JP2007292423A - Refrigeration system and storage equipment - Google Patents

Abstract

In a refrigeration system having a relatively low evaporation temperature used for refrigeration or refrigeration, the refrigeration capacity at power-on and the refrigeration system performance at stability are improved without impairing the durability of the compressor.
An evaporation temperature detection sensor for detecting the temperature of an evaporator and a suction pipe inlet temperature detection sensor for detecting a temperature of an inlet part of the suction pipe connecting the evaporator and the compressor are provided. If the measured value detected by the suction pipe inlet temperature detection sensor 25 is higher than the target temperature determined from the evaporation temperature detected by the temperature detection sensor 23, the opening of the expansion valve is increased, and the suction pipe inlet temperature detection sensor. If the measured value detected at 25 is low, the evaporation temperature is controlled by reducing the opening of the expansion valve to prevent oil retention in the suction pipe, and the compressor 21 at the time of power-on and when it is stable. The temperature of the discharged refrigerant can be kept substantially constant, and the refrigeration capacity can be improved without impairing the durability of the compressor 21.
[Selection] Figure 1

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 a storage device such as a cool box equipped with the refrigeration system.

  In recent years, in order to reduce the influence of the refrigerant used in the refrigeration system on global warming, a refrigeration system using carbon dioxide as a natural refrigerant has been proposed. In addition, the refrigeration system using carbon dioxide is mainly applied to hot water heaters that obtain a high hot water temperature using the transcritical cycle, and is applied to car air conditioners using the nonflammable point. ing.

  Here, since the refrigeration system using the carbon dioxide transcritical cycle can be operated more efficiently by controlling to a high high pressure at a high outside air temperature, it stays in the accumulator installed at the outlet of the evaporator. A configuration in which the amount of liquid 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 internal heat exchange amount is controlled to suppress an increase in the discharge gas temperature (see, for example, Patent Document 2).

  In general, in a refrigeration system using carbon dioxide as a refrigerant, a polyalkylene glycol refrigeration having a kinematic viscosity at 40 ° C. of about 100 mm 2 / s and a kinematic viscosity at 100 ° C. of about 20 mm 2 / s as a refrigerating machine oil for a compressor. Machine oil is used (for example, refer nonpatent literature 1).

  The main reason for using the polyalkylene glycol refrigerating machine oil in the refrigerating machine oil is that the oil phase separated under low temperature and low pressure conditions in the evaporator dissolves the carbon dioxide refrigerant well and has a low viscosity, and the supercritical state in the compressor This is because the viscosity required for lubricating the compressor can be maintained without dissolving the carbon dioxide refrigerant so much.

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

  FIG. 6 is a circuit configuration diagram of a conventional refrigeration system, and FIG. 7 is a Mollier diagram of the conventional refrigeration system.

  As shown in FIG. 6, 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 accumulator 5. Moreover, the internal heat exchanger 6 which performs heat exchange with the gas refrigerant which goes to the expansion valve 3 from the heat radiator 2, and the gas refrigerant which goes to the compressor 1 from the accumulator 5, and the heat radiation which air-cools the heat radiator 2 and the compressor 1 with external air An evaporator fan 8 that circulates the cool air generated by the evaporator fan 7 and the evaporator 4 to the inside of the cool box (not shown), and a sensor 9 that detects the refrigerant pressure and temperature at the outlet of the radiator 2 are provided. .

  Here, the expansion amount of the expansion valve 3 is optimally controlled by an expansion valve control device (not shown) based on the refrigerant pressure and temperature at the outlet of the radiator 2 detected by the sensor 9.

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

  The refrigerant compressed and discharged by the compressor 1 is cooled to the vicinity of the outside temperature by the radiator 2, further cooled by the internal heat exchanger 6, decompressed by the expansion valve 3, and evaporated by the evaporator 4. . Then, while the liquid refrigerant that could not be evaporated by the evaporator 4 is stored in the accumulator 5, only the gas refrigerant returns from the accumulator 5 to the compressor 1 via the internal heat exchanger 6.

  Here, when the outside air temperature is high, the refrigerant temperature at the outlet of the radiator 2 detected by the sensor 9 is increased, and the refrigerant pressure at the outlet of the radiator 2 is increased to an optimum predetermined amount by the expansion valve control device. The opening degree of the expansion valve 3 is reduced. The refrigerant pressure at the outlet of the radiator 2 is increased by reducing the opening degree of the expansion valve 3 because the evaporation temperature is lowered by reducing the opening degree of the expansion valve 3 and the heat exchange amount in the evaporator 4 is reduced. This is because the refrigerant circulation rate decreases as the flow rate increases, and as a result, the degree of dryness of the refrigerant at the outlet of the evaporator 4 increases and the amount of refrigerant stored in the accumulator 5 decreases.

  When the outside air temperature is low, the refrigerant temperature at the outlet of the radiator 2 detected by the sensor 9 is lowered, and the refrigerant pressure at the outlet of the radiator 2 is reduced to an optimum predetermined amount by an expansion valve control device (not shown). The opening degree of the expansion valve 3 is adjusted in the opening direction so as to be lowered. The refrigerant pressure at the outlet of the radiator 2 decreases by adjusting the opening of the expansion valve 3 because the evaporation temperature rises by opening the expansion valve 3 and the amount of heat exchange in the evaporator 4. This is because, as a result of the decrease in the refrigerant circulation amount, the refrigerant circulation amount increases, and as a result, the degree of dryness of the refrigerant at the outlet of the evaporator 4 decreases and the amount of refrigerant stored in the accumulator 5 increases.

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

  FIG. 7 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 a, b, c, d, e represents the inside of the cool box (not shown). 1) shows a change in the state of the refrigerant in a steady state in which the temperature is lowered to a predetermined temperature, and each point indicated by a ′, b ′, c ′, d ′, e ′ indicates the inside of the cool box (see FIG. (Not shown) shows a change in the state of the refrigerant when the power is turned on in the vicinity of the outside air temperature.

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

  Next, the pressure is reduced by the expansion valve 3 to become a point c in a gas-liquid mixed state and supplied to the evaporator 4. The refrigerant evaporated in the evaporator 4 becomes a point d, passes through the accumulator 5 where the liquid refrigerant stays, and is then heated by the internal heat exchanger 6 or the like to return to the compressor 1 as a point e at a temperature T0.

  Here, the temperature T1 is in the vicinity of the outside air temperature, and changes depending on the fluctuation of the outside air temperature. At this time, the expansion valve control device adjusts the high pressure indicated by points a and b to a higher predetermined value if the outside air temperature is high, and increases the high pressure indicated by points a and b if the outside air temperature is low. It is adjusted to a low predetermined value.

  As a result, the optimum refrigeration efficiency obtained at a wide range of outside air temperatures can be realized. Further, if the liquid refrigerant is stored in the accumulator 5 within this adjustment range, the point d is on the saturated gas phase line of the refrigerant, and the temperature T0 at the point e is kept lower than T1, so that the compressor 1 It is possible to suppress an abnormal rise in the refrigerant temperature T2 discharged from the point a.

  On the other hand, when the power is turned on, the refrigerant discharged from the compressor 1 is at the point a 'at the temperature T3 and is cooled by the radiator 2 to become the point b' at the temperature T1. At the point b ', the refrigerant is in a supercritical state as in the stable state.

  Next, the pressure is reduced by the expansion valve 3 to become a point c ′ in the gas-liquid mixed state, and the vapor is supplied to the evaporator 4. In the evaporator 4, the refrigerant completely evaporates and reaches the d ′ point, passes through the accumulator 5 as it is, is heated by the internal heat exchanger 6 or the like, becomes the e ′ point of the temperature T 1, and is returned to the compressor 1.

  Here, when the power is turned on, in the evaporator 4 and the accumulator 5, the refrigerant completely evaporates and reaches a point d ′ that is higher than the saturated vapor phase line of the refrigerant (not shown). This is because the evaporating ability of the evaporator 4 is remarkably increased as compared with when the temperature is stable. Then, the liquid refrigerant that should stay in the accumulator 5 at the stable time is supplied to the high pressure side, and the high pressure indicated by the points a ′ and b ′ is higher than the high pressure at the time indicated by the points a and b. Will keep.

  When the power is turned on, the liquid refrigerant does not stay in the accumulator 5 even if the expansion amount of the expansion valve 3 is changed by the expansion valve control device, and the high pressure does not change greatly. The throttle amount is set to a fixed value so that the evaporation temperature is about the same as that at the time of stabilization until the steady state where the temperature is lowered to a predetermined temperature is reached.

As a result, the refrigeration effect when the power is turned on, which is indicated by the difference between the enthalpies h at the d ′ point and the c ′ point, may be greater than the refrigeration effect at the time indicated by the difference between the enthalpies h at the d point and the c point. It is possible to shorten the time required to reach a steady state required for refrigeration or refrigeration equipment.
Japanese National Patent Publication No. 3-503206 JP 2000-346466 A Idemitsu Tribo Review, No. 25, P1552-1557 (2002)

  However, in the above conventional configuration, in order to maintain the viscosity necessary for the lubrication of the compressor 1 in the supercritical state in the compressor, a high-viscosity refrigerating machine oil that does not dissolve the carbon dioxide refrigerant must be used. Refrigerating or refrigeration equipment operated at a relatively low evaporation temperature of −50 ° C. to 0 ° C. compared to a car air conditioner operated at a relatively high evaporation temperature of 0 ° C. to 20 ° C. Because the refrigerant temperature at point or e 'point is high and the refrigerant pressure is low, the refrigerant does not dissolve very much in the refrigerating machine oil separated in the pipe, and the high-viscosity refrigerating machine oil accumulates and the pipe is blocked or started. Occasionally, the oil that stayed at a time returned to a large amount at a time, and the durability of the compressor 1 could be impaired.

  In particular, in the refrigeration or refrigeration equipment in which the refrigeration system is arranged at the upper part, the head when returning from the evaporator 4 to the compressor 1 is large, and this problem appears notably.

  On the other hand, if the refrigerant temperature at the point e or e ′ returning to the compressor 1 is lowered until it becomes equal to the evaporation temperature, the liquid refrigerant continuously flows back to the compressor 1, thereby eliminating the problem of refrigerating machine oil retention. However, there is a risk that the durability of the compressor 1 may be impaired as the liquid refrigerant is compressed.

  Furthermore, since the refrigerant temperature at point e or e ′ is high and the refrigerant pressure is low, the refrigerant temperature T3 at point a ′ discharged from the compressor 1 when the power is turned on abnormally rises and the durability of the compressor is increased. There was a risk of damaging sex.

  The present invention solves the conventional problems and improves the refrigeration system performance such as the refrigeration capacity at the time of power-on and the refrigeration efficiency at the stable time without impairing the durability of the compressor required for refrigeration or refrigeration equipment. An object of the present invention is to provide a refrigeration system that achieves the above.

  In order to solve the above-described conventional problems, the refrigeration system of the present invention and the storage device including the refrigeration system do not include an accumulator and an internal heat exchanger, and do not include an accumulator and an intake temperature that connects the evaporator and the compressor. The temperature difference of the piping is kept within 20 ° C.

  This ensures the amount of refrigerant dissolved in the refrigerating machine oil separated in the suction pipe, thereby suppressing the kinematic viscosity to 30 mm2 / s or less, desirably 10 mm2 / s or less, and preventing oil retention in the pipe. Can do. Furthermore, the refrigerant circulation rate can be increased by keeping the evaporation temperature high when the power is turned on without losing the durability of the compressor by keeping the temperature of the refrigerant discharged from the compressor substantially constant when the power is turned on and stable. The refrigeration capacity can be improved.

  The refrigeration system of the present invention and the storage device equipped with the same impair the durability of the compressor required for refrigeration or refrigeration equipment by controlling the opening of the expansion valve and the capacity of the compressor with a simple configuration. In addition, it is possible to improve the refrigeration system performance such as the refrigeration capacity when the power is turned on and the refrigeration efficiency when the power is stable.

  Invention of Claim 1 of this invention uses the natural refrigerant | coolant which has a carbon dioxide as a main component as a refrigerant | coolant in the refrigeration system which comprised the compressor, the heat radiator, the expansion valve, and the evaporator, The said The evaporation temperature of the evaporator is in the range of −50 ° C. to 0 ° C., and the difference between the evaporation temperature of the evaporator and the suction pipe temperature of the compressor is kept within 20 ° C.

  Thereby, the refrigerant | coolant dissolution amount in the refrigerating machine oil isolate | separated within the suction piping of the said compressor can be ensured, and the oil stagnation in piping can be prevented.

  The invention according to claim 2 of the present invention uses a polyalkylene glycol refrigerating machine oil having a kinematic viscosity at 40 ° C. of 30 mm 2 / s to 300 mm 2 / s as the lubricating oil of the compressor.

  As a result, the amount of refrigerant dissolved in the refrigerating machine oil separated in the suction pipe can be ensured, the kinematic viscosity is suppressed to 30 mm2 / s or less, preferably 10 mm2 / s or less, and oil retention in the pipe is prevented. Can do.

  The invention according to claim 3 of the present invention includes an evaporation temperature sensor that detects an evaporation temperature of the evaporator, and a suction pipe outlet temperature sensor that detects a temperature in the vicinity of the compressor in the suction pipe of the compressor, When the suction pipe temperature detected by the suction pipe outlet temperature sensor is higher than the target temperature determined from the evaporation temperature detected by the evaporation temperature sensor, the opening of the expansion valve is increased. The evaporating temperature is controlled by reducing the opening degree.

  This ensures the amount of refrigerant dissolved in the refrigerating machine oil separated in the suction pipe, suppresses the kinematic viscosity to 30 mm2 / s or less, preferably 10 mm2 / s or less, and prevents oil retention in the pipe. In addition, the temperature of the refrigerant discharged from the compressor when the power is turned on and when it is stable can be kept substantially constant. As a result, it is possible to improve the refrigerating capacity by increasing the refrigerant circulation amount by keeping the evaporation temperature high when the power is turned on without impairing the durability of the compressor.

  The invention according to claim 4 of the present invention includes an evaporation temperature sensor that detects an evaporation temperature of the evaporator, and an inlet pipe inlet temperature sensor that detects a temperature in the vicinity of the evaporator in the inlet pipe of the compressor, When the suction pipe temperature detected by the suction pipe inlet temperature sensor is higher than the target temperature determined from the evaporation temperature detected by the evaporation temperature sensor, the opening of the expansion valve is increased. The evaporation temperature is controlled by reducing the opening.

  As a result, it is possible to control based on the temperature in the vicinity of the evaporator in the suction pipe of the compressor that is relatively unaffected by the outside air temperature, and to accurately adjust the temperature of the suction pipe while preventing liquid back. it can. In addition, by securing the amount of refrigerant dissolved in the refrigerating machine oil separated in the suction pipe, the kinematic viscosity is suppressed to 30 mm2 / s or less, preferably 10 mm2 / s or less, and oil retention in the pipe is prevented. The temperature of the refrigerant discharged from the compressor when the power is turned on and when it is stable can be kept substantially constant, and the evaporation temperature can be kept high when the power is turned on without impairing the durability of the compressor. It can be increased to improve the refrigerating capacity.

  According to a fifth aspect of the present invention, the compressor is a compressor whose capacity can be varied, and the capacity of the compressor is controlled by the air temperature in the cooled room.

  This makes it possible to quickly reduce the evaporator outlet temperature and the suction pipe temperature by increasing the capacity of the compressor, particularly when the air temperature in the cooled room is high. It is possible to prevent oil stagnation in the suction pipe, and at the stable time when the air temperature in the cooled room is lowered, it is possible to realize highly efficient operation by reducing the capacity of the compressor.

  The invention according to claim 6 of the present invention includes a high temperature protection detection sensor for detecting the temperature of the shell of the compressor or the temperature in the vicinity of the compressor in the discharge pipe, and the temperature detected by the high temperature protection detection sensor is predetermined. When the value is exceeded, control is performed to reduce the capacity of the compressor every predetermined time.

  As a result, the heat radiator is clogged with dust or the like, resulting in a decrease in heat dissipation capability, resulting in a decrease in the compressor performance, and an abnormally high temperature resulting in a decrease in the compressor durability. Can be prevented.

  The invention according to claim 7 of the present invention is a storage device that is equipped with the above-described refrigeration system and stores food at refrigeration or freezing temperature.

  Such a storage device can control the opening of the expansion valve and the capacity of the compressor with a simple configuration even under operating conditions where the evaporation temperature is particularly low, so that the durability of the compressor is not impaired and the power is turned on. Refrigerating capacity and refrigeration system performance such as refrigeration efficiency when stable can be improved, and a highly reliable storage device can be obtained.

  Hereinafter, embodiments of a refrigeration system according to the present invention will be described with reference to the drawings.

  In addition, about the same structure as the past, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted. Further, the present invention is not limited to the present embodiment.

(Embodiment 1)
1 is a refrigerant circuit diagram of a refrigeration system according to Embodiment 1 of the present invention, FIG. 2 is a diagram showing a control reference line of the refrigeration system according to Embodiment 1, and FIG. 3 is a refrigeration according to Embodiment 1. FIG. 4 is a Mollier diagram of the refrigeration system according to the first embodiment.

  As shown in FIG. 1, the refrigeration system of the first embodiment uses carbon dioxide as a refrigerant, and the compressor 21 is a variable capacity compressor (hereinafter referred to as a capacity changing type compressor) whose capacity changes in proportion to the rotational speed. It is called a compressor. And the refrigerating cycle of this refrigerating system is comprised by connecting the compressor 21, the heat radiator 2, the electric expansion valve 22, and the evaporator 4 cyclically | annularly by piping.

  The refrigeration cycle includes an evaporation temperature detection sensor 23 that detects the evaporation temperature of the evaporator 4, and a suction pipe inlet temperature detection sensor that detects the temperature of the inlet portion of the suction pipe 24 that connects the evaporator 4 and the compressor 21. 25 and an indoor temperature sensor 26 for detecting the indoor air temperature of the room to be cooled (not shown).

  Here, a polyalkylene glycol refrigerating machine oil having a kinematic viscosity at 40 ° C. of about 100 mm 2 / s is used as the lubricating oil of the compressor 21. Moreover, the solid line arrow in FIG. 1 shows the flow of the refrigerant, and the broken line arrow shows the flow of the wind passing through the evaporator 4 and the radiator 2.

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

  The refrigerant compressed and discharged by the compressor 21 is cooled to the vicinity of the outside air temperature by the radiator 2, then decompressed by the electric expansion valve 22, and evaporated by the evaporator 4. Then, the gas refrigerant evaporated in the evaporator 4 is returned to the compressor 21.

  Here, the rotation speed of the compressor 21 is optimally controlled by the compressor control device 27 based on the indoor air temperature Tr of the room to be cooled detected by the indoor temperature sensor 26 and the set temperature.

  The electric expansion valve 22 controls the expansion valve based on the evaporation temperature of the evaporator 4 detected by the evaporation temperature detection sensor 23 and the temperature of the inlet portion of the suction pipe 24 detected by the suction pipe inlet temperature detection sensor 25. The aperture amount is optimally controlled by the device 28.

  Specifically, as shown in FIG. 2, the expansion valve 22 is controlled at the inlet portion of the suction pipe 24 that is defined in advance corresponding to the evaporation temperature Te of the evaporator 4 detected by the evaporation temperature detection sensor 23. When the target temperature Ts is compared with the actual temperature detected by the suction pipe inlet temperature detection sensor 25 and the actual temperature is higher (region A in FIG. 2), the opening degree of the electric expansion valve 22 is determined. When the fixed temperature is opened and the actual temperature is lower (region B in FIG. 2), the opening of the electric expansion valve 22 is closed by a predetermined amount.

  Accordingly, the evaporation temperature of the evaporator 4 is increased in the region A of FIG. 2 and the temperature of the inlet portion of the suction pipe 24 is decreased, and the evaporation temperature of the evaporator 4 is decreased in the region B of FIG. The temperature of the inlet portion of the suction pipe 24 can be changed high, and as a result, the state of the refrigeration system can be stabilized on the control reference line shown in FIG.

  Further, the control reference line that defines the target temperature Ts at the inlet of the suction pipe 24 corresponding to an arbitrary evaporation temperature Te of the evaporator 4 is compressed by the compressor 21 and the temperature of the discharged refrigerant is If it is determined in advance so as to be substantially the same, the temperature of the refrigerant compressed and discharged by the compressor 21 is substantially reduced even if the indoor air temperature of the chamber to be cooled (not shown) or the capacity of the compressor 21 changes. Can be kept the same.

  For example, if the design value of the high pressure is 9 MPa and the control reference line is set based on the following (Equation 1), the target temperature Ts becomes −5 ° C. when the evaporation temperature Te of the evaporator 4 is −9 ° C., It is estimated that the temperature rises by about 3 ° C. until the refrigerant flows into the compressor 21 from the suction pipe 24 and reaches about −2 ° C. When the refrigerant is further compressed to 9 MPa, the temperature of the discharged refrigerant becomes about 120 ° C.

Ts = αTe · Te + βTe + γ (Formula 1)
α = 0.0037, β = 1.26, γ = 6
Similarly, according to Equation 1, when the evaporation temperature Te of the evaporator 4 is −15 ° C., the target temperature Ts becomes −12 ° C., and similarly, the refrigerant is about 3 ° C. before flowing into the compressor 21 from the suction pipe 24. It is estimated that the temperature is raised to about −9 ° C., and when the pressure is further compressed to 9 MPa, the temperature of the discharged refrigerant becomes about 120 ° C.

  Thus, when the evaporation temperature Te of the evaporator 4 is low, the target temperature Ts is controlled to be low so that the difference between the evaporation temperature and the temperature of the refrigerant and the refrigerating machine oil in the suction pipe 24 is within 10 ° C. In addition, the temperature of the refrigerant discharged from the compressor 21 can be suppressed to within 120 ° C. by lowering the temperature of the refrigerant in the suction pipe 24.

  It should be noted that it is desirable to design the evaporation capacity of the evaporator 4 so that the target temperature Ts at the time of stabilization is approximately the same as the set temperature of the chamber to be cooled. In other words, if the target temperature Ts is approximately the same as the set temperature of the room to be cooled, the refrigeration effect of the refrigerant can be utilized to the maximum, so that high refrigeration efficiency can be expected.

  If the evaporation capacity of the evaporator 4 is insufficient, the target temperature Ts falls below the set temperature of the chamber to be cooled, and the evaporation temperature Te is stabilized at a lower level.

  In addition, it is desirable to reinforce the heat insulation of the suction pipe 24 and suppress the temperature rise until the refrigerant flows into the compressor 21 from the suction pipe 24. This is because it is necessary to further lower the temperature of the refrigerant flowing into the compressor 21 in order to suppress an increase in the temperature of the refrigerant discharged from the compressor 21.

  Here, the change of the kinematic viscosity of the refrigerating machine oil in the suction pipe 24 will be described with reference to FIG.

  FIG. 3 shows the relationship between the temperature of the refrigerating machine oil and the mixture of the refrigerating machine oil and the refrigerant and the kinematic viscosity, with the horizontal axis representing temperature and the vertical axis representing kinematic viscosity. For example, the line indicated by the refrigerant weight ratio = 0% indicates the relationship between the temperature of the refrigerating machine oil and the kinematic viscosity. The kinematic viscosity at 40 ° C. is about 100 mm 2 / s, and the kinematic viscosity at 100 ° C. is about 16 mm 2 / s. It is. In addition, for the mixture of refrigerating machine oil and refrigerant, the relationship between the temperature and the kinematic viscosity at a weight ratio of 10%, 20%, 30%, 40%, 50% of the refrigerant in the mixture is different from each other (○, □, ◇, Each line is indicated by a line connecting it.

  In FIG. 3, line A, line B, line C, and line D represent the mixture of refrigerant oil and refrigerant in the suction pipe 24 at evaporation temperatures of −20 ° C., −10 ° C., 0 ° C., and 10 ° C., respectively. The relationship between temperature and kinematic viscosity is shown. These lines are obtained by estimating the kinematic viscosity of the mixture of refrigerating machine oil and refrigerant from the results of measuring the amount of refrigerant dissolved under the refrigerant pressure corresponding to each evaporation temperature.

  From the shape of these lines A, B, C and D, the kinematic viscosity is 10 mm 2 / s when the temperature of the mixture of the refrigerating machine oil and the refrigerant in the suction pipe 24 is in the range of 20 ° C. to 40 ° C. near normal temperature. It can be seen that the maximum value of the kinematic viscosity increases as the evaporation temperature decreases.

  This is because the lower the evaporation temperature, the lower the refrigerant pressure in the suction pipe 24, so that the amount of refrigerant dissolved in the refrigerating machine oil becomes smaller and approaches the kinematic viscosity of the refrigerating machine oil alone. From this, it is estimated that the maximum value of the kinematic viscosity is further increased when the evaporation temperature is further lower than −20 ° C.

  From this result, the difference between the evaporation temperature and the temperature of the refrigerant and the refrigerating machine oil in the suction pipe 24 is within 10 ° C. compared to the conventional configuration in which the suction pipe 24 is heated to about room temperature using an internal heat exchanger. In the first embodiment, the kinematic viscosity of the mixture of the refrigerating machine oil and the refrigerant in the suction pipe 24 can be suppressed to about 10 mm 2 / s or less, and oil retention in the suction pipe 24 can be prevented. Accordingly, the temperature of the refrigerant discharged from the compressor 21 when the power is turned on and when it is stable can be kept substantially constant, and the evaporation temperature is kept high when the power is turned on without impairing the durability of the variable capacity compressor 21. It can be seen that the refrigerating capacity can be improved by increasing the refrigerant circulation rate.

  In addition, in order to ensure the oil retention characteristic equivalent to a car air conditioner operated at a relatively high evaporation temperature of 0 ° C. to 20 ° C., the kinematic viscosity of the mixture of the refrigerating machine oil and the refrigerant in the suction pipe 24 is 30 mm 2 / s or less Need to keep. Furthermore, in the case of a refrigerator such as a refrigerator with the refrigeration system installed on the upper side, the evaporator 4 is located below the compressor 21 and the head of the suction pipe 24 becomes large, so that the kinematic viscosity is further reduced to 10 mm2 / s or less. It is desirable.

  Next, the state change of the refrigerant in the refrigeration system in the first embodiment 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. The points indicated by p, q, r, s, and t are the chambers to be cooled (in the case of a refrigerator). This shows the state change of the refrigerant in the steady state in which the indoor air temperature Tr of the refrigerator compartment or the freezer compartment is lowered to a predetermined temperature, and is indicated by p ′, q ′, r ′, s ′, t ′. The point indicates the change in state of the refrigerant when the power is turned on, where the indoor air temperature Tr is in the vicinity of the outside air temperature.

  In FIG. 4, when stable, the refrigerant discharged from the variable capacity compressor 21 is at the point p at the temperature T6 and is cooled by the radiator 2 to the point q at the temperature T5. 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 electric expansion valve 22 to reach the r point in the gas-liquid mixed state, which is supplied to the evaporator 4. The refrigerant evaporated in the evaporator 4 becomes the s point, and after it flows into the inlet portion of the suction pipe 24, it is heated until it flows into the compressor 21 from the suction pipe 24 and becomes the t point of the temperature T4. Reflux.

  Here, the temperature at the point s of the refrigerant evaporated by the evaporator 4 is detected by the suction pipe inlet temperature detection sensor 25 and, as described above, the electric expansion valve is operated by the expansion valve controller 28 so as to approach the target temperature Ts. The opening degree of 22 is adjusted. The temperature change from the s point to the t point is determined by the heat insulating structure of the suction pipe 24, and the temperature change from the t point to the p point is determined by the evaporating temperature Te, the design value of the high pressure and the compressor 21. It is almost determined by the compressor efficiency. For these reasons, when the temperature at the point s is brought close to the target temperature Ts determined in advance with respect to the arbitrary evaporation temperature Te, the temperature T6 at the point p can be maintained at an almost arbitrary value.

  Even if the capacity of the compressor 21 is changed in accordance with the change in the indoor air temperature Tr, if the temperature at the point s is brought close to the target temperature Ts determined in advance for an arbitrary evaporation temperature Te, the point p The temperature T6 can be maintained at an almost arbitrary value (predetermined value). However, when the compressor 21 is designed so that the maximum efficiency is obtained at the time of stable operation, the temperature rise from the point t to the point p becomes small during low speed operation, so that the room air temperature Tr is exceeded. The target temperature Ts may be set higher than that during high speed operation within a range that does not exist.

  Furthermore, setting the target temperature Ts higher within a range that does not exceed the indoor air temperature Tr can enhance the refrigeration effect indicated by the enthalpy change from the r point to the s point, thereby improving the refrigeration efficiency. .

  Further, the temperature T5 is in the vicinity of the outside air temperature, and changes due to fluctuations in the outside air temperature. At this time, the pressure at the point q hardly changes and the enthalpy changes. This is because there is no structure such as an accumulator in which the liquid refrigerant stays in the evaporator 4.

  As a result, when the high pressure is designed to be about 9 to 12 MPa that is normally used, the refrigeration effect indicated by the enthalpy change from the r point to the s point becomes large at a low outside temperature of 25 ° C. or less, and high refrigeration efficiency can be realized. However, at a high outside air temperature of 35 ° C. or higher, the refrigeration effect indicated by the enthalpy change from the r point to the s point is reduced, and the refrigeration efficiency is significantly reduced.

  Therefore, when always used at a high outside air temperature, it is desirable to set the design value of the high pressure to a higher value of about 15 MPa.

  On the other hand, when the power is turned on, the refrigerant discharged from the compressor 21 is at the p ′ point of the temperature T6 and is cooled by the radiator 2 to become the q ′ point of the temperature T5. These p ′ point and q ′ point are substantially in the same state as the stable p point and q point, respectively.

  Next, the pressure is reduced by the electric expansion valve 22 to become the r ′ point in the gas-liquid mixed state, and is supplied to the evaporator 4. The refrigerant evaporated in the evaporator 4 becomes the s ′ point, and after it flows into the inlet portion of the suction pipe 24, it is heated until it flows into the compressor 21 from the suction pipe 24, and becomes the t ′ point of the temperature T5. Reflux to 21.

  Here, the low pressure pressure at the time of turning on the power indicated by the points r ′, s ′, and t ′ is higher than the stable low pressure pressure indicated by the points r, s, and t. This is because the opening degree of the electric expansion valve 22 is adjusted by the valve control device 28, and when the temperature Ts at the point s' detected by the suction pipe inlet temperature detection sensor 25 becomes higher than the normal time, the evaporation temperature Te is increased. The result is higher than normal.

  Further, the reason why the temperature Ts at the point s ′ detected by the intake pipe inlet temperature detection sensor 25 is higher than in the normal state is that the evaporation capacity in the evaporator 4 is excessive due to the high indoor air temperature Tr. In addition, the ambient temperature around the inlet of the suction pipe 24 is high.

  As a result, by keeping the temperature of the refrigerant discharged from the compressor 21 when the power is turned on substantially constant while keeping the evaporation temperature Te high when the power is turned on, the refrigerant circulation amount can be increased and the refrigeration capacity can be improved. Furthermore, since the room temperature Tr is high when the power is turned on, it can be expected that the compressor control device 27 speeds up the compressor 21 to improve the refrigeration capacity.

  As described above, in the first embodiment, the refrigeration system does not include the accumulator and the internal heat exchanger, and the evaporation temperature detection sensor 23 that detects the temperature of the evaporator 4, the evaporator 4, and the capability A suction pipe inlet temperature detection sensor 25 for detecting the temperature of the inlet part of the suction pipe 24 connecting the variable compressor 21 is provided and compared with a target temperature Ts determined from the evaporation temperature Te detected by the evaporation temperature detection sensor 23. If the measured value detected by the suction pipe inlet temperature detection sensor 25 is high, the opening of the electric expansion valve 22 is increased, and conversely, if the measured value detected by the suction pipe inlet temperature detection sensor 25 is low. The control for reducing the opening of the electric expansion valve 22 is performed.

  Such control makes it possible to control the evaporation temperature Te. As a result, by keeping the temperature difference of the suction pipe connecting the evaporator 4 and the compressor 21 within 10 ° C., the refrigeration in the suction pipe 24 can be controlled. The kinematic viscosity of the mixture of machine oil and refrigerant can be suppressed to about 10 mm 2 / s or less, and oil stagnation in the suction pipe 24 can be prevented. Furthermore, by keeping the temperature of the refrigerant discharged from the compressor 21 when the power is turned on and stable, the evaporation temperature Te can be kept high when the power is turned on without impairing the durability of the compressor 21. As a result, the refrigerant circulation amount can be increased to improve the refrigeration capacity.

  In the first embodiment, the single refrigerant of carbon dioxide is used as the natural refrigerant, but the thermophysical properties such as the refrigerant temperature discharged from the variable capacity compressor 21 indicated by T6 in FIG. 4 are improved. Therefore, even if a mixed refrigerant in which a natural refrigerant such as hydrocarbon is mixed with carbon dioxide is used, the same effect can be expected if a transcritical cycle is formed without liquefaction at the q point.

  In the first embodiment, in order to make it less susceptible to the influence of the outside air temperature, the suction pipe inlet temperature detection sensor 25 is provided at the inlet of the suction pipe 24 close to the evaporator 4, and the temperature of the suction pipe 24 is adjusted. Although it is controlled, as shown by reference numeral 25a in FIG. 1, it detects the temperature near the outlet 21 of the suction pipe 24, which is close to the variable capacity compressor 21 and receives the highest ambient temperature or heat conduction from the compressor. Thus, the temperature of the suction pipe 24 may be controlled. In this case, it is desirable to cover the sensor 25a for detecting the temperature near the outlet of the suction pipe 24 with a heat insulating material so as not to be affected by the outside air temperature.

  Furthermore, in the first embodiment, the capacity of the variable capacity compressor 21 is controlled by the compressor control device 27 based on the indoor air temperature Tr. The indoor temperature detection sensor 26 is denoted by reference numeral 26a in FIG. As shown, the temperature of the discharge pipe through which the refrigerant discharged from the compressor 21 passes or a sensor that detects the temperature of the outer surface of the compressor 21 as shown by reference numeral 26b is replaced or added, and the detected temperature is used as a reference value. When exceeding the above, it is desirable to perform control so that the capacity of the compressor 21 is reduced every predetermined time in preference to the above-described control (expansion valve control). As a result, when the heat dissipating capacity of the radiator 7 is reduced for some reason, the capacity of the compressor 21 is reduced, resulting in an abnormally high temperature of the refrigeration system and a decrease in durability of the compressor 21. Can be prevented.

(Embodiment 2)
FIG. 5 is a schematic diagram of the structure of the cool box in the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the structure same as the refrigerating system in previous Embodiment 1, and detailed description is abbreviate | omitted.

  As shown in FIG. 5, the refrigerating system of the cool box in the second embodiment uses carbon dioxide as a refrigerant and can vary the capacity by varying the number of revolutions, as in the first embodiment. The variable capacity compressor 21, the spiral fin radiator 30, the electric expansion valve 22, and the evaporator 4 are connected in an annular shape to constitute a refrigerant circulation circuit. Further, an evaporation temperature detection sensor 23 for detecting the evaporation temperature of the evaporator 4, a suction pipe inlet temperature detection sensor 25 for detecting the temperature of the inlet portion of the suction pipe 24 connecting the evaporator 4 and the compressor 21, and the object to be cooled An indoor temperature sensor 26 that detects the indoor air temperature of the storage chamber 32 that is a chamber is provided.

  Here, as is well known, the spiral fin radiator 30 is formed by crimping and fixing a spiral fin plate 31 to one refrigerant pipe. According to the temperature gradient, one fin plate 31 is also characterized by a similar temperature gradient.

  Moreover, since the spiral fin radiator 30 is based on a configuration in which one refrigerant pipe is bent in a meandering manner, a high pressure resistance design is easy, and it is applied to a refrigeration system having a relatively high high pressure of 9 to 15 MPa. In this case, it can be realized at a lower cost than a finned tube heat exchanger having the same heat dissipation capability.

  Further, as shown in FIG. 5, the cool box of the second embodiment is provided with a machine room 33 in an upper part of a storage room 32 that refrigerates a heat load such as food, and the variable capacity compressor 21 and spiral fin heat dissipation. A container 30 and the like are arranged. Further, the evaporator 4, the electric expansion valve 22, and the like are disposed in the heat insulating wall 34 provided between the storage chamber 32 and the machine chamber 33.

  Thus, in a cold storage such as a commercial refrigerator provided with a refrigeration system in the upper part, the evaporator 4 is often arranged below the compressor 21, and the head of the suction pipe 24 becomes large. The behavior of the kinematic viscosity in the mixture of refrigerating machine oil and refrigerant in the suction pipe 24 is particularly important.

  The operation of the cool box of the second embodiment configured as described above will be described below.

  The refrigerant compressed and discharged by the variable capacity type compressor 21 exchanges heat with the outside air by the spiral fin radiator 30 and is cooled to the vicinity of the outside air temperature. Then, the refrigerant is depressurized by the electric expansion valve 22 and then the evaporator 4. Where it evaporates. Then, the gas refrigerant evaporated in the evaporator 4 is returned to the compressor 21, and the above-described flow is repeated thereafter.

  Here, the spiral fin radiator 30 is disposed so as to substantially face the flow of air (outside air) introduced into the machine chamber 33 by the radiator fan 7 as indicated by broken line arrows. Therefore, inside the spiral fin radiator 30, a temperature gradient is formed such that the refrigerant temperature is highest on the side close to the compressor 21, and the refrigerant temperature decreases as it approaches the radiator fan 7. Accordingly, the refrigerant temperature at the outlet of the spiral fin radiator 30 can be lowered to substantially the outside air temperature with a relatively small heat dissipation capability, and the refrigeration efficiency can be improved simply and inexpensively.

  Similarly to the refrigeration system in the first embodiment, the electric expansion valve 22 includes the evaporation temperature of the evaporator 4 detected by the evaporation temperature detection sensor 23 and the suction pipe detected by the suction pipe inlet temperature detection sensor 25. The expansion amount is optimally controlled by the expansion valve control device 28 based on the temperature of the 24 inlet portions.

  As a result, the difference between the evaporation temperature and the temperature of the refrigerant and the refrigerating machine oil in the suction pipe 24 is made to be within 10 ° C. as compared with the conventional configuration in which the suction pipe 24 is heated to about room temperature using an internal heat exchanger. In the second embodiment, the kinematic viscosity of the mixture of the refrigerating machine oil and the refrigerant in the suction pipe 24 can be suppressed to about 10 mm 2 / s or less, and the stagnation of oil in the suction pipe 24 can be prevented.

  Further, similarly to the refrigeration system in the first embodiment, the variable capacity compressor 21 is based on the indoor air temperature and the set temperature of the storage chamber 32 detected by the indoor temperature sensor 26. The rotational speed is optimally controlled by 27.

  As described above, in the second embodiment, like the refrigeration system in the first embodiment, the evaporating temperature for detecting the temperature of the evaporator 4 without mounting the accumulator and the internal heat exchanger in the refrigeration system. An evaporating temperature detected by the evaporating temperature detecting sensor 23 is provided with a detecting sensor 23 and a suction piping inlet temperature detecting sensor 25 for detecting the temperature of the inlet portion of the suction piping 24 connecting the evaporator 4 and the variable capacity compressor 21. If the measured value detected by the suction pipe inlet temperature detection sensor 25 is higher than the target temperature Ts determined from Te, the opening of the electric expansion valve 22 is increased, and conversely the suction pipe inlet temperature detection sensor. If the actual measurement value detected at 23 is low, the opening of the electric expansion valve 22 is controlled to be small, and the evaporation temperature Te is controlled to control the suction between the evaporator 4 and the compressor 21. The difference between the temperature of the pipe 24 can be kept within 10 ° C..

  As a result, the kinematic viscosity of the mixture of the refrigerating machine oil and the refrigerant in the suction pipe 24 can be suppressed to about 10 mm 2 / s or less, and in the configuration in which the machine room 33 is arranged at the upper part, the suction pipe 24 having a large head Oil retention can be prevented, and the temperature of the refrigerant discharged from the compressor 21 when the power is turned on and when the compressor 21 is stable can be kept substantially constant, thereby not impairing the durability of the compressor 21. Further, it is possible to keep the evaporation temperature Te high when the power is turned on, thereby increasing the refrigerant circulation amount and improving the refrigerating capacity.

  In the second embodiment, the pipe from the spiral fin radiator 30 to the electric expansion valve 22 is connected with the shortest distance, but instead of the dew condensation prevention heater used in refrigeration or refrigeration equipment, the spiral fin radiator A pipe from 30 to the electric expansion valve 22 may be used. With such a configuration, it is possible to reduce the temperature of the refrigerant flowing into the electric expansion valve 22 using the cold heat leaked to the outside, and further improve the refrigeration efficiency.

  In addition, this invention is not restricted to the cool box of embodiment, It can apply also to storage apparatuses, such as a refrigerator, a freezer, or a vending machine.

  As described above, the refrigeration system and the storage device including the refrigeration system according to the present invention can prevent the oil from staying in the suction pipe, and the temperature of the refrigerant discharged from the compressor when the power is turned on and when it is stable. Can be maintained substantially constant, thereby improving the refrigeration system performance such as the refrigeration capacity at the time of power-on and the refrigeration efficiency at the time of stability required for refrigeration or refrigeration equipment without impairing the durability of the compressor. be able to. Therefore, the present invention can also be applied to refrigeration or refrigeration equipment such as showcases, commercial refrigeration refrigerators, and vending machines that require non-fluorocarbon refrigerants and energy saving equipment.

Refrigerant circuit diagram of the refrigeration system in Embodiment 1 of the present invention The figure which shows the control reference line of the refrigerating system in Embodiment 1 The figure which shows the kinematic viscosity characteristic of the refrigerating machine oil of the refrigerating system in the same Embodiment 1. Mollier diagram of the refrigeration system in the first embodiment Configuration schematic diagram of cold storage in Embodiment 2 of the present invention Refrigerant circuit diagram of conventional refrigeration system Mollier diagram of conventional refrigeration system

Explanation of symbols

2 radiator 4 evaporator 21 compressor (variable capacity compressor)
22 Electric expansion valve 24 Suction pipe 23 Evaporation temperature detection sensor 25 Suction pipe inlet temperature detection sensor 26 Indoor temperature detection sensor

Claims (7)

  In a refrigeration system including a compressor, a radiator, an expansion valve, and an evaporator, a natural refrigerant mainly composed of carbon dioxide is used as a refrigerant, and the evaporation temperature of the evaporator is set to −50 ° C. to 0 ° C. The refrigeration system in which the difference between the evaporation temperature of the evaporator and the suction pipe temperature of the compressor is kept within 20 ° C.   The refrigerating system according to claim 1, wherein a polyalkylene glycol refrigerating machine oil having a kinematic viscosity at 40 ° C of 30 mm2 / s to 300 mm2 / s is used as the lubricating oil of the compressor.   An evaporation temperature sensor for detecting the evaporation temperature of the evaporator and a suction pipe outlet temperature sensor for detecting a temperature in the vicinity of the compressor in the suction pipe of the compressor are determined from the evaporation temperature detected by the evaporation temperature sensor. When the suction pipe temperature detected by the suction pipe outlet temperature sensor is higher than the target temperature, the opening degree of the expansion valve is increased, and when it is lower, the evaporation temperature is controlled by decreasing the opening degree of the expansion valve. The refrigeration system according to claim 1 or 2.   An evaporation temperature sensor for detecting the evaporation temperature of the evaporator and a suction pipe inlet temperature sensor for detecting the temperature in the vicinity of the evaporator in the suction pipe of the compressor are determined from the evaporation temperature detected by the evaporation temperature sensor. When the suction pipe temperature detected by the suction pipe inlet temperature sensor is higher than the target temperature, the opening degree of the expansion valve is increased, and when it is lower, the evaporation temperature is controlled by decreasing the opening degree of the expansion valve. The refrigeration system according to claim 1 or 2.   The refrigeration system according to any one of claims 1 to 4, wherein the compressor is a compressor whose capacity is variable, and the capacity of the compressor is controlled based on a level of air temperature in a room to be cooled.   The compressor has a high-temperature protection detection sensor that detects the temperature of the shell of the compressor or the temperature in the vicinity of the compressor in the discharge pipe, and the capability of the compressor when the temperature detected by the high-temperature protection detection sensor exceeds a predetermined value. The refrigeration system according to claim 5, wherein control is performed to lower the value at predetermined time intervals.   The storage apparatus carrying the refrigeration system as described in any one of Claim 1 to 6.

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