阅读说明：本技术 复叠式热泵系统 (Cascade heat pump system ) 是由 唐明生 田长青 邹慧明 于 2021-07-08 设计创作，主要内容包括：本发明提供一种复叠式热泵系统,包括高温级循环回路包括：依次相连形成回路的第一压缩机、冷凝器、风冷过冷器、第一节流装置和换热器的一级换热侧；低温级循环回路包括：依次相连形成回路的第二压缩机、换热器的二级换热侧、第二节流装置和蒸发器；风冷过冷器与蒸发器相邻设置,空气流经风冷过冷器形成第一风源,第一风源吹入蒸发器。本发明提供的复叠式热泵系统,通过在第一节流装置前设置风冷过冷器对管道内的液体进行降温,提高第一节流装置的使用寿命,提高可靠性；通过将风冷过冷器与蒸发器相邻设置,使得冷空气依次流过风冷过冷器和蒸发器,冷空气通过风冷过冷器进行加温后吹向蒸发器,从而减少蒸发器结霜的可能,提升整个热泵系统的性能。(The invention provides a cascade heat pump system, which comprises a high-temperature stage circulation loop, and comprises: the first compressor, the condenser, the air-cooled subcooler, the first throttling device and the first-stage heat exchange side of the heat exchanger are sequentially connected to form a loop; the low temperature stage circulation loop comprises: the second compressor, the secondary heat exchange side of the heat exchanger, the second throttling device and the evaporator are sequentially connected to form a loop; the air-cooled subcooler is arranged adjacent to the evaporator, air flows through the air-cooled subcooler to form a first air source, and the first air source is blown into the evaporator. According to the cascade heat pump system, the air cooling subcooler is arranged in front of the first throttling device to cool liquid in the pipeline, so that the service life of the first throttling device is prolonged, and the reliability is improved; through setting up air-cooled subcooler and evaporator are adjacent for cold air flows through air-cooled subcooler and evaporator in proper order, and cold air blows to the evaporator after heating through air-cooled subcooler, thereby reduces the possibility that the evaporator frosted, promotes whole heat pump system's performance.)

1. A cascade heat pump system, comprising:

a high temperature stage circulation loop comprising: the first compressor, the condenser, the air-cooled subcooler, the first throttling device and the first-stage heat exchange side of the heat exchanger are sequentially connected to form a loop;

a low temperature stage circulation loop comprising: the second compressor, the secondary heat exchange side of the heat exchanger, the second throttling device and the evaporator are sequentially connected to form a loop;

the air-cooled subcooler is adjacent to the evaporator, air flows through the air-cooled subcooler to form a first air source, and the first air source blows into the evaporator.

2. The cascade heat pump system of claim 1, further comprising a second wind source that is mixed with the first wind source and blown into the evaporator.

3. The cascade heat pump system according to claim 1 or 2, wherein the low temperature stage circulation loop further comprises: a four-way reversing valve and a heat storage water tank,

wherein, the first valve port of the four-way reversing valve is connected with the outlet of the second compressor, the second valve port is connected with the inlet of the second stage heat exchange side of the heat exchanger, the third valve port is connected with the inlet of the second compressor, the fourth valve port is connected with the outlet of the evaporator,

the heat storage water tank is installed between an outlet of the secondary heat exchange side of the heat exchanger and the second throttling device.

4. The cascade heat pump system of claim 1, wherein the high temperature stage recirculation loop further comprises: a flow diversion circuit, said first compressor including a gas makeup port,

the inlet of the shunting loop is connected with the air-cooled subcooler, the branch outlet of the shunting loop is connected with the air supplementing port, and the main outlet of the shunting loop is connected with the first throttling device.

5. The cascade heat pump system of claim 4, wherein the shunt circuit comprises an economizer comprising a three-stage heat exchanging side and a four-stage heat exchanging side,

the three-stage heat exchange sideIs/are as followsThe inlet is connected with the air-cooled subcooler, and the three-stage heat exchange sideIs/are as followsThe outlet is connected with the first throttling device,

and the inlet of the four-stage heat exchange side is communicated with the inlet of the three-stage heat exchange side, and the outlet of the four-stage heat exchange side is connected with the air supplementing port.

6. The cascade heat pump system of claim 5, wherein the shunt circuit further comprises a third throttling device disposed between an inlet of the tertiary heat exchange side and an inlet of the quaternary heat exchange side.

7. The cascade heat pump system of claim 4, wherein the shunt circuit comprises a flash tank, the flash tank comprising a flash inlet, a first flash outlet, and a second flash outlet,

the flash entrance is connected with the air-cooled subcooler, the first flash exit is connected with the air supplementing port, and the second flash exit is connected with the first throttling device.

8. The cascade heat pump system of claim 7, wherein the shunt loop further comprises a fourth throttle device disposed between the flash inlet and the air-cooled subcooler,

or the fourth throttling device is arranged between the air supplementing port and the first flashing port.

9. The cascade heat pump system of claim 1, wherein a gas-liquid separator is mounted at an inlet of the first compressor and at an inlet of the second compressor.

10. The cascade heat pump system according to claim 1, wherein the first compressor and the second compressor are each provided with a compressor frequency converter, the heat exchanger is further provided with a target parameter sensor,

the target parameter sensor is connected with the compressor frequency converter and comprises a temperature sensor and/or a pressure sensor.

Technical Field

The invention relates to the technical field of heat pump systems, in particular to a cascade type heat pump system.

Background

With the increasing severity of global energy situation and environmental pollution, energy conservation and emission reduction become the focus of worldwide attention, and energy conservation technology becomes the target of active research and development in various countries. The heat pump is a research hotspot in the field of energy application because of the advantages of high heating efficiency, energy conservation, environmental protection and the like. The majority of the heat pumps applied at present are steam compression type single-stage circulating heat pumps, and after the technology of air supply and enthalpy increase is adopted, higher efficiency can be kept at low ambient temperature.

Whereas the heating temperature of a conventional single-stage heat pump system does not typically exceed 70 c. In industrial production, the production processes of drying, heating and the like which are commonly used need to reach the temperature of more than 80 ℃ so as to meet most process requirements. Therefore, the existing production process with large heat demand generally adopts an oil/gas boiler for heat supply, and the production process with small heat demand mostly adopts an electric heating or electric boiler form. Therefore, in order to apply the heat pump system to industrial production, it is necessary to increase the heating temperature of the heat pump.

At present, the heating temperature of the conventional single-stage air source heat pump can only meet the low-temperature heating requirement of part of industrial production processes. Therefore, in order to increase the heating temperature, a cascade heat pump system is required. However, the throttling device used in the cascade heat pump system is limited due to the problem of high temperature of the unit.

For example, the conventional electronic throttle valve is in a high-temperature working state for a long time, so that the service life and reliability of the throttle device are seriously reduced, and the thermal expansion valve cannot be well adapted to the quick response of the adjustment performance of the heat pump unit, so that the pressure and temperature of the heat pump system oscillate to influence the heating capacity of the heat pump system and the reliability of the compressor. The throttling elements such as the capillary tube or the throttling short tube cannot adapt to the requirement of the high-temperature heat pump unit on variable working condition operation regulation. In addition, for the cascade heat pump system, when the ambient temperature is reduced, the reduction of the evaporation temperature of the unit obviously causes the serious attenuation of the heating performance, and meanwhile, the frosting problem of the evaporator at low ambient temperature can further reduce the heat pump performance and the operation time of the heat pump.

Disclosure of Invention

The invention provides a cascade heat pump system, which is used for solving the defects that the service life of a throttling device is shortened in a high-temperature heat supply environment, the working efficiency is reduced, and the working performance and the efficiency of the whole system are reduced due to frosting of an evaporator in a low-temperature environment in the prior art, so that the service life and the service temperature of the throttling device are ensured while the heat supply temperature is increased, the frosting condition of the evaporator is effectively relieved, and long-term stable and efficient system operation is realized.

The invention provides a cascade heat pump system, comprising:

a high temperature stage circulation loop comprising: the first compressor, the condenser, the air-cooled subcooler, the first throttling device and the first-stage heat exchange side of the heat exchanger are sequentially connected to form a loop;

a low temperature stage circulation loop comprising: the second compressor, the secondary heat exchange side of the heat exchanger, the second throttling device and the evaporator are sequentially connected to form a loop;

the air-cooled subcooler is adjacent to the evaporator, air flows through the air-cooled subcooler to form a first air source, and the first air source blows into the evaporator.

The cascade heat pump system further comprises a second air source, and the second air source and the first air source are mixed and then blown into the evaporator.

According to the cascade heat pump system provided by the present invention, the low temperature stage circulation circuit further includes: a four-way reversing valve and a heat storage water tank,

wherein, the first valve port of the four-way reversing valve is connected with the outlet of the second compressor, the second valve port is connected with the inlet of the second stage heat exchange side of the heat exchanger, the third valve port is connected with the inlet of the second compressor, the fourth valve port is connected with the outlet of the evaporator,

the heat storage water tank is installed between an outlet of the secondary heat exchange side of the heat exchanger and the second throttling device.

According to the cascade heat pump system provided by the invention, the high-temperature stage circulation loop further comprises: a flow diversion circuit, said first compressor including a gas makeup port,

the inlet of the shunting loop is connected with the air-cooled subcooler, the branch outlet of the shunting loop is connected with the air supplementing port, and the main outlet of the shunting loop is connected with the first throttling device.

According to the cascade heat pump system provided by the invention, the shunt loop comprises an economizer, the economizer comprises a three-stage heat exchange side and a four-stage heat exchange side,

the inlet of the three-stage heat exchange side is connected with the air-cooled subcooler, the outlet of the three-stage heat exchange side is connected with the first throttling device,

and the inlet of the four-stage heat exchange side is communicated with the inlet of the three-stage heat exchange side, and the outlet of the four-stage heat exchange side is connected with the air supplementing port.

According to the cascade heat pump system provided by the invention, the shunt loop further comprises a third throttling device, and the third throttling device is arranged between the inlet of the third stage heat exchange side and the inlet of the fourth stage heat exchange side.

According to the cascade heat pump system provided by the invention, the shunt circuit comprises a flash tank, the flash tank comprises a flash inlet, a first flash outlet and a second flash outlet,

the flash entrance is connected with the air-cooled subcooler, the first flash exit is connected with the air supplementing port, and the second flash exit is connected with the first throttling device.

According to the cascade heat pump system provided by the invention, the shunt circuit further comprises a fourth throttling device, the fourth throttling device is arranged between the flash evaporation inlet and the air-cooled subcooler,

or the fourth throttling device is arranged between the air supplementing port and the first flashing port.

According to the cascade heat pump system provided by the invention, the gas-liquid separator is arranged at the inlet of the first compressor and the inlet of the second compressor.

According to the present invention there is provided a cascade heat pump system,

the first compressor and the second compressor are both provided with compressor frequency converters, the heat exchanger is also provided with a target parameter sensor,

the target parameter sensor is connected with the compressor frequency converter and comprises a temperature sensor and/or a pressure sensor.

According to the cascade heat pump system, the high-temperature-level circulation loop and the low-temperature-level circulation loop are connected and heat exchange is carried out through the heat exchanger, and the air cooling subcooler is arranged in front of the first throttling device to cool liquid in the pipeline, so that the temperature of the liquid flowing through the first throttling device is reduced, the service life of the first throttling device is prolonged, and the reliability is improved; through placing air-cooled subcooler and evaporator adjacent for cold air flows through air-cooled subcooler and evaporator in proper order, and cold air blows to the evaporator after heating through air-cooled subcooler, thereby improves low temperature level evaporating temperature, reduces the evaporator frosting's of low temperature level probably, promotes whole heat pump system's performance.

Drawings

In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.

Fig. 1 is a block diagram of a cascade heat pump system according to the present invention;

FIG. 2 is a schematic diagram of a cascade heat pump system according to the present invention;

fig. 3 is a second schematic structural diagram of the cascade heat pump system provided by the present invention;

fig. 4 is a third schematic structural diagram of the cascade heat pump system according to the present invention.

Reference numerals:

100: a first compressor; 101: condenser 102: an air-cooled subcooler;

103: a first throttling device; 110: a shunt loop; 111: an economizer;

112: a third throttling means; 113: a flash tank; 114: a fourth throttling device;

120: use of a side fluid outlet; 200: a second compressor; 300: a heat exchanger;

121: use of a side fluid inlet; 202: an evaporator; 203: a four-way reversing valve;

204: a heat storage water tank; 201: a second throttling device; 400: a gas-liquid separator;

301: a target parameter sensor; 401: a low voltage switch; 402: a high voltage switch;

500: drying the filter; 501: a liquid viewing mirror.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the embodiments of the present invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the embodiments of the present invention and simplifying the description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be configured in a specific orientation, and operate, and thus, should not be construed as limiting the embodiments of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the embodiments of the present invention, it should be noted that, unless explicitly stated or limited otherwise, the terms "connected" and "connected" are to be interpreted broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. Specific meanings of the above terms in the embodiments of the present invention can be understood in specific cases by those of ordinary skill in the art.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of an embodiment of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

An embodiment of the present invention will be described below with reference to fig. 1 to 4. It is to be understood that the following description is only exemplary embodiments of the present invention and is not intended to limit the present invention.

As shown in fig. 1, the present invention provides a cascade heat pump system comprising:

a high temperature stage circulation loop comprising: the first compressor 100, the condenser 101, the air-cooled subcooler 102, the first throttling device 103 and the first-stage heat exchange side of the heat exchanger 300 are sequentially connected to form a loop;

a low temperature stage circulation loop comprising: a second compressor 200, a secondary heat exchange side of the heat exchanger 300, a second throttling device 201 and an evaporator 202 which are sequentially connected to form a loop;

the air-cooled subcooler 102 is disposed adjacent to the evaporator 202, and air flows through the air-cooled subcooler 102 to form a first air source, which is blown into the evaporator 202. In other words, air flows through the air-cooled subcooler 102 and the evaporator 202 in sequence.

In other words, the outlet of the first compressor 100 is connected to the inlet of the condenser 101, the outlet of the condenser 101 is connected to the inlet of the air-cooled subcooler 102, the outlet of the air-cooled subcooler 102 is connected to the inlet of the first throttling device 103, the outlet of the first throttling device 103 is connected to the inlet of the first heat exchanging side of the heat exchanger 300, and the outlet of the first heat exchanging side is connected to the inlet of the first compressor 100, so as to form a high-temperature stage circulation loop.

Similarly, the outlet of the second compressor 200 is connected to the inlet of the secondary heat exchange side of the heat exchanger 300, the outlet of the secondary heat exchange side is connected to the inlet of the second throttling device 201, the outlet of the second throttling device 201 is connected to the inlet of the evaporator 202, and the outlet of the evaporator 202 is connected to the inlet of the second compressor 200, so as to form a low-temperature stage circulation loop.

For the arrangement of the air-cooled subcooler 102 and the evaporator 202 of the invention, the air-cooled subcooler 102 and the evaporator 202 are adjacently arranged in the same air duct, and cold air firstly enters the air-cooled subcooler 102 to become a hot air port and blows the hot air port onto the evaporator 202, thereby solving the problem that the evaporator 202 is frosted due to low environmental temperature.

Further, in the high-temperature stage circulation loop, the temperature of the liquid flowing out of the first compressor 100 through the condenser 101 is higher, and the liquid is further cooled by the air-cooled subcooler 102. Therefore, the temperature of the liquid reaching the first throttling device 103 is low, the first throttling device 103 is not damaged, and the service life and the working efficiency of the first throttling device 103 are ensured.

For the heat exchanger 300 of the present invention, in the high temperature stage circulation loop, the first stage heat exchange side of the heat exchanger 300 converts the liquid passing through the first throttling device 103 into gas, heats and gasifies the liquid, the gas released from the first stage heat exchange side enters the first compressor 100,

in contrast, in the low-temperature stage circulation loop, the two-stage heat exchange side of the heat exchanger 300 converts the high-temperature gas released by the second compressor 200 into liquid, liquefies the gas, and the liquid flowing out through the two-stage heat exchange side enters the second throttling device 201.

In summary, the air-cooled subcooler 102 and the evaporator 202 are arranged adjacently, so that the air sequentially flows through the air-cooled subcooler 102 and the evaporator 202, and the efficient operation of the whole cascade heat pump system is ensured.

According to the cascade heat pump system, the high-temperature-level circulation loop and the low-temperature-level circulation loop are connected and heat exchange is carried out through the heat exchanger, and the air cooling subcooler is arranged in front of the first throttling device to cool liquid in the pipeline, so that the temperature of the liquid flowing through the first throttling device is reduced, the service life of the first throttling device is prolonged, and the reliability is improved; through setting up air-cooled subcooler and evaporator are adjacent for the cold air flows through air-cooled subcooler and evaporator in proper order, and the cold air blows to the evaporator after heating through air-cooled subcooler, thereby improves low temperature level evaporating temperature, reduces the possibility that the evaporator of low temperature level frosted, and then promotes whole heat pump system's performance.

Further, in an alternative embodiment of the present invention, the cascade heat pump system further comprises a second wind source, which is mixed with the first wind source and then blown into the evaporator 202. In this embodiment, the second air source may be cold air or hot air, or air in the air, or air blown from other devices.

As shown in fig. 2, in one embodiment of the invention, the low temperature stage circulation loop further comprises: a four-way reversing valve 203 and a hot water storage tank 204.

The first port a of the four-way reversing valve 203 is connected to the outlet of the second compressor 200, the second port b is connected to the inlet of the second heat exchange side of the heat exchanger 300, the third port c is connected to the inlet of the second compressor 200, and the fourth port d is connected to the outlet of the evaporator 202.

Further, a hot water storage tank 204 is installed between the outlet of the secondary heat exchange side of the heat exchanger 300 and the second throttling means 201. The hot water storage tank 204 is provided with an electric heater therein.

When the ambient temperature is not too low, for example, higher than-20 degrees, the air-cooled subcooler 102 heats the cold air and blows the heated cold air onto the evaporator 202, so that the evaporator 202 is prevented from frosting, and the normal working efficiency of the evaporator is not affected.

Then, when the ambient temperature is too low, for example, below-20 degrees, the hot air blown out through the air-cooled subcooler 102 is far from the purpose of preventing the evaporator 202 from defrosting, and therefore, the four-way reversing valve 203 needs to be adjusted to achieve the defrosting purpose.

Specifically, the four-way selector valve 203 is adjusted so that the first port a communicates with the fourth port d and, correspondingly, the second port b communicates with the third port c.

Such that the outlet of the second compressor 200 is connected to the outlet of the evaporator 202 and the inlet of the second compressor 200 is connected to the inlet of the secondary heat exchanging side of the heat exchanger 300.

Thereby, the high-temperature and high-pressure gas flowing out from the outlet of the second compressor 200 directly enters the evaporator 202, and the evaporator 202 is defrosted. The liquid flowing out from the evaporator 202 enters the hot water storage tank 204 to be heated into gas, enters the secondary heat exchange side of the heat exchanger 300 and then returns to the second compressor 200.

After defrosting the evaporator 202, the four-way selector valve 203 is adjusted to communicate the first port a with the second port b and to communicate the third port c with the fourth port d. And carrying out normal operation of the low-temperature stage circulation loop.

With continued reference to FIG. 2, in an alternative embodiment of the invention, the high temperature stage recirculation loop further comprises: a shunt loop 110. The first compressor 100 includes a make-up port e.

Further, an inlet of the bypass circuit 110 is connected to the air-cooled subcooler 102, a bypass outlet of the bypass circuit 110 is connected to the air supply port e, and a main outlet of the bypass circuit 110 is connected to the first throttling device 103.

With continued reference to fig. 2, in another embodiment of the present invention, the shunt circuit 110 includes an economizer 111, the economizer 111 including a three-stage heat exchanging side and a four-stage heat exchanging side.

Wherein, the inlet of the three-stage heat exchange side is connected with the air-cooled subcooler 102, and the outlet of the three-stage heat exchange side is connected with the first throttling device 103.

In addition, the inlet of the four-stage heat exchange side is communicated with the inlet of the three-stage heat exchange side, and the outlet of the four-stage heat exchange side is connected with the air supplementing port e.

In other words, the economizer 111 delivers a part of the liquid entering through the air-cooled subcooler 102 to the first throttling device 103, and another part of the liquid is converted into gas, which enters the first compressor 100 through the air supplement port e of the first compressor 100, so as to achieve the air supplement function, thereby increasing the cooling capacity of the high-temperature stage.

Further, in another optional embodiment of the present invention, the shunt circuit 110 further comprises a third throttling device 112, and the third throttling device 112 is disposed between the inlet of the third stage heat exchanging side and the inlet of the fourth stage heat exchanging side.

In an alternative embodiment of the present invention, as shown in fig. 3, the shunt circuit 110 includes a flash tank 113, the flash tank 113 includes a flash inlet, a first flash outlet and a second flash outlet,

the flash inlet is connected with the air-cooled subcooler 102, the first flash outlet is connected with the air supplementing port e, and the second flash outlet is connected with the first throttling device 103.

With continued reference to FIG. 3, in another alternative embodiment of the present invention, the bypass circuit 110 further includes a fourth throttling arrangement 114, the fourth throttling arrangement 114 being disposed between the flash inlet and the air-cooled subcooler 102.

Or as shown in fig. 4, the fourth throttle device 114 is disposed between the air supplement port e and the first flash outlet.

Referring to fig. 2 to 4, in an alternative embodiment of the present invention, gas-liquid separators 400 are installed at the inlet of the first compressor 100 and at the inlet of the second compressor 200.

Referring to fig. 2 to 4, in an alternative embodiment of the present invention, both the inlet of the second throttling means 201 and the inlet of the air-cooled subcooler 102 are provided with a dry filter 500.

In another embodiment of the present invention, condenser 101 includes a use-side fluid outlet 120 and a use-side fluid inlet 121.

Wherein the use-side fluid outlet 120 and the use-side fluid inlet 121 are used for heat exchange with external equipment.

In an alternative embodiment of the present invention, the first throttling device 103, the second throttling device 201, the third throttling device 112 and the fourth throttling device 114 may employ electronic expansion valves or capillary tube assemblies.

Wherein, the capillary subassembly includes many capillaries and with the solenoid valve of capillary one-to-one correspondence.

Referring to fig. 3 and 4, in an embodiment of the present invention, the liquid level observation mirror 501 is disposed on the pipeline of the high-temperature stage circulation loop and the low-temperature stage circulation loop, and particularly, the liquid level observation mirror 501 is disposed behind the dry filter 500, so that the conversion degree of gas and liquid can be better observed. Thereby timely adjusting the parameters of each part.

Further, the first compressor 100 and the second compressor 100 are each provided with a compressor inverter. As shown in fig. 3, the heat exchanger 300 is further provided with a target parameter sensor 301, wherein the target parameter sensor 301 is electrically connected to the compressor inverter. The target parameter sensor 301 comprises a temperature sensor and/or a pressure sensor.

Further, the target parameter sensor 301 includes temperature sensors provided at the primary heat exchanging side and the secondary heat exchanging side of the heat exchanger 300, and one or both of pressure sensors provided at the primary heat exchanging side and the secondary heat exchanging side of the heat exchanger 300. The energy balance between the circuits of the high temperature stage and the low temperature stage can be adjusted according to the target parameter sensor 301, which plays a good role in control.

As shown in fig. 4, in one embodiment of the present invention, a high-pressure switch 402 is installed at both the outlet of the first compressor 100 and the outlet of the second compressor 200; a low pressure switch 401 is installed at both the inlet of the first compressor 100 and the inlet of the second compressor 200.

The cascade heat pump system comprises a high-temperature-stage circulation loop and a low-temperature-stage circulation loop, wherein the two stages are connected and exchange heat through a heat exchanger, and the heat is finally transferred to a fluid loop on the use side through a condenser in the high-temperature-stage circulation loop.

The cascade heat pump system of the invention arranges the air-cooled subcooler at one side of the evaporator, so that the cold air flows through the air-cooled subcooler and the evaporator in sequence; therefore, the low-temperature circulating evaporation temperature of the heat pump can be effectively increased, the possibility of frosting of an evaporator is reduced, and the performance of the heat pump unit is improved. Meanwhile, the front temperature of the throttling device can be effectively reduced, and the reliability of the throttling device is improved.

The cascade heat pump system can enable the temperature of the using side fluid loop to reach the temperature required by the process heating in the industrial and agricultural fields, and provides a technical solution which is more energy-saving and environment-friendly for the high-temperature heating requirement in the industrial and agricultural fields.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.