JP2018204805A - Refrigeration unit, refrigeration system and control method for refrigerant circuit - Google Patents

Abstract

To avoid deterioration of oil return performance to a compressor caused by an increase in viscosity of refrigerator oil retained in a gas liquid separator.SOLUTION: A refrigeration unit 1 includes: a gas liquid separator 14; a bypass passage 15 for causing at least part of a refrigerant flowing via a heat exchanger 12 toward a decompression section 13 to flow into the gas liquid separator 14; a bypass valve 16 for opening/closing the bypass passage 15; and a control section 20 for controlling the bypass valve 16. The gas liquid separator 14 includes an oil return mechanism 142 for collecting and returning refrigerator oil retained inside and dissolved to a liquid phase of a refrigerant to a compressor 11. A low-temperature side two-layer separation temperature of a mixed solution of the liquid phase of the refrigerant and the refrigerator oil is lower than a lower limit of a specified evaporation temperature set in the refrigeration unit 1. The control section 20 takes bypass measures for opening the bypass passage 15 or increasing a flow rate of the refrigerant flowing in the bypass passage 15 by controlling the bypass valve 16 on the basis of a predetermined condition where deterioration of oil return performance caused by an increase in viscosity of the refrigerator oil is assumed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a refrigeration unit constituting a refrigeration cycle, a refrigeration system including the refrigeration unit, and a refrigerant circuit control method.

  A refrigeration system such as a refrigerator or an air conditioner includes a heat source side unit including a compressor and a condenser, and a heat utilization side unit (such as a refrigeration case and an indoor air conditioner) including an evaporator. The refrigerant discharged from the compressor of the unit on the heat source side and condensed by the condenser flows out to the unit on the heat utilization side, and returns to the unit on the heat source side through the evaporator.

In order to protect the compressor from liquid compression, the heat source unit (hereinafter referred to as a refrigeration unit) is often provided with a gas-liquid separator that separates liquid refrigerant from refrigerant sucked into the compressor (for example, Patent Documents 1 and 2).
In patent document 1, in order to avoid the fall of the lubricity by the viscosity increase of the refrigerator oil inside a compressor, the heater is provided in the casing of the compressor and the viscosity increase of the refrigerator oil is prevented.

  The refrigerating machine oil used for lubricating the sliding portion of the compressor flows out to the heat utilization side unit together with the refrigerant discharged from the compressor. In order to return the refrigeration oil to the compressor, the refrigeration oil accumulated in the liquid refrigerant at the bottom inside the gas-liquid separator is sucked up and collected by an oil return mechanism such as a U-tube or capillary tube with a pickup hole. Like to do. The sucked refrigeration oil is returned to the compressor.

  In Patent Document 2, when the discharge temperature of the refrigerant discharged from the compressor, or the suction temperature or superheat degree of the refrigerant sucked into the compressor exceeds a set value, the liquid refrigerant condensed and liquefied by the condenser is discharged. A part of the refrigerant is sucked into the compressor through the gas-liquid separator together with the gas refrigerant passed through the evaporator, thereby suppressing an increase in the temperature of the gas refrigerant sucked into the compressor.

JP 2010-210208 A Japanese Utility Model Publication No. 5-79357

The refrigeration unit and the refrigeration system are given a specified refrigerant evaporation temperature. The evaporation temperature can be set within the range of the specified evaporation temperature.
If the evaporating temperature set according to the purpose of use of the refrigeration system and the temperature is so low as to greatly affect the viscosity of the refrigerating machine oil, the viscosity of the refrigerating machine oil accumulated in the liquid refrigerant in the gas-liquid separator increases. Accordingly, the suction of the refrigerating machine oil to the oil return mechanism provided in the gas-liquid separator is slowed down. Therefore, the return of the refrigeration oil from the gas-liquid separator to the compressor is deteriorated.
Here, the hole diameter of the oil return mechanism is designed so that the dilution rate of the refrigeration oil in the compressor by the liquid refrigerant is not more than an appropriate value that can ensure lubricity. If the hole diameter of the oil return mechanism is increased in order to improve the oil return property at low temperature settings where the viscosity of the refrigerating machine oil is increasing, the refrigerating machine oil will return to the compressor together with the liquid refrigerant at the normal viscosity. End up.

Although it is conceivable to prevent an increase in the viscosity of the refrigerating machine oil by heating the gas-liquid separator using the heater in the same manner as in Patent Document 1 described above, the addition of the heater leads to an increase in manufacturing cost and running cost. .
In Patent Document 2 described above, since the refrigeration oil hardly dissolves in the gas refrigerant when the temperature of the gas refrigerant sucked into the compressor rises, the refrigeration oil accumulated in the gas-liquid separator is transported to the compressor by the gas refrigerant. This is related to a phenomenon that does not occur, and does not deal with an increase in the viscosity of the refrigerating machine oil at a low temperature setting.

  In light of the above, an object of the present invention is to avoid deterioration in oil return to the compressor due to an increase in the viscosity of the refrigerating machine oil accumulated in the gas-liquid separator.

The present invention has a refrigerant circuit including a compressor that compresses a refrigerant, a heat exchanger that exchanges heat between the refrigerant and air, and a decompression unit that decompresses the refrigerant, and the refrigerant that has passed through the decompression unit is used as a heat utilization destination. A gas-liquid separator interposed between the heat utilization destination and the compressor, and at least a part of the refrigerant that goes to the decompression unit through the heat exchanger flows into the gas-liquid separator. A bypass path, a bypass valve that opens and closes the bypass path or adjusts the flow rate of the refrigerant flowing through the bypass path, and a control unit that controls the bypass valve are provided.
The gas-liquid separator has an oil return mechanism that recovers refrigeration oil accumulated inside in a state dissolved in the liquid phase of the refrigerant and returns it to the compressor.
The low temperature side two-layer separation temperature of the mixed liquid of the refrigerant liquid phase and the refrigerating machine oil is less than the lower limit of the prescribed evaporation temperature defined for the refrigeration unit.
The control unit opens the bypass path or increases the flow rate of the refrigerant flowing through the bypass path by controlling the bypass valve based on a predetermined condition in which deterioration of oil return property due to increase in the viscosity of the refrigerating machine oil is assumed. Take bypass measures.

  In the refrigeration unit of the present invention, the index used for the condition is a saturation temperature corresponding to the pressure of the refrigerant sucked into the compressor, and the control unit sets the bypass valve when the saturation temperature is lower than the specified value. By controlling, it is preferable to perform a bypass measure.

  In the refrigeration unit of the present invention, it is preferable that the control unit intermittently performs bypass measures at predetermined time intervals based on conditions.

  In the refrigeration unit of the present invention, the control unit is configured such that the saturation temperature corresponding to the pressure of the refrigerant sucked into the compressor is lower than the specified value, and the level of the refrigeration oil in the compressor is lower than the specified level. When it is low, it is preferable to take a bypass measure.

  In the refrigeration unit of the present invention, the control unit detects that the bypass valve is used when the specified time has elapsed from the start of the bypass measure or when the level of the refrigeration oil in the compressor reaches at least the specified liquid level due to the bypass measure. It is preferable to end the bypass measure by controlling.

  In the refrigeration unit of the present invention, the control unit is configured such that the saturation temperature corresponding to the pressure of the refrigerant sucked into the compressor is lower than the specified value, and the superheat degree of the refrigeration oil in the compressor is less than the specified superheat degree. When it is high, it is preferable to take a bypass measure.

  In the refrigeration unit of the present invention, the control unit, if the specified time has elapsed from the start of the bypass measure, or if the superheat degree of the refrigeration oil in the compressor is suppressed to at least the specified superheat degree by the bypass measure, It is preferable to end the bypass measure by controlling the bypass valve.

The present invention is also a refrigeration system comprising a compressor that compresses a refrigerant, a heat exchanger that exchanges heat between the refrigerant and air, a decompression unit that depressurizes the refrigerant, and an evaporator that evaporates the refrigerant. A gas-liquid separator interposed between the compressor and the compressor, a bypass path for allowing at least a part of the refrigerant going to the decompression section via the heat exchanger to flow into the gas-liquid separator, or opening or closing the bypass path, Or the bypass valve which adjusts the flow volume of the refrigerant | coolant which flows through a bypass path | route, and the control part which controls a bypass valve are provided.
The gas-liquid separator has an oil return mechanism that recovers refrigeration oil accumulated inside in a state dissolved in the liquid phase of the refrigerant and returns it to the compressor.
The low-temperature two-layer separation temperature of the refrigerant liquid phase and the mixed solution of the refrigeration oil is less than the lower limit of the prescribed evaporation temperature defined for the refrigeration system.
The control unit opens the bypass path or increases the flow rate of the refrigerant flowing through the bypass path by controlling the bypass valve based on a predetermined condition in which deterioration of oil return property due to increase in the viscosity of the refrigerating machine oil is assumed. Take bypass measures.

  Furthermore, the present invention is a control method for a refrigerant circuit including a compressor that compresses a refrigerant, a heat exchanger that exchanges heat between the refrigerant and air, and a decompression unit that decompresses the refrigerant. A gas-liquid separator interposed between the heat utilization destination to which the refrigerant having passed through the section is supplied and the compressor, and a bypass for allowing at least part of the refrigerant to flow to the decompression section through the heat exchanger into the gas-liquid separator Path and a bypass valve that opens and closes the bypass path or adjusts the flow rate of the refrigerant flowing through the bypass path. Based on the conditions, the bypass valve is opened or the bypass valve is controlled to increase the flow rate of the refrigerant flowing through the bypass path, so that the oil return mechanism provided in the gas-liquid separator dissolves in the refrigerant liquid phase. Shi State to recover refrigerating machine oil accumulated inside the gas-liquid separator back to the compressor.

  According to the present invention, an appropriate amount of the refrigerating machine oil accumulated in the gas-liquid separator is appropriately passed through the bypass path based on the condition that the oil return property is deteriorated due to the increase in the viscosity of the refrigerating machine oil in the gas-liquid separator. Mix the liquid phase of the refrigerant. Therefore, even at a low temperature, an increase in the viscosity of the entire mixed solution of the refrigerating machine oil and the liquid refrigerant accumulated in the gas-liquid separator is suppressed. Therefore, without adding a heater to the gas-liquid separator, the oil return mechanism maintains the proper refrigeration oil dilution rate in the compressor and the role of liquid compression by the gas-liquid separator. A sufficient amount of the refrigeration oil accumulated in the liquid separator can be recovered as a mixed solution and returned to the compressor.

It is a schematic diagram which shows the refrigeration unit which concerns on 1st Embodiment. It is a schematic diagram which shows the refrigeration unit which concerns on 2nd Embodiment. It is a schematic diagram which shows the refrigeration unit which concerns on 3rd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[First Embodiment]
The refrigeration unit 1 (condensing unit) shown in FIG. 1 includes a heat source circuit 10 including a compressor 11, a heat exchanger 12, and a decompression unit 13, a gas-liquid separator 14, a bypass path 15, and a bypass valve 16. The control unit 20 is provided. A housing that houses the elements 11 to 13 of the heat source circuit 10, the gas-liquid separator 14, the bypass path 15, and the bypass valve 16 is installed outside the room.
The refrigeration unit 1 exchanges heat between the refrigerant compressed by the compressor 11 and air as a heat source by the heat exchanger 12, and then depressurizes the refrigerant by the decompression unit 13 such as an expansion valve. The refrigerant is supplied to the indoor heat utilization destination A.

  The heat utilization destination A includes an evaporator (not shown) that constitutes a refrigeration cycle together with the heat source circuit 10 of the refrigeration unit 1. A refrigeration system is configured including a heat utilization destination unit (not shown) provided with the evaporator, a refrigeration unit 1 and a pipe connecting the units. The heat utilization destination unit corresponds to, for example, a refrigerated case or a freezing case that is installed in a store and accommodates food or the like.

  The refrigeration unit 1 is given a prescribed refrigerant evaporation temperature. The evaporation temperature can be set within the range of the specified evaporation temperature.

For the refrigeration system of the present embodiment, an appropriate refrigerant such as an HFC refrigerant such as R404A or a natural refrigerant such as CO ₂ can be used.
The refrigerant discharged from the compressor 11 and heat-exchanged with the outside air in the heat exchanger 12 flows out to the heat utilization destination A, and returns to the refrigeration unit 1 through the evaporator of the heat utilization destination A.
The refrigeration system of the present embodiment can be applied to both the subcritical cycle and the transcritical cycle. The heat exchanger 12 functions as a condenser that condenses and liquefies the gas refrigerant that has flowed in by heat exchange with air in the subcritical cycle. On the other hand, the heat exchanger 12 functions as a gas cooler that cools the supercritical refrigerant that has flowed in by heat exchange with air, for example, in a transcritical cycle in which CO ₂ refrigerant is used.

Refrigerating machine oil is enclosed in the housing 11A of the compressor 11 in order to lubricate sliding portions such as bearings of a built-in compression mechanism. As refrigerating machine oil, what has compatibility with the refrigerant | coolant used for the refrigerating system of this embodiment can be selected suitably. From the viewpoint of compatibility, for example, an ester-based synthetic oil can be selected for CO ₂ . An example of a selectable ester-based synthetic oil is “Diamond Freeze MA68”, a product of JXTG Energy Corporation. For R404A, which is a kind of HFC refrigerant, “Diamond Freeze MA32R”, a product of JXTG Energy Co., Ltd., can be selected.
Since the refrigeration oil is dissolved in the refrigerant, it is discharged from the compressor 11 together with the refrigerant, and flows out to the heat utilization destination A through the heat exchanger 12 and the pressure reducing unit 13.

  The present embodiment is mainly characterized in the configuration of the refrigerant circuit including the heat source circuit 10, the gas-liquid separator 14, the bypass path 15, and the bypass valve 16, and the method of controlling the refrigerant circuit by the control unit 20. Have

The refrigerant sucked into the compressor 11 is received by the gas-liquid separator 14 interposed between the heat utilization destination A and the compressor 11 in order to protect the compressor 11 from liquid compression. And separated.
The gas-liquid separator 14 (accumulator) collects the tank 141 that receives the refrigerant returned from the heat utilization destination A, and the refrigerating machine oil that is stored in the state of being dissolved with the liquid refrigerant at the bottom inside the tank 141 to the compressor 11. An oil return mechanism 142 is provided.
Since liquid refrigerant accumulates at the bottom of the tank 141, gas refrigerant is sucked into the compressor 11 from the upper part of the tank 141.

The oil return mechanism 142 includes, for example, a U-shaped tube having a pickup hole 142A (small hole) and a capillary tube.
The oil return mechanism 142 sucks up the refrigerating machine oil accumulated in the tank 141 and sucks it into the compressor 11 together with the gas refrigerant, thereby returning it to the inside of the housing 11 </ b> A of the compressor 11. Refrigerating machine oil is also stored in the housing 11A of the compressor 11 in a state of being dissolved in the liquid refrigerant.
The hole diameter of the oil return mechanism 142 is designed so that the dilution rate of the refrigeration oil by the liquid refrigerant in the compressor 11 is not more than an appropriate value that can ensure lubricity.

Now, the viscosity of refrigeration oil increases with a decrease in temperature. Therefore, if the refrigerant evaporating temperature is low enough to significantly affect the viscosity of the refrigerating machine oil, it is assumed that the refrigerating machine oil accumulated in the gas-liquid separator 14 deteriorates in oil return to the compressor 11. This evaporation temperature corresponds to the outlet temperature of the evaporator of the heat utilization destination unit.
The evaporation temperature of the refrigeration unit 1 is set to, for example, -5 ° C to -45 ° C. This temperature range is referred to as a specified evaporation temperature. An arbitrary evaporation temperature can be set by the user in accordance with the use of the refrigeration system including the refrigeration unit 1, the temperature, and the like within the range of the specified evaporation temperature. The set evaporation temperature is referred to as the set evaporation temperature.
When the viscosity of the refrigerating machine oil increases and the suction of the refrigerating machine oil to the oil return mechanism 142 slows down, the return of the refrigerating machine oil from the gas-liquid separator 14 to the compressor 11 becomes worse.

In order to avoid deterioration of the oil return property from the gas-liquid separator 14 to the compressor 11 due to the increase in the viscosity of the refrigerating machine oil, the refrigeration unit 1 according to the present embodiment supplies the liquid refrigerant to the gas-liquid separator 14 through the bypass path 15 at appropriate times. By taking measures to mix, the viscosity increase of the mixed solution of the refrigerating machine oil and the liquid refrigerant accumulated in the gas-liquid separator 14 is suppressed.
Therefore, the refrigeration unit 1 includes a bypass path 15 that allows a part of the refrigerant that has passed through the heat exchanger 12 to flow into the gas-liquid separator 14, and a bypass valve 16 that opens and closes the bypass path 15. The bypass valve 16 is controlled based on a predetermined condition in which deterioration of the oil return property due to an increase in the viscosity of the refrigerating machine oil in the gas-liquid separator 14 is assumed. In this embodiment, a pressure sensor 21 that detects the pressure of the refrigerant sucked into the compressor 11 is used in order to obtain a suction pressure saturation temperature as an index used for a condition assumed to deteriorate oil return. The suction pressure saturation temperature changes according to the set evaporation temperature.

The bypass path 15 includes a pipe connecting the outlet side of the heat exchanger 12 and the inlet side of the gas-liquid separator 14, a joint, and the like.
The bypass valve 16 is an electromagnetic valve, and opens and closes the bypass path 15 by being driven according to a command issued from the control unit 20. When the bypass path 15 is opened by the bypass valve 16, a part of the refrigerant going to the decompression unit 13 through the heat exchanger 12 flows into the gas-liquid separator 14 through the bypass path 15. The refrigerant that has flowed through the bypass path 15 and reached the gas-liquid separator 14 is decompressed and becomes a gas-liquid two-phase state.

The refrigerant that has passed through the evaporator at the heat utilization destination A and the refrigerant that has flowed through the bypass path 15 flow into the gas-liquid separator 14. The refrigerant flowing into the tank 141 of the gas-liquid separator 14 is separated due to the difference in density between the gas phase and the liquid phase of the refrigerant, and a liquid phase having a density higher than that of the gas phase is accumulated at the bottom of the tank 141.
Since the refrigerating machine oil is transported through the refrigerant circuit together with the refrigerant in the state of being dissolved in the refrigerant as described above, the refrigerating machine oil contained in the refrigerant from the heat utilization destination A and the refrigerant from the bypass path 15 is also gas. It flows into the liquid separator 14 and accumulates at the bottom of the tank 141. The refrigerating machine oil is mixed with the liquid refrigerant at the bottom of the tank 141 and dissolved in the liquid refrigerant.

  In the present embodiment, the refrigerant that has flowed through the bypass path 15 merges with the refrigerant from the heat utilization destination A toward the gas-liquid separator 14 and flows into the gas-liquid separator 14. However, the present invention is not limited to this, and the refrigerant flowing through the bypass path 15 may be configured to directly flow into the gas-liquid separator 14 without joining the refrigerant flow from the heat utilization destination A.

When the deterioration of the oil return due to the increase in the viscosity of the refrigerating machine oil is assumed, the control unit 20 sends a command to open the bypass path 15 to the bypass valve 16 to open the bypass path 15. With this, the bypass measure is started.
In the present embodiment, the control unit 20 calculates a saturation temperature corresponding to the suction pressure using the suction pressure detected by the pressure sensor 21. If the suction pressure saturation temperature in the gas-liquid separator 14 is lower than the specified value, the oil return property is assumed to deteriorate. Therefore, a command is sent to the bypass valve 16 to open the bypass path 15 and the bypass path 15 Through which the refrigerant flows into the gas-liquid separator 14.
Although the pressure sensor 21 is installed on the inlet side of the gas-liquid separator 14 in this embodiment, the pressure sensor 21 may be provided at an appropriate position where the pressure representing the pressure of the refrigerant sucked into the compressor 11 can be detected. it can. For example, the pressure sensor 21 can be provided between the gas-liquid separator 14 and the compressor 11 or near the end of the bypass path 15.

When the liquid phase of the gas-liquid two-phase refrigerant that has flowed into the gas-liquid separator 14 through the bypass path 15 is mixed into the mixed solution stored in the tank 141, the ratio of the liquid refrigerant in the mixed solution increases.
Therefore, even at a low temperature near the lower limit of the specified evaporation temperature, the entire liquid mixture of the refrigerating machine oil and the liquid refrigerant accumulated in the gas-liquid separator 14 is obtained by mixing the liquid phase of the refrigerant through the bypass path 15. As a result, an increase in viscosity is suppressed. Therefore, the oil return mechanism 142 can collect a sufficient amount of the refrigeration oil accumulated in the tank 141 as a mixed solution and return it to the compressor 11. Therefore, poor lubrication and seizure in the compressor 11 can be prevented in advance.

  The bypass measure for mixing the liquid refrigerant into the refrigerating machine oil in the gas-liquid separator 14 through the bypass path 15 is performed only for a specified time when the suction pressure saturation temperature is lower than the specified value. In implementation, specific temperature and time conditions can be determined as appropriate.

  In the bypass measure according to the present embodiment, the concentration of the refrigeration oil in the mixed solution in the gas-liquid separator 14 is reduced by mixing the liquid phase of the refrigerant into the refrigeration oil in the gas-liquid separator 14 through the bypass path 15. Based on. According to such a bypass measure, it is possible to suppress an increase in the viscosity of the mixed solution as a whole even under temperature conditions in which the viscosity increases when viewed as a single refrigeration oil.

Here, the state in which the liquid refrigerant and the refrigerating machine oil are separated into two layers without being melted together, or the state in which it is emulsified is called two-layer separation, and the temperature at which such a state is reached is called the two-layer separation temperature.
The two-layer separation temperature between the refrigerating machine oil and the liquid refrigerant can be represented by a two-layer separation temperature curve indicating the relationship between the concentration and the temperature of the refrigerating machine oil. The two-layer separation temperature curve includes a two-layer separation temperature curve on the high temperature side that starts separation when the temperature is increased (a convex curve downward), and a low-temperature side that begins separation when the temperature is decreased. There is a two-layer separation temperature curve (upward convex curve).
When the temperature falls below the two-layer separation temperature curve on the low temperature side, the mixed solution of liquid refrigerant and refrigerating machine oil separates from one phase having a uniform concentration into two phases having different concentrations.
As described above, the mixed solution of the refrigerant liquid phase and the refrigerating machine oil is prevented from increasing in viscosity as a whole, and the refrigerating machine oil is uniformly made into a liquid refrigerant without separating the mixed solution in order to sufficiently ensure the oil return. Dissolve in. For this reason, the refrigerant is set so that the low temperature side two-layer separation temperature, which is the maximum value (UCST: Upper Critical Solution Temperature) of the low temperature side two-layer separation temperature curve, is less than the lower limit of the specified evaporation temperature set for the refrigeration unit. And refrigeration oil shall be selected. The low temperature side two-layer separation temperature is preferably lower by 10 ° C. or more, for example, with a margin with respect to the lower limit of the specified evaporation temperature. For example, when the lower limit of the specified evaporation temperature is −45 ° C., it is preferable to employ a combination of refrigerant and refrigerating machine oil such that the low temperature side two-layer separation temperature is −55 ° C. or lower. As an example of a combination in which the low temperature side two-layer separation temperature is −55 ° C. or lower, a CO ₂ refrigerant and the above-described diamond freeze MA68 can be cited.

Here, an example of conditions for implementing the bypass measure is shown.
While monitoring the suction pressure saturation temperature obtained by calculating using the pressure detected by the pressure sensor 21, the control unit 20 has a suction pressure saturation temperature of −30 ° C. or less as a specified value, Every time the integrated operation time of the refrigeration unit 1 reaches 60 minutes, a bypass measure for opening the bypass path 15 is performed for five minutes as a specified time from the start of the bypass measure. In other words, when the refrigeration system including the refrigeration unit 1 is operated at the time of low temperature setting, by performing bypass measures intermittently every 60 minutes, the oil return to the compressor 11 is not delayed and gas-liquid separation is performed. The refrigerating machine oil accumulated in the container 14 can be smoothly returned to the compressor 11.

  In the refrigeration unit 1, the set evaporation temperature can be changed within a range of a specified evaporation temperature as wide as, for example, -5 ° C to -45 ° C. For this reason, in the low temperature range at the specified evaporation temperature, the viscosity of the refrigerating machine oil is greatly affected, and the oil return property from the gas-liquid separator 14 is affected. The viscosity is adequately recoverable and may not affect oil return.

If the viscosity of the refrigeration oil increases at the low temperature setting, the diameter of the pickup hole 142A of the oil return mechanism 142 and the oil return so that a sufficient amount of the refrigeration oil can be recovered from the tank 141 to the oil return mechanism 142. If the diameter of the capillary tube used in the mechanism is increased, the liquid will be returned too much from the gas-liquid separator 14 to the compressor 11 by the oil return mechanism 142 when setting the temperature range other than that. An appropriate amount of refrigeration oil accumulated in the gas-liquid separator 14 is supplied to the compressor 11 so that the compressor 11 is protected from liquid compression and sufficient lubricity is obtained by the refrigeration oil diluted with the liquid refrigerant. It is necessary to return.
Further, it is conceivable that the lower part of the tank 141 of the gas-liquid separator 14 is heated by a heater so that the viscosity of the refrigerating machine oil in the gas-liquid separator 14 does not increase even at a low temperature setting. This leads to an increase in manufacturing cost of the refrigeration unit 1 including the control device and an increase in running cost.

  According to the present embodiment, the refrigerant is stored in the gas-liquid separator 14 through the bypass path 15 based on the conditions that the oil return property is deteriorated due to the increase in the viscosity of the refrigerator oil in the gas-liquid separator 14. By mixing the liquid phase, without adding a heater to the gas-liquid separator 14, the proper refrigeration oil dilution rate in the compressor 11 and the role of liquid compression by the gas-liquid separator 14 are maintained, and the temperature setting is low. Sometimes, an appropriate amount of refrigeration oil can be smoothly returned to the compressor 11.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.
In the following, the description will be focused on matters that differ from the first embodiment. The same code | symbol is attached | subjected to the structure similar to 1st Embodiment. The same applies to a third embodiment to be described later.

The refrigeration unit 2 of the second embodiment shown in FIG. 2 includes a refrigerant circuit having the same configuration as the refrigeration unit 1 of the first embodiment, a control unit 22, a pressure sensor 21, and an oil level sensor 23.
The oil level sensor 23 detects the liquid level (oil level) of the refrigeration oil that accumulates in the housing 11A of the compressor 11 while being dissolved in the liquid refrigerant. This liquid level is used as an index for returning the refrigeration oil to the compressor 11.

  While the bypass path 15 is open, the flow rate of the refrigerant flowing to the heat utilization destination A is reduced by an amount corresponding to the flow of a part of the refrigerant that has passed through the heat exchanger 12 into the bypass path 15, and the entire refrigerant circuit is circulated. Since the refrigerant flow rate to be reduced is reduced, the refrigeration capacity is reduced. In consideration of this, in the present embodiment, the bypass path 15 is opened and closed based on conditions related to the detected refrigerant level in the compressor 11 in addition to the suction pressure saturation temperature.

Hereinafter, an example of control using the pressure sensor 21 and the oil level sensor 23 will be described.
In this control, the first oil level switch 231 that detects that the liquid level of the refrigerating machine oil accumulated in the compressor 11 has fallen below the prescribed first liquid level, and the liquid level of the refrigerating machine oil accumulated in the compressor 11 are It is assumed that the oil level sensor 23 is composed of a second oil level switch 232 that detects that the specified second level is higher than the first level. The first oil level switch 231 and the second oil level switch 232 are turned on and off according to the corresponding liquid level.
Here, in order to avoid hunting in which the bypass measure is frequently repeated, two liquid levels (first liquid level and second liquid level) as the predetermined liquid levels are used for control. However, it is also permissible to perform control related to the bypass measure using only one specified liquid level. In that case, only one oil level switch is required.

  The suction pressure saturation temperature calculated by the control unit 22 using the pressure detected by the pressure sensor 21 is equal to or lower than a specified value, that is, the evaporation temperature of the refrigeration unit 1 is set to a low temperature, and the refrigeration oil in the compressor 11 When the first oil level switch 231 is turned on (or off) because the liquid level is lower than the first liquid level, the bypass valve 16 is controlled by the control unit 22 to open the bypass path 15. With this, the bypass measure is started.

Since the liquid phase of the refrigerant that has flowed into the gas-liquid separator 14 through the bypass path 15 is mixed into the refrigeration oil accumulated in the gas-liquid separator 14, the oil return property is improved. A sufficient amount of refrigerating machine oil returns to the compressor 11.
Thereafter, when the liquid level of the refrigeration oil accumulated in the compressor 11 reaches the second liquid level and the second oil level switch 232 is turned on (or off), the control unit 22 controls the bypass valve 16. As a result, the bypass path 15 is closed.
In order to prevent excessive dilution of the refrigerating machine oil due to the liquid phase of the refrigerant flowing into the gas-liquid separator 14 through the bypass path 15, the level of the refrigerating machine oil in the compressor 11 reaches at least the first liquid level. Preferably, when the oil reaches the second liquid level and the oil return property does not need to be improved, it is preferable to close the bypass passage 15 and end the bypass measure to prevent further dilution.

  According to the second embodiment, on the basis of the actual oil return state that can be detected by the oil level sensor 23, the bypass is only performed when the oil return property needs to be improved because the oil return property is deteriorating. Measures can be implemented in a limited way. Therefore, it is possible to prevent poor lubrication and seizure in the compressor 11 while suppressing a decrease in refrigeration capacity.

The control in the second embodiment can be changed as follows.
For example, when the suction pressure saturation temperature is −30 ° C. or less as a specified value and the accumulated operation time of the refrigeration unit 1 reaches 60 minutes, the liquid level of the refrigerating machine oil accumulated in the compressor 11 becomes the specified liquid level. However, the control unit 22 may control the bypass valve 16 so that the bypass path 15 is opened only when it is low.
After that, if the level of the refrigeration oil in the compressor 11 reaches at least the specified level, or if, for example, 5 minutes have passed as the specified time from the start of the bypass measure for opening the bypass path 15, the bypass is performed. By controlling the valve 16, the bypass path 15 can be closed and the bypass measure can be terminated.

[Third Embodiment]
Next, a third embodiment of the present invention will be described.
The refrigeration unit 3 of the third embodiment shown in FIG. 3 includes a refrigerant circuit having the same configuration as that of the refrigeration unit 1 of the first embodiment, a control unit 24, a pressure sensor 21, and a temperature sensor 25.
In this embodiment, the temperature of the refrigerating machine oil in the compressor 11 or the temperature at which the temperature can be estimated is used for control. In order to detect the temperature of the refrigerating machine oil accumulated in the housing 11A of the compressor 11, the temperature sensor 25 is installed on the lower outer peripheral portion of the housing 11A.

The control unit 24 calculates the degree of superheat of the refrigerating machine oil (hereinafter referred to as oil superheat degree) from the difference between the temperature detected by the temperature sensor 25 and the suction pressure saturation temperature detected by the pressure sensor 21. This degree of oil superheat is used as an index of the return status of the refrigeration oil to the compressor 11.
Here, when the pressure inside the housing 11A of the compressor 11 is set to a high pressure, such as CO ₂ refrigerant, the oil superheat degree is equal to the saturation temperature corresponding to the discharge pressure and the temperature of the refrigerating machine oil of the compressor 11. Or it calculates from the difference with estimated temperature. In that case, the saturation temperature is calculated from the discharge pressure detected by the pressure sensor installed on the discharge side of the compressor 11.

Also in the present embodiment, the bypass measure is implemented only when there is a request for improving the oil return property based on the degree of oil superheat in consideration of the refrigerating capacity.
Hereinafter, an example of control using the suction pressure saturation temperature and the oil superheat degree will be shown. In this control, regarding the oil superheat degree of the compressor 11, it is assumed that a first superheat degree indicating that the oil return property is deteriorating and a second superheat degree lower than that are set.
Also in this embodiment, in order to avoid hunting, two liquid levels (first superheat degree and second superheat degree) as the specified superheat degree are used for control. However, it is also permissible to perform control related to the bypass measure using only one specified superheat degree.

  If the suction pressure saturation temperature calculated by the control unit 24 using the pressure detected by the pressure sensor 21 is equal to or lower than a specified value and the oil superheat degree of the compressor 11 is higher than the first superheat degree, the control unit 24 By controlling the bypass valve 16, the bypass path 15 is opened.

If the oil superheat degree of the compressor 11 is suppressed to the second superheat degree by the above bypass measure, the bypass valve 16 is controlled by the control unit 24, whereby the bypass path 15 is closed.
If the oil superheat degree is suppressed to at least the first superheat degree, and preferably to the second superheat degree, a sufficient amount of mixed solution of refrigeration oil and liquid refrigerant is accumulated in the compressor 11. Therefore, it is preferable to close the bypass path 15 to prevent further dilution progress.

  According to the third embodiment, the bypass measure is limited only when the oil return property needs to be improved based on the degree of oil superheat that can estimate the amount of refrigerating machine oil dissolved in the liquid refrigerant inside the compressor 11. Can be implemented automatically. Therefore, it is possible to prevent poor lubrication and seizure in the compressor 11 while suppressing a decrease in refrigeration capacity.

The control in the third embodiment can be changed as follows.
For example, when the suction pressure saturation temperature is −30 ° C. or less as a specified value and the accumulated operation time of the refrigeration unit 1 reaches 60 minutes, the superheat degree of the refrigerating machine oil accumulated in the compressor 11 is the specified superheat degree. However, the control unit 24 may control the bypass valve 16 so that the bypass path 15 is opened only when it is high.
Thereafter, if the superheat degree of the refrigeration oil in the compressor 11 is suppressed to at least the specified superheat degree, or if, for example, 5 minutes have elapsed since the start of the bypass measure for opening the bypass path 15, the control of the bypass valve 16 is performed. Thus, the bypass path 15 can be closed and the bypass measure can be terminated.

  Different indicators can be used for the start condition of the bypass measure and the end condition of the bypass measure. For example, when the level of the refrigeration oil in the compressor 11 falls below a specified liquid level, the bypass measure is started, and after a lapse of a specified time from the start of the bypass measure or by the bypass measure, the degree of superheat of the refrigeration oil in the compressor 11 is increased. Control can be made to end the bypass measure if at least the specified degree of superheat is suppressed.

  In addition to the above, as long as the gist of the present invention is not deviated, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

  The present invention is not limited to a refrigeration system having a refrigeration / freezing case and a condensing unit constituting the system, but also to a refrigeration system relating to an air conditioner, a container, etc., and a refrigeration unit constituting the system. Can do.

The bypass valve 16 is not necessarily an open / close valve, and may be configured as a flow rate adjusting valve that adjusts the flow rate of the refrigerant flowing through the bypass path 15.
In that case, for example, the following control is also possible.
Even if the evaporating temperature is not set to a low temperature that greatly affects the viscosity of the refrigerating machine oil, the opening degree of the bypass valve 16 is controlled by the control unit 20 so that the refrigerant slightly flows in the bypass path 15. When the evaporation temperature is set to a low temperature, the flow rate of the refrigerant flowing through the bypass passage 15 is increased based on the condition that deterioration of the oil return property from the gas-liquid separator 14 to the compressor 11 is assumed. The control unit 20 controls the bypass valve 16. Then, the amount of liquid refrigerant mixed into the mixed solution accumulated in the gas-liquid separator 14 through the bypass path 15 increases, and the concentration of the refrigeration oil in the mixed solution decreases accordingly, so that the mixing returned to the compressor 11 is performed. The increase in viscosity of the entire solution can be suppressed, and deterioration of oil return can be avoided.

The bypass measure for increasing the flow rate of the refrigerant flowing through the bypass path 15 is an oil return property intermittently every predetermined time or according to the return level of the refrigeration oil indicated by the level of the refrigeration oil in the compressor 11 and the degree of oil superheat. It is preferable to carry out the process only when there is a need for improvement.
If a predetermined time elapses after increasing the flow rate of the refrigerant to be bypassed or if there is no need for the bypass from the oil return situation, the flow rate of the refrigerant flowing through the bypass path 15 may be reduced by controlling the bypass valve 16. preferable.

  In each of the above embodiments, only a part of the refrigerant that goes to the decompression unit 13 through the heat exchanger 12 is caused to flow into the gas-liquid separator 14 through the bypass path 15, but it is necessary to immediately improve the oil return property. In some cases, it is allowed to allow all of the refrigerant that passes through the heat exchanger 12 to the decompression unit 13 to flow into the gas-liquid separator 14 through the bypass path 15. In this case, the bypass valve 16 can be provided, for example, at the start end of the bypass path 15 branched from the main stream on the outlet side of the heat exchanger 12.

1-3 Refrigeration unit 10 Heat source circuit 11 Compressor 11A Housing 12 Heat exchanger 13 Decompression unit 14 Gas-liquid separator 15 Bypass path 16 Bypass valves 20, 22, 24 Control unit 21 Pressure sensor 23 Oil level sensor 25 Temperature sensor 141 Tank 142 Oil return mechanism 142A Pickup hole 231 First oil level switch 232 Second oil level switch A Heat utilization destination

Claims (9)

A compressor that compresses the refrigerant; a heat exchanger that exchanges heat between the refrigerant and air; and a refrigerant circuit that includes a decompression unit that decompresses the refrigerant, and the refrigerant that has passed through the decompression unit is used as a heat utilization destination A refrigeration unit to supply
A gas-liquid separator interposed between the heat utilization destination and the compressor;
A bypass path through which at least a part of the refrigerant going to the decompression unit via the heat exchanger flows into the gas-liquid separator;
A bypass valve that opens and closes the bypass path or adjusts the flow rate of the refrigerant flowing through the bypass path;
A control unit for controlling the bypass valve,
The gas-liquid separator has an oil return mechanism that recovers refrigeration oil accumulated inside in a state dissolved in the liquid phase of the refrigerant and returns it to the compressor.
The low-temperature two-layer separation temperature of the liquid phase of the refrigerant and the mixed solution of the refrigerating machine oil is less than the lower limit of the prescribed evaporation temperature defined in the refrigeration unit;
The control unit opens the bypass path or flows through the bypass path by controlling the bypass valve based on a predetermined condition in which deterioration of oil return property due to an increase in the viscosity of the refrigerator oil is assumed. Increase the refrigerant flow rate, take bypass measures,
A refrigeration unit characterized by that. The index used for the condition is a saturation temperature corresponding to the pressure of the refrigerant sucked into the compressor,
The controller is
When the saturation temperature is lower than a specified value, the bypass measure is performed by controlling the bypass valve.
The refrigeration unit according to claim 1. The controller is
Based on the conditions, the bypass measure is intermittently performed at predetermined time intervals.
The refrigeration unit according to claim 1 or 2. The controller is
When the saturation temperature corresponding to the pressure of the refrigerant sucked into the compressor is lower than a specified value and the level of the refrigerating machine oil in the compressor is lower than the specified level, the bypass measure I do,
The refrigeration unit according to claim 2 or 3. The controller is
If the specified time has elapsed from the start of the bypass measure, or if the level of the refrigerating machine oil in the compressor reaches at least the specified liquid level by the bypass measure,
By controlling the bypass valve, the bypass measure is terminated.
The refrigeration unit according to claim 4. The controller is
When the saturation temperature corresponding to the pressure of the refrigerant sucked into the compressor is lower than a specified value and the degree of superheat of the refrigerating machine oil in the compressor is higher than the specified superheat degree, the bypass measure I do,
The refrigeration unit according to any one of claims 2, 3, and 5. The controller is
If the specified time has passed since the start of the bypass measure, or if the degree of superheat of the refrigerating machine oil in the compressor is suppressed to at least the specified superheat degree by the bypass measure,
By controlling the bypass valve, the bypass measure is terminated.
The refrigeration unit according to claim 4 or 6. A refrigeration system comprising a compressor that compresses a refrigerant, a heat exchanger that exchanges heat between the refrigerant and air, a decompression unit that depressurizes the refrigerant, and an evaporator that evaporates the refrigerant,
A gas-liquid separator interposed between the evaporator and the compressor;
A bypass path through which at least a part of the refrigerant going to the decompression unit via the heat exchanger flows into the gas-liquid separator;
A bypass valve that opens and closes the bypass path or adjusts the flow rate of the refrigerant flowing through the bypass path;
A control unit for controlling the bypass valve,
The gas-liquid separator has an oil return mechanism that recovers refrigeration oil accumulated inside in a state dissolved in the liquid phase of the refrigerant and returns it to the compressor.
The low-temperature two-layer separation temperature of the refrigerant liquid phase and the refrigerating machine oil mixed solution is less than the lower limit of the prescribed evaporation temperature defined in the refrigeration system,
The control unit opens the bypass path or flows through the bypass path by controlling the bypass valve based on a predetermined condition in which deterioration of oil return property due to an increase in the viscosity of the refrigerator oil is assumed. Increase the refrigerant flow rate, take bypass measures,
A refrigeration system characterized by that. A method of controlling a refrigerant circuit including a compressor that compresses a refrigerant, a heat exchanger that exchanges heat between the refrigerant and air, and a decompression unit that depressurizes the refrigerant,
The refrigerant circuit includes: a heat utilization destination to which the refrigerant having passed through the decompression unit is supplied; a gas-liquid separator interposed between the compressor; and at least the refrigerant that travels to the decompression unit through the heat exchanger A bypass path that allows a part to flow into the gas-liquid separator, and a bypass valve that opens and closes the bypass path or adjusts the flow rate of the refrigerant flowing through the bypass path,
Controlling the bypass valve so as to open the bypass path or increase the flow rate of the refrigerant flowing through the bypass path based on a predetermined condition in which deterioration of oil return property due to an increase in the viscosity of the refrigerating machine oil is assumed. so,
By the oil return mechanism provided in the gas-liquid separator, the refrigerating machine oil collected inside the gas-liquid separator in a state dissolved in the liquid phase of the refrigerant is recovered and returned to the compressor.
And a refrigerant circuit control method.

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