A variable frequency air source heat pump defrosting operation method based on a defrosting performance map

Abstract

The application discloses a variable frequency air source heat pump frost control operation method based on a frost control performance graph, and belongs to the technical field of frost control. First, a variable frequency unit frost control performance graph under a current working condition is drawn. Second, according to a heating capacity range and a frost control potential reflected by the frost control performance graph, a heating target and a frost control operation target are determined according to a building load demand at the moment. Third, a compressor frequency and an outdoor fan frequency of the variable frequency air source heat pump are determined according to the above demand and target. Finally, the compressor and the fan frequency output are controlled by a unit frost control operation controller, so that the heating and the frost control demand are realized. On the basis of meeting the heating capacity, effective frost control operation of the unit is realized.

Description

Technical Field

[0001] This invention relates to a defrosting operation method for variable frequency air source heat pumps based on defrosting performance diagrams, and involves the fields of air source heat pump defrosting technology and operation control. Background Technology

[0002] Air source heat pumps, as a renewable energy technology, have been widely used in building heating, cooling, and domestic hot water applications. With the escalating global energy crisis and environmental degradation, air source heat pumps have seen significant development in many countries and sectors due to their energy-saving, low-carbon, environmentally friendly, and easy-to-install characteristics.

[0003] However, when used for building space heating in winter, the application potential of air source heat pumps is often hindered by unnecessary frosting. When the surface temperature of the outdoor coil of an air source heat pump is below the triple point of water and the dew point of ambient air, frost will form on the surface of the outdoor coil. As frost accumulates on the outdoor coil surface, the airflow channels of the outdoor coil will gradually become blocked. This will lead to many operational problems for the air source heat pump unit, such as reduced compressor suction superheat, increased compression ratio, decreased output heating capacity, and a significant decrease in the coefficient of performance (COP), and in severe cases, even unit shutdown. Studies have shown that frosting can cause a 30%–57% decrease in unit heating capacity and a 35%–60% decrease in COP. To ensure the efficient and safe operation of air source heat pumps, regular defrosting must be implemented, but this will lead to additional energy consumption. Therefore, the problem of outdoor coil frosting remains a key issue affecting the overall development of heat pump units.

[0004] To address the negative impacts of frosting and defrosting, numerous measures exist to suppress or delay frost formation on the outdoor coil surface of high-temperature heat pumps. These include reducing the humidity of the air inlet to the outdoor coil, increasing its temperature, altering the surface wind speed, increasing the heat exchange area, surface modification of the hydrophobic coating, mechanical vibration, applying an external electric field, applying an external magnetic field, and ultrasonic waves. However, these technologies have not yet been successfully applied to actual heat pump units due to their high cost, short lifespan, and complex manufacturing processes. Therefore, further development of effective defrosting technologies is essential. On the other hand, variable frequency air source heat pumps have become the mainstream for space heating because they can adjust their output heating capacity and achieve higher efficiency under partial load conditions. Variable frequency units, by adjusting the frequency of the compressor and outdoor fan to change the output heating capacity, also possess defrosting capabilities. Therefore, for variable frequency air source heat pumps, frosting can be suppressed by changing the frequency of their compressor and outdoor fan.

[0005] Therefore, from an operational control perspective, a defrosting performance diagram can be used to determine the heating capacity range and defrosting potential of variable frequency units. Combined with the building's load requirements, this guides the adjustment of compressor and outdoor fan frequencies, achieving effective defrosting operation of the unit while meeting heating capacity requirements. This will promote the application and development of air source heat pumps throughout my country. Summary of the Invention

[0006] The purpose of this invention is to provide a defrosting operation method for variable frequency air source heat pumps based on defrosting performance diagrams. For variable frequency air source heat pumps, under frosting conditions, the developed defrosting performance diagrams are used to understand the heating capacity range and defrosting control potential of the unit. Based on the building load demand at this time, the operating frequencies of the compressor and outdoor fan are optimized to effectively suppress defrosting while meeting heating requirements, thereby achieving efficient operation of the unit under all operating conditions.

[0007] To achieve the above objectives, the technical solution adopted by this invention to solve its technical problem is: a defrosting operation method for a variable frequency air source heat pump based on a defrosting performance diagram, comprising: first, drawing a defrosting performance diagram of the variable frequency unit under the current operating conditions; second, determining the heating target and defrosting operation target based on the heating capacity range and defrosting potential reflected in the defrosting performance diagram, and then based on the current building load demand; third, determining the compressor frequency and outdoor fan frequency of the variable frequency air source heat pump according to the above requirements and targets; and finally, controlling the output of the compressor and fan frequencies through the unit's defrosting operation controller to achieve the heating and defrosting requirements. The specific steps are as follows:

[0008] The first step is to first determine the ambient temperature T based on real-time data. a Calculate the dew point temperature T from the relative humidity RH. a,d Combined with the outdoor heat exchanger coil temperature T of the unit c Through the frost suppression model The real-time defrosting parameter Fs, or F, of the computer group determines whether the unit is frosted at the current moment. If the unit is operating in a frost-free or condensation-free zone, the unit operation control will not be adjusted; otherwise, proceed to the second step.

[0009] The second step, if located in the frosting zone, is to draw a frosting performance diagram for the inverter unit based on the environmental conditions at the time of operation: by adjusting the inverter unit compressor to the maximum frequency f... cmax Minimum frequency f cmin Outdoor fan up to maximum frequency f fmax Minimum frequency f fmin The operating frequencies of the compressor and outdoor fan are respectively matched to f. cmax f fmax f cmax f fmim f cmin f fmim and f cminf fmax The heating capacity range and defrosting potential range of the unit are determined based on four points;

[0010] The third step is to determine the required frost suppression capacity F of the unit on the frost suppression performance diagram based on the building load demand Q at this moment.

[0011] The fourth step is to adjust the compressor operating frequency f through the unit's defrost control controller, based on the determined heating capacity requirement Q and defrost capability requirement F. c outdoor fan operating frequency f f And calculate in real time the actual values ​​Qs and Fs of the unit's output heating capacity and defrosting capacity;

[0012] Fifth, after the unit stabilizes, make the following judgment: if |Qs-Q| / Q < 0.05 and |Fs-F| / F < 0.05, the unit continues to operate stably to meet the heating and defrosting requirements; otherwise, redetermine the operating frequency of the compressor and outdoor fan according to the target values ​​of Qs and Fs until |Qs-Q| / Q < 0.05 and |Fs-F| / F < 0.05 are satisfied.

[0013] The present invention has the following advantages:

[0014] (1) For variable frequency air source heat pumps, under the guidance of the defrosting performance diagram, the operating frequency of the compressor and outdoor fan is adjusted during the frosting operation process, so as to achieve the defrosting capability under the condition of ensuring the building load demand. This fully utilizes the partial load adjustment capability of the variable frequency unit and opens up a brand-new defrosting operation method.

[0015] (2) This method can effectively suppress frost, alleviate the problem of frost formation in the actual operation of air source heat pump, improve the operating efficiency of the unit, and realize the efficient and stable operation of air source heat pump under all operating conditions;

[0016] (3) This method does not add any equipment or system, achieves the goal of effective frost suppression operation of the unit, has no cost increase, and is highly practical. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a certain brand of variable frequency air source heat pump (chilled water) unit.

[0018] Figure 2 This is a graph showing the anti-frost performance of a certain brand of variable frequency unit under a specific operating condition.

[0019] Figure 3 This is a flowchart of a defrosting operation method for a variable frequency air source heat pump based on a defrosting performance diagram according to the present invention. Detailed Implementation

[0020] The following description is only a preferred embodiment of the present invention and does not limit the scope of protection of the present invention.

[0021] The defrosting operation method for variable frequency air source heat pumps based on defrosting performance diagrams proposed in this invention achieves defrosting operation capability while ensuring building heating needs, opening up a completely new direction for defrosting. The following is a further detailed description of the implementation process of this invention, using a specific brand of variable frequency air source heat pump (chilled water) unit as an example, with reference to the accompanying drawings:

[0022] (1) Figure 1 The schematic diagram of this unit includes 1. a variable frequency compressor, 2. an outdoor heat exchanger, 3. an outdoor variable frequency fan, 4. an electronic expansion valve, 5. a shell-and-tube heat exchanger, 6. a four-way reversing valve, and 7. a unit defrost control. Specifically, the compressor 1, outdoor heat exchanger 2, outdoor fan 3, electronic expansion valve 4, shell-and-tube heat exchanger 5, four-way reversing valve 6, and unit controller 7 are included. The outlet of the outdoor heat exchanger 2 is connected to one port of the four-way reversing valve 6; the second port of the four-way reversing valve 6 is connected to the outlet of the compressor 1, and the inlet of the compressor 1 is connected to the third port of the four-way reversing valve 6 to form a circulation loop; the inlet of the outdoor heat exchanger 2 is connected sequentially via the electronic expansion valve 4, the shell-and-tube heat exchanger 5, and the fourth port of the four-way reversing valve 6; these connections are piping connections, and the connecting components are filled with refrigerant.

[0023] The outdoor heat exchanger 2 is equipped with an outdoor fan 3. The outdoor fan 3 and the compressor 1 are respectively connected to the unit controller 7, and signal feedback transmission and control are carried out through electrical signals.

[0024] Copper pipes are used to connect units 2 and 6, 6 and 1, 1 and 5, 5 and 4, and 4 and 2. These connections are filled with refrigerant. Units 7, 1, and 3 are connected via a controller, using electrical signals for feedback transmission and control. The parameters of the unit's variable frequency compressor and outdoor variable frequency fan are as follows: Compressor 1's operating frequency f... c The operating frequency of outdoor fan 3 is 30-85Hz. f The frequency range is 10–45 Hz.

[0025] (2) First, based on the real-time collected ambient temperature T a Calculate the dew point temperature T from the relative humidity RH. a,d Combined with the outdoor heat exchanger coil temperature T of the unit c Through the frost suppression model The real-time defrosting parameter Fs (F) of the computer group determines whether the unit is frosted at the current moment. If Fs ≥ 0, there is no frosting; if Fs < 0, the unit is in a frosted state. If there is no frosting, continue operating at the current frequency; if there is frosting, combine... Figure 2The frost suppression performance diagram is adjusted as follows: The diagram is drawn by adjusting the operating frequencies of the compressor and fan to combination 1: 30Hz, 10Hz; combination 2: 30Hz, 45Hz; combination 3: 85Hz, 10Hz; and combination 4: 85Hz, 45Hz. This yields four points corresponding to Q and F, which are then used to plot the unit's frost suppression performance diagram. The diagram is an irregular quadrilateral formed by four curves drawn from these four points. The quadrilateral area represents the current heating capacity and frost suppression capacity range of the unit. The horizontal axis represents the unit's heating capacity Q, and the vertical axis represents the corresponding frost suppression parameter value F. A larger F indicates lighter frost, and a smaller F indicates more severe frost. If F ≥ 0, there is no frost (F = 0 is the critical frost line), and F < 0 indicates a frosting state. Based on the building's heating load demand Q, the optimal frost suppression target is found within the range of F ≥ 0 (no frost).

[0026] (3) The combination described in step (2) above Figure 2 Adjust the anti-frost performance graph as follows: Combine with Figure 2 Given that the building heating load demand Q is 7kW, according to the frost suppression performance diagram, under the same Q, there will be four frost suppression targets: F1, F2, F3, and F4. F1, F2, and F3 are all below the critical frost line, indicating that the unit is in a frosting state, but their frost suppression capabilities are different. Only F4 is above the critical frost line, indicating that it can guarantee Q of 7kW without frost. Therefore, F4 is the optimal frost suppression target, which is the frost suppression demand under this operating condition.

[0027] (4) Combination Figure 3 The unit's defrosting operation controller adjusts the operating frequency f of the variable frequency unit's compressor. c outdoor fan operating frequency f f To meet the load demand of 7kW and the frost suppression demand of F4;

[0028] (5) After the unit has been running stably, calculate Qs and Fs based on the actual operating parameters. If |Qs-7| / 7 < 0.05 and |Fs-F4| / F4 < 0.05, the unit continues to run stably, meets the building heating demand, and has the ability to suppress frost. Otherwise, readjust the compressor frequency and outdoor fan frequency according to Q = 7kW and F4 until |Qs-7| / 7 < 0.05 and |Fs-F4| / F4 < 0.05.

[0029] In the embodiments of the present invention, under frosting conditions, the air source heat pump can effectively suppress frequent frosting while fully ensuring the building's heating needs, thus ensuring stable and efficient operation of the unit under all operating conditions.

Claims

1. A defrosting operation method for a variable frequency air source heat pump based on a defrosting performance diagram, characterized in that, The process includes: first, drawing a defrosting performance diagram of the variable frequency unit under the current operating conditions; second, based on the heating capacity range and defrosting potential reflected in the defrosting performance diagram, and according to the current building load demand, determining the heating target and defrosting operation target; third, determining the compressor frequency and outdoor fan frequency of the variable frequency air source heat pump based on the above requirements and targets; and finally, controlling the output frequency of the compressor and fan through the unit's defrosting operation controller to achieve the heating and defrosting requirements. The specific steps are as follows: The first step is to first determine the ambient temperature T based on real-time data. a Calculate the dew point temperature T from the relative humidity RH. a,d Combined with the outdoor heat exchanger coil temperature T of the unit c Through the frost suppression model The real-time defrosting parameter Fs, or F, of the computer group determines whether the unit is frosted at the current moment. If the unit is operating in a frost-free or condensation-free zone, the unit operation control will not be adjusted; otherwise, proceed to the second step. The second step, if located in the frosting zone, is to draw a frosting performance diagram for the inverter unit based on the environmental conditions at the time of operation: by adjusting the inverter unit compressor to the maximum frequency f... cmax Minimum frequency f cmin Outdoor fan up to maximum frequency f fmax Minimum frequency f fmin The operating frequencies of the compressor and outdoor fan are respectively matched to f. cmax f fmax f cmax f fmim f cmin f fmim and f cmin f fmax The heating capacity range and defrosting potential range of the unit are determined based on four points; The third step is to determine the required frost suppression capacity F of the unit on the frost suppression performance diagram based on the building load demand Q at this moment. The fourth step is to adjust the compressor operating frequency f through the unit's defrost control controller, based on the determined heating capacity requirement Q and defrost capability requirement F. c outdoor fan operating frequency f f And calculate in real time the actual values ​​Qs and Fs of the unit's output heating capacity and defrosting capacity; Fifth, after the unit stabilizes, make the following judgment: if |Qs-Q| / Q < 0.05 and |Fs-F| / F < 0.05, the unit continues to operate stably to meet the heating and defrosting requirements; otherwise, redetermine the operating frequency of the compressor and outdoor fan according to the target values ​​of Qs and Fs until |Qs-Q| / Q < 0.05 and |Fs-F| / F < 0.05 are satisfied.

2. The method according to claim 1, characterized in that, The second step involves obtaining the Q and F values ​​corresponding to the four points and then plotting the unit's frost suppression performance diagram. This diagram consists of four curves drawn from the four points as fixed points, forming an irregular quadrilateral. The quadrilateral area represents the current unit's heating capacity and frost suppression capacity range. The horizontal axis of the diagram represents the unit's heating capacity Q, and the vertical axis represents the corresponding frost suppression parameter value F. A larger F indicates lighter frost formation, while a smaller F indicates more severe frost formation. If F ≥ 0, there is no frost formation. F = 0 is the critical frost line, and Fs < 0 indicates a frost-forming state. Based on the building's heating load demand Q, the optimal frost suppression target is found within the range of F ≥ 0 without frost formation.

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