Frost layer monitoring and defrost control device and control method

Abstract

The present invention provides a frost layer monitoring and defrost control device and a control method for a refrigeration system. The refrigeration system includes an evaporator and a fan. The frost layer detection and control device includes: a pressure differential sensor, which collects static pressure difference data before and after the evaporator at a specified time interval t1 under low-temperature refrigeration conditions; a control module, which is communicatively connected to the pressure differential sensor module, calculates and outputs a real-time pressure loss coefficient PLF of the evaporator based on the static pressure differential data; and controls whether the refrigeration system enters a defrost mode based on the pressure loss coefficient PLF. The present invention only needs to measure the static pressure difference before and after the evaporator, and based on the theory of a one-dimensional constant flow energy equation, performs dimensionless processing on the measured static pressure difference data, and obtains the pressure loss coefficient PLF to determine whether to defrost. It does not require a complex control method or a frost diagram, has a moderate cost, and is conducive to promotion. It effectively solves the problem that the traditional defrosting method controlled by the pressure differential sensor is affected by the evaporator type and fin structure, and realizes precise defrosting.

Description

Technical Field

[0001] The present invention relates to the field of air conditioning or heat pumps, and in particular to a frost layer monitoring and defrosting control device and a control method. Background Art

[0002] For refrigeration systems (air-source heat pumps), frost forms on the system's evaporator (outdoor unit) when the heat exchanger surface temperature falls below the air dew point and below 0°C. When the frost layer accumulates to a certain thickness, the spacing between the evaporator's heat exchange fins decreases, blocking the air flow path and increasing the pressure drop and heat transfer resistance. This significantly reduces the evaporator's heat transfer performance and lowers the system's energy efficiency ratio (COP). Therefore, to ensure efficient and long-term stable operation of the system, the evaporator needs to be periodically defrosted.

[0003] Time control and time-temperature control methods are widely used in practical projects due to their simple operation and low construction costs. The time control method records the compressor's operating time and activates defrost mode when the compressor's operating time reaches a set value. The time-temperature control method uses the evaporation temperature or superheat and the compressor's operating time as a basis for controlling the start and stop of defrost. However, because frost formation is an extremely complex process, influenced by numerous factors such as air temperature and humidity, fan speed, and refrigerant temperature, these two defrost control methods can cause "false defrosts," such as defrosting without frost in low-temperature and low-humidity operating conditions. The occurrence of "false defrosts" can cause the system's average COP to drop to 40%, reducing heating capacity by 43.4%.

[0004] To avoid or reduce the occurrence of "false defrosts," researchers have proposed more advanced control strategies. For example, a frost spectrum map based on a temperature and humidity chart was developed to guide the determination of defrost timing, and frost areas were divided into light, moderate, and heavy frosting zones. The defrost start and stop points were determined by the minimum loss coefficient of the output heating energy, and the defrost start time was predicted using a topological multivariable nonlinear model. Other researchers have proposed defrost control based on defrost thickness measurement using a photoelectric sensor. Experimental comparisons with time-based control methods showed that the system's unnecessary defrost frequency decreased by 62.2%. Although these methods can improve the efficiency of system defrost cycle control to a certain extent, they require strict system specifications (artificial neural network control) or high cost or complex defrost control procedures (multivariable nonlinear pattern prediction, high-precision photoelectric sensors), which may restrict their application in practical projects. Other traditional defrost control systems based on air static pressure differential measurement have low accuracy due to limitations in evaporator type and fin structure, limiting their widespread use.

[0005] Therefore, it is necessary to develop a low-cost, highly universal, and easy-to-operate defrost control method. Summary of the Invention

[0006] In response to the above problems, the present invention provides a method for accurately detecting the growth of frost layer by simply monitoring the static pressure difference data before and after the fan and obtaining the pressure loss coefficient PLF after dimensionless processing. This can effectively improve the accuracy of the system in detecting frost layer, and has moderate cost. It effectively solves the problem of "false defrosting" caused by inaccurate control of existing refrigeration systems, thereby ensuring long-term stable and efficient operation of the system.

[0007] The present invention provides a frost layer monitoring and defrosting control device for a refrigeration system. The refrigeration system includes an evaporator and a fan. The frost layer detection and control device includes:

[0008] The differential pressure sensor collects the static pressure difference data before and after the evaporator at the specified time interval t1 under low-temperature refrigeration conditions;

[0009] The control module is in communication with the pressure difference sensor module, calculates and outputs a real-time pressure loss coefficient PLF of the evaporator according to the static pressure difference data, and controls whether the refrigeration system enters a defrost mode according to the pressure loss coefficient PLF;

[0010] Pressure loss coefficient

[0011] Where ΔP is the total pressure of the evaporator; ΔP0 is the initial static pressure difference of the evaporator; ΔP1 is the static pressure difference of the evaporator at time t1.

[0012] According to the present invention, the pressure loss coefficient PLF represents the ratio of the change in the static pressure difference before and after the evaporator due to the growth of the frost layer, wherein ΔP1-ΔP0 represents the degree of increase in the resistance along the path and the local resistance loss due to the growth of the frost at time t1; ΔP-ΔP0 represents the degree of increase in the resistance along the path and the local resistance loss when the frost layer covers the entire evaporator. At this time, the static pressure difference before and after the evaporator is the largest, that is, the total pressure ΔP of the fan at this fan speed. Theoretically, P f The maximum value is equal to the total pressure ΔP of the fan minus ΔP0. Whether to enter defrost control is determined according to the pressure loss coefficient PLF, thereby improving the accuracy of defrost control. The present invention only needs to measure the static pressure difference before and after the evaporator, and based on the theory of the one-dimensional constant flow energy equation, the measured static pressure difference data is dimensionlessly processed to obtain the pressure loss coefficient PLF; no complicated control method or frosting diagram is required, and except for the fan speed, the static pressure difference control is independent of the refrigerant state and the system operating conditions, ensuring moderate cost and facilitating promotion; and effectively solves the problem that the traditional defrost control method controlled by the pressure difference sensor is affected by the evaporator type and fin structure, thereby achieving precise defrosting.

[0013] In an optional technical solution of the present invention, the differential pressure sensor is installed on the central axis of the evaporator.

[0014] According to this technical solution, the accuracy of static pressure difference measurement can be improved, thereby improving the accuracy of defrost judgment.

[0015] In an optional technical solution of the present invention, when the pressure loss coefficient PLF is greater than a set threshold, the control module controls the refrigeration system to enter the defrost mode; the set threshold is the pressure loss coefficient corresponding to when the heat transfer efficiency of the evaporator drops significantly.

[0016] According to this technical solution, when the heat transfer efficiency of the evaporator drops significantly, it reflects that the thickness of the frost layer causes the performance of the evaporator to decline. When the pressure loss coefficient calculated in real time is greater than the pressure loss coefficient corresponding to the significant drop in heat transfer efficiency, the defrost mode is entered, which improves the accuracy of the defrost judgment and can prevent the frost layer from further thickening.

[0017] The optional technical solution of the present invention further includes a temperature detection module for detecting the inlet air temperature, outlet air temperature and evaporation temperature of the evaporator. The real-time heat transfer efficiency is related to the inlet air temperature, outlet air temperature and evaporation temperature.

[0018] According to this technical solution, the heat transfer efficiency Where Tin is the inlet air temperature; Tout is the outlet air temperature; Tube is the evaporation temperature.

[0019] The optional technical solution of the present invention also includes a timing module, which is communicated with the control module. The timing module is used to set the defrost time and collect the defrost time. When the defrost time is greater than the set time, the control module controls the refrigeration system to exit the defrost mode.

[0020] According to this technical solution, the defrost mode can be exited in time to avoid incomplete defrosting caused by too short a defrost time or too long a defrost time, which affects the user's comfort experience.

[0021] In an optional technical solution of the present invention, the refrigeration system is an air source heat pump system or an air conditioning system.

[0022] According to the technical solution, the frost layer monitoring and defrosting control device of the present invention is suitable for air source heat pump systems and air conditioning systems and has strong applicability.

[0023] The present invention further provides a frost layer monitoring and defrost control method for a refrigeration system, wherein the refrigeration system includes an evaporator and a fan, and the frost layer monitoring and defrost control method includes the following steps:

[0024] S1: Collect static pressure difference data before and after the evaporator under low temperature conditions at time interval t1.

[0025] S2: Calculate and output the real-time pressure loss coefficient PLF of the evaporator based on the static pressure difference data;

[0026] Pressure loss coefficient

[0027] Where ΔP is the total pressure of the evaporator; ΔP0 is the initial static pressure difference of the evaporator; ΔP1 is the static pressure difference of the evaporator at time t1.

[0028] S3: Control whether the refrigeration system enters the defrost mode according to the pressure loss coefficient PLF.

[0029] In an optional technical solution of the present invention, “controlling whether the refrigeration system enters the defrost mode according to the pressure loss coefficient PLF” includes: determining whether the pressure loss system PLF is not less than a set threshold, and if so, controlling the refrigeration system to enter the defrost mode; if not, returning to S1;

[0030] In an optional technical solution of the present invention, the threshold value is set as the pressure loss coefficient corresponding to a significant decrease in the real-time heat transfer efficiency of the evaporator.

[0031] The optional technical solution of the present invention also includes setting the defrost time and collecting the defrost time. When the defrost time is greater than the set time, the refrigeration system is controlled to exit the defrost mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the frost layer monitoring and defrost control device in an embodiment of the present invention.

[0033] Figure 2 Schematic diagram of the flow of the frost layer monitoring and defrost control method in an embodiment of the present invention.

[0034] Reference numerals:

[0035] Refrigeration system 1; pressure difference sensor 2; control module 3; temperature detection module 4; timing module 5. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0037] like Figure 1As shown, the present invention provides a frost layer monitoring and defrost control device for a refrigeration system. The refrigeration system 1 includes an evaporator and a fan. The frost layer detection and control device includes: a pressure differential sensor 2 and a control module 3. Under low-temperature refrigeration conditions, the pressure differential sensor 2 collects static pressure difference data before and after the evaporator at a specified time interval t1; the signal output end of the pressure differential sensor 2 is connected to the signal input end of the control module 3, and the control module 3 calculates and outputs the real-time pressure loss coefficient PLF of the evaporator based on the static pressure difference data;

[0038] Pressure loss coefficient

[0039] Wherein, ΔP is the total pressure of the evaporator; ΔP0 is the initial static pressure difference of the evaporator; ΔP1 is the static pressure difference of the evaporator at time t1; the control signal output end of the control module 3 is connected to the defrost signal input end of the refrigeration system 1, and the control module 3 determines whether to send a defrost signal to the refrigeration system 1 according to the pressure loss coefficient PLF. The refrigeration system 1 enters / exits the defrost mode according to the defrost signal.

[0040] Measuring the static pressure difference across the evaporator eliminates the need for complex control methods or frost maps. Pressure difference control is independent of the refrigerant state and system operating conditions, except for the fan speed. Frost formation, which leads to a decrease in air flow, is one of the main reasons for the reduction in evaporator heat exchange capacity. Therefore, the pressure difference across the evaporator can directly reflect the degree of frost formation and the heat exchange capacity of the system. According to this embodiment, the pressure loss coefficient PLF represents the ratio of the change in the static pressure difference across the evaporator due to the growth of the frost layer, where P f =ΔP1-ΔP0 represents the degree of increase in the along-the-line resistance and local resistance loss due to the growth of frost at time t1; P f max=ΔP-ΔP0 represents the degree of increase in resistance along the way and local resistance loss when the frost layer covers the entire evaporator. At this time, the static pressure difference before and after the evaporator is the largest, that is, the total pressure ΔP of the fan at this fan speed. In theory, P f The maximum value is equal to the total pressure ΔP of the fan minus ΔP0. Whether to enter defrost control is determined according to the pressure loss coefficient PLF, thereby improving the accuracy of defrost control. The present invention only needs to measure the static pressure difference before and after the evaporator, and based on the theory of the one-dimensional constant flow energy equation, the measured static pressure difference data is dimensionlessly processed to obtain the pressure loss coefficient PLF; no complicated control method or frosting diagram is required. Except for the fan speed, the static pressure difference control is independent of the refrigerant state and the system operating conditions, ensuring moderate cost and facilitating promotion; and effectively solves the problem that the traditional defrost control method of the pressure difference sensor 2 is affected by the evaporator type and fin structure, thereby achieving precise defrosting.

[0041] In a preferred embodiment of the present invention, the differential pressure sensor 2 is installed on the front and rear sides of the fan. Furthermore, the differential pressure sensor 2 is installed above the central axis of the evaporator, specifically, 10 cm from the top of the central axis of the evaporator. The differential pressure sensor 2 is preferably TRD150-205A / 0-500Pa.

[0042] In a preferred embodiment of the present invention, a temperature detection module 4 is also included, which is installed on the air inlet side, air outlet side and pipe wall of the evaporator to detect the air inlet temperature, air outlet temperature and evaporation temperature of the evaporator. The real-time heat transfer efficiency of the evaporator is related to the air inlet temperature, air outlet temperature and evaporation temperature.

[0043] Specifically, the real-time heat transfer efficiency of the evaporator Where Tin is the inlet air temperature; Tout is the outlet air temperature; and Tube is the evaporation temperature. During system operation, the evaporator's heat transfer efficiency is calculated. When the heat transfer efficiency drops significantly, the time t is recorded. The corresponding pressure loss coefficient PLF at this time is the set threshold for initiating system defrost. Preferably, this set threshold is 0.48, which is data obtained through multiple experiments. In the experiments, the pressure loss coefficient corresponding to the moment when the heat transfer efficiency drops significantly is 0.48. This set threshold is preset in control module 3. When the pressure loss coefficient PLF is greater than the set threshold of 0.48, control module 3 controls refrigeration system 1 to enter defrost mode. When the evaporator's heat transfer efficiency drops significantly, it reflects that the thickness of the frost layer has caused the evaporator's performance to decline. When the real-time calculated pressure loss coefficient is greater than the pressure loss coefficient corresponding to the significant drop in heat transfer efficiency, the defrost mode is entered, which improves the accuracy of the defrost judgment and can prevent the frost layer from further thickening. Furthermore, the temperature detection module 4 is also used to detect the outdoor ambient temperature. Under the low-temperature refrigeration conditions specified in the present invention, the outdoor ambient temperature may be lower than 0°C or lower than 4°C. When the outdoor ambient temperature is lower than the specified temperature and is in the refrigeration mode, the defrost judgment is performed, which can avoid frequent execution of the defrost judgment, affecting the normal use of the refrigeration system, and improving the user's comfort.

[0044] In a preferred embodiment of the present invention, a timing module 5 is further included, which is in communication with the control module 3. The timing module 5 is used to set the defrost duration and collect the defrost time. When the defrost time exceeds the set duration, the control module 3 controls the refrigeration system 1 to exit the defrost mode. Furthermore, the timing module 5 is installed in the refrigeration system 1, and the output end of the timing module 5 is connected to the input end of the control module 3.

[0045] Through the above method, the defrost mode can be exited in time to avoid incomplete defrosting caused by too short defrosting time and too long defrosting time, which affects the user's comfort experience.

[0046] In a preferred embodiment of the present invention, the refrigeration system 1 is an air source heat pump system or an air conditioning system.

[0047] In the above manner, the frost layer monitoring and defrosting control device of the present invention is applicable to air source heat pump systems and air conditioning systems, and has strong applicability.

[0048] like Figure 2 As shown, the present invention further provides a frost layer monitoring and defrost control method for a refrigeration system. The refrigeration system 1 includes an evaporator and a fan. The frost layer monitoring and defrost control method includes the following steps:

[0049] S1: Collect static pressure difference data before and after the evaporator under low temperature conditions at time interval t1.

[0050] S2: Calculate and output the real-time pressure loss coefficient PLF of the evaporator based on the static pressure difference data;

[0051] Pressure loss coefficient

[0052] Where ΔP is the total pressure of the evaporator; ΔP0 is the initial static pressure difference of the evaporator; ΔP1 is the static pressure difference of the evaporator at time t1.

[0053] S3: Controlling whether the refrigeration system 1 enters the defrost mode according to the pressure loss coefficient PLF.

[0054] In particular, the method for determining the pressure loss coefficient PLF is as follows: the static pressure difference data before and after the evaporator is processed. Under constant wind speed, the static pressure difference ΔP1 collected at the current time t1 is subtracted from the static pressure difference ΔP0 collected by the evaporator at time t0. The resulting difference is divided by the difference between the total pressure ΔP of the fan at the wind speed and the static pressure difference ΔP0 collected by the evaporator at time t0. The result is the pressure loss coefficient PLF at the current time t1.

[0055] It should be noted that the method for determining the static pressure difference ΔP0 collected by the evaporator at time t0 is as follows: if the fan is a fixed-frequency fan, the static pressure difference before and after the evaporator is collected at the constant wind speed when the system is initially running as ΔP0; if the fan is a variable-frequency fan, each time the frequency is changed, the static pressure difference of the evaporator at the constant wind speed is input as ΔP0.

[0056] It should be noted that the fan's total pressure ΔP is determined by the fan's total pressure at a specific wind speed. This pressure can be obtained from the fan performance curve provided by the manufacturer. For fixed-frequency fans, the control system only needs to input the fan's total pressure at that wind speed. For variable-frequency fans, the control system must re-enter the fan's total pressure at a constant wind speed after each frequency change.

[0057] Processing of static pressure difference data:

[0058] (1) Based on the fan performance curve of the selected evaporator (outdoor unit), the initial static pressure difference ΔP0 before and after the evaporator and the fan total pressure ΔP at a specific wind speed can be determined. After obtaining the initial static pressure difference ΔP0 and the evaporator fan total pressure ΔP, perform the following steps:

[0059] (1) The static pressure difference before and after the evaporator is collected in real time at a time interval of t1. The measured static pressure difference is ΔP1. Preferably, t1 is 60s;

[0060] (2) Determine the pressure loss coefficient PLF of the evaporator as the frost layer grows at the current time t1:

[0061] According to the steady flow energy equation of the gas, formula (1) can be obtained:

[0062]

[0063] Where: v1 and v2 are the gas velocities at time t1 and t2, respectively, in m / s; ρ is the gas density, in kg / m 3 ; P1 and P2 are the absolute pressures of the gas at time t1 and t2, Pa; P w It is the sum of the gas loss along the way and the local resistance, Pa.

[0064] Under the condition that the evaporator type is determined, the static pressure difference before and after the evaporator is only related to the fan speed. Therefore, the initial static pressure difference ΔP0 of the evaporator can be determined by the fan performance curve corresponding to the selected evaporator type.

[0065] When frost forms on the fins of the evaporator, the frost attached to the evaporator will reduce the flow channel area of ​​the air through the evaporator, causing the difference between the inlet and outlet flow velocities v of the fan and P w This will increase the static pressure difference before and after the evaporator. Therefore, the difference between the two is P f It is used to qualitatively express the degree of increase in the along-the-line resistance and local resistance loss due to frost growth, as shown in formula (2):

[0066] P f =ΔP l -ΔP0 (2)

[0067] When the frost layer covers the entire evaporator, the static pressure difference before and after the evaporator is the largest, that is, the total pressure of the fan ΔP at this fan speed. f The maximum value is equal to the total pressure of the fan ΔP minus ΔP0, as shown in formula (3):

[0068] P fmax =ΔP-ΔP0 (3)

[0069] Combining the above formulas (2) and (3), a dimensionless number can be calculated, namely the pressure loss coefficient PLF, which is expressed as the ratio of the change in the static pressure difference before and after the evaporator due to the growth of the frost layer, as shown in formula (4):

[0070]

[0071] In a preferred embodiment of the present invention, “controlling whether the refrigeration system 1 enters the defrost mode according to the pressure loss coefficient PLF” includes: determining whether the pressure loss coefficient PLF is not less than a set threshold value, and if so, controlling the refrigeration system 1 to enter the defrost mode; if not, returning to S1;

[0072] In a preferred embodiment of the present invention, the threshold value is set to the pressure loss coefficient corresponding to a significant decrease in the heat transfer efficiency of the evaporator.

[0073] In a preferred embodiment of the present invention, it further includes setting a defrost duration and collecting the defrost time. When the defrost time is greater than the set duration, the refrigeration system 1 is controlled to exit the defrost mode.

[0074] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A frost layer monitoring and defrosting control device for an air source heat pump, characterized in that: The air source heat pump includes an evaporator and a corresponding fan, and the frost layer monitoring and defrost control device includes: The pressure differential sensor collects static pressure differential data before and after the evaporator at a predetermined time interval t1 under low-temperature refrigeration conditions; A control module is in communication with the pressure difference sensor module, calculates and outputs the real-time pressure loss coefficient PLF of the evaporator according to the static pressure difference data; controls whether the air source heat pump enters the defrost mode according to the pressure loss coefficient PLF, Pressure loss coefficient Wherein, ΔP is the total pressure of the evaporator; ΔP0 is the initial static pressure difference of the evaporator; ΔP1 is the static pressure difference of the evaporator at time t1, The differential pressure sensor is mounted on the central axis of the evaporator.

2. The frost layer monitoring and defrosting control device for an air source heat pump according to claim 1, characterized in that: When the pressure loss coefficient PLF is greater than a set threshold, the control module controls the air source heat pump to enter the defrost mode; the set threshold is the pressure loss coefficient corresponding to when the heat transfer efficiency of the evaporator drops significantly.

3. The frost layer monitoring and defrosting control device for an air source heat pump according to claim 2, characterized in that: It also includes a temperature detection module for detecting the inlet air temperature, outlet air temperature and evaporation temperature of the evaporator, and the real-time heat transfer efficiency is related to the inlet air temperature, the outlet air temperature and the evaporation temperature.

4. The frost layer monitoring and defrosting control device for an air source heat pump according to claim 1, characterized in that: It also includes a timing module, which is in communication with the control module. The timing module is used to set the defrost time and collect the defrost time. When the defrost time is greater than the set defrost time, the control module controls the air source heat pump to exit the defrost mode.

5. A frost layer monitoring and defrosting control method for an air source heat pump, wherein the air source heat pump comprises an evaporator and a corresponding fan, characterized in that: The frost layer monitoring and defrost control method includes the following steps: S1: Using a pressure differential sensor installed on the central axis of the evaporator, collect static pressure differential data before and after the evaporator under low temperature conditions at time intervals of t1. S2: Calculate and output the real-time pressure loss coefficient PLF of the evaporator according to the static pressure difference data; Pressure loss coefficient Wherein, ΔP is the total pressure of the evaporator; ΔP0 is the initial static pressure difference of the evaporator; ΔP1 is the static pressure difference of the evaporator at time t1, S3: Control whether the air source heat pump enters the defrost mode according to the pressure loss coefficient PLF.

6. The frost layer monitoring and defrosting control method of an air source heat pump according to claim 5, characterized in that: The "controlling whether the air source heat pump enters the defrost mode according to the pressure loss coefficient PLF" includes: determining whether the pressure loss coefficient PLF is not less than a set threshold; if so, controlling the air source heat pump to enter the defrost mode; if not, returning to S1.

7. The frost layer monitoring and defrosting control method of an air source heat pump according to claim 6, characterized in that: The set threshold is a pressure loss coefficient corresponding to a significant decrease in the heat transfer efficiency of the evaporator.

8. The frost layer monitoring and defrosting control method of an air source heat pump according to claim 5, characterized in that: It also includes setting a defrost time and collecting the defrost time. When the defrost time is greater than the set defrost time, the air source heat pump is controlled to exit the defrost mode.

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