An EVI low-temperature heat pump device and its control method

Abstract

This invention discloses an EVI (Electronic Ventilation and Refrigerant) low-temperature heat pump device and its control method. The EVI low-temperature heat pump device includes a compressor, a four-way reversing valve, a water-side heat exchanger, a liquid receiver, an economizer, a main electronic expansion valve, an air-side heat exchanger, and a gas-liquid separator, connected in sequence to form the refrigerant main circuit. When the EVI low-temperature heat pump device is in heating mode, if the exhaust temperature is too high, the amount of gas supplied is increased by closing the main electronic expansion valve and opening the auxiliary electronic expansion valve when the auxiliary electronic expansion valve is open, thereby reducing the exhaust temperature. When the auxiliary electronic expansion valve is closed, the return gas superheat is reduced by opening the main electronic expansion valve, thereby reducing the exhaust temperature. This invention uses liquid to be taken after the economizer for gas supply and enthalpy increase, which can avoid the situation where liquid cannot be taken in traditional systems. When the exhaust temperature is high, different control methods are used depending on whether the auxiliary electronic expansion valve is open or closed, to achieve the purpose of reducing the exhaust temperature.

Description

Technical Field

[0001] This invention relates to an EVI low-temperature heat pump device and its control method. Background Technology

[0002] In recent years, heat pump heating technology, represented by low ambient temperature air source heat pumps, has developed rapidly. The market demand for high water temperatures poses a significant challenge to the long-term reliability of air source heat pump products. Low-temperature heat pumps, when heating at high outlet water temperatures, are prone to excessively high exhaust temperatures, affecting unit reliability.

[0003] There are currently three main technologies for solving the problem of excessively high exhaust temperature in heat pumps. The first is to appropriately open the throttle valve to reduce the superheat of the return gas and thus lower the exhaust temperature. However, this method may cause liquid slugging in the return gas, resulting in poor reliability. The second is liquid injection cooling, where the auxiliary circuit takes liquid from the condenser outlet, throttles it through the throttle valve, and then enters the compressor's liquid injection port. However, the heat pump capacity and efficiency of liquid injection cooling are relatively low. The third is liquid intake before enthalpy boosting, where the auxiliary circuit takes liquid from the condenser outlet, throttles it through the throttle valve, and then exchanges heat with the main circuit through the economizer. The superheated gas is then drawn into the compressor's injection port. The injection enthalpy boosting method has good efficiency at low temperatures, but it is prone to insufficient injection volume, resulting in a still high exhaust temperature. In addition, the electronic expansion valve is usually controlled with a fixed number of steps, and the exhaust control only considers the water temperature, not the condensing temperature. When the exhaust temperature is too high, it cannot be reduced quickly, leading to a shortened compressor life. Summary of the Invention

[0004] To address the above problems, the present invention provides an EVI low-temperature heat pump device and its control method, which effectively solves the problems pointed out in the background art.

[0005] The technical solution adopted in this invention is:

[0006] An EVI low-temperature heat pump unit includes a compressor, a four-way reversing valve, a water-side heat exchanger, a liquid receiver, an economizer, a main circuit electronic expansion valve, an air-side heat exchanger, and a gas-liquid separator, connected in sequence to form a refrigerant main circuit; wherein:

[0007] The four-way reversing valve includes control valve port D, control valve port S, control valve port E, and control valve port C. The compressor's discharge port is connected to control valve port D. Control valve port C is connected to the refrigerant inlet of the water-side heat exchanger. The refrigerant outlet of the water-side heat exchanger is connected to one end of the liquid receiver. The other end of the liquid receiver is connected to the fourth port of the economizer. Control valve port S is connected to the inlet of the gas-liquid separator. The outlet of the gas-liquid separator is connected to the compressor's suction port. Control valve port E is connected to the first port of the air-side heat exchanger. The second port of the air-side heat exchanger is connected to one end of the main electronic expansion valve. The other end of the main electronic expansion valve is connected to the second port of the economizer.

[0008] A first auxiliary pipeline is connected between the main electronic expansion valve and the second port of the economizer. The other end of the first auxiliary pipeline is connected to the first port of the economizer. An auxiliary electronic expansion valve is installed on the first auxiliary pipeline. A second auxiliary pipeline is connected to the third port of the economizer. The other end of the second auxiliary pipeline is connected to the air supply port of the compressor.

[0009] The EVI low-temperature heat pump device includes a cooling mode and a heating mode.

[0010] Preferably, the EVI low-temperature heat pump device is in heating mode, with control valve port D connected to control valve port C, and control valve port S connected to control valve port E. The refrigerant discharged from the compressor passes sequentially through control valve port D, control valve port C, water-side heat exchanger, liquid receiver, fourth port of the economizer, and second port of the economizer, and is divided into main refrigerant and auxiliary refrigerant, wherein:

[0011] The refrigerant in the main circuit passes sequentially through the main circuit electronic expansion valve, the air-side heat exchanger, control valve port E, control valve port S, the gas-liquid separator, and the compressor's suction port.

[0012] The auxiliary refrigerant passes sequentially through the auxiliary electronic expansion valve, the first port of the economizer, the third port of the economizer, the second auxiliary pipeline, and the compressor's gas supply port.

[0013] Preferably, the EVI low-temperature heat pump device is in cooling mode, control valve port D is connected to control valve port E, and control valve port C is connected to control valve port S. The refrigerant discharged from the compressor passes sequentially through control valve port D, control valve port E, air-side heat exchanger, and main electronic expansion valve, and is divided into main refrigerant and auxiliary refrigerant, wherein:

[0014] The main refrigerant passes sequentially through the second port of the economizer, the fourth port of the economizer, the liquid receiver, the water-side heat exchanger, control valve port C, control valve port S, the gas-liquid separator, and the compressor suction port.

[0015] The auxiliary refrigerant passes sequentially through the auxiliary electronic expansion valve, the first port of the economizer, the third port of the economizer, the second auxiliary pipeline, and the compressor's gas supply port.

[0016] This invention addresses the problem of excessively high exhaust temperature in EVI low-temperature heat pump units during low-temperature heating by employing a method of replenishing gas and increasing enthalpy by taking liquid from the economizer, and simultaneously controlling the main and auxiliary electronic expansion valves to reduce exhaust temperature and ensure reliable unit operation.

[0017] Meanwhile, for the aforementioned EVI low-temperature heat pump device, the present invention also provides a low-temperature heating control method for the EVI low-temperature heat pump device. When the EVI low-temperature heat pump device is in heating mode, when T... pq ≥T pqset And T s ≥T sset If the exhaust temperature is too high, then the system will enter the over-temperature control mode; otherwise, it will enter the normal control mode.

[0018] The above-mentioned control of excessive exhaust temperature includes the following steps:

[0019] Step 1) Check if the auxiliary electronic expansion valve is open. If the auxiliary electronic expansion valve is open, proceed to step 2); if the auxiliary electronic expansion valve is closed, proceed to step 3.

[0020] Step 2) At every time interval t, adjust the opening of the main electronic expansion valve and the auxiliary electronic expansion valve as follows: adjust the opening of the main electronic expansion valve to 0.95 times the previous opening, and adjust the opening of the auxiliary electronic expansion valve to 1.1 times the previous opening, and when T... pq <T pqset -5 or T c -T s When the temperature exceeds ΔT, discontinue the exhaust temperature overheat control.

[0021] Step 3) Adjust the opening of the main electronic expansion valve at time intervals t as follows: Adjust the opening of the main electronic expansion valve to 1.1 times the previous opening, and when T... pq <T pqset At -5, the exhaust temperature overheat control is deactivated;

[0022] The general control is as follows: the opening degree of the main circuit electronic expansion valve is controlled according to the target return gas superheat, and the opening degree of the auxiliary circuit electronic expansion valve is controlled according to the target exhaust gas superheat.

[0023] Among them, T pq T represents the current exhaust temperature. pqset T is the system setpoint. s T represents the current outlet water temperature. sset T is the system setpoint. c Here, ΔT represents the condensation temperature corresponding to the system's high pressure, and ΔT is the system setpoint.

[0024] Preferably, when the refrigerant used in the EVI low-temperature heat pump device is R410A, the T... pqset The temperature is 92℃, T sset When the refrigerant used in the EVI low-temperature heat pump device is R32, the temperature is 50°C. pqset At 95℃, T sset When the refrigerant used in the EVI low-temperature heat pump device is R290, the temperature is 50℃.pqset At 90℃, T sset The temperature is 70℃.

[0025] Preferably, when the water-side heat exchanger used in the EVI low-temperature heat pump device is a plate heat exchanger, the ΔT is 5°C; when the water-side heat exchanger used in the EVI low-temperature heat pump device is a shell-and-tube heat exchanger, the ΔT is 8°C.

[0026] This invention employs a method of replenishing gas and increasing enthalpy by taking liquid from the economizer, which avoids the possibility of insufficient liquid intake in traditional systems. When the exhaust temperature is high, it distinguishes between the open and closed states of the auxiliary electronic expansion valve and uses different control methods to reduce the exhaust temperature. When the auxiliary electronic expansion valve is open and the main electronic expansion valve is partially closed, the exhaust temperature trend is predicted comprehensively by using the condensate temperature, outlet water temperature, and exhaust temperature, enabling precise adjustment of the main electronic expansion valve. When the exhaust temperature is too high, it is adjusted proportionally to the current opening degree, which can quickly reduce the exhaust temperature and avoid slow adjustment that could cause the compressor temperature to rise too high and continuously damage the compressor, thereby avoiding affecting the compressor's service life. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the EVI low-temperature heat pump device of the present invention;

[0028] Figure 2 This is a schematic diagram of the refrigerant flow in the heating state of the present invention;

[0029] Figure 3 This is a schematic diagram of the refrigerant flow in the cooling state of the present invention;

[0030] Figure 4 This is a flowchart illustrating the low-temperature heating control method of the present invention. Detailed Implementation

[0031] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] Furthermore, in the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more, unless explicitly defined otherwise.

[0035] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0037] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0038] Example 1

[0039] like Figure 1As shown, an EVI low-temperature heat pump device includes a compressor 1, a four-way reversing valve 2, a water-side heat exchanger 3, a liquid receiver 4, an economizer 5, a main circuit electronic expansion valve 6, an air-side heat exchanger 7, and a gas-liquid separator 8, which are connected in sequence to form the refrigerant main circuit; wherein:

[0040] The four-way reversing valve 2 includes control valve port D21, control valve port S22, control valve port E23 and control valve port C24. The discharge port of the compressor 1 is connected to control valve port D21. The control valve port C24 is connected to the refrigerant inlet of the water-side heat exchanger 3. The refrigerant outlet of the water-side heat exchanger 3 is connected to one end of the liquid receiver 4. The other end of the liquid receiver 4 is connected to the fourth port 54 of the economizer. The control valve port S22 is connected to the inlet end of the gas-liquid separator 8. The outlet end of the gas-liquid separator 8 is connected to the suction port of the compressor 1. The control valve port E23 is connected to the first port of the air-side heat exchanger 7. The second port of the air-side heat exchanger 7 is connected to one end of the main circuit electronic expansion valve 6. The other end of the main circuit electronic expansion valve 6 is connected to the second port 52 of the economizer.

[0041] A first auxiliary pipeline 9 is connected between the main electronic expansion valve 6 and the second port 52 of the economizer. The other end of the first auxiliary pipeline 9 is connected to the first port 51 of the economizer. An auxiliary electronic expansion valve 10 is provided on the first auxiliary pipeline 9. A second auxiliary pipeline 11 is connected to the third port 53 of the economizer. The other end of the second auxiliary pipeline 11 is connected to the air supply port of the compressor 1.

[0042] The EVI low-temperature heat pump device includes a cooling mode and a heating mode.

[0043] Furthermore, the EVI low-temperature heat pump device is in heating mode, such as... Figure 2 As shown, control valve port D21 is connected to control valve port C24, and control valve port S22 is connected to control valve port E23. The refrigerant discharged from the compressor 1 passes sequentially through control valve port D21, control valve port C24, water-side heat exchanger 3, liquid receiver 4, fourth port 54 of the economizer, and second port 52 of the economizer, and is divided into main refrigerant and auxiliary refrigerant, wherein:

[0044] The main refrigerant passes sequentially through the main electronic expansion valve 6, the air-side heat exchanger 7, the control valve port E23, the control valve port S22, the gas-liquid separator 8, and the suction port of the compressor 1.

[0045] The auxiliary refrigerant passes sequentially through the auxiliary electronic expansion valve 10, the first port 51 of the economizer, the third port 53 of the economizer, the second auxiliary pipeline 11, and the gas supply port of the compressor 1.

[0046] Furthermore, the EVI low-temperature heat pump device is in cooling mode, such as... Figure 3 As shown, control valve port D21 is connected to control valve port E23, and control valve port C24 is connected to control valve port S22. The refrigerant discharged from compressor 1 passes sequentially through control valve port D21, control valve port E23, air-side heat exchanger 7, and main electronic expansion valve 6, and is divided into main refrigerant and auxiliary refrigerant.

[0047] The main refrigerant passes sequentially through the second port 52 of the economizer, the fourth port 54 of the economizer, the liquid receiver 4, the water-side heat exchanger 3, the control valve port C24, the control valve port S22, the gas-liquid separator 8, and the suction port of the compressor 1.

[0048] The auxiliary refrigerant passes sequentially through the auxiliary electronic expansion valve 10, the first port 51 of the economizer, the third port 53 of the economizer, the second auxiliary pipeline 11, and the gas supply port of the compressor 1.

[0049] Meanwhile, for this EVI low-temperature heat pump device, the present invention also provides a low-temperature heating control method for the EVI low-temperature heat pump device, such as... Figure 4 As shown, when the EVI low-temperature heat pump device is in heating mode, when T pq ≥T pqset And T s ≥T sset If the exhaust temperature is too high, then the system will enter the over-temperature control mode; otherwise, it will enter the normal control mode.

[0050] The above-mentioned control of excessive exhaust temperature includes the following steps:

[0051] Step 1) Check if the auxiliary electronic expansion valve is open. If the auxiliary electronic expansion valve is open, proceed to Step 2), that is, increase the amount of supplementary gas by closing the main electronic expansion valve and opening the auxiliary electronic expansion valve to reduce the exhaust temperature. If the auxiliary electronic expansion valve is closed, proceed to Step 3), that is, reduce the return gas superheat by opening the main electronic expansion valve to reduce the exhaust temperature.

[0052] Step 2) At every time interval t, adjust the opening of the main circuit electronic expansion valve and the auxiliary circuit electronic expansion valve as follows: the opening of the main circuit electronic expansion valve is adjusted to 0.95 times the previous opening, rounded down; the opening of the auxiliary circuit electronic expansion valve is adjusted to 1.1 times the previous opening, rounded down. And when T... pq <T pqset -5 or T c -T s When the temperature exceeds △T, the exhaust temperature overheat control is deactivated, and normal control is activated after deactivation.

[0053] Step 3) Adjust the opening of the main electronic expansion valve at time intervals t as follows: Adjust the opening of the main electronic expansion valve to 1.1 times the previous opening, rounding the opening data, and when T...pq <T pqset At -5, the exhaust temperature overheat control is deactivated, and after deactivating the exhaust temperature overheat control, normal control is activated.

[0054] The general control is as follows: the opening degree of the main circuit electronic expansion valve is controlled according to the target return gas superheat, and the opening degree of the auxiliary circuit electronic expansion valve is controlled according to the target exhaust gas superheat.

[0055] Among them, T pq T represents the current exhaust temperature. pqset T is the system setpoint. s T represents the current outlet water temperature. sset T is the system setpoint. c Here, ΔT is the condensation temperature corresponding to the system high pressure, t is the system setpoint, and t is the system setpoint. For example, t can be preferably set to 30s.

[0056] Furthermore, when the refrigerant used in the EVI low-temperature heat pump device is R410A, the aforementioned T pqset The temperature is 92℃, T sset When the refrigerant used in the EVI low-temperature heat pump device is R32, the temperature is 50°C. pqset At 95℃, T sset When the refrigerant used in the EVI low-temperature heat pump device is R290, the temperature is 50℃. pqset At 90℃, T sset The temperature is 70℃.

[0057] Furthermore, the setting of △T is to prevent the condensing temperature from being too high, which would affect the unit's energy efficiency and reliability. Its setting value is related to the type of water-side heat exchanger. When the EVI low-temperature heat pump unit uses a plate heat exchanger, the △T is 5°C. When the EVI low-temperature heat pump unit uses a shell-and-tube heat exchanger, the △T is 8°C.

[0058] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. A low-temperature heating control method of an EVI low-temperature heat pump device, characterized by, The device comprises a compressor (1), a four-way reversing valve (2), a water-side heat exchanger (3), a liquid accumulator (4), an economizer (5), a main circuit electronic expansion valve (6), an air-side heat exchanger (7), and a gas-liquid separator (8) connected in sequence to form a refrigerant main circuit. The four-way reversing valve (2) comprises a control valve port D (21), a control valve port S (22), a control valve port E (23), and a control valve port C (24). The discharge port of the compressor (1) is connected to the control valve port D (21). The control valve port C (24) is connected to the refrigerant inlet of the water-side heat exchanger (3). The refrigerant outlet of the water-side heat exchanger (3) is connected to one end of the liquid accumulator (4). The other end of the liquid accumulator (4) is connected to the fourth port (54) of the economizer. The control valve port S (22) is connected to the inlet end of the gas-liquid separator (8). The outlet end of the gas-liquid separator (8) is connected to the suction port of the compressor (1). The control valve port E (23) is connected to the first port of the air-side heat exchanger (7). The second port of the air-side heat exchanger (7) is connected to one end of the main circuit electronic expansion valve (6). The other end of the main circuit electronic expansion valve (6) is connected to the second port (52) of the economizer. A first auxiliary circuit pipeline (9) is connected between the main circuit electronic expansion valve (6) and the second port (52) of the economizer. The other end of the first auxiliary circuit pipeline (9) is connected to the first port (51) of the economizer. An auxiliary circuit electronic expansion valve (10) is arranged on the first auxiliary circuit pipeline (9). A second auxiliary circuit pipeline (11) is connected to the third port (53) of the economizer. The other end of the second auxiliary circuit pipeline (11) is connected to the air injection port of the compressor (1). The EVI low-temperature heat pump device comprises a refrigeration mode and a heating mode. The control method is: when the EVI low-temperature heat pump device starts the heating mode, if T pq ≥T pqset and T s ≥T sset , then enter the exhaust temperature is too high control, otherwise enter the normal control; The exhaust gas temperature control comprises the following steps: Step 1), detecting whether the auxiliary circuit electronic expansion valve is opened. If the auxiliary circuit electronic expansion valve is opened, step 2) is entered. If the auxiliary circuit electronic expansion valve is closed, step 3) is entered. Step 2), every time t, the opening degree of the main route electronic expansion valve and the auxiliary route electronic expansion valve is adjusted as follows: the opening degree of the main route electronic expansion valve is adjusted to 0.95 times the opening degree of the last time, the opening degree of the auxiliary route electronic expansion valve is adjusted to 1.1 times the opening degree of the last time, and when T pq <T pqset -5 or T c -T s >△T, the exhaust gas temperature is too high control is exited; Step 3), every time t, the opening of the main passage electronic expansion valve is adjusted as follows: the opening of the main passage electronic expansion valve is adjusted to 1.1 times the opening of the last time, and when T pq <T pqset -5, exhaust gas temperature is too high control is exited; The normal control is that the opening degree of the main circuit electronic expansion valve is controlled according to the target return gas superheat degree, and the opening degree of the auxiliary circuit electronic expansion valve is controlled according to the target exhaust gas superheat degree. Wherein, T pq is the current exhaust temperature, T pqset is the system set value, T s is the current outlet water temperature, T sset is the system set value, T c is the system high pressure corresponding condensing temperature, and ΔT is the system set value.

2. The low-temperature heating control method of the EVI low-temperature heat pump device according to claim 1, characterized by, When the EVI low-temperature heat pump device is in the heating mode, the control valve port D (21) is connected to the control valve port C (24), and the control valve port S (22) is connected to the control valve port E (23). The refrigerant discharged from the compressor (1) passes through the control valve port D (21), the control valve port C (24), the water-side heat exchanger (3), the liquid accumulator (4), the fourth port (54) of the economizer, and the second port (52) of the economizer in sequence, and is divided into main circuit refrigerant and auxiliary circuit refrigerant. The main circuit refrigerant passes through the main circuit electronic expansion valve (6), the air-side heat exchanger (7), the control valve port E (23), the control valve port S (22), the gas-liquid separator (8), and the suction port of the compressor (1) in sequence. The auxiliary refrigerant passes through the auxiliary electronic expansion valve (10), the first port (51) of the economizer, the third port (53) of the economizer, the second auxiliary pipeline (11) and the air supplement port of the compressor (1) in sequence.

3. The low-temperature heating control method of the EVI low-temperature heat pump device according to claim 2, characterized by, When the refrigerant used in the EVI low-temperature heat pump device is R410A, the T pqset is 92°C, the T sset is 50°C, when the refrigerant used in the EVI low-temperature heat pump device is R32, the T pqset is 95°C, the T sset is 50°C, when the refrigerant used in the EVI low-temperature heat pump device is R290, the T pqset is 90°C, the T sset is 70°C.

4. The low-temperature heating control method of the EVI low-temperature heat pump device according to claim 2, characterized by, When the water-side heat exchanger of the EVI low-temperature heat pump device is a plate heat exchanger, the △T is 5℃, and when the water-side heat exchanger of the EVI low-temperature heat pump device is a tube-in-tube heat exchanger, the △T is 8℃.

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