Air-conditioning apparatus with safety measure for ventilation of inflammable refrigerant from heat exchanger

A refrigerant circuit device includes a compressor, a heat exchanger that is capable of exchanging heat between the refrigerant and a heat medium, and other components that are connected by pipes, in which the refrigerant circuit circulates a refrigerant. A heat medium circulating circuit circulates the heat medium in the heat exchanger. At least the compressor is housed in an outdoor unit, at least the heat exchanger is housed in a heat medium relay unit, and an indoor unit is housed in a use side heat exchanger. The outdoor unit, the heat medium relay unit, and the indoor unit are formed separately and can be disposed in separate positions. A housing of the heat medium relay unit has an opening that allows ventilation between the housing space of the heat exchanger related to heat medium and the space outside the housing space.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of PCT/JP2010/007048 filed on Dec. 3, 2010.

TECHNICAL FIELD

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

BACKGROUND ART

For example, there is a multi-air-conditioning apparatus for a building that performs air conditioning by exchanging heat between a refrigerant, which circulates between an outdoor unit and a relay unit, and a heat medium such as water, which circulates between the relay unit and indoor units. During the heat exchange, power for conveying the heat medium is reduced so as to save energy (see Patent Literature 1, for example).

Furthermore, there is an air-conditioning apparatus devised with a countermeasure for refrigerant leakage in a case in which hydrocarbon is employed as a refrigerant. In this air-conditioning apparatus, a refrigerant passage is shut-off with a solenoid valve when there is refrigerant leakage (see Patent Literature 2, for example).

Moreover, there is an air-conditioning apparatus that averts explosion in a case of refrigerant leakage when a combustible refrigerant is employed. In this air-conditioning apparatus, a damper for discharging the refrigerant is activated when leakage of the refrigerant is detected by a refrigerant leak sensor disposed inside a housing of an outdoor unit. Further, the air-conditioning apparatus is configured to operate an air-sending device such that air is sent into the housing (see Patent Literature 3, for example).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

An air-conditioning apparatus, such as a multi-air-conditioning apparatus for a building described in the above-described Patent Literature 1, is configured such that a refrigerant is made to circulate between an outdoor unit and a relay unit, a heat medium such as water is made to circulate between the relay unit and indoor units, and heat is exchanged in the relay unit between the refrigerant and the heat medium such as water. Accordingly, the refrigerant can be prevented from leaking into the indoor side. However, there is a problem in that no countermeasure in particular to prevent leakage into the housing of the outdoor unit and the like, which becomes a problem when the refrigerant is flammable, is taken.

Furthermore, the air-conditioning apparatus described in Patent Literature 2 performs a processing operation of stopping refrigerant leakage such that a passage is shut off with a solenoid valve when there is refrigerant leakage. However, there is no detailed description of the operation in Patent Literature 2. Moreover, the air volume of the air-sending device is not stipulated.

Additionally, the air-conditioning apparatus described in Patent Literature 3 activates the damper for discharging the refrigerant by reverse rotating the air-sending device when leakage of the refrigerant is detected while the unit is in operation. However, the air-sending device cannot be operated while the unit is suspended. Moreover, the air volume of the air-sending device is not stipulated.

The present invention addresses to solve the above problems and to obtain an air-conditioning apparatus that is capable of further increasing safety by preventing increase in refrigerant concentration inside a housing caused by refrigerant leakage inside the housing and increased its safety

Solution to Problem

The air-conditioning apparatus according to the invention includes a refrigeration cycle including a refrigerant circuit for circulating a refrigerant, the refrigerant circuit being constituted by connecting with pipes a compressor that sends out a combustible refrigerant, a refrigerant flow switching device configured to switch circulation paths of the refrigerant, a heat source side heat exchanger configured to exchange heat of the refrigerant, a refrigerant expansion device configured to control a pressure of the refrigerant, and a heat exchanger related to heat medium capable of exchanging heat between the refrigerant and a heat medium that is different from the refrigerant, in which the refrigerant circuit circulates the refrigerant; and a heat medium side device constituted by a heat medium circulating circuit by connecting with pipes a heat medium sending device configured to circulate the heat medium pertaining to heat exchange of the heat exchanger related to heat medium, and a use side heat exchanger exchanging heat between the heat medium and air related to a conditioned space, in which at least the compressor, the refrigerant flow switching device, the heat source side heat exchanger are housed in an outdoor unit, at least the heat exchanger related to heat medium and the refrigerant expansion device are housed in a heat medium relay unit, and the use side heat exchanger is housed in an indoor unit, while each of the outdoor unit, the heat medium relay unit, and the indoor unit is separately formed and are allowed to be disposed at separate positions, and a housing of the heat medium relay unit includes an opening allowing ventilation between a housing space of the heat exchanger related to heat medium and a space other than the housing space; hence, the air-conditioning apparatus is capable of providing safety when there is refrigerant leakage and is capable of improving energy efficiency.

Advantageous Effects of Invention

In the air-conditioning apparatus of the invention, an opening is provided to a heat medium relay unit allowing a refrigerant that has leaked out to be discharged. As such, since refrigerant concentration can be maintained under a predetermined concentration, ignition or the like owing to refrigerant leakage of a combustible refrigerant can be prevented, and a heat medium relay unit and an air-conditioning apparatus with high safety can be obtained. Furthermore, since the length of pipes circulating a heat medium can be shortened compared to that of the air-conditioning apparatus such as a chiller, conveyance power can be smaller. Hence, energy saving can be achieved.

DESCRIPTION OF EMBODIMENT

An embodiment of the invention will be described with reference to the drawings.FIGS. 1 and 2are schematic diagrams illustrating exemplary installations of an air-conditioning apparatus according to the embodiment of the invention. The exemplary installations of the air-conditioning apparatus will be described with reference toFIGS. 1 and 2. In this air-conditioning apparatus, an apparatus is used that includes devices and the like that constitute a circuit (a refrigerant circuit (refrigeration cycle circuit) A and a heat medium circulating circuit B) that circulate a flammable heat source side refrigerant (refrigerant) and a heat medium such as water serving as a refrigerant, respectively, such that a cooling mode or a heating mode is allowed to be selected freely as the operation mode in each indoor unit. It should be noted that the dimensional relationships of components inFIG. 1and other subsequent drawings may be different from the actual ones. Furthermore, like devices that are distinguished by their suffix may omit their suffix when there is no need to particularly distinguish or specify the devices.

Referring toFIG. 1, the air-conditioning apparatus according to the embodiment includes a single outdoor unit1functioning as a heat source unit, a plurality of indoor units2, and a heat medium relay unit3disposed between the outdoor unit1and the indoor units2. The heat medium relay unit3exchanges heat between the heat source side refrigerant that circulates in the refrigerant circuit and a heat medium that becomes a load (subject of heat exchange) to the heat source side refrigerant. The outdoor unit1and the heat medium relay unit3are connected with refrigerant pipes4through which the heat source side refrigerant flows. The heat medium relay unit3and each indoor unit2are connected with pipes (heat medium pipes)5through which the heat medium flows. Cooling energy or heating energy generated in the outdoor unit1is delivered to the indoor units2through the heat medium relay unit3.

Referring toFIG. 2, the air-conditioning apparatus according to the embodiment includes the single outdoor unit1, the plurality of indoor units2, a plurality of separated heat medium relay units3(a main heat medium relay unit3aand sub heat medium relay units3b) disposed between the outdoor unit1and the indoor units2. The outdoor unit1and the main heat medium relay unit3aare connected with the refrigerant pipes4. The main heat medium relay unit3aand the sub heat medium relay units3bare connected with the refrigerant pipes4. Each sub heat medium relay unit3band corresponding indoor units2are connected with the pipes5. Cooling energy or heating energy (quantity of heat) generated in the outdoor unit1is delivered to the indoor units2through the main heat medium relay unit3aand the sub heat medium relay units3b.

The outdoor unit1is typically disposed in an outdoor space6, which is a space (e.g., a roof) outside a structure9, such as a building, and is configured to supply cooling energy or heating energy to the indoor units2through the heat medium relay unit3. Each indoor unit2is disposed at a position that can supply cooling air or heating air to an indoor space7, which is a space (e.g., a living room) inside the structure9, and supplies the cooling air or heating air to the indoor space7that is a space to be conditioned. The heat medium relay unit3is configured with a housing separate from the outdoor unit1and the indoor units2such that the heat medium relay unit3can be disposed at a position different from those of the outdoor space6and the indoor space7. Furthermore, the heat medium relay unit3is connected to the outdoor unit1and the indoor units2with refrigerant pipes4and pipes5, respectively, to convey heating energy or cooling energy from the outdoor unit1to the indoor units2.

As illustrated inFIGS. 1 and 2, in the air-conditioning apparatus according to the embodiment, the outdoor unit1is connected to the heat medium relay unit3using two refrigerant pipes4, and the heat medium relay unit3is connected to each indoor unit2using two pipes5. As described above, in the air-conditioning apparatus according to the embodiment, each of the units (the outdoor unit1, the indoor units2, and the heat medium relay unit3) is connected using two pipes (the refrigerant pipes4or the pipes5), thus construction is facilitated.

As illustrated inFIG. 2, the heat medium relay unit3can be separated into a single main heat medium relay unit3aand two sub heat medium relay units3b(a sub heat medium relay unit3b(1) and a sub heat medium relay unit3b(2)) derived from the main heat medium relay unit3a. This separation allows a plurality of sub heat medium relay units3bto be connected to the single main heat medium relay unit3a. In this configuration, the number of refrigerant pipes4connecting the main heat medium relay unit3ato each sub heat medium relay unit3bis three. Details of this circuit will be described in detail later (seeFIG. 3A).

Furthermore,FIGS. 1 and 2illustrate an exemplary state in which each heat medium relay unit3is disposed in the structure9but in a space different from the indoor space7, for example, a space above a ceiling (hereinafter, simply referred to as a “space8”). Space8is not a closed space and is structured to allow ventilation to the outdoor space6by means of a vent hole9A provided in the structure. Note that the vent hole9A of the structure may be any type of ventilation that is configured to allow ventilation to the outdoor space6by natural convection or forced convection when there is leakage of the heat source side refrigerant into the space8such that concentration of the heat source side refrigerant in the space8does not become excessively high. In addition, althoughFIGS. 1 and 2illustrate a case in which the indoor units2are of a ceiling-mounted cassette type, the indoor units are not limited to this type and, for example, a ceiling-concealed type, a ceiling-suspended type, or any type of indoor unit may be used as long as the unit can blow out air for heating or air for cooling into the indoor space7directly or through a duct or the like.

The air-conditioning apparatus ofFIG. 1andFIG. 2employs a combustible refrigerant as the heat source side refrigerant that circulates in the refrigerant circuit. As the combustible refrigerant, tetrafluoropropene represented by the chemical formula of C3H2F4(HFO1234yf represented by CF3CF=CH2, HFO1234ze represented by CF3CH═CHF, for example) or difluoromethane (R32) represented by the chemical formula of CH2F2is employed. Moreover, the combustible refrigerant may be a mixed refrigerant and, in the case of a mixed refrigerant, the refrigerant is, for example, 80% of HFO1234yf and 20% of R32. Furthermore, a highly combustible refrigerant such as R290 (propane) may be employed.

Accordingly, other than the space above a ceiling, the heat medium relay unit3may be disposed in any place that is a space other than a living space and that has a ventilation of some kind to the outside. For example, the heat medium relay unit3can be disposed in a common space where an elevator or the like is installed, which is a space that has ventilation to the outside.

AlthoughFIGS. 1 and 2illustrate a case in which the outdoor unit1is disposed in the outdoor space6, the arrangement is not limited to this case. For example, such as a machine room with a ventilation opening, the outdoor unit1may be disposed in an enclosed space, or the outdoor unit1can be disposed any space where ventilation is provided to the outdoor space6.

Additionally, the numbers of connected outdoor units1, indoor units2, and heat medium relay units3are not limited to those illustrated inFIGS. 1 and 2. The numbers thereof can be determined in accordance with the structure9where the air-conditioning apparatus according to the embodiment is installed.

Further, in order to prevent the heat source side refrigerant from leaking into the indoor space7in a case where there is leakage of a heat source side refrigerant from the heat medium relay unit3, it is desirable to configure the space8, where the heat medium relay unit3is disposed, and the indoor space7such that there is no ventilation of air therebetween. However, even if there is a small vent hole between the space8and the indoor space7such as, for example, a through hole for a pipe, the heat source side refrigerant that has leaked out will be discharged outdoors if the ventilation resistance between the space8and the indoor space7is set larger than the ventilation resistance of the vent hole between the space8and the outdoor space6; accordingly, there will be no problem.

Furthermore, as illustrated inFIGS. 1 and 2, the refrigerant pipes4that connect the outdoor unit1and the heat medium relay unit3are passed through the outdoor space6or through a pipe shaft20. Since the pipe shaft is a duct for passing the pipes through and its outer surface is surrounded with metal and the like, even if the heat source side refrigerant were to leak out from the refrigerant pipe4, the heat source side refrigerant will not be diffused to the surroundings. Additionally, since the pipe shaft is disposed in a non-air-conditioned space other than the living space or outdoors, the heat source side refrigerant that has leaked out from the refrigerant pipe4is discharged outdoors from the pipe shaft through the non-air-conditioned space8or directly from the pipe shaft, and will not leak into the indoor space. Alternatively, the heat medium relay unit3may be disposed in the pipe shaft.

Note that in the heat medium relay unit3, a relay-unit air-sending device60is provided that is driven with a predetermined air volume (larger than a ventilation volume) to ventilate air inside the housing.

Now, in the housing of the heat medium relay unit3, an opening61is disposed at a position where air of the relay-unit air-sending device60can pass through such that the heat source side refrigerant that has leaked into the housing of the heat medium relay unit3is discharged, and thus, no heat source side refrigerant is stagnated inside the housing. In this case, by disposing the relay-unit air-sending device60at a position (a position facing the relay-unit air-sending device60or in a free space in the panel of the housing, for example) that does not impede the fanned air flow (a position where ventilation resistance is small), it will be possible to discharge the heat source side refrigerant to the outdoor space6through the space8.

The opening61includes a first hole61A and one or more second hole61B opened at a different position (seeFIG. 3). The functions of the relay-unit air-sending device60, the first hole61A, and the second hole61B allows the heat source side refrigerant that has leaked into the housing of the heat medium relay unit3to be discharged from the housing, and it is possible to maintain the refrigerant concentration inside the housing under a constant value. Note that if the total opening area of the first hole and the second hole is too small with respect to the size of the housing, the ventilation resistance becomes excessively high and, thus, it will not be possible to obtain sufficient air volume (amount of discharge).

For example, it is empirically known that the housing is sufficiently ventilated therein when the total opening area of the first hole61A and the second hole61B is 10% or more of the surface area (including the total opening area) of the housing of the heat medium relay unit3. Accordingly, when configured as above, it is possible to efficiently discharge the heat source side refrigerant that has leaked into the heat medium relay unit3and to maintain the refrigerant concentration under a constant value, and, thus, obtain a safe apparatus. Note that, based on a study on ventilation of buildings, it is known that the resistance coefficient during ventilation does not drop much when the opening ratio of the building is 10% or higher. As such, if the opening ratio of the hole(s) opened in the housing of the heat medium relay unit3is equivalent or higher than this, it will be possible to sufficiently ventilate the inside of the housing and, thus, efficiently reduce the refrigerant concentration to a constant value or less.

Furthermore, a hole with a size allowing air sent to the heat medium relay unit3from the outside to pass therein, for example, a hole with a size that is 10% or more of the surface area of the housing of the heat medium relay unit may be provided, and an air-sending device may be provided in the space8. Hereby, air can be made to flow inside the housing of the heat medium relay unit3without directly installing an air-sending device to the heat medium relay unit3.

FIG. 3is a schematic circuit diagram illustrating an exemplary circuit configuration of the air-conditioning apparatus (hereinafter, referred to as an “air-conditioning apparatus100”) according to Embodiment 1. The detailed configuration of the air-conditioning apparatus100will be described with reference toFIG. 3. As illustrated inFIG. 3, the outdoor unit1and the heat medium relay unit3are connected with the refrigerant pipes4through heat exchangers related to heat medium15aand15bincluded in the heat medium relay unit3. Furthermore, the heat medium relay unit3and the indoor units2are connected with the pipes5through the heat exchangers related to heat medium15aand15b. Note that the refrigerant pipe4will be described in detail later.

The outdoor unit1includes a compressor10, a first refrigerant flow switching device11, such as a four-way valve, a heat source side heat exchanger12, and an accumulator19, which are connected in series with the refrigerant pipes4. The outdoor unit1is further provided with a first connecting pipe4a, a second connecting pipe4b, a check valve13a, a check valve13b, a check valve13c, and a check valve13d. By providing the first connecting pipe4a, the second connecting pipe4b, the check valve13a, the check valve13b, the check valve13c, and the check valve13d, the heat source side refrigerant can be made to flow into the heat medium relay unit3in a constant direction irrespective of the operation requested by the indoor units2.

The compressor10sucks in the heat source side refrigerant and compresses the heat source side refrigerant to a high-temperature high-pressure state. The compressor10may include, for example, a capacity-controllable inverter compressor. The first refrigerant flow switching device11switches the flow of the heat source side refrigerant between a heating operation (a heating only operation mode and a heating main operation mode) and a cooling operation (a cooling only operation mode and a cooling main operation mode). The heat source side heat exchanger12functions as an evaporator during the heating operation and functions as a condenser (or a radiator) during the cooling operation.

During the above, heat is exchanged between air supplied from an outdoor-unit air-sending device (not shown) and the heat source side refrigerant to evaporate and gasify or condense and liquefy the heat source side refrigerant. The accumulator19is provided on the suction side of the compressor10and retains excess heat source side refrigerant.

The check valve13ais provided in the refrigerant pipe4between the heat source side heat exchanger12and the heat medium relay unit3and permits the heat source side refrigerant to flow only in a predetermined direction (the direction from the outdoor unit1to the heat medium relay unit3). The check valve13bis provided in the first connecting pipe4aand allows the heat source side refrigerant discharged from the compressor10to flow through the heat medium relay unit3during the heating operation. The check valve13cis disposed in the second connecting pipe4band allows the heat source side refrigerant, returning from the heat medium relay unit3, to flow to the suction side of the compressor10during the heating operation. The check valve13dis provided in the refrigerant pipe4between the heat medium relay unit3and the first refrigerant flow switching device11and permits the heat source side refrigerant to flow only in a predetermined direction (the direction from the heat medium relay unit3to the outdoor unit1).

In the outdoor unit1, the first connecting pipe4aconnects the refrigerant pipe4, between the first refrigerant flow switching device11and the check valve13d, to the refrigerant pipe4, between the check valve13aand the heat medium relay unit3. In the outdoor unit1, the second connecting pipe4bconnects the refrigerant pipe4, between the check valve13dand the heat medium relay unit3, to the refrigerant pipe4, between the heat source side heat exchanger12and the check valve13a. It should be noted that althoughFIG. 3illustrates a case in which the first connecting pipe4a, the second connecting pipe4b, the check valve13a, the check valve13b, the check valve13c, and the check valve13dare disposed, the outdoor unit is not limited to this case, and they may be omitted.

Each of the indoor units2includes a use side heat exchanger26. The use side heat exchanger26connects to a heat medium flow control device25and a second heat medium flow switching device23in the heat medium relay unit3with the pipes5. Each of the use side heat exchangers26exchanges heat between air supplied from an air-sending device, such as a fan, (not shown) and the heat medium in order to generate air for heating or air for cooling supplied to the indoor space7.

FIG. 3illustrates a case in which four indoor units2are connected to the heat medium relay unit3. Illustrated are, from the bottom of the drawing, an indoor unit2a, an indoor unit2b, an indoor unit2c, and an indoor unit2d. In addition, the use side heat exchangers26are illustrated as, from the bottom of the drawing, a use side heat exchanger26a, a use side heat exchanger26b, a use side heat exchanger26c, and a use side heat exchanger26deach corresponding to the indoor units2ato2d. Note that the number of connected indoor units2is not limited to four that are illustrated inFIG. 3, as well as the examples ofFIGS. 1 and 2.

The heat medium relay unit3includes the two heat exchangers related to heat medium15, two expansion devices16, two opening and closing devices17, two second refrigerant flow switching devices18, two pumps21, four first heat medium flow switching devices22, the four second heat medium flow switching devices23, and the four heat medium flow control devices25. An air-conditioning apparatus in which the heat medium relay unit3is separated into the main heat medium relay unit3aand the sub heat medium relay unit3bwill be described later with reference toFIG. 3A.

Each of the two heat exchangers related to heat medium15(the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15b) functions as a condenser (radiator) or an evaporator, exchanges heat, and serves as a load side heat exchanger that transfers cooling energy or heating energy, generated in the outdoor unit1and stored in the heat source side refrigerant, to the heat medium. The heat exchanger related to heat medium15ais disposed between an expansion device16aand a second refrigerant flow switching device18ain the refrigerant circuit A and is used to cool the heat medium in a cooling and heating mixed operation mode. Additionally, the heat exchanger related to heat medium15bis disposed between an expansion device16band a second refrigerant flow switching device18bin the refrigerant circuit A and is used to heat the heat medium in the cooling and heating mixed operation mode. Although two heat exchangers related to heat medium15are disposed herein, one heat exchanger related to heat medium may be disposed or three or more heat exchangers related to heat medium may be disposed.

The two expansion devices16(the expansion device16aand the expansion device16b) each have functions of a reducing valve and an expansion valve and are configured to decompress and expand the heat source side refrigerant. The expansion device16ais disposed upstream of the heat exchanger related to heat medium15a, in the heat source side refrigerant flow during the cooling operation. The expansion device16bis disposed upstream of the heat exchanger related to heat medium15b, in the heat source side refrigerant flow during the cooling operation. Each of the two expansion devices16may include a component that can variably control its opening degree, such as an electronic expansion valve.

The two opening and closing devices17(an opening and closing device17aand an opening and closing device17b) each include, for example, a two-way valve and open and close the refrigerant pipe4. The opening and closing device17ais disposed in the refrigerant pipe4on the inlet side of the heat source side refrigerant. The opening and closing device17bis disposed in a pipe connecting the refrigerant pipe4on the inlet side of the heat source side refrigerant and the refrigerant pipe4on the outlet side thereof. The two second refrigerant flow switching devices18(the second refrigerant flow switching devices18aand18b) each include, for example, a four-way valve and switch the flow of the heat source side refrigerant in accordance with the operation mode. The second refrigerant flow switching device18ais disposed downstream of the heat exchanger related to heat medium15a, in the heat source side refrigerant flow during the cooling operation. The second refrigerant flow switching device18bis disposed downstream of the heat exchanger related to heat medium15b, in the heat source side refrigerant flow during the cooling only operation.

The two pumps21(a pump21aand a pump21b) are each provided in accordance with the corresponding one of the heat exchangers related to heat medium15and circulate the heat medium flowing through the pipes5. The pump21ais disposed in the pipe5between the heat exchanger related to heat medium15aand the second heat medium flow switching devices23. The pump21bis disposed in the pipe5between the heat exchanger related to heat medium15band the second heat medium flow switching devices23. Each of the two pumps21may include, for example, a capacity-controllable pump.

The four first heat medium flow switching devices22(first heat medium flow switching devices22ato22d) each include, for example, a three-way valve and switches passages of the heat medium. The first heat medium flow switching devices22are arranged so that the number thereof (four in this case) corresponds to the installed number of indoor units2. Each of the first heat medium flow switching devices22is disposed on an outlet side of a heat medium passage of the corresponding use side heat exchanger26such that one of the three ways is connected to the heat exchanger related to heat medium15a, another one of the three ways is connected to the heat exchanger related to heat medium15b, and the other one of the three ways is connected to the corresponding heat medium flow control device25. Note that illustrated from the bottom of the drawing are the first heat medium flow switching device22a, the first heat medium flow switching device22b, the first heat medium flow switching device22c, and the first heat medium flow switching device22d, so as to correspond to the respective indoor units2.

The four second heat medium flow switching devices23(second heat medium flow switching devices23ato23d) each include, for example, a three-way valve and are configured to switch passages of the heat medium. The second heat medium flow switching devices23are arranged so that the number thereof (four in this case) corresponds to the installed number of indoor units2. Each of the second heat medium flow switching devices23is disposed on an inlet side of the heat medium passage of the corresponding use side heat exchanger26such that one of the three ways is connected to the heat exchanger related to heat medium15a, another one of the three ways is connected to the heat exchanger related to heat medium15b, and the other one of the three ways is connected to the corresponding use side heat exchanger26. Note that illustrated from the bottom of the drawing are the second heat medium flow switching device23a, the second heat medium flow switching device23b, the second heat medium flow switching device23c, and the second heat medium flow switching device23dso as to correspond to the respective indoor units2.

The four heat medium flow control devices25(heat medium flow control devices25ato25d) each include, for example, a two-way valve capable of controlling the area of opening and controls the flow rate of the flow in the corresponding pipe5. The heat medium flow control devices25are arranged so that the number thereof (four in this case) corresponds to the installed number of indoor units2. Each of the heat medium flow control devices25is disposed on the outlet side of the heat medium passage of the corresponding use side heat exchanger26such that one way is connected to the use side heat exchanger26and the other way is connected to the first heat medium flow switching device22. Note that illustrated from the bottom of the drawing are the heat medium flow control device25a, the heat medium flow control device25b, the heat medium flow control device25c, and the heat medium flow control device25dso as to correspond to the respective indoor units2. In addition, each of the heat medium flow control devices25may be disposed on the inlet side of the heat medium passage of the corresponding use side heat exchanger26.

Furthermore, the heat medium relay unit3according to the embodiment includes a refrigerant concentration detection device40and shut-off devices50. The refrigerant concentration detection device40includes a refrigerant concentration sensor (concentration detection means)41, for example. When it is determined that a detection value of the refrigerant concentration detected by the refrigerant concentration sensor41is equivalent to or higher than a certain value, an instruction signal is transmitted to the shut-off devices50so as to carry out a refrigerant passage closing process. Note that in the embodiment, description is made such that the refrigerant concentration detection device40is disposed inside the heat medium relay unit3; however, for example, the refrigerant concentration detection device40may be disposed outside the heat medium relay unit3at a position near the heat medium relay unit3, and the refrigerant concentration inside the housing of the heat medium relay unit3may be detected by using a hose or the like. Furthermore, at the refrigerant inlet or outlet of the heat medium relay unit3, the shut-off devices50stop the heat source side refrigerant from flowing in or out by closing the refrigerant passage on the basis of the instruction signal.

Now, a case in which the heat source side refrigerant has leaked into the heat medium relay unit3from a joint of pipe in the heat medium relay unit3, for example, will be discussed. When a combustible refrigerant that is poorly combustible or highly combustible is employed as the heat source side refrigerant that is circulated in the refrigerant circuit, there is a possibility of catching fire, being ignited, or the like (hereinafter, referred to as “ignited or the like”) as to the leaked heat source side refrigerant. It is related to the refrigerant concentration in the space whether the combustible refrigerant is ignited or the like. The lower the concentration, the lower the possibility of being ignited or the like, and when lower than a limit, the combustible refrigerant does not become ignited or the like. Herein, the limit concentration (kg/m3) not allowing the combustible refrigerant to be ignited or the like is referred to as an “LFL” (Lower Flammability Limit). For example, even if the heat source side refrigerant were to leak into the housing of the heat medium relay unit3, if the refrigerant concentration can be suppressed under the “LFL”, then, it will not lead to any ignition or the like in the housing and safety can be provided. Now, the “LFL” of each refrigerant is different. For example, the “LFL” of R32 is 0.306 (kg/m3), the “LFL” of HFO1234yf is 0.289 (kg/m3).

Change of concentration in a space when refrigerant is leaking into the space can be computed from the following Equation (1). Note that V is spatial volume (m3), C is refrigerant concentration in the space (kg/m3), Mr is refrigerant leakage rate (kg/s), and Q is ventilation volume (m3/s).
V×dC/dt=Mr−C×Q(1)

FIG. 4is an exemplary diagram illustrating results of an experiment on the changes of refrigerant concentration in a space. When a refrigerant leaks out of a joint of pipe in a space where a constant volume of ventilation is carried out, the refrigerant concentration in the space increases instantaneously from the start of leakage. Next, with the drop of the refrigerant pressure inside the pipe, the refrigerant amount leaking from the pipe decreases and the increase in the refrigerant concentration becomes slow. Then, after the refrigerant concentration exhibits its maximum value, the refrigerant concentration becomes lower when the amount of refrigerant leakage becomes smaller than a ventilation volume Q.

Now, an experiment has been conducted on the change of refrigerant concentration in a case in which a refrigerant is leaked from an air-conditioning apparatus into a space where ventilation is being carried out while conditions such as the amount of charged refrigerant, point of leakage, and the like are changed. As illustrated inFIG. 4, it has been understood from the results that, in a general-purpose air-conditioning apparatus, the time it takes from the start of leakage until the maximum refrigerant concentration is indicated is 250 seconds or less (regardless of the conditions).

In an air-conditioning apparatus including the refrigerant concentration detection device40disposed inside the heat medium relay unit3and the shut-off devices50disposed in each of the refrigerant inlet/outlet of the heat medium relay unit3, a case will be discussed in which, after the refrigerant concentration detection device40detects refrigerant leakage, the refrigerant passage is shut off by closing the shut-off devices50when the detection value becomes equivalent to or higher than a predetermined value. Here, when assuming that the refrigerant amount existing in the refrigerant pipe in the heat medium relay unit3is 1 (kg), for example, it is suffice to assume that the refrigerant leakage rate Mr is leaking at Mr=0.004 (kg/s) (=1 (kg)/250 (s)). The refrigerant amount existing in the refrigerant pipe in the heat medium relay unit3is the maximum refrigerant amount during operation when each of the operation modes under each of the environmental conditions is taken into consideration, or is the refrigerant amount obtained by multiplying the refrigerant density (kg/m3) to the total value (m3) of the internal volumes of the refrigerant pipes and each refrigerant component in the heat medium relay unit3. Here, for example, when assuming that the refrigerant is a liquid refrigerant, then the refrigerant density will be about 1000 (kg/m3). Accordingly, the largest refrigerant amount existing in the refrigerant pipes in the heat medium relay unit3is the refrigerant amount obtained by multiplying 1000 (kg/m3) to the total value (m3) of the internal volumes of the refrigerant pipes and the components, through which the refrigerant passes, in the heat medium relay unit3. It is possible to obtain a safer air-conditioning apparatus by obtaining the ventilation volume Q from Equation (1) on the basis of the largest refrigerant amount.

The ultimate refrigerant concentration obtained by solving Equation (1) is the same irrespective of the spatial volume V (m3). In a case in which the refrigerant is R32, the refrigerant concentration inside the heat medium relay unit3can be suppressed under 0.306 (kg/m3), which is the “LFL” of R32, when the ventilation volume Q of the relay-unit air-sending device60is set to 0.01307 (m3/s) or greater, that is 0.784 (m3/min) or greater. Furthermore, in a case in which the refrigerant is HFO1234yf, the refrigerant concentration inside the heat medium relay unit3can be suppressed under 0.289 (kg/m3), which is the “LFL” of HFO1234yf, when the ventilation volume Q of the relay-unit air-sending device60is set to 0.01384 (m3/s) or greater, that is 0.830 (m3/min) or greater.

Here, the refrigerant leakage rate Mr is proportional to the refrigerant amount m. Accordingly, in a case in which the refrigerant amount existing in the refrigerant pipes of the heat medium relay unit3is m (kg), the ventilation volume Q of the relay-unit air-sending device60may be set to m times or greater than the value described above in order to suppress the refrigerant concentration inside the housing of the heat medium relay unit3under the “LFL”. For example, in a case in which R32 is employed as the heat source side refrigerant, the ventilation volume Q of the relay-unit air-sending device60is set to 0.784×m (m3/min) or greater. Furthermore, in a case in which HFO1234yf is employed as the heat source side refrigerant, the ventilation volume Q of the relay-unit air-sending device60is set to 0.830×m (m3/min) or greater. Suppressing of the refrigerant concentration inside the housing of the heat medium relay unit3under the “LFL” corresponding to the refrigerant allows the system to be used safely.

Furthermore, in a case of a mixed refrigerant, calculation is conducted using the composition ratio of each refrigerant. For example, in a case of a mixed refrigerant of HFO1234yf and R32, the ventilation volume Q of the relay-unit air-sending device60may be set to (0.784×ratio (%) of R32+0.830×ratio (%) of HFO1234yf)×m (m3/min) or greater. For example, when the mixed refrigerant includes 20% (0.2) of R32 and 80% (0.8) of HFO1234yf, then, the ventilation volume Q is (0.1568+0.664)×m=0.8228×m (m3/min) or greater.

Furthermore, when R411B that has an “LFL” of 0.239 (kg/m3) is employed as the heat source side refrigerant, then, a ventilation volume Q of 1.004×m (m3/min) or greater is needed. Moreover, when R141b that has an “LFL” of 0.43 (kg/m3) is employed, then, a ventilation volume Q of 0.55×m (m3/min) or greater is needed.

From the above, as to each of the heat source side refrigerants used in the air-conditioning apparatus (refrigerant circuit A), the refrigerant concentration inside the housing of the heat medium relay unit3can be suppressed under the “LFL” if a relay-unit air-sending device60that can achieve these ventilation volume Q is disposed. Hence, a safe system can be configured.

Additionally, in a case in which R290 (propane) that is a highly combustible refrigerant is employed as the heat source side refrigerant, since the “LFL” of R290 is 0.038 (kg/m3), a ventilation volume Q of 6.3×m (m3/min) or greater is needed. Furthermore, in a case in which R1270 (propylene) is employed as the heat source side refrigerant, since the “LFL” of R1270 is 0.043 (kg/m3), a ventilation volume Q of 5.5×m (m3/min) or greater is needed.

Note that in the above description, the amount of refrigerant leaking from the air-conditioning apparatus is reduced to the extent possible by disposing the shut-off devices50. However, the arrangement is not limited to the above. For example, if the relay-unit air-sending device60has the capacity of suppressing the refrigerant concentration inside the housing of the heat medium relay unit3under the “LFL”, taking into account the total refrigerant amount of the air-conditioning apparatus (refrigerant circuit), then the shut-off devices50do not need to be disposed. For example, assuming that the refrigerant amount charged in the overall air-conditioning apparatus is m (kg), when m (kg) is 10 (kg), then, it is only sufficient that the ventilation volume Q of the relay-unit air-sending device60is 0.784 (m3/min) or greater in a case in which R32 is employed as the heat source side refrigerant. Furthermore, when HFO1234yf is employed as the heat source side refrigerant, it is only sufficient that the ventilation volume Q is 0.830×m (m3/min) or greater. As above, it is possible to achieve safety of the air-conditioning apparatus even when no shut-off devices50are disposed.

Note that the relay-unit air-sending device60may be controlled such that an ON/OFF operation of the relay-unit air-sending device60is carried out or a rotation speed control of the relay-unit air-sending device60is carried out, based on the output of the refrigerant concentration detection device40.

Moreover, the outdoor fan60may be stopped when it is determined that the detection value of the refrigerant concentration has continuously been under a predetermined value for a predetermined time. Alternatively, an increase/decrease control of the air volume may be carried out.

Furthermore, refrigerant leakage may occur while the operation of the air-conditioning apparatus is suspended (while the compressor1suspended). Accordingly, the refrigerant concentration detection device40performs determination on the basis of the refrigerant concentration while the operation of the air-conditioning apparatus is suspended. That is, even when the compressor10is in a suspended state, if the detection value of the refrigerant concentration detection device40exceeds a predetermined value, there is refrigerant leakage. In such a case, the relay-unit air-sending device60is operated to suppress the refrigerant concentration inside the housing of the heat medium relay unit3under the “LFL”. As such, it is possible to obtain a safe apparatus. Further, if the refrigerant passage is shut off by the shut-off devices50, then, a safer apparatus can be obtained. Furthermore, if the refrigerant concentration inside the housing of the heat medium relay unit3is suppressed under the “LFL” by driving the relay-unit air-sending device60at the ventilation volume or higher at all times (including when the operation of the air-conditioning apparatus is suspended), then, the refrigerant concentration detection device40does not need to be provided. Moreover, the relay-unit air-sending device60may be driven at the ventilation volume or higher at constant intervals such as every minute.

Additionally, it is preferable that a refrigerant concentration detection device that has a similar function to that of the refrigerant concentration detection device40is provided in the space8where the heat medium relay unit3is disposed and that a second air-sending device for ventilation is provided in a position allowing air to be sent out to the outdoor space6from the space8. Similar to the relay-unit air-sending device60, by suppressing the refrigerant concentration of the space8under the “LFL”, it is possible to assure safety of the building9that uses the air-conditioning apparatus. Here, similar to the relay-unit air-sending device60, on the basis of the output of the refrigerant concentration detection device, an ON/OFF operation, a rotation speed control, constant operation, or the like may be carried out.

Furthermore, the heat medium relay unit3is provided with various detection devices (two heat medium outflow temperature detection devices31, four heat medium outlet temperature detection devices34, four refrigerant inflow/outflow temperature detection devices35, and a refrigerant pressure detection device36). Information (temperature information and pressure information) detected by these detection devices is transmitted to, for example, an outdoor unit control device70that performs integrated control of the operation of the air-conditioning apparatus100. The information is used to control the driving frequency of the compressor10, the rotation speed of the air-sending device (not shown), switching of the first refrigerant flow switching device11, the driving frequency of the pumps21, switching of the second refrigerant flow switching devices18, switching of the heat medium passage, and the like.

Each of the two heat medium outflow temperature detection devices31(a heat medium outflow temperature detection device31aand a heat medium outflow temperature detection device31b) detects the temperature of the heat medium that has flowed out of the corresponding heat exchanger related to heat medium15, namely, the heat medium at an outlet of the corresponding heat exchanger related to heat medium15and may include, for example, a thermistor. The heat medium outflow temperature detection device31ais disposed in the pipe5on the inlet side of the pump21a. The heat medium outflow temperature detection device31bis disposed in the pipe5on the inlet side of the pump21b.

Each of the four heat medium outlet temperature detection devices34(heat medium outlet temperature detection devices34ato34d) is disposed between the corresponding first heat medium flow switching device22and heat medium flow control device25and detects the temperature of the heat medium flowing out of the corresponding use side heat exchanger26. The heat medium outlet temperature detection device34may include, for example, a thermistor. The heat medium outlet temperature detection devices34are arranged so that the number thereof (four in this case) corresponds to the installed number of indoor units2. Note that illustrated from the bottom of the drawing are the heat medium outlet temperature detection device34a, the heat medium outlet temperature detection device34b, the heat medium outlet temperature detection device34c, and the heat medium outlet temperature detection device34dso as to correspond to the respective indoor units2.

Each of the four refrigerant inflow/outflow temperature detection devices35(refrigerant inflow/outflow temperature detection devices35ato35d) is disposed on the inlet side or the outlet side of the heat source side refrigerant of the heat exchanger related to heat medium15and detects the temperature of the heat source side refrigerant flowing into the heat exchanger related to heat medium15or the temperature of the heat source side refrigerant flowing out of the heat exchanger related to heat medium15and may include, for example, a thermistor. The refrigerant inflow/outflow temperature detection device35ais disposed between the heat exchanger related to heat medium15aand the second refrigerant flow switching device18a. The refrigerant inflow/outflow temperature detection device35bis disposed between the heat exchanger related to heat medium15aand the refrigerant expansion device16a. The refrigerant inflow/outflow temperature detection device35cis disposed between the heat exchanger related to heat medium15band the second refrigerant flow switching device18b. The refrigerant inflow/outflow temperature detection device35dis disposed between the heat exchanger related to heat medium15band the refrigerant expansion device16b.

The refrigerant pressure detection device (pressure sensor)36is disposed between the heat exchanger related to heat medium15band the refrigerant expansion device16b, similar to the installation position of the refrigerant inflow/outflow temperature detection device35d, and is configured to detect the pressure of the heat source side refrigerant flowing between the heat exchanger related to heat medium15band the expansion device16b.

Further, the indoor side control device70includes, for example, a microcomputer and controls the driving frequency of the compressor10, switching of the first refrigerant flow switching device11, driving of the pumps21, the opening degree of each expansion device16, opening and closing of each opening and closing device17, switching of the second refrigerant flow switching devices18, switching of the first heat medium flow switching devices22, switching of the second heat medium flow switching devices23, and the opening degree of each heat medium flow control device25, on the basis of signals associated to detection by the various detection devices and an instruction from a remote control to carry out the operation. Furthermore, in the present embodiment, a relay unit control device71constituted by a microcomputer or the like is also included. The relay unit control device71controls the relay-unit air-sending device60on the basis of the detection of the refrigerant concentration detection device40. While the refrigerant concentration detection device40and the relay unit control device71are provided separately, the controller may carry out the process carried out by the refrigerant concentration detection device40. Moreover, the indoor side control device70and the relay unit control device71may be integrated and the indoor side control device70may carry out control of the relay-unit air-sending device60.

The pipes5in which the heat medium flows include the pipes connected to the heat exchanger related to heat medium15aand the pipes connected to the heat exchanger related to heat medium15b. The pipes5are branched into pipes5ato pipes5d(into four branches in this case) in accordance with the number of indoor units2connected to the heat medium relay unit3. Further, the pipes5are connected by the first heat medium flow switching devices22and the second heat medium flow switching devices23. Control of the first heat medium flow switching devices22and the second heat medium flow switching devices23determines whether the heat medium flowing from the heat exchanger related to heat medium15ais allowed to flow into the use side heat exchanger26or whether the heat medium flowing from the heat exchanger related to heat medium15bis allowed to flow into the use side heat exchanger26. For example, when the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15bare both cooling or heating the heat medium, control is carried out such that each heat medium that has exchanged heat in both the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15bare merged in the second heat medium flow switching devices23, the resultants are made to flow into the use side heat exchangers26, thereafter, the heat medium are branched in the first heat medium flow switching devices22, and are returned to the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15b. Furthermore, when the heat exchanger related to heat medium15ais cooling the heat medium and when the heat exchanger related to heat medium15bis heating the heat medium, control is carried out such that each of the first heat medium flow switching devices22and each of the second heat medium flow switching devices23is switched so that either the cooled heat medium or the heated heat medium is selected to be made to flow into the respective use side heat exchangers26.

Now, in the air-conditioning apparatus100, the compressor10, the first refrigerant flow switching device11, the heat source side heat exchanger12, the opening and closing devices17, the second refrigerant flow switching devices18, a refrigerant passage of the heat exchanger related to heat medium15a, the refrigerant expansion devices16, and the accumulator19are connected by the refrigerant pipes4, thus forming the refrigerant circuit A. In addition, a heat medium passage of the heat exchanger related to heat medium15a, the pumps21, the first heat medium flow switching devices22, the heat medium flow control devices25, the use side heat exchangers26, and the second heat medium flow switching devices23are connected by the pipes5, thus forming the heat medium circulating circuit B. In other words, the plurality of use side heat exchangers26are connected in parallel to each of the heat exchangers related to heat medium15, thus forming the heat medium circulating circuit B into a multiple system.

Accordingly, in the air-conditioning apparatus100, the outdoor unit1and the heat medium relay unit3are connected through the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15barranged in the heat medium relay unit3. The heat medium relay unit3and each indoor unit2are also connected through the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15b. In other words, in the air-conditioning apparatus100, the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15beach exchange heat between the heat source side refrigerant circulating in the refrigerant circuit A and the heat medium circulating in the heat medium circulating circuit B.

FIG. 3Ais a schematic circuit diagram illustrating another exemplary circuit configuration of the air-conditioning apparatus (hereinafter, referred to as an “air-conditioning apparatus100A”) according to the embodiment of the invention. The configuration of the air-conditioning apparatus100A in a case in which the heat medium relay unit3is separated into a main heat medium relay unit3aand a sub heat medium relay unit3bwill be described with reference toFIG. 3A. As illustrated inFIG. 3A, the housing of the heat medium relay unit3is separated such that the heat medium relay unit3is composed of the main heat medium relay unit3aand the sub heat medium relay unit3b. This separation allows a plurality of sub heat medium relay units3bto be connected to the single main heat medium relay unit3aas illustrated inFIG. 2.

The main heat medium relay unit3aincludes a gas-liquid separator14and an expansion device16c. Other components are arranged in the sub heat medium relay unit3b. The gas-liquid separator14is connected to a single refrigerant pipe4connected to the outdoor unit1and is connected to two refrigerant pipes4connected to the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15bin the sub heat medium relay unit3b, and is configured to separate the heat source side refrigerant supplied from the outdoor unit1into a vapor refrigerant and a liquid refrigerant. The expansion device16c, disposed on the downstream side regarding the flow direction of the liquid refrigerant flowing out of the gas-liquid separator14, has functions of a reducing valve and an expansion valve and decompresses and expands the heat source side refrigerant. During the cooling and heating mixed operation, the expansion device16cis controlled such that an outlet thereof is at an intermediate pressure. The expansion device16cmay include a component that can variably control its opening degree, such as an electronic expansion valve. This arrangement allows a plurality of sub heat medium relay units3bto be each connected to the main heat medium relay unit3awith three pipes.

The air-conditioning apparatus100according to the present embodiment is provided with several operation modes. In these operation modes, the heat source side refrigerant flows through the pipes4connecting the outdoor unit1and the heat medium relay unit3.

In the several operation modes carried out by the air-conditioning apparatus100according to the embodiment, a heat medium, such as water or antifreeze, flows through the pipes5connecting the heat medium relay unit3and the indoor units2.

The operation modes carried out by the air-conditioning apparatus100will now be described. The air-conditioning apparatus100allows each indoor unit2to perform a cooling operation or a heating operation on the basis of a command from the indoor unit2. That is, the air-conditioning apparatus100allows all of the indoor units2to perform the same operation and also allows each of the indoor units2to perform different operations.

The operation modes carried out by the air-conditioning apparatus100includes a cooling only operation mode in which all of the operating indoor units2perform the cooling operation, a heating only operation mode in which all of the operating indoor units2perform the heating operation, a cooling main operation mode in which a cooling load is larger, and a heating main operation mode in which a heating load is larger. Note that the air-conditioning apparatus100A carries out various operation modes similar to those above.

Now, in the air-conditioning apparatus100, when only the heating load or the cooling load is occurring in the use side heat exchangers26, the corresponding first heat medium flow switching devices22and the corresponding second heat medium flow switching devices23are set to a medium opening degree such that the heat medium flows into both of the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15b. Consequently, since both the heat exchanger related to heat medium15aand the heat exchanger related to heat medium15bcan be used for the heating operation or the cooling operation, the heat transfer area can be increased, and, accordingly, an efficient heating operation or cooling operation can be performed.

In addition, when the heating load and the cooling load are simultaneously occurring in the use side heat exchangers26, the first heat medium flow switching device22and the second heat medium flow switching device23corresponding to the use side heat exchanger26which performs the heating operation are switched to the passage connected to the heat exchanger related to heat medium15bfor heating, and the first heat medium flow switching device22and the second heat medium flow switching device23corresponding to the use side heat exchanger26which performs the cooling operation are switched to the passage connected to the heat exchanger related to heat medium15afor cooling, so that the heating operation or cooling operation can be freely performed in each indoor unit2.

Furthermore, each of the first heat medium flow switching devices22and the second heat medium flow switching devices23described in the embodiment may be any of the sort as long as they can switch passages, for example, a three-way valve capable of switching between three passages or a combination of two opening and closing valves and the like switching between two passages. Alternatively, components such as a stepper motor driven mixing valve capable of changing flow rates of three passages or electronic expansion valves capable of changing flow rates of two passages used in combination may be used as each of the first heat medium flow switching devices22and the second heat medium flow switching devices23. In this case, water hammer caused when a passage is suddenly opened or closed can be prevented. Furthermore, in the embodiment, while an exemplary description has been given in which each of the heat medium flow control devices25is a two-way valve, each of the heat medium flow control devices25may be a control valve having three passages and may be disposed with a bypass pipe that bypasses the corresponding use side heat exchanger26.

Furthermore, as regards each of the use side heat medium flow control devices25, a stepping-motor-driven type that is capable of controlling the flow rate in the passage is preferably used. A two-way valve or a three-way valve with a closed end may be used. Alternatively, as regards each of the use side heat medium flow control devices25, a component, such as an opening and closing valve, which is capable of opening or closing a two-way passage, may be used while ON/OFF operations are repeated to control the average flow rate.

Furthermore, while each second refrigerant flow switching device18has been described as if it is a four-way valve, the device is not limited to this type. The device may be configured such that the heat source side refrigerant flows in the same manner using a plurality of two-way flow switching valves or three-way flow switching valves.

While a description has been given that the air-conditioning apparatus100according to the present embodiment is capable of performing the cooling and heating mixed operation, the apparatus is not limited to this case. The same advantages can be obtained even in an apparatus that is configured by a single heat exchanger related to heat medium15and a single expansion device16having a plurality of use side heat exchangers26and heat medium flow control valves25connected in parallel thereto allowing only a cooling operation or a heating operation to be carried out.

In addition, it is needless to mention that the same holds true for the case in which only a single use side heat exchanger26and a single heat medium flow control valve25are connected. Moreover, it is needless to mention that no problem will arise even if the heat exchanger related to heat medium15and the expansion device16acting in the same manner are arranged in plural numbers. Furthermore, while a case has been described in which the heat medium flow control valves25are equipped in the heat medium relay unit3, the arrangement is not limited to this case. Each heat medium flow control valve25may be disposed in the indoor unit2. The heat medium relay unit3and the indoor unit2may be constituted in different housings.

As regards the heat medium, for example, brine (antifreeze), water, a mixed solution of brine and water, or a mixed solution of water and an additive with high anticorrosive effect can be used. Accordingly, in the air-conditioning apparatus100, even if the heat medium leaks into the indoor space7through the indoor unit2, because the employed heat medium is highly safe, contribution to improvement of safety can be made.

Further, the heat source side heat exchanger12and the use side heat exchangers26ato26dare typically arranged with an air-sending device in which condensing or evaporation is promoted by sending air; however, the heat source side heat exchanger12and the use side heat exchangers26ato26dare not limited to the above, a panel heater using radiation can be used as the use side heat exchangers26ato26dand a water-cooled heat exchanger which transfers heat using water or antifreeze can be used as the heat source side heat exchanger12. Any component structured to radiate or absorb heat may be used.

Furthermore, while an exemplary description with four use side heat exchangers26ato26dhas been given, the number is not limited in particular and any number thereof can be connected.

Furthermore, description has been made illustrating a case in which there are two heat exchangers related to heat medium15, namely, the heat exchanger related to heat mediums15aand15b. As a matter of course, the arrangement is not limited to this case, and any number of heat exchangers related to heat medium may be disposed as long as it is arranged such that cooling and/or heating of the heat medium can be carried out.

Furthermore, each of the number of pumps21aand21bis not limited to one. A plurality of pumps having a small capacity may be used in parallel.

Moreover, the air-sending device disposed in the outdoor unit1is not limited to the described system. The same holds true for a direct expansion air conditioner that circulates a refrigerant into the indoor unit and the same advantages can be enjoyed.

As described above, in the air-conditioning apparatus (the air-conditioning apparatus100and the air-conditioning apparatus100A) according to the present embodiment, since the relay-unit air-sending device(s)60is driven such that the heat source side refrigerant is discharged at a predetermined ventilation volume, even when a heat source side refrigerant with combustibility leaks into the housing of the heat medium relay unit3, increase of the refrigerant concentration inside the heat medium relay unit3can be prevented, ignition or the like can be prevented, and safety of the outdoor unit1and the air-conditioning apparatus can be increased. Here, by setting the ventilation volume in accordance with the “LFL” of the employed refrigerant, ignition or the like can be readily prevented. At this time, with respect to the refrigerant amount m (kg), the ventilation volume of 0.55×m (m3/min) or greater is secured; hence, it is possible to correspond to a variety of refrigerants used in the air-conditioning apparatus. Here, by setting the refrigerant amount on the basis of the internal volume of the refrigerant pipes and devices of the heat medium relay unit3, it is possible to efficiently set the needed ventilation volume for maintaining safety. Moreover, by assuming the refrigerant density to be 1000 (kg/m3) and by setting the ventilation volume on the basis of the maximum refrigerant amount that can be assumed, ignition or the like can be readily prevented.

Further, since the refrigerant concentration detection device40is provided and the relay-unit air-sending device60is driven based on the refrigerant concentration according to the detection of the refrigerant concentration sensor41, it is possible to efficiently drive the relay-unit air-sending device60when the refrigerant concentration is equivalent to or higher than a predetermined concentration. Furthermore, since the shut-off devices50are provided in each of the refrigerant inlet/outlet of the heat medium relay unit3and each of the shut-off devices50is made to shut off the flow of the heat source side refrigerant flowing in or out of the heat medium relay unit3on the basis of the determination of the refrigerant concentration detection device40, it is possible to suppress the amount of heat source side refrigerant leakage to only the refrigerant amount confined in the heat medium relay unit3. Additionally, since the amount of refrigerant leakage is small, the ventilation volume Q of the relay-unit air-sending device60can be small.

In addition, by opening the portions of the housing of the heat medium relay unit3and forming the first hole61A and the second hole61B that serve as the opening61, the heat source side refrigerant that has leaked into the housing of the heat medium relay unit3can be discharged and, thus, it is possible to maintain the refrigerant concentration inside the housing under a constant value. Here, since the opening61is opened such that the total opening area of the opening61is equivalent to or larger than 10% of the surface area of the housing of the heat medium relay unit3, the heat source side refrigerant can be efficiently discharged to the outside of the housing of the heat medium relay unit3and the refrigerant concentration can be suppressed under a predetermined value without increase in the ventilation resistance. Hence, a safe apparatus can be obtained.