 with valve 43 may be used to accelerate a defrost operation. In this operation, refrigerant flows after compressor 1 through the first four-way valve 3 and then to conduit 25, now connected to conduit 21. Then refrigerant passes to the second four-way valve 7, now connecting conduits 25 and 31. Hot gaseous refrigerant then cools and liquefies in the second heat exchanger 8, thereby defrosting the outside surface of the heat exchanger 8. After expansion in metering device 13, refrigerant then flows through thermal storage device 9, which acts as an evaporator, to the second four-way valve 7. From valve 7 and conduit 29 refrigerant passes through by¬ pass line 37 with valve 43 in open position to the first four-way valve 3 and conduit 33 back to compressor 1.

When heat pump system 10 is operating in a cooling mode, the first reversing valve 3 communicates compressed refrigerant to conduit 25. From conduit 25 the refrigerant flows to second reversing valve 7 which now connects conduit 25 and conduit 31. Then gaseous refrigerant condenses in the second heat exchanger 8 and flows to conduit 27. If there is an optional check valve 48 in line 29, refrigerant does not flow through thermal storage device 9. In the absence of check valve 48, some amount of refrigerant may flow through thermal storage device 9. After conduit 27, refrigerant reaches first metering device 51 where it expands and flows to the first heat exchanger 5, which now acts as an evaporator. Further, refrigerant flows through conduit 23 and first four-way reversing valve 3 and to conduit 33 and then to the suction side of compressor 1. A controller 19 controls positioning of first and second reversing valves 3 and 7, as well as a coil of solenoid valve 43, the fan 65 and optional heater 41. Fig. la illustrates another heat pump system 10a, having elements similar and correspondingly numbered to those illustrated in Fig. 1. In system 10a, thermal storage device 9 can be used to increase the capacity of the heat pump system in a cooling mode. In addition to the elements noted ^sin system 10 of Fig. 1, two further bypass lines 34 and 38 are provided, having respective solenoid valves 36 and 40. To charge the thermal storage device 9 with negative thermal potential, refrigerant after exiting compressor 1 passes through first reversing valve 3 in a cooling mode, and to heat exchanger 8 which functions as a condenser. Valve 36 is in a closed position, and valve 43 is in an open position thus allowing refrigerant to flow from by-pass line 37 to compressor 1, and not allowing flow through heat exchanger 5. Thus, liquid refrigerant after exiting the condenser 8 expands in the metering device 13 and evaporates in the thermal storage device 9 extracting heat from the thermal storage medium. At peak demand for cooling, valve 36 is open, and valve 40 is positioned so as to connect conduit 38 to that part of conduit 27 leading to metering device 51, and preventing the flow of refrigerant through the other part of conduit 27. Valve 43 is positioned to allow refrigerant to flow through conduit 23 and to block flow through conduit 37. In this manner, refrigerant exiting heat exchanger/condenser 8 flows throughout conduit 34 to thermal storage device 9, is there subcooled, and then passes to metering device 51, evaporator 5 and then back to compressor 1.

Another heat pump with a defrost system is shown in Fig. lb. A heat pump system 10b includes a compressor 1 discharging compressed refrigerant through a conduit 21 to a first four-way reversing valve 3. The first reversing valve 3 communicates compressed refrigerant to either conduit 23 when the heat pump is operating in a heating mode or to conduit 25 when the heat pump is operating in a cooling mode. In the heating mode, after passage through conduit 23, hot compressed refrigerant flows to a first heat exchanger 5 where it rejects heat to a space and condenses. Still warm liquid refrigerant then passes through conduit 29. A check valve 48, prevents refrigerant from flowing into conduit 27. After conduit 29 refrigerant passes through an optional pressure- reducing device 17, e.g. and orifice, and then flows to second four-way reversing valve 7. During a thermal storage charging cycle, four-way valve 7 connects conduit 29 and conduit 35 such that liquid refrigerant flows to a thermal storage device 9 containing a thermal storage medium, e.g., phase change material, as, for example, water. In the thermal storage device 9, refrigerant subcools and conveys heat to the thermal storage medium, e.g., heat from the refrigerant melts ice when water is used as a thermal storage medium. Subcooled liquid refrigerant exiting thermal storage device 9 passes through a second metering device 13 which can for example include a capillary tube, an - I I

orifice, or two thermostatic expansion valves with check valves, or a check-flo-rater 14 and a check-flo- rater 15. In second metering device 13, liquid refrigerant expands and then is evaporated in second heat exchanger 8, after which it passes through conduit 31, second four-way valve 7, conduit 25, first four-way valve 3, and conduit 33 to compressor 1. The above- described cycle can then be repeated.

If the thermal storage medium in thermal storage device 9 does not have negative thermal potential, e.g., there is no ice left (only warm water), it will neither condense nor subcool the refrigerant in the thermal storage device 9 and thus refrigerant flows in a conventional heat pump cycle. If the evaporating temperature in second heat exchanger 8 is below about 32°F (0°C), ice may start to form on the outside surface of a coil of heat exchanger 8.

If the thermal storage medium is charged with positive thermal potential, such may be used to defrost heat exchanger 8 and to increase the heating capacity of the heat pump. In such an operation, second four- way valve 7 connects conduit 29 with conduit 31 and conduit 35 with conduit 25. Liquid refrigerant after condensing in first heat exchanger 5 flows to second heat exchanger 8, where the refrigerant subcools, thereby defrosting second heat exchanger 8 by rejecting heat. To reduce heat flux to cold air, a fan 65 for moving air through heat exchanger 8 during other conventional operations of system 10 may run at a reduced speed or may be off. After second heat exchanger 8, refrigerant flows through second metering device 13 to thermal storage 9 which now acts as an evaporator. Refrigerant evaporates in thermal storage device 9, thereby cooling down the thermal storage medium, e.g. freezing water. Refrigerant thereafter flows through conduits 35, 25 and 33 and returns to compressor 1. Another way to increase energy flow and the rate of energy saving in thermal storage device 9 during a thermal storage charge period, and/or to increase the defrost rate in second heat exchanger 8 during a thermal storage discharge, is to reduce the speed of a fan 67 moving air through the first heat exchanger 5 or to turn this fan off. In this manner, thermal storage device 99 will act at least partly as a condenser in addition to subcooling. On the other hand, first heat exchanger 5 will act as a desuperheater and partly as a condenser.

In some heat pumps, e.g., PTAC units or window heat pumps, fans for both first and second heat exchangers 67 and 65 are driven by the same motor. In this case speed reduction or stoppage of both fans will be done simultaneously. Heat pump 10b may also have a suction accumulator (not shown) in line 33 between suction in the compressor 1 and the first reversing valve 3. A filter/dryer (not shown) may be also installed either in the discharge line 21 or in suction line 33. An auxiliary electrical or gas heater (not shown) may be also employed after the first (inside) heat exchanger 5. When heat pump system 10b is operating in a cooling mode, the first reversing valve 3 communicates compressed refrigerant to conduit 25. From conduit 25 the refrigerant flows to second reversing valve 7 which now connects conduit 25 and conduit 31. Then gaseous refrigerant condenses in the second heat exchanger 8 and flows through metering device 13 and then to conduit 27 and further through check valve 48 to first heat exchanger 5. Some amount of refrigerant may also flow through thermal storage device 9. Expanded refrigerant flows through the first heat exchanger 5, which now acts as an evaporator. Further, refrigerant flows through conduit 23 and first four-way reversing valve 3 and to conduit 33 and then to the suction side of compressor 1. A controller 19 controls positioning of first and second reversing valves 3 and 7, as well as fans 67 and 65.

Change of the positioning of the second reversing valve 7 can be controlled on a temperature-timing basis. A temperature sensor (not shown) attached to the outside coil (second heat exchanger 8) signals when reversing valve 7 should be activated. Further, a timer (not shown) can control the time share between charging and discharging cycles of the thermal storage 9, activating and deactivating reversing valve 7 and managing both fans 65, 67 to reduce the speed of or stop the fans and thereafter return them to original speed, as appropriate. If the temperature sensor senses that the temperature of coil 8 is above a predetermined set point, valve 7 is deactivated and refrigerant will flow initially through thermal storage device 9 and then through outside heat exchanger 8, which acts as an evaporator. Another heat pump system 20 is illustrated in Fig. 2. Similar to the system of Fig. 1, system 20 includes a compressor 1 discharging compressed refrigerant through conduit 21 to first four-way reversing valve 3. The first reversing valve 3 communicates compressed refrigerant to either conduit 23 when the heat pump is operating in a heating mode or to conduit 25 if the heat pump is operating in a cooling mode. After conduit 23, hot compressed refrigerant flows to first heat exchanger 5 where it rejects heat to a space and condenses. First metering device 51 prevents refrigerant to flow in conduit 27. Still warm liquid refrigerant flows through conduit 29 with check valve 48 to second four-way valve 7. Four- way valve 7 connects conduit 29 either to conduit 35 leading to third heat exchanger 61, or to conduit 31 leading to second heat exchanger 8. During part of the heating cycle, warm liquid refrigerant flows to the second heat exchanger 8 where it subcools, simultaneously melting ice on the outside heat transfer surface (defrost) . The refrigerant then flows through metering device 13, e.g., check-flo-raters 15 and 14, and expanded refrigerant passes to third heat exchanger 61 which acts as an evaporator. After heat exchanger 61, refrigerant vapor flows through second reversing valve 7, conduit 25, first reversing valve 3, and conduit 33 and back to compressor 1. After defrosting the outside surface of heat exchanger 61, in a second part of the heating cycle, reversing valve 7 connects conduit 29 with conduit 35 and conduit 31 with conduit 25, such that warm liquid refrigerant flows from conduit 29 to the third heat exchanger 61 where it subcools, simultaneously defrosting ice on the outside heat transfer surface of exchanger 61. The refrigerant then passes through metering device 13, e.g., check- flo-raters 15 and 14, and expanded refrigerant flows to the second heat exchanger 8 which now acts as an evaporator. After heat exchanger 8, vaporized refrigerant flows through second reversing valve 7, conduit 25, first reversing valve 3, and conduit 33 and back to compressor 1. Fans 63 and 65, which flow air through third and second heat exchangers, may be controllable. For example, during the function of third heat exchanger 61 as a subcooler, fan 63 is off, and fan 65 is on. Alternatively, only a single fan with reversible flow may be used for air flow selectively to heat exchangers 8 and 61. Optional by- pass line 37 with three-way valve 43 allows part or all hot gaseous refrigerant after compressor 1 to pass to the second or third heat exchanger to push liquid refrigerant out of the heat exchanger before reversing liquid refrigerant flow to the other heat exchanger with second reversing valve 7.

Operation of the heat pump 20 in the cooling mode is similar to the cooling mode operation of the heat pump 10 (Fig. 1) . First reversing valve 3 communicates compressed refrigerant to conduit 25. From conduit 25, refrigerant flows to second reversing valve 7 which now connects conduit 25 and conduit 31. Then, gaseous refrigerant condenses in the second heat exchanger 8 and flows to conduit 27. Because of check valve 48 in line 29, refrigerant does not flow through third heat exchanger 61. After conduit 27, refrigerant reaches first metering device 51 where it expands and flows to first heat exchanger 5, which now acts as an evaporator. The refrigerant then flows through conduit 23 and first four-way reversing valve 3 to a conduit 33 and to the suction side of compressor 1. A controller 19 controls positioning of first 3 and second 7 reversing valves, and also fans 63 and 65 and optional valve 43.

Heat pump system 20 may also operate in the fashion presented in Fig. lb, with the difference that the thermal storage 9 in Fig. lb is substituted by the third heat exchanger 61 with a fan 63 of Fig. 2.

Figures 3 and 4 illustrate defrost systems and operations for refrigeration systems. Except where specifically discussed herein, the features of operation of defrost systems and methods of the invention for refrigeration is analogous to that in heat pumps as discussed above, and components of the systems of Figures 3 and 4 are numbered correspondingly to those of the systems of the prior Figures, except being within the 100 and 200 series, e.g. 101 (Fig. 3) and 201 (Fig 4) correspond to 1 (Fig. 1), etc.

Refrigeration system 30 of Fig 3 is similar to the heat pump 10 of Fig. 1, with the exception of the omission of line 27 and first four-way reversing valve 3. Refrigerant after compressor 101 and condenser 105 flows to a four-way reversing valve 107 which in turn connects either conduit 129 with conduit 135 and conduit 131 with conduit 125, or conduit 129 with conduit 131 and conduit 135 with conduit 125. During one part of a refrigeration cycle, refrigerant after condenser 105 flows to a thermal storage device 109 containing a thermal storage medium. In thermal storage device 109, refrigerant subcools and transfers heat to the thermal storage medium, e.g., melting ice. After thermal storage device 109, refrigerant flows to metering device 113 which is an analogue of the metering device 13 (Fig. 1). Expanded refrigerant then flows to heat exchanger 108 which is acts as an evaporator. Air to be cooled is passed across heat exchanger 108 with the assistance of fan 165. After heat exchanger 108, refrigerant vapor passes to conduits 131 and 125 and back to compressor 101. During a second phase of the cycle, refrigerant after condenser 105 flows to the heat exchanger 108, subcools there and defrosts outside surfaces of heat exchanger 108, expands in metering device 113 and evaporates in thermal storage 109 thereby charging the thermal storage medium with negative potential. Fan 165 in this operation may be off. After thermal storage device 109, refrigerant flows back to compressor 101 as described above. A controller 119 controls positioning of the reversing valve 107 and the operation of fan 165, and optional valve 143. Fig. 4 illustrates another refrigeration system similar to heat pump system 20 (Fig. 2) with the exception of the omission of line 27 and first four-way reversing valve 3. Refrigerant after compressor 201 and condenser 205 flows to four-way reversing valve 207 which in turn connects either conduit 229 with conduit 235 and conduit 231 with conduit 225, or conduit 229 with conduit 231 and conduit 235 with conduit 225. During a first phase of a cycle, refrigerant after condenser 215 flows to second heat exchanger 261 which acts as a subcooler. During this period, fan 263 for moving air through heat exchanger 261 may be off. Refrigerant subcools in heat exchanger 261 and extracts heat to defrost its outside heat transfer surfaces, and flows to metering device 213 which is an analogue of metering device 13 (Fig. 2) . Expanded refrigerant then flows to first heat exchanger 208 which acts as an evaporator. Fan 265 moving air through heat exchanger 208 is now on. After evaporation, refrigerant vapor passes to conduits 231 and 225 and back to compressor 201.

During a second phase of the cycle, refrigerant after condenser 205 flows to the first heat exchanger 208, subcools there and defrosts outside surfaces of heat exchanger 208, expands in metering device 213 and evaporates in the second heat exchanger 261. Then, the refrigerant flows back to compressor 201 as described above. In this phase of the operation, fan 263 is on and fan 265 is off. A controller 219 controls positioning of the reversing valve and also the operation of fans 263 and 265, and valve 243 in optional bypass line 237.

Similar operations can be employed in a refrigeration system having three or more evaporators, as for example illustrated in Fig. 5. Refrigerant after compressor 301 and condenser 305 flows through an optional receiver 371 to conduit 329. After conduit 329, refrigerant passes either to liquid manifold 383, if valve 375 is open, or to conduit 393 and further to three-way valves 377, 379 and 381. In the normal refrigeration cycle, valve 375 is open, and three way valves 377, 379 and 381 connect evaporators 373, 361 and 308 to suction manifold 385 and prevent liquid refrigerant flow from conduit 393 to manifold 385. In this manner, liquid refrigerant expands in metering devices 314, 315 and 316, which can be thermostatic expansion valves or any other expansion devices, and evaporates in evaporators or evaporator groups 308, 361 and 373. Refrigerant then flows through three-way valves 377, 379 and 381 to manifold 385 and then to conduit 325 and to the suction side of compressor 301.

During a defrost operation, e.g. of evaporator 373, valve 375 is closed and three-way valve 377 is positioned to allow refrigerant flow from conduit 393 to conduit 395, and to prevent liquid refrigerant flow to manifold 385. Thus, after compressor 301, condenser 305, and optional receiver 371, liquid refrigerant flows through conduits 329, 393 and 395 to evaporator 373, is there subcooled thereby defrosting evaporator 373, and then flows through check valve 387 and to manifold 383. The refrigerant then flows to metering devices 315 and 316, whereafter the expanded refrigerant passes to evaporators 361 and 308 and is evaporated. The gaseous refrigerant then flows to manifold 385 and further through conduit 325 to the suction side of compressor 301. Of course, analogous subcooling operations can be carried out in the other evaporators for purposes of defrosting them. In addition, an optional bypass line 337 with valve 343 can allow all or part of the hot gaseous refrigerant after compressor 301 to pass to evaporator 373 to push liquid refrigerant out of this evaporator or a group of evaporators before reversing liquid refrigerant flow to the other groups of evaporators to implement defrost operations or revert to normal operation. As described before, a controller (not shown) can be provided to control the positioning of valves 375, 377, 379 and 381, as well as the operation of evaporator fans (not shown) and valve 343.

Claims

WHAT IS CLAIMED IS:

1. A space conditioning system operable in a primary space conditioning cycle and a subcooling defrost cycle, comprising: a compressor; a condenser which condenses compressed refrigerant from the compressor; a heat exchanger which evaporates refrigerant exiting the condenser during the primary space conditioning cycle, and which subcools refrigerant exiting the condenser during the subcooling defrost cycle; an evaporation device which evaporates subcooled refrigerant exiting the heat exchanger during the subcooling defrost cycle; a first fluid path which returns refrigerant exiting the heat exchanger to the compressor during the primary space conditioning cycle; and a second fluid path which returns refrigerant exiting said evaporation device to the compressor during the subcooling defrost cycle.

2. The system of claim 1 wherein said evaporation device is a thermal storage device having a thermal storage medium.

3. The system of claim 1 wherein said evaporation device is a heat exchanger.

4. The system of claim 1, which is a heat pump system operable in at least a heating mode for heating a space to be conditioned, comprising: a compressor; a condenser for condensing compressed refrigerant from the compressor and providing positive thermal potential to the space to be conditioned during the heating mode; a refrigerant loop for receiving condensed refrigerant from the condenser during the heating mode, the refrigerant loop including a thermal storage device, a heat exchanger and a metering device in between the thermal storage device and heat exchanger; means for causing refrigerant flow in first and second directions in the loop to provide thermal storage charging and discharging cycles; wherein during the thermal storage charging cycle refrigerant flows in the first direction and the thermal storage device and heat exchanger operate as a subcooler and or condenser and an evaporator, respectively, whereby the thermal storage device can be charged with positive thermal potential; wherein during the thermal storage discharging cycle refrigerant flows in the second direction in the loop and the thermal storage device and heat exchanger operate as an evaporator and a subcooler and/or condenser, respectively, whereby operation of the heat exchanger as a subcooler can defrost the second heat exchanger; and means for returning refrigerant exiting refrigerant loop to the compressor.

5. The system of claim 1, which is a heat pump system operable in at least one of a heating and a cooling mode, the heat pump system comprising: a refrigerant circuit including a compressor, a first four-way reversing valve, and in serial connection, a first heat exchanger providing said condenser in a heating mode, a first metering device, and a second heat exchanger; a first bypass circuit including a second four-way reversing valve, a thermal storage device with a thermal storage medium, and a second metering device; means for controlling operation of the first four- way reversing valve to operate the first heat exchanger either as a condenser in the heating mode to supply positive thermal potential to a conditioned space, or as an evaporator in a cooling mode to supply negative thermal potential to the conditioned space; and control means for controlling operation of the second four-way reversing valve to manage the thermal storage device to operate either as a subcooler or an evaporator.

6. A heat pump system of claim 5, wherein the first bypass circuit further comprises a pressure regulating device between the first heat exchanger and the second four-way valve to reduce refrigerant pressure before subcooling.

7. A heat pump system of claim 5, further comprising a fan operable to move air through the second heat exchanger and means for controlling operation of the fan.

8. A heat pump system of claim 5 wherein the thermal storage further comprises an external source of heat.

9. A heat pump system of claim 5 further comprising a second bypass circuit with a valve positioned between the first four-way valve and the first heat exchanger to operate the thermal storage device or the outdoor heat exchanger as a condenser, and means for controlling operation of the valve.

10. A system of claim 1, which is a heat pump system operable in at least one of a heating and a cooling mode, the heat pump system comprising: a refrigerant circuit including a compressor, a first four-way reversing valve, and in serial connection, a first heat exchanger having associated therewith a fan for moving air through the first heat exchanger, a check valve, a metering device, and a second heat exchanger having associated therewith a fan for moving air through the second heat exchanger; a first bypass circuit including a second four-way reversing valve, a thermal storage device with a thermal storage medium; means for controlling operation of the first four- way reversing valve to operate the first heat exchanger either as a condenser in a heating mode to supply positive thermal potential to a conditioned space, or as an evaporator in a cooling mode to supply negative thermal potential to the conditioned space; and control means for controlling operation of the second four-way reversing valve to manage the thermal storage device to operate either (i) as a condenser and/or a subcooler or (ii) as an evaporator, and for controlling the speed of said fans.

11. A heat pump system of claim 2 wherein the thermal storage medium is a phase change material.

12. The system of claim 1, which is a heat pump system operable in at least one of a heating and a cooling mode, the heat pump system comprising: a refrigerant circuit including a compressor, a first four-way reversing valve, and in serial connection, a first heat exchanger, a first metering device, and a second heat exchanger; a first bypass circuit including a second four-way reversing valve, a third heat exchanger, and a second metering device; means for controlling operation of the first four- way reversing valve to operate the first heat exchanger either as a condenser in heating mode to supply positive thermal potential to a conditioned space or as an evaporator to supply negative thermal potential to a conditioned space; means for controlling operation of the second four-way reversing valve in the heating mode to operate either the second heat exchanger as a subcooler and the third heat exchanger as an evaporator, or the third heat exchanger as a subcooler and the second heat exchanger as an evaporator.

13. The system of claim 1, which is a heat pump system operable in at least one of a heating and a cooling mode, the heat pump system comprising: a refrigerant circuit including a compressor, a first four-way reversing valve, and in serial connection, a first heat exchanger, a check valve, and a second heat exchanger; a first bypass circuit including a second four-way reversing valve and a third heat exchanger; means for controlling operation of the first four- way reversing valve to operate the first heat exchanger either as a condenser in heating mode to supply positive thermal potential to a conditioned space or as an evaporator to supply negative thermal potential to a conditioned space; means for controlling operation of the second four-way reversing valve in the heating mode to operate either the second heat exchanger as a condenser and/or subcooler and the third heat exchanger as an evaporator, or the third heat exchanger as a condenser and/or subcooler and the second heat exchanger as an evaporator.

14. A heat pump system of claim 10 further comprising fans operable to move air flowing through the second and the third heat exchanger, and means for controlling operation of the fans.

15. A heat pump system of claim 13 further comprising fans operable to move air flowing through the second and the third heat exchanger, and means for controlling operation of the fans.

16. A heat pump system of claim 12 wherein the first bypass circuit further comprises a check valve positioned between the first heat exchanger and the second four-way valve to prevent refrigerant from flowing through the third heat exchanger in a heat pump system cooling operation.

17. A refrigeration system with multiple evaporators and operable for the conduct of a subcooling defrost cycle, comprising: a compressor for compressing refrigerant; a condenser for condensing compressed refrigerant after exiting the compressor; a plurality of metering devices for expanding refrigerant after exiting the compressor; a plurality of evaporators for evaporating refrigerant after exiting the metering devices, each metering device having one or more associated evaporators which receive expanded refrigerant from the metering device; and means for causing refrigerant to selectively bypass a metering device so as to cause its associated one or more evaporators to function as a subcooler while a second group including one or more of said evaporators functions as an evaporator, whereby said first group can be defrosted during said function as a subcooler.

18. A space conditioning system operable in a defrost cycle, comprising: a first heat exchanger for condensing compressed refrigerant from the compressor; a refrigerant loop for receiving condensed refrigerant from the first heat exchanger, the refrigerant loop including a thermal storage device, a second heat exchanger and a metering device in between the thermal storage device and second heat exchanger; means for causing refrigerant flow in first and second directions in the loop to provide thermal storage charging and discharging cycles; wherein during the thermal storage charging cycle refrigerant flows in the first direction and the thermal storage device and second heat exchanger operate as a subcooler and/or condenser and an evaporator, respectively, whereby the thermal storage device can be charged with positive thermal potential; wherein during the thermal storage discharging cycle refrigerant flows in the second direction and the thermal storage device and second heat exchanger operate as an evaporator and a subcooler, respectively, whereby operation of the second heat exchanger as a subcooler can defrost the second heat exchanger; and means for returning refrigerant exiting refrigerant loop to the compressor.

19. A method for heating a space using a heat pump system with a thermal storage device, comprising: charging the thermal storage device with positive thermal potential during operation of the thermal storage as a condenser and/or subcooler in the system; discharging the charged positive thermal potential from the thermal storage device during operation of the thermal storage as an evaporator and an outside evaporator as a subcooler, thereby defrosting the outside evaporator.

20. A method of claim 19, wherein during operation of an outside heat exchanger of the system as condenser and/or a subcooler, a fan operable to move air through the outside heat exchanger is off or runs at a reduced speed.

21. A method of claim 20 wherein during charge of the thermal storage device with positive thermal potential, at least a portion of the refrigerant condenses in the thermal storage device.

22. A method of claim 21, wherein during a thermal storage device discharge the thermal storage device operates as an evaporator, thereby returning stored energy from the refrigeration cycle.

23. A method for heating a space using a heat pump system with a thermal storage device, wherein during a defrost cycle of the system an outdoor heat exchanger of the system operates as a subcooler and optionally partially as a condenser.

24. A method of claim 23 wherein further during the defrost operation, the thermal storage device operates as an evaporator.

25. A method of claim 24 wherein during the defrost operation at least a portion of the refrigerant condenses in an outdoor heat exchanger.

26. A method of claim 24, which is method for heating a space with a defrost operation using a heat pump system with first and second outdoor heat exchangers, comprising: defrosting the first outdoor heat exchanger by operating the first outdoor heat exchanger as a subcooler and the second outdoor heat exchanger as an evaporator; and thereafter defrosting the second outdoor heat exchanger by operating the second outdoor heat exchanger as a subcooler and a first outdoor heat exchanger as an evaporator.

27. A method of claim 26 wherein during operation of the first or second outdoor heat exchanger as a subcooler, a fan operable to move air through the heat exchanger is off or runs at reduced speed.

28. A method of claim 27 wherein a timer controls operation of the first and second heat exchangers as subcoolers and evaporators.

29. A method of claim 28 wherein during operation of the first or the second outdoor heat exchangers as a subcooler at least a portion of the refrigerant condenses in the heat exchanger.

30. A method for cooling a space with defrost operations using a refrigeration system having a thermal storage device, wherein the thermal storage device is charged with positive thermal potential during operation of the thermal storage device as a subcooler thereby extracting heat from liquid refrigerant.

31. A method of claim 30, comprising: compressing refrigerant in a compressor; condensing compressed refrigerant after exiting the compressor in a condenser; in a thermal storage device charging cycle, subcooling liquid refrigerant after exiting the condenser in the thermal storage device while charging the thermal storage device with positive thermal potential; expanding the refrigerant in a metering device; and evaporating the refrigerant in a heat exchanger; and in a thermal storage discharging cycle, subcooling liquid refrigerant after exiting the condenser in the heat exchanger thereby defrosting the heat exchanger; expanding the subcooled refrigerant in the metering device; and then evaporating the expanded refrigerant in the thermal storage device thereby discharging the charged thermal potential from the thermal storage device.

32. A method of claim 31 wherein during a thermal storage device discharge, the thermal storage device operates as an evaporator thereby returning energy stored during a cooling cycle.

33. A method of claim 31, wherein during the thermal storage device charging cycle and or the thermal storage device discharge cycle, said refrigerent is also at least partially condensed in said thermal storage device.

34. A method for cooling a space using a refrigeration system having a defrost operation, wherein at least one of a plurality of evaporating coils of the system operates as a subcooler during the defrost operation.

35. A method for defrosting evaporators of a refrigeration system with multiple evaporators, comprising: sequentially defrosting evaporator groups of the refrigeration system, each evaporator group including one or more evaporators, said defrosting including sequentially operating each evaporator group as a subcooler while at least one of the remainder of the evaporator groups is operated as an evaporator.

36. A method of claim 35 wherein said sequentially operating is controlled by a timer.