JP2003004316A - Method for controlling refrigeration unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigeration cycle capable of making an adjustment to a pressure for surely obtaining an optimum efficiency, i.e., surely enabling change of refrigerating capacity, and having a high efficiency and a high capacity by employing the steps of detecting pressure and temperature at an inlet of an expansion valve and calculating a specific enthalpy value of a refrigerant as shown in the table of Fig. 5, in a refrigeration unit using the refrigeration cycle wherein a supercritical fluid is used as the refrigerant and the refrigerant is heat-exchanged at an inlet side and an outlet side of a gas cooler. SOLUTION: The refrigeration unit comprises a flow control valve 11 for controlling quantity of internal heat exchange, a pressure detecting means 7 at an inlet of the expansion valve and a temperature detecting means 8. The specific enthalpy of the refrigerant is calculated so that an operation by employing an optimum refrigeration cycle is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a vapor compression cycle having an internal heat exchanger for exchanging heat between refrigerant flowing through an inlet side pipe of a compressor and an outlet side pipe of a gas cooler. The present invention relates to a method for controlling a refrigeration system that uses a fluid that exceeds a critical point on the high pressure side as a refrigerant.

[0002]

2. Description of the Related Art In recent years, a vapor compression refrigeration cycle using, for example, carbon dioxide (CO2) has been proposed as one of the measures for dechlorofluorocarbon removal of the refrigerant used in the vapor compression refrigeration cycle. However, in the vapor compression refrigeration cycle using carbon dioxide whose high pressure side exceeds the critical point, the supercooling degree control method used in the Freon cycle cannot be used, and some kind of capacity control method is required. . Further, in the CO2 cycle, the refrigerating capacity and COP (coefficient of performance) are inferior to those in the Freon cycle. Therefore, in order to improve this, there is an example of a cycle control method as disclosed in Japanese Patent Publication No. 7-294033. . This example will be described with reference to FIG. 11. First, the refrigerant temperature at the gas cooler outlet is detected (S100), and the optimum high pressure of the refrigerant flowing through the high pressure passage is calculated from this refrigerant temperature (S10).
1) It is determined whether the actual high pressure in the high pressure passage is higher than the optimum high pressure (S102). As a result, when it is determined that the actual high pressure is large, the opening of the expansion valve is controlled to be increased to reduce the high pressure (S103). When it is determined that the actual high pressure is small, the high pressure is increased by controlling the opening degree of the expansion valve to a smaller direction. As mentioned above,
In the CO2 cycle in which the pressure of the gas cooler exceeds the critical pressure, the refrigerating capacity and the COP depend on the high pressure, and it is known that the COP becomes the best at a certain pressure (10 to 15 MPa). For example, in the summer when the temperature at the inlet of the expansion valve is around 40 degrees, as shown in FIG. 12, the high pressure β at which the COP becomes maximum α exists. This is because, when CO2 is used as a refrigerant, there is an optimum high pressure value that is efficient and efficient with respect to the refrigerant temperature on the inlet side of the expansion valve.

[0003]

By the way, although the method of calculating the optimum high pressure from the refrigerant temperature is simple as described above, the discharge pressure of the compressor and the inlet pressure of the expansion valve are different when the refrigerant circulation amount changes. Since the loss also greatly changes, the calculation formula becomes very complicated in order to actually adjust the discharge pressure to a pressure that provides optimum efficiency. In particular, when the high pressure is in the range of 8 MPa to 10 MPa, the slope of the isotherm in the supercritical region becomes extremely small. Therefore, in consideration of the correction when performing calculations with multiple detectors, it is necessary to actually control to the optimum high pressure. Is difficult in reality. That is, since it is difficult to adjust the pressure to obtain the optimum efficiency, it is also difficult to provide a refrigeration cycle with high efficiency and high capacity.

Therefore, in the present invention, in a refrigeration cycle in which a supercritical fluid is used as a refrigerant and an internal heat exchanger for exchanging heat between the gas cooler outlet side and the compressor inlet side is provided, By detecting the temperature and pressure at the inlet of the expansion valve and calculating the specific enthalpy value of the refrigerant as in the table shown in FIG. 5, it is possible to reliably adjust the pressure to the optimum efficiency, that is, reliably. It is an object of the present invention to provide a highly efficient and highly efficient refrigeration cycle by making it possible to increase or decrease the refrigeration capacity.

[0005]

A method for controlling a refrigerating apparatus according to the present invention is a fluid flowing through a compressor, a gas cooler, an outlet side pipe of the gas cooler and an inlet side pipe of the compressor. An internal heat exchanger for exchanging heat, an expansion valve, and an evaporator are annularly connected to each other to form a vapor compression cycle, and the fluid that exceeds the critical point on the high pressure side of the vapor compression cycle A method for controlling a refrigeration apparatus used as a refrigerant, comprising: a temperature detecting means for detecting a refrigerant temperature on the expansion valve inlet side; and a pressure detecting means for detecting a refrigerant pressure on the expansion valve inlet side, wherein the temperature detection Calculating a specific enthalpy value at the expansion valve inlet from the detected temperature detected by the means and the detected pressure detected by the pressure detecting means, and controlling the opening degree of the expansion valve based on the specific enthalpy value. The features. The method for controlling a refrigeration system of the present invention according to claim 2 is a compressor, a gas cooler, and an internal heat exchanger for exchanging heat between fluids flowing through an outlet side pipe of the gas cooler and an inlet side pipe of the compressor. , An expansion valve, a receiver, and an evaporator are annularly connected to each other to form a vapor compression cycle, and a pipe from the receiver and the outlet of the evaporator to the inlet of the internal heat exchanger Of a refrigerating apparatus that has a bypass circuit connecting with and an internal heat exchange amount adjusting valve that adjusts the flow rate of the refrigerant flowing through the bypass circuit, and that uses the fluid that exceeds the critical point on the high pressure side of the vapor compression cycle as the refrigerant. A control method, comprising: temperature detection means for detecting the refrigerant temperature at the inlet side of the expansion valve; and pressure detection means for detecting the pressure in the high pressure side pipe of the vapor compression cycle, the temperature detection means Therefore, the specific enthalpy value of the expansion valve inlet refrigerant is calculated from the detected temperature and the pressure detected by the pressure detection means, and the opening degree of the internal heat exchange amount control valve is controlled based on the specific enthalpy value. Is characterized by. The method for controlling a refrigeration system of the present invention according to claim 3 is a compressor, a gas cooler, and an internal heat exchanger for exchanging heat between fluids flowing through an outlet side pipe of the gas cooler and an inlet side pipe of the compressor. , A first expansion valve, a receiver, a second expansion valve, and an evaporator are connected in an annular shape via pipes to form a vapor compression cycle, and a critical point is set on the high pressure side of the vapor compression cycle. A method of controlling a refrigeration apparatus using a fluid exceeding a refrigerant, comprising temperature detecting means for detecting a refrigerant temperature at an inlet side of the expansion valve, and pressure detecting means for detecting a pressure of a high pressure side pipe of the vapor compression cycle. Comprising, the specific enthalpy value of the expansion valve inlet refrigerant is calculated from the temperature detected by the temperature detection means and the pressure detected by the pressure detection means, and based on the specific enthalpy value, the first expansion valve And controlling the opening degree of the second expansion valve. According to a fourth aspect of the present invention, there is provided a method of controlling a refrigerating apparatus, wherein a compressor, an oil separator, a gas cooler, an outlet side pipe of the gas cooler and an inlet side pipe of the compressor are heat-exchanged. An internal heat exchanger, an expansion valve, and an evaporator are annularly connected to each other to form a vapor compression cycle, and the bottom of the oil separator and the outlet of the internal heat exchanger form the compressor. An oil return circuit that connects a pipe to the inlet and an oil return amount control valve that adjusts the amount of oil return flowing through the oil return circuit are provided, and the fluid that exceeds a critical point on the high pressure side of the vapor compression cycle A method of controlling a refrigerating apparatus used as a refrigerant, comprising: a temperature detecting means for detecting a refrigerant temperature at an inlet side of the expansion valve; and a pressure detecting means for detecting a pressure of a high pressure side pipe of the vapor compression cycle. , By the temperature detecting means The specific enthalpy value of the expansion valve inlet refrigerant is calculated from the temperature that is output and the pressure detected by the pressure detection means, and the opening degree of the oil return amount control valve is controlled based on the specific enthalpy value. And According to a fifth aspect of the present invention, in the method for controlling a refrigerating apparatus according to any of the first to fourth aspects, the cooling amount of the gas cooler or the rotation speed of the compressor is based on the specific enthalpy value. It is characterized by controlling. According to a sixth aspect of the present invention, in the refrigeration apparatus control method according to the second or fourth aspect, a temperature detection unit that detects a refrigerant temperature of the compressor is provided, and the refrigerant temperature detected by the temperature detection unit is included. According to, the flow rate of the refrigerant flowing through the bypass circuit or the oil return amount flowing through the oil return circuit is controlled. According to a seventh aspect of the present invention, in the method for controlling a refrigerating apparatus according to any one of the first to fourth aspects, the opening degree of the expansion valve is set to 10 to 30 seconds from the start of operation of the compressor. The feature is that the diameter is controlled to be 5% or less of the area. The present invention according to claim 8 is the method for controlling a refrigerating apparatus according to any one of claims 1 to 4, wherein the evaporator is provided with a refrigerant temperature detecting means, and a value detected by the temperature detecting means is It is characterized in that the opening degree of the expansion valve is controlled when it becomes 0 to 3 degrees. According to a ninth aspect of the present invention, in the method for controlling a refrigerating apparatus according to any one of the first to fourth aspects, the evaporator is provided with a refrigerant temperature detecting means, and the refrigerant temperature detected by the temperature detecting means is set to the refrigerant temperature. Accordingly, the opening degree of the expansion valve, the cooling amount of the gas cooler, or the flow rate of the refrigerant flowing through the bypass circuit is controlled. The present invention according to claim 10 relates to claim 2 or claim 4.
In the method for controlling a refrigerating apparatus according to item 1, there is provided a rotation speed detection means for detecting the rotation speed of the compressor, and depending on the rotation speed detected by the rotation speed detection means, a refrigerant flow rate or the oil flowing through the bypass circuit. It is characterized by controlling the amount of oil returned to the return circuit. The present invention according to claim 11 is the method for controlling a refrigerating apparatus according to any one of claims 1 to 4, wherein carbon dioxide is used as the refrigerant. According to a twelfth aspect of the present invention, in the refrigerating apparatus control method according to any one of the first to fourth aspects, a natural refrigerant such as carbon dioxide or ammonia is used as the refrigerant, and an amount of lubricating oil to be filled is set. 5
10 to 10 g, and a linear compressor is used as the compressor.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the first embodiment of the present invention, the temperature detected by the temperature detecting means by detecting the refrigerant temperature at the inlet side of the expansion valve and the pressure in the high pressure side pipe of the vapor compression cycle. The specific enthalpy value of the expansion valve inlet refrigerant is calculated from the pressure detected by the pressure detecting means and the expansion valve opening degree. According to the present embodiment, the heat exchange amount can be controlled to be high when the required load is high, and the COP can be controlled to be high when the required load is low, so that the performance of the refrigeration cycle can be surely improved. Can be achieved.

In the second embodiment of the present invention, the temperature of the refrigerant at the inlet side of the expansion valve and the pressure of the high-pressure side pipe of the vapor compression cycle are detected, and the temperature and the pressure detecting means are detected by the temperature detecting means. The specific enthalpy of the refrigerant at the inlet of the expansion valve is calculated from the pressure detected by, and the internal heat exchange control valve of the bypass circuit that connects the upper part of the receiver and the pipe from the outlet of the evaporator to the inlet of the internal heat exchanger is opened. It is to increase or decrease the degree. According to the present embodiment, when the required load is high, it is possible to control the internal heat exchange amount so that the heat exchange amount is increased while lowering the high pressure, and when the required load is low, the COP is increased. Therefore, it is possible to further improve the performance of the refrigeration cycle.

In the third embodiment of the present invention, the temperature of the refrigerant at the inlet side of the expansion valve and the pressure of the high pressure side pipe of the vapor compression cycle are detected, and the temperature and the pressure detecting means are detected by the temperature detecting means. The specific enthalpy of the refrigerant at the inlet of the expansion valve is calculated from the pressure detected by, and the opening degrees of the first expansion valve and the second expansion valve are increased or decreased. According to the present embodiment, the amount of refrigerant stored in the receiver can be controlled so that the heat exchange amount becomes high when the required load is high, and the COP can be controlled so that it becomes high when the required load is low.
The performance of the refrigeration cycle can be improved at a lower cost.

The fourth embodiment of the present invention detects the refrigerant temperature at the inlet side of the expansion valve and the pressure of the high pressure side pipe of the vapor compression cycle, and the temperature and pressure detecting means detected by the temperature detecting means. The specific enthalpy of the refrigerant at the inlet of the expansion valve is calculated from the pressure detected by, and the oil return amount of the oil return circuit that connects the bottom of the oil separator and the pipe from the outlet of the internal heat exchanger to the compressor inlet is adjusted. This is to increase or decrease the valve opening. According to the present embodiment, the compressor performance can be controlled to increase the heat exchange amount when the required load is high, and the COP can be controlled to increase when the required load is low. Thus, the performance of the refrigeration cycle can be improved.

The fifth embodiment of the present invention is a method for controlling a refrigeration system according to any one of the first to fourth embodiments, in which a cooling amount of a gas cooler (for example, an air flow amount of a cooling fan for promoting heat dissipation) is expanded. A highly efficient refrigeration cycle operation can be achieved by adjusting the valve enthalpy to be optimum according to the specific enthalpy value and the required load.

The sixth embodiment of the present invention is the method for controlling a refrigerating apparatus according to the second to fourth embodiments, in which the refrigerant temperature of the compressor is detected and the value detected by the temperature detecting means is a constant value. If it exceeds (for example 150 degrees),
The amount of refrigerant flowing through the bypass circuit or the amount of oil returned through the oil return circuit is increased or decreased. According to the present embodiment, it is possible to prevent the discharge temperature of the compressor from rising excessively,
It is possible to prevent the efficiency of the compressor from being lowered, and to improve the performance of the refrigeration cycle while preventing the discharge temperature of the compressor from rising too high.

The seventh embodiment of the present invention is the method for controlling a refrigeration system according to any of the first to fourth embodiments, wherein the expansion valve opening is set to the aperture for 10 to 30 seconds from the start of operation of the compressor. The area is controlled to 5% or less. According to the present embodiment, the high-low pressure difference can be increased immediately after the compressor operates, so that the refrigerating capacity can be improved in a short time.

An eighth embodiment of the present invention is the method for controlling a refrigeration system according to any one of the first to fourth embodiments, in which the refrigerant temperature of the evaporator is detected and the value detected by the temperature detecting means is 0 to 0. When it becomes 3 degrees, the expansion valve opening is controlled. According to the present embodiment, even when the evaporator temperature may decrease and the evaporator may freeze, by controlling the expansion valve opening degree without stopping the compressor,
It is possible to improve the reliability of the compressor by continuing the operation while preventing the refrigeration cycle from fluctuating significantly.

The ninth embodiment of the present invention is the method for controlling a refrigerating apparatus according to any one of the first to fourth embodiments, wherein the evaporator is provided with a refrigerant temperature detecting means, and the refrigerant temperature detected by the temperature detecting means is adjusted. Accordingly, the opening degree of the expansion valve, the cooling amount of the gas cooler, or the flow rate of the refrigerant flowing through the bypass circuit is controlled. According to the present embodiment, the expansion valve opening degree, the gas cooler cooling amount, or the change amount of the flow rate of the refrigerant flowing through the bypass circuit is controlled according to the evaporation temperature that changes per constant time, so that a more stable refrigeration cycle is configured. can do.

The tenth embodiment of the present invention is the method for controlling a refrigeration system according to any one of the first to fourth embodiments.
The rotation speed of the compressor is detected, and the amount of change in the value detected by the rotation speed detection means is a constant value (for example, 1000 rpm / sec).
In the above case, the flow rate of the refrigerant flowing through the bypass circuit or the oil return amount flowing through the oil return circuit is increased or decreased. According to the present embodiment, it is possible to prevent the discharge temperature and discharge pressure of the compressor from rising excessively, prevent the compressor efficiency from decreasing, and ensure the reliability of the refrigeration cycle. You can

An eleventh embodiment of the present invention is a method for controlling a refrigeration system according to any of the first to fourth embodiments, wherein
Carbon dioxide is used as the refrigerant, and according to the first to fourth embodiments, carbon dioxide can be used, and by using carbon dioxide, effective CFC countermeasures can be taken.

The twelfth embodiment of the present invention is the method for controlling a refrigeration system according to any one of the first to fourth embodiments,
A natural refrigerant such as carbon dioxide or ammonia is used as the refrigerant, the amount of lubricating oil filled is 5 to 10 g, and a linear compressor is used as the compressor. According to the present embodiment, since the lubricating oil is small, the heat transfer coefficient of the gas cooler and the evaporator can be improved, and the discharge temperature of the compressor can be raised, so that the refrigerating capacity can be improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIG. 1 shows a block diagram of Embodiment 1 of a refrigerating apparatus according to the present invention. 1 is a compressor, 2 is a gas cooler,
3 is an internal heat exchanger, 4 is an expansion valve, and 5 is an evaporator. These compressor 1, gas cooler 2, and internal heat exchanger 3
The expansion valve 4 and the evaporator 5 are annularly connected to each other through pipes to form a vapor compression cycle. In this vapor compression cycle, pressure detection means (pressure sensor) 7 for detecting the pressure of the high-pressure side pipe, that is, refrigerant pressure at the inlet of the expansion valve 4, and temperature for detecting the refrigerant temperature at the inlet of the expansion valve 4. A detection means (temperature sensor) 8 and an evaporator temperature detection means (temperature sensor) 9 for detecting the temperature of the evaporator 5 are provided. The adjusting means (controller) 10 in the figure is based on the specific enthalpy value of the expansion valve inlet calculated from the temperature detected by the temperature sensor 8 (or the temperature sensors 8 and 9) and the pressure detected by the pressure sensor 7. Thus, the opening degree of the expansion valve 4 is controlled. Here, the internal heat exchanger 3 is the gas cooler 2
Of the refrigerant flowing through the outlet pipe of the compressor and the refrigerant flowing through the inlet pipe of the compressor 1 are exchanged with each other. In this refrigeration cycle,
A refrigerant such as CO2 having a critical temperature near room temperature is used as the fluid, and the refrigerant compressed by the compressor 2 enters the gas cooler 2 as a high-temperature and high-pressure supercritical refrigerant.
It radiates heat here and cools. After that, in the internal heat exchanger 3, it is further cooled by exchanging heat with the low temperature refrigerant in the low pressure pipe,
It is sent to the expansion valve 4 without being liquefied. Then, after the pressure is reduced in the expansion valve 4, it is evaporated and vaporized in the evaporator 6, and heat is exchanged with the high-temperature refrigerant in the high-pressure pipe in the internal heat exchanger 3, and then returns to the compressor 2. Further, the opening of the expansion valve 4 is automatically controlled by the controller 10. Here, the controller 10 is a CPU, RO
Expansion valve 4 with M, RAM and input / output ports
It has a drive circuit for driving the stepping motor, and processes various signals related to the cycle state according to a predetermined program given to the ROM.

An outline of the control method of the first embodiment will be described. First, the specific enthalpy value table for CO2 in FIG. 5 will be described. The table actually stored in the controller 10 is the temperature and pressure change values when the opening degree of the expansion valve 4 is changed by a fixed amount (for example, 2 pulses). (Actually, the amount of change in temperature and pressure with respect to the change in the opening degree of the expansion valve 4 is different for each system, so it must be set for each). The specific enthalpy value calculated from the inlet temperature and inlet pressure of the expansion valve 4 is h. Here, when the opening degree of the expansion valve 4 is reduced, the discharge pressure rises and the inlet temperature of the expansion valve 4 falls, so the position of the specific enthalpy value h moves to the lower left in FIG. h1 and the difference h−h1 = Δh). When the opening degree of the expansion valve 4 is increased, the discharge pressure is decreased and the inlet temperature of the expansion valve 4 is increased, so that the position of the specific enthalpy value h moves to the upper right. In addition, in the specific enthalpy value table of FIG.
The lower left value is defined as "X1" where the specific enthalpy value is larger and "Y1" where the specific enthalpy value is smaller. Here, the entire area is the area of “Y1”, that is, when the expansion valve opening is made smaller, the area moves to the lower left, so the specific enthalpy value decreases and the cooling capacity increases in the entire area.

FIG. 6 shows the control method of the first embodiment.
This will be described with reference to the control flowchart shown in FIG. That is, the controller 10 outputs a signal from the pressure sensor 7 that detects the inlet pressure of the expansion valve, a signal from the temperature sensor 8 that detects the inlet temperature of the expansion valve 4 (step 21), and a temperature sensor 9 that detects the evaporator outlet temperature. Are input (step 22), and the specific enthalpy value of the refrigerant is calculated based on these signals (step 23). Then, it is determined whether the specific enthalpy value is in the region of "X1" or "Y1" (step 24), the temperature t of the evaporator 5 and the set value t1.
The temperature difference Δt (= t−t1) from (for example, 10 degrees) is determined to be positive or negative (step 25, step 26), and the opening degree of the expansion valve 4 is determined so as to change the capacity load, The expansion valve 4 is drive-controlled. In the above-mentioned configuration, for example, when it is desired to increase the capacity, the opening degree of the expansion valve 4 is controlled according to the temperature difference Δt of the evaporator and the change amount Δh of the specific enthalpy value, so that the required cooling capacity can be reliably achieved. Can be increased. In this way, according to the state of the refrigerant at the inlet of the expansion valve, it is possible to control so that the heat exchange amount becomes high when the required load is high and the COP becomes high when the required load is low. In addition, the performance of the refrigeration cycle can be improved.

(Embodiment 2) FIG. 2 is a block diagram of Embodiment 2 of a refrigerating apparatus according to the present invention. The configuration of the second embodiment is
In the configuration of the first embodiment, the receiver 6 and the bypass circuit 1
2 and the internal heat exchange amount control valve 17 are provided, the receiver 6 is disposed between the expansion valve 4 and the inlet of the evaporator 5, and one end of the bypass circuit 12 is connected to the bottom of the receiver 6 to The other end is connected to the inlet side of the low-pressure pipe of the internal heat exchanger 3 via the heat exchange amount control valve 17. Hereinafter, differences from the first embodiment will be mainly described, and the same portions will be denoted by the same reference numerals and description thereof will be omitted. The refrigeration cycle of the second embodiment is characterized by increasing the internal heat exchange amount by bypassing the liquid refrigerant from the bottom of the receiver 6 to the internal heat exchanger 3. An outline of the control method of the second embodiment will be described. The table actually stored in the controller 10 is the temperature and pressure change values when the heat exchange amount of the internal heat exchanger 3 is changed by a constant amount (for example, 100 W). In addition, it is assumed that the discharge temperature of the compressor is operating at a certain constant value (for example, 110 degrees) in the refrigeration cycle. Here, when the internal heat exchange amount is reduced, the inlet temperature of the expansion valve rises and the compressor suction temperature falls, so the compressor discharge temperature also falls. Therefore, the opening degree of the expansion valve 4 is controlled so as to keep the discharge temperature constant, so that it becomes small. Therefore, as the balance of the refrigeration cycle, the discharge pressure rises, and therefore the position of the specific enthalpy value h moves to the lower right in FIG. When the amount of internal heat exchange is increased, the discharge pressure decreases and the position of the specific enthalpy value h moves to the upper left. In the specific enthalpy value table of FIG. 5, a portion where the upper left value has a larger specific enthalpy value is "X2", and a portion where the specific enthalpy value is smaller is "Y2".

FIG. 7 shows the control method of the second embodiment.
This will be described with reference to the control flowchart shown in FIG. That is, it is determined whether the specific enthalpy value is in the region of "X2" or "Y2" (step 34), and the temperature difference Δt between the temperature t of the evaporator 5 and the set value t1 (for example, 10 degrees) is determined. Whether it is positive or negative is determined (step 35 or step 36), the opening degree of the internal heat exchange amount control valve is determined so as to change the capacity load, and the internal heat exchange amount control valve 17 is drive-controlled. In the above configuration, for example, when it is desired to increase the capacity, the temperature difference Δt of the evaporator and the change amount Δh of the specific enthalpy value.
Accordingly, the opening degree of the internal heat exchange amount control valve 17 is controlled, and the required cooling capacity can be reliably increased. Thus, the internal heat exchange amount can be optimally adjusted according to the state of the refrigerant at the inlet of the expansion valve, so that the performance of the refrigeration cycle can be further improved with respect to the required capacity.

(Embodiment 3) FIG. 3 is a block diagram of a refrigeration apparatus according to Embodiment 3 of the present invention. The configuration of the third embodiment is
In the configuration of the second embodiment, the bypass circuit 12 and the internal heat exchange amount control valve 17 are eliminated, and instead the first expansion valve 13 is used.
And a second expansion valve 14 are provided, the first expansion valve 13 is arranged between the internal heat exchanger 3 and the receiver 6, and the second expansion valve 14 is connected to the receiver 6 and the evaporator 5. It is arranged between. Hereinafter, differences from the second embodiment will be mainly described, and the same configurations will be denoted by the same reference numerals and description thereof will be omitted. The refrigeration cycle of the third embodiment is characterized in that the opening amounts of the first expansion valve 13 and the second expansion valve 14 are controlled to change the amount of refrigerant stored in the receiver 6. When it is desired to increase the storage amount, the opening degree of the first expansion valve 13 is increased and the opening degree of the second expansion valve is decreased. An outline of the control method of the third embodiment will be described. The table actually stored in the controller 10 is such that the amount of refrigerant in the receiver 6 is constant (for example, 100
g) Temperature and pressure change values when changed. The discharge temperature of the compressor is a certain constant value (for example, 110 degrees).
Assume that the refrigeration cycle is operating at. here,
When the storage amount is reduced, the amount of refrigerant flowing through the refrigeration cycle increases, so the discharge pressure rises and the compressor suction temperature drops, so the compressor discharge temperature also drops. First expansion valve 1
The opening degrees of the third and second expansion valves 14 are controlled so as to keep the discharge temperature constant, but since the increase and decrease of the respective opening degrees cannot be determined by the system, the first expansion valve 13 is used here.
It is assumed that the opening of the second expansion valve 14 is increased and the opening of the second expansion valve 14 is decreased to control the storage amount. That is, in FIG. 5, the position of the specific enthalpy value h moves to the lower right. Further, when the storage amount is increased, the discharge pressure is decreased and the position of the specific enthalpy value h moves to the upper left. In addition,
In the specific enthalpy value table of FIG. 5, a portion where the upper left value has a larger specific enthalpy value is "X2", and a portion where the specific enthalpy value is smaller is "Y2".

FIG. 8 shows the control method of the third embodiment.
This will be described with reference to the control flowchart shown in FIG. That is, it is determined whether the specific enthalpy value is in the region of "X2" or "Y2" (step 44), and the temperature difference Δt between the temperature t of the evaporator 5 and the set value t1 (for example, 10 degrees) is determined. Whether it is positive or negative is determined (step 45 or 46), the opening degrees of the first expansion valve 13 and the second expansion valve 14 are determined so as to change the capacity load, and the first expansion valve 13 and the second expansion valve 14 are opened. The expansion valve 14 is driven and controlled. In this way, the required capacity can be met by optimally adjusting the amount of refrigerant stored in the receiver according to the state of the refrigerant at the inlet of the expansion valve, so that the performance of the refrigeration cycle can be improved. In addition, Example 3
This configuration does not require a bypass circuit as compared with the second embodiment and can be realized at a lower cost.

(Embodiment 4) FIG. 4 is a block diagram of a refrigerating apparatus according to Embodiment 4 of the present invention. The configuration of the fourth embodiment is
In the configuration of the first embodiment, the oil separator 15 and the oil return circuit 1
6 and the oil return amount control valve 18, the oil separator 15 is disposed between the compressor 1 and the gas cooler 2, and the oil return circuit 1 is provided.
One end of 6 is connected to the bottom of the oil separator 15, and the other end is connected to the inlet of the compressor 1 via the oil return amount control valve 18. Hereinafter, the points different from the first embodiment will be mainly described, and the same components will be denoted by the same reference numerals and the description thereof will be omitted. The refrigeration cycle of the fourth embodiment is characterized by increasing the compressor performance by bypassing the oil from the bottom of the oil separator 15 to the inlet of the compressor 1. The outline of the control method of the fourth embodiment will be described. The table actually stored in the controller 10 shows temperature and pressure change values when the oil return amount is changed by a fixed amount (for example, 1 wt%). In addition, it is assumed that the discharge temperature of the compressor is operating at a certain constant value (for example, 110 degrees) in the refrigeration cycle. Here, if the oil return amount is increased, the leakage in the compressor is reduced, so the volumetric efficiency is improved and the cooling amount is increased because the circulation amount is increased, but the compressor discharge temperature is increased because the compressor suction temperature is increased. Also increases. Therefore, the opening degree of the expansion valve 4 is increased to control the discharge temperature to be constant. Therefore, as the balance of the refrigeration cycle, the discharge pressure decreases, so that the position of the specific enthalpy value h moves to the upper left in FIG.

FIG. 9 shows the control method of the fourth embodiment.
This will be described with reference to the control flowchart shown in FIG. That is, it is determined whether the specific enthalpy value is in the region of "X2" or "Y2" (step 54), and the temperature difference Δt between the temperature t of the evaporator 5 and the set value t1 (for example, 10 degrees) is determined. Whether it is positive or negative is determined (step 55 or step 56), the opening degree of the oil return amount control valve 18 is determined so as to change the capacity load, and the oil return amount control valve 18 is drive-controlled. In the above configuration, for example, when it is desired to increase the capacity, the opening degree of the oil return amount control valve 18 is controlled according to the temperature difference Δt of the evaporator and the change amount Δh of the specific enthalpy value, and the required cooling capacity is obtained. Can be surely increased. in this way,
According to the state of the refrigerant at the inlet of the expansion valve, the oil return amount can be optimally adjusted to greatly change the circulation amount of the compressor, so that the performance of the refrigeration cycle can be broadly improved with respect to the required capacity.

(Fifth Embodiment) The configuration (not shown) of the fifth embodiment is, for example, a cooling fan for a gas cooler as a gas cooler cooling amount adjusting means for promoting heat dissipation of the gas cooler 2 in the first to fourth embodiments. It has a means for adjusting the air flow rate. Then, by using this gas cooler cooling amount adjusting means, based on the specific enthalpy value of the expansion valve inlet, a control method of adjusting the gas cooler cooling amount to be optimal according to the required load, a more efficient refrigeration You get the operation of a cycle. Although the control method of the fifth embodiment is shown in the control flowchart of FIG. 10, the content of the control method is the same as that of the first to fourth embodiments, and the description thereof will be omitted. On the other hand, a means for increasing / decreasing the rotation speed of the compressor is provided, and the control method for increasing / decreasing the rotation speed of the compressor based on the specific enthalpy value at the inlet of the expansion valve so as to be optimal according to the required load is also used. An efficient refrigeration cycle operation can be obtained. The fifth embodiment is particularly effective for highly efficient refrigeration cycle operation when the number of revolutions is low such as idling of a vehicle-mounted refrigeration system.

(Embodiment 6) The configuration of Embodiment 6 (configuration not shown) is provided with temperature detecting means for detecting the refrigerant temperature of the compressor 1 in Embodiments 2 and 4, and the value of the detected temperature is When it becomes a certain value (for example, 150 degrees) or more, the suction temperature is lowered by controlling the flow rate of the refrigerant flowing through the bypass circuit 12 of the second embodiment to reduce the internal heat exchange amount. This is a control method that lowers the temperature. Alternatively, it is a control method of lowering the discharge temperature of the compressor 1 by controlling and reducing the amount of oil returned to the oil return circuit 16 of the fourth embodiment. Not only is the expansion valve opening controlled, but the bypass circuit 1
Since the discharge temperature of the compressor 1 can be lowered by controlling the flow rate of the refrigerant flowing through 2 or the amount of oil returned through the oil return circuit 16, the reliability of the compressor 1 can be further ensured. In the case of Example 6, especially CO
This is effective for highly reliable refrigeration cycle operation when using a refrigerant whose discharge temperature is high, such as 2 or ammonia.

(Embodiment 7) With a refrigerant having a small molecular diameter such as CO2, it is difficult for a high-low pressure difference to occur even if the opening of the expansion valve is reduced. Therefore, the configuration (configuration not shown) of the seventh embodiment has a means for controlling the opening degree of the expansion valve in the first to fourth embodiments, and is 10 to 30 seconds from the start of operation of the compressor 1. By controlling the expansion valve opening to 5% or less of the aperture area, it is possible to quickly increase the high-low pressure difference, so that the refrigerating capacity can be improved in a short time.

(Embodiment 8) When a refrigerant such as CO2 having a pressure much higher than that of a conventional CFC is used, and when the operation and stop are repeated, the impact on the compressor mechanism is very high due to pressure fluctuation and the like. Can be considered. The configuration (configuration not shown) of the eighth embodiment is the same as that of the first to fourth embodiments, having the means for controlling the opening of the expansion valve and the means for detecting the refrigerant temperature of the evaporator. When the temperature becomes 0 to 3 degrees and the temperature of the evaporator 5 decreases and the evaporator 5 may freeze, the opening degree of the expansion valve 4 is increased without stopping the compressor 1. With such a control method, it is possible to continue the operation while preventing the refrigeration cycle from fluctuating significantly and improve the reliability of the compressor 1.

(Embodiment 9) The configuration (configuration not shown) of Embodiment 9 is the opening amount of the expansion valve in Embodiments 1 to 4, the cooling amount of the gas cooler 2, or the flow rate of the refrigerant flowing in the bypass circuit 12. When the evaporation temperature that changes per fixed time when these amounts are increased or decreased exceeds a certain value (for example, 3 deg), the refrigeration cycle or the surrounding air conditioning (environment) ), It is determined that a large abnormality has occurred, and the change amount of the opening amount of the expansion valve 1, the cooling amount of the gas cooler 2, or the flow rate of the refrigerant flowing through the bypass circuit 12 is controlled to 0 (zero). is there. As a result, a more reliable and stable refrigeration cycle can be configured.

(Embodiment 10) The configuration (configuration not shown) of the tenth embodiment has means for detecting the rotation speed of the compressor 1 in the second and fourth embodiments, and changes in the detected value. A fixed amount (eg 1000 rpm / sec)
In the case above, by controlling the flow rate of the bypass circuit 12 so as to reduce the internal heat exchange amount exchanged in the internal heat exchanger 3 to prevent the discharge temperature from rising too much, or By controlling the amount of oil returned from the compressor 15 to be small and preventing the discharge temperature from rising too high, it is possible to suppress the discharge temperature and discharge pressure of the compressor 1 from rising excessively, and to improve the reliability of the refrigeration cycle. The security can be secured.

(Embodiment 11) With the control method of the refrigeration system shown in Embodiments 1 to 4, even if a refrigerant having a large amount of oil discharge such as carbon dioxide is used as a refrigerant, measures such as an oil separator are taken. It is possible to realize a very high-performance refrigeration cycle with an inexpensive system without needing it, and since it is almost unnecessary to consider deterioration of the lubricating oil,
The maximum value of the discharge temperature (for example, 150 degrees) can be made larger than that of the conventional CFC cycle, and the reliability can be further improved.

(Embodiment 12) According to the refrigerating apparatus control methods shown in Embodiments 1 to 4, the natural oil such as carbon dioxide or ammonia is used as the refrigerant, and the lubricating oil to be filled is 5 to 10 g. By using the linear compressor, it is possible to prevent the refrigerant heat transfer coefficient of the heat exchanger from being lowered due to the lubricating oil staying or flowing together with the refrigerant.

[0035]

According to the present invention, the refrigerant temperature at the inlet side of the expansion valve and the pressure in the high pressure side pipe of the vapor compression cycle are detected, and the temperature detected by the temperature detecting means and the pressure detecting means are detected. Since the specific enthalpy value of the expansion valve inlet refrigerant is calculated from the pressure and the expansion valve opening is increased / decreased, the heat exchange amount can be controlled to be high when the required load is high, and the required load is low. At this time, the COP can be controlled so as to be high, so that the performance of the refrigeration cycle can be surely improved. Further, according to the present invention, the refrigerant temperature at the inlet side of the expansion valve, the pressure of the high pressure side pipe of the vapor compression cycle is detected, from the temperature detected by the temperature detecting means and the pressure detected by the pressure detecting means, The specific enthalpy of the refrigerant at the inlet of the expansion valve is calculated, and the opening degree of the internal heat exchange control valve of the bypass circuit connecting the upper part of the receiver and the pipe from the outlet of the evaporator to the inlet of the internal heat exchanger is increased or decreased. Therefore, when the required load is high, the internal heat exchange amount can be controlled so as to increase the heat exchange amount while lowering the high pressure, and when the required load is low, the COP can be controlled so as to be increased. Performance can be improved. Further, according to the present invention, the refrigerant temperature at the inlet side of the expansion valve and the pressure of the high pressure side pipe of the vapor compression cycle are detected,
Since the specific enthalpy of the expansion valve inlet refrigerant is calculated from the temperature detected by the temperature detecting means and the pressure detected by the pressure detecting means, the opening degrees of the first expansion valve and the second expansion valve are increased or decreased. The amount of refrigerant stored in the receiver can be controlled to increase the heat exchange amount when the required load is high, and the COP can be controlled to increase when the required load is low. Performance can be improved. Further, according to the present invention, the refrigerant temperature at the inlet side of the expansion valve, the pressure of the high pressure side pipe of the vapor compression cycle is detected, from the temperature detected by the temperature detecting means and the pressure detected by the pressure detecting means, A valve that calculates the specific enthalpy of the refrigerant at the inlet of the expansion valve and increases or decreases the oil return amount control valve opening of the oil return circuit that connects the bottom of the oil separator and the pipe from the outlet of the internal heat exchanger to the inlet of the compressor. Therefore, when the required load is high, the compressor performance can be controlled so that the heat exchange amount becomes high, and when the required load is low, the COP can be controlled so that the COP becomes high. Performance can be improved. Further, according to the present invention, by adjusting the cooling amount of the gas cooler (for example, the air flow amount of the cooling fan that promotes heat dissipation) to be optimum according to the specific enthalpy value of the expansion valve inlet and the required load, high efficiency can be obtained. The operation of various refrigeration cycles can be achieved. Further, according to the present invention, the refrigerant temperature of the compressor is detected, and when the value detected by the temperature detecting means becomes a constant value (for example, 150 degrees) or more, the refrigerant flow rate flowing through the bypass circuit or the oil return circuit flows. Since it increases or decreases the amount of oil returned, it suppresses the discharge temperature of the compressor from rising excessively,
It is possible to prevent the efficiency of the compressor from being lowered, and to improve the performance of the refrigeration cycle while preventing the discharge temperature of the compressor from rising too high. Further, according to the present invention, the opening degree of the expansion valve is controlled to 5% or less of the aperture area for 10 to 30 seconds after the start of operation of the compressor. According to the present embodiment, the high-low pressure difference can be increased immediately after the compressor operates, so that the refrigerating capacity can be improved in a short time. Further, according to the present invention, since the refrigerant temperature of the evaporator is detected and the expansion valve opening degree is controlled when the value detected by the temperature detecting means is 0 to 3 degrees, the evaporator temperature is lowered. Even if there is a risk that the evaporator will freeze, the expansion valve opening is controlled without stopping the compressor to prevent the refrigeration cycle from fluctuating significantly and continue operation, thereby ensuring reliability of the compressor. It is possible to improve the property. Further, according to the present invention, in the refrigerating apparatus according to the first to fourth embodiments, the refrigerant temperature at the inlet of the expansion valve, the pressure of the high pressure side pipe of the vapor compression cycle, and the refrigerant temperature of the evaporator are detected. A specific enthalpy of the expansion valve inlet refrigerant is calculated from the temperature detected by the temperature detecting means and the pressure detected by the pressure detecting means to increase or decrease the expansion valve opening degree or the gas cooler cooling amount or the refrigerant flow rate flowing through the bypass circuit. Therefore, the expansion valve opening degree, the gas cooler cooling amount, or the change amount of the flow rate of the refrigerant flowing through the bypass circuit is controlled according to the evaporation temperature that changes per certain time, so that a more stable refrigeration cycle can be configured. . Further, according to the present invention, when the number of revolutions of the compressor is detected and the amount of change in the value detected by the number-of-revolutions detection means becomes a certain value (for example, 1000 rpm / sec) or more, the flow rate of the refrigerant or the oil flowing through the bypass circuit. Since the amount of oil returned through the return circuit is increased or decreased, it is possible to prevent the discharge temperature and discharge pressure of the compressor from rising excessively and prevent the compressor efficiency from decreasing, and at the same time, the refrigeration cycle The reliability of can be secured. Further, according to the present invention, carbon dioxide is used as the refrigerant, and carbon dioxide can be used. By using carbon dioxide, an effective measure against CFCs can be taken. Carbon dioxide is used as the refrigerant. Further, according to the present invention, a natural refrigerant such as carbon dioxide or ammonia is used as the refrigerant, and the lubricating oil to be filled is 5 to 5 times.
Since it is 10 g and a linear compressor is used as a compressor, since the amount of lubricating oil is small, the heat transfer coefficient of the gas cooler and the evaporator can be improved, and the discharge temperature of the compressor can be raised, so that the refrigeration The ability can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a refrigeration cycle in a first embodiment of a refrigeration apparatus according to the present invention.

FIG. 2 is a configuration diagram of a refrigeration cycle in a second embodiment of the refrigeration apparatus according to the present invention

FIG. 3 is a configuration diagram of a refrigeration cycle in a third embodiment of the refrigeration apparatus according to the present invention

FIG. 4 is a configuration diagram of a refrigeration cycle in a fourth embodiment of the refrigeration apparatus according to the present invention.

FIG. 5: Specific enthalpy value table of refrigerant CO2

FIG. 6 is a flowchart of expansion valve control in Embodiment 1 of the refrigeration system according to the present invention.

FIG. 7 is a flowchart of expansion valve control in Embodiment 2 of the refrigeration system according to the present invention.

FIG. 8 is a flowchart of expansion valve control in Embodiment 3 of the refrigeration system according to the present invention.

FIG. 9 is a flowchart of expansion valve control in Embodiment 4 of the refrigeration system according to the present invention.

FIG. 10 is a flowchart of expansion valve control in Embodiment 5 of the refrigeration system according to the present invention.

FIG. 11 is a flowchart of expansion valve control of a refrigeration system according to a conventional example.

FIG. 12: High pressure and C of refrigeration cycle according to conventional example
Characteristic diagram showing the relationship with OP

[Explanation of symbols]

1 compressor 2 gas cooler 3 Internal heat exchanger 4 expansion valve 5 evaporator 6 receiver 7 Pressure sensor (pressure detection means) 8 Temperature sensor (temperature detection means) 9 Temperature sensor (evaporator temperature detection means) 10 controller 12 Bypass circuit 13 First expansion valve 14 Second expansion valve 15 Oil separator 16 Oil return circuit 17 Internal heat exchange amount control valve 18 Oil return amount control valve

Claims (12)

[Claims] 1. A compressor, a gas cooler, an internal heat exchanger for exchanging heat between fluids flowing through an outlet side pipe of the gas cooler and an inlet side pipe of the compressor, an expansion valve, and an evaporator, respectively. A method for controlling a refrigerating apparatus that uses a fluid that exceeds a critical point as a refrigerant on a high pressure side of the vapor compression cycle to form a vapor compression cycle by annularly connecting the refrigerant through the expansion valve inlet side refrigerant. It has a temperature detecting means for detecting a temperature and a pressure detecting means for detecting a refrigerant pressure on the inlet side of the expansion valve, and from the detected temperature detected by the temperature detecting means and the detected pressure detected by the pressure detecting means, Calculate the specific enthalpy value at the inlet of the expansion valve,
A method for controlling a refrigerating apparatus, comprising controlling an opening of the expansion valve based on the specific enthalpy value. 2. A compressor, a gas cooler, an internal heat exchanger for exchanging heat between fluids flowing through an outlet side pipe of the gas cooler and an inlet side pipe of the compressor, an expansion valve, a receiver, and an evaporator. A bypass circuit connecting the upper part of the receiver and the pipe from the outlet of the evaporator to the inlet of the internal heat exchanger by forming a vapor compression cycle by annularly connecting and with each other, and the bypass. A method for controlling a refrigerating device having an internal heat exchange amount control valve for adjusting the flow rate of a refrigerant flowing through a circuit, wherein the fluid exceeding a critical point on the high-pressure side of the vapor compression cycle is used as a refrigerant, comprising: Temperature detection means for detecting the refrigerant temperature at the inlet side,
It has a pressure detection means for detecting the pressure of the high pressure side pipe of the vapor compression cycle, the specific enthalpy value of the expansion valve inlet refrigerant from the temperature detected by the temperature detection means and the pressure detected by the pressure detection means. A method of controlling a refrigerating apparatus, which calculates and controls the opening degree of the internal heat exchange amount control valve based on the specific enthalpy value. 3. A compressor, a gas cooler, an internal heat exchanger for exchanging heat between fluids flowing through an outlet side pipe of the gas cooler and an inlet side pipe of the compressor, and a first expansion valve,
A receiver, a second expansion valve, and an evaporator are connected to each other in an annular shape through pipes to form a vapor compression cycle, and a refrigeration apparatus that uses a fluid exceeding a critical point as a refrigerant on the high pressure side of the vapor compression cycle. The control method of, the temperature detection means for detecting the refrigerant temperature of the inlet side of the expansion valve, and a pressure detection means for detecting the pressure of the high-pressure side pipe of the vapor compression cycle, by the temperature detection means A specific enthalpy value of the expansion valve inlet refrigerant is calculated from the detected temperature and the pressure detected by the pressure detection means, and based on the specific enthalpy value, the first expansion valve and the second
A method for controlling a refrigerating apparatus, comprising controlling the opening of the expansion valve. 4. A compressor, an oil separator, a gas cooler, an internal heat exchanger for exchanging heat between fluids flowing through an outlet side pipe of the gas cooler and an inlet side pipe of the compressor, an expansion valve, An oil return that connects the evaporator and the ring to each other through a pipe to form a vapor compression cycle, and connects the bottom of the oil separator and the pipe from the outlet of the internal heat exchanger to the inlet of the compressor. A control method for a refrigerating device having a circuit and an oil return amount control valve for adjusting the amount of oil return flowing through the oil return circuit, and using the fluid above the critical point on the high pressure side of the vapor compression cycle as a refrigerant. A temperature detecting means for detecting the refrigerant temperature at the inlet side of the expansion valve, and a pressure detecting means for detecting the pressure of the high pressure side pipe of the vapor compression cycle, and the temperature detected by the temperature detecting means. In the pressure detection means Therefore, the specific enthalpy value of the expansion valve inlet refrigerant is calculated from the detected pressure, and the opening degree of the oil return amount control valve is controlled based on the specific enthalpy value. 5. The refrigerating apparatus according to claim 1, wherein the cooling amount of the gas cooler or the rotation speed of the compressor is controlled based on the specific enthalpy value. Control method. 6. A temperature detecting means for detecting a refrigerant temperature of the compressor, wherein a flow rate of a refrigerant flowing through the bypass circuit or an oil return amount flowing through the oil return circuit is provided in accordance with a refrigerant temperature detected by the temperature detecting means. The method for controlling a refrigerating apparatus according to claim 2 or 4, further comprising: 7. 10 to 30 from the start of operation of the compressor
The control method of the refrigerating apparatus according to any one of claims 1 to 4, wherein the opening degree of the expansion valve is controlled to 5% or less of the aperture area for a second. 8. The evaporator is provided with a refrigerant temperature detecting means,
The opening degree of the said expansion valve is controlled when the value detected by the said temperature detection means becomes 0 to 3 degrees, Control of the refrigerating apparatus in any one of Claim 1 to 4 characterized by the above-mentioned. Method. 9. The evaporator is provided with a refrigerant temperature detecting means,
According to the refrigerant temperature detected by the temperature detecting means,
The control method of the refrigerating apparatus according to any one of claims 1 to 4, wherein the opening degree of the expansion valve, the cooling amount of the gas cooler, or the flow rate of the refrigerant flowing through the bypass circuit is controlled. 10. A rotation speed detection means for detecting the rotation speed of the compressor is provided, and according to the rotation speed detected by the rotation speed detection means, the flow rate of the refrigerant flowing through the bypass circuit or the oil flowing through the oil return circuit. The method for controlling a refrigerating apparatus according to claim 2 or 4, wherein the return amount is controlled. 11. The method for controlling a refrigerating apparatus according to claim 1, wherein carbon dioxide is used as the refrigerant. 12. A natural refrigerant such as carbon dioxide or ammonia is used as the refrigerant, and the amount of lubricating oil filled is 5 to 1
The refrigeration apparatus control method according to any one of claims 1 to 4, wherein the compressor is set to 0 g, and a linear compressor is used as the compressor.