JP2019100603A - Hot gas defrosting operation method of refrigeration circuit - Google Patents

Abstract

To provide a defrosting operation method of a refrigeration circuit capable of preventing excessive load from acting on a compressor in restoration to normal operation.SOLUTION: A defrosting operation method is applied to a refrigerant circuit comprising: a bypass pipe conduit connecting between a pipe conduit between a compressor and a condenser, and a pipe conduit between an expander and an evaporator; a bypass pipe conduit opening/closing valve arranged on the bypass pipe conduit; and a main pipe conduit opening/closing valve arranged on the pipe conduit between the condenser and the expander. The defrosting operation method comprises: when ending defrosting performed in a state the bypass pipe conduit opening/closing valve is opened and the main pipe conduit opening/closing valve is closed, stopping the compressor and opening the main pipe conduit opening/closing valve; and keeping the bypass pipe conduit opening/closing valve into an open state until a predetermined condition is established.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a hot gas defrosting operation method of a refrigeration circuit.

  Refrigerant circuits built in cooling equipment such as vending machines and refrigerated / refrigerated showcases include an evaporator, an accumulator, a compressor, a condenser, and an expander sequentially in the flow direction of the refrigerant on a pipe line on which the refrigerant circulates. It is arranged.

  During operation of the refrigeration circuit, the low-temperature and low-pressure liquid-phase refrigerant absorbs heat from the air in the refrigerator of the cooling device introduced by the evaporator fan in the evaporator and evaporates (vaporizes) under a constant pressure. Cool the air inside. The low pressure refrigerant flowing out of the evaporator is separated into gas and liquid in the accumulator, and only the gas phase refrigerant flows into the compressor to be compressed, and is delivered to the condenser as the high temperature and pressure gas phase refrigerant. The high temperature and high pressure gas phase refrigerant releases heat to the atmosphere introduced by the condenser fan in the condenser and condenses (liquefies) under constant pressure. The high-pressure liquid-phase refrigerant is temporarily stored in the liquid reservoir of the condenser, and then isenthalpically expanded in an expander (capillary, electronic expansion valve, etc.) to become a low-temperature low-pressure liquid-phase refrigerant, and the evaporator To reflux.

  During operation of the refrigeration circuit, the evaporator is low in surface temperature because a low temperature refrigerant is flowing inside, and if the air in the cold storage of the cooling device contains moisture, the moisture is contained in the evaporator. May adhere to the surface of the evaporator and freeze, resulting in frost (frost formation).

  Thus, when frost forms on the evaporator, the heat of the evaporator is increased due to an increase in the heat transfer resistance in the frosted area and a decrease in the air flow rate due to partial blocking of the air passage around the frosted area. The exchange efficiency is reduced, which in turn reduces the coefficient of performance of the refrigeration circuit.

  In order to prevent this, in the refrigeration circuit, a defrosting operation is performed to remove the adhered frost when frost formation is detected or at predetermined time intervals at which occurrence of frost formation is expected.

  There are various methods for defrosting operation, but the pipe line downstream of the compressor (between the compressor and the condenser) and the pipe line downstream of the expander (between the expander and the evaporator) are connected A bypass line is provided, and the high temperature gas phase refrigerant discharged from the compressor is returned to the evaporator through the bypass line, thereby utilizing the sensible heat and latent heat to deposit frost adhering to the surface of the evaporator. It is known to melt, so-called hot gas defrosting.

  In order to perform hot gas defrosting, a bypass line and a line from the bypass line branch point downstream of the compressor to the bypass line joint point downstream of the expander through the condenser and the expander (main line The high temperature gas-phase refrigerant discharged from the compressor flows only in the bypass line by providing the on / off valve in each of the two), closing the on / off valve on the main line, and opening the on / off valve on the bypass line. Let's do it.

  However, when the on-off valve on the bypass pipeline is opened, if the on-off valve on the main pipeline is closed at the same time, a large amount of gas phase refrigerant flows into the evaporator through the bypass pipeline and condenses (liquefies). Liquid phase refrigerant is generated. When the amount of the liquid phase refrigerant exceeds the gas-liquid separation capacity of the accumulator, a part of the liquid phase refrigerant may flow into the compressor without being separated and removed by the accumulator and may damage the compressor. In order to prevent this, it is sufficient to increase the size of the accumulator to enhance the gas-liquid separation capacity, but generally, the size of the accumulator that is required to have the minimum necessary size due to restrictions on the installation location and cost is increased. Is not desirable.

  Therefore, it has been proposed that, at the start of the hot gas defrosting operation, the on-off valve on the main pipeline be kept open even after opening the on-off valve on the bypass pipeline and closed after a predetermined time has elapsed (Patent Literature 1).

  According to this method, after the hot gas defrosting operation is started, the gas phase refrigerant flows into the condenser to be condensed (liquefied) and stored in the liquid reservoir until the predetermined time elapses, so the predetermined time After the on-off valve on the main pipeline is closed and the amount of refrigerant flowing into the evaporator through the bypass pipeline is significantly reduced. Thus, the amount of liquid phase refrigerant generated in the evaporator can be contained within the gas-liquid separation capacity of the accumulator, and the inflow of liquid phase refrigerant into the compressor can be prevented.

Japanese Patent Application Laid-Open No. 62-223570

  However, patent document 1 does not mention the operation at the time of returning to normal operation, after the hot gas defrosting operation by the method mentioned above is completed.

  According to the method described above, a large amount of liquid-phase refrigerant is stored in the liquid reservoir of the condenser at the end of the hot gas defrosting operation. In this state, the pressure on the high pressure side of the refrigeration circuit (pipe line from the compressor to the condenser to the expander) is the pressure on the low pressure side of the refrigeration circuit (pipe from the expander to the evaporator to the compressor) It is very high compared to the pressure of the road). That is, the differential pressure between the high pressure side and the low pressure side of the refrigeration circuit is in a very large state. In this state, if the on-off valve on the main conduit is opened at the same time as the on-off valve on the bypass conduit is closed, an excessive load is applied to the compressor. Therefore, there is a problem that it is necessary to increase the size of the motor which is a drive source of the compressor, or power consumption of the motor is increased. In addition, when a small-sized compressor is adopted for the purpose of downsizing and energy saving of the cooling device, the compressor and the electric motor which is a driving source of the compressor are caused due to the above-mentioned excessive load. There is a risk of damage.

  The present invention has been made in view of the above problems, and prevents an excessive load from acting on the compressor when the refrigeration circuit returns to the normal operation after the end of the defrosting operation. It is an object of the present invention to provide a defrosting operation method that can be performed.

  In order to solve the above-mentioned subject, the defrosting operation method of the present invention comprises: an evaporator, a compressor, a condenser, and an expander, which are sequentially disposed in a flowing direction of the refrigerant on a pipe line through which the refrigerant circulates A bypass line connecting the pipeline between the compressor and the condenser, the pipeline between the expander and the evaporator, and a bypass pipeline on-off valve disposed on the bypass pipeline; It is applied to a refrigeration circuit provided with a main pipeline on-off valve disposed on the pipeline between the condenser and the expander, wherein the bypass pipeline on-off valve is opened, and the main pipeline is opened. When the defrosting performed with the on-off valve closed is finished, the compressor is stopped and the main line on-off valve is opened, while the bypass line on-off valve is opened until a predetermined condition is satisfied. It is characterized by being maintained in

  Preferably, the pressure of the refrigerant in a portion of the pipe leading from the compressor to the condenser through the condenser is a high pressure side pressure, and the pipe from the expander to the evaporator through the evaporator. When the pressure of the refrigerant in the portion leading to the pressure side is referred to as the low pressure side pressure, the predetermined condition is that the differential pressure between the high pressure side pressure and the low pressure side pressure is the compressor after the defrosting is completed. The pressure equalization time may be reduced to the maximum differential pressure that can be activated.

  Preferably, the pressure equalization time may be determined in advance.

  Preferably, the pressure of the refrigerant in a portion of the pipe leading from the compressor to the condenser through the condenser is a high pressure side pressure, and the pipe from the expander to the evaporator through the evaporator. When the pressure of the refrigerant in the portion leading to the pressure side is referred to as a low pressure side pressure, the refrigeration circuit further includes pressure sensors for detecting the high pressure side pressure and the low pressure side pressure, and the predetermined condition is the pressure It is preferable that a differential pressure between the high pressure side pressure and the low pressure side pressure detected by a sensor be lower than a maximum differential pressure which the compressor can start.

  Preferably, the expander is a capillary.

  Preferably, the compressor maintaining a stopped state from the end point of the defrosting may be restarted after the predetermined condition is satisfied and the bypass pipe open / close valve is closed.

  According to the present invention, it is possible to prevent an excessive load from acting on the compressor when the refrigeration circuit returns to the normal operation after the end of the hot gas defrosting operation, so the compressor can be miniaturized and By reducing the power consumption of the motor which is the drive source of the compressor, it is possible to obtain an excellent effect that it can contribute to the downsizing and energy saving of the cooling device incorporating the refrigeration circuit. In addition, even when a small compressor is adopted from the beginning, an excellent effect of enabling smooth transition from the defrosting operation to the normal operation can be obtained.

It is a schematic explanatory drawing which shows the refrigerating circuit to which the hot gas defrosting driving | operation method of this invention is applied. It is an explanatory view showing operation of each apparatus in the hot gas defrost operation method of the present invention in time series.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic explanatory view showing a refrigeration circuit to which a hot gas defrosting operation method of the present invention is applied.

  The refrigeration circuit 1 is incorporated in a cooling device such as, for example, a vending machine or a freezer / refrigerated showcase, and the evaporator 10 and the compressor 20 are sequentially arranged in the flow direction of the refrigerant on a conduit along which the refrigerant circulates. , The condenser 30 and the expander 40 are arranged. D is a dryer for removing the water mixed in the refrigerant.

  During operation of the refrigeration circuit 1, the low-temperature low-pressure liquid-phase refrigerant absorbs heat from the air in the refrigerator of the cooling device introduced by the evaporator fan 10F in the evaporator 10 and evaporates (vaporizes) under constant pressure, When cooling the air in the refrigerator. The low pressure refrigerant flowing out of the evaporator 10 is separated into gas and liquid in the accumulator 15, and only the gas phase refrigerant flows into the compressor 20 to be compressed, and is delivered to the condenser 30 as a high temperature and pressure gas phase refrigerant. The high temperature and high pressure gas phase refrigerant releases heat to the cooling medium (atmospheric air, cooling water, etc.) introduced by the condenser fan 30F in the condenser 30, and condenses (liquefies) under a constant pressure. The high-pressure liquid-phase refrigerant is temporarily stored in a liquid reservoir (not shown) of the condenser 30, and then is isenthalpically expanded in the expander 40 (capillary, electronic expansion valve, etc.) to obtain a low-temperature low-pressure liquid-phase refrigerant And return to the evaporator 10 (see the solid arrow in FIG. 1).

  Then, in the refrigeration circuit 1, in order to perform the hot gas defrosting operation, the pipe line downstream of the compressor 20 (between the compressor 20 and the condenser 30) and the downstream of the expander 40 (the expander 40 and the evaporation) A bypass line B is provided which connects the lines between the vessels 10).

  Here, a point at which the bypass pipe line B branches from the pipe line downstream of the compressor 20 is a bypass pipe line branch point BB, and a point at which the bypass pipe line B joins a pipe line downstream of the expander 40 is a bypass pipe line merging The line from the point BM and the bypass line branch point BB to the bypass line joint BM through the condenser 30 and the expander 40 will be referred to as a main line M. Further, the pressure of the refrigerant in the portion from the compressor 20 through the condenser 30 to the expander 40 in the pipe line of the refrigeration circuit 1 is the high-pressure side pressure PH, from the expander 40 through the evaporator 10 to the compressor 20 The pressure of the refrigerant in the portion is referred to as the low pressure side pressure PL.

  The refrigeration circuit 1 further includes a bypass pipeline on-off valve BV on the bypass pipeline B, and a main pipeline on-off valve MV on the main pipeline M between (the liquid reservoir of the condenser 30) and the expander 40. , Each has.

  The procedure of the hot gas defrosting operation in the refrigeration circuit 1 configured as described above will be described with reference to FIG.

  FIG. 2 is an explanatory view showing the operation of each device in the hot gas defrosting operation method of the present invention in time series.

  While the refrigeration circuit 1 is in normal operation (until time T1), the compressor 20, the condenser fan 30F and the evaporator fan 10F are all operating, and the main line on-off valve MV is open. On the other hand, the bypass line on-off valve BV is closed.

  When the hot gas defrosting operation is started at time T1, first, the condenser fan 30F and the evaporator fan 10F are stopped.

  Thereafter, at time T2 after a predetermined time has elapsed, the bypass conduit on-off valve BV is opened, but at this time, the main conduit on-off valve MV is maintained in the opened state. In this state, the high temperature gas phase refrigerant discharged from the compressor 20 flows into the condenser 30 through the main pipe line M to be condensed (liquefied) and stored in the liquid reservoir as liquid phase refrigerant. As a result, in the next step, even when the main pipeline open / close valve MV is closed and the high temperature gas phase refrigerant discharged from the compressor 20 flows only into the bypass pipeline B, The amount of refrigerant flowing in can be significantly reduced.

  At time T3 after a predetermined time has elapsed since the bypass conduit on-off valve BV was opened, the main conduit on-off valve MV is closed. As a result, all the high-temperature gas-phase refrigerant discharged from the compressor 20 flows into the evaporator 10 through the bypass pipeline B (refer to the broken arrow in FIG. 1), and defrosting in the evaporator 10 Proceed in earnest.

  Thereafter, if it is determined that the defrosting is completed, for example, the refrigerant temperature detected by the temperature sensor installed at the outlet of the evaporator 10 becomes equal to or higher than a predetermined value, or a predetermined time passes (time T4), While the compressor 20 is temporarily stopped and the main line on-off valve MV is opened, the bypass line on-off valve BV is maintained in the open state.

  At the time of completion of the defrosting (time T4), a large amount of liquid phase refrigerant is stored in the liquid reservoir of the condenser 30, and the high pressure side pressure PH of the refrigeration circuit 1 is very high compared to the low pressure side pressure PL. It is high. That is, the differential pressure ΔP between the high pressure side and the low pressure side of the refrigeration circuit 1 is in a very large state.

  Therefore, as described above, the compressor 20 is temporarily stopped, the main pipeline open / close valve MV is opened, and the bypass pipeline open / close valve BV is maintained open, thereby existing on the high pressure side of the refrigeration circuit 1 The refrigerant gradually moves to the low pressure side through the expander 40 and the bypass line B, and the above-described differential pressure ΔP between the high pressure side and the low pressure side gradually decreases. That is, pressure equalization of the pipe line of the refrigeration circuit 1 proceeds.

In the pressure equalization of the pipe line of the refrigeration circuit 1, when the compressor 20 is restarted to return the refrigeration circuit 1 to the normal operation, an excessive load is applied to the compressor 20 (ie, the inlet side This is carried out to avoid that the above-mentioned differential pressure .DELTA.P corresponding to the differential pressure on the outlet side is excessive.
This equalization can also be performed in a state where only the main line open / close valve MV is open (ie, the bypass line open / close valve BV is closed), but in this case, it exists on the high pressure side of the refrigeration circuit 1 The refrigerant moves to the low pressure side only through the expander 40. When an electronic expansion valve is employed as the expander 40, the time required for pressure equalization may be shortened by minimizing the aperture (maximum opening) during the pressure equalization process. it can. On the other hand, when a capillary is employed as the expander 40, since the capillary is configured to have a large throttle (small opening) suitable for normal operation, the time required for pressure equalization is very long. become longer. Therefore, as described above, by maintaining the bypass pipe open / close valve BV in the open state, the time required for pressure equalization can be obtained even when either the electronic expansion valve or the capillary is adopted as the expander 40. It can be greatly shortened. The effect of shortening the time required for pressure equalization is particularly remarkable when a capillary is employed as the expander 40, as described above.

  As described above, when the compressor 20 is stopped and the main line on-off valve MV and the bypass line on-off valve BV are open, a predetermined condition is satisfied, ie, the high pressure side of the refrigeration circuit 1. The differential pressure ΔP with the low pressure side is maintained until it falls below the maximum differential pressure ΔPc that the compressor 20 can start. When the predetermined condition is satisfied, the compressor 20 is restarted following the closing of the bypass pipeline on-off valve BV at time T5. Thus, the refrigeration circuit 1 returns to the normal operation. In FIG. 2, for the sake of simplification, the time when the predetermined condition is satisfied and the bypass pipe open / close valve BV is closed is illustrated as being the same as the time when the compressor 20 is restarted. However, in practice, the compressor 20 is restarted after the bypass line on-off valve BV is closed.

  As described above, when the compressor 20, which has been temporarily stopped at the end of defrosting, is restarted to return the refrigeration circuit 1 to the normal operation, an excessive load acts on the compressor 20 (ie, The pressure difference .DELTA.P corresponding to the pressure difference between the inlet side and the outlet side is not excessive. Therefore, a smaller compressor can be adopted as the compressor 20. Alternatively, the power consumption of the motor which is a drive source of the compressor 20 can be suppressed low, and the miniaturization of the cooling device incorporating the refrigeration circuit 1 Energy saving can be achieved. In addition, even when a small compressor is adopted from the beginning as the compressor 20, there is no possibility that the compressor 20 and the motor as a drive source of the compressor 20 may be damaged due to an excessive load, and usually from the defrosting operation A smooth transition to driving is possible.

  It should be noted that the fact that the predetermined condition is satisfied, that is, the fact that the differential pressure ΔP between the high pressure side and the low pressure side of the refrigeration circuit 1 has fallen below the maximum differential pressure ΔPc that can start the compressor 20 It may be detected using a pressure sensor for measuring the pressure difference between the inlet side and the outlet side. However, when installation of a pressure sensor is not preferable from the viewpoint of cost reduction of the entire cooling device, the differential pressure ΔP between the high pressure side and the low pressure side of the refrigeration circuit 1 is less than the maximum differential pressure ΔPc at which the compressor 20 can start. The time (pressure equalization time) until it falls to may be obtained in advance by experiment or the like, and the above-mentioned predetermined condition may be satisfied when the pressure equalization time has elapsed.

Reference Signs List 1 refrigeration circuit 10 evaporator 20 compressor 30 condenser 40 expander B bypass pipeline BV bypass pipeline on-off valve MV main pipeline on-off valve PH high pressure side pressure PL low pressure side pressure ΔP difference between high pressure pressure and low pressure pressure Pressure ΔPc Maximum differential pressure that can be activated by the compressor

Claims (6)

An evaporator, a compressor, a condenser, and an expander, which are sequentially disposed in the flow direction of the refrigerant on a pipe line through which the refrigerant circulates;
A bypass line connecting the line between the compressor and the condenser, and the line between the expander and the evaporator;
A bypass line on-off valve disposed on the bypass line;
A main line on-off valve disposed on the pipe between the condenser and the expander;
In a defrosting operation method of a refrigeration circuit comprising:
When the defrosting performed in a state in which the bypass line on-off valve is opened and the main line on-off valve is closed is finished, the compressor is stopped and the main line on-off valve is opened, and a predetermined condition is satisfied. And maintaining the bypass line on-off valve in an open state until then. The pressure of the refrigerant in the portion of the pipe extending from the compressor to the condenser through the condenser is referred to as the high pressure side, and the portion of the pipe from the expander to the compressor through the evaporator to the compressor When the pressure of the refrigerant at the
The predetermined condition is a pressure equalization time in which a differential pressure between the high-pressure side pressure and the low-pressure side pressure decreases to the maximum differential pressure at which the compressor can start after the defrosting is completed. The method according to claim 1, characterized in that   The method according to claim 2, wherein the equalization time is determined in advance. The pressure of the refrigerant in the portion of the pipe extending from the compressor to the condenser through the condenser is referred to as the high pressure side, and the portion of the pipe from the expander to the compressor through the evaporator to the compressor When the pressure of the refrigerant at the
The refrigeration circuit further includes pressure sensors that detect the high pressure side pressure and the low pressure side pressure, respectively.
The predetermined condition is characterized in that a differential pressure between the high-pressure side pressure and the low-pressure side pressure detected by the pressure sensor is reduced to less than or equal to a maximum differential pressure which can be started by the compressor. The method according to claim 1.   5. A method according to any one of the preceding claims, characterized in that the expander is a capillary.   The compressor, which maintains a stopped state from the end of the defrosting, is restarted after the predetermined condition is satisfied and the bypass pipe open / close valve is closed. The method according to any one of 1 to 5.

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