Control method of heat pump system and heat pump system

Abstract

The invention relates to the heat pump technology, and discloses a control method of a heat pump system and the heat pump system.The control method comprises the steps that if the heat pump system is in a heating standby state and the standby duration reaches the preset standby duration, a two-way valve between an exhaust port and an air return port of a compressor is opened; the first environment temperature is obtained, if the first environment temperature is not smaller than the first temperature threshold value, an expansion valve of the heat pump system is started, and the opening degree of the expansion valve is adjusted based on the first environment temperature. The two-way valve is controlled to be opened when the heat pump system is in the specific state, lubricating oil deposited in the compressor and a pipeline can be redistributed, the interior of the compressor is fully lubricated, and abrasion of the compressor is reduced. Meanwhile, the expansion valve is controlled to be opened when the temperature is larger than the first temperature threshold value, the corresponding opening degree of the expansion valve is determined, and it can be guaranteed that the system pressure is balanced when restarting is conducted.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pumps, and in particular to a control method for a heat pump system and a heat pump system. Background Art

[0002] In a low-temperature heat pump heating system, when the system water temperature reaches the preset temperature, the system will stop running to save energy. When the temperature is extremely low, the temperature difference between the evaporator and the condenser causes the refrigerant pressure in the condenser to be higher than that in the evaporator, thereby causing refrigerant migration. When the downtime is long, part of the refrigerant will migrate from the evaporator to the compressor.

[0003] When the compressor is started, if there is liquid refrigerant inside, it will dilute the lubricating oil, destroy the lubricating oil film, and increase the wear of the moving parts of the compressor. In addition, when the compressor is at a low temperature, the lubricating oil will precipitate and stratify, resulting in poor lubricity and inability to effectively lubricate the moving parts inside the compressor, further exacerbating the wear. Summary of the invention

[0004] The technical problem solved by the present invention is to provide a control method of a heat pump system and a heat pump system, which effectively solves the problem of compressor wear caused by refrigerant migration.

[0005] The first technical problem mentioned above is solved by the following technical solution:

[0006] A control method for a heat pump system, the method comprising:

[0007] If the heat pump system is in the heating standby state and the standby time reaches the preset standby time, open the two-way valve between the compressor exhaust port and the return air port;

[0008] Obtain a first ambient temperature. If the first ambient temperature is not less than a first temperature threshold, open the expansion valve of the heat pump system, and adjust the opening of the expansion valve based on the first ambient temperature. The first temperature threshold is used to characterize the critical temperature of refrigerant migration.

[0009] Compared with the background technology, the control method of the heat pump system described in the present invention has the following beneficial effects: by controlling the two-way valve to open after the heat pump system is smoothly shut down, the lubricating oil precipitated from the compressor will follow the migration of the refrigerant from the two-way valve back to the compressor, thereby lubricating the compressor in time and reducing the wear of the compressor. At the same time, the expansion valve is controlled to open when it is greater than the first temperature threshold, and the corresponding expansion valve opening can be determined according to the first ambient temperature to ensure the pressure balance of the system when it is restarted.

[0010] In one embodiment, the method further comprises:

[0011] If the first ambient temperature is lower than a first temperature threshold, the expansion valve is closed.

[0012] In one embodiment, the method further comprises:

[0013] If the heat pump system is in a heating working state, detecting the operating time of the compressor;

[0014] If the operating time is not less than the preset heating operating time, the two-way valve is controlled to be closed.

[0015] In one embodiment, it also includes:

[0016] If the heat pump system is restarted after being shut down, obtaining the second ambient temperature and the actual outlet water temperature of the condenser;

[0017] If the second ambient temperature is lower than the preset secondary start-up temperature threshold, and the temperature difference between the actual water outlet temperature and the preset water outlet temperature is lower than the preset water outlet temperature threshold, the heat pump system is controlled to operate in the evaporator heating mode.

[0018] In one embodiment, the expansion valve includes a main expansion valve and an auxiliary expansion valve, and controlling the heat pump system to operate in an evaporator heating mode includes:

[0019] Controlling the compressor to operate at a first preset heating frequency and controlling the four-way valve to switch to heat the evaporator;

[0020] When the compressor on time reaches the preset evaporator mode operation time, the auxiliary expansion valve is closed, and the opening of the main expansion valve is adjusted to a preset opening corresponding to the evaporator heating mode.

[0021] In one embodiment, the method further comprises:

[0022] Obtaining the outer coil temperature of the evaporator;

[0023] If the temperature of the outer coil is not less than the preset defrost exit temperature, controlling the heat pump system to exit the evaporator heating mode;

[0024] If the heat pump system exits the evaporator heating mode, controlling the compressor to decrease from the preset heating frequency to a second preset heating frequency;

[0025] If the operating frequency of the compressor is reduced to the second preset heating frequency, the four-way valve is controlled to switch to enter the heating working state.

[0026] In one embodiment, after controlling the heat pump system to exit the evaporator heating mode, the method further includes:

[0027] The frequency of the compressor is adjusted to a third preset heating frequency, and the opening of the main expansion valve is adjusted to a preset third opening. The third preset heating frequency and the third opening indicate that the speed at which the compressor discharges refrigerant is within a preset speed range.

[0028] In one of the embodiments, if the compressor operates based on the third preset heating frequency for a first operation time, the frequency of the compressor is increased from the third preset heating frequency to a target frequency.

[0029] The above second technical problem is solved by the following technical solution:

[0030] A heat pump system includes a compressor, the compressor is provided with an exhaust port, an air return port and an air supply port, a two-way valve is provided between the exhaust port and the air return port, the two-way valve is connected to the exhaust port and the air return port respectively, and the heat pump system is used to execute the method described in the above embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 is a schematic diagram of a heat pump system according to an embodiment of the present invention;

[0033] Figure 2 A schematic flow chart of a control method for a heat pump system according to an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of a heat pump system in an evaporator heating mode according to an embodiment of the present invention.

[0035] Description of reference numerals:

[0036] 1. Compressor; 2. Four-way valve; 3. Condenser; 4. Filter; 5. Main electronic expansion valve; 6. Auxiliary electronic expansion valve; 7. Coaxial shell and tube heat exchanger; 8. Evaporator; 9. Gas-liquid separator; 10. Two-way valve; 11. External coil temperature sensor; 12. Ambient temperature sensor. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0039] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0040] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0041] After the system water temperature of the low-temperature heat pump heating unit reaches the set temperature, the unit will be in a shutdown state. As the shutdown time increases, the temperature of the evaporator in the system will decrease, and the water-side condenser in the heat pump system will be higher than the evaporator due to its heat preservation properties. The temperature difference between the two will lead to a pressure difference, and the refrigerant will migrate from the water-side condenser to the evaporator. When the shutdown time is relatively long, part of the refrigerant will migrate from the evaporator to the compressor, leaving the liquid refrigerant in the compressor cavity, causing the compressor to start with liquid when it is started, increasing the wear of the moving parts of the compressor. In addition, when the compressor is at a low temperature, the lubricating oil will precipitate and stratify, resulting in poor lubricity, and it is impossible to effectively lubricate the moving parts inside the compressor, further aggravating the wear. Based on this, an embodiment of the present invention provides a control method for a heat pump system. It is used to solve the above problems.

[0042] According to an embodiment of the present invention, on the one hand, a heat pump system is provided, which can be used to execute the control method of the heat pump system provided by the present invention. Figure 1 As shown, it includes a compressor 1 arranged on the refrigerant pipeline, the compressor 1 is provided with an exhaust port, an air return port and an air supply port, a two-way valve is arranged between the exhaust port and the air return port, and the two-way valve is connected to the exhaust port and the air return port respectively.

[0043] In one embodiment, the device further comprises: a four-way valve 2, a condenser 3, a filter 4, a main electronic expansion valve 5, an auxiliary electronic expansion valve 6, a coaxial tube heat exchanger 7, an evaporator 8, a gas-liquid separator 9, a two-way valve 10, an external coil temperature sensor 11, and an ambient temperature sensor 12. The compressor 1 is connected to the condenser 3, the evaporator 8, and the gas-liquid separator 9 through the four-way valve 2, respectively. The coaxial tube heat exchanger 7 and the main expansion valve 5 are respectively arranged on the refrigerant pipeline between the condenser 3 and the evaporator 8. The gas outlet of the coaxial tube heat exchanger 7 is connected to the return gas port of the compressor 1, and the liquid outlet of the coaxial tube heat exchanger 7 is connected to the refrigerant pipeline through the auxiliary expansion valve 6. The pipeline of the main expansion valve 5 is provided with a filter 4, and the evaporator 8 is provided with an external coil temperature sensor 11 and an ambient temperature sensor 12.

[0044] Among them, the condenser 3 can adopt a water side heat exchanger, the evaporator 8 can adopt an air side heat exchanger, an outdoor fan can be set on the outside, the main expansion valve 5 and the auxiliary expansion valve 6 can both adopt electronic expansion valves, and the two-way valve 10 can adopt an electromagnetic two-way valve.

[0045] When the heat pump system starts heating mode, the refrigerant flows as follows Figure 1 As shown by the middle arrow, after the refrigerant is compressed into a high-temperature and high-pressure gas by the compressor 1, it is discharged from the exhaust port of the compressor 1, flows to the interface pipe D of the four-way valve, and then flows from the interface pipe D to the interface pipe C, and enters the condenser 3. In the condenser, it condenses through the fluorine outlet of the condenser 3 to release heat, and becomes a high-pressure liquid and comes out from the fluorine outlet of the condenser. At this time, a small part of the refrigerant passes through the auxiliary expansion valve 6 for throttling treatment to reduce the temperature and pressure, and then enters the coaxial tube heat exchanger 7 for heat exchange. After the heat exchange is completed, this part of the refrigerant flows back to the medium-pressure chamber gas replenishment port of the compressor 1 to replenish the amount of refrigerant required for the operation of the compressor 1. The remaining large amount of refrigerant is converted into a low-temperature and low-pressure gas state through the throttling effect of the main expansion valve 5. After that, the refrigerant enters the evaporator 8 to absorb heat and flows out, passes through the interface pipe E and interface pipe S of the four-way valve, and enters the gas-liquid separator 9 for gas-liquid separation. The refrigerant treated by the gas-liquid separator returns to the return air port of the compressor 1, completing the complete heating cycle process.

[0046] It should be noted that, during the startup and operation of the heat pump system, the two-way valve 10 is in a normally closed state and does not participate in the refrigerant circulation.

[0047] According to an embodiment of the present invention, on the other hand, a control method of a heat pump system is provided, which is applied to the heat pump system of the above embodiment, such as Figure 2 As shown, the control method includes:

[0048] Step S101: if the heat pump system is in a heating standby state and the standby time reaches a preset standby time, the two-way valve between the compressor exhaust port and the return air port is opened.

[0049] A two-way valve is arranged between the exhaust port and the return port of the compressor. Two interfaces of the two-way valve are respectively connected to the exhaust port and the return port. The two-way valve can be an electromagnetic two-way valve.

[0050] When the heat pump system reaches the set temperature or other shutdown conditions, it stops working. At this time, the heat pump system is in standby mode. Set the preset standby time to ensure that the compressor has completely stopped running. The specific preset standby time can be set according to the actual application scenario. If the standby time reaches the preset standby time (for example: 30 seconds), the two-way valve is in the energized open state, and the refrigerant and lubricating oil can flow in a specific path. When the two-way valve is energized and opened, the lubricating oil in the compressor will flow out of the exhaust port along with the migration of the refrigerant, pass through the two-way valve, and then return to the compressor from the return port.

[0051] Step S102, obtaining a first ambient temperature, if the first ambient temperature is not less than a first temperature threshold, opening an expansion valve of the heat pump system, and adjusting the opening of the expansion valve based on the first ambient temperature.

[0052] The first temperature threshold is a set environmental threshold used to characterize the critical temperature of refrigerant migration. The first environmental temperature can be set according to the temperature at which refrigerant migration may occur. The specific value can be set in combination with the actual application scenario. For example, the first temperature threshold can be set to -20°C. The first ambient temperature can be measured by a temperature sensor, specifically, by an ambient temperature sensor provided on the evaporator. When the heat pump system is in a heating standby state and the standby time reaches a preset standby time, if the measured first ambient temperature is not less than the first temperature threshold, the expansion valve in the heat pump system is opened. The heat pump system may include one or more expansion valves, and one or more of the expansion valves are opened, which is not limited here. The opening of the expansion valve can be adjusted according to the actually measured first ambient temperature, and the opening size of the expansion valve corresponding to different first ambient temperatures can be pre-set.

[0053] Optionally, multiple temperature intervals can be set, and corresponding expansion valve openings can be set for different temperature intervals. The corresponding expansion valve opening can be determined according to the temperature interval in which the first ambient temperature is located, and the expansion valve can be controlled to open to the corresponding opening. Furthermore, the expansion valve opening corresponding to the high temperature interval can be set to be higher.

[0054] In one embodiment, the control method of the heat pump system in the above embodiment further includes: if the first ambient temperature is less than the first temperature threshold, close the expansion valve.

[0055] When the first ambient temperature is less than the first temperature threshold, it indicates that the first ambient temperature is already less than the critical temperature of refrigerant migration. In this state, refrigerant migration will occur. Control the expansion valve to be in the closed state at this temperature.

[0056] Specifically, it can be set that when it is detected that the first ambient temperature is less than the first temperature threshold, the corresponding expansion valve opening is 0P, indicating that the expansion valve is closed at this temperature, so as to avoid refrigerant migrating from the condenser through the expansion valve to the evaporator, resulting in the refrigerant remaining in the compressor cavity, and further causing wear to the compressor.

[0057] Exemplarily, let the ambient temperature be Ta, and the expansion valve opening can be set according to the following rules:

[0058] Ta < -20°C, standby opening = D1

[0059] -20°C ≤ Ta ≤ 10°C, standby opening = D2

[0060] Ta > 10°C, standby opening = D3

[0061] Among them, the ranges of D1, D2, and D3 can be set to 0 - 500P, D1 = 0P, D2 < D3, and the first temperature threshold is -20°C.

[0062] For the control method of the heat pump system provided by the embodiment of the present invention, if the heat pump system is in the heating standby state and the standby duration reaches the preset standby duration, open the two-way valve between the compressor exhaust port and the suction port; obtain the first ambient temperature. If the first ambient temperature is not less than the first temperature threshold, open the expansion valve of the heat pump system and adjust the opening of the expansion valve based on the first ambient temperature, where the first temperature threshold is used to characterize the critical temperature of refrigerant migration. By controlling the two-way valve to open after the heat pump system shuts down smoothly, the lubricating oil separated by the compressor will follow the refrigerant migration and return to the compressor through the two-way valve, thereby lubricating the compressor in time and reducing the wear of the compressor. At the same time, control the expansion valve to open when it is greater than the first temperature threshold, and the corresponding expansion valve opening can be determined according to the first ambient temperature to ensure the system pressure balance when starting again. Control the expansion valve to close when it is less than the first temperature threshold, so as to avoid refrigerant migrating from the condenser through the expansion valve to the evaporator, resulting in the refrigerant remaining in the compressor cavity, and further avoiding wear to the compressor and extending the service life of the compressor.

[0063] In one embodiment, the control method of the heat pump system provided in the above embodiment further includes the following steps:

[0064] Step S201, if the heat pump system is in a heating working state, detecting the operating time of the compressor;

[0065] Step S202: If the operation time is not less than the preset heating operation time, the two-way valve is controlled to close.

[0066] When the heat pump system is started and in heating mode, and after startup, it is detected that the compressor operation time continues to reach the preset heating operation time (for example, three seconds), the two-way valve in the heat pump system is controlled to be in a power-off normally closed state to prevent gas cross-flow between the exhaust port and the return port of the compressor. The preset heating time can be set according to the specific application scenario.

[0067] In one embodiment, the control method of the heat pump system provided in the above embodiment further includes the following steps:

[0068] Step S301: If the heat pump system is restarted after being shut down, the second ambient temperature and the actual outlet water temperature of the condenser are obtained.

[0069] If the heat pump system reaches the set temperature or shutdown temperature and is in standby mode, if it is started again, the second ambient temperature is measured by the temperature sensor, which can be measured by the ambient temperature sensor installed on the evaporator. The condenser uses a water-side heat exchanger, and the actual water outlet temperature refers to the water outlet temperature of the water-side heat exchanger outlet, which can be measured by the temperature sensor installed on the water-side heat exchanger.

[0070] Step S302: If the second ambient temperature is lower than the preset secondary start-up temperature threshold, and the temperature difference between the actual outlet water temperature and the preset outlet water temperature is lower than the preset outlet water temperature threshold, the heat pump system is controlled to operate in the evaporator heating mode.

[0071] The preset secondary start ambient temperature threshold is set according to the environment. Specifically, the critical temperature of the refrigerant migration can be used as the secondary start ambient temperature threshold. The preset outlet water temperature refers to the ideal outlet water temperature set by the water side heat exchanger. It can be set by the controller of the water side heat exchanger to calculate the temperature difference between the actual outlet water temperature and the preset outlet water temperature. If the temperature difference between the actual outlet water temperature and the preset outlet water temperature is less than the preset outlet water temperature threshold, and the second ambient temperature is less than the preset secondary start temperature threshold, it indicates that the actual outlet water temperature is close to the preset outlet water temperature. At the same time, the evaporator of the heat pump system may frost when it is in a low temperature environment. Therefore, the heat pump system is controlled to operate the evaporator heating mode, that is, the defrost mode. In addition, in order to ensure the accuracy of turning on the evaporator heating mode, additional conditions can be added, that is, the temperature difference between the actual outlet water temperature and the preset outlet water temperature is less than the preset outlet water temperature threshold, and the duration of the second ambient temperature being less than the preset secondary start temperature threshold reaches the preset duration. If the preset duration is reached, the evaporator heating mode is turned on.

[0072] If the above conditions cannot be met at the same time, the two-way valve can be closed for a certain period of time (which can be set by yourself) and then the heat pump system can be controlled to operate according to normal logic.

[0073] For example, let the ambient temperature be Ta, the preset outlet water temperature be To, the actual outlet water temperature be Tk, the preset secondary start temperature threshold be -20°C, the preset outlet water temperature threshold be T1 (2-5°C), if the following two conditions are met at the same time and last for 60 seconds:

[0074] Ta<-20℃

[0075] To-Tk<T1

[0076] The evaporator heating mode is turned on.

[0077] If the above two conditions are not met at the same time, the heat pump system will be controlled to operate according to normal logic after closing the two-way valve for 10 seconds.

[0078] Furthermore, in the above step S302, controlling the heat pump system to operate in the evaporator heating mode includes the following steps:

[0079] Step S3011, controlling the compressor to operate at a first preset heating frequency and controlling the four-way valve to switch to heat the evaporator.

[0080] The compressor is controlled to increase the frequency from the lowest frequency to the first preset heating frequency, and to operate at the first preset heating frequency, and the four-way valve is controlled to switch. Specifically, after the four-way valve is energized, the coil slides to the other end under the action of the magnetic force, and the direction of the refrigerant changes, thereby turning on the evaporator heating mode.

[0081] When the compressor is running at the first preset heating frequency, the outdoor fan is turned off. For example, when controlling the compressor to heat up to the first preset heating frequency, the frequency increase speed (for example, 1 Hz per second) can be set, and the first preset heating frequency can be set to 30 Hz, which can be set according to actual conditions.

[0082] Step S3012: When the compressor on time reaches the preset evaporator mode operation time, the auxiliary expansion valve is closed, and the opening of the main expansion valve is adjusted to a preset opening corresponding to the evaporator heating mode.

[0083] The expansion valve includes the main expansion valve and the auxiliary expansion valve. The preset evaporator mode operation time is set according to demand (for example, 3 seconds). When the compressor is turned on for a certain period of time, the main electronic expansion valve is closed and the auxiliary electronic expansion valve is adjusted to a preset opening. The size of the preset opening can be set according to actual conditions. Figure 3 As shown, the direction Figure 1 on the contrary.

[0084] According to the method provided in the embodiment of the present invention, when the heat pump system is shut down and restarted, and the refrigerant migrates from the condenser to the evaporator, due to the low ambient temperature of the evaporator, the refrigerant and the refrigeration oil of the compressor will be deposited at the bottom of the evaporator, and the compressor lubricating oil will be stratified and precipitated, and the kinematic viscosity will increase. The lubricating oil cannot follow the refrigerant back to the compressor for lubrication. By turning on the evaporator heating mode and increasing it to the first preset heating frequency, the temperature of the evaporator can be increased, thereby preventing the compressor lubricating oil from stratifying and precipitating, reducing the kinematic viscosity of the lubricating oil, allowing the lubricating oil to quickly return to the compressor cavity to lubricate the moving parts of the compressor, and reducing compressor wear.

[0085] In one embodiment, the control method of the heat pump system provided in the above embodiment further includes the following steps:

[0086] Step S401, obtaining the outer coil temperature of the evaporator.

[0087] Step S402: If the temperature of the external coil is not less than the preset defrosting exit temperature, the heat pump system is controlled to exit the evaporator heating mode.

[0088] Step S403: the heat pump system exits the evaporator heating mode and controls the compressor to reduce the preset heating frequency to a second preset heating frequency.

[0089] Step S404: if the operating frequency of the compressor is reduced to the second preset heating frequency, the four-way valve is controlled to switch to enter the heating working state.

[0090] The outer coil temperature of the evaporator can be measured by the ambient temperature sensor. If the outer coil temperature is not less than the preset exit defrost temperature, it means that the evaporator heating mode is completed. At this time, the heat pump system can be controlled to exit the evaporator heating mode. The preset exit defrost temperature can be set according to the actual situation, for example, it can be set to 17°C.

[0091] The preset heating frequency is the heating temperature in the evaporator heating mode, and the compressor is controlled to decrease from the preset heating frequency to the second preset heating frequency. When the operating frequency of the compressor decreases to the second preset heating frequency, it indicates that the heat pump system exits the evaporator heating mode, and the four-way valve loses power and switches direction, so that the refrigerant in the pipeline changes its flow direction, and the heat pump system enters the heating working state. For example, when the compressor is controlled to decrease to the second preset heating frequency, the frequency reduction speed can be set (for example, 1 Hz per second), and the second preset heating frequency can be set to 30 Hz, which can be set according to actual conditions.

[0092] When the compressor operates at the second preset frequency, the outdoor fan is turned on.

[0093] In one embodiment, after the outdoor fan is turned on, the openings of the main expansion valve and the auxiliary expansion valve can be automatically adjusted according to the return air superheat.

[0094] The return air temperature is obtained by measuring the temperature of the evaporator outlet or the compressor return air port. When the difference between the return air temperature and the external coil temperature is less than C2, the opening degree of the main expansion valve P = Pn1-[Kp1*C2].

[0095] When the difference between the return air temperature and the external coil temperature is greater than C2, the opening degree of the main expansion valve P = Pn1 + [Kp1*C2].

[0096] Among them, the range of the adjustment cycle can be set to 10-60 seconds, the default is 10 seconds, Pn1 represents the opening value of the main expansion valve in the previous cycle (0~500P); Kp1 represents the proportional coefficient (the range can be set to 0.1~1) and can be set by yourself; C2 represents the return air target superheat value (0~5) and can be set by yourself.

[0097] Measure the outlet temperature and inlet temperature of the coaxial shell and tube heat exchanger. When the difference between the outlet temperature and the inlet temperature is less than C1, the opening of the auxiliary expansion valve = Pn2-[Kp2*C1].

[0098] When the difference between the outlet temperature and the inlet temperature is greater than C1, the opening of the auxiliary expansion valve = Pn2 + [Kp2*C1]

[0099] Among them, the range of the adjustment cycle can be set to 10-60 seconds, the default is 10 seconds, Pn2 represents the opening value of the auxiliary expansion valve in the previous cycle (0~500P); Kp2 represents the proportional coefficient (the range can be set to 0.1~1) and can be set by yourself; C1 represents the return air target superheat value (0~5) and can be set by yourself.

[0100] Furthermore, in the above embodiment, after controlling the heat pump system to exit the evaporator heating mode, the method further includes: adjusting the frequency of the compressor to a third preset heating frequency, and adjusting the opening of the main expansion valve to a preset third opening. The third preset heating frequency and the third opening indicate that the speed at which the compressor discharges the refrigerant is within a preset speed range.

[0101] When the heat pump system exits the evaporator heating mode and enters the heating mode, after the compressor is started, the frequency of the compressor is controlled to rise to the third preset heating frequency, and the opening of the main expansion valve is adjusted to the third opening. When the compressor is in the third preset heating frequency and the main expansion valve is in the third opening, the speed of the compressor discharging the refrigerant is in the preset speed range. The preset speed range indicates that the speed of discharging the refrigerant is moderate, and the specific range can be set according to actual conditions.

[0102] There is a positive correlation between the third preset heating frequency and the third opening degree. Exemplarily, the relationship between the two is as follows:

[0103] B2=A2*K

[0104] Assume that A2 represents the third preset heating frequency (for example, the value range is 30-45Hz), B2 represents the third opening (for example, the value range is 70-450P, when B2 is calculated to be lower than 70, 70 is taken; when B2 is calculated to be higher than 450, 450 is taken), K represents the proportionality coefficient (for example, the value range is 2-5), and correspondingly, the refrigerant discharge speed ranges from 10 to 15, and the specific discharge speed unit is related to the refrigerant amount. The speed of rising to the third preset heating frequency can be 1Hz per second.

[0105] Further, if the compressor operates based on the third preset heating frequency for a first operation time, the frequency of the compressor is increased from the third preset heating frequency to the target frequency.

[0106] The first operating time can be set according to actual conditions (for example, the value range is 30 to 600 seconds), and the frequency increase process can be controlled to increase the frequency at a certain speed (for example, 2 Hz per second). After reaching the target frequency, the heating is operated according to the target frequency, and the main circuit is adjusted according to the return air superheat.

[0107] According to the method provided in the embodiment of the present invention, when the compressor is at the third preset heating frequency and the main expansion valve is at the third opening, the speed at which the compressor discharges the refrigerant is moderate and will not be too fast or too slow, thereby preventing the lubricating oil in the compressor from being quickly discharged into the refrigeration system and causing oil shortage inside the compressor, thereby avoiding wear of the compressor due to lack of lubricating oil.

[0108] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] The specific contents of the above specific embodiments only express several embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A control method for a heat pump system, characterized in that: The method comprises: If the heat pump system is in the heating standby state and the standby time reaches the preset standby time, open the two-way valve between the compressor exhaust port and the return air port; Obtain a first ambient temperature. If the first ambient temperature is not less than a first temperature threshold, open the expansion valve of the heat pump system, and adjust the opening of the expansion valve based on the first ambient temperature. The first temperature threshold is used to characterize the critical temperature of refrigerant migration.

2. The control method of the heat pump system according to claim 1, characterized in that: The method further comprises: If the first ambient temperature is lower than a first temperature threshold, the expansion valve is closed.

3. The control method of the heat pump system according to claim 1, characterized in that: The method further comprises: If the heat pump system is in a heating working state, detecting the operating time of the compressor; If the operating time is not less than the preset heating operating time, the two-way valve is controlled to be closed.

4. The control method of the heat pump system according to claim 1, characterized in that: Also includes: If the heat pump system is restarted after being shut down, obtaining the second ambient temperature and the actual outlet water temperature of the condenser; If the second ambient temperature is lower than the preset secondary start-up temperature threshold, and the temperature difference between the actual water outlet temperature and the preset water outlet temperature is lower than the preset water outlet temperature threshold, the heat pump system is controlled to operate in the evaporator heating mode.

5. The control method of the heat pump system according to claim 4, characterized in that: The expansion valve includes a main expansion valve and an auxiliary expansion valve, and the controlling the heat pump system to operate in an evaporator heating mode includes: Controlling the compressor to operate at a first preset heating frequency and controlling the four-way valve to switch to heat the evaporator; When the compressor on time reaches the preset evaporator mode operation time, the auxiliary expansion valve is closed, and the opening of the main expansion valve is adjusted to a preset opening corresponding to the evaporator heating mode.

6. The method according to claim 5, characterized in that The method further comprises: Obtaining the outer coil temperature of the evaporator; If the temperature of the outer coil is not less than the preset defrost exit temperature, controlling the heat pump system to exit the evaporator heating mode; If the heat pump system exits the evaporator heating mode, controlling the compressor to decrease from the preset heating frequency to a second preset heating frequency; If the operating frequency of the compressor is reduced to the second preset heating frequency, the four-way valve is controlled to switch to enter the heating working state.

7. The method according to claim 6, characterized in that After controlling the heat pump system to exit the evaporator heating mode, the method further includes: The frequency of the compressor is adjusted to a third preset heating frequency, and the opening of the main expansion valve is adjusted to a preset third opening. The third preset heating frequency and the third opening indicate that the speed at which the compressor discharges refrigerant is within a preset speed range.

8. The method according to claim 7, characterized in that The method further includes increasing the frequency of the compressor from the third preset heating frequency to a target frequency if the compressor operates based on the third preset heating frequency for a first operation time.

9. A heat pump system, characterized in that: The heat pump system includes a compressor, which is provided with an exhaust port, an air return port and an air supply port. A two-way valve is provided between the exhaust port and the air return port, and the two-way valve is connected to the exhaust port and the air return port respectively. The heat pump system is used to perform the method described in any one of claims 1 to 8 above.

10. The heat pump system according to claim 9, characterized in that: Also includes: A four-way valve, a condenser, an evaporator, a gas-liquid separator, a coaxial shell and tube heat exchanger and a main expansion valve are arranged on the refrigerant pipeline; the compressor is connected to the condenser, the evaporator and the gas-liquid separator respectively through the four-way valve, the coaxial shell and tube heat exchanger and the main expansion valve are respectively arranged on the refrigerant pipeline between the condenser and the evaporator, the air outlet of the coaxial shell and tube heat exchanger is connected to the return air port of the compressor, the liquid outlet of the coaxial shell and tube heat exchanger is connected to the refrigerant pipeline through an auxiliary expansion valve, a filter is arranged on the pipeline of the main expansion valve, and the evaporator is provided with an external coil temperature sensor and an ambient temperature sensor.

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