Heat pump system and control method thereof

Abstract

The invention provides a heat pump system and a control method thereof. The heat pump system comprises a main loop, a slave loop, a pressure sensor and an emptying pipeline. The main loop comprises a compressor, a first heat exchanger and a second heat exchanger which are sequentially connected. The slave loop comprises a third heat exchanger connected with the main loop. The pressure sensor is arranged in an exhaust pipeline of the compressor and used for detecting the exhaust pressure of the compressor. The emptying pipeline is connected with a second port of the first heat exchanger and a first port of the second heat exchanger, and an emptying control valve is arranged in the emptying pipeline. The controller is configured to control the evacuation control valve based on an exhaust pressure of the compressor when the heat pump system operates in a reheat dehumidification mode in which the slave circuit is connected in parallel with the main circuit. The application can reduce the occurrence of frosting and shutdown at the low-voltage side.

Description

Technical Field

[0001] This application relates to the field of refrigeration technology, and in particular, to a heat pump system and a control method thereof. Background Art

[0002] Currently, for heat pump products with a reheat dehumidification option, especially small-tonnage machines with only one constant-speed outdoor fan, when operating in the reheat dehumidification mode, in addition to the conventional outdoor coil condenser, there is an additional reheat condenser and heat exchange is very good on the indoor air outlet side. If the constant-speed outdoor fan is kept running, there is no risk of high pressure and high temperature, and frosting or low-pressure tripping is the key concern; if the constant-speed outdoor fan is turned off and the reheat coil alone is relied on to bear the main condensation heat, high-pressure and high-temperature tripping will occur. In addition, when the constant-speed outdoor fan is turned off, the outdoor ambient temperature probe has no circulating outdoor ambient air coming in, resulting in inaccurate measurement and difficulties in control due to different differences between each working condition and the actual ambient temperature.

[0003] In addition to overly good condensation heat transfer, combined with another factor, when the opening degree of the three-way valve in a heat pump product with a reheat dehumidification option is at both ends, the refrigerant is likely to be trapped in one of the condensation coils, and the evaporator lacks refrigerant, leading to frosting or low-pressure tripping, resulting in a very small adjustable opening degree range for the three-way valve. When the three-way valve is at a small opening degree, it is likely to accumulate in the reheat coil, and when the three-way valve is at a large opening degree, it is likely to accumulate in the outdoor condenser. Since the volume inside the outdoor condenser is much larger than that of the indoor reheat coil, it is more difficult to achieve a large opening degree. Summary of the Invention

[0004] The purpose of this application is to provide a heat pump system and a control method thereof, which can solve at least one of the technical problems existing in the above prior art.

[0005] One aspect of this application provides a heat pump system. The heat pump system includes a main circuit, a slave circuit, a pressure sensor, and an evacuation pipeline. The main circuit includes a compressor, a first heat exchanger, and a second heat exchanger connected in sequence. The slave circuit includes a third heat exchanger connected to the main circuit. The pressure sensor is disposed in the exhaust pipeline of the compressor for detecting the exhaust pressure of the compressor. The evacuation pipeline connects the second port of the first heat exchanger and the first port of the second heat exchanger, and an evacuation control valve is provided in the evacuation pipeline. The controller is configured to control the evacuation control valve based on the exhaust pressure of the compressor when the heat pump system is operating in the reheat dehumidification mode, wherein, in the reheat dehumidification mode, the slave circuit is connected in parallel with the main circuit.

[0006] Further, the compressor includes a suction port and a discharge port, and the main circuit includes a three-way adjustable valve and a four-way reversing valve. Among them, the first valve port of the three-way adjustable valve is connected to the discharge port, the second valve port of the three-way adjustable valve is connected to the first valve port of the four-way reversing valve, and the third valve port of the three-way adjustable valve is connected to the first port of the third heat exchanger; the second valve port of the four-way reversing valve is connected to the second port of the second heat exchanger, the third valve port of the four-way reversing valve is connected to the suction port, and the fourth valve port of the four-way reversing valve is connected to the first port of the first heat exchanger.

[0007] Further, the heat pump system includes two constant-speed outdoor fans or variable-frequency outdoor fans. Among them, when one of the two constant-speed outdoor fans is turned off and the other is running, or when the variable-frequency outdoor fan runs at the lowest speed allowed by the control, and the opening degree of the three-way adjustable valve still cannot reach the expected opening degree range, the controller is used to control the evacuation control valve based on the discharge pressure of the compressor.

[0008] Further, the heat pump system includes a constant-speed outdoor fan. Among them, when the constant-speed outdoor fan is running, the controller is used to control the evacuation control valve based on the discharge pressure of the compressor.

[0009] Another aspect of the present application provides a control method for a heat pump system. The heat pump system includes a main circuit and a secondary circuit. The main circuit includes a compressor, a first heat exchanger, and a second heat exchanger connected in sequence. The secondary circuit includes a third heat exchanger. The heat pump system has a reheat and dehumidification mode. In the reheat and dehumidification mode, the secondary circuit is connected in parallel with the main circuit. The control method includes: when the heat pump system is operating in the reheat and dehumidification mode, monitoring the discharge pressure of the compressor; controlling the evacuation control valve disposed in the evacuation pipeline between the outlet of the first heat exchanger and the inlet of the second heat exchanger based on the discharge pressure of the compressor.

[0010] Further, controlling the evacuation control valve based on the discharge pressure of the compressor includes: when the discharge pressure of the compressor is higher than a preset upper limit value of the discharge pressure, controlling to close the evacuation control valve; when the discharge pressure of the compressor is lower than a preset lower limit value of the discharge pressure, controlling to open the evacuation control valve, where the preset upper limit value of the discharge pressure is greater than the preset lower limit value of the discharge pressure.

[0011] Further, the control method further includes: when the switching cycle of the evacuation control valve is lower than a predetermined frequency, controlling to adjust the lower limit value of the discharge pressure and / or the upper limit value of the discharge pressure.

[0012] Further, the control for adjusting the lower limit value and / or the upper limit value of the exhaust pressure includes: controlling to reduce the lower limit value of the exhaust pressure by a first pressure value; and / or controlling to increase the upper limit value of the exhaust pressure by a second pressure value, wherein the adjusted lower limit value of the exhaust pressure and the adjusted upper limit value of the exhaust pressure do not exceed a preset maximum adjustment range.

[0013] Further, the evacuation control valve is an adjustable valve. Controlling the evacuation control valve based on the exhaust pressure of the compressor includes: adjusting the opening degree of the evacuation control valve based on the exhaust pressure of the compressor and the target exhaust pressure.

[0014] Further, the control method further includes: when the exhaust pressure of the compressor is between the upper limit value and the lower limit value of the exhaust pressure, maintaining the state of the evacuation control valve unchanged.

[0015] In the heat pump system and its control method according to one or more embodiments of the present application, when the heat pump system operates in the reheating and dehumidifying mode, by monitoring the exhaust pressure of the compressor to control the evacuation control valve in the evacuation pipeline between the outlet of the first heat exchanger and the inlet of the second heat exchanger, it is possible to partially or completely evacuate the refrigerant in the second heat exchanger located outdoors to increase the evaporation pressure of the first heat exchanger located indoors, help reduce the occurrence of low-pressure side frosting and tripping, and meet the customer's demand for reheating temperature rise under various loads. Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of a heat pump system according to an embodiment of the present application.

[0017] Figure 2 is Figure 1 a schematic diagram of the heat pump system shown operating in the reheating and dehumidifying mode.

[0018] Figure 3 It is a flowchart of a control method of a heat pump system according to an embodiment of the present application.

[0019] Figure 4 It is a specific flowchart of the control method of the heat pump system of the present application. Detailed Description of the Embodiments

[0020] Here, the exemplary embodiments will be described in detail, and the examples are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices consistent with some aspects of the present application as detailed in the appended claims.

[0021] The following will describe in detail the heat pump system and its control method of the present application in conjunction with the accompanying drawings. Without conflict, the features in the following embodiments and implementation manners can be combined with each other.

[0022] The present application provides a heat pump system. Figure 1 The structural schematic diagram of a heat pump system 100 according to an embodiment of the present application is disclosed. As Figure 1 shown, a heat pump system 100 according to an embodiment of the present application includes a main circuit and a slave circuit. The main circuit includes a compressor 110, a first heat exchanger 121, and a second heat exchanger 122 connected in sequence. The slave circuit includes a third heat exchanger 123 connected to the main circuit. The first heat exchanger 121 is located outdoors, and the second heat exchanger 122 and the third heat exchanger 123 are located indoors.

[0023] The compressor 110 includes a suction port 111 and an exhaust port 112. The main circuit includes a three-way adjustable valve 141 and a four-way reversing valve 142. Among them, the first valve port of the three-way adjustable valve 141 is connected to the exhaust port 112, the second valve port of the three-way adjustable valve 141 is connected to the first valve port of the four-way reversing valve 142, and the third valve port of the three-way adjustable valve 141 is connected to the first port of the third heat exchanger 123; the second valve port of the four-way reversing valve 142 is connected to the second port of the second heat exchanger 122, the third valve port of the four-way reversing valve 142 is connected to the suction port 111, and the fourth valve port of the four-way reversing valve 142 is connected to the first port of the first heat exchanger 121.

[0024] The heat pump system 100 of the present application further includes a dryer filter 150, a first throttle valve 161, a second throttle valve 162, a first check valve 171, and a second check valve 172. The dryer filter 150 is used to absorb moisture and filter impurities. The first throttle valve 161 and the second throttle valve 162 can include, for example, a thermostatic expansion valve (TXV).

[0025] Among them, the first end of the first throttle valve 161 is connected to the second port of the first heat exchanger 121, and the second end of the first throttle valve 161 is connected to the first end of the dryer filter 150; the first check valve 171 is connected in parallel at both ends of the first throttle valve 161, and the inlet of the first check valve 171 is connected to the first end of the first throttle valve 161, and the outlet of the first check valve 171 is connected to the second end of the first throttle valve 161. The first end of the second throttle valve 162 is connected to the first port of the second heat exchanger 122, and the second end of the second throttle valve 162 is connected to the second end of the dryer filter 150; the second check valve 172 is connected in parallel at both ends of the second throttle valve 162, and the inlet of the second check valve 172 is connected to the first end of the second throttle valve 162, and the outlet of the second check valve 172 is connected to the second end of the second throttle valve 162.

[0026] The heat pump system 100 of the present application further includes a third control valve 163 and a third check valve 173. The third control valve 163 may include, for example, a solenoid valve. The second port of the third heat exchanger 123 is connected to the first end of the third control valve 163 and is connected to the second end of the second throttle valve 162 through the third check valve 173. Among them, the inlet of the third check valve 173 is connected to the second port of the third heat exchanger 123, and the outlet of the third check valve 173 is connected to the second end of the second throttle valve 162; the second end of the third control valve 163 is connected to the suction port 111 of the compressor 110.

[0027] The heat pump system 100 of the present application further includes a first distribution head 181 and a second distribution head 182. Among them, the second port of the first heat exchanger 121 is connected to the first end of the first throttle valve 161 through the first distribution head 181, and the first port of the second heat exchanger 122 is connected to the first end of the second throttle valve 162 through the second distribution head 182.

[0028] The heat pump system 100 of the present application has a reheat dehumidification mode. Figure 2 A schematic diagram of the heat pump system 100 of the present application operating in the reheat dehumidification mode is disclosed. As Figure 2 shown, when the heat pump system 100 of the present application operates in the reheat dehumidification mode, the slave circuit is connected in parallel with the main circuit. In the reheat dehumidification mode, the first heat exchanger 121 operates as a condenser, and the second heat exchanger 122 operates as an evaporator. The compressor 110 compresses the low-temperature and low-pressure refrigerant inhaled from the suction port 111 into a high-temperature and high-pressure refrigerant and then discharges it from the exhaust port 112. In the reheat dehumidification mode, the three-way adjustable valve 141 opens the third valve port for the refrigerant to flow to the slave circuit, so that the slave circuit is connected in parallel with the main circuit. Therefore, the refrigerant is branched at the three-way adjustable valve 141, a part of the refrigerant flows into the main circuit, and the remaining part flows into the slave circuit.

[0029] The circulation path of the main circuit is as follows: After the refrigerant flows out of the compressor 110, it first enters the outdoor side and then the indoor side. The refrigerant is discharged from the exhaust port 112 of the compressor 110, enters the first valve port of the three-way adjustable valve 141 and flows out from the second valve port, enters the first valve port of the four-way reversing valve 142 and flows out from the fourth valve port of the four-way reversing valve 142, and then enters the first heat exchanger 121. The refrigerant flowing out of the first heat exchanger 121 enters the dryer filter 150 through the second check valve 172. After being dried and filtered by the dryer filter 150, the refrigerant enters the second throttle valve 162, which can throttle and reduce the pressure of the high-temperature and high-pressure refrigerant condensed by the condenser, becoming a low-temperature and low-pressure gas-liquid mixture that is easy to evaporate. The low-temperature and low-pressure gas-liquid mixture then enters the second heat exchanger 122, that is, the evaporator, and the gas-liquid mixture absorbs the heat in the air passing through the evaporator and turns into a gas state. The refrigerant that has completely changed back to the gas state flows out from the second port of the second heat exchanger 122 and enters the suction port 111 of the compressor 110 through the second valve port and the third valve port of the four-way reversing valve 142 respectively, and then enters the compressor 110 again for a new round of circulation.

[0030] The circulation path of the secondary loop is as follows: A part of the refrigerant enters the third heat exchanger 123 through the third valve port of the three-way adjustable valve 141, bringing about a temperature rise of the indoor air. In the reheating and dehumidifying mode, the third heat exchanger 123 also works as a condenser. After the refrigerant flows out of the third heat exchanger 123, it returns to the main circuit through the third check valve 173, converges with the refrigerant in the main circuit, and all enters the second throttle valve 162 in the room for throttling and continues the circulation process.

[0031] In addition, since the third heat exchanger 123 is located behind the second heat exchanger 122, the indoor air will first pass through the second heat exchanger 122, that is, the evaporator, to cool and dehumidify, and then pass through the third heat exchanger 123, that is, the condenser, to warm up, thereby reducing the indoor humidity without making the room too cold.

[0032] As Figure 1 and Figure 2 shown, the heat pump system 100 of the present application further includes a pressure sensor 131 and an evacuation pipeline 132. The pressure sensor 131 is arranged in the exhaust pipeline of the compressor 110 and can be used to detect the exhaust pressure of the compressor 110. The evacuation pipeline 132 connects the second port of the first heat exchanger 121 and the first port of the second heat exchanger 122, and an evacuation control valve 133 is provided in the evacuation pipeline 132. The evacuation control valve 133 can perform corresponding actions according to the exhaust pressure of the compressor 110 detected by the pressure sensor 131, and the evacuation control valve 133 can control the partial or complete evacuation of the refrigerant from the second heat exchanger 122 located outdoors.

[0033] The heat pump system 100 of the present application may further include a controller (not shown). When the heat pump system 100 operates in the reheating and dehumidifying mode, the controller may perform corresponding control on the evacuation control valve 133 based on the discharge pressure of the compressor 110.

[0034] In some embodiments, the heat pump system 100 of the present application may include a constant-speed outdoor fan. When the constant-speed outdoor fan is operating, the controller may control the evacuation control valve 133 based on the discharge pressure of the compressor 110.

[0035] In some other embodiments, the heat pump system 100 of the present application may include two constant-speed outdoor fans. When one of the two constant-speed outdoor fans is closed and the other is operating, and the opening degree of the three-way adjustable valve 141 still cannot reach the expected opening range, the controller may control the evacuation control valve 133 based on the discharge pressure of the compressor 110.

[0036] In still some other embodiments, the heat pump system 100 of the present application may include a variable-frequency outdoor fan. When the variable-frequency outdoor fan operates at the lowest speed allowed by the control, and the opening degree of the three-way adjustable valve 141 still cannot reach the expected opening range, the controller may control the evacuation control valve 133 based on the discharge pressure of the compressor 110.

[0037] If the heat pump system 100 of the present application is configured with two constant-speed outdoor fans or uses a variable-frequency outdoor fan, the speed of the outdoor fan may be preferentially reduced to increase the high pressure. When the opening degree of the three-way adjustable valve 141 still cannot reach the expected opening range, the evacuation control valve 133 may be controlled based on the discharge pressure of the compressor 110, so as to further help expand the opening range of the three-way adjustable valve 141 from the perspective of refrigerant shortage and achieve better effects.

[0038] The present application also provides a control method for the heat pump system 100. Figure 3 The flowchart of the control method for the heat pump system 100 according to an embodiment of the present application is disclosed. As Figure 3 shown, the control method for the heat pump system 100 according to an embodiment of the present application may include step S31 and step S32.

[0039] In step S31, when the heat pump system 100 operates in the reheating and dehumidifying mode, the discharge pressure of the compressor 110 is monitored.

[0040] In step S32, the evacuation control valve 133 in the evacuation pipeline 132 provided between the outlet of the first heat exchanger 121 and the inlet of the second heat exchanger 122 is controlled based on the discharge pressure of the compressor 110.

[0041] In some embodiments, when the evacuation control valve 133 is a solenoid valve with only on or off functions, step S32 may include step S321 and step S322.

[0042] In step S321, when the discharge pressure of the compressor 110 is higher than a preset upper limit value of the discharge pressure, control is performed to close the evacuation control valve 133.

[0043] In step S322, when the discharge pressure of the compressor 110 is lower than a preset lower limit value of the discharge pressure, control is performed to open the evacuation control valve 133, where the preset upper limit value of the discharge pressure is greater than the preset lower limit value of the discharge pressure.

[0044] When the discharge pressure of the compressor 110 is between the upper limit value and the lower limit value of the discharge pressure, the state of the evacuation control valve 133 is maintained unchanged.

[0045] To avoid frequent operation of the evacuation control valve 133, which affects the stability of control, and to ensure the energy efficiency and reliability of the heat pump system 100, the discharge pressure is controlled within a reasonable range, and it is allowed to adjust the upper limit value and the lower limit value of the discharge pressure within a certain range. Therefore, in some embodiments, the control method of the heat pump system 100 of the present application may further include step S33.

[0046] In step S33, when the switching cycle of the evacuation control valve 133 is lower than a predetermined frequency, control is performed to adjust the lower limit value and / or the upper limit value of the discharge pressure.

[0047] Optionally, controlling the adjustment of the lower limit value and / or the upper limit value of the discharge pressure may include: controlling to reduce the lower limit value of the discharge pressure by a first pressure value; and / or controlling to increase the upper limit value of the discharge pressure by a second pressure value. Wherein, the adjusted lower limit value of the discharge pressure and the adjusted upper limit value of the discharge pressure do not exceed a preset maximum adjustment range to prevent the risk of tripping.

[0048] For example, the default values of the lower limit value and the upper limit value of the discharge pressure are 250 psi (pounds per square inch) and 465 psi respectively. When the switching cycle of the evacuation control valve 133 occurs less than once every 30 minutes, the lower limit value of the discharge pressure can be correspondingly reduced and the upper limit value of the discharge pressure can be increased by 20 psi each, but it cannot exceed the maximum adjustment range of 150 - 565 psi.

[0049] In some other embodiments, when the evacuation control valve 133 is an adjustable valve, for example, when the evacuation control valve 133 uses an electric control stepper motor, step S32 may include step S323.

[0050] In step S323, the opening degree of the evacuation control valve 133 can be adjusted based on the exhaust pressure of the compressor 110 and the target exhaust pressure. For example, the number of steps of the electronically controlled stepper motor valve can be adjusted to adapt to the corresponding opening degree, so as to maintain the exhaust pressure of the compressor 110 at a predetermined target exhaust pressure, and the default value of the target exhaust pressure can be 350 psi.

[0051] Figure 4 A specific flowchart of the control method of the heat pump system 100 of the present application is disclosed. As Figure 4 shown, in step S41, the heat pump system 100 enters the reheating and dehumidifying mode. In step S42, when the heat pump system 100 is operating in the reheating and dehumidifying mode, the exhaust pressure of the compressor 110 detected by the pressure sensor 131 is obtained. In step S43, it is judged whether the exhaust pressure of the compressor 110 satisfies being greater than 465 psi. When the judgment result is "yes", the process proceeds to step S44; otherwise, the process proceeds to step S45. In step S44, when the exhaust pressure of the compressor 110 is greater than 465 psi, it indicates that the heat pump system 100 does not need to evacuate to maintain a relatively high condensation pressure and there is no risk of frosting and tripping. At this time, the evacuation control valve 133 can be closed. In step S45, it is judged whether the exhaust pressure of the compressor 110 satisfies being less than 250 psi. When the judgment result is "yes", the process proceeds to step S46; otherwise, the process proceeds to step S47. In step S46, when the exhaust pressure of the compressor 110 is less than 250 psi, the evacuation control valve 133 is opened to evacuate the refrigerant in the coil of the first heat exchanger 121 located outdoors to the evaporator, increase the evaporation pressure, and then close the evacuation control valve 133 until the high pressure rises to 465 psi, ending the evacuation operation; if it cannot rise to 465 psi, the evacuation control valve 133 is kept open for evacuation. In step S47, if the exhaust pressure of the compressor 110 is not less than 250 psi, the state of the evacuation control valve 133 remains unchanged. The principle of the control method of the heat pump system 100 of the present application is similar to the phased control of the outdoor fan by the discharge pressure or the periodic start and stop of the outdoor fan in a low-temperature environment. However, the control method of the heat pump system 100 of the present application does not start from the perspective of reducing outdoor heat exchange, but evacuates the refrigerant in the outdoor condenser to help the phenomenon of lack of refrigerant in the evaporator.

[0052] When the heat pump system 100 of the present application and its control method operate in the reheating and dehumidifying mode, the evacuation control valve 133 in the evacuation pipeline 132 between the outlet of the first heat exchanger 121 and the inlet of the second heat exchanger 122 is controlled by using the exhaust pressure of the compressor 110 detected by the pressure sensor 131 on the exhaust pipeline of the compressor 110. Thus, it is possible to partially or completely evacuate the refrigerant in the second heat exchanger 122 located outdoors to increase the evaporation pressure of the first heat exchanger 121 located indoors, helping to reduce the occurrence of compressor trips due to frosting on the low-pressure side, so as to expand the operating range of the three-way adjustable valve 141, achieve a greater adjustment range of the opening degree of the three-way adjustable valve 141, and meet the customer's requirements for reheating temperature rise under various loads.

[0053] The heat pump system and its control method provided by the embodiments of the present application have been introduced in detail above. Specific examples are used in this article to elaborate on the heat pump system and its control method of the embodiments of the present application. The description of the above embodiments is only used to help understand the core idea of the present application and is not intended to limit the present application. It should be noted that for those of ordinary skill in the art in the technical field, without departing from the spirit and principle of the present application, several improvements and modifications can still be made to the present application, and these improvements and modifications should also fall within the protection scope of the appended claims of the present application.

Claims

1. A heat pump system, characterized in that: Comprising: A main circuit, including a compressor, a first heat exchanger, and a second heat exchanger connected in sequence; A secondary circuit, including a third heat exchanger connected to the main circuit; A pressure sensor, disposed in the exhaust pipeline of the compressor, for detecting the exhaust pressure of the compressor; An evacuation pipeline, connecting the second port of the first heat exchanger and the first port of the second heat exchanger, and an evacuation control valve is provided in the evacuation pipeline; A controller, configured to control the evacuation control valve based on the exhaust pressure of the compressor when the heat pump system operates in the reheating and dehumidifying mode. Wherein, in the reheating and dehumidifying mode, the secondary circuit is connected in parallel with the main circuit.

2. The heat pump system according to claim 1, characterized in that: The compressor includes a suction port and an exhaust port, and the main circuit includes a three-way adjustable valve and a four-way reversing valve. Wherein, The first valve port of the three-way adjustable valve is connected to the exhaust port, the second valve port of the three-way adjustable valve is connected to the first valve port of the four-way reversing valve, and the third valve port of the three-way adjustable valve is connected to the first port of the third heat exchanger; The second valve port of the four-way reversing valve is connected to the second port of the second heat exchanger, the third valve port of the four-way reversing valve is connected to the suction port, and the fourth valve port of the four-way reversing valve is connected to the first port of the first heat exchanger.

3. The heat pump system according to claim 2, characterized in that: The heat pump system includes two constant-speed outdoor fans or a variable-frequency outdoor fan, Wherein, the controller is configured to control the evacuation control valve based on the exhaust pressure of the compressor when one of the two constant-speed outdoor fans is turned off and the other is running, or when the variable-frequency outdoor fan runs at the lowest speed allowed by the control, and the opening degree of the three-way adjustable valve still cannot reach the expected opening degree range.

4. The heat pump system according to claim 1, characterized in that: The heat pump system includes a constant-speed outdoor fan, Wherein, the controller is configured to control the evacuation control valve based on the exhaust pressure of the compressor when the constant-speed outdoor fan is running.

5. A control method for a heat pump system, the heat pump system comprising a main circuit and a slave circuit, the main circuit including a compressor, a first heat exchanger and a second heat exchanger connected in sequence, the slave circuit including a third heat exchanger, the heat pump system having a reheating and dehumidifying mode, in the reheating and dehumidifying mode, the slave circuit is connected in parallel with the main circuit, characterized in that: The control method includes: When the heat pump system operates in the reheating and dehumidifying mode, monitoring the exhaust pressure of the compressor; Based on the exhaust pressure of the compressor, controlling the evacuation control valve disposed in the evacuation pipeline between the outlet of the first heat exchanger and the inlet of the second heat exchanger.

6. The control method according to claim 5, characterized in that: Controlling the evacuation control valve based on the exhaust pressure of the compressor includes: When the exhaust pressure of the compressor is higher than a preset exhaust pressure upper limit value, controlling to close the evacuation control valve; When the exhaust pressure of the compressor is lower than a preset exhaust pressure lower limit value, controlling to open the evacuation control valve, wherein the preset exhaust pressure upper limit value is greater than the preset exhaust pressure lower limit value.

7. The control method according to claim 6, characterized in that: Further comprising: When the switching cycle of the evacuation control valve is lower than a predetermined frequency, controlling to adjust the exhaust pressure lower limit value and / or the exhaust pressure upper limit value.

8. The control method according to claim 7, wherein: The control to adjust the exhaust pressure lower limit value and / or the exhaust pressure upper limit value includes: Controlling to reduce the exhaust pressure lower limit value by a first pressure value; and / or Controlling to increase the exhaust pressure upper limit value by a second pressure value, Among them, the adjusted lower limit value of the exhaust pressure and the adjusted upper limit value of the exhaust pressure do not exceed the preset maximum adjustment range.

9. The control method according to claim 5, wherein: The evacuation control valve is an adjustable valve. Controlling the evacuation control valve based on the exhaust pressure of the compressor includes: Adjusting the opening degree of the evacuation control valve based on the exhaust pressure of the compressor and the target exhaust pressure.

10. The control method according to any one of claims 6 to 9, characterized in that: It also includes: When the exhaust pressure of the compressor is between the upper limit value of the exhaust pressure and the lower limit value of the exhaust pressure, maintaining the state of the evacuation control valve unchanged.

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