EVI low-temperature heat pump device and control method thereof

Abstract

The invention discloses an EVI low-temperature heat pump device and a control method thereof.The EVI low-temperature heat pump device comprises a compressor, a four-way reversing valve, a water side heat exchanger, a liquid storage device, an economizer, a main path electronic expansion valve, an air side heat exchanger and a gas-liquid separator which are sequentially connected to form a refrigerant main loop; when the auxiliary path electronic expansion valve is opened, the air supply amount is increased by turning down the main path electronic expansion valve and turning up the auxiliary path electronic expansion valve, so that the exhaust temperature is reduced, and when the auxiliary path electronic expansion valve is closed, the return air superheat degree is reduced by turning up the main path electronic expansion valve, so that the exhaust temperature is reduced. According to the system, the mode that liquid is taken after the economizer is adopted for gas supplementing and enthalpy increasing is adopted, the situation that liquid cannot be taken possibly in a traditional system can be avoided, when the exhaust temperature is high, the situation that the auxiliary electronic expansion valve is opened and the situation that the auxiliary electronic expansion valve is not opened are distinguished, different control modes are adopted, and the purpose of reducing the exhaust temperature is achieved.

Description

Technical Field

[0001] The invention relates to an EVI low-temperature heat pump device and a control method thereof. Background Art

[0002] In recent years, heat pump heating technology represented by low ambient temperature air source has developed rapidly. The market demand for high water temperature is a big challenge to the long-term reliability of air source heat pump products. When low temperature heat pumps are heating with high outlet water temperature, the exhaust temperature is easy to be too high, affecting the reliability of the unit.

[0003] There are three main technologies for solving the problem of excessively high exhaust temperature in heat pumps. The first is to open the throttle valve appropriately to reduce the superheat of the return air and thus reduce the exhaust temperature. However, this method may cause liquid in the return air, resulting in liquid hammer in the compressor, and has poor reliability. The second is liquid spray cooling, that is, the auxiliary circuit takes liquid from the condenser outlet and enters the compressor liquid spray port after throttling through the throttle valve, but the heat pump capacity and energy efficiency of liquid spray cooling is relatively low. The third is to take liquid before replenishing air and increasing enthalpy, that is, the auxiliary circuit takes liquid from the condenser outlet, throttles through the throttle valve, and then exchanges heat with the main circuit through the economizer. The superheated gas is sucked into the compressor air replenishment port. The jet enthalpy increase method has good capacity and energy efficiency at low temperatures, but it is easy to have insufficient air replenishment, resulting in a situation where the exhaust temperature is still very high. In addition, a fixed number of steps is usually used to control the electronic expansion valve, and the exhaust control only considers the water temperature, not the condensing temperature. When the exhaust temperature is too high, the exhaust temperature cannot be quickly reduced, resulting in a shortened compressor life. Summary of the invention

[0004] In view of the above problems, the present invention provides an EVI low-temperature heat pump device and a control method thereof, which effectively solves the problems pointed out in the background technology.

[0005] The technical solution adopted by the present invention is:

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

[0007] The four-way reversing valve includes a control valve port D, a control valve port S, a control valve port E and a control valve port C. The exhaust port of the compressor is connected to the control valve port D, the 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 reservoir, the other end of the liquid reservoir is connected to the fourth port of the economizer, the control valve port S is connected to the inlet end of the gas-liquid separator, the outlet end of the gas-liquid separator is connected to the air intake port of the compressor, the 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, and 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, the first auxiliary pipeline is provided with an auxiliary electronic expansion valve, the third port of the economizer is connected to a second auxiliary pipeline, 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, the control valve port D is connected to the control valve port C, the control valve port S is connected to the control valve port E, and the refrigerant discharged from the compressor passes through the control valve port D, the control valve port C, the water-side heat exchanger, the liquid storage device, the fourth port of the economizer, and the second port of the economizer in sequence and is divided into the main refrigerant and the auxiliary refrigerant, wherein:

[0011] The main refrigerant passes through the main electronic expansion valve, the air side heat exchanger, the control valve port E, the control valve port S, the gas-liquid separator, and the air intake of the compressor in sequence;

[0012] The auxiliary refrigerant passes through the auxiliary electronic expansion valve, the first port of the economizer, the third port of the economizer, the second auxiliary pipeline, and the air supply port of the compressor in sequence.

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

[0014] The main refrigerant passes through the second port of the economizer, the fourth port of the economizer, the liquid receiver, the water-side heat exchanger, the control valve port C, the control valve port S, the gas-liquid separator, and the air intake of the compressor in sequence;

[0015] The auxiliary refrigerant passes through the auxiliary electronic expansion valve, the first port of the economizer, the third port of the economizer, the second auxiliary pipeline, and the air supply port of the compressor in sequence.

[0016] Aiming at the problem of excessively high exhaust temperature of high water temperature in low-temperature heating of EVI low-temperature heat pump device, the present invention adopts the method of taking liquid after the economizer to replenish air and increase enthalpy, and synchronously controls the main electronic expansion valve and the auxiliary electronic expansion valve to reduce the exhaust temperature and ensure the reliable operation of the unit.

[0017] At the same time, for the above-mentioned EVI low-temperature heat pump device, the present invention also provides a low-temperature heating control method of the EVI low-temperature heat pump device. When the EVI low-temperature heat pump device starts the heating mode, when T pq ≥T pqset And T s ≥T sset When the exhaust temperature is too high, it will enter the exhaust temperature too high control, otherwise it will enter the normal control;

[0018] The exhaust temperature over-high control comprises the following steps:

[0019] Step 1), detect whether the auxiliary circuit electronic expansion valve is open, when the auxiliary circuit electronic expansion valve is open, enter step 2), when the auxiliary circuit electronic expansion valve is closed, enter step 3);

[0020] Step 2), the opening of the main electronic expansion valve and the auxiliary electronic expansion valve is adjusted as follows at every time t: the opening of the main electronic expansion valve is adjusted to 0.95 times the previous opening, and the opening of the auxiliary electronic expansion valve is adjusted to 1.1 times the previous opening, and when T pq <T pqset -5 or T c -T s >△T, exit the exhaust temperature too high control;

[0021] Step 3), adjust the opening of the main electronic expansion valve at every time t as follows: the opening of the main electronic expansion valve is adjusted to 1.1 times the previous opening, and when T pq <T pqset -5, exit the high exhaust temperature control;

[0022] The normal control is as follows: the opening of the main electronic expansion valve is controlled according to the target return air superheat, and the opening of the auxiliary electronic expansion valve is controlled according to the target exhaust gas superheat;

[0023] Among them, T pq is the current exhaust temperature, T pqset is the system setting value, T s is the current outlet water temperature, T sset is the system setting value, T c is the condensing temperature corresponding to the system high pressure, and △T is the system setting value.

[0024] As a preferred embodiment, when the refrigerant used in the EVI low-temperature heat pump device is R410A, the T pqset 92℃, T sset When the refrigerant used in the EVI low-temperature heat pump device is R32, the T pqset At 95°C, T sset When the temperature is 50℃, and the refrigerant used in the EVI low-temperature heat pump device is R290, the Tpqset At 90°C, T sset 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] The present invention adopts a method of taking liquid after the economizer to replenish air and increase enthalpy, which can avoid the situation that the traditional system may not be able to take liquid. When the exhaust temperature is high, the auxiliary electronic expansion valve is distinguished between being opened and not opened, and different control methods are adopted to achieve the effect of lowering the exhaust temperature. When the auxiliary electronic expansion valve is opened and the main electronic expansion valve is closed, the exhaust temperature trend is predicted in all directions through the three temperatures of condensing temperature, water outlet temperature and exhaust temperature, so as to achieve accurate adjustment of the main electronic expansion valve. When the exhaust temperature is too high, it is adjusted in proportion to the current opening, which can quickly reduce the exhaust temperature, avoid excessively high compressor temperature due to slow adjustment and continuous damage to the compressor, thereby avoiding affecting the service life of the compressor. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0030] Figure 4 The figure is a working flow chart of the low temperature heating control method of the present invention. DETAILED DESCRIPTION

[0031] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0033] In addition, in the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more, unless otherwise clearly specified.

[0035] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0037] The present invention is further described in detail below through specific embodiments in conjunction with the 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 storage device 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 sequentially connected to form a refrigerant main circuit; wherein:

[0040] The four-way reversing valve 2 includes a control valve port D21, a control valve port S22, a control valve port E23 and a control valve port C24. The exhaust port of the compressor 1 is connected to the 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 reservoir 4, the other end of the liquid reservoir 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 air intake 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 electronic expansion valve 6, and the other end of the main 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, and 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, the control valve port D21 is connected to the control valve port C24, the control valve port S22 is connected to the control valve port E23, and the refrigerant discharged from the compressor 1 passes through the control valve port D21, the control valve port C24, the water side heat exchanger 3, the liquid storage tank 4, the fourth port 54 of the economizer, and the second port 52 of the economizer in sequence and is divided into the main refrigerant and the auxiliary refrigerant, wherein:

[0044] The main refrigerant passes 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 air intake port of the compressor 1 in sequence;

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

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

[0047] The main refrigerant passes through the second port 52 of the economizer, the fourth port 54 of the economizer, the liquid storage tank 4, the water-side heat exchanger 3, the control valve port C24, the control valve port S22, the gas-liquid separator 8, and the air intake port of the compressor 1 in sequence;

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

[0049] At the same time, for the EVI low-temperature heat pump device, the present invention also provides a low-temperature heating control method of the EVI low-temperature heat pump device, such as Figure 4 As shown in the figure, when the EVI low-temperature heat pump device starts the heating mode, when T pq ≥T pqset And T s ≥T sset When the exhaust temperature is too high, it will enter the exhaust temperature too high control, otherwise it will enter the normal control;

[0050] The exhaust temperature over-high control comprises the following steps:

[0051] Step 1), detect whether the auxiliary electronic expansion valve is open, and when the auxiliary electronic expansion valve is open, enter step 2), that is, increase the air supply volume by closing the main electronic expansion valve and opening the auxiliary electronic expansion valve, thereby reducing the exhaust temperature, and when the auxiliary electronic expansion valve is closed, enter step 3), that is, reduce the return air superheat by opening the main electronic expansion valve, thereby reducing the exhaust temperature;

[0052] Step 2), the opening of the main electronic expansion valve and the auxiliary electronic expansion valve is adjusted as follows at every time t: the opening of the main electronic expansion valve is adjusted to 0.95 times the previous opening, the opening data is rounded, the opening of the auxiliary electronic expansion valve is adjusted to 1.1 times the previous opening, the opening data is rounded, and when T pq <T pqset -5 or T c -T s >△T, exit the exhaust temperature too high control, and then enter the normal control;

[0053] Step 3), adjust the opening of the main electronic expansion valve at every time t as follows: adjust the opening of the main electronic expansion valve to 1.1 times of the previous opening, round the opening data, and when Tpq <T pqset -5, exit the exhaust temperature too high control, and then enter the normal control;

[0054] The normal control is as follows: the opening of the main electronic expansion valve is controlled according to the target return air superheat, and the opening of the auxiliary electronic expansion valve is controlled according to the target exhaust gas superheat;

[0055] Among them, T pq is the current exhaust temperature, T pqset is the system setting value, T s is the current outlet water temperature, T sset is the system setting value, T c is the condensation temperature corresponding to the system high pressure, △T is the system setting value, and t is the system setting value. 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 T pqset 92℃, T sset When the refrigerant used in the EVI low-temperature heat pump device is R32, the T pqset At 95°C, T sset When the temperature is 50℃, and the refrigerant used in the EVI low-temperature heat pump device is R290, the T pqset At 90°C, T sset is 70℃.

[0057] Furthermore, △T is set to prevent the condensing temperature from being too high, which will affect the energy efficiency and reliability of the unit. Its setting value is related to the type of water-side heat exchanger. When the water-side heat exchanger used in the EVI low-temperature heat pump device is a plate heat exchanger, the △T 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 △T is 8°C.

[0058] Finally, it should be noted that the above examples are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. An EVI low-temperature heat pump device, characterized in that: The invention comprises a compressor (1), a four-way reversing valve (2), a water-side heat exchanger (3), a liquid storage device (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 sequentially connected to form a refrigerant main circuit; wherein: 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 exhaust 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 reservoir (4); the other end of the liquid reservoir (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 air intake 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 electronic expansion valve (6); the other end of the main electronic expansion valve (6) is connected to the second port (52) of the economizer; 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), the third port (53) of the economizer is connected to a second auxiliary pipeline (11), the other end of the second auxiliary pipeline (11) is connected to the air supply port of the compressor (1); The EVI low-temperature heat pump device includes a cooling mode and a heating mode.

2. An EVI low-temperature heat pump device according to claim 1, characterized in that: The EVI low-temperature heat pump device is in a heating mode, the control valve port D (21) is connected to the control valve port C (24), the control valve port S (22) is connected to the control valve port E (23), and 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 storage device (4), the fourth port (54) of the economizer, and the second port (52) of the economizer in sequence and is divided into a main refrigerant and an auxiliary refrigerant, wherein: The main refrigerant passes through the main 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 air intake port of the compressor (1) in sequence; The auxiliary circuit refrigerant passes through the auxiliary circuit electronic expansion valve (10), the first port (51) of the economizer, the third port (53) of the economizer, the second auxiliary circuit pipeline (11), and the air supply port of the compressor (1) in sequence.

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

4. A low temperature heating control method for an EVI low temperature heat pump device according to any one of claims 1 to 2, characterized in that: When the EVI low-temperature heat pump device starts the heating mode, when T pq ≥T pqset And T s ≥T sset When the exhaust temperature is too high, it will enter the exhaust temperature too high control, otherwise it will enter the normal control; The exhaust temperature over-high control comprises the following steps: Step 1), detect whether the auxiliary circuit electronic expansion valve is open, when the auxiliary circuit electronic expansion valve is open, enter step 2), when the auxiliary circuit electronic expansion valve is closed, enter step 3); Step 2), the opening of the main electronic expansion valve and the auxiliary electronic expansion valve is adjusted as follows at every time t: the opening of the main electronic expansion valve is adjusted to 0.95 times the previous opening, and the opening of the auxiliary electronic expansion valve is adjusted to 1.1 times the previous opening, and when T pq <T pqset -5 or T c -T s >△T, exit the exhaust temperature too high control; Step 3), adjust the opening of the main electronic expansion valve at every time t as follows: the opening of the main electronic expansion valve is adjusted to 1.1 times the previous opening, and when T pq < T pqset -5, exit the high exhaust temperature control; The normal control is as follows: the opening of the main electronic expansion valve is controlled according to the target return air superheat, and the opening of the auxiliary electronic expansion valve is controlled according to the target exhaust gas superheat; Among them, T pq is the current exhaust temperature, T pqset is the system setting value, T s is the current outlet water temperature, T sset is the system setting value, T c is the condensing temperature corresponding to the system high pressure, and △T is the system setting value.

5. The low-temperature heating control method of an EVI low-temperature heat pump device according to claim 2, characterized in that: When the refrigerant used in the EVI low-temperature heat pump device is R410A, the T pqset 92℃, T sset When the refrigerant used in the EVI low-temperature heat pump device is R32, the T pqset At 95°C, T sset When the temperature is 50℃, and the refrigerant used in the EVI low-temperature heat pump device is R290, the T pqset At 90°C, T sset is 70℃.

6. A low temperature heating control method of an EVI low temperature heat pump device according to claim 2, characterized in that: 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.

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