JP2001255024A - Air conditioner and its control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner and its control method capable of improving operation efficiency. SOLUTION: An air conditioner 1 includes an indoor heat exchange unit 2, an outdoor heat exchange unit 3, a refrigerant circuit 4 for circulating a refrigerant between these heat exchange units 2, 3, a compressor 5 for increasing pressure of the refrigerant in the refrigerant circuit 4, an expansion valve 6 for reducing the pressure of the refrigerant, a temperature sensor 7 for detecting the temperature of the refrigerant in the indoor heat exchange unit 2, a temperature sensor 8 for detecting the temperature of the refrigerant in the outdoor heat exchange unit 3, and a control section 9 for adjusting an opening of the expansion valve 6 based upon the temperature of the refrigerant detected by the temperature sensors 7, 8. Upon operating the air conditioner 1, the opening of the expansion valve 6 is adjusted based upon the temperature of the refrigerant detected by the temperature sensors 78, 8 to keep the degree of overheating of the refrigerant in a predetermined range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioner for adjusting indoor air to a desired state by cooling or heating, and a control method thereof.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a conventional air conditioner. An air conditioner 21 shown here comprises an indoor heat exchange unit 2, an outdoor heat exchange unit 3, these heat exchange units 2, A refrigerant circuit 4 for circulating the refrigerant between the refrigerant circuits 3, a compressor 5 'for increasing the pressure of the refrigerant in the refrigerant circuit 4, an expansion valve 6 for decompressing the refrigerant condensed in the indoor heat exchange unit 2 or the outdoor heat exchange unit 3, and A control unit 29 for adjusting the opening of the expansion valve 6 based on the rotation speed of the motor 5a 'of the compressor 5';
And an accumulator (excess liquid refrigerant holding container) 22 for temporarily storing the excess liquid refrigerant. In the refrigerant circuit 4,
A four-way valve 10 is provided for selectively flowing the refrigerant, the pressure of which has been increased in the compressor 5 ', to one of the indoor heat exchange unit 2 and the outdoor heat exchange unit 3.

In the air conditioner 21, during the cooling operation, the gas refrigerant which has become high temperature and high pressure in the compressor 5 'is sent to the outdoor heat exchange unit 3 through the refrigerant circuit 4, as indicated by the solid line arrow in FIG. Here, the refrigerant is cooled and condensed to become a high-temperature and high-pressure liquid refrigerant, and then decompressed by the expansion valve 6 to become a low-temperature and low-pressure liquid refrigerant. To become a low-temperature low-pressure gas refrigerant, and then returned to the compressor 5 ′ via the accumulator 22 to become a high-temperature high-pressure gas refrigerant,
Thereafter, this process is repeated. Also, during the heating operation, as indicated by the dashed arrow, the gas refrigerant which has become high-temperature and high-pressure in the compressor 5 'is sent to the indoor heat exchange unit 2, where it heats and condenses the room air and converts the high-temperature and high-pressure liquid. The refrigerant is decompressed by the expansion valve 6 to become a low-temperature and low-pressure liquid refrigerant, then sent to the outdoor heat exchanger 3 where it is heated and evaporated to become a low-temperature and low-pressure gas refrigerant, and then passes through the accumulator 22 to the compressor 5 ′ And becomes a high-temperature and high-pressure gas refrigerant, and this process is repeated thereafter.

FIG. 6 is a Mollier diagram showing the thermodynamic change of the refrigerant during the operation of the air conditioner 21.
Hereinafter, this figure will be described. (1) In the process of compressing the gas refrigerant in the compressor 5 ', the state of the refrigerant changes upward to the right in the figure (from point a' to point b '). Hereinafter, this process is called a compression process. (2) In the process of cooling the gas refrigerant into a liquid refrigerant in the indoor heat exchange unit 2 or the outdoor heat exchange unit 3, the state of the refrigerant changes leftward in the drawing (from point b 'to point c').
point). Hereinafter, this process is referred to as a condensation process. (3) In the process in which the liquid refrigerant becomes low temperature and low pressure in the expansion valve 6, the state of the refrigerant changes downward in the figure (from point c 'to d').
point). Hereinafter, this process is referred to as a decompression process. (4) In the process in which the liquid refrigerant is heated and turned into a gas refrigerant in the indoor heat exchange unit 2 or the outdoor heat exchange unit 3, the state of the refrigerant changes rightward in the figure and reaches the saturated vapor line G ( It evaporates completely at point e ') and is brought into a superheated state with a slight degree of superheat SH' (point a '). Hereinafter, this process is called an evaporation process. In the operation process shown in (1) to (4), the compressor 5 ′
When the number of rotations of the motor 5a 'increases or decreases, the compressor 5'
The discharge pressure of the refrigerant changes and the pressure of the refrigerant increases or decreases.
Thus, the opening of the expansion valve 6 is adjusted in accordance with the rotation speed of the motor 5a ', thereby preventing the state of the refrigerant from fluctuating extremely.

[0005]

However, in the above-described conventional air conditioner 21, the change in the state of the refrigerant during operation is likely to vary, and the operation efficiency may decrease. For example, in the pressure reducing process, the opening of the expansion valve 6 becomes excessively large, and the high pressure of the refrigerant decreases and the low pressure increases. As shown by the broken line in FIG. As a result, the heat exchange efficiency is reduced, and the operation efficiency is sometimes reduced. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air conditioner capable of maintaining high operation efficiency and a control method thereof.

[0006]

In order to solve the above-mentioned problems, the present invention employs an air conditioner having the following configuration and a control method thereof. The air conditioner according to claim 1 includes an indoor heat exchange unit, an outdoor heat exchange unit, a refrigerant circuit that circulates refrigerant between the heat exchange units, and a compressor that increases the pressure of the refrigerant in the refrigerant circuit. An expansion valve for reducing the pressure of the refrigerant condensed in the indoor or outdoor heat exchange unit, an indoor refrigerant state detecting means for detecting the state of the refrigerant in the indoor heat exchange unit, and an outdoor refrigerant for detecting the state of the refrigerant in the outdoor heat exchange unit It is characterized by comprising a state detecting means, and a control unit for adjusting the degree of opening of the expansion valve based on the state of the refrigerant detected by the refrigerant state detecting means. In this air conditioner, the opening of the expansion valve can be adjusted by the control unit such that the degree of superheat of the refrigerant in the evaporation process falls within a predetermined range. Therefore, it is possible to reliably prevent the pressure of the refrigerant from becoming low and insufficient evaporation during the evaporation process, to maintain a high heat exchange efficiency during operation, and to improve the operation efficiency.

The air conditioner according to the present invention is characterized in that a temperature sensor for detecting the temperature of the refrigerant is used as the indoor and outdoor refrigerant state detecting means. In this air conditioner, equipment cost can be reduced by using an inexpensive temperature sensor as the refrigerant state detecting means.

The air conditioner according to a third aspect of the present invention is characterized in that a pressure sensor for detecting the pressure of the refrigerant is used as the indoor and outdoor refrigerant state detecting means. In this air conditioner, by using the pressure sensor, the pressure of the refrigerant in the condensation and evaporation processes can be accurately known. For this reason, the degree of superheat can be accurately maintained in the predetermined range, and a more excellent efficiency improving effect can be obtained.

[0009] The control method of the air conditioner according to claim 4 is as follows.
An indoor heat exchange unit, an outdoor heat exchange unit, a refrigerant circuit for circulating refrigerant between the heat exchange units, a compressor for increasing the pressure of the refrigerant in the refrigerant circuit, and a refrigerant condensed in the indoor or outdoor heat exchange unit Expansion valve for reducing pressure, indoor refrigerant state detecting means for detecting the state of the refrigerant in the indoor heat exchange unit, outdoor refrigerant state detecting means for detecting the state of the refrigerant in the outdoor heat exchange unit, and these refrigerant state detecting means And a control unit that adjusts the opening of the expansion valve based on the state of the refrigerant detected by the refrigerant state detecting means, and the refrigerant state detected by the indoor and outdoor refrigerant state detecting means. The degree of superheat of the refrigerant in the indoor or outdoor heat exchange unit is maintained in a predetermined range by adjusting the degree of opening of the expansion valve based on the state. . According to this control method, it is possible to reliably prevent the pressure of the refrigerant from becoming low and insufficient evaporation in the evaporation process, to maintain a high heat exchange efficiency during operation, and to improve the operation efficiency.

[0010]

FIG. 1 shows an embodiment of an air conditioner according to the present invention. An air conditioner 1 shown here comprises an indoor heat exchange unit 2, an outdoor heat exchange unit 3, A refrigerant circuit 4 for circulating the refrigerant between the heat exchange units 2 and 3, a compressor 5 for increasing the pressure of the refrigerant in the refrigerant circuit 4,
An expansion valve 6 for reducing the pressure of the refrigerant condensed in the indoor heat exchange unit 2 or the outdoor heat exchange unit 3, an indoor temperature sensor 7 serving as an indoor refrigerant state detecting means for detecting the temperature of the refrigerant in the indoor heat exchange unit 2, Outdoor heat exchange unit 3
An outdoor temperature sensor 8 which is an outdoor refrigerant state detecting means for detecting the temperature of the refrigerant in the air conditioner;
And a controller 9 for adjusting the opening degree of the expansion valve 6 based on the temperature of the refrigerant detected by the controller 9.

The refrigerant circuit 4 is provided with a four-way valve 10 for selectively flowing the refrigerant whose pressure has been increased in the compressor 5 to either the indoor heat exchange unit 2 or the outdoor heat exchange unit 3. .

The indoor heat exchange unit 2 includes an indoor heat exchanger 11 connected to the refrigerant circuit 4, and an indoor fan 12 for increasing the efficiency of heat exchange between the indoor air and the refrigerant in the indoor heat exchanger 11. I have. The indoor heat exchange unit 2 may adopt a structure embedded in a ceiling, that is, a structure that is installed so as to be embedded in a ceiling surface, or a ceiling suspension type, that is, a structure that can be hung from a ceiling. It can also be a wall-mounted type. Further, the indoor heat exchange unit 2 may be provided with a mechanism for suspending and lifting the suction grill with a wire so that the air filter can be replaced and the suction grill can be easily cleaned.

The outdoor heat exchange unit 3 includes an outdoor heat exchanger 13 connected to the refrigerant circuit 4, and an outdoor fan 14 for increasing the efficiency of heat exchange between the outdoor air and the refrigerant in the outdoor heat exchanger 13. I have.

The heat exchangers 11 and 13 have a heat transfer tube having an inner diameter of 7 mm or less, for example, 6.35 mm.
It is preferable to use a small-diameter high-density heat exchanger that is as follows. In addition, it is preferable to use a heat transfer tube having a groove on the inner surface since the heat transfer efficiency of the refrigerant to the heat transfer tube can be increased and the heat exchange efficiency can be improved. In addition, heat transfer plates (heat transfer fins)
The use of antler louver fins that adopt louver cuts that are inclined with respect to the flow of wind can increase the heat transfer area and increase the heat exchange efficiency. This is preferable because it can be a heat exchanger. Also, when using small-diameter heat transfer tubes, it is necessary to increase the number of refrigerant distribution circuits, so one stabilizes the flow rate of refrigerant in each circuit distribution pipe. It is preferred to use a refrigerant distributor which is possible and well distributable.

The compressor 5 is configured to compress a low-temperature and low-pressure gas refrigerant in the refrigerant circuit 4 and discharge it as a high-temperature and high-pressure gas refrigerant. As the compressor 5,
It is preferable to use a scroll compressor, a rotary compressor, or the like. As the scroll compressor, a type that can reduce leakage loss and increase efficiency by adopting a high-strength material as a material for the scroll is preferable.

As the motor 5a of the compressor 5, a reluctance DC motor can be employed. This motor 5
It is preferable that a is connected to a DC inverter (not shown) that can drive a DC motor and that the inverter can be controlled by a. It is preferable that the inverter employs a "position sensorless system" so that the instantaneous rotation angle of the rotor can be detected from the terminal voltage of the DC motor. In addition, by employing "field weakening control" for the inverter, the motor current in the low / medium speed range can be reduced and the efficiency can be improved.

The temperature sensors 7, 8 are connected to the heat exchange unit 2,
3 is configured to be able to output a detection signal corresponding to the temperature of the refrigerant to the control unit 9, and a general-purpose temperature sensor such as a thermistor, a copper sensor, and a platinum sensor can be used.

The control unit 9 outputs a control signal corresponding to the detection signals from the temperature sensors 7 and 8 to the expansion valve 6 so that the degree of opening of the expansion valve 6 is changed to the refrigerant temperature in the heat exchange units 2 and 3. It can be set accordingly.

Hereinafter, a method of operating the air conditioner 1 will be described. During the cooling operation, the four-way valve 10 is set so that the refrigerant that has passed through the compressor 5 flows to the outdoor heat exchange unit 3. During the cooling operation, as shown by the solid line arrow in FIG. 1, the gas refrigerant which has become high temperature and high pressure in the compressor 5 is sent to the outdoor heat exchange unit 3 through the refrigerant circuit 4 and cooled by heat exchange with the outdoor air. Is condensed and becomes a high-temperature and high-pressure liquid refrigerant. At this time, the outdoor heat exchanger 13 functions as a condenser for condensing the gas refrigerant. The high-temperature and high-pressure liquid refrigerant is reduced in pressure in the expansion valve 6 to become a low-temperature and low-pressure liquid refrigerant. The low-temperature and low-pressure liquid refrigerant is sent to the indoor heat exchange unit 2 through the refrigerant circuit 4, and cools the indoor air by exchanging heat with the indoor air. Becomes At this time, the indoor heat exchanger 11 functions as an evaporator for evaporating the liquid refrigerant. This low-temperature and low-pressure gas refrigerant is returned to the compressor 5 via the four-way valve 10 to become a high-temperature and high-pressure gas refrigerant, and this process is repeated thereafter.

During the heating operation, the refrigerant having passed through the compressor 5 is supplied to the indoor heat exchange unit 2 as indicated by the dashed arrow.
The four-way valve 10 is set to flow to During the heating operation, the gas refrigerant that has become high temperature and high pressure in the compressor 5 is sent to the indoor heat exchange unit 2 to heat the indoor air by exchanging heat with the indoor air and to cool and condense itself. It becomes a high-temperature and high-pressure liquid refrigerant. At this time, the indoor heat exchanger 11 functions as a condenser for condensing the gas refrigerant. The high-temperature and high-pressure liquid refrigerant is reduced in pressure in the expansion valve 6 to become a low-temperature and low-pressure liquid refrigerant. The low-temperature and low-pressure liquid refrigerant is sent to the outdoor heat exchanger 3 through the refrigerant circuit 4, where the liquid refrigerant is heated and evaporated by heat exchange with the outdoor air to become a low-temperature and low-pressure gas refrigerant.
At this time, the outdoor heat exchanger 13 functions as an evaporator for evaporating the liquid refrigerant. The low-temperature and low-pressure gas refrigerant is supplied to the four-way valve 1
After passing through 0, the refrigerant is returned to the compressor 5 and becomes a high-temperature and high-pressure gas refrigerant. Thereafter, this process is repeated.

FIG. 2 is a Mollier diagram showing the thermodynamic change of the refrigerant during the operation of the air conditioner 1. Hereinafter, this figure will be described. (1) In the process of compressing the gaseous refrigerant in the compressor 5, the pressure and the enthalpy both increase, so that the state of the refrigerant changes upward to the right in the figure (from point a to point b). Hereinafter, this process is called a compression process. (2) In the process of cooling the gas refrigerant into the liquid refrigerant in the indoor heat exchange unit 2 or the outdoor heat exchange unit 3, since the enthalpy decreases without changing the pressure, the state of the refrigerant changes leftward in the drawing. Then, when the saturated vapor line G is reached, condensation starts, and when the saturated liquid line L is reached, the refrigerant completely liquefies and is further cooled to have a slight degree of supercooling (SC) (point b). To c). Hereinafter, this process is referred to as a condensation process. (3) In the process in which the liquid refrigerant becomes low-temperature and low-pressure in the expansion valve 6, since the heat does not flow in and out, the enthalpy does not change and the pressure drops, so that the state of the refrigerant changes downward in the figure (from point c). d point). Hereinafter, this process is called a pressure reduction process. (4) In the indoor heat exchange unit 2 or the outdoor heat exchange unit 3, in the process in which the liquid refrigerant is heated and turned into a gas refrigerant, the enthalpy increases without a change in pressure, and the state of the refrigerant moves rightward in the figure. Then, when the temperature reaches the saturated vapor line G (point e), it completely evaporates and is further superheated so as to have a slight degree of superheat SH (point a). Hereinafter, this process is called an evaporation process.

If the degree of superheat SH (temperature difference between point e and point a in the figure) is too large, the operating efficiency is reduced, and if it is too small, the refrigerant tends to be insufficiently evaporated in the evaporation process. , Preferably 3-5 ° C.

In the operation process of the air conditioner 1, the condensation process (point b to point c) and the evaporation process (point d to point a)
Progresses in the heat exchange units 2 and 3, the temperature CT of the refrigerant in the condensation process and the temperature ET of the refrigerant in the evaporation process can be detected by the temperature sensors 7 and 8. For this reason, the pressure of the refrigerant in the condensation and evaporation processes can be known from the refrigerant temperatures CT and ET. That is, the height positions of the line segments bc and da in FIG. 2 can be known. The efficiency of the compressor 5 depends on the motor 5
Since it can be known from the operating frequency of a, etc., the slope of the line segment ab in the compression process can be known. in this way,
Since the pressure of the refrigerant in the condensation and evaporation processes and the slope of the line segment ab in the compression process can be known,
The temperature of the refrigerant at the outlet (point b) of the compressor 5 required to bring the degree of superheat SH (the temperature difference between points e and a in the figure) into the above-mentioned suitable predetermined range (for example, 3 to 5 ° C.) Hereinafter, target discharge refrigerant temperature) can be calculated.

The curve 15 shown in FIG. 3 shows the relationship between the refrigerant temperature (CT) in the condensation process and the target discharge refrigerant temperature. Curve 16 shows the relationship between the refrigerant temperature CT and the target discharge refrigerant temperature when the refrigerant temperature ET in the evaporation process is lower than the refrigerant temperature ET in curve 15. Curve 17 shows the relationship between the refrigerant temperature CT and the target discharge refrigerant temperature when the refrigerant temperature ET in the evaporation process is still lower than the refrigerant temperature ET in curve 16. As shown in this figure, the higher the refrigerant temperature CT in the condensation process and the lower the refrigerant temperature ET in the evaporation process, the higher the target discharge refrigerant temperature.

In the control method of the present embodiment, the controller 9 controls the refrigerant temperature at the outlet of the compressor 5 (discharge refrigerant temperature).
However, the opening of the expansion valve 6 is adjusted so as to reach the target discharge refrigerant temperature. For example, as shown by a broken line BL1 in FIG. 2, when the pressure of the refrigerant in the evaporation process decreases, and as a result, the superheat degree SH becomes less than the above range and the discharged refrigerant temperature falls below the target discharged refrigerant temperature, The control unit 9 outputs to the expansion valve 6 a control signal corresponding to a calculation result based on the detection signals from the temperature sensors 7 and 8 and a previously input efficiency of the compressor 5, and expands the control valve in accordance with the calculation result. The degree of opening of the valve 6 is increased, the amount of pressure decrease of the refrigerant during the pressure reduction process is suppressed to a low level, and the pressure of the refrigerant during the evaporation process is increased. Accordingly, the discharged refrigerant temperature reaches the target discharged refrigerant temperature, and the degree of superheat SH increases to the above-described predetermined range.

As shown by the broken line BL2 in FIG. 2, the pressure of the refrigerant in the evaporation process increases, and as a result, the superheat degree S
When H exceeds the above range and the discharged refrigerant temperature exceeds the target discharged refrigerant temperature, the control unit 9 determines whether the detection signals from the temperature sensors 7 and 8 and the efficiency of the compressor 5 input in advance are sufficient. The control signal corresponding to the calculation result based on the calculation result is output to the expansion valve 6, the opening degree of the expansion valve 6 decreases according to the calculation result, the amount of pressure decrease of the refrigerant in the pressure reduction process increases, and the pressure of the refrigerant in the evaporation process increases. Can be kept low. Accordingly, the discharged refrigerant temperature reaches the target discharged refrigerant temperature, and the degree of superheat SH decreases to the above-described predetermined range.
In the control method of the present invention, for example, PI control or fuzzy control can be adopted.

In the air conditioner 1 of this embodiment, an indoor temperature sensor 7 for detecting the temperature of the refrigerant in the indoor heat exchange unit 2 and an outdoor temperature sensor 8 for detecting the temperature of the refrigerant in the outdoor heat exchange unit 3 And the control unit 9 for adjusting the opening of the expansion valve 6 based on the temperature of the refrigerant detected by the temperature sensors 7 and 8, so that the state of the refrigerant changes and the superheat degree SH becomes excessively large or small. In this case, the opening degree of the expansion valve 6 can be adjusted by the control unit 9 so that the superheat degree SH falls within a predetermined range. Therefore, the degree of superheat SH in the evaporation process can be maintained in a predetermined range (for example, 3 to 5 ° C.). Therefore, it is possible to reliably prevent the pressure of the refrigerant from becoming low and insufficient evaporation during the evaporation process, to maintain a high heat exchange efficiency during operation, and to improve the operation efficiency. Further, since the refrigerant can be surely evaporated at the end of the evaporation process, an accumulator (an excess liquid refrigerant holding container) can be dispensed with. For this reason, it is possible to reduce the equipment cost of the accumulator, prevent pressure loss of the refrigerant in the accumulator, and increase energy efficiency during operation. In addition, the size of the air conditioner can be reduced, and the installation space and weight can be reduced.

The use of inexpensive temperature sensors 7 and 8 as refrigerant state detecting means for detecting the state of the refrigerant can reduce equipment costs.

In the present invention, a pressure sensor can be used instead of the temperature sensors 7 and 8. In this case, the pressure sensor is configured to output a detection signal corresponding to the pressure of the refrigerant in the heat exchange units 2 and 3 to the control unit 9. A semiconductor sensor can be used as the pressure sensor. In this case, the control unit 9 is configured to adjust the opening of the expansion valve 6 by outputting a control signal corresponding to the detection signal from the pressure sensor to the expansion valve 6.

In the operation using the pressure sensor, as in the case of using the temperature sensor, the control unit 9 outputs a control signal corresponding to the detection signal from the pressure sensor to the expansion valve 6 so that the discharged refrigerant temperature is reduced. However, the opening degree of the expansion valve 6 is adjusted so as to reach the target discharge refrigerant temperature, so that the superheat degree SH falls within a predetermined range. That is, when the pressure of the refrigerant in the evaporation process increases or decreases and the discharged refrigerant temperature increases or decreases with respect to the target discharged refrigerant temperature, the control unit 9 detects the detection signal from the pressure sensor and the efficiency of the compressor 5 input in advance. Is output to the expansion valve 6, the opening degree of the expansion valve 6 is adjusted according to the calculation result, the discharge refrigerant temperature reaches the target discharge refrigerant temperature, and the superheat degree SH is set to the predetermined value. Adjusted to the range.

When a pressure sensor is used, the degree of superheat SH in the evaporation process can be easily maintained in a predetermined range (for example, 3 to 5 ° C.), similarly to the case where a temperature sensor is used. Therefore, it is possible to reliably prevent the pressure of the refrigerant from becoming low and insufficient evaporation during the evaporation process, maintain a high operating efficiency, eliminate the need for an accumulator, reduce equipment costs, improve energy efficiency during operation, and reduce installation space. Thus, the weight can be reduced.

Further, by using a pressure sensor as the refrigerant state detecting means for detecting the state of the refrigerant, the pressure of the refrigerant during the evaporation process can be directly detected. This refrigerant pressure can be known more accurately than when the pressure is calculated. For this reason, the degree of superheat SH can be accurately maintained in a predetermined range, and a more excellent operation efficiency improving effect can be obtained.

In the above embodiment, the control method for maintaining the degree of superheating of the refrigerant in the evaporation process in a predetermined range has been described. However, the present invention is not limited to this. It is also possible to employ. That is, as shown in FIG. 4, the air conditioner is operated so as to be in a supercooled state so that the refrigerant has a slight degree of supercooling SC during the condensation process. At this time, for example, a heat exchange unit functioning as a condenser By adjusting the degree of opening of the expansion valve based on the refrigerant temperature at the heat exchange unit outlet detected by the temperature sensor installed at the outlet and the efficiency of the compressor, the degree of supercooling SC in the condensation process can be adjusted to a predetermined value. A control method for maintaining the range can be adopted.

In the above-described embodiment, the example in which the inverter control is employed for the compressor is described. However, the present invention is not limited to this, and a control method for maintaining the discharge refrigerant temperature substantially constant is employed, and the rotational speed is substantially reduced. It is also possible to use a constant compressor. Further, the air conditioner of the present invention can be applied to a commercial air conditioner having a compressor output of, for example, 4 kW or more, a so-called packaged air conditioner, or to an air conditioner having an output less than the above range. it can.

[0035]

According to the air conditioner of the present invention, an indoor heat exchange unit, an outdoor heat exchange unit, a refrigerant circuit for circulating a refrigerant between these heat exchange units, and a pressure of the refrigerant in the refrigerant circuit. Compressor, an expansion valve for reducing the pressure of the refrigerant condensed in the indoor or outdoor heat exchange unit, an indoor refrigerant state detecting means for detecting the state of the refrigerant in the indoor heat exchange unit, and the state of the refrigerant in the outdoor heat exchange unit And a control unit that adjusts the degree of opening of the expansion valve based on the state of the refrigerant detected by the refrigerant state detection means. By adjusting the degree, the degree of superheating of the refrigerant during the evaporation process can be maintained within a predetermined range. Therefore, it is possible to reliably prevent the pressure of the refrigerant from becoming low and insufficient evaporation during the evaporation process, to maintain a high heat exchange efficiency during operation, and to improve the operation efficiency.

In the method for controlling an air conditioner according to the present invention, the degree of opening of the expansion valve is adjusted based on the state of the refrigerant detected by the indoor and outdoor refrigerant state detecting means, so that the indoor or outdoor state is controlled. Since the degree of superheat of the refrigerant in the heat exchange unit is maintained within a predetermined range, it is possible to reliably prevent the pressure of the refrigerant from being lowered during the evaporation process and insufficient evaporation, to maintain a high heat exchange efficiency during operation, and to improve the operation efficiency. Improvement can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an overall configuration of an embodiment of an air conditioner of the present invention.

FIG. 2 is a state diagram of a refrigerant in an operation process of the air conditioner shown in FIG.

FIG. 3 is a graph showing a relationship between a refrigerant temperature in a condensation process and a target discharge refrigerant temperature.

FIG. 4 is a state diagram of a refrigerant in an example of a method for controlling an air conditioner of the present invention.

FIG. 5 is an explanatory diagram showing an overall configuration of an embodiment of a conventional air conditioner.

6 is a state diagram of a refrigerant in an operation process of the air conditioner shown in FIG.

[Explanation of symbols]

1 ... air conditioner, 2 ... indoor heat exchange unit, 3 ... outdoor heat exchange unit, 4 ... refrigerant circuit, 5 ... compressor, 6 ...
・ Expansion valve, 7 ・ ・ ・ Indoor temperature sensor (indoor refrigerant state detecting means), 8 ・ ・ ・ Outdoor temperature sensor (outdoor refrigerant state detecting means) 9 ・ ・ ・ Control unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Mitsuru Nakamura 1F, Takamichi, Iwazuka-cho, Nakamura-ku, Nagoya-shi, Aichi F-term in Mitsubishi Heavy Industries, Ltd. Nagoya Research Laboratories 3L060 AA03 CC04 CC16 DD08 EE09

Claims (4)

[Claims] An indoor heat exchange unit, an outdoor heat exchange unit, a refrigerant circuit for circulating a refrigerant between the heat exchange units, a compressor for increasing the pressure of the refrigerant in the refrigerant circuit, and indoor or outdoor heat exchange. An expansion valve for reducing the pressure of the refrigerant condensed in the unit, an indoor refrigerant state detecting means for detecting the state of the refrigerant in the indoor heat exchange unit, and an outdoor refrigerant state detecting means for detecting the state of the refrigerant in the outdoor heat exchange unit, An air conditioner comprising: a controller that adjusts an opening degree of an expansion valve based on a state of the refrigerant detected by the refrigerant state detecting means. 2. The air conditioner, wherein the indoor and outdoor refrigerant state detecting means is a temperature sensor for detecting a temperature of the refrigerant. 3. The air conditioner, wherein the indoor and outdoor state refrigerant detection means is a pressure sensor for detecting a pressure of the refrigerant. 4. An indoor or outdoor heat exchange unit, an outdoor heat exchange unit, a refrigerant circuit for circulating refrigerant between the heat exchange units, a compressor for increasing the pressure of the refrigerant in the refrigerant circuit, and indoor or outdoor heat exchange. An expansion valve that decompresses the refrigerant condensed in the unit, an indoor refrigerant state detector that detects the state of the refrigerant in the indoor heat exchange unit, and an outdoor refrigerant state detector that detects the state of the refrigerant in the outdoor heat exchange unit, A control unit that adjusts the opening of the expansion valve based on the state of the refrigerant detected by the refrigerant state detection means, and wherein the indoor and outdoor refrigerant state detection means By controlling the degree of opening of the expansion valve based on the detected state of the refrigerant, the degree of superheat of the refrigerant in the indoor or outdoor heat exchange unit is maintained within a predetermined range. Control method of an air conditioner which is characterized and.