GB2545112A - Refrigeration cycle device and air-conditioning device - Google Patents

Abstract

A refrigeration cycle device provided with a refrigerant circuit that is provided with a compressor, indoor heat exchanger, throttle device, and outdoor heat exchanger which are connected by refrigerant piping. The refrigeration cycle device is provided with a control device that controls the execution of defrost operation on the basis of the temperature of the outdoor heat exchanger and outside air temperature. The outdoor heat exchanger is provided with at least a first heat exchanger and a second heat exchanger disposed below the first heat exchanger. The control device is configured so as to perform on-defrost operation in which one of the first heat exchanger and the second heat exchanger serves as an evaporator and the hot gas discharged from the compressor is supplied to the other heat exchanger, without passing through the indoor heat exchanger, if the outside air temperature satisfies a preset condition, and to perform reverse defrost operation in which the refrigerant after passing through the indoor heat exchanger is supplied from the compressor to the first heat exchanger and the second heat exchanger if the temperature of the outdoor heat exchanger satisfies a preset condition after the execution of the on-defrost operation.

Description

DESCRIPTION Title of Invention REFRIGERATION CYCLE APPARATUS AND AIR-CONDITIONING APPARATUS Technical Field [0001]

The present invention relates to a refrigeration cycle apparatus and an air-conditioning apparatus.

Background Art [0002] A refrigeration cycle apparatus includes a refrigerant circuit, for example composed of a compressor, a four-way valve, an outdoor heat exchanger, an expansion device and an indoor heat exchanger, which are connected via refrigerant piping. For example, the compressor and the outdoor heat exchanger are mounted in the outdoor unit installed outside a room. When the refrigeration cycle apparatus performs a heating operation, the outdoor heat exchanger acts as evaporator.

[0003]

The heating operation of the refrigeration cycle apparatus, in which the outdoor heat exchanger acts as evaporator, is primarily performed in winter, and hence frost may stick to the outdoor heat exchanger. When frost sticks to the outdoor heat exchanger, the heat exchange efficiency between refrigerant supplied to a heat transfer pipe of the outdoor heat exchanger and air passing through a plurality of fins attached to the heat transfer pipe is degraded, which results in degraded efficiency of the heating operation performed by the refrigeration cycle apparatus.

[0004]

Accordingly, some refrigeration cycle apparatuses are configured, in order to melt the frost stuck to the outdoor heat exchanger, to perform a reverse-defrost operation including suspending the heating operation, switching the flow path of the four-way valve so as to perform a cooling operation, and supplying the refrigerant to the outdoor heat exchanger through the indoor heat exchanger.

[0005]

In addition, a refrigeration cycle apparatus in which the outdoor heat exchanger is divided into two stages, namely an upper and a lower stage, has been proposed (see, for example, Patent Literature 1). The refrigeration cycle apparatus according to Patent Literature 1 is configured to perform an on-defrost operation, while performing the heating operation, including supplying hot gas the upper or lower outdoor heat exchanger to defrost, and causing the lower or upper outdoor heat exchanger to serve as evaporator. By performing such an on-defrost operation, the heating operation can be continuously performed while the defrosting operation is performed with respect to the upper or lower outdoor heat exchanger.

Citation List Patent Literature [0006]

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-085484 Summary of Invention Technical Problem [0007]

The on-defrost operation includes, for example instead of utilizing the heat collected through the indoor unit, raising the refrigerant temperature with the compressor and supplying the refrigerant with the raised temperature to the outdoor heat exchanger. With the on-defrost operation performed by the refrigeration cycle apparatus according to Patent Literature 1, the frost may remain on the outdoor heat exchanger after the on-defrost operation, owing to insufficient defrosting capacity.

[0008]

Therefore, the refrigeration cycle apparatus according to Patent Literature 1 has a drawback in that the heating operation efficiency may be degraded owing to the frost formed on the outdoor heat exchanger (residual frost), when the heating operation is performed after the on-defrost operation is finished.

[0009]

The present invention has been accomplished in view of the foregoing problem, and provides a refrigeration cycle apparatus and an air-conditioning apparatus capable of preventing degradation in efficiency of a heating operation performed after an on-defrost operation is finished.

Solution to Problem [0010]

In one embodiment, the present invention provides a refrigeration cycle apparatus compressor, an indoor heat exchanger, an expansion device and an outdoor heat exchanger which are connected via refrigerant piping, the refrigeration cycle apparatus comprising: a controller configured to control execution of a defrosting operation according to a refrigerant temperature of the outdoor heat exchanger and an outdoor air temperature, the outdoor heat exchanger including at least a first heat exchanger and a second heat exchanger located under the first heat exchanger, and the controller being configured to cause the refrigeration cycle apparatus to perform, when the outdoor air temperature satisfies a predetermined condition, an on-defrost operation including causing one of the first heat exchanger and the second heat exchanger to serve as an evaporator, and an other to supply hot gas discharged from the compressor without allowing the hot gas to pass through the indoor heat exchanger, and perform, when the temperature of the outdoor heat exchanger satisfies a predetermined condition after the on-defrost operation is performed, a reverse-defrost operation including supplying refrigerant having passed through the indoor heat exchanger to the first heat exchanger and the second heat exchanger, from the compressor.

Advantageous Effects of Invention [0011]

The refrigeration cycle apparatus configured as above according to an embodiment of the present invention is capable of preventing degradation in efficiency of a heating operation performed after the on-defrost operation is finished.

Brief Description of Drawings [0012] [Fig. 1] Fig. 1 is a schematic diagram showing a refrigerant circuit configuration of a refrigeration cycle apparatus 500 according to Embodiment of the present invention.

[Fig. 2] Fig. 2 includes schematic drawings of an outdoor heat exchanger 103.

[Fig. 3A] Fig. 3A is a schematic diagram showing a flow of refrigerant in a heating operation performed by the refrigeration cycle apparatus 500 according to Embodiment of the present invention.

[Fig. 3B] Fig. 3B is a schematic diagram showing a flow of refrigerant in a cooling operation performed by the refrigeration cycle apparatus 500 according to Embodiment of the present invention.

[Fig. 4A] Fig. 4A is a schematic diagram showing how the refrigerant is supplied to a first heat exchanger 103a in an on-defrost operation performed by the refrigeration cycle apparatus 500 according to Embodiment of the present invention.

[Fig. 4B] Fig. 4B is a schematic diagram showing how the refrigerant is supplied to a second heat exchanger 103b in the on-defrost operation performed by the refrigeration cycle apparatus 500 according to Embodiment of the present invention.

[Fig. 4C] Fig. 4C is a schematic diagram showing a flow of refrigerant in a reverse-defrost operation performed by the refrigeration cycle apparatus 500 according to Embodiment of the present invention.

[Fig. 5] Fig. 5 includes schematic drawings showing a melting process of frost stuck to the outdoor heat exchanger 103 during the on-defrost operation.

[Fig. 6A] Fig. 6A includes schematic drawings showing a reverse-defrost operation process performed after the on-defrost operation which has failed to remove the frost because the frost was frozen on the second heat exchanger 103b.

[Fig. 6B] Fig. 6B includes schematic drawings showing a reverse-defrost operation process performed after the on-defrost operation which has failed to remove the frost from neither of the first heat exchanger 103a and the second heat exchanger 103b because of excessive frost formation.

[Fig. 7] Fig. 7 includes schematic drawings showing a reverse-defrost operation process performed without being preceded by the on-defrost operation, because of excessive frost formation on both of the first heat exchanger 103a and the second heat exchanger 103b.

[Fig. 8] Fig. 8 is a flowchart showing a control process for switching from the heating operation to the defrosting operation performed by the refrigeration cycle apparatus 500 according to Embodiment of the present invention.

[Fig. 9] Fig. 9 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 1 of Embodiment of the present invention.

[Fig. 10] Fig. 10 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 2 of Embodiment of the present invention.

[Fig. 11] Fig. 11 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 3 of Embodiment of the present invention.

[Fig. 12] Fig. 12 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 4 of Embodiment of the present invention.

[Fig. 13] Fig. 13 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 5 of Embodiment of the present invention.

Description of Embodiments [0013]

Flereafter, a refrigeration cycle apparatus and an air-conditioning apparatus according to Embodiment of the present invention will be described with reference to the drawings. It is to be noted that the present invention is in no way limited to the following Embodiment. In Fig. 1 and all other drawings, dimensional relationships among the elements illustrated in the drawings may differ from actual ones.

[0014]

Embodiment

Fig. 1 is a schematic diagram showing a refrigerant circuit configuration of a refrigeration cycle apparatus 500 according to Embodiment of the present invention. Fig. 2 includes schematic drawings of an outdoor heat exchanger 103. Referring to Fig. 1, the refrigerant circuit configuration of the refrigeration cycle apparatus 500 will be described. In Embodiment the refrigeration cycle apparatus 500 is exemplified by an air-conditioning apparatus.

The refrigeration cycle apparatus 500 according to Embodiment has been improved so as to perform an on-defrost operation and a reverse-defrost operation according to an outdoor air temperature and a temperature of the outdoor heat exchanger 103.

[0015] [Outdoor unit 100]

An outdoor unit 100 is a heat source unit that supplies cooling energy or heating energy to an indoor unit 300. The outdoor unit 100 includes a compressor 101 that compresses and discharges refrigerant, a four-way valve 102 for switching between a cooling operation and a heating operation, the outdoor heat exchanger 103 that acts as condenser in the cooling operation and acts as evaporator in the heating operation, and an accumulator 104 for storing surplus refrigerant from a refrigerant circuit C, which are connected via refrigerant piping.

[0016]

The outdoor unit 100 also includes a switching valve 105a, a switching valve 105b, a switching valve 106a, and a switching valve 106b for selecting one or more of the cooling operation, the heating operation, the reverse-defrost operation, and the on-defrost operation. In addition, the outdoor unit 100 includes an outdoor fan 109 attached to the outdoor heat exchanger 103 to supply air thereto.

[0017]

Further, the outdoor unit 100 includes a controller 119 that controls the rotation speed of the compressor 101 when performing the cooling operation, the heating operation, the reverse-defrost operation, and the on-defrost operation. The outdoor unit 100 also includes an outdoor air temperature sensor 153, a refrigerant temperature detection unit 151, a high-pressure sensor 141, and a low-pressure sensor 142, utilized by the controller 119 to decide whether to switch between the heating operation, the reverse-defrost operation, and the on-defrost operation.

[0018]

The on-defrost operation and the reverse-defrost operation will now be described hereunder. In the on-defrost operation, the indoor unit 300 is not utilized as source for collecting heat. Accordingly, the on-defrost operation is inferior to the reverse-defrost operation in defrosting capacity, since the heat collected from the indoor unit 300 is not utilized. On the other hand, in the on-defrost operation the heating operation can be continuously performed by causing one of the heat exchangers constituting the outdoor heat exchanger 103, namely one of the first heat exchanger 103a and the second heat exchanger 103b, to serve as evaporator. In the on-defrost operation, hot gas refrigerant discharged from the compressor 101 is supplied to the outdoor heat exchanger 103, through a bypass circumventing an indoor heat exchanger 312.

[0019]

In the reverse-defrost operation, the indoor unit 300 is utilized as source for collecting heat to utilize the latent heat of the refrigerant, and therefore higher defrosting capacity can be attained than in the on-defrost operation, in which the hot gas is supplied to the outdoor heat exchanger 103. Accordingly, the defrosting of the outdoor heat exchanger 103 can be completed in a shorter time than the on-defrost operation. In the reverse-defrost operation, the four-way valve 102 is set for the cooling operation, so that the refrigerant flows in the reverse direction with respect to the flow in the heating operation.

[0020] (Compressor 101)

The compressor 101 sucks low-temperature and low-pressure gas refrigerant and compresses such refrigerant to turn it into high-temperature and high-pressure gas refrigerant, to thereby circulate the refrigerant in the refrigerant circuit C. Preferably, the compressor 101 may be an inverter-based compressor the capacity of which is variable. However, without limitation to the inverter-based compressor with variable capacity, the compressor 101 may be a constant-speed compressor, or a combination type of the constant-speed compressor and the inverter-based compressor. The discharge side of the compressor 101 is connected to the four-way valve 102, and the suction side is connected to the accumulator 104.

[0021]

The type of the compressor 101 is not specifically limited provided that the sucked refrigerant can be compressed. The compressor 101 may be, for example, of a reciprocating type, a rotary type, a scroll type, or a screw type.

[0022] (Four-way Valve 102)

The four-way valve 102 is located on the discharge side of the compressor 101, and serves to switch the refrigerant flow path between the cooling operation and the heating operation. In other words, the four-way valve 102 controls the flow of the refrigerant so as to cause the outdoor heat exchanger 103 to serve as evaporator or condenser, depending on the operation mode. The four-way valve 102 is switched so as to connect the indoor heat exchanger 312 to the compressor 101, and the outdoor heat exchanger 103 to the accumulator 104, in the heating operation. In the cooling operation, the four-way valve 102 is switched so as to connect the outdoor heat exchanger 103 to the compressor 101, and the indoor heat exchanger 312 to the accumulator 104.

[0023] (Outdoor Heat Exchanger 103)

The outdoor heat exchanger 103 exchanges heat between a heat medium (e.g., ambient air, water) and the refrigerant, and acts as evaporator to evaporate and gasify the refrigerant in the heating operation, and as condenser (radiator) to condense and liquefy the refrigerant in the cooling operation. The outdoor heat exchanger 103 may be constituted of, for example a fin tube heat exchanger including a heat transfer pipe through which the refrigerant flows and a plurality of fin tubes connected to the heat transfer pipe. The condensing capacity and the evaporating capacity of the outdoor heat exchanger 103 is controlled through the rotation speed of the outdoor fan 109. The outdoor heat exchanger 103 includes a plurality of heat exchangers. More specifically, the outdoor heat exchanger 103 includes a first heat exchanger 103a and a second heat exchanger 103b located under the first heat exchanger 103a.

[0024]

The first heat exchanger 103a has one end connected to the four-way valve 102, and the other end connected to an expansion device 311 via the switching valve 105a. The second heat exchanger 103b has one end connected to the four-way valve 102, and the other end connected to the expansion device 311 via the switching valve 105b. Although in Embodiment the first heat exchanger 103a is mounted on top of the second heat exchanger 103b as shown in Fig. 2, different configurations may be adopted. For example, the second heat exchanger 103b and the first heat exchanger 103a may be separated from each other.

[0025] (Accumulator 104)

The accumulator 104 is provided on the suction side of the compressor 101, and serves to store surplus refrigerant and separate liquid refrigerant and gas refrigerant from each other. The accumulator 104 has one end connected to the suction side of the compressor 101, and the other end connected to the four-way valve 102.

[0026] (Controller 119)

The controller 119 controls the execution of the cooling operation, the heating operation, the reverse-defrost operation, and the on-defrost operation, according to detection results of the outdoor air temperature sensor 153, the refrigerant temperature detection unit 151, the high-pressure sensor 141, and the low-pressure sensor 142. The controller 119 controls, for the execution of the mentioned operations, the rotation speed (activating and stopping inclusive) of the indoor fan 313, the outdoor fan 109, and the compressor 101, the switching of the four-way valve 102, the opening and closing of the switching valve 105a, the switching valve 105b, the switching valve 106a, and the switching valve 106b, and the opening degree of the expansion device 311.

[0027]

Although the controller 119 for controlling the operation of the refrigeration cycle apparatus 500 is mounted in the outdoor unit 100 in Fig. 1, the controller 119 may be provided in the indoor unit 300. Alternatively, the controller 119 may be provided outside the outdoor unit 100 and the indoor unit 300. Further, the controller 119 may be divided into a plurality of units according to the functions, and allocated to the outdoor unit 100 and the indoor unit 300. In this case, preferably, the plurality of units may be connected to each other wirelessly or via wire.

[0028]

The controller 119 is configured to execute the on-defrost operation when the detection result of a first refrigerant temperature sensor 151a of the refrigerant temperature detection unit 151, to be subsequently described, is equal to or lower than a first refrigerant temperature Ta, and the detection result of the outdoor air temperature sensor 153 is higher than a predetermined outdoor air temperature (see step S2 and step S3 in Fig. 8). In addition, the controller 119 is configured to execute the reverse-defrost operation when the detection result of a second refrigerant temperature sensor 151 b of the refrigerant temperature detection unit 151 is equal to or lower than a second refrigerant temperature Tb (see step S6 in Fig. 8). For example, the first refrigerant temperature Ta and the second refrigerant temperature Tb may be set to 2 degrees Celsius, and the predetermined outdoor air temperature Tair may be set to 1 degree Celsius. In Embodiment, the first refrigerant temperature Ta and the second refrigerant temperature Tb are set, for example, to a value higher than the outdoor air temperature Tair.

[0029]

Embodiment Although the first refrigerant temperature Ta and the second refrigerant temperature Tb are set to the same value in Embodiment, different settings may be adopted. For example, the second refrigerant temperature Tb may be set to a lower value than the first refrigerant temperature Ta, so that the reverse-defrost operation is not entered even though a small amount of frost remains. Alternatively, the second refrigerant temperature Tb may be set to a higher value than the first refrigerant temperature Ta, to facilitate the reverse-defrost operation to be activated so as to assure that the frost is completely removed.

[0030]

When executing the on-defrost operation and the reverse-defrost operation, it is preferable that the controller 119 causes the compressor 101 to work at a maximum rotation speed. In this case, gas refrigerant of a higher temperature can be supplied to the outdoor heat exchanger 103, so that the defrosting of the outdoor heat exchanger 103 can be performed with higher efficiency.

[0031] (Sensors)

The outdoor air temperature sensor 153 detects the outdoor air temperature. The outdoor air temperature sensor 153 is, for example, attached to the casing of the outdoor unit 100. The outdoor air temperature sensor 153 is utilized to decide which of the on-defrost operation and the reverse-defrost operation is to be executed. The refrigeration cycle apparatus 500 is configured, when performing the defrosting operation, to perform the on-defrost operation when the outdoor air temperature is higher than the predetermined temperature, and perform the reverse-defrost operation when the outdoor air temperature is equal to or lower than the predetermined temperature.

[0032]

The refrigerant temperature detection unit 151 is attached to the outdoor heat exchanger 103, to be utilized to detect the temperature of the refrigerant in the outdoor heat exchanger 103. The refrigerant temperature detection unit 151 is utilized to decide whether the on-defrost operation or the reverse-defrost operation is to be executed. The refrigerant temperature detection unit 151 includes the first refrigerant temperature sensor 151a attached to the first heat exchanger 103a to detect the refrigerant in the first heat exchanger 103a, and the second refrigerant temperature sensor 151b attached to the second heat exchanger 103b to detect the refrigerant in the second heat exchanger 103b.

The first refrigerant temperature sensor 151a is located on the inlet side of the first heat exchanger 103a, in other words at a position where the temperature of the refrigerant at inlet of the first heat exchanger 103a can be detected. The second refrigerant temperature sensor 151 b is located on the inlet side of the second heat exchanger 103b, in other words at a position where the temperature of the refrigerant at inlet of the second heat exchanger 103b can be detected.

The first refrigerant temperature sensor 151a may be attached, for example, to the refrigerant pipe connecting between the first heat exchanger 103a and the switching valve 105a, and the second refrigerant temperature sensor 151b may be attached to the refrigerant pipe connecting between the second heat exchanger 103b and the switching valve 105b.

[0033]

The first refrigerant temperature sensor 151a and the second refrigerant temperature sensor 151 b may be located at different positions. For example, these sensors may be provided on the outlet side of the outdoor heat exchanger 103.

[0034]

The high-pressure sensor 141 detects the pressure of the refrigerant discharged from the compressor 101. The high-pressure sensor 141 is attached to the refrigerant pipe connecting between the discharge side of the compressor 101 and the four-way valve 102. In the refrigeration cycle apparatus 500, the controller 119 causes the compressor 101 to work at a maximum rotation speed in the on-defrost operation and the reverse-defrost operation. Such an arrangement facilitates the pressure of the refrigerant discharged from the compressor 101 to be increased. With the increase in refrigerant pressure, the refrigerating machine oil for lubrication of the driving mechanism of the compressor 101 may deteriorate owing to an increase in refrigerant temperature resultant from the increase in refrigerant pressure. Therefore, the controller 119 reduces the rotation speed of the compressor 101 or even stops the compressor 101, when the pressure of the discharged refrigerant provided by the high-pressure sensor 141 is higher than a predetermined value.

[0035]

The low-pressure sensor 142 detects the pressure of the refrigerant sucked into the compressor 101. The low-pressure sensor 142 is attached to the refrigerant pipe connecting between the refrigerant inlet side of the accumulator 104 and the four-way valve 102. When frost sticks to the outdoor heat exchanger 103 (evaporator) in the heating operation, the fins are clogged and the heat exchange efficiency of the outdoor heat exchanger 103 between the refrigerant and air is degraded. Therefore, the refrigerant becomes difficult to be gasified in the outdoor heat exchanger 103 during the heating operation, which may lead to a drop of the low pressure. The low-pressure sensor 142 serves to detect such abnormality of the low pressure. In Embodiment, a process of performing the on-defrost operation and the reverse-defrost operation when a predetermined time has elapsed from the start of the heating operation (step S1 in Fig. 8 to be subsequently described), and the refrigerant temperature and the outdoor air temperature satisfy predetermined conditions will be described as an example, however different arrangements may be adopted. For example, the controller 119 may be configured to execute the on-defrost operation and the reverse-defrost operation when the detection result of the low-pressure sensor 142 becomes lower than a predetermined value during the heating operation.

[0036] [Indoor Unit 300]

The indoor unit 300 is a load-side unit to which cooling energy or heating energy is supplied from the outdoor unit 100. The indoor unit 300 includes the indoor heat exchanger 312 and the expansion device 311, connected in series to each other. It is desirable to provide a non-illustrated fan for supplying air to the indoor heat exchanger 312. Here, the indoor heat exchanger 312 may be configured to exchange heat between the refrigerant and a heat medium different from refrigerant, such as water.

[0037] (Indoor Heat Exchanger 312)

The indoor heat exchanger 312 exchanges heat between a heat medium (e.g., ambient air, water) and the refrigerant, and acts as condenser (radiator) to condense and liquefy the refrigerant in the heating operation, and as evaporator to evaporate and gasify the refrigerant in the cooling operation. The indoor heat exchanger 312 may be constituted of, for example a fin tube heat exchanger including a heat transfer pipe through which the refrigerant flows and a plurality of fin tubes connected to the heat transfer pipe. The condensing capacity and the evaporating capacity of the indoor heat exchanger 312 is controlled through the rotation speed of the indoor fan 313.

[0038] (Expansion Device 311)

The expansion device 311 depressurizes the refrigerant so as to expand the same. The expansion device 311 may be constituted of a device with variable opening degree, such as an electronic expansion valve. Alternatively, a capillary tube which is inexpensive compared with the electronic expansion valve, though unable to adjust the opening degree unlike the electronic expansion valve, may be employed as the expansion device 311.

[0039]

Further, various types of refrigerant may be loaded in the refrigerant circuit C of the refrigeration cycle apparatus 500. For example, natural refrigerant such as carbon dioxide refrigerant, hydrocarbon refrigerant, or helium may be adopted. Otherwise, an alternative refrigerant free from chlorine may be adopted, such as HFC410A refrigerant, HFC407C refrigerant, or HFC404A refrigerant. Further, a freon-based refrigerant such as R22 refrigerant, or R134a refrigerant may be utilized.

[0040] [Details of Fleating Operation and Cooling Operation]

Fig. 3A is a schematic diagram showing a flow of the refrigerant in the heating operation performed by the refrigeration cycle apparatus 500 according to Embodiment. Fig. 3B is a schematic diagram showing a flow of the refrigerant in the cooling operation performed by the refrigeration cycle apparatus 500 according to Embodiment. Referring to Fig. 3A and Fig. 3B, the process of the heating operation and the cooling operation performed by the refrigeration cycle apparatus 500 will be described hereunder.

[0041]

The refrigeration cycle apparatus 500 starts the cooling operation or the heating operation upon receipt or a signal to start the cooling operation or a signal to start the heating operation, for example from a remote controller provided in a room.

[0042]

In the heating operation, the controller 119 sets the four-way valve 102 for the heating operation, so as to connect the discharge side of the compressor 101 to the indoor heat exchanger 312, and the refrigerant inlet of the accumulator 104 to the outdoor heat exchanger 103. The controller 119 also sets the rotation speed of the compressor 101 to a predetermined speed, the rotation speed of the outdoor fan 109 and the indoor fan 313 to a predetermined speed, and the opening degree of the expansion device 311 to a predetermined degree.

Further, the controller 119 opens the switching valve 105a and the switching valve 105b, and closes the switching valve 106a and the switching valve 106b.

As shown in Fig. 3A, the refrigerant discharged from the compressor 101 passes through the four-way valve 102 and then flows into the indoor heat exchanger 312, to be condensed and liquefied therein. The refrigerant which has flowed out of the indoor heat exchanger 312 is depressurized in the expansion device 311 and then gasified in the outdoor heat exchanger 103. The refrigerant which has flowed out of the outdoor heat exchanger 103 flows into the accumulator 104 through the four-way valve 102. Then the gas refrigerant out of the refrigerant in the accumulator 104 flows into the suction side of the compressor 101.

[0043]

In the cooling operation, the controller 119 sets the four-way valve 102 for the cooling operation, so as to connect the discharge side of the compressor 101 to the outdoor heat exchanger 103, and the refrigerant inlet of the accumulator 104 to the indoor heat exchanger 312. The controller 119 also sets the rotation speed of the compressor 101 to a predetermined speed, the rotation speed of the outdoor fan 109 and the indoor fan 313 to a predetermined speed, and the opening degree of the expansion device 311 to a predetermined degree.

Further, the controller 119 opens the switching valve 105a and the switching valve 105b, and closes the switching valve 106a and the switching valve 106b.

As shown in Fig. 3B, the refrigerant discharged from the compressor 101 passes through the four-way valve 102 and then flows into the outdoor heat exchanger 103, to be condensed and liquefied therein. The refrigerant which has flowed out of the outdoor heat exchanger 103 is depressurized in the expansion device 311 and then gasified in the indoor heat exchanger 312. The refrigerant which has flowed out of the indoor heat exchanger 312 flows into the accumulator 104 through the four-way valve 102. Then the gas refrigerant out of the refrigerant in the accumulator 104 flows into the suction side of the compressor 101.

[0044] [Details of On-Defrost Operation and Reverse-Defrost Operation]

Fig. 4A is a schematic diagram showing how the refrigerant is supplied to the first heat exchanger 103a in the on-defrost operation performed by the refrigeration cycle apparatus 500 according to Embodiment. Fig. 4B is a schematic diagram showing how the refrigerant is supplied to the second heat exchanger 103b in the on-defrost operation performed by the refrigeration cycle apparatus 500 according to Embodiment. Fig. 4C is a schematic diagram showing a flow of the refrigerant in the reverse-defrost operation performed by the refrigeration cycle apparatus 500 according to Embodiment.

[0045]

The controller 119 is configured to switch, in the on-defrost operation, such that one of the first heat exchanger 103a and the second heat exchanger 103b is caused to serve as evaporator and the hot gas is supplied to the other. In other words, in the on-defrost operation the controller 119 is configured to perform a first operation mode including causing the first heat exchanger 103a to serve as evaporator and supplying the hot gas to the second heat exchanger 103b, and a second operation mode including causing the second heat exchanger 103b to serve as evaporator and supplying the hot gas to the first heat exchanger 103a.

Fig. 4A corresponds to the first operation mode and Fig. 4B corresponds to the second operation mode.

[0046] (On-Defrost Operation: First Operation Mode)

As shown in Fig. 4A, in the first operation mode the controller 119 sets the four-way valve 102 for the heating operation. In Embodiment, the four-way valve 102 is made to maintain the setting for the heating operation, so as to perform the on-defrost operation while the heating operation is being performed. Accordingly, the controller 119 does not switch the four-way valve 102. In addition, the controller 119 sets the rotation speed of the compressor 101 to the maximum speed, and the rotation speed of the outdoor fan 109 and the indoor fan 313 to a predetermined speed. Since the heating operation is continued during the on-defrost operation, the outdoor fan 109 and the indoor fan 313 are driven. The controller 119 sets the expansion device 311 to a predetermined opening degree. The controller 119 also opens the switching valve 105a and closes the switching valve 105b. Further, the controller 119 closes the switching valve 106a and opens the switching valve 106b. Thus, the first heat exchanger 103a is caused to serve as evaporator and the hot gas refrigerant discharged from the compressor 101 is supplied to the second heat exchanger 103b (see Fig. 5(a), Fig. 5(b), Fig. 6(a), and Fig. 6(b)).

[0047]

As shown in Fig. 4A, a part of the refrigerant discharged from the compressor 101 passes through the four-way valve 102 and then flows into the indoor heat exchanger 312, to be condensed and liquefied therein. The remaining part of the refrigerant discharged from the compressor 101 flows through the switching valve 106b and then flows into the second heat exchanger 103b, so as to melt the frost. The refrigerant which has flowed out of the indoor heat exchanger 312 is depressurized in the expansion device 311 and then gasified in the first heat exchanger 103a.

[0048]

As shown in Fig. 4A, the refrigerant which has flowed out of the first heat exchanger 103a and the refrigerant which has flowed out of the second heat exchanger 103b are merged on the downstream side of the outdoor heat exchanger 103, and the merged refrigerant flows into the accumulator 104 through the four-way valve 102. Then the gas refrigerant out of the refrigerant in the accumulator 104 flows into the suction side of the compressor 101.

[0049] (On-Defrost Operation: Second Operation Mode)

As shown in Fig. 4B, in the second operation mode the controller 119 closes the switching valve 105a and opens the switching valve 105b. In addition, the controller 119 opens the switching valve 106a and closes the switching valve 106b. The control of the remaining components is performed in the same way as in the first operation mode. Thus, the second heat exchanger 103b is caused to serve as evaporator and the hot gas refrigerant discharged from the compressor 101 is supplied to the first heat exchanger 103a (see Fig. 5(c), Fig. 5(d), Fig. 6(c), and Fig. 6(d)).

[0050]

As shown in Fig. 4B, in the second operation mode a part of the refrigerant discharged from the compressor 101 passes through the four-way valve 102 and then flows into the indoor heat exchanger 312, to be condensed and liquefied therein. The refrigerant which has flowed out of the indoor heat exchanger 312 is depressurized in the expansion device 311 and then gasified in the second heat exchanger 103b. The remaining part of the refrigerant discharged from the compressor 101 flows through the switching valve 106b and then flows into the s first heat exchanger 103a, so as to melt the frost.

[0051]

For example, the controller 119 executes the first operation mode for ten minutes, and then executes the second operation mode for ten minutes. Here, the duration may be longer or shorter than ten minutes. In addition, when different periods of time are required to defrost the first heat exchanger 103a and the second heat exchanger 103b, for example because the first heat exchanger 103a and the second heat exchanger 103b are different in size from each other, the duration may be set to different values.

[0052] (Reverse-Defrost Operation)

Since the reverse-defrost operation is performed after the heating operation or the on-defrost operation is performed, the controller 119 is set for the heating operation. Accordingly, the controller 119 switches the four-way valve 102 from the setting for the heating operation to the setting for the cooling operation, as shown in Fig. 4C.

[0053]

The controller 119 sets the rotation speed of the compressor 101 to the maximum speed. The controller 119 also stops driving the outdoor fan 109 and the indoor fan 313. The outdoor fan 109 is stopped because cold outside air is supplied to the outdoor heat exchanger 103, which makes it difficult to melt the frost, if the outdoor fan 109 is driven during the reverse-defrost operation. Likewise, the indoor fan 313 is stopped because cold air having passed through the indoor heat exchanger 312 acting as evaporator is supplied into the room, if the indoor fan 313 is driven during the reverse-defrost operation.

[0054]

The controller 119 sets the expansion device 311 to a predetermined opening degree. Further, the controller 119 opens the switching valve 105a and the switching valve 105b, and closes the switching valve 106a and the switching valve 106b. In the reverse-defrost operation, the first heat exchanger 103a and the second heat exchanger 103b are caused to serve as condenser, so as to remove the frost more effectively than in the on-defrost operation (see Fig. 6(e) and Fig. 6(f)). The controller 119 executes the reverse-defrost operation, for example, for seven to twelve minutes.

[0055]

The reverse-defrost operation is switched from the heating operation or the on-defrost operation. Accordingly, the indoor heat exchanger 312, set to serve as condenser in the heating operation or the on-defrost operation, possesses the heat thereby acquired. In the reverse-defrost operation, the temperature of the refrigerant flowing out of the indoor heat exchanger 312 is increased by passing therethrough, and the refrigerant having the increased temperature is compressed in the compressor 101 and supplied to the outdoor heat exchanger 103. Therefore, by performing the reverse-defrost operation following the on-defrost operation, residual frost that is left after the on-defrost operation can be removed (see step S4 and step S7 Fig. 8 to be subsequently described). In addition, performing the reverse-defrost operation following the on-defrost operation prevents the defrosting time by the on-defrost operation from being excessively prolonged because of a large amount of frost (see step S3 and step S7 Fig. 8 to be subsequently described).

[0056]

The heated refrigerant which has flowed out of the indoor heat exchanger 312 flows into the suction side of the compressor 101 through the four-way valve 102. Then the refrigerant discharged from the compressor 101 passes through the four-way valve 102 and then flows into the outdoor heat exchanger 103 to be condensed and liquefied, and melts the frost stuck to the outdoor heat exchanger 103. The refrigerant which has flowed out of the outdoor heat exchanger 103 is depressurized in the expansion device 311 and flows into the indoor heat exchanger 312.

[0057] [Frost Melting in On-Defrost Operation]

Fig. 5 includes schematic drawings showing a melting process of frost stuck to the outdoor heat exchanger 103 during the on-defrost operation. Fig. 5(a) illustrates a state where the hot gas is supplied to the first heat exchanger 103a while the second heat exchanger 103b is acting as evaporator, and Fig. 5(b) illustrates a state where the frost F on the first heat exchanger 103a has melted after the operation of Fig. 5(a). Fig. 5(c) illustrates a state where the hot gas is supplied to the second heat exchanger 103b while the first heat exchanger 103a is acting as evaporator, and Fig. 5(d) illustrates a state where the frost F on the second heat exchanger 103b has melted after the operation of Fig. 5(c).

[0058]

After the frost on the first heat exchanger 103a of the upper stage has melted and flowed into the second heat exchanger 103b, the water has been frozen and frozen ice FI has been formed on the second heat exchanger 103b. Fig. 5 is based on the assumption that the frost F stuck to the outdoor heat exchanger 103 can be removed without performing the reverse-defrost operation. For example, when only a small amount of frost is formed on the outdoor heat exchanger 103, the amount of water that melts on the first heat exchanger 103a and flows into the second heat exchanger 103b is also small. Accordingly the amount of the frozen ice FI is also small, and therefore the frozen ice FI on the outdoor heat exchanger 103 can be removed by the on-defrost operation.

[0059] [Frost Melting in On-Defrost Operation and Reverse-Defrost Operation]

Fig. 6A includes schematic drawings showing the reverse-defrost operation process performed after the on-defrost operation which has failed to remove the frost because the frost was frozen on the second heat exchanger 103b. When the on-defrost operation is performed, the water melted by the heat of the first heat exchanger 103a of the upper stage flows into the second heat exchanger 103b of the lower stage acting as evaporator. The water melted from ice, not moisture out of the ambient air, directly flows into the second heat exchanger 103b, and therefore the fins of the second heat exchanger 103b may be frozen, so that the frost may be additionally formed. Accordingly, the defrosting of the second heat exchanger 103b may fail, or it may take an excessively long time to defrost, despite supplying the hot gas to the second heat exchanger 103b after supplying the hot gas to the first heat exchanger 103a.

[0060]

For example, while the hot has is supplied to the first heat exchanger 103a and the second heat exchanger 103b is acting as evaporator, the water melted on the first heat exchanger 103a flows along the fins and sticks to the second heat exchanger 103b. Since the second heat exchanger 103b is acting as evaporator, the water flowing from the first heat exchanger 103a may be frozen on the fins of the second heat exchanger 103b, which may lead to additional frost formation.

Therefore, the refrigeration cycle apparatus 500 is configured, on the assumption that the frost is unable to be removed or it takes an excessively long time to defrost by the on-defrost operation, to perform the reverse-defrost operation under predetermined conditions.

[0061]

Fig. 6A(a) illustrates a state where the hot gas is supplied to the first heat exchanger 103a while the second heat exchanger 103b is acting as evaporator, and Fig. 6A(b) illustrates a state where the frost on the first heat exchanger 103a has not completely melted after the operation of Fig. 6A(a). As shown in Fig. 6A(a) and Fig. 6A(b), the frost on the first heat exchanger 103a of the upper stage has melted and flowed into the second heat exchanger 103b, and the frozen ice FI has been formed on the second heat exchanger 103b.

[0062]

Fig. 6A(c) illustrates a state where the hot gas is supplied to the second heat exchanger 103b while the first heat exchanger 103a is acting as evaporator, and Fig. 6A(d) illustrates a state where the frost on the second heat exchanger 103b has not completely melted after the operation of Fig. 6(c). Thus, the defrosting capacity of the hot gas has failed to remove the frozen ice FI.

[0063]

Fig. 6(e) illustrates a state where the refrigerant having passed through the indoor heat exchanger 312 in the reverse-defrost operation is supplied to the first heat exchanger 103a and the second heat exchanger 103b, and Fig. 6(f) illustrates a state where the frost on the first heat exchanger 103a and the second heat exchanger 103b has melted after the operation of Fig. 6(d). Since the reverse-defrost operation is superior to the on-defrost operation in defrosting capacity, the frozen ice FI can be removed.

[0064]

Fig. 6B includes schematic drawings showing the reverse-defrost operation process performed after the on-defrost operation which has failed to remove the frost from neither of the first heat exchanger 103a and the second heat exchanger 103b because of excessive frost formation. Fig. 6B(a) to Fig. 6B(f) respectively correspond to Fig. 6A(a) to Fig. 6(f).

As shown in Fig. 6B, when a large amount of frost F is formed on the outdoor heat exchanger 103, the majority of the frost F may remain although a part of the frost has been removed, as shown in Fig. 6B(b). By performing the reverse-defrost operation, the frost stuck to the outdoor heat exchanger 103 can be removed despite a large amount of frost having been formed.

[0065] [Frost Melting in Reverse-Defrost Operation]

Fig. 7 includes schematic drawings showing the reverse-defrost operation process performed without being preceded by the on-defrost operation, because of excessive frost formation on both of the first heat exchanger 103a and the second heat exchanger 103b. Fig. 7(a) illustrates a state where the refrigerant having passed through the indoor heat exchanger 312 in the reverse-defrost operation is supplied to the first heat exchanger 103a and the second heat exchanger 103b, and Fig. 7(b) illustrates a state where the frost on the first heat exchanger 103a and the second heat exchanger 103b has melted after the operation of Fig. 7(a). As shown in Fig. 7, when a large amount of frost is formed, the reverse-defrost operation is performed without the on-defrost operation having been performed. Such an arrangement prevents the defrosting time from being excessively prolonged in vain. The decision corresponding to the decision of the frost formation amount is made at step S3 to be subsequently described.

[0066] [Control Flow]

Fig. 8 is a flowchart showing a control process for switching from the heating operation to the defrosting operation (on-defrost operation and reverse-defrost operation) performed by the refrigeration cycle apparatus 500 according to Embodiment. Referring to Fig. 8, the control flow performed by the refrigeration cycle apparatus 500 will be described hereunder.

[0067] (Step S1: Heating Operation Time Decision)

The controller 119 makes decision on the heating operation time. The heating operation time t is set in advance according to the operation capacity of the outdoor unit 100 and the performance of the outdoor heat exchanger 103. The heating operation time t is stored, for example, in a microcomputer of the controller 119.

[0068] (Step S2: Decision Whether Frost Formed)

The controller 119 makes the decision according to a predetermined first refrigerant temperature Ta and a detection result of the first refrigerant temperature sensor 151 a. When the detection result of the first refrigerant temperature sensor 151a is equal to or lower than the first refrigerant temperature Ta (e.g., 2 degrees Celsius), the process proceeds to step S3. When the detection result of the first refrigerant temperature sensor 151a is higher than the first refrigerant temperature Ta, the process returns to step SO.

[0069]

At step S2, decision is made on the presence of frost. More specifically, at step S2 decision is made according to the temperature of the refrigerant at inlet of the first heat exchanger 103a, so as to decide whether frost exceeding a predetermined amount has been formed on the outdoor heat exchanger 103 to the extent that the defrosting operation is necessary. When the heating operation is performed, the refrigerant about to be supplied to the outdoor heat exchanger 103 is cooled while passing through the indoor heat exchanger 312 acting as condenser. When such cooled refrigerant is supplied to the outdoor heat exchanger 103, frost is more prone to be formed on the outdoor heat exchanger 103. Accordingly, when the detection result of the first refrigerant temperature sensor 151a is equal to or lower than the first refrigerant temperature Ta, it is decided that the defrosting operation is to be performed.

The defrosting operation includes (1) performing only the on-defrost operation and returning to the heating operation, (2) performing only the reverse-defrost operation and returning to the heating operation, and (3) performing both of the on-defrost operation and the reverse-defrost operation, and then returning to the heating operation.

[0070] (Step S3: Decision of Frost Formation Extent)

The controller 119 makes decision according to a predetermined outdoor air temperature Tair. At this step, the decision is made on the type of the defrosting operation to be performed. When the detection result of the outdoor air temperature sensor 153 is higher than the predetermined outdoor air temperature Tair (e.g., 1 degree Celsius), the process proceeds to the step S4. When the outdoor air temperature is not so low, it can be assumed that the frost formed on the outdoor heat exchanger 103 can be removed only by the on-defrost operation. For such a reason step S3 is followed by step S4, where the on-defrost operation is performed.

[0071]

When the detection result of the outdoor air temperature sensor 153 is equal to or lower than the predetermined outdoor air temperature Tair, step S3 is followed by step S8. When the outdoor air temperature is substantially low, it is assumed that a large amount of frost is formed on the outdoor heat exchanger 103, as described with reference to Fig. 7. Accordingly, step S3 is followed by step S8 since it is difficult to melt the frost or it takes a long time to melt the frost, by the on-defrost operation. Thus, at step S3 the duration of the defrosting operation, which differs depending on the extent of frost formation, is determined according to the outdoor air temperature. Here, the value of the outdoor air temperature Tair may be determined, for example, on the basis of a result of experiments carried out in advance.

[0072] (Step S4 and Step S5: On-Defrost Operation)

The controller 119 executes the on-defrost operation. More specifically, the controller 119 executes the second operation mode after executing the first operation mode. Upon finishing the on-defrost operation, the controller 119 proceeds to step S6.

[0073] (Step S6: Decision Whether Residual Frost Present)

The controller 119 makes the decision according to a predetermined second refrigerant temperature Tb and a detection result of the second refrigerant temperature sensor 151 b. When the detection result of the second refrigerant temperature sensor 151 b is equal to or lower than the second refrigerant temperature Tb (e.g., 2 degrees Celsius), the process proceeds to step S7. It is because it has been decided that residual frost is still present after the on-defrost operation is finished, that step S6 is followed by step S7. More specifically, at step S6 it is decided whether the frost has completely melted by the on-defrost operation of step S4, according to the detection result of the second refrigerant temperature sensor 151 b. When the detection result of the second refrigerant temperature sensor 151b is equal to or lower than the second refrigerant temperature, it is probable that the frost has not completely melted, and therefore the process proceeds to step S7.

[0074]

Here, it is not mandatory that the decision of step S6 is made immediately after the on-defrost operation is finished at step S5. This is because although residual frost is present on the outdoor heat exchanger 103, the detection result of the second refrigerant temperature sensor 151 b may be decided to be higher than the second refrigerant temperature Tb, because the refrigerant pipe on the inlet side of the outdoor heat exchanger 103 is heated by the hot gas passing through the mentioned refrigerant pipe, within a short time after the on-defrost operation is finished.

[0075] (Step S7 and Step S8: Reverse-Defrost Operation)

The controller 119 executes the reverse-defrost operation. When the on-defrost operation is finished, the controller 119 returns to step SO.

[0076] [Advantageous Effects of Refrigeration Cycle Apparatus 500 according to Embodiment]

The refrigeration cycle apparatus 500 according to Embodiment makes the decision on the presence of residual frost according to the temperature of the outdoor heat exchanger 103 (second heat exchanger 103b), after the on-defrost operation is performed. For example when the frozen ice FI is formed on the second heat exchanger 103b (see Fig. 6A(d)), or when residual frost is present all over the outdoor heat exchanger 103 (see Fig. 6B(d)), the controller 119 decides that the detection result of the second refrigerant temperature sensor 151b is equal to or lower than the second refrigerant temperature Tb, and executes the reverse-defrost operation. Accordingly, even though frost remains on the outdoor heat exchanger 103 after the on-defrost operation is finished, such residual frost can be removed. Therefore, the heat exchange efficiency between the refrigerant flowing in the outdoor heat exchanger 103 and the air can be prevented from being degraded. In other words, the refrigeration cycle apparatus 500 according to Embodiment is capable of preventing degradation in heat exchange efficiency between the refrigerant flowing in the outdoor heat exchanger 103 and the air, thereby preventing degradation in heating operation efficiency.

[0077]

The refrigeration cycle apparatus 500 according to Embodiment is configured to make the decision on the frost formation according to the temperature of the outdoor heat exchanger 103 (first heat exchanger 103a), so as to decide whether it is necessary to perform at least one of the on-defrost operation and the reverse-defrost operation.

The refrigeration cycle apparatus 500 according to Embodiment also makes the decision on the frost formation amount according to the outdoor air temperature, to thereby decide which of the on-defrost operation and the reverse-defrost operation is to be performed. Therefore, an increase in time required for the defrosting operation time can be prevented.

[0078]

Although the refrigeration cycle apparatus 500 according to Embodiment includes the outdoor air temperature sensor 153 and the refrigerant temperature detection unit 151, different configurations may be adopted. For example, outdoor air temperature information and temperature information of the refrigerant at inlet of the outdoor heat exchanger 103 may be acquired from a centralized controller or the like that collectively controls a plurality of refrigeration cycle apparatuses 500, so as to decide whether the on-defrost operation and the reverse-defrost operation are to be performed.

[0079]

Further, although the refrigeration cycle apparatus 500 according to Embodiment is configured to supply the hot gas to the second heat exchanger 103b after supplying the hot gas to the first heat exchanger 103a in the on-defrost operation, different configurations may be adopted. For example, the hot gas may be supplied to the first heat exchanger 103a after being supplied to the second heat exchanger 103b. In this case, however, the second heat exchanger 103b of the lower stage acts as evaporator while the hot gas is supplied to the first heat exchanger 103a, and the on-defrost operation is finished. Therefore, the residual frost is more likely to remain on the second heat exchanger 103b, compared with the case of the control flow according to Embodiment shown in Fig. 8.

[0080] [Variation 1]

Fig. 9 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 1 of Embodiment. Fig. 9(a) is a perspective view of an outdoor heat exchanger 103B, and Fig. 9(b) is a vertical cross-sectional view of the outdoor heat exchanger 103B. In the outdoor heat exchanger 103B the first heat exchanger 103a is located on the upper side of the second heat exchanger 103b, but shifted therefrom in a horizontal direction. The outdoor heat exchanger 103B thus configured also provides the same advantageous effects as those provided by the refrigeration cycle apparatus 500 according to Embodiment.

[0081] [Variation 2]

Fig. 10 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 2 of Embodiment. Fig. 10(a) is a perspective view of an outdoor heat exchanger 103C, and Fig. 10(b) is a vertical cross-sectional view of the outdoor heat exchanger 103C. In the outdoor heat exchanger 103C, a plate-shaped installation base T, on which the first heat exchanger 103a is to be placed, is provided on the second heat exchanger 103b. The same advantageous effects as those provided by the refrigeration cycle apparatus 500 according to Embodiment can equally be attained, even when such an installation base is interposed between the first heat exchanger 103a and the second heat exchanger 103b.

[0082] [Variation 3]

Fig. 11 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 3 of Embodiment.

Fig. 11(a) is a perspective view of an outdoor heat exchanger 103D, and Fig. 10(b) is a vertical cross-sectional view of the outdoor heat exchanger 103D.

The outdoor heat exchanger 103D includes a pair of first heat exchangers 103a on the upper stage, and a pair of second heat exchangers 103b in the lower stage. Thus, the outdoor heat exchanger 103D includes four heat exchangers. As in this Variation, the number of heat exchangers constituting the outdoor heat exchanger 103D is not limited to two, but may be three or more. Variation 3 also provides the same advantageous effects as those provided by the refrigeration cycle apparatus 500 according to Embodiment.

[0083] [Variation 4]

Fig. 12 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 4 of Embodiment.

Fig. 12(a) is a perspective view of an outdoor heat exchanger 103E, and Fig. 12(b) is a vertical cross-sectional view of the outdoor heat exchanger 103E.

The first heat exchanger 103a of the outdoor heat exchanger 103E is tilted such that one end portion is located on the lower side and the other end portion is located on the upper side. The second heat exchanger 103b is tilted such that one end portion is located on the upper side and the other end portion is located on the lower side. The same advantageous effects as those provided by the refrigeration cycle apparatus 500 according to Embodiment can equally be attained, even when the heat exchangers constituting the outdoor heat exchanger 103 are tilted as above.

[0084] [Variation 5]

Fig. 13 includes schematic drawings of an outdoor heat exchanger 103 of the refrigeration cycle apparatus 500 according to Variation 5 of Embodiment.

Fig. 13(a) is a perspective view of an outdoor heat exchanger 103F, and Fig. 13(b) is a vertical cross-sectional view of the outdoor heat exchanger 103F. The outdoor heat exchanger 103F includes three stages of heat exchangers superposed on each other, instead of two. The number of stages of the outdoor heat exchanger 103F is not limited to two, but may be three or more. When the outdoor heat exchanger 103F includes three stages of heat exchangers for example, the on-defrost operation and the reverse-defrost operation may be performed as follows.

[0085]

In the on-defrost operation, the hot gas is supplied to an uppermost heat exchanger 103c and the other heat exchangers are caused to serve as evaporator, in the first operation mode. In the second operation mode, the hot gas is supplied to a heat exchanger 103aa of the intermediate stage and the other heat exchangers are caused to serve as evaporator. In the third operation mode, the hot gas is supplied to a lowermost heat exchanger 103bb and the other heat exchangers are caused to serve as evaporator.

In the reverse-defrost operation, the refrigerant is supplied to all of the uppermost heat exchanger 103c, the intermediate heat exchanger 103aa, and the lowermost heat exchanger 103bb.

[0086]

The configuration according to Variation 5 also provides the same advantageous effects as those provided by the refrigeration cycle apparatus 500 according to Embodiment.

Reference Signs List [0087] 100: outdoor unit, 101: compressor, 102: four-way valve, 103: outdoor heat exchanger, 103B: outdoor heat exchanger, 103C: outdoor heat exchanger, 103D: outdoor heat exchanger, 103E: outdoor heat exchanger, 103F: outdoor heat exchanger, 103a: first heat exchanger, 103aa: heat exchanger, 103b: second heat exchanger, 103bb: heat exchanger, 103c: heat exchanger, 104: accumulator, 105a: switching valve, 105b: switching valve, 106a: switching valve, 106b: switching valve, 109: outdoor fan, 119: controller, 141: high-pressure sensor, 142: low-pressure sensor, 151: refrigerant temperature detection unit, 151a: first refrigerant temperature sensor, 151b: second refrigerant temperature sensor, 153: outdoor air temperature sensor, 300: indoor unit, 311: expansion device, 312: indoor heat exchanger, 313: indoor fan, 500: refrigeration cycle apparatus, C: refrigerant circuit, F: frost, FI: frozen ice, T: installation base, Ta: first refrigerant temperature, Tair: outdoor air temperature, Tb: second refrigerant temperature, t: heating operation time

Claims (1)

1. CLAIMS [Claim 1] A refrigeration cycle apparatus comprising a refrigerant circuit including a compressor, an indoor heat exchanger, an expansion device and an outdoor heat exchanger which are connected via refrigerant piping, the refrigeration cycle apparatus comprising: a controller configured to control execution of a defrosting operation according to a refrigerant temperature of the outdoor heat exchanger and an outdoor air temperature, the outdoor heat exchanger including at least a first heat exchanger and a second heat exchanger located under the first heat exchanger, and the controller being configured to cause the refrigeration cycle apparatus to perform, when the outdoor air temperature satisfies a predetermined condition, an on-defrost operation including causing one of the first heat exchanger and the second heat exchanger to serve as an evaporator, and an other to supply hot gas discharged from the compressor without allowing the hot gas to pass through the indoor heat exchanger, and perform, when the temperature of the outdoor heat exchanger satisfies a predetermined condition after the on-defrost operation is performed, a reverse-defrost operation including supplying refrigerant having passed through the indoor heat exchanger to the first heat exchanger and the second heat exchanger, from the compressor. [Claim 2] The refrigeration cycle apparatus of claim 1, further comprising: a refrigerant temperature detection unit attached to the outdoor heat exchanger to detect a refrigerant temperature; and an outdoor air temperature sensor configured to detect an outdoor air temperature, the controller being configured to cause the refrigeration cycle apparatus to perform the on-defrost operation when a detection result of the outdoor air temperature sensor satisfies a predetermined condition, and perform the reverse-defrost operation when a detection result of the refrigerant temperature detection unit satisfies a predetermined condition after the on-defrost operation. [Claim 3] The refrigeration cycle apparatus of claim 1 or 2, wherein the controller is configured to perform switching, in the on-defrost operation, such that one of the first heat exchanger and the second heat exchanger is caused to serve as an evaporator and the hot gas is supplied to an other thereof. [Claim 4] The refrigeration cycle apparatus of claim 3, wherein the controller is configured to cause the first heat exchanger to serve as an evaporator and supply the hot gas to the second heat exchanger, after supplying the hot gas to the first heat exchanger and causing the second heat exchanger to serve as evaporator. [Claim 5] The refrigeration cycle apparatus of claim 4, wherein the refrigerant temperature sensor includes a first refrigerant temperature sensor attached to the first heat exchanger to detect a refrigerant temperature of the first heat exchanger; and a second refrigerant temperature sensor attached to the second heat exchanger to detect a refrigerant temperature of the second heat exchanger, and the controller is configured to cause the refrigeration cycle apparatus to perform the on-defrost operation when a detection result of the first refrigerant temperature sensor is equal to or lower than a predetermined first refrigerant temperature and a detection result of the outdoor air temperature sensor is higher than a predetermined temperature, and perform the reverse-defrost operation when a detection result of the second refrigerant temperature sensor is equal to or lower than a predetermined second refrigerant temperature. [Claim 6] The refrigeration cycle apparatus of claim 5, wherein the first refrigerant temperature sensor is located at a position to detect a temperature of the refrigerant at inlet of the first heat exchanger, and the second refrigerant temperature sensor is located at a position to detect a temperature of the refrigerant at inlet of the second heat exchanger. [Claim 7] The refrigeration cycle apparatus of any one of claims 1 to 6, further comprising an outdoor fan annexed to the outdoor heat exchanger to supply air to the outdoor heat exchanger; and an indoor fan annexed to the indoor heat exchanger to supply air to the indoor heat exchanger, wherein the controller is configured to stop the outdoor fan and the indoor fan during the reverse-defrost operation. [Claim 8] An air-conditioning apparatus comprising the refrigeration cycle apparatus of any one of claims 1 to 7, including an outdoor unit having at least a compressor and an outdoor heat exchanger, and an indoor unit having at least an indoor heat exchanger.