Control method for opening degree of electronic expansion valve of heat pump fixed-frequency unit

Abstract

The invention relates to a method for controlling the opening degree of an electronic expansion valve of a heat pump fixed-frequency unit, which comprises the following steps of: acquiring environment temperature Ta, environment relative humidity phi and finned coil temperature Tc, and judging whether the heat pump fixed-frequency unit is in an easy-to-frost working condition or not: if so, calculating environment dew point temperature Tdp, and if not, calculating the temperature Tdp; an electronic expansion valve is controlled to be adjusted with the aim that the temperature Tc of a fin coil of the heat pump fixed-frequency unit reaches the environment dew point temperature Tdp; and if not, the electronic expansion valve is controlled to be adjusted with the return air superheat degree threshold Ts-0 as the target. Compared with the prior art, the defrosting control of the air side heat exchanger can be considered while the operation reliability in the low-temperature environment is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of heat pumps, and particularly to a control method for the opening degree of an electronic expansion valve of a heat pump fixed-frequency unit. Background Art

[0002] As an efficient and energy-saving heat energy conversion device, an air-conditioning heat pump system is widely used in fields such as hot water supply, heating, and refrigeration. A traditional air-conditioning heat pump system includes a compressor, a condenser, a throttling component, and an evaporator that are sequentially connected by a refrigerant circulation pipeline; among them, the throttling component is usually an electronic expansion valve, and the evaporator is usually a finned heat exchanger.

[0003] During the operation of the air-conditioning heat pump system, when the temperature of the refrigerant flowing through the finned heat exchanger is lower than the dew point temperature of the air, and the water vapor content in the air is relatively high, when the temperature of the fin surface is lower than 0 °C, water vapor will condense and freeze on the fin surface; the frost layer increases the heat transfer thermal resistance, reduces the heat transfer effect, causes the evaporation temperature of the heat pump unit to drop, and the capacity of the compressor also decreases accordingly, resulting in a rapid attenuation of the heating capacity. Especially in low-temperature and high-humidity environments, such as high-humidity regions in the south of China and ultra-low-temperature and high-humidity regions along the coast in the north, frosting occurs quickly and thickly, and defrosting needs to be carried out frequently, affecting the stability of the indoor temperature.

[0004] In the prior art, a fixed-frequency unit can adjust the temperature of the refrigerant flowing through the finned heat exchanger by controlling the opening degree of the electronic expansion valve. When the exhaust temperature is less than 90 °C, the opening degree of the electronic expansion valve is controlled with the superheat of the return gas as the target. When the exhaust temperature is greater than or equal to 90 °C, the opening degree of the electronic expansion valve is controlled with the exhaust temperature as the target.

[0005] However, in this process, due to the recovery of the superheat of the return gas in the fixed-frequency unit, the evaporation temperature is likely to be too low, resulting in the temperature of the fin heat exchanger being lower than the dew point temperature, and the fin heat exchanger is prone to frosting. When the dry bulb temperature is -4 to 4 °C and the relative humidity is above 85%, the frosting situation will be more serious, seriously affecting the heating capacity of the unit. When the capacity attenuation exceeds 20%, defrosting is required, resulting in frequent defrosting of the unit and easy fluctuations in the water temperature or indoor temperature; at the same time, since the use end becomes refrigeration during defrosting, it has a certain offset effect on the heating capacity, so within a certain time range, the average heating capacity decreases. Summary of the Invention

[0006] Based on this, the purpose of the present invention is to overcome the defects or deficiencies of the prior art and provide a control method for the opening degree of an electronic expansion valve of a heat pump fixed-frequency unit.

[0007] A control method for the opening degree of an electronic expansion valve of a heat pump fixed-frequency unit includes the following steps:

[0008] S10 Obtain the exhaust gas temperature Tp of the heat pump fixed-frequency unit, and determine whether the exhaust gas temperature Tp is greater than or equal to the exhaust gas temperature threshold Tp-0:

[0009] If so, control the electronic expansion valve to adjust with the exhaust gas temperature threshold Tp-0 as the target;

[0010] If not, execute step S20;

[0011] S20 Obtain the superheat degree ΔTs of the return gas of the heat pump fixed-frequency unit, and determine whether the superheat degree ΔTs of the return gas is less than the superheat degree threshold ΔTs-0 of the return gas:

[0012] If so, control the electronic expansion valve to adjust with the superheat degree threshold ΔTs-0 of the return gas as the target;

[0013] If not, execute step S30;

[0014] S30 Obtain the ambient temperature Ta, the ambient relative humidity φ and the finned coil temperature Tc, and determine whether the heat pump fixed-frequency unit is in an easy frosting condition:

[0015] If so, calculate the ambient dew point temperature T dp , and control the electronic expansion valve to adjust with the finned coil temperature Tc of the heat pump fixed-frequency unit reaching the ambient dew point temperature T dp as the target;

[0016] If not, control the electronic expansion valve to adjust with the superheat degree threshold ΔTs-0 of the return gas as the target.

[0017] In one embodiment, the easy frosting condition includes the following conditions:

[0018] The first easy frosting condition is: Ta > 7°C, and φ ≥ 90%, and Tc < -1°C;

[0019] The second easy frosting condition is: -7°C ≤ Ta ≤ 7°C, and φ ≥ 70%;

[0020] The third easy frosting condition is: Ta < -7°C, and φ ≥ 85%.

[0021] In one embodiment, the average ambient dew point temperature is calculated according to the ambient temperature Ta and the ambient relative humidity φ in the following manner

[0022] SA1 Obtain the ambient temperature Ta and the ambient relative humidity φ at a frequency F within a set period M1, and obtain the ambient temperature Ta sequence and the ambient relative humidity φ sequence {φ 1 , φ 2 , φ 2 ,..., φ N}; Subsequently, according to the ambient temperature at the i-th sampling and the ambient relative humidity φ i , the ambient dew point temperature calculated at the i-th sampling is obtained by the following formula and the ambient dew point temperature sequence T dp is obtained

[0023]

[0024] where N is the total number of samplings, and its value is is the ceiling function; i is the i-th sampling point, and its value range is i ∈ {1, 2, 3,..., N}; a and b are empirical constants, and their values depend on the ambient temperature Ta;

[0025] SA2 obtains the ambient dew point temperature sequence T dp and obtains the average ambient dew point temperature by calculation

[0026] In one embodiment, it further includes a control method for correcting the average ambient dew point temperature based on the ambient temperature Ta and the finned coil temperature Tc :

[0027] When controlling the electronic expansion valve to adjust the finned coil temperature Tc of the heat pump fixed-frequency unit to reach the ambient dew point temperature T dp as the target, the adjustment is performed at a set period M2. After performing the adjustment action three times, the ambient temperature Ta and the finned coil temperature Tc at the current moment are obtained, and the temperature difference △T between the ambient temperature Ta and the finned coil temperature Tc is calculated. According to the interval where the ambient temperature Ta is located and the interval where the obtained temperature difference △T is located, the average ambient dew point temperature is corrected to obtain the corrected average ambient dew point temperature and the corrected average ambient dew point temperature replaces the average ambient dew point temperature

[0028] In one embodiment, according to the interval where the ambient temperature Ta is located and the interval where the obtained temperature difference △T is located, the average ambient dew point temperature is corrected, including:

[0029] When the heat pump fixed-frequency unit is in the first easy frosting condition, if △T > 14°C, if 9°C < △T < 14°C, if △T < 9°C,

[0030] When the heat pump fixed-frequency unit is in the second frosting-prone working condition, if △T>12℃, if 8℃<△T<12℃, if △T<8℃,

[0031] When the heat pump fixed-frequency unit is in the third frosting-prone working condition, if △T>10℃, if 6℃<△T<10℃, if △T<6℃,

[0032] In one embodiment, the exhaust temperature threshold value Tp-0 is taken as 90℃.

[0033] In one embodiment, controlling the electronic expansion valve to adjust with the exhaust temperature threshold value Tp-0 as the target includes: increasing the opening degree of the electronic expansion valve until Tp<90℃.

[0034] In one embodiment, the suction superheat threshold value △Ts-0 is taken as 2℃.

[0035] In one embodiment, controlling the electronic expansion valve to adjust with the suction superheat threshold value △Ts-0 as the target includes: decreasing the opening degree of the electronic expansion valve until △Ts≥2℃.

[0036] In addition, the present invention also provides a heat pump fixed-frequency unit, which includes a compressor, a four-way reversing valve, a first heat exchanger, an electronic expansion valve and a second heat exchanger connected in sequence by a refrigerant circulation pipeline; the second heat exchanger includes a coil pipe and fins arranged on the outer wall of the coil pipe;

[0037] It further includes an environmental temperature and humidity sensor for detecting the environmental temperature Ta and the environmental relative humidity φ, a first temperature sensor for detecting the exhaust temperature Tp of the compressor, a second temperature sensor for detecting the suction temperature Ts of the compressor, a pressure sensor for detecting the suction pressure Ps of the compressor, and a third temperature sensor for detecting the fin coil temperature Tc of the second heat exchanger; the pressure sensor is used to collect the pressure signal Ps of the low-temperature and low-pressure gaseous refrigerant inhaled by the compressor, and combined with the temperature-pressure conversion table, the evaporation temperature Tz of the refrigerant at this pressure can be accurately obtained. Through the suction temperature Ts and the evaporation temperature Tz of the compressor, the suction superheat △Ts can be obtained;

[0038] And a controller, the controller is electrically connected or communicatively connected to the environmental temperature and humidity sensor, the first temperature sensor, the second temperature sensor, the pressure sensor and the third temperature sensor, and the controller controls the electronic expansion valve by using the control method as claimed in claims 1 to 9.

[0039] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0040] Figure 1 It is a schematic structural diagram of the heat pump system of the present invention;

[0041] Figure 2 It is a flowchart of the opening control method of the electronic expansion valve in the present invention;

[0042] Figure 3 It is a flowchart of the control method for correcting the average ambient dew point temperature in the present invention. Detailed Embodiments

[0043] The solution of the present invention will be described in detail below with reference to the drawings.

[0044] Please refer to Figure 1 , a heat pump system 10 with a control method for the opening of the electronic expansion valve of a heat pump fixed-frequency unit of the present invention, which includes a compressor 11, a four-way reversing valve 12, a first heat exchanger 13, an electronic expansion valve 14, and a second heat exchanger 15 that are sequentially connected by a refrigerant circulation pipeline.

[0045] The first heat exchanger 13 is a heat exchanger that exchanges heat with the user terminal 16; in some embodiments, the first heat exchanger 13 can exchange heat with the water or air of the user terminal 16 to achieve heating or hot water supply.

[0046] The second heat exchanger 15 is a finned heat exchanger, which includes a coil (not shown in the figure) and fins (not shown in the figure) provided on the outer wall of the coil.

[0047] Specifically, it further includes an ambient temperature and humidity sensor 21 for detecting the ambient temperature Ta and ambient relative humidity φ, a first temperature sensor 22 for detecting the exhaust temperature Tp of the compressor 11, a second temperature sensor 23 for detecting the suction temperature Ts of the compressor 11, a pressure sensor 24 for detecting the suction pressure Ps of the compressor 11, and a third temperature sensor 25 for detecting the finned coil temperature Tc of the second heat exchanger 15.

[0048] Specifically, the position of the ambient temperature and humidity sensor 21 is not specifically limited in the present invention, and it is only used to collect the external ambient temperature and humidity where the evaporator is located to obtain the ambient temperature Ta and ambient relative humidity φ.

[0049] Specifically, the first temperature sensor 22 is arranged on the exhaust pipeline of the compressor 11 to obtain the exhaust temperature Tp of the compressor 11.

[0050] Specifically, the second temperature sensor 23 is arranged on the suction pipeline of the compressor 11 to obtain the suction temperature Ts of the compressor 11.

[0051] Specifically, the pressure sensor 24 is arranged on the suction pipeline of the compressor 11 and is used to collect the pressure signal Ps of the low-temperature and low-pressure gaseous refrigerant inhaled by the compressor 11. By combining with the temperature-pressure comparison table, the evaporation temperature Tz of the refrigerant at this pressure can be accurately obtained.

[0052] Specifically, the third temperature sensor 25 is arranged on the coil of the second heat exchanger 15 and is used to obtain the fin coil temperature Tc of the second heat exchanger 15.

[0053] Furthermore, a controller is included. The controller is electrically connected or communicatively connected to the ambient temperature and humidity sensor 21, the first temperature sensor 22, the second temperature sensor 23, the pressure sensor 24, and the third temperature sensor 25.

[0054] Please refer to Figure 2 , the controller in the present invention realizes the opening control of the electronic expansion valve in the following manner:

[0055] S10 Obtain the exhaust gas temperature Tp of the heat pump fixed-frequency unit, and judge whether the exhaust gas temperature Tp is greater than or equal to the exhaust gas temperature threshold Tp-0:

[0056] If it is yes, control the electronic expansion valve to adjust with the exhaust gas temperature threshold Tp-0 as the target;

[0057] If it is no, execute step S20;

[0058] S20 Obtain the suction superheat △Ts of the heat pump fixed-frequency unit, and judge whether the suction superheat △Ts is less than the suction superheat threshold △Ts-0:

[0059] If it is yes, control the electronic expansion valve to adjust with the suction superheat threshold △Ts-0 as the target;

[0060] If it is no, execute step S30;

[0061] S30 Obtain the ambient temperature Ta, the ambient relative humidity φ, and the fin coil temperature Tc, and judge whether the heat pump fixed-frequency unit is in an easy frosting condition:

[0062] If it is yes, calculate the ambient dew point temperature T dp , control the electronic expansion valve to adjust with the fin coil temperature Tc of the heat pump fixed-frequency unit reaching the ambient dew point temperature T dp as the target;

[0063] If it is no, control the electronic expansion valve to adjust with the suction superheat threshold △Ts-0 as the target.

[0064] During specific implementation, the easy frosting condition includes the following conditions:

[0065] The first frosting-prone operating condition is: Ta > 7°C, and φ ≥ 90%, and Tc < -1°C;

[0066] The second frosting-prone operating condition is: -7°C ≤ Ta ≤ 7°C, and φ ≥ 70%;

[0067] The third frosting-prone operating condition is: Ta < -7°C, and φ ≥ 85%.

[0068] During specific implementation, the exhaust gas temperature threshold Tp-0 is taken as 90°C.

[0069] During specific implementation, controlling the electronic expansion valve to adjust with the exhaust gas temperature threshold Tp-0 as the target includes: increasing the opening degree of the electronic expansion valve until Tp < 90°C.

[0070] During specific implementation, the suction superheat threshold ΔTs-0 is taken as 2°C.

[0071] During specific implementation, controlling the electronic expansion valve to adjust with the suction superheat threshold ΔTs-0 as the target includes: reducing the opening degree of the electronic expansion valve until ΔTs ≥ 2°C.

[0072] During specific implementation, the average ambient dew point temperature is calculated according to the ambient temperature Ta and the ambient relative humidity φ by the following method

[0073] SA1 obtains the ambient temperature Ta and the ambient relative humidity φ at a frequency F within the set period M1, and obtains the ambient temperature Ta sequence and the ambient relative humidity φ sequence {φ 1 , φ 2 , φ 3 ,..., φ N}; Subsequently, according to the ambient temperature and the ambient relative humidity φ i at the i-th sampling, the ambient dew point temperature calculated at the i-th sampling is calculated by the following formula and the ambient dew point temperature T dp sequence

[0074]

[0075] where N is the total number of samplings, and its value is is the ceiling function; i is the i-th sampling point, and its value range is i ∈ {1, 2, 3,..., N}; a and b are empirical constants, and their values depend on the ambient temperature Ta.

[0076] SA2 obtains the ambient dew point temperature T dp sequence through The average ambient dew point temperature is calculated

[0077] Further, please refer to Figure 3 , and it also includes a control method for correcting the average ambient dew point temperature based on the ambient temperature Ta and the finned coil temperature Tc :

[0078] S40 When controlling the electronic expansion valve to adjust the finned coil temperature Tc of the heat pump fixed-frequency unit to reach the ambient dew point temperature T dp as the target, it is adjusted with a set period M2. After performing the adjustment action three times, the ambient temperature Ta and the finned coil temperature Tc at the current moment are obtained, and the temperature difference △T between the ambient temperature Ta and the finned coil temperature Tc is calculated. According to the interval where the ambient temperature Ta is located and the interval where the obtained temperature difference △T is located, the average ambient dew point temperature is corrected to obtain the corrected average ambient dew point temperature and the corrected average ambient dew point temperature replaces the average ambient dew point temperature

[0079] Specifically, when implementing, according to the interval where the ambient temperature Ta is located and the interval where the obtained temperature difference △T is located, the average ambient dew point temperature is corrected, including:

[0080] When the heat pump fixed-frequency unit is in the first easy frosting condition, if △T > 14°C, if 9°C < △T < 14°C, if △T < 9°C,

[0081] When the heat pump fixed-frequency unit is in the second easy frosting condition, if △T > 12°C, if 8°C < △T < 12°C, if △T < 8°C,

[0082] When the heat pump fixed-frequency unit is in the third easy frosting condition, if △T > 10°C, if 6°C < △T < 10°C, if △T < 6°C,

[0083] For the prior art, the control method for the opening degree of the electronic expansion valve proposed by the present invention can ensure the operation reliability in a low-temperature environment while taking into account the defrost control of the air-side heat exchanger.

[0084] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application. The singular forms "a", "the", and "said" used in the embodiments of the present application and the claims 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 only used for distinction and not for describing a specific order or sequence, nor can they be understood as indicating or implying relative importance. The term "and / or" used herein means any or all possible combinations of one or more of the associated listed items. When the above description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of the present application, for those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0085] The above-described embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for controlling the opening of an electronic expansion valve of a heat pump fixed frequency unit, characterized in that: S10 obtains the exhaust temperature Tp of the heat pump fixed-frequency unit and determines whether the exhaust temperature Tp is greater than or equal to the exhaust temperature threshold Tp-0: If yes, the electronic expansion valve is controlled to adjust with the exhaust temperature threshold Tp-0 as the target; If no, execute step S20; S20 obtains the return air superheat △Ts of the heat pump fixed frequency unit and determines whether the return air superheat △Ts is less than the return air superheat threshold △Ts-0: If yes, the electronic expansion valve is controlled to adjust with the return air superheat threshold △Ts-0 as the target; If no, execute step S30; S30 obtains the ambient temperature Ta, ambient relative humidity φ and fin coil temperature Tc to determine whether the heat pump fixed-frequency unit is in a frosting-prone condition: If yes, calculate the ambient dew point temperature T dp , control the electronic expansion valve to make the fin coil temperature Tc of the heat pump fixed frequency unit reach the ambient dew point temperature T dp Adjust for the goal; If not, the electronic expansion valve is controlled to adjust with the return air superheat threshold △Ts-0 as the target.

2. The control method according to claim 1, characterized in that: The frosting prone conditions include the following conditions: The first frosting condition is: Ta>7℃, φ≥90%, and Tc<-1℃; The second frosting prone condition is: -7℃≤Ta≤7℃, and φ≥70%; The third frosting prone condition is: Ta<-7℃, and φ≥85%.

3. The control method according to claim 2, characterized in that: The average ambient dew point temperature is calculated from the ambient temperature Ta and the ambient relative humidity φ in the following way SA1 obtains the ambient temperature Ta and ambient relative humidity φ at a frequency F within the set period M1, and obtains the ambient temperature Ta sequence and the relative humidity φ sequence {φ 1 ,φ 2 ,φ 3 ,...,φ N }; Then, according to the ambient temperature at the time of the i-th sampling and ambient relative humidity φ i The ambient dew point temperature calculated at the i-th sampling time is calculated by the following formula: And obtain the ambient dew point temperature T dp sequence Among them, N is the total number of samples, and its value is is the upward rounding function; i is the i-th sampling point, and its value range is i∈{1,2,3,...,N}; a and b are empirical constants, and their values ​​depend on the ambient temperature Ta; SA2 obtains the ambient dew point temperature T dp sequence pass Calculate the average ambient dew point temperature 4. The control method according to claim 3, characterized in that: It also includes the average ambient dew point temperature correction based on the ambient temperature Ta and the fin coil temperature Tc Control method: S40 controls the electronic expansion valve to make the finned coil temperature Tc of the heat pump fixed frequency unit reach the ambient dew point temperature T dp When adjusting for the target, adjust with the set cycle M2. After performing the adjustment action three times, obtain the current ambient temperature Ta and the fin coil temperature Tc, and calculate the temperature difference △T between the ambient temperature Ta and the fin coil temperature Tc. According to the interval of the ambient temperature Ta and the interval of the obtained temperature difference △T, the average ambient dew point temperature Make corrections to obtain the corrected average ambient dew point temperature The corrected average ambient dew point temperature Replaces the average ambient dew point temperature 5. The control method according to claim 4, characterized in that: According to the range of the ambient temperature Ta and the range of the obtained temperature difference △T, the average ambient dew point temperature Make corrections, including: When the heat pump fixed frequency unit is in the first frosting condition, if △T>14℃, If 9℃<△T<14℃, If △T<9℃, When the heat pump fixed frequency unit is in the second frosting condition, if △T>12℃, If 8℃<△T<12℃, If △T<8℃, When the heat pump fixed frequency unit is in the third frosting condition, if △T>10℃, If 6℃<△T<10℃, If △T<6℃, 6. The control method according to claim 5, characterized in that: The exhaust temperature threshold Tp-0 is set to 90°C.

7. The control method according to claim 5, characterized in that: The electronic expansion valve is controlled to be adjusted with the exhaust temperature threshold value Tp-0 as a target, including: increasing the opening of the electronic expansion valve until Tp<90°C.

8. The control method according to claim 5, characterized in that: The return air superheat threshold ΔTs-0 is set at 2°C.

9. The control method according to claim 5, characterized in that: The electronic expansion valve is controlled to be adjusted with the return air superheat threshold value △Ts-0 as a target, including: reducing the opening of the electronic expansion valve until △Ts≥2℃.

10. A heat pump fixed frequency unit, comprising a compressor, a four-way reversing valve, a first heat exchanger, an electronic expansion valve and a second heat exchanger connected in sequence by a refrigerant circulation pipeline; the second heat exchanger comprises a coil and fins arranged on the outer wall of the coil; It also includes an ambient temperature and humidity sensor for detecting the ambient temperature Ta and the ambient relative humidity φ, a first temperature sensor for detecting the exhaust temperature Tp of the compressor, a second temperature sensor for detecting the return air temperature Ts of the compressor, a pressure sensor for detecting the return air pressure Ps of the compressor, and a third temperature sensor for detecting the fin coil temperature Tc of the second heat exchanger; the pressure sensor is used to collect the pressure signal Ps of the low-temperature and low-pressure gaseous refrigerant sucked by the compressor, and in combination with the temperature-pressure comparison table, the evaporation temperature Tz of the refrigerant under the pressure can be accurately obtained, and the return air superheat △Ts can be obtained through the return air temperature Ts and the evaporation temperature Tz of the compressor; and a controller, wherein the controller is electrically connected or communicatively connected to the ambient temperature and humidity sensor, the first temperature sensor, the second temperature sensor, the pressure sensor and the third temperature sensor, characterized in that: The controller controls the electronic expansion valve using the control method as claimed in claims 1 to 9.

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