The present invention relates to the control of an air conditioner's operation such that the air conditioner's coefficient of performance is optimized.

In a conventional refrigeration apparatus, which comprises a refrigerant circuit that comprises and connects a compressor, a condenser, an expansion valve, and an evaporator, control is performed to improve the coefficient of performance (COP).

Accordingly, in an air conditioner described in Patent Document 1 below, for example, controlling each component in the refrigerant circuit such that a degree of supercooling remains constant at a target value improves the COP.

• Patent Document 1
  Japanese Unexamined Patent Application Publication No. 2001-263831

However, because the target degree of supercooling differs both between a cooling operation and a heating operation and in accordance with the output during these operations, the air conditioner control recited in the abovementioned Patent Document 1 cannot optimize the COP under various conditions.

The present invention was conceived considering the points discussed above, and it is an object of the present invention to provide an air conditioner that can optimize the COP under any of various conditions.

An air conditioner according to a first aspect of the invention comprises a refrigerant circuit, a fluid feeding mechanism, a condensing temperature ascertaining means, a fluid temperature ascertaining means, and a control unit. The refrigerant circuit comprises and connects a compressor, a condenser, an expansion mechanism, and an evaporator such that a refrigerant circulates therein. The fluid feeding mechanism feeds a fluid toward the condenser. The condensing temperature ascertaining means senses a physical quantity in order to derive a condensing temperature of the refrigerant. The fluid temperature ascertaining means senses a physical quantity in order to derive the temperature of the fluid, which exchanges heat with the refrigerant inside the condenser. The control unit controls at least one member selected from the group consisting of the compressor, the expansion mechanism, and the fluid feeding mechanism using as a target value a value calculated by dividing a degree of supercooling of the refrigerant in the vicinity of the condenser outlet by the difference between the condensing temperature ascertained by a detection value of the condensing temperature ascertaining means and a fluid temperature ascertained by a detection value of the fluid temperature sensing means.

Furthermore, herein, the means of sensing the physical quantity includes, for example, not only sensing the temperature directly with a temperature sensor, but also converting the pressure sensed by a pressure sensor and the like to a temperature.

Here, it is possible to improve the COP using a simple method of control even if the usage conditions of the air conditioner fluctuate.

An air conditioner according to a second aspect of the invention is the air conditioner according to the first aspect of the invention that comprises a first fluid temperature ascertaining means and a second fluid temperature ascertaining means. The first fluid temperature ascertaining means senses a physical quantity in order to derive the temperature of the fluid prior to exchanging heat with the refrigerant inside the condenser. The second fluid temperature ascertaining means senses a physical quantity in order to derive the temperature of the fluid after exchanging heat with the refrigerant inside the condenser. Furthermore, the control unit sets the condensing temperature to the temperature ascertained by calculating the average of the detection value of the first fluid temperature ascertaining means and the detection value of the second fluid temperature ascertaining means.

Here, the COP can be improved even more because a condensing temperature suited to the calculation of the COP is obtained.

An air conditioner according a third aspect of the invention is the air conditioner according to the first or second aspects of the invention, wherein the target value is greater than or equal to 0.15 and less than 0.75.

Here, the COP can be even more reliably improved even if ambient environmental conditions fluctuate during operation.

An air conditioner according a fourth aspect of the invention is an air conditioner according to the first or second aspects of the invention, wherein the target value is greater than or equal to 0.4 and less than 0.6.

Here, the COP can be even more reliably improved even if ambient environmental conditions fluctuate during operation.

An air conditioner according to a fifth aspect of the invention is the air conditioner according to any of the first through third aspects of the invention, wherein the fluid temperature ascertaining means senses an outside air temperature in the state wherein the refrigerant circuit is undergoing a cooling operation cycle.

Here, the outdoor heat exchanger functions as a condenser of the refrigerant during the cooling operation; however, by making the fluid temperature ascertaining means sense the outdoor temperature, the temperature of the air that passes through the outdoor heat exchanger, which functions as the condenser, can be sensed.

An air conditioner according to a sixth aspect of the invention is the air conditioner according to any of the first through fifth aspects of the invention, wherein the fluid temperature ascertaining means senses an indoor temperature in the state wherein the refrigerant circuit is undergoing a heating operation cycle.

Here, the indoor heat exchanger functions as a condenser of the refrigerant during the heating operation; however, by making the fluid temperature ascertaining means sense the indoor temperature, the temperature of the air that passes through the indoor heat exchanger, which functions as the condenser, can be sensed.

In an air conditioner according to the first aspect of the invention, the COP can be improved using a simple method of control even if usage conditions of the air conditioner fluctuate.

In an air conditioner according to the second aspect of the invention, the COP can be improved even more because a condensing temperature suited to the calculation of the COP is obtained.

In an air conditioner according to the third aspect of the invention, the COP can be more reliably improved even if ambient environmental conditions fluctuate during operation.

In an air conditioner according to the fourth aspect of the invention, the COP can be more reliably improved even if ambient environmental conditions fluctuate during operation.

In an air conditioner according to the fifth aspect of the invention, the temperature of the air that passes through an outdoor heat exchanger, which functions as a condenser, can be sensed.

In an air conditioner according to the sixth aspect of the invention, the temperature of the air that passes through an indoor heat exchanger, which functions as a condenser, can be sensed.

• FIG. 1 is a schematic view of an air conditioner according to one embodiment of the present invention.
• FIG. 2 is a control block diagram of the air conditioner.
• FIG. 3 is a control flow chart showing a flow when an optimal COP control operation is performed.
• FIG. 4 is a graph showing a coefficient of performance versus a value that is calculated by dividing a degree of supercooling by the difference between a condensing temperature and an air temperature.
• FIG. 5 is a graph showing a relationship between the condensing temperature and the degree of supercooling that satisfies a prescribed relationship.
• FIG. 6 is a schematic drawing of the air conditioner according to a modified example (C).
• FIG. 7 is a control block diagram of the air conditioner according to the modified example (C).
• FIG. 8 is a graph showing for an air conditioner according to a modified example (G), an APF ratio versus the value that is calculated by dividing the degree of supercooling by the difference between the condensing temperature and the air temperature.

FIG. 9 is a conventional graph showing the coefficient of performance versus the degree of supercooling.

1

Air conditioner

8

Control unit

10

Refrigerant circuit

21

Compressor

23

Outdoor heat exchanger (condenser)

28

Outdoor fan (fluid feeding mechanism)

33

Heat exchanging temperature sensor (condensing temperature ascertaining means)

36

Outdoor temperature sensor (fluid)

361

Pre-passage outdoor temperature sensor (first fluid temperature ascertaining means)

362

Post-passage outdoor temperature sensor (second fluid temperature ascertaining means)

41, 51

Indoor expansion valves (expansion mechanisms)

42, 52

Indoor heat exchangers (evaporators)

The following text explains the embodiments of an air conditioner according to the present invention, referencing the drawings.

FIG. 1 is a schematic drawing of an air conditioner 1 according to one embodiment of the present invention.

The air conditioner 1 is used to cool and heat an indoor space of, for example, a building by performing a vapor compression type refrigeration cycle operation. The air conditioner 1 principally comprises: a single outdoor unit 2, which serves as a heat source unit; a plurality of indoor units 4, 5 (in the present embodiment, two), which are connected in parallel with the outdoor unit 2 and serve as utilization units; and a liquid refrigerant connection piping 6 and a gas refrigerant connection piping 7, which connect the outdoor unit 2 and the indoor units 4, 5 and serve as refrigerant connection pipings. Namely, a vapor compression type refrigerant circuit 10 of the air conditioner 1 of the present embodiment is configured by the connection of the outdoor unit 2, the indoor units 4, 5, the liquid refrigerant connection piping 6, and the gas refrigerant connection piping 7.

The indoor units 4, 5 are, for example, embedded in or suspended from the indoor ceiling of a building or attached to an indoor wall surface. The indoor units 4, 5 are connected to the outdoor unit 2 via the liquid refrigerant connection piping 6 and the gas refrigerant connection piping 7 and constitute part of the refrigerant circuit 10.

The following text explains the configuration of the indoor units 4, 5. Furthermore, because the indoor unit 4 and the indoor unit 5 are configured similarly, only the configuration of the indoor unit 4 will be explained herein; in addition, the constituent parts of the indoor unit 5 are assigned reference numerals in the 50s instead of the 40s, which are used for the constituent components of the indoor unit 4, and the explanation of each constituent part of the indoor unit 5 is omitted.

The indoor unit 4 principally comprises an indoor side refrigerant circuit 10a (in the indoor unit 5, an indoor side refrigerant circuit 10b), which constitutes part of the refrigerant circuit 10. The indoor side refrigerant circuit 10a principally comprises an indoor expansion valve 41, which serves as an expansion mechanism, and an indoor heat exchanger 42, which serves as a utilization side heat exchanger.

In the present embodiment, the indoor expansion valve 41 is a motor operated expansion valve that is connected to a liquid side of the indoor heat exchanger 42 and serves to, for example, regulate the flow volume of the refrigerant that flows inside the indoor side refrigerant circuit 10a; furthermore, the opening and closing of the indoor expansion valve 41 is controlled in accordance with a pulse signal. During the optimal COP control operation discussed below, a control unit 8 controls the indoor expansion valves 41, 51 by, for example, adjusting or fixing their degrees of opening, so as to optimize the COP of the refrigeration cycle.

In the present embodiment, the indoor heat exchanger 42 is a cross fin type fin and tube heat exchanger that comprises a heat transfer pipe and numerous fins and functions during the cooling operation as an evaporator of the refrigerant, thereby cooling the indoor air, and during the heating operation as a condenser of the refrigerant, thereby heating the indoor air.

In the present embodiment, the indoor unit 4 comprises an indoor fan 43, which serves as a ventilation fan that sucks the indoor air into the unit, exchanges heat between that air and the refrigerant via the indoor heat exchanger 42, and then supplies that air to the indoor space as supplied air. The indoor fan 43 is capable of varying the volume of the air supplied to the indoor heat exchanger 42 and, in the present embodiment, is a centrifugal fan, a multiblade fan, or the like that is driven by a motor 43a, which has a DC fan motor.

In addition, the indoor unit 4 is provided with various sensors. A liquid side temperature sensor 44, which detects the temperature of the refrigerant (i.e., the condensing temperature during the heating operation or the refrigerant temperature that corresponds to the evaporating temperature during the cooling operation), is provided to the liquid side of the indoor heat exchanger 42. A gas side temperature sensor 45, which detects the temperature of the refrigerant, is provided to a gas side of the indoor heat exchanger 42. An indoor temperature sensor 46, which detects the temperature of the indoor air (i.e., the indoor temperature) that flows into the unit, is provided to the indoor air inlet side of the indoor unit 4. In the present embodiment, the liquid side temperature sensor 44, the gas side temperature sensor 45, and the indoor temperature sensor 46 each has a thermistor. In addition, the indoor unit 4 comprises an indoor side control unit 47, which controls the operation of all parts that constitute the indoor unit 4. Furthermore, the indoor side control unit 47 comprises a microcomputer, memory, and the like, which are provided so that the indoor side control unit 47 can control the indoor unit 4; furthermore, the indoor side control unit 47 can exchange both control signals with a remote control (not shown), which is for the purpose of separately operating the indoor unit 4, and control signals and the like with the outdoor unit 2 via a transmission line 8a.

The outdoor unit 2 is installed on the outside of a building, is connected to the indoor units 4, 5 via the liquid refrigerant connection piping 6 and the gas refrigerant connection piping 7, and constitutes the refrigerant circuit 10 between the indoor units 4, 5.

The following text explains the configuration of the outdoor unit 2. The outdoor unit 2 principally comprises an outdoor side coolant circuit 10c, which constitutes part of the refrigerant circuit 10. The outdoor side coolant circuit 10c principally comprises: a compressor 21; a four-way switching valve 22; an outdoor heat exchanger 23, which serves as a heat source side heat exchanger; an outdoor expansion valve 38, which serves as an expansion mechanism; an accumulator 24; a supercooler 25, which serves as a temperature regulating mechanism; a liquid side shutoff valve 26; and a gas side shutoff valve 27.

The compressor 21 is capable of varying its operating capacity and, in the present embodiment, is a positive-displacement compressor that is driven by a motor 21a whose rotational speed is controlled by an inverter. In the present embodiment, there is only one compressor 21, but the present invention is not limited thereto; two or more compressors may be connected in parallel in accordance with, for example, the number of indoor units connected.

The four-way switching valve 22 switches the refrigerant's flow direction; furthermore, during the cooling operation, the four-way switching valve 22 can both connect a discharge side of the compressor 21 and a gas side of the outdoor heat exchanger 23 as well as an inlet side of the compressor 21 (specifically, the accumulator 24) and the gas refrigerant connection piping 7 side of the four-way switching valve 22 (refer to the solid lines of the four-way switching valve 22 in FIG. 1) in order to cause both the outdoor heat exchanger 23 to function as a condenser of the refrigerant compressed by the compressor 21 and the indoor heat exchangers 42, 52 to function as evaporators of the refrigerant condensed in the outdoor heat exchanger 23; in addition, during the heating operation, the four-way switching valve 22 can both connect the discharge side of the compressor 21 and the gas refrigerant connection piping 7 side of the four-way switching valve 22 as well as the inlet side of the compressor 21 and the gas side of the outdoor heat exchanger 23 (refer to the broken lines of the four-way switching valve 22 in FIG. 1) in order to cause both the indoor heat exchangers 42, 52 to function as condensers of the refrigerant compressed by the compressor 21 and the outdoor heat exchanger 23 to function as an evaporator of the refrigerant condensed in the indoor heat exchangers 42, 52.

In the present embodiment, the outdoor heat exchanger 23 is a cross fin type fin and tube heat exchanger that comprises a heat transfer pipe and numerous fins, functions as a condenser of the refrigerant during the cooling operation, and functions as an evaporator of the refrigerant during the heating operation. The gas side of the outdoor heat exchanger 23 is connected to the four-way switching valve 22, and the liquid side of the outdoor heat exchanger 23 is connected to the liquid refrigerant connection piping 6.

In the present embodiment, the outdoor expansion valve 38 is a motor operated expansion valve that is connected to the liquid side of the outdoor heat exchanger 23 and serves to regulate the pressure, flow volume, and the like of the refrigerant that flows inside the outdoor side refrigerant circuit 10c.

In the present embodiment, the outdoor unit 2 comprises an outdoor fan 28, which serves as a ventilation fan for the purpose of sucking outdoor air into the unit, exchanging heat between that air and the refrigerant via the outdoor heat exchanger 23, and then discharging that air to the outdoor space. The outdoor fan 28 is capable of varying the air volume Wo of the air supplied to the outdoor heat exchanger 23 and, in the present embodiment, is a propeller fan or the like that is driven by a motor 28a, which has a DC fan motor.

The accumulator 24 is a vessel that is connected to and disposed between the four-way switching valve 22 and the compressor 21 and is capable of accumulating surplus refrigerant generated inside the refrigerant circuit 10 in accordance with, for example, fluctuations in the operating loads of the indoor units 4, 5.

In the present embodiment, the supercooler 25 is a double pipe type heat exchanger that is provided in order to cool the refrigerant fed to the indoor expansion valves 41, 51 after the refrigerant has been condensed in the outdoor heat exchanger 23. In the present embodiment, the supercooler 25 is connected to and disposed between the outdoor expansion valve 38 and the liquid side shutoff valve 26.

The present embodiment provides a bypass refrigerant circuit 61, which serves as a cooling source of the supercooler 25. Furthermore, in the explanation below, the portion of the refrigerant circuit 10 that excludes the bypass refrigerant circuit 61 is called a main refrigerant circuit for the sake of convenience.

The bypass refrigerant circuit 61 is connected to the main refrigerant circuit such that some of the refrigerant that is fed from the outdoor heat exchanger 23 to the indoor expansion valves 41, 51 branches off from the main refrigerant circuit and returns to the inlet side of the compressor 21. Specifically, the bypass refrigerant circuit 61 comprises: a branching circuit 61a, which is connected such that some of the refrigerant that is fed from the outdoor expansion valve 38 to the indoor expansion valves 41, 51 branches from a position between the outdoor heat exchanger 23 and the supercooler 25; and a merging circuit 61b, which is connected to the inlet side of the compressor 21 such that the refrigerant returns from an outlet on the bypass refrigerant circuit side of the supercooler 25 to the inlet side of the compressor 21. Furthermore, a bypass expansion valve 62, which serves to regulate the flow volume of the refrigerant that flows through the bypass refrigerant circuit 61, is provided to the branching circuit 61a. Here, the bypass expansion valve 62 has a motor operated expansion valve. Thereby, the refrigerant that is fed from the outdoor heat exchanger 23 to the indoor expansion valves 41, 51 is decompressed by the bypass expansion valve 62 and then is cooled by the refrigerant that flows through the bypass refrigerant circuit 61 in the supercooler 25. Namely, the performance of the supercooler 25 is controlled by regulating the degree of opening of the bypass expansion valve 62. Furthermore, the control unit 8 also controls the bypass expansion valve 62 by, for example, adjusting or fixing the degree of opening in order to optimize the COP of the refrigeration cycle during optimal COP control operation discussed below.

The liquid side shutoff valve 26 and the gas side shutoff valve 27 are provided to a connection port that connects to external equipment and piping (specifically, the liquid refrigerant connection piping 6 and the gas refrigerant connection piping 7). The liquid side shutoff valve 26 is connected to the outdoor heat exchanger 23. The gas side shutoff valve 27 is connected to the four-way switching valve 22.

In addition, various sensors are provided to the outdoor unit 2. Specifically, an inlet pressure sensor 29, which detects an inlet pressure of the compressor 21, a discharge pressure sensor 30, which detects a discharge pressure of the compressor 21, an inlet temperature sensor 31, which detects an inlet temperature Ts of the compressor 21, and a discharge temperature sensor 32, which detects a discharge temperature Td of the compressor 21, are provided to the outdoor unit 2. The inlet temperature sensor 31 is provided at a position between the accumulator 24 and the compressor 21. A heat exchanging temperature sensor 33, which detects the temperature of the refrigerant that flows inside the outdoor heat exchanger 23 (i.e., the refrigerant temperature that corresponds to the condensing temperature during the cooling operation or the evaporating temperature during the heating operation) is provided to the outdoor heat exchanger 23. A liquid side temperature sensor 34, which detects the temperature of the refrigerant, is provided to the liquid side of the outdoor heat exchanger 23. A liquid pipe temperature sensor 35, which detects the temperature of the refrigerant (i.e., a liquid pipe temperature), is provided to an outlet on the main refrigerant circuit side of the supercooler 25. A bypass temperature sensor 63, which serves to detect the temperature of the refrigerant that flows through the outlet on the bypass refrigerant circuit side of the supercooler 25, is provided to the merging circuit 61b of the bypass refrigerant circuit 61. An outdoor temperature sensor 36, which detects the temperature of the outdoor air that flows inside the unit (i.e., the outdoor temperature), is provided to the outdoor air inlet side of the outdoor unit 2.

In the present embodiment, the inlet temperature sensor 31, the discharge temperature sensor 32, the heat exchanging temperature sensor 33, the liquid side temperature sensor 34, the liquid pipe temperature sensor 35, the outdoor temperature sensor 36, and the bypass temperature sensor 63 each has a thermistor.

In addition, the outdoor unit 2 comprises an outdoor side control unit 37, which controls the operation of all parts that constitute the outdoor unit 2. Furthermore, the outdoor side control unit 37 comprises, for example, a microcomputer and memory, which are provided to control the outdoor unit 2, and an inverter circuit, which controls the motor 21a, and is capable of exchanging control signals and the like with the indoor side unit 47 in the indoor unit 4 and the indoor side unit 57 in the indoor unit 5 via the transmission line 8a. Namely, the control unit 8, which controls the operation of the entire air conditioner 1, comprises the indoor side control units 47, 57, the outdoor side control unit 37, and the transmission line 8a, which connects the control units 37, 47, 57.

As shown in FIG. 2, which is a control block diagram of the air conditioner 1, the control unit 8 is connected such that it can both receive the detection signals of the various sensors 29 to 36, 44 to 46, 54 to 56, 63 and can control the various equipment and valves 21, 22, 24, 28a, 38, 41, 43a, 51, 62 based on these detection signals.

The refrigerant connection pipings 6, 7 are refrigerant pipings that are laid onsite when the air conditioner 1 is installed at an installation location, such as a building, and comprise pipes of various lengths and pipe diameters in accordance with the installation location and the installation conditions, such as the particular combination of outdoor units and indoor units to be configured.

As described above, in the air conditioner 1 of the present embodiment, the control unit 8, which comprises the indoor side control units 47, 57 and the outdoor side control unit 37, both switches between the cooling operation and the heating operation via the four-way switching valve 22 and controls each piece of equipment of the outdoor unit 2 and the indoor units 4, 5 in accordance with the operating load of each of the indoor units 4, 5.

First, the optimal COP control operation, which is performed during the cooling operation, will be explained, referencing FIG. 1 and FIG. 2.

If the control unit 8 (more specifically, the indoor side control units 47, 57, the outdoor side control unit 37, and the transmission line 8a that connects the control units 37, 47, 57) receives an instruction from, for example, the external remote control (not shown) to perform the cooling operation, then, during the refrigeration cycle, the control unit 8 controls the connection state of the four-way switching valve 22 such that the four-way switching valve 22 is in the state indicated by the solid lines in FIG. 1, namely, the state wherein the discharge side of the compressor 21 is connected to the gas side of the outdoor heat exchanger 23 and, further, the inlet side of the compressor 21 is connected to the gas side of the indoor heat exchangers 42, 52 via the gas side shutoff valve 27 and the gas refrigerant connection piping 7.

At this time, the outdoor expansion valve 38 is set to the fully open state. The liquid side shutoff valve 26 and the gas side shutoff valve 27 are set to an open state.

In optimal COP control during the cooling operation, the control unit 8 first calculates a value by dividing a degree of supercooling SCr by the difference between a condensing temperature Tc of the refrigerant and an air temperature Ta, as shown in the flow chart in FIG. 3 (i.e., step S10).

Furthermore, the method determines whether the value calculated in step S10 is 0.5 (i.e., step S20). Here, if the value calculated in step S10 is 0.5, then control continues as is.

Furthermore, if the value calculated in step S10 is not 0.5, then the control unit 8 performs compensatory control by regulating the degree of opening of each of the indoor expansion valves 41, 51 and the degree of opening of the bypass expansion valve 62 such that the refrigeration cycle can be carried out in the state wherein the value calculated by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta is 0.5 (i.e., step S30). Furthermore, the step S20 is repeated.

Here, in the present embodiment, each value is detected as described below.

First, the control unit 8 calculates the degree of supercooling SCr of the refrigerant at the outlet of the outdoor heat exchanger 23 by subtracting the value sensed by the heat exchanging temperature sensor 33, which detects the temperature of the refrigerant flowing through the outdoor heat exchanger 23, from the value sensed by the liquid pipe temperature sensor 35, which detects the temperature of the refrigerant at the outlet of the supercooler 25 on the main refrigerant circuit side. In addition, the control unit 8 uses the value sensed by the heat exchanging temperature sensor 33 of the outdoor heat exchanger 23 to ascertain the condensing temperature Tc of the refrigerant. Furthermore, the control unit 8 uses the value sensed by the outdoor temperature sensor 36 of the outdoor unit 2 to ascertain a temperature Ta of the outdoor air.

When the refrigerant circuit 10 is in this state, the control unit 8 activates the compressor 21, the outdoor fan 28, and the indoor fans 43, 53. In so doing, low pressure gas refrigerant is sucked into and compressed by the compressor 21, thereby turning into high pressure gas refrigerant. Subsequently, the high pressure gas refrigerant is fed to the outdoor heat exchanger 23 via the four-way switching valve 22, is condensed by the exchange of its heat with the outdoor air supplied by the outdoor fan 28, and turns into high pressure liquid refrigerant.

Furthermore, this high pressure liquid refrigerant passes through the outdoor expansion valve 38, flows into the supercooler 25, exchanges heat with the refrigerant that flows through the bypass refrigerant circuit 61, and thereby is further cooled such that it transitions to the supercooled state. At this time, some of the high pressure liquid refrigerant condensed in the outdoor heat exchanger 23 branches to the bypass refrigerant circuit 61 and, after its pressure is reduced by the bypass expansion valve 62, returns to the inlet side of the compressor 21. Here, that portion of the refrigerant that passes through the bypass expansion valve 62 evaporates as a result of its pressure being reduced to a level close to that of the inlet pressure of the compressor 21. Furthermore, the refrigerant that flows from the outlet of the bypass expansion valve 62 of the bypass refrigerant circuit 61 toward the inlet side of the compressor 21 passes through the supercooler 25 and exchanges heat with the high pressure liquid refrigerant that is fed from the outdoor heat exchanger 23 on the main refrigerant circuit side to the indoor units 4, 5.

Furthermore, the high pressure liquid refrigerant, which is now in a supercooled state, transits the liquid side shutoff valve 26 and the liquid refrigerant connection piping 6 and is fed to the indoor units 4, 5. The indoor expansion valves 41, 51 reduce the pressure of the high pressure liquid refrigerant fed to the indoor units 4, 5 such that this pressure almost reaches the inlet pressure of the compressor 21, and thereby the high pressure liquid refrigerant turns into low pressure refrigerant in the vapor-liquid two-phase state, is subsequently fed to the indoor heat exchangers 42, 52, exchanges heat with the indoor air via the indoor heat exchangers 42, 52, evaporates, and turns into low pressure gas refrigerant.

This low pressure gas refrigerant transits the gas refrigerant connection piping 7, is fed to the outdoor unit 2, transits the gas side shutoff valve 27 and the four-way switching valve 22, and flows into the accumulator 24. Furthermore, the low pressure gas refrigerant that flows into the accumulator 24 is once again sucked into the compressor 21.

The control unit 8 performs the abovementioned optimal COP control operation during the cooling operation by regulating the degree of opening of each of the indoor expansion valves 41, 51 and of the bypass expansion valve 62 and thereby can optimize the coefficient of performance (COP) during the cooling operation.

The following text explains the optimal COP control operation during the heating operation.

If the control unit 8 (more specifically, the indoor side control units 47, 57, the outdoor side control unit 37, and the transmission line 8a that connects the control units 37, 47, 57) receives an instruction from, for example, an external remote control (not shown) to perform the heating operation, then, during the refrigeration cycle, the control unit 8 controls the connection state of the four-way switching valve 22 such that the four-way switching valve 22 is in the state indicated by the broken lines in FIG. 1, namely, the state wherein the discharge side of the compressor 21 is connected to the gas side of the indoor heat exchangers 42, 52 via the gas side shutoff valve 27 and the gas refrigerant connection piping 7 and, further, the inlet side of the compressor 21 is connected to the gas side of the outdoor heat exchanger 23.

In addition, the control unit 8 sets the liquid side shutoff valve 26 and the gas side shutoff valve 27 to the open state and closes the bypass expansion valve 62.

Furthermore, to reduce the pressure of the refrigerant that flows into the outdoor heat exchanger 23 to an extent such that the refrigerant can evaporate (i.e., the evaporating pressure) in the outdoor heat exchanger 23, the control unit 8 regulates the degree of opening of the outdoor expansion valve 38.

In optimal COP control during the heating operation, too, as in the cooling operation, the control unit 8 first calculates a value by dividing a degree of supercooling SCr by the difference between a condensing temperature Tc of the refrigerant and an air temperature Ta, as shown in the flow chart in FIG. 3 (i.e., step S10).

Furthermore, the method determines whether the value calculated in step S10 is 0.5 (i.e., step S20). Here, if the value calculated in step S10 is 0.5, then control continues as is.

Furthermore, if the value calculated in step S10 is not 0.5, then the control unit 8 performs compensatory control by regulating the degree of opening of each of the indoor expansion valves 41, 51 such that the refrigeration cycle can be carried out in the state wherein the value calculated by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta is 0.5. Furthermore, the step S20 is repeated.

Here, in the present embodiment, each value is detected as described below. First, the control unit 8 detects the degree of supercooling SCr of the refrigerant at the outlet of each of the indoor heat exchangers 42, 52 by converting the discharge pressure of the compressor 21 detected by the discharge pressure sensor 30 to the saturation temperature value that corresponds to the condensing temperature and then subtracting the refrigerant temperature value detected by the liquid side temperature sensors 44, 54 from this refrigerant saturation temperature value. In addition, the control unit 8 uses the value sensed by the liquid side temperature sensors 44, 54 of the indoor heat exchangers 42, 52 to ascertain the condensing temperature Tc of the refrigerant. Furthermore, the control unit 8 uses the value sensed by the indoor temperature sensors 46, 56 of the indoor units 4, 5 to ascertain the temperature Ta of the indoor air.

If the control unit 8 activates the compressor 21, the outdoor fan 28, and the indoor units 43, 53 when the refrigerant circuit 10 is in this state, the low pressure gas refrigerant is sucked into and compressed by the compressor 21, turns into a high pressure gas refrigerant, and is then fed to the indoor units 4, 5 via the four-way switching valve 22, the gas side shutoff valve 27, and the gas refrigerant connecting pipe 7.

Furthermore, the high pressure gas refrigerant fed to the indoor units 4, 5 exchanges heat with the indoor air in the indoor heat exchangers 42, 52 and is thereby condensed and transitions to high pressure liquid refrigerant, after which it passes through the indoor expansion valves 41, 51, at which time its pressure is reduced in accordance with the degree of opening of each of the indoor expansion valves 41, 51.

The refrigerant that passes through the indoor expansion valves 41, 51 is fed to the outdoor unit 2 via the liquid refrigerant connection piping 6, the refrigerant's pressure is further reduced via the liquid side shutoff valve 26, the supercooler 25, and the outdoor expansion valve 38, and the refrigerant then flows into the outdoor heat exchanger 23. Furthermore, the vapor-liquid two-phase low pressure refrigerant that flows into the outdoor heat exchanger 23 exchanges heat with the outdoor air supplied by the outdoor fan 28, evaporates, turns into low pressure gas refrigerant, transits the four-way switching valve 22, and flows into the accumulator 24. Furthermore, the low pressure gas refrigerant that flows into the accumulator 24 is once again sucked into the compressor 21.

The control unit 8 performs the abovementioned optimal COP control operation during the heating operation by regulating the degree of opening of each of the indoor expansion valves 41, 51 and thereby can optimize the coefficient of performance (COP) during the heating operation.

The air conditioner 1 of the present embodiment has the following features.

In a conventional air conditioner, a degree of supercooling index that enables COP optimization is defined, and control is performed such that the degree of supercooling remains constant at the value of this index.

However, with this approach, as shown in, for example, FIG. 9, the relationship between the COP and a degree of supercooling SC corresponds to the state in which the air conditioner is driven, which is not particularly exceptional. Namely, the optimal degree of supercooling during the cooling rated operation is 7 degree, during the cooling season operation is 3 degree, during the heating rated operation is 9 degree, and during the heating season operation is 4 degree. Furthermore, if the refrigeration cycle is controlled using a specific value as the target degree of supercooling, then the optimal degree of supercooling will vary with the conditions, thereby making it impossible to optimize the COP. Furthermore, if a target degree of supercooling that corresponds to the abovementioned state is used and the refrigeration cycle is controlled such that the target degree of supercooling is maintained at a constant level, then not only would it be necessary to retain numerous target values, but control would become complicated and optimizing the COP may not be possible. Furthermore, here, it is assumed that, for example, the outside air temperature is in the range of 18°C through 20°C during the cooling season and in the range of 13°C through 18°C during the heating season.

In contrast, in the air conditioner 1 of the present embodiment, the control unit 8 performs control wherein the degree of opening of, for example, each of the indoor expansion valves 41, 51 is regulated such that the refrigeration cycle can be performed in the state wherein the value calculated by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta is 0.5. Here, with reference to the relationship between the COP and the value calculated by dividing the degree of supercooling by the difference between the condensing temperature and the air temperature as shown in FIG. 4, then it is evident that under every condition, regardless of whether it is during the cooling rated operation, the cooling season operation, the heating rated operation, or the heating season operation, the optimal value of the COP as calculated by dividing the degree of supercooling by the difference between the condensing temperature and the air temperature will fall within the range of 0.4 through 0.6.

Consequently, as discussed above, the control unit 8 performs optimal COP control such that the value calculated by dividing the degree of supercooling by the difference between the condensing temperature and the air temperature is 0.5, which makes it possible both to optimize the COP using a simple method of control-that is, merely by setting a single value to a target of 0.5 without maintaining a target value for every condition-and to save energy, whether during the cooling rated operation, the cooling season operation, the heating operation, or the heating season operation.

The above text explained an embodiment of the present invention based on the drawings, but the specific configuration of the present invention is not limited to these embodiments, and it is understood that variations and modifications may be effected without departing from the spirit and scope of the invention.

The abovementioned embodiment explained an exemplary case wherein the control unit 8 controls the degree of opening of each of the indoor expansion valves 41, 51 such that the value calculated by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta is 0.5.

However, the present invention is not limited thereto; for example, FIG. 5 shows a graph derived by transforming a relational expression between Tc and SC that satisfies SCr/(Tc - Ta) = 0.5. Specifically, the relational expression is Tc = 2SC + Ta.

Furthermore, from among the coordinate values that satisfy this relational expression, for example, the control unit 8 may derive a target coordinate value (S) that is closest to a coordinate value (P) of an actual measured value in the current state and may perform various types of control, such as controlling the indoor expansion valves 41, 51, the bypass expansion valve 62, and the like, controlling the rotational speed of the motor 43a of the indoor fan 43, controlling the rotational speed of the motor 21a of the compressor 21, controlling both the adjustment and fixing of the degree of opening of the outdoor expansion valve 38, controlling the rotational speed of the motor 28a of the outdoor fan 28, and so on, such that the degree of supercooling and the condensing temperature at the target coordinate value (S) are achieved.

Even in this case, effects equal to those in the abovementioned embodiments can be achieved.

The abovementioned embodiment explained an exemplary case wherein, when optimal COP control is performed during the heating operation, the control unit 8 detects the degree of supercooling SCr by calculating the degree of supercooling SCr through converting the discharge pressure of the compressor 21 detected by the discharge pressure sensor 30 to the saturation temperature value that corresponds to the condensing temperature and then subtracting the refrigerant temperature value detected by the liquid side temperature sensors 44, 54 from the refrigerant's saturation temperature value.

However, the present invention is not limited thereto; for example, temperature sensors that detect the temperature of the refrigerant flowing inside each of the indoor heat exchangers 42, 52 may be provided in advance, and the control unit 8 may detect the degree of supercooling SCr of the refrigerant at the outlets of the indoor heat exchangers 42, 52 by calculating the degree of supercooling SCr of optimal COP control during the heating operation through subtracting the refrigerant temperature value that corresponds to the condensing temperature detected by the temperature sensors from the refrigerant temperature value detected by the liquid side temperature sensors 44, 54.

The abovementioned embodiment explained an exemplary case wherein optimal COP control operation is performed using the value sensed by a single sensor that senses a single heat exchanger (i.e., the outdoor temperature sensor 36, and the indoor temperature sensors 46, 56) as the air temperature Ta.

However, the present invention is not limited thereto; for example, optimal COP control operation may be performed using the average of values obtained by two temperature sensors per heat exchanger as the air temperature Ta.

Specifically, for example, as shown in FIG 6 and FIG. 7, a pre-passage outdoor temperature sensor 361, which senses the indoor temperature before air passes through the outdoor heat exchanger 23, and a post-passage outdoor temperature sensor 362, which senses the temperature of the air after the air has passed through the outdoor heat exchanger 23 and exchanged heat, may be provided, and the average of the detection values sensed by these sensors may be used as the value of the air temperature Ta.

In such a case, it would be possible to more accurately ascertain the temperature of the air subjected to the exchange of heat, to further optimize the COP, and to save energy.

The abovementioned embodiment explained an exemplary case wherein optimal COP control is performed in the refrigerant circuit 10, which is provided with the bypass refrigerant circuit 61.

However, the present invention is not limited thereto; for example, optimal COP control may be performed as it is in the abovementioned embodiment, but on a refrigeration cycle that comprises, for example, only the main refrigerant circuit and not the bypass refrigerant circuit 61 discussed above. In this case as well, it is possible to achieve the energy saving effect of the present invention.

The abovementioned embodiment explained an exemplary case of an air cooled air conditioner.

However, the present invention is not limited thereto; for example, the air conditioner may be a water cooled type wherein water is used as the fluid that passes through the heat exchanger.

The abovementioned embodiment explained an exemplary case wherein the control unit 8 controls the degree of opening of each of the indoor expansion valves 41, 51 such that the value calculated by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta is 0.5.

However, the present invention is not limited thereto; for example, the control unit 8 may control the degree of opening of each of the indoor expansion valves 41, 51 such that the value calculated by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta falls within a range of greater than or equal to 0.4 and less than 0.6. Even in this case, it is possible to achieve the same effects as those achieved in the abovementioned embodiments.

The abovementioned embodiment explained an exemplary case wherein a COP related target value that can yield a satisfactory COP ratio is specified by comparing the value (i.e., the COP related target value) obtained by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta with the COP ratio (i.e., the COP ratio at each degree of supercooling (SC) for the case wherein the COP is 100% at a certain degree of supercooling (SC)), and then controlling the degree of opening of each of the indoor expansion valves 41, 51 such that the COP related target value falls within the specified range.

However, the present invention is not limited thereto. For example, as shown in FIG. 8, an optimal AFP control may be performed. The optimal AFP control, for example, controlls the degree of opening of each of the indoor expansion valves 41, 51 such that a AFP related target value falls within a specified range. The range of the AFP related target value which can yield a satisfactory AFP (Annual Performance factor) may be specified by comparing the AFP with a value (i.e., the AFP related target value) obtained by dividing the degree of supercooling SCr by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta. Here, when the range of the APF related target value is specified, for example, a range may be derived such that an APF ratio indicated by the ordinate in FIG. 8 is 100% or greater. This APF ratio is called the APF ratio at each degree of supercooling (SC) when the APF is 100% at a certain degree of supercooling (SC).

This APF is a value that indicates the cooling and heating capacity per 1 KW of power consumption when an air conditioner is operated for one year under certain fixed conditions. Here, APF can be calculated by the expression APF = (the aggregate of performance exhibited during the cooling season + the aggregate of performance exhibited during the heating season)/(the aggregate of the amount of power consumed during the cooling season + the aggregate of the amount of power consumed during the heating season).

Furthermore, APF can be calculated more finely by, for example, complying with the conditions specified in JRA 4048:2006 (i.e., the standard for implementing JIS B8616:2006) created by the Japan Refrigeration and Air Conditioning Industry Association Standards.

When creating the graph in FIG. 8, first, based on measurement conditions specified in the standard, the weighting factor for each COP ratio-that is, the COP ratio during the cooling rated operation, the COP ratio during the cooling season operation, the COP ratio during the heating rated operation, the COP ratio during the heating season operation, and the COP ratio during the heating low temperature operation-is back calculated. Furthermore, each calculated weighting factor is multiplied by the corresponding COP ratio-that is, the COP ratio during the cooling rated operation, the COP ratio during the cooling season operation, the COP ratio during the heating rated operation, the COP ratio during the heating season operation, and the COP ratio during the heating low temperature operation-these values are totaled, and thereby the APF ratio is obtained as a value that can fully evaluate the aggregate of cooling and heating.

Furthermore, performing an evaluation that is closer to actual usage-by performing optimal APF control that targets a satisfactory APF value-than can be achieved using the COP-which evaluates the performance for a case (i.e., the rated condition) wherein operation is performed under a certain constant temperature condition-makes it possible to obtain a greater energy saving effect.

The abovementioned embodiment explained an exemplary case wherein the control unit 8 controls the degree of opening of each of the indoor expansion valves 41, 51 such that the value calculated by dividing by the difference between the condensing temperature Tc of the refrigerant and the air temperature Ta is 0.5.

However, the present invention is not limited thereto; for example, so that values suited to, for example, the season and operating environmental conditions for the COP related target value, the APF related target value, discussed in the modified example (G) section can be used, control may be performed such that, for example, the COP related target value and the APF related target value are modified according to the season, the operating environmental conditions, and the like.

For example, operation may be performed wherein two different COP related target values and two different APF related target values-one for the circuit connection state wherein the cooling operation is performed and one for the circuit connection state wherein the heating operation is performed-are prescribed.

The present invention is particularly useful for operating an air conditioner such that it saves energy under various conditions, thereby optimizing the COP even when usage conditions vary.