A refrigeration and antifreeze control method for air-conditioning plate heat exchanger

Abstract

The present invention mainly relates to the field of air conditioner control technology. In order to solve the problems of antifreeze protection hysteresis and poor sensitivity when using the inlet and outlet water temperatures collected from the water side to control the refrigeration antifreeze protection of a plate heat exchanger, and rough and easy misjudgment of the refrigeration antifreeze protection control of the plate heat exchanger from the fluorine side, the present invention provides an air-conditioning plate heat exchanger refrigeration antifreeze control method, wherein temperature sensors are respectively arranged at the refrigerant inlet and outlet of the plate heat exchanger and the water outlet on the water side to collect the refrigerant inlet temperature Tin, the refrigerant outlet temperature Tout, and the water temperature Tw at the water side outlet; when a fixed-frequency compressor is used, the opening of an electronic expansion valve is controlled by analyzing the water temperature of the inlet and outlet of the plate heat exchanger on the water side and the refrigerant temperature of the inlet and outlet to perform refrigeration antifreeze protection control; when a variable-frequency compressor is used, the frequency of the compressor and the opening of the electronic expansion valve are controlled by analyzing the temperature of the refrigerant inlet and outlet of the plate heat exchanger and the water temperature of the water side inlet and outlet to perform refrigeration antifreeze protection control.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of air conditioner control, and in particular to a refrigeration and antifreeze control method for an air conditioner plate heat exchanger. Background Art

[0002] As a heat exchange device, plate heat exchanger is often used in air conditioning cooling water system due to its small size, high heat exchange efficiency, strong anti-corrosion performance and low price. However, due to its special internal structure, it is very easy to freeze and fail under refrigeration conditions, so plate heat exchanger refrigeration antifreeze protection is required. Traditional plate heat exchanger refrigeration antifreeze protection methods are mainly divided into two directions, namely refrigeration antifreeze protection from the water side or the fluorine side. The antifreeze protection from the water side is mainly carried out by collecting the parameters such as the inlet and outlet water temperature, water flow, inlet and outlet water pressure drop of the plate heat exchanger for comprehensive judgment, and then the antifreeze protection action is performed. This method has a certain hysteresis and cannot judge the current heat exchange state of the water side and the fluorine side of the plate heat exchanger well. When the water side of the plate heat exchanger is partially dirty and blocked, the plate heat exchanger is prone to freezing failure; the antifreeze protection from the fluorine side is mainly carried out by collecting the evaporation pressure on the fluorine side of the plate heat exchanger to perform antifreeze protection on the plate heat exchanger. Compared with the protection from the water side, this antifreeze protection method has lower hysteresis and can more effectively protect the plate heat exchanger, but it needs to be configured with corresponding pressure sensors, which is expensive. At the same time, this antifreeze protection method usually controls the start and stop of the unit to perform antifreeze protection on the plate heat exchanger by comparing the collected evaporator pressure value with the set threshold value. It is not associated with the compressor frequency, electronic expansion valve control, etc., and the control is rough, which is easy to cause misjudgment. Summary of the invention

[0003] The technical problems to be solved by the present invention are:

[0004] A refrigeration antifreeze control method for an air-conditioning plate heat exchanger is provided to solve the following problems: 1. The refrigeration antifreeze protection control of the plate heat exchanger is performed by collecting the inlet and outlet water temperatures from the water side, which has the problems of antifreeze protection lag and poor sensitivity; 2. The refrigeration antifreeze protection of the plate heat exchanger is performed from the fluorine side by using a pressure sensor, which has high cost, rough control and is prone to misjudgment.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0006] A refrigeration antifreeze control method for an air-conditioning plate heat exchanger, wherein temperature sensors are respectively arranged on the refrigerant side and the water side of the plate heat exchanger to collect the refrigerant inlet temperature Tin, the refrigerant outlet temperature Tout, and the water side outlet water temperature Tw; when the air-conditioning compressor is a fixed-frequency compressor, the opening of an electronic expansion valve is controlled by analyzing the water side outlet water temperature Tw of the plate heat exchanger and the refrigerant inlet temperature Tin and the refrigerant outlet temperature Tout to perform refrigeration antifreeze protection control; when the air-conditioning compressor is a variable-frequency compressor, the frequency of the compressor and the opening of the electronic expansion valve are controlled by analyzing the water side outlet water temperature Tw of the plate heat exchanger, the refrigerant inlet temperature Tin and the refrigerant outlet temperature Tout to perform refrigeration antifreeze protection control.

[0007] Furthermore, when the air-conditioning compressor is a fixed-frequency compressor, the method includes the following steps:

[0008] Step 1: Determine whether Tw is greater than T1, where T1 is the set refrigeration antifreeze protection temperature of the water side of the plate heat exchanger. If so, trigger the refrigeration antifreeze protection action; if not, proceed to step 2;

[0009] Step 2: Determine whether Tout is less than or equal to T2, where T2 is the set refrigeration antifreeze protection temperature of the fluorine side of the plate heat exchanger. If so, proceed to step 3; if not, proceed to step 6;

[0010] Step 3: Determine whether Tin is less than or equal to T2; if so, trigger the refrigeration antifreeze protection action, if not, go to step 4;

[0011] Step 4: Determine whether Tout is less than Tout_old+ΔT, or whether KD is less than or equal to KD1. If so, trigger the refrigeration antifreeze protection action. If not, go to step 5; Tout_old is the refrigerant outlet temperature of the plate heat exchanger in the previous temperature sampling cycle, ΔT is the sampling error of the temperature sensor, KD is the current opening value of the electronic expansion valve, and KD1 is the set lower limit of the plate heat exchanger refrigeration antifreeze protection opening;

[0012] Step 5: Close the opening of the electronic expansion valve by [the absolute value of (Tout-Tin)*e] steps every m seconds to increase the refrigerant outlet temperature of the plate heat exchanger, and return to step 2; where m is the adjustment cycle of the electronic expansion valve for refrigeration antifreeze protection of the plate heat exchanger, and e is the amplification factor;

[0013] Step 6: Determine whether Tin is greater than T2. ​​If so, the air conditioner operates normally. If not, proceed to step 7.

[0014] Step 7: Determine whether Tout-Tin is less than A, or whether KD is greater than or equal to KD2. If so, trigger the refrigeration antifreeze protection action. If not, go to step 8; A is the set plate heat exchanger refrigeration antifreeze protection superheat judgment standard value, KD2 is the set plate heat exchanger refrigeration antifreeze protection opening upper limit value;

[0015] Step 8: Increase the opening of the electronic expansion valve by [the absolute value of (Tout-Tin)*f] steps every m seconds, and return to step 2, where f is the amplification factor.

[0016] Furthermore, when the air-conditioning compressor is a variable frequency compressor, the method comprises the following steps:

[0017] Step 1: Determine whether Tw is greater than T1, where T1 is the set refrigeration antifreeze protection temperature of the water side of the plate heat exchanger. If so, trigger the refrigeration antifreeze protection action; if not, proceed to step 2;

[0018] Step 2: Determine whether Tout is less than or equal to T2, where T2 is the set refrigeration antifreeze protection temperature of the fluorine side of the plate heat exchanger. If so, proceed to step 3; if not, proceed to step 8;

[0019] Step 3: Determine whether Tin is less than or equal to T2. If so, trigger the antifreeze protection action. If not, go to step 4.

[0020] Step 4: Determine whether the frequency of the variable frequency compressor is the lowest frequency C, if so, proceed to step 5, if not, proceed to step 6;

[0021] Step 5: Determine whether Tout is less than Tout_old+ΔT, or whether KD is less than or equal to KD1. If so, trigger the refrigeration antifreeze protection action. If not, go to step 7; Tout_old is the refrigerant outlet temperature of the plate heat exchanger in the previous cycle, ΔT is the sampling error of the temperature sensor, KD is the current opening value of the electronic expansion valve, and KD1 is the set lower limit of the plate heat exchanger refrigeration antifreeze protection opening;

[0022] Step 6: Reduce the frequency of the compressor by gHz every n seconds until it reaches the lowest frequency C, and control the compressor to operate at the frequency C; where n is the frequency adjustment cycle of the plate heat exchanger refrigeration antifreeze protection compressor, and g is the frequency change of the compressor within each adjustment cycle;

[0023] Step 7: Close the opening of the electronic expansion valve every m seconds [the absolute value of (Tout-Tin)*e] to increase the refrigerant outlet temperature of the plate heat exchanger; where m is the adjustment cycle of the electronic expansion valve for refrigeration antifreeze protection of the plate heat exchanger, and e is the amplification factor;

[0024] Step 8: Determine whether Tin is greater than T2. ​​If so, the air conditioner works normally. If not, go to step 9.

[0025] Step 9: Determine whether Tout-Tin is less than A, or whether KD is greater than or equal to KD2. If so, proceed to step 11; if not, proceed to step 10; wherein A is the plate heat exchanger refrigeration antifreeze protection superheat judgment setting value, and KD1 is the set plate heat exchanger refrigeration antifreeze protection opening upper limit value;

[0026] Step 10: increase the opening of the electronic expansion valve by [the absolute value of (Tout-Tin)*f] steps per m seconds, where f is the amplification factor;

[0027] Step 11: Determine whether the compressor is running at the minimum frequency C. If so, trigger the refrigeration antifreeze protection action. If not, go to step 12.

[0028] Step 12: Reduce the frequency of the compressor by gHz every n seconds, where g is the frequency change of the compressor in each cycle.

[0029] Furthermore, the triggering of the antifreeze protection action specifically includes controlling the compressor to stop running, circulating the water pump, and controlling the air-conditioning unit to shut down.

[0030] Beneficial effects of the present invention:

[0031] The plate heat exchanger refrigeration antifreeze method described in the present invention collects the inlet and outlet refrigerant temperatures of the plate heat exchanger on the fluorine side, and performs refrigeration antifreeze protection for the plate heat exchanger in combination with the compressor frequency and the electronic valve opening control. Compared with the traditional control method of collecting the inlet and outlet water temperatures from the water side for antifreeze protection, this method collects the inlet and outlet refrigerant temperatures of the plate heat exchanger from the fluorine side for refrigeration antifreeze protection, has small hysteresis, rapid protection, and can more effectively perform antifreeze protection, especially in situations such as water shortage and dirty plate heat exchanger blockage; compared with the control method of collecting the fluorine side pressure of the plate heat exchanger for antifreeze protection, this method uses a temperature sensor and has extremely low cost; by associating the inlet and outlet temperatures of the plate heat exchanger with the compressor frequency control and the electronic expansion valve control, the antifreeze misjudgment caused by the electronic expansion valve control and the frequency control is eliminated, and the antifreeze control is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Refrigeration cycle diagram for plate heat exchanger refrigeration antifreeze control method.

[0033] Figure 2 It is the thermodynamic cycle process of the plate heat exchanger refrigeration cycle system.

[0034] Figure 3 This is a flow chart of refrigeration and antifreeze control of the fixed-frequency compressor plate heat exchanger.

[0035] Figure 4 This is the flow chart of refrigeration antifreeze control for variable frequency compressor plate heat exchanger. DETAILED DESCRIPTION

[0036] like Figure 1 As shown, a temperature sensor is provided at the refrigerant inlet and outlet of the fluorine side of the plate heat exchanger of the air conditioner and the inlet and outlet of the water side of the plate heat exchanger to collect the inlet and outlet temperatures of the refrigerant on the fluorine side and the inlet and outlet water temperatures on the water side, and combined with the compressor frequency and the opening of the electronic expansion valve to prevent the plate heat exchanger from freezing during cooling.

[0037] like Figure 2 As shown, the high-temperature and high-pressure gaseous refrigerant at the outlet of the compressor 2 is cooled by the condenser 3 and converted into a high-temperature liquid refrigerant, which enters the electronic expansion valve 4, is throttled by the electronic expansion valve 4, and is converted into a low-temperature and low-pressure gas-liquid mixed refrigerant, which enters the plate heat exchanger 1, and performs heat exchange with the water side of the plate heat exchanger in the plate heat exchanger 1 to cool the water side. The refrigerant after heat exchange is a gas-liquid mixed state or a gas state, which enters the inlet of the compressor 2 for compression, completing the refrigeration cycle. Its thermodynamic cycle process is as follows: Figure 2 As shown, the gaseous refrigerant at state 1 is transformed into the high-temperature and high-pressure gaseous refrigerant at state point 2 after compression, the refrigerant at state point 2 is transformed into the high-temperature liquid refrigerant at state point 3 after condensation, the refrigerant at state point 3 is further cooled by the condenser and becomes the high-temperature liquid refrigerant with a certain degree of supercooling at state point 4, the refrigerant at state point 4 is transformed into the gas-liquid mixed refrigerant at state point 5 after throttling by the electronic expansion valve, the refrigerant at state point 5 enters the plate heat exchanger for heat exchange, and the refrigerant after heat exchange becomes the refrigerant at state point 6. The refrigerant at state point 6 may be in three states: gas-liquid mixed state, saturated steam state, and superheated steam state according to the evaporation of the refrigerant in the plate heat exchanger. The state of the refrigerant in the plate heat exchanger undergoes a transformation process from point 5 to point 6. In this area, there is a good linear correspondence between the refrigerant pressure and the refrigerant temperature. As the pressure decreases from state point 5 to state point 6, the refrigerant temperature decreases accordingly. Therefore, in the refrigeration mode, when the refrigerant at the inlet and outlet of the plate heat exchanger is at a certain superheat, the compressor frequency and the electronic expansion valve opening are controlled to ensure that the refrigerant inlet and outlet temperatures are greater than the freezing point of water, thereby preventing the plate heat exchanger from freezing.

[0038] The refrigeration antifreeze control method for an air-conditioning plate heat exchanger described in the present invention adopts different control methods for variable frequency compressors and fixed frequency compressors. Therefore, before executing the refrigeration antifreeze control method, it is necessary to determine whether the frequency of the compressor is variable.

[0039] For fixed frequency compressors, the control process is as follows: Figure 3As shown, step S201 determines whether the outlet water temperature is greater than the refrigeration antifreeze protection temperature of the water side of the plate heat exchanger. If Tw>T1, step S203 is executed, otherwise step S202 is executed, wherein Tw is the current outlet water temperature of the plate heat exchanger, and T1 is the refrigeration antifreeze protection setting value of the water side of the plate heat exchanger, and its value range is 1 to 5, the unit is ℃, and one decimal place is retained.

[0040] Step S202 triggers the refrigeration antifreeze protection action, the compressor stops immediately, and the circulating water pump runs for 60 seconds before the unit shuts down.

[0041] Step S203 determines whether the current refrigerant outlet temperature of the plate heat exchanger is less than or equal to the refrigeration antifreeze protection setting value of the fluorine side of the plate heat exchanger. If Tout<=T2, execute step S204, otherwise execute step S209, wherein Tout is the current refrigerant outlet temperature of the plate heat exchanger, and T2 is the refrigeration antifreeze protection setting value of the fluorine side of the plate heat exchanger, and its value range is 0 to 5, the unit is ℃, and one decimal place is retained.

[0042] Step S204 determines whether the current refrigerant inlet temperature of the plate heat exchanger is less than or equal to the refrigeration antifreeze protection setting value of the fluorine side of the plate heat exchanger. If Tin<=T2, step S205 is executed, otherwise step S206 is executed, where Tin is the current refrigerant inlet temperature of the plate heat exchanger. When Tin<=T2, Tout<=T2, it indicates that the refrigerant temperature on the refrigerant side of the plate heat exchanger is not higher than the refrigeration antifreeze protection setting value of the fluorine side of the plate heat exchanger, and the freezing risk of the plate heat exchanger is extremely high. When Tin>T2, Tout<=T2, it indicates that part of the refrigerant near the refrigerant outlet area is lower than the refrigeration antifreeze protection setting value of the fluorine side of the plate heat exchanger, and there is a certain freezing risk. This situation may be caused by the excessive opening of the electronic expansion valve causing the refrigerant outlet to carry liquid. Therefore, it is necessary to make a comprehensive judgment based on the refrigerant outlet temperature change trend and the current opening value of the current electronic expansion valve to avoid misjudgment of antifreeze.

[0043] Step S205 triggers the refrigeration antifreeze protection action, the compressor stops immediately, and the circulating water pump runs for 60 seconds before the unit shuts down.

[0044] Step S206 determines the current change trend of the refrigerant outlet temperature of the plate heat exchanger and the current opening value of the electronic expansion valve. If Tout < Tout_old + ΔT or KD <= KD1, step S207 is executed; otherwise, step S208 is executed. Here, Tout_old is the refrigerant outlet temperature of the plate heat exchanger in the previous cycle, KD is the current opening value of the electronic expansion valve, and KD1 is the lower limit value for comparison of refrigeration and anti-freezing protection of the plate heat exchanger, with a value range of 50 - 500 and being an integer. When Tout < Tout_old + ΔT, it indicates that the rising trend of the refrigerant outlet temperature of the plate heat exchanger is not obvious. Here, ΔT is used to eliminate the sampling error of the temperature sensor. When KD <= KD1, it indicates that the effect of using the closing measure to increase the refrigerant outlet temperature of the plate heat exchanger is not obvious. In both of the above cases, step S207 should be executed.

[0045] Step S207 triggers the refrigeration and anti-freezing protection action. The compressor stops immediately, and after the circulating water pump runs for 60 seconds, the unit shuts down.

[0046] Step S208 performs the valve closing action to increase the refrigerant outlet temperature of the plate heat exchanger. The electronic expansion valve opening is closed by [the absolute value of (Tout - Tin) * e] steps every m seconds, and the calculation result is rounded down, with a maximum action step of h steps. Here, m is the adjustment period of the electronic expansion valve for refrigeration and anti-freezing protection of the plate heat exchanger, with a value range of 1 - 30 and being an integer. Tout - Tin is the superheat at the inlet and outlet of the refrigerant side of the current plate heat exchanger, h is the maximum allowable action steps in a single cycle, with a value of 1 - 100, and e is the amplification factor, with a value range of 1 - 10 and retaining one decimal place. After step S208 is executed, it returns to step S203 for re-judgment.

[0047] Step S209 determines whether the current refrigerant inlet temperature of the plate heat exchanger is greater than the set value of the fluorine side refrigeration and anti-freezing protection of the plate heat exchanger. If Tin > T2, step S210 is executed; otherwise, step S211 is executed.

[0048] Step S210 performs normal control of the unit without triggering the anti-freezing protection action. When Tin > T2 and Tout > T2, it indicates that at this time, the refrigerant on the refrigerant side of the plate heat exchanger is higher than the set value of the fluorine side refrigeration and anti-freezing protection of the plate heat exchanger, and there is no risk of freezing for the plate heat exchanger, and the unit can be normally controlled.

[0049] Step S211 determines the superheat at the inlet and outlet of the refrigerant side of the current plate heat exchanger and the current opening of the electronic expansion valve. If Tout - Tin = KD2, then step S212 is executed; otherwise, step S213 is executed. Here, Tout - Tin is the superheat at the inlet and outlet of the refrigerant side of the current plate heat exchanger, A is the set value for judging the superheat for refrigeration and anti-freezing protection of the plate heat exchanger, and its value range is 0 to 5, with the unit of °C and one decimal place reserved. KD2 is the upper limit value for comparison of refrigeration and anti-freezing protection of the plate heat exchanger, and its value range is 50 to 500, and it is an integer, and its value is greater than or equal to KD1.

[0050] Step S212 triggers the refrigeration and anti-freezing protection action. The compressor stops immediately, and after the circulating water pump runs for 60 seconds, the unit shuts down.

[0051] In step S213, the opening of the electronic expansion valve is increased by the absolute value of [(Tout - Tin) * f] steps every m seconds, and the calculation result is rounded down, with a maximum action step of h steps. Here, m is the adjustment period of the electronic expansion valve for refrigeration and anti-freezing protection of the plate heat exchanger, and its value range is 1 to 30 and it is an integer. Tout - Tin is the superheat at the inlet and outlet of the refrigerant side of the current plate heat exchanger, h is the maximum allowable action steps in a single period, with a value of 1 to 100, and f is the amplification factor, and its value range is 1 to 10 with one decimal place reserved.

[0052] For the variable-frequency compressor, the refrigeration and anti-freezing control of the plate heat exchanger is carried out by combining the frequency of the compressor and the opening of the electronic expansion valve. The control flow chart is as Figure 4 shown, and the detailed steps are as follows:

[0053] Step S301 determines whether the outlet water temperature is greater than the refrigeration and anti-freezing protection temperature. If Tw > T1, then step S303 is executed; otherwise, step S302 is executed. Here, Tw is the current outlet water temperature of the plate heat exchanger, and T1 is the set value for water-side refrigeration and anti-freezing protection of the plate heat exchanger, and its value range is 1 to 5, with the unit of °C and one decimal place reserved.

[0054] Step S302 triggers the refrigeration and anti-freezing protection action. The compressor stops immediately, and after the circulating water pump runs for 60 seconds, the unit shuts down.

[0055] Step S303 determines whether the current refrigerant outlet temperature of the plate heat exchanger is less than or equal to the set value for refrigerant-side refrigeration and anti-freezing protection of the plate heat exchanger. If Tout <= T2, then step S304 is executed; otherwise, step S311 is executed. Here, Tout is the current refrigerant outlet temperature of the plate heat exchanger, and T2 is the set value for refrigerant-side refrigeration and anti-freezing protection of the plate heat exchanger, and its value range is 1 to 5, with the unit of °C and one decimal place reserved.

[0056] Step S304 determines whether the current refrigerant inlet temperature of the plate heat exchanger is less than or equal to the set value of the fluorine-side refrigeration anti-freezing protection of the plate heat exchanger. If Tin <= T2, step S305 is executed; otherwise, step S306 is executed, where Tin is the current refrigerant inlet temperature of the plate heat exchanger. When Tin < T2 and Tout < T2, it indicates that at this time, the refrigerants on the refrigerant side of the plate heat exchanger are not higher than the set value of the fluorine-side refrigeration anti-freezing protection of the plate heat exchanger, and the risk of freezing of the plate heat exchanger is extremely high. When Tin > T2 and Tout <= T2, it indicates that at this time, some refrigerants in the area near the refrigerant outlet are lower than the set value of the fluorine-side refrigeration anti-freezing protection of the plate heat exchanger, and there is a certain risk of freezing. This situation may be caused by the excessive opening of the electronic expansion valve or the too high operating frequency of the compressor, resulting in liquid carrying at the refrigerant outlet. Therefore, it is necessary to comprehensively judge according to the change trend of the refrigerant outlet temperature and the current opening value of the current electronic expansion valve to avoid misjudgment of anti-freezing.

[0057] Step S305 triggers the refrigeration anti-freezing protection action. The compressor stops immediately, and after the circulating water pump runs for 60 seconds, the unit shuts down.

[0058] Step S306 determines whether the compressor has run to the minimum frequency set value C. If so, step S307 is executed; otherwise, step S308 is executed, where C is the minimum frequency set value for the compressor operation, and its value range is: 10 - 50, and it is an integer.

[0059] Step S307 determines the change trend of the current refrigerant outlet temperature of the plate heat exchanger and the current opening value of the electronic expansion valve. If Tout < Tout_old + ΔT or KD <= KD1, step S309 is executed; otherwise, step S310 is executed, where Tout_old is the refrigerant outlet temperature of the plate heat exchanger in the previous cycle, KD is the current opening value of the electronic expansion valve, and KD1 is the lower limit value for comparison of the refrigeration anti-freezing protection of the plate heat exchanger, and its value range is 50 - 500, and it is an integer. When Tout < Tout_old + ΔT, it indicates that the rising trend of the refrigerant outlet temperature of the plate heat exchanger is not obvious, where ΔT is to eliminate the sampling error of the temperature sensor. In this embodiment, the sampling error of the sensor is 0.2; when KD <= KD1, it indicates that the effect of reducing the opening of the electronic expansion valve to increase the refrigerant outlet temperature of the plate heat exchanger is not obvious, and at this time, the operating frequency of the compressor has been reduced to the minimum frequency set value of the compressor operation, and the frequency cannot be further reduced to increase the refrigerant inlet and outlet temperatures. In both of these cases, step S309 should be executed.

[0060] In step S308, the frequency is decreased by g Hz every n seconds with a maximum frequency of j Hz. When the decreased frequency is less than the minimum frequency setting value C, it operates at the C value. Here, n is the frequency adjustment period for the refrigeration anti-freezing protection of the plate heat exchanger, and its value range is from 1 to 30 and is an integer. j is the maximum operating frequency of the compressor, and its value range is from 50 to 120 and is an integer. g is the compressor frequency change amount in each period, and its value range is from 1 to 50 and is an integer. After step S308 is executed, it returns to step S303 for re-judgment.

[0061] Step 309 triggers the refrigeration anti-freezing protection action, and the compressor stops immediately. After the circulating water pump operates for 60 seconds, the unit shuts down.

[0062] In step S310, the valve closing action is executed to increase the refrigerant outlet temperature of the plate heat exchanger. Every m seconds, the opening of the electronic expansion valve is closed by the absolute value of [(Tout - Tin) * e] steps, rounded down, and the maximum number of action steps is h steps. Here, m is the electronic expansion valve adjustment period for the refrigeration anti-freezing protection of the plate heat exchanger, and its value range is from 1 to 30 and is an integer. Tout - Tin is the superheat at the inlet and outlet of the refrigerant side of the current plate heat exchanger. h is the maximum number of action steps allowed in a single period, with a value of 1 to 100. e is the amplification factor, and its value range is from 1 to 10 and is reserved to one decimal place. After step S310 is executed, it returns to step S303 for re-judgment.

[0063] In step S311, it is judged whether the current refrigerant inlet temperature of the plate heat exchanger is greater than the refrigeration anti-freezing protection setting value on the fluorine side of the plate heat exchanger. If Tin > T2, step S312 is executed; otherwise, step S313 is executed.

[0064] In step S312, the unit is normally controlled without triggering the anti-freezing protection action. When Tin > T2 and Tout > T2, it indicates that at this time, the refrigerant on the refrigerant side of the plate heat exchanger is higher than the refrigeration anti-freezing protection setting value on the fluorine side of the plate heat exchanger, and there is no risk of freezing for the plate heat exchanger, and the unit can be normally controlled.

[0065] In step S313, it is judged the superheat at the inlet and outlet of the current refrigerant side of the plate heat exchanger and the current opening of the electronic expansion valve. If Tout - Tin = KD2, step S314 is executed; otherwise, step S315 is executed. Here, Tout - Tin is the superheat at the inlet and outlet of the current refrigerant side of the plate heat exchanger. A is the superheat judgment setting value for the refrigeration anti-freezing protection of the plate heat exchanger, and its value range is from 0 to 3, reserved to one decimal place. KD2 is the upper limit value for comparison of the refrigeration anti-freezing protection of the plate heat exchanger, and its value range is from 50 to 500 and is an integer, and its value is greater than or equal to KD1.

[0066] Step S314 determines whether the compressor runs to the minimum frequency setting value C. If so, step S316 is executed, otherwise step S317 is executed, where C is the minimum frequency setting value of the compressor, and its value range is: 10~50, and it is an integer.

[0067] Step S315 increases the opening degree of the electronic expansion valve by [the absolute value of (Tout-Tin)*f] steps every m seconds, rounds down the calculated result, and the maximum number of action steps is h steps, wherein m is the adjustment cycle of the electronic expansion valve for refrigeration antifreeze protection of the plate heat exchanger, and its value range is 1 to 30 and is an integer, Tout-Tin is the inlet and outlet superheat of the refrigerant side of the current plate heat exchanger, h is the maximum number of action steps allowed in a single cycle, and its value range is 1 to 100, f is the amplification factor, and its value range is 1 to 10 and retains one decimal place. After executing step S315, return to step S303 for another judgment.

[0068] Step 316 triggers the refrigeration antifreeze protection action, the compressor stops immediately, and the circulating water pump runs for 60 seconds before the unit shuts down.

[0069] Step S317 reduces gHz every n seconds and the maximum frequency is jHz, where n is the frequency adjustment cycle of the plate heat exchanger refrigeration antifreeze protection compressor, and its value range is 1 to 30 and is an integer, and j is the maximum change of the compressor frequency in each cycle, and its value range is: 1 to 50 and is an integer. After executing step S317, return to step S303 for re-judgment.

[0070] Fixed frequency compressor plate heat exchanger refrigeration antifreeze control embodiment 1:

[0071] 1) Basic system information:

[0072] The air conditioner compressor is a fixed-frequency compressor, and the compressor frequency cannot be adjusted. The current cooling water outlet temperature of the plate heat exchanger is Tw = 4°C, the refrigerant outlet temperature is Tout = 1.4°C, the current refrigerant inlet temperature of the plate heat exchanger is Tin = 4.3°C, the refrigerant outlet temperature of the plate heat exchanger in the previous cycle is Tout_old = 1.1°C, and the current opening of the electronic expansion valve is KD = 370 steps.

[0073] 2) User set value:

[0074] Serial number name default value Setting range 1 T1 2.0 1～5 2 T2 1.5 0～5 3 KD1 200 50～500 4 KD2 450 50～500 5 m 10 1～30 6 h 30 1～100 7 e 5.0 1～10 8 f 2.0 1～10 9 A 3.0 0～5

[0075] 3) Control process:

[0076] Because the compressor is a fixed-frequency compressor and the frequency is not adjustable, step S2 is executed;

[0077] Because the outlet water temperature is Tw=4 which is greater than the refrigeration antifreeze protection temperature T1=2.0, step S203 is executed;

[0078] Since Tout = 1.4 °C < T2 = 1.5, step S204 is executed;

[0079] Since Tin = 4.3 > T2 = 1.5, step S206 is executed;

[0080] Since Tout = 1.4 > Tout_old = 1.1 + 0.2 = 1.3 and KD = 370 > KD1 = 200, step S208 is executed;

[0081] Since (Tout - Tin) * e = (1.4 - 4.3) * 5.0 = -14.5, after taking the absolute value and rounding down, the result is 14;

[0082] Since h = 30 > 14 and m = 10 seconds, the electronic expansion valve opening is reduced by 14 steps every 10 - second cycle to increase the refrigerant outlet temperature and avoid freezing failure.

[0083] Fixed - frequency compressor plate - type heat exchanger refrigeration and anti - freezing control example 2:

[0084] 1) System basic information:

[0085] The compressor is a fixed - frequency compressor with an adjustable frequency. The current refrigeration water outlet temperature of the plate - type heat exchanger is Tw = 5 °C, the current refrigerant outlet temperature of the plate - type heat exchanger is Tout = 6.5 °C, the current refrigerant inlet temperature of the plate - type heat exchanger is Tin = 0.7 °C, and the current opening of the electronic expansion valve is KD = 240 steps.

[0086] 2) User - set values:

[0087]

[0088]

[0089] 3) Control process:

[0090] Since the compressor is a fixed - frequency compressor with an adjustable frequency, step S2 is executed;

[0091] Since the water outlet temperature Tw = 5 is greater than the refrigeration and anti - freezing protection temperature T1 = 2.0, step S203 is executed;

[0092] Since Tout = 6.5 °C > T2 = 1.5, step S209 is executed;

[0093] Since Tin = 0.7 < T2 = 1.5, step S211 is executed;

[0094] Since Tout - Tin = 6.5 - 0.7 = 5.8 > A = 3 and KD = 240 < KD2 = 450, step S213 is executed;

[0095] Since (Tout - Tin)*f = (6.5 - 0.7)*2.0 = 11.6, after taking the absolute value and then rounding down, the result is 11;

[0096] Since h = 30 > 11 and m = 10 seconds, the electronic expansion valve opening is increased by 11 steps every 10 - second cycle to raise the refrigerant inlet temperature and avoid freezing failure.

[0097] Refrigeration and anti - freezing control example 1 of variable - frequency compressor plate heat exchanger

[0098] 1) System basic information:

[0099] The compressor is a variable - frequency compressor with adjustable frequency. The current refrigeration outlet water temperature Tw of the plate heat exchanger is 4°C, the current refrigerant outlet temperature Tout of the plate heat exchanger is 1.4°C, the current refrigerant inlet temperature Tin of the plate heat exchanger is 4.3°C, the refrigerant outlet temperature Tout_old of the plate heat exchanger in the previous cycle is 1.1°C, the current opening KD of the electronic expansion valve is 370 steps, and the current operating frequency of the compressor is 80 Hz.

[0100] 2) User - set values:

[0101] Serial number name default value Setting range 1 T1 2.0 1～5 2 T2 1.5 0～5 3 C 30 10～50 4 KD1 80 50～500 5 KD2 450 50～500 6 m 10 1～30 7 n 5 1～30 8 g 30 1～50 9 j 100 1～120 10 h 30 1～100 11 e 5 1～10 12 f 2.0 1～10 13 A 3.0 0～5

[0102] 3) Control process:

[0103] Since the compressor is a variable - frequency compressor with adjustable frequency, step S3 is executed;

[0104] Since the outlet water temperature Tw = 4 is greater than the refrigeration and anti - freezing protection temperature T1 = 2.0, step S303 is executed;

[0105] Since Tout = 1.4°C < T2 = 1.5, step S304 is executed;

[0106] Since Tin = 4.3 > T2 = 1.5, step S306 is executed;

[0107] Since the current operating frequency of the compressor is 80 Hz, which is greater than the minimum operating frequency C = 30 Hz, step S308 is executed to reduce the compressor frequency by 30 Hz every 5 seconds to increase the refrigerant outlet temperature and avoid freezing failure.

[0108] The following is refrigeration and anti - freezing control example 2 of variable - frequency compressor plate heat exchanger:

[0109] 1) System basic information:

[0110] The compressor is a variable-frequency compressor with adjustable frequency. The current refrigerating water outlet temperature Tw of the plate heat exchanger is 5°C, the current refrigerant outlet temperature Tout of the plate heat exchanger is 7.4°C, the current refrigerant inlet temperature Tin of the plate heat exchanger is 1.1°C, the current opening KD of the electronic expansion valve is 170 steps, and the current operating frequency of the compressor is 70 Hz.

[0111] 2) User settings:

[0112] Serial number name default value Setting range 1 T1 2.0 1～5 2 T2 1.5 0～5 3 C 30 10～50 4 KD1 80 50～500 5 KD2 450 50～500 6 m 10 1～30 7 n 5 1～30 8 g 30 1～50 9 j 100 1～120 10 h 30 1～100 11 e 5 1～10 12 f 2.0 1～10 13 A 3.0 0～5

[0113] 3) Control process:

[0114] Since the compressor is a variable-frequency compressor with adjustable frequency, step S3 is executed;

[0115] Since the water outlet temperature Tw = 5 is greater than the refrigerating anti-freezing protection temperature T1 = 2.0, step S303 is executed;

[0116] Since Tout = 7.4°C > T2 = 1.5, step S311 is executed;

[0117] Since Tin = 1.1 < T2 = 1.5, step S313 is executed;

[0118] Since Tout - Tin = 7.4 - 1.1 = 6.3 > A = 3 and KD = 170 < KD2 = 450, step S315 is executed;

[0119] Since (Tout - Tin) * f = (7.4 - 1.1) * 2.0 = 12.6, and the result after taking the absolute value and rounding is 12;

[0120] Since h = 30 > 12, the opening of the electronic expansion valve is increased by 12 steps every 10-second control cycle to increase the refrigerant inlet temperature and avoid freezing failure.

Claims

1. A refrigeration antifreeze control method for an air-conditioning plate heat exchanger, characterized in that: Temperature sensors are respectively set on the refrigerant side and water side of the plate heat exchanger to collect the refrigerant inlet temperature Tin, the refrigerant outlet temperature Tout, and the water side outlet water temperature Tw; when the air-conditioning compressor is a fixed-frequency compressor, the opening of the electronic expansion valve is controlled by analyzing the water side outlet water temperature Tw of the plate heat exchanger, the refrigerant inlet temperature Tin, and the refrigerant outlet temperature Tout to perform refrigeration antifreeze protection control; when the air-conditioning compressor is a variable-frequency compressor, the frequency of the compressor and the opening of the electronic expansion valve are controlled by analyzing the water side outlet water temperature Tw of the plate heat exchanger, the refrigerant inlet temperature Tin, and the refrigerant outlet temperature Tout to perform refrigeration antifreeze protection control; When the air-conditioning compressor is a fixed-frequency compressor, the method comprises the following steps: Step 1: Determine whether Tw is greater than T1, where T1 is the set refrigeration antifreeze protection temperature of the water side of the plate heat exchanger. If so, trigger the refrigeration antifreeze protection action; if not, proceed to step 2; Step 2: Determine whether Tout is less than or equal to T2, where T2 is the set refrigeration antifreeze protection temperature of the fluorine side of the plate heat exchanger. If so, proceed to step 3; if not, proceed to step 6; Step 3: Determine whether Tin is less than or equal to T2; if so, trigger the refrigeration antifreeze protection action, if not, go to step 4; Step 4: Determine whether Tout is less than Tout_old+ΔT, or whether KD is less than or equal to KD1. If so, trigger the refrigeration antifreeze protection action. If not, go to step 5; Tout_old is the refrigerant outlet temperature of the plate heat exchanger in the previous temperature sampling cycle, ΔT is the sampling error of the temperature sensor, KD is the current opening value of the electronic expansion valve, and KD1 is the set lower limit of the plate heat exchanger refrigeration antifreeze protection opening; Step 5: Close the opening of the electronic expansion valve by [the absolute value of (Tout-Tin)*e] steps every m seconds to increase the refrigerant outlet temperature of the plate heat exchanger, and return to step 2; where m is the adjustment cycle of the electronic expansion valve for refrigeration antifreeze protection of the plate heat exchanger, and e is the amplification factor; Step 6: Determine whether Tin is greater than T2. ​​If so, the air conditioner operates normally. If not, proceed to step 7. Step 7: Determine whether Tout-Tin is less than A, or whether KD is greater than or equal to KD2. If so, trigger the refrigeration antifreeze protection action. If not, go to step 8; A is the set plate heat exchanger refrigeration antifreeze protection superheat judgment standard value, KD2 is the set plate heat exchanger refrigeration antifreeze protection opening upper limit value; Step 8: Increase the opening of the electronic expansion valve by [the absolute value of (Tout-Tin)*f] steps every m seconds, and return to step 2, where f is the amplification factor.

2. The air conditioning plate heat exchanger refrigeration antifreeze control method according to claim 1, characterized in that: When the air-conditioning compressor is a variable frequency compressor, the method comprises the following steps: Step 1: Determine whether Tw is greater than T1, where T1 is the set refrigeration antifreeze protection temperature of the water side of the plate heat exchanger. If so, trigger the refrigeration antifreeze protection action; if not, proceed to step 2; Step 2: Determine whether Tout is less than or equal to T2, where T2 is the set refrigeration antifreeze protection temperature of the fluorine side of the plate heat exchanger. If so, proceed to step 3; if not, proceed to step 8; Step 3: Determine whether Tin is less than or equal to T2. If so, trigger the refrigeration antifreeze protection action. If not, go to step 4. Step 4: Determine whether the frequency of the variable frequency compressor is the lowest frequency C, if so, proceed to step 5, if not, proceed to step 6; Step 5: Determine whether Tout is less than Tout_old+ΔT, or whether KD is less than or equal to KD1. If so, trigger the refrigeration antifreeze protection action. If not, go to step 7; Tout_old is the refrigerant outlet temperature of the plate heat exchanger in the previous cycle, ΔT is the sampling error of the temperature sensor, KD is the current opening value of the electronic expansion valve, and KD1 is the set lower limit of the plate heat exchanger refrigeration antifreeze protection opening; Step 6: Reduce the frequency of the compressor by gHz every n seconds until it reaches the lowest frequency C, and control the compressor to operate at the frequency C; where n is the frequency adjustment cycle of the plate heat exchanger refrigeration antifreeze protection compressor, and g is the frequency change of the compressor within each adjustment cycle; Step 7: Close the opening of the electronic expansion valve every m seconds [the absolute value of (Tout-Tin)*e] to increase the refrigerant outlet temperature of the plate heat exchanger; where m is the adjustment cycle of the electronic expansion valve for refrigeration antifreeze protection of the plate heat exchanger, and e is the amplification factor; Step 8: Determine whether Tin is greater than T2. ​​If so, the air conditioner works normally. If not, go to step 9. Step 9: Determine whether Tout-Tin is less than A, or whether KD is greater than or equal to KD2. If so, proceed to step 11; if not, proceed to step 10; wherein A is the plate heat exchanger refrigeration antifreeze protection superheat judgment setting value, and KD1 is the set plate heat exchanger refrigeration antifreeze protection opening upper limit value; Step 10: increase the opening of the electronic expansion valve by [the absolute value of (Tout-Tin)*f] steps per m seconds, where f is the amplification factor; Step 11: Determine whether the compressor is running at the minimum frequency C. If so, trigger the refrigeration antifreeze protection action. If not, go to step 12. Step 12: Reduce the frequency of the compressor by gHz every n seconds, where g is the frequency change of the compressor in each cycle.

3. A refrigeration antifreeze control method for an air-conditioning plate heat exchanger according to claim 1 or 2, characterized in that: The triggering of the refrigeration antifreeze protection action specifically includes controlling the compressor to stop running, circulating the water pump, and controlling the air conditioning unit to shut down.

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