A control method of an electronic expansion valve of an EVI system of a low-temperature air source heat pump unit

Abstract

The present application relates to air source heat pump technical field, specifically to a kind of low-temperature air source heat pump unit EVI system electronic expansion valve control method.Equipment includes first electronic expansion valve, second electronic expansion valve, set on the fin temperature bulb of air side heat exchanger, set on the evaporation temperature bulb of water side heat exchanger, outlet water temperature bulb, detect ambient temperature Th and return water temperature Ts by fin temperature bulb, outlet water temperature bulb, evaporation temperature bulb is used to detect exhaust temperature, detect exhaust temperature Tp, if Tp>Tmax, second electronic expansion valve opening degree is controlled according to exhaust overhigh;If Tmin≤Tp≤Tmax, then enter step 5;If Tp<Tmin, then cycle step 3;Wherein Tmax It is the maximum value set, Tmin It is the minimum value set, Tmax-Tmin≥10 ℃.Through setting ambient temperature Thset and return water temperature Tsset control, the control of electronic expansion valve in low-temperature environment is solved, the problem that equipment often appears control fluctuation without attention of the person skilled in the art is solved.

Description

Technical Field

[0001] This invention relates to the field of air source heat pump technology, and specifically to a method for controlling the electronic expansion valve of an EVI system in a low-temperature air source heat pump unit. Background Technology

[0002] To improve energy efficiency and achieve economic and environmental benefits, air source heat pumps are receiving increasing attention and application. In northern my country, where winter outdoor temperatures are low, traditional air source heat pumps struggle to adapt to low-temperature conditions. This is primarily because excessively high compressor exhaust temperatures can disrupt their normal operation in such environments. Chinese patent CN113432336A discloses a "vapor injection enthalpy-increasing air source heat pump system and dynamic exhaust superheat control method," which addresses the problem in existing technologies where maintaining the same exhaust superheat under different operating conditions fails to maximize system efficiency; that is, the exhaust superheat does not continuously change with operating conditions. This achieves optimal energy efficiency for ultra-low temperature air source heat pump systems under varying ambient and water temperatures.

[0003] However, for low-temperature air-source heat pump units with EVI (Emission Enthalpy) systems, under low ambient and water temperature conditions, the exhaust temperature is low due to the low water temperature. For example, the electronic expansion valve opens when the exhaust temperature is ≥50℃ and closes when the exhaust temperature is <50℃. If the exhaust temperature reaches the critical point of 50℃, the auxiliary electronic expansion valve may open and close repeatedly, causing exhaust temperature fluctuations and fluctuations in the overall heating capacity of the unit, resulting in system stability issues. The usual solution to this problem is to disable the auxiliary electronic expansion valve. However, this directly reduces the unit's heating capacity and overall energy efficiency. Summary of the Invention

[0004] To address at least one of the technical problems existing in the prior art, such as the auxiliary electronic expansion valve opening and closing repeatedly at the exhaust temperature critical point, resulting in exhaust temperature fluctuations, this invention provides a method for controlling the electronic expansion valve of the EVI system in a low-temperature air source heat pump unit.

[0005] This patent discloses a method for controlling the electronic expansion valve of an EVI system in a low-temperature air-source heat pump unit. The unit includes a first electronic expansion valve, a second electronic expansion valve, a finned temperature sensor mounted on the air-side heat exchanger, an evaporation temperature sensor mounted on the water-side heat exchanger, and an outlet water temperature sensor. The finned temperature sensor and the outlet water temperature sensor detect the ambient temperature Th and the return water temperature Ts. The evaporation temperature sensor detects the exhaust temperature. Controlling the unit includes the following steps:

[0006] Step 1: Start the unit and begin heating operation;

[0007] Step 2: Detect the ambient temperature and return water temperature. If the ambient temperature Th ≤ the set temperature Thset and the return water temperature Ts ≤ the set temperature Tsset, proceed to the next step; otherwise, proceed to step 5.

[0008] Step 3: Adjust the opening of the first electronic expansion valve according to the target superheat.

[0009] Step 4: Control the second electronic expansion valve to open, maintain the set time T and set opening degree K, and then proceed to step 5;

[0010] Step 5: Detect the exhaust temperature Tp. If Tp > Tmax, the opening of the second electronic expansion valve is controlled according to the exhaust overheating control. If Tmin ≤ Tp ≤ Tmax, proceed to step 5. If Tp < Tmin, repeat step 3. Where Tmax is the set maximum value, Tmin is the set minimum value, and Tmax - Tmin ≥ 10℃.

[0011] Step 6: The opening degree of the first electronic expansion valve 4 is adjusted according to the target superheat, and the opening degree of the second electronic expansion valve is controlled according to the fixed opening degree corresponding to the ambient temperature and return water temperature.

[0012] Step 3 can be interchanged with step 2.

[0013] This application controls the electronic expansion valve in low-temperature environments by setting the ambient temperature Thset and the return water temperature Tsset, which solves the problem of control fluctuations that are often overlooked by those skilled in the art. This makes the unit operate stably and improves the unit's heating capacity and overall energy efficiency.

[0014] As a preferred embodiment, a method for controlling the electronic expansion valve of an EVI system in a low-temperature air source heat pump unit is characterized in that: in step 2, Thset≤-20℃, Tsset≤20℃.

[0015] As a preferred embodiment, a method for controlling the electronic expansion valve of an EVI system in a low-temperature air source heat pump unit is characterized in that: in step 3, after the second electronic expansion valve is opened, the set time T is maintained at 5 min to 15 min, and the opening degree K is 30 pls to 80 pls.

[0016] As a preferred embodiment, a method for controlling the electronic expansion valve of a low-temperature air source heat pump unit EVI system is characterized in that: after the second electronic expansion valve is opened, it is maintained for a set time of 10 minutes and the opening degree is 50pls.

[0017] As a preferred embodiment, a method for controlling the electronic expansion valve of an EVI system in a low-temperature air source heat pump unit is characterized in that: in step 4, the value range of Tmin is 70-80℃, and the value range of Tmax is 90-100℃.

[0018] As a preferred embodiment, a method for controlling the electronic expansion valve of an EVI system in a low-temperature air source heat pump unit is characterized in that: in step 4, Tmin is 70°C and Tmax is 95°C. Attached Figure Description

[0019] Figure 1 This is a low-temperature air source heat pump unit EVI system.

[0020] Figure 2 This is a flowchart of the electronic expansion valve control method.

[0021] The image is labeled as follows:

[0022] 1-Compressor, 2-Four-way reversing valve, 3-Air-side heat exchanger, 31-Finned temperature sensor, 32-Axial flow fan, 4-First electronic expansion valve, 5-Economizer, 6-Liquid receiver, 7-Water-side heat exchanger, 71-Evaporation temperature sensor, 8-Second electronic expansion valve, 9-Gas-liquid separator, 10-Water temperature sensor, 11-Outlet water temperature sensor, 101-Temperature sensing device, 102-High-pressure switch, 103-High-pressure sensor. Detailed Implementation

[0023] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0024] This invention discloses a method for controlling the electronic expansion valve of an EVI system in a low-temperature air-source heat pump unit. The EVI system includes a compressor 1, a four-way reversing valve 2, an air-side heat exchanger 3, a first electronic expansion valve 4, an economizer 5, a liquid receiver 6, a water-side heat exchanger 7, a second electronic expansion valve 8, and a gas-liquid separator 9. The compressor 1 is connected to the four-way reversing valve 2, and a temperature sensing device 101, a high-pressure switch 102, and a high-pressure sensor 103 are installed on the connecting pipe.

[0025] In this embodiment, the vapor injection enthalpy-enhancing air source heat pump system is abbreviated as EVI system, also known as Economist 5 (or flash evaporator, intercooler) system, and its refrigerant circulation diagram is shown in [reference needed]. Figure 1 The process is as follows:

[0026] 1. Refrigeration cycle system: The refrigerant flows as shown by the arrow in the diagram: After being compressed by the compressor to form a high-temperature, high-pressure refrigerant, the refrigerant enters the air-side heat exchanger 3 through the four-way reversing valve 2. Under the action of the axial flow fan 32, it rapidly exchanges heat with the air and then becomes a medium-temperature, high-pressure liquid. Then, it enters the economizer 5 and the liquid receiver 6 through the first electronic expansion valve 4, becoming a low-temperature, low-pressure liquid. Then, it enters the water-side heat exchanger 7 for refrigeration, becoming a low-temperature, low-pressure gas. Finally, the refrigerant returns to the compressor through the four-way reversing valve 2 to continue the cycle, thus achieving refrigeration.

[0027] 2. Heating circulation system: The refrigerant flows as shown by the arrow in the diagram: After being compressed by the compressor to form a high-temperature, high-pressure refrigerant, the refrigerant enters the water inlet heat exchanger 7 through the four-way reversing valve 2, absorbing cold and releasing heat to become a medium-temperature, high-pressure liquid; then it passes sequentially through the liquid receiver 6, the economizer 5, and the first electronic expansion valve 4, becoming a low-temperature, low-pressure liquid; then it enters the air-side heat exchanger 3, where it rapidly exchanges heat with the air under the action of the axial flow fan 32, absorbing heat and releasing cold to become a low-temperature, low-pressure gas; then, the refrigerant returns to the compressor through the four-way reversing valve 2 to continue the circulation, thus achieving heating.

[0028] Economizer 5 is a heat exchanger that controls the auxiliary refrigerant flow rate via a second electronic expansion valve 8. Through heat exchange between the main and auxiliary refrigerants, the main refrigerant is subcooled, increasing the system's subcooling degree and thus enhancing heat exchange capacity. In this embodiment, during heating or cooling cycles, the second electronic expansion valve 8 controls the auxiliary flow rate of economizer 5 along the circulation path. Specifically, as follows... Figure 1 As shown, taking the heating cycle as an example, one end of the auxiliary circuit of the economizer 5 is connected between the economizer 5 and the liquid receiver 6. After passing through the liquid receiver 6, the refrigerant branches through the second electronic expansion valve 8 and enters the auxiliary circuit of the economizer 5 to subcool the refrigerant in the main circuit, and then enters the compressor.

[0029] The control method of the auxiliary second electronic expansion valve 8 of the air source heat pump unit under low ambient temperature and low water temperature (generally, low ambient temperature is below -10 degrees Celsius and low water temperature is below 25 degrees Celsius) is to adjust the opening of the main first electronic expansion valve 4 according to the target return gas superheat and adjust the exhaust temperature through the second electronic expansion valve 8.

[0030] A finned temperature sensor 31 is installed in the air-side heat exchanger 3, and an evaporation temperature sensor 71 is installed in the water-side heat exchanger 7. An inlet water temperature sensor 10 and an outlet water temperature sensor 11 are also installed.

[0031] According to the heating cycle system of this patent, after the unit starts up, the ambient temperature Th and return water temperature Ts are detected by the finned temperature sensor 31 and the outlet water temperature sensor 11, and the evaporation temperature sensor 71 is used to detect the exhaust temperature Tp. If the ambient temperature Th ≤ Thset (e.g., -20℃) and the return water temperature Ts ≤ Tsset (e.g., 20℃), the first electronic expansion valve 4 and the second electronic expansion valve 8 of the unit are controlled as follows:

[0032] Step 1: Start the unit and begin heating operation;

[0033] Step 2: Detect the ambient temperature and return water temperature. If the ambient temperature Th≤Thset and the return water temperature Ts≤Tsset, proceed to the next step; otherwise, proceed to step 6.

[0034] Step 3: Adjust the opening of the first electronic expansion valve 4 according to the target superheat.

[0035] Step 4: Control the second electronic expansion valve 8 to open, maintain the set time T and the minimum set opening degree K, and then proceed to step 5;

[0036] As a preferred embodiment, after the second electronic expansion valve 8 is opened, it is maintained for a set time T of 5 to 15 minutes, and the opening degree K is 30 to 80 pls. In this embodiment, after the second electronic expansion valve 8 is opened, it is maintained at a minimum opening degree of 50 pls for 10 minutes before proceeding to step 4. Maintaining the second electronic expansion valve at a minimum opening degree of 50 pls for 10 minutes allows the unit to quickly pass through the low ambient temperature and low water temperature fluctuation state. The purpose of maintaining the time and opening degree is to stabilize the system, because the exhaust temperature rises relatively slowly at low water temperatures; maintaining the temperature for a period of time before control is implemented prevents fluctuations.

[0037] Step 5: Detect the exhaust temperature Tp. If Tp > Tmax, the opening of the second electronic expansion valve 8 is controlled according to the exhaust overheat control. If Tmin ≤ Tp ≤ Tmax, proceed to step 5. If Tp < Tmin, repeat step 3. Where Tmax is the set maximum value, Tmin is the set minimum value, and Tmax - Tmin ≥ 10℃.

[0038] Step 6: The opening degree of the first electronic expansion valve 4 is adjusted according to the target superheat, and the opening degree of the second electronic expansion valve 8 is controlled according to the fixed opening degree corresponding to the ambient temperature and return water temperature.

[0039] In step 2, Thset ≤ -20℃ and Tsset ≤ 20℃. Under this ring condition, the unit is prone to critical temperature fluctuations, and this problem exists in existing low-temperature air source heat pump unit EVI systems.

[0040] Through extensive experiments, in step 4, the value range of Tmin is 70-80℃, and the value range of Tmax is 90-100℃. An exhaust temperature above 70℃ ensures reasonable exhaust superheat in the system, which is beneficial to system stability; at the same time, it cannot be too high to protect the compressor and prevent exhaust protection shutdown.

[0041] In some embodiments, in step 4, Tmin is 70°C and Tmax is 95°C.

[0042] According to the exhaust over-pressure control, the second electronic expansion valve 8 of the auxiliary road is gradually opened until the maximum opening degree of 480pls. This is a conventional control method for the second electronic expansion valve 8.

[0043] Superheat refers to the temperature at the intake temperature sensor minus the temperature at the evaporation temperature sensor. Adjustment based on the target superheat is performed by adjusting and controlling the relationship between the pre-set superheat temperature of the unit and the opening degree of the first electronic expansion valve 4.

[0044] In this embodiment, 70℃-95℃ is optimal, and optimal control may occur at 80-100℃ in some units. The opening degree of the second electronic expansion valve 8 is adjusted according to a fixed value corresponding to the return water temperature. The current control logic is to fix one opening degree of the second electronic expansion valve 8 for each return water temperature. The table below shows the corresponding fixed opening degree control of the second electronic expansion valve 8 of the applicant's 7P air source heat pump product with ambient temperature and return water temperature.

[0045]

[0046] Note: "X" represents different opening values ​​set by the second electronic expansion valve 8. Different manufacturers' air source heat pump products have their own different setting values. The value of X is not disclosed by the applicant in this patent. In some products, it can also be set as a function relationship, which all belong to the prior art.

[0047] The following embodiments are illustrative of the present invention, but the present invention is not limited to the following embodiments.

[0048] The ambient temperature setting threshold Thset and return water temperature setting threshold Tsset in this invention are not fixed and can be adjusted accordingly based on different units or systems. During the electronic expansion valve adjustment process, the opening degree is limited by the maximum and minimum opening degrees set by the unit.

[0049] Problem solved: By controlling the electronic expansion valve in low-temperature environments through setting the ambient temperature Thset and return water temperature Tsset, the problem of control fluctuations that often occur in units, which has not been addressed by those skilled in the art, was resolved. This also solves the problem of fluctuating exhaust temperature and heating capacity caused by the repeated opening and closing of the second electronic expansion valve 8 during operation of the EVI system in low-temperature air source heat pump units at low ambient and low water temperatures.

[0050] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for controlling the electronic expansion valve of an EVI system for a low-temperature air source heat pump unit, wherein the unit includes a first electronic expansion valve (4), a second electronic expansion valve (8), a finned temperature sensor (31) installed on an air-side heat exchanger (3), an evaporation temperature sensor (71) installed on a water-side heat exchanger (7), and an outlet water temperature sensor (11). The ambient temperature Th and the return water temperature Ts are detected by the finned temperature sensor (31) and the outlet water temperature sensor (11), and the evaporation temperature sensor (71) is used to detect the exhaust temperature. The unit includes a refrigerant circulation main circuit, where the compressor (1) discharges and returns gas to the D and S ports of the four-way valve (2). The E port of the four-way valve (2), the air-side heat exchanger (3), the first electronic expansion valve (4), the economizer (5), the water-side heat exchanger (7), and the C port of the four-way valve (2) are connected in sequence through pipelines to form the refrigerant circulation main circuit. It also includes a refrigerant auxiliary circuit, one end of which is connected between the economizer (5) and the water-side heat exchanger (7). The refrigerant auxiliary circuit enters the economizer (5) through the second electronic expansion valve (8) and then enters the compressor. The control of the unit includes the following steps: Step 1: Start the unit and begin heating operation; Step 2: Detect the ambient temperature and return water temperature. If the ambient temperature Th ≤ the set temperature Thset and the return water temperature Ts ≤ the set temperature Tsset, proceed to the next step; otherwise, proceed to step 6. Step 3: Adjust the opening of the first electronic expansion valve (4) according to the target superheat. Step 4: The second electronic expansion valve (8) is opened and maintained at the set opening time T and the set opening degree K; Step 5: Detect the exhaust temperature Tp. If Tp > Tmax, the opening of the second electronic expansion valve (8) is controlled according to the exhaust temperature. If Tmin ≤ Tp ≤ Tmax, proceed to step 6. If Tp < Tmin, repeat step 3. Where Tmax is the set maximum value and Tmin is the set minimum value. Tmax - Tmin ≥ 10℃. Step 6: The opening degree of the first electronic expansion valve (4) is adjusted according to the target superheat, and the opening degree of the second electronic expansion valve (8) is controlled according to the fixed opening degree corresponding to the ambient temperature and the return water temperature; Step 3 can be interchanged with step 2.

2. The electronic expansion valve control method for a low-temperature air source heat pump unit EVI system according to claim 1, characterized in that: In step 2, Thset ≤ -20℃ and Tsset ≤ 20℃.

3. The electronic expansion valve control method for a low-temperature air source heat pump unit EVI system according to claim 1, characterized in that: In step 3, after the second electronic expansion valve (8) is opened, the set time T is maintained at 5 min to 15 min and the opening degree K is 30 pls to 80 pls.

4. The electronic expansion valve control method for a low-temperature air source heat pump unit EVI system according to claim 3, characterized in that: After the second electronic expansion valve (8) is opened, it is maintained for a set time of 10 minutes and the opening degree is 50pls.

5. The electronic expansion valve control method for a low-temperature air source heat pump unit EVI system according to claim 1, characterized in that: In step 4, the value of Tmin ranges from 70 to 80℃, and the value of Tmax ranges from 90 to 100℃.

6. The electronic expansion valve control method for a low-temperature air source heat pump unit EVI system according to claim 5, characterized in that: In step 4, Tmin is 70℃ and Tmax is 95℃.

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