Control method for an electronic expansion valve of a low-temperature heat pump system

Abstract

A control method for an electronic expansion valve of a low-temperature heat pump system, in which a main circuit electronic expansion valve and a heating auxiliary circuit electronic expansion valve are provided in the low-temperature heat pump system, and the method includes the following steps: Step 1, start the low-temperature heat pump system and run it; Step 2, timely detect the running time t of the compressor of the low-temperature heat pump system. When the running time t≥2 min, enter Step 3; otherwise, enter Step 1; Step 3, timely detect the ambient temperature Ta. When the ambient temperature Ta < C1 and lasts for 60 seconds, enter Step 4; otherwise, enter Step 1; Step 4, timely detect the exhaust superheat ES and the condensation temperature tk. When the exhaust superheat ES > the condensation temperature tk + C3 and lasts for 60 seconds, enter Step 5; otherwise, enter Step 1; Step 5, open the heating auxiliary circuit electronic expansion valve; enter Step 6. The present invention has the characteristics of easy operation, safety and reliability.

Description

Technical Field

[0001] The present invention relates to a control method for an electronic expansion valve of a low-temperature heat pump system. Background Art

[0002] In the prior art, in a low-temperature heat pump heating system at a low ambient temperature, the normal operation of the heat pump system is usually achieved by controlling the flow rate through the opening of a two-loop electronic expansion valve, that is, the main-loop electronic expansion valve and the auxiliary-loop electronic expansion valve are respectively controlled and adjusted according to their respective superheat degrees.

[0003] However, in actual applications, the changes in the respective openings of the two-loop electronic expansion valves will affect each other, resulting in frequent adjustment of the openings. Especially in the case of low ambient temperature and high water temperature, since the refrigerant circulation amount in the system decreases, the opening of the main-loop electronic expansion valve is very small, causing the compressor discharge temperature to be very high, even exceeding 110°C. At this time, the auxiliary-loop electronic expansion valve will quickly open wide, even fully open to 450 steps.

[0004] In this state, two adverse phenomena will occur in the heat pump heating system: 1) The opening of the main-loop electronic expansion valve is opened to the minimum, causing poor oil return or serious liquid return in the heat pump heating system, which seriously affects the reliability of the compressor;

[0005] 2) The compressor discharge temperature of the heat pump heating system drops rapidly, causing the superheat degree of the main loop of the heat pump heating system to increase, resulting in a rapid increase in the opening of the main-loop electronic expansion valve. The heat pump heating system performs a large-scale adjustment of the electronic expansion valve, leading to poor stability of the heat pump heating system; ultimately, it will cause poor reliability and stability of the heat pump heating system, resulting in a decline in the comprehensive performance of the heat pump heating system, low energy efficiency, and even the occurrence of compressor burnout. Summary of the Invention

[0006] The purpose of the present invention is to provide an easy-to-operate control method for an electronic expansion valve of a low-temperature heat pump system to overcome the deficiencies in the prior art.

[0007] A control method for an electronic expansion valve of a low-temperature heat pump system designed according to this purpose, in which a main-loop electronic expansion valve and a heating auxiliary-loop electronic expansion valve are provided in the low-temperature heat pump system, is characterized by including the following steps:

[0008] Step 1, start the low-temperature heat pump system and run it;

[0009] Step 2, timely detect the running time t of the compressor of the low-temperature heat pump system. When the running time t≥2 min, enter Step 3; otherwise, enter Step 1;

[0010] Step 3: Detect the ambient temperature Ta in a timely manner. When the ambient temperature Ta < C1 and lasts for 60 seconds, proceed to Step 4; otherwise, proceed to Step 1.

[0011] Step 4: Detect the exhaust superheat ES and the condensing temperature tk in a timely manner. When the exhaust superheat ES > the condensing temperature tk + C3 and lasts for 60 seconds, proceed to Step 5; otherwise, proceed to Step 1. Wherein, C3 = 18 - 30°C.

[0012] Step 5: Open the heating auxiliary electronic expansion valve; proceed to Step 6.

[0013] Step 6: According to the ambient temperature detected in a timely manner, the central controller of the low-temperature heat pump system adjusts the operating opening of the heating auxiliary electronic expansion valve to its initial heating opening and maintains the operating modulation time t1 = 10 seconds; proceed to Step 7.

[0014] Wherein, the initial heating opening includes an initial heating first opening A1, an initial heating second opening A2, an initial heating third opening A3, and an initial heating fourth opening A4.

[0015] When the ambient temperature Ta ≥ 5°C, the operating opening of the heating auxiliary electronic expansion valve is the initial heating first opening A1.

[0016] When -5°C < the ambient temperature Ta < 5°C, the operating opening of the heating auxiliary electronic expansion valve is the initial heating second opening A2.

[0017] When -10°C < the ambient temperature Ta ≤ -5°C, the operating opening of the heating auxiliary electronic expansion valve is the initial heating third opening A3.

[0018] When the ambient temperature Ta ≤ -10°C, the operating opening of the heating auxiliary electronic expansion valve is the initial heating fourth opening A4.

[0019] A1 = 90 - 110P, A2 = 120 - 140P, A3 = 150 - 160P, A4 = 180 - 240P.

[0020] Step 7: Judge according to the superheat of the heating auxiliary detected in a timely manner, and use the suction superheat of the heating auxiliary to control the adjustment of the operating opening of the heating auxiliary electronic expansion valve. The maximum adjustment range of the operating opening of the heating auxiliary electronic expansion valve ≤ C5; proceed to Step 8.

[0021] Step 8: Detect the exhaust temperature TP of the compressor in a timely manner. When the exhaust temperature TP ≥ C4, proceed to Step 9.

[0022] Step 9: The compressor is directly used with frequency reduction; proceed to Step 1.

[0023] Among them, the value range of C1 is 10 to 15 °C, C4 = 100 to 105 °C, and C5 = 12 to 30P.

[0024] Furthermore, during the operation of the heating auxiliary circuit electronic expansion valve, when any one of the following three conditions is satisfied and maintained for 60 seconds, the heating auxiliary circuit electronic expansion valve closes;

[0025] Condition 1: Timely detect that the ambient temperature Ta ≥ C1 + 2 °C;

[0026] Condition 2: The exhaust superheat ES < the condensation temperature tk + C3 (parameter adjustable) - 5 °C;

[0027] Condition 3: Timely detect that the operating current i of the compressor = 0.

[0028] Furthermore, the operating opening degree adjustment of the main circuit electronic expansion valve is controlled by the main circuit suction superheat.

[0029] Furthermore, the main circuit electronic expansion valve and the heating auxiliary circuit electronic expansion valve are respectively set with upper and lower limit values of the operating opening degree.

[0030] After the present invention adopts the above technical solution, during the opening of the heating auxiliary circuit electronic expansion valve, the exhaust superheat is used as the criterion for judging the opening. That is to say, the exhaust superheat index is used to replace the original exhaust temperature and inlet water temperature indexes. Therefore, not only can the exhaust superheat of the low-temperature heat pump system be ensured at any time to improve the reliability of the compressor, but also the phenomenon that the inlet water temperature is not high and the exhaust temperature of the low-temperature heat pump system is high but cannot be reduced in time at low ambient temperatures can be avoided. Therefore, the working stability of the low-temperature heat pump system is fundamentally improved.

[0031] When the present invention has a high exhaust temperature in the low-temperature heat pump system, it is processed by reducing the frequency, which can quickly make the low-temperature heat pump system reach a stable state, and avoid the phenomenon that the operating opening degree of the heating auxiliary circuit electronic expansion valve is fully opened in the low ambient temperature and high inlet water temperature, thereby improving the safety performance. When the operating opening degree of the heating auxiliary circuit electronic expansion valve is fully opened, it will disrupt the flow control of the operating opening degree of the electronic expansion valve, and even cause problems such as oil return and liquid return in the low-temperature heat pump system, greatly reducing the reliability of the product.

[0032] The main circuit electronic expansion valve and the heating auxiliary circuit electronic expansion valve in the present invention are respectively set with upper and lower limit values of the operating opening degree, which can further reduce the influence of poor opening control on the unit, weaken the influence of poor opening on the stability of the unit, especially at different outdoor ambient temperatures, and this is particularly important.

[0033] In summary, the present invention has the characteristics of easy operation, safety and reliability. Detailed implementation manners

[0034] The present invention will be further described below in conjunction with embodiments.

[0035] A control method for an electronic expansion valve of a low-temperature heat pump system, wherein a main circuit electronic expansion valve and a heating auxiliary circuit electronic expansion valve are provided in the low-temperature heat pump system, and the method is characterized by comprising the following steps:

[0036] Step 1, start the low-temperature heat pump system and run it.

[0037] Step 2, timely detect the running time t of the compressor of the low-temperature heat pump system. When the running time t≥2 min, enter Step 3; otherwise, enter Step 1.

[0038] In this embodiment, the detection period for timely detection can be 0.5 - 2 seconds / time.

[0039] Preferably, the detection period for timely detection can be 0.5 - 1.5 seconds / time.

[0040] It should be noted that the detection period is generally fixed, but it does not prevent the previous detection period from being different from the next one. As for the running time, the above 2 min is only an example, which means that the low-temperature heat pump system has completed initialization; if not, continue to wait for initialization to be completed. The initialization time of different low-temperature heat pump systems determines whether the comparison threshold of the above t is 2 min or other time.

[0041] Step 3, timely detect the ambient temperature Ta. When the ambient temperature Ta < C1 and lasts for 60 seconds, enter Step 4; otherwise, enter Step 1.

[0042] In this embodiment, the value range of C1 is 10 - 15 °C. Usually, C1 can take the value of 12 °C.

[0043] It should be noted that since the present invention is directed to the requirements of low-temperature heat pump heating, when the C1 temperature is higher than 15 °C, in principle, only the main circuit is used for heating; when the value range of C1 is exemplarily 10 - 15 °C, it is a judgment threshold for turning on the auxiliary circuit for heating. As for only using the main circuit for heating, it is not the technical contribution to be made by the present invention, and this can be adjusted according to the existing technology. As for the 60 seconds in Step 3, it is also an exemplary description, aiming to eliminate the influence caused by the adjustment lag of the entire heat pump system in the environment where it acts as much as possible.

[0044] Step 4, timely detect the exhaust superheat ES and the condensation temperature tk. When the exhaust superheat ES > the condensation temperature tk + C3 and lasts for 60 seconds, enter Step 5; otherwise, enter Step 1.

[0045] Among them, C3 = 18 - 30 °C; in practice, C3 can be taken as 25 °C.

[0046] Combined with the above, it can be understood that the judgment of the exhaust superheat degree belongs to another judgment threshold for turning on the auxiliary heating circuit. Only when the judgment conditions of Step 3 and Step 4 are both satisfied, the method disclosed in the present invention enters Step 5 to turn on the electronic expansion valve of the heating auxiliary circuit. It should be noted that the two judgment logics of Step 3 and Step 4 are always established during the operation of the method disclosed in the present invention. The 60 seconds in Step 4 is also an example description, for the same reason as the 60 seconds in Step 3 above. Since the function of the heating auxiliary circuit also includes reducing the exhaust superheat degree, when the exhaust superheat degree can be effectively reduced during the main heating process, naturally the participation of the heating auxiliary circuit is not required. Therefore, to examine whether the exhaust superheat degree ES is high enough to require the assistance of the heating auxiliary circuit, the following judgment condition summarized according to experience in the present invention is: ES > the condensation temperature tk + C3 and lasts for 60 seconds.

[0047] Step 5, turn on the electronic expansion valve of the heating auxiliary circuit; enter Step 6;

[0048] Step 6, according to the timely detected ambient temperature, the central controller of the low-temperature heat pump system adjusts the operating opening of the electronic expansion valve of the heating auxiliary circuit to its initial heating opening and maintains the operating modulation time t1 = 10 seconds; enter Step 7;

[0049] Among them, the initial heating opening includes an initial heating first opening A1, an initial heating second opening A2, an initial heating third opening A3, and an initial heating fourth opening A4;

[0050] When the ambient temperature Ta ≥ 5 °C, the operating opening of the electronic expansion valve of the heating auxiliary circuit is the initial heating first opening A1;

[0051] When -5 °C < Ta < 5 °C, the operating opening of the electronic expansion valve of the heating auxiliary circuit is the initial heating second opening A2;

[0052] When -10 °C < Ta ≤ -5 °C, the operating opening of the electronic expansion valve of the heating auxiliary circuit is the initial heating third opening A3;

[0053] When Ta ≤ -10 °C, the operating opening of the electronic expansion valve of the heating auxiliary circuit is the initial heating fourth opening A4;

[0054] A1 = 90 - 110P, A2 = 120 - 140P, A3 = 150 - 160P, A4 = 180 - 240P;

[0055] In practice, fixed values can also be taken. For example, A1 = 100P, A2 = 140P, A3 = 160P, and A4 = 210P.

[0056] It should be noted that the correspondence between different levels of ambient temperature and the initial opening degree of the heating auxiliary electronic expansion valve during heating determines the speed of heating and whether the entire heat pump system can operate stably during heating. It can be understood that the control method disclosed in the present invention is always aimed at reaching the heating target temperature set by the user as quickly as possible while ensuring the stability of the system, and can avoid the problems faced by the prior art pointed out in the background art. It can be understood that the temperature division in step six and the initial opening degree in the corresponding temperature range are not the only ways pointed to by the above parameters, which mainly depend on coordinating the system stability and the speed of adjustment.

[0057] Step seven, judge according to the timely detection of the superheat degree of the heating auxiliary circuit, and use the suction superheat degree of the heating auxiliary circuit to control the operation opening degree adjustment of the heating auxiliary electronic expansion valve. The maximum adjustment range of the operation opening degree of the heating auxiliary electronic expansion valve ≤ C5; enter step eight;

[0058] It can be understood that the C5 threshold value in step seven is also an empirical value, which needs to be determined through repeated tests. During the test process, it is not only necessary to ensure the stability of the entire system during the adjustment process, but also to make the entire heat pump system reach the heating target temperature set by the user as quickly as possible, and can avoid the problems faced by the prior art pointed out in the background art.

[0059] Step eight, timely detect the exhaust temperature TP of the compressor. When the exhaust temperature TP ≥ C4, enter step nine;

[0060] Step nine, directly reduce the frequency of use of the compressor; enter step one;

[0061] Among them, C4 = 100 - 105 °C, C5 = 12 - 30P.

[0062] It should be noted that when the exhaust gas temperature TP ≥ C4, it means that the exhaust gas temperature is too high at this time and energy efficiency needs to be considered, so the compressor operates at a reduced frequency. If in step eight, the condition of exhaust gas temperature TP ≥ C4 is not met, the state after the most recent adjustment of the heating auxiliary electronic expansion valve is maintained, and it is re-detected whether both step three and step four are satisfied. If one of the conditions in step three and step four is not satisfied, it means that the heating auxiliary is not required to assist the main circuit at this time, and the heating auxiliary can be closed, that is, the heating auxiliary electronic expansion valve is closed. If both step three and step four are satisfied, then steps five to eight are naturally executed again. Once the frequency is reduced, it means that the entire low-temperature heat pump system has entered a new working state, so it is equivalent to entering step one. Therefore, at this time, it is necessary to re-enter the entire control logic of the present invention from step one, step two, etc. in sequence. The auxiliary electronic expansion valve operates in the last state. When executing step three and step four, as described above, when any one of the conditions in step three and step four is not satisfied, the heating auxiliary electronic expansion valve is closed.

[0063] In practice, fixed values can also be taken. For example, A1 = 100P, A2 = 140P, A3 = 160P, A4 = 210P. C4 = 105°C, C5 = 20P.

[0064] During the operation of the heating auxiliary electronic expansion valve, when any one of the following three conditions is satisfied and maintained for 60 seconds, the heating auxiliary electronic expansion valve is closed;

[0065] Condition 1: Timely detect that the ambient temperature Ta ≥ C1 + 2°C;

[0066] Condition 2: The exhaust superheat ES < the condensation temperature tk + C3 - 5°C;

[0067] Condition 3: Timely detect that the operating current i of the compressor = 0.

[0068] In this embodiment, when the operating current i is detected as 0, it means the compressor is shut down, and when i is detected as 1, it means the compressor is started.

[0069] It should be noted that the above three conditions for closing the heating auxiliary electronic expansion valve are the conditions that will be judged as long as the heating auxiliary electronic expansion valve is in operation. All the above parameters are based on empirical values to achieve a balance between the adjustment efficiency and system stability on the premise of system stability. The final values of these parameters are related to the working ability of the compressor involved in the present invention, the working ability of the entire heat pump system, the adjustment ability of the main circuit electronic expansion valve, and the adjustment ability of the electronic expansion valve on the auxiliary circuit. Therefore, it needs to be based on experiments and weighed. All the empirical parameters given in the above embodiments are obtained based on experiments under the selection conditions of a compressor with a displacement of 65, a main circuit electronic expansion valve with a 2.4 - inch diameter, and a heating auxiliary electronic expansion valve with a 1.8 - inch diameter.

[0070] The opening degree adjustment of the main circuit electronic expansion valve is controlled by the superheat degree of the main circuit return air.

[0071] The main circuit electronic expansion valve and the heating auxiliary circuit electronic expansion valve are respectively set with upper limit values and lower limit values of the operating opening degree.

[0072] In practice, after adopting the above technical solution, through long-term repeated operation for a period of time, it is possible to ensure the long-term stable and reliable operation of the low-temperature heat pump system.

[0073] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A control method for an electronic expansion valve of a low-temperature heat pump system, wherein a main circuit electronic expansion valve and a heating auxiliary circuit electronic expansion valve are provided in the low-temperature heat pump system, characterized in that, The control method includes the following steps: Step 1: Start the low-temperature heat pump system and run it; Step 2: Detect the running time t of the compressor of the low-temperature heat pump system in a timely manner. When the running time t ≥ 2 min, go to Step 3; otherwise, go back to Step 1; Step 3: Detect the ambient temperature Ta in a timely manner. When the ambient temperature Ta < C1 and lasts for 60 seconds, go to Step 4; otherwise, go back to Step 1; Step 4: Detect the exhaust superheat ES and the condensation temperature tk in a timely manner. When the exhaust superheat ES > the condensation temperature tk + C3 and lasts for 60 seconds, go to Step 5; otherwise, go back to Step 1; Step 5: Open the heating auxiliary electronic expansion valve; go to Step 6; Step 6: According to the ambient temperature detected in a timely manner, the central controller of the low-temperature heat pump system adjusts the running opening of the heating auxiliary electronic expansion valve to its initial heating opening and maintains the running modulation time for t1 seconds; go to Step 7; Among them, the initial heating opening includes an initial heating first opening A1, an initial heating second opening A2, an initial heating third opening A3, and an initial heating fourth opening A4; When the ambient temperature Ta ≥ 5°C, the running opening of the heating auxiliary electronic expansion valve is the initial heating first opening A1; When -5°C < the ambient temperature Ta < 5°C, the running opening of the heating auxiliary electronic expansion valve is the initial heating second opening A2; When -10°C < the ambient temperature Ta ≤ -5°C, the running opening of the heating auxiliary electronic expansion valve is the initial heating third opening A3; When the ambient temperature Ta ≤ -10°C, the running opening of the heating auxiliary electronic expansion valve is the initial heating fourth opening A4; Step 7: Judge according to the superheat detected in a timely manner in the heating auxiliary circuit, and use the suction superheat in the heating auxiliary circuit to control the adjustment of the running opening of the heating auxiliary electronic expansion valve. The maximum adjustment range of the running opening of the heating auxiliary electronic expansion valve ≤ C5; go to Step 8; Step 8: Detect the exhaust temperature TP of the compressor in a timely manner. When the exhaust temperature TP ≥ C4, go to Step 9; Step 9: The compressor directly reduces the frequency for use; go back to Step 1.

2. The control method of the electronic expansion valve of the low-temperature heat pump system according to claim 1, characterized in that During the operation of the heating auxiliary electronic expansion valve, when any one of the following three conditions is satisfied and lasts for 60 seconds, the heating auxiliary electronic expansion valve closes; Condition 1: Detect the ambient temperature Ta ≥ C1 + 2°C in a timely manner; Condition 2: The exhaust superheat ES < the condensation temperature tk + C3 - 5°C; Condition 3: Detect that the running current i of the compressor = 0 in a timely manner.

3. The control method of the electronic expansion valve of the low-temperature heat pump system according to claim 1 or 2, characterized in that, The adjustment of the running opening of the main electronic expansion valve is controlled by the suction superheat of the main circuit.

4. The control method of the electronic expansion valve of the low-temperature heat pump system according to claim 1 or 2, characterized in that, The main electronic expansion valve and the heating auxiliary electronic expansion valve are respectively set with upper and lower limit values of the running opening.