GB2555298A

GB2555298A - Air conditioning device

Info

Publication number: GB2555298A
Application number: GB1719778.1A
Authority: GB
Inventors: Morimoto Hiroyuki; Motomura Yuji; Hatomura Takeshi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2015-05-22
Filing date: 2015-05-22
Publication date: 2018-04-25
Anticipated expiration: 2035-05-22
Also published as: GB2555298B; JP6537603B2; GB201719778D0; WO2016189599A1; JPWO2016189599A1

Abstract

A heat transfer medium of a heat transfer medium circulation circuit B is a non-burnable refrigerant that exchanges heat as latent heat in each of an inter-heat-transfer-medium heat exchanger 15 and a usage-side heat exchanger 26, and a plurality of pumps 21, 37 are configured as liquid pumps for suctioning in the heat transfer medium, which is in a liquid state, and circulating the heat transfer medium through the heat transfer medium circulation circuit B.

Description

(56) Documents Cited:

WO 2012/049704 A1 JP 2006258390 A JPH0317475

JP 2008209111 A (58) Field of Search:

INT CL F24F

Other: Jitsuyo Shinan Koho 1922-1996; Jitsuyo Shinan Toroku Koho 1996-2015; Kokai Jitsuyo Shinan Koho 1971-2015; Toroku Jitsuyo Shinan Koho 1994-2015 (71) Applicant(s):

Mitsubishi Electric Corporation (Incorporated in Japan)

7-3, Marunouchi 2-chome, Chiyoda-ku, Tokyo 100-8310, Japan (72) Inventor(s):

Hiroyuki Morimoto Yuji Motomura Takeshi Hatomura (74) Agent and/or Address for Service:

Mewburn Ellis LLP

City Tower, 40 Basinghall Street, LONDON, Greater London, EC2V 5DE, United Kingdom (54) Title of the Invention: Air conditioning device Abstract Title: Air conditioning device (57) A heat transfer medium of a heat transfer medium circulation circuit B is a non-burnable refrigerant that exchanges heat as latent heat in each of an inter-heattransfer-medium heat exchanger 15 and a usage-side heat exchanger 26, and a plurality of pumps 21, 37 are configured as liquid pumps for suctioning in the heat transfer medium, which is in a liquid state, and circulating the heat transfer medium through the heat transfer medium circulation circuit B.

[02]

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FIG. 1

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FIG. 4

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FIG. 5

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FIG. 6

h

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FIG. 7

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h

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10/10

h

DESCRIPTION

Title of Invention

AIR-CONDITIONING APPARATUS

Technical Field [0001]

The present invention relates to an air-conditioning apparatus used for, for example, a multi-air-conditioning unit for a building.

Background Art [0002]

In conventional air-conditioning apparatuses such as a multi-air-conditioning unit for a building, refrigerant is circulated between an outdoor unit, which is a heat source unit disposed outside a building, and an indoor unit disposed in an indoor space inside the building. Air is heated or cooled as the refrigerant rejects heat to the air or removes heat from the air, and the cooled or heated air is used to cool or heat the air-conditioned space. Such a multi-air-conditioning unit for a building often includes a plurality of interconnected indoor units, with some indoor units stopped and some indoor units running. In some instances, the pipe connecting the outdoor unit with each indoor unit can be as long as up to 100 m. The longer the pipe, the greater the amount of refrigerant charged into the system.

[0003]

Typically, an indoor unit of such a multi-air-conditioning apparatus for a building is placed and used in an indoor space in which people reside (for example, an office space, a habitable room, or a shop). If the refrigerant is a low GWP refrigerant, such as R32 or HFO1234yf, which has flammability and toxicity, and if, for any cause, the refrigerant leaks from the indoor unit placed in the indoor space, its effects on the human body, and safety issues, are a serious concern.

[0004]

To address the above-described problem, there exists a technique that employs a secondary loop system for an air-conditioning apparatus (see, for example,

Patent Literature 1). According to a method proposed by this technique, refrigerant is used for the primary loop (refrigerant cycle circuit), and a nontoxic heat medium such as water or brine is used for the secondary loop (heat medium cycle circuit). In a heat exchanger provided to the secondary loop, heat is exchanged between the heat medium, and the air in the space in which people reside to perform airconditioning ofthe indoor space.

Citation List

Patent Literature [0005]

Patent Literature 1: International Publication No. 2012/049704 Summary of Invention Technical Problem [0006]

With the technique according to Patent Literature 1, the primary loop utilizes changes in the latent heat of the refrigerant to perform cooling or heating, thus enabling a decrease in the amount of refrigerant to be transported. By contrast, the secondary loop utilizes changes in the sensible heat of the heat medium to perform cooling or heating, which makes it necessary to increase the amount of refrigerant to be transported. This results in increased transport capacity required for a transport unit to transport the heat medium, leading to increased size of the transport unit and reduced freedom of layout.

[0007]

If water is used for the secondary loop, this presents another problem as the water freezes and damages a heat exchanger, a pipe, or other components.

[0008]

The present invention has been made to address the above-described problems, and provides an air-conditioning apparatus that makes it possible to reduce required transport power, increase freedom of system layout, and enhance reliability. Solution to Problem [0009]

An air-conditioning apparatus according to an embodiment of the present invention includes a heat source-side refrigerant cycle circuit in which a compressor, a heat source-side heat exchanger, an expansion device, and a refrigerant flow path of each of a plurality of intermediate heat exchangers are connected by pipes to circulate a heat source-side refrigerant; a heat medium cycle circuit in which a plurality of pumps, a plurality of use-side heat exchangers, and a heat medium flow path of each of the plurality of intermediate heat exchangers are connected by a pipe to circulate a heat medium; a heat medium flow switching device provided to the heat medium cycle circuit in correspondence with each of the plurality of use-side heat exchangers, the heat medium flow switching device allowing each of the plurality of use-side heat exchangers to communicate with one of the plurality of intermediate heat exchangers to switch flow paths of the heat medium, wherein the heat medium comprises an inflammable refrigerant that, in each ofthe intermediate heat exchangers and the use-side heat exchangers, undergoes heat exchange using latent heat, and wherein the plurality of pumps each comprise a liquid pump that sucks the heat medium in a liquid state and circulates the sucked heat medium in the heat medium cycle circuit.

Advantageous Effects of Invention [0010]

An embodiment ofthe present invention provides an air-conditioning apparatus that makes it possible to reduce required transport power, increase freedom of system layout, and enhance reliability.

Brief Description of Drawings [0011] [Fig. 1] Fig. 1 schematically illustrates an exemplary installation of an airconditioning apparatus according to an embodiment of the present invention.

[Fig. 2] Fig. 2 is a schematic circuit configuration diagram illustrating an exemplary circuit configuration of the air-conditioning apparatus according to

Embodiment of the present invention.

[Fig. 3] Fig. 3 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling only operation mode of the air-conditioning apparatus according to Embodiment of the present invention.

[Fig. 4] Fig. 4 is a P-h diagram of each of Refrigerant Cycle Circuit A and Heat 5 Medium Cycle Circuit B in cooling only operation mode of the air-conditioning apparatus according to Embodiment of the present invention.

[Fig. 5] Fig. 5 is a refrigerant circuit diagram illustrating the flow of refrigerant in heating only operation mode of the air-conditioning apparatus according to Embodiment of the present invention.

[Fig. 6] Fig. 6 is a P-h diagram of each of Refrigerant Cycle Circuit A and Heat

Medium Cycle Circuit B in heating only operation mode of the air-conditioning apparatus according to Embodiment of the present invention.

[Fig. 7] Fig. 7 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling main operation mode of the air-conditioning apparatus according to

Embodiment of the present invention.

[Fig. 8] Fig. 8 is a P-h diagram of each of Refrigerant Cycle Circuit A and Heat

Medium Cycle Circuit B in cooling main operation mode of the air-conditioning apparatus according to Embodiment of the present invention.

[Fig. 9] Fig. 9 is a refrigerant circuit diagram illustrating the flow of refrigerant in heating main operation mode of the air-conditioning apparatus according to Embodiment of the present invention.

[Fig. 10] Fig. 10 is a P-h diagram of each of Refrigerant Cycle Circuit A and Heat Medium Cycle Circuit B in heating main operation mode of the air-conditioning apparatus according to Embodiment of the present invention.

Description of Embodiments [0012]

Hereinafter, Embodiment of the present invention will be described with reference to the drawings.

[0013]

Embodiment

Fig. 1 schematically illustrates an exemplary installation of an air-conditioning apparatus according to Embodiment of the present invention. An exemplary installation of the air-conditioning apparatus will be described with reference to Fig. 1. This air-conditioning apparatus uses a refrigeration cycle (Refrigerant Cycle Circuit A and Heat Medium Cycle Circuit B) in which refrigerant (a heat source-side refrigerant and a heat medium) is circulated to allow each indoor unit to freely select a cooling mode or a heating mode as its operation mode.

[0014]

The air-conditioning apparatus according to Embodiment employs a system (indirect system) that indirectly uses refrigerant (heat source-side refrigerant) to perform air-conditioning of an air-conditioned space. That is, cooling energy or heating energy stored in the heat source-side refrigerant is transferred to a refrigerant different from the heat source-side refrigerant (to be referred to as heat medium hereinafter), and the cooling energy or heating energy stored in the heat medium is used to cool or heat the air-conditioned space.

[0015]

In Fig. 1, the air-conditioning apparatus according to Embodiment has a single outdoor unit 1, which is a heat source unit, a plurality of indoor units 2, and a heat medium relay unit 3 interposed between the outdoor unit 1 and the indoor unit 2.

The heat medium relay unit 3 exchanges heat between the heat source-side refrigerant and the heat medium. The outdoor unit 1 and the heat medium relay unit 3 are connected by a refrigerant pipe 4 through which the heat source-side refrigerant passes. The heat medium relay unit 3 and the indoor unit 2 are connected by a pipe (heat medium pipe) 5 through which the heat medium passes. The cooling energy or heating energy generated in the outdoor unit 1 is delivered to the indoor unit 2 via the heat medium relay unit 3.

[0016]

The outdoor unit 1 is usually placed in an outdoor space 6, which is a space outside a construction 9 such as a building (for example, the rooftop). The outdoor unit 1 supplies cooling energy or heating energy to the indoor unit 2 via the heat medium relay unit 3. The indoor unit 2 is placed at a position that enables supply of cooling air or heating air to an indoor space 7, which is a space inside the construction 9 (e.g., a habitable room), to supply cooling air or heating air to the indoor space 7 that is the air-conditioned space. The heat medium relay unit 3 can be installed in a space different from the outdoor space 6 and the indoor space 7, as an enclosure separate from the outdoor unit 1 and the indoor unit 2. The heat medium relay unit 3 is connected to the outdoor unit 1 and the indoor unit 2 by the refrigerant pipe 4 and the pipe 5, respectively, and transfers cooling energy or heating energy supplied from the outdoor unit 1 to the indoor unit 2.

[0017]

As illustrated in Fig. 1, in the air-conditioning apparatus according to Embodiment, the outdoor unit 1 and the heat medium relay unit 3 are connected by using two refrigerant pipes 4. Further, the heat medium relay unit 3 and each indoor unit 2 are connected by using two pipes 5. In this way, in the air-conditioning apparatus according to Embodiment, individual units (the outdoor unit 1, the indoor unit 2, and the heat medium relay unit 3) are connected by using two pipes (two refrigerant pipes 4 and two pipes 5), thus allowing easy construction.

[0018]

Fig. 1 illustrates an exemplary state in which the heat medium relay unit 3 is installed in a space that is located inside the construction 9 but is separate from the indoor space 7, such as a space above a ceiling (e.g., a space such as a space above a ceiling in the construction 9, which will be simply referred to as space 8 hereinafter). Alternatively, the heat medium relay unit 3 can be also installed in a space such as a common use space where an elevator or other facilities are located. Although Fig. 1 illustrates an exemplary case where the indoor unit 2 is of a ceiling cassette type, the type of the indoor unit is not limited to this. The indoor unit 2 may be of any type that allows heating air or cooling air to be blown out to the indoor space 7 either directly or through a duct or other components, such as a ceiling concealed type or ceiling suspended type.

[0019]

Although Fig. 1 illustrates an exemplary case where the outdoor unit 1 is installed in the outdoor space 6, the location of installation is not limited thereto. For example, the outdoor unit 1 may be installed in an enclosed space such as a machine room with ventilation openings. Alternatively, the outdoor unit 1 may be installed inside the construction 9 as long as waste heat can be exhausted to the outside of the construction 9 by an exhaust duct, or the outdoor unit 1 may be installed inside the construction 9 also if the outdoor unit 1 used is of a water-cooled type. Installing the outdoor unit 1 in such locations does not present any particular problems.

[0020]

The heat medium relay unit 3 may be installed near the outdoor unit 1.

However, if the distance from the heat medium relay unit 3 to the indoor unit 2 is too long, significantly more power is required to transport the heat medium, resulting in diminished energy saving effect. Further, the respective numbers of the outdoor units 1, indoor units 2, and heat medium relay units 3 to be connected are not particularly limited to those illustrated in Fig. 1. The respective numbers of these units may be determined in accordance with the construction 9 in which the airconditioning apparatus according to Embodiment is installed.

[0021]

Fig. 2 is a schematic circuit configuration diagram illustrating an exemplary circuit configuration of the air-conditioning apparatus (to be referred to as airconditioning apparatus 100 hereinafter) according to Embodiment of the present invention. A detailed configuration of the air-conditioning apparatus 100 will be described with reference to Fig. 2. As illustrated in Fig. 2, the outdoor unit 1 and the heat medium relay unit 3 are connected by the refrigerant pipe 4 via an intermediate heat exchanger 15a and an intermediate heat exchanger 15b, which are provided to the heat medium relay unit 3, to form Refrigerant Cycle Circuit A that serves as a refrigeration cycle in which the heat source-side refrigerant is circulated. The heat medium relay unit 3 and the indoor unit 2 are connected by the pipe 5 via the intermediate heat exchanger 15a and the intermediate heat exchanger 15b to form

Heat Medium Cycle Circuit B in which the heat medium is circulated. The refrigerant pipe 4 and the pipe 5 will be described later in detail.

[0022]

Since Refrigerant Cycle Circuit A is basically installed outdoors, a flammable refrigerant such as R32 or HFO1234yf is used as a refrigerant. For Heat Medium Cycle Circuit B, an inflammable refrigerant such as R410Aor CO2 is used to provide the air-conditioning apparatus 100 with enhanced safety.

[0023]

Hereinafter, the respective configurations of the outdoor unit 1, the indoor unit 2, and the heat medium relay unit 3 of the air-conditioning apparatus 100 having Refrigerant Cycle Circuit A and Heat Medium Cycle Circuit B will be described in the stated order.

[0024] [Outdoor Unit 1]

The outdoor unit 1 is equipped with a compressor 10, a first refrigerant flow switching device 11 such as a four-way valve, a heat source-side heat exchanger 12, and an accumulator 19 that are connected in series by the refrigerant pipe 4. The outdoor unit 1 is also provided with a first connection pipe 4a, a second connection pipe 4b, a check valve 13a, a check valve 13b, a check valve 13c, and a check valve 13d. The presence of the first connection pipe 4a, the second connection pipe 4b, the check valve 13a, the check valve 13b, the check valve 13c, and the check valve 13d ensures that the heat source-side refrigerant routed into the heat medium relay unit 3 from the outdoor unit 1 flows in a fixed direction, irrespective of the mode of operation requested by the indoor unit 2.

[0025]

The compressor 10 sucks the heat source-side refrigerant, and compresses the heat source-side refrigerant into a high-temperature and high-pressure state.

The compressor 10 is preferably formed by, for example, an inverter compressor whose capacity can be controlled. The first refrigerant flow switching device 11 switches between the flow of the heat source-side refrigerant in heating operation mode (heating only operation mode and heating main operation mode), and the flow of the heat source-side refrigerant in cooling operation mode (cooling only operation mode and cooling main operation mode).

[0026]

The heat source-side heat exchanger 12 serves as an evaporator in heating operation, and serves as a radiator (gas cooler) in cooling operation. The heat source-side heat exchanger 12 exchanges heat between air supplied from an airblowing device (not illustrated) such as a fan, and the heat source-side refrigerant. The accumulator 19 is disposed on the suction side of the compressor 10 to store surplus refrigerant resulting from the difference in operation between the heating operation mode and the cooling operation mode, or surplus refrigerant for transient changes in operation (e.g., a change in the number of indoor units 2 that are running). [0027] [Indoor Unit 2]

Each indoor unit 2 is equipped with a use-side heat exchanger 26 (use-side heat exchanger 26a, 26b, 26c, or 26d). The use-side heat exchanger 26 is connected to a heat medium flow control device 25 (heat medium flow control device 25a, 25b, 25c, or 25d) and a second heat medium flow switching device 23 (second heat medium flow switching device 23a, 23b, 23c, or 23d) of the heat medium relay unit 3 via the pipe 5. The use-side heat exchanger 26 exchanges heat between air supplied from an air-blowing device such as a fan (not illustrated) and the heat medium to generate the heating air or cooling air that is to be supplied to the indoor space 7.

[0028] [Heat Medium Relay Unit 3]

The heat medium relay unit 3 includes two intermediate heat exchangers 15 (intermediate heat exchangers 15a and 15b), two expansion devices 16 (expansion devices 16a and 16b), two valve devices 17 (valve devices 17a and 17b), and two second refrigerant flow switching devices 18 (second refrigerant flow switching devices 18a and 18b). The heat medium relay unit 3 is further equipped with four refrigerant liquid pumps (to be simply referred to as liquid pumps hereinafter), that is, liquid pumps 21 (liquid pumps 21a and 21b) and liquid pumps 37 (liquid pumps 37a and 37b), four first heat medium flow switching devices 22 (first heat medium flow switching devices 22a to 22d), four second heat medium flow switching devices 23 (second heat medium flow switching devices 23a to 23d), four heat medium flow control devices 25 (heat medium flow control devices 25a to 25d), four backflow prevention devices, that is, backflow prevention devices 38 (backflow prevention devices 38a and 38b) and backflow prevention devices 39 (backflow prevention devices 39a and 39b), and four bypasses, that is, bypasses 40 (bypasses 40a and 40b) and bypasses 41 (bypasses 41a and 41b).

[0029]

The two intermediate heat exchangers 15 (intermediate heat exchangers 15a and 15b) each function as a condenser (radiator) or an evaporator. The intermediate heat exchanger 15 exchanges heat between the heat source-side refrigerant and the heat medium, and transfers, to the heat medium, the cooling energy or heating energy generated in the outdoor unit 1 and stored in the heat source-side refrigerant. The intermediate heat exchanger 15a is disposed between the expansion device 16a and the second refrigerant flow switching device 18a in Refrigerant Cycle Circuit A, and is used to cool the heat medium in cooling and heating mixed operation mode. The intermediate heat exchanger 15b is disposed between the expansion device 16b and the second refrigerant flow switching device 18b in Refrigerant Cycle Circuit A, and is used to heat the heat medium in cooling and heating mixed operation mode. [0030]

The two expansion devices 16 (expansion devices 16a and 16b), which each serve as a pressure reducing valve or an expansion valve, cause the heat sourceside refrigerant to be reduced in pressure and expand. The expansion device 16a is disposed upstream of the intermediate heat exchanger 15a with respect to the flow of the heat source-side refrigerant in cooling only operation mode. The expansion device 16b is disposed upstream of the intermediate heat exchanger 15b with respect to the flow of the heat source-side refrigerant in cooling only operation mode. The two expansion devices 16 may each be formed by a device whose opening degree can be variably controlled, for example, an electronic expansion valve.

[0031]

The valve devices 17a and 17b, which are each formed by a two-way valve or other devices, open and close the refrigerant pipe 4.

[0032]

The two second refrigerant flow switching devices 18 (second refrigerant flow switching devices 18a and 18b) are each formed by, for example, a four-way valve or other devices, and switch the flows of the heat source-side refrigerant in accordance with the operation mode. The second refrigerant flow switching device 18a is disposed downstream of the intermediate heat exchanger 15a with respect to the flow of the heat source-side refrigerant in cooling only operation mode. The second refrigerant flow switching device 18b is disposed downstream of the intermediate heat exchanger 15b with respect to the flow of the heat source-side refrigerant in cooling only operation mode.

[0033]

The four liquid pumps 21a, 21 b, 37a, and 37b cause the heat medium passing through the pipe 5 to circulate within Heat Medium Cycle Circuit B. The liquid pumps 21a and 21b are used for cooling, and the liquid pumps 37a and 37b are used for heating. The liquid pump 21a is disposed between the intermediate heat exchanger 15a and the heat medium flow control device 25b. The liquid pump 21 b is disposed between the intermediate heat exchanger 15b and the heat medium flow control device 25d. The two liquid pumps 21 may each be formed by, for example, a pump whose capacity can be controlled.

[0034]

The liquid pump 37a is disposed upstream of the heat medium flow control device 25a with respect to the flow of the heat medium in Heat Medium Cycle Circuit

B. The liquid pump 37b is disposed upstream of the heat medium flow control device 25c with respect to the flow of the heat medium in Heat Medium Cycle Circuit

B. The two liquid pumps 37 may each be formed by, for example, a pump whose capacity can be controlled.

[0035]

The four first heat medium flow switching devices 22 (first heat medium flow switching devices 22a to 22d) are each formed by a three-way valve or other devices, and switch the flows of the heat medium. The number of first heat medium flow switching devices 22 to be provided (four in this case) corresponds to the number of indoor units 2 to be installed. Of the three ports of the first heat medium flow switching device 22, one is connected to the intermediate heat exchanger 15a, one is connected to the intermediate heat exchanger 15b, and one is connected to the useside heat exchanger 26. The first heat medium flow switching device 22 is disposed on the outlet side of the heat medium flow path of the use-side heat exchanger 26.

In association with the corresponding indoor units 2, the first heat medium flow switching device 22a, the first heat medium flow switching device 22b, the first heat medium flow switching device 22c, and the first heat medium flow switching device 22d are illustrated in this order from the lower side of the drawing.

[0036]

The four second heat medium flow switching devices 23 (second heat medium flow switching devices 23a to 23d) are each formed by a three-way valve or other devices, and switch the flows of the heat medium. The number of second heat medium flow switching devices 23 to be provided (four in this case) correspond to the number of indoor units 2 to be installed. Of the three ports of the second heat medium flow switching device 23, one is connected to the intermediate heat exchanger 15a, one is connected to the intermediate heat exchanger 15b, and one is connected to the use-side heat exchanger 26. The second heat medium flow switching device 23 is disposed on the inlet side of the heat medium flow path of the use-side heat exchanger 26. In association with the corresponding indoor units 2, the second heat medium flow switching device 23a, the second heat medium flow switching device 23b, the second heat medium flow switching device 23c, and the second heat medium flow switching device 23d are illustrated in this order from the lower side of the drawing.

[0037]

The four heat medium flow control devices 25 (heat medium flow control devices 25a to 25d) are each formed by an electronic expansion valve or other devices whose opening area can be controlled, and control the flow rate of the heat medium flowing through the pipe 5. The number of heat medium flow control devices 25 to be provided (four in this case) correspond to the number of indoor units 2 to be installed. The heat medium flow control devices 25a and 25c are respectively disposed downstream of the liquid pumps 37a and 37b with respect to the flow of the heat medium in Heat Medium Cycle Circuit B. The heat medium flow control devices 25b and 25d are respectively disposed downstream of the liquid pumps 21 a and 21 b with respect to the flow of the heat medium in Heat Medium Cycle Circuit B. In association with the corresponding indoor units 2, the heat medium flow control device 25a, the heat medium flow control device 25b, the heat medium flow control device 25c, and the heat medium flow control device 25d are illustrated in this order from the lower side of the drawing.

[0038]

The heat medium relay unit 3 includes various detection units (two first temperature sensors 31, four second temperature sensors 34 (34a, 34b, 34a, and 34b), four third temperature sensors 35 (35a, 35b, 35c, and 35d), and a pressure sensor 36). Pieces of information detected by these detection units (e.g., temperature information, pressure information, and information about the concentration of the heat source-side refrigerant) are sent to a controller (not illustrated) that controls the operation of the air-conditioning apparatus 100 in a centralized manner, and are used to control the driving frequency of the compressor 10, the rotation speed of an air-blowing device (not illustrated) disposed near each of the heat source-side heat exchanger 12 and the use-side heat exchanger 26, switching of the first refrigerant flow switching device 11, the driving frequency of the liquid pump 21, switching of the second refrigerant flow switching device 18, switching of the flow paths of the heat medium, or other operational states.

[0039]

The two first temperature sensors 31 (first temperature sensors 31a and 31b) detect the temperature of the heat medium exiting the intermediate heat exchanger 15, that is, the temperature of the heat medium at the outlet of the intermediate heat exchanger 15. The two first temperature sensors 31 may each be formed by, for example, a thermistor or other devices. The first temperature sensor 31 a is provided to the pipe 5 on the inlet side of the liquid pump 21a. The first temperature sensor 31 b is provided to the pipe 5 on the inlet side of the liquid pump 21 b.

[0040]

The four second temperature sensors 34 (second temperature sensors 34a to 34d) are disposed upstream of the first heat medium flow switching device 22 to detect the temperature of the heat medium exiting the use-side heat exchanger 26. The four second temperature sensors 34 may each be formed by, for example, a thermistor or other devices. The number of second temperature sensors 34 to be provided (four in this case) corresponds to the number of indoor units 2 to be installed. In association with the corresponding indoor units 2, the second temperature sensor 34a, the second temperature sensor 34b, the second temperature sensor 34c, and the second temperature sensor 34d are illustrated in this order from the lower side of the drawing.

[0041]

The four third temperature sensors 35 (third temperature sensors 35a to 35d) are disposed on the inlet side or outlet side of the heat source-side refrigerant of the intermediate heat exchanger 15 to detect the temperature of the heat source-side refrigerant entering the intermediate heat exchanger 15 or the temperature of the heat source-side refrigerant exiting the intermediate heat exchanger 15. The four third temperature sensors 35 may be each formed by a thermistor or other devices. The third temperature sensor 35a is disposed between the intermediate heat exchanger 15a and the second refrigerant flow switching device 18a. The third temperature sensor 35b is disposed between the intermediate heat exchanger 15a and the expansion device 16a. The third temperature sensor 35c is disposed between the intermediate heat exchanger 15b and the second refrigerant flow switching device 18b. The third temperature sensor 35d is disposed between the intermediate heat exchanger 15b and the expansion device 16b.

[0042]

As with the third temperature sensor 35d, the pressure sensor 36 is located between the intermediate heat exchanger 15b and the expansion device 16b to detect the pressure of the heat source-side refrigerant flowing between the intermediate heat exchanger 15b and the expansion device 16b.

[0043]

The controller (not illustrated) is implemented by a microcomputer or other devices. The controller controls, based on information detected by various detection units and an instruction from a remote controller, the driving frequency of the compressor 10, the rotation speed (including ON/OFF) of the air-blowing device, switching of the first refrigerant flow switching device 11, driving of the liquid pump 21, the opening degree ofthe expansion device 16, opening and closing of the valve device 17, switching ofthe second refrigerant flow switching device 18, switching of the first heat medium flow switching device 22, switching of the second heat medium flow switching device 23, the opening degree of the heat medium flow control device 25, or other operational states to thereby execute various operational modes described later. The controller may be provided to each individual unit, or may be provided to the outdoor unit 1 or the heat medium relay unit 3.

[0044]

The pipes 5 through which the heat medium passes include the pipe 5 connected to the intermediate heat exchanger 15a, and the pipe 5 connected to the intermediate heat exchanger 15b. The pipe 5 is divided into a number of branches (four in this case) corresponding to the number of indoor units 2 connected to the heat medium relay unit 3. The pipe 5 connected to the intermediate heat exchanger 15a, and the pipe 5 connected to the intermediate heat exchanger 15b are connected to each other by the first heat medium flow switching device 22 and the second heat medium flow switching device 23. The first heat medium flow switching device 22 and the second heat medium flow switching device 23 are controlled to determine whether to direct the heat medium flowing from the intermediate heat exchanger 15a into the use-side heat exchanger 26 or direct the heat medium flowing from the intermediate heat exchanger 15b into the use-side heat exchanger 26.

[0045]

Now, the configuration of Refrigerant Cycle Circuit A is summarized again. Refrigerant Cycle Circuit A is formed by connecting the compressor 10, the first refrigerant flow switching device 11, the heat source-side heat exchanger 12, the valve device 17, the second refrigerant flow switching device 18, the refrigerant flow path of the intermediate heat exchanger 15a, the expansion device 16, and the accumulator 19 by the refrigerant pipe 4. Heat Medium Cycle Circuit B is formed by connecting the heat medium flow path of the intermediate heat exchanger 15a, the liquid pump 21, the first heat medium flow switching device 22, the heat medium flow control device 25, the use-side heat exchanger 26, and the second heat medium flow switching device 23 by the pipe 5. That is, a plurality of use-side heat exchangers 26 are connected in parallel to each of the intermediate heat exchangers 15, and thus Heat Medium Cycle Circuit B is made up of a plurality of lines.

[0046]

Accordingly, in the air-conditioning apparatus 100, the outdoor unit 1 and the heat medium relay unit 3 are connected via the intermediate heat exchanger 15a and the intermediate heat exchanger 15b that are provided to the heat medium relay unit 3, and the heat medium relay unit 3 and the indoor unit 2 are also connected via the intermediate heat exchanger 15a and the intermediate heat exchanger 15b. That is, in the air-conditioning apparatus 100, the heat source-side refrigerant circulated in Refrigerant Cycle Circuit A, and the heat medium circulated in Heat Medium Cycle Circuit B exchange heat in the intermediate heat exchanger 15a and the intermediate heat exchanger 15b.

[0047]

Now, features of Embodiment are described.

Features of Embodiment reside in that as a refrigerant for use in Heat Medium Cycle Circuit B, an inflammable refrigerant such as R410Aor CO2 is used as described above, and this inflammable refrigerant undergoes changes in latent heat. Use of such an inflammable refrigerant ensures safety. Since a refrigerant that undergoes changes in latent heat is used, changes in latent heat are utilized to exchange heat in the intermediate heat exchanger 15 and the use-side heat exchanger 26. This enables efficient heat transfer and allows for reduced amount of heat medium to be transported, in comparison to use of typical conventional heat mediums for which changes in sensible heat are utilized to effect heat exchange, such as water. This enables downsizing of a liquid pump that serves as a unit to transport the heat medium.

[0048]

Next, various operation modes executed by the air-conditioning apparatus 100 will be described. The air-conditioning apparatus 100 is capable of performing, based on an instruction from each indoor unit 2, either a cooling operation or a heating operation in the corresponding indoor unit 2. That is, the air-conditioning apparatus 100 allows all of the indoor units 2 to perform the same operation, and also allows each individual indoor unit 2 to perform a different operation.

[0049]

Operation modes executed by the air-conditioning apparatus 100 include a cooling only operation mode in which all ofthe indoor units 2 that are running execute a cooling operation, a heating only operation mode in which all of the indoor units 2 that are running execute a heating operation, a cooling main operation mode as a cooling and heating mixed operation mode in which the cooling load is greater than the heating load, and a heating main operation mode as a cooling and heating mixed operation mode in which the heating load is greater than the cooling load.

Hereinafter, each ofthe operation modes will be described together with the corresponding flows ofthe heat source-side refrigerant and heat medium.

[0050] [Cooling Only Operation Mode]

Fig. 3 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling only operation mode ofthe air-conditioning apparatus according to Embodiment of the present invention. With reference to Fig. 3, the cooling only operation mode will be described for an exemplary case where a cooling load is generated only in the use-side heat exchanger 26a and the use-side heat exchanger 26b. In Fig. 3, pipes indicated by thick lines represent pipes through which the refrigerant (the heat source-side refrigerant and the heat medium) flows. In Fig. 3, the flow direction of the heat source-side refrigerant is indicated by solid arrows, and the flow direction of the heat medium is indicated by broken arrows.

[0051]

In the case of the cooling only operation mode illustrated in Fig. 3, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched to direct the heat source-side refrigerant discharged from the compressor 10 into the heat sourceside heat exchanger 12. In the heat medium relay unit 3, the heat medium flow control device 25b and the heat medium flow control device 25d are opened, and the heat medium flow control device 25a and the heat medium flow control device 25c are fully closed. Then, the liquid pump 21a used for cooling and the liquid pump 21 b used for cooling are driven, and the heat medium is circulated between the intermediate heat exchanger 15a and the use-side heat exchanger 26a, and between the intermediate heat exchanger 15b and the use-side heat exchanger 26b.

[0052]

Fig. 4 is a P-h diagram (a diagram illustrating the relationship between the pressure of refrigerant and specific enthalpy) of each of Refrigerant Cycle Circuit A and Heat Medium Cycle Circuit B in the cooling only operation mode of the airconditioning apparatus according to Embodiment of the present invention.

[0053] (Refrigerant Cycle Circuit A)

First, the flow of the heat source-side refrigerant in Refrigerant Cycle Circuit A will be described.

A low-temperature and low-pressure refrigerant is compressed by the compressor 10, and discharged as a high-temperature and high-pressure gas refrigerant that is in a state (1) illustrated in Fig. 4. The high-temperature and highpressure gas refrigerant (State (1)) discharged from the compressor 10 enters the heat source-side heat exchanger 12 via the first refrigerant flow switching device 11. After entering the heat source-side heat exchanger 12, the refrigerant turns into a high-pressure liquid refrigerant (State (2)) while rejecting heat to the outdoor air at the heat source-side heat exchanger 12.

[0054]

The high-pressure refrigerant exiting the heat source-side heat exchanger 12 passes through the check valve 13a and exits the outdoor unit 1, and then passes through the refrigerant pipe 4 into the heat medium relay unit 3. The high-pressure refrigerant entering the heat medium relay unit 3 is routed through the valve device 17a, and then divided into respective branch streams that enter the expansion device 16a and the expansion device 16b. The respective refrigerant streams entering the expansion device 16a and the expansion device 16b undergo expansion and turn into a low-temperature and low-pressure two-phase refrigerant (State (3)). The valve device 17b is closed at this time.

[0055]

The respective streams of two-phase refrigerant (State (3)) enter the intermediate heat exchanger 15a and the intermediate heat exchanger 15b serving as evaporators, and remove heat from the heat medium circulated in Heat Medium Cycle Circuit B and thus turn into a low-temperature and low-pressure gas refrigerant (State (4)) while cooling the heat medium. The respective streams of gas refrigerant exiting the intermediate heat exchanger 15a and the intermediate heat exchanger 15b pass through the second refrigerant flow switching device 18a and the second refrigerant flow switching device 18b, and merge before exiting the heat medium relay unit 3. After exiting the heat medium relay unit 3, the refrigerant passes through the refrigerant pipe 4 and enters the outdoor unit 1 again. After entering the outdoor unit 1, the resulting refrigerant passes through the check valve 13d, and sucked into the compressor 10 again via the first refrigerant flow switching device 11 and the accumulator 19.

[0056]

At this time, the second refrigerant flow switching device 18a and the second refrigerant flow switching device 18b communicate with a low pressure-side pipe. Further, the opening degree of the expansion device 16a is controlled such that the superheat (degree of superheat) obtained as the difference between the temperature detected by the third temperature sensor 35a and the temperature detected by the third temperature sensor 35b becomes constant. Likewise, the opening degree of the expansion device 16b is controlled such that the superheat obtained as the difference between the temperature detected by the third temperature sensor 35c and the temperature detected by the third temperature sensor 35d becomes constant. [0057] (Heat Medium Cycle Circuit B)

Next, the flow of the heat medium in Heat Medium Cycle Circuit B will be described.

In the cooling only operation mode, the cooling energy of the heat source-side refrigerant is transferred to the heat medium in both the intermediate heat exchanger 15a and the intermediate heat exchanger 15b to cool the heat medium. The respective streams of heat medium in a liquid state (State a in Fig. 4) sucked by the liquid pump 21a and the liquid pump 21 b, which are liquid pumps used for cooling, are pressurized into State b illustrated in Fig. 4, and reduced in pressure in the heat medium flow control device 25c and the heat medium flow control device 25d (State c in Fig. 4). The respective streams of heat medium, which are now at a reduced pressure, are routed through the pipe 5 into the use-side heat exchanger 26a and the use-side heat exchanger 26b, and turn into a gas state by heat exchange with the surrounding air (cooling) (State d in Fig. 4).

[0058]

The respective streams of heat medium in a gas state turn into State e in Fig.

due to pressure loss in the pipe 5 and the first heat medium flow switching devices

22a and 22b. The respective streams of heat medium in State e pass through the backflow prevention devices 39a and 39b of the bypasses 40a and 40b and enter the intermediate heat exchangers 15a and 15b, and exchange heat with the refrigerant circulated in Refrigerant Cycle Circuit A and condense into a liquid state (State a in Fig. 4). Then, the respective streams of heat medium exiting the intermediate heat exchangers 15a and 15b are pressurized by the liquid pumps 21a and 21b. At this time, the liquid pumps 37a and 37b used for heating are in their stopped state. The indoor space 7 is cooled through the above-described operation.

[0059]

Within the pipe 5 of the use-side heat exchanger 26, the heat medium flows in such a direction that the heat medium reaches the first heat medium flow switching device 22 from the second heat medium flow switching device 23. Further, the air conditioning load required for the indoor space 7 can be covered by controlling the opening degree of the heat medium flow control device 25 such that the difference between the temperature detected by the first temperature sensor 31a or the temperature detected by the first temperature sensor 31b, and the temperature detected by the second temperature sensor 34 (i.e., the difference in heat medium temperature between the outlet and inlet of the intermediate heat exchanger 15) is kept at a target value. As the outlet temperature of the intermediate heat exchanger 15, either one of the temperature detected by the first temperature sensor 31 a and the temperature detected by the first temperature sensor 31 b may be used, or the mean of the two temperatures may be used.

[0060]

At this time, the first heat medium flow switching device 22 and the second heat medium flow switching device 23 are switched such that each use-side heat exchanger 26 in which a thermal load is generated communicates with the intermediate heat exchanger 15a or the intermediate heat exchanger 15b to secure a flow path. The first heat medium flow switching device 22 and the second heat medium flow switching device 23 may be each controlled to an intermediate opening degree such that each use-side heat exchanger 26 in which a thermal load is generated communicates with both the intermediate heat exchanger 15a and the intermediate heat exchanger 15b to secure a flow path. The same applies to the heating only operation described later.

[0061]

In executing the cooling only operation mode, there is no need to pass the heat medium to the use-side heat exchanger 26 in which no thermal load is generated (including thermo-OFF). Accordingly, the flow path to the corresponding use-side heat exchanger 26 is closed by the first heat medium flow switching device 22 and the second heat medium flow switching device 23 so that the heat medium does not flow to the use-side heat exchanger 26. In Fig. 3, although a thermal load is generated in the use-side heat exchanger 26a and the use-side heat exchanger 26b and hence the heat medium is passed to these heat exchangers, no thermal load is generated in the use-side heat exchanger 26c and the use-side heat exchanger 26d, and hence the corresponding first heat medium flow switching devices 22a and 22b, and the corresponding second heat medium flow switching devices 23a and 23b are fully closed. When a thermal load is generated in the use-side heat exchanger 26c or the use-side heat exchanger 26d, the first heat medium flow switching device 22c or 22d, and the second heat medium flow switching device 23c or 23d may be opened to circulate the heat medium.

[0062]

The liquid pumps 21a and 21 b each serve as a transport unit with a variable flow rate. The liquid pumps 21a and 21 b have their flow rate controlled to obtain an optimum cooling output, based on temperature information from the second temperature sensor 34 at the use-side outlet.

[0063] [Heating Only Operation Mode]

Fig. 5 is a refrigerant circuit diagram illustrating the flow of refrigerant in heating only operation mode of the air-conditioning apparatus according to Embodiment of the present invention. With reference to Fig. 5, the heating only operation mode will be described for an exemplary case where a heating load is generated only in the use-side heat exchanger 26a and the use-side heat exchanger 26b. In Fig. 5, pipes indicated by thick lines represent pipes through which the refrigerant (the heat source-side refrigerant and the heat medium) flows. In Fig. 5, the flow direction of the heat source-side refrigerant is indicated by solid arrows, and the flow direction of the heat medium is indicated by broken arrows.

[0064]

In the case of the heating only operation mode illustrated in Fig. 5, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched such that the heat source-side refrigerant discharged from the compressor 10 is directed into the heat medium relay unit 3 without being routed through the heat source-side heat exchanger 12. In the heat medium relay unit 3, the heat medium flow control device 25b and the heat medium flow control device 25d are opened, and the heat medium flow control device 25a and the heat medium flow control device 25c are fully closed. Then, the liquid pump 37a used for heating and the liquid pump 37b used for heating are driven, and the heat medium is circulated between the intermediate heat exchanger 15a and the use-side heat exchanger 26a, and between the intermediate heat exchanger 15b and the use-side heat exchanger 26b.

[0065]

Fig. 6 is a P-h diagram (a diagram illustrating the relationship between the pressure of refrigerant and specific enthalpy) of each of Refrigerant Cycle Circuit A and Heat Medium Cycle Circuit B in heating only operation mode of the airconditioning apparatus according to Embodiment of the present invention.

[0066] (Refrigerant Cycle Circuit A)

A low-temperature and low-pressure refrigerant is compressed by the compressor 10, and discharged as a high-temperature and high-pressure gas refrigerant (State (1) in Fig. 6). The high-temperature and high-pressure gas refrigerant discharged from the compressor 10 passes through the first refrigerant flow switching device 11 and the check valve 13b, and exits the outdoor unit 1. The high-temperature and high-pressure gas refrigerant exiting the outdoor unit 1 passes through the refrigerant pipe 4 into the heat medium relay unit 3. After entering the heat medium relay unit 3, the high-temperature and high-pressure gas refrigerant is split into branch streams, which respectively pass through the second refrigerant flow switching device 18a and the second refrigerant flow switching device 18b into the intermediate heat exchanger 15a and the intermediate heat exchanger 15b.

[0067]

The respective streams of high-temperature and high-pressure gas refrigerant entering the intermediate heat exchanger 15a and the intermediate heat exchanger 15b turn into a high-pressure liquid refrigerant (State (2) in Fig. 6) while rejecting heat to the heat medium circulated in Heat Medium Cycle Circuit B. The respective streams of liquid refrigerant exiting the intermediate heat exchanger 15a and the intermediate heat exchanger 15b undergo expansion in the expansion device 16a and the expansion device 16b and turn into a low-temperature and low-pressure twophase refrigerant (State (3) in Fig. 6). These two-phase refrigerant streams merge, and then the merged two-phase refrigerant exits the heat medium relay unit 3 through the valve device 17b, and enters the outdoor unit 1 again through the refrigerant pipe

4. The valve device 17a is closed at this time.

[0068]

After entering the outdoor unit 1, the refrigerant passes through the check valve 13c into the heat source-side heat exchanger 12 that serves as an evaporator.

Then, the refrigerant entering the heat source-side heat exchanger 12 removes heat from the outdoor air in the heat source-side heat exchanger 12, and turns into a lowtemperature and low-pressure gas refrigerant (State (4) in Fig. 6). The lowtemperature and low-pressure gas refrigerant exiting the heat source-side heat exchanger 12 is sucked into the compressor 10 again via the first refrigerant flow switching device 11 and the accumulator 19.

[0069]

At this time, the second refrigerant flow switching device 18a and the second refrigerant flow switching device 18b communicate with a high pressure-side pipe. Further, the opening degree of the expansion device 16a is controlled such that the subcooling (degree of subcooling) obtained as the difference between a value obtained by converting the pressure detected by the pressure sensor 36 into a saturation temperature, and the temperature detected by the third temperature sensor 35b becomes constant. Likewise, the opening degree of the expansion device 16b is controlled such that the subcooling obtained as the difference between a value obtained by converting the pressure detected by the pressure sensor 36 into a saturation temperature, and the temperature detected by the third temperature sensor 35d becomes constant. If the temperature at the middle position of the intermediate heat exchanger 15 can be measured, the temperature at the middle position may be used instead of the pressure sensor 36. This allows the system to be configured inexpensively.

[0070] (Heat Medium Cycle Circuit B)

In the heating only operation mode, the heating energy of the heat source-side refrigerant is transferred to the heat medium in both the intermediate heat exchanger 15a and the intermediate heat exchanger 15b to heat the heat medium. The respective streams of heat medium in a liquid state (State a in Fig. 6) sucked by the liquid pump 37a and the liquid pump 37b, which are liquid pumps used for heating, are pressurized into State b illustrated in Fig. 6, and reduced in pressure in the heat medium flow control device 25a and the heat medium flow control device 25c (State c in Fig. 6). The respective streams of heat medium, which are now at a reduced pressure, flow into the intermediate heat exchanger 15a and the intermediate heat exchanger 15b, and turn into a gas state by heat exchange with the refrigerant circulated in Refrigerant Cycle Circuit A (State d in Fig. 6).

[0071]

The respective streams of heat medium in a gas state pass through the backflow prevention devices 38a and 39b of the bypasses 41a and 41 b, further pass through the second heat medium flow switching devices 23a and 23b, and are routed through the pipe 5 into the use-side heat exchangers 26a and 26b. The respective streams of heat medium entering the use-side heat exchangers 26a and 26b turn into a liquid state by heat exchange with the surrounding air at the use-side heat exchangers 26a and 26b. The respective streams of heat medium in a liquid state pass through the first heat medium flow switching devices 22a and 22b, and sucked and pressurized by the liquid pump 37a and the liquid pump 37b again. At this time, the liquid pumps 21 a and 21 b used for cooling are in their stopped state. The indoor space 7 is heated through the above-described operation.

[0072] [Cooling Main Operation Mode]

Fig. 7 is a refrigerant circuit diagram illustrating the flow of refrigerant in cooling main operation mode of the air-conditioning apparatus according to Embodiment of the present invention. In Fig. 7, the cooling main operation mode will be described for an exemplary case where a cooling load is generated in the use-side heat exchanger 26a and a heating load is generated in the use-side heat exchanger 26b.

In Fig. 7, pipes indicated by thick lines represent pipes through which the refrigerant (the heat source-side refrigerant and the heat medium) circulates. In Fig. 7, the flow direction of the heat source-side refrigerant is indicated by solid arrows, and the flow direction of the heat medium is indicated by broken arrows.

[0073]

In the cooling main operation mode illustrated in Fig. 7, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched such that the heat source-side refrigerant discharged from the compressor 10 is routed into the heat source-side heat exchanger 12. In the heat medium relay unit 3, the heat medium flow control device 25b and the heat medium flow control device 25d are opened, and the heat medium flow control device 25a and the heat medium flow control device 25c are fully closed. Then, the liquid pump 21a used for cooling and the liquid pump 37b used for heating are driven, and the heat medium is circulated between the intermediate heat exchanger 15a and the use-side heat exchanger 26a, and between the intermediate heat exchanger 15b and the use-side heat exchanger 26b.

[0074]

Fig. 8 is a P-h diagram (a diagram illustrating the relationship between the pressure of refrigerant and specific enthalpy) of each of Refrigerant Cycle Circuit A and Heat Medium Cycle Circuit B in cooling main operation mode of the airconditioning apparatus according to Embodiment of the present invention.

[0075] (Refrigerant Cycle Circuit A)

A low-temperature and low-pressure refrigerant is compressed by the compressor 10, and discharged as a high-temperature and high-pressure gas refrigerant (State (1) in Fig. 8). The high-temperature and high-pressure gas refrigerant discharged from the compressor 10 enters the heat source-side heat exchanger 12 via the first refrigerant flow switching device 11. After entering the heat source-side heat exchanger 12, the refrigerant turns into a liquid refrigerant while rejecting heat to the outdoor air at the heat source-side heat exchanger 12. The refrigerant exiting the heat source-side heat exchanger 12 exits the outdoor unit 1, and passes through the check valve 13a and the refrigerant pipe 4 into the heat medium relay unit 3. The refrigerant entering the heat medium relay unit 3 passes through the second refrigerant flow switching device 18b into the intermediate heat exchanger 15b that serves as a condenser.

[0076]

The refrigerant entering the intermediate heat exchanger 15b further decreases in temperature while rejecting heat to the heat medium circulated in Heat Medium Cycle Circuit B (State (2) in Fig. 8). The refrigerant exiting the intermediate heat exchanger 15b undergoes expansion in the expansion device 16b and turns into a low-pressure two-phase refrigerant (State (3) in Fig. 8). This low-pressure two27 phase refrigerant enters the intermediate heat exchanger 15a, which serves as an evaporator, via the expansion device 16a that is now fully open. The low-pressure two-phase refrigerant entering the intermediate heat exchanger 15a removes heat from the heat medium circulated in Heat Medium Cycle Circuit B, and thus turns into a low-pressure gas refrigerant while cooling the heat medium (State (4) in Fig. 8).

This gas refrigerant exits the intermediate heat exchanger 15a, and then exits the heat medium relay unit 3 via the second refrigerant flow switching device 18a. The gas refrigerant then travels through the refrigerant pipe 4, and enters the outdoor unit 1 again. The refrigerant entering the outdoor unit 1 is sucked into the compressor 10 again via the check valve 13d, the first refrigerant flow switching device 11, and the accumulator 19.

[0077]

At this time, the second refrigerant flow switching device 18a communicates with a low pressure-side pipe, and the second refrigerant flow switching device 18b communicates with a high-pressure side pipe. Further, the opening degree of the expansion device 16b is controlled such that the superheat obtained as the difference between the temperature detected by the third temperature sensor 35a and the temperature detected by the third temperature sensor 35b becomes constant. The valve device 17b is in its closed state at this time. Alternatively, the opening degree of the expansion device 16b may be controlled such that the subcooling obtained as the difference between a value obtained by converting the pressure detected by the pressure sensor 36 into a saturation temperature, and the temperature detected by the third temperature sensor 35d becomes constant. Alternatively, the expansion device 16b may be fully opened, and the superheat or subcooling may be controlled by the expansion device 16a.

[0078] (Heat Medium Cycle Circuit B)

Next, the flow of the heat medium in Heat Medium Cycle Circuit B in cooling main operation mode will be described.

[0079]

First, the heating side will be described.

The heat medium in a liquid state (State a1 in Fig. 8) sucked by the liquid pump 37b used for heating is pressurized into State b1 in Fig. 8, and reduced in pressure in the heat medium flow control device 25c (State c1 in Fig. 8). The heat medium in State c1 flows into the intermediate heat exchanger 15b, where the heat medium turns into a gas state by heat exchange with the refrigerant circulated in Refrigerant Cycle Circuit A (State d1 in Fig. 8).

[0080]

The heat medium in the gas state passes through the backflow prevention device 38b of the bypass 41 b, and further passes through the second heat medium flow switching device 23b and the pipe 5. The heat medium in the gas state turns into State e1 of Fig. 8 due to pressure loss in the second heat medium flow switching device 23b and the pipe 5. The heat medium in State e1 flows into the use-side heat exchanger 26b. The heat medium entering the use-side heat exchanger 26b turns into a liquid state by heat exchange with the surrounding air at the use-side heat exchanger 26b (State a1 in Fig. 8). The heat medium now in its liquid state passes through the first heat medium flow switching device 22b, and is sucked again into the liquid pump 37b used for cooling. At this time, the liquid pump 21b used for cooling, and the liquid pump 37a used for heating are in their stopped state. As the heat medium condenses in the use-side heat exchanger 26b, the indoor space 7 is heated.

[0081]

Next, the cooling side will be described.

The heat medium in a liquid state (State a in Fig. 8) sucked by the liquid pump 21a used for cooling is pressurized into State b in Fig. 8, and reduced in pressure in the heat medium flow control device 25b (State c in Fig. 8). The heat medium in State c is routed through the second heat medium flow switching device 23a and the pipe 5, and sent to the use-side heat exchanger 26b. The heat medium sent to the use-side heat exchanger 26b turns into a gas state by heat exchange with the surrounding air (cooling) in the use-side heat exchanger 26b (State d in Fig. 8).

[0082]

The heat medium in a gas state turns into State e in Fig. 8 due to pressure loss in the pipe 5 and the first heat medium flow switching device 22a. The heat medium in State e passes through the backflow prevention device 39a of the bypass 40a into the intermediate heat exchanger 15a. The heat medium entering the intermediate heat exchanger 15a exchanges heat with the refrigerant circulated in Refrigerant Cycle Circuit A and condenses into a liquid state (State a in Fig. 8).

The heat medium in a liquid state is pressurized again by the liquid pump 21a used for cooling. At this time, the liquid pump 37a used for heating, and the liquid pump 21 b used for cooling are in their stopped state. As the heat medium removes heat from the indoor air to evaporate at the use-side heat exchanger 26a, the indoor space 7 is cooled.

[0083] [Heating Main Operation Mode]

Fig. 9 is a refrigerant circuit diagram illustrating the flow of refrigerant in heating main operation mode of the air-conditioning apparatus according to Embodiment of the present invention. In Fig. 9, the heating main operation mode will be described for an exemplary case where a heating load is generated in the use-side heat exchanger 26a and a cooling load is generated in the use-side heat exchanger 26b.

In Fig. 9, pipes indicated by thick lines represent pipes through which the refrigerant (the heat source-side refrigerant and the heat medium) circulates. In Fig. 9, the flow direction of the heat source-side refrigerant is indicated by solid arrows, and the flow direction of the heat medium is indicated by broken arrows.

[0084]

In the case of the heating main operation mode illustrated in Fig. 9, in the outdoor unit 1, the first refrigerant flow switching device 11 is switched such that the heat source-side refrigerant discharged from the compressor 10 is directed into the heat medium relay unit 3 without being routed through the heat source-side heat exchanger 12. In the heat medium relay unit 3, the heat medium flow control device 25b and the heat medium flow control device 25d are opened, and the heat medium flow control device 25a and the heat medium flow control device 25c are fully closed. Then, the liquid pump 21a used for cooling and the liquid pump 37b used for heating are driven, and the heat medium is circulated between the intermediate heat exchanger 15a and the use-side heat exchanger 26a, and between the intermediate heat exchanger 15b and the use-side heat exchanger 26b.

[0085]

Fig. 10 is a P-h diagram (a diagram illustrating the relationship between the pressure of refrigerant and specific enthalpy) of each of Refrigerant Cycle Circuit A and Heat Medium Cycle Circuit B in heating main operation mode of the airconditioning apparatus according to Embodiment of the present invention.

[0086] (Refrigerant Cycle Circuit A)

A low-temperature and low-pressure refrigerant is compressed by the compressor 10, and discharged as a high-temperature and high-pressure gas refrigerant (State (1) in Fig. 10). The high-temperature and high-pressure gas refrigerant discharged from the compressor 10 passes through the first refrigerant flow switching device 11 and the check valve 13b, and exits the outdoor unit 1. The high-temperature and high-pressure gas refrigerant exiting the outdoor unit 1 passes through the refrigerant pipe 4 into the heat medium relay unit 3. The hightemperature and high-pressure gas refrigerant entering the heat medium relay unit 3 passes through the second refrigerant flow switching device 18b into the intermediate heat exchanger 15b that serves as a condenser.

[0087]

The gas refrigerant entering the intermediate heat exchanger 15b turns into a liquid refrigerant while rejecting heat to the heat medium circulated in Heat Medium

Cycle Circuit B (State (2) in Fig. 10). The refrigerant exiting the intermediate heat exchanger 15b undergoes expansion in the expansion device 16b and turns into a low-pressure two-phase refrigerant (State (3) in Fig. 10). This low-pressure two31 phase refrigerant enters the intermediate heat exchanger 15a, which serves as an evaporator, via the expansion device 16a that is now fully open. The low-pressure two-phase refrigerant entering the intermediate heat exchanger 15a removes heat from the heat medium circulated in Heat Medium Cycle Circuit B and thus evaporates into a low-pressure two-phase refrigerant while cooling the heat medium. This lowpressure two-phase refrigerant exits the intermediate heat exchanger 15a, and then exits the heat medium relay unit 3 via the second refrigerant flow switching device 18a. The low-pressure two-phase refrigerant then enters the outdoor unit 1 again. [0088]

Then, the refrigerant entering the heat source-side heat exchanger 12 removes heat from the outdoor air in the heat source-side heat exchanger 12, and turns into a lowtemperature and low-pressure gas refrigerant (State (4) in Fig. 10). The lowtemperature and low-pressure gas refrigerant exiting the heat source-side heat exchanger 12 is sucked into the compressor 10 again via the first refrigerant flow switching device 11 and the accumulator 19.

[0089]

At this time, the second refrigerant flow switching device 18a communicates with a low-pressure side pipe, and the second refrigerant flow switching device 18b communicates with a high-pressure side pipe. Further, the opening degree of the expansion device 16b is controlled such that the subcooling obtained as the difference between a value obtained by converting the pressure detected by the pressure sensor 36 into a saturation temperature, and the temperature detected by the third temperature sensor 35b becomes constant. The valve device 17a is in its closed state at this time. Alternatively, the expansion device 16b may be fully opened, and the subcooling may be controlled by the expansion device 16a.

[0090] (Heat Medium Cycle Circuit B)

Next, the flow of the heat medium in Heat Medium Cycle Circuit B in heating main operation mode will be described.

[0091]

First, the heating side will be described.

The heat medium in a liquid state (State a1 in Fig. 10) sucked by the liquid pump 37b used for heating is pressurized into State b1 in Fig. 10, and reduced in pressure in the heat medium flow control device 25c (State c1 in Fig. 10). The heat medium in State c1 flows into the intermediate heat exchanger 15b, and turns into a gas state by heat exchange with the refrigerant circulated in Refrigerant Cycle Circuit A (State d1 in Fig. 10).

[0092]

The heat medium in the gas state passes through the backflow prevention device 38b of the bypass 41 b, and further passes through the second heat medium flow switching device 23b and the pipe 5. The heat medium in the gas state turns into State e1 of Fig. 10 due to pressure loss in the second heat medium flow switching device 23b and the pipe 5. This heat medium in State e1 flows into the use-side heat exchanger 26b. The heat medium entering the use-side heat exchanger 26b turns into a liquid state by heat exchange with the surrounding air at the use-side heat exchanger 26b (State a1 in Fig. 10). The heat medium now in its liquid state passes through the first heat medium flow switching device 22b, and sucked by the liquid pump 37b again. At this time, the liquid pump 21 b used for cooling, and the liquid pump 37a used for heating are in their stopped state. As the heat medium condenses in the use-side heat exchanger 26b, the indoor space 7 is heated.

[0093]

Next, the cooling side will be described.

The heat medium in a liquid state (State a in Fig. 10) sucked by the liquid pump 21a used for cooling is pressurized (State b in Fig. 10), and reduced in pressure in the heat medium flow control device 25b (State c in Fig. 10). The heat medium in State c is routed through the second heat medium flow switching device

23a and the pipe 5, and sent to the use-side heat exchanger 26b. The heat medium sent to the use-side heat exchanger 26b turns into a gas state by heat exchange with the surrounding air (cooling) in the use-side heat exchanger 26b (State d in Fig. 10). [0094]

The heat medium now in its gas state turns into State e in Fig. 10 due to pressure loss in the pipe 5 and the first heat medium flow switching device 22a. The heat medium in State e passes through the backflow prevention device 39a of the bypass 40a into the intermediate heat exchanger 15a. The heat medium entering the intermediate heat exchanger 15a exchanges heat with the refrigerant circulated in Refrigerant Cycle Circuit A and condenses into a liquid state (State a in Fig. 10).

The heat medium in the liquid state is pressurized again by the liquid pump 21a used for cooling. At this time, the liquid pump 37a used for heating, and the liquid pump 21 b used for cooling are in their stopped state. As the heat medium rejects heat to the indoor air at the use-side heat exchanger 26a, the indoor space 7 is cooled.

[0095]

Cooling operation, heating operation, cooling main operation, and heating main operation can be performed as describe above.

[0096]

As described above, in Embodiment, a liquid pump is employed as a transport device for Heat Medium Cycle Circuit B, and a refrigerant that undergoes heat changes is used as a heat medium for Heat Medium Cycle Circuit B. Heat exchange is performed by using latent heat in each ofthe intermediate heat exchanger 15 and the use-side heat exchanger 26. This configuration enables heat exchange to be effected by changes in latent heat, thus allowing the flow rate of heat medium to be reduced. This results in reduced power required to transport the heat medium. Further, the use of a non-toxic inflammable refrigerant as a heat medium also ensures safety.

[0097]

Further, Heat Medium Cycle Circuit B has the pipe (supply pipe) 5 that runs from the intermediate heat exchanger 15 toward the use-side heat exchanger 26, and the pipe (return pipe) 5 that runs back from the use-side heat exchanger 26 to the intermediate heat exchanger 15. The liquid pumps 21 and the heat medium flow control device 25 are arranged in the named order from the upstream side in the portion of the supply pipe 5 between the intermediate heat exchanger 15 and the second heat medium flow switching device 23, and the liquid pump 37 and the heat medium flow control device 25 are arranged in the named order from the upstream side in the portion of the return pipe 5 between the intermediate heat exchanger 15 and the first heat medium flow switching device 22. The supply pipe 5 is connected with the bypass 41 to bypass the liquid pump 21 and the heat medium flow control device 25, and the return pipe 5 is connected with the bypass 40 to bypass the liquid pump 37 and the heat medium flow control device 25. The bypasses 40 and 41 are respectively provided with the backflow prevention devices 38 and 39.

[0098]

Briefly, the main point of the configuration of Heat Medium Cycle Circuit B described above is that two liquid pumps 21 and 37 are used separately, one for cooling and the other for heating, for each individual intermediate heat exchanger 15. This configuration is employed for the following reason.

[0099]

Since refrigerant is used as the heat medium to be circulated in Heat Medium Cycle Circuit B, while the heat medium is circulated in Heat Medium Cycle Circuit B, the heat medium changes into a gas state, a two-phase state, or a liquid state. Accordingly, from the viewpoint of sucking the heat medium with the liquid pump at a position where the heat medium is in its liquid state, different liquid pumps are used separately for cooling and heating.

[0100]

In Patent Literature 1 mentioned above, a single liquid pump is used for each individual intermediate heat exchanger 15, contrary to that in Embodiment of the present invention where two liquid pumps are used for each individual intermediate heat exchanger 15. Although this may seem that the number of liquid pumps simply increased, in Embodiment, a refrigerant that undergoes changes in latent heat is used as a heat medium as described above to thereby reduce the transport capacity required for the liquid pump. This means that even through two liquid pumps are used, each individual liquid pump may be small in size. Therefore, the installation space can be reduced in comparison to conventional configurations. This results in increased freedom of system layout.

[0101]

Further, use of refrigerant as a heat medium makes it possible to obviate problems such as damage to heat exchangers or pipes caused by freezing of water if water is used as a heat medium. This leads to enhanced reliability.

[0102]

In Embodiment, two liquid pumps are used for each individual intermediate heat exchanger 15, one for heating and the other for cooling. However, instead of using different liquid pumps separately for heating and cooling, a single liquid pump may be used for each intermediate heat exchanger 15. In this case, a plurality of solenoid valves or other devices may be used in combination such that a heat medium in its liquid state is sucked into the liquid pump.

Reference Signs List [0103] outdoor unit 2 indoor unit 3 heat medium relay unit 4 refrigerant pipe 4a first connecting pipe 4b second connecting pipe 5 pipe (supply pipe, return pipe) 6 outdoor space 7 indoor space 8 space 9 building 10 compressor 11 first refrigerant flow switching device 12 heat source-side heat exchanger 13a checkvalve 13b checkvalve 13c checkvalve 13d check valve 15 intermediate heat exchanger 15a intermediate heat exchanger 15b intermediate heat exchanger 16 expansion device 16a expansion device 16b expansion device 17 valve device 17a valve device 17b valve device 18 second refrigerant flow switching device 18a second refrigerant flow switching device 18b second refrigerant flow switching device 19 accumulator 21 liquid pump 21a liquid pump 21b liquid pump 22 first heat medium flow switching device 22a first heat medium flow switching device 22b first heat medium flow switching device 22c first heat medium flow switching device 22d first heat medium flow switching device 23 second heat medium flow switching device 23a second heat medium flow switching device 23b second heat medium flow switching device 23c second heat medium flow switching device

23d second heat medium flow switching device 25 heat medium flow control device 25a heat medium flow control device 25b heat medium flow control device 25c heat medium flow control device 25d heat medium flow control device 26 use-side heat exchanger 26a use-side heat exchanger 26b useside heat exchanger 26c use-side heat exchanger 26d use-side heat exchanger 31 first temperature sensor 31a first temperature sensor 31b first temperature sensor 34 second temperature sensor 34a second temperature sensor 34b second temperature sensor 34c second temperature sensor 34d second temperature sensor 35 third temperature sensor 35a third temperature sensor 35b third temperature sensor 35c third temperature sensor 35d third temperature sensor 36 pressure sensor 37 liquid pump 37a liquid pump 37b liquid pump 38 backflow prevention device 38a backflow prevention device 38b backflow prevention device 39 backflow prevention device 39a backflow prevention device 39b backflow prevention device 40 bypass 40a bypass 40b bypass 41 bypass 41a bypass 41b bypass 100 air20 conditioning apparatus A Refrigerant Cycle Circuit B Heat Medium Cycle Circuit

Claims

CLAIMS [Claim 1]

An air-conditioning apparatus comprising:

a heat source-side refrigerant cycle circuit in which a compressor, a heat source-side heat exchanger, an expansion device, and a refrigerant flow path of each of a plurality of intermediate heat exchangers are connected by pipes to circulate a heat source-side refrigerant;

a heat medium cycle circuit in which a plurality of pumps, a plurality of use-side heat exchangers, and a heat medium flow path of each of the plurality of intermediate heat exchangers are connected by a pipe to circulate a heat medium;

a heat medium flow switching device provided to the heat medium cycle circuit in correspondence with each of the plurality of use-side heat exchangers, the heat medium flow switching device allowing each of the plurality of use-side heat exchangers to communicate with one of the plurality of intermediate heat exchangers to switch flow paths of the heat medium, wherein the heat medium comprises an inflammable refrigerant that, in each of the intermediate heat exchangers and the use-side heat exchangers, undergoes heat exchange using latent heat, and wherein the plurality of pumps each comprise a liquid pump that sucks the heat medium in a liquid state and circulates the sucked heat medium in the heat medium cycle circuit.
[Claim 2]

The air-conditioning apparatus of claim 1, wherein the heat medium cycle circuit includes, for each of the plurality of intermediate heat exchangers, a supply pipe that runs from the intermediate heat exchanger toward the use-side heat exchanger, and a return pipe that runs back from the use-side heat exchanger to the intermediate heat exchanger, wherein the liquid pump and a heat medium flow control device are arranged in named order from an upstream side, in each of the supply pipe between the intermediate heat exchanger and the heat medium flow switching device and the return pipe between the intermediate heat exchanger and the heat medium flow switching device, wherein each of the supply pipe and the return pipe is connected with a bypass to bypass the liquid pump and the heat medium flow control device, and

5 wherein a backflow prevention device is provided to the bypass.
[Claim 3]

The air-conditioning apparatus of claim 1 or 2, wherein carbon dioxide is used as the heat medium.