Control method for preventing frequent triggering of low-temperature protection and heat pump system

Abstract

The invention relates to a heat pump system capable of preventing frequent triggering and low-temperature protection control, which comprises the following steps of: when a system startup demand is received, acquiring an environment temperature Ta at the current moment, judging whether the environment temperature Ta meets a startup operation condition or not, and if the environment temperature Ta meets the startup operation condition, controlling a compressor to start and operate at the lowest gear F1 and the initial opening degree EV0 of an electronic expansion valve; the air return pressure Pp at the previous moment and the air return pressure Pn at the current moment in the current pressure collection period T are obtained, and the air return pressure change rate P of the current collection period T is obtained through calculation; and the opening degree of the electronic expansion valve and the gear of the compressor are controlled according to the interval where the air return pressure change rate P is located. By dynamically adjusting the opening degree of the electronic expansion valve and the gear of the compressor, the problem that the heat pump system frequently triggers low-temperature protection under the extremely-low-temperature working condition is solved, the starting reliability of the heat pump system is remarkably improved, the service life of the compressor is remarkably prolonged, and the low-temperature energy efficiency is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat pump, in particular to a control method for preventing frequent triggering of low-temperature protection and a heat pump system. BACKGROUND

[0002] The heat pump system is a kind of high-efficiency energy-saving equipment that utilizes low-grade heat energy in air or water to realize heat transfer from low-temperature environment to high-temperature environment through a small amount of electric energy. It mainly includes a compressor, a condenser, a main electronic expansion valve and an evaporator connected by a refrigerant circulation pipeline.

[0003] Under the condition of extremely low temperature, when the system is shut down for a long time, the saturation pressure of the refrigerant decreases due to the continuous decrease of the system temperature, that is, the pressure inside the system continuously decreases. At the same time, the refrigerant flow resistance increases when the system is started up subsequently after being shut down for a long time, because the gaseous refrigerant will condense at low temperature and preferentially deposit in the pipeline (including but not limited to the bottom of the evaporator), forming a "liquid column" of liquid refrigerant; in addition, the dynamic viscosity of the refrigerant increases exponentially with temperature, so that the liquid refrigerant forms an "oily" adhesive layer in the pipeline.

[0004] When the system is started up again after being shut down for a long time, a rarefaction zone (similar to a vacuum front) is immediately established at the suction side of the compressor, and the liquid / gaseous refrigerant is swept away at high speed, resulting in a sharp pressure drop at the suction side in milliseconds to seconds. Since there is liquid refrigerant in the pipeline at this time, and the refrigerant flow resistance is high, the air supply speed of the suction side of the compressor cannot keep up with the air extraction speed, which will trigger the low-pressure protection shutdown of the compressor, affecting the system performance and the service life of the compressor. SUMMARY

[0005] Based on this, the purpose of the present application is to overcome the defects or deficiencies of the prior art, and to provide a heat pump system comprising a control for preventing frequent triggering of low-temperature protection.

[0006] A heat pump system comprising a control for preventing frequent triggering of low-temperature protection, comprising a compressor, a condenser, an electronic expansion valve and an evaporator connected by a refrigerant circulation pipeline, a pressure sensor for detecting the back pressure P of the compressor, a second temperature sensor for detecting the ambient temperature Ta, and a controller in communication with the pressure sensor, the second temperature sensor, the compressor and the electronic expansion valve, the controller comprising a system initial state control unit, a pressure change rate calculation unit, an electronic expansion valve opening degree adjustment unit and a compressor gear adjustment unit.

[0007] The system initial state control unit is configured to, when receiving a system start-up demand, acquire the ambient temperature Ta at the current time, determine whether the ambient temperature Ta satisfies the start-up running condition, and control the compressor to start running at the lowest gear F1 and the initial opening degree EV0 of the electronic expansion valve if the start-up running condition is satisfied.

[0008] The pressure change rate calculation unit is used to obtain the return gas pressure P at the previous moment within the current pressure acquisition period T. p Current return pressure P n The rate of change of return gas pressure ΔP in the current sampling period T is calculated.

[0009] The electronic expansion valve opening adjustment unit is used to control the opening of the electronic expansion valve according to the range of the return gas pressure change rate ΔP.

[0010] The compressor gear adjustment unit is used to control the compressor gear according to the range of the return gas pressure change rate ΔP.

[0011] Compared with existing technologies, this invention solves the problem of frequent triggering of low-temperature protection when the heat pump system starts up under extremely low temperature conditions because the gas replenishment speed on the compressor suction side cannot keep up with the gas extraction speed. This is achieved by monitoring the rate of change of the compressor return gas pressure in real time and dynamically adjusting the opening of the electronic expansion valve and the operating frequency (i.e., gear) of the compressor. This significantly improves the start-up reliability, compressor life and low-temperature energy efficiency of the heat pump system.

[0012] In one embodiment, the power-on operating condition in the system initial state control unit is that the ambient temperature Ta is less than or equal to 20°C.

[0013] In one embodiment, the rate of change of return gas pressure ΔP during the current sampling period T is calculated using the following formula:

[0014] In one embodiment, the electronic expansion valve opening adjustment unit controls the opening of the electronic expansion valve according to the range of the return gas pressure change rate ΔP, including:

[0015] If ΔP ≤ -0.1 Bar / s, then the opening degree EV of the electronic expansion valve is set to a first opening degree EV1, which is determined by the following formula:

[0016] EV1 = K1 × EV0

[0017] Wherein, K1 is the first opening adjustment coefficient, and its specific value is 2;

[0018] If -0.1 Bar / s < ΔP < -0.02 Bar / s, then the opening degree EV of the electronic expansion valve is set to the second opening degree EV2, which is determined by the following formula:

[0019] EV2 = K2 × EV0

[0020] Wherein, K2 is the second opening adjustment coefficient, and its specific value is 1.5;

[0021] If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, then the opening degree EV of the electronic expansion valve is set to the third opening degree EV3, which is determined by the following formula:

[0022] EV3 = K3 × EV0

[0023] K3 is the third opening adjustment coefficient, and its specific value is 1.2.

[0024] In one embodiment, the compressor gear adjustment unit controls the compressor gear according to the range of the return gas pressure change rate ΔP, including:

[0025] If -0.1 Bar / s < ΔP < -0.02 Bar / s, and the duration in this range is five minutes, then the compressor speed is increased by one level, i.e., the compressor speed is set to F2.

[0026] If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, and the duration within this range is two minutes, then the compressor speed is increased by two levels, i.e., the compressor speed is set to F3.

[0027] Furthermore, the present invention also provides a control method for preventing frequent triggering of low-temperature protection, comprising the following steps:

[0028] S10: When a system startup request is received, the current ambient temperature Ta is obtained, and it is determined whether the ambient temperature Ta meets the startup conditions. If it does, the compressor is controlled to start running at the lowest gear F1 and the initial opening of the electronic expansion valve EV0.

[0029] S20: Obtain the return gas pressure P at the previous moment within the current pressure acquisition period T. p Current return pressure P n The rate of change of return gas pressure ΔP in the current sampling period T is calculated.

[0030] S30: Control the opening degree of the electronic expansion valve according to the range of the return gas pressure change rate ΔP;

[0031] S40: Control the compressor speed according to the range of the return gas pressure change rate ΔP.

[0032] In one embodiment, the power-on condition in step S10 is that the ambient temperature Ta is less than or equal to 20°C.

[0033] In one embodiment, step S20 calculates the rate of change of return gas pressure ΔP for the current sampling period T using the following formula:

[0034] In one embodiment, step S30, controlling the opening of the electronic expansion valve according to the range of the return gas pressure change rate ΔP, includes:

[0035] If ΔP ≤ -0.1 Bar / s, then the opening degree EV of the electronic expansion valve is set to a first opening degree EV1, which is determined by the following formula:

[0036] EV1 = K1 × EV0

[0037] Wherein, K1 is the first opening adjustment coefficient, and its specific value is 2;

[0038] If -0.1 Bar / s < ΔP < -0.02 Bar / s, then the opening degree EV of the electronic expansion valve is set to the second opening degree EV2, which is determined by the following formula:

[0039] EV2 = K2 × EV0

[0040] Wherein, k2 is the second opening adjustment coefficient, and its specific value is 1.5;

[0041] If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, then the opening degree EV of the electronic expansion valve is set to the third opening degree EV3, which is determined by the following formula:

[0042] EV3 = K3 × EV0

[0043] K3 is the third opening adjustment coefficient, and its specific value is 1.2.

[0044] In one embodiment, step S40, controlling the compressor speed based on the range of the return gas pressure change rate ΔP, includes:

[0045] If -0.1 Bar / s < ΔP < -0.02 Bar / s, and the duration in this range is five minutes, then the compressor speed is increased by one level, i.e., the compressor speed is set to F2.

[0046] If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, and the duration within this range is two minutes, then the compressor speed is increased by two levels, i.e., the compressor speed is set to F3.

[0047] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the air conditioning heat pump system of the present invention;

[0049] Figure 2 This is a schematic diagram of the controller of the present invention;

[0050] Figure 3 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings.

[0052] like Figure 1 As shown, a heat pump system 10 of the present invention includes a low-temperature protection control to prevent frequent triggering. The system includes a compressor 11, a condenser 12, an electronic expansion valve 13 and an evaporator 14 connected by a refrigerant circulation pipe.

[0053] Specifically, the compressor 11 can be either a fixed-frequency compressor or a variable-frequency compressor; the condenser 12 can be either a water source heat exchanger or an air source heat exchanger. After the refrigerant flows out of the compressor 11, it flows through the condenser 12 to exchange heat with the external water or air, causing the temperature of the external water or air to rise; the evaporator 14 can be either a water source heat exchanger or an air source heat exchanger. After the refrigerant flows out of the electronic expansion valve 13, it flows through the evaporator 14 to exchange heat with the external water or air, causing the temperature of the external water or air to drop.

[0054] The heat pump system further includes a pressure sensor 21 for detecting the return gas pressure P of the compressor, and a second temperature sensor 22 for detecting the ambient temperature Ta.

[0055] Specifically, the pressure sensor 21 is installed on the return gas pipe of the compressor; the location of the second temperature sensor 22 is not specifically limited in this invention, and is only used to collect the ambient temperature Ta of the heat pump system 10.

[0056] Specifically, it also includes a controller, which is communicatively connected to the pressure sensor 21, the compressor 11, and the electronic expansion valve 13.

[0057] like Figure 2 and Figure 3 As shown, the controller includes: a system initial state control unit 31, a pressure change rate calculation unit 32, an electronic expansion valve opening adjustment unit 33, and a compressor gear adjustment unit 34.

[0058] The system initial state control unit 31 is used to execute step S10: When the system starts up request is received, the system initial state control unit is used to obtain the current ambient temperature Ta, determine whether the ambient temperature Ta meets the start-up conditions, and if it does, control the compressor to start up at the lowest gear F1 and the initial opening of the electronic expansion valve EV0.

[0059] Specifically, the operating condition is that the ambient temperature Ta is less than or equal to 20℃.

[0060] Specifically, the compressor frequency of the existing heat pump system 10 is divided into 11 levels from F0 to F10. Each level corresponds to a certain frequency range. By adjusting the frequency, different operating requirements can be met. Level F10 represents the highest operating frequency of the compressor, level F1 represents the lowest operating frequency of the compressor, and level F0 represents the compressor being stopped.

[0061] The pressure change rate calculation unit 32 is used to execute step S20: obtain the return gas pressure P at the previous moment within the current pressure acquisition cycle T. p Current return pressure P n The rate of change of return gas pressure ΔP in the current sampling period T is calculated.

[0062] Specifically, the pressure acquisition period T of the return gas pressure P is a fixed value. In this application, the pressure acquisition period T is 5s.

[0063] Specifically, the rate of change of return gas pressure ΔP during the current sampling period T is calculated using the following formula:

[0064] The electronic expansion valve opening adjustment unit 33 is used to perform step S30: control the opening of the electronic expansion valve according to the range of the return gas pressure change rate ΔP.

[0065] Specifically, controlling the opening degree of the electronic expansion valve based on the range of the return gas pressure change rate ΔP includes:

[0066] If ΔP ≤ -0.1 Bar / s, then the opening degree EV of the electronic expansion valve is set to a first opening degree EV1, which is determined by the following formula:

[0067] EV1 = K1 × EV0

[0068] Wherein, K1 is the first opening adjustment coefficient, and its specific value is 2;

[0069] If -0.1 Bar / s < ΔP < -0.02 Bar / s, then the opening degree EV of the electronic expansion valve is set to the second opening degree EV2, which is determined by the following formula:

[0070] EV2 = K2 × EV0

[0071] Wherein, K2 is the second opening adjustment coefficient, and its specific value is 1.5;

[0072] If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, then the opening degree EV of the electronic expansion valve is set to the third opening degree EV3, which is determined by the following formula:

[0073] EV3 = K3 × EV0

[0074] K3 is the third opening adjustment coefficient, and its specific value is 1.2.

[0075] The compressor gear adjustment unit 34 is used to perform step S40: control the compressor gear according to the range of the return gas pressure change rate ΔP.

[0076] Specifically, controlling the compressor speed based on the range of the return gas pressure change rate ΔP includes:

[0077] If -0.1 Bar / s < ΔP < -0.02 Bar / s, and the duration in this range is five minutes, then the compressor speed is increased by one level, i.e., the compressor speed is set to F2.

[0078] If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, and the duration within this range is two minutes, then the compressor speed is increased by two levels, i.e., the compressor speed is set to F3.

[0079] Compared with existing technologies, the present invention proposes a control method and heat pump system for preventing frequent triggering of low-temperature protection. By monitoring the rate of change of the compressor return gas pressure in real time and dynamically adjusting the opening of the electronic expansion valve and the operating frequency (i.e., the gear) of the compressor, the problem of frequent triggering of low-temperature protection caused by the compressor suction side's gas replenishment speed not keeping up with the gas extraction speed when the heat pump system is started under extremely low temperature conditions is solved. This significantly improves the start-up reliability, compressor life and low-temperature energy efficiency of the heat pump system.

[0080] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this application are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; the terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description relates to drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this application, those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0081] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A heat pump system including a low-temperature protection control to prevent frequent triggering, comprising a compressor, a condenser, an electronic expansion valve, and an evaporator connected by a refrigerant circulation pipe, a pressure sensor for detecting the return gas pressure P of the compressor, a second temperature sensor for detecting the ambient temperature Ta, and a controller, wherein the controller is communicatively connected to the pressure sensor, the second temperature sensor, the compressor, and the electronic expansion valve, characterized in that: The controller includes a system initial state control unit, a pressure change rate calculation unit, an electronic expansion valve opening adjustment unit, and a compressor gear adjustment unit; The system initial state control unit is used to obtain the current ambient temperature Ta when it receives the system start-up request, determine whether the ambient temperature Ta meets the start-up conditions, and if it does, control the compressor to start running at the lowest gear F1 and the initial opening of the electronic expansion valve EV0. The pressure change rate calculation unit is used to obtain the return gas pressure P at the previous moment within the current pressure acquisition period T. p Current return pressure P n The rate of change of return gas pressure ΔP in the current sampling period T is calculated. The electronic expansion valve opening adjustment unit is used to control the opening of the electronic expansion valve according to the range of the return gas pressure change rate ΔP. The compressor gear adjustment unit is used to control the compressor gear according to the range of the return gas pressure change rate ΔP.

2. The heat pump system according to claim 1, characterized in that: The startup condition in the initial state control unit of the system is that the ambient temperature Ta is less than or equal to 20℃.

3. The heat pump system according to claim 1, characterized in that, The rate of change of return gas pressure ΔP during the current sampling period T is calculated using the following formula:

4. The heat pump system according to claim 1, characterized in that, The electronic expansion valve opening adjustment unit controls the opening of the electronic expansion valve according to the range of the return gas pressure change rate ΔP, including: If ΔP ≤ -0.1 Bar / s, then the opening degree EV of the electronic expansion valve is set to a first opening degree EV1, which is determined by the following formula: EV1 = K1 × EV0 Wherein, K1 is the first opening adjustment coefficient, and its specific value is 2; If -0.1 Bar / s < ΔP < -0.02 Bar / s, then the opening degree EV of the electronic expansion valve is set to the second opening degree EV2, which is determined by the following formula: EV2 = K2 × EV0 Wherein, K2 is the second opening adjustment coefficient, and its specific value is 1.5; If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, then the opening degree EV of the electronic expansion valve is set to the third opening degree EV3, which is determined by the following formula: EV3 = K3 × EV0 K3 is the third opening adjustment coefficient, and its specific value is 1.

2.

5. The heat pump system according to claim 1, characterized in that, The compressor gear adjustment unit controls the compressor gear according to the range of the return gas pressure change rate ΔP, including: If -0.1 Bar / s < ΔP < -0.02 Bar / s, and the duration in this range is five minutes, then the compressor speed is increased by one level, i.e., the compressor speed is set to F2. If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, and the duration within this range is two minutes, then the compressor speed is increased by two levels, i.e., the compressor speed is set to F3.

6. A control method for preventing frequent triggering of low-temperature protection, characterized in that, Includes the following steps: S10: When a system startup request is received, the current ambient temperature Ta is obtained, and it is determined whether the ambient temperature Ta meets the startup conditions. If it does, the compressor is controlled to start running at the lowest gear F1 and the initial opening of the electronic expansion valve EV0. S20: Obtain the return gas pressure P at the previous moment within the current pressure acquisition period T. p Current return pressure P n The rate of change of return gas pressure ΔP in the current sampling period T is calculated. S30: Control the opening degree of the electronic expansion valve according to the range of the return gas pressure change rate ΔP; S40: Control the compressor speed according to the range of the return gas pressure change rate ΔP.

7. The heat pump system according to claim 6, characterized in that: The startup condition in step S10 is that the ambient temperature Ta is less than or equal to 20℃.

8. The heat pump system according to claim 6, characterized in that, Step S20 calculates the rate of change of return gas pressure ΔP during the current sampling period T using the following formula:

9. The heat pump system according to claim 6, characterized in that, Step S30, controlling the opening of the electronic expansion valve according to the range of the return gas pressure change rate ΔP, includes: If ΔP ≤ -0.1 Bar / s, then the opening degree EV of the electronic expansion valve is set to a first opening degree EV1, which is determined by the following formula: EV1 = K1 × EV0 Wherein, K1 is the first opening adjustment coefficient, and its specific value is 2; If -0.1 Bar / s < ΔP < -0.02 Bar / s, then the opening degree EV of the electronic expansion valve is set to the second opening degree EV2, which is determined by the following formula: EV2 = K2 × EV0 Wherein, K2 is the second opening adjustment coefficient, and its specific value is 1.5; If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, then the opening degree EV of the electronic expansion valve is set to the third opening degree EV3, which is determined by the following formula: EV3 = K3 × EV0 K3 is the third opening adjustment coefficient, and its specific value is 1.

2.

10. The heat pump system according to claim 6, characterized in that, Step S40, which involves controlling the compressor speed based on the range of the return gas pressure change rate ΔP, includes: If -0.1 Bar / s < ΔP < -0.02 Bar / s, and the duration in this range is five minutes, then the compressor speed is increased by one level, i.e., the compressor speed is set to F2. If -0.02 Bar / s ≤ ΔP ≤ -0.01 Bar / s, and the duration within this range is two minutes, then the compressor speed is increased by two levels, i.e., the compressor speed is set to F3.

Images