A co2 heat pump system and a defrosting control method thereof

Abstract

The application discloses a CO2 heat pump system and a defrosting control method thereof, and relates to the technical field of air source heat pump systems. The application is used to solve the problem of slow defrosting speed of the existing air source heat pump system. The application comprises a CO2 refrigerant circulation path and a water supply circulation path. The CO2 refrigerant circulation path comprises a compressor, a gas cooler, a first throttling device and an evaporator which are sequentially connected in a head-tail mode. The water supply circulation path comprises a water tank and a water circuit connecting pipe assembly. The water circuit connecting pipe assembly comprises a cold water supply pipe, a hot water return pipe, a water circuit control valve and a hot water supply pipe. The water inlet of the water tank is communicated with the hot water supply pipe, and the water outlet of the water tank is communicated with the hot water return pipe. The water inlet of the gas cooler, the cold water supply pipe, the hot water return pipe and the water circuit control valve are connected. The hot water supply pipe is communicated with the water outlet of the gas cooler. The water circuit control valve is used to control the water inlet of the gas cooler to be communicated with or disconnected from the cold water supply pipe, and to control the water inlet of the gas cooler to be communicated with or disconnected from the hot water return pipe.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of air source heat pump system, and particularly relates to a CO2 heat pump system and a defrosting control method thereof. BACKGROUND

[0002] The air source heat pump system is used for absorbing low-temperature heat in air into a heat transfer medium, converting the low-temperature heat into high-temperature heat after compression by a compressor, and using the high-temperature heat to heat water. Compared with an electric water heater and a gas water heater, the air source heat pump system has the advantages of high efficiency and energy saving. CO2 is a heat transfer medium existing in nature, and has ODP (Ozone Depletion Potential) = 0 and GWP (Global Warming Potential) = 1. In a situation where flammability and toxicity are strictly limited, CO2 is a very ideal refrigerant, and the high discharge temperature and temperature glide of the transcritical cycle of CO2 are very suitable for water heating. Therefore, the CO2 heat pump system has a good application prospect.

[0003] Since the CO2 heat pump system adopts an air source heat pump, the CO2 heat pump system still has the problem of frosting. When the CO2 heat pump system operates in a situation where the outdoor temperature is low and the humidity is high, the surface of the air-side evaporator is prone to frosting. When the surface of the air-side evaporator is frosted, defrosting needs to be performed for the air-side evaporator. Common defrosting methods for the air source heat pump system in the art include four-way valve reversing defrosting and hot gas bypass defrosting.

[0004] For the CO2 heat pump system, the overall operating pressure of the CO2 heat pump system is high, and there is no suitable four-way valve component that can be used. Therefore, the four-way valve reversing defrosting is not suitable for defrosting of the CO2 heat pump system. In addition, when the hot gas bypass defrosting is used to defrost the CO2 heat pump system, the heat for defrosting is derived from the heat storage of the compressor housing and the power consumption during operation of the compressor. Therefore, the available heat is extremely small during defrosting. As a result, the time consumed for defrosting is long. Furthermore, after the hot gas bypass defrosting is started, the only high-low pressure difference of the CO2 heat pump system is derived from the resistance loss of the pipeline components in the CO2 heat pump system. Since the pressure difference caused by the pipeline components in the CO2 heat pump system is extremely small, the high-low pressure difference of the compressor during defrosting is very small, the discharge pressure is very low, and the discharge temperature is also very low. Therefore, the temperature of the refrigerant at the inlet of the evaporator is further reduced, and the time consumed for defrosting is longer. Therefore, when the frosting is more serious, the time consumed for the hot gas bypass defrosting is longer, which seriously affects the user experience. SUMMARY

[0005] The CO2 heat pump system and the defrosting control method thereof provided by the present application are used for solving the problem of slow defrosting speed and long defrosting time of the existing air source heat pump system.

[0006] To achieve the above object, the CO2 heat pump system provided by the application comprises a CO2 refrigerant circulation path and a water supply circulation path, the CO2 refrigerant circulation path comprises a compressor, a gas cooler, a first throttling device and an evaporator connected in sequence, the water supply circulation path comprises a water tank and a water circuit connecting pipe assembly, the water tank is provided with a water inlet and a water return outlet, the water circuit connecting pipe assembly comprises a cold water supply pipe, a hot water return pipe, a water circuit control valve and a hot water supply pipe, the water inlet of the water tank is communicated with the hot water supply pipe, the water return outlet of the water tank is communicated with the hot water return pipe, the water inlet of the gas cooler, the cold water supply pipe, the hot water return pipe and the water circuit control valve are connected, the hot water supply pipe is communicated with the water outlet of the gas cooler, and the water circuit control valve is used for controlling the water inlet of the gas cooler to be communicated with or disconnected from the cold water supply pipe and controlling the water inlet of the gas cooler to be communicated with or disconnected from the hot water return pipe.

[0007] In another aspect, the application further provides a defrosting control method for the CO2 heat pump system, comprising the following steps: when it is detected that the CO2 heat pump system reaches a first defrosting condition, the first throttling device is opened, the water circuit control valve controls the water inlet of the gas cooler to be communicated with the hot water return pipe, and the first defrosting condition at least comprises that the suction pressure of the compressor exceeds a first preset pressure range, and the duration that the suction pressure of the compressor exceeds the first preset pressure range reaches a first preset time.

[0008] Compared with the prior art, the CO2 heat pump system and the defrosting control method thereof provided by the embodiment of the present application have the following advantages: the water supply circulation passage of the CO2 heat pump system comprises a water tank and a water connection pipe assembly, the water tank is provided with a water inlet and a water return port, the water connection pipe assembly comprises a cold water supply pipe, a hot water return pipe, a water control valve and a hot water supply pipe, the water inlet of the water tank is in communication with the hot water supply pipe, the water return port of the water tank is in communication with the hot water return pipe, the water inlet of the gas cooler, the cold water supply pipe and the hot water return pipe are connected with the water control valve, the hot water supply pipe is in communication with the water outlet of the gas cooler, and the water control valve is used to control the water inlet of the gas cooler to be in communication with the cold water supply pipe or the hot water return pipe. When the CO2 heat pump system is used to heat the water in the water tank, the water control valve controls the water inlet of the gas cooler to be in communication with the cold water supply pipe, and cold water flows into the gas cooler, so that the high-temperature and high-pressure refrigerant (i.e. CO2 refrigerant) discharged by the compressor can transfer heat to the cold water flowing into the water inlet of the gas cooler to heat the water. When the above CO2 heat pump system is used for defrosting, if the suction pressure of the compressor exceeds the first preset pressure range and the duration that the suction pressure of the compressor exceeds the first preset pressure range reaches the first preset time, the CO2 heat pump system reaches the first defrosting condition, that is, the suction pressure of the compressor exceeds the first preset pressure range and the duration that the suction pressure of the compressor exceeds the first preset pressure range reaches the first preset time, which indicates that the evaporator surface is frosted, and defrosting of the evaporator is needed at this time. Subsequently, the water control valve controls the water inlet of the gas cooler to be in communication with the hot water return pipe, and a first throttling device is opened, so that the hot water return pipe guides the hot water in the water tank into the gas cooler, and thus the refrigerant discharged by the compressor can absorb the heat of the hot water when passing through the gas cooler, so that the temperature of the refrigerant is increased, the defrosting speed is accelerated, the defrosting time is shortened, and the user experience is better. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0010] Figure 1 The structure schematic diagram of the CO2 heat pump system provided by the embodiment of the present application;

[0011] Figure 2 The structure schematic diagram of the CO2 heat pump system provided by the embodiment of the present application comprises multiple heating modules;

[0012] Figure 3 The control method flow chart of the embodiment 1;

[0013] Figure 4 The control method flow chart of the embodiment 2;

[0014] Figure 5 The control method flow chart of the first throttling device opening adjustment of the embodiment of the application. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the application will be apparently and completely described in combination with the drawings of the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments of the application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0016] It is known that CO2 is a natural environment-friendly refrigerant which does not destroy atmospheric ozone layer and cause global warming, so the CO2 heat pump system is very ideal for heating water. However, when the CO2 heat pump system is operated in the case of low outdoor temperature and high humidity, the evaporator surface of the air side of the CO2 heat pump system is prone to frost formation, which reduces the heating capacity of the CO2 heat pump system.

[0017] With reference to Figure 1 The CO2 heat pump system provided by the embodiment of the application comprises a CO2 refrigerant circulation passage and a water supply circulation passage. The CO2 refrigerant circulation passage comprises a compressor 1, a gas cooler 3, a first throttling device 6 and an evaporator 7 which are sequentially and circularly connected. Wherein, Figure 1 The direction indicated by the arrow is the flow direction of the refrigerant. The water supply circulation passage comprises a water tank 11 and a waterway connecting pipe assembly. The water tank 11 is provided with a water inlet 12 and a water outlet 13. The waterway connecting pipe assembly comprises a cold water supply pipe 14, a hot water return pipe 15, a waterway control valve 32 and a hot water supply pipe 16. The water inlet 12 of the water tank 11 is communicated with the hot water supply pipe 16, and the water outlet 13 of the water tank 11 is communicated with the hot water return pipe 15. The water inlet 17 of the gas cooler, the cold water supply pipe 14 and the hot water return pipe 15 are connected with the waterway control valve 32. The hot water supply pipe 16 is communicated with the water outlet 18 of the gas cooler. The waterway control valve 32 is used to control the water inlet 17 of the gas cooler 3 to be communicated with or disconnected from the cold water supply pipe 14, and to control the water inlet 17 of the gas cooler 3 to be communicated with or disconnected from the hot water return pipe 15.

[0018] The CO2 heat pump system provided by the embodiment of the present application is used to heat water in the water tank 11, the water path control valve 32 controls the water inlet 17 of the gas cooler 3 to communicate with the cold water supply pipe 14, and cold water flows into the gas cooler 3, at this time, the high-temperature and high-pressure refrigerant (i.e. CO2 refrigerant) discharged by the compressor 1 can transfer heat to the cold water flowing into the water inlet 17 of the gas cooler 3 when passing through the gas cooler 3, so as to heat the water, and the heated water flows into the water tank 11 through the water outlet 18 of the gas cooler 3, at the same time, the refrigerant passing through heat exchange in the gas cooler 3 enters the evaporator 7 through the first throttling device 6 to evaporate and absorb heat, and finally returns to the suction port of the compressor 1 to complete a heating cycle. When the above-mentioned CO2 heat pump system is used for defrosting, the water path control valve 32 controls the water inlet 17 of the gas cooler 3 to communicate with the hot water return pipe 15, and the first throttling device 6 is opened, the hot water return pipe 15 guides the hot water in the water tank 11 into the gas cooler 3, so that the refrigerant discharged by the compressor 1 can absorb the heat of the hot water when passing through the gas cooler 3, thereby increasing the temperature of the refrigerant entering the evaporator, accelerating the defrosting speed, shortening the defrosting time, and providing a better user experience.

[0019] Optionally, the CO2 heat pump system in the embodiment of the present application further comprises a gas-liquid separator 8, the gas-liquid separator 8 is connected to the connecting pipeline between the evaporator 7 and the compressor 1, the gas inlet of the gas-liquid separator 8 communicates with the outlet of the evaporator 7, and the gas outlet of the gas-liquid separator 8 communicates with the suction port of the compressor 1. During the operation of the CO2 heat pump system, the gas-liquid separator 8 not only can play a role of gas-liquid separation for the refrigerant in the gas-liquid two-phase state discharged by the evaporator 7, but also can prevent the compressor 1 from sucking liquid, and compared with the refrigerant directly returned to the suction port of the compressor 1 from the evaporator 7, the setting of the gas-liquid separator 8 can buffer the pressure of the refrigerant, thereby ensuring that the suction pressure of the compressor 1 is stable, safe and reliable. The above-mentioned cold water supply pipe 14 can be connected to the municipal water inlet or the water in the water tank 10.

[0020] Further, the above-mentioned CO2 refrigerant circulation path further comprises a first control valve 9, the first control valve 9 is connected in parallel at both ends of the first throttling device 6, and the refrigerant from the gas cooler 3 can directly enter the evaporator 7 through the first control valve 9. Compared with the refrigerant from the gas cooler 3 introduced into the evaporator 7 through the first throttling device 6, the pressure loss of the refrigerant from the gas cooler 3 introduced into the evaporator 7 through the first control valve 9 is smaller, that is, the temperature of the refrigerant introduced into the inlet of the evaporator 7 through the first control valve 9 is higher, the defrosting speed of the CO2 heat pump system is faster, and the defrosting time is shorter. The above-mentioned CO2 refrigerant circulation path further comprises a bypass pipeline 19, and the first control valve 9 is arranged on the bypass pipeline 19, that is, the inlet of the first control valve 9 communicates with the refrigerant outlet 20 of the gas cooler 3, and the outlet of the first control valve 9 communicates with the inlet of the evaporator 7.

[0021] Optionally, the CO2 refrigerant circulation path further comprises a heat recovery branch 22 connected in parallel with the first throttling device 6, the heat recovery branch 22 is used for heat exchange with the connecting pipe at the exhaust port of the compressor 1, so that the refrigerant in the heat recovery branch 22 can absorb the heat of the refrigerant at the exhaust port of the compressor 1, further increasing the temperature of the refrigerant at the inlet of the evaporator 7, thereby further improving the defrosting speed of the CO2 heat pump system and shortening the defrosting time of the CO2 heat pump system.

[0022] The heat recovery branch 22 comprises a heat recovery device 2 and a second control valve 10 connected in series, the heat recovery device 2 comprises a heat exchange pipe wound around the connecting pipe between the exhaust port of the compressor 1 and the refrigerant inlet 21 of the gas cooler 3, and the second control valve 10 is used for controlling the on or off of the heat recovery branch 22. Optionally, the heat recovery branch 22 comprises a heat recovery device 2 and a second control valve 10 connected in series, the heat recovery device 2 comprises a heat exchange pipe wound around the connecting pipe between the refrigerant outlet 20 of the gas cooler 3 and the first throttling device 6, and the second control valve 10 is used for controlling the on or off of the heat recovery branch 22. Since the temperature of the refrigerant will decrease after passing through the gas cooler 3, the heat exchange pipe can absorb less heat, therefore, in the embodiment of the present application, the heat exchange pipe is wound around the connecting pipe between the exhaust port of the compressor 1 and the refrigerant inlet 21 of the gas cooler 3, so that the heat exchange pipe can absorb the heat at the exhaust port of the compressor 1, thereby further increasing the temperature of the refrigerant entering the evaporator 7 and shortening the defrosting time of the CO2 heat pump system.

[0023] Further, the CO2 refrigerant circulation path further comprises a heat regenerator 5, a first heat exchange flow path in the heat regenerator 5 is connected in series between the outlet of the evaporator 7 and the suction port of the compressor 1, and a second heat exchange flow path in the heat regenerator 5 is connected in series between the refrigerant outlet 20 of the gas cooler 3 and the inlet of the first throttling device 6. During the defrosting process of the CO2 heat pump system, the temperature of the refrigerant discharged after condensation and heat release in the evaporator 7 is relatively low, that is, the temperature of the refrigerant in the second heat exchange flow path of the heat regenerator 5 is higher than that of the refrigerant in the first heat exchange flow path of the heat regenerator 5, so that the refrigerant can absorb the heat of the second heat exchange flow path of the heat regenerator 5 when passing through the first heat exchange flow path of the heat regenerator 5, ensuring that the refrigerant flowing out of the first heat exchange flow path of the heat regenerator 5 has a suitable superheat degree, avoiding liquid suction of the compressor 1, and ensuring safe and reliable operation of the compressor 1. Optionally, the heat regenerator 5 is connected in parallel with the first control valve 9, and the flow of the refrigerant passing through the heat regenerator 5 can be adjusted through the first control valve 9 (and / or the first throttling device 6), thereby ensuring stable operation of the CO2 heat pump system.

[0024] Optionally, the CO2 refrigerant circulation passage further comprises a gas supplement assembly, which is in communication with the gas supplement port of the compressor 1 and capable of supplementing gas to the compressor 1, thereby increasing the discharge capacity of the compressor 1 and reducing the discharge temperature of the compressor 1.

[0025] Further, the gas supplement assembly comprises the economizer 4 and a gas supplement branch 23 in communication with the suction port of the compressor 1, the first heat exchange flow path in the economizer 4 is in series with the gas supplement branch 23, the second heat exchange flow path in the economizer 4 is in series between the refrigerant outlet 20 of the gas cooler 3 and the inlet of the first throttling device 6, the gas supplement branch 23 comprises the second throttling device 41 and the third control valve 42 in series with each other, the second throttling device 41 is located at the inlet side of the first heat exchange flow path in the economizer 4, and the third control valve 42 is used to control the communication or disconnection of the gas supplement branch 23. Optionally, the economizer 4 in the gas supplement assembly can also be replaced by a flash evaporator, but considering that the vapor pressure of the refrigerant in the flash evaporator is not easy to control, it is necessary to set electronic expansion valves at the front end and the rear end of the flash evaporator, resulting in a complex structure of the gas supplement assembly and a high cost, therefore, the former scheme is adopted in the embodiment of the present application. Specifically, the third controller 42 is installed at the outlet side of the first heat exchange flow path in the economizer 4.

[0026] Optionally, the inlet of the second throttling device 41 can be connected to the connecting pipeline between the gas cooler 3 and the economizer 4; or the inlet of the second throttling device 41 can be connected to the connecting pipeline between the economizer 4 and the first throttling device 6. The latter scheme is more suitable for the temperature of the refrigerant introduced into the second throttling device 41, and can better balance the pros and cons of gas supplement and enthalpy increase, therefore, the latter scheme is adopted in the embodiment of the present application.

[0027] It should be noted that for the scheme in which the CO2 heat pump system comprises both the economizer 4 and the regenerator 5, the economizer 4 can be arranged on the connecting pipeline between the regenerator 5 and the gas cooler 3, or arranged on the connecting pipeline between the regenerator 5 and the first throttling device 6. Considering that the temperature drop of the refrigerant after passing through the regenerator 5 is greater than the temperature drop of the refrigerant after passing through the economizer 4, the former can better prevent the CO2 heat pump system from supplementing liquid, and ensure the reliability of the operation of the compressor 1. In addition, the inlet of the second throttling device 41 can be arranged on the connecting pipeline between the economizer 4 and the regenerator 5, or arranged on the connecting pipeline between the regenerator 5 and the inlet of the first throttling device 6, and for the same reason, the former scheme is adopted in the embodiment of the present application.

[0028] Based on the above embodiment, the economizer 4 is connected in parallel with the first control valve 9, and the flow of the refrigerant into the economizer 4 can be adjusted by the opening and closing of the first control valve 9. The first control valve 9, the second control valve 10 and the third control valve 42 can be selected as solenoid valves or electronic expansion valves.

[0029] Further, the valve aperture of the first control valve 9 is larger than the valve aperture of the first throttling device 6 when fully open, so that the flow resistance of the refrigerant when the first control valve 9 is fully open is smaller than the flow resistance in the first throttling device 6. When the first control valve 9 is opened, most of the high-temperature refrigerant directly enters the evaporator 7 through the first control valve 9, and the defrosting effect is good.

[0030] If the valve aperture of the second control valve 10 is larger than the valve aperture of the first throttling device 6 when fully open, most of the refrigerant passes through the heat recovery device 2 to absorb the heat at the exhaust port of the compressor 1, so that the temperature of the refrigerant at the exhaust port of the compressor 1 is reduced more, and if the reduced temperature of the refrigerant cannot be compensated in time when passing through the gas cooler 3, the temperature of the refrigerant entering the evaporator 7 is low, and the defrosting effect is poor. Therefore, the valve aperture of the second control valve 10 in the embodiment of the present application is smaller than the valve aperture of the first throttling device 6 when fully open.

[0031] For the scheme of the CO2 heat pump system including the first throttling device 6, the first control valve 9 and the second control valve 10, when the first throttling device 6, the first control valve 9 and the second control valve 10 are all fully open, most of the high-temperature refrigerant can directly enter the evaporator 7 through the first control valve 9, only a small part of the refrigerant enters the heat recovery device 2 after throttling through the second control valve 10 to recover heat, and the refrigerant flow in each branch is appropriate, so that the defrosting effect of the CO2 heat pump system is better.

[0032] The above-mentioned CO2 heat pump system includes a plurality of heating modules, each of which is composed of a CO2 refrigerant circulation path and a water supply circulation path, and is suitable for the case where a large amount of water needs to be heated. Of course, the CO2 heat pump system can also include only one of the above-mentioned heating modules, such as Figure 1 . The CO2 heat pump system in the above-mentioned Figure 2 includes a first heating module 100, a second heating module 200 and a third heating module 300, and the water supply circulation paths in the three heating modules are in communication with the same water tank 11. Here, the number of heating modules in the CO2 heat pump system is not specifically limited.

[0033] The embodiment of the present application also provides a defrosting control method for the above-mentioned CO2 heat pump system, which includes the following steps:

[0034] When it is detected that the CO2 heat pump system reaches the first defrosting condition, the first throttling device is opened, and the waterway control valve controls the water inlet of the gas cooler to be in communication with the hot water return pipe, and the first defrosting condition at least includes that the suction pressure of the compressor exceeds the first preset pressure range, and the duration that the suction pressure of the compressor exceeds the first preset pressure range reaches the first preset time.

[0035] The CO2 heat pump system comprises a controller configured to detect the suction pressure of the compressor from a suction pressure sensor installed at the suction port of the compressor, and a timing module configured to record the duration when the suction pressure of the compressor exceeds the first preset pressure range. The controller is configured to control the first throttling device to open and the waterway control valve to connect the water inlet of the gas cooler to the hot water return pipe. When the controller determines that the obtained suction pressure exceeds the first preset pressure range and the duration recorded by the timing module reaches the first preset time, the controller controls the first throttling device to open and the waterway control valve to connect the water inlet of the gas cooler to the hot water return pipe. When the refrigerant discharged by the compressor passes through the gas cooler, the refrigerant can absorb the heat of the hot water, so that the temperature of the refrigerant is increased, the defrosting speed of the CO2 heat pump system is increased, the defrosting time is shortened, and the user experience is good.

[0036] It should be noted that the first defrosting condition further comprises an ambient temperature T a exceeds the first preset ambient temperature range and the evaporator liquid pipe temperature T e exceeds the first preset liquid pipe temperature range, or the ambient temperature T a exceeds the second preset ambient temperature range and the evaporator liquid pipe temperature T e exceeds the ambient temperature T a and the first preset temperature value, and the CO2 heat pump system satisfies any one of the above three first defrosting conditions.

[0037] Further, the defrosting control method further comprises:

[0038] When it is detected that the CO2 heat pump system reaches a defrosting end condition, the waterway control valve controls the water inlet of the gas cooler to be disconnected from the hot water return pipe. The defrosting end condition comprises that the main gas pipe temperature of the evaporator exceeds the first preset main gas pipe temperature range. The controller obtains the main gas pipe temperature from a gas pipe temperature sensor installed at the main gas pipe of the evaporator. When the main gas pipe temperature is greater than or equal to the first preset main gas pipe temperature, the controller sends a control signal to the waterway control valve. After the waterway control valve receives the control signal, the water inlet of the gas cooler is disconnected from the hot water return pipe, and the defrosting ends.

[0039] Further, the CO2 heat pump system further comprises a first control valve connected in parallel across the first throttling device. The defrosting control method of the CO2 heat pump system further comprises:

[0040] When the CO2 heat pump system is detected to reach the first defrosting condition, the first control valve is opened. The controller controls the first control valve to open, and most of the refrigerant enters the evaporator through the first control valve, so that the amount of refrigerant entering the evaporator is large, and the defrosting effect is good. Alternatively, the above defrosting control method further comprises: when the CO2 heat pump system is detected to reach the first defrosting end condition, the first control valve is closed. Of course, the closing operation of the first control valve is also controlled and executed by the controller.

[0041] Based on the above embodiment, the defrosting control method of the CO2 heat pump system further comprises:

[0042] When the CO2 heat pump system is detected to reach the second defrosting condition, the first control valve is opened, the first throttling device is closed, and the waterway control valve controls the water inlet of the gas cooler to be disconnected with the hot water return pipe. The second defrosting condition at least includes that the suction pressure of the compressor exceeds the second preset pressure range, and the duration that the suction pressure of the compressor exceeds the second preset pressure range reaches the second preset time.

[0043] It should be noted that: the above second defrosting condition further includes that the ambient temperature Ta of the CO2 heat pump system exceeds the third preset ambient temperature range and the evaporator liquid pipe temperature T e exceeds the third preset liquid pipe temperature range, or the ambient temperature Ta of the CO2 heat pump system exceeds the fourth preset ambient temperature range and the evaporator liquid pipe temperature T a exceeds the fourth preset ambient temperature range, and the evaporator liquid pipe temperature T e exceeds the ambient temperature Ta, and the evaporator liquid pipe temperature T a exceeds the ambient temperature Ta, and the evaporator liquid pipe temperature T

[0044] Similarly, the above operations of opening the first control valve, closing the first throttling device, and the waterway control valve controlling the water inlet of the gas cooler to be disconnected with the hot water return pipe are all controlled and executed by the controller, and are more suitable for the case that the surface frost layer of the evaporator is thin.

[0045] Further, the CO2 refrigerant circulation passage in the CO2 heat pump system further comprises a heat recovery branch connected in parallel across the first throttling device, the heat recovery branch comprising a heat recovery device and a second control valve connected in series with each other, the heat recovery device comprising a heat exchange pipe wound around a connecting pipe between the discharge port of the compressor and the gas cooler, and the second control valve being used to control the on or off of the heat recovery branch; the defrosting control method of the CO2 heat pump system further comprises: when it is detected that the CO2 heat pump system reaches the first defrosting condition, opening the second control valve. The controller controls the opening of the second control valve, so that part of the refrigerant can absorb the heat at the discharge port of the compressor, thereby increasing the temperature of the refrigerant in the heat recovery branch, and further increasing the temperature of the refrigerant entering the evaporator, so as to further improve the defrosting speed of the CO2 heat pump system and shorten the defrosting time. Alternatively, the defrosting control method further comprises: when it is detected that the CO2 heat pump system reaches the first defrosting end condition, controlling the second control valve to be closed. Of course, the closing operation of the second control valve is also controlled by the controller.

[0046] The CO2 heat pump system comprises a plurality of heating modules, each of which is composed of a CO2 refrigerant circulation passage and a water supply circulation passage; the defrosting control method of the CO2 heat pump system specifically comprises: if the total number of the heating modules to be defrosted is less than or equal to the maximum defrosting number, controlling the first throttling device included in all the heating modules to be defrosted to be opened, and controlling the waterway control valve included in the water supply circulation passage to be defrosted to control the water inlet of the gas cooler to be communicated with the hot water return pipe; if the total number of the heating modules to be defrosted is greater than the maximum defrosting number, after at least one heating module completes defrosting, the first throttling device included in the heating module to be defrosted is controlled to be opened, and the waterway control valve corresponding to the water supply circulation passage to be defrosted is controlled to control the water inlet of the gas cooler to be communicated with the hot water return pipe. When the controller performs the above operation, according to the specific design parameters of the CO2 heat pump system, the number of the heating modules defrosting at the same time is controlled, so that the water temperature in the water tank fluctuates less under the condition of ensuring the defrosting speed.

[0047] It should be noted that: the maximum defrosting number N is calculated by the formula: N = 5L x M / Q, wherein the total capacity of the heat pump is Q (unit: kW), M (unit: pieces) is the total number of the heating modules, and L (unit: m3) is the volume of the water tank. 3 ) for the water tank.

[0048] When the host receives the defrost request signal of the heating module to be defrosted, the number of the heating module being defrosted is increased by 1, and then the relationship between the number of the heating module being defrosted and the maximum defrosting number is judged. Alternatively, if the total number m of the heating module to be defrosted is less than 5L×M / Q, it indicates that defrosting the heating module to be defrosted will not cause the water temperature in the water tank to decrease, and then the host sends a defrost permission signal to the heating module to be defrosted. If the total number m of the heating module to be defrosted is greater than 5L×M / Q, it indicates that defrosting the heating module to be defrosted will cause the water temperature in the water tank to decrease, and then the host sends a defrost waiting signal to the heating module to be defrosted, and after at least one heating module completes defrosting, the controller controls the heating module to be defrosted to send a defrost permission signal.

[0049] Further, the first throttling device is an electronic expansion valve, and the opening of the first throttling device specifically includes: opening the first throttling device at a preset opening degree; and adjusting the opening degree of the first throttling device according to the suction superheat degree of the compressor. The suction port of the compressor is provided with a suction temperature sensor and a suction pressure sensor, and the controller calculates the suction superheat degree T according to the suction temperature value detected by the suction temperature sensor and the suction pressure value detected by the suction pressure sensor. so Specifically, the suction superheat degree T so is a difference value obtained by subtracting the saturated temperature of the refrigerant corresponding to the suction pressure value from the suction temperature of the compressor.

[0050] The adjustment of the opening degree of the first throttling device specifically includes:

[0051] When the suction superheat degree of the compressor is greater than a preset suction superheat degree, the opening degree of the first throttling device is decreased. When the suction superheat degree of the compressor is greater than the preset suction superheat degree, it indicates that most of the refrigerant in the CO2 heat pump system passes through the first throttling device at this time, so that only a small amount of refrigerant passes through the first control valve. By decreasing the opening degree of the first throttling device, the refrigerant flow rate passing through the first control valve is increased, and the defrosting speed of the CO2 heat pump system is relatively fast at this time.

[0052] When the suction superheat degree of the compressor is less than the preset suction superheat degree, the opening degree of the first throttling device is increased. When the suction superheat degree of the compressor is less than the preset suction superheat degree, it indicates that the CO2 heat pump system is prone to liquid entrainment at this time. By increasing the opening degree of the first throttling device, the suction superheat degree of the compressor can be increased.

[0053] When the suction superheat degree of the compressor is equal to the preset suction superheat degree, the current opening degree of the first throttling device is maintained. When the suction superheat degree of the compressor is equal to the preset suction superheat degree, it indicates that the defrosting speed of the CO2 heat pump system is relatively fast and liquid entrainment will not occur at this time, and the current opening degree of the first throttling device can be maintained.

[0054] Optionally, the increasing the opening of the first throttling device is increasing the opening of the first throttling device to a set opening, or increasing the opening of the first throttling device by a preset opening based on the current opening of the first throttling device. Similarly, the decreasing the opening of the first throttling device can also be calculated in a similar manner.

[0055] Further, the water supply circulation passage further comprises a water supply pump for introducing or discharging water into or out of the gas cooler. The defrosting control method of the CO2 heat pump system further comprises:

[0056] When the CO2 heat pump system reaches the first defrosting condition, the water supply pump is turned on; when the CO2 heat pump system reaches the second defrosting condition, the water supply pump is turned off. The controller controls the opening and closing of the water supply pump, when the CO2 heat pump system reaches the first defrosting condition, the water supply pump introduces hot water in the water tank into the gas cooler through the hot water return pipe, thereby accelerating the heat exchange efficiency of the hot water and the refrigerant in the gas cooler; when the CO2 heat pump system reaches the second defrosting condition, the water supply pump stops introducing hot water in the water tank into the gas cooler through the hot water return pipe.

[0057] Based on the above embodiment, the turning on of the water supply pump specifically comprises: turning on the water supply pump at a preset speed; and adjusting the speed of the water supply pump according to the discharge temperature value of the compressor and the outlet temperature value of the gas cooler. According to the different discharge temperature values of the compressor and the outlet temperature values of the gas cooler in different working conditions, the water supply pump is adjusted to run at a suitable speed to control the heat exchange efficiency of the hot water and the refrigerant in the gas cooler, thereby controlling the temperature at the refrigerant outlet of the gas cooler.

[0058] It should be noted that the speed of the water supply pump is inversely proportional to the voltage duty cycle signal for controlling the speed of the water supply pump, and the speed of the water supply pump is adjusted by adjusting the size of the voltage duty cycle signal. Specifically, the target voltage duty cycle signal PWM(n) of the water supply pump = PWM(n-1) + ΔPWM, wherein PWM(n-1) is the voltage duty cycle signal of the last time, and ΔPWM is the water supply pump voltage duty cycle signal correction value caused by the discharge temperature of the compressor and the outlet refrigerant temperature of the gas cooler. The water supply pump voltage duty cycle signal correction value ΔPWM can be obtained by looking up a table, for example, as shown in Table 1:

[0059] Table 1 Parameter table of water supply pump voltage duty cycle signal correction value ΔPWM

[0060]

[0061] The defrosting control method of the CO2 heat pump system according to the embodiments of the present application will be further described below in combination with two specific embodiments.

[0062] Embodiment 1

[0063] Figure 3 For the condition that the frost layer on the evaporator in the CO2 heat pump system is thick, the first defrosting condition is that the suction pressure P S ≤1.9Mpa, and the suction pressure P S ≤1.9Mpa for a duration t1≥1min, that is, the first preset pressure range is that the suction pressure is greater than 1.9Mpa, and the first preset time is 1min; or the first defrosting condition is that the ambient temperature T a ≥6℃, and the evaporator liquid pipe temperature T e ≤-4℃, that is, the first preset ambient temperature range is that the ambient temperature T a is less than 6℃, and the first preset liquid pipe temperature range is that the evaporator liquid pipe temperature is greater than -4℃; or the first defrosting condition is that -5℃ a <6℃, and the evaporator liquid pipe temperature T e ≤T a -10℃, that is, the second preset ambient temperature range is that the ambient temperature T a is less than or equal to -5℃ or the ambient temperature T a is greater than or equal to 6℃, and the evaporator liquid pipe temperature range is greater than the ambient temperature T a by the first preset temperature value 10℃; or the first defrosting condition is that the ambient temperature T a ≤-5℃, and the evaporator liquid pipe temperature T e ≤T a -9℃, that is, the second preset ambient temperature range is that the ambient temperature T a is greater than -5℃, and the evaporator liquid pipe temperature range is greater than the ambient temperature T a by the first preset temperature value 9℃. The first defrosting end condition is that the main gas pipe temperature T g1 of the evaporator is greater than or equal to 8℃, that is, the first preset main gas pipe temperature range is that the main gas pipe temperature is less than 8℃.

[0064] The specific process of defrosting of the CO2 heat pump system is as follows: when the suction pressure value P S1 ≤1.9Mpa, and t1≥1min, or T a ≥6℃, and T e ≤-4℃; or -5℃ a <6℃, and T e ≤T a -10℃; or T a ≤-5℃, and T e ≤T a -9℃, the controller controls the water supply pump to be opened, the first throttling device to be opened, the first control valve to be opened, and the second control valve to be opened. When T g1When the temperature reaches ≥8℃, the CO2 heat pump system reaches the first defrosting termination condition.

[0065] During the defrosting process of a CO2 heat pump system, the controller adjusts the speed of the water supply pump according to specific logic, and controls the opening degree of the first throttling device to be calculated according to specific logic. The speed adjustment of the water supply pump and the opening degree calculation of the first throttling device have been introduced previously, so they will not be repeated here.

[0066] Example 2

[0067] Figure 4 For a CO2 heat pump system with a thin frost layer on the evaporator, the second defrosting condition mentioned above is the compressor suction pressure P. S ≤2.2 MPa, and the compressor's suction pressure P S The duration t2 ≤ 2.2 MPa is ≥ 1 min, that is, the second preset pressure range is when the intake pressure is greater than 2.2 MPa and the second preset time is 1 min; or the above-mentioned second defrosting condition is when the ambient temperature T a ≥6℃, and evaporator liquid line temperature T e ≤-2℃, that is, the third preset ambient temperature range is ambient temperature T. a The third preset liquid pipe temperature range is less than 6℃, where the evaporator liquid pipe temperature is greater than -2℃; or the second defrosting condition mentioned above is -5℃ < T. a <6℃, and the evaporator liquid tube temperature T a ≤Ta-8℃, that is, the fourth preset ambient temperature range is the ambient temperature T. a Less than or equal to -5℃ or ambient temperature T a The evaporator liquid pipe temperature range is greater than or equal to 6℃ and is greater than the ambient temperature T. a A temperature difference of 8°C from the second preset temperature value; or the second defrosting condition is an ambient temperature T. a ≤-5℃, and evaporator liquid line temperature T e ≤T a -7℃, which is the fourth preset ambient temperature range, is ambient temperature T. a The evaporator liquid line temperature range is greater than -5℃ and greater than the ambient temperature T. a The temperature difference between the second preset temperature value and the second preset temperature value is 7°C. The above-mentioned second defrosting termination condition is the main gas pipe temperature T of the evaporator. g2 The second preset main air pipe temperature range is ≥5℃, or the defrosting time t3≥9min, meaning the main air pipe temperature is less than 5℃, and the third preset time is 9min.

[0068] The specific process of defrosting a CO2 heat pump system is as follows: when the suction pressure value P... s ≤2.2 MPa, and t2≥1 min, or T a ≥6℃, and Te ≤-2℃; or -5℃ < T a <6℃, and T e ≤T a -8℃; or T a ≤-5℃, and T e ≤T a -7℃, the controller controls the water supply pump to be closed, the first throttling device to be closed, and the first control valve to be opened. When T g2 ≥5℃ or t3≥9min, the CO2 heat pump system reaches the second defrosting end condition.

[0069] Figure 5 is a specific embodiment of the opening degree adjustment of the first throttling device in the CO2 heat pump system, the preset suction superheat degree of the compressor is 1℃, and the preset opening degree of the first throttling device is 2% EVO max , EVO max is the maximum opening degree of the first throttling device, assuming that the maximum opening degree EVO max of the first throttling device is 500 pls (pulse), and the preset opening degree is 10 pls. When the suction superheat degree of the compressor is greater than 1℃, the target opening degree EVO(i) of the first throttling device is reduced by the preset opening degree 2% on the basis of the current opening degree EVO(i-1) of the first throttling device; when the suction superheat degree of the compressor is equal to 1℃, the target opening degree EVO(i) of the first throttling device remains unchanged; when the suction superheat degree of the compressor is less than 1℃, the target opening degree EVO(i) of the first throttling device is increased by the preset opening degree 2% on the basis of the current opening degree EVO(i-1) of the first throttling device. After the above operation is performed, when the opening time of the target opening degree EVO(i) of the first throttling device reaches the control period t, the judgment is started again, and the next cycle is entered. The control period t is in the range of 10s to 90s. For example, Figure 5 the control period t in the above formula is 50s.

[0070] In the description of the present specification, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0071] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A CO2 heat pump system, characterized by, The CO2 refrigerant circulation passage comprises a compressor, a gas cooler, a first throttling device and an evaporator connected in sequence, and the water circulation passage comprises a water tank and a water connection pipe assembly, the water tank is provided with a water inlet and a water outlet, the water connection pipe assembly comprises a cold water supply pipe, a hot water return pipe, a water control valve and a hot water supply pipe, the water inlet of the water tank is communicated with the hot water supply pipe, the water outlet of the water tank is communicated with the hot water return pipe, the water inlet of the gas cooler, the cold water supply pipe, the hot water return pipe and the water control valve are connected, the hot water supply pipe is communicated with the water outlet of the gas cooler, and the water control valve is used for controlling the water inlet of the gas cooler to be communicated with or disconnected from the cold water supply pipe and controlling the water inlet of the gas cooler to be communicated with or disconnected from the hot water return pipe. The CO2 refrigerant circulation passage further comprises a heat recovery branch connected in parallel at both ends of the first throttling device, and the heat recovery branch is used for heat exchange with a connecting pipe at an exhaust port of the compressor. The heat recovery branch comprises a heat recovery device and a second control valve connected in sequence, the heat recovery device comprises a heat exchange pipe wound around the connecting pipe between the exhaust port of the compressor and the gas cooler, and the second control valve is used for controlling the heat recovery branch to be conducted or disconnected. The CO2 refrigerant circulation passage further comprises a bypass pipe connected with a refrigerant outlet of the gas cooler and an air inlet of the evaporator.

2. The CO2 heat pump system of claim 1, wherein, The CO2 refrigerant circulation passage further comprises a first control valve arranged on the bypass pipe and connected in parallel at both ends of the first throttling device.

3. The CO2 heat pump system of claim 1, wherein, The CO2 refrigerant circulation passage further comprises a heat recovery device, a first heat exchange flow path in the heat recovery device is connected in sequence between an outlet of the evaporator and a suction port of the compressor, and a second heat exchange flow path in the heat recovery device is connected in sequence between a refrigerant outlet of the gas cooler and an inlet of the first throttling device.

4. The CO2 heat pump system according to claim 1 or 3, characterized by, The CO2 refrigerant circulation passage further comprises a gas supplement assembly communicated with a gas supplement port of the compressor.

5. The CO2 heat pump system of claim 4, wherein, The gas supplement assembly comprises an economizer and a gas supplement branch communicated with the suction port of the compressor, a first heat exchange flow path in the economizer is connected in sequence on the gas supplement branch, a second heat exchange flow path in the economizer is connected in sequence between the refrigerant outlet of the gas cooler and the inlet of the first throttling device, the gas supplement branch comprises a second throttling device and a third control valve connected in sequence, the second throttling device is located on the inlet side of the first heat exchange flow path in the economizer, and the third control valve is used for controlling the gas supplement branch to be connected or disconnected.

6. The CO2 heat pump system of claim 2, wherein, The valve port diameter of the first control valve is greater than the valve port diameter of the first throttling device when the first throttling device is fully opened.

7. The CO2 heat pump system of claim 1, wherein, The valve port diameter of the second control valve is less than the valve port diameter of the first throttling device when the first throttling device is fully opened.

8. The CO2 heat pump system of claim 5, wherein, The inlet of the second throttling device is connected to a connecting pipe between the economizer and the first throttling device.

9. The CO2 heat pump system of claim 1, wherein, Each of the plurality of heating modules is formed by one of the CO2 refrigerant circulation paths and one of the water supply circulation paths.

10. A defrosting control method for the CO2 heat pump system according to any one of claims 1 to 9, characterized by, The method comprises the following steps: When the CO2 heat pump system is detected to reach the first defrosting condition, the first throttling device is opened, the waterway control valve controls the water inlet of the gas cooler to be communicated with the hot water return pipe, and the first defrosting condition at least comprises that the suction pressure of the compressor exceeds a first preset pressure range and the duration that the suction pressure of the compressor exceeds the first preset pressure range reaches a first preset time.

11. The defrosting control method of the CO2 heat pump system according to claim 10, characterized by, The CO2 heat pump system further comprises a first control valve connected in parallel at both ends of the first throttling device, and the defrosting control method further comprises: When the CO2 heat pump system is detected to reach the first defrosting condition, the first control valve is opened.

12. The defrosting control method of a CO2 heat pump system according to claim 11, characterized by, The defrosting control method further comprises: When the CO2 heat pump system is detected to reach the second defrosting condition, the first control valve is opened and the first throttling device is closed, and the waterway control valve controls the water inlet of the gas cooler to be disconnected from the hot water return pipe, and the second defrosting condition at least comprises that the suction pressure of the compressor exceeds a second preset pressure range and the duration that the suction pressure of the compressor exceeds the second preset pressure range reaches a second preset time.

13. The defrosting control method of a CO2 heat pump system according to claim 11, characterized by, The CO2 refrigerant circulation path in the CO2 heat pump system further comprises a heat recovery branch connected in parallel at both ends of the first throttling device, the heat recovery branch comprises a heat recovery device and a second control valve connected in series, the heat recovery device comprises a heat exchange pipe wound around a connecting pipe between the gas cooler and the exhaust port of the compressor, and the second control valve is used to control the conduction or disconnection of the heat recovery branch. The defrosting control method further comprises: When the CO2 heat pump system is detected to reach the first defrosting condition, the second control valve is opened.

14. The defrosting control method of a CO2 heat pump system according to claim 10, characterized by, The CO2 heat pump system comprises a plurality of heating modules, each of which is formed by one of the CO2 refrigerant circulation paths and one of the water supply circulation paths. The defrosting control method further comprises: If the total number of the heating modules requiring defrosting is less than or equal to the maximum defrosting number, the first throttling devices included in all the heating modules requiring defrosting are controlled to be opened, and the waterway control valves included in all the water supply circulation paths requiring defrosting are controlled to control the water inlet of the gas cooler to be communicated with the hot water return pipe. If the total number of the heating modules requiring defrosting is greater than the maximum defrosting number, after defrosting of at least one heating module is completed, the first throttling devices included in the heating modules to be defrosted are controlled to be opened, and the waterway control valves included in the water supply circulation paths to be defrosted are controlled to control the water inlet of the gas cooler to be disconnected from the hot water return pipe.

15. The defrosting control method of a CO2 heat pump system according to claim 10, characterized by, The first throttling device is an electronic expansion valve, and the opening of the first throttling device specifically comprises: The first throttling device is opened at a preset opening degree. The opening degree of the first throttling device is adjusted according to the suction superheat degree of the compressor.

16. The defrost control method of a CO2 heat pump system according to claim 12, characterized by, The water supply circulation passage further comprises a water supply pump for leading water into or out of the gas cooler; the defrosting control method further comprises: opening the water supply pump when it is detected that the CO2 heat pump system reaches a first defrosting condition; closing the water supply pump when it is detected that the CO2 heat pump system reaches a second defrosting condition.

17. The defrosting control method of a CO2 heat pump system according to claim 16, characterized by, The opening of the water supply pump specifically comprises: opening the water supply pump at a preset rotating speed; adjusting the rotating speed of the water supply pump according to the exhaust temperature value of the compressor and the outlet temperature value of the gas cooler.

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