Refrigeration apparatus

A refrigeration apparatus uses R32 as refrigerant, and includes a compressor, a condenser, an expansion mechanism, an evaporator, a branch flow channel branching from a main refrigerant channel joining the condenser and the evaporator, a first opening adjustable valve disposed along the branch flow channel, an injection heat exchanger, a first injection channel, a refrigerant storage tank disposed along the main refrigerant channel, and a second injection channel. The injection heat exchanger exchanges heat between refrigerant in the main refrigerant channel and refrigerant passing through the first opening adjustable valve. The first injection channel guides refrigerant that flows in the branch flow channel and that exits from the injection heat exchanger to the compressor or the suction passage. The second injection channel guides a gas component of refrigerant accumulated inside the refrigerant storage tank to the compressor or the suction passage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application Nos. 2012-121213, filed in Japan on May 28, 2012, and 2012-276152, filed in Japan on Dec. 18, 2012, the entire contents of which are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a refrigeration apparatus, and more specifically, a refrigeration apparatus that uses R32 as a refrigerant.

BACKGROUND ART

In the conventional art, among refrigeration apparatuses such as air conditioning apparatuses and like, are apparatuses that use R32 as the refrigerant. When using R32 as the refrigerant, the discharge temperature of the compression mechanism tends to be higher in comparison to the case of using R410A or R22 as the refrigerant. Recognizing this problem, an air conditioning apparatus that lowers the refrigerant discharge temperature while using R32 is described in Japanese Laid-open Patent Application No. 2009-127902. In this air conditioning apparatus, part of the liquid refrigerant exiting from a gas liquid separator disposed in a high-pressure line is caused to bypass to a compression mechanism, that bypassed refrigerant then being converted to a flash gas state in an internal heat exchanger. That refrigerant, bypassed to the compression mechanism and converted into a flash gas is injected, lowering the enthalpy of refrigerant in an intermediate-pressure state in the compressor, causing a decrease in the discharge temperature of refrigerant in the compression mechanism.

SUMMARY

Technical Problem

If the refrigerant from the high-pressure main refrigerant channel is caused to bypass and is depressurized, and then that refrigerant is evaporated in an internal heat exchanger and supplied to a compressor, it is certainly possible to lower the discharge temperature of the compressor.

However, in the case in which the outdoor unit of an air conditioning apparatus is positioned higher in comparison to the indoor unit, the pressure of refrigerant coming out of the gas liquid separator of the outdoor unit during the heating operation may become very low. Further, in the case in which the refrigerant communication tubes joining the outdoor unit and the indoor unit are long, it is conceivable that the pressure of refrigerant coming out of the gas liquid separator will decrease. When the pressure of such refrigerant that is caused to bypass is low, the room for depressurizing the refrigerant that is caused to bypass prior to entry into the internal heat exchanger decreases and the temperature difference between the refrigerant that is caused to bypass and the refrigerant flowing in the main refrigerant channel in the internal heat exchanger becomes small, causing concern that the quantity of flash gas or the dryness may not be maintained. In order to prevent these problems it becomes necessary to increase the size of the internal heat exchanger, which then raises production costs and makes it necessary to increase the size of the outdoor unit.

An object of the present invention is to provide a refrigeration apparatus having a heat exchanger that exchanges heat between refrigerant flowing in the main refrigerant channel and refrigerant diverged from the main refrigerant channel, in which the refrigerant diverged from the main refrigerant channel is supplied to a compressor or a suction pipe, lowering the discharge temperature of the compressor, while minimizing increase in the size of the heat exchanger and maintaining the function of reducing the discharge temperature of the compressor.

Solution to the Problem

A refrigeration apparatus according to a first aspect of the present invention uses R32 as the refrigerant, and is provided with a compressor, a condenser, an expansion mechanism, an evaporator, a branch flow channel, a first opening adjustable valve, a heat exchanger for injection, a first injection channel, a refrigerant storage tank, and a second injection channel. The compressor sucks in low-pressure refrigerant from a suction passage, compresses the refrigerant and discharges high-pressure refrigerant. The condenser condenses high-pressure refrigerant discharged from the compressor. The expansion mechanism expands the high-pressure refrigerant that comes out of the condenser. The evaporator evaporates the refrigerant expanded by the expansion mechanism. The branch flow channel is a channel that branches from the main refrigerant channel joining the condenser and the evaporator. The first opening adjustable valve is disposed in the branch flow channel, and the degree of opening can be adjusted. The heat exchanger for injection exchanges heat between the refrigerant that flows in the main refrigerant channel and refrigerant that passes through the first opening adjustable valve of the branch flow channel. The first injection channel guides refrigerant that flows in the branch flow channel and exits from the heat exchanger for injection, to the compressor or the suction passage. The refrigerant storage tank is disposed along the main refrigerant channel. The second injection channel guides the gas component of refrigerant accumulated inside the refrigerant storage tank to the compressor or the suction passage.

This refrigeration apparatus according to the present invention, furnished with the heat exchanger for injection and the first injection channel, depressurizes refrigerant branched from the main refrigerant channel connecting the condenser and the evaporator at the first opening adjustable valve of the branch flow channel, and heats the refrigerant in the heat exchanger for injection. The depressurized, heated refrigerant, that has become flash gas in a gas-liquid two-phase state, saturated gas or superheated gas, is flowed to the compressor or the suction passage by passing through the first injection channel, enabling the discharge temperature of the compressor to be lowered. On the other hand, as the refrigeration apparatus is further furnished with the refrigerant storage tank and the second injection channel, the gas component (saturated gas) of refrigerant accumulated inside the refrigerant storage tank, is flowed to the compressor or the suction passage via the second injection channel, which also enables the discharge temperature of the compressor to be lowered. Thus, as there are two injection routes, in the refrigeration apparatus according to the present invention, even in the case in which the pressure of the refrigerant diverged from the main refrigerant channel is low, and the dryness and quantity of refrigerant flowing to the compressor is unable to be maintained even after being heated at the heat exchanger for injection, it is possible to lower the discharge temperature of the compressor using the refrigerant from the refrigerant storage tank. Further, as it is possible to use either of the two routes, it becomes unnecessary to increase the size of the heat exchanger for injection in order to maintain the dryness of refrigerant flowing to the compressor, regardless of the refrigerant state, thereby minimizing an increase in the size of the heat exchanger, and enabling the function of reducing the discharge temperature of the compressor to be maintained.

A refrigeration apparatus according to a second aspect of the present invention is the refrigeration apparatus according to the first aspect of the present invention further provided with a control unit. The control unit switches between a first injection control that flows refrigerant to primarily the first injection channel, and a second injection control that flows refrigerant to primarily the second injection channel.

Here, when the first injection control is performed, refrigerant diverged from the main refrigerant channel joining the condenser and the evaporator, is depressurized by the first opening adjustable valve of the branch flow channel, and heated in the heat exchanger for injection. Then, the depressurized, heated refrigerant that is a gas-liquid two-phase flash gas, saturated gas or superheated gas, passes through the first injection channel, flowing to the compressor or the suction passage, serving to lower the discharge temperature of the compressor. On the other hand, when the second injection control is performed, the gas component (saturated gas) of refrigerant accumulated in the refrigerant storage tank passes through the second injection channel and flows to the compressor or the suction passage, serving to lower the discharge temperature of the compressor. In this way, this refrigeration apparatus according to the present invention is configured to enable switching between the first injection control that flows refrigerant to primarily the first injection channel and the second injection control that flows refrigerant to primarily the second injection channel. Accordingly, even in the case in which the pressure of the refrigerant diverged from the main refrigerant channel is low, and the dryness and quantity of refrigerant flowing to the compressor is unable to be maintained even after being heated at the heat exchanger for injection, it is possible to switch to the second injection control and lower the discharge temperature of the compressor. Further, as it is possible to use the second injection control as well as the first injection control, regardless of the state of the refrigerant, it becomes unnecessary to increase the size of the heat exchanger for injection in order to maintain the dryness of refrigerant flowing to the compressor, thereby minimizing an increase in the size of the heat exchanger, while enabling the function of reducing the discharge temperature of the compressor to be maintained.

The first injection control is control for lowering the discharge temperature of the compressor through refrigerant flowing in primarily the first injection channel. The first injection control operates such that almost no refrigerant flows in the second injection channel or the quantity of refrigerant that flows in the second injection channel is less than the quantity of refrigerant that flows in the first injection channel. The second injection control is control for lowering the discharge temperature of the compressor with refrigerant flowing in primarily the second injection channel. The second injection control operates such that almost no refrigerant flows in the first injection channel or the quantity of refrigerant that flows in the first injection channel is less than the quantity of refrigerant that flows in the second injection channel.

A refrigeration apparatus according to a third aspect of the present invention is the refrigeration apparatus according to the second aspect of the present invention, in which the control unit switches between the first injection control and the second injection control based on the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism.

Here, in the case in which the pressure is low in the refrigerant flowing via the first opening adjustable valve and the heat exchanger for injection to the compressor or the suction passage, given that it is not possible to maintain the quantity and dryness of refrigerant exiting from the heat exchanger for injection, the switching between the first injection control and the second injection control is performed based on the pressure of refrigerant in the main refrigerant channel that is diverged by the branch flow channel (basically, the pressure of refrigerant between the condenser and the expansion mechanism). Accordingly, even in the case in which injection using the first injection channel largely cannot be performed, the discharge temperature of the compressor can be lowered.

Note that the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism can be directly detected by for example, installing a pressure gauge. Further, by obtaining the quantity of circulating refrigerant from the compressor frequency, the pressure of low-pressure refrigerant in the suction passage or the pressure of high-pressure refrigerant discharged from the compressor, and calculating the amount of depressurization in the expansion mechanism of the main refrigerant channel, it is possible to calculate the pressure of refrigerant in the main refrigerant channel from the amount of depressurization of the expansion mechanism and the difference between the high and low pressures. For the pressure of high-pressure refrigerant or of low-pressure refrigerant, it is suitable to detect these using a pressure gauge, and it is also suitable to calculate from the refrigerant saturation temperature or the like.

Moreover, the switching between the first injection control and the second injection control performed based on the pressure of refrigerant in the main refrigerant channel diverged by the branch flow channel, includes switching performed based on a detected value or estimated value of the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism, and also includes switching performed based on a detected value related to the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism.

A refrigeration apparatus according to a fourth aspect of the present invention is the refrigeration apparatus according to either the second aspect or the third aspect of the present invention further provided with a second opening adjustable valve. The second opening adjustable valve is disposed along the second injection channel and the degree of opening can be adjusted. The first injection channel and the second injection channel cause the refrigerant to merge with intermediate-pressure refrigerant of the compressor. The control unit, in the first injection control, causes refrigerant from primarily the first injection channel to merge with intermediate-pressure refrigerant of the compressor, and in the second injection control, causes refrigerant from primarily the second injection channel to merge with intermediate-pressure refrigerant of the compressor.

Here, as the refrigerant flowing in each of the injection channels is caused to merge with intermediate-pressure refrigerant of the compressor, it is possible to suppress the rotational speed of the compressor while maintaining capacity, thereby improving the efficiency of the refrigeration apparatus. Further, during the first injection control the first opening adjustable valve is adjusted, and during the second injection control the second opening adjustable valve is adjusted, such that the discharge temperature of the compressor can be lowered through performing the appropriate injection.

A refrigeration apparatus according to a fifth aspect of the present invention is the refrigeration apparatus according to the second aspect of the present invention, in which the control unit switches between the first injection control, the second injection control and a third injection control, the third injection control being a control that flows refrigerant to both the first injection channel and the second injection channel.

Here, in addition to the first injection control that flows refrigerant to primarily the first injection channel and the second injection control that flows refrigerant to primarily the second injection channel, the third injection control is provided. The control unit, through the third injection control, flows refrigerant to the first injection channel and the second injection channel. That is, the third injection control flows refrigerant from the heat exchanger for injection via the first injection channel to the compressor or the suction passage, and also flows refrigerant from the refrigerant storage tank via the second injection channel to the compressor or the suction passage. In this way, as the first, second and third injection controls are provided, the appropriate injection control is selected based on the operating condition and installation conditions of the refrigeration apparatus, leading to improved operating capacity and a reduction in the discharge temperature of the compressor.

A refrigeration apparatus according to a sixth aspect of the present invention is the refrigeration apparatus according to the fifth aspect of the present invention, in which the control part, in the third injection control, changes the ratio between the quantity of refrigerant flowed to the first injection channel and the quantity of refrigerant flowed to the second injection channel, based on the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism.

If the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism decreases, depending on the size of the heat exchanger for injection, the dryness and quantity of refrigerant flowing from the heat exchanger for injection to the first injection channel may not reach the desired levels. Further, if the pressure of refrigerant in the main refrigerant channel decreases, in the case in which there is substantial difference between the height of the position of the condenser and the height of the position of the evaporator, such that there is substantial difference between the elevation of the condenser and the evaporator, it is not preferable to control accumulation (control that further decreases the pressure) of the gas component of the refrigerant in the refrigerant storage tank.

However, in the third injection control of the refrigeration apparatus according to the sixth aspect of the present invention that flows refrigerant from the heat exchanger for injection and the refrigerant storage tank simultaneously to the compressor and the like, the ratio of the quantity of refrigerant subject to injection that flows from the heat exchanger for injection to the first injection channel and the quantity of refrigerant subject to injection that flows from the refrigerant storage tank to the second injection channel, is changed based on the pressure of refrigerant in the main refrigerant channel. Control implemented in this way enables injection to be implemented as appropriate and prevents adverse effects occurring at other places in the refrigeration apparatus due to injection of refrigerant.

A refrigeration apparatus according to a seventh aspect of the present invention is the refrigeration apparatus according to the second aspect of the present invention, in which the control unit switches between the first injection control, the second injection control, and non-injection control. The non-injection control is control such that refrigerant does not flow in the first injection channel or the second injection channel.

Here, as the discharge temperature is low, it is not necessary to decrease the temperature of the compressor through suction injection or intermediate injection, moreover, in the case for example in which the rotational speed of the compressor is low as low capacity is required, the control unit can switch to non-injection control. If the switch to non-injection control is made, increase of capacity through suction injection or intermediate injection and the occurrence of substantially decreased operating efficiency are minimized, enabling operating efficiency to be maintained while fulfilling the requirement of low capacity.

Advantageous Effects of Invention

The refrigeration apparatus according to the first aspect of the present invention uses refrigerant from the refrigerant storage tank, thereby enabling the discharge temperature of the compressor to be reduced, even in the case in which the pressure of refrigerant diverged from the main refrigerant line is low and though heated by the heat exchanger for injection, the dryness and quantity of the refrigerant flowed to the compressor cannot be maintained.

The refrigeration apparatus according to the second aspect of the present invention switches to the second injection control thereby enabling the discharge temperature of the compressor to be reduced, even in the case in which the pressure of refrigerant diverged from the main refrigerant line is low and though heated by the heat exchanger for injection, the dryness and quantity of the refrigerant flowed to the compressor cannot be maintained.

The refrigeration apparatus according to the third aspect of the present invention switches to the second injection control, such that appropriate operation to reduce the discharge temperature of the compressor is performed even in the case in which due to the refrigerant pressure injection using the first injection channel is largely unable to be performed.

The refrigeration apparatus according to the fourth aspect of the present invention merges the refrigerant from the injection channel with intermediate-pressure refrigerant of the compressor, thereby improving the efficiency of the refrigeration apparatus, and enabling the appropriate injection to be performed by adjusting the degree of opening of each opening adjustable valve.

The refrigeration apparatus according to the fifth aspect of the present invention selects the appropriate injection control based on the operating condition and installation conditions of the refrigeration apparatus, leading to improved operating capacity and a reduction in the discharge temperature of the compressor.

The refrigeration apparatus according to the sixth aspect of the present invention enables injection to be performed as appropriate and suppresses adverse effects occurring at other places in the refrigeration apparatus due to injection of refrigerant.

In the refrigeration apparatus according to the seventh aspect of the present invention, increase of capacity through suction injection or intermediate injection and the occurrence of decreased operating efficiency are minimized, enabling operating efficiency to be maintained while fulfilling the requirement of low capacity.

DESCRIPTION OF EMBODIMENTS

First Embodiment

(1)FIG. 1shows the refrigerant piping system of an air conditioning apparatus10, being a refrigeration apparatus according to the first embodiment of the present invention. The air conditioning apparatus10is a distributed refrigerant piping system air conditioning apparatus, that cools and heats each room inside a building by vapor compression type refrigerant cycle operation. The air conditioning apparatus10is provided with an outdoor unit11as a heat source unit, a plurality of indoor units12as usage-side units, and a liquid refrigerant communication pipe13and gas refrigerant communication pipe14as refrigerant communication pipes that connect the outdoor unit11to the indoor units12. That is, the refrigerant circuit of the air conditioning apparatus10shown inFIG. 1, is configured such that the outdoor unit11, the indoor units12, the liquid refrigerant communication pipe13and the gas refrigerant communication pipe14are connected. The liquid refrigerant communication pipe13and the gas refrigerant communication pipe14are, in the case of a long piping configuration, 150 m long or longer. The total length of the piping of the liquid refrigerant communication pipe13and the gas refrigerant communication pipe14in order to connect the plurality of indoor units12with the single outdoor unit11can be up to 1000 m. Further, although it is envisaged that there may be a difference in the elevations in which the outdoor unit11and the indoor units12are installed, in the case that the outdoor unit11is installed in a low place and the indoor units12are installed in a higher place, the difference in elevation between the highest positioned indoor unit12and the outdoor unit11can be up to 40 m. On the other hand, in the case in which the outdoor unit11is installed in a high place such as on a roof or the like, and the indoor units12are installed in a low place, the difference in elevation between the lowest positioned indoor unit12and the outdoor unit11can be up to 90 m.

Refrigerant is sealed in the refrigerant circuit shown inFIG. 1, and as described subsequently, is subjected in that circuit to the operations of a refrigerant cycle in which the refrigerant is compressed, cooled and condensed, depressurized, then heated and evaporated, after which the refrigerant is compressed again. R32 is used as the refrigerant. R32 is a low GWP refrigerant with a low warming coefficient, a type of HFC refrigerant. Further, an ether-based synthetic oil having some degree of compatibility with R32 is used as the refrigerator oil.

(2) Detailed Configuration of the Air Conditioning Apparatus

(2-1) Indoor Units

The indoor units12are installed on the ceiling or a side wall in each room and are connected to the outdoor unit11via the refrigerant communication pipes13and14. The indoor unit12has primarily, an indoor expansion valve42that is a pressure reducer and an indoor heat exchanger50as a usage-side heat exchanger.

The indoor expansion valve42is an expansion mechanism that depressurizes the refrigerant, being an electric valve having an adjustable opening. One end of the indoor expansion valve42is connected to the liquid refrigerant communication pipe13and the other end is connected to the indoor heat exchanger50.

The indoor heat exchanger50is a heat exchanger that functions as an evaporator or a condenser of refrigerant. One end of the indoor heat exchanger50is connected to the indoor expansion valve42and the other end is connected to the gas refrigerant communication pipe14.

The indoor unit12has an indoor fan55for sucking in indoor air and resupplying the air indoors, facilitating exchange of heat between the indoor air and the refrigerant flowing in the indoor heat exchanger50.

Further, the indoor unit12has an indoor controller90bfor controlling the operation of each part that configures the indoor unit12and each kind of sensor. The indoor controller90bhas a microcomputer or memory or the like installed for controlling the indoor unit12, exchanges control signals or the like with a remote control unit (not shown in the drawing) to facilitate individual operation of the indoor unit12, and exchanges control signals or the like via a transmission line90cwith an outdoor controller90aof the outdoor unit11, described subsequently. The various sensors include an indoor liquid pipe temperature sensor97and an indoor gas pipe temperature sensor98that are installed in the indoor unit12. The indoor liquid pipe temperature sensor97is attached to a refrigerant pipe that connects the indoor expansion valve42and the indoor heat exchanger50. The indoor gas pipe temperature sensor98is attached to a refrigerant pipe extending from the indoor heat exchanger50to the gas refrigerant communication pipe14.

(2-2) Outdoor Unit

The outdoor unit11is installed either outside or in the basement of the building having each room in which the indoor unit12is deployed, and is connected to the indoor units12via the refrigerant communication pipes13and14. Primarily, the outdoor unit11has a compressor20, a four-way switching valve15, an outdoor heat exchanger30, an outdoor expansion valve41, a bridge circuit70, a high-pressure receiver80, a first electric injection valve63, a heat exchanger for injection64, a second electric injection valve84, a liquid-side shut off valve17and a gas-side shut off valve18.

The compressor20is a hermetically sealed compressor driven by a compressor motor. In this embodiment there is one compressor20, however this embodiment is not limited to this number, and it is suitable to have two or more compressors20connected in parallel, depending on the number of connected indoor unit12. The compressor20sucks the gas refrigerant from a suction passage27via a vessel28appurtenant to the compressor20. A discharge pressure sensor91for detecting the pressure of discharged refrigerant, and a discharge temperature sensor93for detecting the temperature of discharged refrigerant are mounted to a discharge-side refrigerant pipe29of the compressor20. Further, an intake temperature sensor94for detecting the temperature of the refrigerant sucked into the compressor20is mounted to the suction passage27. Note that the compressor20has an intermediate injection port23described subsequently.

The four-way switching valve15is a mechanism for switching the direction of refrigerant flow. The four-way switching valve15connects the discharge-side refrigerant pipe29of the compressor20and one end of the outdoor heat exchanger30, and connects the suction passage27of the compressor20(including the vessel28) to the gas-side shut off valve18(refer the solid line of the four-way switching valve15inFIG. 1), such that during the cooling operation, the outdoor heat exchanger30is caused to function as a condenser of refrigerant compressed by the compressor20and the indoor heat exchanger50is caused to function as an evaporator of refrigerant cooled in the outdoor heat exchanger30. Further, the four-way switching valve15connects the discharge-side refrigerant pipe29of the compressor20and the gas-side shut off valve18, and connects the suction passage27to one end of the outdoor heat exchanger30(refer the dashed line of the four-way switching valve15inFIG. 1), such that during the heating operation, the indoor heat exchanger50is caused to function as a condenser of refrigerant compressed by the compressor20and the outdoor heat exchanger30is caused to function as an evaporator of refrigerant cooled in the indoor heat exchanger50. In this embodiment, the four-way switching valve15is a four-way valve connected to the suction passage27, the discharge-side refrigerant pipe29of the compressor20, the outdoor heat exchanger30and the gas-side shut off valve18.

The outdoor heat exchanger30is a heat exchanger that functions as an evaporator or a condenser of the refrigerant. One end of the outdoor heat exchanger30is connected to the four-way switching valve15and the other end is connected to the outdoor expansion valve41. An outdoor liquid pipe temperature sensor95is mounted to the refrigerant pipe connecting the outdoor heat exchanger30and the outdoor expansion valve41, in order to detect the temperature of the refrigerant flowing in that pipe.

The outdoor unit11has an outdoor fan35that sucks in outdoor air into the unit and expels the air again outdoors. The outdoor fan35facilitates exchange of heat between outdoor air and the refrigerant flowing in the outdoor heat exchanger30, and is driven by an outdoor fan motor. Note that the heat source of the outdoor heat exchanger30is not limited to outside air and it is suitable to use a different heating medium such as water or the like.

The outdoor expansion valve41is an expansion mechanism for depressurizing the refrigerant, and is an electric valve having an adjustable opening. One end of the outdoor expansion valve41is connected to the outdoor heat exchanger30and the other end is connected to the bridge circuit70.

The bridge circuit70has four check valves,71,72,73and74. The inlet check valve71allows the refrigerant from the outdoor heat exchanger30to flow only toward the high-pressure receiver80. The outlet check valve72allows the refrigerant from the high-pressure receiver80to flow only toward the indoor heat exchanger50. The inlet check valve73allows the refrigerant from the indoor heat exchanger50to flow only toward the high-pressure receiver80. The outlet check valve74allows the refrigerant from the high-pressure receiver80to flow only toward the indoor heat exchanger30via the outdoor expansion valve41. That is, the inlet check valves71and73fulfill the function of flowing refrigerant from one of the outdoor heat exchanger30and the indoor heat exchanger50to the high-pressure receiver80, while the outlet check valves72and74fulfill the function of flowing refrigerant from the high-pressure receiver80to the other of the outdoor heat exchanger30and the indoor heat exchanger50.

The high-pressure receiver80is a container disposed between the outdoor expansion valve41and the liquid-side shut off valve17that functions as a refrigerant storage tank. During the cooling operation and during the heating operation, the high-pressure receiver80, into which high-pressure refrigerant has flowed, is not subject to the occurrence of the adverse phenomena in which excess refrigerant, including refrigerator oil, separates into two layers, with the refrigerator oil accumulating in the upper portion, because the surplus refrigerant that accumulates in the high-pressure receiver80is kept at a relatively high temperature.

Further, normally liquid refrigerant resides in the lower part of the internal space of the high-pressure receiver80and gas refrigerant resides in the upper part. A second injection channel82extends from the upper part of that internal space toward the compressor20. The second injection channel82fulfills the function of guiding the gas component of refrigerant accumulated inside the high-pressure receiver80to the compressor20. An adjustable opening second electric injection valve84is provided in the second injection channel82.

A heat exchanger for injection64is provided between the outlet of the high-pressure receiver80and the outlet check valves72and74of the bridge circuit70. A branch flow pipe62branches from a part of the main refrigerant channel11aconnecting the outlet of the high-pressure receiver80and the heat exchanger for injection64. The main refrigerant channel11ais the main channel for liquid refrigerant, and connects the outdoor heat exchanger30and the indoor heat exchanger50. The high-pressure receiver80is disposed between the outdoor expansion valve41and the liquid-side shut off valve17along the main refrigerant channel11a.

A first electric injection valve63having an adjustable opening, is disposed in the branch flow pipe62. The branch flow pipe62is connected to a second flow path64bof the heat exchanger for injection64. That is, when the first electric injection valve63is open, the refrigerant diverged from the main refrigerant channel11ato the branch flow pipe62is depressurized at the first electric injection valve63and flows to the second channel64bof the heat exchanger for injection64.

The refrigerant depressurized at the first electric injection valve63and flowed to the second channel64bof the heat exchanger for injection64, is subject to heat exchange with refrigerant flowing in a first channel64aof the heat exchanger for injection64. The first channel64aof the heat exchanger for injection64configures a part of the main refrigerant channel11a. The refrigerant that has flowed through the branch flow pipe62and the second channel64bafter heat exchange at the heat exchanger for injection64, is delivered toward the compressor20by means of a first injection channel65. A first injection temperature sensor96for detecting the temperature of the refrigerant that has been subject to heat exchange after passing through the second channel64bof the heat exchanger for injection64, is mounted to the first injection channel65.

The heat exchanger for injection64is an internal heat exchanger employing a double tube structure that performs heat exchange between the refrigerant flowing in the main refrigerant channel11athat is the main path, and the refrigerant diverged from the main refrigerant channel11afor injection, as described above. One end of the first channel64aof the heat exchanger for injection64is connected to the outlet of the high-pressure receiver80, while the other end connects to the outlet check valves72and74of the bridge circuit70.

The liquid-side shut off valve17is a valve connected to the liquid refrigerant communication pipe13that functions to exchange refrigerant between the outdoor unit11and the indoor unit12. The gas-side shut off valve18is a valve connected to the gas refrigerant communication pipe14that functions to exchange refrigerant between the outdoor unit11and the indoor unit12, the gas-side shut off valve18being connected to the four-way switching valve15. Here, the liquid-side shut off valve17and the gas-side shut off valve18are three-way valves provided with service ports.

The vessel28is arranged in the suction passage27between the four-way switching valve15and the compressor20, and fulfills the function of preventing liquid refrigerant from being sucked into the compressor20when refrigerant that includes excessive liquid component flows in. Here, while the vessel28is provided, it is also suitable to additionally deploy in the suction passage27, an accumulator for preventing liquid flow back to the compressor20.

As described above, the intermediate injection port23is provided in the compressor20. The intermediate injection port23is a port that introduces refrigerant in order to flow refrigerant from outside into the intermediate-pressure refrigerant in the course of compression in the compressor20. The above described first injection channel65and second injection channel82are connected to an intermediate injection pipe23athat is connected to the intermediate injection port23. When the first electric injection valve63is open, intermediate injection is performed that flows refrigerant to the intermediate injection port23from the first injection channel65, and when the second electric injection valve84is open, intermediate injection is performed that flows refrigerant to the intermediate injection port23from the second injection channel82. Note that it is possible to replace the compressor20with two compressors connected in series and connect the intermediate injection pipe23ato the refrigerant piping connecting the discharge port of a low stage compressor and the suction port of a high-stage compressor.

As shown inFIG. 3, soundproof material20ais wound around the compressor20. A notch20bthat prevents contact with the intermediate injection pipe23ais formed in the soundproof material20a. The soundproof material20ais divided into two parts in consideration of the difficulties that would be incurred in attaching and removing the soundproof material20aif the whole of the soundproof material20aaround the notch20bwere a single integrated body, when another member such as a casing member of the outdoor unit11or the like is provided around the intermediate injection pipe23a. Specifically, the soundproof material20ais divided into a main body section20cand a small piece section20d. The small piece section20dattaches to the main body section20cvia a plurality of hook and loop fasteners20e. When the soundproof material20ais removed from the compressor20for a reason such as performing maintenance or the like, firstly the small piece section20dis detached from the main body section20c, then the main body section20cis slid to the left side inFIG. 3, removing the soundproof material20afrom the intermediate injection pipe23aand the compressor20.

Further, the outdoor unit11has various sensors, and an outdoor controller90a. The outdoor controller90ais provided with memory or a microcomputer or the like, for performing control of the outdoor unit11, and exchanges control signals and the like via a transmission line8awith the indoor controller90bof the indoor unit12. The various sensors include the discharge pressure sensor91, the discharge temperature sensor93, the intake temperature sensor94, the outdoor liquid pipe temperature sensor95and the first injection temperature sensor96described above, a receiver outlet pressure sensor92, and an outdoor air temperature sensor99for detecting the outside air temperature. The receiver outlet pressure sensor92, mounted to a part of the main refrigerant channel11abetween the outlet of the high-pressure receiver80and the heat exchanger for injection64, is a sensor for detecting the pressure of refrigerant exiting the high-pressure receiver80.

(2-3) Refrigerant Communication Pipes

The refrigerant communication pipes13and14are refrigerant pipes that are installed on site when the outdoor unit11and the indoor units12are installed on location.

The controller90, control device for performing the various operation controls of the air conditioning apparatus10, comprises the outdoor controller90aand the indoor controller90bjoined via a transmission line90cas shown inFIG. 1. As shown inFIG. 2, the controller90receives detection signals from the above described various sensors91-99, and implements control of the various devices including the compressor20, the outdoor fan35, the outdoor expansion valve41, the indoor fan55, the first electric injection valve63, the second electric injection valve84and the like, based on these detection signals.

The controller90is provided with function parts including a cooling operation control part for when the cooling operation is performed, that uses the indoor heat exchanger50as an evaporator, a heating operation control part for when the heating operation is performed, that uses the indoor heat exchanger50as a condenser, and an injection control part that performs injection control for the cooling operation or the heating operation.

(3) Operation of the Air Conditioning Apparatus

The operation of the air conditioning apparatus10according to this embodiment will now be described. The controls for each operation explained subsequently are performed from the controller90that functions as a device for operation control.

(3-1) Basic Operations for the Cooling Operation

During the cooling operation the four-way switching valve15is in the condition indicated by the solid line inFIG. 1, that is, liquid refrigerant discharged from the compressor20flows to the outdoor heat exchanger30, moreover the suction passage27is connected to the gas-side shut off valve18. With the outdoor expansion valve41fully open, the indoor expansion valve42comes to be adjusted. Note that the shut off valves17and18are in the open condition.

With the refrigerant circuit in this condition, the high-pressure gas refrigerant discharged from the compressor20is delivered via the four-way switching valve15to the outdoor heat exchanger30functioning as a condenser of refrigerant, where the refrigerant is cooled by being subjected to heat exchange with outdoor air supplied from the outdoor fan35. The high-pressure refrigerant cooled in the outdoor heat exchanger30and liquefied, becomes refrigerant in a supercooled state at the heat exchanger for injection64, and is then delivered via the liquid refrigerant communication pipe13to each of the indoor units12. The refrigerant delivered to each of the indoor units12is depressurized by the respective indoor expansion valves42, becoming low-pressure refrigerant in a gas-liquid two-phase state, and is then subjected to heat exchange with indoor air in the indoor heat exchanger50, functioning as an evaporator of refrigerant, becoming evaporated, and becoming low-pressure gas refrigerant. The low-pressure gas refrigerant heated in the indoor heat exchanger50is delivered via the gas refrigerant communication pipe14to the outdoor unit11and sucked into the compressor20again via the four-way switching valve15. This is how the air conditioning apparatus cools indoors.

In the case in which some of the indoor units12from among the indoor units12are not operating, the indoor expansion valve42of the indoor unit12that is not operating has the opening closed (for example completely closed). In this case, almost no refrigerant passes through the indoor unit12that has stopped operating and the cooling operation is only carried out in the indoor unit12that is operating.

(3-2) Basic Operations During the Heating Operation

During the heating operation the four-way switching valve15is in the condition indicated by the dashed line inFIG. 1, that is, the discharge-side refrigerant pipe29of the compressor20is connected to the gas-side shut off valve18, moreover, the suction passage27is connected to the outdoor heat exchanger30. The outdoor expansion valve41and the indoor expansion valve42come to be adjusted. Note that the shut off valves17and18are in the open condition.

With the refrigerant circuit in this condition, the high-pressure gas refrigerant discharged from the compressor20is delivered via the four-way switching valve15and the gas refrigerant communication pipe14to each of the indoor units12. The high-pressure gas refrigerant delivered to each of the indoor units12is cooled by being subjected to heat exchange with indoor air in the respective indoor heat exchangers50, each functioning as a condenser of refrigerant. Thereafter the refrigerant passes through the indoor expansion valve42and is delivered via the liquid refrigerant communication pipe13to the outdoor unit11. As the refrigerant is subjected to heat exchange with indoor air and cooled, the indoor air is heated. The high-pressure refrigerant delivered to the outdoor unit11is separated into liquid and gas at the high-pressure receiver80, the high-pressure liquid refrigerant comes into a subcooled state at the heat exchanger for injection64, being depressurized by the outdoor expansion valve41to become low-pressure refrigerant in a gas-liquid two-phase state, which is then flowed into the outdoor heat exchanger30, functioning as an evaporator of refrigerant. The low-pressure refrigerant in a gas-liquid two-phase state flowed into the outdoor heat exchanger30is subjected to heat exchange with outdoor air supplied from the outdoor fan35and heated, becoming evaporated, low-pressure refrigerant. The low-pressure gas refrigerant exiting from the outdoor heat exchanger30is sucked into the compressor20again via the four-way switching valve15. This is how the air conditioning apparatus warms indoors.

(3-3) Injection Control for Each Operation

During the cooling operation and during the heating operation, the injection control part comprising one of the function parts of the controller90, selectively performs either the first injection control that flows refrigerant to primarily the first injection channel65, or the second injection control that flows refrigerant to primarily the second injection channel82. These injection controls are performed in order to reduce the discharge temperature as there is a tendency for the discharge temperature of the compressor20using R32 as refrigerant to be high, the refrigerant being delivered to the intermediate injection port23of the compressor20using the first injection channel65or the second injection channel82, reducing the discharge temperature of the compressor20. The intermediate-pressure refrigerant delivered to the intermediate injection port23is of lower temperature than intermediate-pressure refrigerant in the course of compression in the compressor20, thereby reducing the discharge temperature of the compressor20.

The controller90normally performs the first injection control. The first injection control flows refrigerant to primarily the first injection channel65and is therefore a control that performs intermediate injection. During the first injection control the first electric injection valve63functions as an expansion valve, the opening normally being adjusted based on the detected temperature Tsh from the first injection temperature sensor96. At this time, the opening of the first electric injection valve63is adjusted such that the refrigerant flowing in the first injection channel65becomes superheated gas, that is, such that the refrigerant becomes refrigerant gas superheated as required. In this way, the discharge temperature of the compressor20is reduced and the operating efficiency of the air conditioning apparatus10is improved.

The controller90, in the first injection control monitors the discharge temperature Tdi of the compressor20detected by the discharge temperature sensor93, and if the discharge temperature Tdi exceeds a first upper limit value, stops adjusting the degree of the opening of the first electric injection valve63based on the detected temperature Tsh of the first injection temperature sensor96and transitions to adjustment of the degree of opening of the first electric injection valve63based on the detected temperature Tdi of the discharge temperature sensor93. At this time the opening of the first electric injection valve63is adjusted such that the refrigerant flowing in the first injection channel65becomes humid gas (flash gas). If the detected temperature Tdi of the discharge temperature sensor93is below the first upper limit value, the controller90returns to adjusting the degree of opening of the first electric injection valve63based on the detected temperature Tsh of the first injection temperature sensor96again. On the other hand, if the detected temperature Tdi of the discharge temperature sensor93exceeds a second upper limit value that is higher than the first upper limit value, droop control of the compressor20commences, reducing the rotational speed of the compressor20, moreover if the detected temperature Tdi exceeds a third upper limit value that is still higher than the second upper limit value, an instruction is issued to stop the compressor20.

Basically, the first injection control lowers the discharge temperature of the compressor20and improves the operating efficiency of the air conditioning apparatus10as described above, however, the controller90, through the receiver outlet pressure sensor92, constantly monitors the pressure Ph2 (outdoor liquid pipe pressure Ph2) of the refrigerant in the vicinity of the connection point of the main refrigerant channel11awith the branch flow pipe62. When the outdoor liquid pipe pressure Ph2 of the main refrigerant channel11ais lower than a threshold value, the controller90switches from the first injection control to the second injection control. This is because if the outdoor liquid pipe pressure Ph2 becomes low, it becomes necessary to considerably reduce the opening degree of the first electric injection valve63in order that the refrigerant flowing in the first injection channel65becomes superheated gas, and it is not possible to maintain the quantity of injected refrigerant (the quantity of refrigerant flowing into the intermediate injection port23). In the second injection control, performed when the outdoor liquid pipe pressure Ph2 is below the threshold value, the first electric injection valve63is closed and the second electric injection valve84is opened instead, the gas component of the refrigerant accumulated inside the high-pressure receiver80passes through the second injection channel82, being supplied from the intermediate injection port23to the compressor20. Because the outdoor liquid pipe pressure Ph2 is low, it often occurs that refrigerant returning to the outdoor unit11from the indoor unit12is flashed, with the gas component of the refrigerant residing in the high-pressure receiver80.

In this second injection control it may be possible for the first electric injection valve63to not be closed, and to continue adjustment of the opening of the first electric injection valve63based on the detected temperature Tsh of the first injection temperature sensor96. However, as the outdoor liquid pipe pressure Ph2 is below the threshold value, in the second injection control the quantity of refrigerant flowing in the second injection channel82becomes larger than the quantity of refrigerant flowing in the first injection channel65. Further, in the second injection control, the opening of the second electric injection valve84is adjusted based on the detected temperature Tdi of the discharge temperature sensor93.

Note that even when the air conditioning apparatus10is started up, in the case in which a small number of the indoor units12are operated, as it is envisaged that the discharge temperature of the compressor20will rise, intermediate injection is performed at times when predetermined conditions are met. Specifically, the determination on whether or not to implement intermediate injection is dependent on the outside air temperature conditions or conditions of the capacity for thermo-on (the total capacity of the indoor units12that flow refrigerant with the indoor expansion valve42open). In this case in which intermediate injection is implemented at startup, the control operates such that the opening of the first electric injection valve63is gradually increased in order that the compressor20does not cause liquid compression.

(4) Characteristics of the Air Conditioning Apparatus

The air conditioning apparatus10according to this embodiment of the present invention, when performing the first injection control, primarily depressurizes at the first electric injection valve63of the branch flow pipe62, the refrigerant diverged from the main refrigerant channel11a, and heats the refrigerant in the heat exchanger for injection64. The depressurized, heated refrigerant that has become flash gas in a gas-liquid two-phase state, saturated gas or superheated gas, flows through the first injection channel65to the compressor20, the discharge temperature of the compressor20being reduced. On the other hand, when the second injection control is performed, primarily, the gas component (saturated gas) of the refrigerant accumulated inside the high-pressure receiver80is flowed through the second injection channel82to the compressor20, operating to lower the discharge temperature of the compressor20. In this way, the air conditioning apparatus10is configured so as to be capable of switching between the first injection control that flows refrigerant primarily in the first injection channel65, and the second injection control that flows refrigerant primarily in the second injection channel82.

Accordingly, even in the case in which the pressure of the liquid refrigerant in the outdoor unit11that has been diverged from the main refrigerant channel11ais low, and though the refrigerant is heated in the heat exchanger for injection64it is not possible to maintain the quantity of the refrigerant flowing from the first injection channel65to the compressor20, it is possible to switch to the second injection control and lower the discharge temperature of the compressor20. Further, as it is possible to perform the second injection control in addition to the first injection control, it becomes unnecessary to substantially increase the size of the heat exchanger for injection64so that the dryness of the refrigerant flowing to the compressor20is maintained, regardless of the refrigerant condition, thereby minimizing any increase in the size of the heat exchanger for injection64and enabling the function of reducing the discharge temperature of the compressor20to be maintained.

In the air conditioning apparatus10according to this embodiment, as the quantity of refrigerant required for the cooling operation is sealed in the refrigerant circuit, during the heating operation, while also depending on the condition of load, the high-pressure refrigerant that returns to the outdoor unit11flashes easily. However, in the case in which the pressure of the refrigerant about to be flowed to the compressor20via the first electric injection valve63and the heat exchanger for injection64is low (the pressure of refrigerant prior to depressurization at the first electric injection valve63), it is conceivable that it would not be possible to maintain the dryness and quantity of refrigerant exiting the heat exchanger for injection64.

In light of this, in the air conditioning apparatus10, the switching between the first injection control and the second injection control is performed based on the pressure of the refrigerant of the main refrigerant channel11adiverged by the branch flow pipe62. Specifically, the pressure Ph2 (outdoor liquid pipe pressure Ph2) of the refrigerant in the vicinity of the connection point of the main refrigerant channel11aand the branch flow pipe62, is constantly monitored by the receiver outlet pressure sensor92, and when the outdoor liquid pipe pressure Ph2 of the main refrigerant channel11ais below the threshold value, the controller90switches from the first injection control to the second injection control. The receiver outlet pressure sensor92is disposed in the part of the main refrigerant channel11abetween the indoor expansion valve42in the role of an expansion mechanism and the outdoor heat exchanger30in the role of a condenser in the cooling operation. Further, the receiver outlet pressure sensor92is disposed in the part of the main refrigerant channel11abetween the outdoor expansion valve41in the role of an expansion mechanism and the indoor heat exchanger50in the role of a condenser in the heating operation. That is, in the air conditioning apparatus10, switching between the first injection control and the second injection control is performed based on the pressure of refrigerant in the main refrigerant channel11abetween the condenser and the expansion mechanism.

In this way, even in the case in which intermediate injection using the first injection channel65is largely not able to be performed, the gas component of the refrigerant accumulated in the high-pressure receiver80comes to be supplied after passing through the second injection channel82, to the intermediate injection port23of the compressor20, thereby enabling the discharge temperature of the compressor20to be lowered. This air conditioning apparatus10envisages switching from the first injection control to the second injection control particularly in the heating operation.

Note that the controller90, basically through the first injection control, reduces the discharge temperature of the compressor20and improves the operating efficiency of the air conditioning apparatus10. This is because by adjusting the opening of the first electric injection valve63, the refrigerant that flows in the first injection channel65and is subject to intermediate injection, can be made into superheated gas and can also be made into humid gas (flash gas). The controller90, in the first injection control, stops adjusting the opening degree of the first electric injection valve63based on the detected temperature Tsh of the first injection temperature sensor96if the discharge temperature Tdi exceeds the first upper limit value, and transitions to adjusting the opening degree of the first electric injection valve63based on the detected temperature Tdi of the discharge temperature sensor93, such that humid gas that has high cooling effect flows in the first injection channel65and is subject to intermediate injection. Further, the second injection control, in the case in which the pressure of high-pressure refrigerant returning to the outdoor unit11becomes low, could be said to be the preferable control as it enables gas to be simply ensured at the high-pressure receiver80, on the other hand because only saturated gas can be subject to intermediate injection, the cooling effect is low. Moreover, in the case of intentionally dropping the pressure of high-pressure refrigerant that is returned to the outdoor unit11for the purpose of the second injection control, when the indoor expansion valve42cannot shut perfectly, a large amount of the refrigerant will flow at different pressures in an indoor unit12in the thermo-off condition or an indoor unit12that is stopped in the heating operation, leading to wasteful energy consumption due to superfluous heating. Accordingly, the air conditioning apparatus10according to this embodiment, primarily through the first injection control, reduces the discharge temperature of the compressor20and improves the operating efficiency of the air conditioning apparatus10.

The air conditioning apparatus10according to this embodiment of the present invention operates such that refrigerant flowing in each of the first injection channel65and the second injection channel82is caused to merge with intermediate-pressure refrigerant inside the compressor20, thereby suppressing the rotational speed of the compressor20while maintaining capacity, providing improved operating efficiency.

(5-1) Modification A

In the air conditioning apparatus10according to the above described embodiment, the pressure Ph2 (outdoor liquid pipe pressure Ph2) of the refrigerant is continually monitored by the receiver outlet pressure sensor92in the vicinity of the connection point of the main refrigerant channel11aand the branch flow pipe62, and switching between the first injection control and the second injection control is performed based on that outdoor liquid pipe pressure Ph2. It is also possible however, to not have the receiver outlet pressure sensor92installed and to estimate the outdoor liquid pipe pressure. For example, it is possible to obtain the quantity of circulating refrigerant from the operating frequency of the compressor20, the pressure of low-pressure refrigerant in the suction passage27or the pressure of high-pressure refrigerant discharged from the compressor20(detected value from the discharge pressure sensor91), calculate the amount of depressurization in the indoor expansion valve42or the outdoor expansion valve41, then calculate the refrigerant pressure in the vicinity of the heat exchanger for injection64of the main refrigerant channel11afrom that amount of depressurization and the difference between the high and low pressures. It is also possible to install a pressure gauge to detect the pressure of low-pressure refrigerant in the suction passage27, or to calculate from the refrigerant saturation temperature or the like.

(5-2) Modification B

In the above described embodiment, switching between the first injection control and the second injection control is performed based on the pressure of the refrigerant (outdoor liquid pipe pressure Ph2) in the vicinity of the connection point of the main refrigerant channel11aand the branch flow pipe62, however it is also possible for the switching to be performed based on a detected value related to the outdoor liquid pipe pressure Ph2, rather than being based on an estimated value or detected value of the outdoor liquid pipe pressure Ph2 itself. For example, in the case in which it is determined from the temperature (value detected by the first injection temperature sensor96) and the pressure of refrigerant after depressurized at the first electric injection valve63and the refrigerant has been subject to heat exchange at the heat exchanger for injection64, that the dryness of refrigerant or the quantity of refrigerant flow at the intermediate injection from the first injection channel65is outside the desired range, it is possible to recognize that the outdoor liquid pipe pressure Ph2 is decreased and to change from the first injection control to the second injection control.

(5-3) Modification C

In the air conditioning apparatus10according to the above described embodiment, intermediate injection is performed in which refrigerant flowing in each of the injection channels65and82is flowed into the intermediate injection port23of the compressor20, however as shown inFIG. 4, it is also possible to reduce the discharge temperature of the compressor20by flowing the refrigerant flowing in each of the injection channels65and82into the suction passage27.

An air conditioning apparatus110shown inFIG. 4replaces the outdoor unit11of the air conditioning apparatus10in the above described embodiment with an outdoor unit111. The outdoor unit111has a compressor120instead of the compressor20of the outdoor unit11, and changes the connecting ends of the first injection channel65and the second injection channel82to the suction passage27.

The compressor120of the outdoor unit111sucks in refrigerant gas from the suction passage27via the vessel28appurtenant to the compressor and discharges compressed, high-pressure refrigerant to the refrigerant pipe29, such that an intermediate injection port is not provided. Further, in the outdoor unit111, the end of the second injection channel82extending toward the compressor120from the high-pressure receiver80and the end of the first injection channel65extending towards the compressor120from the heat exchanger for injection64, connect to a merge pipe27a. As shown inFIG. 4, the end of the merge pipe27aconnects to the suction passage27. Thus the refrigerant that has flowed through each of the injection channels65and82merges with low-pressure gas refrigerant flowing in the suction passage27and comes to be sucked into the compressor120. In this case also, it is possible to reduce the discharge temperature of the compressor120using injection control. Further, the switch between the first injection control and the second injection control can be performed in the same way as in the above described embodiment, moreover, the same effects as are achieved in the above described embodiment are realized.

Second Embodiment

(1) Configuration of the Air Conditioning Apparatus

In the air conditioning apparatus according to the second embodiment of the present invention, the outdoor unit11of the air conditioning apparatus10in the above described first embodiment using R32 as the refrigerant, is replaced by an outdoor unit211shown inFIG. 5. In this air conditioning apparatus according to the second embodiment, the outdoor unit211is disposed in a position lower than the indoor unit12, and there is a substantial difference between the positional height of the outdoor unit211and the positional height of the highest part of the indoor unit12, such that there is substantial difference in their respective elevations. The outdoor unit211will now be described, some of those elements which are substantially similar to the corresponding elements of the outdoor unit11in the first embodiment described above will be given the same reference numerals in the figures and their description is omitted.

The outdoor unit211has primarily, the compressor20, the four way switching valve15, the outdoor heat exchanger30, the outdoor expansion valve41, the bridge circuit70, a high-pressure receiver280, a first electric injection valve263, a heat exchanger for injection264, a second electric injection valve284, an intermediate injection switching valve266, a suction injection switching valve268, the liquid-side shut off valve17and the gas-side shut off valve18.

The compressor20, the vessel28appurtenant to the compressor, the suction passage27, the discharge-side refrigerant pipe29of the compressor20, the discharge temperature sensor93, the intermediate injection port23, the four-way switching valve15, the liquid-side shut off valve17, the gas-side shut off valve18, the outdoor heat exchanger30, the outdoor expansion valve41, the outdoor fan35and the bridge circuit70are the same as their corresponding members in the first embodiment, accordingly their descriptions are omitted.

The high-pressure receiver280is a vessel that functions as a refrigerant storage tank, and is disposed between the outdoor expansion valve41and the liquid-side shut off valve17. The high-pressure receiver280, into which high-pressure refrigerant flows during the cooling operation and during the heating operation, does not have the problem in which the excess refrigerant including refrigerant oil separates into two layers, with the refrigerant oil collecting in the upper portion, as the temperature of excess refrigerant accumulated therein is maintained relatively high. A receiver outlet pressure sensor292is provided to the receiver outlet pipe that extends from the lower portion of the high-pressure receiver280to the heat exchanger for injection264. The receiver outlet pipe is part of the main refrigerant channel211adescribed subsequently. The receiver outlet pressure sensor292is a sensor that detects a pressure value (high-pressure value) for high-pressure liquid refrigerant.

Liquid refrigerant normally resides in the lower part of the internal space of the high-pressure receiver280, and gas refrigerant normally resides in the upper part of that space, while a bypass channel282extends from that upper part of the internal space toward the compressor20. The bypass channel282is a pipe that plays the role of guiding the gas component of refrigerant accumulated inside the high-pressure receiver280to the compressor20. A second bypass electric injection valve284having an adjustable opening, is provided in the bypass channel282. When this second bypass electric injection valve284opens, gas refrigerant flows via a common injection tube202to an intermediate injection channel265or a suction injection channel267described subsequently.

A heat exchanger for injection264is provided between the outlet check valves72and74of the bridge circuit70and the outlet of the high-pressure receiver280. Further, a branch flow pipe262branches from a part of the main refrigerant channel211athat connects the outlet of the high-pressure receiver280and the heat exchanger for injection264. The main refrigerant channel211ais the main channel for liquid refrigerant, and connects the outdoor heat exchanger30and the indoor heat exchanger50.

The first electric injection valve263, having an adjustable opening, is disposed in the branch flow pipe262. The branch flow pipe262is attached to a second flow path264bof the heat exchanger for injection264. That is, when the first electric injection valve263is open, refrigerant diverged from the main refrigerant channel211ato the branch flow pipe262is depressurized at the first electric injection valve263and flows to the second flow path264bof the heat exchanger for injection264.

The refrigerant depressurized at the first electric injection valve263and flowed to the second flow path264bof the heat exchanger for injection264is subject to heat exchange with refrigerant flowing in a first flow path264aof the heat exchanger for injection264. The refrigerant that flows through the branch flow pipe262after heat exchange at the heat exchanger for injection264, flows via the shared injection tube202and into the intermediate injection channel265or the suction injection channel267described subsequently. An injection temperature sensor296for detecting the temperature of refrigerant after heat exchange at the heat exchanger for injection264, is mounted to the down flow side of the heat exchanger for injection264of the branch flow pipe262.

The heat exchanger for injection264is an internal heat exchanger employing a double tube structure. One end of the first flow path264aconnects to the outlet of the high-pressure receiver280, and the other end of the first flow path264aconnects to the outlet check valves72and74of the bridge circuit70.

The common injection tube202is a pipe connecting to an end of the bypass channel282extending from the high-pressure receiver280and an end of the branch flow pipe262extending from the main refrigerant channel211avia the heat exchanger for injection264, and connecting to the intermediate injection switching valve266and the suction injection switching valve268. If at least one from among the first electric injection valve263and the second bypass electric injection valve284is open, and either the intermediate injection switching valve266or the suction injection switching valve268opens, refrigerant flows in the common injection tube202, and intermediate injection or suction injection is implemented.

The intermediate injection channel265extends from the intermediate injection switching valve266connected to the common injection tube202, to the compressor20. Specifically, one end of the intermediate injection channel265is connected to the intermediate injection switching valve266, and the other end of the intermediate injection channel265is connected to the intermediate injection port23of the compressor20.

The suction injection channel267extends from the suction injection switching valve268connected to the common injection tube202to the suction passage27. Specifically, one end of the suction injection channel267is connected to the suction injection switching valve268, and the other end of the suction injection channel267is connected to the part of the suction passage27connecting the vessel28appurtenant to the compressor and the compressor20.

The intermediate injection switching valve266and the suction injection switching valve268are solenoid valves that switch between an open condition and a closed condition.

(2) Operation of the Air Conditioning Apparatus

The operation of the air conditioning apparatus according to the second embodiment of the present invention will now be described. The controls for each operation explained subsequently are performed by the control unit of the outdoor unit211that functions as a means for operation control.

(2-1) Basic Operations for the Cooling Operation

During the cooling operation the four-way switching valve15is in the condition indicated by the solid line inFIG. 5, that is, gas refrigerant discharged from the compressor20flows to the outdoor heat exchanger30, moreover the suction passage27is connected to the gas-side shut off valve18. With the outdoor expansion valve41in the fully open condition, the degree of opening of the indoor expansion valve42comes to be adjusted. Note that the shut off valves17and18are in the open condition.

With the refrigerant circuit in this condition, the high-pressure gas refrigerant discharged from the compressor20is delivered via the four-way switching valve15to the outdoor heat exchanger30functioning as a condenser of refrigerant, where the refrigerant is cooled by being subjected to heat exchange with outdoor air supplied from the outdoor fan35. The liquefied high-pressure refrigerant cooled in the outdoor heat exchanger30, becomes refrigerant in a subcooled state at the heat exchanger for injection264, and is then delivered to each of the indoor units12. The operation of each of the indoor units12is the same as in the first embodiment described above. Low-pressure gas refrigerant returning to the outdoor unit11from each of the indoor units12is sucked into the condenser20again, via the four-way switching valve15. Basically, this is how the air conditioning apparatus cools indoors.

(2-2) Basic Operations for the Heating Operation

During the heating operation the four-way switching valve15is in the condition shown by the dashed line inFIG. 5, that is the discharge-side refrigerant pipe29of the compressor20is connected to the gas-side shut off valve18, moreover the suction passage27is connected to the outdoor heat exchanger30. The degrees of opening of the outdoor expansion valve41and the indoor expansion valve42come to be adjusted. Note that the shut off valves17and18are in the open condition.

With the refrigerant circuit in this condition, high-pressure gas refrigerant discharged from the compressor20passes via the four-way switching valve15and the gas refrigerant communication pipe14and is delivered to each of the indoor units12. The operation of each of the indoor units12is the same as for the first embodiment described above. The high-pressure refrigerant returning to the outdoor unit11again, passes via the high-pressure receiver280and becomes refrigerant in a subcooled state at the heat exchanger for injection264, flowing to the outdoor expansion valve41. The refrigerant depressurized at the outdoor expansion valve41and now low-pressure refrigerant in a gas-liquid two-phase state, flows into the outdoor heat exchanger30functioning as an evaporator. The low-pressure, gas-liquid two-phase state refrigerant that flows into the outdoor heat exchanger30is heated by being subject to heat exchange with outdoor air supplied from the outdoor fan35, and is evaporated, becoming low-pressure refrigerant. The low-pressure gas refrigerant coming out of the outdoor heat exchanger30passes via the four-way switching valve15and is sucked into the compressor20again. Basically, this is how the air conditioning apparatus heats indoors.

(2-3) Injection Control for Each Operation

During the cooling operation and during the heating operation, the control unit performs intermediate injection or suction injection, the object being to improve operating capacity or decrease the discharge temperature of the compressor20. Intermediate injection means that the refrigerant that has flowed into the common injection tube202from the heat exchanger for injection264and/or the high-pressure receiver280, flows through the intermediate injection channel265and is injected into the intermediate injection port23of the compressor20. Suction injection means that the refrigerant that has flowed into the common injection tube202from the heat exchanger for injection264and/or the high-pressure receiver280, is injected into the suction passage27by way of the suction injection channel267and caused to be sucked into the compressor20. Both intermediate injection and suction injection have the effect of decreasing the discharge temperature of the compressor20. Intermediate injection has the further effect of improving operating capacity.

The control unit performs injection control based on the rotational speed (or frequency) of the inverter controlled compressor20, the discharge temperature Tdi of refrigerant detected from the discharge temperature sensor93with respect to refrigerant discharged from the compressor20, and the temperature of injected refrigerant as detected by the injection temperature sensor296to the downstream side of the heat exchanger for injection264. Specifically, the control unit implements intermediate injection control that causes intermediate injection, or implements suction injection control that causes suction injection. Further, when the conditions are such that the control unit should not perform either intermediate injection or suction injection, neither form of injection is performed and operations are carried out in the non-injection condition. In other words, the control unit may selectively perform intermediate injection control, suction injection control, or non-injection control, in which neither form of injection is implemented.

The flow of injection control from the control unit will now be described with reference toFIG. 6AthroughFIG. 6D.

Firstly, at step S21, the control unit determines whether the rotational speed of the compressor20is above or below a predetermined threshold. The predetermined threshold is set for example, at a significantly low rotational speed, a value below which a lower rotational speed could not be set, or, a value at which, were the rotational speed to be lowered even further, there would be a decrease in the efficiency of the compressor motor.

(2-3-1) Intermediate Injection Control

If the control unit determines at step S21that the rotational speed of the compressor20is greater than or equal to the threshold, the control unit transitions to step S22to determine whether the air conditioning apparatus is performing the cooling operation or the heating operation. In the case of the heating operation, intermediate injection is performed, that flows gas refrigerant taken from primarily the high-pressure receiver280, to the intermediate injection channel265.

(2-3-1-1) Intermediate Injection Control During Heating

If the determination at step S22is that the air conditioning apparatus is in the heating operation, the control unit transitions to step S23and determines whether or not the discharge temperature Tdi of refrigerant discharged from the compressor20as detected by the discharge temperature sensor93, is higher than the first upper limit value. The first upper limit value can be set at for example 95° C. If the discharge temperature is not higher than the first upper limit value, the control unit transitions to step S24and puts the intermediate injection switching valve266into the open condition and the suction injection switching valve268into the closed condition. If those valves are already in those respective conditions, the valves are maintained as they are. Further, at step S24the respective degrees of opening of the first electric injection valve263and the second bypass electric injection valve284are adjusted. As the discharge temperature Tdi is in the normal range, the opening of the first electric injection valve263is adjusted, in accordance with basic heating operation control, such that liquid refrigerant out from the high-pressure receiver280and flowing in the main refrigerant channel211areaches a predetermined degree of subcooling. Moreover, the opening of the second bypass electric injection valve284is adjusted such that the gas refrigerant in the high-pressure receiver280, flows to the intermediate injection channel265. On the other hand, if, at step S23, the control unit determines that the discharge temperature Tdi is higher than the first upper limit value, step S25is transitioned to. Here, as it is necessary to reduce the discharge temperature Tdi, the respective openings of the first electric injection valve263and the second bypass electric injection valve284are adjusted based on that discharge temperature Tdi. Specifically, at step S25, moisture control is performed that moistens gas refrigerant to be subject to intermediate injection such that the discharge temperature Tdi can be swiftly brought below the first upper limit value. That is, in order to raise the cooling effect of intermediate injection, the opening of the first electric injection valve263and the like is adjusted such that gas refrigerant for intermediate injection becomes gas-liquid, two-phase flash gas.

(2-3-1-2) Intermediate Injection Control During Cooling

If the determination at step S22is that the air conditioning apparatus is in the cooling operation, the control unit transitions to step S26and determines whether or not the discharge temperature Tdi is higher than the first upper limit value. If the discharge temperature Tdi is higher than the first upper limit value, the control unit transitions to step S27, and in order to perform moisture control that moistens gas refrigerant to be subject to intermediate injection, refrigerant flows from primarily the heat exchanger for injection264to the intermediate injection channel265. Specifically, at step S27, the intermediate injection switching valve266is put into the open condition and the suction injection switching valve268is put into the closed condition, further, the degree of opening of the first electric injection valve263is controlled based on the discharge temperature Tdi. Moreover, at step S27, the second bypass electric injection valve284is opened as required. At this step S27, moist gas refrigerant in a gas-liquid two-phase state from the heat exchanger for injection264is subject to intermediate injection to the compressor20, and the elevated discharge temperature Tdi can be expected to decrease rapidly.

At step S26, if the discharge temperature Tdi is lower than the first upper limit value the control unit determines there is no necessity to lower the discharge temperature Tdi, and intermediate injection is performed using both refrigerant from the high-pressure receiver280and refrigerant from the heat exchanger for injection264. Specifically, the system transitions via step S28or step S29to step S30, the intermediate injection switching valve266is put into the open condition, the suction injection switching valve268is put into the closed condition, moreover the degree of opening of the first electric injection valve263and the degree of opening of the second bypass electric injection valve284are adjusted. At step S28the control unit determines whether or not a high-pressure value of liquid refrigerant detected by the receiver outlet pressure sensor292at the outlet of the high-pressure receiver280is below a threshold value. This threshold value is an initially set value, based on for example the elevational difference (difference in the height of their respective places of installation) between the outdoor unit211and the indoor unit12of the air conditioning apparatus, and is set such that if the high-pressure value is lower than this threshold value, prior to passing through the indoor expansion valve42of the indoor unit12, the refrigerant would become refrigerant in a flash gas state and the sound of passing refrigerant would increase substantially. If it is determined at step S28that the high-pressure value is below the threshold value, as it is necessary to increase the high-pressure value, the outdoor expansion valve41in a state of being slightly constricted, is opened more, relieving the degree of depressurization by the outdoor expansion valve41. Thus, the gas component of refrigerant in the high-pressure receiver280is reduced, the quantity of gas refrigerant from the high-pressure receiver280comprising the total quantity of refrigerant for injection decreases, and the ratio of injection from the high-pressure receiver280becomes smaller. On the other hand, if at step S28the high-pressure value exceeds the threshold value, the system transitions to step S30maintaining that injection ratio. At step S30, in the same manner as above, the intermediate injection switching valve266is open, and both refrigerant flowing from the high-pressure receiver280and refrigerant flowing from the heat exchanger for injection264flow from the intermediate injection channel265to the intermediate injection port23of the compressor20. Moreover at step S30the degree of opening of the first electric injection valve263is adjusted based on the temperature Tsh of refrigerant used for injection, to the down flow side of the heat exchanger for injection264, further, based on the injection ratio, the opening of the second bypass electric injection valve284is adjusted in conjunction with the degree of opening of the outdoor expansion valve41.

(2-3-2) Control to Maintain Low Capacity

From step S22up to step S30above, relates to control when it is determined at step S21that the rotational speed of the compressor20is greater than or equal to the threshold value, however as there is room to drop the rotational speed of the compressor20further lowering capacity, basically improved operating capacity is achieved through injection. Accordingly, intermediate injection is selected and not suction injection.

However, if at step S21it is determined that the rotational speed of the compressor20is less than the threshold value, this means that the compressor20has already dropped to low capacity, and as raising the operating capacity right up would be contrary to the needs of users, control is implemented to maintain the capacity of the compressor20as it is, in that low capacity condition.

(2-3-2-1) Suction Injection Control

If at step S21it is determined that the rotational speed of the compressor20is below the threshold value, the control unit transitions to step S31and the determination is made whether or not the discharge temperature Tdi is higher than the first upper limit value. If the discharge temperature Tdi is higher than the first upper limit value, as it is needed to lower the discharge temperature Tdi, step S33or step S34is transitioned to, and suction injection is implemented.

(2-3-2-1-1) Suction Injection Control During the Heating Operation

If it is determined at step S31that the discharge temperature Tdi is higher than the first upper limit value, moreover at step S32it is determined that the heating operation is being performed, suction injection is performed in which primarily refrigerant from the high-pressure receiver280flows from the suction injection channel267to the suction passage27. Specifically, at step S33, the intermediate injection switching valve266is put into the closed condition and the suction injection switching valve268is put into the open condition. Then, based on the discharge temperature Tdi, the degree of opening of the second bypass electric injection valve284is adjusted such that gas refrigerant accumulated in the high-pressure receiver280in the heating operation flows mostly to the suction injection channel267, further, the degree of opening of the first electric injection valve263is adjusted such that refrigerant flowing from the heat exchanger for injection264to the suction injection channel267becomes flash gas.

(2-3-2-1-2) Suction Injection Control During the Cooling Operation

If it is determined at step S31that the discharge temperature Tdi is higher than the first upper limit value, moreover at step S32it is determined that the cooling operation is being performed, suction injection is performed in which primarily refrigerant from the heat exchanger for injection264flows to the suction injection channel267. Specifically, at step S34, the intermediate injection switching valve266is put into the closed condition and the suction injection switching valve268is put into the open condition. Then, based on the discharge temperature Tdi, the degree of opening of the first electric injection valve263is adjusted such that refrigerant flowing from the heat exchanger for injection264to the suction injection channel267becomes flash gas. Further at step S34, the second bypass electric injection valve284is opened as necessary.

If at step S31the discharge temperature Tdi is lower than the first upper limit value, it is determined that it is not necessary to reduce the discharge temperature Tdi, and the control unit selects the non-injection condition. That is, intermediate injection and suction injection in order to lower the discharge temperature Tdi and intermediate injection in order to improve operation capacity are not required, and as it is desirable to stop those forms of injection, the non-injection condition is implemented. At step S35, the control unit puts the intermediate injection switching valve266and the suction injection switching valve268into the closed condition, and adjusts the degree of opening of the first electric injection valve263and the degree of opening of the second bypass electric injection valve284to the minimum. When the minimum degree of opening is zero, the first electric injection valve263and the second electric injection valve284are in the completely closed condition.

Thus, in the air conditioning apparatus according to this second embodiment of the present invention, it is not necessary to lower the discharge temperature of the compressor20by intermediate injection or suction injection as the discharge temperature Tdi is low, moreover, in the case in which the rotational speed of the compressor20is decreased as low capacity is required, the non-injection control is selected and implemented. Thus, increase of capacity through intermediate injection or suction injection and the occurrence of decreased operating efficiency are minimized, and in this air conditioning apparatus according to the second embodiment, it is possible to maintain operating efficiency while satisfying the requirement of low capacity.