REFRIGERATION CYCLE APPARATUS

Abstract

A refrigeration cycle apparatus includes a compressor, a first heat exchanger, an expansion valve in which refrigerant flows from the first heat exchanger, a second heat exchanger having a plurality of heat transfer tubes and a header, a first refrigerant pipe connecting the expansion valve with a refrigerant inlet of the header, a second refrigerant pipe connecting the second heat exchanger with a refrigerant suction inlet of the compressor, a bypass circuit having a bypass inlet connected to the header at a position different from that of the refrigerant inlet of the header and a bypass outlet connected to the second refrigerant pipe, a bypass valve configured to make a pressure of the refrigerant in the bypass circuit lower than a pressure of the refrigerant in the header, and a refrigerant circuit auxiliary unit configured to deliver gas-phase refrigerant from the bypass circuit to the bypass outlet.

Description

TECHNICAL FIELD

The present disclosure relates to a refrigeration cycle apparatus including a refrigerant circuit.

BACKGROUND ART

As an example of a conventional heat exchanger, there has been proposed a heat exchanger including a gas-liquid separation mechanism configured to separate refrigerant into gas refrigerant and liquid refrigerant before the refrigerant flows into the heat exchanger (see, for example, Patent Literature 1).

The heat exchanger disclosed in Patent Literature 1 includes a plurality of heat transfer tubes, a first header, a second header, the gas-liquid separation mechanism, a first outlet pipe, and a second outlet pipe. The first header and the second header each have an internal space extending in a particular horizontal direction. The second header is disposed above the first header. The gas-liquid separation mechanism is disposed above the second header. The first header has a first inlet located at one of both ends thereof in the particular direction and connected to the gas-liquid separation mechanism via the first outlet pipe and a second inlet located at the other of both ends thereof in the particular direction and connected to the gas-liquid separation mechanism via the second outlet pipe.

The heat exchanger disclosed in Patent Literature 1 is configured such that the gas refrigerant flows from the gas-liquid separation mechanism into the first header via the first outlet pipe and that the liquid refrigerant flows from the gas-liquid separation mechanism into the first header via the second outlet pipe.

CITATION LIST

Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2017-223386

SUMMARY OF INVENTION

Technical Problem

In the heat exchanger disclosed in Patent Literature 1, the flow rate of the gas refrigerant flowing into the first header and the flow rate of the liquid refrigerant flowing into the first header depend on the situation of two-phase gas-liquid separation in the gas-liquid separation mechanism. Therefore, for example, if the liquid refrigerant flows unevenly to one or some of the plurality of heat transfer tubes, the refrigerant cannot be distributed appropriately to the plurality of heat transfer tubes. In this case, there is a decrease in heat exchange efficiency, undesirably.

The present disclosure was made to solve problems such as those noted above and has as an object to provide a refrigeration cycle apparatus configured to improve heat exchange efficiency according to the amount of refrigerant that circulates.

Solution to Problem

A refrigeration cycle apparatus according to an embodiment of the present disclosure includes a compressor configured to compress and discharge refrigerant, a first heat exchanger into which the refrigerant discharged from the compressor flows, an expansion valve configured to expand the refrigerant flowing from the first heat exchanger, a second heat exchanger having a plurality of heat transfer tubes and a header configured to distribute, to the plurality of heat transfer tubes, the refrigerant flowing from the expansion valve, a first refrigerant pipe connecting the expansion valve to a refrigerant inlet of the header, a second refrigerant pipe connecting the second heat exchanger to a refrigerant suction inlet of the compressor, a bypass circuit having a bypass inlet connected to the header at a position different from that of the refrigerant inlet of the header and a bypass outlet connected to the second refrigerant pipe, a bypass valve provided in the bypass circuit and configured to make a pressure of the refrigerant in the bypass circuit lower than a pressure of the refrigerant in the header, and a refrigerant circuit auxiliary unit configured to deliver gas-phase refrigerant from the bypass circuit to the bypass outlet.

Advantageous Effects of Invention

According to the embodiment of the present disclosure, in the header, which functions as a distributor of the second heat exchanger, liquid-phase refrigerant flowing into the header through the refrigerant inlet is caused by the bypass circuit to be subjected to a force by which the liquid-phase refrigerant is suctioned in a direction different from that of the refrigerant inlet. This makes it easy for the liquid-phase refrigerant flowing into the header to be more equally distributed from the header to the plurality of heat transfer tubes. This results in improvement in the heat exchange efficiency of the second heat exchanger.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a refrigerant circuit diagram showing an example configuration of a refrigeration cycle apparatus according to Embodiment 1.

FIG. 2 is a side schematic view for explaining a configuration of a second heat exchanger shown in FIG. 1.

FIG. 3 is a phase diagram of a refrigeration cycle by the refrigeration cycle apparatus shown in FIG. 1.

FIG. 4 is a block diagram showing an example of a control substrate configured to control equipment provided in the refrigeration cycle apparatus shown in FIG. 1.

FIG. 5 is a schematic view showing an example configuration of a bypass valve shown in FIG. 1.

FIG. 6 is a diagram showing an example configuration of a refrigeration cycle apparatus according to Modification 6.

FIG. 7 is a functional block diagram showing an example configuration of a controller shown in FIG. 6.

FIG. 8 is a hardware configuration diagram showing an example configuration of the controller shown in FIG. 7.

FIG. 9 is a hardware configuration diagram showing another example configuration of the controller shown in FIG. 7.

FIG. 10 is a side schematic view showing another example of installation of the second heat exchanger shown in FIG. 2.

FIG. 11 is a refrigerant circuit diagram showing an example configuration of a refrigeration cycle apparatus according to Embodiment 2.

FIG. 12 is a partially enlarged side schematic view of an integrated combination of a refrigerant circuit auxiliary unit and a second heat exchanger in the refrigeration cycle apparatus shown in FIG. 11.

FIG. 13 is a refrigerant circuit diagram showing an example configuration of a refrigeration cycle apparatus according to Modification 8.

FIG. 14 is a refrigerant circuit diagram showing an example configuration of a refrigeration cycle apparatus according to Embodiment 3.

FIG. 15 is a phase diagram of a refrigeration cycle by the refrigeration cycle apparatus shown in FIG. 14.

FIG. 16 is a refrigerant circuit diagram showing an example configuration of a refrigeration cycle apparatus according to Embodiment 4.

FIG. 17 is a functional block diagram showing an example configuration of a controller shown in FIG. 16.

FIG. 18 is a flow chart showing steps of a control method that is executed by the controller shown in FIG. 17.

FIG. 19 is a refrigerant circuit diagram showing an example configuration of a refrigeration cycle apparatus according to Embodiment 5.

FIG. 20 is a phase diagram of a refrigeration cycle by the refrigeration cycle apparatus shown in FIG. 19.

DESCRIPTION OF EMBODIMENTS

Embodiment 1

A configuration of a refrigeration cycle apparatus of Embodiment 1 is described. FIG. 1 is a refrigerant circuit diagram showing an example configuration of the refrigeration cycle apparatus according to Embodiment 1. As shown in FIG. 1, the refrigeration cycle apparatus 1 includes a compressor 2, a first heat exchanger 3, an expansion valve 5, a second heat exchanger 6, and a bypass circuit 7. The compressor 2, the first heat exchanger 3, the expansion valve 5, and the second heat exchanger 6 are connected via refrigerant pipes 16 to constitute a refrigerant circuit 10 through which refrigerant circulates. The expansion valve 5 is connected to the second heat exchanger 6 via a first refrigerant pipe 16a. The second heat exchanger 6 is connected to a refrigerant suction inlet 18 of the compressor 2 via a second refrigerant pipe 16b. The refrigerant pipes 16 include the first refrigerant pipe 16a and the second refrigerant pipe 16b.

FIG. 2 is a side schematic view for explaining a configuration of the second heat exchanger shown in FIG. 1. For explanatory convenience, FIG. 2 shows the arrows of three axes (namely an X axis, a Y axis, and a Z axis) that define directions. A direction opposite to the direction of the Z-axis arrow is a direction of gravitational force.

The second heat exchanger 6 includes a plurality of heat transfer tubes 11, a first header 12, and a second header 13. The plurality of heat transfer tubes 11 extend in parallel to the Y axis. The first header 12 and the second header 13 are each a columnar or cuboidal hollow structure linearly extending in parallel to the Z axis. As shown in FIG. 2, the second heat exchanger 6 has a plurality of radiating fins 17 provided between the first header 12 and the second header 13. Each radiating fin 17 is placed at equal spacing from an adjacent radiating fin 17 in a direction parallel with the Y axis. Each radiating fin 17 is a plate structure parallel to an X-Y plane. The plurality of heat transfer tubes 11 penetrate through the plurality of radiating fins 17. An illustration of the radiating fins 17 shown in FIG. 2 is omitted from the illustration of the second heat exchanger 6 shown in FIG. 1.

The first header 12 serves as a distributor configured to distribute, to the plurality of heat transfer tubes 11, the refrigerant flowing from the expansion valve 5 via the first refrigerant pipe 16a. The first refrigerant pipe 16a is connected to a refrigerant inlet 19 provided in the first header 12. The second header 13 serves as a converging device configured to cause flows of refrigerant through the plurality of heat transfer tubes 11 to converge into one flow of refrigerant that then flows out to the compressor 2 via the second refrigerant pipe 16b. The second refrigerant pipe 16b is connected to a refrigerant outlet 22 of the second header 13.

The first header 12 and the second header 13 each have a hollow structure in which to store refrigerant diverging into the plurality of heat transfer tubes 11 or refrigerant flowing from the plurality of heat transfer tubes 11. The plurality of heat transfer tubes 11 are connected to the first header 12 at positions of different heights in the direction of gravitational force. A detailed description of the first heat exchanger 3 is omitted, as the first heat exchanger 3 is similar in configuration to the second heat exchanger 6.

Although the case of a configuration in which the second heat exchanger 6 has the radiating fins 17 has been described with reference to FIG. 2, the second heat exchanger 6 may be a heat exchanger having no radiating fins 17.

In the configuration shown in FIG. 1, the bypass circuit 7 has a bypass inlet 21 located at one end and connected to the first header 12 at a position higher than that of the refrigerant inlet 19 of the first header 12 and a bypass outlet 20 located at the other end and connected to the second refrigerant pipe 16b. That is, in the example configuration shown in FIGS. 1 and 2, the bypass circuit 7 is connected to the first header 12 downstream in the direction in which the refrigerant flows through the first header 12, as the refrigerant is blown off into the first header 12 through the refrigerant inlet 19 in the direction of the Z-axis arrow.

The bypass circuit 7 is provided with a bypass valve 14 and a refrigerant circuit auxiliary unit 15. In Embodiment 1, the refrigerant circuit auxiliary unit 15 is disposed downstream of the bypass valve 14 in the direction in which the refrigerant flows through the bypass circuit 7. The bypass valve 14 is a pressure regulating valve configured to make the pressure of the refrigerant in the bypass circuit 7 lower than the pressure of the refrigerant in the first header 12. The refrigerant circuit auxiliary unit 15 is a piece of equipment configured to cause gas-phase refrigerant to flow out from the bypass circuit 7 to the bypass outlet 20. In Embodiment 1, the refrigerant circuit auxiliary unit 15 is a secondary heat exchanger functioning in the bypass circuit 7 as a heat exchanger configured to gasify liquid-phase refrigerant by heating the refrigerant flowing out from the bypass valve 14.

The compressor 2 is configured to suction, compress, and discharge refrigerant. The compressor 2 is an inverter compressor whose capacity can be changed by regulating its operating frequency. The compressor 2 is for example a reciprocating compressor or a rotary compressor. The expansion valve 5 is an expansion device configured to decompress and expand the refrigerant. The expansion valve 5 is for example a temperature expansion valve. There are two types of temperature expansion valve, namely an external pressure equalizing valve and an internal pressure equalizing valve. In a case in which the expansion valve 5 is an external pressure equalizing valve, a temperature sensitive cylinder (not illustrated) provided in a refrigerant pipe 16 between the first heat exchanger 3 and the compressor 2 and a pressure equalizer (not illustrated) provided in a refrigerant pipe 16 that is closer to the compressor 2 than the temperature sensitive cylinder are connected to the expansion valve 5. The expansion valve 5 is configured to automatically regulate its opening degree according to a pressure-volume difference between the pressure of a substance (substance with properties identical to those of the refrigerant) sealed into the temperature sensitive cylinder (not illustrated) and a refrigerant pressure that is inputted via the pressure equalizer (not illustrated).

Next, a refrigeration cycle of operation of the refrigeration cycle apparatus 1 shown in FIG. 1 is described. A case in which the second heat exchanger 6 functions as an evaporator is described. FIG. 3 is a phase diagram of a refrigeration cycle by the refrigeration cycle apparatus shown in FIG. 1. In the phase diagram shown in FIG. 3, the horizontal axis represents specific enthalpy h [kJ/kg], and the vertical axis represents pressure P [MPa]. In the phase diagram shown in FIG. 3, the thick solid line represents a saturation liquid line and a saturation vapor line of refrigerant. P1 to P8 shown in FIG. 3 represent states of the refrigerant at positions p1 to p8 in the refrigerant circuit 10 shown in FIG. 1.

The compressor 2 suctions gas-phase refrigerant, and compresses and discharges the gas-phase refrigerant thus suctioned (see the position p1 in FIG. 3). The gas-phase refrigerant discharged from the compressor 2 is condensed by exchanging heat with air in the third heat exchanger 3 and turns into liquid-phase refrigerant that then flows out from the first heat exchanger 3 (see the position p2 in FIG. 3). The liquid-phase refrigerant flowing out of the first heat exchanger 3 is decompressed by the expansion valve 5 into two-phase gas-liquid refrigerant (see the position p3 in FIG. 3). The two-phase gas-liquid refrigerant flows into the first header 12 via the first refrigerant pipe 16a.

A portion of the two-phase gas-liquid refrigerant flowing into the first header 12 flows into the bypass circuit 7. The two-phase gas-liquid refrigerant flowing into the bypass circuit 7 has its flow rate adjusted by the bypass valve 14, and is decompressed (see the positions p4 and p5 in FIG. 3). The refrigerant flowing out of the bypass valve 14 flows into the refrigerant circuit auxiliary unit 15. The refrigerant flowing into the refrigerant circuit auxiliary unit 15 is heat by the refrigerant circuit auxiliary unit 15, which functions as a secondary heat exchanger. Liquid-phase refrigerant contained in the refrigerant flowing out of the bypass valve 14, if any, is completely gasified by the refrigerant circuit auxiliary unit 15 (see the position p6 in FIG. 3). The gas-phase refrigerant flows into the second refrigerant pipe 16b through the bypass outlet 20.

Meanwhile, a remaining portion of the two-phase gas-liquid refrigerant flowing into the first header 12 diverges into the plurality of heat transfer tubes 11. The flows of refrigerant gasified in the plurality of heat transfer tubes 11 converge at the second header 13 into one flow of refrigerant that then flows out to the second refrigerant pipe 16b (see the position p7 in FIG. 3). The gas-phase refrigerant flowing out from the bypass circuit 7 and the gas-phase refrigerant flowing out from the second header 13 converge at the bypass outlet 20 into one flow of refrigerant that then flows through the second refrigerant pipe 16b (see the position p8 in FIG. 3). The gas-phase refrigerant flowing through the second refrigerant pipe 16b flows into the compressor 2 through the refrigerant suction inlet 18 of the compressor 2.

In a case in which the flow rate of the two-phase gas-liquid refrigerant flowing into the first header 12 via the first refrigerant pipe 16a is low, the refrigerant accumulates more easily in a lower part of the first header 12 (situated in a direction opposite to the direction of the Z-axis arrow in FIG. 2) than in an upper part of the first header 12 (situated in the direction of the Z-axis arrow in FIG. 2) due to the influence of gravity. This makes it hard for the refrigerant to flow to upper ones of the plurality of heat transfer tubes 11, causing less refrigerant to flow to the upper heat transfer tubes 11 than to lower ones. To address this problem, Embodiment 1 is configured such that the bypass valve 14 makes the pressure of the refrigerant in the bypass circuit 7 lower than the pressure of the refrigerant in the first header 12 (see the positions p4 and p5 in FIG. 3). Therefore, the refrigerant in the first header 12 is suctioned upward in the direction of the Z-axis arrow. This makes it easy for the refrigerant to also flow to the upper ones of the plurality of heat transfer tubes 11.

Although, in Embodiment 1, FIG. 1 shows a configuration in which the bypass inlet 21 is connected to the upper part of the first header 12 and the refrigerant inlet 19 is connected to the lower part of the first header 12, the positions of the bypass inlet 21 and the refrigerant inlet 19 are not limited to the case shown in FIG. 1. In the first header 12 shown in FIG. 2, the bypass inlet 21 needs only be at a position away from the refrigerant inlet 19 in the direction of the Z-axis arrow. That is, the bypass circuit 7 needs only be connected to the first header 12 further downstream in the direction in which the two-phase gas-liquid refrigerant flows through the first header 12 than a position at which the first refrigerant pipe 16a is connected to the first header 12. Described with reference to FIG. 2, the direction in which the refrigerant flows through the first header 12 is the direction of the Z-axis arrow. Therefore, the two-phase gas-liquid refrigerant flowing into the first header 12 is suctioned upward in the direction of the Z-axis arrow shown in FIG. 2 from downstream in the direction in which the two-phase gas-liquid refrigerant flows through the first header 12.

In a case in which the flow rate of the refrigerant flowing into the first header 12 is high, liquid-phase refrigerant easily reaches the upper part of the first header 12; however, in a case in which the flow rate of the refrigerant is low, it becomes hard for the liquid-phase refrigerant to reach the upper part of the first header 12. To address this problem, Embodiment 1 is configured such that the liquid-phase refrigerant is pulled up by the bypass circuit 7 provided on top of the first header 12, which functions as a distributor. This brings about improvement in the ratio of distribution to the plurality of heat transfer tubes 11 even in a case in which the amount of refrigerant that circulates through the refrigerant circuit 10 is small. Although intrusion of liquid-phase refrigerant into the bypass circuit 7 is anticipated, the liquid-phase refrigerant is evaporated and gasified by the refrigerant circuit auxiliary unit 15, which functions as a secondary heat exchanger. A decrease in the amount of refrigerant that circulates needs only be countered by a reduction in the flow passage resistance of the bypass valve 14.

A refrigeration cycle apparatus 1 of Embodiment 1 includes a compressor 2, a first heat exchanger 3, an expansion valve 5, a second heat exchanger 6, and a bypass circuit 7 provided with a bypass valve 14 and a refrigerant circuit auxiliary unit 15. The second heat exchanger 6 includes a plurality of heat transfer tubes 11 and a first header 12 configured to distribute, to the plurality of heat transfer tubes 11, refrigerant flowing from the expansion valve 5. The expansion valve 5 is connected to a refrigerant inlet 19 of the first header 12 via a first refrigerant pipe 16a. The second heat exchanger 6 is connected to a refrigerant suction inlet 18 of the compressor 2 via a second refrigerant pipe 16b. The bypass circuit 7 has a bypass inlet 21 connected to the first header 12 at a position different from that of the refrigerant inlet 19 of the first header 12 and a bypass outlet 20 connected to the second refrigerant pipe 16b. The bypass circuit 7 is provided with the bypass valve. The bypass valve 14 is configured to make a pressure of the refrigerant in the bypass circuit 7 lower than a pressure of the refrigerant in the first header 12. The refrigerant circuit auxiliary unit 15 is configured to deliver gas-phase refrigerant from the bypass circuit 7 to the bypass outlet 20.

According to Embodiment 1, in the first header 12, which functions as a distributor of the second heat exchanger 6, liquid-phase refrigerant flowing into the first header 12 through the refrigerant inlet 19 is caused by the bypass circuit 7 to be subjected to a force by which the liquid-phase refrigerant is suctioned in a direction different from that of the refrigerant inlet 19. For example, in the example configuration shown in FIG. 2, the liquid-phase refrigerant flowing into the first header 12 through the refrigerant inlet 19 is subjected to a force by which the liquid-phase refrigerant is suctioned in the direction of the Z-arrow direction. This makes it easy for the liquid-phase refrigerant flowing into the first header 12 to be more equally distributed from the first header 12 to the plurality of heat transfer tubes 11. This results in improvement in the heat exchange efficiency of the second heat exchanger 6.

Even when the flow rate of the refrigerant flowing into the second heat exchanger 6 is low, the effect of the bypass circuit 7 suctioning the refrigerant upward brings about improvement in the ratio of distribution of the refrigerant to the plurality of heat transfer tubes 11, making it possible to improve the heat exchanging performance of the second heat exchanger 6 according to the amount of refrigerant that circulates. Further, even if liquid-phase refrigerant flows to the bypass circuit 7, the refrigerant circuit auxiliary unit 15 evaporates the liquid-phase refrigerant, whereby a decrease in coefficient of performance (COP) can be prevented.

Modification 1

In Modification 1, the refrigerant circuit auxiliary unit 15 is configured such that in a case in which the second heat exchanger 6 and the refrigerant circuit auxiliary unit 15 perform heat exchange under the same condition, the refrigerant circuit auxiliary unit 15 is smaller in heat exchange amount than the second heat exchanger 6.

For the flow rate of refrigerant, it is desirable that a relationship “Flow Rate of Refrigerant through Second Heat Exchanger 6>Flow Rate of Refrigerant through Refrigerant Circuit Auxiliary Unit 15” hold. Therefore, for heat exchanging performance, it is only necessary that a relationship “Heat Exchanging Performance of Second Heat Exchanger 6>Heat Exchanging Performance of Refrigerant Circuit Auxiliary Unit 15” hold. In Modification 1, the refrigerant circuit auxiliary unit 15 is configured such that in a case in which the second heat exchanger 6 and the refrigerant circuit auxiliary unit 15 perform heat exchange under the same condition, the refrigerant circuit auxiliary unit 15 is smaller in heat exchange amount than the second heat exchanger 6.

According to Modification 1, the refrigerant circuit auxiliary unit 15 can be made a heat exchanger of an appropriate size. This makes it possible to prevent an increase in size of installation space for the refrigerant circuit auxiliary unit 15 in installing the refrigeration cycle apparatus 1.

Modification 2

In Embodiment 1, the refrigerant circuit auxiliary unit 15 may exchange heat with a substrate that generates heat. In Modification 2, the refrigerant circuit auxiliary unit 15 is configured to make contact with a substrate that generates heat. The substrate that generates heat is a control substrate configured to control equipment provided in the refrigeration cycle apparatus 1.

FIG. 4 is a block diagram showing an example of a control substrate configured to control equipment provided in the refrigeration cycle apparatus shown in FIG. 1. The refrigeration cycle apparatus 1 includes a control substrate configured to control equipment including the compressor 2. A control substrate 70 is a control substrate configured to control the compressor 2. In a case in which there is provided a fan (not illustrated) configured to supply air to the second heat exchanger 6, there may be provided a control substrate (not illustrated) configured to control a motor of the fan.

The control substrate 70 includes a noise filter 72 connected to an AC power source, a diode bridge 73, a capacitor 74, an inverter 75 connected to a motor 71 of the compressor 2, and a control circuit 76 configured to control the inverter 75. The control substrate 70 generates heat with the passage of a current through an electrical circuit mounted therein. In Modification 2, the refrigerant circuit auxiliary unit 15 is heated by heat generated by the control substrate 70, as the refrigerant circuit auxiliary unit 15 is in contact with the control substrate 70. Further, the absorption into the refrigerant circuit auxiliary unit 15 of heat generated by the control substrate 70 is higher in cooling efficiency than natural heat radiation and makes it possible to prevent overheating. This results in making it possible to prevent the control substrate 70 from malfunctioning due to overheating.

Modification 2 makes it possible to improve the ratio of distribution of the refrigerant to the plurality of heat transfer tubes 11 and prevent overheating of the control substrate. This makes it unnecessary to separately provide a heat source for heating the refrigerant circuit auxiliary unit 15, thus making it possible to save installation space and to improve reliability by preventing malfunction of an electrical system.

Modification 3

The bypass valve 14 of Modification 3 is for example a mechanical differential pressure regulating valve configured to keep a pressure difference between a refrigerant flow inlet and a refrigerant flow outlet of the bypass valve 14 within a certain range.

A specific example configuration of the bypass valve 14 of Modification 3 is a valve configured to operate under a principle that is similar to that of a temperature expansion valve. The bypass valve 14 has a regulating valve (not illustrated), such as a diaphragm, configured to detect a refrigerant pressure difference between a refrigerant flow inlet and a refrigerant flow outlet and adjusts its opening degree according to the operation of the regulating valve. In this case, it is not necessary to provide a special component such as a controller to control the opening degree of the bypass valve 14.

An example of a configuration of the bypass valve 14 of Modification 3 is described. FIG. 5 is a schematic view showing an example configuration of the bypass valve shown in FIG. 1. The bypass valve 14 has a refrigerant flow inlet 51 connected to the bypass inlet 21 via the bypass circuit 7 and a refrigerant flow outlet 52 connected to the refrigerant circuit auxiliary unit 15 via the bypass circuit 7. The bypass valve 14 includes a diaphragm chamber 53, a pressure chamber 55 provided with a spring 54, an orifice plate provided with an orifice 56 through which the refrigerant flows from the refrigerant flow inlet 51 to the refrigerant flow outlet 52, and a needle 57 configured to adjust the opening degree of the orifice 56.

The diaphragm chamber 53 is connected via a first pressure equalizer 61 to part of the bypass circuit 7 that is close to the refrigerant flow inlet 51. The pressure chamber 55 is connected via a second pressure equalizer 62 to part of the bypass circuit 7 that is close to the refrigerant flow outlet 52. The diaphragm chamber 53 has a diaphragm 53a at a boundary surface between the diaphragm chamber 53 and the pressure chamber 55, with a shaft 58 attached to the diaphragm 53a. The needle 58 is attached to an end of the shaft 58 opposite to the diaphragm 53a. The diaphragm 53a moves along an axial direction of the shaft 58 due to a refrigerant pressure difference ΔPd between the refrigerant flow inlet 51 and the refrigerant flow outlet 52 and the elastic force of the spring 54. By the needle 57 moving as the diaphragm 53a moves in the axial direction of the shaft 58, the opening degree of the orifice 56 is adjusted. As a result of that, the flow rate of the refrigerant flowing through the orifice 56 is adjusted, so that the refrigerant pressure difference ΔPd is held constant.

A decrease in the flow rate of the refrigerant flowing into the first header 12 makes it harder for the liquid-phase refrigerant to rise in the first header 12 and leads to a decrease in the heat exchanging performance of the second heat exchanger 6, thus making it is necessary to reduce the flow passage resistance of the bypass valve 14. A decrease in the flow rate of refrigerant leads to a reduction in pressure loss, that is, refrigerant pressure difference between the refrigerant flow inlet 51 and the refrigerant flow outlet 52 of the bypass valve 14. Therefore, Modification 3 uses a mechanical differential pressure regulating valve as the bypass valve 14, so that the bypass valve 14 automatically lowers the flow passage resistance to increase the refrigerant pressure difference by increasing the flow rate of the refrigerant.

According to Modification 3, even when the flow rate of refrigerant flowing into the first header 12 is low, the liquid-phase refrigerant is suctioned upward to the bypass valve 14, as a decrease in the flow rate of refrigerant allows a reduction in the flow passage resistance of the bypass valve 14. This makes it unnecessary to electrically control the bypass valve 14 and makes it possible to improve the ratio of distribution of the refrigerant to the plurality of heat transfer tubes 11, bringing about improvement in the heat exchanging performance of the second heat exchanger.

Modification 4

In Modification 4, in a case in which refrigerant flows through the bypass circuit 7 and the second heat exchanger 6 at the same flow rate, the bypass circuit 7 is smaller in pressure loss than the second heat exchanger 6 with the opening degree of the bypass valve 14 fully open.

An increase in the number of passes, that is, the number of folds, of the heat transfer tubes 11 in the heat exchanger leads to an increase in pressure loss. Further, a reduction in cross-sectional area of the heat transfer tubes 11 in the heat exchanger leads to an increase in pressure loss. In Modification 4, the number of passes of the refrigerant circuit auxiliary unit 15 per unit flow rate of refrigerant is smaller than the number of passes of the second heat exchanger 6 per unit flow rate of refrigerant with the opening degree of the bypass valve 14 fully open. Therefore, the bypass circuit 7 is smaller in pressure loss than the second heat exchanger 6 with the opening degree of the bypass valve 14 fully open. When the bypass circuit 7 is smaller in pressure loss than the second heat exchanger 6, the flow rate of the refrigerant flowing through the bypass circuit 7 increases. This makes it easy for the bypass circuit 7 of Modification 4 to assist the liquid-phase refrigerant in the first header 12 in rising even in a case in which the flow rate of refrigerant is low.

Modification 4 increases a force by which the refrigerant flowing into the first header 12 is suctioned toward the bypass circuit 7. This brings about improvement in the ratio of distribution to the refrigerant to the plurality of heat transfer tubes 11 and improvement in the heat exchanging performance of the second heat exchanger 6 in a case in which the flow rate of refrigerant is low.

Modification 5

Modification 5 is configured such that the bypass outlet 20 of the bypass circuit 7 is connected to the second refrigerant pipe 16b at a position closer to the compressor 2 than an intermediate position between a refrigerant outlet 22 of the second heat exchanger 6 and the refrigerant suction inlet 18 of the compressor 2. Modification 5 is described in detail.

To raise the liquid-phase to the upper part of the first header 12 even in a case in which the flow rate of the refrigerant flowing into the first header 12 is low, it is desirable to increase the flow rate of refrigerant to the bypass circuit 7. As a method for increasing the flow rate of refrigerant to the bypass circuit 7, there is a method for reducing the flow passage resistance of the bypass circuit 7. As an alternative method, there is a method for increasing the pressure difference between the refrigerant in the bypass circuit 7 and the refrigerant in the first header 12. Modification 5 uses the alternative method. Modification 5 is configured such that the bypass outlet 20 is connected to the second refrigerant pipe 16b at a position closer to the compressor 2 than an intermediate position between the refrigerant outlet 22 and the refrigerant suction inlet 18. Modification 5 makes it possible to increase the pressure difference between the refrigerant in the bypass circuit 7 and the refrigerant in the first header 12 by bringing the refrigerant pressure of the bypass outlet 20 of the bypass circuit 7 close to the refrigerant pressure of the refrigerant suction inlet 18 of the compressor 2, which is the lowest pressure in the refrigerant circuit 10.

Modification 5 increases a force by which the refrigerant flowing into the first header 12 is suctioned toward the bypass circuit 7. This brings about improvement in the ratio of distribution to the refrigerant to the plurality of heat transfer tubes 11 and improvement in the heat exchanging performance of the second heat exchanger 6 in a case in which the flow rate of refrigerant is low.

Modification 6

Modification 6 is intended to adjust the opening degree of the bypass valve 14 in response to changes in the operating frequency of the compressor 2. Specifically, Modification 6 is intended to increase the opening degree of the bypass valve 14 before the operating frequency of the compressor 2 decreases and decrease the opening degree of the bypass valve 14 before the operating frequency of the compressor 2 increases.

A configuration of a refrigeration cycle apparatus of Modification 6 is described. FIG. 6 is a diagram showing an example configuration of the refrigeration cycle apparatus according to Modification 6. The refrigeration cycle apparatus 1a shown in FIG. 6 is configured such that a room temperature sensor 45 and a controller 40 are added to the components shown in FIG. 1. The room temperature sensor 45 is configured to detect room temperature Tr, which is the temperature of air in a room to be air-conditioned by the second heat exchanger 6. The room temperature sensor 45 is for example a thermistor. The room temperature sensor 45, the bypass valve 14, and the compressor 2 are each connected to the controller 40 via a signal line (not illustrated). The bypass valve 14 of Modification 6 is for example a solenoid valve.

FIG. 7 is a functional block diagram showing an example configuration of the controller shown in FIG. 6. The controller 40 is for example a microcomputer. The controller 40 includes a compressor control unit 41 configured to control the operating frequency of fc of the compressor 2 and a valve control unit 44 configured to control the opening degree of the bypass valve 14.

The compressor control unit 41 controls the operating frequency fc of the compressor 2 so that the room temperature Tr detected by the room temperature sensor 45 falls within an allowable range Rg determined in advance with reference to setting temperature Ts. For example, in a case in which the room temperature Tr detected by the room temperature sensor 45 is higher than the allowable range Rg, the compressor control unit 41 makes the operating frequency fc of the compressor 2 higher than the present frequency. In a case in which the room temperature Tr detected by the room temperature sensor 45 is lower than the allowable range Rg, the compressor control unit 41 makes the operating frequency fc of the compressor 2 lower than the present frequency. Meanwhile, in a case in which the room temperature Tr detected by the room temperature sensor 45 falls within the allowable range Rg, the compressor control unit 41 keeps the operating frequency fc of the compressor 2 at the present frequency. In changing the operating frequency fc of the compressor 2, the compressor control unit 41 transmits change information to the valve control unit 44 before changing the operating frequency fc. The change information is information that indicates whether the operating frequency fc becomes higher or lower than the present frequency.

Upon receiving the change information from the compressor control unit 41, the valve control unit 44 regulates the opening degree of the bypass valve 14 in accordance with the change information. For example, in a case in which the change information indicates that the operating frequency fc of the compressor 2 becomes lower than the present frequency, the valve control unit 44 makes the opening degree of the bypass valve 14 larger than the present opening degree before the operating frequency fc of the compressor 2 is changed. In a case in which the change information indicates that the operating frequency fc of the compressor 2 becomes higher than the present frequency, the valve control unit 44 makes the opening degree of the bypass valve 14 smaller than the present opening degree before the operating frequency fc of the compressor 2 is changed.

In a case in which the operating frequency fc of the compressor 2 decreases, it becomes harder for the liquid-phase refrigerant in the first header 12 to rise toward the upper part of the first header 12 than before the operating frequency fc of the compressor 2 decreases. On the other hand, in a case in which the operating frequency fc of the compressor 2 increases, it becomes excessively easier for the liquid-phase refrigerant in the first header 12 to rise toward the upper part of the first header 12 than before the operating frequency fc of the compressor 2 increases. When the liquid-phase refrigerant in the distributor does not rise or, to the contrary, abruptly rises in response to changes in the operating frequency of the compressor 2, there is deterioration in the ratio of distribution of the refrigerant to the plurality of heat transfer tubes 11, and there is a decrease in the heat exchanging performance of the second heat exchanger 6. Therefore, Modification 6 makes it possible to reduce deterioration of the distribution of the refrigerant to the plurality of heat transfer tubes 11 by the controller 40 adjusting the opening degree of the bypass valve 14 according to increases and decreases in the operating frequency fc of the compressor 2.

Modification 6 makes it possible to reduce deterioration of efficiency in the distribution of the refrigerant to the plurality of heat transfer tubes 11 due to the operating action of the compressor 2.

An example of a hardware configuration of the controller 40 shown in FIG. 7 is described here. FIG. 8 is a hardware configuration diagram showing an example configuration of the controller 40 shown in FIG. 7. In a case in which the various functions of the controller 40 are implemented by dedicated hardware, the controller 40 shown in FIG. 7 is constituted by a processing circuit 80 as shown in FIG. 8. The functions of the compressor control unit 41 and the valve control unit 44 shown in FIG. 7 are implemented by the processing circuit 80.

In a case in which the various functions are implemented by the hardware, the processing circuit 80 corresponds to a single circuit, a complex circuit, a programed processor, a parallel-programed processor an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a combination thereof. The functions of the compressor control unit 41 and the valve control unit 44 may be implemented by each separate processing circuits 80. Alternatively, the functions of the compressor control unit 41 and the valve control unit 44 may be implemented by one processing circuit 80.

Further, an example of another hardware configuration of the controller 40 shown in FIG. 7 is described. FIG. 9 is a hardware configuration diagram showing another example configuration of the controller shown in FIG. 7. In a case in which the various functions of the controller 40 are implemented by software, the controller 40 shown in FIG. 7 is constituted by a processor 81 such as a central processing unit (CPU) and a memory 82 as shown in FIG. 9. The functions of the compressor control unit 41 and the valve control unit 44 are implemented by the processor 81 and the memory 82. FIG. 9 shows that the processor 81 and the memory 82 are connected via a bus 83.

In a case in which the various functions are implemented by the software, the functions of the compressor control unit 41 and the valve control unit 44 are implemented by the software, firmware, or a combination of the software and the firmware. The software and the firmware are described as programs and stored in the memory 82. The processor 81 implements the functions of the units by reading out and executing the programs stored in the memory 82.

Usable examples of the memory 82 include a nonvolatile semiconductor memory such as a read-only memory (ROM), a flash memory, an erasable and programmable ROM (EPROM), and an electrically erasable and programmable ROM (EEPROM). Further, usable examples of the memory may include a volatile semiconductor memory such as a random-access memory (RAM). Furthermore, usable examples of the memory 82 may include a detachable storage medium such as a magnetic disc, a flexible disc, an optical disc, a compact disc (CD), a mini disc (MD), and a digital versatile disc (DVD).

Modification 7

Modification 7 is a modification of the second heat exchanger 6. Although FIG. 1 shows a case in which the first header 12 and the second header 13 of the second heat exchanger 6 are vertical headers parallel to the direction of gravitational force, they may be horizontal headers orthogonal to the direction of gravitational force. For example, in Embodiment 1, the first header 12 and the second header 13 shown in FIG. 1 may be disposed to extend in parallel to the Y axis shown in FIG. 2.

FIG. 10 is a side schematic view showing another example of installation of the second heat exchanger shown in FIG. 2. As with FIG. 2, FIG. 10 shows the arrows of three axes that define directions. FIG. 10 shows a configuration in which the second heat exchanger 6 is installed so that the direction in which the first header 12 extends is parallel with a plane orthogonal to the direction of gravitational force. In the example of installation shown in FIG. 10, one of the plurality of heat transfer tubes 11 that is furthest away from the refrigerant inlet 19 in a direction opposite to the direction of the Y-axis arrow is referred to as “first heat transfer tube 25”, and one of the plurality of heat transfer tubes 11 that is closest to the refrigerant inlet 19 in the direction of the Y-axis arrow is referred to as “second heat transfer tube 26”.

In the case of the example of installation shown in FIG. 10, two-phase gas-liquid refrigerant flowing into the first header 12 via the first refrigerant pipe 16a flows in the direction of a dashed arrow through the first header 12 under the force of inertia with which the two-phase gas-liquid refrigerant flows into the first header 12. However, in a case in which the amount of refrigerant that flows into the first header 12 is small, it becomes hard for the two-phase gas-liquid refrigerant to reach the first heat transfer tube 25, so that it becomes harder for the refrigerant to flow toward the first heat transfer tube 25 than toward the second heat transfer tube 26. On the other hand, in Embodiment 1, the two-phase gas-liquid refrigerant in the first header 12 is suctioned upward to the bypass circuit 7 by the bypass valve 14. This results in making it easy for the two-phase gas-liquid refrigerant to also flow toward the first heat transfer tube 25. In this way, the direction in which the first header 12 extends may be a direction parallel with the ground. Further, in the example of installation shown in FIG. 10, the second heat exchanger 6 may be inclined with respect to the ground.

Embodiment 2

A refrigeration cycle apparatus of Embodiment 2 is configured such that a second heat exchanger 6 described in Embodiment 1 and a secondary heat exchanger are integrated with each other. Components in Embodiment 2 that are identical to those described in Embodiment 1 are given identical reference signs, and a detailed description of those components is omitted.

A configuration of the refrigeration cycle apparatus of Embodiment 2 is described. FIG. 11 is a refrigerant circuit diagram showing an example configuration of the refrigeration cycle apparatus according to Embodiment 2. In comparison with the configuration shown in FIG. 1, the refrigeration cycle apparatus 1b of Embodiment 2 is configured such that a refrigerant circuit auxiliary unit 15a functioning as a secondary heat exchanger is integrated with the second heat exchanger 6.

FIG. 12 is a partially enlarged side schematic view of the integrated combination of the refrigerant circuit auxiliary unit and the second heat exchanger in the refrigeration cycle apparatus shown in FIG. 11. As with FIG. 2, FIG. 12 shows the arrows of three axes that define directions. FIG. 12 omits to illustrate the first refrigerant pipe 16a, the refrigerant inlet 19, or other components shown in FIG. 11.

The refrigerant circuit auxiliary unit 15a includes a first secondary header 34, a second secondary header 35, and a plurality of heat transfer tubes 11. The refrigerant circuit auxiliary unit 15a has two of the plurality of heat transfer tubes 11, and the second heat exchanger 6 has eight of the plurality of heat transfer tubes 11. Although the first secondary header 34 and the first header 12 are integrated with each other, a partition wall 36 is provided between the first secondary header 34 and the first header 12. Although the second secondary header 35 and the second header 13 are integrated with each other, a partition wall 36 is provided between the second secondary header 35 and the second header 13. As with the first header 12 and the second header 13, the first secondary header 34 and the second secondary header 35 too are hollow structures.

Although the refrigerant circuit auxiliary unit 15a is integrated with the second heat exchanger 6, a partition wall 36 is provided between the first header 12 and the first secondary header 34, and a partition wall 36 is provided between the second header 13 and the second secondary header 35. This causes refrigerant to be separated without flowing from the refrigerant circuit auxiliary unit 15a to the second heat exchanger 6 or from the second heat exchanger 6 to the refrigerant circuit auxiliary unit 15a.

Even in a configuration such as Embodiment 2 in which the refrigerant circuit auxiliary unit 15a, which functions as a secondary heat exchanger, and the second heat exchanger 6 are integrated with each other, liquid-phase refrigerant is pulled up to the upper part of the first header 12. Further, liquid-phase refrigerant flowing out of the bypass valve 14 flows out to the bypass outlet 20 after being gasified in the refrigerant circuit auxiliary unit 15a.

Although FIG. 12 illustrates a case in which the number of heat transfer tubes 11 of the refrigerant circuit auxiliary unit 15a is 2, the number of heat transfer tubes 11 is not limited to 2. A detailed description of a refrigeration cycle of operation by the refrigeration cycle apparatus 1a of Embodiment 2 is omitted, as the operation is similar to that described with reference to FIG. 3 in Embodiment 1.

According to Embodiment 2, the refrigerant circuit auxiliary unit 15a, which functions as a secondary heat exchanger, does not need to be a component separate from the second heat exchanger 6. This makes it possible to save installation space for the second heat exchanger 6.

Modification 8

The refrigeration cycle apparatus 1b of Embodiment 2 may include a fan configured to send air to the second heat exchanger 6 and the refrigerant circuit auxiliary unit 15a. Modification 8 is configured such that in a case in which the fan has a wind speed distribution, the refrigerant circuit auxiliary unit 15a is disposed at such a position that the speed of air sent by the fan to the refrigerant circuit auxiliary unit 15a is lower than the speed of air sent by the fan to the second heat exchanger 6.

FIG. 13 is a refrigerant circuit diagram showing an example configuration of a refrigeration cycle apparatus according to Modification 8. As shown in FIG. 13, the refrigeration cycle apparatus 1b may include a fan 30 configured to send air to the second heat exchanger 6 and the refrigerant circuit auxiliary unit 15a. The refrigerant circuit auxiliary unit 15a is disposed at such a position that the speed of air sent by the fan 30 to the refrigerant circuit auxiliary unit 15a is lower than the speed of air sent by the fan 30 to the second heat exchanger 6.

For the flow rate of refrigerant, it is desirable that a relationship “Flow Rate of Refrigerant through Second Heat Exchanger 6>Flow Rate of Refrigerant through Refrigerant Circuit Auxiliary Unit 15a” hold. Therefore, for heat exchanging performance, it is only necessary that a relationship “Heat Exchanging Performance of Second Heat Exchanger 6>Heat Exchanging Performance of Refrigerant Circuit Auxiliary Unit 15a” hold. In the case of a heat exchanger configured to exchange heat with air, a decrease in speed of air sent by a fan leads to a decrease in heat exchanging performance. Therefore, the heat exchanging performance of the second heat exchanger 6, which is large in amount of heat exchange, can be increased by disposing the refrigerant circuit auxiliary unit 15a, which is relatively smaller in required amount of heat exchange than the second heat exchanger 6, in a portion in which the speed of air is low.

According to Modification 8, in a case in which the refrigerant circuit auxiliary unit 15a is integrated with the second heat exchanger 6, the refrigerant circuit auxiliary unit 15a can be made a heat exchanger of an appropriate size.

Modification 9

In Modification 9, the refrigerant circuit auxiliary unit 15a is configured such that the refrigerant circuit auxiliary unit 15a is smaller in heat transfer area than the second heat exchanger 6.

In the example configuration shown in FIG. 12, the refrigerant circuit auxiliary unit 15a has two of the plurality of heat transfer tubes 11, and the second heat exchanger 6 has eight of the plurality of heat transfer tubes 11. The number of heat transfer tubes 11 of the refrigerant circuit auxiliary unit 15a is smaller than the number of heat transfer tubes 11 of the second heat exchanger 6. The refrigerant circuit auxiliary unit 15a is smaller in heat transfer area than the second heat exchanger 6. For the flow rate of refrigerant, it is desirable that a relationship “Flow Rate of Refrigerant through Second Heat Exchanger 6>Flow Rate of Refrigerant through Refrigerant Circuit Auxiliary Unit 15a” hold. Therefore, for heat exchanging performance, it is only necessary that a relationship “Heat Exchanging Performance of Second Heat Exchanger 6>Heat Exchanging Performance of Refrigerant Circuit Auxiliary Unit 15a” hold.

According to Modification 9, in a case in which the refrigerant circuit auxiliary unit 15a is integrated with the second heat exchanger 6, the refrigerant circuit auxiliary unit 15a can be made a heat exchanger of an appropriate size.

In Embodiment 2, Modifications 3 to 7 described in Embodiment 1 may be applied, although Modifications 8 and 9 have been described as applicable modifications.

Embodiment 3

A refrigeration cycle apparatus of Embodiment 3 is configured such that a gas-liquid separator is provided instead of the secondary heat exchanger in the bypass circuit 7 described in Embodiment 1. Components in Embodiment 3 that are identical to those described in Embodiment 1 are given identical reference signs, and a detailed description of those components is omitted.

A configuration of the refrigeration cycle apparatus of Embodiment 3 is described. FIG. 14 is a refrigerant circuit diagram showing an example configuration of the refrigeration cycle apparatus according to Embodiment 3. In comparison with the configuration shown in FIG. 1, the refrigeration cycle apparatus 1c of Embodiment 3 is configured such that a refrigerant circuit auxiliary unit 15b functioning as a gas-liquid separator is provided instead of the secondary heat exchanger in the bypass circuit 7.

The refrigerant circuit auxiliary unit 15b is connected by a liquid pipe 38 to a refrigerant return port 37 provided in the first refrigerant pipe 16a. The refrigerant circuit auxiliary unit 15b is configured to separate the two-phase gas-liquid refrigerant flowing from the first header 12 via the bypass circuit 7 into gas-phase refrigerant and liquid-phase refrigerant. The refrigerant circuit auxiliary unit 15b is configured to cause the gas-phase refrigerant to flow out to the bypass valve 14 via the bypass circuit 7. The refrigerant circuit auxiliary unit 15b is configured to cause the liquid-phase refrigerant to flow out to the refrigerant return port 37 via the liquid pipe 38.

In Embodiment 3, the gas-liquid separator is configured to separate the two-phase gas-liquid refrigerant into the gas-phase refrigerant and the liquid-phase refrigerant, return the liquid-phase refrigerant toward the refrigerant inlet 19 of the second heat exchanger 6, and cause the gas-phase refrigerant to converge at the refrigerant outlet 22 of the second heat exchanger 6 with refrigerant flowing out from the second heat exchanger 6. This eliminates the need for the secondary heat exchanger described in Embodiment 1.

Next, a refrigeration cycle of operation of the refrigeration cycle apparatus 1c shown in FIG. 14 is described. A case in which the second heat exchanger 6 functions as an evaporator is described. FIG. 15 is a phase diagram of a refrigeration cycle by the refrigeration cycle apparatus shown in FIG. 14. In the phase diagram shown in FIG. 15, the horizontal axis represents specific enthalpy h [kJ/kg], and the vertical axis represents pressure P [MPa]. In the phase diagram shown in FIG. 15, the thick solid line represents a saturation liquid line and a saturation vapor line of refrigerant. P1 to P8 shown in FIG. 15 represent states of the refrigerant at positions p1 to p8 in the refrigerant circuit 10 shown in FIG. 14.

The compressor 2 suctions gas-phase refrigerant, and compresses and discharges the gas-phase refrigerant thus suctioned (see the position p1 in FIG. 15). The gas-phase refrigerant discharged from the compressor 2 is condensed by exchanging heat with air in the third heat exchanger 3 and turns into liquid-phase refrigerant that then flows out from the first heat exchanger 3 (see the position p2 in FIG. 15). The liquid-phase refrigerant flowing out of the first heat exchanger 3 is decompressed by the expansion valve 5 into two-phase gas-liquid refrigerant (see the position p3 in FIG. 15). The two-phase gas-liquid refrigerant flows into the first header 12 via the first refrigerant pipe 16a.

A portion of the two-phase gas-liquid refrigerant flowing into the first header 12 flows into the bypass circuit 7. The two-phase gas-liquid refrigerant flowing into the bypass circuit 7 flows into the refrigerant circuit auxiliary unit 15b. The two-phase gas-liquid refrigerant flowing into the refrigerant circuit auxiliary unit 15b is separated by the refrigerant circuit auxiliary unit 15b into gas-phase refrigerant and liquid-phase refrigerant. The liquid-phase refrigerant flows from the refrigerant circuit auxiliary unit 15b to the refrigerant return port 37 via the liquid pipe 38 (see the position p10 in FIG. 15). The liquid-phase refrigerant flowing into the first refrigerant pipe 16a from the liquid pipe 38 and the two-phase gas-liquid refrigerant flowing through the first refrigerant pipe 16a from the expansion valve 5 converge at the refrigerant return port 37 to flow through the first header 12 (see the position p4 in FIG. 15).

Flowing out from the refrigerant circuit auxiliary unit 15b (see the position p6 in FIG. 15), the gas-phase refrigerant flows into the bypass valve 14. The gas-phase refrigerant flowing into the bypass valve 14 has its flow rate adjusted by the bypass valve 14 (see the position p7 in FIG. 15). After that, the gas-phase refrigerant flows through the bypass circuit 7 and flows into the second refrigerant pipe 16b through the bypass outlet 20.

Meanwhile, a remaining portion of the two-phase gas-liquid refrigerant flowing into the first header 12 diverges into the plurality of heat transfer tubes 11. The flows of refrigerant gasified in the plurality of heat transfer tubes 11 converge at the second header 13 into one flow of refrigerant that then flows out to the second refrigerant pipe 16b (see the position p8 in FIG. 3). The gas-phase refrigerant flowing out from the bypass circuit 7 and the gas-phase refrigerant flowing out from the second header 13 converge at the bypass outlet 20 into one flow of refrigerant that then flows through the second refrigerant pipe 16b (see the position p9 in FIG. 15). The gas-phase refrigerant flowing through the second refrigerant pipe 16b flows into the compressor 2 through the refrigerant suction inlet 18 of the compressor 2.

The refrigeration cycle apparatus 1c of Embodiment 3 separates the two-phase gas-liquid refrigerant flowing through the bypass circuit 7 into liquid-phase refrigerant and gas-phase refrigerant with the gas-liquid separator and evaporates the liquid-phase refrigerant with the second heat exchanger 6. Embodiment 3 eliminates the need for the secondary heat exchanger and also eliminates the need for a heat source for evaporating the liquid-phase refrigerant flowing through the bypass circuit 7.

In Embodiment 3, Modifications 3 to 7 described in Embodiment 1 may be applied.

Embodiment 4

A refrigeration cycle apparatus of Embodiment 4 is configured to control the opening degree of the bypass valve in accordance with the temperature of refrigerant flowing through a heat transfer tube of the second heat exchanger. Components in Embodiment 4 that are identical to those described in Embodiments 1 to 3 are given identical reference signs, and a detailed description of those components is omitted. Although Embodiment 4 is described based on the refrigeration cycle apparatus of Embodiment 1, Embodiment 4 may be applied to the refrigeration cycle apparatus of Embodiment 2 or 3.

A configuration of the refrigeration cycle apparatus of Embodiment 4 is described. FIG. 16 is a refrigerant circuit diagram showing an example configuration of the refrigeration cycle apparatus according to Embodiment 4. The refrigeration cycle apparatus 1d shown in FIG. 16 is configured such that a temperature sensor 31 configured to detect the temperature of the refrigerant and a controller 40a are added to the components shown in FIG. 1. The temperature sensor 31 is for example a thermistor. The temperature sensor 31 and the bypass valve 14 are each connected to the controller 40a via a signal line (not illustrated). The bypass valve 14 of Embodiment 4 is for example a solenoid valve.

In FIG. 16, the temperature sensor 31 is provided on a first heat transfer tube 25 located at the highest position of the plurality of heat transfer tubes 11 of the second heat exchanger 6 in terms of height in the direction of gravitational force (opposite to the direction of the Z-axis arrow) shown in FIG. 2. The position of the temperature sensor 31 in a height direction is not limited to the case shown in FIG. 16. The temperature sensor 31 needs only be provided at a position higher than an intermediate position in the second heat exchanger 6 in terms of height in the direction of gravitational force shown in FIG. 2. Further, the temperature sensor 31 is provided near an outlet of a heat transfer tube 11 situated downstream in the direction in which the refrigerant flows through the heat transfer tube 11.

FIG. 17 is a functional block diagram showing an example configuration of the controller shown in FIG. 16. The controller 40a is for example a microcomputer. The controller 40a includes a determination unit 42 and a valve control unit 43. The determination unit 42 makes a determination on whether refrigerant temperature Te, which is a detected value of the temperature sensor 31, is higher than a predetermined threshold Tth, and transmits information on a result of the determination to the valve control unit 43.

In a case in which the refrigerant temperature Te is higher than the threshold Tth, the valve control unit 43 increases the opening degree of the bypass valve 14 to reduce the flow passage resistance of the bypass valve 14. In a case in which the refrigerant temperature Te is lower than the threshold Tth, the valve control unit 43 decreases the opening degree of the bypass valve 14 to increase the flow passage resistance of the bypass valve 14.

It becomes hard due to the influence of gravity for the liquid-phase refrigerant of the two-phase gas-liquid refrigerant flowing into the first header 12 to rise upward (in the direction of the Z-axis arrow) in the first header 12 shown in FIG. 2. Therefore, a heat transfer tube 11 located at a higher position than the intermediate position in the second heat exchanger 6 allows the gas-phase to flow therethrough more easily and allows the gas-phase refrigerant to exchange heat with air more efficiently. As a result of that, the refrigerant temperature of a heat transfer tube 11 located at a higher position than the intermediate position in the second heat exchanger 6 is more likely to rise than the refrigerant temperature of a heat transfer tube 11 located at a lower position than the intermediate position in the second heat exchanger 6.

In connection with this phenomenon, in Embodiment 4, the determination unit 42 determines that the higher the temperature of refrigerant flowing through a heat transfer tube 11 located at a higher position than the intermediate position in the second heat exchanger 6 is, the more insufficient the liquid-phase refrigerant is in a heat transfer tube 11 located at a higher position than the intermediate position. Therefore, the determination unit 42 reduces the flow passage resistance of the bypass valve 14 to raise the liquid-phase refrigerant to the upper part of the first header 12. The reduction in the flow passage resistance of the bypass valve 14 makes it easy for the liquid-phase refrigerant to rise to a higher position in the first header 12.

Next, an operation of the refrigeration cycle apparatus 1d of Embodiment 4 is described. FIG. 18 is a flow chart showing steps of a control method that is executed by the controller shown in FIG. 17. A case in which the second heat exchanger 6 functions as an evaporator is described here. The controller 40a operates in accordance with the flow chart of FIG. 17 with certain periodicity.

The determination unit 42 acquires a detected value from the temperature sensor 31 (step S101). The determination unit 42 makes a determination on whether the refrigerant temperature Te detected by the temperature sensor 31 is higher than the threshold value Tth (step S102). In a case in which as a result of the determination made in step S102, the refrigerant temperature Te is higher than the threshold value Tth, the determination unit 42 transmits information on the result of the determination to the valve control unit 43. Upon receiving, as the result of the determination from the determination unit 42, information indicating that the refrigerant temperature Te is higher than the threshold value Tth, the valve control unit 43 increases the opening degree of the bypass valve 14 (step S103). This makes it easy for the liquid-phase refrigerant to rise toward the upper part of the first header 12.

On the other hand, in a case in which as a result of the determination made in step S102, the refrigerant temperature Te is lower than or equal to the threshold value Tth, the determination unit 42 makes a determination on whether the refrigerant temperature Te is lower than the threshold value Tth (step S104). The determination unit 42 transmits, to the valve control unit 43, information on a result of the determination made in step S104. Upon receiving, from the determination unit 42 as the result of the determination made in step S104, information indicating that the refrigerant temperature Te is lower than the threshold value Tth, the valve control unit 43 decreases the opening degree of the bypass valve 14 (step S105). This makes it hard for the liquid-phase refrigerant to rise toward the upper part of the first header 12. Further, upon receiving, from the determination unit 42 as the result of the determination made in step S104, information indicating that the refrigerant temperature Te is equal to the threshold value Tth, the valve control unit 43 maintains the opening degree of the bypass valve 14 (step S106).

A detailed description of a refrigeration cycle of operation by the refrigeration cycle apparatus 1d of Embodiment 4 is omitted, as the operation is similar to that described with reference to FIG. 3 in Embodiment 1.

The refrigeration cycle apparatus 1d of Embodiment 4 determines that the higher the temperature of refrigerant in a higher position than the intermediate position in the second heat exchanger 6 is, the more insufficient the liquid-phase refrigerant is, and reduces the flow passage resistance of the bypass valve 14 to raise the liquid-phase refrigerant to the upper part of the first header 12. The reduction in the flow passage resistance of the bypass valve 14 makes it easy for the liquid-phase refrigerant to rise to a higher position in the first header 12. Embodiment 4 inhibits an insufficient rise of the liquid-phase refrigerant in the first header 12 by adjusting the flow rate of refrigerant flowing through the bypass circuit 7, making it possible to improve the heat exchanging performance of the second heat exchanger 6.

In Embodiment 4, Modifications 1 to 7 described in Embodiment 1 may be applied. A detailed description of a hardware configuration of the controller 40a is omitted, as the hardware configuration is similar to that described with reference to FIGS. 8 and 9.

Embodiment 5

A refrigeration cycle apparatus of Embodiment 5 includes, instead of the secondary heat exchanger, a gas-liquid separator configured to heat refrigerant flowing through the bypass circuit. Components in Embodiment 5 that are identical to those described in Embodiments 1 to 4 are given identical reference signs, and a detailed description of those components is omitted.

A configuration of the refrigeration cycle apparatus of Embodiment 5 is described. FIG. 19 is a refrigerant circuit diagram showing an example configuration of the refrigeration cycle apparatus according to Embodiment 5. The refrigeration cycle apparatus 1e is configured such that a refrigerant circuit auxiliary unit 15b is provided in the first refrigerant pipe 16a. The refrigerant circuit auxiliary unit 15b is a gas-liquid separator configured to separate refrigerant flowing from the expansion valve 5 into the first header 12 into gas-phase refrigerant and liquid-phase refrigerant. The bypass circuit 7 is disposed to pass through the refrigerant circuit auxiliary unit 15b to cause the refrigerant flowing out from the bypass valve 14 to exchange heat with the liquid-phase refrigerant stored in the refrigerant circuit auxiliary unit 15b. The refrigerant circuit auxiliary unit 15b causes refrigerant flowing through the bypass circuit 7 to exchange heat with the refrigerant flowing from the expansion valve 5 into the first header 12.

Next, a refrigeration cycle of operation of the refrigeration cycle apparatus 1e shown in FIG. 19 is described. A case in which the second heat exchanger 6 functions as an evaporator is described. FIG. 20 is a phase diagram of a refrigeration cycle by the refrigeration cycle apparatus shown in FIG. 19. In the phase diagram shown in FIG. 20, the horizontal axis represents specific enthalpy h [kJ/kg], and the vertical axis represents pressure P [MPa]. In the phase diagram shown in FIG. 20, the thick solid line represents a saturation liquid line and a saturation vapor line of refrigerant. P1 to P9 shown in FIG. 20 represent states of the refrigerant at positions p1 to p9 in the refrigerant circuit 10 shown in FIG. 19.

The compressor 2 suctions gas-phase refrigerant, and compresses and discharges the gas-phase refrigerant thus suctioned (see the position p1 in FIG. 20). The gas-phase refrigerant discharged from the compressor 2 is condensed by exchanging heat with air in the third heat exchanger 3 and turns into liquid-phase refrigerant that then flows out from the first heat exchanger 3 (see the position p2 in FIG. 20). The liquid-phase refrigerant flowing out of the first heat exchanger 3 is decompressed by the expansion valve 5 into two-phase gas-liquid refrigerant (see the position p3 in FIG. 20). The two-phase gas-liquid refrigerant flowing out from the expansion valve 5 flows into the refrigerant circuit auxiliary unit 15b, which functions as a gas-liquid separator.

The two-phase gas-liquid refrigerant flowing into the refrigerant circuit auxiliary unit 15b is separated by the refrigerant circuit auxiliary unit 15b into gas-phase refrigerant and liquid-phase refrigerant. The liquid-phase refrigerant flows out from the refrigerant circuit auxiliary unit 15b (see the position p4 in FIG. 20). The liquid-phase refrigerant flows through the first refrigerant pipe 16a and flows into the first header 12 through the refrigerant inlet 19. In the first header 12, the liquid-phase refrigerant is suctioned upward to the bypass inlet 21, and a portion of the liquid-phase refrigerant is gasified.

A portion of the two-phase gas-liquid refrigerant in the first header 12 flows into the bypass circuit 7 (see the position p5 in FIG. 20). The two-phase gas-liquid refrigerant flowing into the bypass circuit 7 has its flow rate adjusted by the bypass valve 14, and is decompressed (see the position p6 in FIG. 20). The refrigerant flowing out of the bypass valve 14 flows into the refrigerant circuit auxiliary unit 15b. The refrigerant flowing into the refrigerant circuit auxiliary unit 15b is heated by exchanging heat with the liquid-phase refrigerant stored in the refrigerant circuit auxiliary unit 15b and evaporates. Liquid-phase refrigerant contained in the refrigerant flowing out of the bypass valve 14, if any, is completely gasified by exchanging heat with the liquid-phase refrigerant in the refrigerant circuit auxiliary unit 15b (see the position p7 in FIG. 20). The gas-phase refrigerant flows into the second refrigerant pipe 16b through the bypass outlet 20.

Meanwhile, a remaining portion of the two-phase gas-liquid refrigerant flowing into the first header 12 diverges into the plurality of heat transfer tubes 11. The flows of refrigerant gasified in the plurality of heat transfer tubes 11 converge at the second header 13 into one flow of refrigerant that then flows out to the second refrigerant pipe 16b (see the position p8 in FIG. 20). The gas-phase refrigerant flowing out from the bypass circuit 7 and the gas-phase refrigerant flowing out from the second header 13 converge at the bypass outlet 20 into one flow of refrigerant that then flows through the second refrigerant pipe 16b (see the position p9 in FIG. 20). The gas-phase refrigerant flowing through the second refrigerant pipe 16b flows into the compressor 2 through the refrigerant suction inlet 18 of the compressor 2.

The refrigeration cycle apparatus 1e of Embodiment 5 is configured such that a refrigerant circuit auxiliary unit 15b functioning as a gas-liquid separator is provided in the first refrigerant pipe 16a. The bypass circuit 7 is disposed to pass through the refrigerant circuit auxiliary unit 15b to cause the refrigerant flowing out from the bypass valve 14 to exchange heat with the liquid-phase refrigerant stored in the refrigerant circuit auxiliary unit 15b.

Embodiment 5 makes it possible to, by causing refrigerants to exchange heat with each other in the refrigerant circuit auxiliary unit 15b, eliminate the need for an external heat source for evaporating the liquid-phase refrigerant flowing through the bypass circuit 7. This makes it possible to, even without providing a heating source, evaporate and gasify the liquid-phase refrigerant flowing through the bypass circuit 7. As in the cases of Embodiments 1 to 4, a decrease in COP can be prevented.

In Embodiment 5, Modifications 3 to 7 described in Embodiment 1 may be applied.

Although Embodiments 1 to 5 have been described with reference to a case in which the refrigerant circuit 10 is configured such that refrigerant flows in one direction, the refrigerant circuit 10 may be provided with a flow switching device (not illustrated) such as a four-way valve and configured such that refrigerant flows in either one direction or the opposite direction. In this case, the refrigeration cycle apparatus may be configured such that an evaporator is equivalent to the second heat exchanger 6 described in any of Embodiments 1 to 5.

REFERENCE SIGNS LIST

1, 1a to 1e: refrigeration cycle apparatus, 2: compressor, 3: first heat exchanger, 5: expansion valve, 6: second heat exchanger, 7: bypass circuit, 10: refrigerant circuit, 11: heat transfer tube, 12: first header, 13: second header, 14: bypass valve, 15, 15a, 15b: refrigerant circuit auxiliary unit, 16: refrigerant pipe, 16a: first refrigerant pipe, 16b: second refrigerant pipe, 17: radiating fin, 18: refrigerant suction inlet, 19: refrigerant inlet, 20: bypass outlet, 21: bypass inlet, 22: refrigerant outlet, 25: first heat transfer tube, 26: second heat transfer tube, 30: fan, 31: temperature sensor, 34: first secondary header 35: second secondary header, 36: partition wall, 37: refrigerant return port, 38: liquid pipe, 40, 40a: controller, 41: compressor control unit, 42: determination unit, 43, 44: valve control unit, 45: room temperature sensor, 51: refrigerant flow inlet, 52: refrigerant flow outlet, 53: diaphragm chamber, 53a: diaphragm, 54: spring, 55: pressure chamber, 56: orifice, 57: needle, 58: shaft, 61: first pressure equalizer, 62: second pressure equalizer, 70: control substrate, 71: motor, 72: noise filter, 73: diode bridge, 74: capacitor, 75: inverter, 76: control circuit, 80: processing circuit, 81: processor, 82: memory, 83: bus

Claims

1. A refrigeration cycle apparatus comprising:

a compressor configured to compress and discharge refrigerant;

a first heat exchanger into which the refrigerant discharged from the compressor flows;

an expansion valve configured to expand the refrigerant flowing from the first heat exchanger;

a second heat exchanger having a plurality of heat transfer tubes and a header configured to distribute, to the plurality of heat transfer tubes, the refrigerant flowing from the expansion valve;

a first refrigerant pipe connecting the expansion valve with a refrigerant inlet of the header;

a second refrigerant pipe connecting the second heat exchanger with a refrigerant inlet of the compressor;

a bypass circuit having a bypass inlet connected to the header at a position different from that of the refrigerant inlet of the header and a bypass outlet connected to the second refrigerant pipe;

a bypass valve provided in the bypass circuit and configured to make a pressure of the refrigerant in the bypass circuit lower than a pressure of the refrigerant in the header; and

a refrigerant circuit auxiliary unit configured to deliver gas-phase refrigerant from the bypass circuit to the bypass outlet.

2. The refrigeration cycle apparatus of claim 1, wherein the refrigerant circuit auxiliary unit is a secondary heat exchanger provided between the bypass valve and the bypass outlet in the bypass circuit and configured to heat the refrigerant flowing out from the bypass valve.

3. The refrigeration cycle apparatus of claim 2, further comprising a control substrate configured to control equipment including the compressor,

wherein the refrigerant circuit auxiliary unit is configured to be in contact with the control substrate.

4. The refrigeration cycle apparatus of claim 2, wherein the refrigerant circuit auxiliary unit is integrated with the second heat exchanger.

5. The refrigeration cycle apparatus of claim 4, further comprising a fan configured to send air to the second heat exchanger and the secondary heat exchanger,

wherein the refrigerant circuit auxiliary unit is disposed at such a position that a speed of air sent by the fan to the refrigerant circuit auxiliary unit is lower than a speed of air sent by the fan to the second heat exchanger.

6. The refrigeration cycle apparatus of claim 4, wherein the refrigerant circuit auxiliary unit is configured such that the refrigerant circuit auxiliary unit is smaller in heat transfer area than the second heat exchanger.

7. The refrigeration cycle apparatus of claim 2, wherein the refrigerant circuit auxiliary unit is configured such that the refrigerant circuit auxiliary unit is smaller in amount of heat exchange than the second heat exchanger.

8. The refrigeration cycle apparatus claim 2, wherein the bypass valve is configured such that the bypass valve is smaller in pressure loss than the second heat exchanger in a case in which an opening degree of the bypass valve is fully open.

9. The refrigeration cycle apparatus of claim 2, wherein

the plurality of heat transfer tubes are placed at different heights in the second heat exchanger in a direction of gravitational force,

the refrigeration cycle apparatus further comprising:

a temperature sensor provided on one of the plurality of heat transfer tubes that is above an intermediate position of the heights in the second heat exchanger and configured to detect a temperature of refrigerant flowing through the heat transfer tube; and

a controller configured to control an opening degree of the bypass valve based on a detected value of the temperature sensor,

wherein the controller is configured to increase the opening degree of the bypass valve in a case in which the detected value is higher than a predetermined threshold and decrease the opening degree of the bypass valve in a case in which the detected value is lower than the threshold.

10. The refrigeration cycle apparatus of claim 1, further comprising a liquid pipe connecting a refrigerant return port provided in the first refrigerant pipe with the refrigerant circuit auxiliary unit,

wherein

the refrigerant circuit auxiliary unit is a gas-liquid separator provided between the header and the bypass valve in the bypass circuit and configured to separate the refrigerant flowing from the header into gas-phase refrigerant and liquid-phase refrigerant, and

the refrigerant circuit auxiliary unit is configured to cause the gas-phase refrigerant to flow out to the bypass valve via the bypass circuit and cause the liquid-phase refrigerant to flow out to the refrigerant return port via the liquid pipe.

11. The refrigeration cycle apparatus of claim 1, wherein

the refrigerant circuit auxiliary unit is a gas-liquid separator provided in the first refrigerant pipe and configured to separate refrigerant flowing from the expansion valve into the header into gas-phase refrigerant and liquid-phase refrigerant, and

the bypass circuit is disposed to pass through the refrigerant circuit auxiliary unit to cause the refrigerant flowing out from the bypass valve to exchange heat with the liquid-phase refrigerant stored in the refrigerant circuit auxiliary unit.

12. The refrigeration cycle apparatus of claim 1, wherein the bypass valve is a mechanical differential pressure regulating valve configured to keep a pressure difference of the refrigerant between a refrigerant flow inlet and a refrigerant flow outlet of the bypass valve within a certain range.

13. The refrigeration cycle apparatus of claim 1, wherein the bypass outlet is connected to the second refrigerant pipe at a position closer to the compressor than an intermediate position between a refrigerant outlet of the second heat exchanger and the refrigerant suction inlet of the compressor.

14. The refrigeration cycle apparatus of claim 1, further comprising a controller configured to control an operating frequency of the compressor and an opening degree of the bypass valve,

wherein

in making the operating frequency of the compressor lower than a present frequency, the controller is configured to make the opening degree of the bypass valve larger than a present opening degree before changing the operating frequency, and

in making the operating frequency of the compressor higher than the present frequency, the controller makes the opening degree of the bypass valve smaller than the present opening degree before changing the operating frequency.

15. The refrigeration cycle apparatus of claim 1, wherein

the header is configured to linearly extend in parallel to a direction of gravitational force, and

the bypass inlet is connected to the header at a position away from the refrigerant inlet in a direction opposite to the direction of gravitational force.

16. The refrigeration cycle apparatus of claim 1, wherein

the header is configured to linearly extend in parallel to a plane orthogonal to a direction of gravitational force, and

the bypass inlet is connected to the header downstream of the refrigerant inlet in a direction in which the refrigerant flows through the header.