A defrosting control method and system for air source heat pump unit

Abstract

The present invention discloses a defrost control method and system for an air source heat pump unit, and relates to the technical field of air source heat pumps. The main scheme is: collecting multiple data of an air source heat pump; respectively calculating the frosting rate, frosting thickness and heat exchange efficiency reduction rate, further calculating the frosting degree index, comparing with a preset threshold and judging whether the air source heat pump unit needs defrosting; calculating the total defrost heat, calculating the defrost time based on the total defrost heat, and then calculating the temperature change rate of an outdoor heat exchanger; calculating the defrost effect index based on the temperature change rate of the outdoor heat exchanger; comparing with a preset threshold and judging whether the defrost is completed; this method can monitor and accurately control the defrost process in real time, and ensure that the defrost operation is timely, appropriate and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of air source heat pumps, and in particular to a defrosting control method and system for an air source heat pump unit. Background Art

[0002] As a widely used device for heating and cooling, the diversity of the operating environment of air source heat pumps brings many challenges to the performance of the equipment. Among them, when operating in a low temperature environment, the outdoor heat exchanger of the air source heat pump unit is very prone to frost. Frosting will increase the heat transfer resistance of the heat exchanger, resulting in a significant decrease in the heating capacity of the unit, which in turn affects the heating effect of the entire system. In addition, frosting will also cause the operating stability of the unit to deteriorate, increase energy consumption, and even shorten the service life of the equipment. This series of problems are key issues that need to be solved in the field of air source heat pump technology.

[0003] At present, there are some corresponding solutions to the frosting problem of air source heat pump units. For example, temperature difference defrosting is based on the inlet and outlet temperature difference of the outdoor heat exchanger to determine whether defrosting is needed. When the inlet and outlet temperature difference reaches a certain threshold, it is determined that the outdoor heat exchanger is severely frosted and the defrosting program needs to be started.

[0004] However, existing defrosting technologies have certain limitations. Temperature difference defrosting is easily affected by ambient temperature fluctuations. For example, when the ambient temperature changes rapidly, even if there is no frost or the frost is very slight, the temperature difference between the inlet and outlet reaches the threshold due to temperature fluctuations, thereby erroneously triggering the defrost program. This misjudgment not only causes energy waste, but is also not conducive to the long-term stable operation of the unit. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the deficiencies in the prior art, the present invention provides a defrost control method and system for an air source heat pump unit, which comprises: collecting multiple data of the air source heat pump; respectively calculating the frosting rate, frosting thickness and heat exchange efficiency reduction rate, further calculating the frosting degree index, and comparing and judging whether the air source heat pump unit needs defrosting based on preset thresholds; calculating the total defrost heat, and calculating the defrost time based on the total defrost heat, and then calculating the temperature change rate of the outdoor heat exchanger; calculating the defrost effect index; and comparing and judging whether the defrost is completed based on preset thresholds, thereby solving the problem of inaccurate single parameter judgment in traditional defrost control methods.

[0007] (II) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: A defrosting control method for an air source heat pump unit, comprising:

[0009] Real-time collection of air source heat pump temperature data, unit operation data and unit heating data;

[0010] Calculate the frosting rate based on temperature data and unit operation data ; According to the frosting rate Calculate the frost thickness based on the unit operation data ; Calculate the heat exchange efficiency drop rate based on the unit heating data ;

[0011] According to the frosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index ; Preset the frost index threshold value and set the frost index Compare with the frost degree index threshold, and judge whether the air source heat pump unit needs to be defrosted according to the result;

[0012] When the air source heat pump unit needs to defrost, the defrost instruction is executed and based on the frost thickness Calculate the total defrosting heat with the unit operation data ; Based on total defrosting heat , calculate the defrost time ; According to temperature data and defrosting time , calculate the temperature change rate of the outdoor heat exchanger ; Based on the outdoor heat exchanger temperature change rate , calculate defrost effect index ; Preset the defrost effect index threshold value, and set the defrost effect index The result is compared with the defrost effect index threshold, and whether the defrost is completed is determined according to the result; if the defrost is not completed, the defrost instruction is continued to be executed until the defrost completion condition is met, and then the defrost instruction is stopped.

[0013] In the preferred embodiment of the defrosting control method of the air source heat pump unit described above: calculating the frosting rate The method is:

[0014] Temperature data includes the surface temperature of the outdoor heat exchanger at the current moment , the surface temperature of the outdoor heat exchanger at the last moment and outdoor air temperature ;

[0015] Unit operating data including the heat exchange area of ​​the outdoor heat exchanger ;

[0016] According to the surface temperature , surface temperature , Outdoor air temperature and heat exchange area , calculate the frosting rate , the formula based on is:

[0017]

[0018] in, is the time interval; is the convective heat transfer coefficient of the outdoor heat exchanger; is the air mass flow rate; is the specific heat of air at constant pressure.

[0019] In the preferred embodiment of the defrosting control method of the air source heat pump unit described above: calculating the frost thickness The method is:

[0020] The unit operation data also includes the average wall temperature of the outdoor heat exchanger ;

[0021] According to the frosting rate , the average wall temperature of the outdoor heat exchanger and heat exchange area , calculate the frosting thickness , the formula based on is:

[0022]

[0023] in, It is the time for frosting; is the humidity content of outdoor air; is the molar mass of air; is the universal gas constant; is the saturated humidity content of outdoor air; is the dynamic viscosity of air.

[0024] In the preferred embodiment of the defrosting control method of the air source heat pump unit described above: calculating the heat exchange efficiency decrease rate The method is:

[0025] The unit heating data includes the evaporator inlet air temperature of the air source heat pump unit in the non-frost state. and evaporator outlet temperature And the evaporator inlet air temperature of the air source heat pump unit under frosting conditions and evaporator outlet temperature ;

[0026] Calculate the heat exchange efficiency drop rate based on the unit heating data , the calculation formula is:

[0027] .

[0028] In the preferred embodiment of the defrosting control method of the air source heat pump unit, the method for judging whether the air source heat pump unit needs defrosting is:

[0029] According to the frosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index , the calculation formula is:

[0030]

[0031] in, Frosting rate The weight coefficient is between 0.1 and 0.3; Frosting thickness The weight coefficient is between 0.3 and 0.4; Heat transfer efficiency decrease rate The weight coefficient is between 0.3 and 0.5; ;

[0032] Preset frost level indicator threshold ;when When the air source heat pump unit does not need to defrost; When the air source heat pump unit needs to be defrosted, the defrost instruction is executed.

[0033] In the preferred embodiment of the defrosting control method of the air source heat pump unit described above: calculating the total heat of defrosting The method is:

[0034] When the air source heat pump unit needs to defrost, according to the thickness of the frost Heat exchange area of ​​outdoor heat exchanger , calculate the total heat of defrosting , the calculation formula is:

[0035]

[0036] in, is the frost layer density; is the latent heat of melting of frost; is the average specific heat capacity of the frost layer and the heat exchanger surface; is the melting point of frost; is the initial average temperature of the frost layer and the heat exchanger surface.

[0037] In the preferred embodiment of the defrosting control method of the air source heat pump unit described above: calculating the defrosting time The method is:

[0038] Based on total heat of defrosting , calculate the defrost time , the calculation formula is:

[0039]

[0040] in, It is the mass flow rate of high-temperature refrigerant discharged from the compressor; is the constant pressure specific heat capacity of the refrigerant; is the temperature of the refrigerant entering the outdoor heat exchanger; It is the temperature of the refrigerant leaving the outdoor heat exchanger.

[0041] In the preferred embodiment of the defrosting control method of the air source heat pump unit described above: calculating the temperature change rate of the outdoor heat exchanger The method is:

[0042] The temperature data also includes the inlet temperature of the outdoor heat exchanger when defrosting starts. , outlet temperature And the inlet temperature of the outdoor heat exchanger at the end of defrosting and outlet temperature ;

[0043] According to defrosting time , inlet temperature , outlet temperature and inlet temperature and outlet temperature , calculate the temperature change rate of the outdoor heat exchanger , the calculation formula is:

[0044] .

[0045] In the preferred embodiment of the defrosting control method of the air source heat pump unit, the method for judging whether the defrosting is completed is:

[0046] Based on the outdoor heat exchanger temperature change rate , calculate defrost effect index , the calculation formula is:

[0047]

[0048] in, It is the defrost water discharge speed; It is the compressor operation status indicator; is the temperature change rate of the outdoor heat exchanger The weight coefficient is between 0.2 and 0.3; Defrost water discharge speed The weight coefficient is between 0.3 and 0.4; Compressor operating status indicator The weight coefficient is between 0.4 and 0.5; and ;

[0049] Preset defrost effect index threshold ;when When , it is judged that defrosting is completed; when When the defrost is not completed, it is judged that the defrost is not completed, and the defrost instruction is continued to be executed until the defrost completion conditions are met, and then the defrost instruction is stopped.

[0050] The present invention also discloses an air source heat pump unit defrost control system, which is used to implement the above air source heat pump unit defrost control method, comprising:

[0051] Data acquisition module, used to collect temperature data, unit operation data and unit heating data of air source heat pump in real time;

[0052] Frosting degree calculation module, used to calculate the frost rate based on temperature data and unit operation data ; According to the frosting rate Calculate the frost thickness based on the unit operation data ; Calculate the heat exchange efficiency drop rate based on the unit heating data ;

[0053] Defrost judgment module, used to judge the defrosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index ; Preset the frost index threshold value and set the frost index Compare with the frost degree index threshold, and judge whether the air source heat pump unit needs to be defrosted according to the result;

[0054] The defrost monitoring module is used to execute the defrost instruction when the air source heat pump unit needs to defrost, and based on the frost thickness Calculate the total defrosting heat with the unit operation data ; Based on total defrosting heat , calculate the defrost time ; According to temperature data and defrosting time , calculate the temperature change rate of the outdoor heat exchanger ; Based on the outdoor heat exchanger temperature change rate , calculate defrost effect index ; Preset the defrost effect index threshold value, and set the defrost effect index The result is compared with the defrost effect index threshold, and whether the defrost is completed is determined according to the result; if the defrost is not completed, the defrost instruction is continued to be executed until the defrost completion condition is met, and then the defrost instruction is stopped.

[0055] (III) Beneficial effects

[0056] The present invention provides a defrosting control method and system for an air source heat pump unit, which has the following beneficial effects:

[0057] (1) Real-time collection of the temperature data, unit operation data, and unit heating data of the air source heat pump can fully grasp the operating status of the unit, discover potential problems in all aspects of the unit operation, and provide the possibility for subsequent precise analysis and control, ensuring that the unit can operate in the optimal state.

[0058] (2) Calculating the frosting rate and thickness helps to accurately determine the frosting condition of the unit and intuitively understand the speed and degree of frosting. Calculating the heat exchange efficiency drop rate can timely reflect the impact of frosting on the heating performance of the unit. This indicator can help to promptly detect performance degradation caused by frosting so that corresponding measures can be taken.

[0059] (3) Calculate the frost degree index and preset the threshold for comparison to determine whether the air source heat pump unit needs to be defrosted; this judgment mechanism can decide whether to defrost based on the actual frosting situation of the unit, avoiding unnecessary defrosting operations and untimely defrosting, and effectively improving the stability of the unit's operation and energy utilization.

[0060] (4) Calculate the total defrosting heat and defrosting time, which can reasonably plan the heat and time required for defrosting, ensuring that the defrosting process can effectively remove the frost layer without over-defrosting. Calculate the temperature change rate of the outdoor heat exchanger and the defrosting effect index, and then judge whether the defrosting is completed by comparing with the preset threshold. This can prevent energy waste and unit performance damage caused by over-defrosting, while ensuring that the frost layer is completely removed, ensuring the subsequent efficient operation of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 The present invention is a schematic diagram of the steps of a defrosting control method for an air source heat pump unit. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] See also Figure 1 The present invention provides a defrosting control method for an air source heat pump unit, comprising:

[0064] Step 1: Collect the temperature data, unit operation data and unit heating data of the air source heat pump in real time.

[0065] Comprehensive step one:

[0066] Through comprehensive and real-time data collection, the operating status of the unit can be fully understood, potential problems can be discovered in all aspects of the unit's operation, and the possibility of subsequent precise analysis and control is provided.

[0067] Step 2: Calculate the frosting rate based on the temperature data and unit operation data ; According to the frosting rate Calculate the frost thickness based on the unit operation data ; Calculate the heat exchange efficiency drop rate based on the unit heating data .

[0068] Step 201: Calculate the frosting rate , the specific steps are:

[0069] Temperature data includes the surface temperature of the outdoor heat exchanger at the current moment , the surface temperature of the outdoor heat exchanger at the last moment and outdoor air temperature .

[0070] It should be noted that by installing a temperature sensor on the surface of the outdoor heat exchanger, the surface temperature of the outdoor heat exchanger at the current moment is obtained. and the surface temperature of the outdoor heat exchanger at the previous moment By installing an air temperature sensor outdoors, the outdoor air temperature can be monitored and obtained in real time. .

[0071] Unit operating data including the heat exchange area of ​​the outdoor heat exchanger .

[0072] It should be noted that the heat exchange area of ​​the outdoor heat exchanger can be obtained according to the product manual or technical specification of the air source heat pump unit. .

[0073] According to the surface temperature , surface temperature , Outdoor air temperature and heat exchange area , calculate the frosting rate , the formula based on is:

[0074]

[0075] in, is the time interval; is the convective heat transfer coefficient of the outdoor heat exchanger; is the air mass flow rate; is the specific heat capacity of air at constant pressure, which is .

[0076] It should be noted that the time interval , by installing a temperature sensor on the surface of the outdoor heat exchanger, recording the time points of two measurements, and then calculating the difference between the two time points, the time interval can be obtained. .

[0077] Get the convective heat transfer coefficient of the outdoor heat exchanger , by obtaining the thermal conductivity of air and the length of the outdoor heat exchanger , calculate the convective heat transfer coefficient of the outdoor heat exchanger ;in, is the Nusselt number. This is used to obtain the convective heat transfer coefficient of the outdoor heat exchanger .

[0078] Get air mass flow , by obtaining the volume flow rate of air and air density , calculate the air mass flow .

[0079] It should be noted that Indicates the time interval The rate of change of the surface temperature of the indoor and outdoor heat exchangers. When the surface temperature drops rapidly, A larger value of means a faster frost formation rate. The effect of heat exchange between outdoor air and the outdoor heat exchanger surface on the frosting rate is taken into account. This term overall represents the effect of temperature change caused by heat exchange between air and the heat exchanger surface on the frosting rate. When the air temperature is higher than the heat exchanger surface temperature, the heat transfer will increase the surface temperature, thereby slowing down the frosting rate, so this term is a minus term in the formula. Frosting rate It is obtained by subtracting the temperature change caused by heat exchange between the air and the heat exchanger surface from the surface temperature change rate. In this way, the effects of surface temperature change and heat exchange on the frosting rate can be comprehensively considered, so as to calculate the frosting rate more accurately.

[0080] Step 202: Calculate frosting thickness , the specific steps are:

[0081] The unit operation data also includes the average wall temperature of the outdoor heat exchanger .

[0082] It should be noted that by installing multiple thermal resistors on the wall of the heat exchanger, the wall temperature is measured at multiple points on the heat exchanger using the thermal resistors. The average wall temperature of the outdoor heat exchanger is obtained by adding the wall temperatures measured each time and dividing by the number of measurements. .

[0083] According to the frosting rate , the average wall temperature of the outdoor heat exchanger and heat exchange area , calculate the frosting thickness , the formula based on is:

[0084]

[0085] in, It is the time for frosting; is the humidity content of outdoor air; is the molar mass of air, which is 28.97 g / mol; is the universal gas constant, which is ; is the saturated humidity content of outdoor air; is the dynamic viscosity of air.

[0086] It should be noted that obtaining the frosting time , use a timer to count from the moment the frosting starts until the frosting process ends, and record the elapsed time, which is the frosting time .

[0087] Get the humidity of outdoor air , by using a dry-bulb and wet-bulb thermometer to measure the dry-bulb temperature and wet-bulb temperature of the outdoor air. Then, based on the dry-bulb and wet-bulb temperature difference, the humidity content of the outdoor air is obtained by consulting the humidity calculation table. .

[0088] Get the outdoor air saturation humidity , by obtaining the saturated water vapor pressure es and atmospheric pressure p, the saturated humidity of outdoor air is calculated , the calculation formula is:

[0089] .

[0090] Get the dynamic viscosity of air , according to the measured air temperature, directly refer to the air property table to obtain the corresponding air dynamic viscosity .

[0091] It should be noted that This means that the faster the frosting rate and the longer the frosting time, the thicker the frosting will naturally be. It shows that the lower the wall temperature, the easier it is to frost; the larger the heat exchange area, the greater the possibility and thickness of frost. This formula takes into account factors such as air humidity conditions, physical properties, frost time, frost rate, and characteristics of the heat exchanger to calculate the frost thickness.

[0092] Step 203: Calculate the heat exchange efficiency drop rate , the specific steps are:

[0093] The unit heating data includes the evaporator inlet air temperature of the air source heat pump unit in the non-frost state. and evaporator outlet temperature And the evaporator inlet air temperature of the air source heat pump unit under frosting conditions and evaporator outlet temperature .

[0094] It should be noted that by installing a temperature sensor on the air inlet side of the evaporator of the air source heat pump unit, the temperature change can be accurately measured in real time to obtain the evaporator inlet temperature of the air source heat pump unit in the non-frost state. ; At the same time, a temperature sensor is installed on the air outlet side of the evaporator to measure the air temperature flowing out of the evaporator and obtain the evaporator air outlet temperature By operating the air source heat pump unit in a low temperature and high humidity environment, the evaporator surface is frozen. A temperature sensor is installed on the air inlet side to accurately measure the temperature change in real time, and the evaporator inlet temperature of the air source heat pump unit in the frosted state is obtained. ; Install a temperature sensor on the air outlet side of the evaporator to measure the air temperature flowing out of the evaporator and obtain the evaporator air outlet temperature .

[0095] Calculate the heat exchange efficiency drop rate based on the unit heating data , the calculation formula is:

[0096] .

[0097] It should be noted that It indicates the amount of heat transferred through the evaporator per unit time in an air source heat pump unit without frost. It indicates the amount of heat transferred through the evaporator per unit time when the air source heat pump unit is in a frosted state. Subtracting the two results in the amount of heat exchange reduction caused by frosting. Finally, multiply by , which indicates the percentage of heat transfer reduction to heat transfer in the non-frost state, i.e. the heat transfer efficiency decrease rate .

[0098] Comprehensive steps 201 to 203:

[0099] The frosting rate can intuitively reflect the speed of frosting, the frosting thickness shows the severity of frosting from a spatial scale, and the heat exchange efficiency reduction rate reflects the impact of frosting on the unit's working efficiency from the perspective of unit performance.

[0100] Step 3: According to the frosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index ; Preset the frost index threshold value and set the frost index Compare with the frost degree index threshold and determine whether the air source heat pump unit needs to be defrosted based on the result.

[0101] Step 301: Calculate the frost degree index , the specific steps are:

[0102] According to the frosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index , the calculation formula is:

[0103]

[0104] in, Frosting rate The weight coefficient is between 0.1 and 0.3; Frosting thickness The weight coefficient is between 0.3 and 0.4; Heat transfer efficiency decrease rate The weight coefficient is between 0.3 and 0.5; .

[0105] It should be noted that this formula takes into account the frosting rate , Frost thickness and heat transfer efficiency drop rate These three important parameters. Each parameter has a corresponding weight coefficient, indicating the importance of the weight coefficient in calculating the frost degree index. By multiplying each parameter by its corresponding weight coefficient and then summing them up, we can get an index that can fully describe the frost degree of the air source heat pump unit. .

[0106] Step 302: Determine whether the air source heat pump unit needs to be defrosted. The specific steps are:

[0107] Preset frost level indicator threshold ; By conducting operation tests on the air source heat pump unit under different outdoor temperature, humidity and other environmental conditions, the operating performance data of the unit under different degrees of frost were recorded. In the experiment, when the frost thickness reached a certain value, the heating efficiency of the unit began to decline significantly, and the corresponding frost degree index value at this time was used as the frost degree index threshold. For example, when the frost thickness reached 3mm, it was found that the heating efficiency of the unit dropped from the initial 4.0 to 3.2, a decrease of 20%. At this time, the frost degree index value corresponding to the frost thickness of 3mm is used as the frost degree index threshold.

[0108] when When the air source heat pump unit does not need to defrost; When the air source heat pump unit needs to be defrosted, the defrost instruction is executed.

[0109] Comprehensive step 301~step 302:

[0110] By calculating the frost degree index, the frost degree of the unit is accurately measured, thus providing a scientific and reliable basis for whether defrosting is needed. The preset threshold value can ensure the timeliness and necessity of defrosting operation. It avoids the problems of untimely or excessive defrosting that may occur in traditional timed defrosting or single temperature difference defrosting methods.

[0111] Step 4: When the air source heat pump unit needs to defrost, execute the defrost instruction and Calculate the total defrosting heat with the unit operation data ; Based on total defrosting heat , calculate the defrost time ; According to temperature data and defrosting time , calculate the temperature change rate of the outdoor heat exchanger ; Based on the outdoor heat exchanger temperature change rate , calculate defrost effect index ; Preset the defrost effect index threshold value, and set the defrost effect index The result is compared with the defrost effect index threshold, and whether the defrost is completed is determined according to the result; if the defrost is not completed, the defrost instruction is continued to be executed until the defrost completion condition is met, and then the defrost instruction is stopped.

[0112] Step 401: Calculate total defrosting heat , the specific steps are:

[0113] When the air source heat pump unit needs to defrost, according to the thickness of the frost Heat exchange area of ​​outdoor heat exchanger , calculate the total heat of defrosting , the calculation formula is:

[0114]

[0115] in, is the frost layer density; is the melting latent heat of frost, which is 334KJ / kg; is the average specific heat capacity of the frost layer and the heat exchanger surface; is the melting point of frost, which is 0°C; is the initial average temperature of the frost layer and the heat exchanger surface.

[0116] It should be noted that obtaining the frost density , according to the frost mass ml and frost volume vl, calculate the frost layer density , .

[0117] Get the average specific heat capacity of the frost layer and heat exchanger surface , through calorimetric experiments, the temperature changes of the system consisting of frost layer and heat exchanger surface are measured in a cooling environment T, heat transfer Qm and total mass mm, then calculate .

[0118] Get the initial average temperature of the frost layer and heat exchanger surface By arranging multiple temperature sensors on the heat exchanger surface and in the frost layer, measuring their initial temperatures, and then taking the average value, the initial average temperature of the frost layer and the heat exchanger surface is obtained. .

[0119] It should be noted that The mass of the frost layer is calculated. Then multiply it by the latent heat of melting of the frost. , and obtain the heat required to change the frost layer from solid to liquid, that is, the latent heat of melting. This part calculates the temperature of the frost layer and the heat exchanger surface from the initial average temperature Heat to melting point This formula calculates the total heat required for defrosting by calculating the latent heat required to melt the frost layer and the sensible heat required to heat the frost layer and the heat exchanger surface to the melting point. .

[0120] Step 402: Calculate defrost time , the specific steps are:

[0121] Based on total heat of defrosting , calculate the defrost time , the calculation formula is:

[0122]

[0123] in, It is the mass flow rate of high-temperature refrigerant discharged from the compressor; is the constant pressure specific heat capacity of the refrigerant; is the temperature of the refrigerant entering the outdoor heat exchanger; It is the temperature of the refrigerant leaving the outdoor heat exchanger.

[0124] It should be noted that the mass flow rate of the high-temperature refrigerant discharged from the compressor is obtained , by installing a mass flow meter on the refrigerant pipe at the compressor outlet. The mass flow meter can directly measure the mass flow of the refrigerant and obtain the mass flow of the high-temperature refrigerant discharged by the compressor. .

[0125] Get the constant pressure specific heat capacity of the refrigerant , by consulting the refrigerant physical properties table, obtain the constant pressure specific heat capacity of the refrigerant .

[0126] Get the temperature of the refrigerant entering the outdoor heat exchanger , install a temperature sensor on the pipe where the refrigerant enters the outdoor heat exchanger to directly measure the temperature of the refrigerant when it enters the heat exchanger, and obtain the temperature of the refrigerant entering the outdoor heat exchanger .

[0127] Get the temperature of the refrigerant leaving the outdoor heat exchanger , install a temperature sensor on the pipe where the refrigerant leaves the outdoor heat exchanger to directly measure the temperature of the refrigerant when it leaves the heat exchanger, and obtain the temperature of the refrigerant leaving the outdoor heat exchanger. .

[0128] It should be noted that Indicates the amount of heat that the refrigerant can transfer per unit time. Multiply by the constant pressure specific heat capacity of the refrigerant , and obtain the heat that the refrigerant can carry per unit mass flow rate. The product of these two temperatures reflects to some extent the effect of the temperature change of the refrigerant in the heat exchanger on the heat transfer. Divide by the heat that the refrigerant can provide for defrosting per unit time to get the defrosting time .

[0129] Step 403: Calculate the temperature change rate of the outdoor heat exchanger , the specific steps are:

[0130] The temperature data also includes the inlet temperature of the outdoor heat exchanger when defrosting starts. , outlet temperature And the inlet temperature of the outdoor heat exchanger at the end of defrosting and outlet temperature .

[0131] It should be noted that by installing the temperature sensor on the pipe where the refrigerant enters the outdoor heat exchanger at the beginning and end of defrosting, the temperature change is measured in real time to obtain the inlet temperature and inlet temperature The temperature sensor is installed on the pipe where the refrigerant leaves the outdoor heat exchanger at the beginning and end of defrosting, and the temperature change is measured in real time to obtain the outlet temperature. and outlet temperature .

[0132] According to defrosting time , inlet temperature , outlet temperature and inlet temperature and outlet temperature , calculate the temperature change rate of the outdoor heat exchanger , the calculation formula is:

[0133] .

[0134] It should be noted that This part calculates the average rate of change of the outdoor heat exchanger inlet temperature during the defrosting process. This part calculates the average rate of change of the outdoor heat exchanger outlet temperature during the defrosting process. The denominator is 2, which means that the inlet temperature change rate and the outlet temperature change rate are averaged. This formula calculates the average rate of change of the outdoor heat exchanger inlet temperature and outlet temperature during the defrosting process, and takes the average value to get the outdoor heat exchanger temperature change rate. .

[0135] Step 404: Calculate defrosting effect index , the specific steps are:

[0136] Based on the outdoor heat exchanger temperature change rate , calculate defrost effect index , the calculation formula is:

[0137]

[0138] in, It is the defrost water discharge speed; It is the compressor operation status indicator; is the temperature change rate of the outdoor heat exchanger The weight coefficient is between 0.2 and 0.3; Defrost water discharge speed The weight coefficient is 0.3~0.4; Compressor operating status indicator The weight coefficient is between 0.4 and 0.5; and .

[0139] It should be noted that the defrost water discharge speed is , by placing a container under the defrost water discharge pipe, collecting defrost water during the defrosting process, and using a stopwatch to record the time required to collect a certain amount of defrost water. The defrost water discharge speed can be estimated by calculating the volume of defrost water collected and the time used. For example, if the volume of defrost water collected is vn and the time used is tn, then the defrost water discharge speed is .

[0140] Get compressor operating status indicators , the operating parameters of the compressor are monitored by the sensor installed on the compressor to obtain the current ,Voltage ,power and pressure ;

[0141] According to the current ,Voltage ,power and pressure , calculate the compressor operating status index , the calculation formula is:

[0142]

[0143] in, For current The weight coefficient is between 0.2 and 0.3; For voltage The weight coefficient is between 0.2 and 0.4; Power The weight coefficient is 0.3~0.4; For pressure The weight coefficient is between 0.1 and 0.3; .

[0144] It should be noted that this formula takes into account the temperature change rate of the outdoor heat exchanger. , defrost water discharge speed and compressor operating status indicators These three important parameters. Each parameter has a corresponding weight coefficient, which indicates the weight of the defrosting effect index. By multiplying each parameter with its corresponding weight coefficient and then summing them up, we can get the defrosting effect index. .

[0145] Step 405: Determine whether defrosting is completed. The specific steps are:

[0146] Preset defrost effect index threshold ; By conducting operation tests on the air source heat pump unit under different outdoor temperature, humidity and other environmental conditions, the operating performance data of the unit under different defrosting degrees was recorded. In the experiment, when the defrost water discharge rate reached a certain value, and the temperature change rate of the outdoor heat exchanger and the operating status of the compressor were both stable within a certain range, the heating efficiency of the unit began to recover significantly, and the corresponding defrost effect index value at this time was used as the defrost effect index threshold. For example, when the defrost water discharge rate reached 10L / h, the temperature change rate of the outdoor heat exchanger was stable at 2℃ / h, and the compressor operating status fluctuated within the range of ±5%, it was found that the heating efficiency of the unit increased from 3.0 before defrosting to 3.8, and the recovery was obvious. At this time, the corresponding defrost effect index is used as the defrost effect index threshold.

[0147] when When , it is judged that defrosting is completed; when When the defrost is not completed, it is judged that the defrost is not completed, and the defrost instruction is continued to be executed until the defrost completion conditions are met, and then the defrost instruction is stopped.

[0148] Comprehensive steps 401 to 405:

[0149] By calculating the total defrosting heat and defrosting time, the energy and time resources required for defrosting can be reasonably allocated to avoid energy waste. The temperature change rate of the outdoor heat exchanger and the defrosting effect index are calculated, and the defrosting is judged by comparing with the preset threshold value to ensure that the defrosting operation can completely remove the frost layer without causing damage to the unit due to excessive defrosting, thus achieving precise control and optimization of the defrosting process.

[0150] On the other hand, the present invention further discloses an air source heat pump unit defrost control system, which is used to implement the above-mentioned air source heat pump unit defrost control method, comprising:

[0151] Data acquisition module, used to collect temperature data, unit operation data and unit heating data of air source heat pump in real time;

[0152] Frosting degree calculation module, used to calculate the frost rate based on temperature data and unit operation data ; According to the frosting rate Calculate the frost thickness based on the unit operation data ; Calculate the heat exchange efficiency drop rate based on the unit heating data ;

[0153] Defrost judgment module, used to judge the defrosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index ; Preset the frost index threshold value and set the frost index Compare with the frost degree index threshold, and judge whether the air source heat pump unit needs to be defrosted according to the result;

[0154] The defrost monitoring module is used to execute the defrost instruction when the air source heat pump unit needs to defrost, and based on the frost thickness Calculate the total defrosting heat with the unit operation data ; Based on total defrosting heat , calculate the defrost time ; According to temperature data and defrosting time , calculate the temperature change rate of the outdoor heat exchanger ; Based on the outdoor heat exchanger temperature change rate , calculate defrost effect index ; Preset the defrost effect index threshold value, and set the defrost effect index The result is compared with the defrost effect index threshold, and whether the defrost is completed is determined according to the result; if the defrost is not completed, the defrost instruction is continued to be executed until the defrost completion condition is met, and then the defrost instruction is stopped.

[0155] The above embodiments may be implemented in whole or in part by software, hardware, firmware or any other combination thereof. When implemented using software, the above embodiments may be implemented in whole or in part in the form of a computer program product. A person of ordinary skill in the art may appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein may be implemented in electronic hardware or in combination with computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution.

[0156] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0157] The above description is only a specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application.

Claims

1. A defrosting control method for an air source heat pump unit, characterized in that: include: Real-time collection of air source heat pump temperature data, unit operation data and unit heating data; Calculate the frosting rate based on temperature data and unit operation data ; According to the frosting rate Calculate the frost thickness based on the unit operation data ; Calculate the heat exchange efficiency drop rate based on the unit heating data ; According to the frosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index ; Calculate the frost degree index The method is: according to the frosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index , the calculation formula is: in, Frosting rate The weight coefficient is between 0.1 and 0.3; Frosting thickness The weight coefficient is 0.3~0.4; Heat transfer efficiency decrease rate The weight coefficient is between 0.3 and 0.5; ; Preset frost index threshold value, set frost index Compare with the frost degree index threshold, and judge whether the air source heat pump unit needs to be defrosted according to the result; When the air source heat pump unit needs to defrost, the defrost instruction is executed and based on the frost thickness Calculate the total defrosting heat with the unit operation data ; Based on total defrosting heat , calculate the defrost time ; According to temperature data and defrosting time , calculate the temperature change rate of the outdoor heat exchanger ; Based on the outdoor heat exchanger temperature change rate , calculate the defrosting effect index ; Preset the defrost effect index threshold value, and set the defrost effect index Compare with the defrost effect index threshold, and judge whether defrost is completed according to the result; if defrost is not completed, continue to execute the defrost instruction until the defrost completion condition is met, and then stop the defrost instruction; The method to judge whether defrosting is completed is: Based on the outdoor heat exchanger temperature change rate , calculate the defrosting effect index , the calculation formula is: in, It is the defrost water discharge speed; It is the compressor operation status indicator; is the temperature change rate of the outdoor heat exchanger The weight coefficient is between 0.2 and 0.3; Defrost water discharge speed The weight coefficient is 0.3~0.4; Compressor operating status indicator The weight coefficient is between 0.4 and 0.5; and ; Preset defrost effect index threshold ;when When , it is judged that defrosting is completed; when When the defrost is not completed, it is judged that the defrost is not completed, and the defrost instruction is continued to be executed until the defrost completion conditions are met, and then the defrost instruction is stopped.

2. The defrosting control method of an air source heat pump unit according to claim 1, characterized in that: Calculating the frost rate The method is: Temperature data includes the surface temperature of the outdoor heat exchanger at the current moment , the surface temperature of the outdoor heat exchanger at the last moment and outdoor air temperature ; Unit operating data including the heat exchange area of ​​the outdoor heat exchanger ; According to the surface temperature , surface temperature , Outdoor air temperature and heat exchange area , calculate the frosting rate , the formula based on is: in, is the time interval; is the convective heat transfer coefficient of the outdoor heat exchanger; is the air mass flow rate; is the specific heat of air at constant pressure.

3. The defrosting control method of an air source heat pump unit according to claim 2, characterized in that: Calculate frost thickness The method is: The unit operation data also includes the average wall temperature of the outdoor heat exchanger ; According to the frosting rate , the average wall temperature of the outdoor heat exchanger and heat exchange area , calculate the frosting thickness , the formula based on is: in, It is the time for frosting; is the humidity content of outdoor air; is the molar mass of air; is the universal gas constant; is the saturated humidity content of outdoor air; is the dynamic viscosity of air.

4. The defrosting control method of an air source heat pump unit according to claim 3, characterized in that: Calculate the heat transfer efficiency drop rate The method is: The unit heating data includes the evaporator inlet air temperature of the air source heat pump unit in the non-frost state. and evaporator outlet temperature And the evaporator inlet air temperature of the air source heat pump unit under frosting conditions and evaporator outlet temperature ; Calculate the heat exchange efficiency drop rate based on the unit heating data , the calculation formula is: 。 5. The defrosting control method of an air source heat pump unit according to claim 4, characterized in that: The method to determine whether the air source heat pump unit needs defrosting is: Preset frost level indicator threshold ;when When the air source heat pump unit does not need to defrost; When the air source heat pump unit needs to be defrosted, the defrost instruction is executed.

6. The defrosting control method of an air source heat pump unit according to claim 5, characterized in that: Calculate total defrost heat The method is: When the air source heat pump unit needs to defrost, according to the thickness of the frost Heat exchange area with outdoor heat exchanger , calculate the total heat of defrosting , the calculation formula is: in, is the frost layer density; is the latent heat of melting of frost; is the average specific heat capacity of the frost layer and the heat exchanger surface; is the melting point of frost; is the initial average temperature of the frost layer and the heat exchanger surface.

7. The defrosting control method of an air source heat pump unit according to claim 6, characterized in that: Calculate defrost time The method is: Based on total heat of defrosting , calculate the defrost time , the calculation formula is: in, It is the mass flow rate of high-temperature refrigerant discharged from the compressor; is the constant pressure specific heat capacity of the refrigerant; is the temperature of the refrigerant entering the outdoor heat exchanger; It is the temperature of the refrigerant leaving the outdoor heat exchanger.

8. The defrosting control method of an air source heat pump unit according to claim 7, characterized in that: Calculate the rate of change of outdoor heat exchanger temperature The method is: The temperature data also includes the inlet temperature of the outdoor heat exchanger when defrosting starts. , outlet temperature And the inlet temperature of the outdoor heat exchanger at the end of defrosting and outlet temperature ; According to defrosting time , inlet temperature , outlet temperature and inlet temperature and outlet temperature , calculate the temperature change rate of the outdoor heat exchanger , the calculation formula is: 。 9. A defrost control system for an air source heat pump unit, characterized in that: A defrosting control method for an air source heat pump unit for implementing any one of claims 1 to 8, comprising: Data acquisition module, used to collect temperature data, unit operation data and unit heating data of air source heat pump in real time; Frosting degree calculation module, used to calculate the frost rate based on temperature data and unit operation data ; According to the frosting rate Calculate the frost thickness based on the unit operation data ; Calculate the heat exchange efficiency drop rate based on the unit heating data ; Defrost judgment module, used to judge the defrosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index ; Calculate the frost degree index The method is: according to the frosting rate , Frost thickness and heat transfer efficiency drop rate , calculate the frost degree index , the calculation formula is: in, Frosting rate The weight coefficient is between 0.1 and 0.3; Frosting thickness The weight coefficient is 0.3~0.4; Heat transfer efficiency decrease rate The weight coefficient is between 0.3 and 0.5; ; Preset frost index threshold value, set frost index Compare with the frost degree index threshold, and judge whether the air source heat pump unit needs to be defrosted according to the result; The defrost monitoring module is used to execute the defrost instruction when the air source heat pump unit needs to defrost, and based on the frost thickness Calculate the total defrosting heat with the unit operation data ; Based on total defrosting heat , calculate the defrost time ; According to temperature data and defrosting time , calculate the temperature change rate of the outdoor heat exchanger ; Based on the outdoor heat exchanger temperature change rate , calculate the defrosting effect index ; Preset the defrost effect index threshold value, and set the defrost effect index The result is compared with the defrost effect index threshold, and whether the defrost is completed is determined according to the result; if the defrost is not completed, the defrost instruction is continued to be executed until the defrost completion condition is met, and then the defrost instruction is stopped.

Images