Variable-frequency refrigerating system adopting hot gas bypass valve for oil return

Abstract

The utility model relates to the technical field of variable-frequency refrigeration, in particular to a variable-frequency refrigeration system adopting a hot gas bypass valve for oil return. Comprising an evaporator, a condenser and an inverter compressor, the oil return module is used for returning lubricating oil retained in the evaporator through the inverter compressor; the variable-frequency refrigerating system further comprises a liquid supply module used for adjusting the frequency of the variable-frequency compressor to supply liquid to the evaporator by controlling the air suction superheat degree of the variable-frequency compressor. The auxiliary oil return module is used for assisting the variable-frequency compressor to return the lubricating oil retained in the evaporator; by synchronously increasing the opening degree of the hot gas bypass electronic expansion valve, the opening degree of the liquid supply electronic expansion valve and the frequency of the inverter compressor, the air flow rate in the evaporator and the air suction pipe is increased, the refrigerating capacity of the evaporator is guaranteed, oil return of the inverter compressor is guaranteed, long-term operation of a refrigerating system is achieved, and temperature control precision is not affected.

Description

Technical Field

[0001] The utility model relates to the technical field of variable frequency refrigeration, in particular to a variable frequency refrigeration system adopting a hot gas bypass valve for oil return. Background Art

[0002] In a refrigeration system using a variable frequency compressor, when the cooling capacity required on the load side is low, the compressor frequency is reduced, the refrigerant flow rate is reduced, and the refrigerant flow rate from the evaporator to the compressor is reduced. In the suction pipe, the gaseous refrigerant cannot dissolve the lubricating oil, and the lubricating oil droplets will adhere to the inner wall of the pipe and be pushed back into the compressor by the airflow. When the gaseous refrigerant flow rate in the suction pipe is lower than 4m / s, the airflow speed is not enough to drive the lubricating oil back to the compressor. In addition, the lower the suction temperature of the compressor, the greater the viscosity of the lubricating oil, and the higher the minimum flow rate of the refrigerant in the suction pipe to bring back the lubricating oil.

[0003] In order to ensure the long-term stable operation of the refrigeration system, the compressor needs to return oil normally. For conventional variable frequency refrigeration systems, when running at low frequency, the lubricating oil retained in the heat exchanger or pipeline can be brought back to the compressor by loading the compressor frequency after a certain period of operation, thereby achieving long-term operation of the refrigeration system. However, for equipment that requires precise temperature control, such as chiller refrigeration systems, temperature fluctuations within a large range caused by compressor frequency loading are not allowed during adjustment and control, which affects the accuracy of temperature control. Utility Model Content

[0004] In view of the shortcomings of the prior art, the utility model provides a variable frequency refrigeration system with a hot gas bypass valve for oil return, which solves the problem of affecting the temperature control accuracy by only returning oil by loading the compressor frequency. It has the advantages of ensuring the oil return of the compressor without affecting the temperature control accuracy.

[0005] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0006] A variable frequency refrigeration system using a hot gas bypass valve to return oil, comprising an evaporator, a condenser and a variable frequency compressor; and an oil return module for returning the lubricating oil retained in the evaporator through the variable frequency compressor; the variable frequency refrigeration system also includes a liquid supply module for supplying liquid to the evaporator by controlling the suction superheat of the variable frequency compressor and adjusting the frequency of the variable frequency compressor; and an auxiliary oil return module for assisting the variable frequency compressor in returning the lubricating oil retained in the evaporator; the liquid supply module includes a liquid return module connected to the output end of the condenser The auxiliary oil return module comprises a hot gas bypass electronic expansion valve, and an exhaust pipe is connected between the input end of the evaporator and the liquid supply electronic expansion valve through the liquid supply pipe.

[0007] Furthermore, the oil return module includes an intake pipe connected to the output end of the evaporator, and an intake pressure test, a gas-liquid separator, a low-pressure sensor and an intake thermometer are sequentially arranged on the intake pipe. The intake thermometer is connected to one end of the variable frequency compressor through the intake pipe, and the other end of the variable frequency compressor is connected to the exhaust thermometer through the exhaust pipe.

[0008] Furthermore, the output end of the evaporator and the suction pressure test are connected to the liquid injection electronic expansion valve through the suction pipe.

[0009] Furthermore, the exhaust thermometer and the hot gas bypass electronic expansion valve are connected to the input end of the condenser through the exhaust pipe.

[0010] Furthermore, the input end of the condenser is also connected to a cooling water inlet pipe, and the output end of the condenser is also connected to a cooling water outlet pipe.

[0011] Furthermore, the input end of the evaporator is also connected to a chilled water inlet pipe, on which an inlet thermometer is provided, and the output end of the evaporator is also connected to a chilled water outlet pipe, on which an outlet thermometer is provided.

[0012] Compared with the prior art, the utility model provides a variable frequency refrigeration system using a hot gas bypass valve to return oil, which has the following beneficial effects:

[0013] 1. The utility model increases the gas flow rate in the evaporator and the suction pipe and ensures the cooling capacity of the evaporator by synchronously increasing the opening of the hot gas bypass electronic expansion valve, the opening of the liquid supply electronic expansion valve and the frequency of the variable frequency compressor, thereby ensuring the oil return of the variable frequency compressor, realizing the long-term operation of the refrigeration system without affecting the temperature control accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0015] Figure 1 This is a schematic diagram of a variable frequency refrigeration system using a hot gas bypass valve to return oil according to the utility model;

[0016] Figure 2 It is a schematic diagram of the connection between the oil return module, the liquid supply module and the auxiliary oil return module of the utility model;

[0017] Figure 3 This is a flow calculation formula table for the electronic expansion valve of the utility model.

[0018] In the figure:

[0019] 1. Evaporator; 2. Condenser; 3. Variable frequency compressor;

[0020] 4. Oil return module; 41. Suction pipe; 42. Suction pressure test; 43. Gas-liquid separator; 44. Low pressure sensor; 45. Suction thermometer; 46. Exhaust thermometer;

[0021] 5. Liquid supply module; 51. Liquid supply pipe; 52. High pressure sensor; 53. Liquid supply thermometer; 54. Liquid supply electronic expansion valve; 55. Liquid spray pipe; 56. Liquid spray electronic expansion valve;

[0022] 6. Auxiliary oil return module; 61. Hot gas bypass electronic expansion valve; 62. Exhaust pipe. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0024] For a refrigeration system using a variable frequency compressor, in order to ensure that the refrigeration system can operate stably for a long time, it is necessary to make the compressor return oil normally. For a conventional variable frequency refrigeration system, when operating at a low frequency, after a certain period of operation, the lubricating oil retained in the heat exchanger or pipeline can be brought back to the compressor by loading the compressor frequency, thereby realizing long-term operation of the refrigeration system. However, for equipment that requires precise temperature control, temperature fluctuations within a large range caused by compressor frequency loading are not allowed during adjustment and control, which affects the accuracy of temperature control. The utility model assists the compressor in oil return through a hot gas bypass electronic expansion valve. The hot gas bypass electronic expansion valve is an electronic expansion valve with adjustable opening. During normal operation, in order to reduce system energy consumption, the refrigeration system only opens the liquid supply electronic expansion valve, and the liquid injection electronic expansion valve controls the suction superheat. The compressor frequency is adjusted to make the unit output cooling capacity meet the demand. When low-frequency operation of the compressor and other abnormalities are detected, the hot gas bypass electronic expansion valve is adjusted to assist the compressor in oil return, thereby realizing long-term operation of the refrigeration system without affecting the temperature control accuracy.

[0025] Figure 1-Figure 3 This is an embodiment of the utility model: a variable frequency refrigeration system using a hot gas bypass valve to return oil, comprising an evaporator 1, a condenser 2 and a variable frequency compressor 3; an oil return module 4 is used to return the lubricating oil retained in the evaporator 1 through the variable frequency compressor 3, and the refrigerant in the evaporator 1 is evaporated back to the variable frequency compressor 3 through the oil return module 4, and the refrigerant returning to the variable frequency compressor 3 carries the lubricating oil; the variable frequency refrigeration system also includes a liquid supply module 5 for supplying liquid to the evaporator 1 by controlling the suction superheat of the variable frequency compressor 3 and adjusting the frequency of the variable frequency compressor 3; an auxiliary oil return module 6 assists the variable frequency compressor 3 in returning the lubricating oil retained in the evaporator 1; the liquid supply module 5 comprises a liquid supply pipe 51 connected to the output end of the condenser 2, the output end of the condenser 2 is connected to a high-pressure sensor 52, a liquid supply thermometer 53 and a liquid supply electronic expansion valve 54 in sequence through the liquid supply pipe 51, the liquid supply electronic expansion valve 54 is connected to the input end of the evaporator 1 through the liquid supply pipe 51, a liquid spray pipe 55 is connected between the high-pressure sensor 52 and the liquid supply thermometer 53 through the liquid supply pipe 51, and a liquid spray electronic expansion valve 56 is arranged on the liquid spray pipe 55; the auxiliary oil return module 6 comprises a hot gas bypass electronic expansion valve 61, and an exhaust pipe 62 is connected between the input end of the evaporator 1 and the liquid supply electronic expansion valve 54 through the liquid supply pipe 51 and the hot gas bypass electronic expansion valve 61.

[0026] During normal operation, in order to reduce system energy consumption, the refrigeration system only opens the liquid supply electronic expansion valve 54, and the liquid supply electronic expansion valve 54 controls the suction superheat, and adjusts the frequency of the variable frequency compressor 3 so that the cooling capacity output by the unit meets the demand. When the variable frequency compressor 3 is detected to be running at a low frequency, the low frequency running time is recorded. When the running time is greater than 40 minutes, and the difference between the saturated temperature of the refrigerant in the evaporator 1 and the average temperature difference between the inlet and outlet water on the liquid supply side increases, it is determined that the thermal conductivity of the evaporator 1 decreases due to excessive retained lubricating oil, and the heat exchange temperature difference increases. The system needs to increase the refrigerant flow in the evaporator 1 to return the retained lubricating oil to the compressor, and the hot gas bypass electronic expansion valve 61 is adjusted. The auxiliary variable frequency compressor 3 returns oil, and the hot gas bypass electronic expansion valve 61 is an electronic expansion valve with adjustable opening. The lubricating oil retained in the heat exchanger or pipeline is brought back to the variable frequency compressor 3 only by loading the frequency of the variable frequency compressor 3. There will be temperature fluctuations in a large range due to the frequency loading of the variable frequency compressor 3, affecting the accuracy of temperature control. By synchronously increasing the opening of the hot gas bypass electronic expansion valve 61, the opening of the liquid supply electronic expansion valve 54 and the frequency of the variable frequency compressor 3, the gas flow rate in the evaporator 1 is increased and the cooling capacity of the evaporator 1 is guaranteed, thereby ensuring the oil return of the variable frequency compressor 3 and realizing long-term operation of the refrigeration system without affecting the temperature control accuracy.

[0027] As a preferred technical solution of this embodiment, the oil return module 4 includes an intake pipe 41 connected to the output end of the evaporator 1, and an intake pressure test 42, a gas-liquid separator 43, a low pressure sensor 44 and an intake thermometer 45 are sequentially arranged on the intake pipe 41. The intake thermometer 45 is connected to one end of the variable frequency compressor 3 through the intake pipe 41, and the other end of the variable frequency compressor 3 is connected to the exhaust thermometer 46 through the exhaust pipe 62. The output end of the evaporator 1 and the intake pressure test 42 are connected to the liquid injection electronic expansion valve 56 through the intake pipe 41. The intake superheat or the amount of liquid in the intake pipe 41 is adjusted by the liquid injection electronic expansion valve 56 to reduce the exhaust temperature in the exhaust pipe 62. When the opening of the hot gas bypass electronic expansion valve 61, the opening of the liquid supply electronic expansion valve 54 and the frequency of the variable frequency compressor 3 are increased synchronously, the gas flow rate in the evaporator 1 is increased, and thus the gas flow rate in the intake pipe 41 is also increased.

[0028] As a preferred technical solution of this embodiment, the exhaust thermometer 46 and the hot gas bypass electronic expansion valve 61 are connected to the input end of the condenser 2 through the exhaust pipe 62. The input end of the condenser 2 is also connected to a cooling water inlet pipe, and the output end of the condenser 2 is also connected to a cooling water outlet pipe. The gas in the exhaust pipe 62 enters the condenser 2, is cooled and liquefied into liquid by the condenser 2, and is output through the liquid supply pipe 51.

[0029] As a preferred technical solution of this embodiment, the input end of the evaporator 1 is also connected to a chilled water inlet pipe, on which an inlet thermometer is provided, and the output end of the evaporator 1 is also connected to a chilled water outlet pipe, on which an outlet thermometer is provided.

[0030] The variable frequency refrigeration system using hot gas bypass valve oil return proposed in this embodiment ensures oil return of the compressor by adjusting the electronic expansion valve and the variable frequency compressor, thereby achieving long-term operation of the refrigeration system without affecting the temperature control accuracy. The specific adjustment process is as follows:

[0031] The NIST software is called in the control program, and the system exhaust temperature, high pressure, liquid supply temperature, suction temperature, low pressure, etc. are calculated based on the system exhaust temperature, high pressure, liquid supply temperature, suction temperature, low pressure, etc. Figure 1 As shown, the enthalpy and density parameters of the first state point, the second state point, the third state point and the fourth state point can be found; Figure 3 As shown, according to the electronic expansion valve flow calculation formula and the parameter values ​​of each state point, the following parameters can be calculated according to the formula: the increase in liquid refrigerant flow corresponding to the opening of the liquid supply electronic expansion valve 54 by one step; the increase in gaseous refrigerant flow corresponding to the opening of the hot gas bypass electronic expansion valve 61 by one step; the enthalpy difference between the second state point and the fourth state point; the enthalpy difference between the first state point and the fourth state point; based on the calculated refrigerant flow change and the enthalpy difference of each state point, calculate the increase in system cooling capacity ΔQ1 for each step opening of the liquid supply electronic expansion valve 54 and the decrease in system cooling capacity ΔQ2 for each step opening of the hot gas bypass electronic expansion valve 61; during the adjustment process, the liquid supply electronic expansion valve 54 and the hot gas bypass electronic expansion valve 61 are adjusted in inverse proportion to ΔQ1 / ΔQ2.

[0032] According to the number of steps of increase of the liquid supply electronic expansion valve 54 and the hot gas bypass electronic expansion valve 61, the mass flow rate of the increase in the refrigerant flow rate is calculated and converted into the increase in the volume flow rate at the fourth state point; according to the increase in the volume flow rate and the exhaust volume of the variable frequency compressor 3, the frequency increase of the variable frequency compressor 3 is calculated; the frequency target of the variable frequency compressor 3 is set to the minimum oil return frequency, and the final valve opening steps of the liquid supply electronic expansion valve 54 and the hot gas bypass electronic expansion valve 61 are calculated according to this frequency; when the variable frequency compressor 3 is actually adjusted, after the frequencies of the electronic expansion valve and the variable frequency compressor 3 are both turned on to the target values, the PID adjustment method can be used to control the liquid supply temperature on the evaporator 1 side, so that the liquid supply temperature is finally stabilized near the target value. By using this method for adjustment, the cooling capacity output by the evaporator 1 is relatively stable.

[0033] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0034] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A variable frequency refrigeration system using a hot gas bypass valve for oil return, comprising an evaporator (1), a condenser (2) and a variable frequency compressor (3); and an oil return module (4) for returning lubricating oil retained in the evaporator (1) through the variable frequency compressor (3); characterized in that: The variable frequency refrigeration system further comprises a liquid supply module (5) for supplying liquid to the evaporator (1) by controlling the suction superheat of the variable frequency compressor (3) and adjusting the frequency of the variable frequency compressor (3); and an auxiliary oil return module (6) for assisting the variable frequency compressor (3) in returning the lubricating oil retained in the evaporator (1); The liquid supply module (5) comprises a liquid supply pipe (51) connected to the output end of the condenser (2); the output end of the condenser (2) is connected to a high-pressure sensor (52), a liquid supply thermometer (53) and a liquid supply electronic expansion valve (54) in sequence through the liquid supply pipe (51); the liquid supply electronic expansion valve (54) is connected to the input end of the evaporator (1) through the liquid supply pipe (51); a liquid spray pipe (55) is connected between the high-pressure sensor (52) and the liquid supply thermometer (53) through the liquid supply pipe (51); and a liquid spray electronic expansion valve (56) is arranged on the liquid spray pipe (55); The auxiliary oil return module (6) comprises a hot gas bypass electronic expansion valve (61), and an exhaust pipe (62) is connected between the input end of the evaporator (1) and the liquid supply electronic expansion valve (54) via the liquid supply pipe (51) and the hot gas bypass electronic expansion valve (61).

2. A variable frequency refrigeration system using a hot gas bypass valve for oil return according to claim 1, characterized in that: The oil return module (4) comprises an intake pipe (41) connected to the output end of the evaporator (1); an intake pressure tester (42), a gas-liquid separator (43), a low pressure sensor (44) and an intake thermometer (45) are sequentially arranged on the intake pipe (41); the intake thermometer (45) is connected to one end of the variable frequency compressor (3) through the intake pipe (41); and the other end of the variable frequency compressor (3) is connected to the exhaust thermometer (46) through the exhaust pipe (62).

3. A variable frequency refrigeration system using a hot gas bypass valve for oil return according to claim 2, characterized in that: The output end of the evaporator (1) and the suction pressure test (42) are connected to the liquid injection electronic expansion valve (56) through the suction pipe (41).

4. A variable frequency refrigeration system using a hot gas bypass valve for oil return according to claim 3, characterized in that: The exhaust gas thermometer (46) and the hot gas bypass electronic expansion valve (61) are connected to the input end of the condenser (2) via the exhaust pipe (62).

5. The variable frequency refrigeration system using hot gas bypass valve oil return according to claim 1, characterized in that: The input end of the condenser (2) is also connected to a cooling water inlet pipe, and the output end of the condenser (2) is also connected to a cooling water outlet pipe.

6. The variable frequency refrigeration system using hot gas bypass valve oil return according to claim 1, characterized in that: The input end of the evaporator (1) is also connected to a chilled water inlet pipe, on which a water inlet thermometer is provided; the output end of the evaporator (1) is also connected to a chilled water outlet pipe, on which a water outlet thermometer is provided.

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