JP2007187358A - Refrigerating system and cold insulation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress discharge gas temperature with a simple configuration wherein an oil separator is installed on the downstream side of a heat radiator to improve refrigerating system performance without impairing durability of a compressor required in refrigerating equipment or freezing equipment, in a refrigerating system having comparatively low evaporation temperature used for refrigeration or freezing. <P>SOLUTION: Because this refrigerating system is a refrigerating system wherein the oil separator 5 is provided on the downstream side of the heat radiator 20 of a preceding stage, a temperature of lubricating oil circulated to the compressor 1 is reduced, a refrigerant is dissolved into the lubricating oil, and the refrigerant is evaporated when circulating the refrigerant to the compressor 1. Thereby, the temperature can be further reduced, a system circulation amount of the lubricating oil can be reduced by use of the oil separator 5 while suppressing a temperature rise of the discharge gas, and the refrigerating system performance can be improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a refrigeration system having a relatively low evaporation temperature used for refrigeration or refrigeration in a refrigeration system using carbon dioxide as a refrigerant, and to a cold insulation apparatus equipped with the refrigeration system.

  In recent years, there has been an increasing demand for reducing the influence of refrigerants used in refrigeration systems on global warming, and refrigeration systems using carbon dioxide have been proposed as natural refrigerants that have little influence on global warming.

  In addition, a refrigeration system using carbon dioxide is applied to a hot water heater that obtains a high hot water temperature by using the transcritical cycle, and the amount of refrigerant leakage at the time of use is non-flammable. Applied to large car air conditioners.

  Here, a refrigeration system that uses a transcritical cycle of carbon dioxide can be operated more efficiently if it is controlled at a high high pressure at a high outdoor temperature, so that the liquid staying in the accumulator installed at the outlet of the evaporator A configuration in which the amount of refrigerant is adjusted to control the high pressure is applied (see, for example, Patent Document 1).

  On the other hand, in a refrigeration system having a relatively low evaporation temperature used for refrigeration or freezing, there is a problem that the discharge gas temperature becomes very high as the evaporation temperature decreases, and its application has not progressed. In view of this, a refrigeration system has been proposed in which the oil return pipe from the oil separator is cooled using air-cooling fins or the like to suppress an increase in the discharge gas temperature (see, for example, Patent Document 2 or Patent Document 3).

  Hereinafter, a conventional refrigeration system will be described with reference to the drawings.

  FIG. 5 is a circuit configuration diagram of a conventional refrigeration system, and FIG. 6 is a Mollier diagram of the conventional refrigeration system.

  As shown in FIG. 5, the conventional refrigeration system uses carbon dioxide as a refrigerant and has a circuit configuration including a compressor 1, a radiator 2, an expansion valve 3, an evaporator 4, and an oil separator 5.

  In addition, the oil return pipe 6 that recirculates the lubricating oil separated by the oil separator 5 to the compressor 1, the radiator 2 and the oil separator 5, the radiator fan 7 that air-cools the compressor 1 with the outside air, and the cold air generated by the evaporator 4. Are circulated to the inside of the refrigerator (not shown), an evaporation temperature sensor 9 for detecting the evaporation temperature of the evaporator 4, a suction pipe 10 for returning from the evaporator 4 to the compressor 1, and a suction pipe 10 Are provided with a suction pipe temperature sensor 11 for detecting the temperature of the inlet portion and an internal temperature sensor 12 for detecting the temperature of the air flowing into the evaporator 4.

  Here, the expansion valve 3 is throttled by an expansion valve control device (not shown) based on the evaporation temperature detected by the evaporation temperature sensor 9 and the suction pipe temperature sensor 11 and the inlet temperature of the suction pipe 10, respectively. Is optimally controlled. This prevents a large amount of liquid refrigerant from flowing back to the compressor 1 and lowers the temperature of the inlet of the suction pipe 11 when the evaporation temperature is low, thereby reducing the temperature of the gas refrigerant flowing back to the compressor 1. By lowering the temperature, the increase in the discharge gas temperature is suppressed.

  The operation of the conventional refrigeration system configured as described above will be described below.

  The high-temperature discharged gas refrigerant compressed and discharged by the compressor 1 is supplied to the radiator 2 after separating the lubricating oil contained in the oil separator 5. Then, after being cooled to near the outside air temperature by the radiator 2, the pressure is reduced by the expansion valve 3 and evaporated by the evaporator 4. Further, the relatively low-temperature gas refrigerant evaporated in the evaporator 4 returns to the compressor 1 via the suction pipe 10.

  Further, the lubricating oil separated by the oil separator 5 returns to the compressor 1 through the oil return pipe 6. At this time, the refrigerant inside the radiator 2 is in a supercritical state, and the temperature gradually decreases from a high temperature of about 100 ° C. to an outside air temperature as heat is radiated in the path of the radiator 2. Further, the refrigerant inside the evaporator 4 is in a two-phase region, and when the internal temperature is a refrigeration temperature of 0 to 5 ° C, the evaporation temperature of the refrigerant is kept at a relatively low temperature of about -20 to -10 ° C. The air is dried near the path outlet of the evaporator 4 and controlled between the evaporation temperature and the temperature of the air in the cabinet.

  Here, the lubricating oil of the compressor 1 is separated from the refrigerant circulating using the oil separator 5 in order to prevent a decrease in heat exchange efficiency in the radiator 2 and the evaporator 4. In particular, when a large amount of lubricating oil flows into the evaporator 4 at a low temperature, the viscosity of the liquid refrigerant mixed with the lubricating oil is increased, the fluidity is impaired, and the heat exchange efficiency is significantly reduced.

  Further, by controlling the throttle amount of the expansion valve 3, the inlet temperature of the suction pipe 10 is kept about 5 to 10 ° C. higher than the evaporation temperature, thereby preventing the liquid refrigerant from flowing into the compressor 1, The temperature of the discharge gas can be suppressed by lowering the temperature of the refrigerant returning to the compressor 1.

  Next, the state change of the refrigerant in the conventional refrigeration system will be described in detail with reference to FIG.

  FIG. 6 is a Mollier diagram in which the horizontal axis indicates the enthalpy h of the refrigerant and the vertical axis indicates the pressure P of the refrigerant. The points indicated by p, q, r, s, and t are lowered to a predetermined temperature in the refrigerator. The state change of the refrigerant | coolant at the time of the stable in the steady state which showed is shown.

  At the stable time, the refrigerant discharged from the compressor 1 is at the point p at the temperature T2, and is cooled by the radiator 2 to become the point q at the temperature T1. The characteristic of the transcritical cycle is that the refrigerant is in a supercritical state at point q and does not liquefy.

  Next, the pressure is reduced by the expansion valve 3 to reach the r point in the gas-liquid mixed state and supplied to the evaporator 4. The refrigerant evaporated in the evaporator 4 becomes the s point at the inlet of the suction pipe 11 and is heated while passing through the suction pipe 11 to return to the compressor 1 as the point e at the temperature T0.

  Here, the refrigerant in the oil separator 5 is at a point p ′ in the vicinity of the point p, and the lubricating oil returning to the compressor 1 through the oil return pipe 6 has a temperature T2 ′ near the point p, and the compressor 1 The temperature of the gas refrigerant is increased by mixing with the gas refrigerant that is refluxed.

  As a result, under the condition that the amount of lubricating oil returning to the compressor 1 through the oil return pipe 6 increases, there is a risk that the temperature of the refrigerant flowing into the compressor 1 rises and the discharge gas temperature becomes abnormally high. .

Therefore, an attempt has been proposed to lower the temperature of the lubricating oil returning to the compressor 1 by providing an air cooling fin or the like in the oil return pipe 6.
Japanese National Patent Publication No. 3-503206 Japanese Patent Laid-Open No. 2002-127739 JP 2004-101114 A

  However, in the above-described conventional configuration, the temperature of the lubricating oil separated by the oil separator 5 is at a high temperature in the vicinity of the discharge gas temperature and cannot be easily cooled. As a result, the inlet temperature of the suction pipe 10 is further increased. There is a problem that unless the temperature is lowered, the temperature of the refrigerant returning to the compressor 1 cannot be suppressed.

  As a result, the refrigeration effect in the evaporator 4 is reduced, leading to a reduction in efficiency, and the inlet portion of the compressor 1 in the suction pipe 10 is too close to the two-phase region, making it difficult to control the expansion valve 3. Problems also arise. This is because the detection temperature of the suction pipe temperature sensor 11 does not fall below the evaporation temperature, and it is difficult to detect the liquid back under conditions near the evaporation temperature.

  An object of the present invention is to solve the conventional problems and to provide a refrigeration system that improves the performance of the refrigeration system without impairing the durability of the compressor required for refrigeration or refrigeration equipment.

  In order to solve the above-described conventional problems, the refrigeration system of the present invention and the cold insulation device including the refrigeration system are characterized in that an oil separator is provided on the downstream side of the radiator.

  Accordingly, the temperature of the lubricating oil returning to the compressor can be reduced, and the refrigerant can be dissolved in the lubricating oil and evaporated when the refrigerant is returned to the compressor to further reduce the temperature.

  As a result, the temperature rise of the gas refrigerant flowing into the compressor is suppressed without lowering the temperature at the inlet of the suction pipe, and the performance of the refrigeration system is reduced without impairing the durability of the compressor required for refrigeration or refrigeration equipment. Improvements can be made.

  Further, in order to solve the above-described conventional problems, the refrigeration system of the present invention and the cold insulation device provided with the refrigeration system are characterized in that a flow control valve is provided in the oil return pipe.

  As a result, the amount of oil return can be adjusted according to the operating condition, and the refrigerant temperature flowing into the compressor can be actively lowered by increasing the amount of oil return, especially under relatively severe operating conditions where the discharge gas temperature rises. In order to ensure the durability of the compressor, and under relatively loose operating conditions where the discharge gas temperature does not rise, the lubricating oil and the refrigerant dissolved in the oil separator are stored in the oil separator to ease the operating conditions such as high pressure, Furthermore, the performance of the refrigeration system can be improved.

  The refrigeration system of the present invention and a cool box equipped with the refrigeration system have a simple configuration in which an oil separator is installed on the downstream side of the radiator to suppress the discharge gas temperature, so that the durability of the compressor required for refrigeration or refrigeration equipment The performance of the refrigeration system can be improved without impairing the performance.

  According to the first aspect of the present invention, there is provided a refrigeration cycle in which a compressor enclosing a lubricating oil, a radiator, an expansion valve, and an evaporator are connected in an annular shape, and a refrigerant is enclosed therein. The oil separator which isolate | separates the lubricating oil mixed in the said refrigerant | coolant is provided in the downstream of this.

  As described above, when the oil separator is provided on the downstream side of the radiator, the temperature of the lubricating oil returning to the compressor is lowered, and the refrigerant is dissolved in the lubricating oil and returned to the compressor. By evaporating the refrigerant, the temperature can be further lowered, and the system circulation amount of the lubricating oil can be reduced by using an oil separator while suppressing an increase in the discharge gas temperature, thereby improving the refrigeration system performance. Can be achieved.

  According to a second aspect of the present invention, an oil return pipe that connects the oil separator and the suction pipe of the compressor is provided, a flow control valve is provided in the oil return pipe, and the flow control valve is operated. And adjusting means for adjusting the amount of oil returned from the oil separator to the compressor.

  By adopting such a configuration, the amount of oil return can be adjusted according to the operating state, and in a relatively loose operating condition where the discharge gas temperature does not increase, an appropriate amount of oil return is secured to prevent an increase in the discharge gas temperature. However, the oil separator system circulation amount can be reduced by using the oil separator, and the performance of the refrigeration system can be improved.

  Also, under relatively severe operating conditions where the target temperature decreases to the refrigeration zone, particularly when the discharge gas temperature rises, the refrigerant temperature flowing into the compressor is actively reduced by increasing the oil return amount, thereby increasing the discharge gas temperature. And the durability of the compressor can be ensured.

  According to a third aspect of the present invention, when a discharge temperature sensor is provided in a discharge pipe of the compressor and the adjusting means increases the oil return amount when the discharge temperature is high and the discharge temperature is low. Reduces the oil return.

  With this configuration, when it is not necessary to lower the discharge gas temperature by directly detecting the discharge gas temperature, the oil separator is secured while ensuring an appropriate oil return amount and suppressing an increase in the discharge gas temperature. It is possible to reduce the system circulation amount of the lubricating oil and improve the refrigeration system performance.

  In addition, when it becomes difficult to ensure the durability of the compressor because the discharge gas temperature exceeds the limit value, the refrigerant flowing into the compressor is increased by increasing the oil return amount at the expense of the refrigerant circulation amount of the system. The temperature can be actively lowered to reduce the discharge gas temperature, and the durability of the compressor can be ensured.

  According to a fourth aspect of the present invention, there is provided an outside air temperature sensor for detecting an ambient temperature around the refrigeration cycle, and the adjusting means increases the oil return amount at a high outside air temperature, and the oil return at a low outside air temperature. The amount is to be reduced.

  By adopting such a configuration, especially when the refrigeration load is small and the outside temperature of the radiator is low and the refrigeration effect is large, the oil return is reduced and lubricating oil and refrigerant dissolved in the oil separator are stored. By relieving the high pressure, the performance of the refrigeration system can be further improved.

  The invention according to claim 5 of the present invention is provided with a control device for increasing or decreasing the rotational speed of the compressor, and the compressor increases the oil return amount during high speed operation and decreases the oil return amount during low speed operation. It is.

  As a result, especially during low speed operation where the concentration of lubricating oil in the refrigerant increases due to increased leakage inside the compressor, the amount of oil returned is reduced and lubricating oil and refrigerant dissolved therein are stored in the oil separator. Thus, the high pressure can be relieved, and further, leakage inside the compressor can be reduced to suppress the concentration of the lubricating oil in the refrigerant, thereby improving the performance of the refrigeration system.

  The invention according to claim 6 of the present invention is provided with a flow path switching valve for switching the forward path of the radiator and the oil separator, and the flow path switching valve controls the control of giving priority to the refrigeration capacity and suppresses the discharge temperature. Control is to be selected.

  By adopting such a configuration, when performing control giving priority to refrigeration capacity during pull-down, the discharge gas temperature is lowered by raising the evaporation temperature and reducing the compression ratio, and an oil separator is disposed upstream of the radiator. The amount of the refrigerant returning to the compressor via the oil return pipe is reduced. Thereby, the refrigerating capacity at the time of pull-down is securable.

  On the other hand, when control is performed to suppress the discharge temperature when the evaporation temperature is low or the like, an oil separator is disposed on the downstream side of the radiator to increase the amount of refrigerant that flows back to the compressor via the oil return pipe. As a result, it is possible to reduce the system circulation amount of the lubricating oil using the oil separator while suppressing an increase in the discharge gas temperature, and it is possible to improve the refrigeration system performance.

  The invention according to claim 7 of the present invention uses a natural refrigerant mainly composed of carbon dioxide as a refrigerant, and a polyalkylene glycol refrigerating machine oil having a viscosity at 40 ° C. of 5 to 300 cSt as a lubricating oil used in a compressor. Is used.

  Generally, in the refrigerant state downstream from the middle of the radiator having a high pressure of 8 to 12 MPa and a temperature of 20 to 40 ° C., 10 to 30% by weight of the refrigerant is saturated and dissolved in the lubricating oil. Lubricating oil and refrigerant can be stored inside an oil separator installed on the downstream side of the radiator. In particular, under relatively severe operating conditions in which the discharge gas temperature rises, it is possible to ensure the durability of the compressor by actively reducing the temperature of the refrigerant flowing into the compressor by ensuring the amount of refrigerant in the oil return. In the relatively loose operating conditions where the discharge gas temperature does not rise, the lubricating oil and the refrigerant dissolved in the oil separator are stored in the oil separator, and the operating conditions such as high pressure are relaxed to further improve the refrigeration system performance. Can do.

  The invention described in claim 8 of the present invention is a cold storage device equipped with the above refrigeration system, and is a cold storage device for storing food at refrigeration or freezing temperature. In addition, it is possible to control the discharge gas temperature with a simple configuration that installs an oil separator downstream of the radiator, and as a result, the performance of the refrigeration system without compromising the durability of the compressor required for refrigeration or refrigeration equipment. Can be improved.

  Hereinafter, embodiments of a refrigeration system according to the present invention will be described with reference to the drawings. In addition, about the component which performs the same structure or the same function as the past, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

(Embodiment 1)
FIG. 1 is a refrigerant circuit diagram of a refrigeration system according to Embodiment 1 of the present invention, and FIG. 2 is a Mollier diagram of the refrigeration system according to Embodiment 1. In addition, the same number is attached | subjected about the component which has the same structure or the same function as before, and detailed description is abbreviate | omitted.

  As shown in FIG. 1, the refrigeration system of Embodiment 1 is described by taking the case of a cold storage as an example, using carbon dioxide as a refrigerant and a polyalkylene glycol having a viscosity at 40 ° C. of 100 cSt as a lubricating oil In the refrigerating cycle using the compressor oil, the compressor 1, the radiator 2, the electric expansion valve 3, the evaporator 4, and the oil separator 5, a pre-stage radiator between the compressor 1 and the oil separator 5. 20.

  Here, the pre-stage radiator 20 located upstream of the oil separator 5 is a spiral fin tube having a known configuration having one continuous fin and a piping path, and is structurally opposed to the radiator 2. The outlet refrigerant temperature is efficiently reduced by exchanging heat with the high-temperature discharged gas refrigerant by the radiator fan 7.

  The oil separator 5 is provided with an oil return pipe 6 whose tip is connected to the return side (suction side) of the compressor 1, and the lubricating oil separated inside the oil separator 5 is returned to the compressor 1. Is configured to do. Further, the oil return pipe 6 is provided with a flow rate adjusting valve 21 that adjusts the amount of oil returned to the compressor 1, and the outlet (discharge) pipe of the compressor 1 is a discharge temperature sensor that detects the discharge gas temperature. 22 is provided.

  Here, the oil return amount of the flow rate adjustment valve 21 is based on the evaporation temperature detected by the evaporation temperature sensor 9 and the discharge gas temperature detected by the discharge temperature sensor 22. The amount is controlled and optimally controlled by this.

  Further, the compressor 1 is operation-controlled as is well known by an operation control device 25 that uses the temperatures of the suction pipe temperature sensor 11 and the internal temperature sensor 12 as basic input information, and also detects the evaporation temperature sensor 9 as necessary. The temperature is also controlled by the control device 25 as input information. Further, the opening degree of the expansion valve 3 is similarly controlled by the operation control device 25 based on the basic input information.

  The operation of the refrigeration system according to Embodiment 1 configured as described above will be described below.

  The high-temperature discharged gas refrigerant compressed and discharged by the compressor 1 is precooled by the pre-stage radiator 20 and supplied to the oil separator 5, and the lubricating oil contained in the oil separator 5 is separated as is well known. Thereafter, the heat is supplied to the radiator 2, cooled to the vicinity of the outside temperature by the radiator 2, depressurized by the expansion valve 3, and evaporated by the evaporator 4. Then, the relatively low-temperature gas refrigerant evaporated in the evaporator 4 is returned to the compressor 1 through the suction pipe 10, and the above-described flow is repeated to cool the inside of the refrigerator.

  Here, when the evaporation temperature is higher than −20 ° C., the evaporation temperature sensor 9 detects this, and the flow rate control device 24 reduces the opening of the flow rate adjustment valve 21. Therefore, the lubricating oil separated by the oil separator 5 returns to the compressor 1 through the oil return pipe 6 at a small flow rate.

  Thus, since the lubricating oil returning to the compressor 1 through the oil return pipe 6 is precooled by the pre-stage radiator 20, the discharge gas temperature does not increase, and the flow rate adjusting valve 21 Since the amount of refrigerant flowing back to the compressor 1 is reduced by reducing the valve opening, the refrigerating capacity can be secured without greatly reducing the refrigerant circulation amount supplied to the evaporator 4.

  Further, in this state, the refrigerant inside the front-stage heat radiator 20 is in a supercritical state, but heat dissipation proceeds as it passes through the path of the front-stage heat radiator 20, and finally the high temperature from about 100 ° C. to the outside air temperature +10 to 10 The temperature gradually decreases to about 15 ° C. For example, when the outside air temperature is about 25 ° C., the outlet temperature of the pre-stage radiator 20 is about 40 ° C., and about 40 ° C. lubricating oil and 20-30 wt% refrigerant dissolved in the oil separator 5 are separated and stored. The

  In the first embodiment, in order to lower the temperature of the lubricating oil returning from the oil return pipe 6, the amount of refrigerant dissolved in the return oil is preferably about 10 to 40% by weight. It is optimal to keep the oil separator 5 at about 40 ° C. using polyalkylene glycol refrigerating machine oil compatible with the refrigerant.

  That is, if a refrigerating machine oil that is incompatible with the carbon dioxide refrigerant is used, the amount of refrigerant dissolved in the oil return becomes very small, and the effect of lowering the temperature of the lubricating oil that circulates is lost. If the compatibility with the carbon dioxide refrigerant is too high, it becomes difficult to separate the lubricating oil in the oil separator 5, and the system circulation amount of the lubricating oil cannot be reduced.

  In addition, the refrigerant inside the radiator 2 is in a supercritical state near the outside air temperature, has a small temperature difference from the outside air, and it is desirable to prevent mixing of lubricating oil in order to improve heat exchange efficiency. Further, the refrigerant inside the evaporator 4 is in a two-phase region, and when the internal temperature is in a refrigeration temperature zone of 0 to 5 ° C, the evaporation temperature of the refrigerant is kept at a relatively low temperature of about -20 to -10 ° C. As in the conventional case, the operation control device 25 controls the throttle amount (valve opening degree) of the expansion valve 3 to the optimum value, so that it dries near the route outlet of the evaporator 4 and the temperature of the air in the chamber changes from the evaporation temperature. Controlled between.

  On the other hand, when the internal temperature becomes a refrigeration temperature of -20 to -10 ° C, the evaporation temperature of the evaporator 4 is relatively low at -20 ° C or less, and the discharge gas temperature rises and exceeds the limit value. By increasing the valve opening degree of the flow rate adjusting valve 21 and increasing the oil return amount, an increase in the discharge gas temperature is suppressed. Thereby, a relatively low temperature lubricating oil stored in the oil separator 5 and a liquid refrigerant of about 20 to 30% by weight dissolved therein can be recirculated in a large amount to the suction side of the compressor 1, thereby An increase in the discharge gas temperature can be suppressed by further lowering the intake gas (intake refrigerant) temperature.

  Next, the state change of the refrigerant in the refrigeration system in Embodiment 1 will be described in detail with reference to FIG.

  FIG. 2 is a Mollier diagram in which the horizontal axis indicates the enthalpy h of the refrigerant and the vertical axis indicates the pressure P of the refrigerant, and points indicated by p, q, r, s, t, and u are inside the refrigerator (see FIG. (Not shown) indicates the state change (change point) of the refrigerant at the stable state in a steady state where the temperature is lowered to a predetermined temperature.

  When stable, the refrigerant discharged from the compressor 1 is at the point p at the temperature T2, and is cooled by the pre-stage radiator 20 to become the point u at the temperature T3. And it further cools with the heat radiator 2, and becomes q point of temperature T1. The feature of the transcritical cycle is that the refrigerant is in a supercritical state at point q and does not liquefy.

  Next, the refrigerant is decompressed by the expansion valve 3, becomes a point r in a gas-liquid mixed state, and is supplied to the evaporator 4. The refrigerant evaporated in the evaporator 4 becomes the s point at the inlet of the suction pipe 11 and is heated while passing through the suction pipe 11 to return to the compressor 1 as the point e at the temperature T0.

  Here, the refrigerant and the lubricating oil in the oil separator 5 are at the point u of the temperature T3 cooled by the pre-stage radiator 20, and 20 to 30% by weight of the refrigerant is dissolved in the lubricating oil due to the temperature drop. Then, the refrigerant and the lubricating oil dissolved in the refrigerant return to the compressor 1 through the oil return pipe 6 in an amount corresponding to the valve opening degree of the flow rate adjustment valve 21. The recirculation to the compressor 1 is such that the pressure of the recirculation refrigerant decreases while mixing with the gas refrigerant that recirculates from the suction pipe 11 to the compressor 1. It evaporates and suppresses the temperature of the gas refrigerant sucked by the compressor 1.

  As a result, when the evaporation temperature is relatively high, such as over −20 ° C., the opening degree of the flow rate adjusting valve 21 is made small, so that the amount of lubricating oil returning to the compressor 1 via the oil return pipe 6 is small. Thus, the system circulation amount of the lubricating oil using the oil separator can be reduced while suppressing an increase in the discharge gas temperature due to this, and the refrigeration system performance can be improved.

  On the other hand, when the evaporation temperature is relatively low at −20 ° C. or lower and the discharge gas temperature rises and exceeds a limit value, the opening degree of the flow rate adjustment valve 21 is increased. Therefore, although the amount of the refrigerant circulating in the system is sacrificed, the amount of oil returned to the compressor 1 via the oil return pipe 6 can be increased, whereby the temperature of the refrigerant flowing into the compressor 1 is increased. Can be positively lowered to reduce the discharge gas temperature, and the durability of the compressor 1 can be ensured.

  As described above, in the first embodiment, the oil separator 5 is installed on the downstream side of the pre-stage radiator 20, and based on the evaporation temperature and the discharge gas temperature detected by the evaporation temperature sensor 9 and the discharge temperature sensor 22, respectively. The flow control valve 21 provided in the oil return pipe 6 is optimally controlled. With this control, when the evaporation temperature is relatively high, such as over -20 ° C., the opening degree of the flow control valve 21 is reduced. The oil separator 5 can be used to reduce the system circulation amount of the lubricating oil while ensuring an appropriate oil return amount and suppressing the rise in the discharge gas temperature, and the refrigeration system performance can be improved.

  Conversely, when the evaporation temperature is relatively low at −20 ° C. or lower and the discharge gas temperature rises and exceeds a limit value, the opening degree of the flow rate adjustment valve 21 is increased and the oil return amount is increased. . By such control, although the amount of refrigerant circulation in the system is sacrificed, by increasing the oil return amount into the refrigeration cycle, the refrigerant temperature flowing into the compressor 1 is actively lowered to reduce the discharge gas temperature, The durability of the compressor 1 can be ensured.

  In Embodiment 1, priority is given to ensuring the durability of the compressor 1 when the evaporation temperature is relatively low at −20 ° C. or lower and the discharge gas temperature rises and exceeds a limit value. Although the flow rate adjustment valve 21 has a large opening, a sensor for detecting the outside air temperature is provided in the configuration of FIG. 1, and the flow rate adjustment valve 21 is opened with priority given to ensuring the durability of the compressor 1 at a high outside air temperature. The same effect can be expected even when the degree of control is controlled to be large.

  Further, a variable speed compressor is used as the compressor 1, and based on the information indicating the operation state, the opening degree of the flow rate adjusting valve 21 is controlled to be large in order to ensure the durability of the compressor 1 during high speed operation. The same effect can be expected from the configuration.

  Further, if the opening degree of the flow regulating valve 21 is reduced and the amount of lubricating oil stored in the oil separator 5 and the amount of refrigerant dissolved therein are increased, the effect of reducing the internal pressure of the system, particularly the high pressure can be expected. As a result, the refrigeration system performance can be improved by relieving the high pressure even if the opening degree of the flow rate adjusting valve 21 is reduced only when the outside air temperature is low or when the compressor 1 is operating at a low speed.

  In the present embodiment, the radiator 2 is installed on the downstream side of the oil separator 5. However, even if the performance of the front-stage radiator 20 is improved and the radiator 2 is omitted, the same operation and effect are expected. it can.

  In the first embodiment, when the evaporation temperature is relatively high, such as over −20 ° C., the throttle control amount of the expansion valve 3 is optimally controlled by the operation control device (expansion valve control device) 25 as in the prior art. Thus, although the rise in the discharge gas temperature is suppressed, even if a fixed throttle means such as a capillary tube selected so as to operate within the range where the discharge gas temperature is allowed, the evaporation temperature is relatively −20 ° C. or lower. If the discharge gas temperature is low and exceeds the limit value, the same effect as in this embodiment can be expected by suppressing the increase in the discharge gas temperature by increasing the opening of the flow rate adjustment valve 21. .

(Embodiment 2)
FIG. 3 is a refrigerant circuit diagram of the refrigeration system in the second embodiment of the present invention, and FIG. 4 is a Mollier diagram of the refrigeration system in the second embodiment. In addition, the same number is attached | subjected about the component which performs the same structure as the previous Embodiment 1, or the same function, and detailed description is abbreviate | omitted. Further, the configuration of the flow control device 24 and the operation control device 25 shown in the first embodiment is also omitted, and the operation content of each component will be mainly described.

  As shown in FIG. 3, the refrigeration system according to the second embodiment uses carbon dioxide as a refrigerant and polyalkylene glycol refrigeration oil having a viscosity of 100 cSt at 40 ° C. as a lubricating oil. The circuit configuration including the vessel 2, the electric expansion valve 3, the evaporator 4, the oil separator 5, and the front radiator 20 is the same, and the flow path switching valve 23 is newly provided. The flow path switching valve 23 replaces the normal path through which the refrigerant of the upstream radiator 20 and the oil separator 5 flows between paths from the compressor 1 to the radiator 2 and has a well-known configuration.

  The operation of the refrigeration system of Embodiment 2 configured as described above will be described below.

  When performing control giving priority to the refrigerating capacity at the time of pull-down or the like, the flow path switching valve 23 is set so that the pre-stage radiator 20 is on the downstream side of the oil separator 5. At this time, the high-temperature discharged gas refrigerant compressed and discharged by the compressor 1 is supplied to the radiator 2 via the pre-stage radiator 20 after separating the lubricating oil contained in the oil separator 5. After being cooled to near the outside air temperature at 2, the pressure is reduced by the expansion valve 3 and evaporated by the evaporator 4. Then, the relatively low temperature gas refrigerant evaporated in the evaporator 4 returns to the compressor 1 through the suction pipe 10.

  As a result, the oil separator 5 is maintained at a high temperature close to the discharge gas temperature, and the refrigerant hardly dissolves in the retained lubricating oil. As a result, the amount of refrigerant recirculated to the compressor 1 through the oil return pipe 6 can be reduced, and the accompanying reduction in refrigeration capacity can be suppressed. If the load during pull-down is large, the inlet temperature of the suction pipe 10 can be optimally controlled by increasing the evaporation temperature of the evaporator 4 and adjusting the throttle degree of the expansion valve 3. An increase in the discharge gas temperature can be suppressed.

  On the other hand, when performing control to suppress the discharge temperature when the evaporation temperature is low, the flow path switching valve 23 is set so that the pre-stage radiator 20 is on the upstream side of the oil separator 5.

  As a result, the high-temperature discharged gas refrigerant compressed and discharged by the compressor 1 is pre-cooled by the pre-stage radiator 20 and supplied to the oil separator 5, and after separating the lubricating oil contained by the oil separator 5, It is supplied to the radiator 2. Then, after being cooled to near the outside air temperature by the radiator 2, the pressure is reduced by the expansion valve 3 and evaporated by the evaporator 4. Then, the relatively low temperature gas refrigerant evaporated in the evaporator 4 returns to the compressor 1 through the suction pipe 10. Hereinafter, the inside of the cool box can be cooled by repeating the above-described flow.

  Therefore, the oil separator 5 is cooled by the pre-stage radiator 20, and the temperature of the staying lubricating oil decreases, and the refrigerant dissolves in the staying lubricating oil, and returns to the compressor 1 through the oil return pipe 6. When the refrigerant evaporates, an increase in the discharge gas temperature can be suppressed. At the same time, since the refrigerant is stored in the oil separator 5, an effect of relieving the high pressure and improving the refrigeration system performance can be expected.

  It should be noted that the system circulation amount of the lubricating oil can be reduced by the oil separator 5 regardless of which the flow path switching valve 23 is switched, and the refrigeration system performance can be improved.

  Next, the state change of the refrigerant in the refrigeration system in Embodiment 2 will be described in detail with reference to FIG.

  FIG. 4 is a Mollier diagram in which the horizontal axis represents the enthalpy h of the refrigerant and the vertical axis represents the pressure P of the refrigerant. Each point indicated by p, q, r, s, t, u represents the inside of the cool box (see FIG. (Not shown) indicates the state change (change point) of the refrigerant at the stable state in a steady state where the temperature is lowered to a predetermined temperature.

  When performing control giving priority to the refrigerating capacity at the time of pull-down or the like, the flow path switching valve 23 is set so that the pre-stage radiator 20 is on the downstream side of the oil separator 5. At this time, the refrigerant in the oil separator 5 is indicated by a point p ′ where the refrigerant discharged from the compressor 1 is in the vicinity of the point p of the temperature T2. The lubricating oil staying in the oil separator 5 is also at a high temperature, and the refrigerant is hardly dissolved.

  On the other hand, when performing control to suppress the discharge temperature when the evaporation temperature is low, the flow path switching valve 23 is set so that the pre-stage radiator 20 is on the upstream side of the oil separator 5. At this time, the refrigerant and the lubricating oil in the oil separator 5 are at the point u of the temperature T3 cooled by the front radiator 20, and 20 to 30% by weight of the refrigerant is dissolved in the lubricating oil due to the temperature drop.

  Here, in order to lower the temperature of the lubricating oil returning from the oil return pipe 6 into the refrigerant circulation circuit (refrigeration cycle), the amount of refrigerant dissolved in the return oil is preferably about 10 to 40% by weight, In order to realize this, it is optimal to keep the oil separator 5 at about 40 ° C. by using polyalkylene glycol refrigerating machine oil compatible with the carbon dioxide refrigerant.

  If a refrigerating machine oil that is incompatible with the carbon dioxide refrigerant is used, the amount of refrigerant that dissolves in the return oil becomes very small, and the effect of lowering the temperature of the refluxing lubricating oil is lost. If the compatibility with the carbon dioxide refrigerant is too high, it becomes difficult to separate the lubricating oil in the oil separator 5, and the system circulation amount of the lubricating oil cannot be reduced.

  As described above, in the second embodiment, the flow path switching valve 23 for switching the forward paths of the pre-stage radiator 20 and the oil separator 5 is provided, and different paths are controlled by the control that gives priority to the refrigerating capacity and the control that controls the discharge temperature. Just choose.

  And when performing control giving priority to the refrigerating capacity at the time of pull-down or the like, the refrigerant is hardly dissolved in the staying lubricating oil by maintaining the oil separator 5 at a high temperature close to the discharge gas temperature. The amount of refrigerant flowing back to the compressor 1 via the oil return pipe 6 can be reduced. Furthermore, the accompanying decline in the refrigerating capacity can be suppressed.

  Also, when performing control to suppress the discharge temperature when the evaporation temperature is low, etc., the oil separator 5 is cooled by the pre-stage radiator 20, thereby lowering the temperature of the retained lubricating oil, As a result, the refrigerant dissolves in the staying lubricating oil, and the refrigerant evaporates when returning to the compressor 1 via the oil return pipe 6, thereby suppressing an increase in the discharge gas temperature.

  In the second embodiment, the radiator 2 is installed on the downstream side of the flow path switching valve 23, but the same effect can be obtained even if the performance of the front-stage radiator 20 is improved and the radiator 2 is omitted. I can expect.

  Further, in the second embodiment, when priority is given to the refrigerating capacity at the time of pull-down or the like, the throttle amount of the expansion valve 3 is optimally controlled by the expansion valve control function that is a function of the operation control device as in the conventional case. Thus, although the rise in the discharge gas temperature is suppressed, a fixed throttle means such as a capillary tube selected so as to operate within a range where the discharge gas temperature is allowed may be used. That is, when performing control to suppress the discharge temperature when the evaporation temperature is low or the like, the discharge gas temperature can be controlled by setting the flow path switching valve 23 so that the upstream radiator 20 is on the upstream side of the oil separator 5. The rise can be suppressed and the same effect can be expected.

  As described above, the refrigeration system according to the present invention and the cold storage apparatus equipped with the refrigeration system suppress an increase in the discharge gas temperature due to the recirculating lubricating oil while reducing the system circulation amount of the lubricating oil using the oil separator. Therefore, it can be widely applied as refrigeration equipment or refrigeration equipment such as showcases, commercial refrigerators and vending machines that require non-fluorocarbon refrigerants and energy saving equipment. is there.

1 is a refrigerant circuit diagram of a refrigeration system according to Embodiment 1 of the present invention. Mollier diagram of the refrigeration system according to Embodiment 1 of the present invention. Refrigerant circuit diagram of a refrigeration system according to Embodiment 2 of the present invention Mollier diagram of a refrigeration system according to Embodiment 2 of the present invention Refrigerant circuit diagram of conventional refrigeration system Mollier diagram of conventional refrigeration system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 2 Radiator 3 Expansion valve 4 Evaporator 5 Oil separator 6 Oil return pipe 20 Pre-stage radiator 21 Flow rate adjustment valve 22 Discharge temperature sensor 23 Flow path switching valve

Claims (8)

  In a refrigeration cycle in which a compressor, a radiator, an expansion valve, and an evaporator are connected in an annular shape and the refrigerant is sealed inside, the lubricant mixed in the refrigerant is disposed downstream of the radiator. A refrigeration system with an oil separator that separates oil.   An oil return pipe connecting the oil separator and the suction pipe of the compressor is provided, a flow control valve is provided in the oil return pipe, and the flow rate control valve is operated to return the oil separator to the compressor. The refrigeration system according to claim 1, further comprising an adjusting means for adjusting the oil amount.   The discharge temperature sensor is provided in the discharge pipe of the compressor, and the oil return amount is increased when the discharge temperature is high and the oil return amount is decreased when the discharge temperature is low by the adjusting means. Refrigeration system.   The outside air temperature sensor for detecting the ambient temperature around the refrigeration cycle is provided, and the adjusting means increases the oil return amount at a high outside air temperature and decreases the oil return amount at a low outside air temperature. The refrigeration system described.   The control apparatus which increases / decreases the rotation speed of the compressor is provided, and the compressor increases the oil return amount when operating at high speed, and decreases the oil return amount when operating at low speed. The refrigeration system described.   6. A flow path switching valve for switching a forward path between the heat radiator and the oil separator is provided, and the flow path switching valve selects control for giving priority to refrigeration capacity and control for suppressing discharge temperature. The refrigeration system as described in any one of Claims.   7. The refrigerant according to claim 1, wherein a natural refrigerant mainly composed of carbon dioxide is used as a refrigerant, and a polyalkylene glycol refrigerating machine oil having a viscosity at 40 ° C. of 5 to 300 cSt is used as a lubricating oil for a compressor. A refrigeration system according to claim 1.   A cold storage device equipped with the refrigeration system according to any one of claims 1 to 7.

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