Air-conditioning apparatus including intermediate heat exchangers

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.

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 compressor11, an outdoor heat exchanger13, a first refrigerant branch part21connected to the compressor11, a second refrigerant branch part22and a third refrigerant branch part23connected to the outdoor heat exchanger13, a first refrigerant flow control device24provided between a branch pipe40and the second refrigerant branch part22, intermediate heat exchangers25nwhose one side is connected to the first refrigerant branch part21and the third refrigerant branch part23via three-way valves26nand whose other side is connected to the second refrigerant branch part22, and second refrigerant flow control devices27nprovided between each of the intermediate heat exchangers25nand the second refrigerant branch part22, and a use-side refrigerant circuit Bn having indoor heat exchangers31nconnected to the intermediate heat exchangers25n, 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

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.

DESCRIPTION OF EMBODIMENTS

FIG. 1is 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. 2is a schematic diagram of the air-conditioning apparatus, illustrating the flow of refrigerant in the heating operation. Of the arrows inFIGS. 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 compressor3, an outdoor heat exchanger4, an expansion mechanism5, a four-way valve6, and an intermediate heat exchanger7. The primary-side refrigerant circuit is configured by connecting the compressor3, the four-way valve6, the outdoor heat exchanger4, the expansion mechanism5, the intermediate heat exchanger7, the four-way valve6, and the compressor3in this order by refrigerant pipes.

The secondary-side refrigerant circuit includes at least the intermediate heat exchanger7, an indoor heat exchanger8, a pump9, and valves10ato10d. The secondary-side refrigerant circuit is configured by connecting the pump9, the indoor heat exchanger8, the valve10b, the intermediate heat exchanger7, the valve10a, and the pump9in this order by refrigerant pipes. In the secondary-side refrigerant circuit, a branch part30aon the refrigerant pipe connecting the indoor heat exchanger8and the valve10bis connected to a branch part30bon the refrigerant pipe connecting the valve10aand the intermediate heat exchanger7, by a refrigerant pipe via the valve10d. Also, in the secondary-side refrigerant circuit, a branch part30con the refrigerant pipe connecting the intermediate heat exchanger7and the valve10bis connected to a branch part30don the refrigerant pipe connecting the pump9and the valve10a, by a refrigerant pipe via the valve10c.

The intermediate heat exchanger7includes at least heat transfer units7aand7b, check valves11ato11c, and check valves12ato12c. As will be described later, each of the heat transfer units7aand7bexchanges 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 unit7b, one refrigerant outlet/inlet of the refrigerant flow path through which the primary-side refrigerant flows is connected to the four-way valve6by a refrigerant pipe. The other refrigerant outlet/inlet is connected to the expansion mechanism5by a refrigerant pipe via the check valve11b.

In the heat transfer unit7a, one refrigerant outlet/inlet of the refrigerant flow path through which the primary-side refrigerant flows is connected to a branch part20bon the refrigerant pipe connecting the heat transfer unit7band the check valve11b, by a refrigerant pipe. The other refrigerant outlet/inlet is connected to a branch part20don the refrigerant pipe connecting the heat transfer unit7band the four-way valve6, by a refrigerant pipe via the check valve11a.

Further, a branch part20con the refrigerant pipe connecting the heat transfer unit7aand the check valve11ais connected to a branch part20aon the refrigerant pipe connecting the expansion mechanism5and the check valve11b, by a refrigerant pipe via the check valve11c.

In the heat transfer unit7b, one refrigerant outlet/inlet of the refrigerant flow path through which the secondary-side refrigerant flows is connected to the valve10aby a refrigerant pipe. The other refrigerant outlet/inlet is connected to the valve10bby a refrigerant pipe via the check valve12b.

In the heat transfer unit7a, one refrigerant outlet/inlet of the refrigerant flow path through which the secondary-side refrigerant flows is connected to a branch part31con the refrigerant pipe connecting the heat transfer unit7band the check valve12b, by a refrigerant pipe. The other refrigerant outlet/inlet is connected to a branch part31aon the refrigerant pipe connecting the heat transfer unit7band the valve10a, by a refrigerant pipe via the check valve12a.

Further, a branch part31don the refrigerant pipe connecting the check valve12band the valve10bis connected to a branch part31bon the refrigerant pipe connecting the heat transfer unit7aand the check valve12a, by a refrigerant pipe via the check valve12c.

The compressor3sucks 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 compressor3may be configured by, for example, an inverter compressor or the like whose capacity can be controlled.

The outdoor heat exchanger4functions as a radiator in the cooling operation, and functions as an evaporator in the heating operation. The outdoor heat exchanger4exchanges heat between the outdoor air supplied from a fan4aand the primary-side refrigerant.

The expansion mechanism5expands and reduces the pressure of the primary-side refrigerant that has flowed out of the outdoor heat exchanger4in the cooling operation, and the primary-side refrigerant that has flowed out of the intermediate heat exchanger7in the heating operation.

The four-way valve6has the function of switching the refrigerant flow path. Specifically, in the cooling operation, the four-way valve6switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor3flows to the outdoor heat exchanger4, and that the primary-side refrigerant that has flowed out of the intermediate heat exchanger7flows to the compressor3. In the heating operation, the four-way valve6switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor3flows to the intermediate heat exchanger7, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger4flows to the compressor3.

The heat transfer units7aand7bare 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 units7aand7bincludes 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 units7aand7bcauses 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 units7aand7b, by taking phase change of the primary-side refrigerant into consideration, each of the heat transfer units7aand7bis preferably installed in such an orientation that the primary-side refrigerant flows into each of the heat transfer units7aand7bfrom the lower side when the primary-side refrigerant absorbs heat, and that the primary-side refrigerant flows into each of the heat transfer units7aand7bfrom the upper side when the primary-side refrigerant radiates heat.

The indoor heat exchanger8functions as a cooler in the cooling operation, and functions as a radiator in the heating operation. The indoor heat exchanger8exchanges heat between the indoor air supplied from a fan8aand the secondary-side refrigerant.

The pump9causes the secondary-side refrigerant to circuit within the secondary-side refrigerant circuit as the pump9is driven.

The valves10ato10dare 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 valves10ato10dhave the function of switching the outlet/inlet through which the secondary-side refrigerant that has flowed out of the indoor heat exchanger8flows into the intermediate heat exchanger7.

The check valves11ato11ccause the primary-side refrigerant to flow in only one direction. Specifically, the check valve11acauses the primary-side refrigerant to flow only in a direction from the branch part20ctoward the branch part20d. The check valve11bcauses the primary-side refrigerant to flow only in a direction from the branch part20atoward the branch part20b. The check valve11ccauses the primary-side refrigerant to flow only in a direction from the branch part20ctoward the branch part20a.

The check valves12ato12ccause the secondary-side refrigerant to flow in only one direction. Specifically, the check valve12acauses the secondary-side refrigerant to flow only in a direction from the branch part31atoward the branch part31b. The check valve12bcauses the secondary-side refrigerant to flow only in a direction from the branch part31ctoward the branch part31d. The check valve12ccauses the secondary-side refrigerant to flow only in a direction from the branch part31dtoward the branch part31b.

While the branch parts20ato20d,30ato30d, and31ato31dare provided on refrigerant pipes as illustrated inFIGS. 1 and 2for 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 valve11band the check valve11care both connected to the expansion mechanism5via the branch part20a, the check valve11band the check valve11cmay be connected to the expansion mechanism5directly without passing through a clear branch part20a. This configuration does not alter the function of the refrigerant circuit at all. Furthermore, for example, while the branch part30band the branch part31aare configured as separate branch parts for the convenience of explanation of the refrigerant circuit, the branch part30band the branch part31amay 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 inFIGS. 1 and 2remains 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 exchanger4and the indoor heat exchanger8correspond to the “heat source-side heat exchanger” and the “use-side heat exchanger”, respectively, in the invention according to claim9of the present invention. The four-way valve6and the valves10ato10dcorrespond to the “first flow switching means” and the “second flow switching means”, respectively, in the invention according to claim9of the present invention. The check valves11ato11cand the check valves12ato12ceach correspond to the “third flow switching means” according to claim9of the present invention.

Next, the cooling operation of an air-conditioning apparatus according to Embodiment 1 will be described with reference toFIG. 1.

In the primary-side refrigerant circuit, the four-way valve6is switched in advance so that the primary-side refrigerant discharged from the compressor3flows to the outdoor heat exchanger4, and that the primary-side refrigerant that has flowed out of the intermediate heat exchanger7flows to the compressor3. In the secondary-side refrigerant circuit, the valve10aand the valve10bare closed, and the valve10cand the valve10dare 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 compressor3, and discharged in a high-temperature, high-pressure state. The high-temperature, high-pressure primary-side refrigerant discharged from the compressor3flows into the outdoor heat exchanger4via the four-way valve6. The primary-side refrigerant that has flowed into the outdoor heat exchanger4radiates heat to the outdoor air sent by the fan4a, 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 exchanger4flows into the expansion mechanism5, 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 mechanism5flows into the intermediate heat exchanger7.

After the primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger7passes through the branch part20aand the check valve11b, the primary-side refrigerant divides into branch flows at the branch part20b, and the branch flows flow into the heat transfer unit7aand the heat transfer unit7bin parallel, respectively. At this time, at the branch part20a, the primary-side refrigerant does not flow in a direction from the branch part20atoward the branch part20cowing to the action of the check valve11c. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the heat transfer unit7aand the heat transfer unit7babsorb 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 unit7apasses though the branch part20cand the check valve11a, merges at the branch part20dwith the primary-side refrigerant in a gas state that has flowed out of the heat transfer unit7b, and the merged primary-side refrigerant flows out of the intermediate heat exchanger7.

The primary-side refrigerant in a gas state that has flowed out of the intermediate heat exchanger7is sucked into the compressor3via the four-way valve6, 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 pump9flows into the indoor heat exchanger8. The secondary-side refrigerant that has flowed into the indoor heat exchanger8cools the indoor air sent by the fan8a, and flows into the intermediate heat exchanger7via the branch part30a, the valve10d, and the branch part30b. At this time, at the branch part30a, the secondary-side refrigerant does not flow in a direction from the branch part30atoward the branch part30cbecause the valve10bis closed. Also, at the branch part30b, the secondary-side refrigerant does not flow in a direction from the branch part30btoward the branch part30dbecause the valve10ais closed.

The secondary-side refrigerant that has flowed into the intermediate heat exchanger7divides into branch flows at the branch part31a, one of which flows into the heat transfer unit7b, and the other flows into the heat transfer unit7avia the check valve12aand the branch unit31b. At this time, at the branch part31b, the secondary-side refrigerant does not flow in a direction from the branch part31btoward the branch part31dowing to the action of the check valve12c. The flows of the secondary-side refrigerant that have flowed into the heat transfer unit7aand the heat transfer unit7bin 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 unit7aand the heat transfer unit7b, respectively. The respective flows of the secondary-side refrigerant that have flowed out of the heat transfer unit7aand the heat transfer unit7bmerge at the branch part31c, and the merged secondary-side refrigerant flows out of the intermediate heat exchanger7via the check valve12band the branch part31d.

The secondary-side refrigerant that has flowed out of the intermediate heat exchanger7flows into the pump9via the branch part30c, the valve10c, and the branch part30d, and is sent out again. At this time, at the branch part30c, the secondary-side refrigerant does not flow in a direction from the branch part30ctoward the branch part30abecause the valve10bis closed. Also, at the branch part30d, the secondary-side refrigerant does not flow in a direction from the branch part30dtoward the branch part30bbecause the valve10ais closed.

Next, the heating operation in the air-conditioning apparatus according to Embodiment 1 will be described with reference toFIG. 2.

In the primary-side refrigerant circuit, the four-way valve6is switched in advance so that the primary-side refrigerant discharged from the compressor3flows to the intermediate heat exchanger7, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger4flows to the compressor3. In the secondary-side refrigerant circuit, the valve10aand the valve10bare open, and the valve10cand the valve10dare 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 compressor3, and discharged in a high-temperature, high-pressure state. The high-temperature, high-pressure primary-side refrigerant discharged from the compressor3flows into the intermediate heat exchanger7via the four-way valve6.

The primary-side refrigerant that has flowed into the intermediate heat exchanger7flows into the heat transfer unit7bvia the branch part20d, and radiates heat to the secondary-side refrigerant flowing in counterflow to the primary-side refrigerant. At this time, at the branch part20d, the primary-side refrigerant does not flow in a direction from the branch part20dtoward the branch part20cowing to the action of the check valve11a. The primary-side refrigerant that has flowed out of the heat transfer unit7bflows into the heat transfer unit7avia the branch part20b. In the heat transfer unit7aas 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 part20b, the primary-side refrigerant does not flow in a direction from the branch part20btoward the branch part20aowing to the action of the check valve11b. In this way, unlike the cooling operation described above, the primary-side refrigerant flows through the heat transfer unit7band the heat transfer unit7ain 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 unit7aflows out of the intermediate heat exchanger7via the branch part20c, the check valve11c, and the branch part20a.

The primary-side refrigerant in a two-phase gas-liquid state or liquid state that has flowed out of the intermediate heat exchanger7flows into the expansion mechanism5, 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 mechanism5flows into the outdoor heat exchanger4. The primary-side refrigerant that has flowed into the outdoor heat exchanger4absorbs heat from the outdoor air sent by the fan4a, 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 exchanger4is sucked into the compressor3via the four-way valve6, 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 pump9flows into the indoor heat exchanger8. The secondary-side refrigerant that has flowed into the indoor heat exchanger8heats the indoor air sent by the fan8a, and flows into the intermediate heat exchanger7via the branch part30a, the valve10b, and the branch part30c. At this time, at the branch part30a, the secondary-side refrigerant does not flow in a direction from the branch part30atoward the branch part30bbecause the valve10dis closed. Also, at the branch part30c, the secondary-side refrigerant does not flow in a direction from the branch part30ctoward the branch part30dbecause the valve10cis closed.

The secondary-side refrigerant that has flowed into the intermediate heat exchanger7flows into the heat transfer unit7avia the branch part31d, the check valve12c, and the branch part31b, and is heated by the primary-side refrigerant flowing in counterflow to the secondary-side refrigerant. At this time, at the branch part31d, the secondary-side refrigerant does not flow in a direction from the branch part31dtoward the branch part31cowing to the action of the check valve12b. Also, at the branch part31b, the secondary-side refrigerant does not flow in a direction from the branch part31btoward the branch part31aowing to the action of the check valve12a. The secondary-side refrigerant that has flowed out of the heat transfer unit7aflows into the heat transfer unit7bvia the branch part31c, 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 unit7aand the heat transfer unit7bin series. The secondary-side refrigerant that has flowed out of the heat transfer unit7bflows out of the intermediate heat exchanger7via the branch part31a.

The secondary-side refrigerant that has flowed out of the intermediate heat exchanger7flows into the pump9via the branch part30b, the valve10a, and the branch part30d, and is sent out again. At this time, at the branch part30b, the secondary-side refrigerant does not flow in a direction from the branch part30btoward the branch part30abecause the valve10dis closed. Also, at the branch part30d, the secondary-side refrigerant does not flow in a direction from the branch part30dtoward the branch part30cbecause the valve10cis closed.

(Heat Exchange Operation in Intermediate Heat Exchanger7)

FIG. 3illustrates the temperature relationship between the primary-side refrigerant and the secondary-side refrigerant in the intermediate heat exchanger7in 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. 4illustrates the temperature relationship between the primary-side refrigerant and the secondary-side refrigerant in the intermediate heat exchanger7in 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 inFIG. 3, the primary-side refrigerant at a high discharge pressure as illustrated inFIG. 4has high discharge temperature, and does not become a two-phase state in the intermediate heat exchanger7, 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 exchanger7through which the secondary-side refrigerant flows, or for the outlet-inlet temperature difference in the indoor heat exchanger8, thereby making it possible to reduce the input to the pump9.

Advantageous Effects of Embodiment 1

According to the configuration and the operation mentioned above, in the intermediate heat exchanger7, 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 unit7aand the heat transfer unit7bin 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 unit7aand the heat transfer unit7bin 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 exchanger7, and flows through the heat transfer unit7aand the heat transfer unit7bin 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 compressor3. In the heating operation, the primary-side refrigerant performs a heat radiation operation in the intermediate heat exchanger7, and flows through the heat transfer unit7aand the heat transfer unit7bin 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 inFIGS. 1 and 2, the heat transfer unit7aexists 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 exchanger7changes 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 exchanger8only 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 exchanger7can 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 pump9.

In the air-conditioning apparatus illustrated inFIGS. 1 and 2, use of the check valves11ato11cand12ato12cmakes it unnecessary to perform operations other than operations of the four-way valve6and valves10ato10d, for switching of the overall cross-sectional area of the flow path in the intermediate heat exchanger7due to switching of cooling and the heating operations. Consequently, in the vicinity of the intermediate heat exchanger7, problems such as leakage of refrigerant from valves can be prevented, thereby enabling safe operation.

While the air-conditioning apparatus illustrated inFIGS. 1 and 2is configured so that the intermediate heat exchanger7includes two heat transfer units such as the heat transfer unit7aand the heat transfer unit7b, this should not be construed restrictively. The intermediate heat exchanger7may include three or more heat transfer units. As an example in this case,FIG. 5illustrates the flow of refrigerant in the cooling operation in a case where the intermediate heat exchanger7includes three heat transfer units (heat transfer units7ato7c), andFIG. 6illustrates 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 inFIGS. 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 exchanger7(the check valves11ato11cinFIGS. 1 and 2), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves12ato12cinFIGS. 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 inFIGS. 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 exchanger7(the check valves11aand11binFIGS. 5 and 6), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves12aand12binFIGS. 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 exchanger7is 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 exchanger7is 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 valves11ato11cand12ato12cwithin the intermediate heat exchanger7in the air-conditioning apparatus illustrated inFIGS. 1, 2, 5, and 6may 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 inFIGS. 1 and 2, in the cooling operation, the valves corresponding to the check valves11a,11b,12a, and12bmay be opened, and the valves corresponding to the check valves11cand12cmay 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 pump9may 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 exchanger7, or the outlet-inlet temperature difference of the secondary-side refrigerant in the indoor heat exchanger8can 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 valves10ato10dused to switch the direction of the secondary-side refrigerant flowing into the intermediate heat exchanger7, 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 exchanger8is illustrated as an indoor unit as inFIG. 1or the like, this should not be construed restrictively. The number of indoor units may be two or more.

FIG. 7is 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 inFIG. 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 compressor103, an outdoor heat exchanger104, expansion mechanisms105aand105b, a four-way valve106, intermediate heat exchangers107aand107b, and valves111ato111e. Roughly speaking, the primary-side refrigerant circuit is configured by connecting the compressor103, the four-way valve106, the outdoor heat exchanger104, the expansion mechanisms105aand105b, the intermediate heat exchangers107aand107b, the four-way valve106, and the compressor103in this order by refrigerant pipes.

The secondary-side refrigerant circuit includes at least the intermediate heat exchangers107aand107b, indoor heat exchangers108n(n is a natural number not smaller than 2, and represents the number of indoor heat exchangers. The same applies hereinafter.FIG. 7illustrates a case where n=3.), pumps109aand109b, and valves110ato110hand112nato112nd(n in this case is the same as mentioned above). Roughly speaking, the secondary-side refrigerant circuit is configured by connecting the pumps109aand109b, the indoor heat exchangers108n, the intermediate heat exchangers107aand107b, and the pumps109aand109bin 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 exchangers107aand107b.

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 inFIG. 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 C1to 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 C1to 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 compressor103, the outdoor heat exchanger104, and the four-way valve106.

The compressor103sucks 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 compressor103may be configured by, for example, an inverter compressor or the like whose capacity can be controlled.

The outdoor heat exchanger104functions as a radiator in the cooling operation, and functions as an evaporator in the heating operation. The outdoor heat exchanger104exchanges heat between the outdoor air supplied from a fan and the primary-side refrigerant.

The four-way valve106switches 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 valve106switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor103flows to the outdoor heat exchanger104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor103. In the heating operation, the four-way valve106switches the refrigerant flow path so that the primary-side refrigerant discharged from the compressor103flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger104flows to the compressor103.

(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 exchangers107aand107b, the expansion mechanisms105aand105b, the pumps109aand109b, and the valves110ato110h,111ato111e, and112nato112nd.

The intermediate heat exchangers107aand107bare 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 exchangers107aand107bincludes 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 exchangers107aand107bfunctions as a radiator or an evaporator to exchange heat between the primary-side refrigerant and the secondary-side refrigerant. Of these, the intermediate heat exchanger107ais provided between the expansion mechanism105aand the valve111cin the primary-side refrigerant circuit, and is provided between the valve110aand the valve110bin the secondary-side refrigerant circuit. The intermediate heat exchanger107bis provided between the expansion mechanism105band the valve111din the primary-side refrigerant circuit, and is provided between the valve110eand the valve110fin the secondary-side refrigerant circuit.

In a case where a plate heat exchanger is used as each of the intermediate heat exchangers107aand107b, by taking phase change of the primary-side refrigerant into consideration, each of the intermediate heat exchangers107aand107bis preferably installed in such an orientation that the primary-side refrigerant flows into each of the intermediate heat exchangers107aand107bfrom the lower side when the primary-side refrigerant absorbs heat, and that the primary-side refrigerant flows into each of the intermediate heat exchangers107aand107bfrom the upper side when the primary-side refrigerant radiates heat.

The expansion mechanisms105aand105bhave 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 mechanism105ais provided between the intermediate heat exchanger107aand the valve111e, and the expansion mechanism105bis provided between the intermediate heat exchanger107band the valve111e. The expansion mechanisms105aand105bmay 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 valves111ato111eare each configured by a two-way valve or the like. The valves111ato111eeach 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 valve111ais provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger107aand the valve111c, and the refrigerant pipe connecting the valve111band the outdoor heat exchanger104(or the valve111e). The valve111bis provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger107band the valve111d, and the refrigerant pipe connecting the valve111aand the outdoor heat exchanger104(or the valve111e). The valve111cis provided in the refrigerant pipe connecting the four-way valve106and the intermediate heat exchanger107a. The valve111dis provided in the refrigerant pipe connecting the four-way valve106and the intermediate heat exchanger107b. The valve111eis provided in the refrigerant pipe connecting the outdoor heat exchanger104and the expansion mechanism105a(or the expansion mechanism105b).

Each of the pumps109aand109bpumps and circulates the secondary-side refrigerant within the secondary-side refrigerant circuit. The pumps109aand109bmay 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 pump109adivides into branches, which are respectively connected to the valves1121a,1122a, and1123a. The refrigerant pipe connected to the suction side of the pump109ais connected to the valve110a. The refrigerant pipe connected to the discharge side of the pump109bdivides into branches, which are respectively connected to the valves1121b,1122b, and1123b. The refrigerant pipe connected to the suction side of the pump109bis connected to the valve110e.

The valves110ato110hare each configured by a two-way valve or the like. In the secondary-side refrigerant circuit, the valves110ato110heach open and close a refrigerant pipe, and switch the flow path of the secondary-side refrigerant sent to each of the pumps109aand109b. The valve110ais provided in the refrigerant pipe connecting the pump109aand the intermediate heat exchanger107a. The refrigerant pipe connected to one side of the valve110bis connected to the intermediate heat exchanger107a, and the refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves1121c,1122c, and1123c. The valve110cis provided in the refrigerant pipe that connects between the refrigerant pipe connecting the pump109aand the valve110a, and the refrigerant pipe connecting the intermediate heat exchanger107aand the valve110b. The valve110dis provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger107aand the valve110a, and the refrigerant pipe connecting the valve110band each of the valves1121c,1122c, and1123c. The valve110eis provided in the refrigerant pipe connecting the pump109band the intermediate heat exchanger107b. The refrigerant pipe connected to one side of the valve110fis connected to the intermediate heat exchanger107b, and the refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves1121d,1122d, and1123d. The valve110gis provided in the refrigerant pipe that connects between the refrigerant pipe connecting the pump109band the valve110e, and the refrigerant pipe connecting the intermediate heat exchanger107band the valve110f. The valve110his provided in the refrigerant pipe that connects between the refrigerant pipe connecting the intermediate heat exchanger107band the valve110e, and the refrigerant pipe connecting the valve110fand each of the valves1121d,1122d, and1123d.

The valves112nato112nd(n is a natural number not smaller than 2) switch the flow path of the secondary-side refrigerant sent to the indoor heat exchangers108nof the indoor units C1to C3. By adjusting the opening degree (opening area) of the valves112nato112nd, the flow rate of the secondary-side refrigerant flowing to the indoor heat exchangers108ncan be controlled.

(Configuration of Indoor Unit C)

The indoor units C1to C3include indoor heat exchangers1081,1082, and1083, respectively. The indoor units C1to C3perform air conditioning by performing cooling or heating for the indoor space in which the indoor units C1to C3are provided.

The indoor heat exchangers108n(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 exchangers108nexchange 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 exchanger1081divides into branches, which are respectively connected to the valves1121aand1121b. The refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves1121cand1121d. The refrigerant pipe connected to one side of the indoor heat exchanger1082divides into branches, which are respectively connected to the valves1122aand1122b. The refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves1122cand1122d. The refrigerant pipe connected to one side of the indoor heat exchanger1083divides into branches, which are respectively connected to the valves1123aand1123b. The refrigerant pipe connected to the other side divides into branches, which are respectively connected to the valves1123cand1123d.

While the number of indoor units C connected is three inFIG. 7, this should not be construed restrictively. The number of indoor units C connected may be other than three.

The outdoor heat exchanger104and the indoor heat exchangers108ncorrespond to the “heat source-side heat exchanger” and the “use-side heat exchangers”, respectively, in the invention according to claim1of the present invention. The four-way valve106, the valves111ato111e, the valves110ato110h, and the valves112nato112ndcorrespond 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 claim1of 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.

FIG. 8is 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. InFIG. 8, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. InFIG. 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 toFIGS. 9 to 11. Hereinafter, the cooling only operation mode will be described with reference toFIG. 8.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the outdoor heat exchanger104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor103, and the valves111aand111bare closed and the valves111cto111eare open. In the secondary-side refrigerant circuit, the valves110a,110b,110e, and110fare closed, the valves110c,110d,110g, and110hare open, and the valves112nato112ndare 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger104via the four-way valve106, 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 exchanger104flows 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 valve111e, the primary-side refrigerant divides into branch flows. The branch flows flow into the expansion mechanisms105aand105b, 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 exchangers107aand107bin parallel, respectively. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the intermediate heat exchangers107aand107babsorb 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 exchangers107aand107bmerge after passing through the valves111cand111d, 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 compressor103via the four-way valve106, 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 pump109adivides into branch flows. The branch flows flow out of the relay unit B after passing through the valves1121a,1122a, and1123a, and flow into the indoor heat exchanger1081of the indoor unit C1, the indoor heat exchanger1082of the indoor unit C2, and the indoor heat exchanger1083of the indoor unit C3, respectively. The secondary-side refrigerant at low temperature sent out by driving of the pump109bdivides into branch flows. The branch flows flow out of the relay unit B after passing through the valves1121b,1122b, and1123b, and flow into the indoor heat exchanger1081of the indoor unit C1, the indoor heat exchanger1082of the indoor unit C2, and the indoor heat exchanger1083of the indoor unit C3, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers1081,1082, and1083cool 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 valve1121cafter flowing out of the indoor heat exchanger1081, 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 valve1122cafter flowing out of the indoor heat exchanger1082, 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 valve1123cafter flowing out of the indoor heat exchanger1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger107avia the valve110d. Also, the other flow of the secondary-side refrigerant which has passed through the valve1121dafter flowing out of the indoor heat exchanger1081, flowing into the relay unit B, and dividing into branch flows, the other flow of the secondary-side refrigerant which has passed through the valve1122dafter flowing out of the indoor heat exchanger1082, 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 valve1123dafter flowing out of the indoor heat exchanger1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger107bvia the valve110h. The flows of the secondary-side refrigerant that have flowed into the intermediate heat exchangers107aand107bare 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 exchangers107aand107b, respectively. The flows of the secondary-side refrigerant that have flowed out of the intermediate heat exchangers107aand107bflow into the pumps109aand109bvia the valves110cand110g, respectively, and are sent out again.

FIG. 9is 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 toFIG. 9.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger104flows to the compressor103, and the valves111aand111bare closed and the valves111cto111eare open. In the secondary-side refrigerant circuit, the valves110a,110b,110e, and110fare open, the valves110c,110d,110g, and110hare closed, and the valves112nato112ndare 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve106, 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 exchangers107aand107bin parallel via the valves111cand111d, respectively. The flows of the primary-side refrigerant in a high-temperature, high-pressure state that have flowed into the intermediate heat exchangers107aand107bradiate 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 exchangers107aand107bflow into the expansion mechanisms105aand105b, 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 valve111e, 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 exchanger104, 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 compressor103via the four-way valve106, 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 pump109adivides into branch flows. The branch flows flow out of the relay unit B after passing through the valves1121a,1122a, and1123a, and flow into the indoor heat exchanger1081of the indoor unit C1, the indoor heat exchanger1082of the indoor unit C2, and the indoor heat exchanger1083of the indoor unit C3, respectively. The secondary-side refrigerant at high temperature sent out by driving of the pump109bdivides into branch flows. The branch flows flow out of the relay unit B after passing through the valves1121b,1122b, and1123b, and flow into the indoor heat exchanger1081of the indoor unit C1, the indoor heat exchanger1082of the indoor unit C2, and the indoor heat exchanger1083of the indoor unit C3, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers1081,1082, and1083heat 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 valve1121cafter flowing out of the indoor heat exchanger1081, 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 valve1122cafter flowing out of the indoor heat exchanger1082, 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 valve1123cafter flowing out of the indoor heat exchanger1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger107avia the valve110b. Also, the other flow of the secondary-side refrigerant which has passed through the valve1121dafter flowing out of the indoor heat exchanger1081, flowing into the relay unit B, and dividing into branch flows, the other flow of the secondary-side refrigerant which has passed through the valve1122dafter flowing out of the indoor heat exchanger1082, 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 valve1123dafter flowing out of the indoor heat exchanger1083, flowing into the relay unit B, and dividing into branch flows, merge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger107bvia the valve110f. The flows of the secondary-side refrigerant that have flowed into the intermediate heat exchangers107aand107bare 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 exchangers107aand107b, respectively. The flows of the secondary-side refrigerant that have flowed out of the intermediate heat exchangers107aand107bflow into the pumps109aand109bvia the valves110aand110e, respectively, and are sent out again.

FIG. 10is 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 toFIG. 10.

InFIG. 10, it is assumed that the indoor unit C1performs a heating operation, and the indoor units C2and C3perform a refrigerating operation.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the outdoor heat exchanger104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor103, and the valves111a,111d, and111eare closed and the valves111band111care open. In the secondary-side refrigerant circuit, the valves110a,110b,110g, and110hare closed, and the valves110c,110d,110e, and110fare open. Further, the valves1121a,1121c,1122b,1122d,1123b, and1123dare closed, and the valves1121b,1121d,1122a,1122c,1123a, and1123care 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger104via the four-way valve106, 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 exchanger104flows 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 exchanger107bvia the valve111b, 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 exchanger107bpasses through the expansion mechanism105band the expansion mechanism105a, 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 exchanger107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger107aabsorbs 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 exchanger107aflows out of the relay unit B via the valve111c, 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 compressor103via the four-way valve106, 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 pump109adivides into branch flows. The branch flows flow out of the relay unit B after passing through the valves1122aand1123a, and flow into the indoor heat exchanger1082of the indoor unit C2, and the indoor heat exchanger1083of the indoor unit C3, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers1082and1083cool the indoor air and turn into a high-temperature state, flow out of the indoor units C2and C3, respectively, and flow into the relay unit B.

The secondary-side refrigerant that has flowed out of the indoor heat exchanger1082, flowed into the relay unit B, and passed through the valve1122c, and the secondary-side refrigerant that has flowed out of the indoor heat exchanger1083, flowed into the relay unit B, and passed through the valve1123cmerge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger107avia the valve110d. The secondary-side refrigerant that has flowed into the intermediate heat exchanger107ais 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 exchanger107a. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger107aflows into the pump109avia the valve110c, and is sent out again.

The secondary-side refrigerant at high temperature sent out by driving of the pump109bflows out of the relay unit B after passing through the valve1121b, and flows into the indoor heat exchanger1081of the indoor unit C1. The secondary-side refrigerant that has flowed into the indoor heat exchanger1081heats 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 exchanger1081, flowed into the relay unit B, and passed through the valve1121dflows into the intermediate heat exchanger107bvia the valve110f. The secondary-side refrigerant that has flowed into the intermediate heat exchanger107bis 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 exchanger107b. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger107bflows into the pump109bvia the valve110e, and is sent out again.

FIG. 11is 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 toFIG. 11. InFIG. 11, it is assumed that the indoor units C1and C2perform a heating operation, and the indoor unit C3performs a refrigerating operation.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger104flows to the compressor103, and the valves111aand111dare open and the valves111b,111c, and111eare closed. In the secondary-side refrigerant circuit, the valves110a,110b,110g, and110hare closed, and the valves110cto110fare open. Further, the valves1121a,1121c,1122a,1122c,1123b, and1123dare closed, and the valves1121b,1121d,1122b,1122d,1123a, and1123care 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve106, 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 exchanger107bvia the valve111d, 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 exchanger107bpasses through the expansion mechanism105band the expansion mechanism105a, 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 exchanger107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger107aabsorbs 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 exchanger107aflows out of the relay unit B via the valve111a, and flows into the outdoor unit A.

The primary-side refrigerant that has flowed into the outdoor unit A flows into the outdoor heat exchanger104, 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 compressor103via the four-way valve106, 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 pump109aflows out of the relay unit B after passing through the valve1123a, and flows into the indoor heat exchanger1083of the indoor unit C3. The secondary-side refrigerant that has flowed into the indoor heat exchanger1083cools 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 exchanger1083, flowed into the relay unit B, and passed through the valve1123cflows into the intermediate heat exchanger107avia the valve110d. The secondary-side refrigerant that has flowed into the intermediate heat exchanger107ais 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 exchanger107a. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger107aflows into the pump109avia the valve110a, and is sent out again.

The secondary-side refrigerant at high temperature sent out by driving of the pump109bdivides into branch flows. The branch flows flow out of the relay unit B after passing through the valves1121band1122b, and flow into the indoor heat exchanger1081of the indoor unit C1, and the indoor heat exchanger1082of the indoor unit C2, respectively. The flows of the secondary-side refrigerant that have flowed into the indoor heat exchangers1081and1082heat the indoor air and turn into a low-temperature state, flow out of the indoor units C1and C2, respectively, and flow into the relay unit B.

The secondary-side refrigerant that has flowed out of the indoor heat exchanger1081, flowed into the relay unit B, and passed through the valve1121d, and the secondary-side refrigerant that has flowed out of the indoor heat exchanger1082, flowed into the relay unit B, and passed through the valve1122dmerge, and the merged secondary-side refrigerant flows into the intermediate heat exchanger107bvia the valve110f. The secondary-side refrigerant that has flowed into the intermediate heat exchanger107bis 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 exchanger107b. The secondary-side refrigerant that has flowed out of the intermediate heat exchanger107bflows into the pump109bvia the valve110e, 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 exchangers107aand107b. 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 pumps109aand109b.

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 valves110ato110dused to switch the direction of the secondary-side refrigerant flowing into the intermediate heat exchanger107a, and the four valves110eto110hused to switch the direction of the secondary-side refrigerant flowing into the intermediate heat exchanger107b, 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 valves112naand112nbused to switch the direction of the secondary-side refrigerant flowing into the indoor heat exchangers108nas 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 valves112ncand112ndused to switch the direction of the secondary-side refrigerant that has flowed out of the indoor heat exchangers108n.

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.

FIG. 12is a schematic diagram of an air-conditioning apparatus according to Embodiment 3 of the present invention.

As illustrated inFIG. 12, the outdoor unit A includes the compressor103, the outdoor heat exchanger104, the four-way valve106, and a flow switching unit141including check valves113ato113d.

As will be described later, the flow switching unit141including the check valves113ato113dhas 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 valve113ais provided in the refrigerant pipe connecting the four-way valve106and each of the valves111cand111d, and causes the primary-side refrigerant to flow only in a direction from each of the valves111cand111dtoward the four-way valve106. The check valve113bis provided in the refrigerant pipe connecting the outdoor heat exchanger104and the valve111fdescribed later, and causes the primary-side refrigerant to flow only in a direction from the outdoor heat exchanger104toward the valve111f. The check valve113cis provided in the refrigerant pipe that connects between the refrigerant pipe connecting the four-way valve106and the check valve113a, and the refrigerant pipe connecting the check valve113band the valve111f, and causes the primary-side refrigerant to flow only in a direction from the refrigerant pipe connecting the four-way valve106and the check valve113atoward the refrigerant pipe connecting the check valve113band the valve111f. The check valve113dis provided in the refrigerant pipe that connects between the refrigerant pipe connecting the check valve113aand each of the valves111cand111d, and the refrigerant pipe connecting the indoor heat exchanger104and the check valve113b, and causes the primary-side refrigerant to flow only in a direction from the refrigerant pipe connecting the check valve113aand each of the valves111cand111dtoward the refrigerant pipe connecting the indoor heat exchanger104and the check valve113b.

The relay unit B includes the intermediate heat exchangers107aand107b, the expansion mechanisms105aand105b, the pumps109aand109b, the valves110ato110h,111ato111f, and112nato112nd, and a bypass pipe142.

The valve111fis configured by a two-way valve or the like. The valve111fis provided in the refrigerant pipe between the valve111e, and the point where the refrigerant pipe into which refrigerant pipes connected to the valves111aand111bmerge connects with the refrigerant pipe connecting the check valve113band the valve111e.

The bypass pipe142is a refrigerant pipe that connects between the refrigerant pipe connecting the check valve113aand each of the valves111cand111d, and the refrigerant pipe connecting the valve111eand the valve111f.

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.

FIG. 13is 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. InFIG. 13, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. InFIG. 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 toFIGS. 14 to 16. Hereinafter, the cooling only operation mode will be described with reference toFIG. 13.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the outdoor heat exchanger104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor103, and the valves111aand111bare closed and the valves111cto111fare open. In the secondary-side refrigerant circuit, the valves110a,110b,110e, and110fare closed, the valves110c,110d,110g, and110hare open, and the valves112nato112ndare 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger104via the four-way valve106, 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 exchanger104flows out of the outdoor unit A via the check valve113b, and flows into the relay unit B.

After the primary-side refrigerant that has flowed into the relay unit B passes through the valves111fand the valve111e, the primary-side refrigerant divides into branch flows. The branch flows flow into the expansion mechanisms105aand105b, 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 exchangers107aand107bin parallel, respectively. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the intermediate heat exchangers107aand107babsorb 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 exchangers107aand107bmerge after passing through the valves111cand111d, 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 compressor103via the check valve113aand the four-way valve106, and is compressed again.

FIG. 14is 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 toFIG. 14.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger104flows to the compressor103, and the valves111a,111b, and111eare open and the valves111c,111d, and111fare closed. In the secondary-side refrigerant circuit, the valves110a,110b,110e, and110fare open, the valves110c,110d,110g, and110hare closed, and the valves112nato112ndare 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve106and the check valve113c, 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 exchangers107aand107bin parallel via the valves111aand111b, respectively. The flows of the primary-side refrigerant in a high-temperature, high-pressure state that have flowed into the intermediate heat exchangers107aand107bradiate 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 exchangers107aand107bflow into the expansion mechanisms105aand105b, 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 valve111e, and flows out of the relay unit B after flowing through the bypass pipe142, 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 exchanger104via the check valve113d, 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 compressor103via the four-way valve106, and is compressed again.

FIG. 15is 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 toFIG. 15. InFIG. 15, it is assumed that the indoor unit C1performs a heating operation, and the indoor units C2and C3perform a cooling operation.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the outdoor heat exchanger104, and that the primary-side refrigerant that has flowed out of the relay unit B flows to the compressor103, and the valves111a,111d,111e, and111fare closed and the valves111band111care open. In the secondary-side refrigerant circuit, the valves110a,110b,110g, and110hare closed, and the valves110c,110d,110e, and110fare open. Further, the valves1121a,1121c,1122b,1122d,1123b, and1123dare closed, and the valves1121b,1121d,1122a,1122c,1123a, and1123care 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows into the outdoor heat exchanger104via the four-way valve106, 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 exchanger104flows out of the outdoor unit A via the check valve113b, 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 exchanger107bvia the valve111b, 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 exchanger107bpasses through the expansion mechanism105band the expansion mechanism105a, 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 exchanger107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger107aabsorbs 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 exchanger107aflows out of the relay unit B via the valve111c, 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 compressor103via the check valve113aand the four-way valve106, and is compressed again.

FIG. 16is 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 toFIG. 16. InFIG. 16, it is assumed that the indoor units C1and C2perform a heating operation, and the indoor unit C3performs a cooling operation.

In the primary-side refrigerant circuit, the four-way valve106is switched in advance so that the primary-side refrigerant discharged from the compressor103flows to the relay unit B, and that the primary-side refrigerant that has flowed out of the outdoor heat exchanger104flows to the compressor103, and the valves111a, and111dto111fare closed and the valves111band111care open. In the secondary-side refrigerant circuit, the valves110a,110b,110g, and110hare closed, and the valves110cto110fare open. Further, the valves1121a,1121c,1122a,1122c,1123b, and1123dare closed, and the valves1121b,1121d,1122b,1122d,1123a, and1123care 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 compressor103, and discharged in a high-temperature, high-pressure state. The primary-side refrigerant flows out of the outdoor unit A via the four-way valve106and the check valve113c, 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 exchanger107bvia the valve111b, 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 exchanger107bpasses through the expansion mechanism105band the expansion mechanism105a, 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 exchanger107a. The primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger107aabsorbs 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 exchanger107aflows out of the relay unit B via the valve111c, and flows into the outdoor unit A.

The primary-side refrigerant that has flowed into the outdoor unit A flows into the outdoor heat exchanger104via the check valve113d, 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 compressor103via the four-way valve106, 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.

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.

FIG. 17is a schematic diagram of an air-conditioning apparatus according to Embodiment 4 of the present invention.

As illustrated inFIG. 17, in the air-conditioning apparatus according to Embodiment 4, the intermediate heat exchangers107aand107bin the air-conditioning apparatus according to Embodiment 2 are replaced by intermediate heat exchangers107aaand107ba, respectively. The intermediate heat exchangers107aaand107baare both configured in the same manner as the intermediate heat exchanger7in the air-conditioning apparatus according to Embodiment 1.

First, heat transfer units1071aand1072a, and check valves132ato132cand133ato133cin the intermediate heat exchanger107aacorrespond to the heat transfer units7aand7b, and the check valves11ato11cand12ato12cin the intermediate heat exchanger7in Embodiment 1, respectively. Heat transfer units1071band1072b, and check valves132dto132fand133dto133fin the intermediate heat exchanger107bacorrespond to the heat transfer units7aand7b, and the check valves11ato11cand12ato12cin the intermediate heat exchanger7in 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 exchangers107aaand107ba. Moreover, provided that the primary-side refrigerant and the secondary-side refrigerant flow out of and flow into the intermediate heat exchanger107aaand the intermediate heat exchanger107bain the same direction, the operations in the intermediate heat exchanger107aaand the intermediate heat exchanger107baare the same. Accordingly, hereinafter, the operation in the intermediate heat exchanger107bawill be described.

The check valves132ato132fand133ato133fcorrespond to the “fifth flow switching means” in the invention according to claim5of the present invention.

FIG. 18illustrates the flows of the primary-side refrigerant and secondary-side refrigerant in a case where the intermediate heat exchanger107bain the air-conditioning apparatus according to Embodiment 4 of the present invention functions as an evaporator. InFIG. 18, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. InFIG. 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 toFIG. 19. Hereinafter, the operation in a case where the intermediate heat exchanger107bafunctions as an evaporator will be described with reference toFIG. 18.

After the primary-side refrigerant in a two-phase gas-liquid state that has flowed into the intermediate heat exchanger107bapasses through the check valve132e, the primary-side refrigerant divides into branch flows, and the branch flows flow into the heat transfer unit1071band the heat transfer unit1072bin parallel, respectively. At this time, the primary-side refrigerant does not flow in a direction toward the check valve132dowing to the action of the check valve132f. The flows of the primary-side refrigerant in a two-phase gas-liquid state that have flowed into the heat transfer unit1071band the heat transfer unit1072babsorb 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 unit1071bpasses though the check valve132d, merges with the primary-side refrigerant that has flowed out of the heat transfer unit1072b, and flows out of the intermediate heat exchanger107ba.

The secondary-side refrigerant that has flowed into the intermediate heat exchanger107badivides into branch flows, one of which flows into the heat transfer unit1072b, and the other flows into the heat transfer unit1071bvia the check valve133d. 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 exchanger107baowing to the action of the check valve133f. The flows of the secondary-side refrigerant that have flowed into the heat transfer unit1071band the heat transfer unit1072bin 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 unit1071band the heat transfer unit1072b, respectively. The flows of the secondary-side refrigerant that have respectively flowed out of the heat transfer unit1071band the heat transfer unit1072bmerge, and the merged secondary-side refrigerant flows out of the intermediate heat exchanger107bavia the check valve133e.

FIG. 19illustrates the flows of the primary-side refrigerant and secondary-side refrigerant in a case where the intermediate heat exchanger107bain the air-conditioning apparatus according to Embodiment 4 of the present invention functions as a radiator. InFIG. 19, pipes indicated by thick lines represent pipes through which the primary-side refrigerant and the secondary-side refrigerant flow. InFIG. 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 exchanger107bafunctions as a radiator will be described with reference toFIG. 19.

The primary-side refrigerant that has flowed into the intermediate heat exchanger107baflows into the heat transfer unit1072b, 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 unit1071band the check valve132fowing to the action of the check valve132d. The primary-side refrigerant that has flowed out of the heat transfer unit1072bflows into the heat transfer unit1071b. In the heat transfer unit1071bas 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 exchanger107baowing to the action of the check valve132e. In this way, the primary-side refrigerant flows through the heat transfer unit1072band the heat transfer unit1071bin 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 unit1071bflows out of the intermediate heat exchanger107bavia the check valve132f.

The secondary-side refrigerant that has flowed into the intermediate heat exchanger107baflows into the heat transfer unit1071bvia the check valve133f, 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 unit1072bowing to the action of the check valve133e. The secondary-side refrigerant does not flow in a direction toward the outlet of the secondary-side refrigerant in the intermediate heat exchanger107ba, either, owing to the action of the check valve133d. The secondary-side refrigerant that has flowed out of the heat transfer unit1071bflows into the heat transfer unit1072b, 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 unit1071band the heat transfer unit1072bin series. The secondary-side refrigerant that has flowed out of the heat transfer unit1072bflows out of the intermediate heat exchanger107ba.

(Operation in Each Operation Mode)

In the cooling only operation mode, the intermediate heat exchangers107aaand107baboth act as the evaporator described above with reference toFIG. 18, and in the heating only operation mode, the intermediate heat exchangers107aaand107baboth act as the radiator described above with reference toFIG. 19. In both the cooling main operation mode and the heating main operation mode, the intermediate heat exchanger107aaacts as the evaporator described above with reference toFIG. 18, and the intermediate heat exchanger107baacts as the radiator described above with reference toFIG. 19.

Advantageous Effects of Embodiment 4

According to the configuration and the operation mentioned above, in a case where each of the intermediate heat exchangers107aaand107bafunctions as an evaporator where the primary-side refrigerant absorbs heat from the secondary-side refrigerant, the primary-side refrigerant flows through the heat transfer unit1071a(1071b) and the heat transfer unit1072a(1072b) in parallel, and in a case where each of the intermediate heat exchangers107aaand107bafunctions as a radiator where the primary-side refrigerant radiates heat to the secondary-side refrigerant, the primary-side refrigerant flows through the heat transfer unit1071a(1071b) and the heat transfer unit1072a(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 exchanger107aa(107ba) that functions as an evaporator, the primary-side refrigerant performs a heat absorption operation, and flows through the heat transfer unit1071a(1071b) and the heat transfer unit1072a(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 compressor103. In the intermediate heat exchanger107aa(107ba) that functions as a radiator, the primary-side refrigerant performs a heat radiation operation, and flows through the heat transfer unit1071a(1071b) and the heat transfer unit1072a(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 unit1071binFIGS. 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 exchangers108nonly 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 valves132ato132fand133ato133fmakes it unnecessary to perform operations other than operations of the four-way valve106and each valve, for switching of the overall cross-sectional area of the flow path in each of the intermediate heat exchangers107aaand107badue to switching of operation modes. Consequently, in the vicinity of each of the intermediate heat exchangers107aaand107ba, problems such as leakage of refrigerant from valves can be prevented, thereby enabling safe operation.

The configuration of the intermediate heat exchangers107aaand107baof 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 inFIG. 17is configured so that the intermediate heat exchangers107aaand107baeach include two heat transfer units such as the heat transfer unit1071a(1071b) and the heat transfer unit1072a(1072b), this should not be construed restrictively. The intermediate heat exchangers107aaand107bamay each include three or more heat transfer units. As an example in this case,FIG. 20illustrates a configuration in which the intermediate heat exchangers107aaand107baeach include three heat transfer units (heat transfer units1071ato1073a(1071bto1073b)). In a case where the number of heat transfer units is an even number, the resulting configuration is the same as the configuration illustrated inFIG. 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 exchangers107aaand107ba(the check valves132ato132finFIG. 17), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves133ato133finFIG. 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 inFIG. 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 exchangers107aaand107ba(the check valves132a,132b,132d, and132einFIG. 20), and the number of check valves belonging to the secondary-side refrigerant circuit (the check valves133a,133b,133d, and133einFIG. 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 exchangers107aaand107bais 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 exchangers107aaand107bais 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 exchangers107aaand107bain the air-conditioning apparatus illustrated inFIGS. 17 and 20may 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.

FIG. 21is 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 inFIG. 21, the check valves110eto110hare omitted from the air-conditioning apparatus according to Embodiment 3.

Advantageous Effects of Embodiment 5

When the check valves110eto110hare eliminated as in the configuration mentioned above, the flow of the secondary-side refrigerant flowing through the intermediate heat exchanger107bbecomes a certain direction. Accordingly, in a case where the intermediate heat exchanger107bacts 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 exchanger107bacts as a condenser than in the case where the intermediate heat exchanger107bacts as an evaporator, and of the four operation modes, the intermediate heat exchanger107bacts 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 valves110eto110hare omitted can be also applied to the air-conditioning apparatus according to Embodiment 2.

FIG. 22illustrates an installation example of an air-conditioning apparatus according to Embodiment 6 of the present invention. The air-conditioning apparatus illustrated inFIG. 22will 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 building100illustrated inFIG. 22. In addition, in an indoor space that is an air-conditioning space such as a living space inside the building100, 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 inFIG. 22, a plurality of indoor units C (three indoor units C (indoor units C1to C3) inFIG. 22) are installed in the indoor space on each floor of the building100. The relay unit B is installed in a non-air-conditioned space inside the building100. The relay unit B is connected to the outdoor unit A and each of the indoor units C by refrigerant pipes. As illustrated inFIG. 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 inFIG. 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 exchanger7), 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 exchanger8and the fan8a. The relay unit B corresponds to the intermediate heat exchanger7in the air-conditioning apparatus according to Embodiment 1, and a portion constituting the secondary-side refrigerant circuit which has the pump9and the valves10ato10d.

While the case where the outdoor unit A is installed on the rooftop of the building100as illustrated inFIG. 22has been described, this should not be construed restrictively. For example, the outdoor unit A may be installed in the basement of the building100, in the machine room on each floor, or the like.

While three indoor units C are installed on each floor of the building100as illustrated inFIG. 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