US20190056160A1

US20190056160A1 - Air-conditioning apparatus

Info

Publication number: US20190056160A1
Application number: US16/079,607
Authority: US
Inventors: Misaki KODA; Naomichi TAMURA; Yutaka Aoyama
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2016-05-11
Filing date: 2016-05-11
Publication date: 2019-02-21
Also published as: GB2563536A; GB2563536B; JP6727296B2; GB2563536B8; WO2017195296A1; JPWO2017195296A1; GB201814863D0

Abstract

In plural heat-source-side heat exchangers included in an outdoor unit of an air-conditioning apparatus, bypasses for defrosting are provided with flow-rate adjusting mechanisms for refrigerant flowing into the bypasses. The flow rates of the refrigerant which are to be adjusted by the flow-rate adjusting mechanisms are determined in accordance with ambient environments of plural heat-source-side heat exchangers.

Description

TECHNICAL FIELD

The present invention relates to an air-conditioning apparatus which is applied to, for example, a multi-air-conditioning apparatus for a building.

BACKGROUND ART

When an air-conditioning apparatus performs a heating operation during winter season, water vapor in the air adheres to a heat exchanger in a heat source, and frost is formed on the heat exchanger. If the frost still adheres to the heat exchanger, the heating capacity lowers. Therefore, generally, a defrost operation is performed by an outdoor unit during an interval between heating operations to melt the frost adhering to the heat exchanger, to thereby achieve a stable heating capacity.
When the defrost operation is performed, the frost formed on the heat exchanger is melted into defrost water, which flows to a lower part of the heat exchanger. In a cold region, the temperature of such defrost water is low, and the temperature of outside air is extremely low. Therefore, in the cold region, in the case where such a defrost operation is performed in an air-conditioning apparatus, defrost water sometimes refreezes when it flows to a lower part of a heat exchanger. In order to prevent the defrost water from being refrozen, a bypass is provided at a lowermost part of the heat exchanger, and refrigerant having a high pressure and a high temperature is made to flow into the bypass (patent literature 1).

CITATION LIST

Patent Literature

Patent Literature: Japanese Unexamined Patent Application Publication No. 2006-64381

SUMMARY OF INVENTION

Technical Problem

In many cases, as multi-air-conditioning apparatuses for a building, plural air-conditioning apparatuses are used. In this case, outdoor units of the air-conditioning apparatuses are arranged side by side, that is, they are arranged such that side surfaces of any adjacent two of them face each other. In the case where plural outdoor units are densely installed, the distance between side surfaces of any adjacent two of the outdoor units is only several centimeters. During the above defrost operation, fans of the outdoor units of the air-conditioning apparatuses are stopped, and only outside air thus passes through the outdoor units. Therefore, in multi-air-conditioning apparatuses, in the case where plural outdoor units are densely installed, during the defrost operation, outside air more greatly influences upon front and rear surfaces of the outdoor units than upon the side surfaces of the outdoor units, which are spaced from each other by a slight distance. As a result, defrost water tends to refreeze on the front and rear surfaces of the outdoor units.
Also, in many cases, the external shape of an outdoor unit is a substantially cuboid as a whole. The influence of outside air upon the outdoor unit varies from one surface of the outdoor unit to another surface thereof, since the surfaces of the outdoor unit have different areas. Furthermore, the temperature of refrigerant at part of the above bypass which is the farthest from a header of the heat exchanger is lower than the temperature of refrigerant at any of the other parts of the bypass. Therefore, in a single heat exchanger, the temperature of a bypass for preventing refreeze is not uniform over the bypass, a drainage performance is easily worsened, and there is a possibility that refreeze will occur, and whether or not refreeze occurs depends on the distance between part of the bypass and the header.
The present invention has been made to solve the above problem, and an object of the invention is to improve a defrosting efficiency during a defrost operation in a multi-air-conditioning apparatus in which plural outdoor units are installed, and to prevent defrost water from being refrozen.

Solution to Problem

An air-conditioning apparatus according to an embodiment of the present invention includes: an outdoor unit including a compressor, a flow-path switching unit and plural heat-source-side heat exchangers, the compressor, the flow-path switching unit and the heat-source-side heat exchangers being connected by pipes; and an indoor unit connected to the outdoor unit to air-condition a target space, wherein the outdoor unit includes: plural bypasses each having ends one of which is, in connection by pipes in the outdoor unit, connected to a discharge side of the compressor, and the other of which is connected to a suction side of the compressor, the bypasses being configured to cause refrigerant to flow through lower parts of the plural heat-source-side heat exchangers during a defrost operation of the air-conditioning apparatus; and flow-rate adjusting mechanisms respectively provided in the plural bypasses to adjust flow rates of refrigerant flowing into the plural bypasses.

Advantageous Effects of Invention

In the air-conditioning apparatus according to the embodiment of the present invention, the plural bypasses configured to cause the refrigerant to flow through lower parts of the plural heat-source-side heat exchangers during the defrost operation are provided with flow-rate adjusting mechanisms for adjusting the flow rates of the refrigerant flowing into the bypasses. Therefore, in the multi-air-conditioning apparatus for a building, even in the case where the outdoor units are densely installed, the flow-rate adjusting mechanisms are made to function in accordance with the states of the installation of the outdoor units, whereby defrost water generated during the defrost operation can be reliably prevented from being refrozen.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a refrigerant circuit of an air-conditioning apparatus.

FIG. 2 is a diagram illustrating flows of refrigerant during a heating operation of the air-conditioning apparatus.

FIG. 3 is a diagram illustrating flows of refrigerant during a defrost operation of the air-conditioning apparatus.

FIG. 4 is a schematic diagram of a heat-source-side heat exchanger of the air-conditioning apparatus.

FIG. 5 is a diagram illustrating flows of refrigerant in the case where a solenoid valve for a bypass is opened during the defrost operation of the air-conditioning apparatus.

FIG. 6 is a diagram illustrating an example of dense installation of outdoor units in embodiment 1 of the present invention.

FIG. 7 is a schematic diagram of a refrigerant circuit of the air-conditioning apparatus according to embodiment 1 of the present invention.

FIG. 8 is a control block diagram of the air-conditioning apparatus according to embodiment 1 of the present invention.

FIG. 9 is a schematic diagram illustrating heat-source-side heat exchangers in embodiment 2 of the present invention as seen from above.

FIG. 10 is a schematic diagram of a refrigerant circuit of an air-conditioning apparatus according to embodiment 2 of the present invention.

DESCRIPTION OF EMBODIMENTS

Refrigeration cycle devices according to embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the embodiments, which will be described below. With respect to the figures to be referred to, there is a case where the size of each of structural elements is different from that of an actual apparatus.
FIG. 1 is a schematic diagram of a refrigerant circuit of an air-conditioning apparatus. In the air-conditioning apparatus 100, indoor units 10 a, 10 b, 10 c and 10 d are connected to an outdoor unit (heat source unit) 20 by pipes A and B. The indoor units 10 a, 10 b, 10 c and 10 d are connected in parallel. The pipes A and B are refrigerant pipes which allow refrigerant (heat-source-side refrigerant) to flow therethrough.
The outdoor unit 20 includes a compressor 1, a flow-path switching unit 2 such as a four-way valve, heat-source- side heat exchangers 3 a and 3 b and an accumulator 5, which are connected by pipes. The compressor 1 sucks refrigerant, compresses it to cause it to have a high temperature and a high pressure, and transfers it to a refrigerant circuit. The compressor is provided as, for example, an inverter compressor the capacity of which can be controlled. The flow-path switching unit 2 switches the flow of refrigerant between the flow of refrigerant in a heating operation mode and the flow of refrigerant in a cooling operation mode. The heat-source- side heat exchangers 3 a and 3 b function as evaporators in the heating operation mode and function as radiators in the cooling operation mode and a defrost operation mode, and cause heat exchange to be performed between the refrigerant and air supplied by an air-sending device such as a fan (not shown). The heat-source- side heat exchangers 3 a and 3 b are connected in parallel by refrigerant pipes in the outdoor unit 20. The heat-source- side heat exchangers 3 a and 3 b are formed in an L-shape as their outer shape, and are arranged to form a rectangular frame as a whole in a housing of the outdoor unit 20. The accumulator 5 is installed on a suction side of the compressor 1, and accumulates surplus refrigerant which generates because of the difference between the heating operation mode and the cooling operation mode, and surplus refrigerant which generates because of a change in a transient operation.
Bypasses 6 a and 6 b are connected to pipes in the outdoor unit 20. In the pipes in the outdoor unit 20, one of the ends of each of the bypasses 6 a and 6 b is connected to the discharge side of the compressor 1, and the other is connected to the suction side thereof. Furthermore, the bypass 6 a extends through lower part of the heat-source-side heat exchanger 3 a, and the bypass 6 b extends through lower part of the heat-source-side heat exchanger 3 b. Also, the bypasses 6 a and 6 b are connected by pipes to a solenoid valve 4 which serves as an opening/closing unit. The refrigerant in the pipes does not flow into the bypasses 6 a and 6 b when the solenoid valve 4 is closed, and flows into the bypasses 6 a and 6 b when the solenoid valve 4 is opened. The bypasses 6 a and 6 b and the solenoid valve 4 are used to prevent melted frost from being refrozen after the defrost operation of the air-conditioning apparatus 100.
In the indoor unit 10 a, a use-side heat exchanger (indoor-side heat exchanger) 12 a and an expansion unit 11 a are connected in series to each other. In the indoor unit 10 b, a use-side heat exchanger 12 b and an expansion unit 11 b are connected in series to each other. In the indoor unit 10 c, a use-side heat exchanger 12 c and an expansion unit 11 c are connected in series to each other. In the indoor unit 10 d, a use-side heat exchanger 12 d and an expansion unit 11 d are connected in series to each other. The use- side heat exchangers 12 a, 12 b, 12 c and 12 d function as condensers in the heating operation mode, and function as evaporators in the cooling operation mode, causes heat exchange to be performed between refrigerant and air supplied by the air-sending device (not shown) such as a fan, and generates air for cooling or air for heating, which is to be supplied to a to-be-air-conditioned space. The expansion units 11 a, 11 b, 11 c and 11 d have functions of pressure reducing valves and expansion valves, and reduce the pressure of the refrigerant and expand the refrigerant, and they are also provided as, for example, electronic expansion valves whose opening degrees can be controlled to be changed. In the air-conditioning apparatus 100, the four indoor units 10 a, 10 b, 10 c and 10 d are connected in parallel. This, however, is a mere example, and the number of indoor units is not limited to four.
Each of operation modes of the air-conditioning apparatus 100 will be described.

[Heating Operation Mode]

FIG. 2 is a diagram illustrating flows of refrigerant during the heating operation of the air-conditioning apparatus. In FIG. 2, flows of refrigerant during the heating operation are indicated by arrows. The following description is made referring to FIG. 2 with respect to the case where all the indoor units 10 a, 10 b, 10 c and 10 d are operated. When gas refrigerant having a low temperature and a low pressure is sucked into the compressor 1, it is compressed by the compressor 1 to become gas refrigerant having a high-temperature and a high and pressure, and is discharged from the compressor 1. The gas refrigerant discharged from the compressor 1 flows out from the outdoor unit 20 through the flow-path switching unit 2 and the pipe A, and flows into the use- side heat exchangers 12 a, 12 b, 12 c and 12 d.
In the use- side heat exchangers 12 a, 12 b, 12 c and 12 d, the gas refrigerant having the high temperature and high pressure exchanges heat with air supplied from the air-sending device not shown, and thus becomes liquid refrigerant. The use- side heat exchangers 12 a, 12 b, 12 c and 12 d function as condensers, which transfer heat to the ambient air, and reduce the temperature of the refrigerant in pipes in the heat exchangers. The liquid refrigerant flows out from the use- side heat exchangers 12 a, 12 b, 12 c and 12 d as liquid refrigerant having a high temperature and a high pressure, and is expanded and reduced in pressure by the expansion units 11 a, 11 b, 11 c and 11 d to become two-phase gas-liquid refrigerant having a low temperature and a low pressure, and then the two-phase gas-liquid refrigerant flows from the indoor units 10 a, 10 b, 10 c and 10 d. After flowing from the indoor units 10 a, 10 b, 10 c and 10 d, the two-phase gas-liquid refrigerant flows into the outdoor unit 20 through the pipe B. After flowing into the outdoor unit 20, in the heat-source- side heat exchangers 3 a and 3 b, the two-phase gas-liquid refrigerant exchanges heat with air supplied by the air-sending device (not shown) to become gas refrigerant having a low temperature and a low pressure. The heat-source- side heat exchangers 3 a and 3 b function as evaporators that receive heat from the ambient air and evaporate the refrigerant in the pipes. After flowing from the heat-source- side heat exchangers 3 a and 3 b, the gas refrigerant flows into the accumulator 5 through pipes and the flow-path switching unit 2 in the outdoor unit 20. The refrigerant having flown into the accumulator 5 is separated into liquid refrigerant and gas refrigerant, and the gas refrigerant is sucked into the compressor 1.
When the heating operation is continued at a low external temperature (at an evaporating temperature of 0 degrees C. or less), frost forms on surfaces of the heat-source- side heat exchangers 3 a and 3 b. This is because with moisture contained in air to be subjected to heat exchange at the heat-source- side heat exchangers 3 a and 3 b, dew condensation occurs at the surfaces of the heat-source- side heat exchangers 3 a and 3 b, which serve as evaporators, and the temperature of outside air is low, as a result of which frost forms. When the quantity of frost forming on the heat-source- side heat exchangers 3 a and 3 b increases, the thermal resistance increases, and the quantity of air decreases. Consequently, pipe temperatures (evaporating temperatures) in the heat-source- side heat exchangers 3 a and 3 b lower, and the heating capacity cannot be sufficiently fulfilled. It is therefore necessary to perform defrosting to remove the frost.

[Defrost Operation Mode]

FIG. 3 is a diagram illustrating flows of refrigerant during the defrost operation of the air-conditioning apparatus. In FIG. 3, flows of refrigerant during the defrost operation mode are indicated by arrows. In the defrost operation mode, a normal heating operation is stopped, and the direction of circulation of the refrigerant is changed by the flow-path switching unit 2 to the same direction as that in the cooling operation mode. When gas refrigerant having a low temperature and a low pressure is sucked into the compressor 1, it is compressed by the compressor 1 to become gas refrigerant having a high temperature and a high pressure, and is discharged from the compressor 1. The gas refrigerant discharged from the compressor 1 passes through the flow-path switching unit 2, and flows into the heat-source- side heat exchangers 3 a and 3 b. In the heat-source- side heat exchangers 3 a and 3 b, the gas refrigerant having the high temperature and high pressure exchanges heat with the ambient air to become liquid refrigerant. The heat-source- side heat exchangers 3 a and 3 b function as condensers, which transfer heat to the ambient air and reduce the temperature of refrigerant in the pipes. The heat transferred by the heat-source- side heat exchangers 3 a and 3 b to the air melts the frost on the surfaces of the heat-source- side heat exchangers 3 a and 3 b. At this time, in many cases, the air-sending device (not shown), which is located close to the heat-source- side heat exchangers 3 a and 3 b, is in stopped state. After flowing from the heat-source- side heat exchangers 3 a and 3 b, the liquid refrigerant flows into the indoor units 10 a, 10 b, 10 c and 10 d through the pipe B.
In the indoor units 10 a, 10 b, 10 c and 10 d, the liquid refrigerant is expanded and reduced in pressure by the respective expansion units 11 a, 11 b, 11 c and 11 d to become two-phase gas-liquid refrigerant having a low temperature and a low pressure. The two-phase gas-liquid refrigerant flows from the indoor units 10 a, 10 b, 10 c and 10 d without being subjected to heat exchange at the use- side heat exchangers 12 a, 12 b, 12 c and 12 d. After flowing from the indoor units 10 a, 10 b, 10 c and 10 d, the two-phase gas-liquid refrigerant re-flows into the outdoor unit 20 through the pipe A. In the outdoor unit 20, the two-phase gas-liquid refrigerant passes through the flow-path switching unit 2, and flows into the accumulator 5. The refrigerant having flown into the accumulator 5 is separated into liquid refrigerant and gas refrigerant, and the gas refrigerant is re-sucked into the compressor 1.

[During Defrost Operation]

FIG. 4 is a schematic diagram of the heat-source-side heat exchanger of the air-conditioning apparatus. FIG. 4 illustrates the heat-source-side heat exchanger 3 a as viewed side-on. FIG. 5 is a diagram illustrating flows of refrigerant in the case where the solenoid valve for the bypass is opened during the defrost operation of the air-conditioning apparatus. The heat-source-side heat exchanger 3 a has a structure that plural heat transfer tubes bent in a hairpin manner are inserted into plural fins in a direction perpendicular thereto. The bypass 6 a is provided to extend through the lower part of the heat-source-side heat exchanger 3 a. Since the heat-source-side heat exchanger 3 a is long in a step direction, there is a possibility that after the defrost operation, defrost water will be collected in the part of the heat-source-side heat exchanger 3 a through which the bypass 6 a is provided to extend, and will be refrozen. Therefore, as illustrated in FIG. 5, in the defrost operation or in a last stage of the defrost operation, the solenoid valve 4 is opened to cause the refrigerant in the pipe to flow into the bypass 6 a. As described above, during the defrost operation, the refrigerant in the pipe in the outdoor unit 20 has a high temperature and a high pressure. Therefore, by causing the refrigerant to flow into the bypass 6 a, it is possible to enhance heating of the lower part of the heat-source-side heat exchanger 3 a. As a result, frost is prevented from being re-frozen at the lower part of the heat-source-side heat exchanger 3 a. Similarly, the bypass 6 b is provided to extend through the lower part of the heat-source-side heat exchanger 3 b, and the solenoid valve 4 is connected to the bypass 6 b. Therefore, by opening the solenoid valve 4 in the late stage of the defrost operation, the refrigerant having a high temperature and a high pressure flows into the bypass 6 b, and frost is prevented from being refrozen at the lower part.
In ordinary cases, the defrost operation is ended when it is confirmed that the entire frost adhering to the heat-source- side heat exchangers 3 a and 3 b is completely melted, on the basis of results of detection by temperature detection units (not shown) provided at the heat-source- side heat exchangers 3 a and 3 b. When the defrost operation is ended, the flow-path switching unit 2 is switched, and the operation to be performed is returned to the above heating operation. It is determined to end the defrost operation, for example, by detecting an increase in the temperatures of the pipes in the heat-source- side heat exchangers 3 a and 3 b, which is caused by removal of the entire frost.
In order to prevent frost from being refrozen after the defrost operation, there is a case where it is necessary to consider an influence of an environment in which the air-conditioning apparatus 100, which causes refrigerant to be circulated using the bypasses 6 a and 6 b as illustrated in FIG. 5, is installed. In many cases, a multi-air-conditioning apparatus for a building is used in a large-scale building or facility because of its usage, and a large number of outdoor units are installed on the rooftop. In this description, such installation of the outdoor units of the multi-air-conditioning apparatus for a building is referred to as a dense installation.
FIG. 6 is a diagram showing an example of dense installation of the outdoor units in embodiment 1 of the present invention. FIG. 6, (a), illustrates a state of the dense installation of the outdoor units as viewed side-on. FIG. 6, (b) to (e), illustrate a state of the dense installation of the outdoor units as viewed from above. In FIG. 6, (b) to (e), it is assumed that the front surface of the units are surfaces thereof which faces upward in the figure, and the rear surfaces of the units are surfaces thereof which face downward in the figure. Also, in the figure, arrows indicate the directions of wind.
As illustrated in FIG. 6, (a), in the dense installation, in many cases, the intervals at which the outdoor units are arranged laterally are very short. Of these outdoor units, in an outdoor unit adjacent to other outdoor units on its both sides, the both side surfaces of the outdoor unit respectively face side surfaces of the above adjacent outdoor units, and the front and rear surfaces of the outdoor unit are exposed to outside air at all times. Also, in the dense installation, one of the side surfaces of each of the outermost ones of the outdoor units faces a side surface of an adjacent outdoor unit, and the other side surface and the front and rear surfaces of the above each outermost outdoor unit are exposed to outside air at all times. Therefore, the influence of wind on the outdoor units varies from one outdoor unit to another.
For example, in the case where wind flows as illustrated in FIG. 6, (b), the front surfaces of the outdoor units are more greatly influenced by the wind than the other surfaces of the outdoor units: and in the case where wind flows as illustrated in FIG. 6, (c), the rear surfaces of the outdoor units are more greatly influenced by the wind than the other surfaces of the outdoor units. Furthermore, in the case where wind flows as illustrated in FIG. 6, (d), the left surface of the outermost left one of the outdoor units as illustrated in the figure is more greatly influenced by the wind than the other surfaces of the outermost left outdoor unit and all the surfaces of the other outdoor units, and in the case where wind flows as illustrated in FIG. 6, (e), the right surface of the outermost right one of the outdoor units as illustrated in the figure is more greatly influenced by the wind than the other surfaces of the outermost right outdoor unit and all the surfaces of the other outdoor units.
In ordinary cases, in the case where the air-conditioning apparatus is in the cooling operation or the heating operation, the air-sending device is operated to cause wind to forcefully pass through the heat-source-side heat exchangers. However, in the defrost operation described above, the air-sending devices of the outdoor units are stopped. During the defrost operation, if wind flows as illustrated in FIG. 6, (b), a larger amount of outside air comes into contact with the front surfaces of the outdoor units than the other surfaces thereof, and if wind flows as illustrated in FIG. 6, (c), a larger amount of outside air comes into contact with the rear surfaces of the outdoor units than the other surfaces thereof. Also, during the defrost operation, if wind flows as illustrated in FIG. 6, (d), a larger amount of outside air comes into contact with the left surface of the outermost left one of the outdoor units as illustrated in the figure than the other surfaces of the outermost left outdoor unit and all the surfaces of the other outdoor units, and if wind flows as illustrated in FIG. 6, (e), a larger amount of outside air comes into contact with the right surface of the outermost right one of the outdoor units than the other surfaces of the outermost right outdoor unit and all the surfaces of the other outdoor units.
In forced convection, a value obtained by multiplying the velocity of wind by 0.5 is proportional to a thermal conductivity. Therefore, when the wind velocity increases by A times, a heat radiation amount increases by √A times. Therefore, in the defrost operation mode, if wind flows as illustrated in FIG. 6, (b) or (c), the heat radiation amounts of the front or rear surfaces of the outdoor units are higher than those of the other surfaces of the outdoor units, and heat is removed from the front or rear surfaces, as a result of which there is a stronger possibility that defrost water generated by the defrost operation will be refrozen on the front or rear surfaces. Furthermore, if wind flows as illustrated in FIG. 6, (d), the heat radiation amount of the left surface of the outermost left one of the outdoor units as illustrated in the figure is higher than those of the other surfaces of the outermost left outdoor unit and all the surfaces of the other outdoor units radiation rate, and heat is removed from the left surface of the outermost left outdoor unit, as a result of which there is a stronger possibility that defrost water generated by the defrost operation will be refrozen on the left surface of the outermost left outdoor unit. If wind flows as illustrated FIG. 6, (e), the heat radiation amount of the right surface of the outermost right one of the outdoor units as illustrated in the figure is higher than those of the other surfaces of the outermost right outdoor unit and all the surfaces of the other outdoor units, and heat is removed from the right surface of the outermost right outdoor unit, and there is a stronger possibility that defrost water generated by the defrost operation will be refrozen on the right surface of the outermost right outdoor unit.

Embodiment 1

FIG. 7 is a schematic diagram of a refrigerant circuit of an air-conditioning apparatus according to embodiment 1 of the present invention. Structural elements which are the same as those of the above refrigerant circuit as illustrated in FIG. 1 to 3 will be denoted by the same reference signs, and their descriptions will thus be omitted. In the air-conditioning apparatus 200 according to embodiment 1, the bypass 6 a includes an electronic expansion valve 7 a serving as a flow-rate adjusting mechanism, and a thermistor 8 a serving as a temperature detection unit. The electronic expansion valve 7 a and the thermistor 8 a are provided on a secondary side of the bypass 6 a, with the heat-source-side heat exchanger 3 a interposed between the electronic expansion valve 7 a and thermistor 8 a and secondary side of the bypass 6 a. Similarly, the bypass 6 b includes an electronic expansion valve 7 b serving as a flow-rate adjusting mechanism, and a thermistor 8 b serving as a temperature detection unit. The electronic expansion valve 7 b and the thermistor 8 b are provided on a secondary side of the bypass 6 b, with the heat-source-side heat exchanger 3 b interposed between the electronic expansion valve 7 b and thermistor 8 b and the secondary side of the bypass 6 b. A temperature sensor 9 a which detects an outlet temperature of the heat-source-side heat exchanger 3 a, i.e., the temperature of an outlet thereof from which refrigerant flows, is provided at the heat-source-side heat exchanger 3 a; and a temperature sensor 9 b which detects an outlet temperature of the heat-source-side heat exchanger 3 b, i.e., the temperature of an outlet thereof from which the refrigerant flows, is provided at the heat-source-side heat exchanger 3 b.
When the solenoid valve 4 is opened, and an opening degree of the electronic expansion valve 7 a reaches a predetermined opening degree, gas refrigerant having a high temperature and a high pressure starts to flow into the bypass 6 a. After flowing into the bypass 6 a, the gas refrigerant having the high temperature and high pressure exchanges heat with defrost water, at the lower part of the heat-source-side heat exchanger 3 a. As a result, while liquefying, the gas refrigerant having the high temperature and high pressure heats the bypass 6 a of the heat-source-side heat exchanger 3 a. Thus, the defrost water is prevented from being refrozen. When the solenoid valve 4 is opened, and the opening degree of the electronic expansion valve 7 b reaches a predetermined opening degree, the gas refrigerant having the high temperature and high pressure starts to flow into the bypass 6 b. After flowing into the bypass 6 b, the gas refrigerant having the high temperature and high pressure exchanges heat with defrost water, at the lower part of the heat-source-side heat exchanger 3 b. As a result, while liquefying, the gas refrigerant having the high temperature and high pressure heats the bypass 6 b of the heat-source-side heat exchanger 3 b. Thus, the defrost water is prevented from being refrozen.
FIG. 8 is a control block diagram of the air-conditioning apparatus 200. A controller 201 controls the entire air-conditioning apparatus 200. The temperature sensor 9 a, a temperature sensor 9 b, the thermistor 8 a and a thermistor 8 b are connected to the controller 201. Also, the solenoid valve 4, the electronic expansion valve 7 a and an electronic expansion valve 7 b are connected to the controller 201. The controller 201 outputs a signal for opening the solenoid valve 4 to the solenoid valve 4, when the outlet temperature of the heat-source-side heat exchanger 3 a detected by the temperature sensor 9 a becomes a predetermined temperature or higher immediately after start of the defrost operation or after elapse of a predetermined time from the start of the defrost operation. Also, the controller 201 detects the temperature of the thermistor 8 a to determine the opening degree of the electronic expansion valve 7 a, and outputs a control signal based on the result of the determination to the electronic expansion valve 7 a. Similarly, the controller 201 outputs a signal for opening the solenoid valve 4 to the solenoid valve 4, when the outlet temperature of the heat-source-side heat exchanger 3 b detected by the temperature sensor 9 b becomes the predetermined temperature or higher. Also, the controller 201 detects the temperature of the thermistor 8 b to determine the opening degree of the electronic expansion valve 7 b, and outputs a control signal based on the result of the determination to the electronic expansion valve 7 b. To be more specific, the opening degrees of the electronic expansion valves 7 a and 7 b are determined on the basis of the differences (ΔT=T*+T) between target temperatures T* and the detected temperatures T of the thermistors 8 a and 8 b, respectively. When ΔT>0, the controller 201 outputs control signals for increasing the opening degrees of the electronic expansion valves 7 a and 7 b, and when ΔT<0, the controller 201 outputs control signals for decreasing the opening degrees of the electronic expansion valves 7 a and 7 b.
As described above, according to embodiment 1, in addition to control of opening of the solenoid valve 4, control of the opening degrees of the electronic expansion valves 7 a and 7 b based on the detection results of the thermistors 8 a and 8 b is performed, and the flow rates of refrigerant to the bypasses 6 a and 6 b are adjusted in accordance with ambient environments of the heat-source- side heat exchangers 3 a and 3 b. In other words, the defrosting capacities of the heat-source- side heat exchangers 3 a and 3 b are adjusted in accordance with the ambient environments thereof. Therefore, the flow rates of the refrigerant to the bypasses 6 a and 6 b can be optimized in accordance with defrosting loads on the bypasses 6 a and 6 b. As a result, even if the influences of wind of outside air upon the surfaces of the heat-source- side heat exchangers 3 a and 3 b vary in accordance with the positions of the outdoor units in the dense installation as described with reference to FIG. 6, (a) to 6(e), it is possible to reliably prevent defrost water from being refrozen in accordance with the influences.

Embodiment 2

FIG. 10 is a schematic diagram of a refrigerant circuit of an air-conditioning apparatus according to embodiment 2 of the present invention. With respect to this embodiment, structural elements which are the same as those of the refrigerant circuit as illustrated in FIG. 1 to 3 will be denoted by the same reference signs, and their descriptions will thus be omitted. In an air-conditioning apparatus 300 according to embodiment 2, a pipe resistor 15 a is provided in the bypass 6 a, and a pipe resistor 15 b is provided in the bypass 6 b. The pipe resistors 15 a and 15 b are, for example, capillary tubes. The inflow rate of refrigerant to the bypass 6 a is determined in accordance with the pipe resistor 15 a. The inflow rate of the refrigerant to the bypass 6 b is determined in accordance with the pipe resistor 15 b. Flow resistances of the pipe resistors 15 a and 15 b to the flow of the refrigerant are set different from each other to cause the flow rates of the refrigerant to the bypasses 6 a and 6 b to differ from each other.
The following description is given by referring to by way of example the case where the plural outdoor units 20 in the multi-air-conditioning apparatus for a building are densely installed, and wind of outside air flows in the direction indicated in FIG. 6, (b) or (c). FIG. 9 is a schematic diagram illustrating heat-source-side heat exchangers in embodiment 2 of the present invention as viewed from above. The heat-source- side heat exchangers 3 a and 3 b are L-shaped, and are provided to form a frame that is substantially rectangular as viewed from above in the housing of the outdoor unit 20. The heat-source-side heat exchanger 3 a is provided on the front surface of the outdoor unit 20. In FIG. 9, the front surface of the outdoor unit 20 faces downward in the figure. Also, referring to FIG. 9, an inlet 13 a and an outlet 13 b are an inlet and an outlet of the bypass 6 a of the heat-source-side heat exchanger 3 a, respectively; and an inlet 14 a and an outlet 14 b are an inlet and an outlet of the bypass 6 b of the heat-source-side heat exchanger 3 b, respectively. In the case where wind of outside air flows in the direction indicated in FIG. 6, (b) or (c), a surface 16 a of the heat-source-side heat exchanger 3 a is a surface thereof onto which the wind flows, and a surface 16 b of the heat-source-side heat exchanger 3 a is a surface thereof onto which the wind flows.
The inlet 13 a of the bypass 6 a of the heat-source-side heat exchanger 3 a is located close to the surface 16 a onto which the wind flows. Refrigerant gas having a high temperature flows into part of the surface 16 a of the heat-source-side heat exchanger 3 a. On the other hand, the inlet 14 a of the bypass 6 b of the heat-source-side heat exchanger 3 b is located on a side of a side surface thereof which is orthogonal to the surface 16 b onto which the wind flows. The refrigerant gas passes through part of the side surface of the heat-source-side heat exchanger 3 b, and flows into part of the surface 16 b. Thus, the temperature of the refrigerant gas flowing into the part of the surface 16 b of the heat-source-side heat exchanger 3 b lowers, as compared with the temperature of the refrigerant gas flowing into the part of the surface 16 a of the heat-source-side heat exchanger 3 a. Therefore, the defrosting capacity of the heat-source-side heat exchanger 3 b needs to be set higher than the defrosting capacity of the heat-source-side heat exchanger 3 a. In embodiment 2, the flow resistance of the pipe resistor 15 b is set lower than the flow resistance of the pipe resistor 15 a.
In such a manner, according to embodiment 2, in the dense installation in the multi-air-conditioning apparatus for a building, in the case where it is known which of the defrosting capacities requisite for the heat-source- side heat exchangers 3 a and 3 b of each of the outdoor units 20 is greater or smaller, pipe resistors 15 a and 15 b whose flow resistances are set in accordance with the requisite defrosting capacities are provided.
According to embodiment 2, it is possible to reduce increasing of the number of components. Therefore, in the dense installation, in the case where it is known which of defrosting capacities which are requisite for the heat-source- side heat exchangers 3 a and 3 b in accordance with the position of each of installed outdoor units is greater or smaller, the defrost water at the heat-source- side heat exchangers 3 a and 3 b can be prevented from being refrozen, at the same time as the product cost is reduced.


Reference Signs List

	1	compressor
	2	flow-path switching unit
	3a	heat-source-side heat exchanger
	3b	heat-source-side heat exchanger
	4	solenoid valve
	5	accumulator
	6a	bypass

	6b	bypass
	7a	electronic expansion valve
	7b	electronic expansion valve
	8a	thermistor
	8b	thermistor
	9a	temperature sensor
	9b	temperature sensor
	10a	indoor unit
	10b	indoor unit
	10c	indoor unit
	10d	indoor unit
	11a	expansion unit
	11b	expansion unit
	11c	expansion unit
	11d	expansion unit
	12a	use-side heat exchanger
	12b	use-side heat exchanger
	12c	use-side heat exchanger
	12d	use-side heat exchanger
	13a	inlet

	13b	outlet
	14a	inlet
	14b	outlet

	15a	pipe resistor
	15b	pipe resistor
	16a	surface
	16b	surface

	20	outdoor unit
	100	air-conditioning apparatus
	200	air-conditioning apparatus
	201	controller
	300	air-conditioning apparatus.

Claims

1. An air-conditioning apparatus comprising: an outdoor unit including a compressor, a flow-path switching unit and plural heat-source-side heat exchangers, the compressor, the flow-path switching unit and the heat-source-side heat exchangers being connected by pipes; and an indoor unit connected to the outdoor unit to air-condition a target space,

wherein the outdoor unit includes:

plural bypasses each having ends one of which is, in connection by pipes in the outdoor unit, connected to a discharge side of the compressor, and the other of which is connected to a suction side of the compressor, the bypasses being configured to cause refrigerant to flow through lower parts of the plural heat-source-side heat exchangers during a defrost operation of the air-conditioning apparatus; and

flow-rate adjusting mechanisms provided in the respective bypasses to adjust flow rates of refrigerant flowing into the plural bypasses.

2. The air-conditioning apparatus of claim 1,

wherein the outdoor unit further comprises a controller and detection units configured to detect ambient temperatures of the plural heat-source-side heat exchangers, and

the controller controls the flow-rate adjusting mechanisms based on ambient temperatures which are detected by the respective detection units of the plural heat-source-side heat exchangers, and adjusts flow rates of the refrigerant flowing into the bypasses, immediately after start of the defrost operation of the air-conditioning apparatus, or after elapse of a set time from the start of the defrost operation.

3. The air-conditioning apparatus of claim 2, wherein the flow-rate adjusting mechanisms are electronic expansion valves, and the controller adjusts opening degrees of the electronic expansion valves.

4. The air-conditioning apparatus of claim 1, wherein the flow-rate adjusting mechanisms are capillary tubes, and the flow rates of the refrigerant flowing into the plural bypasses through the capillary tubes are set different from each other with respect to the plural heat-source-side heat exchangers.