A CO2 variable frequency heat pump air conditioning system and control method

Abstract

The present invention discloses a CO2 variable-frequency heat pump air-conditioning system and a control method. The system includes a compressor, a four-way reversing valve, an outdoor heat exchanger, a dryer filter, a regenerator, a two-way expansion valve group, an indoor heat exchanger, and a gas-liquid separator connected in sequence through pipelines. The two-way expansion valve group includes a refrigeration expansion valve group and a heating expansion valve group connected in parallel on the pipeline between the regenerator and the indoor heat exchanger. The refrigeration expansion valve group includes an electronic expansion valve A and a check valve A connected in series. The heating expansion valve group includes an electronic expansion valve B and a check valve B connected in series. In the CO2 variable-frequency heat pump air-conditioning system disclosed by the present invention, the two-way expansion valve group only adopts one-way electronic expansion valves and check valves, reducing the cost of the heat pump, and having the advantages of high operation reliability and low maintenance cost at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of rail transit air conditioning control, in particular to a CO2 variable frequency heat pump air conditioning system and a control method. Background Art

[0002] The safety and reliability of air-conditioning units in rail transit are particularly important. Carbon dioxide refrigerant, as a natural refrigerant, is non-flammable and non-explosive, and has excellent low-temperature heating performance. The throttling expansion of the transcritical carbon dioxide heat pump system is the core component of the refrigeration system. At present, the cost of the two-way electronic expansion valve that realizes two-way expansion under high pressure conditions is very high. It is mainly used in scientific research in universities and scientific research systems and cannot be used commercially. At the same time, in the actual application process, the circulation flow rate under different cooling and heating conditions is different, and a single two-way electronic expansion valve cannot achieve precise control suitable for different conditions.

[0003] Patent CN116222026A introduces an electronic expansion valve solution for heat pumps, which uses only one valve to control both cooling and heating operating conditions. Although the cost is low, the reliability of valve use will be reduced. At the same time, the circulation flow rates of the cooling and heating systems are different, and there will be greater control accuracy problems, resulting in the solution being unable to fully meet the requirements of the two operating conditions.

[0004] Therefore, how to realize the reversing function of the heat pump air conditioner while ensuring the reliable operation of the system under different working conditions and achieving low maintenance costs is an urgent problem to be solved. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention proposes a CO2 variable frequency heat pump air conditioning system and a control method.

[0006] The specific technical solution adopted by the present invention is as follows:

[0007] A CO2 variable frequency heat pump air conditioning system, comprising a compressor, a four-way reversing valve, an outdoor heat exchanger, a drying filter, a regenerator, a two-way expansion valve group, an indoor heat exchanger and a gas-liquid separator;

[0008] The four interfaces of the four-way reversing valve are respectively connected to the compressor, the outdoor heat exchanger, the indoor heat exchanger and the gas-liquid separator through pipelines; the two ends of the a channel of the regenerator are respectively connected to the compressor and the gas-liquid separator through pipelines, the two ends of the b channel of the regenerator are respectively connected to the drying filter and the two-way expansion valve group through pipelines, and the other end of the two-way expansion valve group is connected to the indoor heat exchanger through a pipeline;

[0009] The bidirectional expansion valve group includes a cooling expansion valve group and a heating expansion valve group which are arranged in parallel on the pipeline between the regenerator and the indoor heat exchanger;

[0010] The refrigeration expansion valve group includes an electronic expansion valve A and a check valve A connected in series;

[0011] The heating expansion valve group includes an electronic expansion valve B and a check valve B connected in series.

[0012] Furthermore, in the refrigeration working condition, the refrigeration expansion valve group is connected, and the heat exchange medium flows through the two-way expansion valve group along the electronic expansion valve A and the one-way valve A;

[0013] In the heating condition, the heating expansion valve group is connected, and the heat exchange medium flows through the two-way expansion valve group along the electronic expansion valve B and the one-way valve B.

[0014] Further, the electronic expansion valve A and the electronic expansion valve B have the following relationship:

[0015] Cvbi<Cvh≤Cvb<Cvai<Cvc≤Cva;

[0016] Wherein, Cva is the maximum flow coefficient of electronic expansion valve A, and Cvb is the maximum flow coefficient of electronic expansion valve B;

[0017] Cvai is the actual flow coefficient of the electronic expansion valve A, Cvai = Qc / ((Thh-Tss)*Cp);

[0018] Cvbi is the actual flow coefficient of the electronic expansion valve B, Cvbi = Qh / ((Thh-Tss)*Cp);

[0019] Cvc is the theoretical flow coefficient of the electronic expansion valve A, Cvc = Qc / ((Th-Ts)*Cp);

[0020] Cvh is the theoretical flow coefficient of the electronic expansion valve B, Cvh = Qh / ((Th-Ts)*Cp);

[0021] Qc is the cooling load; Qh is the heating load; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the specific heat of air at constant pressure.

[0022] Furthermore, it also includes an outdoor fan.

[0023] Furthermore, an indoor ventilator is also included.

[0024] The CO2 variable frequency heat pump air conditioning system control method disclosed in the present invention comprises the following steps:

[0025] When the CO2 variable frequency heat pump air conditioning system is used for refrigeration:

[0026] Start the refrigeration mode of the CO2 variable frequency heat pump air conditioning system. According to the collected refrigeration load Qc, the opening control strategy of the electronic expansion valve A is used to control the opening of the electronic expansion valve A. The opening control strategy of the electronic expansion valve A is as follows:

[0027] Calculate the temperature control accuracy K and suction superheat △T;

[0028] Temperature control accuracy K = Th-Tic;

[0029] Suction superheat △T = Tx-To;

[0030] Control the opening of the electronic expansion valve A according to the temperature control accuracy K and the suction superheat △T;

[0031] K>1℃, the opening degree of electronic expansion valve A y=Te×a1+△T×b1+Cvai;

[0032] 0.5<K≤1℃, the opening degree of electronic expansion valve A y=Te×a2+△T×b2+Cvai;

[0033] 0<K≤0.5℃, opening degree of electronic expansion valve A y=Te×a3+△T×b3+Cvai;

[0034] -0.5<K≤0℃, electronic expansion valve A opening y=Te×a4+△T×b4+Cvai;

[0035] Among them, Cvai is the actual flow coefficient of the electronic expansion valve A, Cvai = Qc / ((Thh-Tss)*Cp); Qc = kA(Te-Th); k is the heat transfer coefficient of the vehicle body surface; A is the surface area of ​​the vehicle body; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tx is the suction temperature; To is the suction saturation temperature; Te is the ambient temperature; Tic is the target temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the constant pressure specific heat of air; a1-a4 are the refrigeration temperature coefficients, which are constants obtained from experimental data; b1-b4 are the refrigeration superheat coefficients, which are constants obtained from experimental data;

[0036] When the CO2 variable frequency heat pump air conditioning system is used for heating:

[0037] Start the heating mode of the CO2 variable frequency heat pump air conditioning system. According to the collected heating load Qh, the opening control strategy of the electronic expansion valve B is used to control the opening of the electronic expansion valve B. The opening control strategy of the electronic expansion valve B is as follows:

[0038] Calculate the temperature control accuracy K and suction superheat △T;

[0039] Temperature control accuracy K = Th-Tic;

[0040] Suction superheat △T = Tx-To;

[0041] Control the opening of the electronic expansion valve B according to the temperature control accuracy K and the suction superheat △T;

[0042] K>1℃, the opening degree of electronic expansion valve B y=Te×a5+△T×b5+Cvbi;

[0043] 0.5<K≤1℃, opening degree of electronic expansion valve B y=Te×a6+△T×b6+Cvbi;

[0044] 0<K≤0.5℃, opening degree of electronic expansion valve B y=Te×a7+△T×b7+Cvbi;

[0045] -0.5<K≤0℃, electronic expansion valve B opening y=Te×a8+△T×b8+Cvbi;

[0046] Among them, Cvbi is the actual flow coefficient of the electronic expansion valve B, Cvbi = Qh / ((Thh-Tss)*Cp); Qh = kA(Te-Th); k is the heat transfer coefficient of the vehicle body surface; A is the surface area of ​​the vehicle body; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the constant pressure specific heat of air; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tx is the intake temperature; To is the intake saturation temperature; Te is the ambient temperature; Tic is the target temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the constant pressure specific heat of air; a5-a8 are the heating ring temperature coefficients, which are constants obtained from experimental data; b5-b8 are the heating overheating coefficients, which are constants obtained from experimental data.

[0047] Furthermore, the action time of the electronic expansion valve is delayed by a set time relative to the time of the ambient temperature gradient change.

[0048] Furthermore, the delay setting time is 5s.

[0049] Furthermore, when the CO2 variable frequency heat pump air conditioning system is used for refrigeration, the operating frequency of the compressor Fe=x1Te+y1, where x1 is the ambient temperature coefficient and y1 is the correction coefficient;

[0050] When the CO2 variable frequency heat pump air conditioning system is used for heating conditions, the operating frequency of the compressor is Fe=x2Te+y2, where x2 is the ambient temperature coefficient and y2 is the correction coefficient.

[0051] Compared with the prior art, the bidirectional expansion valve group for the CO2 variable frequency heat pump air-conditioning system disclosed in the present invention has the following beneficial effects: the present application sets two one-way electronic expansion valves and two one-way valves, connects an electronic expansion valve and a one-way valve in series to form an expansion valve group, and then connects the two expansion valve groups in parallel to form a two-way expansion valve group. Since only one-way electronic expansion valves and one-way valves are used, the cost of the heat pump is reduced. At the same time, a method for separate control under different working conditions is designed based on the system, which can comprehensively improve the control accuracy under both cooling and heating conditions, and has the advantages of high operating reliability and low maintenance cost. Compared with the bidirectional electronic expansion valve, the cost of the scheme of the present invention is superior, which is about 1 / 3 of the cost of the bidirectional electronic expansion valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a structural schematic diagram of the CO2 variable frequency heat pump air conditioning system disclosed in the present invention;

[0053] Figure 2 This is a control flow chart of the CO2 variable frequency heat pump air conditioning system disclosed in the present invention;

[0054] In the figure: 1. compressor; 2. four-way reversing valve; 3. outdoor heat exchanger; 4. drying filter; 5. regenerator; 6. outdoor fan; 7. two-way expansion valve group; 7-1. electronic expansion valve A; 7-2. check valve A; 7-3. electronic expansion valve B; 7-4. check valve B; 8. indoor heat exchanger; 9. gas-liquid separator, 10. indoor ventilator. DETAILED DESCRIPTION

[0055] like Figure 1 The figure shows a CO2 variable frequency heat pump air conditioning system disclosed in the present invention, comprising a compressor 1, a four-way reversing valve 2, an outdoor heat exchanger 3, a drying filter 4, a regenerator 5, a two-way expansion valve group 7, an indoor heat exchanger 8 and a gas-liquid separator 9;

[0056] Among them, the four interfaces of the four-way reversing valve 4 (including the D interface, the C interface, the E interface and the S interface in the figure) are respectively connected to the compressor 1, the outdoor heat exchanger 3, the indoor heat exchanger 8 and the gas-liquid separator 9 through pipelines; the two ends of the a channel of the regenerator are respectively connected to the compressor 1 and the gas-liquid separator 9 through pipelines, and the two ends of the b channel of the regenerator are respectively connected to the drying filter 4 and the two-way expansion valve group 7 through pipelines, and the other end of the two-way expansion valve group 7 is connected to the indoor heat exchanger 8 through a pipeline;

[0057] The bidirectional expansion valve group 7 includes a cooling expansion valve group and a heating expansion valve group which are arranged in parallel on the pipeline between the regenerator 5 and the indoor heat exchanger 8;

[0058] The refrigeration expansion valve group includes an electronic expansion valve A7-1 and a one-way valve A7-2 connected in series;

[0059] The heating expansion valve group includes an electronic expansion valve B7-3 and a one-way valve B7-4 connected in series.

[0060] Specifically, the compressor 1 is connected to the D interface of the four-way reversing valve 2, the C interface of the four-way reversing valve 2 is connected to the inlet of the outdoor heat exchanger 3, the inlet of the drying filter 4 is connected to the outlet of the outdoor heat exchanger 3, one end of the b channel of the regenerator 5 is connected to the drying filter 4, the other end of the b channel of the regenerator 5 is connected to the one-way valve A7-2, the other end of the one-way valve A7-2 is connected to the electronic expansion valve A7-1, the other end of the electronic expansion valve A7-1 is connected to one end of the indoor heat exchanger 8, and the electronic expansion valve A7-1 is connected to one end of the indoor heat exchanger 8. One end of the expansion valve B7-3 is connected to the low-pressure side of the regenerator 5, the other end of the electronic expansion valve B7-3 is connected to one end of the one-way valve B7-4, the other end of the one-way valve B7-4 is connected to the indoor heat exchanger 8, the other end of the indoor heat exchanger 8 is connected to the E interface of the four-way reversing valve 2, the S interface of the four-way reversing valve 2 is connected to the gas-liquid separator 9, the outlet of the gas-liquid separator 9 is connected to one end of the a channel of the regenerator 5, and the air intake of the compressor 1 is connected to the other end of the a channel of the regenerator 5. When the CO2 variable frequency heat pump air conditioning system disclosed in the present invention is in refrigeration mode, the refrigeration expansion valve group is connected, and the heat exchange medium flows through the two-way expansion valve group along the electronic expansion valve A and the one-way valve A, and does not flow through the heating expansion valve group;

[0061] In the heating condition, the heating expansion valve group is connected, and the heat exchange medium flows through the two-way expansion valve group along the electronic expansion valve B and the one-way valve B, and does not flow through the cooling expansion valve group.

[0062] Furthermore, an outdoor fan 6 and / or an indoor ventilator 10 are included to further improve the heat exchange efficiency of the air conditioner.

[0063] The working process of the CO2 variable frequency heat pump air conditioning system disclosed in the present invention is as follows:

[0064] 1. CO2 variable frequency heat pump air conditioning system air conditioning refrigeration cycle process:

[0065] After compressor 1 compresses low-temperature and low-pressure carbon dioxide refrigerant (cooling medium) to do work, it forms high-temperature and high-pressure supercritical gas and discharges it into the four-way reversing valve 2. Carbon dioxide enters the outdoor heat exchanger 3 through the outdoor side port of the four-way reversing valve 2. After the heat released by the refrigerant in the outdoor heat exchanger 3 is taken away by the wind blown by the outdoor axial flow fan 6, the refrigerant continues to flow from the outdoor heat exchanger 3 to the drying filter 4. The refrigerant flowing out of the drying filter flows into the high-pressure side (b channel) of the regenerator 5. The refrigerant flowing out of the high-pressure side (b channel) of the regenerator 5 enters the electronic expansion valve B7-3 for throttling expansion. The expanded low-temperature and low-pressure refrigerant flows out of the electronic expansion valve B7-3. The refrigerant continues to flow to the one-way valve B7-4. The refrigerant flowing out of the one-way valve B7-4 enters the inlet of the indoor heat exchanger 8. The heat carried by the wind blown by the indoor fan 10 is taken away by the refrigerant in the indoor heat exchanger 8, and the refrigerant continues to enter the gas-liquid separator 9 through the four-way reversing valve 2. After the meteorological components are separated from the refrigerant from the gas-liquid separator 9, it enters the low-pressure side (channel a) of the regenerator 5, and finally enters the suction port of the compressor 1 to complete the system refrigeration cycle.

[0066] 2. Air conditioning heating cycle process of CO2 variable frequency heat pump air conditioning system:

[0067] The compressor 1 compresses the low-temperature and low-pressure carbon dioxide refrigerant to form a high-temperature and high-pressure supercritical gas and discharges it into the four-way reversing valve 2. The carbon dioxide enters the indoor heat exchanger 8 through the indoor side pipe of the four-way reversing valve 2. The heat released by the refrigerant in the outdoor heat exchanger is taken away by the wind blown by the indoor ventilator 10, so that the indoor temperature rises and the heating is performed. The refrigerant continues to flow from the indoor heat exchanger 8 to the electronic expansion valve A7-1. The expanded low-temperature and low-pressure refrigerant flows out of the electronic expansion valve A7-1 and continues to flow to the one-way valve A7-2. The refrigerant flowing out of A7-2 enters the b channel of the regenerator 5, and the refrigerant flowing out of the b channel of the regenerator 5 enters the drying filter 4, and the refrigerant flowing out of the drying filter 4 enters the outdoor heat exchanger 3. The refrigerant absorbs the heat of the wind blown out by the outdoor axial flow fan 6 and enters the four-way reversing valve 2, and then flows out from the return air pipe port of the four-way reversing valve 2 and enters the gas-liquid separator 9. After the gaseous carbon dioxide refrigerant with separated liquid components enters the a channel of the regenerator 5, it finally flows to the suction port of the compressor 1, and finally completes the system heat pump heating cycle.

[0068] The CO2 variable frequency heat pump air conditioning system disclosed in the present invention is provided with two one-way electronic expansion valves and two one-way valves between the regenerator and the indoor heat exchanger, and an electronic expansion valve and a one-way valve are connected in series to form a cooling expansion valve group and a heating expansion valve group respectively, and then the two expansion valve groups are connected in parallel to form a two-way expansion valve group. Since only one-way electronic expansion valves and one-way valves are used, the cost of the heat pump is reduced, and the system has the advantages of high operating reliability and low maintenance cost. Compared with the two-way electronic expansion valve, the cost of the scheme of the present invention is superior, which is about 1 / 3 of the cost of the two-way electronic expansion valve.

[0069] Further, the electronic expansion valve A and the electronic expansion valve B have the following relationship:

[0070] Cvbi<Cvh≤Cvb<Cvai<Cvc≤Cva;

[0071] Wherein, Cva is the maximum flow coefficient of electronic expansion valve A, and Cvb is the maximum flow coefficient of electronic expansion valve B;

[0072] Cvai is the actual flow coefficient of the electronic expansion valve A, Cvai = Qc / ((Thh-Tss)*Cp);

[0073] Cvbi is the actual flow coefficient of the electronic expansion valve B, Cvbi = Qh / ((Thh-Tss)*Cp);

[0074] Cvc is the theoretical flow coefficient of the electronic expansion valve A, Cvc = Qc / ((Th-Ts)*Cp);

[0075] Cvh is the theoretical flow coefficient of the electronic expansion valve B, Cvh = Qh / ((Th-Ts)*Cp);

[0076] Qc is the cooling load; Qh is the heating load; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the specific heat of air at constant pressure.

[0077] This control strategy can match the appropriate electronic expansion valve control method according to the system load demand to the maximum extent, so that the system's cooling capacity matches the appropriate outdoor load and shortens the time to reach the target temperature.

[0078] like Figure 2 The CO2 variable frequency heat pump air conditioning system control method disclosed in the present invention comprises the following steps:

[0079] When the CO2 variable frequency heat pump air conditioning system is used for refrigeration:

[0080] Start the refrigeration mode of the CO2 variable frequency heat pump air conditioning system. According to the collected refrigeration load Qc, the opening control strategy of the electronic expansion valve A is used to control the opening of the electronic expansion valve A. The opening control strategy of the electronic expansion valve A is as follows:

[0081] Calculate the temperature control accuracy K and suction superheat △T;

[0082] Temperature control accuracy K = Th-Tic;

[0083] Suction superheat △T = Tx-To;

[0084] Control the opening of the electronic expansion valve A according to the temperature control accuracy K and the suction superheat △T;

[0085] K>1℃, the opening degree of electronic expansion valve A y=Te×a1+△T×b1+Cvai;

[0086] 0.5<K≤1℃, the opening degree of electronic expansion valve A y=Te×a2+△T×b2+Cvai;

[0087] 0<K≤0.5℃, opening degree of electronic expansion valve A y=Te×a3+△T×b3+Cvai;

[0088] -0.5<K≤0℃, electronic expansion valve A opening y=Te×a4+△T×b4+Cvai;

[0089] Among them, Cvai is the actual flow coefficient of the electronic expansion valve A, Cvai = Qc / ((Thh-Tss)*Cp); Qc = kA(Te-Th); k is the heat transfer coefficient of the vehicle body surface; A is the surface area of ​​the vehicle body; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tx is the suction temperature; To is the suction saturation temperature; Te is the ambient temperature; Tic is the target temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the constant pressure specific heat of air; a1-a4 are the refrigeration temperature coefficients, which are constants obtained from experimental data; b1-b4 are the refrigeration superheat coefficients, which are constants obtained from experimental data;

[0090] When the CO2 variable frequency heat pump air conditioning system is used for heating:

[0091] Start the heating mode of the CO2 variable frequency heat pump air conditioning system. According to the collected heating load Qh, the opening control strategy of the electronic expansion valve B is used to control the opening of the electronic expansion valve B. The opening control strategy of the electronic expansion valve B is as follows:

[0092] Calculate the temperature control accuracy K and suction superheat △T;

[0093] Temperature control accuracy K = Th-Tic;

[0094] Suction superheat △T = Tx-To;

[0095] Control the opening of the electronic expansion valve B according to the temperature control accuracy K and the suction superheat △T;

[0096] K>1℃, the opening degree of electronic expansion valve B y=Te×a5+△T×b5+Cvbi;

[0097] 0.5<K≤1℃, opening degree of electronic expansion valve B y=Te×a6+△T×b6+Cvbi;

[0098] 0<K≤0.5℃, opening degree of electronic expansion valve B y=Te×a7+△T×b7+Cvbi;

[0099] -0.5<K≤0℃, electronic expansion valve B opening y=Te×a8+△T×b8+Cvbi;

[0100] Among them, Cvbi is the actual flow coefficient of the electronic expansion valve B, Cvbi = Qh / ((Thh-Tss)*Cp); Qh = kA(Te-Th); k is the heat transfer coefficient of the vehicle body surface; A is the surface area of ​​the vehicle body; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the constant pressure specific heat of air; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tx is the intake temperature; To is the intake saturation temperature; Te is the ambient temperature; Tic is the target temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the constant pressure specific heat of air; a5-a8 are the heating ring temperature coefficients, which are constants obtained from experimental data; b5-b8 are the heating overheating coefficients, which are constants obtained from experimental data.

[0101] The CO2 variable frequency heat pump air conditioning system control method disclosed in the present invention has the purposes of high temperature control accuracy, fast cooling rate, energy saving and consumption reduction.

[0102] At the same time, since the refrigerants in cooling conditions and heating conditions use different flow paths, the mutual influence between cooling conditions and heating conditions can be reduced. Different valve types and flow coefficients are selected for different conditions, which has better adaptability to systems with large differences in load between cooling and heating conditions. In particular, the load difference between summer and winter in southern China is large. Therefore, the adoption of this solution can minimize the energy consumption of the whole machine; by using different flow paths, when the valve in the cooling condition is damaged, it will not affect the heating condition and can continue to be used, which improves the maintainability of the system. At the same time, the frequency of valve use is reduced, the service life of the valve is extended, and the risk of system operation is reduced.

[0103] Furthermore, the action time of the electronic expansion valve is delayed by a setting time relative to the time when the ambient temperature gradient changes. Preferably, the delay setting time is 5s, that is, when the ambient temperature sensor detects that the ambient temperature has changed and the ambient temperature is at different gradients, it is delayed for a certain time. After the ambient temperature reaches the temperature, the opening of the electronic expansion valve is adjusted to achieve adjustment of different ambient temperatures. For example, when the ambient temperature sensor detects that the ambient temperature changes from a first gradient (for example, 17.9°C) to a second gradient (for example, 18.2°C), the electronic expansion valve A is delayed for a certain time (for example, 5s) before adjusting the opening of the electronic expansion valve A from 380 steps to 400 steps. Since the action time of the electronic expansion valve is delayed relative to the time when the ambient temperature gradient changes, the collected ambient temperature can be ensured to be warmer and the electronic expansion valve can be controlled more accurately, thereby ensuring the effect of the heat pump.

[0104] Furthermore, when the CO2 variable frequency heat pump air conditioning system is used for refrigeration, the operating frequency of the compressor Fe=x1Te+y1, where x1 is the ambient temperature coefficient and y1 is the correction coefficient;

[0105] When the CO2 heat pump is used for heating, the operating frequency of the compressor is Fe=x2Te+y2, where x2 is the ambient temperature coefficient and y2 is the correction coefficient.

[0106] The compressor frequency control adopts the above control logic, which can make the compressor adapt to the load change caused by the ambient temperature change as soon as possible, so as to achieve the purpose of improving the cooling rate of the compressor and reducing energy consumption.

[0107] Comparison of cooling modes, assuming target temperature Tic = 24°C, ambient temperature Te = 30°C, initial (0min) return air temperature Thl = 29°C:

[0108]

[0109] It can be seen from the data table that by adopting the scheme of this embodiment, under refrigeration working conditions, the valve control accuracy of this scheme is better, the cooling rate is faster, and the temperature fluctuation is smaller.

[0110] Comparison of heating modes, assuming target temperature Tic = 18°C, ambient temperature Te = 10°C, initial (0min) return air temperature Thl = 12°C:

[0111]

[0112] It can be seen from the data table that by adopting the scheme of this embodiment, the heat pump working condition can shorten the time to reach the target temperature and the temperature fluctuation is small because it adopts an electronic expansion valve aperture and control scheme different from that of the refrigeration working condition.

[0113] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A CO2 variable frequency heat pump air conditioning system control method, characterized in that: The CO2 variable frequency heat pump air conditioning system comprises a compressor (1), a four-way reversing valve (2), an outdoor heat exchanger (3), a drying filter (4), a regenerator (5), a two-way expansion valve group (7), an indoor heat exchanger (8) and a gas-liquid separator (9); The four interfaces of the four-way reversing valve (2) are respectively connected to the compressor (1), the outdoor heat exchanger (3), the indoor heat exchanger (8) and the gas-liquid separator (9) through pipelines; the two ends of the a channel of the regenerator (5) are respectively connected to the compressor (1) and the gas-liquid separator (9) through pipelines, the two ends of the b channel of the regenerator (5) are respectively connected to the drying filter (4) and the two-way expansion valve group (7) through pipelines, and the other end of the two-way expansion valve group (7) is connected to the indoor heat exchanger (8) through a pipeline; The bidirectional expansion valve group comprises a cooling expansion valve group and a heating expansion valve group which are arranged in parallel on the pipeline between the regenerator (5) and the indoor heat exchanger (8); The refrigeration expansion valve group comprises an electronic expansion valve A (7-1) and a check valve A (7-2) connected in series; The heating expansion valve group comprises an electronic expansion valve B (7-3) and a check valve B (7-4) connected in series; The control method comprises the following steps, When the CO2 variable frequency heat pump air conditioning system is used for refrigeration: Start the refrigeration mode of the CO2 variable frequency heat pump air conditioning system. According to the collected refrigeration load Qc, the opening control strategy of the electronic expansion valve A is used to control the opening of the electronic expansion valve A. The opening control strategy of the electronic expansion valve A is as follows: Calculate the temperature control accuracy K and suction superheat △T; Temperature control accuracy K = Th-Tic; Suction superheat △T = Tx-To; Control the opening of the electronic expansion valve A according to the temperature control accuracy K and the suction superheat △T; K>1℃, the opening degree of electronic expansion valve A y=Te×a1+△T×b1+Cvai; 0.5<K≤1℃, the opening degree of electronic expansion valve A y=Te×a2+△T×b2+Cvai; 0<K≤0.5℃, opening degree of electronic expansion valve A y=Te×a3+△T×b3+Cvai; -0.5<K≤0℃, electronic expansion valve A opening y=Te×a4+△T×b4+Cvai; Among them, Cvai is the actual flow coefficient of the electronic expansion valve A, Cvai=Qc / ((Thh-Tss)*Cp); Qc=kA(Te-Th); k is the heat transfer coefficient of the vehicle body surface; A is the surface area of ​​the vehicle body; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tx is the suction temperature; To is the suction saturation temperature; Te is the ambient temperature; Tic is the target temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the constant pressure specific heat of air; a1-a4 is the refrigeration ring temperature coefficient; b1-b4 is the refrigeration superheat coefficient; When the CO2 variable frequency heat pump air conditioning system is used for heating: Start the heating mode of the CO2 variable frequency heat pump air conditioning system. According to the collected heating load Qh, the opening control strategy of the electronic expansion valve B is used to control the opening of the electronic expansion valve B. The opening control strategy of the electronic expansion valve B is as follows: Calculate the temperature control accuracy K and suction superheat △T; Temperature control accuracy K = Th-Tic; Suction superheat △T = Tx-To; Control the opening of the electronic expansion valve B according to the temperature control accuracy K and the suction superheat △T; K>1℃, the opening degree of electronic expansion valve B y=Te×a5+△T×b5+Cvbi; 0.5<K≤1℃, opening degree of electronic expansion valve B y=Te×a6+△T×b6+Cvbi; 0<K≤0.5℃, opening degree of electronic expansion valve B y=Te×a7+△T×b7+Cvbi; -0.5<K≤0℃, electronic expansion valve B opening y=Te×a8+△T×b8+Cvbi; Among them, Cvbi is the actual flow coefficient of the electronic expansion valve B, Cvbi = Qh / ((Thh-Tss)*Cp); Qh = kA(Te-Th); k is the heat transfer coefficient of the vehicle body surface; A is the surface area of ​​the vehicle body; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the air constant pressure specific heat; Ts is the theoretical supply air temperature; Th is the theoretical return air temperature; Tx is the intake temperature; To is the intake saturation temperature; Te is the ambient temperature; Tic is the target temperature; Tss is the actual supply air temperature; Thh is the actual return air temperature; Cp is the air constant pressure specific heat; a5-a8 is the heating ring temperature coefficient; b5-b8 is the heating overheating coefficient.

2. The CO2 variable frequency heat pump air conditioning system control method according to claim 1, characterized in that: The action time of the electronic expansion valve is delayed by the set time relative to the change time of the ambient temperature gradient.

3. The CO2 variable frequency heat pump air conditioning system control method according to claim 2, characterized in that: The delay setting time is 5s.

4. The CO2 variable frequency heat pump air conditioning system control method according to claim 3, characterized in that: When the CO2 variable frequency heat pump air conditioning system is used for refrigeration, the operating frequency of the compressor is Fe=x1Te+y1, where x1 is the ambient temperature coefficient and y1 is the correction coefficient; When the CO2 variable frequency heat pump air conditioning system is used for heating conditions, the operating frequency of the compressor Fe=x2Te+y2, where x2 is the ambient temperature coefficient and y2 is the correction coefficient.

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