Temperature control method of fixed-frequency refrigerating unit and fixed-frequency refrigerating unit

Abstract

According to the temperature control method of the fixed-frequency refrigerating unit and the fixed-frequency refrigerating unit, a bypass is formed in a main passage of the fixed-frequency refrigerating unit, a bypass electronic expansion valve is arranged on the bypass, and according to the actual refrigerating requirement of a to-be-cooled target, the bypass electronic expansion valve is used for adjusting flow distribution of a refrigerant, so that the temperature of the to-be-cooled target is controlled; therefore, flow adjustment of the refrigerant on the main passage is achieved, accurate adjustment of the refrigerating capacity of the main passage is achieved, and the purpose of stably and accurately controlling the temperature of a to-be-cooled target is achieved. According to the temperature control method, the current temperature of the to-be-cooled target is obtained and compared with the preset temperature interval, so that the refrigeration requirement of the to-be-cooled target is obtained in real time, and the opening degree of the main path electronic expansion valve and the opening degree of the bypass electronic expansion valve are reversely adjusted to meet the refrigeration requirement of the to-be-cooled target; and the compressor carries out cooling capacity adjustment and temperature control without shutdown, so that the temperature control precision of the variable load of the fixed-frequency refrigerating unit is improved.

Description

Technical Field

[0001] The present application relates to the technical field of refrigeration control, and in particular to a temperature control method of a fixed-frequency refrigeration unit and a fixed-frequency refrigeration unit. Background Art

[0002] The precision control of chillers is an important technology, which is mainly used in occasions that require precise temperature control, such as data centers, energy storage, etc. The core of the precision control technology of chillers lies in adjusting the flow of refrigerant and the working state of the compressor through advanced control systems, so as to achieve precise control of the outlet water temperature (or return air temperature). The existing technology usually improves the control accuracy through variable frequency drive technology, specifically by using a frequency converter to adjust the motor speed, thereby changing the operating state of the compressor, so as to achieve the purpose of energy saving and consumption reduction, while maintaining a high temperature control accuracy.

[0003] In the process of implementing this application, the inventor found that there are at least the following technical problems in the prior art: the leakage current of the current inverter is relatively large and cannot meet the use in all application scenarios of some industries such as data centers and energy storage, so these industries still use fixed-frequency compressors. However, in many application scenarios, the heat generation of the control target is uncertain, the heating interval is irregular, and the fixed-frequency compressor is usually set with a start-up interval requirement to ensure the reliability of the compressor. If the control target is heated within the start-up interval of the fixed-frequency compressor, the fixed-frequency compressor cannot respond in time, which will cause the control accuracy to be lost.

[0004] Therefore, how to effectively improve the problem that the existing chillers using fixed-frequency compressors cannot cope with the problem of reduced temperature control accuracy due to uncertain control target heating value, irregular heating interval duration and the existence of start-up intervals is a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the invention

[0005] In view of this, the present application provides a temperature control method and a fixed-frequency refrigeration unit for a fixed-frequency refrigeration unit, aiming to effectively solve the problem that the above-mentioned chiller using a fixed-frequency compressor cannot cope with the problem that the temperature control accuracy is reduced due to uncertain control target heating value, irregular heating interval duration and the existence of a start-up interval.

[0006] The present application provides a temperature control method for a fixed-frequency refrigeration unit, the fixed-frequency refrigeration unit comprising a first circulation path and a second circulation path, the first circulation path having a refrigerant circulating therein and comprising a main path and a bypass path, the main path being provided with a compressor, a condenser, a main electronic expansion valve, and a heat exchanger in sequence, the bypass path being connected between the outlet of the condenser and the inlet of the compressor and being provided with a bypass electronic expansion valve and a bypass evaporator, the bypass evaporator being heat exchanged with the condenser, the second circulation path having a secondary coolant circulating therein and being provided with a target to be cooled, the second circulation path being connected to the heat exchanger so that the refrigerant and the secondary coolant exchange heat in the heat exchanger, the temperature control method comprising:

[0007] Obtain the current temperature T0 of the target to be cooled, and compare it with the preset temperature intervals [a1, b] and (b, a2];

[0008] When T0∈[a1,b], the opening of the main electronic expansion valve decreases, and the opening of the bypass electronic expansion valve increases;

[0009] When T0∈(b,a2], the opening of the main electronic expansion valve increases, and the opening of the bypass electronic expansion valve decreases.

[0010] In one embodiment, the sum of the valve opening steps of the main electronic expansion valve and the valve opening steps of the bypass electronic expansion valve is a certain value.

[0011] In one embodiment, the regulation priority of the main electronic expansion valve is greater than the regulation priority of the bypass electronic expansion valve.

[0012] In one embodiment, the caliber of the main electronic expansion valve is the same as the caliber of the bypass electronic expansion valve, and the heat exchange capacity of the heat exchanger is the same as the heat exchange capacity of the bypass evaporator.

[0013] In one embodiment, the temperature control method further comprises:

[0014] Setting a hysteresis range for the end values ​​a1, b, a2 of the temperature range;

[0015] When T0 is within the hysteresis interval of the corresponding end value, the current openings of the main electronic expansion valve and the bypass electronic expansion valve are maintained;

[0016] When T0 exceeds the hysteresis interval of the corresponding end value, the main electronic expansion valve and the bypass electronic expansion valve perform corresponding opening adjustments.

[0017] In one embodiment, a1 is a negative value, and a2 is a positive value.

[0018] In one embodiment, b is 0; and / or the sum of a1 and a2 is 0.

[0019] In one embodiment, the fixed-frequency refrigeration unit further includes an economizer, which is disposed between the outlet of the condenser and the inlet of the bypass passage, and the economizer cooperates with a main passage section of the main passage located between the inlet of the compressor and the outlet of the bypass passage for heat exchange.

[0020] In one embodiment, the refrigerant and the coolant flow directions in the heat exchanger are opposite; and / or, the second circulation passage is provided with a pump, and the pump is used to drive the coolant to circulate in the second circulation passage; and / or, the bypass evaporator and the condenser are equipped with a fan, and the airflow generated by the fan passes through the condenser and the bypass evaporator in sequence.

[0021] The present application also provides a fixed-frequency refrigeration unit, which operates according to the temperature control method of the fixed-frequency refrigeration unit as described above.

[0022] In summary, the present application provides a temperature control method for a fixed-frequency refrigeration unit and a fixed-frequency refrigeration unit, which at least has the following

[0023] Beneficial effects:

[0024] The fixed-frequency refrigeration unit opens a bypass passage on the main passage, and sets a bypass electronic expansion valve on the bypass passage. According to the actual refrigeration demand of the target to be cooled, the bypass electronic expansion valve is used to adjust the flow distribution of the refrigerant, thereby realizing the flow regulation of the refrigerant on the main passage, and then realizing the precise regulation of the refrigeration capacity of the main passage, so as to achieve the purpose of stable and precise temperature control of the target to be cooled. The temperature control method of the present application obtains the current temperature of the target to be cooled and compares it with a preset temperature range to obtain the refrigeration demand of the target to be cooled in real time, reversely adjusts the opening of the main electronic expansion valve and the bypass electronic expansion valve to meet the refrigeration demand of the target to be cooled, and the compressor performs cooling capacity adjustment and temperature control without stopping, thereby improving the temperature control accuracy of the variable load of the fixed-frequency refrigeration unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the system principle of a fixed-frequency refrigeration unit according to an embodiment of the present application.

[0026] Figure 2 This is a schematic diagram of the system principle of a fixed-frequency refrigeration unit according to another embodiment of the present application.

[0027] Figure 3 The figure is a flow chart of a temperature control method of a fixed-frequency refrigeration unit according to an embodiment of the present application.

[0028] Figure 4 It is a flow chart of a temperature control method of a fixed-frequency refrigeration unit according to another embodiment of the present application.

[0029] Figure 5 It is a schematic diagram of the temperature range of a specific embodiment of the present application.

[0030] Reference numerals: 10-fixed frequency refrigeration unit; 10a-refrigeration system; 10b-cooling system; 12-first circulation path; 14-second circulation path; 16-main path; 18-bypass path; 18a-bypass inlet; 18b-bypass outlet; 20-compressor; 20a-compressor inlet; 20b-compressor outlet; 22-condenser; 22a-condenser inlet; 22b-condenser outlet; 24-main electronic expansion valve; 24a-main electronic expansion valve inlet; 24b-main electronic expansion valve outlet; 26-heat exchanger; 26 a-first heat exchange inlet; 26b-first heat exchange outlet; 26c-second heat exchange inlet; 26d-second heat exchange outlet; 28-bypass electronic expansion valve; 28a-bypass electronic expansion valve inlet; 28b-bypass electronic expansion valve outlet; 30-bypass evaporator; 30a-bypass evaporator inlet; 30b-bypass evaporator outlet; 32-target to be cooled; 32a-cooling inlet; 32b-cooling outlet; 34-pump; 36-fan; 38-economizer; 38a-economizer inlet; 38b-economizer outlet; 40-main pipe section. DETAILED DESCRIPTION

[0031] Before describing the embodiments in detail, it should be understood that the present application is not limited to the detailed structure or component arrangement described below or in the drawings in the present application. The present application may be an embodiment implemented in other ways. Moreover, it should be understood that the words and terms used herein are only used for descriptive purposes and should not be interpreted restrictively. The words "including", "comprising", "having" and the like used herein are meant to include the items listed thereafter, their equivalents and other additional items. In particular, when describing "a certain element", the present application does not limit the number of the element to one, but may also include multiple elements.

[0032] Please refer to Figure 1As shown, the present application provides a fixed-frequency refrigeration unit 10, which can be used in data centers, energy storage and other fields that require precise temperature control, so as to cool down and precisely regulate the temperature of the corresponding heating devices. The fixed-frequency refrigeration unit 10 includes a first circulation passage 12 and a second circulation passage 14, wherein the first circulation passage 12 circulates a refrigerant and includes a main passage 16 and a bypass passage 18, wherein the refrigerant is, for example, fluorine, wherein the main passage 16 is a closed-loop passage, and the bypass passage 18 is connected in parallel to the main passage 16. A compressor 20, a condenser 22, a main electronic expansion valve 24, and a heat exchanger 26 are sequentially provided on the main passage 16. The compressor 20 is, for example, a fixed-frequency compressor, and the heat exchanger 26 is, for example, a cold plate heat exchanger. The bypass passage 18 is connected between the outlet of the condenser 22 and the inlet of the compressor 20 and is provided with a bypass electronic expansion valve 28 and a bypass evaporator 30. The bypass evaporator 30 cooperates with the condenser 22 for heat exchange. A refrigerant circulates in the second circulation passage 14 and is provided with a target to be cooled 32. The refrigerant is, for example, water. The second circulation passage 14 is connected to the heat exchanger 26 so that the refrigerant and the refrigerant can exchange heat in the heat exchanger 26.

[0033] Among them, the refrigerant circulates in the main passage 16 and the bypass passage 18 of the first circulation passage 12, that is, the refrigerant circulates between the compressor 20, the condenser 22, the main electronic expansion valve 24, the heat exchanger 26, the bypass electronic expansion valve 28, and the bypass evaporator 30. Specifically, the compressor 20 has a compressor inlet 20a and a compressor outlet 20b, the condenser 22 has a condenser inlet 22a and a condenser outlet 22b, the main electronic expansion valve 24 has a main electronic expansion valve inlet 24a and a main electronic expansion valve outlet 24b, and the heat exchanger 26 includes a first heat exchange inlet 26a, a first heat exchange outlet 26b, a second heat exchange inlet 26c and a second heat exchange outlet 26d, wherein the first heat exchange inlet 26a and the first heat exchange outlet 26b are located on the main passage 16, that is, the refrigerant enters the heat exchanger 26 from the first heat exchange inlet 26a for heat exchange and then flows out from the first heat exchange outlet 26b, and the second heat exchange inlet 26c and the second heat exchange outlet 26d are located on the second circulation passage 14, that is, the coolant enters the heat exchanger 26 from the second heat exchange inlet 26c for heat exchange and then flows out from the second heat exchange outlet 26d. The bypass passage 18 has a bypass inlet 18a and a bypass outlet 18b. The bypass passage 18 is connected between the condenser outlet 22b and the compressor inlet 20a. For example, the bypass inlet 18a is connected to the pipe section between the condenser outlet 22b and the main electronic expansion valve inlet 24a on the main passage 16, and the bypass outlet 18b is connected to the pipe section between the first heat exchange outlet 26b and the compressor inlet 20a on the main passage 16. In other words, the bypass passage 18 is connected in parallel to the main electronic expansion valve 24 and the heat exchanger 26. The bypass electronic expansion valve 28 and the bypass evaporator 30 are in parallel with the main electronic expansion valve 24 and the heat exchanger 26, so that the bypass passage 18 forms a bypass branch on the main passage 16. The bypass electronic expansion valve 28 has a bypass electronic expansion valve inlet 28a and a bypass electronic expansion valve outlet 28b, and the bypass evaporator 30 has a bypass evaporator inlet 30a and a bypass evaporator outlet 30b.

[0034] The brine circulates in the second circulation passage 14. Specifically, the target to be cooled 32 has a cooling inlet 32a and a cooling outlet 32b. The cooling outlet 32b is connected to the second heat exchange inlet 26c, and the second heat exchange outlet 26d is connected to the cooling inlet 32a.

[0035] More specifically, the compressor outlet 20b is connected to the condenser inlet 22a, the condenser outlet 22b is connected to the main electronic expansion valve inlet 24a and the bypass electronic expansion valve inlet 28a, the main electronic expansion valve outlet 24b is connected to the first heat exchange inlet 26a, the bypass electronic expansion valve outlet 28b is connected to the bypass evaporator inlet 30a, and the first heat exchange outlet 26b and the bypass evaporator outlet 30b are connected to the compressor inlet 20a. The refrigerant entering the compressor inlet 20a is pressurized by the compressor 20 and becomes a high-temperature and high-pressure refrigerant gas. The high-temperature and high-pressure refrigerant gas flows out from the compressor outlet 20b and enters the condenser 22 through the condenser inlet 22a. In the condenser 22, the refrigerant releases heat to the air and condenses into a high-temperature and high-pressure supercooled liquid. After the high-temperature and high-pressure refrigerant liquid flows out from the condenser outlet 22b, a part of it enters the main electronic expansion valve 24 through the main electronic expansion valve inlet 24a, and the other part enters the bypass electronic expansion valve 28 through the bypass inlet 18a and the bypass electronic expansion valve inlet 28a. The main electronic expansion valve 24 throttles and reduces the pressure of the inflowing refrigerant to a low-pressure two-phase state. The low-pressure two-phase refrigerant flows out from the main electronic expansion valve outlet 24b and enters the heat exchanger 26 through the first heat exchange inlet 26a. The refrigerant absorbs heat during evaporation and becomes superheated refrigerant gas. The superheated refrigerant gas flows out from the first heat exchange outlet 26b and enters the compressor 20 through the compressor inlet 20a for further compression. The bypass electronic expansion valve 28 throttles and reduces the pressure of the inflowing refrigerant to a low-pressure two-phase state. The low-pressure two-phase refrigerant flows out from the bypass electronic expansion valve outlet 28b and enters the bypass evaporator 30 through the bypass evaporator inlet 30a. The bypass evaporator 30 cooperates with the condenser 22 in heat exchange. Therefore, the refrigerant in the bypass evaporator 30 absorbs the heat released by the refrigerant in the condenser 22 into the air and is converted into superheated refrigerant gas to complete the heat exchange. After this part of the refrigerant gas flows out from the bypass outlet 18b, it merges with the refrigerant gas flowing out of the first heat exchange outlet 26b on the main passage 16 and enters the compressor 20 together to complete a cycle. After the coolant exchanges heat with the target to be cooled 32, it flows out from the cooling outlet 32b and enters the heat exchanger 26 through the second heat exchange inlet 26c, exchanges heat with the refrigerant in the heat exchanger 26, and the heat of the coolant is absorbed by the refrigerant in the heat exchanger 26. After the temperature of the coolant is reduced, it flows out through the second heat exchange outlet 26d and flows into the target to be cooled 32 through the cooling inlet 32a, so as to absorb the heat of the target to be cooled 32 to cool it down, completing one cycle.

[0036] The fixed-frequency refrigeration unit 10 of the present application opens a bypass passage 18 on the main passage 16, and sets a bypass electronic expansion valve 28 on the bypass passage 18. According to the actual refrigeration demand of the target to be cooled 32, the bypass electronic expansion valve 28 is used to adjust the flow distribution of the refrigerant, thereby realizing the flow regulation of the refrigerant on the main passage 16, and then realizing the precise regulation of the refrigeration capacity of the main passage 16, so as to achieve the purpose of stable and precise temperature control of the target to be cooled 32, so as to effectively solve the problem that the existing chillers using fixed-frequency compressors cannot cope with the problem of reduced temperature control accuracy due to uncertain heating value of the control target, irregular heating interval duration and start-up interval.

[0037] Preferably, a pump 34 is provided on the second circulation passage 14, and the pump 34 is used to drive the coolant to circulate in the second circulation passage 14, and the pump 34 can adjust the flow rate of the coolant in the second circulation passage 14 by power regulation, thereby adjusting the flow rate of the coolant in the target to be cooled 32, so as to achieve temperature control and regulation of the target to be cooled 32 by controlling the coolant flow rate. For example, when the cooling demand of the target to be cooled 32 increases, the coolant flow rate can be increased by the pump 34, and when the cooling demand of the target to be cooled 32 decreases, the coolant flow rate can be reduced by the pump 34; or, when the cooling demand of the target to be cooled 32 is extremely low, the pump 34 can also be shut down and restarted when needed. In this embodiment, the pump 34 is arranged between the second heat exchange outlet 26d and the cooling inlet 32a.

[0038] In this embodiment, the bypass evaporator 30 and the condenser 22 are provided with a fan 36, which is used to accelerate the heat exchange rate between the bypass evaporator 30 and the condenser 22. The airflow generated by the fan 36 passes through the condenser 22 and the bypass evaporator 30 in sequence, that is, the airflow generated by the fan 36 first passes through the condenser 22 and then passes through the bypass evaporator 30. When the airflow flows through the condenser 22, it carries the heat dissipated by the condenser 22 and then flows to the bypass evaporator 30, thereby promoting the refrigerant in the bypass evaporator 30 to absorb the heat released by the liquefaction of the refrigerant in the condenser 22 and evaporate.

[0039] The flow direction of the refrigerant in the main passage 16 and the flow direction of the brine in the second circulation passage 14 are as follows: Figure 1 As shown by the arrows on the middle circulation passage, the refrigerant flows in the counterclockwise direction in the main passage 16, and the brine flows in the counterclockwise direction in the second circulation passage 14. The first circulation passage 12 and the second circulation passage 14 are respectively located on both sides of the heat exchanger 26. In a preferred embodiment, the refrigerant and the brine flow in the heat exchanger 26 in opposite directions, which can improve the heat exchange efficiency of the heat exchanger 26. For example, the first heat exchange inlet 26a and the second heat exchange outlet 26d are located at one end of the heat exchanger 26, and the first heat exchange outlet 26b and the second heat exchange inlet 26c are located at the other end of the heat exchanger 26.

[0040] The fixed-frequency refrigeration unit 10 of the present application can be divided into a refrigeration system 10a and a cooling system 10b based on the heat exchanger 26. The refrigerant of the refrigeration system 10a and the coolant of the cooling system 10b exchange heat through the heat exchanger 26 to cool the coolant, and then use the coolant to cool down the target to be cooled 32 and accurately control the temperature. Among them, the refrigeration system 10a includes a first circulation path 12 and a compressor 20, a condenser 22, a main electronic expansion valve 24, a heat exchanger 26, a bypass electronic expansion valve 28, a bypass evaporator 30, and a fan 36 arranged on the first circulation path 12; the cooling system 10b includes a second circulation path 14 and a target to be cooled 32, a heat exchanger 26, and a pump 34 arranged on the second circulation path 14.

[0041] In some other embodiments, the fixed-frequency refrigeration unit 10 further includes an economizer 38. Figure 2 As shown, in this embodiment, the fixed frequency refrigeration unit 10 is Figure 1 An economizer 38 is additionally provided on the basis of the embodiment shown. By adding the economizer 38, the compressor 20 can be guaranteed to have a certain degree of superheat, and the exhaust temperature of the compressor 20 can be reduced to ensure the reliability of the compressor 20 and improve the refrigeration efficiency. The economizer 38 is provided on the pipe section of the main passage 16 between the condenser outlet 22b and the bypass inlet 18a, and the economizer 38 cooperates with the main passage pipe section 40 of the main passage 16 located between the compressor inlet 20a and the bypass outlet 18b for heat exchange. Specifically, the economizer 38 has an economizer inlet 38a and an economizer outlet 38b, the economizer inlet 38a is connected to the condenser outlet 22b, and the economizer outlet 38b is connected to the main electronic expansion valve inlet 24a and the bypass electronic expansion valve inlet 28a. The high-temperature and high-pressure refrigerant supercooled liquid flowing out of the condenser 22 enters the economizer 38 through the economizer inlet 38a, and the main pipe section 40 is connected to the economizer 38, so that the refrigerant gas flowing out of the heat exchanger 26 and the bypass evaporator 30 and merging them enters the economizer 38 to exchange heat with the high-temperature and high-pressure refrigerant supercooled liquid. The refrigerant gas in the main pipe section 40 absorbs heat and its temperature increases, which can increase the suction superheat of the compressor 20 and improve the reliability of the operation of the compressor 20. The high-temperature and high-pressure refrigerant supercooled liquid releases heat and cools down before entering the main electronic expansion valve 24 and the bypass electronic expansion valve 28 respectively. By providing the economizer 38, the subcooling degree of the refrigerant can be increased, the two-phase area of ​​the condenser 22 can be increased, the heat exchange capacity of the condenser 22 can be increased, and thus the cooling capacity can be increased; by utilizing the economizer 38 to increase the subcooling degree of the refrigerant, the subcooling degree of the refrigerant is increased, and the dryness of the refrigerant after the main electronic expansion valve 24 is reduced, thereby increasing the cooling capacity.

[0042] The present application also provides a temperature control method for a fixed-frequency refrigeration unit, wherein the fixed-frequency refrigeration unit may be the fixed-frequency refrigeration unit 10 in the above-mentioned embodiment, please refer to Figure 3As shown, the temperature control method includes:

[0043] S1: obtaining the current temperature T0 of the target to be cooled 32, for example, by setting a temperature sensor to detect the current temperature T0 of the target to be cooled 32 in real time, and comparing it with the preset temperature intervals [a1, b] and (b, a2];

[0044] S2: When T0∈[a1,b], the opening of the main electronic expansion valve 24 decreases, and the opening of the bypass electronic expansion valve 28 increases; specifically, when T0∈[a1,b], it indicates that the refrigeration demand of the target 32 ​​to be cooled is too small or the refrigeration capacity of the main passage 16 of the unit is too large. At this time, the opening of the main electronic expansion valve 24 decreases, and the refrigerant flow rate of the main passage 16 is reduced to reduce the refrigeration capacity of the main passage 16, thereby reducing the temperature drop rate of the coolant to meet the smaller refrigeration demand of the target 32 ​​to be cooled. At the same time, the bypass electronic expansion valve 28 increases its opening according to the current temperature T0 to ensure that the current temperature T0 of the target 32 ​​to be cooled is as close to the control target temperature as possible, wherein the control target temperature is the optimal operating temperature of the heat source end (the target 32 ​​to be cooled). Improving the control accuracy can increase the energy efficiency of the heat source end, etc.;

[0045] S3: When T0∈(b, a2], the opening of the main electronic expansion valve 24 increases, and the opening of the bypass electronic expansion valve 28 decreases; specifically, when T0∈(b, a2], it indicates that the cooling demand of the target 32 ​​to be cooled is too large or the cooling capacity of the main passage 16 of the unit is too small. At this time, the opening of the main electronic expansion valve 24 increases, and the refrigerant flow rate of the main passage 16 is increased to provide a larger cooling capacity for the main passage 16, thereby quickly reducing the refrigerant temperature to meet the larger cooling demand of the target 32 ​​to be cooled. At the same time, the opening of the bypass electronic expansion valve 28 decreases to prevent the refrigerant from flowing through the bypass passage 18 and reducing the cooling capacity of the main passage 16.

[0046] By adopting this temperature control method, the compressor 20 can operate without stopping during the refrigeration and cooling process. The temperature control method of the present application obtains the current temperature of the target to be cooled 32 and compares it with a preset temperature range to obtain the refrigeration demand of the target to be cooled 32 in real time, and reversely adjusts the opening of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 to meet the refrigeration demand of the target to be cooled 32. The compressor 20 performs cooling capacity adjustment and temperature control without stopping, thereby improving the temperature control accuracy of the variable load of the fixed-frequency refrigeration unit 10.

[0047] Preferably, the opening degree of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 are controlled oppositely, that is, when the opening degree of the main electronic expansion valve 24 increases, the opening degree of the bypass electronic expansion valve 28 decreases, and when the opening degree of the main electronic expansion valve 24 decreases, the opening degree of the bypass electronic expansion valve 28 increases. Further, the sum of the opening steps of the main electronic expansion valve 24 and the opening steps of the bypass electronic expansion valve 28 is a certain value, and the selection of the fixed value must meet the requirement of ensuring that the compressor 20 has a certain degree of superheat. Such a setting can ensure that the compressor 20 has a certain degree of suction superheat to ensure the safe operation of the compressor. Since the refrigerant flow rate of the fixed-frequency refrigeration unit 10 remains unchanged, the total opening of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 remains unchanged. By setting the opening control of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 to be opposite, for example, the main electronic expansion valve 24 is opened wider (the bypass electronic expansion valve 28 is closed), the refrigerant flow rate of the main passage 16 can be increased, and the refrigeration capacity can be increased. The core principle is to control the refrigerant flow rate of the main passage 16 according to the heating value of the heat source end.

[0048] In this embodiment, the caliber of the main electronic expansion valve 24 is the same as the caliber of the bypass electronic expansion valve 28, and the heat exchange capacity of the heat exchanger 26 is the same as the heat exchange capacity of the bypass evaporator 30. Such a setting can ensure that when there is no load on the heat source end, the refrigerant flows entirely to the bypass path 18. At this time, the heat exchange capacity of the bypass evaporator 30 is required to be sufficient to ensure the normal operation of the system. Therefore, the heat exchange capacity of the bypass evaporator 30 can be the same as the heat exchange capacity of the heat exchanger 26, or the heat exchange capacity of the bypass evaporator 30 is greater than the heat exchange capacity of the heat exchanger 26.

[0049] In some embodiments, in order to ensure the stability of temperature regulation of the fixed-frequency refrigeration unit 10, the regulation priority of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 can be restricted, that is, the regulation priority of the main electronic expansion valve 24 is greater than the regulation priority of the bypass electronic expansion valve 28. When the temperature of the target 32 ​​to be cooled changes, the main electronic expansion valve 24 is adjusted first. When the main electronic expansion valve 24 reaches the maximum or minimum opening and still fails to control the temperature of the target 32 ​​to be cooled, the bypass electronic expansion valve 28 is adjusted. Such a setting can improve the stability of the unit operation. Specifically, when the main electronic expansion valve 24 and the bypass electronic expansion valve 28 are adjusted at the same time, the control temperature will fluctuate, and the system is not easy to enter a stable state; when the main electronic expansion valve 24 and the bypass electronic expansion valve 28 are adjusted by a single valve, the control parameter is unique, and it is easier to enter a stable state than adjusting at the same time. However, because the temperature control target is the main heat source, it is easier to make the system enter a stable state by adjusting the main electronic expansion valve 24 first, thereby improving the stability of the unit operation.

[0050] Furthermore, if Figure 4 As shown, the temperature control method also includes:

[0051] S1.1: Set the hysteresis interval for the end values ​​a1, b, a2 of the above-mentioned preset temperature intervals [a1, b] and (b, a2];

[0052] S2.1: When T0 is within the hysteresis range of the corresponding end value, the current opening of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 is maintained;

[0053] S3.1: When T0 exceeds the hysteresis interval of the corresponding end value, the main electronic expansion valve 24 and the bypass electronic expansion valve 28 perform corresponding opening adjustments.

[0054] Among them, the b value is the control target temperature of the target to be cooled 32 (heat source end), which can be set according to actual needs and is not specifically limited here; a1 and a2 are control accuracy (the allowable fluctuation range of the heat source end), and the control accuracy (allowable fluctuation range) of different products is different, so no specific limitation is made here.

[0055] For example, the hysteresis value of the hysteresis interval is ±c, and the c value is, for example, 0.5. The c value can be adjusted according to the actual precision design requirements of the product. The hysteresis interval corresponding to the end value a1 is [a1-c, a1+c], the hysteresis interval corresponding to the end value b is [bc, b+c], and the hysteresis interval corresponding to the end value a2 is [a2-c, a2+c]. Specifically, when T0 is within the hysteresis interval [a1-c, a1+c] corresponding to the end value a1, the current valve step requirements of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 are maintained; when T0 exceeds the hysteresis interval [a1-c, a1+c], the main electronic expansion valve 24 and the bypass electronic expansion valve 28 perform corresponding opening adjustments. When T0 is within the hysteresis interval [bc, b+c] corresponding to the end value b, the current valve step requirements of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 are maintained; when T0 exceeds the hysteresis interval [bc, b+c], the main electronic expansion valve 24 and the bypass electronic expansion valve 28 perform corresponding opening adjustments. When T0 is within the hysteresis interval [a2-c, a2+c] corresponding to the end value a2, the current valve step requirements of the main electronic expansion valve 24 and the bypass electronic expansion valve 28 are maintained; when T0 exceeds the hysteresis interval [a2-c, a2+c], the main electronic expansion valve 24 and the bypass electronic expansion valve 28 perform corresponding opening adjustments. Such a setting can ensure the logical operation stability of the above-mentioned temperature control method. By introducing hysteresis, the system fluctuation can be reduced. For example, when the temperature reaches the set value, the temperature value changes near the set value due to problems such as sensor collection, and the two valves have the problem of adjusting back and forth, and the system cannot be stable; the change of valve opening will cause temperature change, aggravate temperature fluctuation, and the system cannot be stable; introducing hysteresis can eliminate this part of the influence.

[0056] Preferably, a1 is a negative value and a2 is a positive value. For example, the sum of a1 and a2 is 0, that is, the absolute values ​​of a1 and a2 are the same. For example, the absolute values ​​of a1 and a2 are both a, that is, a1 = -a, a2 = +a, wherein b is preferably 0, that is, the temperature range set by the fixed-frequency refrigeration unit 10 is [-a, 0] and (0, +a], such as Figure 5 As shown in Table 1, Table 1 shows the control interval division of the temperature intervals [-a, 0] and (0, +a].

[0057] Table 1

[0058] Temperature range [-a,0] (0,+a] Main circuit electronic expansion valve Opening decreases Increased opening Bypass electronic expansion valve Increased opening Opening decreases

[0059] In summary, the present application provides a temperature control method and a fixed-frequency refrigeration unit for a fixed-frequency refrigeration unit. The fixed-frequency refrigeration unit opens a bypass passage on the main passage, and sets a bypass electronic expansion valve on the bypass passage. According to the actual refrigeration demand of the target to be cooled, the bypass electronic expansion valve is used to adjust the flow distribution of the refrigerant, thereby realizing the flow regulation of the refrigerant on the main passage, and then realizing the precise regulation of the refrigeration capacity of the main passage, so as to achieve the purpose of stable and precise temperature control of the target to be cooled. The temperature control method of the present application obtains the current temperature of the target to be cooled and compares it with a preset temperature range to obtain the refrigeration demand of the target to be cooled in real time, reversely adjusts the opening of the main electronic expansion valve and the bypass electronic expansion valve to meet the refrigeration demand of the target to be cooled, and the compressor performs cooling capacity adjustment and temperature control without stopping, thereby improving the temperature control accuracy of the variable load of the fixed-frequency refrigeration unit.

[0060] The concepts described herein may be implemented in other forms without departing from their spirit and characteristics. The specific embodiments disclosed should be considered illustrative rather than restrictive. Therefore, the scope of this application is determined by the appended claims rather than by the preceding description. Any changes within the literal meaning and equivalent scope of the claims should fall within the scope of these claims.

Claims

1. A temperature control method for a fixed-frequency refrigeration unit, characterized in that: The fixed-frequency refrigeration unit includes a first circulation path and a second circulation path, the first circulation path has a refrigerant circulating therein and includes a main path and a bypass path, the main path is provided with a compressor, a condenser, a main electronic expansion valve, and a heat exchanger in sequence, the bypass path is connected between the outlet of the condenser and the inlet of the compressor and is provided with a bypass electronic expansion valve and a bypass evaporator, the bypass evaporator cooperates with the condenser for heat exchange, the second circulation path has a coolant circulating therein and is provided with a target to be cooled, the second circulation path is connected to the heat exchanger so that the refrigerant and the coolant exchange heat in the heat exchanger, and the temperature control method includes: Obtain the current temperature T0 of the target to be cooled, and compare it with the preset temperature intervals [a1, b] and (b, a2]; When T0∈[a1,b], the opening of the main electronic expansion valve decreases, and the opening of the bypass electronic expansion valve increases; When T0∈(b, a2], the opening of the main electronic expansion valve increases, and the opening of the bypass electronic expansion valve decreases.

2. The temperature control method of a fixed-frequency refrigeration unit according to claim 1, characterized in that: The sum of the valve opening steps of the main electronic expansion valve and the valve opening steps of the bypass electronic expansion valve is a certain value.

3. The temperature control method of a fixed-frequency refrigeration unit according to claim 1, characterized in that: The regulation priority of the main electronic expansion valve is greater than the regulation priority of the bypass electronic expansion valve.

4. The temperature control method of a fixed-frequency refrigeration unit according to claim 1, characterized in that: The caliber of the main electronic expansion valve is the same as the caliber of the bypass electronic expansion valve, and the heat exchange capacity of the heat exchanger is the same as the heat exchange capacity of the bypass evaporator.

5. The temperature control method of a fixed-frequency refrigeration unit according to claim 1, characterized in that: The temperature control method further comprises: Setting a hysteresis interval for the end values ​​a1, b, a2 of the temperature interval; When T0 is within the hysteresis interval of the corresponding end value, the current openings of the main electronic expansion valve and the bypass electronic expansion valve are maintained; When T0 exceeds the hysteresis interval of the corresponding end value, the main electronic expansion valve and the bypass electronic expansion valve perform corresponding opening adjustments.

6. The temperature control method of a fixed-frequency refrigeration unit according to claim 1, characterized in that: The a1 is a negative value, and the a2 is a positive value.

7. The temperature control method of a fixed-frequency refrigeration unit according to claim 6, characterized in that: The b is 0; and / or the sum of the a1 and the a2 is 0.

8. The temperature control method for a fixed-frequency refrigeration unit according to any one of claims 1 to 7, characterized in that: The fixed-frequency refrigeration unit also includes an economizer, which is arranged between the outlet of the condenser and the inlet of the bypass passage, and the economizer cooperates with the main passage section of the main passage located between the inlet of the compressor and the outlet of the bypass passage in heat exchange.

9. The temperature control method for a fixed-frequency refrigeration unit according to any one of claims 1 to 7, characterized in that: The refrigerant and the coolant flow directions in the heat exchanger are opposite; and / or, the second circulation passage is provided with a pump, and the pump is used to drive the coolant to circulate in the second circulation passage; and / or, the bypass evaporator and the condenser are equipped with a fan, and the airflow generated by the fan passes through the condenser and the bypass evaporator in sequence.

10. A fixed frequency refrigeration unit, characterized in that: The fixed-frequency refrigeration unit operates according to the temperature control method for a fixed-frequency refrigeration unit according to any one of claims 1 to 9.

Images