A control method for a co2 heat pump system in a cycle heating mode

Abstract

The application discloses a control method of a CO2 heat pump system in a circulating heating mode, and relates to the technical field of household heat pump water heater system control, and solves the technical problem of low operation efficiency of the CO2 heat pump system in the circulating heating mode, and the technical solution is that the control frequency is determined according to the operation stage of the CO2 heat pump system in the circulating heating mode, the water temperature in and out of the air cooler is collected to calculate the optimal opening degree of the electronic expansion valve, and the opening degree of the electronic expansion valve is adjusted to enable the system to operate in the optimal circulating state. The optimization strategy of the control method is to keep the optimal operation state in the dynamic operation process of the system, thereby improving the total operation efficiency and reducing the overall operation power consumption; meanwhile, the optimal opening degree function correlation formula is used as the control method, the rapid control demand is met, and the easy implementation of the control method is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of household heat pump water heater system control, and particularly relates to a control method of a CO2 heat pump system in a circulating heating mode. BACKGROUND

[0002] With the increasing demand for building energy, it is particularly important to improve the operation efficiency of energy systems in the building field to achieve energy saving and decarbonization goals. Heat pump systems can effectively utilize low-grade heat energy, such as air and water, for space heating and domestic hot water production, and thus can be used as a building low-carbon technology with development potential. Carbon dioxide heat pump (CO2) is a heat pump system using carbon dioxide as a circulating working medium. Due to its green environmental protection (GWP value of 1 and OWP value of 0) and high heating potential, it has attracted widespread attention. How to efficiently apply CO2 heat pump to residential buildings or individual families and how to improve the performance of the system under different working conditions have become important research topics.

[0003] Since the transcritical CO2 cycle produces a large temperature glide when heat is released in the supercritical region, the CO2 heat pump is suitable for providing domestic hot water for residential users. However, when CO2 is in the supercritical region, its pressure and temperature are independent of each other, resulting in an optimal state of the cycle, so necessary control measures need to be taken for the CO2 heat pump to optimize its operating state to achieve the goal of high efficiency and energy saving. In daily use, the operating mode of the CO2 heat pump water heater can be divided into direct heating mode and circulating heating mode. In the circulating heating mode, the water inlet temperature of the CO2 heat pump is constantly rising, which will cause the operating condition to deteriorate, resulting in a decrease in system operating efficiency and a decline in energy efficiency performance. However, the existing control optimization method is mainly applied to the CO2 heat pump water heater operating in the direct heating mode, and there is still a lack of control method and optimization strategy for the CO2 heat pump water heater in the circulating mode. SUMMARY

[0004] The present application provides a control method of a CO2 heat pump system in a circulating heating mode, and the technical purpose is to make the CO2 heat pump system achieve an optimal cycle state, improve system energy efficiency and reduce energy consumption.

[0005] The above technical purpose of the present application is achieved by the following technical scheme:

[0006] A control method of a CO2 heat pump system in a circulating heating mode, the control method is used in a CO2 heat pump system, the CO2 heat pump system comprises a compressor, an air cooler, an electronic expansion valve, an evaporator, a gas-liquid separator, a heat storage water tank, a water pump, a first valve, a second valve, a third valve, an inlet water temperature probe, an outlet water temperature probe, a heat storage water tank temperature probe and a controller; the compressor exhaust port is connected with the air cooler refrigerant side inlet, the compressor suction port is connected with the gas-liquid separator outlet, the gas-liquid separator inlet is connected with the evaporator refrigerant side outlet, the electronic expansion valve inlet is connected with the air cooler refrigerant side outlet, and the electronic expansion valve outlet is connected with the evaporator refrigerant side inlet; the heat storage water tank comprises two water inlets and one water outlet, one water inlet is connected with the air cooler water outlet and is provided with the first valve in the pipeline, the other water inlet is used for external water supplement demand and is provided with the second valve on the pipeline, and the water outlet is connected with the air cooler water inlet and is provided with the water pump therebetween; the third valve is installed on the user side pipeline, and the user side pipeline is connected with the air cooler water outlet; the inlet water temperature probe, the outlet water temperature probe and the heat storage water tank temperature probe are arranged at the air cooler water inlet and water outlet and in the heat storage water tank respectively; the controller is used for collecting signals of the inlet water temperature probe, the outlet water temperature probe and the heat storage water tank temperature probe and sending control signals to the electronic expansion valve, and the method comprises the following steps:

[0007] S1: starting the circulating heating mode, setting a target temperature in the heat storage water tank, and monitoring whether the current water temperature in the heat storage water tank reaches the target temperature by the controller; if yes, the CO2 heat pump system is not controlled to run; if not, the CO2 heat pump system is controlled to start running;

[0008] S2: collecting the temperatures of the air cooler water inlet and water outlet by the controller, and judging the current running stage of the CO2 heat pump system after the CO2 heat pump system starts running;

[0009] S3: if the air cooler water inlet temperature is in a stable stage, adjusting the opening degree of the electronic expansion valve once by the controller; if the air cooler water inlet temperature is in a rising stage, adjusting the opening degree of the electronic expansion valve according to a fixed control frequency by the controller; wherein the opening degree of the electronic expansion valve is determined by an optimal opening degree function each time;

[0010] S4: judging whether the water temperature in the heat storage water tank reaches the target temperature by the controller; if yes, stopping heating; if not, returning to step S2 until the water temperature in the heat storage water tank reaches the target temperature.

[0011] Further, in step S2, the current running stage of the CO2 heat pump system is judged, comprising:

[0012] the air cooler water inlet temperature change amount ΔT in a 60-second time period wgi,60The ratio of this time period, i.e. r = (ΔT wgi,60 ) / 60, when r≤0.01, the CO2 heat pump system is in a stable stage; when r>0.01, the CO2 heat pump system is in a rising stage.

[0013] Further, the fixed regulation frequency comprises: the water inlet temperature variation ΔT wgi When 0.5℃≤ΔT wgi ≤1℃ is met, the controller performs one-time adjustment on the electronic expansion valve opening degree.

[0014] Further, the optimal opening degree function is expressed as: E o =f(T wgi ,T wgo ); wherein E o represents the optimal opening degree of the electronic expansion valve each time adjustment, T wgi represents the water inlet temperature of the air cooler, and T wgo represents the water outlet temperature of the air cooler.

[0015] Further, the operation mode of the CO2 heat pump system comprises a direct heating mode and a circulating heating mode.

[0016] When the CO2 heat pump system is in the direct heating mode, the second valve and the third valve are both in an open state, the first valve remains closed, and the water flow direction in the pipeline is: the water supplement is transported to the air cooler by the water pump after passing through the heat storage water tank for heating, and then directly enters the user side pipeline.

[0017] When the CO2 heat pump system is in the circulating heating mode, the third valve remains closed, the water amount in the heat storage water tank is maintained in a normal range through the water supplement pipeline, then the second valve is closed and the first valve is opened, and the water flow direction in the pipeline is: the stored water in the heat storage water tank is heated by the water pump to the air cooler, and then returns to the heat storage water tank again, maintaining the circulating heating state until the water temperature in the heat storage water tank reaches the target temperature.

[0018] Further, the air cooler is a counterflow double-pipe heat exchanger, and the evaporator comprises a counterflow double-pipe heat exchanger and a finned heat exchanger.

[0019] The application has the following beneficial effects:

[0020] (1) This application regulates the dynamic operation of a CO2 heat pump system in cyclic heating mode, improving overall operating efficiency while reducing overall power consumption. Because the operating conditions of the system deteriorate due to the continuous change in the inlet water temperature of the air cooler, in order to prevent the real-time performance of the CO2 heat pump from declining, the system operating state is adjusted multiple times according to the optimal opening degree corresponding to different inlet and outlet water temperatures of the air cooler. This ensures that the CO2 heat pump system remains in the optimal cyclic state when the operating conditions change dynamically, thereby improving the performance of the entire cyclic heating process and enhancing overall energy efficiency.

[0021] (2) This application utilizes the optimal opening function correlation as the control method, which can meet the multiple control requirements brought about by real-time changes in operating conditions and ensure the ease of use and implementability of the control method. During the control process, since the real-time data only requires the inlet and outlet water temperatures of the air cooler, the data volume is low, and the calculation of the optimal opening takes less time, which can meet the high-frequency control operation when the operating conditions are constantly changing. The optimal opening function correlation requires fewer temperature variables, which reduces the number of temperature measuring points installed in the system, which is conducive to reducing the system manufacturing cost and is more beneficial to the promotion and application of this method. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the CO2 heat pump system in an embodiment of this application;

[0023] In the diagram: 1-Compressor; 2-Air cooler; 3-Electronic expansion valve; 4-Evaporator; 5-Gas-liquid separator; 6-Hot water storage tank; 7-Water pump; 8-Valve No. 1; 9-Valve No. 2; 10-Valve No. 3; 11-Inlet water temperature probe; 12-Outlet water temperature probe; 13-Hot water storage tank temperature probe; 14-Controller. Detailed Implementation

[0024] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0025] like Figure 1 As shown, the CO2 heat pump system with a hot water storage tank includes a compressor 1, an air cooler 2, an electronic expansion valve 3, an evaporator 4, a gas-liquid separator 5, a hot water storage tank 6, a water pump 7, a first valve 8, a second valve 9, a third valve 10, an inlet water temperature probe 11, an outlet water temperature probe 12, a hot water storage tank temperature probe 13, and a controller 14.

[0026] The discharge port of compressor 1 is connected to the refrigerant side inlet of air cooler 2, the suction port of compressor 1 is connected to the outlet of gas-liquid separator 5, the inlet of gas-liquid separator 5 is connected to the refrigerant side outlet of evaporator 4, the inlet of electronic expansion valve 3 is connected to the refrigerant side outlet of air cooler 2, and the outlet of electronic expansion valve 3 is connected to the refrigerant side inlet of evaporator 4.

[0027] The heat storage water tank 6 comprises two water inlets and one water outlet, one of the water inlets is connected with the water outlet of the air cooler 2 and a first valve 8 is arranged in the pipeline of the water inlet, the other water inlet is used for external water supplement and a second valve 9 is arranged in the pipeline of the water inlet, and the water outlet is connected with the water inlet of the air cooler 2 and a water pump 7 is arranged between the water outlet and the water inlet.

[0028] The first valve 8, the second valve 9 and the third valve 10 are arranged in the pipeline of the heat storage water tank 6, and a water inlet temperature probe 11, a water outlet temperature probe 12 and a heat storage water tank temperature probe 13 are arranged at the water inlet and the water outlet of the third valve 10 and in the heat storage water tank 6 respectively, and a controller 14 is used for collecting signals of the water inlet temperature probe 11, the water outlet temperature probe 12 and the heat storage water tank temperature probe 13 and sending control signals to the electronic expansion valve 3.

[0029] Figure 1 In the figure, the solid line represents the direct heating mode of the CO2 heat pump system, and the dashed line represents the circulating heating mode of the CO2 heat pump system.

[0030] When the CO2 heat pump system is in the direct heating mode, the second valve 9 and the third valve 10 are both opened, and the first valve 8 is kept closed, and the flow direction of water in the pipeline is that the water supplement is transported to the air cooler 2 by the water pump 7 after passing through the heat storage water tank 6, and then directly enters the user side pipeline after being heated in the air cooler 2.

[0031] When the CO2 heat pump system is in the circulating heating mode, the third valve 10 is kept closed, the water amount in the heat storage water tank 6 is maintained in a normal range through the water supplement pipeline, then the second valve 9 is closed and the first valve 8 is opened, and the flow direction of water in the pipeline is that the stored water in the heat storage water tank 6 is heated in the air cooler 2 by the water pump 7 and then returns to the heat storage water tank 6 again, and the circulating heating state is maintained until the water temperature in the heat storage water tank 6 reaches the target temperature.

[0032] Based on the above CO2 heat pump system and operation modes, the control method of the CO2 heat pump system in the circulating heating mode comprises the following steps.

[0033] S1: opening the circulating heating mode, setting the target temperature in the heat storage water tank 6, and monitoring whether the current water temperature in the heat storage water tank 6 reaches the target temperature by the controller 14, if yes, controlling the CO2 heat pump system not to run, if no, controlling the CO2 heat pump system to start running.

[0034] S2: collecting the temperatures of the water inlets and outlets of the air cooler 2 by the controller 14, and judging the stage of the current operation of the CO2 heat pump system after the CO2 heat pump system starts running.

[0035] Specifically, judging the stage of the current operation of the CO2 heat pump system comprises that the change amount ΔT wgi,60The ratio of this time period, i.e. r = (ΔT wgi,60 ) / 60, when r≤0.01, the CO2 heat pump system is in a stable stage; when r>0.01, the CO2 heat pump system is in a rising stage.

[0036] S3: If the water inlet temperature of the air cooler 2 is in a stable stage, the controller 14 adjusts the opening degree of the electronic expansion valve 3 once to ensure that the CO2 heat pump system maintains the optimal operating state in this stage; if the water inlet temperature of the air cooler 2 is in a rising stage, the controller 14 adjusts the opening degree of the electronic expansion valve 3 according to a fixed control frequency, so as to achieve a multiple optimization effect. The opening degree of the electronic expansion valve 3 is determined by an optimal opening degree function each time.

[0037] Specifically, the fixed control frequency is represented as: the water inlet temperature change amount ΔT wgi in the same time period. wgi When 0.5℃≤ΔT wgi ≤1℃, the controller 14 adjusts the opening degree of the electronic expansion valve 3 once.

[0038] The optimal opening degree function takes the opening degree of the electronic expansion valve corresponding to the optimal cycle state of the CO2 heat pump system as a target value, and the water inlet temperature and the water outlet temperature of the air cooler as independent variable function correlation formula, which is represented as: E o =f(T wgi ,T wgo ); wherein, E o represents the optimal opening degree of the electronic expansion valve each time, T wgi represents the water inlet temperature of the air cooler, and T wgo represents the water outlet temperature of the air cooler. The specific control relationship is obtained by limited experiments according to the quantitative relationship and the above function for different water inlet temperatures and water outlet temperatures of the air cooler.

[0039] Those skilled in the art can understand that the above description is only preferred embodiments of the present application, and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, and those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A control method of a CO2 heat pump system in a circulating heating mode, the control method being used in a CO2 heat pump system comprising a compressor (1), an air cooler (2), an electronic expansion valve (3), an evaporator (4), a gas-liquid separator (5), a heat storage water tank (6), a water pump (7), a first valve (8), a second valve (9), a third valve (10), a water inlet temperature probe (11), a water outlet temperature probe (12), a heat storage water tank temperature probe (13) and a controller (14); the compressor (1) is connected with the refrigerant side inlet of the air cooler (2), the suction port of the compressor (1) is connected with the outlet of the gas-liquid separator (5), the inlet of the gas-liquid separator (5) is connected with the refrigerant side outlet of the evaporator (4), the inlet of the electronic expansion valve (3) is connected with the refrigerant side outlet of the air cooler (2), and the outlet of the electronic expansion valve (3) is connected with the refrigerant side inlet of the evaporator (4); the heat storage water tank (6) comprises two water inlets and one water outlet, one water inlet is connected with the water outlet of the air cooler (2) and is provided with the first valve (8) in the pipeline, and the other water inlet is used for external water supplement demand and is provided with the second valve (9) in the pipeline, and the water outlet is connected with the water inlet of the air cooler (2) and is provided with the water pump (7) therebetween; the third valve (10) is installed on the user side pipeline, and the user side pipeline is connected with the water outlet of the air cooler (2); the water inlet temperature probe (11), the water outlet temperature probe (12) and the heat storage water tank temperature probe (13) are arranged at the water inlets and outlets of the air cooler (2) and in the heat storage water tank (6), respectively; the controller (14) is used for collecting signals of the water inlet temperature probe (11), the water outlet temperature probe (12) and the heat storage water tank temperature probe (13) and sending a control signal to the electronic expansion valve (3), characterized in that, The method comprises: S1: starting a circulating heating mode, setting a target temperature in the heat storage water tank (6), and monitoring whether the water temperature in the current heat storage water tank (6) reaches the target temperature by the controller (14), if yes, controlling the CO2 heat pump system not to run, if no, controlling the CO2 heat pump system to start running; S2: collecting the temperature of the water inlet and outlet of the air cooler (2) by the controller (14), and judging the stage of the current running of the CO2 heat pump system after the CO2 heat pump system starts running; S3: if the water inlet temperature of the air cooler (2) is in a stable stage, adjusting the opening of the electronic expansion valve (3) by the controller (14) once; if the water inlet temperature of the air cooler (2) is in a rising stage, adjusting the opening of the electronic expansion valve (3) according to a fixed control frequency by the controller (14); wherein the opening size of the electronic expansion valve (3) is determined by an optimal opening function each time; S4: judging whether the water temperature in the heat storage water tank (6) reaches the target temperature by the controller (14), if yes, stopping heating, if no, returning to step S2 until the water temperature in the heat storage water tank (6) reaches the target temperature; The fixed control frequency comprises: a water inlet temperature variation ΔT in a same time period wgi When 0.5℃≤ΔT wgi ≤1℃, the controller (14) performs one-time adjustment on the opening of the electronic expansion valve (3). The optimal opening degree function is expressed as: E o = f(T wgi , T wgo ); wherein E o represents the optimal opening degree of the electronic expansion valve for each adjustment, T wgi represents the inlet water temperature of the air cooler, and T wgo represents the outlet water temperature of the air cooler.

2. The method of claim 1, wherein, In step S2, the stage of the current running of the CO2 heat pump system is judged, comprising: The amount of change in the water temperature of the gas cooler (2) in a 60-second period ΔT wgi,60 The ratio to this period, i.e. r = (ΔT wgi,60 ) / 60, when r ≤ 0.01, the CO2 heat pump system is in a stable phase; when r > 0.01, the CO2 heat pump system is in a rising phase.

3. The method of claim 1, wherein, The operation mode of the CO2 heat pump system comprises a direct heating mode and a circulating heating mode; When the CO2 heat pump system is in the direct heating mode, the second valve (9) and the third valve (10) are both in an open state, the first valve (8) remains closed, and the flow direction of water in the pipeline is: the water supplement passes through the heat storage water tank (6), is transported to the air cooler (2) by the water pump (7) for heating, and then directly enters the user side pipeline; When the CO2 heat pump system is in the circulating heating mode, the third valve (10) remains closed, the water amount in the heat storage water tank (6) is maintained in a normal range through the water supplement pipeline, then the second valve (9) is closed, the first valve (8) is opened, and the flow direction of water in the pipeline is: the stored water in the heat storage water tank (6) is heated by the water pump (7) to the air cooler (2), and then returns to the heat storage water tank (6) again, maintaining the circulating heating state until the water temperature in the heat storage water tank (6) reaches the target temperature.

4. The method of claim 1, wherein, The air cooler (2) is a counterflow double-pipe heat exchanger, and the evaporator (4) comprises a counterflow double-pipe heat exchanger and a finned heat exchanger.

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