Cooling device

Abstract

To provide a cooling device capable of enhancing energy-saving performance while simplifying the constitution of a hot gas defrosting circuit.SOLUTION: A cooling device uses a refrigeration cycle 1 which includes: a circulation circuit in which a plurality of stages of compressors 20, 21, a gas cooler 3 and evaporators 5A, 5B are connected; and a hot gas defrosting circuit for defrosting the evaporators 5A, 5B. In the hot gas defrosting circuit, a pipe line 100C for constituting the downstream side of the evaporators 5A, 5B is connected to the circulation circuit at a confluence position C on the upstream side of the gas cooler 3. In the circulation circuit, pressure adjustment means 60 is provided further on the upstream side than the confluence position C which adjusts a heating medium discharged from the compressor 21 to a pressure equal to or less than the heating medium after defrosting of the evaporator 5A.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cooling device using a refrigeration cycle that includes a circulation circuit connected to at least a single-stage or multi-stage compressor, a gas cooler or condenser, and an evaporator, and a hot gas defrost circuit that defrosts the evaporator. [Background technology]

[0002] BACKGROUND ART Cooling devices used to cool objects in various industrial fields are known. Such cooling devices are configured to cool objects by utilizing a refrigeration cycle using a heat medium.

[0003] In a cooling system using a refrigeration cycle, frost forms on the surface of the evaporator during cooling operation, reducing the cooling capacity. Therefore, a defrosting operation is required to remove the frost that has formed on the evaporator. For example, the cooling system disclosed in Patent Document 1 is equipped with a hot gas defrosting circuit that enables the use of a high-pressure heat transfer medium discharged from a high-stage compressor for defrosting operation. Specifically, in the cooling system disclosed in Patent Document 1, during defrosting operation, the defrosted gas-liquid two-phase heat transfer medium that has passed through the evaporator is reduced in pressure by an expansion valve provided downstream of the evaporator in the hot gas defrosting circuit, and then evaporated in a separately provided heat exchanger (heating device) through heat exchange with a medium-pressure heat transfer medium discharged from a low-stage compressor to become a gas-phase heat transfer medium, which is then drawn into the low-stage compressor. This prevents the defrosted heat transfer medium from returning liquid to the low-stage compressor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Microfilm of Utility Model Publication No. 55-10961 (pages 5-7, Figure 2) Summary of the Invention [Problem to be solved by the invention]

[0005] However, although Patent Document 1 is highly reliable in terms of preventing the liquid backflow of the heat transfer medium after defrosting into the low-stage compressor, it requires a separate heating device to evaporate the heat transfer medium after defrosting, which not only complicates the configuration of the hot gas defrost circuit, but also requires that the heat transfer medium after defrosting be compressed in the low-stage compressor, which increases the compression power of the heat transfer medium that does not contribute to cooling capacity, resulting in problems of reduced energy-saving performance.

[0006] The present invention has been made in light of these problems, and aims to provide a cooling device that can simplify the configuration of the hot gas defrost circuit while improving energy-saving performance. [Means for solving the problem]

[0007] In order to solve the above problems, the cooling device of the present invention comprises: A cooling device using a refrigeration cycle including a circulation circuit connected to at least a single-stage or multiple-stage compressor, a gas cooler or condenser, and an evaporator, and a hot gas defrost circuit for defrosting the evaporator, the hot gas defrosting circuit is configured such that a pipe constituting a downstream side of the evaporator is connected to the circulation circuit at a joining position upstream of the gas cooler or the condenser, The circulation circuit is characterized in that a pressure adjustment means is provided further upstream of the junction position to adjust the pressure of the heat medium discharged from the compressor to a pressure equal to or lower than the pressure of the heat medium after defrosting of the evaporator. According to this feature, by adjusting the pressure of the heat transfer medium in the circulation circuit using a pressure adjustment means provided upstream of the gas cooler or condenser, the heat transfer medium after defrosting in the evaporator can be merged with the heat transfer medium flowing in the circulation circuit at the merging point upstream of the gas cooler or condenser, and the entire amount of heat transfer medium discharged from the compressor can be made to contribute to the cooling capacity, thereby simplifying the configuration of the hot gas defrost circuit while improving energy-saving performance.

[0008] The compressor is characterized in that the discharge pressure during the defrosting operation is higher than the discharge pressure during the cooling operation. According to this feature, by increasing the discharge pressure of the compressor during defrost operation, the pressure of the heat transfer medium adjusted by the pressure adjustment means can be made equal to or higher than the pressure inside the gas cooler or condenser, allowing the heat transfer medium to flow smoothly into the gas cooler or condenser.

[0009] The discharge pressure during the defrosting operation is increased by an amount corresponding to a pressure drop of the heat medium after defrosting of the evaporator. According to this feature, the increase in power consumption of the compressor can be minimized, thereby improving energy-saving performance.

[0010] The pressure adjusting means is characterized by comprising a pressure adjusting valve. According to this feature, the structure of the pressure adjusting means can be simplified. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a refrigeration cycle used in a cooling device of an embodiment according to the present invention, and Fig. 1 shows a state in which cooling operation is performed by both evaporators connected in parallel. [Figure 2] FIG. 10 is a diagram showing a state in which one of the evaporators connected in parallel is switched to a defrosting operation in the refrigeration cycle of the embodiment. [Figure 3] FIG. 10 is a diagram showing a state in which the other evaporator connected in parallel is switched to a defrosting operation in the refrigeration cycle of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cooling device according to an embodiment of the present invention will be described below with reference to the accompanying drawings. [Example]

[0013] A cooling device according to an embodiment will be described with reference to Fig. 1 to Fig. 3. In this embodiment, a cooling device using a two-stage compression, one-stage expansion refrigeration cycle 1 (hereinafter referred to as "refrigeration cycle 1") in which carbon dioxide is circulated as a heat medium will be described as an example.

[0014] As shown in Figures 1 to 3, the refrigeration cycle 1 in this embodiment is used in cooling devices such as industrial refrigerators, and is mainly composed of a circulation circuit in which a low-stage compressor 20, a high-stage compressor 21, a gas cooler 3, expansion valves 4A, 4B, evaporators 5A, 5B, and a receiver tank 7 are connected by pipes, a hot gas defrost circuit connected to the circulation circuit at a junction C upstream of the gas cooler 3, and a pressure adjustment mechanism 60 (pressure adjustment means) provided further upstream of the junction C.

[0015] In this embodiment, the hot gas defrost circuit is provided with bypass pipes 100A and 100B that branch off from the downstream side of the high-stage compressor 21, more specifically, between the high-stage compressor 21 and the gas cooler 3, and are connected to the upstream side of the evaporators 5A and 5B, more specifically, between the expansion valves 4A and 4B and the evaporators 5A and 5B, respectively, thereby allowing the high-pressure gas-phase heat transfer medium discharged from the high-stage compressor 21 to be used to defrost the evaporators 5A and 5B.

[0016] The hot gas defrost circuit also includes a bypass pipe 100C (a pipe constituting the downstream side of the evaporators) that branches off downstream of the evaporators 5A, 5B, more specifically between the evaporators 5A, 5B and the solenoid valves 50A, 50B, joins downstream of the solenoid valves 80A, 80B, and is then connected to the circulation circuit at a joining position C upstream of the gas cooler 3.

[0017] In this embodiment, the pressure adjustment mechanism 60 is provided further upstream of the above-mentioned junction position C, more specifically, between the junction position C and the high-stage compressor 21. When a defrosting operation is being performed in one of the evaporators 5A, 5B, the pressure adjustment mechanism 60 adjusts (depressurizes) the pressure of the heat medium discharged from the high-stage compressor 21 to a pressure equal to or lower than the pressure of the heat medium after defrosting in the evaporators 5A, 5B. This allows the defrosted heat medium to be merged (flown into) the high-pressure heat medium flowing through the circulation circuit at the junction position C of the circulation circuit and the hot gas defrosting circuit (bypass pipe 100C).

[0018] Furthermore, in this embodiment, the pressure adjustment mechanism 60 is configured so that the opening degree of the motor-operated valve 6 (pressure adjustment valve) can be electrically controlled by the PIC 91 based on the discharge pressure of the high-stage compressor 21. Note that, although this embodiment describes an embodiment in which the pressure adjustment mechanism 60 is configured from the PIC 61 and the motor-operated valve 6, the present invention is not limited to this, and the valve that configures the pressure adjustment mechanism may be any valve that functions as a proportional automatic pressure adjustment valve, and may be configured as an air-operated valve or the like other than the motor-operated valve.

[0019] Here, a state in which both evaporators 5A and 5B connected in parallel are performing cooling operations will be described with reference to Fig. 1. As shown in Fig. 1, when both evaporators 5A and 5B are performing cooling operations, solenoid valves 9A and 9B provided in bypass pipes 100A and 100B constituting the hot gas defrost circuit and solenoid valves 80A and 80B provided in bypass pipe 100C are closed. Furthermore, when both evaporators 5A and 5B are performing cooling operations, motor-operated valve 6 constituting pressure adjustment mechanism 60 allows the heat medium discharged from high-stage compressor 21 to pass through without adjusting its pressure.

[0020] As shown by the solid arrows in Figure 1, when cooling operation is being performed in both evaporators 5A and 5B, the medium-pressure (PE3) gas-phase heat transfer medium discharged from the low-stage compressor 20 is sucked into the high-stage compressor 21, and the high-pressure (PE1-1) gas-phase heat transfer medium discharged from the high-stage compressor 21 passes directly through the motor-operated valve 6, and then passes through the gas cooler 3 to lower its temperature, becoming a high-pressure (PE1-1) heat transfer medium and storing it in the receiver tank 7.

[0021] The high-pressure (PE1-1) liquid-phase heat transfer medium sent from the receiver tank 7 to the evaporators 5A and 5B passes through solenoid valves 40A and 40B and check valves 41A and 41B in that order, and then passes through expansion valves 4A and 4B, respectively, where it is reduced in pressure to become a low-pressure (PE4) liquid-phase heat transfer medium. This flows into the evaporators 5A and 5B, respectively, and cools the target (external fluid). The low-pressure (PE4) gas-phase heat transfer medium that has passed through the evaporators 5A and 5B passes through solenoid valves 50A and 50B, respectively, before joining and being drawn into the low-stage compressor 20. Note that depending on the cooling capacity of the evaporators 5A and 5B, the heat transfer medium that has passed through the evaporators 5A and 5B may not evaporate sufficiently and become a two-phase gas-liquid heat transfer medium. Therefore, for example, a separate accumulator or the like may be provided between the solenoid valves 50A and 50B and the low-stage compressor 20 to reliably prevent liquid backflow to the low-stage compressor 20.

[0022] Next, a state in which a defrosting operation is being performed in one of the evaporators 5A and 5B will be described with reference to Figures 2 and 3. As shown in Figure 2, when a defrosting operation is being performed in the evaporator 5A, compared to the state in Figure 1, solenoid valve 9A provided in bypass pipe 100A and solenoid valve 80A provided in bypass pipe 100C, which constitute the hot gas defrosting circuit, are opened, and solenoid valve 40A provided upstream of expansion valve 4A and solenoid valve 50A provided downstream of evaporator 5A are closed. Also, as shown in Figure 3, when a defrosting operation is being performed in the evaporator 5B, compared to the state in Figure 1, solenoid valve 9B provided in bypass pipe 100B and solenoid valve 80B provided in bypass pipe 100C, which constitute the hot gas defrosting circuit, are opened, and solenoid valve 40B provided upstream of expansion valve 4B and solenoid valve 50B provided downstream of evaporator 5B are closed.

[0023] Furthermore, in this embodiment, when a defrosting operation is being performed on one of the evaporators 5A and 5B, the discharge pressure of the high-stage compressor 21 is increased above the discharge pressure during cooling operation. Specifically, the discharge pressure (PE1-2) of the high-stage compressor 21 during defrosting operation is increased by a pressure equivalent to the pressure difference α between the discharge pressure (PE1-1) of the high-stage compressor 21 during cooling operation and the pressure (PE2-3) of the heat transfer medium after defrosting in the evaporators 5A and 5B, i.e., the pressure drop of the heat transfer medium after defrosting (PE1-2 = PE1-1 + α). Here, the drop in the pressure of the heat transfer medium after defrosting is caused by a pressure loss and a temperature drop of the heat transfer medium in the hot gas defrosting circuit.

[0024] In this embodiment, the output of the high-stage compressor 21 during defrost operation is controlled based on measurement data relating to the pressure drop of the heat transfer medium after defrosting of the evaporators 5A, 5B. For example, the measurement data may be a data table showing the relationship between the evaporator temperature at the start of defrost operation and the above-mentioned pressure difference α. By controlling the output of the high-stage compressor 21 based on this measurement data, the heat transfer medium can be smoothly flowed into the gas cooler 3 immediately after the start of defrost operation. Alternatively, a pressure sensor may be provided in the hot gas defrost circuit to measure the pressure of the heat transfer medium after defrosting, and the output of the high-stage compressor 21 may be controlled in real time based on this measurement data.

[0025] As shown by the solid arrow in Figure 2, when defrosting operation is being performed in the evaporator 5A, the medium-pressure (PE3) gas-phase heat transfer medium discharged mainly from the low-stage compressor 20 is sucked into the high-stage compressor 21, and a portion of the high-pressure (PE1-2) gas-phase heat transfer medium discharged from the power-increased high-stage compressor 21 passes through the solenoid valve 9A provided in the bypass pipe 100A, and then flows into the evaporator 5A to perform defrosting.

[0026] The defrosted heat medium that has passed through the evaporator 5A passes through the solenoid valve 80A and check valve 81A provided in the bypass pipe 100C in that order, and then flows into the circulation circuit at the junction position C. At this time, in the circulation circuit at the junction position C, there is still a high-pressure (PE2-2) heat medium whose pressure has been adjusted (reduced) by the high-pressure (PE1-2) gas-phase heat medium discharged from the high-stage compressor 21 passing through the motor-operated valve 6 that constitutes the pressure adjustment mechanism 60. However, since the high-pressure (PE2-2) heat medium has been adjusted (reduced) to a pressure lower than that of the defrosted heat medium (PE2-3≧PE2-2), the defrosted heat medium can be smoothly merged (flowed into) into the circulation circuit at the junction position C.

[0027] The high-pressure heat medium that has merged with the circulation circuit at the merge position C flows into the gas cooler 3. At this time, because the discharge pressure of the high-stage compressor 21 during defrosting operation is higher than the discharge pressure during cooling operation, the pressure of the heat medium (PE2-2) adjusted (reduced) by the pressure adjustment mechanism 60, and therefore the pressure of the heat medium that merges with the heat medium after defrosting at the merge position C and flows into the gas cooler 3, can be adjusted to be equal to or higher than the pressure inside the gas cooler 3 (≒PE1-1), thereby ensuring a smooth flow of the heat medium at the inlet of the gas cooler 3.

[0028] The high-pressure liquid-phase heat transfer medium is liquefied by passing through the gas cooler 3 and stored in the receiver tank 7, and is sent to the evaporator 5B to contribute to the cooling capacity of the evaporator 5B. Note that the cooling operation of the evaporator 5B is the same as the state in which the cooling operation is performed by both the evaporators 5A and 5B described above, and therefore a detailed description thereof will be omitted.

[0029] Also, as shown in Figure 3, the state in which defrost operation is being performed in evaporator 5B is substantially the same as the state in which defrost operation is being performed in evaporator 5A described above, except that the operating modes of evaporators 5A and 5B are swapped, so detailed explanation will be omitted.

[0030] As described above, the cooling device of this embodiment adjusts (depressurizes) the pressure of the heat medium in the circulation circuit using the pressure adjustment mechanism 60 provided upstream of the gas cooler 3. This allows the heat medium after defrosting in the evaporator to merge with the heat medium in the circulation circuit at the merging point C upstream of the gas cooler 3, allowing the entire amount of heat medium discharged from the high-stage compressor 21 to contribute to cooling capacity. This eliminates the need for a pressure reduction device that depressurizes the heat medium downstream of the evaporator, which was necessary in conventional hot gas defrost circuits, and a heating device for the heat medium after defrosting. This simplifies the configuration of the hot gas defrost circuit and improves energy-saving performance. Furthermore, the simplification of the hot gas defrost circuit configuration reduces the initial cost of the cooling device and the installation space.

[0031] Furthermore, the discharge pressure of the high-stage compressor 21 during defrosting operation is made higher than the discharge pressure during cooling operation, so that the pressure of the heat medium adjusted by the pressure adjustment mechanism 60 can be made equal to or higher than the pressure inside the gas cooler 3, allowing the heat medium to smoothly flow into the gas cooler 3. Furthermore, the discharge pressure during defrosting operation is increased by the amount of pressure drop (differential pressure α) of the heat medium after defrosting of the evaporator, so that the increase in power of the high-stage compressor 21 can be kept to a minimum, thereby further improving energy-saving performance.

[0032] Furthermore, the pressure adjustment mechanism 60 includes the motor-operated valve 6, which is a pressure adjustment valve, thereby simplifying the configuration of the pressure adjustment means.

[0033] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0034] For example, in the above embodiment, the discharge pressure of the high-stage compressor 21 is increased during defrosting operation of the evaporator. However, this is not limiting, and the compressor may not change its discharge pressure during defrosting operation of the evaporator. In other words, the compressor may be output-controlled to the same discharge pressure as during cooling operation.

[0035] Furthermore, in the above embodiment, the pressure adjustment means has been described as being configured as a pressure adjustment mechanism 60 having an electric valve 6 which is a pressure adjustment valve, but this is not limited thereto. The pressure adjustment means may be configured, for example, as a heat exchanger provided in a bypass pipe line which can flow only during defrosting operation, between the confluence position C and the compressor, as long as it can adjust (reducing pressure) the pressure of the heat medium discharged from the compressor to a pressure lower than that of the heat medium after defrosting of the evaporator.

[0036] In addition, in the above embodiment, the refrigeration cycle 1 is described as having two evaporators 5A, 5B connected in parallel, but this is not limited to this, and the refrigeration cycle 1 may also be configured, for example, with three or more evaporators connected in parallel.

[0037] In addition, in the above embodiment, the refrigeration cycle 1 has been described as a two-stage compression, single-stage expansion system having a low-stage compressor 20 and a high-stage compressor 21, but the refrigeration cycle of the present invention is not limited to this, and may be, for example, a three-stage or more compression system, a single-stage compression system, or a two-stage expansion system.

[0038] Furthermore, the compressor is not limited to the one in which a low-stage compressor and a high-stage compressor are separately provided as in the above embodiment, but may be a single-shaft multi-stage compressor.

[0039] In addition, in the above embodiment, a gas cooler is used because carbon dioxide is circulated as a heat transfer medium. However, if, for example, chlorofluorocarbon, ammonia, or the like is circulated as a heat transfer medium, it is preferable to use a condenser instead of a gas cooler. [Explanation of symbols]

[0040] 1 Refrigeration cycle 3 Gas Cooler 4A, 4B expansion valve 5A, 5B Evaporator 6. Motor-operated valve (pressure regulating valve) 7. Receiver Tank 9A, 9B solenoid valves 20 Low-stage compressor 21 High-stage compressor 40A, 40B solenoid valve 41A, 41B check valve 50A, 50B solenoid valve 60 Pressure adjustment mechanism (pressure adjustment means) 80A, 80B solenoid valve 81A, 81B check valve 100A, 100B Bypass pipeline 100C Bypass pipe (pipe downstream of the evaporator) C Confluence position

Claims

1. A cooling device using a refrigeration cycle including a circulation circuit connected to at least a single-stage or multiple-stage compressor, a gas cooler or condenser, and an evaporator, and a hot gas defrost circuit for defrosting the evaporator, the hot gas defrosting circuit is configured such that a pipe constituting a downstream side of the evaporator is connected to the circulation circuit at a joining position upstream of the gas cooler or the condenser, a pressure adjusting means for adjusting the pressure of the heat transfer medium discharged from the compressor to a pressure equal to or lower than that of the heat transfer medium after defrosting of the evaporator, further upstream of the junction position, in the circulation circuit.

2. 2. The cooling device according to claim 1, wherein the compressor has a discharge pressure higher during a defrosting operation than during a cooling operation.

3. 3. The cooling device according to claim 2, wherein the discharge pressure during the defrosting operation is increased by an amount corresponding to a pressure drop of the heat medium after defrosting of the evaporator.

4. 4. The cooling device according to claim 1, wherein the pressure adjusting means comprises a pressure adjusting valve.

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