CN-122015401-A - Defrosting control method and system of heat pump system and heat pump system

Abstract

The present invention relates to the field of air source heat pump technologies, and in particular, to a defrosting control method and system for a heat pump system, and a heat pump system; the method comprises the steps of obtaining operation working condition parameters of a compression mechanism, calculating a polytropic index under the current working condition, calculating an expected exhaust temperature, calculating an exhaust superheat degree early warning threshold value, calculating a real-time exhaust superheat degree, controlling an auxiliary heating mechanism to start defrosting when the real-time exhaust superheat degree is reduced below a first threshold value, continues for a first preset time and is in a continuous descending trend, and controlling the auxiliary heating mechanism to stop defrosting when the real-time exhaust superheat degree is increased above a second threshold value, continues for a second preset time and the change rate is smaller than a preset change rate threshold value. According to the invention, the defrosting judgment standard can be dynamically adjusted according to the real-time working condition, the defrosting time is accurately controlled, the high-efficiency running time of the heat pump is maximized on the premise of ensuring the safety of the compressor, and the overall energy efficiency of the system is improved.

Inventors

• LIN JINHAO
• DANG HUA

Assignees

• 浙江智马达智能科技有限公司

Dates

Publication Date

20260512

Application Date

20260327

Claims (10)

1. 1. A defrosting control method of a heat pump system, comprising: Acquiring operation condition parameters of the compression mechanism, wherein the operation condition parameters comprise exhaust temperature, exhaust pressure, suction pressure and rotating speed; Inputting the operation condition parameters into a preset thermodynamic characteristic model of the compression mechanism, and calculating the polytropic index of the compression mechanism under the current working condition; Calculating the expected exhaust temperature corresponding to the condition that the suction superheat threshold of the compression cavity is met based on the suction pressure, the exhaust pressure, the polytropic index and a preset suction superheat threshold of the compression cavity; calculating an exhaust superheat degree early warning threshold value, wherein the exhaust superheat degree early warning threshold value is a difference value of the expected exhaust temperature and the saturated condensing temperature corresponding to the exhaust pressure; calculating a real-time exhaust superheat degree which is a difference value between the exhaust temperature and the saturated condensing temperature; When the real-time exhaust superheat degree is reduced to be below a first threshold value, the first preset time is continued and the trend of continuous falling is presented, the auxiliary heating mechanism is controlled to be started so as to defrost the outdoor heat exchanger in a non-reverse circulation manner; when the real-time exhaust superheat degree is raised to be above a second threshold value, the second preset time is continued, and the change rate is smaller than a preset change rate threshold value, controlling the auxiliary heating mechanism to stop so as to exit defrosting; The first threshold is the product of a first coefficient and the exhaust superheat degree early-warning threshold before the defrosting mode is started, the second threshold is the product of a second coefficient and the exhaust superheat degree early-warning threshold recalculated in the defrosting mode, and the second coefficient is smaller than the first coefficient.
2. 2. The defrosting control method of a heat pump system according to claim 1, wherein the compression mechanism thermodynamic characteristic model is a model for describing a functional relationship between the polytropic index and the rotation speed, the discharge pressure, and the suction pressure, which is obtained in advance by fitting performance test data of the compression mechanism.
3. 3. The defrost control method according to claim 2, wherein the functional relationship model is expressed as: , Wherein, the In the form of a polytropic exponent, In order to be the rotational speed, In order to be the pressure of the exhaust gas, For the suction pressure to be applied, To the point of In order to fit the coefficients of the coefficients, As the exhaust pressure at the reference operating condition, Is the suction pressure under the reference working condition.
4. 4. The defrosting control method of a heat pump system according to claim 1, wherein the compression chamber suction superheat threshold is a minimum safe superheat value for preventing the compression mechanism from being hydraulically hit, and the actual suction superheat of the compression chamber inlet is higher than the compression chamber suction superheat threshold in a normal heating operation, and when the outdoor heat exchanger is degraded in heat exchange performance due to frosting, the actual suction superheat of the compression chamber inlet is lowered to the threshold, which indicates that the heat pump system has reached a critical state requiring defrosting.
5. 5. The defrosting control method of a heat pump system according to claim 1, wherein the calculating, by thermodynamic reverse estimation, an expected discharge temperature corresponding to when the compression chamber suction superheat threshold is satisfied includes: inquiring a pre-stored refrigerant physical property data table or calling a refrigerant physical property calculation function according to the suction pressure to obtain a corresponding evaporation temperature; calculating the inlet temperature of a compression cavity, wherein the inlet temperature of the compression cavity is the sum of the evaporation temperature and the suction superheat threshold value of the compression cavity; calculating the temperature of a compressor air suction port, wherein the temperature of the compressor air suction port is obtained by subtracting a preset temperature rise value from the compressor air suction port to a compression cavity from the inlet temperature of the compression cavity; calculating said desired discharge temperature from said compressor suction temperature, said discharge pressure, said suction pressure, and said polytropic exponent by a compression process thermodynamic equation: , Wherein, the In order to achieve the desired exhaust gas temperature, For the temperature of the suction port of the compressor, In order to be the pressure of the exhaust gas, For the suction pressure to be applied, Is a polytropic index.
6. 6. The defrosting control method of a heat pump system according to claim 1, characterized in that the first coefficient is determined by: acquiring a limit allowable minimum suction dryness of the compression mechanism, wherein the limit allowable minimum suction dryness is the minimum mass fraction of a gas phase in wet vapor allowable to be sucked by a compressor; Under the current suction pressure, inquiring a pre-stored refrigerant physical property data table or calling a refrigerant physical property calculation function to obtain the enthalpy value of the saturated liquid refrigerant and the enthalpy value of the saturated gaseous refrigerant corresponding to the suction pressure; calculating the enthalpy of the wet vapor at the current suction pressure and limit to the allowable minimum suction dryness: wherein For the saturated liquid enthalpy at the current suction pressure, For saturated gaseous enthalpy at the current suction pressure, Minimum inhalation dryness is allowed for limit; calculating enthalpy difference: ; Under the current exhaust pressure, inquiring a pre-stored refrigerant physical property data table or calling a refrigerant physical property calculation function to obtain an overheated steam enthalpy value corresponding to the exhaust superheat degree early warning threshold value Wherein To be at the current exhaust pressure temperature of The enthalpy value at the time of the formation, For the saturated condensation temperature, The exhaust superheat degree early warning threshold value; Calculating a target enthalpy value: ; under the current exhaust pressure, inquiring a pre-stored refrigerant physical property data table or calling a refrigerant physical property calculation function, and reversely checking the temperature Ta corresponding to the target enthalpy value Ha; calculating a first coefficient: wherein Is the first coefficient.
7. 7. The defrosting control method of a heat pump system according to claim 1, characterized in that the second coefficient is determined by: in a defrosting mode, acquiring the current suction pressure, the current discharge pressure and the current polytropic index of the compression mechanism; Inquiring a pre-stored refrigerant physical property data table or calling a refrigerant physical property calculation function according to the suction pressure in the defrosting mode to obtain a corresponding evaporation temperature; Calculating the sum of the current evaporation temperature and the suction superheat threshold of the compression cavity to be used as the inlet temperature of the compression cavity in the defrosting mode; Calculating the temperature of an inlet of a compression cavity in a defrosting mode minus a preset temperature rise value from an air suction port of the compressor to the compression cavity, and taking the temperature as the temperature of the air suction port of the compressor in the defrosting mode; Calculating an expected discharge temperature in the defrost mode from the compressor suction temperature, the current discharge pressure, the current suction pressure and the current polytropic index in the defrost mode by a compression process thermodynamic equation: ; Wherein, the For the desired exhaust temperature in defrost mode, Is the compressor suction temperature in defrost mode, For the discharge pressure in the defrost mode, For the suction pressure in the defrost mode, Is a polytropic exponent in defrost mode; Calculating a difference value of a saturated condensing temperature corresponding to the expected exhaust temperature and the current exhaust pressure in the defrosting mode, and taking the difference value as an exhaust superheat degree early warning threshold value in the defrosting mode; calibrating the second coefficient through a system dynamic response test Calibrated to have beta smaller than the first coefficient And selecting the temperature of the real-time exhaust gas to be raised back to the superheat degree in the defrosting exit process Is more than the product of the pre-warning threshold value of the degree of superheat of the exhaust gas in the defrosting mode and has no overshoot oscillation Values.
8. 8. The defrosting control method of a heat pump system according to claim 1, wherein the auxiliary heating mechanism includes at least one of a hot gas bypass circuit, a triangular circulation circuit, a motor active heating device, and a PTC heater.
9. 9. A control system for a heat pump system, comprising: the parameter acquisition module is used for acquiring operation condition parameters of the compression mechanism, wherein the operation condition parameters comprise exhaust temperature, exhaust pressure, suction pressure and rotating speed; the polytropic index calculation module is used for inputting the operation condition parameters into a preset thermodynamic characteristic model of the compression mechanism and calculating the polytropic index of the compression mechanism under the current working condition; the threshold value determining module is used for calculating the expected exhaust temperature corresponding to the compression cavity suction superheat threshold value based on the suction pressure, the exhaust pressure, the polytropic index and the preset compression cavity suction superheat threshold value; The defrosting control module is used for calculating the real-time exhaust superheat degree, wherein the real-time exhaust superheat degree is the difference value between the exhaust temperature and the saturated condensing temperature; when the real-time exhaust superheat degree is reduced to be below a first threshold value, the first preset time is continued and the trend of continuous falling is presented, the auxiliary heating mechanism is controlled to be started so as to defrost the outdoor heat exchanger in a non-reverse cycle; when the real-time exhaust superheat degree is raised to be above a second threshold value, the second preset time is continued, and the change rate is smaller than a preset change rate threshold value, controlling the auxiliary heating mechanism to stop so as to exit defrosting; The first threshold is a product of a first coefficient and an exhaust superheat degree early-warning threshold calculated by the threshold determining module before a defrosting mode is started, the second threshold is a product of a second coefficient and an exhaust superheat degree early-warning threshold recalculated by the threshold determining module in the defrosting mode, and the second coefficient is smaller than the first coefficient.
10. 10. A heat pump system, comprising: Compression mechanism, outdoor heat exchanger, indoor heat exchanger, auxiliary heating mechanism, and A controller comprising a memory storing a computer program and a processor implementing the steps of the defrost control method of the heat pump system according to any one of claims 1 to 8 when the computer program is executed.

Description

Defrosting control method and system of heat pump system and heat pump system Technical Field The present invention relates to the field of air source heat pump technologies, and in particular, to a defrosting control method and system for a heat pump system, and a heat pump system. Background When the heat pump system is in heating operation, the outdoor heat exchanger serves as an evaporator to absorb heat from the outdoor air. When the outdoor environment temperature is low and the humidity is high, the surface of the outdoor heat exchanger is easy to frost, and the existence of a frost layer can increase air flow resistance and reduce heat exchange efficiency, so that the heating capacity of the system is reduced and the energy efficiency is reduced. In order to ensure continuous and efficient operation of the system, the outdoor heat exchanger needs to be defrosted at proper time. In the prior art, a common defrosting mode is reverse circulation defrosting, namely, a four-way valve is switched to enable a system to be switched from a heating mode to a refrigerating mode, and a high-temperature refrigerant is utilized to melt a frost layer on the surface of an outdoor heat exchanger. However, in the reverse cycle defrosting process, the indoor heat exchanger absorbs indoor heat, resulting in indoor temperature fluctuation, affecting user comfort. For this reason, some heat pump systems are equipped with auxiliary heating mechanisms, such as a hot gas bypass circuit or an electric heating device, to defrost in a non-reverse cycle manner, that is, to introduce an auxiliary heat source to heat and defrost the outdoor heat exchanger while maintaining the system heating mode, thereby avoiding indoor temperature fluctuation. In a non-reverse circulation defrosting system, how to accurately judge intervention timing and exit timing of defrosting becomes a technical key. If defrosting intervention is too late, the outdoor heat exchanger is seriously frosted, the heat exchange efficiency is obviously reduced, the energy efficiency of the system is also reduced, and even the compressor is possibly caused to suck air and carry liquid due to insufficient heat exchange of an evaporator, liquid impact is caused, and the compressor is damaged. If the defrosting is out too late, the auxiliary heating mechanism continuously operates to cause energy waste, and control oscillation can be caused by the change of the working condition of the system in the defrosting process. In the prior art, the judgment of defrosting intervention and withdrawal usually depends on a fixed temperature threshold value or a fixed time period, and is difficult to adapt to the change of the ambient temperature and the operation working condition, so that the defrosting control is inaccurate, and the efficient operation time of the heat pump cannot be maximized on the premise of ensuring the safety of the compressor. Disclosure of Invention The invention provides a defrosting control method and a control system of a heat pump system and the heat pump system, wherein the method can be used for dynamically determining a defrosting judgment standard according to the real-time working condition of the heat pump system, accurately identifying defrosting requirements and timely exiting defrosting, so that the effective operation time of a heat pump mode is prolonged and the overall energy efficiency of the heat pump system is improved on the premise of ensuring that a compressor does not generate liquid impact. The invention provides a defrosting control method of a heat pump system, which comprises the following steps: Acquiring operation condition parameters of the compression mechanism, wherein the operation condition parameters comprise exhaust temperature, exhaust pressure, suction pressure and rotating speed; Inputting the operation condition parameters into a preset thermodynamic characteristic model of the compression mechanism, and calculating the polytropic index of the compression mechanism under the current working condition; calculating the expected exhaust temperature corresponding to the condition that the suction superheat threshold of the compression cavity is met through thermodynamic reverse calculation based on the suction pressure, the exhaust pressure, the polytropic index and a preset suction superheat threshold of the compression cavity; calculating an exhaust superheat degree early warning threshold value, wherein the exhaust superheat degree early warning threshold value is a difference value of the expected exhaust temperature and the saturated condensing temperature corresponding to the exhaust pressure; calculating a real-time exhaust superheat degree which is a difference value between the exhaust temperature and the saturated condensing temperature; When the real-time exhaust superheat degree is reduced to be below a first threshold value, the first preset time is continued and the trend of going low continuously is show