# Patent

## Title
Air-conditioning apparatus including intermediate heat exchangers

## Abstract

An air-conditioning apparatus in which a primary-side refrigerant in a two-phase gas-liquid state that has flowed into each of intermediate heat exchangers absorbs heat from a secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and evaporates and turns into a low-temperature, low-pressure gas state. The air-conditioning apparatus ensures high heat exchange efficiency even when a direction of a heat source-side refrigerant (secondary-side refrigerant) flowing through an intermediate heat exchanger changes, and enables an appropriate operation in any operation mode.

## Background
TECHNICAL FIELD
The present invention relates to an air-conditioning apparatus that has two refrigerant circuits including a primary-side refrigerant circuit and a secondary-side refrigerant circuit, and causes heat to be exchanged between a primary-side refrigerant and a secondary-side refrigerant in an intermediate heat exchanger.
BACKGROUND ART
As an air-conditioning apparatus in related art, there has been proposed an air-conditioning apparatus capable of simultaneous cooling and the heating operation which “includes a heat source-side refrigerant circuit A having a compressor 11, an outdoor heat exchanger 13, a first refrigerant branch part 21 connected to the compressor 11, a second refrigerant branch part 22 and a third refrigerant branch part 23 connected to the outdoor heat exchanger 13, a first refrigerant flow control device 24 provided between a branch pipe 40 and the second refrigerant branch part 22, intermediate heat exchangers 25n whose one side is connected to the first refrigerant branch part 21 and the third refrigerant branch part 23 via three-way valves 26n and whose other side is connected to the second refrigerant branch part 22, and second refrigerant flow control devices 27n provided between each of the intermediate heat exchangers 25n and the second refrigerant branch part 22, and a use-side refrigerant circuit Bn having indoor heat exchangers 31n connected to the intermediate heat exchangers 25n, and in which at least one of water and brine circulates through the use-side refrigerant circuit Bn” (see Patent Literature 1).
CITATION LIST
Patent Literature


    Patent Literature 1: WO2009/133640 (Abstract)


SUMMARY OF INVENTION
Technical Problem
However, the air-conditioning apparatus described in Patent Literature 1 has the following problem. That is, while the direction of the heat source-side refrigerant flowing through the intermediate heat exchangers changes depending on the operation mode, the flow of the use-side refrigerant is a certain direction. Therefore, appropriate heat exchange efficiency is not obtained in intermediate heat exchangers in which these refrigerants are in parallel flow, which makes it impossible to perform optimum operation in all operation modes.
The present invention has been made in view of the problem mentioned above, and accordingly it is an object of the present invention to provide an air-conditioning apparatus which ensures high heat exchange efficiency even when the direction of a heat source-side refrigerant (secondary-side refrigerant) flowing through an intermediate heat exchanger changes, and enables an appropriate operation in any operation mode.
Solution to Problem
An air-conditioning apparatus according to the present invention includes a primary-side refrigerant circuit in which a compressor, first flow switching means, a heat source-side heat exchanger, second flow switching means, a plurality of intermediate heat exchangers, and an expansion mechanism are connected by refrigerant pipes, and through which a primary-side refrigerant flows, and a secondary-side refrigerant circuit in which the intermediate heat exchangers, third flow switching means, a pump, fourth flow switching means, and a plurality of use-side heat exchangers are connected by refrigerant pipes, and through which a secondary-side refrigerant different from the primary-side refrigerant flows. Each of the intermediate heat exchangers exchanges heat between the primary-side refrigerant and the secondary-side refrigerant. The first flow switching means switches a refrigerant flow path so that the primary-side refrigerant discharged from the compressor flows to each of the intermediate heat exchangers or the heat source-side heat exchanger. The second flow switching means switches a flow direction of the primary-side refrigerant flowing into each of the intermediate heat exchangers. The third flow switching means switches a flow direction of the secondary-side refrigerant flowing into each of the intermediate heat exchangers. The fourth flow switching means switches a refrigerant flow path to direct one of flows of the secondary-side refrigerant that have flown through the plurality of the intermediate heat exchangers to flow through the corresponding each use-side heat exchanger, so that one of a cooling operation and a heating operation is performed in a selectable manner by each of the use-side heat exchangers. The second flow switching means and the third flow switching means each switch a refrigerant flow path so that the primary-side refrigerant and the secondary-side refrigerant are in counterflow in at least one of the intermediate heat exchangers.
Advantageous Effects of Invention
According to the present invention, the primary-side refrigerant and the secondary-side refrigerant are in counterflow in at least one intermediate heat exchanger. Therefore, thermal effect of the primary-side refrigerant and the secondary-side refrigerant is exerted efficiently, thereby making it possible to reduce the input to the pump.



BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic diagram of an air-conditioning apparatus according to Embodiment 1 of the present invention, illustrating the flow of a refrigerant in a cooling operation.
FIG. 2 is a schematic diagram of an air-conditioning apparatus according to Embodiment 1 of the present invention, illustrating the flow of refrigerant in the heating operation.
FIG. 3 illustrates the temperature relationship between a primary-side refrigerant and a secondary-side refrigerant in an intermediate heat exchanger 7 in the heating operation, in a case where a refrigerant whose discharge pressure is lower than the critical point is used as the primary-side refrigerant in the air-conditioning apparatus according to Embodiment 1 of the present invention.
FIG. 4 illustrates the temperature relationship between the primary-side refrigerant and the secondary-side refrigerant in the intermediate heat exchanger 7 in the heating operation, in a case where a refrigerant whose discharge pressure is higher than the critical point is used as the primary-side refrigerant in the air-conditioning apparatus according to Embodiment 1 of the present invention.
FIG. 5 illustrates the flow of refrigerant in the cooling operation in a case where the intermediate heat exchanger 7 includes three heat transfer units.
FIG. 6 illustrates the flow of refrigerant in the heating operation in a case where the intermediate heat exchanger 7 includes three heat transfer units.
FIG. 7 is a schematic diagram of an air-conditioning apparatus according to Embodiment 2 of the present invention.
FIG. 8 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling only operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention.
FIG. 9 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating only operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention.
FIG. 10 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling main operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention.
FIG. 11 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating main operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention.
FIG. 12 is a schematic diagram of an air-conditioning apparatus according to Embodiment 3 of the present invention.
FIG. 13 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling only operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention.
FIG. 14 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating only operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention.
FIG. 15 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling main operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention.
FIG. 16 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating main operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention.
FIG. 17 is a schematic diagram of an air-conditioning apparatus according to Embodiment 4 of the present invention.
FIG. 18 illustrates the flows of the primary-side refrigerant and secondary-side refrigerant in a case where an intermediate heat exchanger 107ba in the air-conditioning apparatus according to Embodiment 4 of the present invention functions as an evaporator.
FIG. 19 illustrates the flows of the primary-side refrigerant and secondary-side refrigerant in a case where the intermediate heat exchanger 107ba in the air-conditioning apparatus according to Embodiment 4 of the present invention functions as a radiator.
FIG. 20 illustrates a configuration in which intermediate heat exchangers 107aa and 107ba each include three heat transfer units.
FIG. 21 is a schematic diagram of an air-conditioning apparatus according to Embodiment 5 of the present invention.
FIG. 22 illustrates an installation example of an air-conditioning apparatus according to Embodiment 6 of the present invention.



DESCRIPTION OF EMBODIMENTS
Embodiment 1
(Configuration of Air-Conditioning Apparatus)
FIG. 1 is a schematic diagram of an air-conditioning apparatus according to Embodiment 1 of the present invention, illustrating the flow of a refrigerant in the cooling operation. FIG. 2 is a schematic diagram of the air-conditioning apparatus, illustrating the flow of refrigerant in the heating operation. Of the arrows in FIGS. 1 and 2, arrows indicated by thick lines indicate the flow of a primary-side refrigerant, and arrows indicated by narrow lines indicate the flow of a secondary-side refrigerant.
The air-conditioning apparatus according to Embodiment 1 includes two refrigerant circuits, a primary-side refrigerant circuit, and a secondary-side refrigerant circuit.
As the primary-side refrigerant that flows through the primary-side refrigerant circuit of these refrigerant circuits, for example, a fluorocarbon refrigerant such as R410A, a hydrocarbon refrigerant such as propane, a natural refrigerant such as carbon dioxide, or the like is used. It is also possible to use an azeotropic refrigerant mixture such as R410A, or a zeotropic refrigerant mixture such as R407C, R32, and R134a, or R32 and R1234yf.
As the secondary-side refrigerant that flows through the secondary-side refrigerant circuit, for example, brine, water, a liquid mixture of brine and water, a liquid mixture of water and an additive having an anti-corrosion effect, or the like is used.
The primary-side refrigerant circuit includes at least a compressor 3, an outdoor heat exchanger 4, an expansion mechanism 5, a four-way valve 6, and an intermediate heat exchanger 7. The primary-side refrigerant circuit is configured by connecting the compressor 3, the four-way valve 6, the outdoor heat exchanger 4, the expansion mechanism 5, the intermediate heat exchanger 7, the four-way valve 6, and the compressor 3 in this order by refrigerant pipes.
The secondary-side refrigerant circuit includes at least the intermediate heat exchanger 7, an indoor heat exchanger 8, a pump 9, and valves 10a to 10d. The secondary-side refrigerant circuit is configured by connecting the pump 9, the indoor heat exchanger 8, the valve 10b, the intermediate heat exchanger 7, the valve 10a, and the pump 9 in this order by refrigerant pipes. In the secondary-side refrigerant circuit, a branch part 30a on the refrigerant pipe connecting the indoor heat exchanger 8 and the valve 10b is connected to a branch part 30b on the refrigerant pipe connecting the valve 10a and the intermediate heat exchanger 7, by a refrigerant pipe via the valve 10d. Also, in the secondary-side refrigerant circuit, a branch part 30c on the refrigerant pipe connecting the intermediate heat exchanger 7 and the valve 10b is connected to a branch part 30d on the refrigerant pipe connecting the pump 9 and the valve 10a, by a refrigerant pipe via the valve 10c. 
The intermediate heat exchanger 7 includes at least heat transfer units 7a and 7b, check valves 11a to 11c, and check valves 12a to 12c. As will be described later, each of the heat transfer units 7a and 7b exchanges heat between the primary-side refrigerant and the secondary-side refrigerant, and includes a refrigerant flow path through which the primary-side refrigerant flows and a refrigerant flow path through which the secondary-side refrigerant flows.
In the heat transfer unit 7b, one refrigerant outlet/inlet of the refrigerant flow path through which the primary-side refrigerant flows is connected to the four-way valve 6 by a refrigerant pipe. The other refrigerant outlet/inlet is connected to the expansion mechanism 5 by a refrigerant pipe via the check valve 11b. 
In the heat transfer unit 7a, one refrigerant outlet/inlet of the refrigerant flow path through which the primary-side refrigerant flows is connected to a branch part 20b on the refrigerant pipe connecting the heat transfer unit 7b and the check valve 11b, by a refrigerant pipe. The other refrigerant outlet/inlet is connected to a branch part 20d on the refrigerant pipe connecting the heat transfer unit 7b and the four-way valve 6, by a refrigerant pipe via the check valve 11a. 
Further, a branch part 20c on the refrigerant pipe connecting the heat transfer unit 7a and the check valve 11a is connected to a branch part 20a on the refrigerant pipe connecting the expansion mechanism 5 and the check valve 11b, by a refrigerant pipe via the check valve 11c. 
In the heat transfer unit 7b, one refrigerant outlet/inlet of the refrigerant flow path through which the secondary-side refrigerant flows is connected to the valve 10a by a refrigerant pipe. The other refrigerant outlet/inlet is connected to the valve 10b by a refrigerant pipe via the check valve 12b. 
In the heat transfer unit 7a, one refrigerant outlet/inlet of the refrigerant flow path through which the secondary-side refrigerant flows is connected to a branch part 31c on the refrigerant pipe connecting the heat transfer unit 7b and the check valve 12b, by a refrigerant pipe. The other refrigerant outlet/inlet is connected to a branch part 31a on the refrigerant pipe connecting the heat transfer unit 7b and the valve 10a, by a refrigerant pipe via the check valve 12a. 
Further, a branch part 31d on the refrigerant pipe connecting the check valve 12b and the valve 10b is connected to a branch part 31b on the refrigerant pipe connecting the heat transfer unit 7a and the check valve 12a, by a refrigerant pipe via the check valve 12c. 
The compressor 3 sucks the primary-side refrigerant in a gas state, compresses the primary-side refrigerant into a high-temperature, high-pressure state, and discharges the resulting primary-side refrigerant. The compressor 3 may be configured by, for example, an inverter compressor or the like whose capacity can be controlled.
The outdoor heat exchanger 4 functions as a radiator in the cooling operation, and functions as an evaporator in the heating operation. The outdoor heat exchanger 4 exchanges heat between the outdoor air supplied from a fan 4a and the primary-side refrigerant.
The expansion mechanism 5 expands and reduces the pressure of the primary-side refrigerant that has flowed out of the outdoor heat exchanger 4 in the cooling operation, and the primary-side refrigerant that has flowed out of the intermediate heat exchanger 7 in the heating operation.
The four-way valve 6 has the function of switching the refrigerant flow path. Specifically, in the cooling operation, the four-way valve 6 switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor 3 flows to the outdoor heat exchanger 4, and that the primary-side refrigerant that has flowed out of the intermediate heat exchanger 7 flows to the compressor 3. In the heating operation, the four-way valve 6 switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor 3 flows to the intermediate heat exchanger 7, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger 4 flows to the compressor 3.
The heat transfer units 7a and 7b are each configured by, for example, a double-pipe heat exchanger, a plate heat exchanger, a micro-channel water heat exchanger, or the like. As described above, each of the heat transfer units 7a and 7b includes a refrigerant flow path through which the primary-side refrigerant flows, and a refrigerant flow path through which the secondary-side refrigerant flows, and exchanges heat between the primary-side refrigerant and the secondary-side refrigerant. Specifically, each of the heat transfer units 7a and 7b causes the primary-side refrigerant to be heated by the secondary-side refrigerant in the cooling operation, and causes the primary-side refrigerant to be cooled by the secondary-side refrigerant in the heating operation.
In a case where a plate heat exchanger is used as each of the heat transfer units 7a and 7b, by taking phase change of the primary-side refrigerant into consideration, each of the heat transfer units 7a and 7b is preferably installed in such an orientation that the primary-side refrigerant flows into each of the heat transfer units 7a and 7b from the lower side when the primary-side refrigerant absorbs heat, and that the primary-side refrigerant flows into each of the heat transfer units 7a and 7b from the upper side when the primary-side refrigerant radiates heat.
The indoor heat exchanger 8 functions as a cooler in the cooling operation, and functions as a radiator in the heating operation. The indoor heat exchanger 8 exchanges heat between the indoor air supplied from a fan 8a and the secondary-side refrigerant.
The pump 9 causes the secondary-side refrigerant to circuit within the secondary-side refrigerant circuit as the pump 9 is driven.
The valves 10a to 10d are opening and closing valves, which conduct the secondary-side refrigerant when open, and shut off the flow of the secondary-side refrigerant when closed. Specifically, the valves 10a to 10d have the function of switching the outlet/inlet through which the secondary-side refrigerant that has flowed out of the indoor heat exchanger 8 flows into the intermediate heat exchanger 7.
The check valves 11a to 11c cause the primary-side refrigerant to flow in only one direction. Specifically, the check valve 11a causes the primary-side refrigerant to flow only in a direction from the branch part 20c toward the branch part 20d. The check valve 11b causes the primary-side refrigerant to flow only in a direction from the branch part 20a toward the branch part 20b. The check valve 11c causes the primary-side refrigerant to flow only in a direction from the branch part 20c toward the branch part 20a. 
The check valves 12a to 12c cause the secondary-side refrigerant to flow in only one direction. Specifically, the check valve 12a causes the secondary-side refrigerant to flow only in a direction from the branch part 31a toward the branch part 31b. The check valve 12b causes the secondary-side refrigerant to flow only in a direction from the branch part 31c toward the branch part 31d. The check valve 12c causes the secondary-side refrigerant to flow only in a direction from the branch part 31d toward the branch part 31b. 
While the branch parts 20a to 20d, 30a to 30d, and 31a to 31d are provided on refrigerant pipes as illustrated in FIGS. 1 and 2 for the sake of convenience in explaining the refrigerant circuit configuration, this should not be construed restrictively. That is, these branch parts may not necessarily be provided on refrigerant pipes in a clear manner. For example, while the check valve 11b and the check valve 11c are both connected to the expansion mechanism 5 via the branch part 20a, the check valve 11b and the check valve 11c may be connected to the expansion mechanism 5 directly without passing through a clear branch part 20a. This configuration does not alter the function of the refrigerant circuit at all. Furthermore, for example, while the branch part 30b and the branch part 31a are configured as separate branch parts for the convenience of explanation of the refrigerant circuit, the branch part 30b and the branch part 31a may be configured as an integral branch part, and this configuration does not alter the function of the refrigerant circuit at all, either. The same applies to the other branch parts. As long as the function of the refrigerant circuit (such as the flow directions of the respective refrigerants) illustrated in FIGS. 1 and 2 remains the same, as mentioned above, it is not necessary to provide clear branch parts, nor is it necessary for the branch parts to be separated as separate components.
The outdoor heat exchanger 4 and the indoor heat exchanger 8 correspond to the “heat source-side heat exchanger” and the “use-side heat exchanger”, respectively, in the invention according to claim 9 of the present invention. The four-way valve 6 and the valves 10a to 10d correspond to the “first flow switching means” and the “second flow switching means”, respectively, in the invention according to claim 9 of the present invention. The check valves 11a to 11c and the check valves 12a to 12c each correspond to the “third flow switching means” according to claim 9 of the present invention.
(Cooling Operation of Air-Conditioning Apparatus)
Next, the cooling operation of an air-conditioning apparatus according to Embodiment 1 will be described with reference to FIG. 1.
In the primary-side refrigerant circuit, the four-way valve 6 is switched in advance so that the primary-side refrigerant discharged from the compressor 3 flows to the outdoor heat exchanger 4, and that the primary-side refrigerant that has flowed out of the intermediate heat exchanger 7 flows to the compressor 3. In the secondary-side refrigerant circuit, the valve 10a and the valve 10b are closed, and the valve 10c and the valve 10d are open.
First, the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described. The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 3, and discharged in a high-temperature, high-pressure state. The high-temperature, high-pressure primary-side refrigerant discharged from the compressor 3 flows into the outdoor heat exchanger 4 via the four-way valve 6. The primary-side refrigerant that has flowed into the outdoor heat exchanger 4 radiates heat to the outdoor air sent by the fan 4a, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. The primary-side refrigerant in a two-phase gas-liquid state or liquid state that has flowed out of the outdoor heat exchanger 4 flows into the expansion mechanism 5, where the primary-side refrigerant is expanded and reduced in pressure and turns into a two-phase gas-liquid state at low temperature and low pressure. The primary-side refrigerant in a two-phase gas-liquid state at low temperature and low pressure that has flowed out of the expansion mechanism 5 flows into the intermediate heat exchanger 7.
After the primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger 7 passes through the branch part 20a and the check valve 11b, the primary-side refrigerant divides into branch flows at the branch part 20b, and the branch flows flow into the heat transfer unit 7a and the heat transfer unit 7b in parallel, respectively. At this time, at the branch part 20a, the primary-side refrigerant does not flow in a direction from the branch part 20a toward the branch part 20c owing to the action of the check valve 11c. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the heat transfer unit 7a and the heat transfer unit 7b absorb heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant in a gas state that has flowed out of the heat transfer unit 7a passes though the branch part 20c and the check valve 11a, merges at the branch part 20d with the primary-side refrigerant in a gas state that has flowed out of the heat transfer unit 7b, and the merged primary-side refrigerant flows out of the intermediate heat exchanger 7.
The primary-side refrigerant in a gas state that has flowed out of the intermediate heat exchanger 7 is sucked into the compressor 3 via the four-way valve 6, and is compressed again.
Next, the flow of the secondary-side refrigerant in the secondary-side refrigerant circuit will be described. The secondary-side refrigerant sent out by driving of the pump 9 flows into the indoor heat exchanger 8. The secondary-side refrigerant that has flowed into the indoor heat exchanger 8 cools the indoor air sent by the fan 8a, and flows into the intermediate heat exchanger 7 via the branch part 30a, the valve 10d, and the branch part 30b. At this time, at the branch part 30a, the secondary-side refrigerant does not flow in a direction from the branch part 30a toward the branch part 30c because the valve 10b is closed. Also, at the branch part 30b, the secondary-side refrigerant does not flow in a direction from the branch part 30b toward the branch part 30d because the valve 10a is closed.
The secondary-side refrigerant that has flowed into the intermediate heat exchanger 7 divides into branch flows at the branch part 31a, one of which flows into the heat transfer unit 7b, and the other flows into the heat transfer unit 7a via the check valve 12a and the branch unit 31b. At this time, at the branch part 31b, the secondary-side refrigerant does not flow in a direction from the branch part 31b toward the branch part 31d owing to the action of the check valve 12c. The flows of the secondary-side refrigerant that have flowed into the heat transfer unit 7a and the heat transfer unit 7b in parallel are cooled by the primary-side refrigerant in a low-temperature state flowing in counterflow to the secondary-side refrigerant, and flow into the heat transfer unit 7a and the heat transfer unit 7b, respectively. The respective flows of the secondary-side refrigerant that have flowed out of the heat transfer unit 7a and the heat transfer unit 7b merge at the branch part 31c, and the merged secondary-side refrigerant flows out of the intermediate heat exchanger 7 via the check valve 12b and the branch part 31d. 
The secondary-side refrigerant that has flowed out of the intermediate heat exchanger 7 flows into the pump 9 via the branch part 30c, the valve 10c, and the branch part 30d, and is sent out again. At this time, at the branch part 30c, the secondary-side refrigerant does not flow in a direction from the branch part 30c toward the branch part 30a because the valve 10b is closed. Also, at the branch part 30d, the secondary-side refrigerant does not flow in a direction from the branch part 30d toward the branch part 30b because the valve 10a is closed.
(Heating Operation of Air-Conditioning Apparatus)
Next, the heating operation in the air-conditioning apparatus according to Embodiment 1 will be described with reference to FIG. 2.
In the primary-side refrigerant circuit, the four-way valve 6 is switched in advance so that the primary-side refrigerant discharged from the compressor 3 flows to the intermediate heat exchanger 7, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger 4 flows to the compressor 3. In the secondary-side refrigerant circuit, the valve 10a and the valve 10b are open, and the valve 10c and the valve 10d are closed.
First, the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described. The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 3, and discharged in a high-temperature, high-pressure state. The high-temperature, high-pressure primary-side refrigerant discharged from the compressor 3 flows into the intermediate heat exchanger 7 via the four-way valve 6.
The primary-side refrigerant that has flowed into the intermediate heat exchanger 7 flows into the heat transfer unit 7b via the branch part 20d, and radiates heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant. At this time, at the branch part 20d, the primary-side refrigerant does not flow in a direction from the branch part 20d toward the branch part 20c owing to the action of the check valve 11a. The primary-side refrigerant that has flowed out of the heat transfer unit 7b flows into the heat transfer unit 7a via the branch part 20b. In the heat transfer unit 7a as well, the primary-side refrigerant radiates heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant. At this time, at the branch part 20b, the primary-side refrigerant does not flow in a direction from the branch part 20b toward the branch part 20a owing to the action of the check valve 11b. In this way, unlike the cooling operation described above, the primary-side refrigerant flows through the heat transfer unit 7b and the heat transfer unit 7a in series. During this process, the primary-side refrigerant radiates heat to the secondary-side refrigerant, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. The primary-side refrigerant in a two-phase gas-liquid state or liquid state that has flowed out of the heat transfer unit 7a flows out of the intermediate heat exchanger 7 via the branch part 20c, the check valve 11c, and the branch part 20a. 
The primary-side refrigerant in a two-phase gas-liquid state or liquid state that has flowed out of the intermediate heat exchanger 7 flows into the expansion mechanism 5, where the primary-side refrigerant is expanded and reduced in pressure and turns into a two-phase gas-liquid state at low temperature and low pressure. The primary-side refrigerant in a two-phase gas-liquid state at low temperature and low pressure that has flowed out of the expansion mechanism 5 flows into the outdoor heat exchanger 4. The primary-side refrigerant that has flowed into the outdoor heat exchanger 4 absorbs heat from the outdoor air sent by the fan 4a, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant in a gas state that has flowed out of the outdoor heat exchanger 4 is sucked into the compressor 3 via the four-way valve 6, and is compressed again.
Next, the flow of the secondary-side refrigerant in the secondary-side refrigerant circuit will be described. The secondary-side refrigerant sent out by driving of the pump 9 flows into the indoor heat exchanger 8. The secondary-side refrigerant that has flowed into the indoor heat exchanger 8 heats the indoor air sent by the fan 8a, and flows into the intermediate heat exchanger 7 via the branch part 30a, the valve 10b, and the branch part 30c. At this time, at the branch part 30a, the secondary-side refrigerant does not flow in a direction from the branch part 30a toward the branch part 30b because the valve 10d is closed. Also, at the branch part 30c, the secondary-side refrigerant does not flow in a direction from the branch part 30c toward the branch part 30d because the valve 10c is closed.
The secondary-side refrigerant that has flowed into the intermediate heat exchanger 7 flows into the heat transfer unit 7a via the branch part 31d, the check valve 12c, and the branch part 31b, and is heated by the primary-side refrigerant flowing in counterflow to the secondary-side refrigerant. At this time, at the branch part 31d, the secondary-side refrigerant does not flow in a direction from the branch part 31d toward the branch part 31c owing to the action of the check valve 12b. Also, at the branch part 31b, the secondary-side refrigerant does not flow in a direction from the branch part 31b toward the branch part 31a owing to the action of the check valve 12a. The secondary-side refrigerant that has flowed out of the heat transfer unit 7a flows into the heat transfer unit 7b via the branch part 31c, and is heated by the primary-side refrigerant flowing in counterflow to the secondary-side refrigerant. In this way, unlike the cooling operation described above, the secondary-side refrigerant flows through the heat transfer unit 7a and the heat transfer unit 7b in series. The secondary-side refrigerant that has flowed out of the heat transfer unit 7b flows out of the intermediate heat exchanger 7 via the branch part 31a. 
The secondary-side refrigerant that has flowed out of the intermediate heat exchanger 7 flows into the pump 9 via the branch part 30b, the valve 10a, and the branch part 30d, and is sent out again. At this time, at the branch part 30b, the secondary-side refrigerant does not flow in a direction from the branch part 30b toward the branch part 30a because the valve 10d is closed. Also, at the branch part 30d, the secondary-side refrigerant does not flow in a direction from the branch part 30d toward the branch part 30c because the valve 10c is closed.
(Heat Exchange Operation in Intermediate Heat Exchanger 7)
FIG. 3 illustrates the temperature relationship between the primary-side refrigerant and the secondary-side refrigerant in the intermediate heat exchanger 7 in the heating operation, in a case where a refrigerant whose discharge pressure is lower than the critical point is used as the primary-side refrigerant in the air-conditioning apparatus according to Embodiment 1 of the present invention. FIG. 4 illustrates the temperature relationship between the primary-side refrigerant and the secondary-side refrigerant in the intermediate heat exchanger 7 in the heating operation, in a case where a refrigerant whose discharge pressure is higher than the critical point is used as the primary-side refrigerant in the air-conditioning apparatus.
Unlike the primary-side refrigerant at a low discharge pressure as illustrated in FIG. 3, the primary-side refrigerant at a high discharge pressure as illustrated in FIG. 4 has high discharge temperature, and does not become a two-phase state in the intermediate heat exchanger 7, resulting in large amount of heat exchange with the secondary-side refrigerant. Therefore, a large target value can be set for the outlet-inlet temperature difference in the intermediate heat exchanger 7 through which the secondary-side refrigerant flows, or for the outlet-inlet temperature difference in the indoor heat exchanger 8, thereby making it possible to reduce the input to the pump 9.
Advantageous Effects of Embodiment 1
According to the configuration and the operation mentioned above, in the intermediate heat exchanger 7, in the cooling operation in which the primary-side refrigerant absorbs heat from the secondary-side refrigerant, the primary-side refrigerant flows through the heat transfer unit 7a and the heat transfer unit 7b in parallel, and in the heating operation in which the primary-side refrigerant radiates heat to the secondary-side refrigerant, the primary-side refrigerant flows through the heat transfer unit 7a and the heat transfer unit 7b in series. In this regard, generally, with regard to operation efficiency, pressure loss exerts a greater influence than heat transfer capacity in the heat absorption process, whereas heat transfer capacity exerts a greater influence than pressure loss in the heat radiation process. Accordingly, in the air-conditioning apparatus according to Embodiment 1, in the cooling operation, the primary-side refrigerant performs a heat absorption operation in the intermediate heat exchanger 7, and flows through the heat transfer unit 7a and the heat transfer unit 7b in parallel so that the overall cross-sectional area of the flow path becomes large. Therefore, pressure loss that tends to exert a great influence in the heat absorption process can be reduced, thereby making it possible to reduce the input to the compressor 3. In the heating operation, the primary-side refrigerant performs a heat radiation operation in the intermediate heat exchanger 7, and flows through the heat transfer unit 7a and the heat transfer unit 7b in series so that the overall cross-sectional area of the flow path becomes small. Thus, flow velocity increases, thereby making it possible to promote heat transfer. Therefore, highly efficient operation is possible in both the cooling operation and the heating operation.
As illustrated in FIGS. 1 and 2, the heat transfer unit 7a exists in which the flow directions of both the primary-side refrigerant and the secondary-side refrigerant do not change even when the overall cross-sectional area of the flow path in the intermediate heat exchanger 7 changes as cooling and the heating operations are switched. Consequently, it is possible to take measures such as optimization of refrigerant distribution.
In the cooling operation and the heating operation, even when the flow direction of the secondary-side refrigerant is switched, the secondary-side refrigerant flows through the indoor heat exchanger 8 only in one direction, and in either case, heat exchange with the indoor air is performed in the same manner, resulting in high heat exchange efficiency.
In a case where a refrigerant whose discharge pressure is higher than the critical point is used as the primary-side refrigerant, in the heating operation, an effect due to lowering of the outlet temperature of the primary-side refrigerant in the intermediate heat exchanger 7 can be expected. In this case, the outlet-inlet temperature difference of the secondary-side refrigerant can be made large, and the flow rate of the secondary-side refrigerant can be reduced, thereby making it possible to reduce the input to the pump 9.
In the air-conditioning apparatus illustrated in FIGS. 1 and 2, use of the check valves 11a to 11c and 12a to 12c makes it unnecessary to perform operations other than operations of the four-way valve 6 and valves 10a to 10d, for switching of the overall cross-sectional area of the flow path in the intermediate heat exchanger 7 due to switching of cooling and the heating operations. Consequently, in the vicinity of the intermediate heat exchanger 7, problems such as leakage of refrigerant from valves can be prevented, thereby enabling safe operation.
While the air-conditioning apparatus illustrated in FIGS. 1 and 2 is configured so that the intermediate heat exchanger 7 includes two heat transfer units such as the heat transfer unit 7a and the heat transfer unit 7b, this should not be construed restrictively. The intermediate heat exchanger 7 may include three or more heat transfer units. As an example in this case, FIG. 5 illustrates the flow of refrigerant in the cooling operation in a case where the intermediate heat exchanger 7 includes three heat transfer units (heat transfer units 7a to 7c), and FIG. 6 illustrates the flow of refrigerant in the heating operation in the case of the same configuration. In a case where the number of heat transfer units is an even number, the resulting configuration is the same as the configuration illustrated in FIGS. 1 and 2. That is, letting 2n (n is a natural number not smaller than 1) represent the number of heat transfer units, the number of check valves belonging to the primary-side refrigerant circuit within the intermediate heat exchanger 7 (the check valves 11a to 11c in FIGS. 1 and 2), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves 12a to 12c in FIGS. 1 and 2) are each expressed as (2n+1). In a case where the number of heat transfer units is an odd number, the resulting configuration is the same as the configuration illustrated in FIGS. 5 and 6. That is, letting (2n+1) represent the number of heat transfer units, the number of check valves belonging to the primary-side refrigerant circuit within the intermediate heat exchanger 7 (the check valves 11a and 11b in FIGS. 5 and 6), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves 12a and 12b in FIGS. 5 and 6) are each expressed as 2n. Therefore, the number of check valves to be installed relative to the number of heat transfer units can be reduced in the case where the number of heat transfer units is an odd number.
In a case where the number of heat transfer units in the intermediate heat exchanger 7 is an even number, the number of the above-mentioned heat transfer units in which the flow directions of both the primary-side refrigerant and the secondary-side refrigerant do not change equals 50% of the total number of heat transfer units. In a case where the number of heat transfer units in the intermediate heat exchanger 7 is an odd number, provided that the number is three, the number of heat transfer units in which both of the flow directions do not change equals 33.3% of the total number of heat transfer units and its ratio becomes the lowest. That is, in the case where the number of heat transfer units is an odd number, when the number of heat transfer units is larger than three, and as the number of heat transfer units becomes larger, the ratio of the number of heat transfer units in which both of the flow directions do not change to the total number of heat transfer units becomes larger.
The check valves 11a to 11c and 12a to 12c within the intermediate heat exchanger 7 in the air-conditioning apparatus illustrated in FIGS. 1, 2, 5, and 6 may be valves that can be opened and closed. In this case, for example, in a case where there are two heat transfer units as illustrated in FIGS. 1 and 2, in the cooling operation, the valves corresponding to the check valves 11a, 11b, 12a, and 12b may be opened, and the valves corresponding to the check valves 11c and 12c may be closed. In the heating operation, the open/close states of these valves may be reversed. In a case here the number of heat transfer units is an odd number, all valves may be opened in the cooling operation, and all valves may be closed in the heating operation.
The pump 9 may be a pump whose flow rate can be controlled. In this case, the target value of the outlet-inlet temperature difference of the secondary-side refrigerant in the intermediate heat exchanger 7, or the outlet-inlet temperature difference of the secondary-side refrigerant in the indoor heat exchanger 8 can be made larger in the heating operation than in the cooling operation, thereby enabling an appropriate operation in both the cooling operation and the heating operation.
As for the four valves 10a to 10d used to switch the direction of the secondary-side refrigerant flowing into the intermediate heat exchanger 7, as another means, two three-way valves or one four-way valve may be used to form a circuit for switching the flow path direction. In this case, it is possible to reduce the number of components.
While one indoor unit having the indoor heat exchanger 8 is illustrated as an indoor unit as in FIG. 1 or the like, this should not be construed restrictively. The number of indoor units may be two or more.
Embodiment 2
(Configuration of Air-Conditioning Apparatus)
FIG. 7 is a schematic diagram of an air-conditioning apparatus according to Embodiment 2 of the present invention.
The air-conditioning apparatus according to Embodiment 2 allows each individual indoor unit to freely select a cooling operation or the heating operation as an operation mode, by use of a primary-side refrigerant circuit through which the primary-side refrigerant flows and a secondary-side refrigerant circuit through which the secondary-side refrigerant flows.
As illustrated in FIG. 7, as in Embodiment 1, the air-conditioning apparatus according to Embodiment 2 includes two refrigerant circuits, a primary-side refrigerant circuit, and a secondary-side refrigerant circuit. As the primary-side refrigerant that flows through the primary-side refrigerant circuit of these refrigerant circuits, for example, a fluorocarbon refrigerant such as R410A, a hydrocarbon refrigerant such as propane, a natural refrigerant such as carbon dioxide, or the like is used. It is also possible to use an azeotropic refrigerant mixture such as R410A, or a zeotropic refrigerant mixture such as R407C, R32, and R134a, or R32 and R1234yf. As the secondary-side refrigerant that flows through the secondary-side refrigerant circuit, for example, brine, water, a liquid mixture of brine and water, a liquid mixture of water and an additive having an anti-corrosion effect, or the like is used. Use of these kinds of secondary-side refrigerant contributes to improvement of safety because even if the secondary-side refrigerant leaks to the indoor space via an indoor unit C described later, a highly safe refrigerant is used as the secondary-side refrigerant.
The primary-side refrigerant circuit includes at least a compressor 103, an outdoor heat exchanger 104, expansion mechanisms 105a and 105b, a four-way valve 106, intermediate heat exchangers 107a and 107b, and valves 111a to 111e. Roughly speaking, the primary-side refrigerant circuit is configured by connecting the compressor 103, the four-way valve 106, the outdoor heat exchanger 104, the expansion mechanisms 105a and 105b, the intermediate heat exchangers 107a and 107b, the four-way valve 106, and the compressor 103 in this order by refrigerant pipes.
The secondary-side refrigerant circuit includes at least the intermediate heat exchangers 107a and 107b, indoor heat exchangers 108n (n is a natural number not smaller than 2, and represents the number of indoor heat exchangers. The same applies hereinafter. FIG. 7 illustrates a case where n=3.), pumps 109a and 109b, and valves 110a to 110h and 112na to 112nd (n in this case is the same as mentioned above). Roughly speaking, the secondary-side refrigerant circuit is configured by connecting the pumps 109a and 109b, the indoor heat exchangers 108n, the intermediate heat exchangers 107a and 107b, and the pumps 109a and 109b in this order by refrigerant pipes.
While the number of indoor heat exchangers is three (n=3) in Embodiment 2, the number may be two, or may be four or more.
That is, in the air-conditioning apparatus according to Embodiment 2, the primary-side refrigerant that circulates through the primary-side refrigerant circuit, and the secondary-side refrigerant that circulates through the secondary-side refrigerant circuit exchange heat in the intermediate heat exchangers 107a and 107b. 
While the circuit configuration of each of the primary-side refrigerant circuit and the secondary-side refrigerant circuit mentioned above is a configuration based on a refrigerant circuit through which the same kind of refrigerant flows, as illustrated in FIG. 7, when considered on a unit basis, the air-conditioning apparatus according to Embodiment 2 includes an outdoor unit A that is a heat source unit, a plurality of indoor units C1 to C3 (hereinafter, simply referred to as indoor units C when no distinction is made between individual indoor units), and a relay unit B that is interposed between the outdoor unit A and the indoor units C1 to C3. The cooling energy or heating energy generated in the outdoor unit A is transmitted to the indoor units C via the relay unit B.
(Configuration of Outdoor Unit A)
The outdoor unit A is usually installed in an outdoor space such as the rooftop of a building. The outdoor unit A supplies cooling energy or heating energy to the indoor units C via the relay unit B. The outdoor unit A includes the compressor 103, the outdoor heat exchanger 104, and the four-way valve 106.
The compressor 103 sucks the primary-side refrigerant in a gas state, compresses the primary-side refrigerant into a high-temperature, high-pressure state, and discharges the resulting primary-side refrigerant. The compressor 103 may be configured by, for example, an inverter compressor or the like whose capacity can be controlled.
The outdoor heat exchanger 104 functions as a radiator in the cooling operation, and functions as an evaporator in the heating operation. The outdoor heat exchanger 104 exchanges heat between the outdoor air supplied from a fan and the primary-side refrigerant.
The four-way valve 106 switches between the flow of the primary-side refrigerant in the cooling operation (the cooling only operation mode and the cooling main operation mode described later), and the flow of the primary-side refrigerant in the heating operation (the heating only operation mode and the heating main operation mode described later). Specifically, in the cooling operation, the four-way valve 106 switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor 103 flows to the outdoor heat exchanger 104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor 103. In the heating operation, the four-way valve 106 switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor 103 flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger 104 flows to the compressor 103.
(Configuration of Relay Unit B)
The relay unit B is installed at, for example, a position different from the outdoor space and the indoor space, as a separate casing from the outdoor unit A and the indoor units C. The relay unit B serves as a relay connecting the outdoor unit A and the indoor units C by refrigerant pipes. The relay unit B includes the intermediate heat exchangers 107a and 107b, the expansion mechanisms 105a and 105b, the pumps 109a and 109b, and the valves 110a to 110h, 111a to 111e, and 112na to 112nd. 
The intermediate heat exchangers 107a and 107b are each configured by, for example, a double-pipe heat exchanger, a plate heat exchanger, a micro-channel water heat exchanger, a shell-and-tube heat exchanger, or the like. Each of the intermediate heat exchangers 107a and 107b includes a refrigerant flow path through which the primary-side refrigerant flows, and a refrigerant flow path through which the secondary-side refrigerant flows. Each of the intermediate heat exchangers 107a and 107b functions as a radiator or an evaporator to exchange heat between the primary-side refrigerant and the secondary-side refrigerant. Of these, the intermediate heat exchanger 107a is provided between the expansion mechanism 105a and the valve 111c in the primary-side refrigerant circuit, and is provided between the valve 110a and the valve 110b in the secondary-side refrigerant circuit. The intermediate heat exchanger 107b is provided between the expansion mechanism 105b and the valve 111d in the primary-side refrigerant circuit, and is provided between the valve 110e and the valve 110f in the secondary-side refrigerant circuit.
In a case where a plate heat exchanger is used as each of the intermediate heat exchangers 107a and 107b, by taking phase change of the primary-side refrigerant into consideration, each of the intermediate heat exchangers 107a and 107b is preferably installed in such an orientation that the primary-side refrigerant flows into each of the intermediate heat exchangers 107a and 107b from the lower side when the primary-side refrigerant absorbs heat, and that the primary-side refrigerant flows into each of the intermediate heat exchangers 107a and 107b from the upper side when the primary-side refrigerant radiates heat.
The expansion mechanisms 105a and 105b have the function of a pressure reducing/expansion valve in the primary-side refrigerant circuit, and cause the primary-side refrigerant to be reduced in pressure and expand. Of these, in the primary-side refrigerant circuit, the expansion mechanism 105a is provided between the intermediate heat exchanger 107a and the valve 111e, and the expansion mechanism 105b is provided between the intermediate heat exchanger 107b and the valve 111e. The expansion mechanisms 105a and 105b may each be configured by a mechanism whose opening degree (opening area) can be variably controlled, for example, an electronic expansion valve or the like.
The valves 111a to 111e are each configured by a two-way valve or the like. The valves 111a to 111e each open and close a refrigerant pipe in the primary-side refrigerant circuit, and switch the flow path of the primary-side refrigerant flowing into and flowing out of the relay unit B in the primary-side refrigerant circuit. The valve 111a is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger 107a and the valve 111c, and the refrigerant pipe connecting the valve 111b and the outdoor heat exchanger 104 (or the valve 111e). The valve 111b is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger 107b and the valve 111d, and the refrigerant pipe connecting the valve 111a and the outdoor heat exchanger 104 (or the valve 111e). The valve 111c is provided in the refrigerant pipe connecting the four-way valve 106 and the intermediate heat exchanger 107a. The valve 111d is provided in the refrigerant pipe connecting the four-way valve 106 and the intermediate heat exchanger 107b. The valve 111e is provided in the refrigerant pipe connecting the outdoor heat exchanger 104 and the expansion mechanism 105a (or the expansion mechanism 105b).
Each of the pumps 109a and 109b pumps and circulates the secondary-side refrigerant within the secondary-side refrigerant circuit. The pumps 109a and 109b may each be configured by, for example, a pump or the like whose capacity can be controlled. The refrigerant pipe connected to the discharge side of the pump 109a divides into branches, which are respectively connected to the valves 1121a, 1122a, and 1123a. The refrigerant pipe connected to the suction side of the pump 109a is connected to the valve 110a. The refrigerant pipe connected to the discharge side of the pump 109b divides into branches, which are respectively connected to the valves 1121b, 1122b, and 1123b. The refrigerant pipe connected to the suction side of the pump 109b is connected to the valve 110e. 
The valves 110a to 110h are each configured by a two-way valve or the like. In the secondary-side refrigerant circuit, the valves 110a to 110h each open and close a refrigerant pipe, and switch the flow path of the secondary-side refrigerant sent to each of the pumps 109a and 109b. The valve 110a is provided in the refrigerant pipe connecting the pump 109a and the intermediate heat exchanger 107a. The refrigerant pipe connected to one side of the valve 110b is connected to the intermediate heat exchanger 107a, and the refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves 1121c, 1122c, and 1123c. The valve 110c is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the pump 109a and the valve 110a, and the refrigerant pipe connecting the intermediate heat exchanger 107a and the valve 110b. The valve 110d is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger 107a and the valve 110a, and the refrigerant pipe connecting the valve 110b and each of the valves 1121c, 1122c, and 1123c. The valve 110e is provided in the refrigerant pipe connecting the pump 109b and the intermediate heat exchanger 107b. The refrigerant pipe connected to one side of the valve 110f is connected to the intermediate heat exchanger 107b, and the refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves 1121d, 1122d, and 1123d. The valve 110g is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the pump 109b and the valve 110e, and the refrigerant pipe connecting the intermediate heat exchanger 107b and the valve 110f. The valve 110h is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger 107b and the valve 110e, and the refrigerant pipe connecting the valve 110f and each of the valves 1121d, 1122d, and 1123d. 
The valves 112na to 112nd (n is a natural number not smaller than 2) switch the flow path of the secondary-side refrigerant sent to the indoor heat exchangers 108n of the indoor units C1 to C3. By adjusting the opening degree (opening area) of the valves 112na to 112nd, the flow rate of the secondary-side refrigerant flowing to the indoor heat exchangers 108n can be controlled.
(Configuration of Indoor Unit C)
The indoor units C1 to C3 include indoor heat exchangers 1081, 1082, and 1083, respectively. The indoor units C1 to C3 perform air conditioning by performing cooling or heating for the indoor space in which the indoor units C1 to C3 are provided.
The indoor heat exchangers 108n (n is a natural number not smaller than 2) function as a radiator in the heating operation and function as an evaporator in the cooling operation. The indoor heat exchangers 108n exchange heat between the indoor air supplied from a fan and the secondary-side refrigerant, and generates the heating air or cooling air to be supplied to the indoor space. The refrigerant pipe connected to one side of the indoor heat exchanger 1081 divides into branches, which are respectively connected to the valves 1121a and 1121b. The refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves 1121c and 1121d. The refrigerant pipe connected to one side of the indoor heat exchanger 1082 divides into branches, which are respectively connected to the valves 1122a and 1122b. The refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves 1122c and 1122d. The refrigerant pipe connected to one side of the indoor heat exchanger 1083 divides into branches, which are respectively connected to the valves 1123a and 1123b. The refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves 1123c and 1123d. 
While the number of indoor units C connected is three in FIG. 7, this should not be construed restrictively. The number of indoor units C connected may be other than three.
The outdoor heat exchanger 104 and the indoor heat exchangers 108n correspond to the “heat source-side heat exchanger” and the “use-side heat exchangers”, respectively, in the invention according to claim 1 of the present invention. The four-way valve 106, the valves 111a to 111e, the valves 110a to 110h, and the valves 112na to 112nd correspond to the “first flow switching means”, the “second flow switching means”, the “third flow switching means”, and the “fourth flow switching means”, respectively, in the invention according to claim 1 of the present invention.
Operation modes performed by the air-conditioning apparatus according to Embodiment 2 include a cooling only operation mode in which all of the indoor units C perform a cooling operation, a heating only operation mode in which all of the indoor units C perform a heating operation, a cooling main operation mode which allows a cooling operation or a heating operation to be selected for each individual indoor unit C and in which the cooling load is greater than the heating load, and a heating main operation mode which allows a cooling operation or a heating operation to be selected for each individual indoor unit C and in which the heating load is greater than the cooling load. Hereinafter, the operation modes will be described together with the flows of the primary-side refrigerant and secondary-side refrigerant.
(Cooling Only Operation Mode)
FIG. 8 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling only operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention. In FIG. 8, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. In FIG. 8, the flow direction of the primary-side refrigerant is indicated by solid arrows, and the flow direction of the secondary-side refrigerant is indicated by broken arrows. Hereinafter, the same applies to FIGS. 9 to 11. Hereinafter, the cooling only operation mode will be described with reference to FIG. 8.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the outdoor heat exchanger 104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor 103, and the valves 111a and 111b are closed and the valves 111c to 111e are open. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110e, and 110f are closed, the valves 110c, 110d, 110g, and 110h are open, and the valves 112na to 112nd are open.
First, the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger 104 via the four-way valve 106, where the primary-side refrigerant radiates heat to the outdoor air, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. The primary-side refrigerant in a two-phase gas-liquid state or liquid state that has flowed out of the outdoor heat exchanger 104 flows out of the outdoor unit A, and flows into the relay unit B.
After the primary-side refrigerant that has flowed into the relay unit B passes through the valve 111e, the primary-side refrigerant divides into branch flows. The branch flows flow into the expansion mechanisms 105a and 105b, undergo expansion and pressure reduction, turn into a two-phase gas-liquid state at low temperature and low pressure, and flow into the intermediate heat exchangers 107a and 107b in parallel, respectively. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the intermediate heat exchangers 107a and 107b absorb heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and evaporate and turn into a low-temperature, low-pressure gas state. The flows of the primary-side refrigerant that have flowed out of the intermediate heat exchangers 107a and 107b merge after passing through the valves 111c and 111d, respectively. The merged primary-side refrigerant flows out of the relay unit B, and flows into the outdoor unit A.
The primary-side refrigerant in a gas state that has flowed into the outdoor unit A is sucked into the compressor 103 via the four-way valve 106, and is compressed again.
Next, the flow of the secondary-side refrigerant in the secondary-side refrigerant circuit will be described.
The secondary-side refrigerant at low temperature sent out by driving of the pump 109a divides into branch flows. The branch flows flow out of the relay unit B after passing through the valves 1121a, 1122a, and 1123a, and flow into the indoor heat exchanger 1081 of the indoor unit C1, the indoor heat exchanger 1082 of the indoor unit C2, and the indoor heat exchanger 1083 of the indoor unit C3, respectively. The secondary-side refrigerant at low temperature sent out by driving of the pump 109b divides into branch flows. The branch flows flow out of the relay unit B after passing through the valves 1121b, 1122b, and 1123b, and flow into the indoor heat exchanger 1081 of the indoor unit C1, the indoor heat exchanger 1082 of the indoor unit C2, and the indoor heat exchanger 1083 of the indoor unit C3, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers 1081, 1082, and 1083 cool the indoor air and turn into a high-temperature state, flow out of the indoor units C1, C2, and C3, respectively, and flow into the relay unit B.
One of the flows of the secondary-side refrigerant which has passed through the valve 1121c after flowing out of the indoor heat exchanger 1081, flowing into the relay unit B, and dividing into branch flows, one of the flows of the secondary-side refrigerant which has passed through the valve 1122c after flowing out of the indoor heat exchanger 1082, flowing into the relay unit B, and dividing into branch flows, and one of the flows of the secondary-side refrigerant which has passed through the valve 1123c after flowing out of the indoor heat exchanger 1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger 107a via the valve 110d. Also, the other flow of the secondary-side refrigerant which has passed through the valve 1121d after flowing out of the indoor heat exchanger 1081, flowing into the relay unit B, and dividing into branch flows, the other flow of the secondary-side refrigerant which has passed through the valve 1122d after flowing out of the indoor heat exchanger 1082, flowing into the relay unit B, and dividing into branch flows, and the other flow of the secondary-side refrigerant which has passed through the valve 1123d after flowing out of the indoor heat exchanger 1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger 107b via the valve 110h. The flows of the secondary-side refrigerant that have flowed into the intermediate heat exchangers 107a and 107b are cooled by the primary-side refrigerant in a low-temperature state flowing in counterflow to the secondary-side refrigerant, and flow into the intermediate heat exchangers 107a and 107b, respectively. The flows of the secondary-side refrigerant that have flowed out of the intermediate heat exchangers 107a and 107b flow into the pumps 109a and 109b via the valves 110c and 110g, respectively, and are sent out again.
(Heating Only Operation Mode)
FIG. 9 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating only operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention. Hereinafter, the heating only operation mode will be described with reference to FIG. 9.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger 104 flows to the compressor 103, and the valves 111a and 111b are closed and the valves 111c to 111e are open. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110e, and 110f are open, the valves 110c, 110d, 110g, and 110h are closed, and the valves 112na to 112nd are open.
First, the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve 106, and flows into the relay unit B.
The primary-side refrigerant that has flowed into the relay unit B divides into branch flows, and the branch flows flow into the intermediate heat exchangers 107a and 107b in parallel via the valves 111c and 111d, respectively. The flows of the primary-side refrigerant in a high-temperature, high-pressure state that have flowed into the intermediate heat exchangers 107a and 107b radiate heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. The flows of the primary-side refrigerant in a two-phase gas-liquid state or liquid state that have flowed out of the intermediate heat exchangers 107a and 107b flow into the expansion mechanisms 105a and 105b, respectively, where the flows of the primary-side refrigerant are expanded and reduced in pressure and turn into a two-phase gas-liquid state at low temperature and low pressure, and then merge. The merged primary-side refrigerant flows out of the relay unit B via the valve 111e, and flows into the outdoor unit A.
The primary-side refrigerant in a two-phase gas-liquid state that have flowed into the outdoor unit A flows into the outdoor heat exchanger 104, absorbs heat from the outdoor air, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant is sucked into the compressor 103 via the four-way valve 106, and is compressed again.
Next, the flow of the secondary-side refrigerant in the secondary-side refrigerant circuit will be described.
The secondary-side refrigerant at high temperature sent out by driving of the pump 109a divides into branch flows. The branch flows flow out of the relay unit B after passing through the valves 1121a, 1122a, and 1123a, and flow into the indoor heat exchanger 1081 of the indoor unit C1, the indoor heat exchanger 1082 of the indoor unit C2, and the indoor heat exchanger 1083 of the indoor unit C3, respectively. The secondary-side refrigerant at high temperature sent out by driving of the pump 109b divides into branch flows. The branch flows flow out of the relay unit B after passing through the valves 1121b, 1122b, and 1123b, and flow into the indoor heat exchanger 1081 of the indoor unit C1, the indoor heat exchanger 1082 of the indoor unit C2, and the indoor heat exchanger 1083 of the indoor unit C3, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers 1081, 1082, and 1083 heat the indoor air and turn into a low-temperature state, flow out of the indoor units C1, C2, and C3, respectively, and flow into the relay unit B.
One of the flows of the secondary-side refrigerant which has passed through the valve 1121c after flowing out of the indoor heat exchanger 1081, flowing into the relay unit B, and dividing into branch flows, one of the flows of the secondary-side refrigerant which has passed through the valve 1122c after flowing out of the indoor heat exchanger 1082, flowing into the relay unit B, and dividing into branch flows, and one of the flows of the secondary-side refrigerant which has passed through the valve 1123c after flowing out of the indoor heat exchanger 1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger 107a via the valve 110b. Also, the other flow of the secondary-side refrigerant which has passed through the valve 1121d after flowing out of the indoor heat exchanger 1081, flowing into the relay unit B, and dividing into branch flows, the other flow of the secondary-side refrigerant which has passed through the valve 1122d after flowing out of the indoor heat exchanger 1082, flowing into the relay unit B, and dividing into branch flows, and the other flow of the secondary-side refrigerant which has passed through the valve 1123d after flowing out of the indoor heat exchanger 1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger 107b via the valve 110f. The flows of the secondary-side refrigerant that have flowed into the intermediate heat exchangers 107a and 107b are heated by the primary-side refrigerant in a high-temperature state flowing in counterflow to the secondary-side refrigerant, and flow out of the intermediate heat exchangers 107a and 107b, respectively. The flows of the secondary-side refrigerant that have flowed out of the intermediate heat exchangers 107a and 107b flow into the pumps 109a and 109b via the valves 110a and 110e, respectively, and are sent out again.
(Cooling Main Operation Mode)
FIG. 10 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling main operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention. Hereinafter, the cooling main operation mode will be described with reference to FIG. 10.
In FIG. 10, it is assumed that the indoor unit C1 performs a heating operation, and the indoor units C2 and C3 perform a refrigerating operation.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the outdoor heat exchanger 104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor 103, and the valves 111a, 111d, and 111e are closed and the valves 111b and 111c are open. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110g, and 110h are closed, and the valves 110c, 110d, 110e, and 110f are open. Further, the valves 1121a, 1121c, 1122b, 1122d, 1123b, and 1123d are closed, and the valves 1121b, 1121d, 1122a, 1122c, 1123a, and 1123c are open.
First, the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger 104 via the four-way valve 106, where the primary-side refrigerant radiates heat to the outdoor air, and a part of the primary-side refrigerant condenses and turns into a two-phase gas-liquid state. The primary-side refrigerant in a two-phase gas-liquid state that has flowed out of the outdoor heat exchanger 104 flows out of the outdoor unit A, and flows into the relay unit B.
The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the relay unit B flows into the intermediate heat exchanger 107b via the valve 111b, and further condenses as the primary-side refrigerant heats the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant. As the secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107b passes through the expansion mechanism 105b and the expansion mechanism 105a, the secondary-side refrigerant is expanded and reduced in pressure, turns into a two-phase gas-liquid state at low temperature and low pressure, and flows into the intermediate heat exchanger 107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger 107a absorbs heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant in a low-temperature, low-pressure gas state that has flowed out of the intermediate heat exchanger 107a flows out of the relay unit B via the valve 111c, and flows into the outdoor unit A.
The primary-side refrigerant in a gas state that has flowed into the outdoor unit A is sucked into the compressor 103 via the four-way valve 106, and is compressed again.
Next, the flow of the secondary-side refrigerant in the secondary-side refrigerant circuit will be described.
The secondary-side refrigerant at low temperature sent out by driving of the pump 109a divides into branch flows. The branch flows flow out of the relay unit B after passing through the valves 1122a and 1123a, and flow into the indoor heat exchanger 1082 of the indoor unit C2, and the indoor heat exchanger 1083 of the indoor unit C3, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers 1082 and 1083 cool the indoor air and turn into a high-temperature state, flow out of the indoor units C2 and C3, respectively, and flow into the relay unit B.
The secondary-side refrigerant that has flowed out of the indoor heat exchanger 1082, flowed into the relay unit B, and passed through the valve 1122c, and the secondary-side refrigerant that has flowed out of the indoor heat exchanger 1083, flowed into the relay unit B, and passed through the valve 1123c merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger 107a via the valve 110d. The secondary-side refrigerant that has flowed into the intermediate heat exchanger 107a is cooled by the primary-side refrigerant in a low-temperature state flowing in counterflow to the secondary-side refrigerant, and flows out of the intermediate heat exchanger 107a. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107a flows into the pump 109a via the valve 110c, and is sent out again.
The secondary-side refrigerant at high temperature sent out by driving of the pump 109b flows out of the relay unit B after passing through the valve 1121b, and flows into the indoor heat exchanger 1081 of the indoor unit C1. The secondary-side refrigerant that has flowed into the indoor heat exchanger 1081 heats the indoor air and turn into a low-temperature state, flow out of the indoor unit C1, and flows into the relay unit B.
The secondary-side refrigerant that has flowed out of the indoor heat exchanger 1081, flowed into the relay unit B, and passed through the valve 1121d flows into the intermediate heat exchanger 107b via the valve 110f. The secondary-side refrigerant that has flowed into the intermediate heat exchanger 107b is heated by the primary-side refrigerant in a high-temperature state flowing in counterflow to the secondary-side refrigerant, and flows out of the intermediate heat exchanger 107b. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107b flows into the pump 109b via the valve 110e, and is sent out again.
(Heating Main Operation Mode)
FIG. 11 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating main operation mode of the air-conditioning apparatus according to Embodiment 2 of the present invention. Hereinafter, the heating main operation mode will be described with reference to FIG. 11. In FIG. 11, it is assumed that the indoor units C1 and C2 perform a heating operation, and the indoor unit C3 performs a refrigerating operation.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger 104 flows to the compressor 103, and the valves 111a and 111d are open and the valves 111b, 111c, and 111e are closed. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110g, and 110h are closed, and the valves 110c to 110f are open. Further, the valves 1121a, 1121c, 1122a, 1122c, 1123b, and 1123d are closed, and the valves 1121b, 1121d, 1122b, 1122d, 1123a, and 1123c are open.
First, the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve 106, and flows into the relay unit B.
The primary-side refrigerant in a high-temperature, high-pressure state that has flowed into the relay unit B flows into the intermediate heat exchanger 107b via the valve 111d, radiates heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. As the secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107b passes through the expansion mechanism 105b and the expansion mechanism 105a, the secondary-side refrigerant is expanded and reduced in pressure, turns into a two-phase gas-liquid state at low temperature and low pressure, and flows into the intermediate heat exchanger 107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger 107a absorbs heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and partially evaporates. The primary-side refrigerant that has flowed out of the intermediate heat exchanger 107a flows out of the relay unit B via the valve 111a, and flows into the outdoor unit A.
The primary-side refrigerant that has flowed into the outdoor unit A flows into the outdoor heat exchanger 104, absorbs heat from the indoor air, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant is sucked into the compressor 103 via the four-way valve 106, and is compressed again.
Next, the flow of the secondary-side refrigerant in the secondary-side refrigerant circuit will be described.
The secondary-side refrigerant at low temperature sent out by driving of the pump 109a flows out of the relay unit B after passing through the valve 1123a, and flows into the indoor heat exchanger 1083 of the indoor unit C3. The secondary-side refrigerant that has flowed into the indoor heat exchanger 1083 cools the indoor air and turn into a high-temperature state, flows out of the indoor unit C3, and flows into the relay unit B.
The secondary-side refrigerant that has flowed out of the indoor heat exchanger 1083, flowed into the relay unit B, and passed through the valve 1123c flows into the intermediate heat exchanger 107a via the valve 110d. The secondary-side refrigerant that has flowed into the intermediate heat exchanger 107a is cooled by the primary-side refrigerant in a low-temperature state flowing in counterflow to the secondary-side refrigerant, and flows out of the intermediate heat exchanger 107a. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107a flows into the pump 109a via the valve 110a, and is sent out again.
The secondary-side refrigerant at high temperature sent out by driving of the pump 109b divides into branch flows. The branch flows flow out of the relay unit B after passing through the valves 1121b and 1122b, and flow into the indoor heat exchanger 1081 of the indoor unit C1, and the indoor heat exchanger 1082 of the indoor unit C2, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers 1081 and 1082 heat the indoor air and turn into a low-temperature state, flow out of the indoor units C1 and C2, respectively, and flow into the relay unit B.
The secondary-side refrigerant that has flowed out of the indoor heat exchanger 1081, flowed into the relay unit B, and passed through the valve 1121d, and the secondary-side refrigerant that has flowed out of the indoor heat exchanger 1082, flowed into the relay unit B, and passed through the valve 1122d merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger 107b via the valve 110f. The secondary-side refrigerant that has flowed into the intermediate heat exchanger 107b is heated by the primary-side refrigerant in a high-temperature state flowing in counterflow to the secondary-side refrigerant, and flows out of the intermediate heat exchanger 107b. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107b flows into the pump 109b via the valve 110e, and is sent out again.
Advantageous Effects of Embodiment 2
According to the configuration and the operation mentioned above, in any operation mode, the primary-side refrigerant and the secondary-side refrigerant flow in counterflow directions in both of the intermediate heat exchangers 107a and 107b. Therefore, thermal effect of the primary-side refrigerant and the secondary-side refrigerant is efficiently exerted, thereby making it possible to reduce the input to each of the pumps 109a and 109b. 
In a case where a refrigerant whose discharge pressure is higher than the critical point is used as the primary-side refrigerant, the discharge temperature of the refrigerant is higher than that of a refrigerant whose discharge pressure is lower than the critical point, and the refrigerant does not become a two-phase gas-liquid state. Therefore, the target value of the outlet-inlet temperature difference of the secondary-side refrigerant within the intermediate heat exchanger can be set to a large value, thereby making it possible to reduce the input to the pump.
In a case where a zeotropic refrigerant mixture is used as the primary-side refrigerant, because a zeotropic refrigerant mixture undergoes a temperature change when its phase changes, as compared with a case where a single refrigerant or azeotropic refrigerant mixture that does not undergo a temperature change when its phase changes is used, heat exchange can be performed efficiently when the primary-side refrigerant and the secondary-side refrigerant are made to flow in counterflow directions in the intermediate heat exchanger.
As for the four valves 110a to 110d used to switch the direction of the secondary-side refrigerant flowing into the intermediate heat exchanger 107a, and the four valves 110e to 110h used to switch the direction of the secondary-side refrigerant flowing into the intermediate heat exchanger 107b, as another means, two three-way valves or one four-way valve may be used to form a circuit for switching the flow path direction. In this case, it is possible to reduce the number of components.
As for the valves 112na and 112nb used to switch the direction of the secondary-side refrigerant flowing into the indoor heat exchangers 108n as well, as another means, these valves may be configured as one three-way valve, in which case it is possible to reduce the number of components. The same applies to the valves 112nc and 112nd used to switch the direction of the secondary-side refrigerant that has flowed out of the indoor heat exchangers 108n. 
Embodiment 3
An air-conditioning apparatus according to Embodiment 3 will be described while mainly focusing on differences from the air-conditioning apparatus according to Embodiment 2.
(Configuration of Air-Conditioning Apparatus)
FIG. 12 is a schematic diagram of an air-conditioning apparatus according to Embodiment 3 of the present invention.
As illustrated in FIG. 12, the outdoor unit A includes the compressor 103, the outdoor heat exchanger 104, the four-way valve 106, and a flow switching unit 141 including check valves 113a to 113d. 
As will be described later, the flow switching unit 141 including the check valves 113a to 113d has the function of causing the primary-side refrigerant flowing within the refrigerant pipes connecting the outdoor unit A and the relay unit B to flow in a certain direction. The check valve 113a is provided in the refrigerant pipe connecting the four-way valve 106 and each of the valves 111c and 111d, and causes the primary-side refrigerant to flow only in a direction from each of the valves 111c and 111d toward the four-way valve 106. The check valve 113b is provided in the refrigerant pipe connecting the outdoor heat exchanger 104 and the valve 111f described later, and causes the primary-side refrigerant to flow only in a direction from the outdoor heat exchanger 104 toward the valve 111f. The check valve 113c is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the four-way valve 106 and the check valve 113a, and the refrigerant pipe connecting the check valve 113b and the valve 111f, and causes the primary-side refrigerant to flow only in a direction from the refrigerant pipe connecting the four-way valve 106 and the check valve 113a toward the refrigerant pipe connecting the check valve 113b and the valve 111f. The check valve 113d is provided in the refrigerant pipe that connects between the refrigerant pipe connecting the check valve 113a and each of the valves 111c and 111d, and the refrigerant pipe connecting the indoor heat exchanger 104 and the check valve 113b, and causes the primary-side refrigerant to flow only in a direction from the refrigerant pipe connecting the check valve 113a and each of the valves 111c and 111d toward the refrigerant pipe connecting the indoor heat exchanger 104 and the check valve 113b. 
The relay unit B includes the intermediate heat exchangers 107a and 107b, the expansion mechanisms 105a and 105b, the pumps 109a and 109b, the valves 110a to 110h, 111a to 111f, and 112na to 112nd, and a bypass pipe 142.
The valve 111f is configured by a two-way valve or the like. The valve 111f is provided in the refrigerant pipe between the valve 111e, and the point where the refrigerant pipe into which refrigerant pipes connected to the valves 111a and 111b merge connects with the refrigerant pipe connecting the check valve 113b and the valve 111e. 
The bypass pipe 142 is a refrigerant pipe that connects between the refrigerant pipe connecting the check valve 113a and each of the valves 111c and 111d, and the refrigerant pipe connecting the valve 111e and the valve 111f. 
Hereinafter, operation modes will be described together with the flow of the primary-side refrigerant.
The flow of the secondary-side refrigerant is the same as that in Embodiment 1.
(Cooling Only Operation Mode)
FIG. 13 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling only operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention. In FIG. 13, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. In FIG. 13, the flow direction of the primary-side refrigerant is indicated by solid arrows, and the flow direction of the secondary-side refrigerant is indicated by broken arrows. Hereinafter, the same applies to FIGS. 14 to 16. Hereinafter, the cooling only operation mode will be described with reference to FIG. 13.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the outdoor heat exchanger 104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor 103, and the valves 111a and 111b are closed and the valves 111c to 111f are open. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110e, and 110f are closed, the valves 110c, 110d, 110g, and 110h are open, and the valves 112na to 112nd are open.
As described above, only the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger 104 via the four-way valve 106, where the primary-side refrigerant radiates heat to the outdoor air, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. The primary-side refrigerant in a two-phase gas-liquid state or liquid state that has flowed out of the outdoor heat exchanger 104 flows out of the outdoor unit A via the check valve 113b, and flows into the relay unit B.
After the primary-side refrigerant that has flowed into the relay unit B passes through the valves 111f and the valve 111e, the primary-side refrigerant divides into branch flows. The branch flows flow into the expansion mechanisms 105a and 105b, undergo expansion and pressure reduction, turn into a two-phase gas-liquid state at low temperature and low pressure, and flow into the intermediate heat exchangers 107a and 107b in parallel, respectively. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the intermediate heat exchangers 107a and 107b absorb heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and evaporate and turn into a low-temperature, low-pressure gas state. The flows of the primary-side refrigerant that have flowed out of the intermediate heat exchangers 107a and 107b merge after passing through the valves 111c and 111d, respectively. The merged primary-side refrigerant flows out of the relay unit B, and flows into the outdoor unit A.
The primary-side refrigerant in a gas state that has flowed into the outdoor unit A is sucked into the compressor 103 via the check valve 113a and the four-way valve 106, and is compressed again.
(Heating Only Operation Mode)
FIG. 14 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating only operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention. Hereinafter, the heating only operation mode will be described with reference to FIG. 14.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger 104 flows to the compressor 103, and the valves 111a, 111b, and 111e are open and the valves 111c, 111d, and 111f are closed. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110e, and 110f are open, the valves 110c, 110d, 110g, and 110h are closed, and the valves 112na to 112nd are open.
As described above, only the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve 106 and the check valve 113c, and flows into the relay unit B.
The primary-side refrigerant that has flowed into the relay unit B divides into branch flows, and the branch flows flow into the intermediate heat exchangers 107a and 107b in parallel via the valves 111a and 111b, respectively. The flows of the primary-side refrigerant in a high-temperature, high-pressure state that have flowed into the intermediate heat exchangers 107a and 107b radiate heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. The flows of the primary-side refrigerant in a two-phase gas-liquid state or liquid state that have flowed out of the intermediate heat exchangers 107a and 107b flow into the expansion mechanisms 105a and 105b, respectively, undergo expansion and pressure reduction, turn into a two-phase gas-liquid state at low temperature and low pressure, and then merge. The merged primary-side refrigerant passes through the valve 111e, and flows out of the relay unit B after flowing through the bypass pipe 142, and flows into the outdoor unit A.
The primary-side refrigerant in a two-phase gas-liquid state that have flowed into the outdoor unit A flows into the outdoor heat exchanger 104 via the check valve 113d, absorbs heat from the outdoor air, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant is sucked into the compressor 103 via the four-way valve 106, and is compressed again.
(Cooling Main Operation Mode)
FIG. 15 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the cooling main operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention. Hereinafter, the cooling main operation mode will be described with reference to FIG. 15. In FIG. 15, it is assumed that the indoor unit C1 performs a heating operation, and the indoor units C2 and C3 perform a cooling operation.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the outdoor heat exchanger 104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor 103, and the valves 111a, 111d, 111e, and 111f are closed and the valves 111b and 111c are open. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110g, and 110h are closed, and the valves 110c, 110d, 110e, and 110f are open. Further, the valves 1121a, 1121c, 1122b, 1122d, 1123b, and 1123d are closed, and the valves 1121b, 1121d, 1122a, 1122c, 1123a, and 1123c are open.
As described above, only the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger 104 via the four-way valve 106, where the primary-side refrigerant radiates heat to the outdoor air, and a part of the primary-side refrigerant condenses and turns into a two-phase gas-liquid state. The primary-side refrigerant in a two-phase gas-liquid state that has flowed out of the outdoor heat exchanger 104 flows out of the outdoor unit A via the check valve 113b, and flows into the relay unit B.
The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the relay unit B flows into the intermediate heat exchanger 107b via the valve 111b, and further condenses as the primary-side refrigerant heats the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant. As the secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107b passes through the expansion mechanism 105b and the expansion mechanism 105a, the secondary-side refrigerant is expanded and reduced in pressure, turns into a two-phase gas-liquid state at low temperature and low pressure, and flows into the intermediate heat exchanger 107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger 107a absorbs heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant in a low-temperature, low-pressure gas state that has flowed out of the intermediate heat exchanger 107a flows out of the relay unit B via the valve 111c, and flows into the outdoor unit A.
The primary-side refrigerant in a gas state that has flowed into the outdoor unit A is sucked into the compressor 103 via the check valve 113a and the four-way valve 106, and is compressed again.
(Heating Main Operation Mode)
FIG. 16 is a refrigerant circuit diagram illustrating the flows of the primary-side refrigerant and secondary-side refrigerant in the heating main operation mode of the air-conditioning apparatus according to Embodiment 3 of the present invention. Hereinafter, the heating main operation mode will be described with reference to FIG. 16. In FIG. 16, it is assumed that the indoor units C1 and C2 perform a heating operation, and the indoor unit C3 performs a cooling operation.
In the primary-side refrigerant circuit, the four-way valve 106 is switched in advance so that the primary-side refrigerant discharged from the compressor 103 flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger 104 flows to the compressor 103, and the valves 111a, and 111d to 111f are closed and the valves 111b and 111c are open. In the secondary-side refrigerant circuit, the valves 110a, 110b, 110g, and 110h are closed, and the valves 110c to 110f are open. Further, the valves 1121a, 1121c, 1122a, 1122c, 1123b, and 1123d are closed, and the valves 1121b, 1121d, 1122b, 1122d, 1123a, and 1123c are open.
As described above, only the flow of the primary-side refrigerant in the primary-side refrigerant circuit will be described.
The primary-side refrigerant in a low-temperature, low-pressure gas state is compressed by the compressor 103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve 106 and the check valve 113c, and flows into the relay unit B.
The primary-side refrigerant in a high-temperature, high-pressure state that has flowed into the relay unit B flows into the intermediate heat exchanger 107b via the valve 111b, radiates heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. As the secondary-side refrigerant that has flowed out of the intermediate heat exchanger 107b passes through the expansion mechanism 105b and the expansion mechanism 105a, the secondary-side refrigerant is expanded and reduced in pressure, turns into a two-phase gas-liquid state at low temperature and low pressure, and flows into the intermediate heat exchanger 107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger 107a absorbs heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and partially evaporates. The primary-side refrigerant that has flowed out of the intermediate heat exchanger 107a flows out of the relay unit B via the valve 111c, and flows into the outdoor unit A.
The primary-side refrigerant that has flowed into the outdoor unit A flows into the outdoor heat exchanger 104 via the check valve 113d, absorbs heat from the indoor air, and evaporates and turns into a low-temperature, low-pressure gas state. The primary-side refrigerant is sucked into the compressor 103 via the four-way valve 106, and is compressed again.
Advantageous Effects of Embodiment 3
According to the configuration and the operation mentioned above, irrespective of the operation mode, the primary-side refrigerant flowing through the refrigerant pipes connecting the outdoor unit A and the relay unit B flow in a certain direction, and the refrigerant pipes through which a high-pressure refrigerant and a low-pressure refrigerant flow become fixed. Consequently, of the refrigerant pipes connecting the outdoor unit A and the relay unit B, the wall thickness of the refrigerant pipe through which the low-pressure refrigerant flows can be reduced, thereby enabling cost reduction.
Embodiment 4
An air-conditioning apparatus according to Embodiment 4 will be described while mainly focusing on differences from the air-conditioning apparatus according to Embodiment 2.
(Configuration of Air-Conditioning Apparatus)
FIG. 17 is a schematic diagram of an air-conditioning apparatus according to Embodiment 4 of the present invention.
As illustrated in FIG. 17, in the air-conditioning apparatus according to Embodiment 4, the intermediate heat exchangers 107a and 107b in the air-conditioning apparatus according to Embodiment 2 are replaced by intermediate heat exchangers 107aa and 107ba, respectively. The intermediate heat exchangers 107aa and 107ba are both configured in the same manner as the intermediate heat exchanger 7 in the air-conditioning apparatus according to Embodiment 1.
First, heat transfer units 1071a and 1072a, and check valves 132a to 132c and 133a to 133c in the intermediate heat exchanger 107aa correspond to the heat transfer units 7a and 7b, and the check valves 11a to 11c and 12a to 12c in the intermediate heat exchanger 7 in Embodiment 1, respectively. Heat transfer units 1071b and 1072b, and check valves 132d to 132f and 133d to 133f in the intermediate heat exchanger 107ba correspond to the heat transfer units 7a and 7b, and the check valves 11a to 11c and 12a to 12c in the intermediate heat exchanger 7 in Embodiment 1, respectively.
The operation of the air-conditioning apparatus according to Embodiment 4 is the same as that of the air-conditioning apparatus according to Embodiment 2, except for the flow of refrigerant within each of the intermediate heat exchangers 107aa and 107ba. Moreover, provided that the primary-side refrigerant and the secondary-side refrigerant flow out of and flow into the intermediate heat exchanger 107aa and the intermediate heat exchanger 107ba in the same direction, the operations in the intermediate heat exchanger 107aa and the intermediate heat exchanger 107ba are the same. Accordingly, hereinafter, the operation in the intermediate heat exchanger 107ba will be described.
The check valves 132a to 132f and 133a to 133f correspond to the “fifth flow switching means” in the invention according to claim 5 of the present invention.
(Operation of Intermediate Heat Exchanger 107Ba as Evaporator)
FIG. 18 illustrates the flows of the primary-side refrigerant and secondary-side refrigerant in a case where the intermediate heat exchanger 107ba in the air-conditioning apparatus according to Embodiment 4 of the present invention functions as an evaporator. In FIG. 18, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. In FIG. 18, the flow direction of the primary-side refrigerant is indicated by solid arrows, and the flow direction of the secondary-side refrigerant is indicated by broken arrows. Hereinafter, the same applies to FIG. 19. Hereinafter, the operation in a case where the intermediate heat exchanger 107ba functions as an evaporator will be described with reference to FIG. 18.
After the primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger 107ba passes through the check valve 132e, the primary-side refrigerant divides into branch flows, and the branch flows flow into the heat transfer unit 1071b and the heat transfer unit 1072b in parallel, respectively. At this time, the primary-side refrigerant does not flow in a direction toward the check valve 132d owing to the action of the check valve 132f. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the heat transfer unit 1071b and the heat transfer unit 1072b absorb heat from the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant, and partially evaporate, or evaporate and turn into a low-temperature, low-pressure gas state. The primary-side refrigerant that has flowed out of the heat transfer unit 1071b passes though the check valve 132d, merges with the primary-side refrigerant that has flowed out of the heat transfer unit 1072b, and flows out of the intermediate heat exchanger 107ba. 
The secondary-side refrigerant that has flowed into the intermediate heat exchanger 107ba divides into branch flows, one of which flows into the heat transfer unit 1072b, and the other flows into the heat transfer unit 1071b via the check valve 133d. At this time, the secondary-side refrigerant does not flow in a direction toward the outlet of the secondary-side refrigerant in the intermediate heat exchanger 107ba owing to the action of the check valve 133f. The flows of the secondary-side refrigerant that have flowed into the heat transfer unit 1071b and the heat transfer unit 1072b in parallel are cooled by the primary-side refrigerant in a low-temperature state flowing in counterflow to the secondary-side refrigerant, and flow out of the heat transfer unit 1071b and the heat transfer unit 1072b, respectively. The flows of the secondary-side refrigerant that have respectively flowed out of the heat transfer unit 1071b and the heat transfer unit 1072b merge, and the merged secondary-side refrigerant flows out of the intermediate heat exchanger 107ba via the check valve 133e. 
(Operation of Intermediate Heat Exchanger 107ba as Radiator)
FIG. 19 illustrates the flows of the primary-side refrigerant and secondary-side refrigerant in a case where the intermediate heat exchanger 107ba in the air-conditioning apparatus according to Embodiment 4 of the present invention functions as a radiator. In FIG. 19, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. In FIG. 19, the flow direction of the primary-side refrigerant is indicated by solid arrows, and the flow direction of the secondary-side refrigerant is indicated by broken arrows. Hereinafter, the operation in a case where the intermediate heat exchanger 107ba functions as a radiator will be described with reference to FIG. 19.
The primary-side refrigerant that has flowed into the intermediate heat exchanger 107ba flows into the heat transfer unit 1072b, and radiates heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant. At this time, the primary-side refrigerant does not flow in a direction toward the heat transfer unit 1071b and the check valve 132f owing to the action of the check valve 132d. The primary-side refrigerant that has flowed out of the heat transfer unit 1072b flows into the heat transfer unit 1071b. In the heat transfer unit 1071b as well, the primary-side refrigerant radiates heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant. At this time, the primary-side refrigerant does not flow in a direction toward the outlet of the primary-side refrigerant in the intermediate heat exchanger 107ba owing to the action of the check valve 132e. In this way, the primary-side refrigerant flows through the heat transfer unit 1072b and the heat transfer unit 1071b in series, and during this process, the primary-side refrigerant radiates heat to the secondary-side refrigerant, and a part or the entire primary-side refrigerant condenses and turns into a two-phase gas-liquid state or liquid state. The primary-side refrigerant in a two-phase gas-liquid state or liquid state that has flowed out of the heat transfer unit 1071b flows out of the intermediate heat exchanger 107ba via the check valve 132f. 
The secondary-side refrigerant that has flowed into the intermediate heat exchanger 107ba flows into the heat transfer unit 1071b via the check valve 133f, and is heated by the primary-side refrigerant flowing in counterflow to the secondary-side refrigerant. At this time, the secondary-side refrigerant does not flow in a direction toward the heat transfer unit 1072b owing to the action of the check valve 133e. The secondary-side refrigerant does not flow in a direction toward the outlet of the secondary-side refrigerant in the intermediate heat exchanger 107ba, either, owing to the action of the check valve 133d. The secondary-side refrigerant that has flowed out of the heat transfer unit 1071b flows into the heat transfer unit 1072b, and is heated by the primary-side refrigerant flowing in counterflow to the secondary-side refrigerant. In this way, the secondary-side refrigerant flows through the heat transfer unit 1071b and the heat transfer unit 1072b in series. The secondary-side refrigerant that has flowed out of the heat transfer unit 1072b flows out of the intermediate heat exchanger 107ba. 
(Operation in Each Operation Mode)
In the cooling only operation mode, the intermediate heat exchangers 107aa and 107ba both act as the evaporator described above with reference to FIG. 18, and in the heating only operation mode, the intermediate heat exchangers 107aa and 107ba both act as the radiator described above with reference to FIG. 19. In both the cooling main operation mode and the heating main operation mode, the intermediate heat exchanger 107aa acts as the evaporator described above with reference to FIG. 18, and the intermediate heat exchanger 107ba acts as the radiator described above with reference to FIG. 19.
Advantageous Effects of Embodiment 4
According to the configuration and the operation mentioned above, in a case where each of the intermediate heat exchangers 107aa and 107ba functions as an evaporator where the primary-side refrigerant absorbs heat from the secondary-side refrigerant, the primary-side refrigerant flows through the heat transfer unit 1071a (1071b) and the heat transfer unit 1072a (1072b) in parallel, and in a case where each of the intermediate heat exchangers 107aa and 107ba functions as a radiator where the primary-side refrigerant radiates heat to the secondary-side refrigerant, the primary-side refrigerant flows through the heat transfer unit 1071a (1071b) and the heat transfer unit 1072a (1072b) in series. In this regard, as described above, with regard to operation efficiency, pressure loss exerts a greater influence than heat transfer capacity in the heat absorption process, and heat transfer capacity exerts a greater influence than pressure loss in the heat radiation process. Accordingly, in the air-conditioning apparatus according to Embodiment 4, in the intermediate heat exchanger 107aa (107ba) that functions as an evaporator, the primary-side refrigerant performs a heat absorption operation, and flows through the heat transfer unit 1071a (1071b) and the heat transfer unit 1072a (1072b) in parallel so that the overall cross-sectional area of the flow path becomes large. Therefore, pressure loss that tends to exert a great influence in the heat absorption process can be reduced, thereby making it possible to reduce the input to the compressor 103. In the intermediate heat exchanger 107aa (107ba) that functions as a radiator, the primary-side refrigerant performs a heat radiation operation, and flows through the heat transfer unit 1071a (1071b) and the heat transfer unit 1072a (1072b) in series so that the overall cross-sectional area of the flow path becomes small. Thus, flow velocity increases, thereby making it possible to promote heat transfer. Therefore, highly efficient operation is possible in each operation mode.
In the air-conditioning apparatus according to Embodiment 4, there exists a heat transfer unit (the heat transfer unit 1071b in FIGS. 18 and 19) in which the flow directions of both the primary-side refrigerant and the secondary-side refrigerant do not change even when the overall cross-sectional area of the flow path in the intermediate heat exchanger changes in accordance with each operation mode. Consequently, it is possible to take measures such as optimization of refrigerant distribution.
In each operation mode, even when the flow direction of the secondary-side refrigerant is switched, the secondary-side refrigerant flows through the indoor heat exchangers 108n only in one direction, and in either case, heat exchange with the indoor air is performed in the same manner, resulting in high heat exchange efficiency.
Use of the check valves 132a to 132f and 133a to 133f makes it unnecessary to perform operations other than operations of the four-way valve 106 and each valve, for switching of the overall cross-sectional area of the flow path in each of the intermediate heat exchangers 107aa and 107ba due to switching of operation modes. Consequently, in the vicinity of each of the intermediate heat exchangers 107aa and 107ba, problems such as leakage of refrigerant from valves can be prevented, thereby enabling safe operation.
The configuration of the intermediate heat exchangers 107aa and 107ba of the air-conditioning apparatus according to Embodiment 4 can be also applied to the air-conditioning apparatus according to Embodiment 3.
While the air-conditioning apparatus illustrated in FIG. 17 is configured so that the intermediate heat exchangers 107aa and 107ba each include two heat transfer units such as the heat transfer unit 1071a (1071b) and the heat transfer unit 1072a (1072b), this should not be construed restrictively. The intermediate heat exchangers 107aa and 107ba may each include three or more heat transfer units. As an example in this case, FIG. 20 illustrates a configuration in which the intermediate heat exchangers 107aa and 107ba each include three heat transfer units (heat transfer units 1071a to 1073a (1071b to 1073b)). In a case where the number of heat transfer units is an even number, the resulting configuration is the same as the configuration illustrated in FIG. 17. That is, letting 2n (n is a natural number not smaller than 1) represent the number of heat transfer units, the number of check valves belonging to the primary-side refrigerant circuit within each of the intermediate heat exchangers 107aa and 107ba (the check valves 132a to 132f in FIG. 17), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves 133a to 133f in FIG. 17) are each expressed as (2n+1). In a case where the number of heat transfer units is an odd number, the resulting configuration is the same as the configuration illustrated in FIG. 20. That is, letting (2n+1) represent the number of heat transfer units, the number of check valves belonging to the primary-side refrigerant circuit within each of the intermediate heat exchangers 107aa and 107ba (the check valves 132a, 132b, 132d, and 132e in FIG. 20), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves 133a, 133b, 133d, and 133e in FIG. 20) are each expressed as 2n. Therefore, the number of check valves to be installed relative to the number of heat transfer units can be reduced in the case where the number of heat transfer units is an odd number.
In a case where the number of heat transfer units in each of the intermediate heat exchangers 107aa and 107ba is an even number, the number of the above-mentioned heat transfer units in which the flow directions of both the primary-side refrigerant and the secondary-side refrigerant do not change equals 50% of the total number of heat transfer units. In a case where the number of heat transfer units in each of the intermediate heat exchangers 107aa and 107ba is an odd number, provided that the number is three, the number of heat transfer units in which both of the flow directions do not change equals 33.3% of the total number of heat transfer units and its ratio becomes the lowest. That is, in the case where the number of heat transfer units is an odd number, when the number of heat transfer units is larger than three, and as the number of heat transfer units becomes larger, the ratio of the number of heat transfer units in which both of the flow directions do not change to the total number of heat transfer units becomes larger.
The check valves inside each of the intermediate heat exchangers 107aa and 107ba in the air-conditioning apparatus illustrated in FIGS. 17 and 20 may be valves that can be opened and closed. In this case, for example, although an operation according to each operation mode becomes necessary, equipment cost can be reduced.
Embodiment 5
(Configuration of Air-Conditioning Apparatus)
FIG. 21 is a schematic diagram of an air-conditioning apparatus according to Embodiment 5 of the present invention.
In the configuration of the air-conditioning apparatus according to Embodiment 5 illustrated in FIG. 21, the check valves 110e to 110h are omitted from the air-conditioning apparatus according to Embodiment 3.
Advantageous Effects of Embodiment 5
When the check valves 110e to 110h are eliminated as in the configuration mentioned above, the flow of the secondary-side refrigerant flowing through the intermediate heat exchanger 107b becomes a certain direction. Accordingly, in a case where the intermediate heat exchanger 107b acts an evaporator, the primary-side refrigerant and the secondary-side refrigerant are not in counter low, resulting in poor efficiency. However, generally, the effect of counterflow is greater in the case where the intermediate heat exchanger 107b acts as a condenser than in the case where the intermediate heat exchanger 107b acts as an evaporator, and of the four operation modes, the intermediate heat exchanger 107b acts as an evaporator only in the cooling only operation mode. Therefore, a cost reduction that more than compensates for a decrease in performance can be expected.
Such a configuration in which the check valves 110e to 110h are omitted can be also applied to the air-conditioning apparatus according to Embodiment 2.
Embodiment 6
(Installation Example of Air-Conditioning Apparatus)
FIG. 22 illustrates an installation example of an air-conditioning apparatus according to Embodiment 6 of the present invention. The air-conditioning apparatus illustrated in FIG. 22 will be described by way of an example in which the air-conditioning apparatus is the air-conditioning apparatus according to each of Embodiments 2 to 5, and this air-conditioning apparatus is installed in a building or the like having a plurality of floors.
The outdoor unit A is installed in an outdoor space such as the rooftop of a building 100 illustrated in FIG. 22. In addition, in an indoor space that is an air-conditioning space such as a living space inside the building 100, the indoor unit C is installed at a position that allows a cooling operation and a heating operation to be performed for the air in the indoor space. As illustrated in FIG. 22, a plurality of indoor units C (three indoor units C (indoor units C1 to C3) in FIG. 22) are installed in the indoor space on each floor of the building 100. The relay unit B is installed in a non-air-conditioned space inside the building 100. The relay unit B is connected to the outdoor unit A and each of the indoor units C by refrigerant pipes. As illustrated in FIG. 22, the relay unit B is installed for each plurality of indoor units C installed on each floor. That is, heat transport between the outdoor unit A and the relay unit B is performed by the primary-side refrigerant, and heat transport between the indoor unit C and the relay unit B is performed by the secondary-side refrigerant.
The air-conditioning apparatus according to Embodiment 1 may be applied to the air-conditioning apparatus illustrated in FIG. 22. In this case, the outdoor unit A corresponds to the portion constituting the primary-side refrigerant circuit in the air-conditioning apparatus according to Embodiment 1 (excluding the intermediate heat exchanger 7), and the indoor unit C corresponds to a portion constituting the secondary-side refrigerant circuit in the air-conditioning apparatus which has the indoor heat exchanger 8 and the fan 8a. The relay unit B corresponds to the intermediate heat exchanger 7 in the air-conditioning apparatus according to Embodiment 1, and a portion constituting the secondary-side refrigerant circuit which has the pump 9 and the valves 10a to 10d. 
While the case where the outdoor unit A is installed on the rooftop of the building 100 as illustrated in FIG. 22 has been described, this should not be construed restrictively. For example, the outdoor unit A may be installed in the basement of the building 100, in the machine room on each floor, or the like.
While three indoor units C are installed on each floor of the building 100 as illustrated in FIG. 22, this should not be construed restrictively. For example, one or another number of indoor units C may be installed.
Advantageous Effects of Embodiment 6
According to the configuration mentioned above, in the air-conditioning apparatus according to Embodiment 6, the secondary-side refrigerant such as water flows through the refrigerant pipe connected to the indoor unit C installed in an indoor space such as a living space. Therefore, leakage of the primary-side refrigerant to the indoor space can be prevented.
The outdoor unit A and the indoor unit C are installed in places other than an indoor space such as a living space, which allows for easy maintenance of these units.
REFERENCE SIGNS LIST
3 compressor, 4 outdoor heat exchanger, 4a fan, 5 expansion mechanism, 6 four-way valve, 7 intermediate heat exchanger, 7a, 7b heat transfer unit, 8 indoor heat exchanger, 8a fan, 9 pump, 10a, 10b, 10c, 10d valve, 11a to 11c, 12a to 12c check valve, 20a to 20d, 30a to 30d, 31a to 31d branch part, 100 building, 103 compressor, 104 outdoor heat exchanger, 105a, 105b expansion mechanism, 106 four-way valve, 107a, 107b, 107aa, 107ba intermediate heat exchanger, 109a, 109b pump, 110a to 110h, 111a to 111f valve, 113a to 113d, 132a to 132f, 133a to 133f check valve, 141 flow switching unit, 142 bypass pipe, 1071a, 1071b, 1072a, 1072b heat transfer unit, 1081 to 1083 indoor heat exchanger, 1121a to 1121d, 1122a to 1122d, 1123a to 1123d valve, A outdoor unit, B relay unit, C1 to C3 indoor unit.

## Claims

1. An air-conditioning apparatus comprising:
a primary-side refrigerant circuit in which a compressor, first flow switching means, a heat source-side heat exchanger, an expansion mechanism, and an intermediate heat exchanger are connected by refrigerant pipes, and through which a primary-side refrigerant flows; and
a secondary-side refrigerant circuit in which a pump, a use-side heat exchanger, second flow switching means, and the intermediate heat exchanger are connected by refrigerant pipes, and through which a secondary-side refrigerant different from the primary-side refrigerant flows,
wherein the intermediate heat exchanger has a plurality of heat transfer units and third flow switching means,
the heat transfer units perform heat exchange so that the primary-side refrigerant absorbs heat from the secondary-side refrigerant in a cooling operation, and that the primary-side refrigerant radiates heat to the secondary-side refrigerant in a heating operation,
the first flow switching means switches a refrigerant flow path so that the primary-side refrigerant discharged from the compressor flows to the heat source-side heat exchanger in the cooling operation, and switches a refrigerant flow path so that the primary-side refrigerant discharged from the compressor flows to the intermediate heat exchanger in the heating operation,
the second flow switching means switches a flow direction of the secondary-side refrigerant flowing into the intermediate heat exchanger,
the third flow switching means switches a refrigerant flow path so that in the intermediate heat exchanger, a cross-sectional area of a refrigerant flow path through which the primary-side refrigerant flows becomes larger in the cooling operation than that of in the heating operation,
the third flow switching means switches a refrigerant flow path in the cooling operation so that the primary-side refrigerant and the secondary-side refrigerant flow through the heat transfer units in parallel, and
the third flow switching means switches a refrigerant flow path in the heating operation so that the primary-side refrigerant and the secondary-side refrigerant flow through the heat transfer units in series.

2. The air-conditioning apparatus of claim 1, wherein:
the third flow switching means is configured by a check valve; and
the cross-sectional area of the flow path of the primary-side refrigerant is switched by the check valve in accordance with respective inflow directions of the primary-side refrigerant and the secondary-side refrigerant that flow into the intermediate heat exchanger.

3. The air-conditioning apparatus of claim 1, further comprising:
a plurality of the intermediate heat exchangers;
a plurality of the use-side heat exchangers; and
fourth flow switching means provided to the secondary-side refrigerant circuit; wherein
the fourth flow switching means switches a refrigerant flow path to direct the secondary-side refrigerant flown out from any one of the plurality of intermediate heat exchangers toward each of the plurality of use-side heat exchangers, so that one of a cooling operation and a heating operation is performed in a selectable manner by each of the use-side heat exchangers.

4. The air-conditioning apparatus of claim 3, comprising:
an outdoor unit including the compressor, the first flow switching means, the heat source-side heat exchanger, and the expansion mechanism;
an indoor unit including at least one of the plurality of use-side heat exchangers; and
a relay unit including the intermediate heat exchangers, the pump, the second flow switching means, the third flow switching means, and the fourth flow switching means,
wherein the indoor unit is installed in an air-conditioned space,
the outdoor unit and the relay unit is installed in a non-air-conditioned space,
the primary-side refrigerant flows between the outdoor unit and the relay unit, and
the secondary-side refrigerant flows between the indoor unit and the relay unit.

5. The air-conditioning apparatus of claim 1, wherein the intermediate heat exchanger has at least one of the heat transfer units in which respective flows of the primary-side refrigerant and the secondary-side refrigerant flow in a certain direction in both of a case where the intermediate heat exchanger functions as an evaporator and a case where the intermediate heat exchanger functions as a radiator.

6. The air-conditioning apparatus of claim 1, wherein the primary-side refrigerant is a zeotropic refrigerant mixture.