Air conditioning system including pressure control device and bypass valve

An air conditioning system includes: first and second utilization side heat exchangers and a heat source side heat exchanger respectively connected in series; a compressor connected between the first utilization side heat exchanger and the heat source side heat exchanger; an expansion valve connected between the first utilization side heat exchanger and the second utilization side heat exchanger; a pressure control device connected between the second utilization side heat exchanger and the heat source side heat exchanger; and a bypass valve connected between the expansion valve and the heat source side heat exchanger. The bypass valve provides a variable amount of liquid refrigerant flowing from the expansion valve to the heat source side heat exchanger. The pressure control device and the bypass valve cooperate with each other to keep a temperature of the compressor below a maximum allowable temperature predetermined for the compressor.

TECHNICAL FIELD

The technical field relates in general to air conditioning systems, and more particularly to an air conditioning system equipped with a variable bypass valve that reduces the temperature of refrigerant entering a compressor during normal system operation, and that aids in quickly circulating refrigerant that would otherwise be unable to flow during a defrost system operation.

BACKGROUND

Conventional air conditioning systems provide heating and cooling to the interiors of buildings and other contained spaces via interior utilization side heat exchangers. During normal system operation, refrigerant flows through one or more utilization side heat exchangers before flowing through an exterior heat source side heat exchanger. After exiting the heat source side exchanger, the refrigerant enters a compressor, where its pressure and temperature are rapidly increased. The refrigerant then exits the compressor in liquid phase, as is known in the art.

However, the temperature of the refrigerant as it is discharged from the compressor must be below a predetermined maximum allowable temperature associated with the compressor. Specifically, if the temperature of refrigerant exiting the compressor exceeds the predetermined maximum allowable temperature, the compressor will likely fail. Conventionally, it is difficult to downwardly adjust the temperature of the refrigerant entering the heat source side heat exchanger prior to the refrigerant entering the compressor. Therefore, the refrigerant entering the compressor may result in a discharge temperature of the compressor that is above the maximum allowable temperature.

Japanese Patent Application Publication No. 2009-222357 describes an air conditioning system that is equipped with a refrigerant circuit including a compressor, condenser, an expansion mechanism, and first and second evaporators, respectively. A zeotropic refrigerant mixture circulates through the refrigerant circuit.

The refrigerant circuit also includes a pressure control device located between the first and second evaporators for reducing pressure of the refrigerant one or more times during the evaporation process as the refrigerant flows between the first and second evaporators. The decrease in pressure is ultimately helpful in decreasing the suction pressure of the refrigerant entering the compressor.

However, the refrigerant circuit does not decrease suction temperature of the refrigerant as it flows from the second evaporator to the compressor. Thus, the suction temperature of the refrigerant flowing into the compressor from the second evaporator may be above a tolerance, or in other words a predetermined maximum allowable temperature, of the compressor as the refrigerant flows from the compressor.

In addition, in the system above frost forms on the heat source side heat exchanger during system operation. When the system is operated in a defrost mode, the maximum opening degree of the pressure control device is small. As a result, very little refrigerant passes through the pressure control device to circulate through the refrigerant circuit, resulting in a shortage in system defrost capacity. If refrigerant is forced through the pressure control valve during the defrost mode, damage to the pressure control valve can occur.

There is therefore a need for a refrigerant circuit that can reduce the temperature of refrigerant flowing into a compressor from a heat exchanger to a level where the temperature of the refrigerant flowing from the compressor is within a fault tolerance of the compressor. There is also a need for a refrigerant circuit that can provide adequate condenser defrost capacity even when a pressure control device is present in the circuit.

SUMMARY

Accordingly, one embodiments described herein provides an air conditioning system comprising first and second utilization side heat exchangers, a heat source side heat exchanger, a compressor, an expansion valve, a pressure control device, and a bypass valve. The first and second utilization side heat exchangers and the heat source side heat exchanger are respectively connected in series. The compressor is connected between the first utilization side heat exchanger and the heat source side heat exchanger.

The expansion valve is connected between the first utilization side heat exchanger and the second utilization side heat exchanger. The pressure control device is connected between the second utilization side heat exchanger and the heat source side heat exchanger. The bypass valve is connected between the expansion valve and the heat source side heat exchanger.

The pressure control device is configured to maintain refrigerant that flows from the second utilization side heat exchanger to the heat source side heat exchanger at a predefined pressure. The bypass valve is configured to make refrigerant from the expansion valve bypass the second utilization side heat exchanger and the pressure control device. Lastly, the pressure control device and the bypass valve are configured in cooperation with each other to keep a temperature of the compressor below a maximum allowable temperature predetermined for the compressor.

A second embodiment described herein further provides an air conditioning system comprising first and second utilization side heat exchangers, a heat source side heat exchanger, a compressor, an expansion valve, a pressure control device, and a bypass valve. In the second embodiment, the components listed above are disposed as in the first embodiment. However in the second embodiment, during a defrost system operation the bypass valve is configured to be opened so as to make refrigerant from the heat source side heat exchanger bypass the pressure control device.

A third embodiment described herein further provides an air conditioning system comprising first and second utilization side heat exchangers, a heat source side heat exchanger, a compressor, an expansion valve, a pressure control device, and a bypass valve. In the third embodiment, the components listed above are disposed as in the first embodiment. The pressure control device is configured to maintain refrigerant that flows from the second utilization side heat exchanger to the heat source side heat exchanger at a predefined pressure. The bypass valve is configured to provide a variable amount of liquid refrigerant flowing from the expansion valve to the heat source side heat exchanger.

Another embodiment described herein provides a controller that includes a central processing unit (CPU) that is in communication with an air conditioning system. The air conditioning system includes first and second utilization side heat exchangers, a heat source side heat exchanger, a compressor, an expansion valve, a pressure control device, and a bypass valve similar to those described above in the first embodiment.

The CPU is configured to execute instructions that cause the pressure control device to, during a normal system operation, maintain refrigerant that flows from the second utilization side heat exchanger to the heat source side heat exchanger at a predefined pressure. The CPU is further configured to execute instructions that cause the bypass valve to make refrigerant from the expansion valve bypass the second utilization side heat exchanger and the pressure control device. The CPU is further configured to execute instructions that cause the pressure control device and the bypass valve to cooperate with each other to keep a temperature of the compressor below a maximum allowable temperature predetermined for the compressor.

DETAILED DESCRIPTION

It is further understood that the use of relational terms such as first and second, and the like, if any, are used solely to distinguish one from another entity, item, or action without necessarily requiring or implying any actual such relationship or order between such entities, items or actions. It is noted that some embodiments may include a plurality of processes or steps, which can be performed in any order, unless expressly and necessarily limited to a particular order; i.e., processes or steps that are not so limited may be performed in any order.

Exemplary air conditioning systems in accord with various embodiments are now described. Referring now toFIG. 1, a diagram illustrating an air conditioning system100with a pressure control device and bypass valve according to a first embodiment will be discussed and described. Specifically, the air conditioning system100includes a compressor101, such as a rotary, reciprocating, or scroll-type compressor or the like, a four-way valve103, a first utilization side heat exchanger (with fan)105, a first expansion valve107, a second expansion valve111, a second utilization side heat exchanger (with fan)113, and a heat source side heat exchanger117(with fan) that are connected in series by refrigerant piping identified generally at119.

As can generally be seen fromFIG. 1, the compressor101is connected between the first utilization side heat exchanger105and the heat source side heat exchanger117. The first and second expansion valves107,111are connected between the first utilization side heat exchanger105and the second utilization side heat exchanger113. An evaporating pressure control device115is disposed between the second utilization side heat exchanger113and the heat source side heat exchanger117. A bypass valve109connects piping at an inlet of the heat source side heat exchanger117with piping between the first expansion valve107and the second expansion valve111. The air conditioning system100also includes sensors120,121,123and a controller125with a CPU that is in communication with the components of the air conditioning system100. The remaining discussion refers to the sensors120,121,123as “temperature sensors.” However, each sensor120,121,123could alternatively be configured as a pressure sensor.

Since the system components are most dearly understood in terms of refrigerant flow, the operation of the air conditioning system100is now provided, with reference also to the pressure/enthalpy diagram ofFIG. 2. Referring then to bothFIG. 1andFIG. 2, during normal system operation, refrigerant flowing through the air conditioning system100, as identified generally by directional arrows127, attains a high pressure and high temperature state A after the refrigerant is compressed by the compressor101. The refrigerant in state A passes through the four-way valve103and flows into the first utilization side heat exchanger105. The first utilization side heat exchanger105is designed in the current embodiment to operate as a heating unit. As the refrigerant thus passes through the first utilization side heat exchanger105, it condenses into a liquid phase as it is cooled by heat exchange with ambient air surrounding the first utilization side heat exchanger105. It should be noted that during normal system operation, a fan of the first utilization side heat exchanger105may operate and propel warm air from the first utilization side heat exchanger105into the ambient air.

As the refrigerant flows through the first utilization side heat exchanger105and exchanges heat with ambient air surrounding the first utilization side heat exchanger105, its temperature is decreased and its pressure is decreased or not changed, as represented by state B inFIG. 2. The refrigerant in state B then flows through the first expansion valve107. The expansion valve107reduces the pressure and the temperature of the refrigerant. That is to say, at state C the refrigerant is decreased in pressure and temperature relative to state B.

The second expansion valve111then further reduces the pressure of the refrigerant at state D. At state D, the refrigerant is decreased in pressure and temperature relative to state C. The refrigerant at state C then flows into the second utilization side heat exchanger113.

The second utilization side heat exchanger113is designed in the present embodiment to operate as a cooling unit. Therefore, as the refrigerant flows through the second utilization side heat exchanger113, the refrigerant evaporates as it is heated by heat exchange with ambient air surrounding the second utilization side heat exchanger113. It should be noted that during normal system operation, the fan of the second utilization side heat exchanger113may operate and propel cool air from the second utilization side heat exchanger into the ambient air surrounding the second utilization side heat exchanger113.

After flowing through the second utilization side heat exchanger113, at state E the refrigerant is maintained at the same pressure as at state D but increases significantly in temperature. For example, if the refrigerant is R41OA, the pressure of the refrigerant is maintained to a predefined amount, for example 0.985 MPa. As the refrigerant flows through the pressure control device115, the pressure of the refrigerant is decreased by the pressure control device115to attain a high temperature, low pressure state F.

The decrease in pressure of the refrigerant to state F caused by the pressure control device115may not be significant enough to reduce the temperature of the refrigerant entering the compressor101(after exiting the heat source side heat exchanger117) to cause the temperature of the refrigerant to be within a discharge temperature tolerance of the compressor101as the refrigerant exits the compressor101. For example, a scroll type compressor in such an air conditioning system may have a maximum discharge temperature tolerance of approximately 120′C. Therefore, the bypass valve109is provided in order to additionally reduce the temperature of refrigerant entering the heat source side heat exchanger117to thereby subsequently reduce the temperature of the compressed refrigerant flowing out of the compressor101.

As can be seen inFIG. 2, as the bypass valve109is controlled to reduce the pressure of the liquid refrigerant flowing through it, the temperature of the refrigerant remains low. That is to say, after flowing through the bypass valve109, the refrigerant transitions from a relatively high pressure, low temperature state C to a low pressure, low temperature state G. As indicated inFIG. 2, the pressure of the refrigerant after flowing through the pressure control device115at state F is equal to the pressure of the refrigerant after flowing through the bypass valve109at state G.

Although the pressure of the refrigerant at states F and G is substantially equal, the refrigerant differs at state F from the refrigerant at state G in both phase and temperature. Specifically, at state F the refrigerant is in a high temperature gaseous state, while at state G the refrigerant is in a low temperature liquid state. Thus when the refrigerant mixes at state H (a low pressure, lower temperature state), the refrigerant is a two-phase gas/liquid mix that is at a temperature lower than at the gaseous state F.

Once the refrigerant is in a two-phase state H, the refrigerant flows into the heat source side heat exchanger117. The refrigerant evaporates as it is heated by heat exchange with outside ambient air surrounding the heat source side heat exchanger117, which in this embodiment is configured to operate as a cooling unit. As indicated inFIG. 2, the refrigerant flowing through the heat source side heat exchanger117reaches a low pressure, relatively high temperature state I.

It should be noted that by reducing the temperature of the refrigerant flowing into the heat source side exchanger117, the temperature of the refrigerant at state I is low enough to be within a temperature tolerance (that is, below a predetermined maximum allowable temperature) of the compressor101as the refrigerant transitions from a relatively high temperature, low suction pressure state I to a very high temperature, very high pressure state A after being compressed by the compressor101. Thus, it should be clear that if both the pressure control device115and the bypass valve109were absent from the air conditioning system100, the refrigerant would enter the heat source side heat exchanger117at state E, which would shift the line between state I and state A farther to the right (and up), resulting in a much higher temperature endpoint upon flowing from the compressor101.

Additionally, if only the bypass valve109were removed from the air conditioning system100(and the pressure control device115remained), the refrigerant would enter the heat source side heat exchanger117at state F. Although better than the first scenario in terms of resultant pressure after the refrigerant flows from the compressor101, the line between state I and state A would still be shifted farther to the right, resulting in a much higher temperature endpoint after flowing from the compressor101. Under either scenario, the resulting discharge temperature from the compressor101may simply be too high for the compressor101to operate without fault.

Succinctly put, in the air conditioning system ofFIG. 1, the bypass valve109is configured to provide a variable amount of liquid refrigerant flowing from the expansion valve107to the heat source side heat exchanger117. The pressure control device115and the bypass valve109thus cooperate with each other to keep a temperature of the compressor101below a maximum allowable temperature predetermined for the compressor101. As discussed above, this is advantageous.

A brief description of the controller125is now provided. The controller125may be a microcontroller that is a highly integrated circuit and contains a processor core (i.e., a CPU), a read only memory (ROM), and a small amount of random access memory (RAM). The ROM may take several forms, including either NOR or NAND non-volatile flash memory, non-flash EEPROM memory, or any type of programmable read-only memory as would be known in the art.

The controller125will also include input/out (110) ports, and timers. A program for the controller125may be written in the ROM, and the CPU in communication with the air conditioning system100executes the program to control operation of the air conditioning system100through the I/O ports. The controller125is thus able to communicate with components of the air conditioning system, and is configured to control any component with either a variable or on/off setting. For example, the controller125controls a degree of opening of the bypass valve109(not just the on-off state of the bypass valve), and therefore provide the variable amount of liquid refrigerant to the heat source side heater exchanger117that bypasses the second utilization side heat exchanger113though the bypass valve109. The controller125additionally controls the pressure control device115.

The particular disposal of a line inFIG. 1between the controller125and the air conditioning system100is arbitrary and is intended only to show that controller125is generally in communication with the air conditioning system100. Although the line is shown as extending only from the controller125to the bypass valve109, this is a matter of illustrative convenience. The controller125may communicate with all the components of the system100depending upon the specific system configuration. It should be understood that the controller125, and more particularly the CPU, is configured to execute program instructions that cause the components of the air conditioning system100(and the air conditioning systems of the additional embodiments presented in this disclosure) to operate as described herein. This is true as to the operation of components of each air conditioning system during normal system operation and during defrost system operation.

The temperature sensor120is used to measure or detect the temperature of the refrigerant that flows from the second utilization side exchanger113. Temperature measurements taken by the temperature sensor120are used by the controller125to adjust the pressure control device115, to appropriately adjust the flow of refrigerant through this component. Specifically, an opening degree of the pressure control device115will be adjusted to provide a variable amount of refrigerant flowing therethrough based on the refrigerant temperature detected by the temperature sensor120.

The temperature sensor121is used to measure or detect an outdoor air temperature as the refrigerant flows through the heat source side exchanger117. Temperature measurements taken by the temperature sensor121are used by the controller125to adjust the bypass valve109, to appropriately adjust the flow of refrigerant through this component. Specifically, an opening degree of the bypass valve109will be adjusted to provide a variable amount of refrigerant flowing therethrough based on the air temperature detected by the temperature sensor121. For example, the bypass valve109is opened when the air temperature detected by the temperature sensor121is lower than a predetermined value.

The temperature sensor123measures the temperature of the refrigerant discharged through the compressor101that is correlated with the temperature of the compressor101. The temperature measurements taken by the temperature sensor123are used by the controller125to adjust the bypass valve109to appropriately adjust the flow of refrigerant through this component.

As mentioned above, the temperature sensors120,121,123can be replaced by, or supplemented with, pressure sensors that detect pressure of the refrigerant discharged from the pressure control device115, the heat source side heat exchanger117or the compressor100as discussed above. The measurements of such pressure sensors would be used by the controller125in determining adjustments to the bypass valve109, the pressure control device115and/or the compressor101in a manner similar to that discussed above.

As described above, after the air conditioning system100operates in normal system operation for a certain amount of time, frost tends to develop on the heat source side heat exchanger due to the cooling of the refrigerant as it absorbs heat from the ambient air. Therefore, as shown inFIG. 3, the air conditioning system100is also configured to run a system defrost operation. Specifically, the controller operates to switch the four-way valve103so that refrigerant flows in a direction opposite to the direction that the refrigerant flows during normal system operation as shown inFIG. 1.

It should be clear that the four-way valve103, which is disposed between the first utilization side heat exchanger105and the heat source side heat exchanger117, can be selectively switched as between the normal system operation and the system defrost operation. More specifically, during the normal system operation, the four-way valve103connect an outlet of the compressor101and the first utilization side heat exchanger105and an inlet of the compressor101and the heat source side heat exchanger117. During the defrost system operation, the four-way valve103connect the outlet of the compressor101and the heat source side heat exchanger117and the inlet of the compressor101and the first utilization side heat exchanger105.

As indicated above, the controller125operates to open the valve109when the degree of opening of the pressure control device115is very small during start-up of the defrost system operation. At start-up of the system defrost operation, pressure at the pressure control device115is quite low.FIG. 4, which is a pressure/enthalpy diagram, is now discussed to present a general view of refrigerant flowing in the air conditioning system100during defrost system operation.

The refrigerant enters a high temperature high pressure state3A after it is compressed by the compressor101. InFIG. 3, the four-way valve103is adjusted so that the outlet of the compressor101is connected with the inlet of the heat source side heat exchanger117. The refrigerant in state3A thus flows through the four-way valve103and into the heat source side heat exchanger117.

As the refrigerant flows through the heat source side heat exchanger117, the refrigerant is cooled by heat exchange with ambient air surrounding the heat source side heat exchanger117and melts frost on the heat source side heat exchanger117. Therefore, the refrigerant enters a low temperature, slightly lower pressure state3B.

As mentioned above, during the defrost system operation the bypass valve109is opened since pressure at the outlet of the second utilization side heat exchanger113is quite low. The controller125controls the bypass valve109so that the refrigerant in state3B flows through the bypass valve109and decreases in pressure while decreasing its temperature and phase as it enters state3C. At this point, there is little or no refrigerant passing through the pressure control device115and the second utilization side heat exchanger113. Succinctly put, during the defrost system operation, the refrigerant exiting the heat source side heat exchanger117in state313flows through the bypass valve109attaining state3C and enters the first expansion valve107, therefore bypassing entirely the second utilization side heat exchanger113.

The pressure of the refrigerant is lowered even further when it flows into the first expansion valve107, and achieves a very low pressure state3D. In fact, the pressure and temperature are such that the refrigerant is again in a two-phase state at3D. When the two-phase refrigerant enters the first utilization side heater exchanger105, liquid refrigerant is evaporated as the temperature of the refrigerant is increased to state3E. The low pressure state is maintained at3E. Lastly, the gaseous state refrigerant enters the compressor101, where once again the pressure and temperature are increased to state3A and the refrigerant returns to a gas phase.

As mentioned above, the controller125is able to communicate with the components of the air conditioning system100to control any component with a variable setting. For example, the controller125(and more particularly the CPU) controls a varying amount of liquid refrigerant that bypasses the second utilization side heat exchanger113though the bypass valve109such that the refrigerant flows from the heat source side heat exchanger117to the first expansion valve107. The particular disposal of a line inFIG. 3between the controller125and the air conditioning system100is arbitrary and is merely intended to show that controller125is in communication with the air conditioning system100. Although the line extends from the controller125to the piping between the first and second expansion valves107,111this is a matter of illustrative convenience. The controller125in fact may communicate with all the components of the system100.

As discussed above, the temperature sensor120is used to measure or detect the temperature of the refrigerant that flows from the second utilization side exchanger113. The temperature sensor121is used to measure or detect an outdoor air temperature as the refrigerant flows through the heat source side exchanger117. The temperature sensor123measures the temperature of the refrigerant discharged through the compressor101. Temperature sensors may be additionally disposed at other locations as well (although not shown) so that the controller125can appropriately adjust the bypass valve109and the pressure control device115. For example, in the defrost system operation, a temperature sensor would be appropriate at the first utilization side heat exchanger105.

FIG. 5is a diagram illustrating an air conditioning system500with a pressure control device515and a bypass valve509according to a second embodiment, during a defrost system operation. Because many of the components inFIG. 5correspond to like components inFIG. 1andFIG. 3and are identified by like reference numbers, further discussion of the operation of these components is omitted.

In the air conditioning system500, the bypass valve is connected by piping, identified generally at119, to both an inlet side and an outlet side of the pressure control device515. The refrigerant enters a high temperature high pressure state after it is compressed by the compressor101. The four-way valve103is adjusted so that the outlet of the compressor101is connected with the inlet of the heat source side heat exchanger117. The refrigerant thus flows through the four-way valve103and through the heat source side heat exchanger117. Consequently, the refrigerant is cooled by heat exchange with ambient air and melts frost on the heat source side heat exchanger117. Therefore, the refrigerant enters a low temperature, slightly lower pressure state as it exits the heat source side heat exchanger117.

As mentioned above, during the defrost system operation the bypass valve509is opened since pressure at the control device515is quite low. The controller125controls the bypass valve509so that the refrigerant flows from the heat source side heat exchanger117through the bypass valve509, and into the second utilization side heat exchanger113. At this point, there is little or no refrigerant passing through the pressure control device515.

However, unlike in the air conditioning system100shown inFIG. 3, the lower pressure refrigerant does flow through the second utilization side heat exchanger113. As a result, the temperature of the refrigerant is further increased, compared to the refrigerant that completely bypasses the second utilization side heat exchanger113and the second expansion valve111during the system defrost operation inFIG. 3. The bypass valve509in the air conditioning system500according to the second embodiment enables the heat source side heat exchanger117to be more quickly and efficiently defrosted during the defrost system operation.

FIG. 6is a diagram illustrating an air conditioning system600according to a third embodiment during normal system operation. The air conditioning system600includes a third utilization side heat exchanger625in addition to the second utilization side heat exchanger113, a second pressure control device627in addition to the first pressure control device115, and a bypass valve609. Because many of the components inFIG. 6correspond to like components inFIG. 1,FIG. 3andFIG. 5and are identified by like reference numbers, further discussion of the operation of these components is omitted. In addition, although the air conditioning system600inFIG. 6includes two utilization side heat exchangers in parallel, the system may alternatively include three or more utilization side heat exchangers with corresponding pressure control devices.

In the third embodiment, the third utilization side heat exchanger625is connected in parallel with the second utilization side heat exchanger113. The second, or additional, pressure control device627is connected between the third utilization side heat exchanger625and the heat source side heat exchanger117. As with the first pressure control device115, the second pressure control device627is configured to maintain additional gaseous refrigerant that flows from the third utilization side heat exchanger625to the heat source side heat exchanger117at a further predefined pressure. The variable amount of liquid refrigerant flowing from the first expansion valve107to the heat source side heat exchanger117through the bypass valve609includes additional liquid refrigerant that bypasses the third utilization side heat exchanger625and the second pressure control device627to mix with the additional gaseous refrigerant maintained by the second pressure control device627at the further predefined pressure to form the two-phase refrigerant in a manner similar to the air conditioning system100.

As a result, as in the air conditioning system100, the bypass valve109is controlled to reduce the pressure of the liquid refrigerant flowing through it, and the temperature of the refrigerant remains low. That is to say, after flowing through the bypass valve109, the refrigerant transitions from a relatively high pressure, low temperature state to a low pressure, low temperature state and forms a two-phase refrigerant prior to flowing into the heat source side heat exchanger117to thereby maintain the refrigerant at a temperature below the fault tolerance of the compressor101. Succinctly put, the second pressure control device627is additionally configured in cooperation with the pressure control device105and the bypass valve109to keep the temperature of the compressor101below the maximum allowable temperature predetermined for the compressor.

In view of the above, one skilled in the art will appreciate that the embodiments described herein include a bypass valve in combination with a pressure control device in a refrigeration circuit. The pressure control device controls pressure of gaseous refrigerant flowing from a utilization side heat exchanger. The bypass valve is opened such that liquid refrigerant bypasses the utilization side heat exchanger. In this way, the bypass valve controls the state of the refrigerant that flows from the heat source side heat exchanger and thus the temperature of the refrigerant flowing into the compressor.

More specifically, the liquid refrigerant bypasses the utilization side heat exchanger and mixes with the gaseous refrigerant flowing from utilization side heat exchanger. A two-phase refrigerant is formed that is lower in temperature than the gaseous refrigerant that flows into the heat source side heat exchanger. The two-phase refrigerant flows into the heat source side heat exchanger at a temperature that is lower than the gaseous refrigerant that would otherwise only flow into the heat source side heat exchanger. As such, the discharge temperature of refrigerant exiting the compressor will not exceed the predetermined maximum allowable temperature of the compressor.

The bypass valve disclosed herein also aids in a defrost system operation of an air conditioning system. More specifically, when the defrost operation first begins, pressure at the inlet of the pressure control valve is below a predefined level due to the decreased pressure of the refrigerant at the inlet of the compressor, and the valve is substantially closed. As a result, refrigerant cannot flow through the heat source side heat exchanger. In the above described embodiments, in a defrost system operation refrigerant can bypass the pressure control valve through the bypass valve, and can then flow efficiently throughout the refrigerant circuit. As a result, the air conditioning system can efficiently complete the defrost system operation, and can at the same time protect the pressure control valve from damage that might otherwise occur if refrigerant were forced through the device.