Air conditioner

Abstract

To eliminate a pressure control valve for controlling an evaporation pressure of a refrigerant in an air conditioner.SOLUTION: A refrigerant circuit (50) of an air conditioner (10) includes a compressor (51), a condenser (52), an expansion valve (53), and an evaporator (54). The air conditioner (10) performs a refrigeration cycle by circulating a refrigerant in the refrigerant circuit (50), and cools air in the evaporator (54). The air conditioner (10) includes a pressure detecting unit (61) and a controller (70). The pressure detecting unit (61) detects the evaporation pressure of the refrigerant in the evaporator (54). The controller (70) controls the opening of the expansion valve (53) on the basis of the evaporation pressure detected by the pressure detecting unit (61).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an air conditioner.

Background Art

[0002] Conventionally, an air conditioner having a refrigerant circuit has been known. In the refrigerant circuit of the air conditioner, a refrigeration cycle is performed by circulating the refrigerant.

[0003] In an air conditioner, a pressure regulating valve may be provided downstream of the evaporator in the refrigerant circuit. Patent Document 1 discloses an air conditioner equipped with this pressure regulating valve. The air conditioner equipped with the pressure regulating valve adjusts the evaporation pressure of the refrigerant in the evaporator by adjusting the opening degree of the pressure regulating valve.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, in order to perform air conditioning of a test chamber that houses a large object such as a vehicle, a very high-capacity air conditioner is required. In such a high-capacity air conditioner, a very large-diameter (for example, an inner diameter of 200 mm or more) pipe member is used as the pipe through which the gaseous refrigerant flowing out from the evaporator flows. The pressure regulating valve attached to such a large-diameter pipe member becomes very large (for example, a height of 1500 mm or more and a weight of 200 kg or more).

[0006] When installing such a very large pressure regulating valve, the layout constraints when installing the air conditioner become large. In addition, since the pressure regulating valve is expensive, the cost required for introducing the air conditioner increases.

[0007] An object of the present disclosure is to omit a pressure regulating valve for regulating the evaporation pressure of a refrigerant in an air conditioner.

Means for Solving the Problems

[0008] A first aspect of the present disclosure is an air conditioner (10) including a refrigerant circuit (50) having a compressor (51), a condenser (52), an expansion valve (53), and an evaporator (54), circulating a refrigerant in the refrigerant circuit (50) to perform a refrigeration cycle, and cooling air in the evaporator (54), the air conditioner (10) including a pressure detection unit (61) for detecting the evaporation pressure of the refrigerant in the evaporator (54), and a controller (70) for controlling the opening degree of the expansion valve (53) based on the evaporation pressure detected by the pressure detection unit (61).

[0009] In the first aspect, the controller (70) controls the opening degree of the expansion valve (53) based on the evaporation pressure of the refrigerant detected by the pressure detection unit (61). When the opening degree of the expansion valve (53) changes, the pressure of the refrigerant flowing into the evaporator (54) changes, and as a result, the evaporation pressure of the refrigerant in the evaporator (54) changes. Therefore, while maintaining the function of the air conditioner (10) of "controlling the evaporation pressure of the refrigerant in the evaporator (54)", a pressure regulating valve for regulating the evaporation pressure can be omitted from the refrigerant circuit (50) of the air conditioner (10).

[0010] A second aspect of the present disclosure is, in the first aspect, the pressure detection unit (61) is provided between the expansion valve (53) and the evaporator (54) in the refrigerant circuit (50), and is a pressure sensor that measures the pressure of the refrigerant flowing from the expansion valve (53) toward the evaporator (54) as the evaporation pressure.

[0011] In the second aspect, a pressure sensor that measures the pressure of the refrigerant flowing from the expansion valve (53) toward the evaporator (54) constitutes the pressure detection unit (61) that detects the evaporation pressure of the refrigerant in the evaporator (54).

[0012] A third aspect of the present disclosure is that, in the above first or second aspect, the refrigerant circuit (50) includes a gas supply passage (55) that supplies the gas refrigerant discharged by the compressor (51) between the expansion valve (53) and the evaporator (54) in the refrigerant circuit (50), and a control valve (56) with variable opening degree provided in the gas supply passage (55). The controller (70) controls the opening degree of the control valve (56) based on the superheat degree of the refrigerant at the outlet of the evaporator (54) and the rotational speed of the compressor (51).

[0013] In a third aspect, the controller (70) controls the opening degree of the control valve (56) provided in the gas supply passage (55). When the opening degree of the control valve (56) changes, the flow rate of the gas refrigerant flowing through the gas supply passage (55) changes, and as a result, the state of the refrigerant flowing into the evaporator (54) changes. When the state of the refrigerant flowing into the evaporator (54) changes, the state of the refrigerant flowing out of the evaporator (54) changes, and as a result, the rotational speed of the compressor (51) may change. Therefore, the controller (70) controls the opening degree of the control valve (56) based on the superheat degree of the refrigerant at the outlet of the evaporator (54) and the rotational speed of the compressor (51).

[0014] A fourth aspect of the present disclosure is that, in the above third aspect, the controller (70) sets the opening degree of the control valve (56) determined to make the superheat degree of the refrigerant at the outlet of the evaporator (54) the set superheat degree as the first opening degree, and sets the opening degree of the control valve (56) determined to make the rotational speed of the compressor (51) the set speed as the second opening degree, and sets the opening degree of the control valve (56) to the larger one of the first opening degree and the second opening degree.

[0015] In a fourth aspect, the controller (70) sets the opening degree of the control valve (56) to the larger one of the first opening degree and the second opening degree. As a result, the superheat degree of the refrigerant at the outlet of the evaporator (54) is maintained at or above the set superheat degree, and the rotational speed of the compressor (51) is maintained at or above the set speed.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

[0017] An embodiment will be described. The air conditioner (10) of the present embodiment performs air conditioning of a test chamber (100) used for a driving test of an automobile or the like.

[0018] The air conditioner (10) includes a user side unit (20) and a heat source side unit (40). The air conditioner also includes a refrigerant circuit (50).

[0019] - User side unit - As shown in FIG. 1, the user side unit (20) is a so-called air handling unit. The user side unit (20) includes a casing (25). An intake port (27) is formed on one end surface of the casing (25), and an outlet port (28) is formed on the other end surface of the casing (25). An air flow path (26) is formed inside the casing (25) from the intake port (27) to the outlet port (28).

[0020] The user side unit (20) is connected to the test chamber (100) via an intake duct (16) and an outlet duct (17). The intake duct (16) is connected to the intake port (27) of the casing (25) and communicates the air flow path (26) with the internal space of the test chamber (100). The outlet duct (17) is connected to the outlet port (28) of the casing (25) and communicates the air flow path (26) with the internal space of the test chamber (100).

[0021] In the air flow path (26) within the casing (25), a filter (31), an evaporator (54), an electric heater (32), and a user-side fan (33) are provided in order from the suction port (27) side toward the blowout port (28) side. The filter (31) collects dust and the like contained in the air flowing in from the suction port (27). The evaporator (54) is connected to the refrigerant circuit (50) and cools the air. The electric heater (32) heats the air that has passed through the evaporator (54). The user-side fan (33) sucks in the air that has passed through the electric heater (32) and blows the air toward the blowout port (28).

[0022] 〈Operation〉 The operation of the user-side unit (20) will be described.

[0023] When the user-side fan (33) operates, the air in the internal space of the test chamber (100) flows into the air flow path (26) within the casing (25) through the suction duct (16). The air flowing through the air flow path (26) passes through the filter (31), the evaporator (54), and the electric heater (32) in sequence.

[0024] The air is cooled as it passes through the evaporator (54) and heated as it passes through the electric heater (32). Note that the electric heater (32) may temporarily stop heating the air. The air that has passed through the electric heater (32) is blown out from the user-side fan (33) and flows into the blowout duct (17), and then is blown out into the internal space of the test chamber (100).

[0025] -Air temperature sensor, heater controller- The air conditioner (10) includes an air temperature sensor (36) and a heater controller (37).

[0026] The air temperature sensor (36) is provided in the blowout duct (17) and measures the temperature of the air flowing through the blowout duct (17). The measured value of the air temperature sensor (36) indicates the temperature of the air that the user-side unit (20) supplies to the internal space of the test chamber (100).

[0027] The measured value of the air temperature sensor (36) is input to the heater controller (37). Based on the measured value of the air temperature sensor (36), the heater controller (37) controls the heating amount of the electric heater (32). Specifically, the heater controller (37) adjusts the heating amount of the electric heater (32) so that the measured value of the air temperature sensor (36) becomes the set air temperature. When the measured value of the air temperature sensor (36) is lower than the set air temperature, the heater controller (37) increases the heating amount of the electric heater (32). When the measured value of the air temperature sensor (36) is higher than the set air temperature, the heater controller (37) decreases the heating amount of the electric heater (32).

[0028] - Refrigerant circuit - The refrigerant circuit (50) is a closed circuit filled with refrigerant. The refrigerant circuit (50) performs a refrigeration cycle by circulating the refrigerant.

[0029] As shown in FIG. 2, the refrigerant circuit (50) includes a compressor (51), a condenser (52), an expansion valve (53), and an evaporator (54). In the refrigerant circuit (50), the condenser (52), the expansion valve (53), and the evaporator (54) are arranged in order from the discharge port to the suction port of the compressor (51).

[0030] The compressor (51) compresses and discharges the inhaled refrigerant. Although not shown, the compressor (51) includes a compression mechanism and an electric motor that drives the compression mechanism. The condenser (52) is a cross - fin type air heat exchanger that exchanges heat between the refrigerant and outdoor air. The expansion valve (53) is an electric expansion valve with variable opening degree. The evaporator (54) is a cross - fin type air heat exchanger that exchanges heat between the refrigerant and the air in the air flow path (26).

[0031] Also, the refrigerant circuit (50) includes a gas supply pipe (55). The gas supply pipe (55) constitutes a gas supply passage. One end of the gas supply pipe (55) is connected to the pipe between the discharge port of the compressor (51) and the condenser (52). The other end of the gas supply pipe (55) is connected to the pipe between the expansion valve (53) and the evaporator (54). A regulating valve (56) is provided in the gas supply pipe (55). The regulating valve (56) is an electric valve with variable opening degree.

[0032] 〈Refrigeration Cycle〉 The refrigeration cycle performed by the refrigerant circuit (50) will be described.

[0033] When the compressor (51) operates, the refrigerant circulates in the refrigerant circuit (50). The refrigerant discharged from the compressor (51) flows into the condenser (52), releases heat to the outdoor air passing through the condenser (52), and condenses. The refrigerant flowing out from the condenser (52) is depressurized in the process of passing through the expansion valve (53), and then flows into the evaporator (54).

[0034] In a state where the regulating valve is open, a part of the gaseous refrigerant (hot gas) discharged from the compressor flows into the gas supply pipe (55). The gaseous refrigerant flowing through the gas supply pipe (55) flows into the evaporator (54) together with the refrigerant that has passed through the expansion valve (53). The refrigerant flowing into the evaporator (54) absorbs heat from the air passing through the evaporator (54) and evaporates. The refrigerant flowing out from the evaporator (54) is sucked into the compressor (51) and compressed. The compressor (51) compresses and discharges the sucked refrigerant.

[0035] -Heat Source Unit- The heat source side unit (40) is provided with the compressor (51) and the condenser (52) of the refrigerant circuit (50). Further, the heat source side unit (40) includes a heat source side fan (41) and an inverter (42). The heat source side fan (41) supplies outdoor air to the condenser (52). Although not shown, an external power source such as a commercial power supply is connected to the inverter (42). The inverter (42) converts the supplied AC frequency to a set frequency and supplies the AC of the set frequency to the motor of the compressor (51). When the output frequency of the inverter (42) is changed, the rotational speed of the compressor (51) changes.

[0036] -Suction Pressure Sensor, Compressor Controller- The heat source side unit (40) includes a suction pressure sensor (46) and a compressor controller (47).

[0037] The suction pressure sensor (46) is connected to the refrigerant circuit (50). The suction pressure sensor (46) is attached to a pipe connected to the suction port of the compressor (51) and measures the pressure of the refrigerant sucked into the compressor (51).

[0038] The measured value of the suction pressure sensor (46) is input to the compressor controller (47). The compressor controller (47) is configured to control the rotational speed of the compressor (51) based on the measured value of the suction pressure sensor (46).

[0039] Specifically, the compressor controller (47) adjusts the rotational speed of the compressor (51) so that the measured value of the suction pressure sensor (46) becomes the set suction pressure. When the measured value of the suction pressure sensor (46) is lower than the set suction pressure, the compressor controller (47) decreases the rotational speed of the compressor (51) by decreasing the output frequency of the inverter (42). When the measured value of the suction pressure sensor (46) is higher than the set suction pressure, the compressor controller (47) increases the rotational speed of the compressor (51) by increasing the output frequency of the inverter (42).

[0040] - Sensor - The air conditioner (10) includes an inlet side pressure sensor (61), an outlet side pressure sensor (62), an outlet side temperature sensor (63), and a frequency sensor (64).

[0041] The inlet side pressure sensor (61), the outlet side pressure sensor (62), and the outlet side temperature sensor (63) are connected to the refrigerant circuit (50). The inlet side pressure sensor (61) is attached to a pipe connected to the inlet of the evaporator (54) and measures the pressure of the refrigerant flowing into the evaporator (54). The inlet side pressure sensor (61) is a pressure detection unit that detects the evaporation pressure of the refrigerant in the evaporator (54). The outlet side pressure sensor (62) and the outlet side temperature sensor (63) are attached to a pipe connected to the outlet of the evaporator (54). The outlet side pressure sensor (62) measures the pressure of the refrigerant flowing out of the evaporator (54). The outlet side temperature sensor (63) measures the temperature of the refrigerant flowing out of the evaporator (54).

[0042] The frequency sensor (64) is provided on the power supply electrical wiring that connects the inverter (42) to the motor of the compressor (51). The frequency sensor (64) measures the output frequency of the inverter (42). The measured value of the frequency sensor (64) is the frequency of the alternating current that the inverter (42) supplies to the compressor (51).

[0043] -Controller- The air conditioner (10) includes an expansion valve controller (75), a first controller (76), a second controller (77), and a selector (78). The expansion valve controller (75), the first controller (76), the second controller (77), and the selector (78) constitute a controller (70) that controls the expansion valve (53) and the regulating valve (56).

[0044] 〈Expansion Valve Controller〉 The measured value of the inlet side pressure sensor (61) is input to the expansion valve controller (75). The expansion valve controller (75) is configured to control the opening degree of the expansion valve (53) based on the measured value of the inlet side pressure sensor (61).

[0045] Specifically, the expansion valve controller (75) calculates the opening degree of the expansion valve (53) such that the measured value of the inlet side pressure sensor (61) becomes the set evaporation pressure, and determines the calculated opening degree as the third command value regarding the opening degree of the expansion valve (53). The expansion valve controller (75) transmits the determined third command value to the expansion valve (53). As a result, the opening degree of the expansion valve (53) becomes the opening degree corresponding to the third command value.

[0046] When the measured value of the inlet side pressure sensor (61) is lower than the set evaporation pressure, the expansion valve controller (75) transmits, as the third command value, an opening degree larger than the current opening degree of the expansion valve (53) to the expansion valve (53). The opening degree of the expansion valve (53) expands to the opening degree corresponding to the third command value. When the opening degree of the expansion valve (53) expands, the pressure of the refrigerant at the outlet of the expansion valve (53) rises. As a result, the pressure of the refrigerant flowing into the evaporator (54) rises, and the evaporation pressure of the refrigerant in the evaporator (54) rises.

[0047] When the measured value of the inlet-side pressure sensor (61) is higher than the set evaporation pressure, the expansion valve controller (75) sends a smaller opening degree than the current opening degree of the expansion valve (53) to the expansion valve (53) as the third command value. The opening degree of the expansion valve (53) is reduced to the opening degree corresponding to the third command value. When the opening degree of the expansion valve (53) is reduced, the pressure of the refrigerant at the outlet of the expansion valve (53) decreases. As a result, the pressure of the refrigerant flowing into the evaporator (54) decreases, and the evaporation pressure of the refrigerant in the evaporator (54) decreases.

[0048] <First Controller> The measured value of the outlet-side pressure sensor (62) and the measured value of the outlet-side temperature sensor (63) are input to the first controller (76). The first controller (76) is configured to calculate a first command value regarding the opening degree of the regulating valve (56) based on the measured values of the outlet-side pressure sensor (62) and the outlet-side temperature sensor (63).

[0049] First, the first controller (76) calculates the superheat degree of the refrigerant at the outlet of the evaporator (54). The first controller (76) sets the value obtained by subtracting "the saturation temperature Ts of the refrigerant corresponding to the measured value of the outlet-side pressure sensor (62)" from "the measured value T of the outlet-side temperature sensor (63)" as the superheat degree SH (= T - Ts) of the refrigerant at the outlet of the evaporator (54).

[0050] Next, the first controller (76) calculates the opening degree of the regulating valve (56) such that the superheat degree of the refrigerant at the outlet of the evaporator (54) becomes the set superheat degree. The opening degree calculated by this first controller (76) is the first opening degree. The first controller (76) determines the calculated first opening degree as the first command value regarding the opening degree of the regulating valve (56). The first controller (76) sends the determined first command value to the selector (78).

[0051] Here, when the refrigerant at the outlet of the evaporator (54) becomes wet, liquid refrigerant may be sucked into the compressor (51), and as a result, the compressor (51) may be damaged. Therefore, in order to prevent damage to the compressor (51), it is necessary to keep the refrigerant at the outlet of the evaporator (54) in a gas single-phase state.

[0052] On the one hand, when the opening degree of the regulating valve (56) is changed, the flow rate of the gas refrigerant flowing through the gas supply pipe (55) changes. Therefore, the state of the refrigerant flowing into the evaporator (54) changes, and as a result, the state of the refrigerant at the outlet of the evaporator (54) changes. Thus, the first controller (76) calculates the opening degree of the regulating valve (56) such that the superheat degree of the refrigerant at the outlet of the evaporator (54) becomes the set superheat degree.

[0053] When the opening degree of the regulating valve (56) expands, the flow rate of the gas refrigerant flowing through the gas supply pipe (55) increases. Therefore, the moisture content of the refrigerant flowing into the evaporator (54) decreases, and as a result, the superheat degree of the refrigerant at the outlet of the evaporator (54) rises. Thus, when the superheat degree of the refrigerant at the outlet of the evaporator (54) is lower than the set superheat degree, the second controller (77) determines a larger opening degree than the current opening degree of the regulating valve (56) as the first command value.

[0054] On the other hand, when the opening degree of the regulating valve (56) contracts, the flow rate of the gas refrigerant flowing through the gas supply pipe (55) decreases. Therefore, the moisture content of the refrigerant flowing into the evaporator (54) increases, and as a result, the superheat degree of the refrigerant at the outlet of the evaporator (54) drops. Thus, when the superheat degree of the refrigerant at the outlet of the evaporator (54) is higher than the set superheat degree, the second controller (77) determines a smaller opening degree than the current opening degree of the regulating valve (56) as the first command value.

[0055] 〈Second Controller〉 The measured value of the frequency sensor (64) is input to the second controller (77). The second controller (77) is configured to calculate a second command value regarding the opening degree of the regulating valve (56) based on the measured value of the frequency sensor (64).

[0056] Specifically, the second controller (77) calculates the opening degree of the regulating valve (56) such that the measured value of the frequency sensor (64) becomes the set frequency. The opening degree calculated by this second controller (77) is the second opening degree. The second controller (77) determines the calculated second opening degree as the second command value regarding the opening degree of the regulating valve (56). The second controller (77) transmits the determined second command value to the selector (78).

[0057] Here, when the rotational speed of the compressor (51) is low, the flow rate of the refrigerant flowing through the refrigerant circuit (50) becomes low, and the refrigerating machine oil discharged together with the refrigerant from the compressor (51) tends to stay in the evaporator (54), piping, etc. Therefore, when the compressor (51) operates for a long time at a relatively low rotational speed (for example, a state of 20% or less of the maximum rotational speed), the amount of refrigerating machine oil staying outside the compressor (51) increases, and the amount of refrigerating machine oil remaining inside the compressor (51) decreases. As a result, the amount of refrigerating machine oil supplied to the sliding part of the compressor (51) becomes insufficient, and the compressor (51) may be damaged.

[0058] On the other hand, if the rotational speed of the compressor (51) is maintained at a relatively high rotational speed (for example, 80% or more of the maximum rotational speed), the amount of refrigerating machine oil returning to the compressor (51) together with the refrigerant is ensured. Therefore, the amount of refrigerating machine oil stored in the compressor (51) is sufficiently ensured, and damage to the compressor (51) is prevented.

[0059] Therefore, the second controller (77) calculates the opening degree of the regulating valve (56) such that the measured value of the frequency sensor (64) becomes the set frequency. The measured value of the frequency sensor (64) is the actually measured value of the output frequency of the inverter (42). Therefore, when the measured value of the frequency sensor (64) becomes the set frequency, the rotational speed of the compressor (51) becomes the set speed, and as a result, the amount of refrigerating machine oil returning to the compressor (51) together with the refrigerant is ensured.

[0060] Here, when the cooling load of the evaporator (54) (specifically, the amount of heat that the refrigerant takes from the air in the evaporator (54)) becomes small, the amount of refrigerant evaporating in the evaporator (54) decreases, so the measured value of the suction pressure sensor (46) decreases. Therefore, if nothing is done, the compressor controller (47) decreases the rotational speed of the compressor (51) in order to keep the measured value of the suction pressure sensor (46) at the set suction pressure. In such a case, by increasing the flow rate of the gas refrigerant flowing through the gas supply pipe (55), the decrease in the rotational speed of the compressor (51) can be suppressed.

[0061] The reason will be explained. The refrigerant passing through the expansion valve (53) and the gaseous refrigerant flowing through the gas supply pipe (55) flow into the evaporator (54) after being mixed. A part of the liquid refrigerant contained in the refrigerant passing through the expansion valve (53) is heated by the gaseous refrigerant flowing in from the gas supply pipe (55) and evaporates. Therefore, when the opening degree of the regulating valve (56) is enlarged and the flow rate of the gaseous refrigerant flowing through the gas supply pipe (55) increases, the amount of the gaseous refrigerant sucked by the compressor (51) from the evaporator (54) increases. As a result, the decrease in the measured value of the suction pressure sensor (46) is suppressed, and the decrease in the rotational speed of the compressor (51) is also suppressed.

[0062] Therefore, when the measured value of the frequency sensor (64) is lower than the set frequency, the second controller (77) determines a second command value to be an opening degree larger than the current opening degree of the regulating valve (56).

[0063] On the other hand, when the measured value of the frequency sensor (64) is higher than the set frequency, there is a possibility that the rotational speed of the compressor (51) can be maintained at the set speed or higher even if the opening degree of the regulating valve (56) is reduced. Therefore, when the measured value of the frequency sensor (64) is higher than the set frequency, the second controller (77) determines a second command value to be an opening degree smaller than the current opening degree of the regulating valve (56).

[0064] By the way, when the opening degree of the regulating valve (56) changes greatly in a short time, the pressure of the refrigerant flowing into the evaporator (54) changes, and accordingly, the expansion valve controller (75) may change the opening degree of the expansion valve (53). Therefore, the second controller (77) determines the second command value so that the change in the opening degree of the regulating valve (56) is a gentle change to such an extent that the measured value of the inlet side pressure sensor (61) is substantially kept constant.

[0065] 〈Selector〉 The selector (78) receives the first command value output by the first controller (76) and the second command value output by the second controller (77). The selector (78) is configured to compare the first command value and the second command value and transmit the larger one of the first command value and the second command value to the regulating valve (56).

[0066] The regulating valve (56) sets its opening degree to the opening degree corresponding to the received one of the first command value and the second command value. As described above, the opening degree of the regulating valve (56) corresponding to the first command value is the first opening degree, and the opening degree of the regulating valve (56) corresponding to the second command value is the second opening degree. Therefore, the opening degree of the regulating valve (56) is set to the larger one of the first opening degree and the second opening degree.

[0067] The first opening degree is the opening degree of the regulating valve (56) determined by the first controller (76) so that the superheat degree of the refrigerant at the outlet of the evaporator (54) becomes the set superheat degree. The second opening degree is the opening degree of the regulating valve (56) determined by the second controller (77) so that the measured value of the frequency sensor (64) becomes the set frequency.

[0068] When the first command value is larger than the second command value, the selector (78) transmits the first command value to the regulating valve (56). Therefore, the opening degree of the regulating valve (56) is set to the first opening degree, and the superheat degree of the refrigerant at the outlet of the evaporator (54) becomes the set superheat degree. Accordingly, the refrigerant sucked into the compressor (51) is kept in a gas single-phase state, and damage to the compressor (51) caused by sucking liquid refrigerant is avoided.

[0069] In this case, the first opening degree corresponding to the first command value is larger than the second opening degree corresponding to the second command value. Therefore, when the opening degree of the regulating valve (56) is set to the first opening degree, the measured value of the frequency sensor (64) becomes higher than the set frequency, and as a result, the rotational speed of the compressor (51) becomes higher than the set speed. Accordingly, a sufficient amount of the refrigerant oil returning to the compressor (51) together with the refrigerant is ensured, and damage to the compressor (51) caused by a shortage of the refrigerant oil is avoided.

[0070] When the second command value is greater than the first command value, the selector (78) sends the second command value to the control valve (56). Therefore, the opening degree of the control valve (56) is set to the second opening degree, and the output frequency of the inverter (42) becomes the set frequency. As a result, the rotational speed of the compressor (51) becomes the set speed. Accordingly, a sufficient amount of refrigerant oil returning to the compressor (51) together with the refrigerant is ensured, and damage to the compressor (51) caused by a shortage of refrigerant oil is avoided.

[0071] In this case, the second opening degree corresponding to the second command value is larger than the first opening degree corresponding to the first command value. Therefore, when the opening degree of the control valve (56) is set to the second opening degree, the superheat degree of the refrigerant at the outlet of the evaporator (54) becomes higher than the set superheat degree. Accordingly, the refrigerant sucked into the compressor (51) is kept in a gas single-phase state, and damage to the compressor (51) caused by sucking liquid refrigerant is avoided.

[0072] - Feature (1) of the embodiment - In the air conditioner of the present embodiment, the controller (70) controls the opening degree of the expansion valve (53) based on the measured value of the inlet side pressure sensor (61). That is, the controller (70) controls the opening degree of the expansion valve (53) based only on the evaporation pressure of the refrigerant in the evaporator (54). When the opening degree of the expansion valve (53) changes, the pressure of the refrigerant flowing into the evaporator (54) changes, and as a result, the evaporation pressure of the refrigerant in the evaporator (54) changes.

[0073] Therefore, according to the present embodiment, while maintaining the function of the air conditioner (10) of "controlling the evaporation pressure of the refrigerant in the evaporator (54)", a pressure regulating valve for adjusting the evaporation pressure can be omitted from the refrigerant circuit (50) of the air conditioner (10). As a result, the layout constraints when installing the air conditioner (10) can be reduced. In addition, since an expensive pressure regulating valve can be omitted, the cost required for introducing the air conditioner (10) can be reduced.

[0074] - Feature (2) of the embodiment - In the air conditioner according to this embodiment, the controller (70) controls the opening degree of the regulating valve (56) provided in the gas supply pipe (55). When the opening degree of the regulating valve (56) changes, the flow rate of the gas refrigerant flowing through the gas supply pipe (55) changes, and as a result, the state of the refrigerant flowing into the evaporator (54) changes.

[0075] When the state of the refrigerant flowing into the evaporator (54) changes, the state of the refrigerant flowing out of the evaporator (54) changes, and further, the state of the refrigerant sucked by the compressor (51) changes. When the state of the refrigerant sucked by the compressor (51) changes, the rotational speed of the compressor (51) may change by the control operation of the compressor controller (47). Therefore, the controller (70) controls the opening degree of the regulating valve (56) based on the superheat degree of the refrigerant at the outlet of the evaporator (54) and the rotational speed of the compressor (51).

[0076] - Feature (3) of the embodiment - In the air conditioner according to this embodiment, the selector (78) of the controller (70) transmits the larger one of the first command value and the second command value to the regulating valve (56). As a result, the opening degree of the regulating valve (56) is set to the larger one of "the first opening degree corresponding to the first command value" and "the second opening degree corresponding to the second command value".

[0077] Due to the function of this selector (78), the superheat degree of the refrigerant at the outlet of the evaporator (54) is maintained at or above the set superheat degree. As a result, the refrigerant sucked into the compressor (51) is maintained in a gas single-phase state, and damage to the compressor (51) caused by sucking liquid refrigerant is avoided.

[0078] Also, due to the function of this selector (78), the rotational speed of the compressor (51) is maintained at or above the set speed. As a result, a sufficient amount of refrigerant oil returning to the compressor (51) together with the refrigerant is ensured, and damage to the compressor (51) caused by a shortage of refrigerant oil is avoided.

[0079] 《Other embodiments》 Regarding the air conditioner (10) of the above embodiment, the following modifications may be applied. Note that the following modifications may be appropriately combined or replaced as long as the functions of the air conditioner (10) are not impaired.

[0080] The object for which the air conditioner (10) of this embodiment performs air conditioning is not limited to the laboratory (100). The air conditioner (10) of this embodiment may be used, for example, for air conditioning large spaces such as halls.

[0081] Also, in the air conditioner (10) of this embodiment, the controller (70) may be constituted by a single microcomputer. In this case, the control operations performed by each of the expansion valve controller (75), the first controller (76), the second controller (77), and the selector (78) are performed by the microcomputer constituting the controller (70). Further, in this case, the microcomputer constituting the controller (70) may be configured to perform the control operations performed by one or both of the heater controller (37) and the compressor controller (47).

[0082] Although the embodiment and the modification have been described above, it will be understood that various changes in form and detail are possible without departing from the spirit and scope of the claims. Also, the elements according to the above embodiment, modification, and other embodiments may be appropriately combined or replaced. Also, the descriptions such as "first", "second", "third",... in the specification and the claims are used to distinguish the clauses to which these descriptions are attached, and do not limit even the number and order of these clauses.

Industrial Applicability

[0083] As described above, the present disclosure is useful for air conditioners.

Explanation of Signs

[0084] 10 Air conditioner 50 Refrigerant circuit 51 Compressor 52 Condenser 53 Expansion valve 54 Evaporator 55 Gas supply pipe (gas supply passage) 56 Control valve 61 Inlet side pressure sensor (pressure detection unit) 70 Controller

Claims

1. An air conditioner (10) comprising a refrigerant circuit (50) having a compressor (51), a condenser (52), an expansion valve (53), and an evaporator (54), circulating refrigerant in the refrigerant circuit (50) to perform a refrigeration cycle, and cooling air in the evaporator (54), a pressure detection unit (61) for detecting the evaporation pressure of the refrigerant in the evaporator (54), and a controller (70) for controlling the opening degree of the expansion valve (53) based on the evaporation pressure detected by the pressure detection unit (61). Air conditioner.

2. The pressure detection unit (61) is a pressure sensor provided between the expansion valve (53) and the evaporator (54) in the refrigerant circuit (50), and measuring the pressure of the refrigerant flowing from the expansion valve (53) toward the evaporator (54) as the evaporation pressure. The air conditioner according to Claim 1.

3. The refrigerant circuit (50) is provided with a gas supply passage (55) for supplying the gas refrigerant discharged from the compressor (51) between the expansion valve (53) and the evaporator (54) in the refrigerant circuit (50), and an adjustable valve (56) with variable opening degree provided in the gas supply passage (55). The controller (70) controls the opening degree of the adjustable valve (56) based on the superheat degree of the refrigerant at the outlet of the evaporator (54) and the rotational speed of the compressor (51). The air conditioner according to Claim 1 or 2.

4. The controller (70) is taking the opening degree of the adjustable valve (56) determined to set the superheat degree of the refrigerant at the outlet of the evaporator (54) to the set superheat degree as the first opening degree, taking the opening degree of the adjustable valve (56) determined to set the rotational speed of the compressor (51) to the set speed as the second opening degree, and setting the opening degree of the adjustable valve (56) to the larger one of the first opening degree and the second opening degree. The air conditioner according to Claim 3.

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