When indoor units are performing a cooling operation, an air-conditioning apparatus controls four flow passage switching valves, for example a first solenoid valve, a second solenoid valve, a third solenoid valve, and a fourth solenoid valve, so that a number of intermediate heat exchangers operating as evaporators is greater than in a cooling main operation. During the cooling main operation, a target value for suction pressure or evaporating temperature at a compressor is set equal to or lower than that in a case in which the indoor units are performing the cooling operation, and a frequency of the compressor and a capacity of a heat-source-side heat exchanger are controlled.

TECHNICAL FIELD

The present invention relates to an air-conditioning apparatus using a refrigeration cycle and, more particularly, to an air-conditioning apparatus that performs heat transport of cooling energy or heating energy generated in a refrigeration cycle to a use-side heat exchanger using a different heat medium.

BACKGROUND ART

A cooling and heating simultaneous air-conditioning apparatus in which a relay unit and a plurality of indoor units are connected to an outdoor unit and which is capable of performing a cooling operation in which the operation mode of an operating indoor unit is cooling only, a heating operation in which the operation mode of an operating indoor unit is heating only, and a mixed (simultaneous) operation in which indoor units perform cooling and heating, is available (see, for example, Patent Literatures 1 to 3).

Patent Literature 1 describes a method for controlling the compressor frequency of the cooling and heating simultaneous air-conditioning apparatus and the heat exchange capacity of an outdoor heat exchanger.

Furthermore, Patent Literatures 2 and 3 describe a system in which an intermediate heat exchanger is provided in a relay unit and which performs a cooling and heating simultaneous operation in which heat transport from an outdoor unit to the relay unit is performed using a refrigerant, heat exchange between the refrigerant and brine in a refrigeration cycle is performed in the intermediate heat exchanger, and heat transport from the relay unit to an indoor unit is performed using the brine, and a control method on the water side.

CITATION LIST

Patent Literatures

SUMMARY OF INVENTION

Technical Problem

In the cooling and heating simultaneous air-conditioning apparatus described in Patent Literature 1, a method for controlling the condensing temperature and the evaporating temperature of the refrigerant in the compressor and the indoor unit at predetermined target values in order to exhibit a capacity corresponding to the load of the indoor unit is described.

In contrast, in the air-conditioning apparatus described in Patent Literatures 2 and 3, typically, the number of installed intermediate heat exchangers is smaller than the number of connected indoor units. Thus, the heat exchange capacity of the intermediate heat exchangers cannot be changed continuously upon ON or OFF of cooling and heating of the indoor units. This poses a problem that even when the condensing temperature and the evaporating temperature are controlled at predetermined values, the cooling and heating capacities may vary depending on the load and the operation modes of the indoor units.

The present invention has been made to solve the above-mentioned problem, and has as its object to provide an air-conditioning apparatus which maintains cooling and heating capacities even when the load conditions vary and which is capable of operating in a state where the cycle efficiency is high.

Solution to Problem

An air-conditioning apparatus according to the present invention includes a heat source unit including a compressor, a first flow passage switching valve that switches a flow passage of a first refrigerant, and a heat-source-side heat exchanger; a plurality of indoor units each including a use-side heat exchanger; and a relay unit including a plurality of intermediate heat exchangers, second flow passage switching valves that switch operation of the indoor units between heating and cooling, and third flow passage switching valves that switch connection of the intermediate heat exchangers between a condenser and an evaporator. In the air-conditioning apparatus, a primary-side cycle is formed through which a primary-side heat transfer medium circulates between the heat source unit and the relay unit, a secondary-side cycle is formed through which a secondary-side heat transfer medium circulates between the relay unit and the indoor units, and heat exchange is performed between the primary-side cycle and the secondary-side cycle in the intermediate heat exchangers. When all of operating indoor units out of the plurality of indoor units are performing a cooling operation, the third flow passage switching valves are controlled such that the number of the intermediate heat exchangers operating as evaporators is greater than in a cooling main operation in which the indoor unit performing cooling and the indoor unit performing heating exist at the same time and the first flow passage switching valve is controlled so that the heat-source-side heat exchanger operates by being connected to a discharge side of the compressor. During the cooling main operation, a target value for a suction pressure or an evaporating temperature at the compressor is set equal to or lower than a case where all of the operating indoor units are performing the cooling operation, and a frequency of the compressor and a capacity of the heat-source-side heat exchanger are controlled.

An air-conditioning apparatus according to the present invention includes a heat source unit including a compressor, a first flow passage switching valve that switches a flow passage of a first refrigerant, and a heat-source-side heat exchanger; a plurality of indoor units each including a use-side heat exchanger; and a relay unit including a plurality of intermediate heat exchangers, second flow passage switching valves that switch operation of the indoor units between heating and cooling, and third flow passage switching valves that switch connection of the intermediate heat exchangers between a condenser and an evaporator. In the air-conditioning apparatus, a primary-side cycle is formed through which a primary-side heat transfer medium circulates between the heat source unit and the relay unit, a secondary-side cycle is formed through which a secondary-side heat transfer medium circulates between the relay unit and the indoor units, and heat exchange is performed between the primary-side cycle and the secondary-side cycle in the intermediate heat exchangers. When all of operating indoor units out of the plurality of indoor units are performing a heating operation, the third flow passage switching valves are controlled such that the number of the intermediate heat exchangers operating as condensers is greater than in a heating main operation in which the indoor unit performing cooling and the indoor unit performing heating exist at the same time and the first flow passage switching valve is controlled so that the heat-source-side heat exchanger operates by being connected to a suction side of the compressor. During the heating main operation, a target value for a discharge pressure or a condensing temperature at the compressor is set equal to or higher than a case where all of the operating indoor units are performing the heating operation, and a frequency of the compressor and a capacity of the heat-source-side heat exchanger are controlled.

Advantageous Effects of Invention

In an air-conditioning apparatus according to the present invention, even when the load conditions vary, cooling and heating capacities are maintained, and operation can be performed in a state where the cycle efficiency, such as COP, is high.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a refrigerant circuit diagram illustrating an example of the refrigerant circuit configuration of an air-conditioning apparatus100according to Embodiment 1 of the present invention.FIG. 2is a refrigerant circuit diagram illustrating another example of the refrigerant circuit configuration of the air-conditioning apparatus100according to Embodiment 1 of the present invention. The circuit configuration and operation of the air-conditioning apparatus100will be explained with reference toFIGS. 1 and 2. The air-conditioning apparatus allows each indoor unit to freely select a cooling mode or a heating mode using a refrigeration cycle. In the drawings provided below includingFIG. 1, the size relationship of individual components may be different from the actual size relationship.

InFIG. 1, the air-conditioning apparatus100includes a heat source unit (outdoor unit) A, a plurality of indoor units C to E connected in parallel, and a relay unit B interposed between the heat source unit A and the indoor units C to E. In Embodiment 1, the case where one relay unit and three indoor units are connected to one heat source unit will be explained. However, the illustration is not intended to limit the number of the units connected. For example, two or more heat source units, two or more relay units, and two or more indoor units may be connected.

Furthermore, the number of operating indoor units connected to the relay unit B may be larger than the number of intermediate heat exchangers within the relay unit B, which will be described later, and even when the number of installed intermediate heat exchangers is equal to the number of connected indoor units, the variation range of the capacity of the intermediate heat exchangers may be different from the variation range of the capacity of the indoor units. This represents, for example, the case in which two intermediate heat exchangers are mounted in the relay unit B, two indoor units are connected to the relay unit B, the heat exchange capacities of the two intermediate heat exchangers are the same, and the capacities of the two indoor units are different. However, Embodiment 1 assumes that the capacities of the indoor units C to E are the same and the capacities of the two intermediate heat exchangers are the same.

A primary-side cycle through which a primary-side heat transfer medium (referred to as refrigerant, hereinafter) circulates is formed between the heat source unit A and the relay unit B, a secondary-side cycle through which a secondary-side heat transfer medium (referred to as brine, hereinafter) circulates is formed between the relay unit B and each of the indoor units C to E, and heat exchange between the primary-side cycle and the secondary-side cycle is performed in intermediate heat exchangers9aand9barranged within the relay unit B. That is, in the air-conditioning apparatus100, cooling energy and heating energy generated by the heat source unit A are transferred to the indoor units C to E via the intermediate heat exchangers9aand9bof the relay unit B.

As the refrigerant, a refrigerant used in a vapor-compression heat pump, such as a fluorocarbon refrigerant (for example, an HFC-type refrigerant, such as an R32 refrigerant, R125, or R134a, a mixture of the above refrigerants, such as R410A, R407c, R404A, or the like), an HFO refrigerant (for example, HFO-1234yf, HFO-1234ze(E), or HFO-1234ze(Z)), a CO2refrigerant, an HC refrigerant (for example, propane or isobutane refrigerant), an ammonia refrigerant, or a mixed refrigerant of the above refrigerants, such as a mixed refrigerant of R32 and HFO-1234yf, may be used. Furthermore, as the brine, water, antifreeze, or water containing an anti-corrosion material as an additive may be used.

The heat source unit A is typically positioned in a space outside a construction, such as a building (for example, a rooftop or the like), and supplies cooling energy or heating energy to the indoor units C to E via the relay unit B. However, the heat source unit A need not be installed outdoors. For example, the heat source unit A may be installed in an enclosed space, such as a machine room equipped with an ventilation opening. The heat source unit A may be installed inside a construction as long as waste heat can be exhausted outside the construction via an exhaust duct. Alternatively, a heat source unit A of a water-cooled type may be installed inside a construction. The area in which the heat source unit A is installed is irrelevant to any particular problem involved.

The heat source unit A includes a compressor1, a four-way valve2, which serves as a first flow passage switching valve that switches the direction in which a refrigerant circulates, a heat-source-side heat exchanger3, and an accumulator4. The above-mentioned components are connected by a first refrigerant pipe6and a second refrigerant pipe7. In the vicinity of the heat-source-side heat exchanger3, a flow control device3-mfor controlling the flow rate of fluid that exchanges heat with a refrigerant is installed. Hereinafter, a heat-source-side heat exchanger3of an air-cooled type will be explained as an example of the heat-source-side heat exchanger3and a fan3-mwill be explained as an example of the flow control device3-m. However, a heat-source-side heat exchanger3of another type, such as a water-cooled type (in this case, the flow control device3-mis a pump), may be used as long as a refrigerant exchanges heat with another fluid. A method for controlling the compressor1and the fan3-m, and a method for switching the four-way valve2will be described later.

The heat source unit A also includes a first connecting pipe60A, a second connecting pipe60B, a check valve14, a check valve16, a check valve17, and a check valve15. By providing the first connecting pipe60A, the second connecting pipe60B, the check valve14, the check valve16, the check valve17, and the check valve15, a high-pressure refrigerant flows out of the heat source unit A via the first refrigerant pipe6and a low-pressure refrigerant flows into the heat source unit A via the second refrigerant pipe7, regardless of the direction in which the four-way valve2is connected.

The compressor1sucks a heat-source-side refrigerant and compresses the heat-source-side refrigerant into a high-temperature and high-pressure state, and is desirably configured as, for example, a capacity-controllable inverter compressor or the like. The four-way valve2switches between the flow of the heat-source-side refrigerant at the time of a heating operation (in a heating only operation mode and a heating main operation mode) and the flow of the heat-source-side refrigerant at the time of a cooling operation (in a cooling only operation mode and a cooling main operation mode). The heat-source-side heat exchanger (outdoor heat exchanger)3functions as an evaporator during a heating operation while functioning as a condenser (or a radiator) during a cooling operation, exchanges heat between air supplied from the fan3-mand the heat-source-side refrigerant, and transforms the heat-source-side refrigerant into vapor or condensate according to the circumstances involved. The accumulator4is provided on the suction side of the compressor1, and stores an excess refrigerant generated due to the difference between a heating operation and a cooling operation or an excess refrigerant generated due to a transient change in operation.

The check valve14is provided at the first refrigerant pipe6between the heat-source-side heat exchanger3and the relay unit B, and allows the heat-source-side refrigerant to flow only in a predetermined direction (the direction from the heat source unit A to the relay unit B). The check valve15is provided at the second refrigerant pipe7between the relay unit B and the four-way valve2, and allows the heat-source-side refrigerant to flow only in another predetermined direction (the direction from the relay unit B to the heat source unit A). The check valve16is provided at the first connecting pipe60a, and causes the heat-source-side refrigerant discharged from the compressor1to circulate to the relay unit B during a heating operation. The check valve17is provided at the connecting pipe60b, and causes the heat-source-side refrigerant returned from the relay unit B to circulate to the suction side of the compressor1during a heating operation.

The first connecting pipe60aconnects between the second refrigerant pipe7between the four-way valve2and the check valve15, and the first refrigerant pipe6between the check valve14and the relay unit B, within the heat source unit A. The second connecting pipe60bconnects between the second refrigerant pipe7between the check valve15and the relay unit B, and the first refrigerant pipe6between the heat-source-side heat exchanger3and the check valve14, within the heat source unit A.

The heat source unit A moreover includes a pressure gauge31, a pressure gauge32, and a thermometer41. The pressure gauge31is provided on the discharge side of the compressor1and measures the pressure of the refrigerant discharged from the compressor1. The pressure gauge32is provided on the suction side of the compressor1and measures the pressure of the refrigerant sucked into the compressor1. The thermometer41is provided in the vicinity of the heat-source-side heat exchanger3and measures the temperature of the outside air taken in by the fan3-m. The pieces of information (temperature information and pressure information) detected by the above-mentioned detection devices are sent to a controller (for example, control means50) that performs overall control of the operation of the air-conditioning apparatus100, and are used to control each actuator.

The relay unit B is installed in, for example, a space on, for example, the lower side of the roof, which is formed inside a construction but is different from an indoor space, and transfers, to the indoor units C to E, cooling energy or heating energy supplied from the heat source unit A. However, the relay unit B may be installed in a shared space in which an elevator or the like is installed, or the like.

As branch portions on the refrigerant side, the relay unit B includes a first branch portion8ainto which a high-pressure refrigerant flows from the heat source unit A, a second branch portion8bfrom which a low-pressure refrigerant flows out towards the heat source unit A, and a third branch portion8cin which the refrigerant has an intermediate pressure. Furthermore, as branch portions on the brine side, the relay unit B includes a fourth branch portion8dand a fifth branch portion8ecorresponding to the high-pressure side of brine, and a sixth branch portion8fand a seventh branch portion8gcorresponding to the low-pressure side of brine.

Furthermore, the relay unit B includes the first intermediate heat exchanger9aand the second intermediate heat exchanger9bwhich exchange heat between a refrigerant and a second refrigerant, a first pump18aand a second pump18bwhich drive the second refrigerant, a first flow control device10awhich controls the flow rate of the refrigerant, a second flow control device10bwhich controls the flow rate of the refrigerant, a third flow control device12awhich controls the flow rate of the refrigerant, a fourth flow control device12bwhich controls the flow rate of the refrigerant, and a refrigerant-refrigerant heat exchanger13which exchanges heat between refrigerants.

At the first branch portion8a, the first refrigerant pipe6is branched in order to connect the first refrigerant pipe6to each of the intermediate heat exchangers9aand9b. At the second branch portion8b, the second refrigerant pipe7is branched in order to connect the second refrigerant pipe7to each of the intermediate heat exchangers9aand9b. The third branch portion8cis provided between the first flow control device10aand the second flow control device10b, and the third flow control device12aand the fourth flow control device12b, and connects the intermediate heat exchangers9aand9bin series or in parallel.

A first solenoid valve11ais provided at the pipe between the first branch portion8aand the intermediate heat exchanger9a. A second solenoid valve11bis provided at the pipe between the first branch portion8aand the intermediate heat exchanger9b. A third solenoid valve11cis provided at the pipe between the second branch portion8band the intermediate heat exchanger9a. A fourth solenoid valve11dis provided at the pipe between the second branch portion8band the intermediate heat exchanger9b. The first solenoid valve11a, the second solenoid valve11b, the third solenoid valve11c, and the fourth solenoid valve11deach operate as a third flow passage switching valve for selectively switching the connection of the intermediate heat exchanger9aor9bbetween a condenser and an evaporator, and each allow the intermediate heat exchanger9aor9bto be switchably connected to the first branch portion8aor the second branch portion8b.

The first solenoid valve11aand the third solenoid valve11care installed on a side opposite to the side of the first flow control device10awith respect to the intermediate heat exchanger9a. Furthermore, the second solenoid valve11band the fourth solenoid valve11dare installed on a side opposite to the side of the second flow control device10bwith respect to the intermediate heat exchanger9b. The flow of refrigerant in the intermediate heat exchangers9aand9bwill be explained later in [Circuit Configuration].

The fourth branch portion8dbranches the brine that has flowed out of the intermediate heat exchanger9ainto the first brine pipes6c,6d, and6e. The fifth branch portion8ebranches the brine that has flowed out of the intermediate heat exchanger9binto the first brine pipes6c,6dand6e. The sixth branch portion8fcombines the brines that have flowed through the second brine pipes7c,7dand7etogether, and allows the combined brine to flow into the intermediate heat exchanger9a. The seventh branch portion8gcombines the brines that have flowed through the second brine pipes7c,7dand7etogether, and allows the combined brine to flow into the intermediate heat exchanger9b.

A switching valve19cis installed at the first brine pipe6cbetween the fourth branch portion8dand an indoor heat exchanger (use-side heat exchanger)5c. A switching valve19dis installed at the first brine pipe6dbetween the fourth branch portion8dand an indoor heat exchanger5d. A switching valve19eis installed at the first brine pipe6ebetween the fourth branch portion8dand an indoor heat exchanger5e. A switching valve19fis installed at the first brine pipe6cbetween the fifth branch portion8eand the indoor heat exchanger5c. A switching valve19gis installed at the first brine pipe6dbetween the fifth branch portion8eand the indoor heat exchanger5d. A switching valve19his installed at the first brine pipe6ebetween the fifth branch portion8eand the indoor heat exchanger5e.

The switching valves19c,19d,19e,19f,19g, and19hoperate as second flow passage switching valves that switch the flow passage of brine, and allow the indoor units C to E to be switchably connected to the fourth branch portion8dor the fifth branch portion8e.

A switching valve19iis installed at the second brine pipe7cbetween the sixth branch portion8fand the indoor heat exchanger5c. A switching valve19jis installed at the second brine pipe7dbetween the sixth branch portion8fand the indoor heat exchanger5d. A switching valve19kis installed at the second brine pipe7ebetween the sixth branch portion8fand the indoor heat exchanger5e. A switching valve19lis installed at the second brine pipe7cbetween the seventh branch portion8gand the indoor heat exchanger5c. A switching valve19mis installed at the second brine pipe7dbetween the seventh branch portion8gand the indoor heat exchanger5d. A switching valve19nis installed at the second brine pipe7ebetween the seventh branch portion8gand the indoor heat exchanger5e.

The switching valves19i,19j,19k,19l,19m, and19noperate as second flow passage switching valves which switch the flow passage of brine, and allow the indoor units C to E to be switchably connected to the sixth branch portion8for the seventh branch portion8g.

In Embodiment 1, the case in which two sets of intermediate heat exchangers, flow control devices, and pumps are installed will be exemplified. However, the number of the components installed is not limited to that as illustrated. That is, the air-conditioning apparatus100includes a plurality of intermediate heat exchangers installed to be capable of a cooling and heating simultaneous operation. As the number of sets of intermediate heat exchangers, flow control devices, and pumps increases, the heat exchange capacities for cooling and heating of the intermediate heat exchangers can be stably, continuously switched according to the load of an indoor unit.

The relay unit B includes thermometers33ato33dthat measure the temperatures of refrigerant at the inlets and outlets of the intermediate heat exchangers9aand9b, a thermometer33ethat measures the temperature of refrigerant between the refrigerant-refrigerant heat exchanger13and the second branch portion8b, thermometers34aand34bthat measure the temperatures of brine on the downstream sides of the first pump18aand the second pump18b, respectively, and thermometers34cto34ethat measure the temperatures of brine between the indoor heat exchangers5cto5eand flow control devices20cto20e, respectively. The pieces of information (temperature information) detected by the above-mentioned detection devices are sent to a controller (for example, control means51) that performs overall control of the operation of the air-conditioning apparatus100, and are used to control each actuator.

[Indoor Units C to E]

The indoor units C to E are each installed at a position from which conditioned air can be supplied to an air-conditioning target space, such as an indoor space, and each supply cooling air or heating air to the air-conditioning target space using cooling energy or heating energy from the heat source unit A transferred via the relay unit B.

The indoor heat exchanger5is mounted in each of the indoor units C to E. Reference symbols c to e are assigned to the indoor heat exchangers5in correspondence with the indoor units C to E, respectively. The indoor heat exchanger5cis connected to the sixth branch portion8for the seventh branch portion8gof the relay unit B via the second brine pipe7c, and is connected to the fourth branch portion8dor the fifth branch portion8eof the relay unit B via the first brine pipe6c. The indoor heat exchanger5dis connected to the sixth branch portion8for the seventh branch portion8gof the relay unit B via the second brine pipe7d, and is connected to the fourth branch portion8dor the fifth branch portion8eof the relay unit B via the first brine pipe6d. The indoor heat exchanger5eis connected to the sixth branch portion8for the seventh branch portion8gof the relay unit B via the second brine pipe7e, and is connected to the fourth branch portion8dor the fifth branch portion8eof the relay unit B via the first brine pipe6e.

The indoor heat exchangers5each exchange heat between air supplied from an air-sending device of a fan5-mand a heat medium, and generate heating air or cooling air to be supplied to the air-conditioning target space. Furthermore, in the vicinity of each of the indoor heat exchangers5, a flow control device5-mthat controls the flow rate of fluid that exchanges heat with refrigerant is installed. Hereinafter, indoor heat exchangers5of an air-cooled type will be taken as an example of the indoor heat exchangers5, and fans5-mwill be taken as an example of the flow control devices5-m. However, indoor heat exchangers5of a different type, such as a water-cooled type (in this case, the flow control devices5-mare pumps), may be used as long as refrigerant exchanges heat with another fluid. Reference symbols c to e are assigned to the fans5-min correspondence with the indoor units C to E, respectively.

Thermometers42-cto42-ethat measure the current temperatures of air-conditioning target spaces, such as indoor spaces, are provided in the indoor units C to E, respectively. The pieces of information (temperature information) detected by these detection devices are sent to controllers (for example, control means52c,52d, and52e) that perform overall control of the operation of the air-conditioning apparatus100, and are used to control each actuator.

A narrow pipe that connects between the heat-source-side heat exchanger3and the first branch portion8aof the relay unit B is referred to as the first refrigerant pipe6. Pipes that connect between the indoor heat exchangers5c,5d, and5eof the indoor units C, D, and E and the fourth branch portion8dor the fifth branch portion8eof the relay unit B are referred to as the first brine pipes6c,6d, and6e. The first brine pipes6c,6d, and6ecorrespond to the first refrigerant pipe6.

A pipe that has a width larger than that of the first refrigerant pipe6and connects between the four-way valve2and the second branch portion8bof the relay unit B is referred to as the second refrigerant pipe7. Pipes that connect between the indoor heat exchangers5c,5d, and5eof the indoor units C, D, and E and the sixth branch portion8for the seventh branch portion8gof the relay unit B are referred to as the second brine pipes7c,7d, and7e. The second brine pipes7c,7d, and7ecorrespond to the second refrigerant pipe7.

Accordingly, the refrigerant flows from the heat source unit A to the relay unit B in the first refrigerant pipe6and flows from the relay unit B to the heat source unit A in the second refrigerant pipe7. Furthermore, brine, serving as the second refrigerant, flows from the relay unit B to the indoor units C to E in the first brine pipes6cto6e, respectively, and flows from the indoor units C to E to the relay unit B in the second brine pipes7cto7e, respectively.

The circuit configuration of the primary-side cycle in the heat source unit A and the relay unit B will be explained first. The primary-side cycle refers to a cycle through which a refrigerant circulates. In the heat source unit A, the four-way valve2is selectively switched in accordance with the operation of the heat-source-side heat exchanger3. That is, the four-way valve2is switched to the direction represented by the solid lines in the drawing in the case where the heat-source-side heat exchanger3operates as a condenser that transfers heat from the refrigerant to air, and is switched to the direction represented by the broken lines in the drawing in the case where the heat-source-side heat exchanger3operates as an evaporator that receives heat from air.

In the case where a CO2refrigerant is used as the refrigerant, since the critical temperature is as low as about 30 degrees Centigrade, and a supercritical range is reached in the course of heat transfer, the heat-source-side heat exchanger3can rather be said to act as a radiator. However, in the present specification, the heat-source-side heat exchanger3is described as a condenser, in correspondence with an evaporator.

In the relay unit B, when all operating indoor units out of the indoor units C to E are performing cooling, both the intermediate heat exchangers9aand9boperate as evaporators. When all operating indoor units out of the indoor units C to E are performing heating, both the intermediate heat exchangers9aand9boperate as condensers. When operating indoor units out of the indoor units C to E are performing cooling and heating in combination, one of the intermediate heat exchangers9aand9boperates as a condenser and the other one of the intermediate heat exchangers9aand9boperates as an evaporator. In a cooling operation and a heating operation, the capacities of the intermediate heat exchangers are increased using both the intermediate heat exchangers9aand9bas evaporators or condensers, thereby improving their cooling and heating performance.

Here, in the case where the first solenoid valve11aand the second solenoid valve11bare opened and the third solenoid valve11cand the fourth solenoid valve11dare closed, the intermediate heat exchangers9aand9boperate as condensers. Also, in the case where the third solenoid valve11cand the fourth solenoid valve11dare opened and the first solenoid valve11aand the second solenoid valve11bare closed, the intermediate heat exchangers9aand9boperate as evaporators. Since the first solenoid valve11aand the third solenoid valve11care not opened at the same time and the second solenoid valve11band the fourth solenoid valve11dare not opened at the same time, they may be replaced with three-way valves or the like.

The first flow control device10aand the second flow control device10bconnect the intermediate heat exchangers9aand9bto the third branch portion8c. With reference to the pieces of temperature information obtained by the thermometers33ato33d, the first flow control device10aand the second flow control device10bare adjusted on the basis of the degree of superheat of refrigerant at the outlet of an intermediate heat exchanger when the intermediate heat exchanger operates as an evaporator, and are adjusted on the basis of the degree of subcooling of refrigerant at the outlet of an intermediate heat exchanger when the intermediate heat exchanger operates as a condenser. The evaporating temperature and the condensing temperature necessary to calculate the degree of superheat and the degree of subcooling of refrigerant at the outlet of an intermediate heat exchanger may be calculated from the pieces of information obtained using the pressure gauges31and32installed within the heat source unit A, which will be described below, or may be calculated by installing pressure gauges at the first branch portion8aand the second branch portion8bwithin the relay unit B and referring to the values detected by the pressure gauges.

In the following description, assume that in a cooling operation in which all operating indoor units are performing cooling, the third solenoid valve11cand the fourth solenoid valve11dare opened, the first solenoid valve11aand the second solenoid valve11bare closed, and both the intermediate heat exchangers9aand9boperate as evaporators. Assume also that in a heating operation in which all operating indoor units are performing heating, the first solenoid valve11aand the second solenoid valve11bare opened, the third solenoid valve11cand the fourth solenoid valve11dare closed, and both the intermediate heat exchangers9aand9boperate as condensers. Assume moreover that in a cooling and heating simultaneous operation in which an indoor unit performing cooling and an indoor unit performing heating exist at the same time, the first solenoid valve11aand the fourth solenoid valve11dare opened, the second solenoid valve11band the third solenoid valve11care opened, the intermediate heat exchanger9aoperates as a condenser, and the intermediate heat exchanger9boperates as an evaporator.

The third flow control device12aconnects between the first branch portion8aand the third branch portion8c, and adjusts the flow rate of refrigerant bypassing the intermediate heat exchangers9aand9b. The fourth flow control device12bconnects between the third branch portion8cand the second branch portion8b, and adjusts the flow rate of refrigerant bypassing the intermediate heat exchangers9aand9b.

The refrigerant-refrigerant heat exchanger13exchanges heat between the refrigerant flowing through the passage between the first flow control device12aand the third branch portion8cand the refrigerant flowing through the passage between the fourth flow control device12band the second branch portion8b. The refrigerant-refrigerant heat exchanger13cools the refrigerant flowing into the first flow control device10a, the second flow control device10b, and the fourth flow control device12bin the case where the intermediate heat exchanger9aor9boperates as an evaporator. The refrigerant-refrigerant heat exchanger13is installed because the refrigerant flowing into a flow control device changes from a two-phase gas-liquid state into a single-liquid-phase state by cooling the refrigerant, thus achieving stable flow control.

As the operation of the third flow control device12aand the fourth flow control device12bin each operation mode, during, for example, a cooling operation, the third flow control device12ais fully opened, and the opening degree of the fourth flow control device12bis controlled on the basis of the degree of superheat of the low-pressure-side refrigerant at the outlet of the refrigerant-refrigerant heat exchanger13by referring to the thermometer33e. Furthermore, during a cooling and heating simultaneous operation, both the third flow control device12aand the fourth flow control device12bare fully closed. Moreover, during a heating operation, the third flow control device12ais fully closed, and the fourth flow control device12bis fully opened.

Basically, the third flow control device12adoes not adjust the flow rate of the refrigerant bypassing a condenser. Therefore, the third flow control device12amay be an opening and closing valve, such as a solenoid valve, as illustrated inFIG. 1. Furthermore, the refrigerant-refrigerant heat exchanger13may be omitted, and a refrigerant circuit may be arranged in such a manner that the refrigerant flowing out of the intermediate heat exchanger9aserving as a condenser passes through the refrigerant-refrigerant heat exchanger13into the third branch portion8cduring a cooling and heating simultaneous operation.

The circuit configuration of the secondary-side cycle in the relay unit B will be explained next. The secondary-side cycle is a cycle through which the second refrigerant circulates. The intermediate heat exchangers9aand9bare connected by pipes in such a manner that the flow of the refrigerant in the primary-side cycle and the flow of brine in the secondary-side cycle are opposed to each other in the case where the intermediate heat exchangers9aand9boperate as condensers. With this configuration, when the intermediate heat exchangers9aand9boperate as evaporators, only the flow direction of refrigerant changes, and operation is performed in which the flow of the refrigerant and the flow of brine are in parallel to each other. However, by installing valves at an inlet and an outlet of brine of an intermediate heat exchanger so that the flow of brine flowing into or out of the intermediate heat exchangers9aand9bcan be changed, to perform control to achieve opposed flows both for a condenser and an evaporator, efficient heat exchange can be achieved.

As illustrated inFIG. 2, flow passage switching valves21aand21bthat change the flow of brine in an intermediate heat exchanger may not be attached at the intermediate heat exchanger9abut may be attached only at the intermediate heat exchanger9boperating as an evaporator during a cooling and heating simultaneous operation. With this arrangement, in a mode in which the intermediate heat exchanger9boperates as an evaporator, the flow of the refrigerant and the flow of brine are opposed to each other in portions other than the intermediate heat exchanger9aduring a cooling operation. Therefore, the cooling capacity can be efficiently improved while suppressing an increase in cost.

Furthermore, the first pump18aand the second pump18bof an inverter type are connected in proximity to the intermediate heat exchangers9aand9band are connected to the fourth branch portion8dand the fifth branch portion8e, respectively. Furthermore, the other pipes for the intermediate heat exchangers9aand9bare connected to the sixth branch portion8fand the seventh branch portion8g, respectively. The position of the first pump18aand the position of the intermediate heat exchanger9ain the secondary-side cycle may be inverted. Similarly, the position of the second pump18band the position of the intermediate heat exchanger9bin the secondary-side cycle may be inverted.

Since both the intermediate heat exchangers9aand9boperate as evaporators in the case where all operating indoor units are performing cooling and both the intermediate heat exchangers9aand9boperate as condensers in the case where all operating indoor units are performing heating, the switching valves19cto19nmay be connected to either intermediate heat exchanger or all of them may be opened so that brine flows into the switching valves from both intermediate heat exchangers. In contrast, during a cooling and heating simultaneous operation, the switching valves19cto19nare operated in such a manner that an indoor unit performing cooling is connected to the intermediate heat exchanger9boperating as an evaporator and an indoor unit performing heating is connected to the intermediate heat exchanger9aoperating as a condenser.

Furthermore, the flow control devices20cto20ethat adjust the flow rates of brine flowing into corresponding indoor units are installed at the second brine pipes7cto7ebetween the indoor heat exchangers5cto5eand the switching valves switching valves19ito19n. The flow control devices20cto20emay be installed on the side of the first brine pipes6cto6e. The opening degrees of the flow control devices20cto20eare controlled such that, for example, the differences in temperature of brine at inlets and outlets of the indoor units C to E stay constant.

As a method for measuring the temperature of brine, measurement of the inlet and output temperatures of the indoor units C to E is possible. For example, by defining the temperatures of brine flowing out of the intermediate heat exchangers9aand9bas the inlet temperatures of the indoor units C to E and defining the temperature of brine returning from the indoor units C to E to the relay unit B as the outlet temperatures of the indoor units C to E, as illustrated in the drawing, control may be performed such that the differences between the temperatures become equal to a predetermined value. The temperatures of the brine that has flowed out of the intermediate heat exchangers9aand9bcan be measured by the thermometers34aand34barranged on the downstream side of the first pump18aand the second pump18b, respectively. Furthermore, the temperatures of the brine returning from the indoor units C to E to the relay unit B can be measured by the thermometers34cto34eprovided between the indoor heat exchangers5cto5eand the flow control devices20cto20e.

The target value for the temperature difference is set to about 3 to 7 degrees Centigrade for a cooling operation, as described in Patent Literature 2. By setting the control target value larger in a heating operation than in cooling, an efficient operation can be achieved. Furthermore, the first pump18aand the second pump18bmay be driven at a constant speed. However, in the flow control devices20cto20efor brine, temperature difference control of which is in progress, control can be performed by changing the pump capacity in such a manner that the opening degree of the flow control device whose opening degree is largest is set to, for example, 80% to 95% of the maximum opening degree.

A running operation at the time of various operations executed by the air-conditioning apparatus100will be explained next. The running operation of the air-conditioning apparatus100includes four modes: a cooling operation mode, a heating operation mode, a cooling main operation mode, and a heating main operation mode. Hereinafter, the flow of refrigerant and brine in each operation mode will be explained with reference to P-h diagrams.

A cooling operation is an operation mode in which an indoor unit is capable of only cooling and the indoor unit is performing cooling or is stopped. An operation is an operation mode in which an indoor unit is capable of only heating and the indoor unit is performing heating or is stopped. A cooling main operation is an operation mode in which each indoor unit is capable of selecting cooling or heating and in a cooling and heating simultaneous operation mode in which an indoor unit performing cooling and an indoor unit performing heating exist at the same time, the cooling load is heavier than heating load, and the heat-source-side heat exchanger3is connected to the discharge side of the compressor and operates as a condenser. A heating main operation is an operation mode in which in a cooling and heating simultaneous operation, the heating load is heavier than the cooling load, and the heat-source-side heat exchanger3is connected to the suction side of the compressor and operates as an evaporator.

The case where all the indoor units C, D, and E intend to perform cooling will be explained hereinafter. In cooling, the four-way valve2is switched so that the refrigerant discharged from the compressor1flows into the heat-source-side heat exchanger3. The third solenoid valve11cand the fourth solenoid valve11dare opened, and the first solenoid valve11aand the second solenoid valve11bare closed. At this time, both the first intermediate heat exchanger9aand the second intermediate heat exchanger9boperate as evaporators.FIG. 3is a P-h diagram illustrating the transition of refrigerant in a cooling operation. The flow of refrigerant will be explained first, and the flow of brine will be explained next.

In this state, the operation of the compressor1starts. A low-temperature and low-pressure gas refrigerant is compressed by the compressor1and is discharged as a high-temperature and high-pressure gas refrigerant. In the refrigerant compression process by the compressor1, compression is performed in such a manner that the refrigerant is heated more than when the refrigerant is adiabatically compressed based on an isentropic line by an amount corresponding to the adiabatic efficiency of the compressor, and is represented by a line extending from point (a) to point (b) inFIG. 3.

The high-temperature and high-pressure gas refrigerant discharged from the compressor1flows into the heat-source-side heat exchanger3via the four-way valve2. At this time, the refrigerant is cooled while heating outdoor air, and turns into an intermediate-temperature and high-pressure liquid refrigerant. The change of the refrigerant in the heat-source-side heat exchanger3is represented by a slightly-slanted substantially horizontal straight line extending from point (b) to point (c) inFIG. 3, in view of pressure loss in the heat-source-side heat exchanger3.

The intermediate-temperature and high-pressure liquid refrigerant that has flowed out of the heat-source-side heat exchanger3passes through the first refrigerant pipe6and the third flow control device12a, exchanges heat in the refrigerant-refrigerant heat exchanger13with the refrigerant that has flowed out of the fourth flow control device12b, and is cooled. The cooling process at this time is represented by a line extending from point (c) to point (d) inFIG. 3.

The liquid refrigerant cooled at the refrigerant-refrigerant heat exchanger13flows into the first flow control device10aand the second flow control device10bwhile the refrigerant partially bypasses the second branch portion8bthrough the fourth flow control device12b. Then, the high-pressure liquid refrigerant is expanded and decompressed by the first flow control device10aand the second flow control device10b, and turns into a low-temperature and low-pressure, two-phase gas-liquid state. A change of the refrigerant occurs with a constant enthalpy at the first flow control device10aand the second flow control device10b. The change of the refrigerant at this time is represented by a vertical line extending from point (d) to point (e) inFIG. 3.

The low-temperature and low-pressure refrigerant in the two-phase gas-liquid state that has flowed out of the first flow control device10aand the second flow control device10bflows into the first intermediate heat exchanger9aand the second intermediate heat exchanger9b. Then, the refrigerant is heated while cooling brine, and turns into a low-temperature and low-pressure gas refrigerant. The change of the refrigerant at the first intermediate heat exchanger9aand the second intermediate heat exchanger9bis represented by a slightly-slanted substantially horizontal straight line extending from point (e) to point (a) inFIG. 3, in view of pressure loss.

The low-temperature and low-pressure gas refrigerants that have flowed out of the first intermediate heat exchanger9aand the second intermediate heat exchanger9bpass through the third solenoid valve11cand the fourth solenoid valve11d, respectively, and flow into the second branch portion8b. The low-temperature and low-pressure gas refrigerants merge together at the second branch portion8b. The merged refrigerant passes through the second refrigerant pipe7and the four-way valve2, flows into the compressor1, and is compressed.

Next, the flow of brine will be explained. Since all the indoor units C, D, and E are performing cooling, the switching valves19cto19hand19ito19nfor brine are opened, and brines travel from the fourth branch portion8dand the fifth branch portion8eto the first brine pipes6cto6eon the indoor side and from the second brine pipes7cto7eon the indoor side to the sixth branch portion8fand the seventh branch portion8g. The brines cooled by the refrigerant at the first intermediate heat exchanger9aand the second intermediate heat exchanger9bare subjected to pressurization and driven by the first pump18aand the second pump18b, and flow into the fourth branch portion8dand the fifth branch portion8e.

The brines flowing into the fourth branch portion8dand the fifth branch portion8eare mixed at the switching valves19cto19hfor brine, and flow into the indoor units C to E through the first brine pipes6cto6eon the indoor side. The brines cool the indoor air at the indoor heat exchangers5cto5e, and cooling is performed. At the time of cooling, the brines are heated by the indoor air, pass through the second brine pipes7cto7eon the indoor side, and return to the relay unit B. The brines flow into the first intermediate heat exchanger9aand the second intermediate heat exchanger9bwhile being expanded and decompressed by the flow control devices20cto20efor brine.

The case where all the indoor units C, D, E intend to perform heating will now be explained. In a heating operation, the four-way valve2is switched so that the refrigerant discharged from the compressor1flows into the first branch portion8a. The first solenoid valve11aand the second solenoid valve11bare opened, and the third solenoid valve11cand the fourth solenoid valve11dare closed. At this time, both the first intermediate heat exchanger9aand the second intermediate heat exchanger9boperate as condensers.FIG. 4is a P-h diagram illustrating the transition of refrigerant in the heating operation. The flow of refrigerant will be explained first, and the flow of brine will be explained next.

In this state, the operation of the compressor1starts. A low-temperature and low-pressure gas refrigerant is compressed by the compressor1and is discharged as a high-temperature and high-pressure gas refrigerant. The refrigerant compression process by the compressor is represented by a line extending from point (a) to point (b) inFIG. 4.

The high-temperature and high-pressure gas refrigerant discharged from the compressor1flows into the first branch portion8athrough the four-way valve2and the first refrigerant pipe6. The high-temperature and high-pressure gas refrigerant that has flowed into the first branch portion8ais branched at the first branch portion8a, and the branched refrigerants pass through the first solenoid valve11aand the second solenoid valve11b, and flow into the first intermediate heat exchanger9aand the second intermediate heat exchanger9b. The refrigerants are cooled while heating brine, and turn into intermediate-temperature and high-pressure liquid refrigerants. The change of the refrigerants in the first intermediate heat exchanger9aand the second intermediate heat exchanger9bis represented by a slightly-slanted substantially horizontal straight line extending from point (b) to point (c) inFIG. 4.

The intermediate-temperature and high-pressure refrigerants that have flowed out of the first intermediate heat exchanger9aand the second intermediate heat exchanger9bflow into the first flow control device10aand the second flow control device10b, merge together at the third branch portion8c, and the merged refrigerant flows into the fourth flow control device12b. At this time, the high-pressure liquid refrigerants are expanded and decompressed at the first flow control device10a, the second flow control device10b, and the fourth flow control device12b, and turn into a low-temperature and low-pressure, two-phase gas-liquid state. The change of the refrigerants at this time is represented by a vertical line extending from point (c) to point (d) inFIG. 4.

The low-temperature and low-pressure refrigerant in the two-phase gas-liquid state that has flowed out of the fourth flow control device12bpasses through the second refrigerant pipe7, flows into the heat-source-side heat exchanger3, is heated while cooling the outdoor air, and turns into a low-temperature and low-pressure gas refrigerant. The change of the refrigerant at the heat-source-side heat exchanger3is represented by a slightly-slanted substantially horizontal straight line extending from point (d) to point (a) inFIG. 4. The low-temperature and low-pressure gas refrigerant that has flowed out of the heat-source-side heat exchanger3passes through the four-way valve2, flows into the compressor1, and is compressed.

Next, the flow of brine will be explained. The flow of brine is substantially similar to that at the time of a cooling operation. Since all the indoor units C, D, and E are performing heating, the switching valves19cto19hand19ito19nfor brine are opened, and brines travel from the fourth branch portion8dand the fifth branch portion8eto the first brine pipes6cto6eon the indoor side and from the second brine pipes7cto7eon the indoor side to the sixth branch portion8fand the seventh branch portion8g. The brines heated by refrigerants at the first intermediate heat exchanger9aand the second intermediate heat exchanger9bare subjected to pressurization and driven at the first pump18aand the second pump18b, and flow into the fourth branch portion8dand the fifth branch portion8e.

The brines that have flowed into the fourth branch portion8dand the fifth branch portion8eare mixed by the switching valves19cto19hfor brine, and pass through the first brine pipes6cto6eon the indoor side and flow into the indoor units C to E. The brines heat the indoor air at the indoor heat exchangers5cto5e, and heating is performed. At the time of heating, the brines are cooled by the indoor air, pass through the second brine pipes7cto7eon the indoor side, and return to the relay unit B. The brines flow into the first and second intermediate heat exchangers9aand9bwhile being expanded and decompressed by the flow control devices20cto20efor brine.

The case where the indoor units C and D are performing cooling and the indoor unit E is performing heating will now be explained. In this case, the four-way valve2is switched so that the refrigerant discharged from the compressor1flows into the heat-source-side heat exchanger3. The first solenoid valve11aand the fourth solenoid valve11dare opened, and the second solenoid valve11band the third solenoid valve11care closed. At this time, the first intermediate heat exchanger9aoperates as a condenser and the second intermediate heat exchanger9boperates as an evaporator.FIG. 5is a P-h diagram illustrating the transition of refrigerant in the cooling main operation. The flow of refrigerant will be explained first, and the flow of brine will be explained next.

In this state, the operation of the compressor1starts. A low-temperature and low-pressure gas refrigerant is compressed by the compressor1, and is discharged as a high-temperature and high-pressure gas refrigerant. The refrigerant compression process by the compressor is represented by a line extending from point (a) to point (b) inFIG. 5.

The high-temperature and high-pressure gas refrigerant discharged from the compressor1flows into the heat-source-side heat exchanger3via the four-way valve2. At this time, in the heat-source-side heat exchanger3, the refrigerant is cooled while heating the outdoor air with a heat quantity necessary for heating being left intact, and turns into an intermediate-temperature and high-pressure, two-phase gas-liquid state. The change of the refrigerant at the heat-source-side heat exchanger3is represented by a slightly-slanted substantially horizontal straight line extending from point (b) to point (c) inFIG. 5.

The intermediate-temperature and high-pressure, two-phase gas-liquid refrigerant that has flowed out of the heat-source-side heat exchanger3passes through the first refrigerant pipe6, the first branch portion8a, and the first solenoid valve11a, and flows into the first intermediate heat exchanger9a. Then, the refrigerant is cooled while heating brine, and turns into an intermediate-temperature and high-pressure liquid refrigerant. The change of the refrigerant at the first intermediate heat exchanger9ais represented by a slightly-slanted substantially horizontal straight line extending from point (c) to point (d) inFIG. 5. The refrigerant that has flowed out of the intermediate heat exchanger9ais expanded and decompressed by the first flow control device10a. The change of the refrigerant at this time is represented by a vertical line extending from point (d) to point (e) inFIG. 5. The refrigerant is further expanded and decompressed by the second flow control device10b, and turns into a low-temperature and low-pressure, two-phase gas-liquid state. The change of the refrigerant at this time is represented by a vertical line extending from point (e) to point (f) inFIG. 5.

The low-temperature and low-pressure refrigerant in the two-phase gas-liquid state that has flowed out of the second flow control device10bflows into the second intermediate heat exchanger9b. Then, the refrigerant is heated while cooling brine, and turns into a low-temperature and low-pressure gas refrigerant. The change of the refrigerant at the second intermediate heat exchanger9bis represented by a slightly-slanted substantially horizontal straight line extending from point (f) to point (a) inFIG. 5, in view of pressure loss. The low-temperature and low-pressure gas refrigerant that has flowed out of the second intermediate heat exchanger9bpasses through the fourth solenoid valve11dand flows into the second branch portion8b. The low-temperature and low-pressure gas refrigerant that has flowed into the second branch portion8bpasses through the second refrigerant pipe7and the four-way valve2, flows into the compressor1, and is compressed.

The first flow control device10aat this time may be controlled such that the degree of subcooling of the refrigerant at the outlet of the first intermediate heat exchanger9areaches a predetermined value, and the second flow control device10bcan be set to be fully opened. Furthermore, by installing a pressure gauge at the third branch portion8c, the fourth flow control device12bmay be controlled such that the pressure at the third branch portion8cstays constant, the first flow control device10amay be controlled such that the degree of subcooling of the refrigerant at the outlet of the first intermediate heat exchanger9areaches a predetermined value, and the second flow control device10bmay be controlled such that the degree of superheat of the refrigerant at the outlet of the first intermediate heat exchanger9astays constant.

Next, the flow of brine will be explained. Since the indoor units C and D are performing cooling and the indoor unit E is performing heating, the switching valves19e,19f,19g,19k,19l, and19mfor brine are opened, and the switching valves19c,19d,19h,19i,19j, and19nfor brine are closed.

The brine heated by the refrigerant at the first intermediate heat exchanger9ais subjected to pressurization and driven by the first pump18a, and flows into the fourth branch portion8d. The brine that has flowed into the fourth branch portion8dpasses through the switching valve19efor brine and the first brine pipe6eon the indoor side, and flows into the indoor unit E. The brine heats the indoor air at the indoor heat exchanger5e, and heating is performed. At the time of heating, the brine is cooled by the indoor air, passes through the second brine pipe7eon the indoor side, and returns to the relay unit B. The brine flows into the first intermediate heat exchanger9awhile being expanded and decompressed by the flow control device20efor brine.

In contrast, the brine cooled by the refrigerant at the second intermediate heat exchanger9bis subjected to pressurization and driven by the second pump18b, and flows into the fifth branch portion8e. The brine that has flowed into the fifth branch portion8epasses through the switching valves19fand19gfor brine and the first brine pipes6cand6don the indoor side, and flows into the indoor units C and D. The brine cools the indoor air at the indoor heat exchangers5cand5d, and cooling is performed. At the time of cooling, the brine is heated by the indoor air, passes through the second brine pipes7cand7don the indoor side, and returns to the relay unit B. The brine flows into the second intermediate heat exchanger9bwhile being expanded and decompressed by the flow control devices20cand20dfor brine.

The case where the indoor unit C is performing cooling and the indoor units D and E are performing heating will now be explained. In this case, the four-way valve2is switched so that refrigerant discharged from the compressor1is caused to flow into the first branch portion8a. The first solenoid valve11aand the fourth solenoid valve11dare opened, and the second solenoid valve11band the third solenoid valve11care closed. At this time, the first intermediate heat exchanger9aoperates as a condenser and the second intermediate heat exchanger9boperates as an evaporator.FIG. 6is a P-h diagram illustrating the transition of refrigerant in the heating main operation. The flow of refrigerant will be explained first, and the flow of brine will be explained next.

In this state, the operation of the compressor1starts. The low-temperature and low-pressure gas refrigerant is compressed by the compressor1, and is discharged as a high-temperature and high-pressure gas refrigerant. The refrigerant compression process by the compressor is represented by a line extending from point (a) to point (b) inFIG. 6.

The high-temperature and high-pressure gas refrigerant discharged from the compressor1flows into the first branch portion8athrough the four-way valve2and the first refrigerant pipe6. The high-temperature and high-pressure gas refrigerant that has flowed into the first branch portion8apasses through the first branch portion8aand the first solenoid valve11a, and flows into the first intermediate heat exchanger9a. Then, the refrigerant is cooled while heating brine, and turns into an intermediate-temperature and high-pressure liquid refrigerant. The change of the refrigerant at the first intermediate heat exchanger9ais represented by a slightly-slanted substantially horizontal straight line extending from point (b) to point (c) inFIG. 6.

The refrigerant that has flowed out of the first intermediate heat exchanger9ais expanded and decompressed by the first flow control device10aand the second flow control device10b. The change of the refrigerant at this time is represented by a vertical line extending from point (c) to point (d) inFIG. 6. The low-temperature and low-pressure refrigerant in the two-phase gas-liquid state that has flowed out of the second flow control device10bflows into the second intermediate heat exchanger9b. The refrigerant is heated while cooling brine by a heating quantity necessary for an indoor unit, and turns into a low-temperature and low-pressure refrigerant. The change of the refrigerant at the second intermediate heat exchanger9bis represented by a slightly-slanted substantially horizontal straight line extending from point (d) to point (e) inFIG. 6, in view of pressure loss.

The low-temperature and low-pressure refrigerant that has flowed out of the second intermediate heat exchanger9bpasses through the second refrigerant pipe7, flows into the heat-source-side heat exchanger3, is heated while cooling the outdoor air, and turns into a low-temperature and low-pressure gas refrigerant. The change of the refrigerant at the heat-source-side heat exchanger3is represented by a slightly-slanted substantially horizontal straight line extending from point (e) to point (a) inFIG. 6. The low-temperature and low-pressure gas refrigerant that has flowed out of the heat-source-side heat exchanger3passes through the four-way valve2, flows into the compressor1, and is compressed.

The first flow control device10aat this time may be controlled such that the degree of subcooling of the refrigerant at the outlet of the first intermediate heat exchanger9areaches a predetermined value, and the second flow control device10bcan be set to be fully opened. Furthermore, as illustrated inFIG. 7, for example, by operating the fourth flow control device12bso that the pressure at the third branch portion8cstays constant, causing the liquid refrigerant to be split at the third branch portion8c, controlling the first flow control device10aso that the degree of subcooling of the refrigerant at the outlet of the first intermediate heat exchanger9areaches a predetermined value, and controlling the second flow control device10bso that the degree of superheat of the refrigerant at the outlet of the first intermediate heat exchanger9areaches a predetermined value, the flow rate of the refrigerant flowing into the second intermediate heat exchanger9bcan be adjusted, thereby enabling load adjustment to be smoothly performed.

InFIG. 7, point (f) represents the state of the refrigerant at the outlet of the second intermediate heat exchanger9b, point (g) represents the state of the refrigerant that has flowed out of the fourth flow control device12b, and point (e) represents the state after the refrigerant at point (f) and the refrigerant at point (g) merge together at the first branch portion.FIG. 7is a P-h diagram illustrating another example of the transition of refrigerant in the heating main operation.

The flow of brine is substantially the same as that in the explanation of the flow of brine in the cooling main operation, and only connection of the indoor unit D is changed from the second intermediate heat exchanger9bto the first intermediate heat exchanger9a. Therefore, an explanation of the flow of brine will be omitted.

In the air-conditioning apparatus100, the heat source unit A includes the control means50, the relay unit B includes the control means51, and the indoor units C to E include the control means52cto52e, respectively. In this configuration, the control means is installed in each of the heat source unit A, the relay unit B, and the indoor units C to E. However, there will be no problem if control means is integrated into one unit and actuators are controlled by communicating control values among individual units. In the explanation provided below, the control means50,51, and52cto52ewill sometimes be collectively referred to as control means.

The control means52cto52eperform driving control, such as operation, stopping, and the like of fan motors for the fans5c-mto5e-mon the basis of the settings of remote control for the indoor units C to E and the current indoor temperature. As described above, the control means51performs setting of the opening degree of flow control devices, switching of solenoid valves, and driving of pumps in the relay unit B, in accordance with the operation mode based on the operation capacity for cooling and heating of the indoor units C to E. In contrast, the control means50performs driving of the compressor1, switching of the four-way valve2, and driving control of the fan motor for the fan3-m.

Hereinafter, a method for driving the compressor1and the fan motor for the fan3-mwill be discussed. The compressor1and the fan motor for the fan3-mare controlled, for example, as described in Patent Literature 1, on the basis of the pressure gauges31and32attached to the input and output channels of the compressor1, so that a fixed target pressure is reached. In the case where discharge pressure cannot be controlled during a cooling main operation, connection of the four-way valve2is switched. In the case where suction pressure cannot be controlled during a heating main operation, connection of the four-way valve2is switched. Accordingly, the operation mode is switched between the cooling main operation and the heating main operation. Here, there is a possibility that the capacities of the intermediate heat exchangers9aand9bmay not be continuous with respect to a change in the number of operating indoor units among the indoor units C to E during a cooling and heating simultaneous operation and, therefore, the required heat exchange amount in one of the intermediate heat exchangers9aand9bmay be increased.

In this explanation, two intermediate heat exchangers are provided for three indoor units. However, assuming that a plurality of small-capacity indoor units are connected, for example, in a cooling main operation based on an indoor capacity of 90 percent on cooling and 10 percent on heating, although load is reduced by only 10 percent compared to the case of 100 percent on cooling, the capacity of an intermediate heat exchanger for cooling is halved, thus increasing the load of the intermediate heat exchanger. Thus, during the cooling main operation, control is performed such that the evaporating temperature is set low by reducing the suction pressure at the compressor1. The same applies to the relationship between a heating operation and a heating main operation.

FIG. 8illustrates a control flow at the time of a cooling main operation.FIG. 8is a flowchart illustrating the flow of a control process at the time of a cooling main operation of the air-conditioning apparatus100. Here, the case where each type of control is performed by the control means50,51, and52cto52ecommunicating with each other will be explained as an example.

In S1, the control means starts operation control. In S2, since, typically, the evaporating temperature of a refrigeration cycle needs to be about 10 degrees Centigrade to perform cooling and the condensing temperature needs to be about 40 to 50 degrees Centigrade to perform heating, the control means sets an initial value ETm0of a target value for the evaporating temperature and an initial value CTm0of a target value for the condensing temperature by taking pressure loss of refrigerant generated in the interval from the heat source unit A to the relay unit B into consideration for the above values. Since a change in the capacity of the intermediate heat exchangers9aand9bis not continuous with respect to a change in the capacity of the indoor units C to E, the cooling load may be increased with respect to the capacity of the intermediate heat exchanger9boperating as an evaporator during a cooling main operation.

Thus, in S3, the control means performs the following operation. In the case of expression (1) provided below, where At is the heat transfer area of the intermediate heat exchangers9aand9bat the time of a cooling operation, Arc is the heat transfer area of the intermediate heat exchanger9boperating as an evaporator at the time of a cooling main operation, Qct is the rated load of cooling, and Qc is the current cooling load, it is determined that the load of the intermediate heat exchanger9boperating as an evaporator is increased compared to the time of a cooling rated operation, and a change amount ΔEtm in the target value for the evaporating temperature is calculated.
Qc>Qct×(Arc/At)  Expression (1)

Since the heat exchange amount is determined based on the product of the heat transfer area, the heat transfer coefficient, and the difference in temperature between fluids that perform heat exchange, on the assumption that the heat transfer coefficient is constant, the log-mean temperature difference between brine and refrigerant can be set to increase by the reciprocal of the cooling load ratio (Qc/Qct) and the reduction (Ar/At) in the heat transfer area, and the evaporating temperature can be set to reduce. This is represented by expression (2) provided below.
ΔETm=(1−(Qc/Qct)/(Ar/At))×dTc,Expression (2)

where dTc represents the log-mean temperature difference between refrigerant and brine at the time of a rated operation in an intermediate heat exchanger. Furthermore, by taking into consideration an improvement in heat transfer coefficient due to increases in flow rate of refrigerant and brine, control appropriate for the load can be achieved.

In S4, the control means updates the target value Etm for the evaporating temperature. In S5, the control means converts the target values for the evaporating temperature and the condensing temperature into pressures according to the physical property of refrigerant. In S6, the control means controls the frequency of the compressor1and the capacity of the heat-source-side heat exchanger3so that the discharge and suction pressures reach the target values.

FIG. 9illustrates a control method in a heating main operation.FIG. 9is a flowchart illustrating the flow of a control process at the time of a heating main operation of the air-conditioning apparatus100. Here, the case where each type of control is performed by the control means50,51, and52cto52ecommunicating with each other will be exemplified. Thus, the control means50,51, and52cto52ewill be collectively referred to as control means.

Control regarding S9to S16in the heating main operation is similar to that in the cooling main operation, and a change amount ΔCtm of the target value for the condensing temperature may be calculated using expression (3) provided below.
ΔCTm=((Qh/Qht)/(Arh/At)−1)×dTh,Expression (3)

where Qh is the current heating load, Qht is the rated load of heating, Arh represents the heat transfer area of a condenser at the time of a heating main operation, At represents the heat transfer area of the intermediate heat exchanger9aat the time of a heating operation, and dTh represents the log-mean temperature difference between refrigerant and brine at the time of a rated operation in an intermediate heat exchanger.

In an air-conditioning apparatus100capable of a cooling and heating simultaneous operation with the configuration described above, operation is performed such that the control target value for the compressor suction pressure at the time of a cooling main operation is set equal to or lower than that at the time of a cooling operation and the control target value for the compressor discharge pressure at the time of a heating main operation is set equal to or higher than that at the time of a heating operation, thereby improving the efficiency and increasing the heating capacity in the individual operation modes.

Furthermore, ΔETm may be determined based on the capacity of the first pump18aof a brine circuit for cooling, and ΔCTm may be determined based on the capacity of the second pump18bof a brine circuit for heating. When the capacity of a pump has reached 100 percent, it is determined that the conveyance power of the pump is insufficient, the target value for the difference in temperature between outlet and inlet of brine is increased, that is, the required flow rate is reduced to lower the load of the pump. At the same time, when a pump for cooling has reached 100 percent, ΔETm is set so that ETm is reduced, and when a pump for heating has reached 100 percent, ΔCTm is set so that CTm is increased. With this operation, the load is adjusted at the compressor. This method makes it possible to improve the efficiency and increase the heating capacity, irrespective of the indoor temperature and load.

Furthermore, in the case where the capacity of a pump has reached 100 percent or the opening degree of any of the valves of the flow control devices20cto20ehas reached a maximum opening degree, there is a possibility that control appropriate for the capacity of the flow control devices20cto20efor the indoor units cannot be performed. Thus, the flow rate of brine is reduced, and the target value for the difference in temperature between outlet and inlet of brine is increased to enable flow control. When the target value for the difference in temperature between outlet and inlet of brine is increased, it is determined that the required capacity is increased, and ΔETm and ΔCTm may be determined in such a manner that ET is reduced and CT is increased to interlock with control of a water circuit.

As described above, the air-conditioning apparatus100according to Embodiment 1 is controlled such that the first intermediate heat exchanger9aand the second intermediate heat exchanger9beach operate as an evaporator during a cooling operation, the first intermediate heat exchanger9aoperates as a condenser and the second intermediate heat exchanger9boperates as an evaporator during a cooling main operation, and thus the number of intermediate heat exchangers operating as evaporators at the time of the cooling operation is greater than in the cooling main operation. In addition, control is performed such that the first intermediate heat exchanger9aand the second intermediate heat exchanger9beach operate as a condenser during a heating operation, the first intermediate heat exchanger9aoperates as a condenser and the second intermediate heat exchanger9boperates as an evaporator during a heating main operation, and thus the number of intermediate heat exchangers operating as condensers at the time of the heating operation is greater than in the heating main operation. Furthermore, operation is performed in such a manner that the control target value for the compressor suction pressure at the time of a cooling main operation is set equal to or lower than that at the time of a cooling operation, and a control target value for the compressor discharge pressure at the time of a heating main operation is set equal to or higher than that at the time of a heating operation, thereby improving the efficiency and increasing the heating capacity in the individual operation modes. Therefore, with the air-conditioning apparatus100, even if the load conditions change, the cooling and heating capacities are maintained, and operation in a state where the efficiency of cycle, such as COP, is high can be achieved.

FIG. 10is a schematic circuit configuration diagram illustrating an example of a refrigerant circuit configuration of an air-conditioning apparatus200according to Embodiment 2 of the present invention. The air-conditioning apparatus200will be explained with reference toFIG. 10. In Embodiment 2, differences from Embodiment 1 will be mainly explained and explanation of the same portions as those in Embodiment 1, such as a refrigerant circuit configuration, will be omitted. Furthermore, since each operation mode executed by the air-conditioning apparatus200is similar to that performed by the air-conditioning apparatus100according to Embodiment 1, an explanation of the operation mode executed by the air-conditioning apparatus200will be omitted.

The heat transfer areas of the intermediate heat exchangers9aand9bwithin the relay unit B of the air-conditioning apparatus200are different from those of the air-conditioning apparatus100illustrated inFIGS. 1 and 2. For example, by setting the heat transfer area of the intermediate heat exchanger9bto the heat transfer area of the intermediate heat exchanger9ato 2:1, an intermediate heat exchanger9bhaving a larger heat transfer area can be used as an evaporator and an intermediate heat exchanger9ahaving a smaller heat transfer area can be used as a condenser during a cooling main operation, and an intermediate heat exchanger9bhaving a larger heat transfer area can be used as a condenser and an intermediate heat exchanger9ahaving a smaller heat transfer area can be used as an evaporator during a heating main operation. With this configuration, the ratio of the heat exchange capacities of the intermediate heat exchangers can be made closer to the load ratio of the indoor units C to E, thereby efficiently improving the capacity of a cooling and heating simultaneous operation. Since the control method is similar to that in Embodiment 1, an explanation of the control method will be omitted.

As described above, with the air-conditioning apparatus200according to Embodiment 2, operation is performed in such a manner that the control target value for the compressor suction pressure at the time of a cooling main operation is set equal to or lower than that at the time of a cooling operation and the control target value for the compressor discharge pressure at the time of a heating main operation is set equal to or higher than that at the time of a heating operation, thereby improving the efficiency and increasing the heating capacity in the individual operation modes. Therefore, similar to the air-conditioning apparatus100according to Embodiment 1, with the air-conditioning apparatus200, even if the load conditions change, the cooling and heating capacities can be maintained, and operation in a state where the efficiency of cycle, such as COP, is high can be achieved.

FIG. 11is a schematic circuit configuration diagram illustrating an example of a refrigerant circuit configuration of an air-conditioning apparatus300according to Embodiment 3 of the present invention. The air-conditioning apparatus300will be explained with reference toFIG. 11. In Embodiment 2, differences from Embodiment 1 described above will be mainly explained and an explanation of the same portions as those in Embodiment 1, such as a refrigerant circuit configuration, will be omitted. Furthermore, since each operation mode executed by the air-conditioning apparatus300is similar to that executed by the air-conditioning apparatus100according to Embodiment 1, an explanation of the operation mode will be omitted.

The air-conditioning apparatus300is different from the air-conditioning apparatus100illustrated inFIGS. 1 and 2in that the number of pipes connecting the heat source unit A and the relay unit B together is changed from 2 into 3. In the air-conditioning apparatus300, a third refrigerant pipe22is installed so that a discharge pipe of the compressor1in the heat source unit A and the first branch portion8ain the relay unit B are connected together. In the air-conditioning apparatus300, the first refrigerant pipe6is connected to the third branch portion8c, and a fifth flow control device23for adjusting the flow rate of refrigerant flowing into the heat-source-side heat exchanger3is installed between the heat-source-side heat exchanger3and the first refrigerant pipe6. The air-conditioning apparatus300is different from the air-conditioning apparatus100in that in the case where there is an indoor unit performing heating, a refrigerant discharged from the compressor1passes through the third refrigerant pipe22and is supplied to the intermediate heat exchangers9aand9b.

Furthermore, in the case where the heat-source-side heat exchanger3operates as a condenser, a thermometer is installed between the heat-source-side heat exchanger3and the fifth flow control device23, and the fifth flow control device23is controlled such that, for example, the degree of subcooling stays constant based on the difference from the condensing temperature calculated from the discharge pressure of the compressor1, and in the case where the heat-source-side heat exchanger3operates as an evaporator, a thermometer is installed between the heat-source-side heat exchanger3and the four-way valve2, and the fifth flow control device23is controlled such that, for example, the degree of superheat stays constant based on the difference from the evaporating temperature calculated from the suction pressure of the compressor1. The other flow of refrigerant is substantially the same as the flow explained usingFIGS. 3 to 7in Embodiment 1. Therefore, an explanation of the flow will be omitted.

Furthermore, since control is performed in the same way as in Embodiment 1, an explanation thereof will be omitted. With the configuration described above, by controlling the compressor suction pressure at the time of a cooling and heating simultaneous operation to be lower than that at the time of a cooling operation and controlling the discharge pressure at the time of the cooling and heating simultaneous operation to be lower than that at the time of a heating operation as in Embodiments 1 and 2, operation can be performed in a high-efficiency state during a cooling operation and a heating operation, and at the same time, the cooling and heating capacities may be maintained high during a cooling and heating simultaneous operation.

As described above, with the air-conditioning apparatus300according to Embodiment 3, operation is performed in such a manner that the control target value for the compressor suction pressure at the time of a cooling main operation is set equal to or lower than that at the time of a cooling operation and the control target value for the compressor discharge pressure at the time of a heating main operation is set equal to or higher than that at the time of a heating operation, thereby improving the efficiency and increasing the heating capacity in the individual operation modes. Thus, with the air-conditioning apparatus300, similar to the air-conditioning apparatus100according to Embodiment 1, even if the load conditions change, the cooling and heating capacities can be maintained, and operation in the state where the efficiency of cycle, such as a COP, is high can be achieved.

Although the cases where three indoor units are provided have been explained in Embodiments 1 to 3 as examples, any number of indoor units may be connected. In addition, the cases where two intermediate heat exchangers are provided have been explained as example. However, obviously, the number of intermediate heat exchangers provided is not necessarily two. Any number of intermediate heat exchangers may be provided as long as the intermediate heat exchangers are configured to be capable of cooling and/or heating a heat medium and as long as control is performed such that the number of intermediate heat exchangers operating as evaporators during a cooling operation is greater than the number of intermediate heat exchangers operating as evaporators during a cooling main operation and that the number of intermediate heat exchangers operating as condensers during a heating operation is greater than the number of intermediate heat exchangers operating as condensers during a heating main operation. Furthermore, since the distribution performance of a heat exchanger decreases as the flow rate of refrigerant decreases, control may be performed such that a given upper limit value is specified for the number of intermediate heat exchangers to operate as condensers or condensers in accordance with the load of indoor units. Furthermore, each of the number of the first pumps18aprovided and the number of the second pumps18bprovided is not necessarily one. A plurality of small-capacity pumps may be connected in series or in parallel. Furthermore, although the cases where the accumulator4is included have been explained in Embodiments 1 to 3, the accumulator4is not necessarily provided.

REFERENCE SIGNS LIST