A first flow switching device causes part of a refrigerant discharged from an injection compressor to flow through a first bypass pipe and be supplied to an outdoor heat exchanger targeting for defrosting. A second flow switching device causes part of the refrigerant supplied to the outdoor heat exchanger targeting for defrosting to enter a second bypass pipe.

TECHNICAL FIELD

The present invention relates to an air-conditioning apparatus.

BACKGROUND ART

Conventional air-conditioning apparatuses perform defrosting operation by inverting a refrigerant cycle to remove frost in an outdoor heat exchanger acting as an evaporator in a heating operation. However, in that defrosting operation, indoor comfort decreases because heating is halted in the defrosting operation. One example of a technique capable of performing a heating operation and a defrosting operation at a time is a heat pump including an outdoor heat exchanger divided into a plurality of parallel heat exchangers, a bypass that bypasses gas discharged from an injection compressor for each of the divided heat exchangers, and an electromagnetic on-off valve that controls a bypass state (see, for example, Patent Literature 1).

That heat pump includes an outdoor unit, indoor units, and a main pipe connecting them such that a refrigerant circulates therethrough and is a multi-type air-conditioning apparatus in which two indoor units are connected to one outdoor unit. The outdoor unit includes an injection compressor, a four-way valve for switching between a cooling operation and a heating operation, outdoor heat exchangers connected in parallel, a first bypass pipes having a first end connected between the injection compressor and the four-way valve and a second end split and connected in parallel to the pipes connected to the outdoor heat exchangers, a second flow switching device for switching the flow of the refrigerant to either one of the main pipe and the first bypass pipe, and a third flow control valve for controlling the flow rate of the refrigerant flowing in the first bypass pipe. That enables continuous heating without inverting the refrigeration cycle by causing part of the refrigerant from the injection compressor to alternately enter each of the bypasses and by alternately defrosting each of the parallel heat exchangers.

There is a refrigeration machine that includes a plurality of parallel heat exchangers, a plurality of main compressors, and a sub compressor and that injects a refrigerant used in deicing for the heat exchanger into the sub compressor (see, for example, Patent Literature 2).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in the technique in Patent Literature 1, during simultaneous operation of heating operation and defrosting operation, a refrigerant in two-phase gas-liquid state exiting the outdoor heat exchanger targeting for defrosting and a gas refrigerant exiting the outdoor heat exchanger performing heating action are mixed, and the mixture is sucked into the injection compressor. Accordingly, the injection compressor needs to raise not only the pressure of the refrigerant for heating but also that for defrosting from low to high, and thus the efficiency of the air-conditioning apparatus decreases.

Enthalpy usable in defrosting is only sensible heat of the gas, and it is necessary to make a large amount of a high-temperature and high-pressure refrigerant discharged from the injection compressor flow into the first bypass pipes in order to melt frost. That reduces the flow rate of the refrigerant flowing through the outdoor heat exchanger transferring heat to outside the room to perform heating, and thus the heating capacity decreases.

The technique in Patent Literature 2 needs the sub compressor, and is a technique relating to a refrigeration machine capable of performing only refrigeration and freezing, and does not include means for switching the direction of the flow of the refrigerant. Thus it cannot perform heating and cooling required as an air-conditioning apparatus.

The present invention is made to solve the above-described conventional problems. It is an object of the present invention to provide an air-conditioning apparatus capable of improving its energy efficiency and improving its heating capacity during simultaneous operation of heating operation and defrosting operation using a main compressor.

Solution to Problem

An air-conditioning apparatus according to the present invention includes a main pipe that connects indoor units and an outdoor unit such that a refrigerant circulates therethrough. The air-conditioning apparatus further includes an indoor heat exchanger, a flow control valve, an injection compressor, a refrigerant flow switching device, a plurality of outdoor heat exchangers connected in parallel, a first bypass pipe, a second bypass pipe, a first flow switching device, and a second flow switching device. The flow control valve is configured to control a flow rate of the refrigerant entering the indoor heat exchanger. The injection compressor includes an injection port allowing the refrigerant to be injected therethrough into the refrigerant undergoing compression. The refrigerant flow switching device is configured to switch between a cooling operation and a heating operation. The plurality of outdoor heat exchangers are connected in parallel. The first bypass pipe has a first end connected between the injection compressor and the refrigerant flow switching device and a second end connected to a first one of inlet and outlet sides of the plurality of outdoor heat exchangers. The second bypass pipe has a first end connected to the injection port or a pipe connected to the injection port and a second end connected to a second one of the inlet and outlet sides of the plurality of outdoor heat exchangers. The first flow switching device is configured to switch a flow of the refrigerant to the main pipe or the first bypass pipe. The second flow switching device is configured to switch the flow of the refrigerant to the main pipe or the second bypass pipe. In a defrosting operation of removing frost in any of the plurality of outdoor heat exchangers, the first flow switching device causes part of the refrigerant discharged from the injection compressor to flow through the first bypass pipe, and the refrigerant is supplied to the outdoor heat exchanger including the plurality of outdoor heat exchangers, and targeting for defrosting, and the second flow switching device causes part of the refrigerant supplied to the outdoor heat exchanger targeting for defrosting to enter the second bypass pipe.

Advantageous Effects of Invention

According to the present invention, there is no need to lower the pressure of the refrigerant for defrosting to a suction pressure. Accordingly, the injection compressor needs to raise only the pressure of the refrigerant circulating through the main circuit to perform heating from low to high, and needs to raise the pressure of the injected intermediate-pressure two-phase gas-liquid refrigerant only from intermediate to high. Thus, the advantageous effects of reducing the workload of the injection compressor1and improving the efficiency of the heat pump and the heating capacity are obtainable.

DESCRIPTION OF EMBODIMENTS

Embodiment 1 of the present invention is described below with reference toFIGS. 1 to 9. The same reference numerals are used in the same parts.FIG. 1illustrates a refrigerant circuit in an air-conditioning apparatus according to Embodiment 1 of the present invention. An air-conditioning apparatus1000is described below with reference toFIG. 1.

The air-conditioning apparatus1000includes an outdoor unit100, indoor units200aand200b, and a main pipe connecting them such that a refrigerant circulates therethrough. The air-conditioning apparatus1000is a multi-type air-conditioning apparatus in which two indoor units are connected to one outdoor unit.

The outdoor unit100includes an injection compressor1, a temperature sensor2, a four-way valve3, a refrigerant heat exchanger6, a second flow control valve7(corresponding to an outdoor flow control valve in the present invention), two-way valves8aand8b, outdoor heat exchangers9aand9b, two-way valves10aand10b, a first bypass pipe21, two-way valves22aand22b, a second bypass pipe31, third flow control valves32aand32b(corresponding to a second bypass flow control valve in the present invention), a third bypass pipe41, a fourth flow control valve42(corresponding to an injection flow control valve in the present invention), a first flow switching device A, and a second flow switching device B. The indoor unit200aincludes an indoor heat exchanger4aand a first flow control valve5a(corresponding to a flow control valve in the present invention). The indoor unit200bincludes an indoor heat exchanger4band a first flow control valve5b(corresponding to the flow control valve in the present invention).

The injection compressor1is a compressor capable of injecting a refrigerant into a refrigerant undergoing compression. The temperature sensor2measures the temperature of a refrigerant discharged from the injection compressor1. The four-way valve3switches between a cooling operation and a heating operation and corresponds to a refrigerant flow switching device in the present invention. The refrigerant heat exchanger6exchanges heat between a refrigerant flowing in the main pipe and a refrigerant flowing in the third bypass pipe41(described below).

The first bypass pipe21has a first end connected between the injection compressor1and the four-way valve3and a second end split and connected in parallel to the pipes connected to the outdoor heat exchangers9aand9b. The second bypass pipe31has a first end connected to the third bypass pipe41and a second end connected in parallel to the pipe different from the pipes connected to the first bypass pipe21for the two outdoor heat exchangers9aand9b. The third bypass pipe41has a first end connected between the outdoor heat exchangers9aand9band the main pipe connected to the indoor units200aand200band a second end connected to an injection port of the injection compressor1.

The first flow control valves5aand5bcontrol the flow rate of the refrigerant flowing through the indoor units200aand200b. The second flow control valve7controls the flow rate of the refrigerant flowing between the refrigerant heat exchanger6and the two-way valves8aand8b. The third flow control valves32aand32bcontrol the flow rate of the refrigerant flowing from the second flow switching device B to the second bypass pipe31. The fourth flow control valve42adjusts the flow rate of the refrigerant flowing in the third bypass pipe41.

The first flow switching device A is made up of the two-way valves8a,8b,22a, and22b. The second flow switching device B is made up of the two-way valves10aand10band the third flow control valves32aand32b. Each of the two-way valves8a,8b,10a,10b,22a, and22bis openable and closable independently of the magnitude of a pressure at each of an inlet and an outlet of the valve and switches the flow of the refrigerant.

FIG. 5illustrates one example of a structure of each of the two-way valves8a,8b,10a,10b,22a, and22band actions. That two-way valve structure is the one in which the valve is openable and closable independently of the magnitude of a pressure at each of an inlet and an outlet of the valve and the valve can stop the refrigerant in only one direction. That two-way valve includes a valve body V to which a main pipe M1and a main pipe M2are connected, a pressure adjusting device X for adjusting the pressure in each of pressure chambers P1and P2in the valve body V, and pipes T1, T2, T3, and T4connected to the valve body V and the pressure adjusting device X or the refrigerant pipe.

The valve body V includes movable walls W1and W2moving rightward or leftward in accordance with the pressure in each of the pressure chambers P1and P2and a small slide valve S. The small slide valve S is attached to the movable walls W1and W2, moves rightward or leftward on a valve seat U, and opens and closes the valve. The pressure adjusting device X includes the small slide valve S and a small slide valve driving device Y driving the small slide valve S. The small slide valve S is used to selectively switch to either one of the case where the pipes T1and T3are connected and the pipes T2and T4are connected (valve is opened) and the case where the pipes T1and T2are connected and the pipes T3and T4are connected (valve is closed).

The pipe T1is attached to the pressure adjusting device X at a first end and to the main pipe M1at a second end. The pipe T2is attached to the pressure adjusting device X at a first end and to the pressure chamber P1at a second end. The pipe T3is attached to the pressure adjusting device X at a first end and to the pressure chamber P2at a second end. The pipe T4is connected to a location where the pressure is always low in the air-conditioning apparatus, for example, to a low-pressure pipe, a suction pipe of the injection compressor1, or an accumulator.

In the two-way valve with the above-described structure, when the small slide valve driving device Y moves the small slide valve S leftward, as illustrated inFIG. 5(a), the pipe T1and the pipe T3are connected and the pipe T2and the pipe T4are connected. With this, the pressure in the pressure chamber P1becomes smaller than the pressure in the pressure chamber P2, the small slide valve S moves leftward, and the valve is opened.

When the small slide valve driving device Y moves the small slide valve S rightward, as illustrated inFIG. 5(b), the pipe T1and the pipe T2are connected and the pipe T3and the pipe T4are connected. With this, the pressure in the pressure chamber P1becomes larger than the pressure in the pressure chamber P2, the small slide valve S moves rightward, and the valve is closed.

In Embodiment 1, as illustrated inFIG. 1, the two-way valves10aand10bstop the refrigerant in only the direction from the outdoor heat exchangers9aand9btoward the four-way valve3(upward inFIG. 1), and the two-way valves8aand8bstop the refrigerant in only the direction from the outdoor heat exchangers9aand9btoward outside the outdoor unit100through the main pipe (downward inFIG. 1). The arrow on the side of each of the valves inFIG. 1indicates the direction of the refrigerant that the valve can stop.

Next, the description is provided with reference toFIGS. 2 to 4, which illustrate flows of the refrigerant in the apparatus andFIGS. 7 to 9, which are p-h diagrams (diagrams each illustrating a relationship between the pressure of the refrigerant and enthalpy). InFIGS. 2 to 4, the thick solid lines indicate flows of the refrigerant in operation, and the numbers in brackets, [i] (i=1, 2, . . . ), indicate pipe portions corresponding to points i (states of the refrigerant) in the diagrams ofFIGS. 7 to 9.

FIG. 2illustrates a flow occurring when cooling is performed by cooling the air inside a room using each of the indoor heat exchangers and transferring heat to the outside air using the outdoor heat exchangers (hereinafter referred to as cooling only operation).

FIG. 3illustrates a flow occurring when heating is performed by heating the air in a room using each of the indoor heat exchangers and removing receiving heat from the outside air using the outdoor heat exchangers (hereinafter referred to as heating only operation).

FIG. 4illustrates a flow occurring when a first one (outdoor heat exchanger9ainFIG. 1) of parallel heat exchangers constituting the outdoor heat exchangers causes the refrigerant to evaporate and receives heat from the outside air and a second one (outdoor heat exchanger9binFIG. 1) of the parallel heat exchangers heats frost in the outdoor heat exchanger9bto melt it (hereinafter referred to as heating and defrosting simultaneous operation). During the above heating operations, the indoor heat exchangers function as condensers, and the outdoor heat exchangers function as evaporators. The same applies to following Embodiment.

FIG. 2illustrates a refrigerant flow in a cooling only operation in the air-conditioning apparatus according to Embodiment 1 of the present invention.FIG. 7illustrates a relationship between the pressure of the refrigerant and the enthalpy in the cooling only operation of the air-conditioning apparatus according to Embodiment 1 of the present invention. The flow in the cooling only operation is described below with reference toFIGS. 2 and 7.

In the cooling only operation, the four-way valve3is switched to the state indicated by the broken lines inFIG. 2. The second flow switching device B is switched such that the refrigerant exiting the four-way valve3is split into both the outdoor heat exchangers9aand9band the refrigerant exiting each of the outdoor heat exchangers9aand9bflows through the main pipe and is supplied to the refrigerant heat exchanger6and the indoor units200aand200b.

First, a low-temperature and low-pressure gas refrigerant is compressed by the injection compressor1. Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [1]-[2]) in consideration of the efficiency of the injection compressor1.

Then, the refrigerant undergoing compression and the refrigerant flowing from the third bypass pipe41join together. Changes in the refrigerant in the joining are made under the state where the pressure is substantially constant and are represented by a horizontal line (points [2]-[3], points [9]-[3]). The refrigerant is further compressed and is discharged as the high-temperature and high-pressure gas refrigerant.

Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [3]-[4]) in consideration of the efficiency of the injection compressor1.

The high-temperature and high-pressure gas refrigerant discharged from the injection compressor1passes through the four-way valve3and is split, and then the split refrigerants pass through the second flow switching device B. The refrigerants enter the outdoor heat exchangers9aand9b, exchange heat with the outside air outside a room, condense and liquefy, and transfer heat to outside the room. Changes in the refrigerant in the outdoor heat exchangers9aand9bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [4]→point [5]) in the p-h diagram in consideration of the pressure losses in the outdoor heat exchangers9aand9b.

The liquid refrigerants pass through the first flow switching device A and then join together. The joined refrigerant flows in the main pipe and is cooled in the refrigerant heat exchanger6by the refrigerant flowing in the third bypass pipe41, and its temperature decreases. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [5]→point [6]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger6.

The refrigerant exiting the refrigerant heat exchanger6partially enters the third bypass pipe41, and the remaining thereof enters the indoor units200aand200b. The refrigerant entering the indoor units200aand200bis split, and the refrigerants enter the first flow control valves5aand5b, respectively. The refrigerants are decompressed into a low-pressure two-phase gas-liquid state. Changes in the refrigerant in the first flow control valves5aand5bare made under the state where the enthalpy is constant and are represented by a vertical line (point [6]→point [7]) in the p-h diagram.

The refrigerants decompressed to low pressure enter the indoor heat exchangers4aand4b, respectively. Each of the refrigerants exchanges heat with the air inside a room, evaporates, and cools the inside of the room. Changes in the refrigerant in the indoor heat exchangers4aand4bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [7]→point [1]) in the p-h diagram in consideration of the pressure losses in the indoor heat exchangers4aand4b.

The low-temperature and low-pressure gas refrigerants exiting the indoor heat exchangers4aand4bjoin together. The joined refrigerant exits the indoor units200aand200b, enters the outdoor unit100through the main pipe, passes through the four-way valve3again, and is sucked into the injection compressor1. The cooling operation is performed by circulation of the refrigerant through the main circuit in the above-described way.

The refrigerant entering the third bypass pipe41is decompressed by the fourth flow control valve42and changes into a low-temperature two-phase gas-liquid state. Changes in the refrigerant in the fourth flow control valve42are made under the state where the enthalpy is constant and are represented by a vertical line (point [6]→point [8]) in the p-h diagram.

The refrigerant entering the refrigerant heat exchanger6is heated by the refrigerant flowing in the main pipe and evaporates. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [8]→point [9]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger6.

FIG. 3illustrates a refrigerant flow in a heating only operation in the air-conditioning apparatus according to Embodiment 1 of the present invention.FIG. 8illustrates a relationship between the pressure of the refrigerant and the enthalpy in the heating only operation in the air-conditioning apparatus according to Embodiment 1 of the present invention. The flow in the heating only operation is described below with reference toFIGS. 3 and 8.

In the heating only operation, the four-way valve3is switched to the state indicated by the solid lines inFIG. 3. The first flow switching device A and the second flow switching device B are switched such that the refrigerant entering the outdoor unit100from the indoor units200aand200bis split, the split refrigerants are sent to both the outdoor heat exchangers9aand9band join together, and the joined refrigerant passes through the four-way valve3and is sucked into the injection compressor1.

First, a low-temperature and low-pressure gas refrigerant is compressed by the injection compressor1. Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [1]-[2]) in consideration of the efficiency of the injection compressor1.

Then, the refrigerant undergoing compression and the refrigerant flowing from the third bypass pipe41join together. Changes in the refrigerant in the joining are made under the state where the pressure is substantially constant and are represented by a horizontal line (points [2]-[3], points [10]-[3]). The refrigerant is further compressed and is discharged as the high-temperature and high-pressure gas refrigerant.

Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [3]-[4]) in consideration of the efficiency of the injection compressor1. The high-temperature and high-pressure gas refrigerant discharged from the injection compressor1passes through the four-way valve3and is split. The split refrigerants enter the indoor units200aand200bthrough the main pipe, and each of the refrigerants exchanges heat with the air inside a room, condenses and liquefies, and heats on the inside of the room.

Changes in the refrigerant in the indoor heat exchangers4aand4bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [4]→point [5]) in the p-h diagram in consideration of the pressure losses in the indoor heat exchangers4aand4b.

The liquid refrigerants are decompressed by the first flow control valves5aand5b. Changes in the refrigerant in the first flow control valves5aand5bare made under the state where the enthalpy is constant and are represented by a vertical line (point [5]→point [6]) in the p-h diagram.

The decompressed refrigerants join together. The joined refrigerant flows through the main pipe and partially enters the third bypass pipe41, and the remaining thereof enters the refrigerant heat exchanger6. The refrigerant entering the refrigerant heat exchanger6is cooled by the refrigerant flowing in the third bypass pipe41, and its temperature decreases. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [6]→point [7]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger6.

The refrigerant exiting the refrigerant heat exchanger6enters the second flow control valve7and is decompressed into a low-pressure two-phase gas-liquid state. Changes in the refrigerant in the second flow control valve7are made under the state where the enthalpy is constant and are represented by a vertical line (point [7]→point [8]) in the p-h diagram.

The refrigerant decompressed to low pressure is split, and the split refrigerants enter the outdoor heat exchangers9aand9b, exchange heat with the outside air outside a room, evaporate, and transfer heat to outside the room. Changes in the refrigerant in the outdoor heat exchangers9aand9bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [8]→point [1]) in the p-h diagram in consideration of the pressure losses in the outdoor heat exchangers9aand9b. The low-temperature and low-pressure gas refrigerants exiting the outdoor heat exchangers9aand9bjoin together, and the joined refrigerant passes through the four-way valve3again and is sucked into the injection compressor1. The heating operation is performed by circulation of the refrigerant through the main circuit in the above-described way.

The refrigerant entering the third bypass pipe41is decompressed by the fourth flow control valve42and changes into a low-temperature two-phase gas-liquid state. Changes in the refrigerant in the fourth flow control valve42are made under the state where the enthalpy is constant and are represented by a vertical line (point [5]→point [9]) in the p-h diagram.

The refrigerant entering the refrigerant heat exchanger6is heated by the refrigerant flowing in the main pipe and evaporates. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [9]→point [10]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger6. In that operation, when the temperature of the air outside the room is low, frost occurs in the outdoor heat exchangers9aand9b, continuous operation increases the frost, and the amount of heat exchanged decreases.

Next, the flow in a heating and defrosting simultaneous operation (in a heating operation at which the outdoor heat exchanger9bis targeting for defrosting) is described with reference toFIGS. 4 and 9. In the heating and defrosting simultaneous operation, the four-way valve3is switched to the state indicated by the solid lines inFIG. 4, as in the state in the heating only operation.

The first flow switching device A is switched such that the refrigerant flowing from the indoor units200aand200binto the outdoor unit100is sent to only the outdoor heat exchanger9a, passes through the four-way valve3, and is sucked into the injection compressor1.

It is switched such that the refrigerant discharged from the injection compressor1partially flows through the first bypass pipe21, passes through the first flow switching device A, enters the outdoor heat exchanger9b, flows through the second bypass pipe31, and joins with the refrigerant flowing in the third bypass pipe41.

First, the low-temperature and low-pressure gas refrigerant is compressed by the injection compressor1. Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [1]-[2]) in consideration of the efficiency of the injection compressor1.

Then, the refrigerant undergoing compression and the refrigerant flowing from the third bypass pipe41join together. Changes in the refrigerant in the joining are made under the state where the pressure is substantially constant and are represented by a horizontal line (points [2]-[3], points [11]-[3]).

The refrigerant is further compressed and is discharged as the high-temperature and high-pressure gas refrigerant. Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [3]-[4]) in consideration of the efficiency of the injection compressor1.

The high-temperature and high-pressure refrigerant discharged from the injection compressor1partially enters the first bypass pipe21. The remaining thereof passes through the four-way valve3, flows through the main pipe, enters each of the indoor units200aand200b, exchanges heat with the air inside a room, condenses and liquefies, and heats the inside of the room. Changes in the refrigerant in the indoor heat exchangers4aand4bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [4]→point [5]) in the p-h diagram in consideration of the pressure losses in the indoor heat exchangers4aand4b.

Then, the liquid refrigerants pass through the first flow control valves5aand5band are decompressed. Changes in the refrigerant in the first flow control valves5aand5bare made under the state where the enthalpy is constant and are represented by a vertical line (point [5]→point [6]) in the p-h diagram. The decompressed refrigerants join together, and the joined refrigerant flows through the main pipe and partially enters the third bypass pipe41. The remaining thereof enters the refrigerant heat exchanger6.

The refrigerant entering the refrigerant heat exchanger6is cooled by the refrigerant flowing through the third bypass pipe41, and its temperature decreases. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [6]→point [7]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger6.

The refrigerant exiting the refrigerant heat exchanger6enters the second flow control valve7and is decompressed into a low-pressure two-phase gas-liquid state. Changes in the refrigerant in the second flow control valve7are made under the state where the enthalpy is constant and are represented by a vertical line (point [7]→point [8]) in the p-h diagram.

The refrigerant decompressed to low pressure passes through the first flow switching device A, enters the outdoor heat exchanger9a, exchanges heat with the outside air outside a room, evaporates, and transfers heat to outside the room. Changes in the refrigerant in the outdoor heat exchanger9aare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [8]→point [1]) in the p-h diagram in consideration of the pressure loss in the outdoor heat exchanger9a. The low-temperature and low-pressure gas refrigerant exiting the outdoor heat exchanger9apasses through the four-way valve3again and is sucked into the injection compressor1. The heating operation is performed by circulation of the refrigerant through the main circuit in the above-described way.

The refrigerant entering the third bypass pipe41is decompressed by the fourth flow control valve42and changes into a low-temperature two-phase gas-liquid state. Changes in the refrigerant in the fourth flow control valve42are made under the state where the enthalpy is constant and are represented by a vertical line (point [6]→point [9]) in the p-h diagram.

Then, the refrigerant passing through the fourth flow control valve42joins with the refrigerant flowing from the second bypass pipe31. Changes in the refrigerant in the joining are made under the state where the pressure is substantially constant and are represented by a horizontal line (point [9]-point [10], point [13]-point [10]) in the p-h diagram.

The joined refrigerant enters the refrigerant heat exchanger6, is heated by the refrigerant flowing in the main pipe, and evaporates. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [10]→point [11]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger.

The refrigerant entering the first bypass pipe21passes through the first flow switching device A and condenses while melting frost occurring in the outdoor heat exchanger9b. Changes in the refrigerant in the outdoor heat exchanger9bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [4]→point [12]) in the p-h diagram in consideration of the pressure loss in the outdoor heat exchanger9b.

The condensed refrigerant is decompressed by the third flow control valve32band changes into the two-phase gas-liquid refrigerant. Changes in the refrigerant in the third flow control valve32bare made under the state where the enthalpy is constant and are represented by a vertical line (point [12]→point [13]) in the p-h diagram.

The decompressed refrigerant flows through the second bypass pipe31and joins with the refrigerant flowing in the third bypass pipe41.

In the above-described way, in this operation mode, frost in the outdoor heat exchanger9bcan be melted while the inside of a room is heated. In the heating operation at which the outdoor heat exchanger9ais targeting for defrosting, the first flow switching device A and the second flow switching device B are switched, and an operation of melting frost in the outdoor heat exchanger9aand of transferring heat to outside the room in the outdoor heat exchanger9bis performed.

<Method of Adjusting Discharge Temperature of Refrigerant from Injection Compressor1>

Next, a method of adjusting the discharge temperature of the refrigerant from the injection compressor1is described. When the discharge temperature of the refrigerant from the injection compressor1measured by the temperature sensor2is equal to or higher than an upper limit temperature for securing reliability of the injection compressor1, the opening degree of the fourth flow control valve42is increased. When that temperature is lower than the upper limit, the opening degree of the fourth flow control valve42is reduced.

In the heating operation at a low outside temperature, because the discharge temperature of the refrigerant from the injection compressor1increases, monitoring the discharge temperature of the refrigerant from the injection compressor1prevents abnormal increase in the discharge temperature of the refrigerant exiting the injection compressor1.

As described above, the air-conditioning apparatus1000according to Embodiment 1 is operable in three modes of the cooling only operation, the heating only operation, and the heating and defrosting simultaneous operation and can continuously heat the inside of a room by the heating and defrosting simultaneous operation if frost occurs in the outdoor heat exchanger9band the performance starts decreasing because of a decrease in the volume of air or a decrease in the evaporating temperature.

In the air-conditioning apparatus1000according to Embodiment 1, the refrigerant for defrosting is injected not into the suction side but in the course of a compression process in the injection compressor1. Thus, it is not necessary to lower the pressure of the refrigerant for defrosting to a suction pressure. Accordingly, the injection compressor1needs to raise only the pressure of the refrigerant circulating through the main circuit from low to high, and needs to raise the pressure of the injected intermediate-pressure two-phase gas-liquid refrigerant only from intermediate to high. Consequently, the workload of the injection compressor1is reduced, and the efficiency of the heat pump (heating capacity/workload of the injection compressor1) is improved. That also contributes to energy saving.

In the air-conditioning apparatus1000according to Embodiment 1, the two-phase gas-liquid refrigerant entering the injection compressor1through the injection port is heated by the intermediate-pressure gas refrigerant undergoing compression and changes into the gas state inside the injection compressor1. Thus, the reliability of the heat pump is improved. In Embodiment 1 described above, the difference of enthalpies of the refrigerant used in defrosting (length of the segment from point [4] to point [12] inFIG. 9) can be larger than that in a conventional air-conditioning apparatus (length of the segment from point [6] to point [7] inFIG. 8), and defrosting can be performed with a low flow rate of the refrigerant and thus heating capacity is improved.

In addition, the air-conditioning apparatus1000according to Embodiment 1 includes the temperature sensor2for measuring the discharge temperature of the refrigerant from the injection compressor1and controls the fourth flow control valve42in accordance with the discharge temperature. Accordingly, an increase in the discharge temperature under a low outside air temperature condition can be suppressed, and the reliability of the injection compressor1is enhanced.

Additionally, in the heating operation in the air-conditioning apparatus1000according to Embodiment 1, the outdoor heat exchanger9btargeting for defrosting exchanges heat while the refrigerant flows in a direction parallel to the direction in which the outside air flows, whereas the outdoor heat exchanger9anot targeting for defrosting exchanges heat while the refrigerant flows in a direction opposite to the direction of the outside air flows. The flow of the refrigerant in the heating and defrosting simultaneous operation is described below with reference toFIG. 6.

The outdoor heat exchangers9aand9billustrated inFIG. 6are fin-tube heat exchangers in which a plurality of heat transfer tubes extend through a plurality of fins along a direction perpendicular to the plurality of fins and are configured such that two rows of the heat exchangers are arranged in the air flow direction, and the two rows are horizontally divided into two parts. In the outdoor heat exchanger9a, a low-temperature and low-pressure two-phase gas-liquid refrigerant flows from the downstream row with respect to the air flow direction, evaporates while transferring heat to the air, moves to the upstream row, further evaporates, and flows out of the outdoor heat exchanger9a. In contrast, in the outdoor heat exchanger9b, which is performing defrosting, a high-temperature and high-pressure refrigerant flows from the row upstream in the air flow, condenses while heating and melting frost, moves to the downstream row, further condenses, and flows out of the outdoor heat exchanger9b. In the outdoor heat exchanger9a, which is not targeting for defrosting, the difference between the temperature of the air and that of the refrigerant can be large, operation can be efficient. In the outdoor heat exchanger9b, which is targeting for defrosting, a higher-temperature refrigerant can be supplied to the upstream side in the air flow direction on which the amount of frost is largest, and the frost can be melted efficiently.

Two-way valves each capable of being opened and closed independently of the magnitude of the pressure at each of the inlet and outlet of the valve and capable of stopping a refrigerant in only one direction are used in the air-conditioning apparatus1000according to Embodiment 1. Accordingly, two-way valves each having a simple internal structure capable of stopping the refrigerant in only one direction can be used.

The air-conditioning apparatus1000according to Embodiment 1 includes the first flow switching device A and the second flow switching device B for each of the plurality of outdoor heat exchangers9aand9bsuch that the direction of the refrigerant flowing from each of the outdoor heat exchangers9aand9bto the main pipe coincides with the direction in which the two-way valve can stop the refrigerant. In all of the operation modes, the refrigerant in the first flow switching device A and the second flow switching device B can be stopped without leakage.

The air-conditioning apparatus1000according to Embodiment 1 is described as the configuration in which the second bypass pipe31is provided with the third flow control valves32aand32b. The configuration may be used in which each of the two pipes into which the second bypass pipe31is split is provided with two two-way valves and the single pipe after joining is provided with one flow control valve. With that configuration, the temperature of the refrigerant entering the outdoor heat exchanger9btargeting for defrosting can decrease and a change in the refrigerant inside the outdoor heat exchanger9btargeting for defrosting can be reduced, unevenness of deicing can be reduced, and thus the efficiency of deicing can be enhanced.

The air-conditioning apparatus1000according to Embodiment 1 includes the third bypass pipe41having the first end connected between the outdoor heat exchangers9aand9band the first flow control valve5and the second end connected to the injection port of the injection compressor1, the refrigerant heat exchanger6for exchanging heat between the refrigerant flowing between the first flow control valve5and the outdoor heat exchangers9aand9band the refrigerant flowing in the third bypass pipe41, and the fourth flow control valve42for controlling the flow rate of the refrigerant flowing through the third bypass pipe41. The first end of the second bypass pipe31is connected to the third bypass pipe41ahead of the refrigerant heat exchanger6. Thus the refrigerant exiting the outdoor heat exchanger9btargeting for defrosting and the refrigerant flowing in the main pipe can exchange heat with each other in the refrigerant heat exchanger6, and the efficiency can be enhanced.

The order of defrosting in the heating and defrosting simultaneous operation is not described in the air-conditioning apparatus1000according to Embodiment 1. In the case of the heat exchanger illustrated inFIG. 6, the outdoor heat exchanger9bmay be defrosted after the upper outdoor heat exchanger9ais defrosted. With that configuration, even if water after deicing in the upper outdoor heat exchanger (outdoor heat exchanger9ainFIG. 6) freezes in the lower outdoor heat exchanger (outdoor heat exchanger9binFIG. 6) again, the frost can be fully removed by the defrosting operation, and the reliability of the air-conditioning apparatus can be enhanced.

Embodiment 2 of the present invention is described below with reference toFIGS. 10 to 12. The same reference numerals are used in the same parts.FIG. 10illustrates a refrigerant circuit in an air-conditioning apparatus according to Embodiment 2 of the present invention.FIG. 11illustrates a refrigerant flow in the heating and defrosting simultaneous operation in the air-conditioning apparatus according to Embodiment 2 of the present invention.FIG. 12illustrates a relationship between the pressure of the refrigerant and the enthalpy in the heating and defrosting simultaneous operation of a heat pump according to Embodiment 2 of the present invention. The air-conditioning apparatus1000is described below with reference toFIG. 10.

The air-conditioning apparatus1000includes the outdoor unit100, the indoor units200aand200b, and the main pipe connecting them such that a refrigerant circulates therethrough. The air-conditioning apparatus1000is a multi-type air-conditioning apparatus in which two indoor units are connected to one outdoor unit.

The outdoor unit100includes two-way valves51aand51bconnected to the second bypass pipe31and a fifth flow control valve50(corresponding to a first bypass flow control valve in the present invention) disposed on the first bypass pipe21. The outdoor unit100further includes a second pressure sensor56on the discharge side of the injection compressor1and a first pressure sensor55between the refrigerant heat exchanger6and the first flow control valves5aand5b(between the branch point to the third bypass pipe41and the first flow control valves5aand5b).

Each of the two-way valves22a,22b,51a, and51bis configured as a valve substantially the same as in Embodiment 1 illustrated inFIG. 5or an electromagnetic valve openable and closable by a motor.

In Embodiment 2, each of the two-way valves8a,8b,10a,10b,22a,22b,51a, and51bcan stop a refrigerant in only the direction indicated by the arrow inFIGS. 10 and 11, as in Embodiment 1.

A check valve52is disposed between the portion where the two-way valves51aand51bare disposed and the portion where the second bypass pipe31and the third bypass pipe41are connected. The check valve52is used to prevent a refrigerant from flowing from the portion where the second bypass pipe31and the third bypass pipe41are connected toward the direction of the two-way valves51aand51b. The second pressure sensor56measures the discharge pressure of the refrigerant from the injection compressor1. The first pressure sensor55measures the pressure at a location between the refrigerant heat exchanger6and the first flow control valves5aand5b(between the branch point to the third bypass pipe41and the first flow control valves5aand5b).

The other configuration is substantially the same as in Embodiment 1, and the description thereof is omitted here.

Next, the description is provided with reference toFIG. 11, which illustrates a refrigerant flow in the above-described apparatus, andFIG. 12, which is a p-h diagram (diagram illustrating a relationship between the pressure of the refrigerant and the enthalpy). InFIG. 11, the thick solid lines indicate flows of the refrigerant in operation, and the numbers in brackets, [i] (i=1, 2, . . . ), indicate pipe portions corresponding to points i (states of the refrigerant) in the diagram ofFIG. 12.

FIG. 11illustrates a flow occurring when the air inside a room is heated by each of the indoor heat exchangers4aand4b, a first one (outdoor heat exchanger9ainFIG. 11) of parallel heat exchangers constituting the outdoor heat exchangers causes the refrigerant to evaporate and receives heat from the outside air and a second one (outdoor heat exchanger9binFIG. 11) of the parallel heat exchangers heats frost in the outdoor heat exchanger9bto melt it (hereinafter referred to as heating and defrosting simultaneous operation). During the heating operation, the indoor heat exchangers4aand4bfunction as condensers, and the outdoor heat exchangers9aand9bfunction as evaporators. The same applies to Embodiment below.

The other operation modes, the cooling operation and the heating operation, are substantially the same as in Embodiment 1, and the description thereof is omitted here.

Next, a flow in a heating and defrosting simultaneous operation (in the heating operation at which the outdoor heat exchanger9bis targeting for defrosting) is described with reference toFIGS. 11 and 12. In the heating and defrosting simultaneous operation, the four-way valve3is switched to the state indicated by the solid lines inFIG. 11, as in the state in the heating only operation.

The first flow switching device A is switched such that the refrigerant entering the outdoor unit100from the indoor units200aand200bis sent to only the outdoor heat exchanger9a, passes through the four-way valve3, and is sucked into the injection compressor1.

It is switched such that the refrigerant discharged from the injection compressor1partially flows through the first bypass pipe21, passes through the first flow switching device A, enters the outdoor heat exchanger9b, flows through the second bypass pipe31, and joins with the refrigerant flowing in the third bypass pipe41.

First, a low-temperature and low-pressure gas refrigerant is compressed by the injection compressor1. Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [1]-[2]) in consideration of the efficiency of the injection compressor1.

Then, the refrigerant undergoing compression and the refrigerant flowing from the third bypass pipe41join together. Changes in the refrigerant in the joining are made under the state where the pressure is substantially constant and are represented by a horizontal line (points [2]-[3], points [11]-[3]).

The refrigerant is further compressed and is discharged as the high-temperature and high-pressure gas refrigerant. Changes in the refrigerant in the injection compressor1are represented by an oblique line where the enthalpy slightly increases (points [3]-[4]) in consideration of the efficiency of the injection compressor1.

The high-temperature and high-pressure refrigerant discharged from the injection compressor1partially enters the first bypass pipe21, and the remaining thereof passes through the four-way valve3, flows through the main pipe, enters each of the indoor units200aand200b, exchanges heat with the air inside a room, condenses and liquefies, and heats the inside of the room. Changes in the refrigerant in the indoor heat exchangers4aand4bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [4]→point [5]) in the p-h diagram in consideration of the pressure losses in the indoor heat exchangers4aand4b.

Then, the liquid refrigerants pass through the first flow control valves5aand5band are decompressed. Changes in the refrigerant in the first flow control valves5aand5bare made under the state where the enthalpy is constant and are represented by a vertical line (point [5]→point [6]) in the p-h diagram. The decompressed refrigerants join together, and the joined refrigerant flows through the main pipe and partially enters the third bypass pipe41. The remaining thereof enters the refrigerant heat exchanger6.

The refrigerant entering the refrigerant heat exchanger6is cooled by the refrigerant flowing through the third bypass pipe41, and its temperature decreases. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [6]→point [7]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger6.

The refrigerant exiting the refrigerant heat exchanger6enters the second flow control valve7and is decompressed into a low-pressure two-phase gas-liquid state. Changes in the refrigerant in the second flow control valve7are made under the state where the enthalpy is constant and are represented by a vertical line (point [7]→point [8]) in the p-h diagram.

The refrigerant decompressed to low pressure, passes through the first flow switching device A, enters the outdoor heat exchanger9a, exchanges heat with the outside air outside a room, evaporates, and transfers heat to outside the room. Changes in the refrigerant in the outdoor heat exchanger9aare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [8]→point [1]) in the p-h diagram in consideration of the pressure loss in the outdoor heat exchanger9a. The low-temperature and low-pressure gas refrigerant exiting the outdoor heat exchanger9apasses through the four-way valve3again and is sucked into the injection compressor1. The heating operation is performed by circulation of the refrigerant through the main circuit in the above-described way.

The refrigerant entering the third bypass pipe41is decompressed by the fourth flow control valve42and changes into a low-temperature two-phase gas-liquid state. Changes in the refrigerant in the fourth flow control valve42are made under the state where the enthalpy is constant and are represented by a vertical line (point [6]→point [9]) in the p-h diagram.

Then, the refrigerant passing through the fourth flow control valve42joins with the refrigerant flowing from the second bypass pipe31. Changes in the refrigerant in the joining are made under the state where the pressure is substantially constant and are represented by a horizontal line (point [9]-point [10], point [13]-point [10]) in the p-h diagram.

The joined refrigerant enters the refrigerant heat exchanger6, is heated by the refrigerant flowing in the main pipe, and evaporates. Changes in the refrigerant in the refrigerant heat exchanger6are made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [10]→point [11]) in the p-h diagram in consideration of the pressure loss in the refrigerant heat exchanger.

The refrigerant entering the first bypass pipe21is decompressed by the fifth flow control valve50. Changes in the refrigerant in the fifth flow control valve50are made under the state where the enthalpy is constant and are represented by a vertical line (point [4]→point [12]) in the p-h diagram. The decompressed refrigerant passes through the first flow switching device A and condenses while melting frost occurring in the outdoor heat exchanger9b. Changes in the refrigerant in the outdoor heat exchanger9bare made under the state where the pressure is substantially constant and are represented by a slightly oblique nearly horizontal line (point [12]→point [13]) in the p-h diagram in consideration of the pressure loss in the outdoor heat exchanger9b.

The decompressed refrigerant flows through the second bypass pipe31and joins with the refrigerant flowing in the third bypass pipe41.

In the above-described way, in this operation mode, frost in the outdoor heat exchanger9bcan be melted while the inside of a room is heated. In the heating operation at which the outdoor heat exchanger9ais targeting for defrosting, the first flow switching device A and the second flow switching device B are switched, and an operation of melting frost in the outdoor heat exchanger9aand of transferring heat to outside the room in the outdoor heat exchanger9bis performed.

The method of adjusting the discharge temperature of the refrigerant from the injection compressor1is substantially the same as in Embodiment 1, and the description thereof is omitted here.

As described above, the air-conditioning apparatus1000according to Embodiment 2 can reduce the temperature of the refrigerant entering the outdoor heat exchanger9btargeting for defrosting and changes in the temperature, can reduce unevenness of deicing, and can enhance the efficiency of deicing, in addition to achieving substantially the same advantageous effects as in Embodiment 1.

Additionally, the air-conditioning apparatus1000according to Embodiment 2 includes the second pressure sensor56for measuring the discharge temperature of the refrigerant from the injection compressor1and controls the fifth flow control valve50such that the refrigerant is at a predetermined discharge pressure in the heating and defrosting simultaneous operation, and thus heating capacity of each of the indoor heat exchangers4aand4bcan be maintained. Specifically, when the discharge pressure is lower than the predetermined pressure, the opening degree of the fifth flow control valve50is reduced. When the discharge pressure is higher than the predetermined pressure, the opening degree of the fifth flow control valve50is increased.

In addition, the air-conditioning apparatus1000according to Embodiment 2 includes the first pressure sensor55for measuring the pressure at a location between the refrigerant heat exchanger6and the first flow control valves5aand5b(between the branch point to the third bypass pipe41and the first flow control valves5aand5b) and controls the second flow control valve7in accordance with the measured pressure. Thus, the pressure of the refrigerant entering the fourth flow control valve42and the refrigerant heat exchanger6can be controlled to a predetermined value, the amount of heat exchanged in each of the refrigerant heat exchanger6and the outdoor heat exchangers9aand9bcan be controlled, and operation is stabilized. Specifically, when the pressure is lower than the predetermined pressure, the opening degree of the second flow control valve7is increased. When the pressure is higher than the predetermined pressure, the opening degree of the second flow control valve7is reduced.

REFERENCE SIGNS LIST