Carbon dioxide heat pump air conditioner anti-frosting control method and system

Abstract

This invention discloses a method for preventing frost formation in a carbon dioxide heat pump air conditioner, comprising: determining the initial theoretical heating capacity Q0 of the carbon dioxide heat pump air conditioner system and the current theoretical heating capacity Q... N The ratio of the difference to the initial theoretical heating capacity Q0 (Q N Does (-Q0) / Q0 exceed the set first threshold? N If (-Q0) / Q0 does not exceed the set first threshold, obtain the initial frosting measurement index A0 and the current frosting measurement index A. N ; when A N The ratio A to A0 N When / A0 is greater than or equal to the set second threshold, it is determined that the outdoor heat exchanger is not frosted; when A N The ratio A to A0 N When / A0 is less than a set second threshold, it is determined that the outdoor heat exchanger is frosted, and the carbon dioxide heat pump air conditioning system enters anti-frost mode or defrost mode. Accordingly, the present invention also discloses a carbon dioxide heat pump air conditioning anti-frost control system.

Description

Technical Field

[0001] This invention relates to a control method and system, and more particularly to a vehicle air conditioning control method and system. Background Technology

[0002] As the second largest energy-consuming module in electric vehicles, the air conditioning system has a significant impact on the overall vehicle range, thus requiring proper optimization. Currently, CO2 heat pump air conditioning is a hot topic in product research and development.

[0003] However, CO2 heat pump air conditioners suffer from frosting on the outdoor heat exchanger during operation. When heating, the outdoor heat exchanger functions as an evaporator. The refrigerant temperature inside the heat exchanger is lower than the outdoor ambient temperature. When the surface temperature of the heat exchanger drops below zero degrees Celsius, moisture in the environment can condense on its surface, forming a thick layer of frost. This affects the heat exchanger's efficiency and, in severe cases, can cause it to lose its heat exchange capacity. Furthermore, once frost forms on the outdoor heat exchanger, the frost spreads rapidly, quickly covering the entire surface. Frosting on the outdoor heat exchanger will cause several problems: (1) The evaporation temperature of the heat pump air conditioning system will drop, the suction temperature and pressure of the compressor will be too low, and the discharge temperature and pressure will also drop, directly lowering the air outlet temperature of the air conditioner; (2) The channels between the fins of the outdoor heat exchanger will be blocked, making it impossible to absorb low-grade heat from the environment, increasing the power consumption of the compressor, and the energy efficiency ratio will drop significantly, i.e., it will consume more electricity; (3) The refrigerant inside the outdoor heat exchanger will be difficult to evaporate, increasing the possibility of liquid slugging in the compressor, which will also reduce the efficiency of the compressor, leading to increased power consumption, reduced heating effect, and affecting the lifespan of various components.

[0004] Therefore, CO2 heat pump air conditioners need to effectively control frost formation. In existing methods:

[0005] Temperature control method adjusts the air outlet temperature for defrosting inside the vehicle based on whether the outside ambient temperature exceeds a preset temperature threshold. However, this method does not consider the influence of air humidity and cannot accurately determine when defrosting begins and ends.

[0006] The timed defrosting method involves the air conditioning system defrosting at preset time intervals. However, since the time intervals for defrosting are fixed, there may be situations where frost is present but not defrosted, or where defrosting is performed even when there is no frost.

[0007] The evaporator differential pressure method involves defrosting when the pressure difference between the air inlet and outlet of the evaporator is too large. However, this method can lead to incorrect defrosting decisions when there are impurities on the evaporator surface.

[0008] The pressure-controlled heat source method triggers a heat source to defrost the evaporator based on changes in the compressor's suction pressure. However, this method is not only related to frost formation but can also be affected by factors such as the expansion valve opening and solenoid valve malfunction, making it impossible to accurately determine whether frost has formed. Furthermore, an additional heat source, such as an electric heater, is required, resulting in higher costs.

[0009] Computer vision-based judgment involves taking pictures of the evaporator and analyzing the degree of frost to determine whether defrosting control is needed. However, this method requires additional cameras, auxiliary light sources, etc., which is costly and impractical.

[0010] The defrosting method using a heat storage device involves storing the heat released by the vehicle's heat exchanger in a heat storage device during heating mode. During defrosting mode, the high-temperature heat storage medium flows through the heat exchanger, increasing the evaporation temperature. However, this method requires additional heat storage devices and heat storage medium, resulting in higher costs. Furthermore, it places higher demands on the heat exchanger's capacity during heating mode.

[0011] Based on this, it is desirable to provide a method and system for preventing frost formation in a carbon dioxide heat pump air conditioning system, which can control frost formation efficiently, accurately, and at low cost. Summary of the Invention

[0012] One of the objectives of this invention is to provide a method for preventing frost formation in a carbon dioxide heat pump air conditioner. This method can accurately determine the frost formation status of the outdoor heat exchanger, avoiding misjudgment of frost formation. It also activates the defrosting mode at the optimal time after frost formation, thus avoiding activation of the defrosting mode too late or too early, which could affect comfort or cause energy waste. Furthermore, it controls frost formation at low cost without the need for additional auxiliary parts.

[0013] To achieve the above objectives, this invention proposes a method for preventing frost formation in a carbon dioxide heat pump air conditioner, comprising:

[0014] Determine the initial theoretical heating capacity Q0 and the current theoretical heating capacity Q of the carbon dioxide heat pump air conditioning system. N The ratio of the difference to the initial theoretical heating capacity Q0 (Q N Does -Q0) / Q0 exceed the set first threshold?

[0015] In (Q) N If -Q0) / Q0 does not exceed the set first threshold, obtain the initial frosting measurement index A0 at the initial moment corresponding to the initial theoretical heating capacity Q0 and the current frosting measurement index A at the current moment. N Where A0=K×Δh0 / W0, A N =K×Δh N / W NWhere K represents the known proportionality coefficient, Δh0 represents the enthalpy difference between the inlet and outlet of the outdoor heat exchanger at the initial moment, and Δh N W represents the enthalpy difference between the inlet and outlet of the outdoor heat exchanger of the carbon dioxide heat pump air conditioning system at the current moment, and W0 represents the power of the compressor of the carbon dioxide heat pump air conditioning system at the initial moment. N This indicates the compressor's power at the current moment;

[0016] When A N The ratio A to A0 N When / A0 is greater than or equal to the set second threshold, it is determined that the outdoor heat exchanger is not frosted;

[0017] When A N The ratio A to A0 N When / A0 is less than the set second threshold, it is determined that the outdoor heat exchanger is frosted, and the carbon dioxide heat pump air conditioning system enters the anti-frost mode or defrost mode.

[0018] Carbon dioxide heat pump air conditioners that use CO2 as a refrigerant (or cooling medium) have the following characteristics:

[0019] CO2 has a high heat transfer coefficient and high energy content per unit, enabling it to absorb sufficient heat from the external environment even at higher evaporation temperatures. Based on this, the present invention uses a strategy of adjusting the opening of the electronic expansion valve and the compressor speed to control frost formation.

[0020] CO2 working fluid still has high pressure and density at low temperature, resulting in a lower compressor compression ratio and higher compressor efficiency. Therefore, its energy efficiency ratio (COP) is higher and its heating capacity is stronger. Based on this, the present invention uses COP and heating capacity Q as the basis for judging frosting.

[0021] The high-pressure side temperature slip of the transcritical carbon dioxide cycle is large, with the highest temperature reaching over 120°C, resulting in good defrosting effect and faster defrosting time.

[0022] In addition, for carbon dioxide heat pump air conditioners, an effective anti-frost control method should: effectively determine the frosting status of the outdoor heat exchanger, that is, neither delay the response nor predict it in advance; be able to eliminate interference from other factors, avoid misjudgment, and accurately analyze whether frosting has occurred; minimize the investment in auxiliary equipment, and ideally be able to complete the task solely through program calculation and analysis.

[0023] Based on the above considerations, this invention first addresses the problem of accurately determining whether the outdoor heat exchanger is frosted: When a heat pump air conditioning system is heating, if the outdoor heat exchanger frosts, a layer of frost will condense on its outer surface, increasing the heat exchanger's thermal resistance and significantly weakening its heat exchange capacity. This results in the refrigerant inside the heat exchanger being unable to exchange heat effectively with the outside environment. At this point, the change in the thermodynamic state of the refrigerant at the heat exchanger's inlet and outlet will gradually decrease, or even become completely unchanged.

[0024] This invention uses enthalpy difference Δh to represent this problem, setting the inlet enthalpy of the outdoor heat exchanger as h. in The enthalpy at the outlet of the outdoor heat exchanger is set to h. out Then Δh = h out -h in This means that the enthalpy difference Δh tends to decrease after frosting. (The enthalpy value h at the inlet of the outdoor heat exchanger is also mentioned.) in outdoor heat exchanger outlet enthalpy h out It is known in this field that these values ​​can all be expressed as h = f(t, p), where t and p are the refrigerant temperature t and pressure p collected by the PT sensors at the inlet or outlet of the outdoor heat exchanger. Therefore, for example, the corresponding inlet enthalpy value h can be obtained by looking up a table for a given t and p. in and export enthalpy h out .

[0025] For a heat pump air conditioner, a smaller enthalpy difference Δh means that the system absorbs less heat from the outside. If the system wants to maintain the same heating capacity, the compressor power W will increase. (The compressor power W can be directly obtained from the compressor signal, which is a known quantity.)

[0026] Based on this, the present invention utilizes the changes in these two values ​​to set a frosting measurement index A to comprehensively consider the changes in these two values, thereby judging the frosting status of the heat pump system during stable operation. Wherein, A = K * Δh / W, where K is a proportionality coefficient that can be calibrated according to different carbon dioxide heat pump air conditioning systems. When the outdoor heat exchanger frosts, the value of A will decrease.

[0027] However, in actual vehicle use of heat pump air conditioning, the constantly changing environment and user settings can prevent the heat pump from maintaining a consistently stable operating state. Therefore, this invention does not simply rely on changes in the A value to determine the frosting condition, but further introduces the heating capacity of the carbon dioxide heat pump air conditioning system, which represents the system's capability. In this invention, the uppercase parameter Q represents the theoretical heating capacity, which is the energy theoretically required by the carbon dioxide heat pump air conditioning system in the current mode. It is unrelated to the frosting condition of the outdoor heat exchanger and is a known quantity. The lowercase parameter q represents the actual heating capacity, which is a value calculated in real time by the carbon dioxide heat pump air conditioning system and can be directly collected. If the value of q cannot reach the value of Q within a certain period of time, and the difference does not decrease further, it can be determined that the outdoor heat exchanger has frosted and is severely frosted.

[0028] Furthermore, this invention also uses the change in theoretical heating capacity Q over a period of time to extract a relatively stable operating period to determine the A value. This is because the theoretical heating capacity Q generally changes very slowly under relatively stable operating conditions, and it itself has undergone some anti-interference processing. Significant changes only occur when the external environment changes drastically (such as a vehicle entering a long tunnel) or when the user redefines the settings. Therefore, this invention approximates the period during which the theoretical heating capacity Q changes within a certain range as the time when the system is in a stable state. This period can then be used to compare the A value. That is, when the change in theoretical heating capacity over a period of time exceeds a set first threshold (in some embodiments, those skilled in the art can select a setting within the range of -1% to 1% as needed), and the A value decreases by a certain value, making A... N The ratio A to A0 N When / A0 is less than the set second threshold, it is determined that the outdoor heat exchanger has started to frost. This second threshold is a quantity related to the theoretical heating capacity and the ambient temperature. Those skilled in the art can set an appropriate second threshold based on these two quantities. In some embodiments, the second threshold can be selected and set in the range of 55% to 60%.

[0029] Furthermore, in the CO2 heat pump air conditioner anti-frost control method described in this invention, when the CO2 heat pump air conditioner system has an indoor heat exchanger, if it is determined that the outdoor heat exchanger is frosted, the CO2 heat pump air conditioner system directly enters the defrosting mode; in the defrosting mode: the outdoor heat exchanger, the compressor, and the indoor heat exchanger are connected in series in the conductive refrigerant main circuit, and the refrigerant flows out from the compressor, flows through the outdoor heat exchanger and the indoor heat exchanger in sequence, and then returns to the compressor.

[0030] Furthermore, in the carbon dioxide heat pump air conditioner anti-frost control method described in this invention, when it is determined that the outdoor heat exchanger is not frosted, the carbon dioxide heat pump air conditioner system maintains the indoor heating mode. In the indoor heating mode, the outdoor heat exchanger, the compressor, and the indoor heat exchanger are connected in series in the conductive refrigerant main circuit. The refrigerant flows out from the compressor, flows through the indoor heat exchanger and the outdoor heat exchanger in sequence, and then returns to the compressor.

[0031] The control method described in this invention is applicable to both two-heat-exchanger air conditioners and three-heat-exchanger air conditioners.

[0032] In the above embodiments, the control method is applicable to two-heat-exchanger air conditioners. A two-heat-exchanger air conditioner refers to an air conditioning system with one outdoor heat exchanger and one indoor heat exchanger. For this type of carbon dioxide heat pump air conditioning system, when it is determined that the outdoor heat exchanger is frosted, the carbon dioxide heat pump air conditioning system directly enters the defrosting mode.

[0033] Furthermore, in the carbon dioxide heat pump air conditioner anti-frost control method described in this invention, the second threshold is a value related to the ambient temperature and the theoretical heating capacity. Those skilled in the art can set the second threshold based on these two factors.

[0034] Furthermore, in the carbon dioxide heat pump air conditioner anti-frost control method described in this invention, when the carbon dioxide heat pump air conditioner system has at least two indoor heat exchangers, namely a first indoor heat exchanger and a second indoor heat exchanger, in the case where it is determined that the outdoor heat exchanger is frosted:

[0035] Continue to determine whether the initial theoretical heating capacity Q0 of the carbon dioxide heat pump air conditioning system is greater than the initial actual heating capacity q0, or continue to determine the current theoretical heating capacity Q. N Is it greater than the current actual heating capacity q? N :

[0036] If the judgment is negative, enter anti-frosting mode;

[0037] If the judgment is yes, continue to judge Q. N With q N Is the difference greater than the difference between Q0 and q0? If the result is yes, enter defrost mode; if the result is no, enter anti-frost mode.

[0038] In the anti-frost mode: the outdoor heat exchanger, the compressor, and the second indoor heat exchanger are connected in series in the main refrigerant circuit, and the first indoor heat exchanger and the compressor are connected in series in the refrigerant bypass circuit. The refrigerant flows out of the compressor, a part of which flows through the outdoor heat exchanger and the second indoor heat exchanger in sequence and returns to the compressor, and the other part flows through the first indoor heat exchanger and then returns to the compressor.

[0039] In the defrosting mode: the outdoor heat exchanger, the compressor, and the second indoor heat exchanger are connected in series in the main refrigerant circuit. The refrigerant flows out from the compressor, flows through the outdoor heat exchanger and the second indoor heat exchanger in sequence, and then returns to the compressor.

[0040] Furthermore, in the carbon dioxide heat pump air conditioner anti-frost control method described in this invention, when it is determined that the outdoor heat exchanger is not frosted:

[0041] Continue to judge A N Is / A0 greater than the preset third threshold? If yes, maintain indoor heating mode; if no, enter anti-frost mode.

[0042] In the indoor heating mode: the outdoor heat exchanger, the compressor, the first indoor heat exchanger, and the second indoor heat exchanger are connected in series in the main refrigerant circuit. The refrigerant flows out from the compressor, flows through the compressor, the first indoor heat exchanger, the second indoor heat exchanger, and the outdoor heat exchanger in sequence, and then returns to the compressor.

[0043] Furthermore, in the carbon dioxide heat pump air conditioner anti-frost control method of the present invention, the third threshold is obtained based on the corresponding second threshold plus a set compensation value. In some embodiments, the third threshold can be selected and set by those skilled in the art within the range of 57% to 62%.

[0044] In a carbon dioxide heat pump air conditioning system, the necessary condition for the outdoor heat exchanger to frost during heating is that the refrigerant temperature inside the outdoor heat exchanger is below 0°C. Furthermore, under the same environmental conditions, the higher the evaporation temperature, the less likely the heat exchanger is to frost. However, higher evaporation temperatures also make it harder for the heat exchanger to absorb heat from the environment, leading to increased system energy consumption. Therefore, this method of raising the evaporation temperature is a means of preventing frost formation in advance. It does not prevent frost formation on heat exchangers that have already been identified as starting to frost; it can only slow down the frost formation process. Of course, this is a different story in certain operating conditions where the evaporation temperature can be raised above 0°C. In such cases, as long as the evaporation temperature is above 0°C, frost formation on the heat exchanger can be completely avoided. For these conditions, this method is extremely effective and can permanently eliminate the frost problem. Therefore, there are two situations in which this method can be used: (1) In heating conditions where the evaporation temperature can be raised to above 0°C, the method of raising the evaporation temperature can be prioritized after it is determined to be frosting; (2) In heating conditions where the evaporation temperature cannot be raised to above 0°C, the method of raising the evaporation temperature can be used in advance before it is determined to be frosting, thus delaying the time when frosting occurs (this mode is more energy-efficient than the anti-frost mode). Based on this, in the second case, the present invention uses A0 / A N A third threshold is set by adding a set compensation value based on the second threshold. In some embodiments, those skilled in the art can select and set it within the range of 57% to 62%.

[0045] Another object of the present invention is to provide a carbon dioxide heat pump air conditioner anti-frost control system, which executes the control method described above, wherein the carbon dioxide heat pump air conditioner anti-frost control system includes:

[0046] The outdoor heat exchanger, compressor, and indoor heat exchanger are connected in series in the main refrigerant circuit;

[0047] An electronic expansion valve is located between the outdoor heat exchanger and the indoor heat exchanger;

[0048] The first shut-off valve is located between the outdoor heat exchanger and the compressor inlet;

[0049] The second shut-off valve is located between the compressor inlet and the indoor heat exchanger;

[0050] The third shut-off valve is located between the compressor outlet and the indoor heat exchanger;

[0051] The fourth shut-off valve is located between the outdoor heat exchanger and the compressor outlet;

[0052] The first PT sensor and the second PT sensor respectively sense the temperature and pressure of the refrigerant at the inlet and outlet of the outdoor heat exchanger;

[0053] The heat pump controller is connected to the electronic expansion valve, the first shut-off valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve, the compressor, the first PT sensor, and the second PT sensor, respectively.

[0054] The aforementioned anti-frost control system for carbon dioxide heat pump air conditioners is designed for carbon dioxide heat pump air conditioner systems with two heat exchangers.

[0055] Furthermore, the present invention also provides a carbon dioxide heat pump air conditioner anti-frost control system, which executes the control method described above, wherein the carbon dioxide heat pump air conditioner anti-frost control system includes:

[0056] An outdoor heat exchanger, a compressor, a first indoor heat exchanger, and a second indoor heat exchanger are connected in series in the main refrigerant circuit.

[0057] A first electronic expansion valve is located between the outdoor heat exchanger and the second indoor heat exchanger;

[0058] The second electronic expansion valve is located between the first indoor heat exchanger and the second indoor heat exchanger;

[0059] The first shut-off valve is located between the outdoor heat exchanger and the compressor inlet;

[0060] The second shut-off valve is located between the compressor inlet and the second indoor heat exchanger.

[0061] The third shut-off valve is located between the compressor outlet and the first indoor heat exchanger;

[0062] The fourth shut-off valve is located between the outdoor heat exchanger and the compressor outlet;

[0063] The first PT sensor and the second PT sensor respectively sense the temperature and pressure of the refrigerant at the inlet and outlet of the outdoor heat exchanger;

[0064] The heat pump controller is connected to the first electronic expansion valve, the second electronic expansion valve, the first shut-off valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve, the compressor, the first PT sensor, and the second PT sensor, respectively.

[0065] According to the control system described in this invention, increasing the evaporator temperature can be achieved by changing the values ​​of the electronic expansion valve and the compressor speed. Generally, the higher the evaporation temperature, the higher the threshold should be, and the compressor speed should also be increased appropriately.

[0066] The control can be divided into two situations: (1) In the heating condition where the evaporation temperature cannot be raised to above 0℃, the threshold is increased by a certain compensation value on the basis of the original threshold, and the compressor speed changes accordingly with the change of the outlet air temperature; (2) In the heating condition where the evaporation temperature can be raised to above 0℃, the target of the threshold is the evaporation temperature of 0℃, and the compressor speed changes accordingly with the change of the outlet air temperature.

[0067] The carbon dioxide heat pump air conditioner anti-frost control method and system described in this invention have the following beneficial effects:

[0068] Based on the characteristics of CO2 refrigerant, this invention designs a unique anti-frost control method that can accurately determine the frost status of the outdoor heat exchanger, greatly shorten the frost cycle of the outdoor heat exchanger, and even prevent frost from occurring in certain weather conditions that are prone to frost.

[0069] This invention can accurately determine the frosting status of the core by changing the COP and heating value, avoiding misjudgment of frosting; and activate the defrosting mode at the optimal time after frosting.

[0070] In certain high-humidity environments above zero degrees Celsius, the present invention can completely prevent frost formation, which is the condition under which 134a heat pumps are most prone to frost formation.

[0071] This invention uses an existing CO2 heat pump air conditioning system without adding any auxiliary parts. Control can be achieved simply by programming on the basis of the existing hardware system, thus having a significant cost advantage.

[0072] This invention is applicable not only to heat pump air conditioners with two heat exchangers, but also to heat pump systems with three heat exchangers, making it more adaptable.

[0073] This invention offers a variety of anti-frosting and post-frosting strategies for users to choose from. Attached Figure Description

[0074] Figure 1 The diagram schematically illustrates a control flowchart of one embodiment of the carbon dioxide heat pump air conditioner anti-frost control method described in this invention.

[0075] Figure 2 The diagram illustrates the process of determining whether frost has formed in one embodiment of the carbon dioxide heat pump air conditioner anti-frost control method of the present invention.

[0076] Figure 3 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in anti-frost mode with three heat exchangers.

[0077] Figure 4 The flowchart schematically illustrates the process of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention further determining whether to enter defrost mode or anti-frost mode under the premise of having three heat exchangers.

[0078] Figure 5 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in defrosting mode with three heat exchangers.

[0079] Figure 6 The flowchart schematically illustrates the process of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention further determining whether to enter the indoor heating mode and the anti-frost mode, given that it has three heat exchangers.

[0080] Figure 7 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in the indoor heating mode with three heat exchangers.

[0081] Figure 8 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in the indoor heating mode with two heat exchangers.

[0082] Figure 9 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in defrosting mode with two heat exchangers. Detailed Implementation

[0083] The following will further explain and illustrate the anti-frost control method and system for carbon dioxide heat pump air conditioners according to the present invention, in conjunction with the accompanying drawings and specific embodiments. However, this explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

[0084] Figure 1 The diagram schematically illustrates a control flowchart of one embodiment of the carbon dioxide heat pump air conditioner anti-frost control method described in this invention.

[0085] like Figure 1 As shown, in some embodiments, the anti-frost control method described in this invention is triggered only when the carbon dioxide heat pump air conditioning system is in heating mode and the evaporator temperature is less than 0°C.

[0086] Based on this method, the first step is to determine whether the outdoor heat exchanger is frosted. Figure 2 The diagram illustrates the process of determining whether frost has formed in one embodiment of the carbon dioxide heat pump air conditioner anti-frost control method of the present invention.

[0087] like Figure 2 As shown, the initial theoretical heating capacity Q0 and the current theoretical heating capacity Q after a period of time are first recorded. N Determine the initial theoretical heating capacity Q0 and the current theoretical heating capacity Q of the carbon dioxide heat pump air conditioning system. N The ratio of the difference to the initial theoretical heating capacity Q0 (Q N Whether -Q0) / Q0 exceeds a set first threshold, in one specific embodiment, the first threshold is set to 0.5%;

[0088] In (Q) N If -Q0) / Q0 does not exceed the set first threshold, obtain the initial frosting measurement index A0 at the initial moment corresponding to the initial theoretical heating capacity Q0 and the current frosting measurement index A at the current moment. N Where A0=K×Δh0 / W0, A N =K×Δh N / W N Where K represents the known proportionality coefficient, Δh0 represents the enthalpy difference between the inlet and outlet of the outdoor heat exchanger at the initial moment, and Δh N W represents the enthalpy difference between the inlet and outlet of the outdoor heat exchanger of the carbon dioxide heat pump air conditioning system at the current moment, and W0 represents the power of the compressor of the carbon dioxide heat pump air conditioning system at the initial moment. N This indicates the compressor's power at the current moment;

[0089] When A N The ratio A to A0 NWhen / A0 is greater than or equal to the set second threshold R, in a specific embodiment, R can be 60% to determine that the outdoor heat exchanger is not frosted;

[0090] When A N The ratio A to A0 N When / A0 is less than the set second threshold R, it is determined that the outdoor heat exchanger is frosted, and the carbon dioxide heat pump air conditioning system enters the anti-frost mode or defrost mode.

[0091] Continue reading Figure 1 If it is determined that the outdoor heat exchanger is frosted, the frosting situation needs to be further assessed. In some implementations, if it is determined that the outdoor heat exchanger is severely frosted, the defrosting mode is entered to directly and quickly defrost the outdoor heat exchanger, and the indoor heating function is temporarily turned off. If it is determined that the outdoor heat exchanger is not severely frosted, the anti-frost mode is entered, which can not only defrost the outdoor heat exchanger to a certain extent, but also maintain the heating of the passenger cabin.

[0092] In some implementations, if it is determined that the outdoor heat exchanger is not frosted, the heat pump controller will continue to determine whether it is necessary to enter the anti-frost mode in advance (i.e., Figure 1 (Pre-frosting prevention). If it is determined that anti-frosting mode should be entered, the compressor speed and the electronic expansion valve threshold can be increased to raise the evaporator temperature and delay the frosting time. If it is determined that anti-frosting prevention is not necessary, simply maintain the current heating mode.

[0093] Since the control method described in this invention can be used in both two-heat-exchanger air conditioning systems and three-heat-exchanger air conditioning systems, and different air conditioning systems use different control methods, the control method described in this invention will be further explained and illustrated based on a specific carbon dioxide heat pump air conditioning system.

[0094] Figure 3 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in anti-frost mode with three heat exchangers.

[0095] like Figure 3As shown, in this embodiment, the carbon dioxide heat pump air conditioner anti-frost control system includes: an outdoor heat exchanger, a compressor, a first indoor heat exchanger, and a second indoor heat exchanger connected in series in the refrigerant main circuit; a first electronic expansion valve located between the outdoor heat exchanger and the second indoor heat exchanger; a second electronic expansion valve located between the first indoor heat exchanger and the second indoor heat exchanger; a first shut-off valve located between the outdoor heat exchanger and the compressor inlet; a second shut-off valve located between the compressor inlet and the second indoor heat exchanger; a third shut-off valve located between the compressor outlet and the first indoor heat exchanger; a fourth shut-off valve located between the outdoor heat exchanger and the compressor outlet; a first PT sensor and a second PT sensor, which respectively sense the temperature and pressure of the refrigerant at the inlet and outlet of the outdoor heat exchanger; and a heat pump controller, which is data-connected to the first electronic expansion valve, the second electronic expansion valve, the first shut-off valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve, the compressor, the first PT sensor, and the second PT sensor.

[0096] Figure 4 The flowchart schematically illustrates the process of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention further determining whether to enter defrost mode or anti-frost mode under the premise of having three heat exchangers.

[0097] like Figure 4 As shown in this embodiment, when it is determined that the outdoor heat exchanger is frosted:

[0098] Continue to determine whether the initial theoretical heating capacity Q0 of the carbon dioxide heat pump air conditioning system is greater than the initial actual heating capacity q0, or continue to determine the current theoretical heating capacity Q. N Is it greater than the current actual heating capacity q? N :

[0099] If the judgment is negative, enter anti-frosting mode;

[0100] If the judgment is yes, continue to judge Q. N With q N Is the difference greater than the difference between Q0 and q0? If the judgment is yes, it is considered that the frost is serious and enters the defrost mode. If the judgment is no, it is considered that the frost is not serious and enters the anti-frost mode.

[0101] Continue reading Figure 3For a carbon dioxide heat pump air conditioning system with three heat exchangers, in anti-frost mode: the heat pump controller controls the first shut-off valve to close, and all other shut-off valves to open. The heat pump controller adjusts the power of the compressor and the opening of the first and second electronic expansion valves. The outdoor heat exchanger, the compressor, and the second indoor heat exchanger are connected in series in the main refrigerant circuit. The first indoor heat exchanger and the compressor are connected in series in the refrigerant bypass circuit. The refrigerant flows out of the compressor, a portion of which flows sequentially through the outdoor heat exchanger and the second indoor heat exchanger and returns to the compressor. The other portion flows through the first indoor heat exchanger and then returns to the compressor. Figure 3 The solid lines in the diagram represent the refrigerant circuits that are active in anti-frost mode, while the dashed lines and lighter-colored icons represent the refrigerant circuits and components that are shut off in anti-frost mode. Figure 3 The arrows in the diagram indicate the direction of refrigerant flow.

[0102] Figure 5 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in defrosting mode with three heat exchangers. Figure 5 The solid lines in the diagram represent the refrigerant circuits that are active in defrost mode, while the dashed lines and lighter-colored icons represent the refrigerant circuits and components that are shut off in defrost mode. Figure 5 The arrows in the diagram indicate the direction of refrigerant flow.

[0103] like Figure 5 As shown, for a carbon dioxide heat pump air conditioning system with three heat exchangers, in defrost mode: the heat pump controller controls the first and third shut-off valves to close, the second and fourth shut-off valves to open, and the second electronic expansion valve to close, thereby making the first indoor heat exchanger not work. The heat pump controller adjusts the power of the compressor and the opening degree of the first electronic expansion valve. The outdoor heat exchanger, the compressor, and the second indoor heat exchanger are connected in series in the conducting refrigerant main circuit. The refrigerant flows out from the compressor, flows through the outdoor heat exchanger and the second indoor heat exchanger in sequence, and then returns to the compressor.

[0104] Figure 6 The flowchart schematically illustrates the process of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention further determining whether to enter the indoor heating mode and the anti-frost mode, given that it has three heat exchangers.

[0105] like Figure 6 As shown, for a carbon dioxide heat pump air conditioning system with three heat exchangers, assuming the outdoor heat exchanger is not frosted: continue to judge A. NWhether / A0 is greater than a preset third threshold P, in a specific embodiment, P can be 62%: when it is determined to be yes, it is considered that there is no need to prevent frost formation in advance, and the indoor heating mode is maintained; when it is determined to be no, it is considered that there is need to prevent frost formation in advance, and the process proceeds as follows. Figure 3 The anti-frost mode is shown.

[0106] Figure 7 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in the indoor heating mode with three heat exchangers. Figure 7 The solid lines in the diagram represent the refrigerant circuits that are active in indoor heating mode, while the dashed lines and lighter-colored icons represent the refrigerant circuits and components that are shut off in indoor heating mode. Figure 7 The arrows in the diagram indicate the direction of refrigerant flow.

[0107] like Figure 7 As shown, for a carbon dioxide heat pump air conditioning system with three heat exchangers, in indoor heating mode: the heat pump controller controls the second and fourth shut-off valves to close, and the first and third shut-off valves to open. The heat pump controller adjusts the power of the compressor and the opening degree of the first and second electronic expansion valves. The outdoor heat exchanger, the compressor, the first indoor heat exchanger, and the second indoor heat exchanger are connected in series in the conductive refrigerant main circuit. The refrigerant flows out from the compressor, flows through the compressor, the first indoor heat exchanger, the second indoor heat exchanger, and the outdoor heat exchanger in sequence, and then returns to the compressor.

[0108] Figure 8 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in the indoor heating mode with two heat exchangers.

[0109] In this embodiment, the carbon dioxide heat pump air conditioner anti-frost control system includes: an outdoor heat exchanger, a compressor, and an indoor heat exchanger connected in series in the refrigerant main circuit; an electronic expansion valve located between the outdoor heat exchanger and the indoor heat exchanger; a first shut-off valve located between the outdoor heat exchanger and the compressor inlet; a second shut-off valve located between the compressor inlet and the indoor heat exchanger; a third shut-off valve located between the compressor outlet and the indoor heat exchanger; a fourth shut-off valve located between the outdoor heat exchanger and the compressor outlet; a first PT sensor and a second PT sensor, which respectively sense the temperature and pressure of the refrigerant at the inlet and outlet of the outdoor heat exchanger; and a heat pump controller, which is data-connected to the electronic expansion valve, the first shut-off valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve, the compressor, the first PT sensor, and the second PT sensor.

[0110] like Figure 8As shown, for a carbon dioxide heat pump air conditioning system with two heat exchangers, if it is determined that the outdoor heat exchanger is not frosted, the carbon dioxide heat pump air conditioning system maintains the indoor heating mode: the heat pump controller controls the second and fourth shut-off valves to close, and the first and third shut-off valves to open. The heat pump controller adjusts the power of the compressor and the opening of the electronic expansion valve. The outdoor heat exchanger, the compressor, and the indoor heat exchanger are connected in series in the conductive refrigerant main circuit. The refrigerant flows out from the compressor, flows through the indoor heat exchanger and the outdoor heat exchanger in sequence, and then returns to the compressor. Figure 8 The solid lines in the diagram represent the refrigerant circuits that are active in indoor heating mode, while the dashed lines and lighter-colored icons represent the refrigerant circuits and components that are shut off in indoor heating mode. Figure 8 The arrows in the diagram indicate the direction of refrigerant flow.

[0111] Figure 9 The diagram schematically illustrates the structure of the carbon dioxide heat pump air conditioner anti-frost control system of the present invention in defrosting mode with two heat exchangers. Figure 9 The solid lines in the diagram represent the refrigerant circuits that are active in defrost mode, while the dashed lines and lighter-colored icons represent the refrigerant circuits and components that are shut off in defrost mode. Figure 9 The arrows in the diagram indicate the direction of refrigerant flow.

[0112] like Figure 9 As shown, for a carbon dioxide heat pump air conditioning system with two heat exchangers, when it is determined that the outdoor heat exchanger is frosted, the carbon dioxide heat pump air conditioning system directly enters the defrosting mode: the heat pump controller controls the second and fourth shut-off valves to open, and the first and third shut-off valves to close. The heat pump controller adjusts the power of the compressor and the opening of the electronic expansion valve. The outdoor heat exchanger, the compressor and the indoor heat exchanger are connected in series in the conducting refrigerant main circuit. The refrigerant flows out from the compressor, flows through the outdoor heat exchanger and the indoor heat exchanger in sequence, and then returns to the compressor.

[0113] It should be noted that in the control method described in this invention, the heat pump controller can not only adjust the power of the compressor and the opening of the electronic expansion valve, but also change the evaporation temperature.

[0114] It should be noted that the prior art portion of the protection scope of this invention is not limited to the embodiments given in this application. All prior art that does not contradict the solution of this invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the protection scope of this invention.

[0115] Furthermore, the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0116] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A method for preventing frost formation in a carbon dioxide heat pump air conditioner, characterized in that, include: Determine the initial theoretical heating capacity Q0 and the current theoretical heating capacity Q of the carbon dioxide heat pump air conditioning system. N The ratio of the difference to the initial theoretical heating capacity Q0 (Q N Does -Q0) / Q0 exceed the set first threshold? In (Q) N If -Q0) / Q0 does not exceed the set first threshold, obtain the initial frosting measurement index A0 at the initial moment corresponding to the initial theoretical heating capacity Q0 and the current frosting measurement index A at the current moment. N Where A0=K×Δh0 / W0, A N =K×Δh N / W N Where K represents the known proportionality coefficient, Δh0 represents the enthalpy difference between the inlet and outlet of the outdoor heat exchanger at the initial moment, and Δh N W represents the enthalpy difference between the inlet and outlet of the outdoor heat exchanger of the carbon dioxide heat pump air conditioning system at the current moment, and W0 represents the power of the compressor of the carbon dioxide heat pump air conditioning system at the initial moment. N This indicates the compressor's power at the current moment; When A N The ratio A to A0 N When / A0 is greater than or equal to the set second threshold, it is determined that the outdoor heat exchanger is not frosted; When A N The ratio A to A0 N When / A0 is less than the set second threshold, it is determined that the outdoor heat exchanger is frosted, and the carbon dioxide heat pump air conditioning system enters the anti-frost mode or defrost mode.

2. The anti-frost control method for carbon dioxide heat pump air conditioners as described in claim 1, characterized in that, When a carbon dioxide heat pump air conditioning system has an indoor heat exchanger, if it is determined that the outdoor heat exchanger is frosted, the carbon dioxide heat pump air conditioning system directly enters the defrosting mode. In the defrosting mode, the outdoor heat exchanger, the compressor, and the indoor heat exchanger are connected in series in the main refrigerant circuit. The refrigerant flows out from the compressor, flows through the outdoor heat exchanger and the indoor heat exchanger in sequence, and then returns to the compressor.

3. The anti-frost control method for carbon dioxide heat pump air conditioners as described in claim 2, characterized in that, If the outdoor heat exchanger is determined not to be frosted, the carbon dioxide heat pump air conditioning system maintains the indoor heating mode. In the indoor heating mode, the outdoor heat exchanger, compressor and indoor heat exchanger are connected in series in the main refrigerant circuit. The refrigerant flows out from the compressor, flows through the indoor heat exchanger and the outdoor heat exchanger in sequence, and then returns to the compressor.

4. The anti-frost control method for carbon dioxide heat pump air conditioners as described in claim 1, characterized in that, The second threshold is a value related to ambient temperature and theoretical heating capacity.

5. The anti-frost control method for carbon dioxide heat pump air conditioners as described in claim 1, characterized in that, When a carbon dioxide heat pump air conditioning system has at least two indoor heat exchangers, namely a first indoor heat exchanger and a second indoor heat exchanger, the following conditions are considered when frosting is observed on the outdoor heat exchanger: Continue to determine whether the initial theoretical heating capacity Q0 of the carbon dioxide heat pump air conditioning system is greater than the initial actual heating capacity q0, or continue to determine the current theoretical heating capacity Q. N Is it greater than the current actual heating capacity q? N : If the judgment is negative, enter anti-frosting mode; If the judgment is yes, continue to judge Q. N With q N Is the difference greater than the difference between Q0 and q0? If the result is yes, enter defrost mode; if the result is no, enter anti-frost mode. In the anti-frost mode: the outdoor heat exchanger, the compressor, and the second indoor heat exchanger are connected in series in the main refrigerant circuit, and the first indoor heat exchanger and the compressor are connected in series in the refrigerant bypass circuit. The refrigerant flows out of the compressor, a part of which flows through the outdoor heat exchanger and the second indoor heat exchanger in sequence and returns to the compressor, and the other part flows through the first indoor heat exchanger and then returns to the compressor. In the defrosting mode: the outdoor heat exchanger, the compressor, and the second indoor heat exchanger are connected in series in the main refrigerant circuit. The refrigerant flows out from the compressor, flows through the outdoor heat exchanger and the second indoor heat exchanger in sequence, and then returns to the compressor.

6. The anti-frost control method for carbon dioxide heat pump air conditioners as described in claim 5, characterized in that, Assuming the outdoor heat exchanger is not frosted: Continue to judge A N Is / A0 greater than the preset third threshold? If yes, maintain indoor heating mode; if no, enter anti-frost mode. In the indoor heating mode: the outdoor heat exchanger, the compressor, the first indoor heat exchanger, and the second indoor heat exchanger are connected in series in the main refrigerant circuit. The refrigerant flows out from the compressor, flows through the compressor, the first indoor heat exchanger, the second indoor heat exchanger, and the outdoor heat exchanger in sequence, and then returns to the compressor.

7. The anti-frost control method for carbon dioxide heat pump air conditioners as described in claim 6, characterized in that, The third threshold is obtained by adding a set compensation value to the corresponding second threshold.

8. A carbon dioxide heat pump air conditioner anti-frost control system, which executes the method as described in any one of claims 1-4, characterized in that, The carbon dioxide heat pump air conditioner anti-frost control system includes: The outdoor heat exchanger, compressor, and indoor heat exchanger are connected in series in the main refrigerant circuit; An electronic expansion valve is provided between the outdoor heat exchanger and the indoor heat exchanger; The first shut-off valve is located between the outdoor heat exchanger and the compressor inlet; The second shut-off valve is located between the compressor inlet and the indoor heat exchanger; The third shut-off valve is located between the compressor outlet and the indoor heat exchanger; The fourth shut-off valve is located between the outdoor heat exchanger and the compressor outlet; The first PT sensor and the second PT sensor respectively sense the temperature and pressure of the refrigerant at the inlet and outlet of the outdoor heat exchanger; The heat pump controller is connected to the electronic expansion valve, the first shut-off valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve, the compressor, the first PT sensor, and the second PT sensor, respectively.

9. A carbon dioxide heat pump air conditioner anti-frost control system, which performs the method as described in any one of claims 1, 5-7, characterized in that, The carbon dioxide heat pump air conditioner anti-frost control system includes: An outdoor heat exchanger, a compressor, a first indoor heat exchanger, and a second indoor heat exchanger are connected in series in the main refrigerant circuit. A first electronic expansion valve is located between the outdoor heat exchanger and the second indoor heat exchanger; The second electronic expansion valve is located between the first indoor heat exchanger and the second indoor heat exchanger; The first shut-off valve is located between the outdoor heat exchanger and the compressor inlet; The second shut-off valve is located between the compressor inlet and the second indoor heat exchanger. The third shut-off valve is located between the compressor outlet and the first indoor heat exchanger; The fourth shut-off valve is located between the outdoor heat exchanger and the compressor outlet; The first PT sensor and the second PT sensor respectively sense the temperature and pressure of the refrigerant at the inlet and outlet of the outdoor heat exchanger; The heat pump controller is connected to the first electronic expansion valve, the second electronic expansion valve, the first shut-off valve, the second shut-off valve, the third shut-off valve, the fourth shut-off valve, the compressor, the first PT sensor, and the second PT sensor, respectively.

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