An oil return control method for an energy storage chiller

Abstract

The present invention discloses an oil return control method for an energy storage chiller, comprising the following steps: S1: Operate the energy storage chiller and determine the operating conditions of the energy storage chiller; S2: Detect the temperature at the bottom of the compressor and calculate the temperature threshold at the bottom of the compressor based on the operating conditions; S3: Judge the relationships between the bottom temperature, the operating time, and the frequency and their corresponding thresholds and execute the oil return scheme; S4: If the oil return time is greater than the time threshold, execute the corresponding operating conditions; if the oil return time is less than or equal to the time threshold and the verification temperature is greater than the verification temperature threshold, do not execute the oil return scheme and return to step S2. The beneficial effects of the present invention are: It can judge the operating state of the compressor based on the temperature at the bottom of the compressor, execute different oil return modes, and achieve accurate control.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage chillers, and particularly relates to an oil return control method for an energy storage chiller. Background Art

[0002] The refrigerant oil reserve of a compressor is of great significance for the stable operation of the compressor. During long-term refrigeration operation or heating operation, the refrigerant oil of the compressor will enter the heat exchanger and pipeline along with the refrigerant. A large amount of refrigerant oil entering the heat exchanger will cause the compressor to lack oil, resulting in wear of the compressor crankshaft, affecting the normal operation of the compressor and even causing damage.

[0003] In the prior art, by increasing the operation time and frequency of the compressor, timed and fixed-frequency oil return is realized, which cannot truly reflect the operation condition and oil return condition of the compressor, and there are problems that the operation state of the compressor cannot be judged based on the bottom temperature of the compressor and different oil return modes cannot be executed.

[0004] For example, a "Hot Water Energy Storage System and Method for a Thermal Power Generation Unit" disclosed in a Chinese patent document, with the publication number: CN112761745A, and the application date: January 20, 2021. This invention discloses an energy storage method for the hot water energy storage system of the thermal power generation unit. When the power grid has a low load requirement, the steam that has not been fully expanded in the thermal power generation unit is extracted and mixed with the cold water in the cold water storage unit to form nearly saturated hot water and stored in the hot water storage unit; when the power grid has a high load requirement, the hot water in the hot water storage unit is extracted and mixed with the boiler water in the thermal power generation unit and supplied to the boiler; this energy storage technology directly stores and releases thermal energy, without multiple conversion processes of various forms of energy, with a relatively high comprehensive energy storage efficiency, large specific heat capacity, good safety, and low price, but there are problems that the operation state of the compressor cannot be judged based on the bottom temperature of the compressor and different oil return modes cannot be executed. Summary of the Invention

[0005] Aiming at the deficiency that the prior art cannot judge the operation state of the compressor based on the bottom temperature of the compressor and execute different oil return modes, the present invention proposes an oil return control method for an energy storage chiller, which can judge the operation state of the compressor based on the bottom temperature of the compressor, execute different oil return modes, and achieve accurate control.

[0006] The following is the technical solution of the present invention. An oil return control method for an energy storage chiller includes the following steps:

[0007] S1: Operate the energy storage chiller and judge the operation condition of the energy storage chiller;

[0008] S2: Detect the bottom temperature of the compressor and calculate the bottom temperature threshold of the compressor based on the operation condition;

[0009] S3: Determine the relationship between the bottom temperature, operating time, and frequency and their corresponding thresholds, and execute the oil return plan;

[0010] S4: If the oil return time is greater than the time threshold, execute the corresponding operating condition; if the oil return time is less than or equal to the time threshold and the verification temperature is greater than the verification temperature threshold, do not execute the oil return plan and return to step S2.

[0011] In this solution, operate the energy storage chiller. When the energy storage chiller is operating, determine the operating condition of the energy storage chiller, detect the bottom temperature of the compressor through devices such as sensors, and based on the operating condition, judge the magnitude relationship between the bottom temperature of the compressor and the bottom temperature threshold. The expression of the bottom temperature threshold is different under different operating conditions. There are several oil return plans set, and execute the oil return plan according to the magnitude relationship. Judge the oil return situation of the energy storage chiller according to the oil return time and verification temperature, and change the operating condition of the energy storage chiller. It can judge the operating state of the compressor based on the bottom temperature of the compressor, execute different oil return modes, and achieve accurate control.

[0012] Preferably, the operating conditions of the energy storage chiller include a heating mode and a non-heating mode.

[0013] In this solution, the energy storage chiller includes a heating mode and a non-heating mode. Under the heating mode and the non-heating mode, the working states of the relevant modules of the energy storage chiller are different. Perform oil return control according to the operating condition, which can improve the accuracy of oil return control and achieve precise control.

[0014] Preferably, the expression of the bottom temperature threshold in the heating mode is:

[0015] A = f·k 1 ·(k 2 -273 / (273+(T 0 -k 3 )·k 4 ))

[0016] In the above formula, A is the bottom temperature threshold in the heating mode, f is the compressor frequency, k 1 , k 2 , k 3 and k 4 are the first coefficient, the second coefficient, the third coefficient, and the fourth coefficient respectively, and T 0 is the ambient temperature.

[0017] In this solution, in the heating mode, the bottom temperature threshold is related to the compressor frequency and ambient temperature, etc. Calculate the bottom temperature threshold through the expression, and then compare the bottom temperature with the bottom temperature threshold, so as to realize the dynamic comparison of the bottom temperature threshold, which can improve the accuracy of oil return control and achieve precise control.

[0018] Preferably, the expression of the bottom temperature threshold in the non-heating mode is:

[0019] B = f·k 5 ·(273 + T 0 ·k 6 / 273)

[0020] In the above formula, B is the bottom temperature threshold in the heating mode, f is the compressor frequency, k 5 and k 6 are the fifth coefficient and the sixth coefficient respectively, and T 0 is the ambient temperature.

[0021] In this solution, in the non-heating mode, the bottom temperature threshold is related to the compressor frequency and the ambient temperature, etc. The bottom temperature threshold is calculated through the expression, and then the bottom temperature and the bottom temperature threshold are compared, so as to realize the dynamic comparison of the bottom temperature threshold, improve the accuracy of the oil return control, and achieve precise control.

[0022] Preferably, the oil return solution includes:

[0023] The first oil return solution: When the compressor frequency reaches the oil return mode, the frequency f = EHz, the running time is T minutes, the speed of the condenser fan is reduced to the lowest speed, and the speed of the evaporator fan is reduced to the lowest speed;

[0024] The second oil return solution: The compressor frequency is increased to the high-frequency oil return mode, the frequency f = FHz, the running time is T minutes, the valve step of the automatic control electronic expansion valve is adjusted, the speed of the condenser fan is reduced to the lowest speed, and the speed of the evaporator fan is reduced to the lowest speed;

[0025] The third oil return solution: When the compressor frequency reaches the oil return mode, the frequency f = EHz, the running time is T minutes, the valve step of the automatic control electronic expansion valve is adjusted, the speed of the condenser fan is reduced to the lowest speed, and the speed of the evaporator fan is reduced to the lowest speed.

[0026] In this solution, several oil return solutions are set, and the relevant modules in each oil return solution correspond to different working states. The modules include the compressor, the electronic expansion valve, the condenser fan, the evaporator fan, etc. The oil return control is realized by controlling the working states of the modules.

[0027] Preferably, in the heating mode, if the bottom temperature of the compressor is less than the bottom temperature threshold, the running time of the energy storage chiller is greater than or equal to the running time threshold, and the compressor frequency is less than or equal to the frequency threshold, the first oil return solution is executed.

[0028] In this solution, different oil return solutions are executed under different conditions. The conditions for executing the first oil return solution are as follows: the operating condition of the energy storage chiller is in the heating mode, the temperature at the bottom of the compressor is less than the bottom temperature threshold, the operating time of the energy storage chiller is greater than or equal to the operating time threshold, and the compressor frequency is less than or equal to the frequency threshold. Determining the execution conditions of the first oil return solution facilitates automatic switching to the first oil return solution, improves the accuracy of oil return control, and achieves precise control.

[0029] Preferably, in the non - heating mode, if the temperature at the bottom of the compressor is greater than or equal to the bottom temperature threshold and the evaporation temperature is less than or equal to the evaporation temperature threshold, the third oil return solution is executed; otherwise, the second oil return solution is executed. If the temperature at the bottom of the compressor is less than the bottom temperature threshold, the operating time of the energy storage chiller is greater than or equal to the operating time threshold, and the compressor frequency is less than or equal to the frequency threshold, the third oil return solution is executed.

[0030] In this solution, different oil return solutions are executed under different conditions. The conditions for executing the second oil return solution are as follows: the operating condition of the energy storage chiller is in the non - heating mode, the temperature at the bottom of the compressor is greater than or equal to the bottom temperature threshold and the evaporation temperature is less than or equal to the evaporation temperature threshold, the third oil return solution is executed; otherwise, the second oil return solution is executed. If the temperature at the bottom of the compressor is less than the bottom temperature threshold, the operating time of the energy storage chiller is greater than or equal to the operating time threshold, and the compressor frequency is less than or equal to the frequency threshold, the third oil return solution is executed. Determining the execution conditions of the second oil return solution and the third oil return solution facilitates automatic switching to the second oil return solution or the third oil return solution, improves the accuracy of oil return control, and achieves precise control.

[0031] Preferably, the verification temperatures include the exhaust temperature, the condensation temperature, and the bottom temperature.

[0032] In this solution, the effect of oil return control is judged by the exhaust temperature, the condensation temperature, and the bottom temperature, which facilitates timely switching of the operating conditions, improves the accuracy of oil return control, and achieves precise control.

[0033] Preferably, when the exhaust temperature is greater than or equal to the exhaust temperature threshold, the condensation temperature is greater than or equal to the condensation temperature threshold, or the temperature at the bottom of the compressor is greater than the high - temperature warning temperature, the oil return mode is exited.

[0034] In this solution, when the oil return time is less than or equal to the time threshold, the relationship between the verification temperature and the verification temperature threshold is judged. If the exhaust temperature is greater than or equal to the exhaust temperature threshold, the condensation temperature is greater than or equal to the condensation temperature threshold, or the temperature at the bottom of the compressor is greater than the high - temperature warning temperature, the oil return mode is exited, which facilitates timely switching of the operating conditions, improves the accuracy of oil return control, and achieves precise control.

[0035] The beneficial effects of the present invention are as follows: By comparing the temperature at the bottom of the compressor with a threshold value, the operating state of the compressor is judged, and further whether the compressor is lacking oil is judged. The value of the threshold is obtained through a function operation of the ambient temperature, the operating frequency of the compressor and the relevant system, so as to realize intelligent judgment. The specific situation of oil shortage is confirmed through the operating time and the operating frequency; in combination with the evaporation temperature judgment, the system adjustment is confirmed, different oil return modes are executed, the corresponding oil return frequency and the actions of other components are set, and accurate control is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Flow chart of an oil return control method for an energy storage water chiller of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The technical solution of the present invention will be further specifically described below through embodiments and in conjunction with the drawings.

[0038] Embodiment: As Figure 1 shown, an oil return control method for an energy storage water chiller includes the following steps:

[0039] S1: Operate the energy storage water chiller and judge the operating condition of the energy storage water chiller;

[0040] S2: Detect the temperature at the bottom of the compressor and calculate the temperature threshold at the bottom of the compressor based on the operating condition;

[0041] S3: Judge the relationship between the bottom temperature, the operating time and the frequency and the corresponding threshold values and execute the oil return plan;

[0042] S4: If the oil return time is greater than the time threshold, execute the corresponding operating condition; if the oil return time is less than or equal to the time threshold and the verification temperature is greater than the verification temperature threshold, do not execute the oil return plan and return to step S2.

[0043] In S1, the energy storage water chiller is operated, and the operating condition of the energy storage water chiller is judged during the operation of the energy storage water chiller. The operating conditions include a heating mode and a non-heating mode.

[0044] In S2 and S3, the temperature Td at the bottom of the compressor is detected by devices such as sensors, and the size relationship between the temperature at the bottom of the compressor and the temperature threshold at the bottom is judged based on the operating condition. The expression of the temperature threshold at the bottom is different under different operating conditions.

[0045] In the heating mode, the expression of the temperature threshold at the bottom is:

[0046] A = f·k 1 ·(k 2 -273 / (273+(T 0 -k 3 )·k 4 ))

[0047] In the above formula, A is the bottom temperature threshold in the heating mode, f is the compressor frequency, and k 1 , k 2 , k 3 and k 4 are the first coefficient, the second coefficient, the third coefficient, and the fourth coefficient respectively, and T 0 is the ambient temperature. k 1 , k 2 , k 3 and k 4 are set according to the actual situation. In this solution, k 1 is 1.1, k 2 is 2, k 3 is 6, and k 4 is 3.

[0048] In the non-heating mode, the expression for the bottom temperature threshold is:

[0049] B = f·k 5 ·(273 + T 0 ·k 6 / 273)

[0050] In the above formula, B is the bottom temperature threshold in the heating mode, f is the compressor frequency, and k 5 and k 6 are the fifth coefficient and the sixth coefficient respectively, and T 0 is the ambient temperature. k 5 and k 6 are set according to the actual situation. In this solution, k 5 is 1.1 and k 6 is 3.

[0051] Based on the operating conditions, the size relationship between the bottom temperature of the compressor and the bottom temperature threshold is judged. When the energy storage chiller is in heating operation, the lubrication system inside the compressor comes from the compressor's refrigerant oil, which lubricates and dissipates heat from the moving mechanism through the oil film. During the winter heating process, due to the low temperature conditions, in order to achieve the heating effect, the compressor is in a high-frequency operation state for a long time, and the evaporation temperature is too low, resulting in the accumulation of refrigerant oil in the evaporator, causing poor oil return of the compressor, leading to oil shortage in the compressor, resulting in compressor damage. At the same time, in winter, the outdoor temperature is relatively low, and during the compressor shutdown process, refrigerant liquid return occurs, resulting in excessive dissolution of refrigerant in the compressor's refrigerant oil, resulting in poor formation of the oil film and serious wear of the compressor.

[0052] In the heating mode, if the bottom temperature Td of the compressor is greater than or equal to the bottom temperature threshold A, the energy storage chiller operates normally and returns to step S2; if the bottom temperature Td of the compressor is less than the bottom temperature threshold A, then the relationship between the operating time t of the energy storage chiller, the operating time threshold M, the compressor frequency f and the frequency threshold D is judged: if the operating time t of the energy storage chiller is greater than or equal to the operating time threshold M and the compressor frequency f is less than or equal to the frequency threshold D, the first oil return scheme is executed; otherwise, the energy storage chiller operates normally and returns to step S2.

[0053] When operating at high frequency in the non - heating mode, the compressor pumps out more refrigerant oil, resulting in poor oil return. Regular medium - frequency oil return is required. When operating at low frequency, due to the low refrigerant flow rate, it accumulates in the evaporator, resulting in poor oil return. High - frequency operation is required to accelerate the oil return speed of the refrigerant and refrigerant oil in the evaporator to achieve rapid oil return.

[0054] In the non - heating mode, if the bottom temperature Td of the compressor is greater than or equal to the bottom temperature threshold B, it indicates that the compressor lacks oil and the temperature is abnormal. The relationship between the evaporation temperature Te and the evaporation temperature threshold Y is judged. If the evaporation temperature Te is less than or equal to the evaporation temperature threshold Y, the third oil return scheme is executed; otherwise, the second oil return scheme is executed. If the bottom temperature Td of the compressor is less than the bottom temperature threshold B, then the relationship between the operating time t of the energy storage chiller, the operating time threshold M, the compressor frequency f and the frequency threshold D is judged: if the operating time t of the energy storage chiller is greater than or equal to the operating time threshold M and the compressor frequency f is less than or equal to the frequency threshold D, the third oil return scheme is executed; otherwise, the energy storage chiller operates normally and returns to step S2.

[0055] The first oil return scheme: The compressor frequency reaches the oil return mode, the frequency f = EHz, the operating time is 3 minutes, the condensing fan speed is reduced to the lowest speed, and the evaporating fan speed is reduced to the lowest speed.

[0056] The second oil return scheme: The compressor frequency is increased to the high - frequency oil return mode, the frequency f = FHz, the operating time is 3 minutes, the electronic expansion valve valve step is automatically controlled, the condensing fan speed is reduced to the lowest speed, and the evaporating fan speed is reduced to the lowest speed.

[0057] The third oil return scheme: The compressor frequency reaches the oil return mode, the frequency f = EHz, the operating time is 3 minutes, the electronic expansion valve valve step is automatically controlled, the condensing fan speed is reduced to the lowest speed, and the evaporating fan speed is reduced to the lowest speed.

[0058] In S4, after 3 minutes of the oil return mode, the oil return mode automatically exits and returns to the current operating state. If within 3 minutes, the exhaust gas temperature is greater than or equal to the exhaust gas temperature threshold, the condensation temperature is greater than or equal to the condensation temperature threshold, or a high-temperature warning occurs (i.e., the temperature at the bottom of the compressor is greater than the high-temperature warning temperature), the oil return mode is exited and the process returns to step S2 for detection.

[0059] In this solution, by comparing the temperature at the bottom of the compressor with the threshold value, the operating state of the compressor is judged, and then whether the compressor is short of oil is judged. The value of the threshold is obtained through a function operation of the ambient temperature, the operating frequency of the compressor, and the relevant system, so as to achieve intelligent judgment. The specific situation of oil shortage is confirmed through the running time and running frequency; combined with the evaporation temperature judgment, the system adjustment is confirmed, different oil return modes are executed, the corresponding oil return frequency and the actions of other components are set, so as to achieve accurate control.

Claims

1. An oil return control method for an energy storage chiller, characterized in that, it includes the following steps: S1: Operate the energy storage chiller and judge the operating conditions of the energy storage chiller; S2: Detect the temperature at the bottom of the compressor, calculate the temperature threshold at the bottom of the compressor based on the operating conditions. In the heating mode, the bottom temperature threshold A = f·k 1 ·(k 2 -273 / (273+(T 0 -k 3 )·k 4 )),where f is the compressor frequency, and k 1 、k 2 、k 3 and k 4 are the first coefficient, the second coefficient, the third coefficient and the fourth coefficient respectively, and T 0 is the ambient temperature; S3: Judge the relationship between the bottom temperature, operating time and frequency and the corresponding thresholds and execute the oil return plan; S4: If the oil return time is greater than the time threshold, execute the corresponding operating conditions; if the oil return time is less than or equal to the time threshold and the verification temperature is greater than the verification temperature threshold, do not execute the oil return plan and return to step S2. The verification temperature includes the exhaust temperature, condensation temperature and compressor bottom temperature.

2. The oil return control method for an energy storage chiller according to claim 1, characterized in that, the operating conditions of the energy storage chiller include a heating mode and a non - heating mode.

3. The oil return control method for an energy storage chiller according to claim 2, characterized in that, the expression of the bottom temperature threshold in the non - heating mode is: B = f·k 5 ·(273 + T 0 ·k 6 / 273) In the above formula, B is the bottom temperature threshold in the heating mode, f is the compressor frequency, k 5 and k 6 are the fifth coefficient and the sixth coefficient respectively, and T 0 is the ambient temperature.

4. The oil return control method for an energy storage chiller according to claim 1, characterized in that, the oil return plan includes: The first oil return plan: The compressor frequency reaches the oil return mode, the frequency f = EHz, the operating time is T minutes, the speed of the condensation fan is reduced to the lowest speed, and the speed of the evaporation fan is reduced to the lowest speed; The second oil return plan: The compressor frequency is increased to the high - frequency oil return mode, the frequency f = FHz, the operating time is T minutes, the electronic expansion valve valve step is automatically controlled, the speed of the condensation fan is reduced to the lowest speed, and the speed of the evaporation fan is reduced to the lowest speed; The third oil return plan: The compressor frequency reaches the oil return mode, the frequency f = EHz, the operating time is T minutes, the electronic expansion valve valve step is automatically controlled, the speed of the condensation fan is reduced to the lowest speed, and the speed of the evaporation fan is reduced to the lowest speed.

5. The oil return control method for an energy storage chiller according to claim 4, characterized in that, in the heating mode, if the compressor bottom temperature is less than the bottom temperature threshold and the operating time of the energy storage chiller is greater than or equal to the operating time threshold and the compressor frequency is less than or equal to the frequency threshold, execute the first oil return plan.

6. The oil return control method for an energy storage chiller according to claim 4, characterized in that, in the non - heating mode, if the compressor bottom temperature is greater than or equal to the bottom temperature threshold and the evaporation temperature is less than or equal to the evaporation temperature threshold, execute the third oil return plan, otherwise, execute the second oil return plan; if the compressor bottom temperature is less than the bottom temperature threshold and the operating time of the energy storage chiller is greater than or equal to the operating time threshold and the compressor frequency is less than or equal to the frequency threshold, execute the third oil return plan.

7. The oil return control method for an energy storage chiller according to claim 1, characterized in that, when the exhaust temperature is greater than or equal to the exhaust temperature threshold, the condensation temperature is greater than or equal to the condensation temperature threshold or the compressor bottom temperature is greater than the high - temperature warning temperature, exit the oil return mode.

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