REFRIGERATION CYCLE APPARATUS

Abstract

 A refrigeration cycle apparatus 1 includes a main circuit 10 connecting at least a compressor 11, a gas cooler 12, a pressure reducing device 13, and an evaporator 14 by a pipe and configured to circulate refrigerant transitioning to a supercritical state at a high-pressure side; a pressure detector configured to detect refrigerant pressure in a part of the main circuit 10 between the compressor 11 and the gas cooler 12; and a pulsation suppression unit configured to suppress pulsation of the refrigerant pressure to be detected by the pressure detector.

Description

Technical Field

[0001] The present invention relates to refrigeration cycle apparatuses.

Background Art

[0002] In response to the chlorofluorocarbon-free movement in recent years, heat pump apparatuses using natural refrigerant have been actively developed. Among such devices, heat pump apparatuses using carbon dioxide (CO₂) as refrigerant are becoming more popular year by year. Because CO₂ has characteristics in which the ozone depletion potential thereof is 0 and the global warming potential thereof is 1, CO₂ is advantageous in being able to reduce the load on the environment. Moreover, CO₂ is also advantageous in terms of a high level of safety due to having no toxicity and no combustibility and in being readily available and relatively inexpensive.

[0003] Furthermore, unlike fluorocarbon-based refrigerant, CO₂ at the high-pressure side discharged from a compressor has characteristics in which it transitions to a supercritical state. Specifically, when this CO₂ in the supercritical state applies heat to another fluid (e.g., water, air, or refrigerant) by exchanging heat therewith, the CO₂ does not condense and remains in the supercritical state. Because the loss caused by state transition is small, CO₂ having such characteristics is suitable for use in a heat pump apparatus that requires high temperature among various types of heat pump apparatuses. Various heat-pump-type hot water suppliers that use CO₂ as the refrigerant and that make full use of the advantages of CO₂ to boil water to a high temperature of 90 degrees C or higher have been proposed.

Citation List

Patent Literature

[0004] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2010-107162

Summary of Invention

Technical Problem

[0005] A refrigeration cycle apparatus in which refrigerant transitions to a supercritical state at the high-pressure side normally includes a main circuit in which a compressor, a gas cooler, a pressure reducing device, and an evaporator are connected by pipes, and also includes a pressure detection circuit for detecting the refrigerant pressure (high pressure) between the compressor and the gas cooler in the main circuit. The pressure detection circuit has a pressure detection pipe branching off from the main circuit at a branching section provided between the compressor and the gas cooler in the main circuit, and also has a pressure detector (e.g., a pressure sensor, a pressure switch, or other devices) disposed at the terminal end of the pressure detection pipe.

[0006] With regard to refrigerant that is not used in the supercritical state, the pressure detection pipe is normally constituted of a pipe with a diameter smaller than the pipe diameter of the main circuit. This is because, in a case where a constant speed compressor driven with a commercial power source is used as the compressor, for example, a capillary pipe is used as the pressure detection pipe for alleviating an increase in detected pressure to prevent the pressure switch from malfunctioning due to a temporary increase in high pressure in the main circuit when the refrigerant circulation amount increases rapidly, such as at the time of activation. The same applies to CO₂ refrigerant used in a supercritical state. Moreover, in a case where a compressor driven with an inverter is used, because a temporary increase in high pressure also occurs when the frequency of an inverter power source is increased largely toward the high side (i.e., high frequency side), for example, a capillary pipe is used as the pressure detection pipe for similar reasons. Furthermore, in a case where HFC refrigerant is used, a gas portion with high compressibility always exists due to the characteristics of the refrigerant during normal operation even if the pressure detection pipe has a small diameter section. Thus, high-pressure pulsation is not amplified.

[0007] Fig. 12 is a graph illustrating an example of temporal changes in refrigerant pressure at respective positions in a common refrigeration cycle apparatus in a case where refrigerant, such as CO₂ refrigerant, is used in a supercritical state. The abscissa of the graph indicates time (seconds) elapsed from a predetermined reference time point, and the ordinate indicates pressure (MPa). Line a denotes a pressure change at a vicinity of the pressure sensor at the high-pressure side, line b denotes a pressure change at the upstream side of the capillary pipe (i.e., the pressure detection pipe) connected to the pressure switch at the high-pressure side, line c denotes a pressure change at a service port at the high-pressure side, and line d denotes a pressure change at an outlet of a muffler provided at the downstream side of the compressor. The driving frequency of the compressor is decreased from 96 Hz to 86 Hz at the elapsed time point of 48 seconds.

[0008] As shown in Fig. 12, pressure pulsation occurs at any of the positions of the refrigeration cycle apparatus, and the pulsation cycle is about 10 ms. For example, the pulsation width at the elapsed time point of 45 seconds is 1.927 MPa at the vicinity of the pressure sensor (line a), is 0.40 MPa at the upstream side of the capillary pipe (line b), is 0.32 MPa at the service port (line c), and is 0.093 MPa at the outlet of the muffler (line d). The pulsation width at the elapsed time point of 57 seconds (i.e., after retardation of the compressor) is 3.90 MPa at the vicinity of the pressure sensor (line a), is 0.44 MPa at the upstream side of the capillary pipe (line b), is 0.40 MPa at the service port (line c), and is 0.28 MPa at the outlet of the muffler (line d). In particular, the pulsation width after the retardation of the compressor increases at the vicinity of the pressure sensor, and the peak pressure at the high-pressure side is higher than that before the retardation of the compressor.

[0009] Even in the case of CO₂ refrigerant used in a supercritical state, if the difference between a preset value of the pressure switch and the normally-used pressure is large, protection by the pressure switch is not actuated even when high-pressure pulsation occurs. However, if the preset value of the pressure switch is to be reduced and the wall thickness of the pipe is to be reduced for the purpose of cost reduction, it is necessary to accurately detect the refrigerant pressure. Moreover, in a case where a bypass circuit having a pipe diameter smaller than the pipe diameter of the main circuit and larger than the pipe diameter of the pressure detection pipe branches off from the main circuit, the pressure detection pipe may be made to branch off from the bypass circuit so that the costs of processing, such as soldering, can be reduced, thereby achieving cost reduction. Even in this case, pressure pulsation similarly increases.

[0010] As described above, the pressure detection circuit in the related art is problematic in that pressure pulsation is amplified in the pressure detection pipe, thus making it difficult to accurately detect the refrigerant pressure by using the pressure detector disposed at the terminal end of the pressure detection pipe.

[0011] The present invention has been made to solve the aforementioned problem and an object thereof is to provide a refrigeration cycle apparatus that can detect refrigerant pressure more accurately.

Solution to Problem

[0012] A refrigeration cycle apparatus according to the present invention includes a main circuit connecting at least a compressor, a gas cooler, a pressure reducing device, and an evaporator by a pipe and configured to circulate refrigerant transitioning to a supercritical state at a high-pressure side; a pressure detector configured to detect refrigerant pressure in a part of the main circuit between the compressor and the gas cooler; and a pulsation suppression unit configured to suppress pulsation of the refrigerant pressure to be detected by the pressure detector.

Advantageous Effects of Invention

[0013] According to the present invention, refrigerant pressure can be detected more accurately.

Brief Description of Drawings

[0014] 

[Fig. 1] Fig. 1 is a refrigerant circuit diagram illustrating an example of the configuration of a refrigeration cycle apparatus 1 according to Embodiment 1 of the present invention.

[Fig. 2] Fig. 2 illustrates the configuration of a pressure detection circuit 110 of the refrigeration cycle apparatus 1 according to Embodiment 1 of the present invention.

[Fig. 3] Fig. 3 schematically illustrates the configuration of a pressure detection circuit in which the pressure detection circuit has a narrowed pipe section.

[Fig. 4] Fig. 4 illustrates the configuration of a pressure detection circuit 110 of a refrigeration cycle apparatus according to Embodiment 2 of the present invention.

[Fig. 5] Fig. 5 is a graph illustrating the correlation between the temperature and the density of CO₂ refrigerant in high-pressure states.

[Fig. 6] Fig. 6 illustrates the configuration of a pressure detection circuit 110 of a refrigeration cycle apparatus according to Embodiment 3 of the present invention.

[Fig. 7] Fig. 7 illustrates the configuration of a pressure detection circuit 110 of a refrigeration cycle apparatus according to Embodiment 4 of the present invention.

[Fig. 8] Fig. 8 illustrates the relationship between the driving frequency of a compressor 11 and the pressure wavelength.

[Fig. 9] Fig. 9 illustrates a pressure detection algorithm of a refrigeration cycle apparatus according to Embodiment 5 of the present invention.

[Fig. 10] Fig. 10 is a graph illustrating an example of a peak pressure value Hpmpeak calculated in the refrigeration cycle apparatus according to Embodiment 5 of the present invention.

[Fig. 11] Fig. 11 is a graph illustrating an example of detected pressure values in the related art.

[Fig. 12] Fig. 12 is a graph illustrating an example of temporal changes in refrigerant pressure at respective positions in a common refrigeration cycle apparatus.

Description of Embodiments

Embodiment 1

[0015] A refrigeration cycle apparatus according to Embodiment 1 of the present invention will be described. Fig. 1 is a refrigerant circuit diagram illustrating an example of the configuration of a refrigeration cycle apparatus 1 according to Embodiment 1. In Embodiment 1, a refrigeration cycle apparatus (heat pump apparatus) used in a heat-pump-type hot water supplier will be described as an example of the refrigeration cycle apparatus 1. In the following figures including Fig. 1, the dimensional relationships among components, the shapes thereof, and other related aspects may differ from the actual aspects.

[0016] As shown in Fig. 1, the refrigeration cycle apparatus 1 has a main circuit 10 in which a compressor 11, a gas cooler 12, a pressure reducing device 13, and an evaporator 14 are connected by pipes and that circulates refrigerant (e.g., CO₂) that transitions to a supercritical state at the high-pressure side.

[0017] The compressor 11 is a fluid device that suctions low-temperature low-pressure refrigerant, compresses the suctioned refrigerant to supercritical pressure, and discharges the refrigerant as high-temperature high-pressure refrigerant in a supercritical state. In this example, an inverter power source that can change the driving frequency of the compressor 11 within a predetermined range (e.g., about 30 Hz to 100 Hz) is used as a power source supplied to the compressor 11. The gas cooler 12 is a water-side heat exchanger that exchanges heat with an external fluid (i.e., circulation water for hot water supply in this example) to cool the refrigerant discharged from the compressor 11 and also to heat the external fluid. The refrigerant cooled by the gas cooler 12 does not condense to remain in the supercritical state and flows out of the gas cooler 12. The pressure reducing device 13 decompresses and expands the refrigerant cooled by the gas cooler 12 and causes the refrigerant to flow out as low-temperature low-pressure two-phase gas-liquid refrigerant. In this example, an electronic expansion valve is used as the pressure reducing device 13. The evaporator 14 is an air-side heat exchanger that evaporates the two-phase gas-liquid refrigerant flowing out of the pressure reducing device 13 by exchanging heat with the external fluid (i.e., air in this example).

[0018] The main circuit 10 is provided with a high-pressure low-pressure heat exchanger 17 that causes the high-temperature high-pressure refrigerant flowing out of the gas cooler 12 and the low-temperature low-pressure refrigerant flowing out of the evaporator 14 to exchange heat with each other. The high-pressure low-pressure heat exchanger 17 is provided with a high-pressure-refrigerant flow path through which the high-temperature high-pressure refrigerant flowing out of the gas cooler 12 flows, and a low-pressure-refrigerant flow path through which the low-temperature low-pressure refrigerant flowing out of the evaporator 14 flows.

[0019] In the main circuit 10, a strainer 16 is provided at the downstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 and the upstream side of the pressure reducing device 13. A strainer 15 is provided at the downstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 and the upstream side of the compressor 11.

[0020]  In the main circuit 10, a muffler 20 is provided at the downstream side of the compressor 11 and the upstream side of the gas cooler 12. The muffler 20 is connected to an oil recovery circuit 21 that recovers refrigerating machine oil and returns it to the suction side of the compressor 11. The oil recovery circuit 21 connects the muffler 20 and a merging section 28 provided at the downstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 and the upstream side of the compressor 11 (i.e., the upstream side of the strainer 15). In the oil recovery circuit 21, a heat exchanger 22 that heats water for hot water supply (i.e., circulation water) by causing the water to exchange heat with high-temperature refrigerating machine oil and a bypass circuit 23 that bypasses the heat exchanger 22 are provided in parallel with each other. The bypass circuit 23 is provided with a solenoid valve 24 that opens and closes the bypass circuit 23. In the bypass circuit 23, a strainer 25 is provided at the upstream side of a branching section where the heat exchanger 22 and the bypass circuit 23 branch off from each other. A branch pipe 26 branches off from the oil recovery circuit 21. The branch pipe 26 is provided with a service valve 27a and a service port 27b. A pressure sensor 29 that further branches off from the branch pipe 26 and that detects the refrigerant pressure at the low-pressure side is provided via a capillary pipe 30.

[0021] In the main circuit 10, a branching section 31 provided at the downstream side of the muffler 20 and the upstream side of the gas cooler 12 and a merging section 32 provided at the downstream side of the gas cooler 12 and the upstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 are connected to each other by a bypass circuit 33 that bypasses the gas cooler 12. The bypass circuit 33 is provided with a solenoid valve 34 that opens and closes the bypass circuit 33, and is also provided with a strainer 35 at the upstream side of the solenoid valve 34.

[0022] In the main circuit 10, a branching section 36 provided at the downstream side of the branching section 31 and the upstream side of the gas cooler 12 and a merging section 37 provided at the downstream side of the pressure reducing device 13 and the upstream side of the evaporator 14 are connected to each other by a bypass circuit 38 that bypasses the gas cooler 12 and the pressure reducing device 13. The bypass circuit 38 is provided with a solenoid valve 39 that opens and closes the bypass circuit 38, and is also provided with a strainer 40 at the upstream side of the solenoid valve 39.

[0023] In the main circuit 10, a branching section 41 provided at the downstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 (i.e., the downstream side of the strainer 16) and the upstream side of the pressure reducing device 13 and a merging section 42 provided at the downstream side of the pressure reducing device 13 and the upstream side of the evaporator 14 (i.e., the upstream side of the merging section 37) are connected to each other by a bypass circuit 43 that bypasses the pressure reducing device 13. The bypass circuit 43 is provided with an internal heat exchanger 45 that exchanges heat with refrigerant flowing in the main circuit 10 at the downstream side of the compressor 11 and upstream of the gas cooler 12, and is also provided with a solenoid valve 44 that opens and closes the bypass circuit 43.

[0024] In the main circuit 10, a branching section 111 provided at the downstream side of the compressor 11 (i.e., the downstream side of the branching section 31) and the upstream side of the gas cooler 12 (i.e., the upstream side of the branching section 36) is connected to a pressure detection circuit 110. The pressure detection circuit 110 has a pressure switch 112 and a pressure detection pipe 114 that connects the branching section 111 and the pressure switch 112. Furthermore, the pressure detection circuit 110 has a pressure sensor 113 and a pressure detection pipe 115 that branches off from the pressure detection pipe 114 at a branching section 116 provided in the pressure detection pipe 114 and that connects the branching section 116 and the pressure sensor 113. The pressure switch 112 is provided at the terminal end of the pressure detection pipe 114, and the pressure sensor 113 is provided at the terminal end of the pressure detection pipe 115.

[0025] The pressure switch 112 and the pressure sensor 113 both function as pressure detectors that detect the refrigerant pressure (i.e., discharge pressure) between the compressor 11 and the gas cooler 12 of the main circuit 10. The pressure switch 112 cuts off the supply of power to the compressor 11 when the refrigerant pressure between the compressor 11 and the gas cooler 12 reaches an abnormal high pressure. The pressure sensor 113 detects the refrigerant pressure between the compressor 11 and the gas cooler 12 and outputs a detection signal to a controller 100, which will described later.

[0026] The pressure detection pipe 114 extending from the branching section 111 of the main circuit 10 to the pressure switch 112 has the same inside diameter (e.g., φ6.35) and is not narrowed. Furthermore, the pressure detection pipes 114 and 115 extending from the branching section 111 of the main circuit 10 to the pressure sensor 113 have the same inside diameter (e.g., φ6.35) and are not narrowed. Specifically, the pressure detection pipes 114 and 115 have no narrowed pipe sections between the branching section 111 and the pressure switch 112 or the pressure sensor 113. A narrowed pipe section is a section where the flow-path cross-sectional area of a pipe decreases at an intermediate position thereof when the pipe is traced in one direction along the pipe line (i.e., a direction extending from the branching section 111 toward the pressure switch 112 or the pressure sensor 113 in this example). In Embodiment 1, when the pressure detection pipes 114 and 115 are traced in the direction extending from the branching section 111 toward the pressure switch 112 or the pressure sensor 113 along the pipe line, the pressure detection pipes 114 and 115 have no sections where the flow-path cross-sectional areas thereof decrease.

[0027]  A branch pipe 118 branches off from a branching section 117 provided in the pressure detection pipe 114. The branch pipe 118 is provided with a service valve 121 a and a service port 121 b.

[0028] The refrigeration cycle apparatus 1 has various types of temperature sensors. The various types of temperature sensors include a temperature sensor 71 that is provided at the downstream side of the compressor 11 of the main circuit 10 and the upstream side of the muffler 20 and that detects the discharge temperature of the compressor 11, a temperature sensor 72 that is provided at the downstream side of the gas cooler 12 and the upstream side of the high-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 (i.e., the upstream side of the merging section 32) and that detects the outlet temperature of the gas cooler 12, a temperature sensor 73 that is provided at the downstream side of the pressure reducing device 13 (i.e., the downstream side of the merging section 42) and the upstream side of the evaporator 14 (i.e., the upstream side of the merging section 37) and that detects the inlet temperature of the evaporator 14, a temperature sensor 74 that is provided at the downstream side of the evaporator 14 and the upstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 and that detects the outlet temperature of the evaporator 14, a temperature sensor 75 that is provided at the downstream side of the low-pressure-refrigerant flow path of the high-pressure low-pressure heat exchanger 17 and the upstream side of the compressor 11 (i.e., the upstream side of the merging section 28) and that detects the suction temperature of the compressor 11, and a temperature sensor 76 that is provided close to the evaporator 14 and that detects the outside air temperature. These temperature sensors output temperature detection signals to the controller 100, which will be described below.

[0029] The refrigeration cycle apparatus 1 has the controller 100. The controller 100 in this example is a microcomputer equipped with, for example, a CPU, a ROM, a RAM, and an I/O port. The controller 100 controls the compressor 11, the pressure reducing device 13, and other devices based on detection signals input from the above-described temperature sensors 71, 72, 73, 74, 75, and 76, the pressure sensors 29 and 113, and other sensors.

[0030] The heat-pump-type hot water supplier has a boiler circuit 50 that uses the refrigeration cycle apparatus 1 to boil water in a hot-water tank (not shown). The boiler circuit 50 connects a lower section and an upper section of the hot-water tank. The boiler circuit 50 receives low-temperature water from the lower section of the hot-water tank, boils the water by causing it to exchange heat with the refrigerating machine oil at the heat exchanger 22 and to exchange heat with the refrigerant at the gas cooler 12, and returns the water as high-temperature water to the upper section of the hot-water tank. In the boiler circuit 50, a circulation pump 51 that sends the water in the lower section of the hot-water tank as circulation water to the upper section of the hot-water tank is provided at the upstream side of the heat exchanger 22 and the gas cooler 12. In the boiler circuit 50, an electric valve 52 that adjusts the flow of the circulation water is provided at the upstream side of the circulation pump 51, a check valve 53 is disposed at the downstream side of the electric valve 52, and a pressure reducing valve 54 is disposed at the downstream side of the check valve 53. A strainer 55 is provided at the downstream side of the electric valve 52 and the upstream side of the check valve 53.

[0031] In the boiler circuit 50, a merging section 56 provided at the downstream side of the pressure reducing valve 54 and the upstream side of the circulation pump 51 is connected to a water supply circuit 57 that supplies tap water to the boiler circuit 50. The water supply circuit 57 is provided with an electric valve 58 that adjusts the flow of tap water, a check valve 59 disposed at the downstream side of the electric valve 58, and a pressure reducing valve 60 disposed at the downstream side of the check valve 59. A strainer 61 is provided at the downstream side of the electric valve 58 and the upstream side of the check valve 59.

[0032]  In the boiler circuit 50, an electric valve 62 that adjusts the flow of the circulation water is provided at the downstream side of the circulation pump 51 and the upstream side of the heat exchanger 22. A branch pipe provided with a relief valve 63 is connected at the downstream side of the circulation pump 51 and the upstream side of the electric valve 62. A flow rate sensor 64 that detects the flow rate of the circulation water is provided at the downstream side of the electric valve 62 and the upstream side of the heat exchanger 22.

[0033] In the boiler circuit 50, a temperature sensor 77 that detects the temperature of the pre-boiled circulation water is provided at the downstream side of the circulation pump 51 and the upstream side of the heat exchanger 22 (i.e., the upstream side of the electric valve 62). Furthermore, in the boiler circuit 50, a temperature sensor 78 that detects the temperature of the boiled circulation water is provided at the downstream side of the gas cooler 12.

[0034] The above-described temperature sensors 77 and 78, the flow rate sensor 64, and other sensors output detection signals to a controller (not shown) of the heat-pump-type hot water supplier or to the controller 100 of the refrigeration cycle apparatus 1.

[0035] Fig. 2 illustrates the configuration of the pressure detection circuit 110 according to Embodiment 1. In Fig. 2, the pressure detection circuit 110 shown is simplified in configuration relative to the pressure detection circuit 110 shown in Fig. 1 and is provided with only the pressure sensor 113 as a pressure detector. The pressure detection circuit 110 shown in Fig. 2 has the pressure sensor 113 that detects the refrigerant pressure at the high-pressure side, and also has the pressure detection pipe 115 that connects the branching section 111, which is provided at the downstream side of the compressor 11 and the upstream side of the gas cooler 12 in the main circuit 10, and the pressure sensor 113. The pressure detection pipe 115 branches off at the branching section 111 in a direction perpendicular to the main circuit 10. Moreover, the pressure detection pipe 115 has a straight-pipe branch-less configuration. The pressure sensor 113 is provided at the terminal end of the pressure detection pipe 115. The pressure detection pipe 115 extending from the branching section 111 to the pressure sensor 113 has the same inside diameter and is not narrowed.

[0036] Fig. 3 illustrates the configuration of a pressure detection circuit 210 in which the pressure detection pipe 115 has a narrowed pipe section 119. Similar to the pressure detection circuit 110 shown in Fig. 2, the pressure detection circuit 210 shown in Fig. 3 has the pressure sensor 113 that detects the refrigerant pressure at the high pressure side and the pressure detection pipe 115 that connects the branching section 111 and the pressure sensor 113. However, the pressure detection pipe 115 in the pressure detection circuit 210 differs from the pressure detection pipe 115 shown in Fig. 2 in that a part of the pipe line extending from the branching section 111 to the pressure sensor 113 has the narrowed pipe section 119. Specifically, the pipe diameter (i.e., the flow-path cross-sectional area) of the pressure detection pipe 115 at the terminal end where the pressure sensor 113 is provided is smaller than the pipe diameter (i.e., the flow-path cross-sectional area) of the pressure detection pipe 115 close to the branching section 111.

[0037] The refrigerant used in the refrigeration cycle apparatus 1 according to Embodiment 1 transitions to a supercritical state at the high-pressure side. Refrigerant in a supercritical state has extremely low compressibility. Consequently, if the narrowed pipe section 119 exists in the pressure detection pipe 115, pressure pulsation at the terminal side relative to the narrowed pipe section 119 becomes amplified inversely proportional to the rate of change α (0 < α < 1) in the cross-sectional area of the pipe (i.e., flow path) before and after the narrowed pipe section 119. Thus, in the pressure detection circuit 210 shown in Fig. 3, it may be difficult to accurately detect the refrigerant pressure by using the pressure sensor 113 provided at the terminal end of the pressure detection pipe 115.

[0038] In contrast, in the pressure detection circuit 110 according to Embodiment 1 shown in Fig. 2, the pressure detection pipe 115 is not provided with a narrowed pipe section. Consequently, in the pressure detection pipe 115 of the pressure detection circuit 110, the cross-sectional area of the flow path through which the refrigerant flows is fixed and does not change from the branching section 111 to the pressure sensor 113. Thus, pressure pulsation can be suppressed at the terminal end of the pressure detection pipe 115. Consequently, in Embodiment 1, the refrigerant pressure (i.e., discharge pressure) can be detected more accurately with the pressure sensor 113.

[0039] As described above, the refrigeration cycle apparatus 1 according to Embodiment 1 has the main circuit 10 in which at least the compressor 11, the gas cooler 12, the pressure reducing device 13, and the evaporator 14 are connected by pipes and that circulates refrigerant that transitions to a supercritical state at the high-pressure side, the pressure detectors (e.g., the pressure sensor 113 and the pressure switch 112) that detect the refrigerant pressure between the compressor 11 and the gas cooler 12 in the main circuit 10, and a pulsation suppression unit (e.g., the pressure detection pipe 115 not provided with a narrowed pipe section) that suppresses pulsation of the refrigerant pressure to be detected by the pressure detectors.

[0040] According to this configuration, since pulsation of the refrigerant pressure to be detected by the pressure detectors can be suppressed, the refrigerant pressure between the compressor 11 and the gas cooler 12 in the main circuit 10 can be detected more accurately.

[0041] Furthermore, in the refrigeration cycle apparatus 1 according to Embodiment 1, the aforementioned pulsation suppression unit connects the branching section 111 and the pressure detectors (e.g., the pressure sensor 113 and the pressure switch 112) provided between the compressor 11 and the gas cooler 12 in the main circuit 10. Moreover, the refrigeration cycle apparatus 1 according to Embodiment 1 includes the pressure detection pipe 115 that does not have a narrowed pipe section whose flow-path cross-sectional area decreases at an intermediate position between the branching section 111 and the pressure sensors.

[0042] According to this configuration, the cross-sectional area of the flow path from the branching section 111 to the pressure sensors, through which the refrigerant flows, can be prevented from decreasing. Consequently, pulsation of the refrigerant pressure to be detected by the pressure sensors can be suppressed.

Embodiment 2

[0043] A refrigeration cycle apparatus according to Embodiment 2 of the present invention will be described. Fig. 4 illustrates the configuration of the pressure detection circuit 110 in the refrigeration cycle apparatus according to Embodiment 2. Components having the same functions and effects as those in the refrigeration cycle apparatus 1 and the pressure detection circuit 110 according to Embodiment 1 will be given the same reference signs, and descriptions thereof will be omitted.

[0044] As shown in Fig. 4, in the pressure detection pipe 115 of the pressure detection circuit 110 according to Embodiment 2, a part of the pipe line extending from the branching section 111 to the pressure sensor 113 has the narrowed pipe section 119. A path length A of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119 is 100 mm or smaller. The reason for setting the path length A to 100 mm or smaller will be described below.

[0045] Fig. 5 is a graph illustrating the correlation between the temperature and the density of CO₂ refrigerant in high-pressure states (12 MPa and 13 MPa). The abscissa of the graph indicates the temperature (degrees C) of the CO₂ refrigerant, and the ordinate indicates the density (kg/m³) of the CO₂ refrigerant. As shown in Fig. 5, CO₂ refrigerant in a high-pressure state has characteristics in which the density increases with decreasing temperature. The temperature range of the CO₂ refrigerant in a pipe (i.e., a main pipe) of the main circuit 10 is about 30 degrees C to 100 degrees C. The pressure detection pipe 115 has a pipe diameter smaller than that of the pipe of the main circuit 10 and has large heat loss per unit flow-path length. Consequently, the temperature of the refrigerant in the pressure detection pipe 115 decreases with increasing distance from the branching section 111. For example, assuming that the refrigerant temperature in the main pipe is 100 degrees C, the refrigerant temperature in the pressure detection pipe 115 is lower than 100 degrees C and decreases monotonously as the distance from the main pipe (i.e., the distance from the branching section 111) increases (see Fig. 5). Consequently, when the path length A between the branching section 111 and the narrowed pipe section 119 exceeds a predetermined value (e.g., 100 mm), the refrigerant between the branching section 111 and the narrowed pipe section 119 decreases in temperature and increases in density. Thus, pressure pulsation occurs between the branching section 111 and the narrowed pipe section 119, causing pressure pulsation at the terminal side relative to the narrowed pipe section 119 to be amplified.

[0046] In Embodiment 2, the path length A of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119 is set to 100 mm or smaller, so that the density of the refrigerant between the branching section 111 and the narrowed pipe section 119 can be lower than or equal to a value at which pressure pulsation occurs. Consequently, since amplification of pressure pulsation at the terminal side relative to the narrowed pipe section 119 can be suppressed, pulsation of the refrigerant pressure to be detected by the pressure sensor 113 can be suppressed.

[0047] As described above, in the refrigeration cycle apparatus according to Embodiment 2, the aforementioned pulsation suppression unit includes the pressure detection pipe 115 that connects the branching section 111, which is provided between the compressor 11 and the gas cooler 12 in the main circuit 10, and the pressure detectors (e.g., the pressure sensor 113 and the pressure switch 112) and that has the narrowed pipe section 119 whose flow-path cross-sectional area decreases at an intermediate position between the branching section 111 and the pressure sensors. Moreover, the path length A of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119 is 100 mm or smaller.

[0048] According to this configuration, since pulsation of the refrigerant pressure to be detected by the pressure detectors can be suppressed, the refrigerant pressure can be detected more accurately.

Embodiment 3

[0049] A refrigeration cycle apparatus according to Embodiment 3 of the present invention will be described. Fig. 6 illustrates the configuration of the pressure detection circuit 110 in the refrigeration cycle apparatus according to Embodiment 3. Components having the same functions and effects as those in the refrigeration cycle apparatus 1 and the pressure detection circuit 110 according to Embodiment 1 will be given the same reference signs, and descriptions thereof will be omitted.

[0050] As shown in Fig. 6, in the pressure detection pipe 115 of the pressure detection circuit 110 according to Embodiment 3, a part of the pipe line extending from the branching section 111 to the pressure sensor 113 has the narrowed pipe section 119. The path length A of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119 is, for example, larger than 100 mm. Furthermore, the pressure detection circuit 110 is provided with a heater 120 that heats a part of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119. The heater 120 heats the part of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119 to a temperature higher than or equal to that of the main circuit 10 at the vicinity of the branching section 111.

[0051] As mentioned above, when the path length A between the branching section 111 and the narrowed pipe section 119 exceeds 100 mm, the refrigerant between the branching section 111 and the narrowed pipe section 119 decreases in temperature and increases in density. Thus, pressure pulsation occurs between the branching section 111 and the narrowed pipe section 119, causing pressure pulsation at the terminal side relative to the narrowed pipe section 119 to be amplified. In Embodiment 3, the part of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119 is heated by the heater 120. Thus, the refrigerant temperature between the branching section 111 and the narrowed pipe section 119 can be prevented from decreasing, and the density of the refrigerant between the branching section 111 and the narrowed pipe section 119 can be lower than or equal to the value at which pressure pulsation occurs, so that amplification of pressure pulsation at the terminal side relative to the narrowed pipe section 119 can be suppressed. Consequently, pulsation of the refrigerant pressure to be detected by the pressure sensor 113 can be suppressed. Although the pressure detection pipe 115 in this example is described as having a path length A larger than 100 mm, the heater 120 may be provided at a pressure detection pipe 115 with a path length A smaller than or equal to 100 mm.

[0052] As described above, in the refrigeration cycle apparatus according to Embodiment 3, the aforementioned pulsation suppression unit includes the pressure detection pipe 115 that connects the branching section 111, which is provided between the compressor 11 and the gas cooler 12 in the main circuit 10, and the pressure detectors (e.g., the pressure sensor 113 and the pressure switch 112) and that has the narrowed pipe section 119 whose flow-path cross-sectional area decreases at an intermediate position between the branching section 111 and the pressure sensors, and the heater 120 that heats the part of the pressure detection pipe 115 between the branching section 111 and the narrowed pipe section 119.

[0053] According to this configuration, since pulsation of the refrigerant pressure to be detected by the pressure detectors can be suppressed, the refrigerant pressure can be detected more accurately.

Embodiment 4

[0054] A refrigeration cycle apparatus according to Embodiment 4 of the present invention will be described. Fig. 7 illustrates the configuration of the pressure detection circuit 110 in the refrigeration cycle apparatus according to Embodiment 4. Components having the same functions and effects as those in the refrigeration cycle apparatus 1 and the pressure detection circuit 110 according to Embodiment 1 will be given the same reference signs, and descriptions thereof will be omitted.

[0055] As shown in Fig. 7, the pressure detection pipe 115 of the pressure detection circuit 110 according to Embodiment 4 has no narrowed pipe section between the branching section 111 and the pressure sensor 113. A path length B of the pressure detection pipe 115 between the branching section 111 and the pressure sensor 113 (i.e., the overall length of the pressure detection pipe 115) is 1,000 mm or smaller. The reason for setting the path length B to 1,000 mm or smaller will be described below.

[0056] Assuming that the pressure wavelength in the pressure detection pipe 115 is defined as λ, when the path length B between the branching section 111 and the pressure sensor 113 is equal to ((2n - 1)/4)λ (n = 1, 2, 3, ...), such as 1/4λ and 3/4λ, amplification of pressure pulsation at a vicinity of the pressure sensor 113 becomes maximum. Consequently, amplification of pressure pulsation at the vicinity of the pressure sensor 113 can be suppressed by preventing the path length B from being equal to ((2n - -1)/4)λ. A pressure wavelength λ is obtained from the driving frequency of the compressor 11 and the speed of sound in the refrigerant.

[0057] Fig. 8 is a graph illustrating the relationship between the driving frequency of the compressor 11 and the pressure wavelength. The abscissa of the graph indicates the frequency (Hz) of the compressor 11, and the ordinate indicates the length (mm) of the pressure wavelength. As shown in Fig. 8, assuming that the range of the driving frequency (i.e., operating range) of the compressor 11 is about 30 Hz to 100 Hz, ((2n - 1)/4)λ (only 1/4λ and 3/4λ are shown in Fig. 8) may be all values larger than about 1,000 mm at frequencies in the operating range of the compressor 11. In other words, in a case where the path length B is larger than about 1,000 mm, the path length B is always equal to ((2n - 1)/4)λ with respect to at least some of the frequencies in the operating range of the compressor 11. In contrast, if the path length B is smaller than or equal to 1,000 mm, the path length B will not be equal to ((2n - 1)/4)λ at frequencies in the operating range of the compressor 11. Consequently, by setting the path length B smaller than or equal to 1,000 mm, amplification of pressure pulsation at the vicinity of the pressure sensor 113 can be prevented from being the maximum, thereby suppressing pulsation of the refrigerant pressure to be detected by the pressure sensor 113. Although the pressure detection pipe 115 in this example is described as not having a narrowed pipe section, Embodiment 4 is also applicable to a pressure detection pipe 115 having a narrowed pipe section.

[0058] As described above, in the refrigeration cycle apparatus according to Embodiment 4, the aforementioned pulsation suppression unit includes the pressure detection pipe 115 that connects the branching section 111, which is provided between the compressor 11 and the gas cooler 12 in the main circuit 10, and the pressure detectors (e.g., the pressure sensor 113 and the pressure switch 112). Moreover, the path length B of the pressure detection pipe 115 between the branching section 111 and the pressure detectors is 1,000 mm or smaller.

[0059] According to this configuration, since pulsation of the refrigerant pressure to be detected by the pressure detectors can be suppressed, the refrigerant pressure can be detected more accurately.

Embodiment 5

[0060] A refrigeration cycle apparatus according to Embodiment 5 of the present invention will be described. As mentioned above, the pulsation cycle of the refrigerant pressure in the refrigeration cycle apparatus is about 10 ms. Thus, with the sampling cycle of 20 ms commonly used in the pressure detection algorithm in the related art, pressure pulsation (e.g., a peak pressure value) cannot be detected, thus making it not possible to control the compressor 11 based on an accurate refrigerant pressure. In Embodiment 5, it is assumed that the waveform of pressure pulsation is a sine wave, and the pressure detection algorithm in the controller 100 is defined as follows to allow for more accurate detection of the refrigerant pressure.

[0061] Fig. 9 illustrates a pressure detection algorithm of the refrigeration cycle apparatus according to Embodiment 5. The abscissa in Fig. 9 indicates time (ms) elapsed after the power is turned on. In Embodiment 5, a sampling cycle for acquiring a detection value of the refrigerant pressure detected by the pressure sensor 113 (i.e., an output signal of the pressure sensor 113) is set to 1/2 or smaller of one cycle of the frequency (i.e., minimum driving frequency) of the compressor 11. For example, in a case of a compressor whose driving frequency is controlled in a range of about 30 Hz to 100 Hz, the sampling cycle is set to 16.7 ms or smaller, which is 1/2 or smaller of one cycle (33.3 ms) of the minimum driving frequency (30 Hz). In this example, the sampling cycle is set to 5 ms. Specifically, a detection value Hpt of the refrigerant pressure is acquired in a 5-ms cycle.

[0062] Subsequently, an average value Hpa and a half amplitude value Hpb are determined for every predetermined period, which is N times of the sampling cycle (N is an integer larger than or equal to 2) (i.e., every 100 ms, which is 20 times of the sampling cycle), with reference to a time when the power is turned on. The average value Hpa is an average value of N units (20 in this example) of detection values Hpt acquired within the aforementioned predetermined period. The half amplitude value Hpb is an average of absolute values of deviation from the average value Hpa of the N units of detection values Hpt. For example, assuming that a detection value acquired after T (ms) (T = 5, 10, 15, ..., 100) elapsed after the power is turned on is defined as HptT, the half amplitude value Hpb is expressed by (|Hpa - Hpt5| + |Hpa - Hpt10| + |Hpa - Hpt15| + ... + |Hpa - Hpt100|)/20.

[0063] Subsequently, an effective amplitude value Hpc, a peak amplitude value Hpd, and a peak pressure value Hpmpeak are calculated for every predetermined period mentioned above. The effective amplitude value Hpc is an average (moving average) of M units of half amplitude values Hpb (M is an integer larger than or equal to 2) calculated for M times of previous predetermined periods (five previous predetermined periods in this example). The peak amplitude value Hpd is √2 times of the effective amplitude value Hpc. The peak pressure value Hpmpeak is the sum of the peak amplitude value Hpd and the average value Hpa. The peak pressure value Hpmpeak may alternatively be the sum of the peak amplitude value Hpd and an average (moving average) of M units of average values Hpa calculated for M times of previous predetermined periods. If 500 ms have not elapsed after the power is turned on (i.e., if the time elapsed after the power is turned on is 100 ms, 200 ms, 300 ms, or 400 ms), the effective amplitude value Hpc is set as an average value of one to four determined half amplitude values Hpb. Specifically, the effective amplitude value Hpc, the peak amplitude value Hpd, and the peak pressure value Hpmpeak are all calculated for every predetermined period (i.e., 100 ms) elapsed after the power is turned on. Because the effective amplitude value Hpc, the peak amplitude value Hpd, and the peak pressure value Hpmpeak in a case where 500 ms have not elapsed after the power is turned on are calculated based on a method different from that used when 500 ms have elapsed after the power is turned on, these values are denoted by Hpc (*), Hpd (*), and Hpmpeak (*) in Fig. 9.

[0064] Based on the peak pressure value Hpmpeak calculated for every predetermined period, the controller 100 performs control, such as increasing and decreasing the driving frequency of the compressor 11 and stopping the compressor 11 if abnormal pressure is detected. The pressure detection algorithm described above may also be applied to the configuration of the refrigeration cycle apparatus according to any of Embodiment 1 to Embodiment 4 described above and may also be applied to the configuration of a refrigeration cycle apparatus in the related art.

[0065] As described above, the refrigeration cycle apparatus according to Embodiment 5 has the main circuit 10 in which at least the compressor 11, the gas cooler 12, the pressure reducing device 13, and the evaporator 14 are connected by pipes and that circulates refrigerant that transitions to a supercritical state at the high-pressure side, the pressure sensor 113 that detects the refrigerant pressure between the compressor 11 and the gas cooler 12 in the main circuit 10, and the controller 100 that controls the compressor 11 based on the refrigerant pressure. The controller 100 sets a sampling cycle for acquiring a detection value Hpt of the refrigerant pressure detected by the pressure sensor 113 to 1/2 or smaller of one cycle of the minimum frequency of the compressor 11, calculates an average value Hpa of N units of detection values Hpt and a half amplitude value Hpb, which is an average of absolute values of deviation from the average value Hpa of the N units of detection values Hpt, for every predetermined period, which is N times of the sampling cycle (N is an integer larger than or equal to 2), calculates a peak pressure value Hpmpeak, which is the sum of a peak amplitude value Hpd, which is √2 times of the moving average (i.e., an effective amplitude value Hpc) of M units of half amplitude values Hpb (M is an integer larger than or equal to 2) calculated for M times of previous predetermined periods, and the average value Hpa, and controls the compressor 11 based on the peak pressure value Hpmpeak.

[0066] According to this configuration, the refrigerant pressure can be detected more accurately, and the compressor 11 can be controlled based on the more accurate refrigerant pressure.

[0067] The advantageous effects of Embodiment 5 will be described with reference to Fig. 10 and Fig. 11. Fig. 10 is a graph illustrating an example of a pressure value (i.e., a peak pressure value Hpmpeak) calculated in Embodiment 5. In the graph, each solid diamond symbol denotes a pre-input pressure value, each void triangle symbol denotes an average value Hpa, and each void square symbol denotes a peak pressure value Hpmpeak. Fig. 11 is a graph illustrating an example of detected pressure values in the related art. In the graph, each solid diamond symbol denotes a pre-input pressure value and each solid square symbol denotes a detected pressure value in the related art. In both Fig. 10 and Fig. 11, the waveform of pressure pulsation is a sine wave, the pulsation frequency is 96 Hz, the pulsation amplitude is 2 MPa, and the increasing rate of average pressure is 0.05 MPa/s. As shown in Fig. 11, pressure pulsation cannot be detected with the detected pressure values in the related art. In contrast, as shown in Fig. 10, the peak pressure value Hpmpeak calculated in accordance with Embodiment 5 is substantially equal to a high-pressure-side peak value of pressure pulsation. Consequently, a high-pressure-side peak of pressure pulsation can be detected in accordance with Embodiment 5.

Other Embodiments

[0068] The present invention is not limited to Embodiment 1 to Embodiment 5 described above and may be variously modified.

[0069] For example, although the pressure detection pipes 114 and 115 having the same inside diameter (i.e., the same flow-path cross-sectional area) from the branching section 111 to the pressure switch 112 or the pressure sensor 113 are used as examples of pressure detection pipes not having narrowed pipe sections in Embodiment 1, the present invention is not limited to this configuration. The pressure detection pipes 114 and 115 may be expanded between the branching section 111 and the pressure switch 112 or the pressure sensor 113.

[0070] Furthermore, the pressure detection pipes 114 and 115 may each have an expanded pipe section whose flow-path cross-sectional area increases at an intermediate position within a range so that the flow-path cross-sectional area immediately before the pressure switch 112 or the pressure sensor 113 is not smaller than the flow-path cross-sectional area immediately after the branching section 111. Alternatively, the pressure detection pipes 114 and 115 may each have an expanded pipe section and a narrowed pipe section within a range so that the flow-path cross-sectional area immediately before the pressure switch 112 or the pressure sensor 113 is not smaller than the flow-path cross-sectional area immediately after the branching section 111.

[0071] Furthermore, Embodiment 1 to Embodiment 5 described above and the modifications thereof may be combined with one another.

Reference Signs List

[0072] 1 refrigeration cycle apparatus, 10 main circuit, 11 compressor, 12 gas cooler, 13 pressure reducing device, 14 evaporator, 15, 16, 25, 35, 40, 55, 61 strainer, 17 high-pressure low-pressure heat exchanger, 20 muffler, 21 oil recovery circuit, 22 heat exchanger, 23, 33, 38 bypass circuit, 24, 34, 39, 44 solenoid valve, 26 branch pipe, 27a, 121 a service valve, 27b, 121 b service port, 29 pressure sensor, 30 capillary pipe, 31, 36, 41 branching section, 32, 37, 42, 56 merging section, 45 internal heat exchanger, 50 boiler circuit, 51 circulation pump, 52, 58, 62 electric valve, 53, 59 check valve, 54, 60 pressure reducing valve, 63 relief valve, 64 flow rate sensor, 71, 72, 73, 74, 75, 76, 77, 78 temperature sensor, 100 controller, 110, 210 pressure detection circuit, 111, 116, 117 branching section, 112 pressure switch, 113 pressure sensor, 114, 115 pressure detection pipe, 118 branch pipe, 119 narrowed pipe section, 120 heater

Claims

1. A refrigeration cycle apparatus comprising:

a main circuit connecting at least a compressor, a gas cooler, a pressure reducing device, and an evaporator by a pipe and configured to circulate refrigerant transitioning to a supercritical state at a high-pressure side;

a pressure detector configured to detect refrigerant pressure in a part of the main circuit between the compressor and the gas cooler; and

a pulsation suppression unit configured to suppress pulsation of the refrigerant pressure to be detected by the pressure detector.

2. The refrigeration cycle apparatus of Claim 1,
wherein the pulsation suppression unit includes a pressure detection pipe connecting a branching section, provided at a part of the main circuit between the compressor and the gas cooler, and the pressure detector and not having a narrowed pipe section decreasing a flow-path cross-sectional area thereof at an intermediate position from the branching section to the pressure detector.

3. The refrigeration cycle apparatus of Claim 1,
wherein the pulsation suppression unit includes a pressure detection pipe connecting a branching section, provided at a part of the main circuit between the compressor and the gas cooler, and the pressure detector,
wherein a flow-path cross-sectional area immediately before the pressure detector is not smaller than a flow-path cross-sectional area immediately after the branching section, and
wherein the pressure detection pipe has an expanded pipe section or a set of an expanded pipe section and a narrowed pipe section, the expanded pipe section increasing a flow-path cross-sectional area thereof at an intermediate position from the branching section to the pressure detector, the narrowed pipe section decreasing a flow-path cross-sectional area thereof at an intermediate position from the branching section to the pressure detector.

4. The refrigeration cycle apparatus of Claim 1,
wherein the pulsation suppression unit includes a pressure detection pipe connecting a branching section, provided at a part of the main circuit between the compressor and the gas cooler, and the pressure detector and having a narrowed pipe section decreasing a flow-path cross-sectional area thereof at an intermediate position from the branching section to the pressure detector, and
wherein a path length of a part of the pressure detection pipe between the branching section and the narrowed pipe section is 100 mm or smaller.

5. The refrigeration cycle apparatus of Claim 1,
wherein the pulsation suppression unit includes
a pressure detection pipe connecting a branching section, provided at a part of the main circuit between the compressor and the gas cooler, and the pressure detector and having a narrowed pipe section decreasing a flow-path cross-sectional area thereof at an intermediate position from the branching section to the pressure detector, and
a heater configured to heat a part of the pressure detection pipe between the branching section and the narrowed pipe section.

6. The refrigeration cycle apparatus of Claim 1,
wherein the pulsation suppression unit includes a pressure detection pipe connecting a branching section, provided at a part of the main circuit between the compressor and the gas cooler, and the pressure detector, and
wherein a path length of the pressure detection pipe between the branching section and the pressure detector is 1,000 mm or smaller.

7. A refrigeration cycle apparatus comprising:

a main circuit connecting at least a compressor, a gas cooler, a pressure reducing device, and an evaporator by a pipe and configured to circulate refrigerant transitioning to a supercritical state at a high-pressure side;

a pressure detector configured to detect refrigerant pressure at a part of the main circuit between the compressor and the gas cooler; and

a controller configured to control the compressor based on the refrigerant pressure,

wherein the controller is configured to set a sampling cycle for acquiring a detection value of the refrigerant pressure detected by the pressure detector to 1/2 or smaller of one cycle of a minimum frequency of the compressor,

wherein the controller is configured to calculate an average value of N units of the detection values and a half amplitude value being an average of absolute values of deviation from the average value of the N units of the detection values for every time of predetermined period being N times of the sampling cycle, N being an integer larger than or equal to 2,

wherein the controller is configured to calculate a peak pressure value being a sum of a peak amplitude value and the average value for every time of the predetermined period, the peak amplitude value being √2 times of a moving average of M units of the half amplitude values calculated for M times of the previous predetermined periods, M being an integer larger than or equal to 2, and

wherein the controller is configured to control the compressor based on the peak pressure value.

Drawing