Refrigerant active jet heat pump based on low-grade heat source and control method thereof

Abstract

Refrigerant injection can improve the heating capacity and energy efficiency of heat pumps, but the injection heat comes from the heat pump itself, which is a passive injection. The injection characteristics show that the performance of the heat pump is limited, and the heat pump cannot operate in extremely low temperature environments. In response to this problem, the present invention proposes a refrigerant active injection heat pump based on a low-grade heat source, which makes full use of low-grade heat sources, such as solar energy, high-temperature wastewater, exhaust gas, etc., so that the heat of the external heat source and the injected refrigerant are fully exchanged in the supercooler, and the refrigerant that obtains heat is injected into the intermediate pressure chamber of the compressor, so that the external heat is converted into the heat pump unit and thermal work gain is obtained, thereby not only greatly improving the heating capacity and energy efficiency of the heat pump, but also effectively improving the user's comfort, and broadening the scope of application of the heat pump, so that the heat pump can be used in areas below ‑15°C. At the same time, the present invention also proposes a control method for the above-mentioned refrigerant active injection heat pump based on a low-grade heat source.

Description

Technical Field

[0001] The invention relates to a heat pump, in particular to a refrigerant active jet heat pump based on a low-grade heat source and a control method thereof. Background Art

[0002] With the development of economy, the continuous improvement of people's living standards and the development of urbanization, the application of air-conditioning and heating systems is becoming more and more extensive, resulting in huge building energy consumption.

[0003] When heat pumps are used for heating, there are serious problems with heating capacity and energy efficiency attenuation at low ambient temperatures, which has become the main factor hindering the promotion and use of this technology. To solve the above problems, current heat pumps mostly use jet enthalpy increase technology, the principle of which is to inhale a portion of the intermediate pressure refrigerant through the intermediate pressure suction hole, mix it with the partially compressed refrigerant and then compress it, and a single compressor achieves two-stage compression, thereby increasing the refrigerant flow in the condenser, increasing the enthalpy difference of the main circulation loop, and thus improving the efficiency of the compressor.

[0004] Although the above-mentioned jet enthalpy increase technology has improved the heating capacity and energy efficiency of the heat pump to a certain extent, this refrigerant injection with a subcooler adopts internal heat exchange between the injected refrigerant and the refrigerant in the main circuit and does not absorb heat from the outside. It is a passive refrigerant injection. Therefore, in fact, the improvement in the heating capacity and energy efficiency of the heat pump is limited. In actual application, the heating capacity of the above-mentioned passive refrigerant injection heat pump is generally increased by about 10%. After taking optimized control measures, the maximum improvement does not exceed 20%, and the energy efficiency of the heat pump is even more limited. This limits the use of the heat pump. When the ambient temperature is below -15°C, the low-temperature heat pump will not be able to play a heating role. Summary of the invention

[0005] One of the technical problems to be solved by the present invention is to provide a refrigerant active jet heat pump based on a low-grade heat source with good heating capacity and energy efficiency and a wide range of applications.

[0006] In order to solve the above technical problems, the present invention provides a refrigerant active injection heat pump based on a low-grade heat source with the following structure: it includes a heat pump system, an injection system, an external heat source and an external heat source pump, the heat pump system includes a compressor, a condenser, an evaporator, a main throttle valve and a four-way valve that are cyclically connected; the injection system includes a subcooler and a subcooling throttle valve, the subcooler is provided with a refrigerant heat exchange tube and an external heat source heat exchange tube, one end of the subcooling throttle valve is connected to the outlet end of the condenser, the other end of the subcooling throttle valve is connected to the inlet end of the refrigerant heat exchange tube, the outlet end of the refrigerant heat exchange tube is connected to the intermediate pressure chamber of the compressor, and the external heat source pump is connected between the inlet end of the external heat source heat exchange tube and the outlet end of the external heat source.

[0007] After adopting the above structure, compared with the prior art, the present invention has the following advantages: the refrigerant active jet heat pump based on low-grade heat source of the present invention can make full use of external heat source, especially low-grade heat source, and convert the low-grade heat source into high-grade heat source, thereby not only effectively improving the heat exchange performance of the subcooler, thereby greatly improving the heating capacity and energy efficiency of the heat pump, but also solving the problem of serious attenuation of the heating capacity and energy efficiency of the heat pump at low ambient temperature, so that the heat pump can be used in areas with ambient temperature below -15°C, thereby greatly broadening the scope of application of the heat pump.

[0008] The refrigerant active jet heat pump based on a low-grade heat source described in the present invention is characterized in that an external heat source temperature sensor is provided at the outlet end of the external heat source, a subcooler inlet temperature sensor is provided at the inlet end of the refrigerant heat exchange tube, and a subcooler outlet temperature sensor is provided at the outlet end of the refrigerant heat exchange tube.

[0009] The above structure can accurately control the start and stop of the external heat source pump, thereby making the operation of the heat pump more stable and ensuring the heating capacity and energy efficiency of the heat pump.

[0010] Another technical problem to be solved by the present invention is to provide a control method for the above-mentioned refrigerant active injection heat pump based on a low-grade heat source.

[0011] In order to solve the above technical problems, the present invention provides a control method for a refrigerant active jet heat pump based on a low-grade heat source, comprising the following steps:

[0012] During the operation of the heat pump, the external heat source temperature T is detected in real time by the external heat source temperature sensor. h,in The subcooler inlet temperature sensor is used to detect the subcooler injection inlet temperature T at the inlet end of the refrigerant heat exchange tube in real time. inj,in The subcooler outlet temperature sensor is used to detect the subcooler injection inlet temperature T at the outlet of the refrigerant heat exchange tube in real time. inj,out ;

[0013] When the external heat source temperature T h,in ≤Subcooler injection outlet temperature T inj,out When the external heat source pump is controlled to stop running, the external heat source cannot enter the subcooler;

[0014] When the external heat source temperature T h,in > Subcooler injection outlet temperature T inj,out When the external heat source pump is controlled to start running, the external heat source can enter the subcooler.

[0015] After adopting the above control method, compared with the prior art, the control method of the refrigerant active jet heat pump based on the low-grade heat source of the present invention has the following advantages:

[0016] The control method of the refrigerant active jet heat pump based on a low-grade heat source of the present invention enables the heat pump to make full use of the external heat source, especially the low-grade heat source, and convert the low-grade heat source into a high-grade heat source. This not only effectively improves the heat exchange performance of the subcooler in the heat pump, thereby greatly improving the heating capacity and energy efficiency of the heat pump, but also enables the heat pump to be used in areas with an ambient temperature below -15°C, thereby greatly broadening the scope of application of the heat pump.

[0017] The control method of the refrigerant active jet heat pump based on a low-grade heat source of the present invention, wherein, in the refrigerant active jet heat pump based on a low-grade heat source, a suction temperature sensor is provided on the pipeline connected to the compressor suction port, and an evaporator inlet temperature sensor is provided on the pipeline connected to the inlet end of the evaporator;

[0018] The main throttle valve is controlled and adjusted according to the superheat of the heat pump. The superheat of the heat pump is defined as:

[0019] Compressor suction temperature T s -Defrost temperature T def ;

[0020] When the actual superheat is greater than the target superheat, the main throttle valve opens wider;

[0021] When the actual superheat is less than the target superheat, the main throttle valve is closed;

[0022] When the actual superheat = target superheat, the main throttle valve maintains the current opening;

[0023] The target superheat is the preset temperature value of the heat pump system, and the compressor suction temperature T s Obtained by the suction temperature sensor, the defrost temperature T def Obtained by the evaporator inlet temperature sensor.

[0024] The above control and regulation of the main throttle valve can effectively ensure the operational reliability of the heat pump.

[0025] The control method of the refrigerant active jet heat pump based on a low-grade heat source of the present invention, wherein, in the refrigerant active jet heat pump based on a low-grade heat source, a condenser outlet temperature sensor is provided on the pipeline connected to the outlet end of the condenser, and a high-pressure pressure sensor is provided on the pipeline connected to the exhaust port of the compressor;

[0026] The subcooling throttle valve is controlled and adjusted according to the subcooling degree of the heat pump. The subcooling degree of the heat pump is defined as:

[0027] The saturation temperature P corresponding to the heat pump high pressure d_t -Liquid pipe temperature T liq ;

[0028] When the actual subcooling degree is greater than the target subcooling degree, the subcooling throttle valve opens wider;

[0029] When the actual subcooling degree is less than the target subcooling degree, the subcooling throttle valve is closed;

[0030] When the actual subcooling degree = the target subcooling degree, the subcooling throttle valve maintains the current opening degree;

[0031] The target subcooling is the preset temperature value of the heat pump system, and the saturation temperature P corresponding to the high pressure of the heat pump is d_t The liquid pipe temperature T is obtained by converting the high pressure pressure of the heat pump obtained by the high pressure sensor. liq Obtained by the condenser outlet temperature sensor.

[0032] The above control and regulation of the subcooling throttle valve can effectively ensure the operational reliability of the heat pump.

[0033] The control method of the refrigerant active jet heat pump based on a low-grade heat source of the present invention, wherein, in the refrigerant active jet heat pump based on a low-grade heat source, an exhaust temperature sensor is provided on the pipeline connected to the exhaust port of the compressor;

[0034] The subcooling throttle valve is adjusted according to the compressor exhaust superheat of the heat pump. The compressor exhaust superheat of the heat pump is defined as:

[0035] Compressor exhaust temperature T d -Saturation temperature P corresponding to the high pressure of the heat pump d_t ;

[0036] When the actual compressor exhaust superheat is less than the set value B, the subcooling throttle valve is closed;

[0037] When the actual compressor exhaust superheat is greater than the set value C, the subcooling throttle valve opens wider;

[0038] When the set value B ≤ actual compressor exhaust superheat ≤ set value C, the subcooling throttle valve is controlled and adjusted according to the target subcooling of the heat pump;

[0039] Among them, set value B and set value C are both the system preset temperature values ​​of the heat pump, and set value C> set value B; compressor exhaust temperature T d Obtained by the exhaust temperature sensor.

[0040] The above-mentioned correction adjustment of the subcooling throttle valve can further ensure the operational reliability of the heat pump.

[0041] The control method of the refrigerant active jet heat pump based on a low-grade heat source of the present invention further includes the following steps:

[0042] After the external heat source pump starts running,

[0043] When the subcooler injection inlet temperature T inj,in +Set value A≤external heat source temperature T h,in <Subcooler injection outlet temperature T inj,out When the external heat source pump is kept in continuous operation;

[0044] When the external heat source temperature T h,in <Subcooler injection inlet temperature T inj,in +When the setting value is A, the external heat source pump is controlled to stop running;

[0045] The set value A is the preset temperature value of the heat pump system, and the subcooler injection inlet temperature T inj,in + set value A<subcooler injection outlet temperature T inj,out .

[0046] The above control method can effectively prevent the external heat source pump in the heat pump from frequently starting and stopping, thereby making the operation of the heat pump more stable and ensuring the heating capacity and energy efficiency of the heat pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a simplified schematic diagram of the system when the heat pump is used for heating in the prior art;

[0048] Figure 2 It is a cycle pressure-enthalpy diagram of a heat pump heating system in the prior art;

[0049] Figure 3 It is a detailed principle diagram of the system of the present invention when the refrigerant active jet heat pump based on low-grade heat source is heating;

[0050] Figure 4 This is a simplified schematic diagram of the system of the present invention when the refrigerant active jet heat pump is heating based on a low-grade heat source;

[0051] Figure 5 It is a cycle pressure-enthalpy diagram of the refrigerant active jet heat pump based on a low-grade heat source during heating of the present invention.

[0052] Description of reference numerals:

[0053] For the heat pump of the prior art: 101, compressor; 102, condenser; 103, evaporator; 104, main throttle valve; 105, subcooler; 106, cold throttle valve.

[0054] For the refrigerant active jet heat pump based on low-grade heat source of the present invention: 1. compressor; 2. condenser; 3. evaporator; 4. main throttle valve; 5. four-way valve; 6. liquid storage tank; 7. gas-liquid separator; 8. outdoor fan; 9. insulated water tank; 10. main engine water pump; 11. refrigerant conduit; 12. insulated water conduit; 13. high-pressure pressure switch; 14. high-pressure pressure sensor; 15. low-pressure pressure switch; 16. subcooler; 17. subcooling throttle valve; 18. refrigerant heat exchange tube; 19. external heat source heat exchange tube; 20. external heat source; 21. external heat source pump; 22. external heat source temperature sensor; 23. subcooler inlet temperature sensor; 24. subcooler outlet temperature sensor; 25. exhaust temperature sensor; 26. suction temperature sensor; 27. condenser outlet temperature sensor; 28. evaporator inlet temperature sensor. DETAILED DESCRIPTION

[0055] The following is a further detailed description of the refrigerant active jet heat pump based on a low-grade heat source and the control method thereof in conjunction with the accompanying drawings and specific embodiments of the present invention.

[0056] The simplified schematic diagram of the heat pump heating system in the prior art is as follows: Figure 1 As shown:

[0057] When the refrigerant is not injected, the heat pump cycle process is as follows: the subcooling throttle valve 106 is closed, the compressor 101 is running, the refrigerant enters the compressor 101 through the air intake port of the compressor 101 and after being compressed, it will become a high-temperature gaseous refrigerant and be discharged from the exhaust port of the compressor 101, and then flow into the condenser 102 and exchange heat with air or water, and then the heat-releasing refrigerant flows into the evaporator 103 through the subcooler 105 and the main throttle valve 104, exchanges heat with the air in the evaporator 103, and finally returns to the air intake port of the compressor 101 and enters the compressor 101 again;

[0058] When the refrigerant is injected, the heat pump cycle process is as follows: the subcooling throttle valve 106 is opened and adjusted according to a certain target (such as adjusting according to the subcooling or superheating of the heat pump), the refrigerant enters the compressor 101 through the suction port of the compressor 101 and after compression, it will become a high-temperature gaseous refrigerant and be discharged from the exhaust port of the compressor 101, and then flow into the condenser 102 and exchange heat with air or water. Then, the refrigerant will flow through two paths. The main circulation path is to flow through the subcooler 105 and the main throttle valve 104 into the evaporator 103, exchange heat with the air in the evaporator 103, and finally return to the suction port of the compressor 101 and enter the compressor 101 again; the other path is to throttle through the cold throttle valve 106, enter the subcooler 105 and exchange heat with the refrigerant in the main circulation flow path, and finally be injected into the intermediate pressure chamber of the compressor 101 under the action of the pressure difference.

[0059] The corresponding pressure-enthalpy diagram of the heat pump in the prior art is as follows: Figure 2 As shown, where h is the specific enthalpy and P is the pressure.

[0060] Figure 1 and Figure 2 V A 、V B 、V C and V D V1-V9 are the refrigerant state points when the refrigerant is not injected, and correspond to the refrigerant state points of the compressor 101 suction port, the compressor 101 exhaust port, the condenser 102 outlet, and the main throttle valve 104 after throttling; V1-V9 are the refrigerant state points when the refrigerant is injected, and V1, V2, V3, V4 and V8 correspond to the state points of the main circulation flow path refrigerant at the compressor 101 suction port, the compressor 101 exhaust port, the main throttle valve 104 inlet, the main throttle valve 104 outlet, and the compressor 101 after the first stage compression, V5, V6 and V7 correspond to the state points of the injection flow path refrigerant at the supercooling throttle valve 106 inlet, the supercooling throttle valve 106 outlet, and entering the intermediate pressure chamber of the compressor 101, and V9 corresponds to the state point after the main circulation flow path refrigerant and the injection flow path refrigerant are mixed in the intermediate chamber of the compressor 101.

[0061] from Figure 2 It can be seen that the refrigerant undergoes two-stage compression in the compressor 101, wherein V1 to V8 is the first stage compression, and V9 to V2 is the second stage compression.

[0062] According to the heat pump cycle principle, the heating capacity of the heat pump in the prior art is Q h,V Equal to the air energy Q absorbed by the evaporator 103 e,V Compression work EP V The sum of is:

[0063] Q h,V =Q e,V +EP V

[0064] Among them, the air energy Q absorbed by the evaporator 103 e,V The expression is:

[0065]

[0066] A part of the refrigerant returns to the compressor 101 after heat exchange in the evaporator 103, and the other part of the refrigerant is injected into the middle cavity of the compressor 101. The two parts of the refrigerant are mixed and then compressed in the second stage. Therefore, the compression work expression of the heat pump in the prior art is:

[0067]

[0068] Energy efficiency COP of existing heat pumpsV The expression is:

[0069]

[0070] In the above expression, m V and m i,V are the compressor exhaust volume and the refrigerant injection mass flow rate respectively.

[0071] The above shows that the performance gain of the heat pump in the prior art comes from the increased air energy (enthalpy difference between point V5 and point V3) due to the increased supercooling and the increased compression work, while the heat of the refrigerant injection (heating capacity calculated by the enthalpy difference between point V7 and point V6) is not calculated into the heating capacity Q h,V middle.

[0072] It can be seen from this that the heat of the refrigerant injection during heating in the prior art heat pump comes from the heat pump itself, so it is passive injection, and the performance improvement of the heat pump is limited. Therefore, the purpose of the present invention is to develop a refrigerant active injection heat pump based on an external low-grade heat source, so as to make full use of low-grade heat sources, such as solar energy, waste heat, etc., to achieve the purpose of greatly improving the heating capacity and energy efficiency of the heat pump.

[0073] Embodiment 1:

[0074] like Figure 3As shown, the refrigerant active injection heat pump based on low-grade heat source of the present invention comprises a heat pump system, an injection system, an external heat source 20 and an external heat source pump 21, the heat pump system comprises a compressor 1, a condenser 2, an evaporator 3, a main throttle valve 4, a four-way valve 5, a liquid storage tank 6, a gas-liquid separator 7, an outdoor fan 8, a heat preservation water tank 9 and a main water pump 10, a refrigerant conduit 11 and a heat preservation water conduit 12 are provided on the condenser 2, the exhaust port of the compressor 1 is connected to the D port of the four-way valve 5, the E port of the four-way valve 5 is connected to the inlet end of the refrigerant conduit 11 on the condenser 2, the outlet end of the refrigerant conduit 11 is connected to one end of the liquid storage tank 6, the other end of the liquid storage tank 6 is connected to one end of the main throttle valve 4, and the main The other end of the throttle valve 4 is connected to one end of the evaporator 3, the other end of the evaporator 3 is connected to the C port of the four-way valve 5, the S port of the four-way valve 5 is connected to the inlet end of the gas-liquid separator 7, the outlet end of the gas-liquid separator 7 is connected to the suction port of the compressor 1, the main engine water pump 10 is connected between the inlet end of the insulation water conduit 12 and the outlet end of the insulation water tank 9, the outlet end of the insulation water conduit 12 is connected to the inlet end of the insulation water tank 9 through a pipeline, and the outdoor fan 8 is arranged near the evaporator 3; a high-pressure switch 13 and a high-pressure pressure sensor 14 are provided on the pipeline connected to the exhaust port of the compressor 1, and a low-pressure switch 15 is provided on the pipeline connected to the suction port of the compressor 1; the injection system includes a subcooler 16 and a subcooling throttle valve 17, the subcooler 16 is provided with a refrigerant heat exchange pipe 18 and an external heat source heat exchange pipe 19, one end of the subcooling throttle valve 17 is connected to the outlet end of the condenser 2, and one end of the subcooling throttle valve 17 in this embodiment is connected to the pipeline between the outlet end of the refrigerant conduit 11 and one end of the liquid storage tank 6; the other end of the subcooling throttle valve 17 is connected to the inlet end of the refrigerant heat exchange pipe 18, and the outlet end of the refrigerant heat exchange pipe 18 is connected to the intermediate pressure chamber of the compressor 1, the external heat source pump 21 is connected between the inlet end of the external heat source heat exchange pipe 19 and the outlet end of the external heat source 20, and the outlet end of the external heat source heat exchange pipe 19 is connected through a pipeline, and the external heat source 20 in this embodiment It can be hot water, steam or hot air heated by low-grade heat sources such as solar energy and waste heat; an external heat source temperature sensor 22 is provided at the outlet end of the external heat source 20, a subcooler inlet temperature sensor 23 is provided at the inlet end of the refrigerant heat exchange tube 18, and a subcooler outlet temperature sensor 24 is provided at the outlet end of the refrigerant heat exchange tube 18; an exhaust temperature sensor 25 is provided on the pipeline connected to the exhaust port of the compressor 1, an intake temperature sensor 26 is provided on the pipeline connected to the intake port of the compressor 1, a condenser outlet temperature sensor 27 is provided on the pipeline connected to the outlet end of the condenser 2, and an evaporator inlet temperature sensor 28 is provided on the pipeline connected to the inlet end of the evaporator 3.

[0075] The simplified schematic diagram of the system when the low-grade heat source refrigerant active jet heat pump is used for heating is shown in the following figure: Figure 4 As shown:

[0076] When the refrigerant is not injected, the heat pump cycle process is as follows: the subcooling throttle valve 17 is closed, the compressor 1 is running, the refrigerant enters the compressor 1 through the air intake port of the compressor 1 and after being compressed, it will become a high-temperature gaseous refrigerant and be discharged from the exhaust port of the compressor 1, and then flow into the condenser 2 and exchange heat with air or water, and then the refrigerant that releases heat flows into the evaporator 3 through the main throttle valve 4, exchanges heat with the air in the evaporator 3, and finally returns to the air intake port of the compressor 1 and enters the compressor 1 again;

[0077] When the refrigerant is injected, the heat pump cycle process is as follows: the subcooling throttle valve 17 is opened and adjusted according to a certain target (such as adjusting according to the subcooling or superheating of the heat pump), and at the same time, an external heat source 20 is input into the subcooler 16; the compressor 1 is running, and the refrigerant enters the compressor 1 through the suction port of the compressor 1 and, after being compressed, it will become a high-temperature gaseous refrigerant and be discharged from the exhaust port of the compressor 1, and then flow into the condenser 2 and exchange heat with air or water, and then the refrigerant will flow through two paths. The main circulation path is to flow into the evaporator 3 through the main throttle valve 4, exchange heat with the air in the evaporator 3, and finally return to the suction port of the compressor 1 and enter the compressor 1 again; the other path is to throttle through the cold throttle valve 17, enter the subcooler 16 and exchange heat with the external heat source 20, and finally be injected into the intermediate pressure chamber of the compressor 1 under the action of the pressure difference.

[0078] The corresponding pressure-enthalpy diagram of the low-grade heat source refrigerant active jet heat pump during heating is as follows: Figure 5 As shown:

[0079] The heating capacity of the refrigerant active jet heat pump based on the low-grade heat source in this embodiment is expressed as:

[0080] Q h,V =Q e,V +Q sc,inj +EP V

[0081] Among them, Q sc,inj is the heat absorbed by the refrigerant in the subcooler, and its expression is:

[0082]

[0083] The compression work expression of the refrigerant active jet heat pump based on the low-grade heat source in this embodiment is:

[0084]

[0085] As can be seen from the above, the heating capacity of the refrigerant active jet heat pump based on the low-grade heat source in this embodiment is more than the heating capacity of the heat pump in the prior art by the heat Q absorbed by the refrigerant in the subcooler. sc,inj, so the energy efficiency COP of the refrigerant active jet heat pump based on low-grade heat source in this embodiment is V It also increases accordingly.

[0086] Embodiment 2:

[0087] This embodiment discloses a control method for the refrigerant active jet heat pump based on a low-grade heat source in Embodiment 1, comprising the following steps:

[0088] During the operation of the heat pump, the main throttle valve 4 and the subcooling throttle valve 17 are opened according to certain targets, such as the subcooling degree or superheating degree of the heat pump; at the same time, the external heat source temperature T is detected in real time by the external heat source temperature sensor 22. h,in The subcooler injection inlet temperature T at the inlet end of the refrigerant heat exchange tube 18 is detected in real time by the subcooler inlet temperature sensor 23. inj,in The subcooler outlet temperature sensor 24 detects the subcooler injection inlet temperature T at the outlet of the refrigerant heat exchange tube 18 in real time. inj,out ;

[0089] When the external heat source temperature T h,in ≤Subcooler injection outlet temperature T inj,out When the external heat source pump 21 is controlled to stop running, the external heat source 20 cannot enter the subcooler 16;

[0090] When the external heat source temperature T h,in > Subcooler injection outlet temperature T inj,out When the external heat source pump 21 is controlled to start running, the external heat source 20 can enter the subcooler 16.

[0091] In this embodiment, the main throttle valve 4 is controlled and adjusted according to the superheat of the heat pump, and the superheat of the heat pump is defined as:

[0092] Compressor suction temperature T s -Defrost temperature T def ;

[0093] When the actual superheat degree is greater than the target superheat degree, the main throttle valve 4 is opened wide;

[0094] When the actual superheat is less than the target superheat, the main throttle valve 4 is closed;

[0095] When the actual superheat = the target superheat, the main throttle valve 4 maintains the current opening;

[0096] The target superheat is the preset temperature value of the heat pump system, and the compressor suction temperature T s Obtained by the suction temperature sensor 26, the defrost temperature T def It is acquired by the evaporator inlet temperature sensor 28.

[0097] The subcooling throttle valve 17 is controlled and adjusted according to the subcooling degree of the heat pump. The subcooling degree of the heat pump is defined as:

[0098] The saturation temperature P corresponding to the heat pump high pressure d_t -Liquid pipe temperature T liq ;

[0099] When the actual subcooling degree is greater than the target subcooling degree, the subcooling throttle valve 17 is opened wide;

[0100] When the actual subcooling degree is less than the target subcooling degree, the subcooling throttle valve 17 is closed;

[0101] When the actual subcooling degree = the target subcooling degree, the subcooling throttle valve 17 maintains the current opening degree;

[0102] The target subcooling is the preset temperature value of the heat pump system, and the saturation temperature P corresponding to the high pressure of the heat pump is d_t The high pressure sensor 14 obtains the heat pump high pressure and converts it into the liquid pipe temperature T liq It is obtained by the condenser outlet temperature sensor 27.

[0103] In order to ensure the reliability of the operation of the heat pump, the subcooling throttle valve 17 is corrected and adjusted according to the compressor exhaust superheat of the heat pump. The compressor exhaust superheat of the heat pump is defined as:

[0104] Compressor exhaust temperature T d -Saturation temperature P corresponding to the high pressure of the heat pump d_t ;

[0105] When the actual compressor exhaust superheat is less than the set value B, the subcooling throttle valve 17 is closed;

[0106] When the actual compressor exhaust superheat is greater than the set value C, the subcooling throttle valve 17 opens wide;

[0107] When the set value B ≤ actual compressor exhaust superheat ≤ set value C, the subcooling throttle valve 17 is controlled and adjusted according to the target subcooling of the heat pump;

[0108] Among them, set value B and set value C are both the system preset temperature values ​​of the heat pump, and set value C> set value B; compressor exhaust temperature T d Acquired by the exhaust gas temperature sensor 25 .

[0109] Setpoint B and setpoint C can be set at the compressor discharge temperature T d When the temperature is too low or too high, the subcooling throttle valve 17 is used to control and adjust the compressor exhaust temperature T d , to ensure the compressor exhaust temperature T dAlways within the reliability range; for example, current heat pumps generally require the compressor exhaust superheat to be above 10°C, so under the condition of ensuring a certain margin, the set value B can be set at 15-20°C; and the current heat pump compressor exhaust temperature T d The protection value is generally around 120°C. According to the saturation temperature P corresponding to the general heat pump high pressure (limited frequency high pressure 37-38 bar), d_t If the temperature is about 60℃, then the set value C can be set to 45~55℃ while ensuring a certain margin.

[0110] Of course, since the subcooling throttle valve 17 is controlled and adjusted according to the subcooling degree of the heat pump, it is a normal adjustment, and the correction adjustment of the subcooling throttle valve 17 according to the compressor exhaust superheat of the heat pump is to ensure the operating reliability of the heat pump. Therefore, when adjusting the opening of the subcooling throttle valve 17, the operating reliability of the heat pump must be guaranteed first, that is, the subcooling throttle valve 17 is controlled and adjusted according to the subcooling degree of the heat pump only when the operating reliability of the heat pump can be guaranteed.

[0111] Embodiment 3:

[0112] The difference between this embodiment and embodiment 2 is that this embodiment adds a control method for preventing the external heat source pump 21 from frequently starting and stopping, which specifically includes the following steps:

[0113] During the operation of the heat pump, the main throttle valve 4 and the subcooling throttle valve 17 adjust their openings according to certain targets, and at the same time, the external heat source temperature T is detected in real time by the external heat source temperature sensor 22. h,in The subcooler injection inlet temperature T at the inlet end of the refrigerant heat exchange tube 18 is detected in real time by the subcooler inlet temperature sensor 23. inj,in The subcooler outlet temperature sensor 24 detects the subcooler injection inlet temperature T at the outlet of the refrigerant heat exchange tube 18 in real time. inj,out ;

[0114] When the external heat source temperature T h,in > Subcooler injection outlet temperature T inj,out When the external heat source pump 21 is controlled to start running, the external heat source 20 can enter the subcooler 16;

[0115] After the external heat source pump 21 starts running,

[0116] When the subcooler injection inlet temperature T inj,in +Set value A≤external heat source temperature T h,in <Subcooler injection outlet temperature T inj,out When the external heat source pump 21 is kept in continuous operation;

[0117] When the external heat source temperature T h,in <Subcooler injection inlet temperature Tinj,in + When the setting value is A, the external heat source pump 21 is controlled to stop running;

[0118] The set value A is the preset temperature value of the heat pump system, and the subcooler injection inlet temperature T inj,in + set value A<subcooler injection outlet temperature T inj,out .

[0119] The setting of set value A is mainly to prevent frequent switching of heat sources, and can be determined according to the actual changes in Th,in.

[0120] The setting value A is mainly to prevent the external heat source pump 21 from frequently starting and stopping, so its specific value can be determined according to the actual external heat source temperature T h,in Change to determine.

[0121] The manner of adjusting the opening of the main throttle valve 4 and the subcooling throttle valve 17 in this embodiment is the same as that in Embodiment 2, and will not be described in detail here.

[0122] The above embodiments are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A control method for a refrigerant active jet heat pump based on a low-grade heat source, characterized in that: The refrigerant active injection heat pump based on a low-grade heat source comprises a heat pump system, an injection system, an external heat source (20) and an external heat source pump (21); the heat pump system comprises a compressor (1), a condenser (2), an evaporator (3), a main throttle valve (4) and a four-way valve (5) which are cyclically connected; the injection system comprises a subcooler (16) and a subcooling throttle valve (17); the subcooler (16) is provided with a refrigerant heat exchange pipe (18) and an external heat source heat exchange pipe (19); one end of the subcooling throttle valve (17) is connected to the outlet end of the condenser (2); the subcooling throttle valve (17) The other end of the refrigerant heat exchange tube (18) is connected to the inlet end of the refrigerant heat exchange tube (18), the outlet end of the refrigerant heat exchange tube (18) is connected to the intermediate pressure chamber of the compressor (1), and the external heat source pump (21) is connected between the inlet end of the external heat source heat exchange tube (19) and the outlet end of the external heat source (20); an external heat source temperature sensor (22) is provided at the outlet end of the external heat source (20), a subcooler inlet temperature sensor (23) is provided at the inlet end of the refrigerant heat exchange tube (18), and a subcooler outlet temperature sensor (24) is provided at the outlet end of the refrigerant heat exchange tube (18); The control method comprises the following steps: During the operation of the heat pump, the main throttle valve (4) and the subcooling throttle valve (17) adjust their openings according to a certain target, and at the same time, the external heat source temperature sensor (22) detects the external heat source temperature T in real time. h,in The subcooler injection inlet temperature T at the inlet end of the refrigerant heat exchange tube (18) is detected in real time by the subcooler inlet temperature sensor (23). inj,in The subcooler outlet temperature sensor (24) is used to detect the subcooler injection inlet temperature T at the outlet end of the refrigerant heat exchange tube (18) in real time. inj,out ; When the external heat source temperature T h,in ≤Subcooler injection outlet temperature T inj,out When the external heat source pump (21) is controlled to stop running, the external heat source (20) does not enter the subcooler (16); When the external heat source temperature T h,in > Subcooler injection outlet temperature T inj,out When the external heat source pump (21) is controlled to start operation, the external heat source (20) can enter the subcooler (16).

2. The control method of the refrigerant active jet heat pump based on a low-grade heat source according to claim 1 is characterized in that: In the refrigerant active jet heat pump based on a low-grade heat source, a suction temperature sensor (26) is provided on a pipeline connected to the suction port of the compressor (1), and an evaporator inlet temperature sensor (28) is provided on a pipeline connected to the inlet end of the evaporator (3); The main throttle valve (4) is controlled and adjusted according to the superheat of the heat pump, and the superheat of the heat pump is defined as: Compressor suction temperature T s -Defrost temperature T def ; When the actual superheat degree is greater than the target superheat degree, the main throttle valve (4) is opened wider; When the actual superheat is less than the target superheat, the main throttle valve (4) is closed; When the actual superheat degree=the target superheat degree, the main throttle valve (4) maintains the current opening degree; The target superheat is the preset temperature value of the heat pump system, and the compressor suction temperature T s The defrost temperature T is obtained by the suction temperature sensor (26). def Obtained by the evaporator inlet temperature sensor (28).

3. The control method of the refrigerant active jet heat pump based on a low-grade heat source according to claim 1, characterized in that: In the refrigerant active jet heat pump based on a low-grade heat source, a condenser outlet temperature sensor (27) is provided on a pipeline connected to the outlet end of the condenser (2), and a high-pressure pressure sensor (14) is provided on a pipeline connected to the exhaust port of the compressor (1); The subcooling throttle valve (17) is controlled and adjusted according to the subcooling degree of the heat pump, and the subcooling degree of the heat pump is defined as: The saturation temperature P corresponding to the heat pump high pressure d_t -Liquid pipe temperature T liq ; When the actual degree of subcooling is greater than the target degree of subcooling, the subcooling throttle valve (17) is opened wider; When the actual degree of subcooling is less than the target degree of subcooling, the subcooling throttle valve (17) is closed; When the actual degree of subcooling = the target degree of subcooling, the subcooling throttle valve (17) maintains the current opening; The target subcooling is the preset temperature value of the heat pump system, and the saturation temperature P corresponding to the high pressure of the heat pump is d_t The high pressure sensor (14) obtains the high pressure of the heat pump and converts it into the liquid pipe temperature T liq Obtained by the condenser outlet temperature sensor (27).

4. The control method of the refrigerant active jet heat pump based on a low-grade heat source according to claim 3 is characterized in that: In the refrigerant active jet heat pump based on a low-grade heat source, an exhaust temperature sensor (25) is provided on a pipeline connected to the exhaust port of the compressor (1); The subcooling throttle valve (17) is corrected and adjusted according to the superheat of the compressor exhaust of the heat pump. The superheat of the compressor exhaust of the heat pump is defined as: Compressor exhaust temperature T d -Saturation temperature P corresponding to the high pressure of the heat pump d_t ; When the actual compressor exhaust superheat is less than the set value B, the subcooling throttle valve (17) is closed; When the actual compressor exhaust gas superheat degree is greater than the set value C, the subcooling throttle valve (17) is opened wide; When the set value B≤actual compressor exhaust superheat≤set value C, the subcooling throttle valve (17) is controlled and adjusted according to the target subcooling of the heat pump; Among them, set value B and set value C are both the system preset temperature values ​​of the heat pump, and set value C> set value B; compressor exhaust temperature T d Obtained by the exhaust temperature sensor (25).

5. The control method of the refrigerant active jet heat pump based on a low-grade heat source according to claim 1, 2, 3 or 4, characterized in that: The following steps are also included: After the external heat source pump (21) is started, When the subcooler injection inlet temperature T inj,in +Set value A≤external heat source temperature T h,in <Subcooler injection outlet temperature T inj,out When the external heat source pump (21) is kept in a continuous operation state; When the external heat source temperature T h,in <Subcooler injection inlet temperature T inj,in + set value A, the external heat source pump (21) is controlled to stop running; The set value A is the preset temperature value of the heat pump system, and the subcooler injection inlet temperature T inj,in + set value A<subcooler injection outlet temperature T inj,out .

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