Refrigeration cycle apparatus

A refrigeration cycle apparatus includes a refrigerant circuit, through which refrigerant is circulated, including a compressor, a heat source side heat exchanger, a first expansion device, and a load side heat exchanger, a controller controlling the refrigerant circuit, and a bypass pipe that branches off from a high-pressure pipe extending from the compressor to the first expansion device and that is connected to a low-pressure pipe on a suction side of the compressor. The apparatus further includes a precooling heat exchanger that is provided in the bypass pipe and that cools the refrigerant diverted to the bypass pipe, a second expansion device that is provided in the bypass pipe and that reduces a pressure of the refrigerant cooled by the precooling heat exchanger, and a refrigerant cooler that is provided in the bypass pipe and that cools the controller with the refrigerant reduced in pressure by the second expansion device.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of International Application No. PCT/JP2016/052313, filed on Jan. 27, 2016, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a refrigeration cycle apparatus including a cooling mechanism for a controller.

BACKGROUND

For cooling of a controller, a known technique involves diverting part of refrigerant, serving as a high-pressure side main stream flowing through a refrigerant circuit, to a bypass pipe, allowing the refrigerant flowing through the bypass pipe to transfer heat in a precooling heat exchanger, and allowing the refrigerant that has transferred heat to flow through a refrigerant cooler and exchange heat with a controller to cool the controller (refer to Patent Literature 1, for example). The part of the refrigerant, serving as the high-pressure side main stream, diverted to the bypass pipe cools the controller in the refrigerant cooler. After that, the refrigerant flowing through the bypass pipe passes through an expansion device, which adjusts the flow rate of the refrigerant through the refrigerant cooler, and flows to a low-pressure side.

PATENT LITERATURE

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2015-75258

As described in Patent Literature 1, the flow rate of the refrigerant through the refrigerant cooler is adjusted by the expansion device located downstream of the refrigerant cooler. Disadvantageously, this technique fails to provide a sufficient difference in temperature between the controller and the refrigerant in the refrigerant cooler because the refrigerant in the refrigerant cooler is at a high pressure and its evaporating temperature accordingly increases. Consequently, if a large cooling capacity is required, the required cooling capacity fails to be achieved. To achieve the required cooling capacity, a large amount of refrigerant has to be diverted to the bypass pipe. This leads to a reduction in capacity of the refrigeration cycle apparatus.

SUMMARY

The present invention has been made to overcome the above-described disadvantages and aims to provide a refrigeration cycle apparatus capable of improving the performance of cooling a controller.

A refrigeration cycle apparatus according to an embodiment of the present invention includes a refrigerant circuit, through which refrigerant is circulated, including a compressor, a heat source side heat exchanger, a first expansion device, and a load side heat exchanger, a controller controlling the refrigerant circuit, and a bypass pipe that branches off from a high-pressure pipe extending from the compressor to the first expansion device and that is connected to a low-pressure pipe on a suction side of the compressor. The apparatus further includes a precooling heat exchanger that is provided in the bypass pipe and that cools the refrigerant diverted to the bypass pipe, a second expansion device that is provided in the bypass pipe and that reduces a pressure of the refrigerant cooled by the precooling heat exchanger, and a refrigerant cooler that is provided in the bypass pipe and that cools the controller with the refrigerant reduced in pressure by the second expansion device.

According to the embodiment of the present invention, the second expansion device is interposed between the precooling heat exchanger and the refrigerant cooler. The refrigerant cooled through the precooling heat exchanger is reduced in pressure through the second expansion device such that the temperature of the refrigerant is further reduced. Then, the refrigerant is allowed to flow into the refrigerant cooler. Such a configuration can improve the performance of cooling the controller.

DETAILED DESCRIPTION

An air-conditioning apparatus, which is an example of a refrigeration cycle apparatus, will be described below with reference to the drawings, for example. Note that components designated by the same reference signs inFIG. 1and the following figures are the same components or equivalents. This note applies to Embodiments described below. Furthermore, note that the forms of components described in the specification are intended to be illustrative only and are not intended to be limited to those described in the specification. In addition, high and low values of temperature, pressure, or other parameters are not determined in relation to a particular absolute value, but are relatively determined based on, for example, a state and an operation of, for example, a system or an apparatus.

FIG. 1is a schematic diagram illustrating an exemplary configuration of a refrigerant circuit of an air-conditioning apparatus500according to Embodiment 1 of the present invention. A refrigerant flow in a refrigeration cycle will be described before description of refrigerant cooling. The configuration of the refrigerant circuit of the air-conditioning apparatus500will be described with reference toFIG. 1. The air-conditioning apparatus500, which is installed in, for example, a building or a condominium, can perform a cooling operation or a heating operation using a refrigeration cycle (heat pump cycle) through which refrigerant is circulated.

The air-conditioning apparatus500includes a heat source side unit100and a plurality of (inFIG. 1, two) load side units300(a load side unit300aand a load side unit300b). In the air-conditioning apparatus500, the heat source side unit100is connected to the load side units300(load side units300aand300b) by a gas extension pipe401and a liquid extension pipe402, thus forming the refrigeration cycle. The gas extension pipe401includes a gas main pipe401A, a gas branch pipe401a, and a gas branch pipe401b. The liquid extension pipe402includes a liquid main pipe402A, a liquid branch pipe402a, and a liquid branch pipe402b.

The heat source side unit100has a function of supplying cooling energy or heating energy to the load side units300.

The heat source side unit100includes a compressor101, a four-way switching valve102, serving as a flow switching device, a heat source side heat exchanger103, and an accumulator104. These devices are connected in series, thus forming part of a main refrigerant circuit. The heat source side unit100further includes a heat source side fan106.

The compressor101sucks low-temperature, low-pressure gas refrigerant, compresses the refrigerant into high-temperature, high-pressure gas refrigerant, discharges the refrigerant, and circulates the refrigerant through the refrigerant circuit, thus performing an operation related to air-conditioning. The compressor101may be, for example, an inverter-driven compressor whose capacity is controllable. The compressor101is not limited to the capacity-controllable inverter-driven compressor. For example, the compressor101may be a constant-speed compressor or may be of a combined type of, for example, the inverter-driven compressor and the constant-speed compressor. The compressor101may be of any type capable of compressing sucked refrigerant into a high-pressure state. For example, the compressor101may be any of a variety of types, such as reciprocal, rotary, scroll, and screw compressors.

The four-way switching valve102, which is provided on a discharge side of the compressor101, switches between a refrigerant flow passage for the cooling operation and a refrigerant flow passage for the heating operation. The four-way switching valve102controls a flow of the refrigerant so that the heat source side heat exchanger103functions as an evaporator or a condenser in accordance with an operation mode.

The heat source side heat exchanger103exchanges heat between the refrigerant and a heat medium (e.g., ambient air or water). In the heating operation, the heat source side heat exchanger103functions as an evaporator to evaporate and gasify the refrigerant. In the cooling operation, the heat source side heat exchanger103functions as a condenser (radiator) to condense and liquefy the refrigerant.

In the case where the heat source side heat exchanger103is an air-cooled heat exchanger as in Embodiment 1, the heat source side unit100includes an air-sending device, for example, the heat source side fan106. To control a condensing capacity or an evaporating capacity of the heat source side heat exchanger103, for example, a controller118, which will be described later, adjusts the rotation speed of the heat source side fan106. In the case where the heat source side heat exchanger103is a water-cooled heat exchanger, the rotation speed of a water circulating pump (not illustrated) is adjusted to control the condensing capacity or the evaporating capacity of the heat source side heat exchanger103.

The accumulator104, which is provided on a suction side of the compressor101, has a function of separating liquid refrigerant from gas refrigerant and a function of storing an excess of refrigerant.

The heat source side unit100further includes a high-pressure sensor141that detects the pressure (high-pressure side pressure) of the refrigerant discharged from the compressor101. In addition, the heat source side unit100includes a low-pressure sensor142that detects the pressure (low-pressure side pressure) of the refrigerant to be sucked into the compressor101. The heat source side unit100further includes an outdoor air temperature sensor604that detects the temperature of outdoor air, a controller temperature sensor605that detects the temperature of the controller118, and a temperature sensor606that detects the temperature of a pipe located downstream of a refrigerant cooler603. These sensors each transmit a signal indicating the detected pressure or the detected temperature to the controller118controlling an operation of the air-conditioning apparatus500.

The controller118controls, for example, the driving frequency of the compressor101, the rotation speed of the heat source side fan106, and switching of the four-way switching valve102on the basis of the high-pressure side pressure and the low-pressure side pressure. In addition, the controller118controls an expansion device602, which will be described later, on the basis of the pressures and temperatures detected by the respective sensors. The temperature sensor606and the low-pressure sensor142constitute a superheat-degree detection device in the present invention. The superheat-degree detection device has only to detect the degree of superheat at an outlet of the refrigerant cooler603. A temperature sensor that detects the temperature of the refrigerant at an inlet of the refrigerant cooler603may be used instead of the low-pressure sensor142.

The controller118controls the devices included in the heat source side unit100in a centralized manner to control the air-conditioning apparatus500. The controller118includes a microcomputer. The controller118includes a control arithmetic processing unit, such as a central processing unit (CPU). The controller118further includes a storage unit (not illustrated), which stores data on a program for a process related to, for example, control. The control arithmetic processing unit executes the process based on the program data, thus achieving control of, for example, the devices included in the heat source side unit100. Although the controller118is provided in the heat source side unit100in Embodiment 1, the controller118may be provided at any location as long as the controller118can control the devices, for example.

The heat source side unit100further includes a bypass pipe608that branches off from a high-pressure pipe611through which the high-pressure gas refrigerant discharged from the compressor101flows and that is connected to a low-pressure pipe610on the suction side of the compressor101. The bypass pipe608is used to divert the high-pressure gas refrigerant, serving as a main stream. In the bypass pipe608, a precooling heat exchanger601is provided to cool the high-pressure gas refrigerant that has flowed into the bypass pipe608. The expansion device602that adjusts the flow rate through the bypass pipe and the refrigerant cooler603that cools the controller118are arranged downstream of the precooling heat exchanger601. The expansion device602corresponds to a second expansion device in the present invention.

The expansion device602, functioning as a pressure reducing valve or an expansion valve, reduces the pressure of the refrigerant to expand the refrigerant. The expansion device602has the function of reducing the pressure of the high-pressure refrigerant cooled by the precooling heat exchanger601to further reduce the temperature of the refrigerant and allowing the temperature-reduced refrigerant to flow into the refrigerant cooler603. The expansion device602includes a component whose opening degree is variably adjustable, such as an electronic expansion valve.

The precooling heat exchanger601is integrated with the heat source side heat exchanger103into a single integrated heat exchanger. Part of the integrated heat exchanger serves as the precooling heat exchanger601. The precooling heat exchanger601may be a component separate from the heat source side heat exchanger103.

The refrigerant cooler603includes a refrigerant pipe, through which the refrigerant flows, such that the refrigerant pipe is in contact with the controller118. The refrigerant that has flowed into the bypass pipe608is cooled by the precooling heat exchanger601such that the refrigerant turns into liquid refrigerant. The liquid refrigerant is subjected to flow rate adjustment by the expansion device602and then flows into the refrigerant cooler603. The liquid refrigerant that has flowed into the refrigerant cooler603receives heat radiated from the controller118, so that the refrigerant turns into gas refrigerant. The gas refrigerant flows through a refrigerant-cooler downstream pipe609, located downstream of the refrigerant cooler603, and the low-pressure pipe610to the accumulator104.

The load side units300supply cooling energy or heating energy from the heat source side unit100to a cooling load or a heating load. For example, as illustrated inFIG. 1, each component included in the “load side unit300a” has a letter “a” after its reference sign, and each component included in the “load side unit300b” has a letter “b” after its reference sign. Although the letter “a” or “b” after the reference sign may be omitted in the following description, the load side unit300aand the load side unit300binclude those components.

Each of the load side units300includes a load side heat exchanger312(load side heat exchanger312a,312b) and an expansion device311(expansion device311a,311b) such that the load side heat exchanger312and the expansion device311are connected in series. The load side unit300and the heat source side unit100are included in the refrigerant circuit. The expansion device311corresponds to a first expansion device in the present invention. The load side unit300may further include an air-sending device (not illustrated) for supplying air to the load side heat exchanger312. The load side heat exchanger312may exchange heat between the refrigerant and a heat medium different from the refrigerant, for example, water.

The load side heat exchanger312exchanges heat between the heat medium (e.g., ambient air or water) and the refrigerant. In the heating operation, the load side heat exchanger312functions as a condenser (radiator) to condense and liquefy the refrigerant. In the cooling operation, the load side heat exchanger312functions as an evaporator to evaporate and gasify the refrigerant. The load side heat exchanger312is typically used in combination with an air-sending device, whose depiction is omitted. The rotation speed of the air-sending device is used to control the condensing capacity or the evaporating capacity of the load side heat exchanger312.

The expansion device311, functioning as a pressure reducing valve or an expansion valve, reduces the pressure of the refrigerant to expand the refrigerant. The expansion device311may include a component whose opening degree is variably adjustable, for example, an accurate flow control device, such as an electronic expansion valve, or an inexpensive refrigerant flow control unit, such as a capillary tube.

The load side unit300includes at least a temperature sensor314(temperature sensor314a,314b) that detects the temperature of a refrigerant pipe between the expansion device311and the load side heat exchanger312and a temperature sensor313(temperature sensor313a,313b) that detects the temperature of the refrigerant pipe between the load side heat exchanger312and the four-way switching valve102. Information (temperature information) obtained by such detection units is transmitted to the controller118controlling the operation of the air-conditioning apparatus500and is used to control various actuators. In other words, the information from the temperature sensor313and the temperature sensor314is used to adjust, for example, the opening degree of the expansion device311included in the load side unit300and the rotation speed of the air-sending device, whose depiction is omitted.

The refrigerant used in the air-conditioning apparatus500may be of any type. For example, any of natural refrigerants, such as carbon dioxide, hydrocarbon, and helium, chlorine-free alternate refrigerants, such as HFC-410A, HFC-407C, and HFC-404A, and chlorofluorocarbon refrigerants, such as R-22 and R-134a, used in existing products may be used.

Although the configuration in which the controller118controlling the operation of the air-conditioning apparatus500is provided in the heat source side unit100is illustrated as an example inFIG. 1, the controller118may be provided in any of the load side units300. Furthermore, the controller118may be provided outside the heat source side unit100and the load side units300. In addition, the controller118may be divided into a plurality of controllers on the basis of functions, and the controller may be provided in each of the heat source side unit100and the load side units300. In this case, the controllers may be connected to each other in a wireless or wired manner for communication.

Operations performed by the air-conditioning apparatus500will now be described.

The air-conditioning apparatus500receives a cooling request or a heating request from, for example, a remote controller provided in, for example, an indoor space. The air-conditioning apparatus500performs an air-conditioning operation in any of two operation modes in response to the request. The two operation modes are a cooling operation mode and a heating operation mode.

FIG. 2is a diagram illustrating a flow of the refrigerant in the cooling operation mode of the air-conditioning apparatus500according to Embodiment 1 of the present invention. An operation of the air-conditioning apparatus500in the cooling operation mode will now be described with reference toFIG. 2.

The compressor101compresses low-temperature, low-pressure refrigerant into high-temperature, high-pressure gas refrigerant and discharges the refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor101passes through the four-way switching valve102, and flows to the heat source side heat exchanger103. Since the heat source side heat exchanger103functions as a condenser, the refrigerant exchanges heat with the ambient air and thus condenses and liquefies. The liquid refrigerant leaving the heat source side heat exchanger103flows through the liquid main pipe402A, and flows out of the heat source side unit100.

The high-pressure liquid refrigerant leaving the heat source side unit100flows through the liquid branch pipes402aand402b, and flows into the load side units300aand300b. The liquid refrigerant that has flowed into the load side units300aand300bis throttled into low-temperature, two-phase gas-liquid refrigerant by the expansion devices311aand311b. The low-temperature, two-phase gas-liquid refrigerant flows into the load side heat exchangers312aand312b. Since the load side heat exchangers312aand312beach function as an evaporator, the refrigerant exchanges heat with the ambient air and thus evaporates and gasifies. At this time, the refrigerant removes heat from the ambient air, thus cooling the indoor space. After that, the refrigerant leaving the load side heat exchangers312aand312bflows through the gas branch pipes401aand401b, and flows out of the load side units300aand300b.

The refrigerant leaving the load side units300aand300bflows through the gas main pipe401A, and returns to the heat source side unit100. The gas refrigerant that has returned to the heat source side unit100passes through the four-way switching valve102and the accumulator104, and is again sucked into the compressor101. The above-described flow allows the air-conditioning apparatus500to implement the cooling operation mode.

FIG. 3is a refrigerant circuit diagram illustrating a flow of the refrigerant in the heating operation mode of the air-conditioning apparatus500according to Embodiment 1 of the present invention. An operation of the air-conditioning apparatus500in the heating operation mode will now be described with reference toFIG. 3.

The compressor101compresses low-temperature, low-pressure refrigerant into high-temperature, high-pressure gas refrigerant and discharges the refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor101passes through the four-way switching valve102, and flows to a gas main pipe401A. After that, the refrigerant flows out of the heat source side unit100. The high-temperature, high-pressure gas refrigerant leaving the heat source side unit100flows through the gas branch pipes401aand401b, and flows into the load side units300aand300b.

The gas refrigerant that has flowed into the load side units300aand300bflows into the load side heat exchangers312aand312b. Since the load side heat exchangers312aand312beach function as a condenser, the refrigerant exchanges heat with the ambient air and thus condenses and liquefies. At this time, the refrigerant transfers heat to the ambient air, thus heating the indoor space, which serves as an air-conditioned space. After that, the liquid refrigerant leaving the load side heat exchangers312aand312bis reduced in pressure by the expansion devices311aand311b. The refrigerant flows through the liquid branch pipes402aand402b, and flows out of the load side units300aand300b.

The refrigerant leaving the load side units300aand300bflows through the liquid main pipe402A, and returns to the heat source side unit100. The gas refrigerant that has returned to the heat source side unit100flows into the heat source side heat exchanger103. Since the heat source side heat exchanger103functions as an evaporator, the refrigerant exchanges heat with the ambient air and thus evaporates and gasifies. After that, the refrigerant leaving the heat source side heat exchanger103passes through the four-way switching valve102, and flows into the accumulator104. The compressor101sucks the refrigerant in the accumulator104and circulates the refrigerant through the refrigerant circuit, thus establishing the refrigeration cycle. The above-described flow allows the air-conditioning apparatus500to implement the heating operation mode.

Refrigerant cooling control, serving as a feature of Embodiment 1, will now be described.

The refrigerant cooling control, serving as control for cooling the controller118with the refrigerant, is performed in the same manner in both the cooling operation mode and the heating operation mode. For this reason, the refrigerant cooling control will be described below with reference to a diagram illustrating a flow of the refrigerant in the cooling operation mode.

FIG. 4is a refrigerant circuit diagram illustrating a flow of the refrigerant for the refrigerant cooling control in the cooling operation mode of the air-conditioning apparatus500according to Embodiment 1 of the present invention.

For the refrigerant cooling control, part of the high-pressure gas refrigerant flowing through the high-pressure pipe611is diverted to the bypass pipe608, and flows into the precooling heat exchanger601. The gas refrigerant that has flowed into the precooling heat exchanger601exchanges heat with air sent from the heat source side fan106, so that the refrigerant is cooled. The liquid refrigerant that has been cooled and reduced to a low pressure in the precooling heat exchanger601is further reduced to a lower pressure by the expansion device602. After that, the refrigerant flows into the refrigerant cooler603. In the refrigerant cooler603, the refrigerant exchanges heat with the controller118and thus evaporates. At this time, the refrigerant removes heat from the controller118and thus cools the controller118. The refrigerant turns into gas refrigerant or two-phase refrigerant by cooling the controller118. The refrigerant flows through the low-pressure pipe610and flows into the accumulator104.

The flow rate of the refrigerant through the refrigerant cooler603is adjusted by the expansion device602. The expansion device602is controlled based on the information obtained from the low-pressure sensor142, the controller temperature sensor605, the temperature sensor606, and the outdoor air temperature sensor604by the controller118. Specific control of the expansion device602will now be described.

FIG. 5is a flowchart illustrating control of the expansion device602during the refrigerant cooling control in the air-conditioning apparatus500according to Embodiment 1 of the present invention.FIG. 6is a diagram illustrating an operation of the expansion device602based on the flowchart ofFIG. 5. In the following description, it is assumed that temperatures (A) to (E) have the following relation: (B)<(D)<(C)<(E)<(A).

In an initial state, the expansion device602is closed. Upon start of the operation of the air-conditioning apparatus500, the controller118determines whether a temperature detected by the controller temperature sensor605is at or above a preset start temperature (A) (e.g., 75 degrees C.) (S1). If the detected temperature is below the start temperature (A), it is unnecessary to cool the controller118, and the opening degree of the expansion device602is kept as it is, or kept closed, (S2) to keep the refrigerant from flowing through the refrigerant cooler603. If the temperature detected by the controller temperature sensor605is at or above the start temperature (A), the controller118increases the opening degree of the expansion device602to a preset fixed value to open the expansion device602(S3). Consequently, the refrigerant flows through the refrigerant cooler603to start cooling of the controller118, so that the temperature of the controller118decreases.

The controller118checks a temperature detected by the controller temperature sensor605, and determines whether the temperature detected by the controller temperature sensor605is at or below a preset end temperature (B) (e.g., 45 degrees C.) (S4). If the temperature detected by the controller temperature sensor605is at or below the end temperature (B), the controller118closes the expansion device602to terminate cooling of the controller118(S5). The process returns to step S1. If the temperature detected by the controller temperature sensor605is above the end temperature (B), it is necessary to continue cooling, and the controller118then determines whether the temperature detected by the controller temperature sensor605is at or below an outdoor air temperature (D) (S6). This determination is performed to prevent condensation on the controller118.

If the temperature detected by the controller temperature sensor605falls to the outdoor air temperature (D) or lower, condensation will occur on the controller118. For this reason, the controller118closes the expansion device602to terminate cooling of the controller118(S5). The process returns to step S1. If the temperature detected by the controller temperature sensor605is above the outdoor air temperature (D), the controller118then determines whether the temperature detected by the controller temperature sensor605is at or below a preset target temperature (C) (e.g., 60 degrees C.) (S7).

If the temperature detected by the controller temperature sensor605is at or below the target temperature (C), the controller118reduces the opening degree of the expansion device602so that the temperature of the controller118reaches the target temperature (C) (S8). The process returns to determination in step S4. If the temperature detected by the controller temperature sensor605is at the target temperature (C), the present opening degree may be maintained. If the temperature detected by the controller temperature sensor605is above the target temperature (C), the controller118determines whether both the following conditions (1) and (2) are satisfied (S9).

(1) The degree of superheat, calculated from detection values of the temperature sensor606and the low-pressure sensor142, at the outlet of the refrigerant cooler603is at or below a previously set value (e.g., 2 degrees C.).

(2) The temperature detected by the controller temperature sensor605is at or below a certain value (E) (e.g., 70 degrees C.).

The determination in step S9is performed for the following purpose. If the opening degree of the expansion device602is adjusted to reduce the temperature detected by the controller temperature sensor605to the target temperature (C) or lower and, for example, the flow rate of the refrigerant through the bypass pipe608is high relative to the temperature of the controller118during the adjustment, the degree of superheat at the outlet of the refrigerant cooler603may decrease, leading to liquid back. Specifically, a high flow rate of the refrigerant through the bypass pipe608under conditions where the temperature of the controller118is not so high may result in an excess of cooling capacity, causing liquid back. The determination on the condition (1) in step S9is performed to prevent such liquid back.

Fundamentally, if the condition (1) is satisfied and the liquid back is likely to occur as described above, control is performed to reduce the opening degree of the expansion device602. However, if the temperature of the controller118is high and the opening degree is reduced, poor cooling may cause an excessive increase in temperature of the controller118. For this reason, the condition (2) is provided in addition to the condition (1). If the temperature detected by the controller temperature sensor605is not high, control is performed so that the degree of superheat reaches a target value. The condition (2) can be omitted.

Specifically, if both the conditions (1) and (2) are satisfied and cooling is continued, liquid back may occur. For this reason, when determining that both the conditions (1) and (2) are satisfied, the controller118reduces the opening degree of the expansion device602so that the degree of superheat at the outlet of the refrigerant cooler603reaches a target value (S10). The reduction of the opening degree of the expansion device602reduces the flow rate of the refrigerant through the bypass pipe608to increase the degree of superheat at the outlet of the refrigerant cooler603, thus preventing liquid back. If either of the conditions (1) and (2) is not satisfied or neither of the conditions (1) and (2) is satisfied, cooling is performed under conditions where liquid back is unlikely to occur. To continue cooling, therefore, the controller118increases the opening degree of the expansion device602so that the temperature detected by the controller temperature sensor605reaches the target temperature (C) (S11). The process returns to step S4, and the same processing steps are repeated.

In the above-described process, if the temperature detected by the controller temperature sensor605is within a range above the target temperature (C) and below the start temperature (A), the determination to prevent liquid back is performed in step S9. The reason is as follows. If the detected temperature is outside the above-described range, the degree of superheat will not be at or below the set value, or alternatively, control will be performed to reduce the opening degree of the expansion device602as demonstrated inFIG. 6. It is only required that determination in step S9is performed in the case where the detected temperature is within the above-described range.

The controller118is cooled by the above-described refrigerant cooling control. Specific numerical values of the temperatures in the above description are illustrative only, and these values may be set as appropriate in accordance with actual use conditions, for example.

As described above, according to Embodiment 1, the expansion device602is provided upstream of the refrigerant cooler603such that the refrigerant, reduced in pressure and temperature by the expansion device602, flows into the refrigerant cooler603. Before flowing through the refrigerant cooler603, the refrigerant is reduced to a lower pressure by the expansion device602. Its evaporating temperature in the refrigerant cooler603accordingly decreases. Such a configuration achieves a lower evaporating temperature in the refrigerant cooler than the related-art configuration in which the expansion device is provided downstream of the refrigerant cooler. Therefore, the configuration according to Embodiment 1 achieves a greater difference in temperature between the controller118and the refrigerant flowing through the refrigerant cooler603than the related-art configuration, thus increasing the efficiency of heat exchange. Consequently, a small amount of refrigerant can achieve a necessary cooling capacity.

Although a large amount of refrigerant has to be diverted to achieve the necessary cooling capacity in the related-art configuration, the amount of refrigerant to be diverted to the bypass pipe in Embodiment 1 can be reduced by an amount corresponding to an increase in heat exchange efficiency of the refrigerant cooler603. Since a sufficient flow rate of the refrigerant through the refrigerant circuit can be achieved, therefore, the cooling or heating performance of the air-conditioning apparatus can be maintained.

In addition, since the expansion device602is provided not downstream of the refrigerant cooler603but upstream of the refrigerant cooler603, the configuration of the refrigerant circuit can be simplified.

Although the air-conditioning apparatus500according to Embodiment 1 has the above-described exemplary configuration in which the number of heat source side units100is one and the number of load side units300is two, the apparatus may include any number of heat source side units and any number of load side units. In Embodiment 1, the case where the present invention is applied to the air-conditioning apparatus500including the load side units300that can be switched between the cooling operation and the heating operation and can be operated in either one of these operations has been described as an example. The present invention can be applied to any other apparatuses. Examples of the other apparatuses, to which the present invention can be applied, include a refrigeration cycle apparatus that heats a load with capacity supply and an apparatus in which a refrigerant circuit is configured by using a refrigeration cycle, such as a refrigeration cycle system.

In Embodiment 2, an air-conditioning apparatus capable of performing a cooling and heating mixed operation will be described as an example of another apparatus to which the present invention can be applied.

FIG. 7is a schematic diagram illustrating an exemplary configuration of a refrigerant circuit of an air-conditioning apparatus500A according to Embodiment 2 of the present invention. The following description will be focused on the difference between the air-conditioning apparatus500A according to Embodiment 2 and the air-conditioning apparatus500according to Embodiment 1 illustrated inFIG. 1.

The air-conditioning apparatus500A according to Embodiment 2 includes a relay unit200, and is configured such that the relay unit200is provided between the heat source side unit100and the load side units300in the air-conditioning apparatus500according to Embodiment 1 illustrated inFIG. 1. The load side units300in Embodiment 2 have the same configuration as that in Embodiment 1.

In Embodiment 2, the relay unit200is connected to a heat source side unit100A by two pipes (a low-pressure pipe403and a high-pressure pipe404), and is connected to the load side units300aand300bby the gas branch pipe401a, the liquid branch pipe402a, the gas branch pipe401b, and the liquid branch pipe402b.

The heat source side unit100A in Embodiment 2 further includes a check valve112, a check valve113, a check valve114, a check valve115, a first connecting pipe120, and a second connecting pipe121in addition to the components included in the heat source side unit100in Embodiment 1. The check valve112, the check valve113, the check valve114, the check valve115, the first connecting pipe120, and the second connecting pipe121constitute a flow direction device in the present invention.

The first connecting pipe120is a pipe that connects the high-pressure pipe404downstream of the check valve113to the low-pressure pipe403downstream of the check valve112. The second connecting pipe121is a pipe that connects the high-pressure pipe404upstream of the check valve113to the low-pressure pipe403upstream of the check valve112.

As illustrated inFIG. 7, the second connecting pipe121and the high-pressure pipe404join at a junction a. The first connecting pipe120and the high-pressure pipe404join at a junction b (downstream of the junction a). The second connecting pipe121and the low-pressure pipe403join at a junction c. The first connecting pipe120and the low-pressure pipe403join at a junction d (downstream of the junction c).

The check valve112, which is provided between the junction c and the junction d, allows the refrigerant to flow only in a direction from the relay unit200to the heat source side unit100A. The check valve113, which is provided between the junction a and the junction b, allows the refrigerant to flow only in a direction from the heat source side unit100A to the relay unit200. The check valve115, which is provided in the first connecting pipe120, allows the refrigerant to flow only in a direction from the junction d to the junction b. The check valve114, which is provided in the second connecting pipe121, allows the refrigerant to flow only in a direction from the junction c to the junction a.

Such a configuration enables the refrigerant to flow in one direction between the heat source side unit100A and the relay unit200in response to either of a heating request and a cooling request from the load side unit300. In other words, the refrigerant flows through the high-pressure pipe404in the direction from the heat source side unit100A to the relay unit200, and flows through the low-pressure pipe403in the direction from the relay unit200to the heat source side unit100A.

The heat source side unit100A includes a bypass pipe608A instead of the bypass pipe608in Embodiment 1. The bypass pipe608A differs from the bypass pipe608in Embodiment 1 in the position of one end connected to the high-pressure side. The bypass pipe608in Embodiment 1 is connected to the high-pressure pipe611through which the high-pressure refrigerant discharged from the compressor101flows, whereas the bypass pipe608A in Embodiment 2 is connected to the high-pressure pipe404, which extends from the heat source side heat exchanger103toward the expansion devices311, downstream of the junction b. Except for the above-described difference, the route of the bypass pipe608A and the devices arranged in the bypass pipe608A are the same as that of and those in the bypass pipe608in Embodiment 1.

The relay unit200will now be described.

The relay unit200switches between refrigerant flow directions in accordance with operation states of the load side units300so that low-temperature refrigerant is supplied to the load side unit300performing the cooling operation and high-temperature refrigerant is supplied to the load side unit300performing the heating operation. InFIG. 7, some of the components included in the relay unit200have a letter “a” or “b” after their reference sign. The letter “a” or “b” added to the reference sign represents that the relevant component is connected to the “load side unit300a” or the “load side unit300b”. In the following description, the letter “a” or “b” added to the reference sign may be omitted. Although the letter “a” or “b” may be omitted in the following description, the relay unit200includes those components connected to the “load side unit300a” and the “load side unit300b”.

The relay unit200includes a gas-liquid separator211, first on-off valves212(a first on-off valve212a, a first on-off valve212b), second on-off valves213(a second on-off valve213a, a second on-off valve213b), a first expansion device214, a second expansion device215, a first refrigerant heat exchanger216, and a second refrigerant heat exchanger217. The relay unit200further includes a connecting pipe220that branches off from a pipe located downstream of a primary side (where the refrigerant leaving the first expansion device214flows) of the second refrigerant heat exchanger217and that is connected to the low-pressure pipe403.

The gas-liquid separator211, which is provided in the high-pressure pipe404, has a function of separating two-phase refrigerant coming from the high-pressure pipe404into gas refrigerant and liquid refrigerant. The gas refrigerant separated by the gas-liquid separator211is supplied to the first on-off valves212through a connecting pipe221, and the liquid refrigerant is supplied to the first refrigerant heat exchanger216.

The first on-off valves212, which are used to control refrigerant supply to the load side unit300in each operation mode, are arranged between the connecting pipe221and the gas branch pipes401aand401b. Specifically, each of the first on-off valves212is connected at one end to the gas-liquid separator211, and is connected at the other end to the load side heat exchanger312in the load side unit300. The first on-off valve212is controlled to open or close to allow or block the flow of the refrigerant.

The second on-off valves213, which are also used to control refrigerant supply to the load side unit300in each operation mode, are arranged between the low-pressure pipe403and the gas branch pipes401aand401b. Specifically, each of the second on-off valves213is connected at one end to the low-pressure pipe403, and is connected at the other end to the load side heat exchanger312in the load side unit300. The second on-off valve213is controlled to open or close to allow or block the flow of the refrigerant.

The first expansion device214is provided in a pipe connecting the gas-liquid separator211to the liquid branch pipes402aand402b. Specifically, the first expansion device214is provided between the first refrigerant heat exchanger216and the second refrigerant heat exchanger217. The first expansion device214, functioning as a pressure reducing valve or an expansion valve, reduces the pressure of the refrigerant to expand the refrigerant. The first expansion device214may include a component whose opening degree is variably adjustable, for example, an accurate flow control device, such as an electronic expansion valve, or an inexpensive refrigerant flow control unit, such as a capillary tube.

The second expansion device215is provided in the connecting pipe220, and is located between the second refrigerant heat exchanger217and the second on-off valves213. The second expansion device215, functioning as a pressure reducing valve or an expansion valve, reduces the pressure of the refrigerant to expand the refrigerant. Like the first expansion device214, the second expansion device215may include a component whose opening degree is variably adjustable, for example, an accurate flow control device, such as an electronic expansion valve, or an inexpensive refrigerant flow control unit, such as a capillary tube.

The first refrigerant heat exchanger216exchanges heat between the refrigerant flowing through its primary side (where the liquid refrigerant separated by the gas-liquid separator211flows) and the refrigerant flowing through its secondary side (where the refrigerant leaving the second refrigerant heat exchanger217after passing through the second expansion device215flows through the connecting pipe220).

The second refrigerant heat exchanger217exchanges heat between the refrigerant flowing through its primary side (downstream of the first expansion device214) and the refrigerant flowing through its secondary side (downstream of the second expansion device215).

The arrangement of the first expansion device214, the second expansion device215, the first refrigerant heat exchanger216, and the second refrigerant heat exchanger217in the relay unit200allows the first refrigerant heat exchanger216and the second refrigerant heat exchanger217to exchange heat between the refrigerant flowing through a main circuit (the primary side) and the refrigerant flowing through the connecting pipe220(the secondary side), thus subcooling the refrigerant flowing through the main circuit. The opening degree of the second expansion device215is used to adjust the amount of refrigerant to be diverted to the secondary side so that proper subcooling can be achieved at a primary-side outlet of the second refrigerant heat exchanger217.

Although the configuration in which the controller118controlling the operation of the air-conditioning apparatus500A is provided in the heat source side unit100A is illustrated as an example inFIG. 7, the controller118may be provided in any of the relay unit200and the load side units300. Furthermore, the controller118may be provided outside the heat source side unit100A, the relay unit200, and the load side units300. In addition, the controller118may be divided into a plurality of controllers on the basis of functions, and the controller may be provided in each of the heat source side unit100A, the relay unit200, and the load side units300. In this case, the controllers may be connected to each other in a wireless or wired manner for communication.

Operations performed by the air-conditioning apparatus500A will now be described.

The air-conditioning apparatus500A receives a cooling request or a heating request from, for example, a remote controller provided in, for example, an indoor space. The air-conditioning apparatus500A performs an air-conditioning operation in any of four operation modes in response to the request. The four operation modes are as follows:

(1) a cooling only operation mode in which all of the load side units300are required to perform the cooling operation;

(2) a cooling main operation mode in which a cooling operation request and a heating operation request have been received and it is determined that a load to be processed by the cooling operation is large;

(3) a heating main operation mode in which a cooling operation request and a heating operation request have been received and it is determined that a heating load is large; and

(4) a heating only operation mode in which all of the load side units300are required to perform the heating operation.

The operation modes will now be described.

FIG. 8is a diagram illustrating a flow of the refrigerant in the cooling only operation mode of the air-conditioning apparatus500A according to Embodiment 2 of the present invention. An operation of the air-conditioning apparatus500A in the cooling only operation mode will now be described with reference toFIG. 8. For the first on-off valves212and the second on-off valves213inFIG. 8, each filled symbol represents a closed state, and each outlined symbol represents an open state. The same applies to the following figures, which will be described later.

The compressor101compresses low-temperature, low-pressure refrigerant into high-temperature, high-pressure gas refrigerant and discharges the refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor101passes through the four-way switching valve102, and flows to the heat source side heat exchanger103. Since the heat source side heat exchanger103functions as a condenser, the refrigerant exchanges heat with ambient air and thus condenses and liquefies. The liquid refrigerant leaving the heat source side heat exchanger103flows through the high-pressure pipe404, passes through the check valve113, and flows out of the heat source side unit100A.

The high-pressure liquid refrigerant leaving the heat source side unit100A passes through the gas-liquid separator211in the relay unit200, and flows into the primary side (refrigerant inflow side) of the first refrigerant heat exchanger216. The liquid refrigerant that has flowed into the primary side of the first refrigerant heat exchanger216is subcooled by the refrigerant flowing through the secondary side (refrigerant outflow side) of the first refrigerant heat exchanger216. The liquid refrigerant whose degree of subcooling has increased is throttled to an intermediate pressure by the first expansion device214. After that, the liquid refrigerant flows into the second refrigerant heat exchanger217, where the degree of subcooling of the liquid refrigerant is further increased. Then, the flow of the liquid refrigerant divides into two streams. One of the streams passes through a check valve218aand a check valve218band then flows out of the relay unit200. The other stream flows to the second expansion device215.

The liquid refrigerant leaving the relay unit200flows into the load side units300aand300b. The liquid refrigerant that has flowed into the load side units300aand300bis throttled into low-temperature, two-phase gas-liquid refrigerant by the expansion devices311aand311b. The low-temperature, two-phase gas-liquid refrigerant flows into the load side heat exchangers312aand312b. Since the load side heat exchangers312aand312beach function as an evaporator, the refrigerant exchanges heat with ambient air and thus evaporates and gasifies. At this time, the refrigerant removes heat from the ambient air, thus cooling the indoor space. After that, the refrigerant leaving the load side heat exchangers312aand312bflows through the gas branch pipes401aand401b, flows out of the load side unit300aand300b, and flows into the relay unit200.

The refrigerant that has flowed into the relay unit200passes through the second on-off valves213aand213b, joins the refrigerant that has flowed through the connecting pipe220after passing through the first expansion device214and the second expansion device215for subcooling in the second refrigerant heat exchanger217. Then, the refrigerant flows into the low-pressure pipe403.

The refrigerant flowing through the low-pressure pipe403flows out of the relay unit200and then returns to the heat source side unit100A. The gas refrigerant that has returned to the heat source side unit100A passes through the check valve112, the four-way switching valve102, and the accumulator104, and is then sucked again into the compressor101. The above-described flow allows the air-conditioning apparatus500A to implement the cooling only operation mode.

FIG. 9is a diagram illustrating a flow of the refrigerant in the cooling main operation mode of the air-conditioning apparatus500A according to Embodiment 2 of the present invention. In the case where the load side units300perform different operations, or the cooling operation and the heating operation, and a cooling load is larger than a heating load, the apparatus operates in the cooling main operation mode. An operation of the air-conditioning apparatus500A in the cooling main operation mode will be described with reference toFIG. 9. The operation in the cooling main operation mode will now be described on the assumption that the load side unit300aperforms cooling and the load side unit300bperforms heating.

The compressor101compresses low-temperature, low-pressure refrigerant into high-temperature, high-pressure gas refrigerant and discharges the refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor101passes through the four-way switching valve102and flows into the heat source side heat exchanger103. Since the heat source side heat exchanger103functions as a condenser, the refrigerant exchanges heat with the ambient air and thus condenses into a two-phase state. Then, the two-phase gas-liquid refrigerant leaving the heat source side heat exchanger103flows through the high-pressure pipe404, passes through the check valve113, and flows out of the heat source side unit100A.

The two-phase gas-liquid refrigerant leaving the heat source side unit100A flows into the gas-liquid separator211in the relay unit200. The two-phase gas-liquid refrigerant that has flowed into the gas-liquid separator211is separated into gas refrigerant and liquid refrigerant by the gas-liquid separator211. The gas refrigerant flows out of the gas-liquid separator211and flows into the connecting pipe221. The gas refrigerant that has flowed into the connecting pipe221passes through the first on-off valve212b, flows through the gas branch pipe401b, and flows into the load side unit300b. The gas refrigerant that has flowed into the load side unit300btransfers heat to the ambient air in the load side heat exchanger312bto heat an air-conditioned space, and thus condenses and liquefies. Then, the refrigerant flows out of the load side heat exchanger312b. The liquid refrigerant leaving the load side heat exchanger312bis throttled to an intermediate pressure by the expansion device311b.

The intermediate-pressure liquid refrigerant throttled by the expansion device311bflows through the liquid branch pipe402b, and passes through a check valve219b. The liquid refrigerant leaving the check valve219bjoins the liquid refrigerant that has passed through the first refrigerant heat exchanger216and the first expansion device214after being separated by the gas-liquid separator211. Then, the refrigerant flows into the second refrigerant heat exchanger217. The liquid refrigerant that has flowed into the second refrigerant heat exchanger217is further increased in degree of subcooling and then flows out of the second refrigerant heat exchanger217. The flow of the refrigerant leaving the second refrigerant heat exchanger217divides into two streams. One of the streams passes through the check valve218a, flows through the liquid branch pipe402a, and flows out of the relay unit200. The other stream flows to the second expansion device215. The liquid refrigerant leaving the relay unit200flows into the load side unit300a. The liquid refrigerant that has flowed into the load side unit300ais throttled into low-temperature, two-phase gas-liquid refrigerant by the expansion device311a. The low-temperature, two-phase gas-liquid refrigerant flows into the load side heat exchanger312a, where the refrigerant removes heat from the ambient air to cool the air-conditioned space and thus evaporates and gasifies. Then, the refrigerant flows out of the load side heat exchanger312a.

The gas refrigerant leaving the load side heat exchanger312aflows through the gas branch pipe401a, flows out of the load side unit300a, and then flows into the relay unit200. The refrigerant that has flowed into the relay unit200passes through the second on-off valve213a. The refrigerant that has passed through the second on-off valve213ajoins the refrigerant that has flowed through the connecting pipe220after passing through the first expansion device214and the second expansion device215for subcooling in the second refrigerant heat exchanger217. Then, the refrigerant flows into the low-pressure pipe403.

The refrigerant flowing through the low-pressure pipe403flows out of the relay unit200and then returns to the heat source side unit100A. The gas refrigerant that has returned to the heat source side unit100A passes through the check valve112, the four-way switching valve102, and the accumulator104, and is then sucked again into the compressor101. The above-described flow allows the air-conditioning apparatus500A to implement the cooling main operation mode.

FIG. 10is a refrigerant circuit diagram illustrating a flow of the refrigerant in the heating only operation mode in the air-conditioning apparatus500A according to Embodiment 2 of the present invention. An operation of the air-conditioning apparatus500A in the heating only operation mode will be described with reference toFIG. 10.

The compressor101compresses low-temperature, low-pressure refrigerant into high-temperature, high-pressure gas refrigerant and discharges the refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor101passes through the four-way switching valve102and the check valve115, and flows into the high-pressure pipe404. The refrigerant then flows out of the heat source side unit100A. The high-temperature, high-pressure gas refrigerant leaving the heat source side unit100A passes through the gas-liquid separator211in the relay unit200, flows through the connecting pipe221, and passes through the first on-off valves212aand212b. The high-temperature, high-pressure gas refrigerant that has passed through the first on-off valves212aand212bflows through the gas branch pipes401aand401binto the load side units300aand300b.

The gas refrigerant that has flowed into the load side units300aand300bflows into the load side heat exchangers312aand312b. Since the load side heat exchangers312aand312beach function as a condenser, the refrigerant exchanges heat with the ambient air and thus condenses and liquefies. At this time, the refrigerant transfers heat to the ambient air, thus heating the air-conditioned space, or the indoor space. Then, the liquid refrigerant flows out of the load side heat exchangers312aand312b, and is reduced in pressure by the expansion devices311aand311b.

The liquid refrigerant reduced in pressure by the expansion devices311aand311bflows through the liquid branch pipes402aand402b, flows out of the load side units300aand300b, and then flows into the relay unit200. The liquid refrigerant that has flowed into the relay unit200passes through a check valve219aand the check valve219b, and flows into the pipe between the first expansion device214and the second refrigerant heat exchanger217. The refrigerant passes through the second refrigerant heat exchanger217and then passes through the second expansion device215. The refrigerant flows through the connecting pipe220, and flows into the low-pressure pipe403.

The refrigerant flowing through the low-pressure pipe403flows out of the relay unit200and then returns to the heat source side unit100A. The refrigerant that has returned to the heat source side unit100A flows through the second connecting pipe121, passes through the check valve114, and flows into the heat source side heat exchanger103. Since the heat source side heat exchanger103functions as an evaporator, the refrigerant exchanges heat with the ambient air and thus evaporates and gasifies. After that, the refrigerant leaving the heat source side heat exchanger103passes through the four-way switching valve102, and flows into the accumulator104. The compressor101sucks the refrigerant in the accumulator104and circulates the refrigerant through the refrigerant circuit, thus establishing the refrigeration cycle. The above-described flow allows the air-conditioning apparatus500A to implement the heating only operation mode.

FIG. 11is a refrigerant circuit diagram illustrating a flow of the refrigerant in the heating main operation mode of the air-conditioning apparatus500A according to Embodiment 2 of the present invention. An operation of the air-conditioning apparatus500A in the heating main operation mode will be described with reference toFIG. 11. The heating main operation mode implemented in response to a heating request from the load side unit300aand a cooling request from the load side unit300bwill now be described. The flow of the refrigerant from the compressor101in the heat source side unit100A to the load side unit300arequired to perform heating is the same as that in the heating only operation mode, and a description of this flow is omitted.

The liquid refrigerant flowing through the liquid branch pipe402aafter passing through the load side unit300arequired to perform heating passes through the check valve219a. Then, the refrigerant is subcooled by the second refrigerant heat exchanger217, and flows out of the second refrigerant heat exchanger217. The flow of the liquid refrigerant leaving the second refrigerant heat exchanger217divides into two streams. One of the streams passes through the check valve218b, flows through the liquid branch pipe402b, and flows into the load side unit300brequired to perform cooling. The other stream flows to the second expansion device215. The refrigerant that has flowed into the load side unit300bis reduced in pressure by the expansion device311b. The refrigerant reduced in pressure by the expansion device311bflows into the load side heat exchanger312b.

Since the load side heat exchanger312bfunctions as an evaporator, the refrigerant exchanges heat with the ambient air and thus evaporates and gasifies. At this time, the refrigerant removes heat from the ambient air, thus cooling the indoor space. After that, the gas refrigerant leaving the load side heat exchanger312bflows through the gas branch pipe401b, flows out of the load side unit300b, and flows into the relay unit200. The refrigerant that has flowed into the relay unit200passes through the second on-off valve213b. The refrigerant that has passed through the second on-off valve213bjoins the refrigerant that has flowed through the connecting pipe220after passing through the second expansion device215for subcooling in the second refrigerant heat exchanger217. Then, the refrigerant flows into the low-pressure pipe403.

The refrigerant flowing through the low-pressure pipe403flows out of the relay unit200and then returns to the heat source side unit100A. The refrigerant that has returned to the heat source side unit100A passes through the check valve114and flows into the heat source side heat exchanger103. Since the heat source side heat exchanger103functions as an evaporator, the refrigerant exchanges heat with the ambient air and thus evaporates and gasifies. After that, the refrigerant leaving the heat source side heat exchanger103passes through the four-way switching valve102, and flows into the accumulator104. The compressor101sucks the refrigerant in the accumulator104and circulates the refrigerant through the circuit, thus establishing the refrigeration cycle. The above-described flow allows the air-conditioning apparatus500A to implement the heating main operation mode.

The present invention can be applied to the air-conditioning apparatus500A that implements the above-described operation modes. In other words, the refrigerant cooling control illustrated in the flowchart ofFIG. 5can be used in the air-conditioning apparatus500A. Thus, the air-conditioning apparatus500A according to Embodiment 2 can offer the same advantages as those in Embodiment 1 described above.

As described above, the high-pressure side end of the two ends of the bypass pipe608in Embodiment 1 is connected to the high-pressure pipe611, whereas the high-pressure side end of the bypass pipe608A in Embodiment 2 is connected to the high-pressure pipe404downstream of the junction b. Therefore, a flow of the refrigerant for the refrigerant cooling control in Embodiment 2 slightly differs from that in Embodiment 1. The flow of the refrigerant for the refrigerant cooling control will now be described. Since the refrigerant for the refrigerant cooling control flows in the same way in any operation mode, the flow of the refrigerant will be described with reference to a diagram illustrating the flow of the refrigerant in the cooling main operation mode.

FIG. 12is a refrigerant circuit diagram illustrating the flow of the refrigerant for the refrigerant cooling control in the cooling only operation mode of the air-conditioning apparatus500A according to Embodiment 2 of the present invention.

In Embodiment 2, when the expansion device602is opened, part of the refrigerant flowing from the junction b to the relay unit200in the high-pressure pipe404is diverted to the bypass pipe608A. The refrigerant diverted to the bypass pipe608A flows in the same way as the refrigerant flowing through the bypass pipe608in Embodiment 1. Specifically, the refrigerant diverted to the bypass pipe608A flows into the precooling heat exchanger601. The liquid refrigerant that has flowed into the precooling heat exchanger601exchanges heat with air from the heat source side fan106, so that the refrigerant is cooled. The liquid refrigerant cooled and reduced in pressure by the precooling heat exchanger601is further reduced to a lower pressure by the expansion device602. Then, the refrigerant flows into the refrigerant cooler603. In the refrigerant cooler603, the refrigerant exchanges heat with the controller118and thus evaporates. At this time, the refrigerant removes heat from the controller118and thus cools the controller118. The refrigerant turns into gas refrigerant or two-phase refrigerant by cooling the controller118. The refrigerant flows through the low-pressure pipe610, and flows into the accumulator104.

Although the air-conditioning apparatus500A according to Embodiment 2 has the above-described exemplary configuration in which the number of heat source side units100A is one, the number of relay units200is one, and the number of load side units300is two, the apparatus may include any number of heat source side units, any number of relay units, and any number of load side units.

Although Embodiments 1 and 2 have been described on the assumption that the refrigeration cycle apparatus is the air-conditioning apparatus, the refrigeration cycle apparatus may be a cooling apparatus that cools, for example, a refrigerator/freezer warehouse.