Refrigeration cycle apparatus

A refrigeration cycle apparatus includes a refrigerant circuit which allows refrigerant to circulate therethrough, and an outdoor heat exchanger which exchanges heat between the refrigerant and outdoor air. The outdoor heat exchanger has first to third heat exchange sections. The second heat exchange section is located below the first heat exchange section, and the third heat exchange section is located below the second heat exchange section. In a refrigerant passage connecting the second and third heat exchange sections, a first pressure reducing device reduces a pressure of the refrigerant flowing through the refrigerant passage. In an operation mode in which the first and second heat exchange sections each serve as an evaporator, the third heat exchange section is located upstream of the second heat exchange section in the flow of the refrigerant, and refrigerant having a temperature higher than that of the outdoor air flows through the third heat exchange section.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of PCT/JP2016/068971 filed on Jun. 27, 2016, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a refrigeration cycle apparatus including an outdoor heat exchanger.

BACKGROUND ART

Patent Literature 1 discloses an outdoor heat exchanger including a plurality of flat tubes, a first header collecting pipe connected to one of the ends of each of the flat tubes, and a second header collecting pipe connected to the other end of each flat tube. In the outdoor heat exchanger, an upper heat exchange region serves as a main heat exchange region, and a lower heat exchange region serves as an auxiliary heat exchange region. The main heat exchange region is divided into a plurality of main heat exchange sections, and the auxiliary heat exchange region is divided into a plurality of auxiliary heat exchange sections the number of which is equal to that of the main heat exchange sections. In the case where the outdoor heat exchanger serves as a condenser, high-pressure gas refrigerant flows into each of the main heat exchange sections. In each main heat exchange section, the gas refrigerant transfers heat to outdoor air and thus condenses. The refrigerant which has condensed in each main heat exchange section further transfers heat to the outdoor air in the auxiliary heat exchange sections, which are associated with the main heat exchange sections, and the refrigerant is thus subcooled. In the case where the outdoor heat exchanger serves as an evaporator, two-phase refrigerant flows into each of the auxiliary heat exchange sections. In each auxiliary heat exchange section, the refrigerant receives heat from the outdoor air, and as a result part of liquid refrigerant evaporates. After flowing out of each auxiliary heat exchange section, the refrigerant further receives heat from the outdoor air in the main heat exchange sections, which are associated with the auxiliary heat sections, and as a result the refrigerant evaporates to change into single-phase gas refrigerant.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the case where a heating operation is performed in a refrigeration cycle apparatus including the outdoor heat exchanger disclosed in Patent Literature 1, the outdoor heat exchanger serves as an evaporator. Thus, when the temperature of outdoor air is low, moisture in the air deposits as frost on fins included in the main heat exchange sections and the auxiliary heat exchange sections. The frost on the fins inhibits heat exchange in the outdoor heat exchanger. Therefore, a defrosting operation for melting frost by causing high-pressure gas refrigerant to flow into the outdoor heat exchanger is periodically performed. Water obtained by melting the frost in the defrosting operation collects at lower part of the outdoor heat exchanger. In this state, if the heating operation is resumed, there is a possibility that the lower part of the outdoor heat exchanger will freeze, causing breakage of the outdoor heat exchanger.

The present invention has been made to solve the above problem, and aims to provide a refrigeration cycle apparatus which can prevent breakage of an outdoor heat exchanger.

Solution to Problem

A refrigeration cycle apparatus according to an embodiment of the present invention includes a refrigerant circuit which allows refrigerant to circulate therethrough, and an outdoor heat exchanger which is provided to the refrigerant circuit, and exchanges heat between the refrigerant and outdoor air. The outdoor heat exchanger has a first heat exchange section, a second heat exchange section, and a third heat exchange section. The second heat exchange section is located below the first heat exchange section, and is connected to the first heat exchange section. The third heat exchange section is located below the second heat exchange section, and is connected to the second heat exchange section. The apparatus further includes a first pressure reducing device provided at a refrigerant passage which connects the second heat exchange section and the third heat exchange section. The first pressure reducing device reduces a pressure of the refrigerant flowing through the refrigerant passage. The third heat exchange section is located at a position more upstream than a position of the second heat exchange section in a refrigerant circulating direction in an operation mode in which the first heat exchange section and the second heat exchange section each serve as an evaporator, and the refrigerant having a temperature higher than that of the outdoor air flows through the third heat exchange section.

Advantageous Effects of Invention

According to an embodiment of the present invention, refrigerant having a temperature higher than that of outdoor air flows through a third heat exchange section located below a first heat exchange section and a second heat exchange section in an operation mode in which the first and second heat exchange sections each serve as an evaporator, Thereby, it is possible to prevent lower part of an outdoor heat exchanger from freezing even if the above operation mode is resumed under a condition where water formed by melting frost or defrosting stays in the third heat exchange section. Thus, the outdoor heat exchanger can be prevented from being broken.

DESCRIPTION OF EMBODIMENTS

A refrigeration cycle apparatus according to embodiment 1 of the present invention will be described.FIG. 1is a schematic refrigerant-circuit diagram illustrating a configuration of the refrigeration cycle apparatus according to embodiment 1. It should be noted that the relationship in dimension and shape between components as illustrated in the following drawings includingFIG. 1may differ from that between the actual components. The positional relationship between the components (for example, a vertically positional relationship) described in the following, in principle, corresponds to that in the case where the refrigeration cycle apparatus is installed usable.

As illustrated inFIG. 1, the refrigeration cycle apparatus includes a refrigerant circuit10which allows refrigerant to circulate therethrough. The refrigerant circuit10includes a compressor11, a flow switching device15, an indoor heat exchanger12, a pressure reducing device13, and an outdoor heat exchanger14, which are connected by refrigerant pipes. The refrigeration cycle apparatus further includes an outdoor unit22installed in, for example, an outdoor space, and an indoor unit21installed in, for example, an indoor space. The outdoor unit22includes the compressor11, the flow switching device15, the pressure reducing device13, the outdoor heat exchanger14and an outdoor-air sending fan32which sends outdoor air to the outdoor heat exchanger14. The indoor unit21includes the indoor heat exchanger12and an indoor-air sending fan31which sends indoor air to the indoor heat exchanger12.

The compressor11is fluid machinery which compresses sucked low-pressure refrigerant into high-pressure refrigerant, and discharges the high-pressure refrigerant. The flow switching device15switches a passage for refrigerant in the refrigerant circuit10between a passage for a cooling operation and a passage for a heating operation in the refrigerant circuit10. As the flow switching device15, for example, a four-way valve is used. In the cooling operation, the passage in the flow switching device15is switched to a passage indicated by solid lines inFIG. 1. In the heating operation, the passage in the flow switching device15is switched to a passage indicated by broken lines inFIG. 1. The indoor heat exchanger12is a load-side heat exchanger which serves as an evaporator in the cooling operation, and serves as a radiator (e.g., a condenser) in the heating operation. In the indoor heat exchanger12, refrigerant flowing therethrough exchanges heat with indoor air supplied by the indoor-air sending fan31.

The pressure reducing device13reduces the pressure of high-pressure refrigerant. As the pressure reducing device13, for example, an electronic expansion valve whose opening degree can be adjusted under the control by a controller is used. The outdoor heat exchanger14is a heat-source-side heat exchanger which serves mainly as a radiator (e.g., a condenser) in the cooling operation, and serves mainly as an evaporator in the heating operation. In the outdoor heat exchanger14, refrigerant flowing therethrough exchanges heat with outdoor air supplied by the outdoor-air sending fan32.

The controller (not illustrated) includes a microcomputer including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an input-output (I/O) port, a timer, etc. The controller controls an operation of the entire refrigeration cycle apparatus including the compressor11, the pressure reducing device13, the flow switching device15, the indoor-air sending fan31and the outdoor-air sending fan32on the basis of detection signals from a temperature sensor which detects a temperature of the refrigerant and a pressure sensor which detects a pressure of the refrigerant. The controller may be provided in the outdoor unit22or in the indoor unit21. Furthermore, the controller may include an outdoor-unit control unit, which is provided in the outdoor unit22, and an indoor-unit control unit, which is provided in the indoor unit21, and which is capable of communicating with the outdoor-unit control unit.

FIG. 2is a schematic front view illustrating a configuration of the outdoor heat exchanger14in embodiment 1. The outdoor heat exchanger14includes a plurality of heat transfer tubes extending laterally and a plurality of plate-like fins intersecting the heat transfer tubes. As each of the heat transfer tubes, a flat multi-hole tube or a small-diameter tube (e.g., a cylindrical tube) having an inside diameter of 6 mm or less is used. The outdoor heat exchanger14may include a pair of header collecting pipes connected to both ends of each of the heat transfer tubes.

As illustrated inFIG. 2, the outdoor heat exchanger14has a heat exchange region divided into three heat exchange sections vertically arranged parallel to each other. The outdoor heat exchanger14includes a first heat exchange section41which corresponds to the uppermost one of the three heat exchange section, a second heat exchange section42which is located below the first heat exchange section41, and a third heat exchange section43which is located below the second heat exchange section42and corresponds to the lowermost one of the heat exchange sections. In embodiment 1, the first heat exchange section41, the second heat exchange section42and the third heat exchange section43are regions into which the heat exchange region of the single outdoor heat exchanger14are separated. Therefore, in terms of structure, the first heat exchange section41, the second heat exchange section42and the third heat exchange section43are provided as a single body.

The first heat exchange section41, the second heat exchange section42, and the third heat exchange section43are connected in series to each other in a refrigerant circulating direction in the refrigerant circuit10, The first heat exchange section41is connected to a discharge side or a suction side of the compressor11by a refrigerant passage44which is defined by a header of the outdoor heat exchanger14, a refrigerant pipe, the flow switching device15, etc. The first heat exchange section41is connected to the second heat exchange section42by a refrigerant passage45defined by a header, a refrigerant pipe, etc. The second heat exchange section42and the third heat exchange section43are connected to each other by a refrigerant passage46defined by a header, a refrigerant pipe, etc. The third heat exchange section43is connected to the pressure reducing device13or the indoor heat exchanger12by a refrigerant passage47defined by a header, a refrigerant pipe, etc.

In the cooling operation, the refrigerant discharged from the compressor11flows, as indicated by a dashed arrow inFIG. 2, through the first heat exchange section41, the second heat exchange section42and the third heat exchange section43in this order. In the heating operation, the refrigerant to be sucked into the compressor11flows, as indicated by a solid arrow inFIG. 2, through the third heat exchange section43, the second heat exchange section42and the first heat exchange section41in this order.

In the refrigerant passage46between the second heat exchange section42and the third heat exchange section43, a flow control device80is provided as a pressure reducing device which reduces the pressure of refrigerant which flows through the refrigerant passage. As the flow control device80, for example, an electronic expansion valve to be controlled by the controller is used.

For example, in the heating operation, an opening degree of the flow control device80is adjusted such that the degree of superheat of refrigerant at an outlet (point e inFIG. 2) of the first heat exchange section41is made closer to a preset target value. The degree of superheat of the refrigerant at the outlet of the first heat exchange section41is calculated based on a detection value obtained by the temperature sensor which detects a temperature of the refrigerant at the outlet of the first heat exchange section41and a detection value obtained by the pressure sensor which detects a saturation temperature of the refrigerant at the outlet of the first heat exchange section41. Instead of the pressure sensor, a temperature sensor which detects a temperature of refrigerant (at point d) between the second heat exchange section42and the first heat exchange section41may be provided. The degree of superheat of the refrigerant at the outlet of the first heat exchange section41is calculated based on the difference between the temperature of refrigerant at point e and that at point d. Thereby, the refrigerant in the first heat exchange section41can be completely evaporated in the heating operation. Thus, the heat exchanger can be effectively used, whereby a refrigeration cycle can be highly efficiently operated.

The flow control device80may double as the pressure reducing device13in the refrigerant circuit10. In this case, the third heat exchange section43of the outdoor heat exchanger14is located closer to the indoor heat exchanger12than the pressure reducing device13in the refrigerant circuit10as illustrated inFIG. 1. Furthermore, a pressure reducing device13other than the flow control device80may be provided upstream of the third heat exchange section43in the refrigerant circulating direction in the heating operation. In this case, the opening degree of the pressure reducing device13in the heating operation is adjusted such that the temperature of the refrigerant which flows into the third heat exchange section43is higher than the temperature of the outdoor air (which may also be hereinafter referred to as “outside air temperature”). As the flow control device80, a fixed expansion device may also be used.

The first heat exchange section41, the second heat exchange section42and the third heat exchange section43each include one or more heat transfer tubes. In the following description, the number of heat transfer tubes included in each of the first heat exchange section41, the second heat exchange section42and the third heat exchange section43will also be referred to as “the number of heat-transfer-tube stages”. For example, if the number of heat transfer tubes included in the first heat exchange section41is n, the number of heat-transfer-tube stages in the first heat exchange section41is n. Furthermore, the first heat exchange section41, the second heat exchange section42and the third heat exchange section43share the plate-like fins. However, the plate-like fins in the first heat exchange section41and the second heat exchange section42may be physically or thermally separated from those in the third heat exchange section43. Thereby, it is possible to prevent thermal interference between the third heat exchange section43and the first and second heat exchange sections41and42.

FIG. 3is a schematic front view illustrating an example of a distributor connected to the second heat exchange section42of the outdoor heat exchanger14in embodiment 1. A distributor50as illustrated inFIG. 3includes a hollow header51, which is, for example, part of the header collecting pipe, a single inflow pipe52connected to the hollow header51, and a plurality of branch pipes53(the number of which is four in embodiment 1) connected to the hollow header51. The branch pipes53are connected to ends of the heat transfer tubes in the second heat exchange section42, which are located on one side of the heat transfer tubes. Thereby, after flowing into the hollow header51through the inflow pipe52, refrigerant is distributed to a plurality of refrigerant passages in the second heat exchange section42.

FIG. 4is a schematic front view illustrating another example of the distributor connected to the second heat exchange section42of the outdoor heat exchanger14in embodiment 1. A distributor60as illustrated inFIG. 4includes a distributor body61, a single inflow pipe62connected to the distributor body61, and a plurality of capillary tubes63(the number of which is four in embodiment 1) connected to the distributor body61. The capillary tubes63are connected to ends of the heat transfer tubes of the second heat exchange section42, which are located on one side of the heat transfer tubes. Thereby, after flowing into the distributor body61through the inlet pipe62, refrigerant is distributed to a plurality of refrigerant passages in the second heat exchange section42.

FIG. 5is a schematic front view illustrating a further example of the distributor connected to the second heat exchange section42of the outdoor heat exchanger14in embodiment 1. A distributor70as illustrated inFIG. 5is a stacked-type header distributor including a stacked-type header71having distribution passages, an inflow pipe72connected to the stacked-type header71, and a plurality of branch pipes73(the number of which is four in embodiment 1) connected to the stacked-type header71. In the stacked-type header71, a plurality of plates which include plates provided with S-shaped or Z-shaped through grooves and plates provided with circular through holes are stacked together (see, for example, International Publication No, WO 2015/063857). The branch pipes53are connected to ends of the heat transfer tubes in the second heat exchange section42, which are located on one side of the heat transfer tubes, Thereby, after flowing into the stacked-type header71through the inflow pipe72, refrigerant is distributed to a plurality of refrigerant passages in the second heat exchange section42.

Since any of the distributors50,60and70as illustrated inFIGS. 3 to 5is provided, a plurality of refrigerant passages parallel to each other are provided in the second heat exchange section42. In all the configurations as illustrated inFIGS. 3 to 5, the number of refrigerant passages (the number of paths) in the second heat exchange section42is four. For example, in the heating operation, after flowing out of the first heat exchange section41, the refrigerant is distributed to a plurality of flow passages by the distributor, and flows into the plurality of refrigerant passages in the second heat exchange section42. In such a manner, since the refrigerant is distributed to the plurality of refrigerant passages, the flow velocity of the refrigerant is reduced, and the flow loss is thus reduced, as a result of which the refrigeration cycle can be operated with a high efficiency.

Although it is not illustrated, the first heat exchange section41and the third heat exchange section43are also connected to respective distributors which are different from the distributors50,60and70in the number of distribution pipes, as occasion demands.

In embodiment 1, of the first heat exchange section41, the second heat exchange section42and the third heat exchange section43, the first heat exchange section41includes the largest number of refrigerant passages, the second heat exchange section42includes the second largest number of refrigerant passages, and the third heat exchange section43includes the smallest number of refrigerant passages. In other words, the numbers of refrigerant passages in the outdoor heat exchanger14satisfy the following relationship: the number of refrigerant passages in the first heat exchange section41is larger than the number of refrigerant paths in the second heat exchange section42, which is larger than the number of refrigerant paths in the third heat exchange section43. In the heating operation in which the first heat exchange section41and the second heat exchange section42of the outdoor heat exchanger14each serve as an evaporator, refrigerant in the first heat exchange section41has higher quality than that in the second heat exchange section42. Thus, in the case where the flow velocity of the refrigerant in the first heat exchange section41is equal to that in the second heat exchange section42, a pressure loss in the first heat exchange section41is greater than that in the second heat exchange section42. By contrast, in embodiment 1, since the number of refrigerant passages in the first heat exchange section41is larger than that in the second heat exchange section42, the pressure loss in the first heat exchange section41can be reduced, thus improving the operation efficiency of the refrigeration cycle.

In embodiment 1, in the refrigerant passages, the same number of heat transfer tubes are provided. Therefore, the first heat exchange section41includes the largest number of heat-transfer-tube stages, the second heat exchange section42includes the second largest number of heat-transfer-tube stages, and the third heat exchange section43includes the smallest number of heat-transfer-tube stages. In other words, the numbers of heat-transfer-tube stages in the outdoor heat exchanger14satisfy the following relationship: the number of heat-transfer-tube stages in the first heat exchange section41is larger than the number of heat-transfer-tube stages in the second heat exchange section42, which is larger than the number of heat-transfer-tube stages in the third heat exchange section43. As will be described later, the first heat exchange section41and the second heat exchange section42each serve as an evaporator in the heating operation, whereas the third heat exchange section43does not serve as an evaporator. In embodiment 1, the number of heat-transfer-tube stages in the third heat exchange section43is smaller than that in each of the first heat exchange section41and the second heat exchange section42. It is therefore possible to reduce lowering of the heat exchange performance of the outdoor heat exchanger14operating as an evaporator.

Furthermore, in embodiment 1, the pressure loss in the first heat exchange section41is the smallest, the pressure loss in the second heat exchange section42is the second smallest, and the pressure loss in the third heat exchange section43is the greatest. That is, the pressure losses in the outdoor heat exchanger14satisfy the following relationship: the pressure loss in the first heat exchange section41is smaller than the pressure loss in the second heat exchange section42, which is smaller than the pressure loss in the third heat exchange section43.

An operation of the refrigerant circuit10will be described mainly by referring to the outdoor heat exchanger14.FIG. 6is a graph indicating a relationship between the saturation temperature and enthalpy of refrigerant which flows in the outdoor heat exchanger14in embodiment 1. In the graph, the vertical axis represents the saturation temperature of the refrigerant, and the horizontal axis represents the enthalpy. Also, in the graph, points a to e correspond to points a to e indicated inFIG. 2.FIG. 6indicates the state of the refrigerant in the heating operation.

In the heating operation, the refrigerant flows through points a to e in this order and is then sucked into the compressor11. The refrigerant at an inlet (point a) of the third heat exchange section43has a temperature higher than the outside air temperature. This refrigerant is in a single-phase liquid state in which it is condensed by, for example, the indoor heat exchanger12. When the refrigerant flows into the third heat exchange section43, it is cooled by exchanging heat with the outdoor air. Thereby, the enthalpy of the refrigerant lowers (point b). To be more specific, in the heating operation, the third heat exchange section43, which is part of the outdoor heat exchanger14, serves as a radiator, not an evaporator. After the refrigerant passes through the third heat exchange section43, the pressure of the refrigerant is reduced by the pressure loss in the third heat exchange section43.

After flowing out of the third heat exchange section43, the refrigerant flows into the flow control device80. In the flow control device80, the pressure of the refrigerant is enthalpically reduced, and as a result the temperature of the refrigerant is lower than the outside air temperature (point c).

After flowing out of the flow control device80, the refrigerant flows into the second heat exchange section42. In the second heat exchange section42, the refrigerant is heated by exchanging heat with the outdoor air. As a result, the enthalpy of the refrigerant increases (point d). After flowing out of the second heat exchange section42, the refrigerant flows into the first heat exchange section41. In the first heat exchange section41, the refrigerant is further heated by exchanging heat with the outdoor air, Thereby, the enthalpy of the refrigerant further increases (point e), and the refrigerant changes into gas refrigerant, and then flows out of the first heat exchange section41. That is, in the heating operation, the second heat exchange section42and the first heat exchange section41each serve as an evaporator. After flowing out of the first heat exchange section41, the gas refrigerant is sucked by the compressor11, and compressed thereby.

As described above, the refrigeration cycle apparatus according to embodiment 1 includes the refrigerant circuit10which allows the refrigerant to circulate therethrough, and the outdoor heat exchanger14which is provided at the refrigerant circuit10to exchange heat between the refrigerant and the outdoor air. The outdoor heat exchanger14includes the first heat exchange section41, the second heat exchange section42and the third heat exchange section43, which are connected in series in the refrigerant circuit10. The second heat exchange section42is located below the first heat exchange section41, and is connected thereto. The third heat exchange section43is located below the second heat exchange section42, and is connected thereto. In the refrigerant passage46connecting the second heat exchange section42to the third heat exchange section43, the flow control device80(an example of a pressure reducing device) is provided to reduce the pressure of refrigerant which flows through a refrigerant passage. In an operation mode (for example, a heating operation mode) in which the first heat exchange section41and the second heat exchange section42each serve as an evaporator, the third heat exchange section43is located at a position upstream than the position of the second heat exchange section42(for example, at a position upstream than the positions of both the first heat exchange section41and the second heat exchange section42) in the refrigerant circulating direction (for example, in the flow of the refrigerant from discharging of the refrigerant from the compressor11to sucking of the refrigerant by the compressor11). Also, in this operation mode, refrigerant having a temperature higher than the outside air temperature flows in the third heat exchange section43.

In the heating operation, the first heat exchange section41and the second heat exchange section42of the outdoor heat exchanger14each serve as an evaporator. Thus, when the outside air temperature is low (for example, 2 degrees C. or less), moisture in air deposits as frost on the fins of the first heat exchange section41and the second heat exchange section42. Therefore, in the case where the heating operation is performed under a condition wherein the outside air temperature is low, the heating operation is temporarily stopped, and a defrosting operation to melt frost at the first heat exchange section41and the second heat exchange section42is periodically performed. The defrosting operation is performed, for example, by switching the flow switching device15to thereby provide a flow passage similar to that in the cooling operation, and causing each of the first heat exchange section41and the second heat exchange section42to serve as a condenser. Water obtained by melting the frost in the defrosting operation collects at the third heat exchange section43, which is located (for example, in the lowermost part of the outdoor heat exchanger14) under the first heat exchange section41and the second heat exchange section42. In the heating operation, in the third heat exchange section43, the refrigerant having a temperature higher than the outside air temperature flows. Thus, even in the case where the heating operation is resumed under a condition where water obtained by melting frost stays at the third heat exchange section43, lower part of the outdoor heat exchanger14can be prevented from freezing. It is therefore possible to prevent the outdoor heat exchanger14from being broken.

A refrigeration cycle apparatus according to embodiment 2 of the present invention will be described.FIG. 7is a schematic front view illustrating a configuration of the outdoor heat exchanger14in embodiment 2. InFIG. 7, arrows each indicate the refrigerant circulating direction refrigerant in the heating operation. It should be noted that components having the same functions and operations as those in embodiment 1 will be denoted by the same reference signs, and their descriptions will thus be omitted.

As illustrated inFIG. 7, in embodiment 2, a bypass passage90is provided which bypasses the third heat exchange section43and connects the refrigerant passage47located on an inlet side of the third heat exchange section43in the heating operation to the refrigerant passage46located on an outlet side of the third heat exchange section43in the heating operation. In the bypass passage90, a flow resistor91and an opening/closing valve92are provided; and the flow resistor91increases a resistance to the refrigerant circulating direction in the bypass passage90, and the opening/closing valve92is controlled to be opened/closed by the controller. The flow resistor91includes a capillary tube or a pipe having a smaller inside diameter than a refrigerant pipe forming the bypass passage90. As the opening/closing valve92, a flow-rate adjustment valve which adjusts the flow rate of the refrigerant through the bypass passage90in a stepwise manner or continuously may be used.

FIG. 8is a graph indicating a relationship between the saturation temperature and enthalpy of the refrigerant flowing in the outdoor heat exchanger14in embodiment 2. In the graph, points a toe and points b1and b2correspond to points a toe and points b1and b2illustrated inFIG. 7.FIG. 8shows the state of the refrigerant in the heating operation.

In the heating operation, the opening/closing valve92is controlled to be opened. At point a inFIG. 7, the refrigerant flowing in the refrigerant passage47is divided into refrigerant which will flow toward the third heat exchange section43and refrigerant which will flow through the bypass passage90. The refrigerant having flowed into the third heat exchange section43has a temperature higher than the outside air temperature, and is thus cooled by exchanging heat with the outdoor air. Thereby, the enthalpy of the refrigerant lowers (point b1inFIG. 8). Also, when the refrigerant passes through the third heat exchange section43, the pressure of the refrigerant is reduced by the pressure loss in the third heat exchange section43.

By contrast, the pressure of the refrigerant having flowed into the bypass passage90is reduced by the flow resistor91and the opening/closing valve92(point b2). This pressure reduction is isenthalpically carried out because heat exchange is not performed in the bypass passage90.

The refrigerant having passed through the third heat exchange section43and the refrigerant having passed through the bypass passage90join each other at a location (point b) upstream of the flow control device80to form single refrigerant. Then, the single refrigerant flows into the flow control device80, and the pressure of the refrigerant is isenthalpically reduced therein. Thereby, the temperature of the refrigerant is lower than the outside air temperature (point c).

After flowing out of the flow control device80, the refrigerant flows into the second heat exchange section42and then into the first heat exchange section41, and the state of the refrigerant varies in the same manner (points d and e) as in embodiment 1.

In the cooling operation, the opening/closing valve92may be controlled to be in the closed state. Thereby, the entire refrigerant flows in the first heat exchange section41, the second heat exchange section42and the third heat exchange section43in that order. However, in the case where the temperature of the refrigerant flowing through the third heat exchange section43is lower than the outside air temperature, the opening/closing valve92may be controlled to be in the opened state.

In embodiment 2, since the bypass passage90bypassing the third heat exchange section43is provided, the pressure of the refrigerant can be prevented from being excessively reduced in the third heat exchange section43. Thereby, it is possible to increase the difference in pressure between an inlet and an outlet of the flow control device80. As a result, a range within which the flow control device80can adjust the flow rate can be increased, and the flow control device80can be made smaller in capacity and size.

Furthermore, in the heating operation, the transfer amount of heat in the third heat exchange section43can be reduced, thus preventing excessive reduction of enthalpy at point c inFIG. 8. It is therefore possible to reduce an evaporation load at each of the second heat exchange section42and the first heat exchange section41. Thus, it is possible to reduce lowering of the saturation temperature of the refrigerant at the outlet of the first heat exchange section41, thus improving the operation efficiency of the refrigeration cycle.

A refrigeration cycle apparatus according to embodiment 3 of the present invention will be described.FIG. 9is a schematic front view illustrating a configuration of the outdoor heat exchanger14in embodiment 3. InFIG. 9, arrows each indicate the refrigerant circulating direction in the heating operation. It should be noted that components having the same functions and operations as those in embodiment 1 or 2 will be denoted by the same reference signs, and their descriptions will thus be omitted.

As illustrated inFIG. 9, in third embodiment 1, the flow control device80(an example of a pressure reducing device) is provided upstream of the third heat exchange section43in the heating operation. As the flow control device80, for example, an electronic expansion valve is used. Furthermore, a flow resistor93(an example of a pressure reducing device) is provided at the refrigerant passage46between the third heat exchange section43and the second heat exchange section42. The flow resistor93is formed of, for example, a capillary tube or a pipe having a smaller inside diameter than the refrigerant pipe which forms the bypass passage90. Alternatively, for example, the distributor60as illustrated inFIG. 4or the distributor70as illustrated inFIG. 5can be used as the flow resistor93. In this case, the flow resistor93has a refrigerant distributing function of distributing the refrigerant to a plurality of refrigerant passages.

FIG. 10is a graph indicating a relationship between the saturation temperature and enthalpy of the refrigerant flowing through the outdoor heat exchanger14in embodiment 3. In the graph, points a to f correspond to points a to f indicated inFIG. 9.FIG. 10indicates the state of the refrigerant in the heating operation.

As illustrated inFIG. 10, in the heating operation, the refrigerant having a temperature (point a inFIG. 10) higher than the outside air temperature flows into the flow control device80. In the flow control device80, the pressure of the refrigerant is isenthalpically reduced (point b). The refrigerant having flowed out of the flow control device80has a temperature higher than the outside air temperature.

After flowing out of the flow control device80, the refrigerant flows into the third heat exchange section43. In the third heat exchange section43, the refrigerant is cooled by exchanging heat with the outdoor air, since it has a temperature higher than the outside air temperature, the refrigerant is cooled by exchanging heat with the outdoor air. Thereby, the enthalpy of the refrigerant lowers (point c). Furthermore, the pressure of the refrigerant that has passed through the third heat exchange section43is reduced by a pressure loss in the third heat exchange section43.

After flowing out of the third heat exchange section43, the refrigerant flows into the flow resistor93, and the pressure of the refrigerant is isenthalpically reduced. Thus, the temperature of the refrigerant is lower than the outside air temperature (point d).

After flowing out of the flow resistor93, the refrigerant flows into the second heat exchange section42and the first heat exchange section41, and the state of the refrigerant varies in the same manner (points e and f) as in embodiment 1.

In embodiment 3, the difference between the temperature (temperature at point b) of the refrigerant which flows into the third heat exchange section43and the outside air temperature is smaller than that in embodiment 1. Thus, the transfer amount of heat at the third heat exchange section43(or the difference between enthalpy at point b and that at point c) can be reduced. Thus, it is possible to reduce an evaporation load in each of the second heat exchange section42and the first heat exchange section41, thus improving the operation efficiency of the refrigeration cycle.

In embodiment 3, the flow resistor93can be easily attached to the outdoor heat exchanger14, and the flow resistor93and the outdoor heat exchanger14can be easily unitized. Therefore, in the manufacturing process of the outdoor unit22, the workability of connection of the outdoor heat exchanger14can be improved.

In the cooling operation in which the first heat exchange section41and the second heat exchange section42each serve as a condenser, the refrigerant flowing through the third heat exchange section43is in an almost liquid state, and the pressure loss is thus small. Furthermore since the refrigerant has a temperature higher than the outside air temperature, the refrigerant is cooled by the outdoor air.

A refrigeration cycle apparatus according to embodiment 4 of the present invention will be described.FIG. 11is a schematic front view illustrating a configuration of the outdoor heat exchanger14in embodiment 4. InFIG. 11, arrows each indicate the refrigerant circulating direction in the heating operation. It should be noted that components having the same functions and operations as those in any of embodiments 1 to 3 will be denoted by the same reference signs and their descriptions will thus be omitted.

As illustrated inFIG. 11, the flow control device80is provided upstream of the third heat exchange section43in the heating operation. Also, the flow resistor93is provided at the refrigerant passage46between the third heat exchange section43and the second heat exchange section42. Furthermore, the bypass passage90is provided, and connects the refrigerant passage47located on the inlet side of the third heat exchange section43in the heating operation and the refrigerant passage46located on the outlet side of the third heat exchange section43in the heating operation, without extending through the third heat exchange section43. At the bypass passage90, the flow resistor91and the opening/closing valve92are provided.

FIG. 12is a graph showing a relationship between the saturation temperature and enthalpy of the refrigerant flowing through the outdoor heat exchanger14in embodiment 4. In the graph, points a to f and points b1and b2correspond to points a to f and points b1and b2indicated inFIG. 11.FIG. 12indicates the state of the refrigerant in the heating operation.

As illustrated inFIG. 12, in the heating operation, refrigerant having a temperature (point a inFIG. 12) higher than the outside air temperature flows into the flow control device80. In the flow control device80, the pressure of the refrigerant is isenthalpically reduced (point b). The refrigerant have flowed out of the flow control device80has a temperature higher than the outside air temperature.

In the heating operation, the opening/closing valve92is controlled to be in the opened state. Thereby, after flowing out of the flow control device80, the refrigerant is divided into refrigerant which will flow into a passage extending through the third heat exchange section43and refrigerant which will flow into the bypass passage90. Since the refrigerant which has flowed into the third heat exchange section43has a temperature higher than the outside air temperature, the refrigerant is cooled by exchanging heat with the outdoor air. Thus, the enthalpy of the refrigerant lowers (point b1), Furthermore, the pressure of the refrigerant which has passed through the third heat exchange section43is reduced by the pressure loss in the third heat exchange section43.

By contrast, the pressure of the refrigerant having flowed into the bypass passage90is reduced (point b2) by the flow resistor91and the opening/closing valve92. Since heat exchange is not performed in the bypass passage90, this pressure reduction is isenthalpic.

The refrigerant having passed through the third heat exchange section43and the refrigerant having passed through the bypass passage90join each other at a location (point c) upstream of the flow control device80. After these refrigerants are combined into a single refrigerant in such a manner, the single refrigerant flows into the flow resistor93. In the flow resistor93, the pressure of the refrigerant is isenthalpically reduced. Thus, the temperature of the refrigerant is lower than the outside air temperature (point d).

After flowing out of the flow resistor93, the refrigerant flows into the second heat exchange section42and the first heat exchange section41, and the state of the refrigerant varies in the same manner (points e and f) as in embodiment 1.

In the cooling operation, the opening/closing valve92may be controlled to be in the closed state. Thereby, the entire refrigerant flows through the first heat exchange section41, the second heat exchange section42and the third heat exchange section43in that order.

In embodiment 4, since the bypass passage90bypassing the third heat exchange section43is provided, the pressure loss in the third heat exchange section43can be reduced. Thereby, the difference in pressure between the inlet and the outlet of the flow control device80can be increased. A range within which the flow control device80can adjust the flow rate can be increased, and the flow control device80can be made smaller in capacity and size.

Furthermore, in embodiment 4, in the cooling operation, the entire amount of refrigerant can be made to flow into the third heat exchange section43, thus increasing the amount of heat exchange in the outdoor heat exchanger14. However, in the case where the pressure loss in the third heat exchange section43is great, the opening/closing valve92may be controlled to be in the opened state, thereby causing part of the refrigerant or the entire refrigerant to flow into the bypass passage90.

A refrigeration cycle apparatus according to embodiment 5 of the present invention will be described.FIG. 13is a schematic front view illustrating a configuration of the outdoor heat exchanger14in embodiment 5. InFIG. 13, arrows each indicate the refrigerant circulating direction in the heating operation. Components having the same functions and operations as those in any of embodiments 1 to 4 will be denoted by the same reference signs, and their descriptions will thus be omitted.

As illustrated inFIG. 13, in embodiment 5, the refrigeration cycle apparatus includes a check valve94instead of the opening/closing valve92. In this regard, embodiment 5 is different from embodiment 4. The check valve94allows the refrigerant in the bypass passage90to flow in a direction from the flow control device80toward the second heat exchange section42, and inhibits the refrigerant from flowing in the opposite direction to the above direction. That is, during the heating operation, the check valve94allows flowing of the refrigerant, and during the cooling operation, the check valve94inhibits flowing of the refrigerant.

FIG. 14is a graph showing a relationship between the saturation temperature and enthalpy of the refrigerant flowing through the outdoor heat exchanger14in embodiment 5. In the graph, points a to f and points b1and b2correspond to points a to f and points b1and b2indicated inFIG. 13. The graph ofFIG. 14is the same as that ofFIG. 12, and its description will thus be omitted.

In embodiment 5, the check valve94is provided instead of the opening/closing valve92. Therefore, the manufacturing cost of the refrigerant circuit10can be reduced as compared with that in embodiment 4.

A refrigeration cycle apparatus according to embodiment 6 of the present invention will be described.FIG. 15is a schematic front view illustrating a configuration of the outdoor heat exchanger14in embodiment 6. Components having the same functions and operations as those in any of embodiments 1 to 5 will be denoted by the same reference signs, and their descriptions will thus be omitted.

As illustrated inFIG. 15, in addition to the configuration according to embodiment 5, the refrigeration cycle apparatus according to embodiment 6 further includes another bypass passage, i.e., a bypass passage95other than the bypass passage90. The bypass passage95connects the refrigerant passage47located on the inlet side of the third heat exchange section43in the heating operation and the refrigerant passage46located on the outlet side of the third heat exchange section43in the heating operation, without extending through the third heat exchange section43. Also, the bypass passage95is located parallel to the bypass passage90.

In the bypass passage90, the flow resistor91and the check valve94are provided. In the bypass passage95, a check valve96is provided. The check valve96allows the refrigerant in the bypass passage95to flow in a direction from the second heat exchange section42toward the flow control device80, and inhibits the refrigerant from flowing in the opposite direction to the above direction. That is, during the cooling operation, the check valve96allows flowing of the refrigerant, and during the heating operation, the check valve96inhibits flowing of the refrigerant. Thus, the function of the check valve96is opposite to that of the check valve94.

FIG. 16is a graph indicating a relationship between the saturation temperature and enthalpy of the refrigerant flowing through the outdoor heat exchanger14in embodiment 6. In the graph, points a to f correspond to points a to f illustrated inFIG. 15.FIG. 16indicates the state of the refrigerant in the defrosting operation or the cooling operation in which the first heat exchange section41and the second heat exchange section42each serve as a condenser. Since the state of the refrigerant in the heating operation is the same as that in embodiment 5, its description will thus be omitted.

High-temperature, high-pressure refrigerant (point f inFIG. 16) discharged from the compressor11flows into the first heat exchange section41and the second heat exchange section42. In the first heat exchange section41and the second heat exchange section42, the refrigerant is cooled (points e and d) by exchanging heat with frost on the fins or the outdoor air. Thereby, in the defrosting operation, the refrigerant transfers heat to the frost, thus melting the frost. After flowing out of the second heat exchange section42, the refrigerant flows into the flow resistor93. In the flow resistor93, the pressure of the refrigerant is isenthalpically reduced (point c).

After flowing out of the flow resistor93, the refrigerant is divided into refrigerant which will flow into the passage extending through the third heat exchange section43and refrigerant which will flow into the bypass passage95. In this case, most of the refrigerant flows through the bypass passage95(point b) because the check valve96has a smaller pressure loss than the third heat exchange section43. The refrigerant which has passed through the third heat exchange section43and the refrigerant which has passed through the bypass passage95join each other at a location upstream of the flow control device80. After those refrigerants are combined into a single refrigerant in the above manner, the single refrigerant flows into the flow control device80, and the pressure of the refrigerant is isenthalpically reduced (point a).

InFIG. 16, a broken line indicates the state of the refrigerant in the case where the bypass passage95is not provided. In the case where the bypass passage95is not provided, the entire refrigerant which has flowed out of the flow resistor93flows into the third heat exchange section43. The pressure of the refrigerant which has passed through the third heat exchange section43is reduced (point b2) by the pressure loss in the third heat exchange section43, thus reducing the difference in pressure between the inlet and the outlet of the flow control device80(point a2).

In contrast, in embodiment 6, by virtue of provision of the bypass passage95, it is possible to prevent the pressure of the refrigerant from being excessively lowered at the third heat exchange section43. It is therefore possible to increase the difference in pressure between the inlet and the outlet of the flow control device80. Thus, a range within which the flow control device80can adjust the flow rate can be increased, and the flow control device80can be made smaller in capacity and size.

Furthermore, in embodiment 6, the pressure of the refrigerant in the third heat exchange section43can be prevented from being excessively lowered, and the flow rate of the refrigerant in the defrosting operation can thus be increased. Therefore, the time required for the defrosting operation is shortened, thus improving the comfortability of the indoor space.

A refrigeration cycle apparatus according to embodiment 7 of the present invention will be described.FIG. 17is a schematic front view illustrating a configuration of the outdoor heat exchanger14according to embodiment 7. Components having the same functions and operations as those in any of embodiments 1 to 6 will be denoted by the same reference signs, and their descriptions will thus be omitted.

As illustrated inFIG. 17, in embodiment 7, a three-way switching valve97is provided instead of the check valves94and96. In this regard, embodiment 7 is different from embodiment 6. Under the control by the controller, the three-way switching device97switches the bypass passage for use in flowing of the refrigerant between the bypass passage90and the bypass passage95. To be more specific, in the heating operation, switching of the three-way switching valve97is performed to cause the flow control device80to communicate with the third heat exchange section43and the bypass passage90; and in the cooling operation, switching of the three-way switching valve97is performed to cause the flow control device80to communicate with the bypass passage95.

In embodiment 7, the three-way switching valve97is used instead of the check valves94and96, which are greatly restricted in what state they are installed. Thus, the structure of the pipes and peripheral elements thereof can be simplified, and the productivity of products is improved. Furthermore, since the three-way switching valve97is used in embodiment 7 instead of the check valves94and96, which can cause chatter (vibration sound), the quality of the refrigeration cycle apparatus is enhanced. In addition, the use of the three-way switching valve97ensures reliable switching between the refrigerant passages, With respect to embodiment 7, although the three-way switching valve97is described above by way of example, a plurality of two-way valves can be used instead of the three-way switching valve97.

The above embodiments can be put to practical use in combination.

REFERENCE SIGNS LIST