JP2012220111A - Binary refrigerating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binary refrigerating device capable of achieving energy saving effect year-round by defining a radiation ratio of an auxiliary radiator in an integrated radiator.SOLUTION: In this binary refrigerating device using a COrefrigerant, the auxiliary radiator is disposed on a former stage in a low-order side refrigerating cycle of a cascade condenser, and a high-order side condenser and the auxiliary radiator are integrated to constitute the integrated radiator 25. The radiation amount of the auxiliary radiator 15 is 10-20% of the total radiation amount of the integrated radiator 25.

Description

  The present invention relates to a binary refrigeration apparatus, and more particularly to a binary refrigeration apparatus that uses a CO2 refrigerant in a low refrigeration cycle.

  In recent years, there has been an increasing demand for reducing the influence of refrigerants used in refrigeration equipment on global warming, and refrigeration equipment using CO2 has been proposed as a natural refrigerant that has little influence on global warming. In addition, the refrigeration system using CO2 is applied to a hot water heater that obtains a high tapping temperature by utilizing the point that is a transcritical cycle, and the refrigerant leakage amount during use is large by utilizing the point that it is nonflammable. Applied to air conditioners.

  On the other hand, in a refrigeration apparatus having a relatively low evaporation temperature used for refrigeration or freezing, there is a problem that the efficiency is remarkably lowered under a high outside air temperature condition, and the discharge gas temperature becomes very high as the evaporation temperature is lowered. Application of CO2 refrigerant is not progressing.

  Therefore, a refrigeration cycle using a CO2 refrigerant (low refrigeration cycle) and a refrigeration cycle using another refrigerant (high refrigeration cycle) are provided. A binary refrigeration apparatus has been proposed in which a low-source refrigeration cycle and a high-source refrigeration cycle are connected by a cascade condenser configured to exchange heat with a high-source evaporator (see, for example, Patent Document 1). In this dual refrigeration system, an auxiliary radiator is installed in front of the cascade condenser in the low refrigeration cycle, and the discharge refrigerant discharged from the low-source compressor is cooled by the auxiliary radiator to improve the operation efficiency. ing.

  In addition, there is a technique in which an auxiliary radiator and a high-side condenser are integrated in a binary refrigeration apparatus to reduce the size of the apparatus (for example, see Patent Document 2).

Japanese Patent No. 3606043 (2nd page, 3rd page, FIG. 1) JP 2010-127548 A (FIG. 4)

  In the binary refrigeration apparatus of Patent Document 1, the auxiliary radiator and the high-side condenser are configured separately, so that the apparatus becomes large. For this reason, if an auxiliary heat sink and a high-end side condenser are integrated as in Patent Document 2, a binary refrigeration apparatus that improves operational efficiency and makes the apparatus compact can be configured.

  By the way, in the binary refrigeration apparatus of Patent Document 1, if the heat radiation amount of the auxiliary radiator that cools the discharged refrigerant in the low-source refrigeration cycle is increased, the capacity of the high-source refrigeration cycle can be reduced and the operation efficiency can be improved. it can. The extent to which the heat radiation amount of the auxiliary radiator should be increased depends on the outside air temperature. In a binary refrigeration system in which heat is exchanged between the low-side condenser and the high-side evaporator in the cascade condenser, the heat dissipation of the auxiliary radiator and the heat dissipation of the high-order condenser There is an optimal heat dissipation ratio between. This heat dissipation ratio is the ratio of the heat dissipation amount of the auxiliary heat dissipation amount to the heat dissipation amount of the entire integrated radiator when the auxiliary heatsink and the high-side condenser are integrated to reduce the size of the device. Replaced. This heat dissipation rate also varies with the outside air temperature.

  For dual refrigeration equipment, operation with high operational efficiency is desired throughout the year. Therefore, in a dual refrigeration system that integrates an auxiliary radiator and a high-end condenser, the heat dissipation rate is determined so that high operating efficiency is achieved after taking into account changes in the outside air temperature throughout the year. It is desirable to do. However, Patent Document 1 does not discuss this point.

  The present invention has been made in view of such points, and an object thereof is to provide a binary refrigeration apparatus capable of providing an energy saving effect throughout the year by defining a heat dissipation rate of an auxiliary radiator in an integrated radiator. And

  A binary refrigeration apparatus according to the present invention includes a low refrigeration cycle using a CO2 refrigerant and a high refrigeration cycle that assists heat dissipation in the low refrigeration cycle, and the low refrigeration cycle and the high refrigeration cycle are respectively compressed. Machine, condenser, decompression device, and evaporator, heat exchange between the high-end evaporator and the low-end condenser using a cascade condenser, and an auxiliary radiator installed at the front stage of the cascade condenser's low-end refrigeration cycle Furthermore, the high-end side condenser and the auxiliary radiator are integrated to form an integrated radiator, and 10% to 20% of the total radiation amount of the integrated radiator is auxiliary radiation. This is the amount of heat released from the vessel.

  Even when a low-efficiency CO 2 refrigerant is used in the refrigeration system as a natural refrigerant that has little influence on global warming, a compact binary refrigeration system can be obtained throughout the year.

It is a refrigerant circuit figure of the binary refrigeration apparatus concerning one embodiment of the present invention. It is the schematic which shows the structure of the heat-transfer fin part of the integrated radiator of FIG. It is a figure which shows the relationship between enthalpy and saturation temperature in the binary refrigeration apparatus of FIG. It is a figure which shows the relationship between the low original side condensing temperature and a compressor input. It is explanatory drawing of the thermal radiation amount in the case where the low element side condensing temperature is lower than outside temperature, and when it is high. It is explanatory drawing of the relationship between the heat dissipation of an auxiliary radiator and COP. It is a figure which shows the relationship between the low element side condensation temperature and the operating efficiency fluctuation | variation rate of the whole binary refrigeration apparatus. It is an enlarged view of the operation efficiency maximum value part of FIG. It is explanatory drawing of the thermal radiation amount of the integrated radiator of FIG. It is explanatory drawing of the heat dissipation amount ratio of the auxiliary radiator in the integrated radiator of FIG. It is a figure which shows the relationship between the heat dissipation amount ratio of an auxiliary radiator when an outside temperature is 32 degreeC, and an operating efficiency fluctuation rate.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of a binary refrigeration apparatus according to the invention will be described with reference to the accompanying drawings.
Embodiment.
FIG. 1 is a refrigerant circuit diagram of a binary refrigeration apparatus according to an embodiment of the present invention. In FIG. 1, the binary refrigeration apparatus includes a low original refrigeration cycle 10 and a high original refrigeration cycle 20. In the low-source refrigeration cycle 10, a variable-capacity low-source compressor 11, a cascade capacitor C, a low-source expansion valve 13 as a decompression device, a low-source evaporator 14 and an auxiliary radiator 15 are sequentially connected. It is configured. The high-source refrigeration cycle 20 is configured by sequentially connecting a high-side compressor 21 having a variable operating capacity, a high-side condenser 22, a high-side expansion valve 23 as a pressure reducing device, and a cascade capacitor C. In the binary refrigeration apparatus of this example, a CO2 refrigerant is used as the refrigerant in the low refrigeration cycle 10, and an HC refrigerant, an HFC refrigerant, an HFO refrigerant (HFO-) having higher operating efficiency than the CO2 refrigerant is used in the high refrigeration cycle 20. 1234yf, HFO-1234ze, etc.).

  The cascade condenser C includes a high-side evaporator 24 on the high side and a low-side condenser 12 on the low side, and is configured to exchange heat with each other. The integrated radiator 25 is formed by integrating the auxiliary radiator 15 and the high-side condenser 22 as an integrated type, and the high-side condenser 22 condenses the refrigerant flowing through the high-source refrigeration cycle 20. At the same time, the auxiliary radiator 15 disposed in front of the cascade capacitor C in the low-source refrigeration cycle 10 cools the CO 2 gas flowing through the low-source refrigeration cycle 10. The integrated radiator 25 sucks outside air into the integrated radiator 25 and exchanges heat with the refrigerant passing through the integrated radiator 25, and then exhausts the outside air after heat exchange to the outside of the integrated radiator 25. A radiator fan 16 is provided.

FIG. 2 is a schematic view showing a configuration of a heat transfer fin portion of the integrated heat radiator of FIG.
The integrated radiator 25 is a plate fin tube type heat exchanger formed by penetrating a heat transfer tube 25b through a flat heat transfer fin 25a. The high-end side condenser 22 and the auxiliary radiator 15 may be integrated by sharing the heat transfer fin 25a, or the heat transfer fin 25a portion may be divided. If integrated, the structure of the heat exchanger makes it easy to manufacture. In addition, when the heat transfer fins 25a are divided between the auxiliary radiator 15 and the high-end condenser 22 that are at a high temperature, the thermal insulation effect is increased, so that the auxiliary radiator 15 and the high-end condenser are provided. Both units 22 can dissipate heat more efficiently.

  Further, in the integrated radiator 25, the auxiliary radiator 15 that cools the discharge gas of the low-temperature CO2 refrigerant that becomes high temperature is arranged in the upper part of the heat exchanger, and the high-side condenser 22 is arranged in the lower part. Thereby, the heat radiation of the auxiliary radiator 15 does not interfere with the high-side condenser 22 side, that is, the heat transfer fluid heated by the auxiliary radiator 15 moves to the high-side condenser 22 side. Therefore, both the auxiliary radiator 15 and the high-side condenser 22 can efficiently dissipate heat.

  As shown in FIG. 2, this example is characterized in that the ratio of the heat dissipation amount of the auxiliary radiator 15 to the heat dissipation amount of the entire integrated radiator 25 is 10% to 20%. Will be described later.

  In the binary refrigeration apparatus configured as described above, the refrigerant used in the low-source refrigeration cycle 10 is CO2 in this example. This is due to the following reason. The low-source refrigeration cycle 10 is connected to an indoor load device, for example, a supermarket showcase, and the refrigerant circuit is opened due to rearrangement of the showcase and the refrigerant leaks frequently. Therefore, in consideration of refrigerant leakage, CO2 having a small influence on global warming is used. On the other hand, since the refrigerant circuit of the high refrigeration cycle 20 is not opened, the refrigerant used in the high refrigeration cycle 20 has a small amount of refrigerant leakage. For this reason, the refrigerant used in the high-source refrigeration cycle 20 may be a conventional HFC refrigerant having a high global warming potential, but a refrigerant having a small influence on global warming, that is, an HFO refrigerant, an HC refrigerant, CO2, water, etc. desirable.

About the binary refrigeration apparatus comprised as mentioned above, the operation | movement is demonstrated below.
The CO 2 refrigerant compressed and discharged by the low-side compressor 11 is cooled by the auxiliary radiator 15 in the integrated radiator 25 and then the high-side evaporator by the low-side condenser 12 of the cascade capacitor C. It is further cooled by exchanging heat with the HFO refrigerant flowing through 24. The CO 2 refrigerant cooled by the cascade condenser C is depressurized by the low-side expansion valve 13, evaporates by the low-side evaporator 14, and returns to the low-side compressor 11 through the suction pipe.

  The HFO refrigerant compressed and discharged by the high-end compressor 21 is radiated and condensed by the high-end condenser 22 in the integrated radiator 25 and then depressurized by the high-end expansion valve 23. It flows into the high-side evaporator 24 of the cascade capacitor C. The HFO refrigerant that has flowed into the high-side evaporator 24 evaporates while exchanging heat with the CO2 refrigerant that flows through the low-side condenser 12, and then returns to the high-side compressor 21.

  In the binary refrigeration apparatus of the present embodiment, the low-source-side high pressure is adjusted by controlling the high-side cooling capacity by controlling the frequency of the motor that drives the high-side compressor 21. This point will be described in detail below.

  FIG. 3 is a diagram showing the relationship between enthalpy and saturation temperature in the binary refrigeration apparatus of FIG. In the binary refrigeration apparatus of this example, a temperature difference ΔT (here, 5 ° C.) between the low-side condensation temperature and the high-side evaporation temperature occurs. Therefore, when the operating frequency of the high-source side compressor 21 is increased from a certain operating state to increase the high-source cooling capacity, the high-source side evaporating temperature is lowered, and the temperature difference ΔT with the reduced high-source side evaporating temperature is It is generated and the low element side condensation temperature (low element side high pressure) is also reduced. Conversely, if the high-source cooling capacity is reduced, the low-source side high pressure increases.

  As is clear from FIG. 3, when the operating frequency of the high-source compressor 21 is increased and the low-source high pressure of the low-source refrigeration cycle 10 is decreased, the input of the high-source compressor 21 is increased (WH1 < In contrast to (WH2), the input of the low-end compressor 11 is small (WL1> WL2). Note that the refrigeration capacity Q = ΔH (enthalpy difference) × Gr (refrigerant flow rate). In the two-way refrigeration system, the cooling load changes according to the outside air temperature, and the refrigeration capacity (low-source refrigeration) This corresponds to the evaporation capacity on the cycle 10 side), and Gr is controlled by the low-side compressor 11 so as to keep the determined refrigeration capacity constant. If ΔH is constant, the low-end compressor 11 is controlled so that Gr is also constant.

  By the way, the CO2 refrigerant used in the low-source refrigeration cycle 10 has a smaller refrigeration effect than the HFO refrigerant used in the high-source refrigeration cycle 20, and requires a large compressor power. Operation efficiency is lower than that of the HFO refrigerant. Therefore, the operation of suppressing the power consumption on the low-source refrigeration cycle 10 side is performed by increasing the capacity of the high-source side compressor 21 and decreasing the low-source side high pressure. That is, the power consumption on the low-source refrigeration cycle 10 side using the CO2 refrigerant having low operating efficiency is reduced, and the power consumption on the high-source refrigeration cycle 20 side using the HFO refrigerant having high operating efficiency is increased to increase the power consumption on the high-source refrigeration cycle. The work amount on the 20 side is increased, and the operation efficiency of the entire binary refrigeration apparatus is improved. In other words, by increasing the power consumption ratio of the high-efficiency high-source refrigeration cycle 20, the operation efficiency of the entire binary refrigeration apparatus is optimized. Therefore, there are many operations in which the high pressure of the low-source refrigeration cycle 10 is not supercritical, and the saturation temperature at which phase change occurs due to the high pressure is determined.

  Arranging the above relationships, the horizontal axis is the low source side condensing temperature, the vertical axis is the total input of the entire dual refrigeration system, and each of the high source side compressor input and the low source side compressor input and their total input When the graph is created, it is as shown in FIG. As shown in FIG. 4, when the compressor inputs on the high-side and low-side are substantially the same, the total input becomes the smallest and COP (= refrigeration capacity / (high-side compressor input + low-source side) It can be seen that the compressor input)) is maximized.

  As described above, in the two-stage refrigeration apparatus, the operation control is performed so that the high-side compressor input and the low-side compressor input are substantially the same so that the COP is maximized. Referring to FIG. 3, operation control is performed such that WH1 × Grh corresponding to the high-end compressor input and WL1 × Grl corresponding to the low-end compressor input are the same. Grh is a high-source refrigerant flow rate, and Grl is a low-source refrigerant flow rate.

  Here, in another way of viewing FIG. 4, the total input becomes minimum and the COP becomes maximum when the low-side refrigeration temperature of the low-source refrigeration cycle 10 is Tc. Therefore, the operation control in which the high-source side compressor input and the low-side compressor input are substantially the same is specifically performed in the low-source refrigeration cycle 10 so as to keep the low-source side condensation temperature at the low-source target condensation temperature Tc. Will be controlled. At this time, the high element side performs control to keep a temperature lower by ΔT ° C. lower than the low original target condensation temperature Tc as the target evaporation temperature. With this control, the COP can be maximized. In addition, since the refrigerating capacity calculated | required by a binary refrigeration apparatus changes according to outside air temperature, the low original target condensation temperature Tc which makes COP the maximum also changes with outside air temperature.

  When the above contents are arranged, the refrigerating capacity necessary for the binary refrigeration system is determined based on the outside air temperature, and when the refrigerating capacity is determined, the low original target condensation temperature Tc is determined. When the low element target condensing temperature Tc is determined, the low element refrigeration cycle 10 is controlled to adjust the low element refrigerant flow rate Grl so as to keep the determined refrigeration capacity constant. Control is performed to keep the evaporation temperature constant at the low original target condensation temperature Tc + ΔT ° C. This realizes operation control in which the high-side compressor input and the low-side compressor input are substantially the same, and COP can be maximized. The high-source refrigeration cycle 20 may directly detect and control the low-source condensation temperature. Further, the high-source refrigeration cycle 20 may directly detect and control the high-source input and the low-source input.

  In the above description, the low-source-side high pressure (low-source-side condensation temperature) is reduced in order to suppress the power consumption of the low-efficiency low-source refrigeration cycle 10, but this is an explanation on the control principle. This does not mean that the low-side high pressure is reduced in actual operation. In actual operation, as described above, control is performed to keep the low original target condensing temperature Tc constant. Further, to explain supplementarily the control principle for reducing the low-source-side high pressure, the HFO refrigerant used in the high-source refrigeration cycle 20 is a highly efficient refrigerant compared to the CO2 refrigerant used in the low-source refrigeration cycle 10. Therefore, the inclination θh of the high-end compressor 21 on the diagram of FIG. 3 is larger than the inclination θl on the low-end compressor 11 side. Therefore, even if the low-side condensation temperature is lowered, the input of the high-side compressor 21 exceeds the input of the low-side compressor 11 until the low-side condensation temperature reaches the low-side target condensation temperature Tc. In other words, the input of the high-side compressor 21 and the input of the low-side compressor 11 become equal at the low-side target condensation temperature Tc.

  The operation efficiency of the refrigerant will be specifically described. If COP (= evaporator enthalpy difference / compression enthalpy difference), which is an index of operation efficiency, is high, a large latent heat of vaporization can be obtained with a small amount of compression power, resulting in a highly efficient refrigerant. Operating state of a general refrigerator operating at an outside air temperature of 32 ° C., that is, an evaporation temperature of −40 ° C., a condensation temperature of 40 ° C. (supercritical CO 2 high pressure is 8.8 MPa), a suction superheat degree of 5 ° C., and a liquid supercooling degree of 5 ° C. The theoretically obtained COP of each refrigerant under the conditions of CO2: 1.25, R404A: 1.76, R410A: 1.91, R134a: 2.01, R32: 1.98, propane: 1.99, isobutane : 2.05, HFO-1234yf: 1.83. CO2 is a low-efficiency refrigerant with a low COP compared to HFC refrigerant, HC refrigerant, and HFO refrigerant.

  Here, in this example, the CO2 refrigerant is used in the low-source refrigeration cycle 10, and in this case, the low-source target condensation temperature Tc is lower than the outside air temperature. Specifically, when the outside air condition is 32 ° C., which is a high outside air condition based on the JRA standard (Japan Refrigeration and Air Conditioning Industry Association), the low original target condensation temperature Tc is about 20 ° C., and the outside air condition is a low outside air condition based on the JIS standard. At a certain 7 ° C., the low original target condensation temperature Tc is about 0 ° C. As described above, when the low-source-side high pressure (low-source-side condensation temperature) is lowered, the input of the low-source side compressor 11 is lowered. In other words, the compressor input on the low-source refrigeration cycle 10 side having poor operating efficiency may be lowered. Therefore, the low original target condensation temperature Tc is located in a temperature region lower than the outside air temperature.

(Difference in heat dissipation of auxiliary radiator 15 when the low-side condensation temperature is lower and higher than the outside air temperature)
Next, the heat radiation amount of the auxiliary radiator 15 will be considered. In the binary refrigeration apparatus of this example, the low original target condensing temperature Tc is lower than the outside air temperature because the low original refrigeration cycle 10 uses a CO2 refrigerant with low operating efficiency. Since the auxiliary radiator 15 is a radiator that radiates heat to the outside air, even if the refrigerant discharged from the low-side compressor 11 exchanges heat with the outside air by the auxiliary radiator 15, the refrigerant only falls to the outside temperature at the maximum. . In addition, the amount of heat released differs even when the refrigerant at the discharge temperature is lowered to the same outside air temperature by the auxiliary radiator 15 depending on whether the low side condensing temperature of the low source refrigeration cycle 10 is lower or higher than the outside air temperature. It becomes. In this example, the low source side condensation temperature is controlled to be constant at the low source target condensation temperature Tc. Since the low source target condensation temperature Tc is lower than the outside air temperature, the low source side condensation temperature is the outside air temperature. Considering the heat dissipation amount of the auxiliary radiator 15 when the temperature is lower than the above. For comparison, the amount of heat released from the condenser when the condensation temperature is higher than the outside air temperature in a general refrigerant circuit including a compressor, a radiator, an expansion valve, and an evaporator will also be considered.

  FIG. 5 is an explanatory diagram of the amount of heat released when the low-side condensation temperature is lower and higher than the outside air temperature. FIG. 5 (1) is a Mollier diagram in a general refrigeration cycle when the condensation temperature is higher than the outside air temperature, and FIG. 5 (2) is a low source refrigeration when the low-side condensation temperature is lower than the outside air temperature. It is a Mollier diagram of cycle 10.

(1) When the low-side condensing temperature is higher than the outside air temperature The temperature of the refrigerant discharged from the compressor (temperature at point a) is, for example, 80 ° C to 90 ° C, the outside air temperature is 20 ° C, and the condensation temperature is 25 ° C. Think about the case.
Since the radiator is a radiator that radiates heat to the outside air, as shown in FIG. 5 (1), the refrigerant (point a) of 80 ° C. to 90 ° C. is exchanged with the outside air by the radiator, It falls to 25 degreeC (point b) which is a condensation temperature with a gas state. And it is condensed and liquid state is maintained while maintaining 25 ° C. (point c). Since the outside air temperature is 20 ° C., the refrigerant can further dissipate heat and falls to 20 ° C. (point d) in a liquid state. As described above, since condensation occurs when the condensation temperature is higher than the outside air temperature, cooling with phase change can be performed, and the amount of heat released can be increased as compared with cooling without phase change.

(2) When the low-end side condensing temperature is lower than the outside air temperature The temperature of the refrigerant discharged from the low-end side compressor 11 (the temperature at the point a) is, for example, 80 ° C. to 90 ° C., and the outside air temperature is 20 ° C. Consider the case where the side condensation temperature is 10 ° C. Since the auxiliary radiator 15 is a radiator that radiates heat to the outside air, as described above, the refrigerant of 80 ° C. to 90 ° C. can reach the maximum outside air temperature of 20 ° C. by heat exchange with the outside air in the auxiliary radiator 15. It only goes down. That is, as shown in FIG. 5 (2), the refrigerant (point a) at 80 ° C. to 90 ° C. becomes 20 ° C. (point b) in the gas state in the auxiliary radiator 15. The heat exchange for condensing the refrigerant lowered to 20 ° C. and further lowering to 10 ° C. (point c) is performed on the low-source side condenser 12 side. In other words, when the low-side condensation temperature is lower than the outside air temperature, the auxiliary radiator 15 cannot perform cooling with phase change and performs gas cooling without phase change. That is, the auxiliary radiator 15 is used in the gas cooling region.

  Here, since the heat radiation from the point a to the point b in FIG. 5 (2) is the heat radiation in the gas state, even if the temperature is lowered to the same outside air temperature 20 ° C., the heat is condensed and lowered to 20 ° C. (1 ) Cannot be increased in the auxiliary radiator 15 as compared with the case of). Therefore, if the low-side condensation temperature is lower than the outside air temperature, even if the airflow of the radiator fan 16 of the auxiliary radiator 15 is increased or a radiator having a large heat transfer area is adopted as the auxiliary radiator 15, The amount of heat released from the auxiliary radiator 15 cannot be increased, and at most, the amount of heat dissipated before the discharged refrigerant is reduced to the outside temperature while being in a gas state.

  In summary, the auxiliary radiator 15 of the present example is used in the gas cooling region, and the amount of heat released is the amount of heat dissipated before the discharged refrigerant is reduced to the outside temperature in the gas state even at the maximum.

(Relationship between heat dissipation of auxiliary radiator 15 and COP)
FIG. 6 is an explanatory diagram of the relationship between the heat dissipation amount of the auxiliary radiator 15 and the COP, and shows a Mollier diagram of the low-source refrigeration cycle 10.
In constituting the low-stage refrigeration cycle 10, the heat radiation amount of the auxiliary radiator 15 compared to the case of when the Q _sub2 you Q _sub1 6, it is low-stage-side condenser when made into a Q _sub2 The heat dissipation amount Qc2 (<Qc1) of the container 12 can be reduced. In the cascade condenser C, the heat exchange amount between the high-side evaporator 24 and the low-side condenser 12 is always equal. Therefore, when the heat dissipation amount at the low-side condenser 12 is Qc2, the heat dissipation amount of the auxiliary radiator 15 is _Qsub1 because the high-source refrigeration cycle 20 side may be balanced with the heat dissipation amount _Qc2. As compared with the above, the input of the high-end compressor 21 can be reduced.

  In the two-stage refrigeration system, the constant refrigeration capacity is controlled, and COP = refrigeration capacity / (high source side compressor input + low side compressor input), so the high side compressor input can be reduced. COP can be increased.

  If the above contents are arranged, the COP can be maximized by the operation control in which the high-side compressor input and the low-side compressor input are substantially the same, and the heat radiation amount of the auxiliary radiator 15 is increased. As a result, the value of COP can be increased.

FIG. 7 is a diagram showing the relationship between the low-side condensation temperature and the operating efficiency fluctuation rate of the entire binary refrigeration apparatus. FIG. 7 is a calculation result obtained by examining the operating efficiency fluctuation rate when the low-side condensation temperature is changed at an outside air temperature of 7 ° C. In this example, the auxiliary radiator 15 with respect to the heat transfer area of the entire integrated heat exchanger is illustrated. The calculation results are shown when the ratio of the heat transfer area is 10%, 20%, 30%, and 40%. FIG. 7 shows the operating efficiency fluctuation rate based on the maximum value (100%) when there is no auxiliary radiator (that is, all the integrated heat exchangers are configured as a high-end condenser). FIG. 7A is an enlarged view of the maximum operating efficiency value portion of FIG.
7 and 7A, regardless of the division ratio of the heat transfer area, a certain low-side condensation temperature in the gas cooling region lower than the outside air temperature (in this example, a temperature around 0 ° C., It is shown that the operating efficiency of the binary refrigeration apparatus is maximized at a time corresponding to the low original target condensation temperature Tc). Further, in FIG. 7, when the low heat source side condensation temperature is raised above the outside air temperature and the auxiliary heat sink 15 is used in the condensing region in order to increase the heat radiation amount of the auxiliary heat sink 15, the low-source refrigeration cycle 10 It has been shown that the power consumption ratio of the system becomes too large and the overall operation efficiency decreases. Although only 40% is shown in FIG. 7, even if it is 100%, the maximum operating efficiency in the gas cooling zone is not exceeded.

  Here, in the binary refrigeration apparatus of this example, since the auxiliary radiator 15 is used in the gas cooling region as described above, the maximum heat dissipation is possible regardless of the structure of the heat transfer area of the auxiliary radiator 15 and the like. Even if it is possible, the refrigerant at the discharge temperature is lowered to the outside temperature. Further, as described above, the COP can be increased as the heat radiation amount of the auxiliary radiator 15 is increased. Therefore, the heat radiation amount of the auxiliary radiator 15 is ensured to such an extent that the temperature of the refrigerant at the discharge temperature can be lowered to near the outside air temperature by the auxiliary radiator 15. Hereinafter, this heat dissipation amount is referred to as a required heat dissipation amount. In order to achieve this required heat dissipation amount, for example, the air volume of the radiator fan 16 is controlled or the structural design of the auxiliary radiator 15 itself is performed. Thus, by setting the heat dissipation amount of the auxiliary radiator 15 as the required heat dissipation amount, the COP can be increased as compared with the case where the heat dissipation amount is smaller than the required heat dissipation amount.

  By the way, the required heat dissipation varies depending on the outside air temperature. Therefore, in order to secure a large COP throughout the year, it is necessary to grasp the required heat dissipation amount under low outdoor air conditions and the required heat dissipation amount under high outdoor air conditions. In the binary refrigeration apparatus of this example, the high condenser side evaporator 24 and the low condenser side condenser 12 are configured to perform heat exchange with the cascade condenser C, and CO2 refrigerant is used in the low condenser refrigeration cycle 10. In addition, when other contents described below are taken into consideration, a predetermined heat dissipation amount ratio corresponding to the outside air condition exists between the required heat dissipation amount of the auxiliary radiator 15 and the heat dissipation amount of the high-side condenser 22. . In this example, since the auxiliary radiator 15 and the high-side condenser 22 are configured by the integrated radiator 25, the predetermined heat dissipation amount ratio is that of the auxiliary radiator 15 with respect to the total heat dissipation of the integrated radiator 25. Replaced by the rate of heat dissipation. Therefore, a dual refrigeration system capable of increasing the COP throughout the year by setting the heat release rate ratio within the range of the heat release rate ratio in the low outside air condition and the heat release rate ratio in the high outside air condition is configured. it can.

  Hereinafter, prior to the description of the heat dissipation rate in the low outside air condition (7 ° C.) and the high outside air condition (32 ° C.), the heat dissipation amount of the integrated radiator 25 as a whole will be described.

(Heat dissipation amount of integrated radiator 25)
FIG. 8 is an explanatory diagram of the heat radiation amount of the integrated radiator 25 of FIG. 1 and shows a Mollier diagram of the dual refrigeration apparatus.
The heat radiation amount Q _ALL of the integrated radiator 25 is an amount obtained by adding the heat radiation amount Q _CH of the high-side condenser 22 and the heat radiation amount Q _sub of the auxiliary radiator 15 as in the following equation (1).

Q _ALL = Q _sub + Q _CH (1)

Here, the heat release amount Q _CH of the high-end side condenser 22 corresponds to a value obtained by adding the input amount WH of the high-end side compressor 21 and the heat exchange amount Q _eH of the high-end side evaporator 24. ) Is rewritten to the following (2).
Q _ALL = Q _sub + WH + Q _eH (2)

In this example, control is performed so that the high-side compressor input WH and the low-side compressor input WL are substantially the same, and the heat exchange amount Q _eH of the high-side evaporator 24 is low. Since the heat exchange amount Q _CL of the side condenser 12 is equal, when these are substituted into the equation (2), the equation (3) is obtained.
Q _ALL = Q _sub + WL + Q _CL (3)

The low-stage-side compressor input frequency WL because substantially equal to the heat radiation amount Q _sub auxiliary radiator 15, and substituting this into equation (3) is obtained (4).
Q _ALL = Q _sub + Q _sub + Q _C (4)

Here, the heat exchange amount Q _WL and the heat radiation amount Q _sub of the auxiliary radiator 15 are substantially equal because the binary refrigeration apparatus of this example performs the operation shown in the following four points.
1. The degree of superheat of the low-source refrigeration cycle 10 is 5 ° C.
2. The low original target side condensation temperature Tc is a little lower than the outside air temperature.
3. In order to maximize the COP, the compressor input on the high side and the low side are made substantially the same.
4). The inclination θ of the saturated vapor line 1 of CO 2 has an inclination close to 90 ° (see FIG. 6).

(Heat dissipation ratio of the auxiliary radiator 15 in the integrated radiator 25)
When the required heat discharge the heat radiation amount Q _sub auxiliary radiator 15, between the heat radiation amount Q _sub integral radiator 25 total radiation amount Q _ALL, according to the physical properties of the ambient temperature and CO2 refrigerants There is. This relationship will be described below.

FIG. 9 is an explanatory diagram of the heat dissipation rate of the auxiliary radiator in the integrated radiator of FIG. 1, and shows a Mollier diagram of the low-source refrigeration cycle when the outside air temperature is 32 ° C. The dotted line in FIG. 9 is a Mollier diagram of the low-source refrigeration cycle when the outside air temperature is 7 ° C.
As described above, when the outside air temperature is 32 ° C. (high outside air condition), the low-order target condensation temperature Tc is set to about 20 ° C. in the binary refrigeration apparatus of this example. When the outside air temperature is 32 ° C., the ratio of the latent heat of condensation A1 in FIG. 9 to the heat release amount B1 between the points a1 and c1 is 3: 1 based on the physical properties of the CO2 refrigerant. Yes.
Further, when the outside air temperature is 7 ° C. (low outside air condition), the low original target condensation temperature is set to about 0 ° C. At this time, the condensation latent heat amount A2 and the heat radiation amount B2 between the points a2 and c2 are The ratio is 8: 1 based on the physical properties of the CO2 refrigerant.

Here, the amount of heat released when the refrigerant that has fallen to 32 ° C. (b1 point) outside air temperature in the high outside air condition is reduced to the low-side condensation temperature 20 ° C. in the gas region is the total amount of heat released from the low-source refrigeration cycle 10. for small relative to the ratio of the condensation latent heat amount A1 and the heat radiation amount B1 is (5) approximates to the ratio of the heat radiation amount Q _CL1 of the required heat radiation quantity Q _sub1 and low-stage-side evaporator 14, as shown in equation Can do. Similarly, when the outside air temperature is 7 ° C., it can be approximated as shown in equation (6).
When the outside air temperature is 32 ° C Q _CL1 : Q _sub1 ≒ 3: 1 ... (5)
When the outside air temperature is 7 ° C Q _CL2 : Q _sub2 ≒ 8: 1 ... (6)

  If each of the above formulas (5) and (6) is substituted into formula (4), formulas (7) and (8) are obtained.

When the outside air temperature is 32 ° C. Q _ALL = Q _sub + Q _sub + 3Q _sub = 5Q _sub (7)
When the outside air temperature is _{7 ℃ Q ALL = Q sub +} Q sub + 8Q sub = 10Q sub ··· (8)

  From the above, in order to obtain a high COP by operating the binary refrigeration apparatus with the control that maximizes the COP and securing the maximum heat dissipation possible with the auxiliary radiator 15 used in the gas region, The ratio of the heat dissipation amount of the auxiliary radiator 15 to the total heat dissipation amount of the integrated radiator 25 is preferably 20% when the outside air temperature is 32 ° C. and 10% when the outside air temperature is 7 ° C. In view of the fact that this binary refrigeration apparatus is used throughout the year, it is desirable that 10% to 20% of the total heat dissipation amount of the integrated radiator 25 is radiated by the auxiliary radiator 15. Become.

  Any specific configuration can be adopted for the heat dissipation rate ratio in this way, and the auxiliary radiator 15 and the high-end condenser 22 have a common fan as shown in FIG. In this case, the heat transfer area of the auxiliary radiator 15 is set to 10% to 20% of the heat transfer area of the integrated radiator 25. Further, when separate fans are used for the auxiliary radiator 15 and the high-side condenser 22, respectively, the heat dissipation rate ratio may be controlled by changing the rotation speed of the fans. In this case, each fan is controlled by a control device (not shown) according to the outside air temperature so that the heat release rate is 10% when the outside air temperature is 7 ° C. and the heat release rate is 20% when the outside air temperature is 32 ° C. May be controlled.

  Here, FIG. 10 shows an example of a specific heat balance during steady operation in the binary refrigeration apparatus of the present embodiment. The low-source refrigeration cycle 10 uses CO2 refrigerant, and the high-source refrigeration cycle 20 uses H410 refrigerant R410A. When the low-end evaporator 14 has an evaporation temperature of −10 ° C., the cooling capacity is 25 kW, and the outside air temperature is 32 ° C., the low If the original side condensing temperature is 10 ° C., the operation efficiency of the entire binary refrigeration apparatus becomes optimal. At this time, the heat dissipation amount of the auxiliary radiator 15 is 6.3 kW, and the heat dissipation amount of the high source side condenser 22 is 31 kW. That is, the heat dissipation amount of the auxiliary radiator 15 is 20% with respect to the total heat dissipation amount of the integrated radiator 25.

  Reference is again made to FIG. 7A. As shown in FIG. 7A, when the ratio of the heat transfer area of the auxiliary radiator 15 to the heat transfer area of the entire integrated radiator 25 is 10%, the COP is highest. . In addition, FIG. 7A is a division | segmentation ratio of the heat-transfer area to the last, and is not a heat dissipation amount ratio.

  Since the auxiliary radiator 15 is used in the gas cooling zone, the amount of heat dissipation increases in proportion to the increase in the heat transfer area until the amount of heat dissipation from the auxiliary radiator 15 reaches the required heat dissipation amount. Even if the area is increased, the heat dissipation does not increase. Further, since the auxiliary radiator 15 is integrated with the high-source side condenser 22, if the division ratio of the auxiliary radiator 15 is increased, the heat transfer area of the high-side condenser 22 is reduced accordingly, and the high-source side condenser 22 is increased. The condensing capacity of the side condenser 22 is lowered and the operation efficiency is lowered. Therefore, as shown in FIG. 7, the operation efficiency decreases as the division ratio of the heat transfer area of the auxiliary radiator 15 is increased.

  As described above, according to the present embodiment, since the heat radiation amount of the auxiliary radiator 15 is 10% to 20% with respect to the total heat radiation amount of the integrated radiator 25, the influence on global warming is increased. Even when a CO2 refrigerant with low operating efficiency is used as a small natural refrigerant in the binary refrigeration apparatus, the operation efficiency of the entire binary refrigeration apparatus can be improved, and a large energy saving effect can be obtained throughout the year. In other words, for the two-stage refrigeration system using CO2 refrigerant, the heat dissipation rate was selected in consideration of the year-round outdoor temperature change, load fluctuations, CO2 characteristics, and high and low power consumption ratios. So you can get energy saving effect throughout the year. Moreover, a compact binary refrigeration apparatus can be obtained by integrally forming the auxiliary radiator 15 and the high-side condenser 22.

  Further, when the heat dissipation amount of the auxiliary radiator 15 is changed from 10% to 20% with respect to the total heat dissipation amount of the integrated radiator 25, the auxiliary radiator 15 and the high-side condenser 22 of the integrated radiator 25 are By adopting a configuration in which the heat transfer area is divided, the integrated radiator 25 can be used without waste, and a compact binary refrigeration apparatus having a large energy saving effect throughout the year can be obtained.

  The dual refrigeration system of this example is also widely applicable to refrigeration or refrigeration equipment such as showcases, commercial refrigerators, and vending machines that require non-fluorocarbons, reduced CFC refrigerants, and energy-saving equipment. it can.

  10 Low-source refrigeration cycle, 11 Low-source side compressor, 12 Low-source side condenser, 13 Low-source side expansion valve, 14 Low-source-side evaporator, 15 Auxiliary radiator, 16 Radiator fan, 20 High-source refrigeration cycle, 21 High side compressor, 22 High side condenser, 23 High side expansion valve, 24 High side evaporator, 25 Integrated radiator, 25a Heat transfer fin, 25b Heat transfer tube, C Cascade condenser.

Claims (5)

A low-source refrigeration cycle using a CO2 refrigerant, and a high-source refrigeration cycle for assisting heat dissipation in the low-source refrigeration cycle,
The low-source refrigeration cycle and the high-source refrigeration cycle each include a compressor, a condenser, a decompression device, and an evaporator, and the high-end evaporator and the low-end condenser exchange heat with a cascade condenser, Having a configuration in which an auxiliary radiator is installed in the previous stage in the low-source refrigeration cycle of the cascade capacitor;
Furthermore, the high-source side condenser and the auxiliary radiator are integrated to form an integrated radiator,
A dual refrigeration apparatus characterized in that 10% to 20% of the total heat dissipation amount of the integrated radiator is defined as the heat dissipation amount of the auxiliary radiator.   2. The dual refrigeration apparatus according to claim 1, wherein 10% to 20% of a total heat transfer area of the integrated radiator is defined as a heat transfer area of the auxiliary radiator.   The two-way refrigeration according to claim 1 or 2, wherein the integrated radiator has a configuration in which the auxiliary radiator is disposed in an upper portion and the high-side condenser is disposed in a lower portion. apparatus.   The integrated radiator is a plate fin tube type heat exchanger formed by passing a heat transfer tube through a flat fin, and the high-side condenser is integrated by sharing the heat transfer fin with the auxiliary radiator. The binary refrigeration apparatus according to any one of claims 1 to 3, wherein the binary refrigeration apparatus is provided.   The binary refrigeration apparatus according to any one of claims 1 to 4, wherein the refrigerant used in the high-source refrigeration cycle has higher operating efficiency than the CO2 refrigerant used in the low-source refrigeration cycle. .

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