CN111623555A - Refrigerant active injection heat pump based on low-grade heat source and control method thereof - Google Patents

Abstract

Refrigerant injection can improve the heating capacity and energy efficiency of the heat pump, but the injection heat comes from the heat pump itself, which is passive injection. In view of this problem, the present invention proposes an active refrigerant 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, waste gas, etc., so that the heat of the external heat source and the injected refrigerant are supercooled. The heat is fully exchanged in the compressor, 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 the thermal power gain is obtained, which not only greatly improves the heating capacity and energy efficiency of the heat pump, but also can effectively Improve the user's comfort and expand the scope of application of the heat pump, so that the heat pump can be used in areas below ‑15℃. At the same time, the present invention also proposes the above-mentioned control method of the refrigerant active injection heat pump based on the low-grade heat source.

Description

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

technical field

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 technique

With the development of the economy, the continuous improvement of people's living standards and the development of urbanization, the application of air conditioning and heating systems has become increasingly widespread, resulting in huge building energy consumption. Globally, building energy consumption in developed countries accounts for about 37-40% of the total social energy consumption, and my country's building energy consumption accounts for more than 33% of the total social energy consumption. than the largest, as high as 65% or more. On the other hand, people put forward higher requirements for the comfort and hygiene of the living environment. Conventional air conditioners are generally low in energy efficiency, and the heating capacity and energy efficiency are seriously attenuated in low temperature environments; while heating by coal-fired boilers is not only unsanitary, but also It also pollutes the environment, is the main culprit in the generation of smog, and easily causes gas poisoning. Therefore, it is difficult for conventional air conditioning and heating equipment to meet the demands of high-quality life and energy efficiency. The current "coal-to-electricity" project, which uses electric energy-driven heat pumps to gradually replace traditional heating equipment, has become a general trend. With the promotion of this project, heat pumps have begun to enter ordinary households and are accepted by consumers.

When the heat pump is used for heating and heating, there are serious problems of heating capacity and energy efficiency attenuation at low ambient temperature, which has become the main factor hindering the popularization and use of this technology. In order to solve the above problems, most of the current heat pumps use jet enthalpy increasing technology. , so as to increase the refrigerant flow in the condenser, increase the enthalpy difference of the main circulation loop, and then improve the efficiency of the compressor.

Although the above-mentioned jet enthalpy increase technology improves the heating capacity and energy efficiency of the heat pump to a certain extent, the refrigerant injection with a subcooler, because the injected refrigerant and the refrigerant in the main circuit use internal heat. Exchange, does not absorb heat from the outside, is a kind of passive injection of refrigerant, so in fact, the improvement of heating capacity and energy efficiency of heat pump is limited. The heating capacity of the heat pump is generally increased by about 10%. After the optimization control measures are taken, the maximum increase is not more than 20%, and the energy efficiency of the heat pump is even more limited, which limits the use of the heat pump. When the ambient temperature is lower than - When the temperature is below 15°C, the low-temperature heat pump will not be able to perform heating.

SUMMARY OF THE INVENTION

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 wide application range.

In order to solve the above-mentioned technical problems, the present invention provides a refrigerant active injection heat pump based on a low-grade heat source with the following structure: including a heat pump system, an injection system, an external heat source and an external heat source pump, and the heat pump system Condenser, evaporator, main throttle valve and four-way valve; the injection system includes a subcooler and a subcooling throttle valve, and the subcooler is provided with a refrigerant heat exchange tube and an external heat source heat exchange tube, and the subcooling throttle One end of the valve is communicated with the outlet end of the condenser, the other end of the subcooling throttle valve is communicated with the inlet end of the refrigerant heat exchange tube, the outlet end of the refrigerant heat exchange tube is communicated with the intermediate pressure chamber of the compressor, and the external heat source pump is communicated Between the inlet end of the external heat source heat exchange tube and the outlet end of the external heat source.

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 the low-grade heat source of the present invention can fully utilize the external heat source, especially the low-grade heat source, and convert the low-grade heat source into It is a high-grade heat source, which can not only effectively improve the heat exchange performance of the subcooler, thereby greatly improving the heating capacity and energy efficiency of the heat pump, but also solve the serious attenuation of the heating capacity and energy efficiency of the heat pump at low ambient temperature. Therefore, the heat pump can be used in areas where the ambient temperature is lower than -15 °C, thus greatly broadening the application scope of the heat pump.

In the low-grade heat source-based refrigerant active jet heat pump of the present invention, an external heat source temperature sensor is provided at the outlet end of the external heat source, and a subcooler inlet temperature sensor is provided at the inlet end of the refrigerant heat exchange tube, The outlet end of the refrigerant heat exchange tube is provided with a subcooler outlet temperature sensor.

The above structure can precisely 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.

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

In order to solve the above-mentioned technical problems, the present invention provides a control method of a refrigerant active injection heat pump based on a low-grade heat source, comprising the following steps:

During the operation of the heat pump, the external heat source temperature T _h,in is detected in real time by the external heat source temperature sensor, and the subcooler injection inlet temperature T _inj,in at the inlet end of the refrigerant heat exchange tube is detected in real time by the subcooler inlet temperature sensor, The subcooler injection inlet temperature T _inj,out at the outlet end of the refrigerant heat exchange tube is detected in real time by the subcooler outlet temperature sensor;

When the external heat source temperature T _h,in ≤ the subcooler injection outlet temperature T _inj,out , control the external heat source pump to stop running, so that the external heat source cannot enter the subcooler;

When the external heat source temperature _Th,in > the subcooler injection outlet temperature T _inj,out , the external heat source pump is controlled to start running, so that the external heat source can enter the subcooler.

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

The control method of the refrigerant active jet heat pump based on the low-grade heat source of the present invention can make the heat pump 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, thereby not only effectively improving the heat pump efficiency The heat exchange performance of the subcooler is greatly improved, which greatly improves the heating capacity and energy efficiency of the heat pump, and also enables the heat pump to be used in areas where the ambient temperature is lower than -15 °C, thus greatly broadening the scope of application of the heat pump.

The control method of the refrigerant active injection heat pump based on the low-grade heat source according to the present invention, wherein, in the refrigerant active injection heat pump based on the low-grade heat source, the pipeline connected to the suction port of the compressor is provided with an air suction The temperature sensor is provided with an evaporator inlet temperature sensor on the pipeline connected to the inlet end of the evaporator;

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

compressor suction temperature T _s - defrost temperature T _def ;

When the actual superheat degree > the target superheat degree, the main throttle valve is opened;

When the actual superheat degree < target superheat degree, the main throttle valve is closed;

When the actual degree of superheat = the target degree of superheat, the main throttle valve maintains the current opening degree;

Wherein, the target superheat is the system preset temperature value of the heat pump, the compressor suction temperature T _s is obtained by the suction temperature sensor, and the defrosting temperature T _def is obtained by the evaporator inlet temperature sensor.

The above-mentioned control and adjustment of the main throttle valve can effectively ensure the operational reliability of the heat pump.

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

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:

The saturation temperature P _{d_t} corresponding to the high pressure of the heat pump - the liquid pipe temperature T _liq ;

When the actual subcooling degree is greater than the target subcooling degree, the subcooling throttle valve opens large;

When the actual subcooling degree < target subcooling degree, the subcooling throttle valve is closed small;

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

The target subcooling degree is the system preset temperature value of the heat pump, the saturation temperature P _{d_t} corresponding to the high pressure of the heat pump is obtained by converting the high pressure of the heat pump from the high pressure pressure sensor, and the liquid pipe temperature T _liq is obtained by the condenser outlet temperature sensor.

The above-mentioned control and adjustment of the subcooling throttle valve can effectively ensure the operational reliability of the heat pump.

The control method of the refrigerant active injection heat pump based on the low-grade heat source according to the present invention, wherein, in the refrigerant active injection heat pump based on the low-grade heat source, the pipeline connected to the exhaust port of the compressor is provided with an exhaust gas Temperature Sensor;

The subcooling throttle valve is corrected and adjusted according to the superheat degree of the compressor exhaust of the heat pump. The superheat degree of the compressor exhaust of the heat pump is defined as:

compressor discharge temperature T _d - saturation temperature P _{d_t} corresponding to the high pressure of the heat pump;

When the actual compressor discharge superheat degree < set value B, the subcooling throttle valve is closed;

When the actual compressor discharge superheat degree > the set value C, the supercooling throttle valve opens large;

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

Wherein, the set value B and the set value C are both the system preset temperature values of the heat pump, and the set value C > the set value B; the compressor discharge temperature T _d is obtained by the discharge temperature sensor.

The above correction and adjustment of the subcooling throttle valve can further ensure the operational reliability of the heat pump.

The control method of the refrigerant active injection heat pump based on a low-grade heat source according to the present invention, wherein, further comprises the following steps:

After the external heat source pump starts running,

When the subcooler injection inlet temperature T _inj,in + set value A≤external heat source temperature _Th,in < subcooler injection outlet temperature T _inj,out , keep the external heat source pump running continuously;

When the external heat source temperature _Th,in < subcooler injection inlet temperature T _inj,in + set value A, control the external heat source pump to stop running;

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

The above control method can effectively prevent the external heat source pump in the heat pump from starting and stopping frequently, thereby making the operation of the heat pump more stable and ensuring the heating capacity and energy efficiency of the heat pump.

Description of drawings

1 is a simplified schematic diagram of a system during heating by a heat pump in the prior art;

Fig. 2 is the cycle pressure enthalpy diagram during the heat pump heating of the prior art;

3 is a detailed schematic diagram of the system when the refrigerant active jet heat pump based on a low-grade heat source of the present invention is heated;

4 is a simplified schematic diagram of the system when the refrigerant active injection heat pump based on a low-grade heat source of the present invention is heated;

5 is a cycle pressure and enthalpy diagram of the low-grade heat source-based refrigerant active injection heat pump of the present invention for heating.

Description of reference numbers:

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

For the refrigerant active injection 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. Insulation water tank; 10. Main engine water pump; 11. Refrigerant conduit; 12. Insulation water conduit; 13. High pressure switch; 14. High pressure pressure sensor; 15, Low pressure pressure switch; 16, subcooler; 17, subcooling throttle valve; 18, refrigerant heat exchange pipe; 19, external heat source heat exchange pipe; 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 ways

The low-grade heat source-based refrigerant active jet heat pump and its control method of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

The simplified schematic diagram of the system of the prior art heat pump heating is shown in Figure 1:

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 suction port of the compressor 101 and after being compressed, it will become a high-temperature gaseous refrigerant The refrigerant is discharged from the discharge port of the compressor 101, and then flows into the condenser 102 and exchanges heat with air or water. Then the refrigerant that releases heat flows into the evaporator 103 through the subcooler 105 and the main throttle valve 104. Exchange heat with air in 103, and finally return to the suction port of compressor 101 and enter into compressor 101 again;

When the refrigerant is injected, the heat pump cycle process is as follows: the subcooling throttle valve 106 is opened, adjusted according to a certain target (for example, according to the degree of subcooling or superheat of the heat pump), the refrigerant enters through the suction port of the compressor 101 After being compressed by the compressor 101, it will become a high-temperature gaseous refrigerant and discharged from the discharge port of the compressor 101, and then flow into the condenser 102 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 103 through the cooler 105 and the main throttle valve 104, 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; another path In order to pass through the cold throttle valve 106 for throttling, it enters the subcooler 105 and exchanges heat with the refrigerant in the main circulation flow path, and is finally injected into the intermediate pressure chamber of the compressor 101 under the action of the pressure difference.

The corresponding pressure-enthalpy diagram of the prior art heat pump for heating is shown in Figure 2, where h is the specific enthalpy and P is the pressure.

V _A , V _B , V _C and V _D in FIG. 1 and FIG. 2 are the refrigerant state points when the refrigerant is not injected, and correspond to the suction port of the compressor 101 , the exhaust port of the compressor 101 , and the condenser 102 respectively The outlet, the refrigerant state point after the main throttle valve 104 is throttled; V ₁ -V ₉ are the refrigerant state points when the refrigerant is injected, and V ₁ , V ₂ , V ₃ , V ₄ and V ₈ correspond to the main The refrigerant in the circulating flow path corresponds to the state points at the suction port of the compressor 101, the exhaust port of the compressor 101, the inlet of the main throttle valve 104, the outlet of the main throttle valve 104, and the corresponding state points after the first stage compression of the compressor 101, V ₅ , _V6 and _V7 correspond to the state points of the refrigerant in the injection flow path at the inlet of the subcooling throttle valve 106, the outlet of the subcooling throttle valve 106, and entering the intermediate pressure chamber of the compressor 101, respectively, and _V9 corresponds to the refrigerant in the main circulation flow path and The state point where the refrigerant in the injection flow path is mixed in the intermediate chamber of the compressor 101 .

It can be seen from FIG. 2 that the refrigerant undergoes two stages of compression in the compressor 101, wherein V ₁ to V ₈ are the first stage compression, and V ₉ to V ₂ are the second stage compression.

According to the principle of heat pump cycle, the heating amount Q _{h, V} of the heat pump in the prior art is equal to the sum of the air energy Q _{e, V} absorbed by the evaporator 103 and the compression work EP _V , and the expression is:

Q _h,V =Q _e,V +EP _V

The expression of the air energy Q _e,V absorbed by the evaporator 103 is:

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, and the two parts of the refrigerant are mixed to perform the second-stage compression. Therefore, the compression work of the heat pump in the prior art is The expression is:

The expression of the energy efficiency COP _V of the heat pump in the prior art is:

In the above expressions, m _V and m _i,V are the compressor displacement and the refrigerant injection mass flow, respectively.

The above shows that the performance gain of the heat pump of the prior art comes from the increase of air energy (enthalpy difference between V ₅ point and V ₃ point) and the increase of compression work, while the heat of refrigerant injection (V ₇ point and V The heating capacity calculated by the enthalpy difference at ₆ points) is not calculated into the heating capacity Q _{h, V.}

It can be seen from this that the heat injected by the refrigerant in the prior art heat pump heating comes from the heat pump itself, so it is passive injection, and its performance improvement to the heat pump is limited. Therefore, the purpose of the present invention is to develop an external low-grade heat source The refrigerant under the action of the active jet heat pump can 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.

Example 1:

As shown in FIG. 3 , the low-grade heat source-based refrigerant active injection heat pump of the present invention includes a heat pump system, an injection system, an external heat source 20 and an external heat source pump 21 , and the heat pump system includes a compressor 1 , a condenser 2 , and an evaporator 3 , the main throttle valve 4, the four-way valve 5, the liquid storage tank 6, the gas-liquid separator 7, the outdoor fan 8, the heat preservation water tank 9 and the main engine water pump 10, and the condenser 2 is provided with a refrigerant conduit 11 and a heat preservation water conduit 12 , the discharge port of the compressor 1 is communicated with the D port of the four-way valve 5, the E port of the four-way valve 5 is communicated with the inlet end of the refrigerant conduit 11 on the condenser 2, and the outlet end of the refrigerant conduit 11 is connected to the liquid storage tank. 6 is connected to one end, the other end of the liquid storage tank 6 is connected to one end of the main throttle valve 4, the other end of the main throttle valve 4 is connected to one end of the evaporator 3, and the other end of the evaporator 3 is connected to the C port of the four-way valve 5. Communication, the S port of the four-way valve 5 is communicated with the inlet end of the gas-liquid separator 7, the outlet end of the gas-liquid separator 7 is communicated with the suction port of the compressor 1, and the main engine water pump 10 is communicated with the inlet end of the heat preservation water conduit 12. Between the outlet ends of the heat preservation water tank 9, the outlet end of the heat preservation water conduit 12 is communicated with the inlet end of the heat preservation water tank 9 through a pipeline, and the outdoor fan 8 is arranged close to the evaporator 3; The high pressure pressure switch 13 and the high pressure pressure sensor 14 are provided with a low pressure pressure switch 15 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, and the subcooler 16 is provided with The refrigerant heat exchange pipe 18 and the external heat source heat exchange pipe 19, one end of the subcooling throttle valve 17 is communicated with the outlet end of the condenser 2, and one end of the subcooling throttle valve 17 in this embodiment is communicated with the outlet of the refrigerant conduit 11 The other end of the subcooling throttle valve 17 is connected to the inlet end of the refrigerant heat exchange tube 18, and the outlet end of the refrigerant heat exchange tube 18 is connected to the intermediate pressure of the compressor 1 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, and the outlet end of the external heat source heat exchange tube 19 is connected through a pipeline. In this embodiment, the external heat source 20 can be hot water, steam or hot air heated by a low-grade heat source 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, and a refrigerant heat exchange tube 18 is provided at the inlet end of the heat exchange tube. A cooler inlet temperature sensor 23, 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, A suction temperature sensor 26 is arranged on the pipeline connected to the suction port, a condenser outlet temperature sensor 27 is arranged on the pipeline connected to the outlet end of the condenser 2, and an evaporator is arranged on the pipeline connected to the inlet end of the evaporator 3 Inlet temperature sensor 28 .

Figure 4 shows the simplified schematic diagram of the system when the refrigerant active injection heat pump based on the low-grade heat source is used for heating in this embodiment:

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 suction port of the compressor 1 and after being compressed, it will become a high-temperature gaseous refrigerant It is discharged from the exhaust port of compressor 1, and then flows into condenser 2 and exchanges heat with air or water. Then the refrigerant that releases heat flows into evaporator 3 through main throttle valve 4, and exchanges with air in evaporator 3. heat, and finally returns to the suction port of compressor 1 and enters into compressor 1 again;

When the refrigerant is injected, the cycle process of the heat pump is as follows: the subcooling throttle valve 17 is opened and adjusted according to a certain target (for example, according to the degree of subcooling or superheat of the heat pump), and an external heat source is input into the subcooler 16 at the same time. 20; Compressor 1 operates, the refrigerant enters into compressor 1 through the suction port of compressor 1 and after being compressed, it will turn into a high-temperature gaseous refrigerant and be discharged from the exhaust port of compressor 1, and then flow into condenser 2 and mix with the refrigerant. Air or water conducts heat exchange, and then the refrigerant will flow through two paths. The main circulation path is to flow into evaporator 3 through main throttle valve 4, exchange heat with air in evaporator 3, and finally return to compressor 1 for suction. 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 inject into the middle of the compressor 1 under the action of the pressure difference in the pressure chamber.

The corresponding pressure-enthalpy diagram of the low-grade heat source-based refrigerant active injection heat pump for heating in this embodiment is shown in Figure 5:

The expression of the heating capacity of the refrigerant active injection heat pump based on the low-grade heat source in this embodiment is:

Q _h,V =Q _e,V +Q _sc,inj +EP _V

Among them, Q _sc,inj is the heat absorbed by the refrigerant in the subcooler, and its expression is:

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

It can be seen from the above that the heating capacity of the refrigerant active injection heat pump based on the low-grade heat source in this embodiment is more than the heat quantity Q _sc,inj absorbed by the refrigerant in the subcooler than the heat pump of the prior art. Therefore, The energy efficiency COP _V of the refrigerant active injection heat pump based on the low-grade heat source in this embodiment is also improved accordingly.

Example 2:

This embodiment discloses the control method of the refrigerant active injection heat pump based on the low-grade heat source in the embodiment 1, which includes the following steps:

During the operation of the heat pump, the opening of the main throttle valve 4 and the subcooling throttle valve 17 is adjusted according to a certain target, such as the degree of subcooling or superheating of the heat pump; at the same time, the external heat source is detected in real time by the external heat source temperature sensor 22 The temperature T _h,in is detected in real time by the subcooler inlet temperature sensor 23 at the inlet end of the refrigerant heat exchange tube 18 , and the subcooler injection inlet temperature T _inj,in is detected in real time by the subcooler outlet temperature sensor 24 . subcooler injection inlet temperature T _inj,out at the outlet end of heat pipe 18;

When the external heat source temperature T _h, in≤subcooler injection outlet temperature T _inj,out , control the external heat source pump 21 to stop running, so that the external heat source 20 cannot enter the subcooler 16;

When the external heat source temperature _Th,in > the subcooler injection outlet temperature T _inj,out , the external heat source pump 21 is controlled to start running, so that the external heat source 20 can enter the subcooler 16 .

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

compressor suction temperature T _s - defrost temperature T _def ;

When the actual superheat degree > the target superheat degree, the main throttle valve 4 is opened large;

When the actual superheat degree < target superheat degree, the main throttle valve 4 is closed small;

When the actual degree of superheat=target degree of superheat, the main throttle valve 4 maintains the current opening degree;

The target superheat is the system preset temperature value of the heat pump, the compressor suction temperature T _s is obtained by the suction temperature sensor 26 , and the defrosting temperature T _def is obtained by the evaporator inlet temperature sensor 28 .

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 _{d_t} corresponding to the high pressure of the heat pump - the liquid pipe temperature T _liq ;

When the actual subcooling degree is greater than the target subcooling degree, the subcooling throttle valve 17 is opened large;

When the actual subcooling degree is less than the target subcooling degree, the subcooling throttle valve 17 is closed small;

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

The target subcooling degree is the system preset temperature value of the heat pump, the saturation temperature P _{d_t} corresponding to the high pressure of the heat pump is obtained by converting the high pressure of the heat pump obtained by the high pressure pressure sensor 14 , and the liquid pipe temperature T _liq is obtained by the condenser outlet temperature sensor 27 . .

In order to ensure the operational reliability of the heat pump, the subcooling throttle valve 17 is corrected and adjusted according to the superheat degree of the compressor exhaust of the heat pump, and the superheat degree of the compressor exhaust of the heat pump is defined as:

compressor discharge temperature T _d - saturation temperature P _{d_t} corresponding to the high pressure of the heat pump;

When the actual compressor discharge superheat degree < set value B, the subcooling throttle valve 17 is closed;

When the actual compressor discharge superheat degree > the set value C, the supercooling throttle valve 17 is opened large;

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

The set value B and the set value C are both system preset temperature values of the heat pump, and the set value C > the set value B; the compressor discharge temperature T _d is obtained by the discharge temperature sensor 25 .

The set value B and the set value C can make the subcooling throttle valve 17 participate in the control and adjustment of the compressor discharge temperature T _d when the compressor discharge temperature T _d is too low or too high, so as to ensure the compressor discharge temperature T _d is always within the reliability range; for example, the current heat pump generally requires the compressor exhaust superheat to be above 10 °C, then the set value B can be set at 15 to 20 °C under the condition of ensuring a certain margin; and At present, the protection value of the exhaust temperature T _d of the compressor of the heat pump is generally around 120 °C, and the saturation temperature P _{d_t} corresponding to the general heat pump high pressure (frequency-limited high pressure 37-38 bar) is around 60 °C, so in order to ensure a certain margin In this case, the set value C can be set to 45 to 55°C.

Of course, since the control and adjustment of the subcooling throttle valve 17 according to the subcooling degree of the heat pump is a normal adjustment, the correction adjustment of the subcooling throttle valve 17 according to the superheat degree of the compressor exhaust of the heat pump is to ensure the operation reliability of the heat pump, Therefore, when adjusting the opening degree of the subcooling throttle valve 17, it is necessary to ensure the operational reliability of the heat pump first. adjust.

Example 3:

The difference between this embodiment and Embodiment 2 is that this embodiment adds a control method for preventing the frequent starting and stopping of the external heat source pump 21, which specifically includes the following steps:

During the operation of the heat _pump , the opening of the main throttle valve 4 and the subcooling throttle valve 17 is adjusted according to a certain target. 23 Real-time detection of the subcooler injection inlet temperature T _inj,in at the inlet end of the refrigerant heat exchange tube 18 , and real-time detection of the subcooler injection inlet temperature at the outlet end of the refrigerant heat exchange tube 18 through the subcooler outlet temperature sensor 24 T _inj,out ;

When the external heat source temperature T _h,in > the subcooler injection outlet temperature T _inj,out , control the external heat source pump 21 to start operation, so that the external heat source 20 can enter the subcooler 16;

After the external heat source pump 21 starts to operate,

When the subcooler injection inlet temperature T _inj,in + set value A≤external heat source temperature _Th,in < subcooler injection outlet temperature T _inj,out , keep the external heat source pump 21 in a continuous running state;

When the external heat source temperature _Th,in < subcooler injection inlet temperature T _inj,in + set value A, control the external heat source pump 21 to stop running;

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

The setting of the setting value A is mainly to prevent the frequent switching of the heat source, which can be determined according to the actual change of Th,in.

The setting of the set value A is mainly to prevent the external heat source pump 21 from starting and stopping frequently, so its specific value can be determined according to the change of the actual external heat source temperature _Th,in .

The manner of adjusting the opening degrees of the main throttle valve 4 and the subcooling throttle valve 17 in this embodiment is the same as that in the second embodiment, and will not be repeated here.

The above embodiments are only to describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and variations of the technical solutions of the present invention made by those of ordinary skill in the art can be made. Improvements should all fall within the protection scope determined by the claims of the present invention.

Claims (7)

1. A refrigerant active injection heat pump based on a low-grade heat source is characterized in that: the heat pump system comprises a heat pump system, an injection system, an external heat source (20) and an external heat source pump (21), wherein 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 communicated in a circulating manner; the injection system comprises a subcooler (16) and a subcooling throttle valve (17), a refrigerant heat exchange tube (18) and an external heat source heat exchange tube (19) are arranged on the subcooler (16), one end of the subcooling throttle valve (17) is communicated with the outlet end of a condenser (2), the other end of the subcooling throttle valve (17) is communicated with the inlet end of the refrigerant heat exchange tube (18), the outlet end of the refrigerant heat exchange tube (18) is communicated with the middle pressure cavity of a compressor (1), and an external heat source pump (21) is communicated between the inlet end of the external heat source heat exchange tube (19) and the outlet end of an external heat source (20).

2. A refrigerant active injection heat pump based on a low-grade heat source according to claim 1, characterized in that: an external heat source temperature sensor (22) is arranged at the outlet end of the external heat source (20), a subcooler inlet temperature sensor (23) is arranged at the inlet end of the refrigerant heat exchange tube (18), and a subcooler outlet temperature sensor (24) is arranged at the outlet end of the refrigerant heat exchange tube (18).

3. A method for controlling a low-grade heat source based active injection heat pump for refrigerant, according to claim 2, comprising the steps of:

in the operation process of the heat pump, the opening of the main throttle valve (4) and the supercooling throttle valve (17) is adjusted according to a certain target, and meanwhile, the external heat source temperature sensor (22) detects the opening in real timeTemperature T of external heat source_h,inThe temperature T of the injection inlet of the subcooler at the inlet end of the refrigerant heat exchange tube (18) is detected in real time by the subcooler inlet temperature sensor (23)_inj,inDetecting in real time the subcooler spray inlet temperature T at the outlet end of the refrigerant heat exchange tube (18) by passing through the chiller outlet temperature sensor (24)_inj,out；

When the temperature T of the external heat source_h,inTemperature T of ejection outlet of subcooler is not more than_inj,outWhen the heat source enters the subcooler (16), controlling the external heat source pump (21) to stop running so that the external heat source (20) does not enter the subcooler (16);

when the temperature T of the external heat source_h,inTemperature T of ejection outlet of subcooler_inj,outAnd controlling the external heat source pump (21) to start operation so that the external heat source (20) can enter the subcooler (16).

4. The method of claim 3, wherein the method comprises: in the low-grade heat source-based refrigerant active injection heat pump, a suction temperature sensor (26) is arranged on a pipeline connected with a suction port of the compressor (1), and an evaporator inlet temperature sensor (28) is arranged on a pipeline connected with an inlet end of the evaporator (3);

the main throttle valve (4) is controlled and adjusted according to the superheat degree of the heat pump, and the superheat degree of the heat pump is defined as follows:

compressor suction temperature T_sDefrost temperature T_def；

When the actual superheat degree is larger than the target superheat degree, the main throttle valve (4) is opened to be large;

when the actual superheat degree is smaller than the target superheat degree, the main throttle valve (4) is closed;

when the actual superheat degree is equal to the target superheat degree, the main throttle valve (4) keeps the current opening degree;

wherein the target superheat degree is a system preset temperature value of the heat pump, and the suction temperature T of the compressor_sA defrost temperature T obtained by the suction temperature sensor (26)_defIs acquired by the evaporator inlet temperature sensor (28).

5. The method of claim 3, wherein the method comprises: in the low-grade heat source-based refrigerant active jet heat pump, a pipeline connected with the outlet end of the condenser (2) is provided with a condenser outlet temperature sensor (27), and a pipeline connected with the exhaust port of the compressor (1) is provided with a high-pressure sensor (14);

the supercooling throttle valve (17) is controlled and adjusted according to the supercooling degree of the heat pump, and the supercooling degree of the heat pump is defined as:

saturation temperature P corresponding to high pressure of heat pump_{d_t}Liquid tube temperature T_liq；

When the actual supercooling degree is larger than the target supercooling degree, the supercooling throttle valve (17) is opened to be large;

when the actual supercooling degree is less than the target supercooling degree, the supercooling throttle valve (17) is closed;

when the actual supercooling degree is equal to the target supercooling degree, the supercooling throttle valve (17) keeps the current opening degree;

wherein, the target supercooling degree is a system preset temperature value of the heat pump and a saturation temperature P corresponding to the high pressure of the heat pump_{d_t}The high pressure sensor (14) obtains the high pressure of the heat pump and then converts the high pressure to obtain the temperature T of the liquid pipe_liqIs acquired by the condenser outlet temperature sensor (27).

6. The method for controlling a low-grade heat source based active injection heat pump for refrigerant according to claim 5, wherein: in the refrigerant active injection heat pump based on the low-grade heat source, an exhaust temperature sensor (25) is arranged on a pipeline connected with an exhaust port of the compressor (1);

the supercooling throttle valve (17) is corrected and adjusted according to the exhaust superheat degree of a compressor of the heat pump, and the exhaust superheat degree of the compressor of the heat pump is defined as:

compressor discharge temperature T_d-saturation temperature P corresponding to high pressure of heat pump_{d_t}；

When the actual compressor exhaust superheat degree is less than a set value B, the supercooling throttle valve (17) is closed;

when the actual compressor exhaust superheat degree is larger than a set value C, the supercooling throttle valve (17) is opened greatly;

when the set value B is less than or equal to the actual compressor exhaust superheat degree and less than or equal to the set value C, the supercooling throttle valve (17) is controlled and adjusted according to the target supercooling degree of the heat pump;

the set value B and the set value C are both system preset temperature values of the heat pump, and the set value C is larger than the set value B; compressor discharge temperature T_dIs acquired by the exhaust gas temperature sensor (25).

7. The method for controlling a low-grade heat source based active injection heat pump for refrigerant, according to claim 3, 4, 5 or 6, further comprising the steps of:

after the external heat source pump (21) is started,

when the temperature T of the injection inlet of the subcooler_inj,in+ set value A is less than or equal to external heat source temperature T_h,in< temperature T of ejection outlet of subcooler_inj,outKeeping the external heat source pump (21) in a continuous operation state;

when the temperature T of the external heat source_h,in< temperature T of injection inlet of subcooler_inj,inWhen the external heat source pump (21) is controlled to stop running at the + set value A;

wherein the set value A is a system preset temperature value of the heat pump, and the injection inlet temperature T of the subcooler_inj,in+ set value A < subcooler jet outlet temperature T_inj,out。

Images