Refrigeration circuit

Abstract

To quickly and accurately control the temperature of a cooling load by simplifying the control of the refrigerant flow rate of the evaporator of a refrigerating circuit.SOLUTION: This air conditioner is provided with a compressor 2, a condenser 3, an expansion valve 4 and an evaporator 5 connected by a pipeline 6. The expansion valves 4 include an upstream electronic expansion valves 4a and a downstream electronic expansion valves 4b connected in series. The air conditioner further includes an inlet-side temperature sensor 7a and an outlet-side temperature sensor 7b disposed at a refrigerant inlet and a refrigerant outlet of the evaporators, respectively, a first expansion valve control part 8 that calculates a degree of superheat from a difference between a measurement value of the outlet-side temperature sensor and a measurement value of the inlet-side temperature sensor and controls an opening degree of the upstream electronic expansion valve based on the calculated value, a temperature sensor 9 for measuring a temperature of gas cooled by the evaporators, and a second expansion valve control part 10 that controls an opening degree of the downstream electronic expansion valve based on measurement values of the temperature sensors.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a refrigeration circuit. [Background technology]

[0002] The refrigeration circuit comprises a compressor, a condenser, an expansion valve, and an evaporator connected in this order by pipes in a ring, and the refrigerant sealed in the refrigerant circuit circulates through repeated cycles of compression, condensation, expansion, and evaporation.

[0003] The compressor of the refrigeration circuit compresses the low-pressure gaseous refrigerant and discharges a high-temperature, high-pressure gaseous refrigerant. The high-temperature, high-pressure gaseous refrigerant flows into the condenser, where it is cooled by outside air or cooling water and condenses into a high-pressure liquid refrigerant.

[0004] The high-pressure liquid refrigerant is rapidly decompressed by passing through the expansion valve, during which time some of the refrigerant vaporizes and the refrigerant itself is cooled by the heat of vaporization, becoming a low-temperature, low-pressure gas-liquid mixture. The gas-liquid mixture enters the evaporator, where it continues to evaporate while absorbing heat, cooling the inside of the evaporator.

[0005] The refrigerant vaporizes completely when it leaves the evaporator, becoming a low-pressure gaseous refrigerant. The low-pressure gaseous refrigerant is then drawn into the compressor, where it becomes a high-temperature, high-pressure gaseous refrigerant again, and the cycle is repeated.

[0006] Thus, the evaporator forms a cooling section (a heat exchanger on the cooling side), and the condenser forms a heating section (a heat exchanger on the heating side). The evaporator is disposed, for example, in an air conditioner that circulates indoor air, and the indoor air is cooled while the refrigerant evaporates in the evaporator.

[0007] With this configuration, if a sudden change in the temperature of the indoor air (cooling load) causes the refrigerant flow rate to become excessive for the cooling load (the refrigerant flow rate becomes too high for the indoor air temperature), the refrigerant will not completely vaporize in the evaporator and some of the refrigerant will flow into the compressor in a liquid state (the occurrence of so-called ``liquid back''), which may cause the compressor to malfunction due to liquid compression.

[0008] To prevent this, in conventional technology, the degree of superheat, which is the temperature difference between the refrigerant outlet and inlet of the evaporator, and the temperature of the cooling load are measured, and the opening of the expansion valve is controlled based on the degree of superheat and the temperature of the cooling load to adjust the refrigerant flow rate of the evaporator.

[0009] This can be achieved, for example, by switching between control of the expansion valve opening based on the degree of superheat and control of the expansion valve opening based on the temperature of the cooling load each time (see, for example, Patent Document 1), by switching between controls while continuously and automatically changing the ratio between control of the expansion valve opening based on the degree of superheat and control of the expansion valve opening based on the temperature of the cooling load (see, for example, Patent Document 2), or by setting a suppression value for suppressing the expansion valve opening based on the degree of superheat and the set superheat, and controlling the expansion valve opening based on the temperature of the cooling load within a range that does not exceed the suppression value (see, for example, Patent Document 3).

[0010] However, according to these conventional techniques, the mechanism for controlling the refrigerant flow rate of the evaporator becomes very complicated, and it is not possible to quickly and accurately maintain the temperature of the cooling load at the set temperature. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Special Publication No. 2-39710 [Patent Document 2] Japanese Patent Application Publication No. 9-4955 [Patent Document 3] Special Publication No. 8-16556 Summary of the Invention [Problem to be solved by the invention]

[0012] SUMMARY OF THE INVENTION It is therefore an object of the present invention to simplify the control of the refrigerant flow rate in the evaporator of the refrigeration circuit, and to enable rapid and accurate temperature control of the cooling load. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, according to the present invention, there is provided a refrigeration circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected in this order in a ring shape by pipes, and the refrigeration circuit comprises a pair of electronic expansion valves connected in series to each other, and the expansion valve is provided with: a superheat sensor arranged at a refrigerant outlet of the evaporator, or at the refrigerant outlet and refrigerant inlet, for measuring the superheat of the refrigerant at the refrigerant outlet; a first expansion valve control unit arranged to control an aperture of the upstream electronic expansion valve of the pair of electronic expansion valves based on a measurement value of the superheat sensor; a temperature sensor arranged to measure a temperature of gas cooled by the evaporator; and a second expansion valve control unit arranged to control an aperture of the downstream electronic expansion valve of the pair of electronic expansion valves based on a measurement value of the temperature sensor, wherein the first expansion valve control unit controls the aperture of the upstream electronic expansion valve so that the measurement value of the superheat sensor becomes a predetermined constant value or is within a predetermined numerical range, and the second expansion valve control unit controls the aperture of the downstream electronic expansion valve so that the temperature of the gas to be cooled becomes a predetermined temperature.

[0014] According to a preferred embodiment of the present invention, the superheat sensor comprises an inlet-side temperature sensor arranged at the refrigerant inlet of the evaporator and an outlet-side temperature sensor arranged at the refrigerant outlet of the evaporator, and the degree of superheat is calculated by the first expansion valve control unit as the difference between the measurement value of the outlet-side temperature sensor and the measurement value of the inlet-side temperature sensor.

[0015] According to another preferred embodiment of the present invention, the superheat sensor comprises a pressure sensor arranged at the refrigerant outlet of the evaporator, and the superheat is calculated by the first expansion valve control unit from a measurement value of the pressure sensor. [Effects of the Invention]

[0016] According to the present invention, the expansion valve of the refrigeration circuit is composed of a pair of electronic expansion valves connected in series with each other, and the opening degree of the upstream electronic expansion valve of the pair of electronic expansion valves is controlled based on the superheat degree of the refrigerant at the refrigerant outlet of the evaporator, while the opening degree of the downstream electronic expansion valve of the pair of electronic expansion valves is controlled based on the temperature of the gas (cooling load) cooled by the evaporator.Since the control of the expansion valve based on the superheat degree and the control of the expansion valve based on the temperature of the cooling load are performed independently, control of the refrigerant flow rate in the refrigeration circuit is simplified more than before, thereby enabling faster and more accurate temperature control of the cooling load while preventing liquid backflow. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram showing a schematic configuration of a refrigeration circuit according to an embodiment of the present invention. [Figure 2] 1. FIG. 3 is a view similar to FIG. 1, showing a modification of the refrigeration circuit of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the configuration of the present invention will be described based on a preferred embodiment with reference to the accompanying drawings. FIG. 1 is a diagram showing a refrigeration circuit according to one embodiment of the present invention. Referring to FIG. 1, a refrigeration circuit 1 of the present invention comprises a compressor 2, a condenser 3, an expansion valve 4, and an evaporator 5, which are connected in this order by a pipe 6 in a ring shape.

[0019] The expansion valve 4 is made up of a pair of electronic expansion valves (an upstream electronic expansion valve 4a and a downstream electronic expansion valve 4b) connected in series to each other.

[0020] The refrigeration circuit 1 of the present invention also includes a superheat sensor for measuring the superheat of the refrigerant at the refrigerant outlet of the evaporator 5. In this embodiment, the superheat sensor comprises an inlet temperature sensor 7 a arranged at the refrigerant inlet of the evaporator 5 and an outlet temperature sensor 7 b arranged at the refrigerant outlet of the evaporator 5 .

[0021] Furthermore, the refrigeration circuit 1 of the present invention includes a first expansion valve control unit 8 that controls the opening degree of the upstream electronic expansion valve 4a based on the measurement value of the superheat sensor.

[0022] Then, the first expansion valve control unit 8 calculates the difference Δt = t2 - t1 between the measurement value t2 of the outlet side temperature sensor 7b and the measurement value t1 of the inlet side temperature sensor 7a, and this calculated value is used as the measurement value of the degree of superheat.

[0023] In this embodiment, the superheat sensor is composed of inlet and outlet temperature sensors 7a, 7b arranged at the refrigerant inlet and outlet of the evaporator 5, respectively. However, the configuration of the superheat sensor is not limited to this. Instead, the superheat sensor can be composed of a pressure sensor 11 arranged at the refrigerant outlet of the evaporator 5, for example, as shown in FIG. 2.

[0024] In the configuration example shown in FIG. 2, the degree of superheat is calculated by the first expansion valve control unit 8 from the measurement value of the pressure sensor 11.

[0025] The refrigeration circuit 1 of the present invention further includes a temperature sensor 9 for measuring the temperature of the gas (cooling load) cooled by the evaporator 5, and a second expansion valve control unit 10 for controlling the opening degree of the downstream electronic expansion valve 4b based on the measurement value of the temperature sensor 9.

[0026] The first expansion valve control unit 8 controls the opening degree of the upstream electronic expansion valve 4a so that the measured value of the degree of superheat becomes a predetermined constant value or is within a predetermined numerical range, while the second expansion valve control unit 10 controls the opening degree of the downstream electronic expansion valve 4b so that the temperature of the cooling load becomes a predetermined temperature.

[0027] According to the present invention, the expansion valve of the refrigeration circuit is composed of a pair of electronic expansion valves connected in series with each other, and the opening degree of the upstream electronic expansion valve of the pair of electronic expansion valves is controlled based on the superheat degree of the refrigerant at the refrigerant outlet of the evaporator, while the opening degree of the downstream electronic expansion valve of the pair of electronic expansion valves is controlled based on the temperature of the gas (cooling load) cooled by the evaporator.Since the control of the expansion valve based on the superheat degree and the control of the expansion valve based on the temperature of the cooling load are performed independently, control of the refrigerant flow rate in the refrigeration circuit is simplified more than before, thereby enabling faster and more accurate temperature control of the cooling load while preventing liquid backflow. [Explanation of symbols]

[0028] 1 Refrigeration circuit 2 Compressor 3. Condenser 4 Expansion valve 4a Upstream electronic expansion valve 4b Downstream electronic expansion valve 5. Evaporator 6 conduit 7a Inlet temperature sensor 7b Outlet temperature sensor 8 First expansion valve control section 9 Temperature Sensor 10 Second expansion valve control section 11 Pressure Sensor

Claims

1. A refrigeration circuit in which a compressor, a condenser, an expansion valve, and an evaporator are connected in this order in a ring by pipes, The expansion valve comprises a pair of electronic expansion valves connected in series with each other, a superheat sensor disposed at a refrigerant outlet of the evaporator, or at both the refrigerant outlet and the refrigerant inlet, for measuring a superheat of the refrigerant at the refrigerant outlet; a first expansion valve control unit that controls an opening degree of the upstream electronic expansion valve of the pair of electronic expansion valves based on a measurement value of the superheat sensor; a temperature sensor for measuring the temperature of the gas cooled by the evaporator; a second expansion valve control unit that controls the opening degree of the downstream electronic expansion valve of the pair of electronic expansion valves based on the measurement value of the temperature sensor, The first expansion valve control unit controls the opening degree of the upstream electronic expansion valve so that the measurement value of the superheat sensor becomes a predetermined constant value or is within a predetermined numerical range, and The second expansion valve control unit controls the opening degree of the downstream electronic expansion valve so that the temperature of the gas to be cooled becomes a predetermined temperature.

2. The superheat sensor is an inlet temperature sensor disposed at the refrigerant inlet of the evaporator; an outlet-side temperature sensor disposed at the refrigerant outlet of the evaporator; 2. The refrigeration circuit according to claim 1, wherein the degree of superheat is calculated by the first expansion valve control unit as a difference between a value measured by the outlet-side temperature sensor and a value measured by the inlet-side temperature sensor.

3. The superheat sensor is a pressure sensor disposed at the refrigerant outlet of the evaporator; 2. The refrigeration circuit according to claim 1, wherein the degree of superheat is calculated by the first expansion valve control unit from the measurement value of the pressure sensor.

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