CN114992889A - Cascade heat pump system and control method thereof - Google Patents

Abstract

The invention relates to the technical field of cascade heat pumps, in particular to a cascade heat pump system and a control method thereof, and aims to solve the problem that the existing cascade heat pump system is easily influenced by the ambient temperature and has a narrow operation range. Therefore, the cascade heat pump system comprises a high-pressure refrigerant circulation loop, a first low-pressure refrigerant circulation loop, a second low-pressure refrigerant circulation loop and a bypass branch, wherein the first low-pressure refrigerant circulation loop, the second low-pressure refrigerant circulation loop and the bypass branch can selectively run; based on the above, the cascade heat pump system of the invention controls the operation states of the first low-pressure refrigerant circulation loop and the second low-pressure refrigerant circulation loop according to the acquired environment temperature, so as to effectively reduce the operation energy consumption of the cascade heat pump system; the running state of the bypass branch is controlled according to the obtained running parameters of the high-pressure refrigerant circulating loop, so that the high-pressure refrigerant circulating loop can be effectively ensured to run all the time by controlling the on-off state of the bypass branch, and the running range of the cascade heat pump system is effectively expanded.

Description

Cascade heat pump system and control method thereof

technical field

The invention relates to the technical field of cascade heat pumps, and in particular provides a cascade heat pump system and a control method thereof.

Background technique

With the promotion of energy saving and emission reduction policies, there are more and more applications where high temperature heat pump systems are used for high temperature heating in food processing, textile and chemical industries. The demand for industrial heating is strong, and the application requirements for high-temperature heat pump systems are also getting higher and higher. First of all, the final heating temperature of the high temperature heat pump system is generally greater than 70°C or even more than 90°C. Secondly, the application environment temperature of the heating system ranges from -30°C to 35°C, or even a larger span. High-temperature hot water or hot air needs to be provided in winter or summer.

The high temperature of the high-temperature hot water used in industry is high, which makes the ordinary heat pump system unable to meet the actual heating demand. The technology of using the cascade heat pump system to provide high-temperature hot water is very mature. Cascade heat pump system generally includes high-pressure refrigerant circulation loop and low-pressure refrigerant circulation loop. However, the existing cascade heat pump system is limited by the ambient temperature and cannot operate when the ambient temperature is higher or lower, that is, the existing cascade heat pump system has a narrow operating range and cannot always provide heat to users water, causing inconvenience to users.

Accordingly, there is a need in the art for a new cascade heat pump system and a control method thereof to solve the above technical problems.

SUMMARY OF THE INVENTION

The present invention aims to solve the above-mentioned technical problem, that is, to solve the problem that the existing cascade heat pump system is easily affected by the ambient temperature and has a narrow operating range.

In a first aspect, the present invention provides a control method for a cascade heat pump system, the cascade heat pump system includes a high pressure refrigerant circulation loop, a first low pressure refrigerant circulation loop, a second low pressure refrigerant circulation loop and a bypass branch ,

A first compressor, a first heat exchanger, a first throttling member and an intermediate heat exchanger are arranged on the high-pressure refrigerant circulation circuit, and a second compressor, the intermediate heat exchanger are arranged on the first low-pressure refrigerant circulation circuit A heat exchanger, a second throttling member and a second heat exchanger, the second low-pressure refrigerant circulation loop is provided with a fluorine pump, the second heat exchanger and the intermediate heat exchanger, the fluorine pump is Both ends are connected to the first low-pressure refrigerant circulation circuit, both ends of the second compressor are connected to the second low-pressure refrigerant circulation circuit, the first low-pressure refrigerant circulation circuit and the second low-pressure refrigerant circulation circuit is arranged to be able to selectively exchange heat with the high-pressure refrigerant circulation loop through the intermediate heat exchanger,

The first end of the bypass branch is connected between the connection point between the fluorine pump and the first low-pressure refrigerant circulation loop and the second heat exchanger, and the second end of the bypass branch is connected Between the second compressor and the intermediate heat exchanger, a control valve is arranged on the bypass branch, and the control valve is arranged to be able to control the on-off state of the bypass branch,

The control method includes:

obtaining the ambient temperature where the cascade heat pump system is located;

controlling the operating states of the first low-pressure refrigerant circulation loop and the second low-pressure refrigerant circulation loop according to the ambient temperature;

Obtain the operating parameters of the high-pressure refrigerant circulation loop;

The operating state of the bypass branch is controlled according to the operating parameters of the high-pressure refrigerant circulation loop.

In a preferred technical solution of the above control method, the step of "controlling the operating states of the first low-pressure refrigerant circulation loop and the second low-pressure refrigerant circulation loop according to the ambient temperature" includes:

If the ambient temperature is greater than or equal to a preset ambient temperature, the first low-pressure refrigerant circulation circuit is controlled to not operate, and the second low-pressure refrigerant circulation circuit is controlled to operate.

In the preferred technical solution of the above control method, the step of "controlling the operating states of the first low-pressure refrigerant circulation loop and the second low-pressure refrigerant circulation loop according to the ambient temperature" further includes:

If the ambient temperature is lower than the preset ambient temperature, the first low-pressure refrigerant circulation circuit is controlled to operate, and the second low-pressure refrigerant circulation circuit is controlled to not operate.

In the preferred technical solution of the above control method, the step of "obtaining the operating parameters of the high-pressure refrigerant circulation loop" specifically includes:

obtaining the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger;

The step of "controlling the operating state of the bypass branch according to the operating parameters of the high-pressure refrigerant circulation loop" specifically includes:

The operating state of the bypass branch is controlled according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature.

In the preferred technical solution of the above control method, the step of "controlling the operating state of the bypass branch according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature" specifically includes:

Calculate the difference between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, and record it as the first difference;

If the first difference is less than the first preset difference, controlling the bypass branch to operate; and/or,

If the first difference is greater than or equal to the first preset difference, the bypass branch is controlled to not operate.

In the preferred technical solution of the above control method, the step of "obtaining the operating parameters of the high-pressure refrigerant circulation loop" specifically includes:

obtaining the current suction pressure and the maximum suction pressure of the first compressor;

The step of "controlling the operating state of the bypass branch according to the operating parameters of the high-pressure refrigerant circulation loop" specifically includes:

The operating state of the bypass branch is controlled according to the current suction pressure and the maximum suction pressure.

In the preferred technical solution of the above control method, the step of "controlling the operating state of the bypass branch according to the current suction pressure and the maximum suction pressure" specifically includes:

Calculate the difference between the maximum inspiratory pressure and the current inspiratory pressure, denoted as the second difference;

If the second difference is less than a second preset difference, controlling the bypass branch to operate; and/or,

If the second difference is greater than or equal to the second preset difference, the bypass branch is controlled to not operate.

In a preferred technical solution of the above control method, when the first low-pressure refrigerant circulation loop is running and the bypass branch is not running, the control method further includes:

obtaining the refrigerant temperature at the outlet of the second heat exchanger;

The operating state of the bypass branch is further controlled according to the temperature of the refrigerant at the outlet of the second heat exchanger.

In the preferred technical solution of the above control method, the step of "further controlling the operating state of the bypass branch according to the temperature of the refrigerant at the outlet of the second heat exchanger" specifically includes:

If the temperature of the refrigerant at the outlet of the second heat exchanger is less than or equal to the preset refrigerant temperature, the bypass branch is controlled to operate; and/or,

If the refrigerant temperature at the outlet of the second heat exchanger is greater than the preset refrigerant temperature, the bypass branch is controlled to not operate.

In another aspect, the present invention also provides a cascade heat pump system, the cascade heat pump system includes a controller capable of executing the control method described in any one of the above preferred technical solutions.

In the case of adopting the above technical solutions, the cascade heat pump system of the present invention can control the operating states of the first low-pressure refrigerant circulation loop and the second low-pressure refrigerant circulation loop according to the obtained ambient temperature, so as to effectively reduce the cost of the cascade heat pump system. Operating energy consumption; it can also control the operating state of the bypass branch according to the obtained operating parameters of the high-pressure refrigerant circulation loop, and then effectively ensure that the high-pressure refrigerant circulation loop can always run by controlling the on-off state of the bypass branch, effectively expanding the cascade The operating range of the heat pump system can meet the needs of users.

Description of drawings

Preferred embodiments of the present invention are described below in conjunction with the accompanying drawings, in which:

Fig. 1 is the overall structure schematic diagram of the cascade heat pump system of the present invention;

Fig. 2 is the main step flow chart of the control method of the present invention;

3 is a flow chart of the specific steps of the first preferred embodiment of the control method of the present invention;

4 is a flow chart of the specific steps of the second preferred embodiment of the control method of the present invention;

Reference number:

1. High pressure refrigerant circulation loop; 11. First compressor; 12. First heat exchanger; 13. First throttle member; 14. Intermediate heat exchanger;

2. The first low-pressure refrigerant circulation circuit; 21, the second compressor; 22, the second throttle member; 23, the second heat exchanger; 24, the first one-way valve; 25, the second one-way valve;

3. The second low-pressure refrigerant circulation loop; 31. The fluorine pump; 32. The third one-way valve;

4. Bypass branch; 41. Control valve;

5. Change the hot water circuit.

Detailed ways

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principle of the present invention, and are not intended to limit the protection scope of the present invention. Those skilled in the art can adjust it as needed to adapt to specific applications. For example, the cascade heat pump system described in the present invention may be a domestic cascade heat pump system or an industrial cascade heat pump system, which is not limiting, and those skilled in the art can set their own according to actual use requirements. The application of the cascade heat pump system of the present invention is determined. Such changes in relevant application situations do not deviate from the basic principles of the present invention, and belong to the protection scope of the present invention.

It should be noted that, in the description of the present preferred embodiment, unless otherwise expressly specified and limited, the terms "first", "second" and "third" are only used for the purpose of description, and should not be construed as indicating or imply relative importance. In addition, the terms "connected" and "connected" should be understood in a broad sense, for example, it may be a mechanical connection, an electrical connection, a direct connection, an indirect connection through an intermediate medium, or an internal connection between two elements. , so it should not be construed as a limitation of the present invention. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

In addition, it should be noted that, in the description of the present invention, although the various steps of the control method of the present invention are described in a specific order in the present application, these sequences are not restrictive, and do not deviate from the basic principle of the present invention. Under the premise that those skilled in the art can perform the steps in different orders.

Based on the problem that the existing cascade heat pump system is easily affected by the ambient temperature and has a narrow operating range mentioned in the background art, the present invention provides a new cascade heat pump system and a control method thereof. The first low-pressure refrigerant circulation loop, the second low-pressure refrigerant circulation loop and the bypass branch can be run stably to expand the operating range of the cascade heat pump system, thereby effectively ensuring that the high-pressure refrigerant circulation loop is always running to meet the needs of users.

Referring first to FIG. 1 , FIG. 1 is a schematic diagram of the overall structure of the cascade heat pump system of the present invention. As shown in FIG. 1 , the cascade heat pump system of the present invention includes a high-pressure refrigerant circulation circuit 1, a first low-pressure refrigerant circulation circuit 2 and a second low-pressure refrigerant circulation circuit 3, and the high-pressure refrigerant circulation circuit 1 is provided with a first compressor 11. , the first heat exchanger 12, the first throttling member 13 and the intermediate heat exchanger 14, the first low pressure refrigerant circulation circuit 2 is provided with a second compressor 21, the intermediate heat exchanger 14, the second throttling member 22 and The second heat exchanger 23, the second low pressure refrigerant circulation loop 3 is provided with a fluorine pump 31, the second heat exchanger 23 and the intermediate heat exchanger 14, the first low pressure refrigerant circulation loop 2 and the second low pressure refrigerant circulation loop 3 are provided It can selectively exchange heat with the high-pressure refrigerant circulation circuit 1 through the intermediate heat exchanger 14 .

Based on the above structural arrangement, the cascade heat pump system of the present invention effectively ensures that the high-pressure refrigerant circulation loop 1 is always running by selectively operating the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3, thereby effectively expanding the The operating range of the cascade heat pump system can also be effectively reduced, and the operating energy consumption of the cascade heat pump system can be effectively improved, and the user experience can be improved.

It should be noted that the present invention does not impose any restrictions on the specific types of refrigerants flowing in the high-pressure refrigerant circulating circuit 1, the first low-pressure refrigerant circulating circuit 2 and the second low-pressure refrigerant circulating circuit 3, and those skilled in the art can set their own according to the actual situation. Certainly. As a specific embodiment, the refrigerant in the high-pressure refrigerant circulation circuit 1 is refrigerant R134a, and the refrigerant in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 is refrigerant R410A.

In addition, it should be noted that the present invention does not impose any restrictions on the specific structure of the intermediate heat exchanger 14, which can be a shell-and-tube heat exchanger or a plate-type heat exchanger, and those skilled in the art can make their own choices according to the actual situation. set up. In this specific embodiment, the intermediate heat exchanger 14 is preferably a plate heat exchanger, so as to effectively improve the heat exchange of the refrigerant in the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 in the intermediate heat exchanger 14 efficiency.

Preferably, the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 are connected to simplify the structure of the cascade heat pump system. As shown in FIG. 1 , both ends of the fluorine pump 31 are connected to the first low-pressure refrigerant circulation circuit 2, and both ends of the second compressor 21 are connected to the second low-pressure refrigerant circulation circuit 3; Connected between the second throttle member 22 and the second heat exchanger 23 , the second end of the fluorine pump 31 is connected between the intermediate heat exchanger 14 and the second throttle member 22 . The intermediate heat exchanger 14 includes a first heat exchange channel and a second heat exchange channel, and the second heat exchanger 23 includes a first heat exchange tube, wherein the refrigerant in the high-pressure refrigerant circulation circuit 1 flows through the first heat exchange channel , the refrigerants in the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 flow through the second heat exchange channel and the first heat exchange tube to achieve the purpose of heat exchange.

It should be noted that the present invention does not apply to the first compressor 11 , the second compressor 21 , the fluorine pump 31 , the first throttling member 13 , the second throttling member 22 , the first heat exchanger 12 and the second heat exchanger No limitation is imposed on the specific structure and specific model of 23; the first compressor 11 and the second compressor 21 may be variable frequency compressors or fixed frequency compressors, preferably, the first compressor 11 and the second compressor 21 is a variable frequency compressor to control the operating state of the cascade heat pump system; the fluorine pump 31 can be a fluorine-lined centrifugal pump, a fluorine-lined magnetic pump, or a fluorine-lined self-priming pump; the first throttling member 13 and the second throttling member 22 can be an electronic expansion valve, a capillary tube, or a thermal expansion valve; the first heat exchanger 12 and the second heat exchanger 23 can be a plate heat exchanger or a shell The tubular heat exchanger, which is not limiting, can be set by those skilled in the art according to the actual situation.

In addition, it should be noted that the present invention also does not impose any restrictions on the heat source source of the second heat exchanger 23, which can be an air source or a ground source, which is not limiting, as long as the second heat exchanger 23 can be realized The heat exchange purpose of the heat exchanger 23 is sufficient, and those skilled in the art can set it according to the actual situation. In this preferred embodiment, the heat source of the second heat exchanger 23 is an air source, so as to further reduce the energy consumption of the cascade heat pump system and improve the operation energy efficiency; specifically, the cascade heat pump system further includes a heat exchanger A hot air blower (not shown in the figure) is provided near the second heat exchanger 23 to improve the heat exchange effect between the air and the refrigerant in the second heat exchanger 23 .

Further, in this preferred embodiment, the cascade heat pump system further includes a bypass branch 4, and the first end of the bypass branch 4 is connected to the connection point between the fluorine pump 31 and the first low-pressure refrigerant circulation loop 2 and the second heat exchanger 23, the second end of the bypass branch 4 is connected between the second compressor 21 and the intermediate heat exchanger 14, the setting of the bypass branch 4 can further expand the cascade type The operating range of the heat pump system can effectively ensure that the high-pressure refrigerant circulation loop 1 can always operate to meet the actual needs of users. It should be noted that the present invention does not impose any restrictions on the specific connection positions of the first end and the second end of the bypass branch 4, and those skilled in the art can set them according to the actual situation.

Preferably, the bypass branch 4 is provided with a control valve 41, and the control valve 41 is set to be able to control the on-off state of the bypass branch 4 and the flow direction of the refrigerant. It should be noted that the present invention does not impose any restrictions on the specific structure and type of the control valve 41, and those skilled in the art can set it according to the actual situation.

As a specific embodiment, the control valve 41 is a reversing control valve, and the reversing control valve is configured to enable the refrigerant flowing in the bypass branch 4 to pass from the second side of the bypass branch 4 through the reversing control. The end flows to the first end of the bypass branch 4 , and the refrigerant flowing in the bypass branch 4 can also flow from the first end of the bypass branch 4 to the second end of the bypass branch 4 .

Specifically, the reversing control valve is configured to enable the refrigerant flowing in the first low-pressure refrigerant circulation circuit 2 to pass through the bypass branch when the first low-pressure refrigerant circulation circuit 2 is in operation and the second low-pressure refrigerant circulation circuit 3 is not in operation. The second end of 4 flows to the first end of the bypass branch 4 . After the refrigerant in the first low-pressure refrigerant circulation circuit 2 is discharged from the discharge port of the second compressor 21, a part enters the bypass branch 4 through the second end of the bypass branch 4, and the other part enters the intermediate heat exchanger 14 It exchanges heat with the refrigerant in the high-pressure refrigerant circulation circuit 1, and then passes through the second throttling member 22 to throttle and depressurize, and then merges with the refrigerant flowing out of the first end of the bypass branch 4 and enters the second heat exchanger 23. , and then return to the second compressor 21 from the air inlet of the second compressor 21 .

In addition, the reversing control valve is also configured to enable the refrigerant flowing in the second low-pressure refrigerant circulation circuit 3 to pass through the bypass branch when the first low-pressure refrigerant circulation circuit 2 is not in operation and the second low-pressure refrigerant circulation circuit 3 is in operation. The first end of 4 flows to the second end of the bypass branch 4 . Specifically, a part of the refrigerant circulated through the fluorine pump 31 enters the bypass branch 4 through the first end of the bypass branch 4 , and the other part enters the second heat exchanger 23 to evaporate and absorb heat and then communicate with the bypass branch 4 . The refrigerant flowing out of the second end of the refrigerant is combined, and then enters the intermediate heat exchanger 14 for heat exchange with the refrigerant in the high-pressure refrigerant circulation circuit 1, and the refrigerant after heat exchange enters the fluorine pump 31 again to participate in the circulation.

In addition, when both the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 are in operation, those skilled in the art can control the direction of the reversing control valve, thereby controlling the flow direction of the refrigerant in the bypass branch 4, The present invention does not make any limitation to this.

Preferably, the first low-pressure refrigerant circulation circuit 2 is further provided with a first one-way valve 24, the first one-way valve 24 is disposed between the second compressor 21 and the second end of the bypass branch 4, and the first one-way valve 24 is provided. The check valve 24 is set to only allow the refrigerant to flow from the side of the discharge port of the second compressor 21 to the second end of the bypass branch 4 and the side of the intermediate heat exchanger 14. The first check valve 24 can effectively ensure that When the first low-pressure refrigerant circulation circuit 2 is not in operation and the second low-pressure refrigerant circulation circuit 3 is in operation, the refrigerant flowing out of the second end of the bypass branch 4 will not flow back into the second compressor 21 .

Further, the first low-pressure refrigerant circulation circuit 2 is also provided with a second one-way valve 25, and the second one-way valve 25 is arranged at the first end of the bypass branch 4 and the fluorine pump 31 and the first low-pressure refrigerant circulation circuit 2. Between the connection points, the second one-way valve 25 is set to only allow the refrigerant to flow from the side of the connection point between the fluorine pump 31 and the first low-pressure refrigerant circulation loop 2 to the first end of the bypass branch 4 and the second heat exchange On one side of the device 23, the second one-way valve 25 can effectively ensure that when the first low-pressure refrigerant circulation circuit 2 is running and the second low-pressure refrigerant circulation circuit 3 is not running, the refrigerant flowing out of the first end of the bypass branch 4 will not Backflow into the fluorine pump 31 .

Further preferably, a third one-way valve 32 is also provided on the second low-pressure refrigerant circulation circuit 3, and the third one-way valve 32 is provided between the second heat exchanger 23 and the intermediate heat exchanger 14, specifically, the third one-way valve 32 The check valve 32 is arranged in parallel with the second compressor 21 , and the third check valve 32 is arranged to only allow the refrigerant to flow from the side of the second heat exchanger 23 to the side of the intermediate heat exchanger 14 .

It should be noted that the present invention does not limit the specific structures and models of the first one-way valve 24, the second one-way valve 25 and the third one-way valve 32, which can be set by those skilled in the art according to actual conditions.

In addition, in this preferred embodiment, the cascade heat pump system further includes a hot water exchange circuit 5, and a part of the hot water exchange circuit 5 is arranged in the first heat exchanger 12 to exchange with the refrigerant in the high-pressure refrigerant circulation circuit 1 hot. It should be noted that the present invention does not impose any restrictions on the specific structure of the hot water exchange circuit 5, and those skilled in the art can set it according to the actual situation.

Further, the high-pressure refrigerant circulation circuit 1 is also provided with a first air separation device (not shown in the figure), and the first air separation device is arranged at the air inlet of the first compressor 11 . The first low-pressure refrigerant circulation loop 2 is also provided with a second air separation device (not shown in the figure), and the second air separation device is arranged at the air inlet of the second compressor 21 . The arrangement of the first air separation device and the second air separation device can effectively avoid the problem of liquid hammer in the first compressor 11 and the second compressor 21, and effectively ensure the first compressor 11 and the second compressor 21. service life. It should be noted that the present invention does not impose any restrictions on the specific structures of the first gas separation device and the second gas separation device, and those skilled in the art can set them according to actual conditions.

Further, the cascade heat pump system also includes a temperature sensor, a pressure sensor and a controller, the temperature sensor is used to detect the ambient temperature, the current refrigerant evaporation temperature of the intermediate heat exchanger 14 and the outlet of the second heat exchanger 23 The temperature of the refrigerant at the first compressor 11 is used to detect the current suction pressure of the first compressor 11 . It should be noted that the present invention does not impose any restrictions on the specific structure, model, number and location of the temperature sensor and the pressure sensor, which can be set by those skilled in the art according to the actual situation.

The controller can control the operation state of the cascade heat pump system, for example, the controller can control the operation state of the first low-pressure refrigerant circulation circuit 2, the second low-pressure refrigerant circulation circuit 3 and the bypass branch 4, The controller can also acquire the detection results of the temperature sensor and the pressure sensor, etc., which are not limitative. It can be understood by those skilled in the art that the present invention does not limit the specific structure and model of the controller, and the controller may be the original controller of the cascade heat pump system, or the controller For a controller set separately for implementing the control method of the present invention, those skilled in the art can set the structure and model of the controller by themselves according to actual use requirements.

Referring first to FIG. 2, FIG. 2 is a flow chart of the main steps of the control method of the present invention. As shown in FIG. 2, based on the cascade heat pump system described in the above embodiment, the control method of the present invention mainly includes the following steps:

S1: Obtain the ambient temperature where the cascade heat pump system is located;

S2: Control the operating states of the first low-pressure refrigerant circulation loop and the second low-pressure refrigerant circulation loop according to the ambient temperature;

S3: Obtain the operating parameters of the high-pressure refrigerant circulation loop;

S4: Control the operating state of the bypass branch according to the operating parameters of the high-pressure refrigerant circulation loop.

First, in step S1, the controller acquires the ambient temperature of the cascade heat pump system detected by the temperature sensor; of course, the present invention does not make any specific acquisition timing and acquisition method of the ambient temperature. Restriction, the controller may acquire in real time, or acquire in a certain period of time, which is not restrictive, and those skilled in the art can set by themselves according to the actual situation. Preferably, the controller acquires the ambient temperature in real time, so as to be able to adjust the operating state of the cascade heat pump system in a timely and effective manner, thereby effectively improving the operating energy efficiency of the cascade heat pump system and expanding the The operating range of the cascade heat pump system.

Next, in step S2, the controller controls the operating states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature.

It should be noted that the present invention does not impose any restrictions on the specific control logic of step S2, and the controller can control the on-off state of the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 according to the ambient temperature, and also The operating speeds of the refrigerants in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 can be controlled, which are not limiting, and can be set by those skilled in the art according to actual conditions.

Further, in step S3, the controller obtains the operating parameters of the high-pressure refrigerant circulating circuit 1; of course, the present invention does not limit the specific parameter types of the obtained operating parameters of the high-pressure refrigerant circulating circuit 1, which may be the first The operating frequency of the compressor 11 may also be the discharge pressure or the suction pressure of the first compressor 11, etc., which are not limiting, and can be set by those skilled in the art according to the actual situation.

Next, in step S4 , the controller controls the operating state of the bypass branch 4 according to the operating parameters of the high-pressure refrigerant circulation circuit 1 .

It should be noted that the present invention does not impose any restrictions on the specific control logic of step S4. The controller can control the on-off state of the bypass branch 4 according to the operating parameters of the high-pressure refrigerant circulation loop 1, and can also control the on-off state of the bypass branch 4 according to the operating parameters of the high-pressure refrigerant circulation loop The operating parameters of 1 are controlled by controlling the opening of the control valve 41, thereby controlling the operating state of the bypass branch 4, which are not restrictive, and can be set by those skilled in the art according to the actual situation.

In addition, it should be noted that the present invention does not impose any restrictions on the specific execution order of step S1 and step S3, and can be executed simultaneously or sequentially without any order, which can be set by those skilled in the art according to the actual situation.

Next, referring to FIG. 3 , FIG. 3 is a flow chart of the specific steps of the first preferred embodiment of the control method of the present invention. As shown in FIG. 3, based on the cascade heat pump system described in the above embodiments, the control method of the first preferred embodiment of the present invention includes the following steps:

S101: Obtain the ambient temperature where the cascade heat pump system is located;

S102: if the ambient temperature is greater than or equal to the preset ambient temperature, control the first low-pressure refrigerant circulation circuit to not operate, and control the second low-pressure refrigerant circulation circuit to operate;

S103: if the ambient temperature is lower than the preset ambient temperature, control the first low-pressure refrigerant circulation loop to operate, and control the second low-pressure refrigerant circulation loop to not operate;

S104: Obtain the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger;

S105: Calculate the difference between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, and record it as the first difference;

S106: if the first difference is less than the first preset difference, control the bypass branch to operate;

S107: If the first difference is greater than or equal to the first preset difference, control the bypass branch not to operate.

First, in step S101, the controller acquires the ambient temperature of the cascade heat pump system detected by the temperature sensor; of course, the present invention does not make any specific acquisition timing and acquisition method of the ambient temperature. Restriction, the controller may acquire in real time, or acquire in a certain period of time, which is not restrictive, and those skilled in the art can set by themselves according to the actual situation. Preferably, the controller acquires the ambient temperature in real time, so as to be able to adjust the operating state of the cascade heat pump system in a timely and effective manner, thereby effectively improving the operating energy efficiency of the cascade heat pump system and expanding the The operating range of the cascade heat pump system.

Next, the controller controls the operating states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature.

It should be noted that the present invention does not impose any restrictions on the specific control logic of the above steps, and the controller can control the on-off state of the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 according to the ambient temperature, and also The operating speeds of the refrigerants in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 can be controlled, which are not limiting, and can be set by those skilled in the art according to actual conditions.

Preferably, in step S102, if the ambient temperature is greater than or equal to the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation circuit 2 to not operate, and controls the second low-pressure refrigerant circulation circuit 3 to operate, In order to effectively reduce the operating energy consumption of the cascade heat pump system.

Further, in step S103, if the ambient temperature is lower than the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation loop 2 to operate, and controls the second low-pressure refrigerant circulation loop 3 to not operate, so as to effectively It is ensured that the heat exchange of the intermediate heat exchanger 14 can make the high-pressure refrigerant circulation circuit 1 operate normally, so as to meet the user's use requirements.

It should be noted that the present invention does not impose any restrictions on the specific set value of the preset ambient temperature. Those skilled in the art can set it according to the actual operation of the cascade heat pump system, or according to the actual use of the user. Demand acquisition, which is not restrictive.

Further preferably, in step S104, the controller acquires the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger 14 detected by the temperature sensor. It should be noted that the present invention does not impose any restrictions on the specific acquisition timing and acquisition method of the current refrigerant evaporation temperature, and those skilled in the art can set it according to the actual situation.

Next, the controller controls the operation state of the bypass branch 4 according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature; of course, the present invention does not impose any restrictions on the specific control logic of this step, for example, the The controller may compare the current evaporation temperature of the refrigerant with the maximum evaporation temperature of the refrigerant, and control the operation state of the bypass branch 4 according to the result of the comparison.

Preferably, in step S105, the controller calculates the difference between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, which is recorded as the first difference.

Next, the controller controls the operation state of the bypass branch 4 according to the first difference value. Specifically, in step S106, if the first difference is smaller than the first preset difference, it means that the current refrigerant evaporation temperature is close to the maximum refrigerant evaporation temperature at this time, and the first compressor 11 has a malfunction due to If the air temperature is too high and shut down, thereby causing the risk that the high-pressure refrigerant circulation circuit 1 does not operate, the controller controls the operation of the bypass branch 4 to reduce the refrigerant condensation temperature of the intermediate heat exchanger 14. Refrigerant evaporation temperature, thereby effectively ensuring the normal operation of the high-pressure refrigerant circulation circuit 1.

Further, in step S107, if the first difference is greater than or equal to the first preset difference, it means that the difference between the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature is large, and the current refrigerant evaporation temperature The evaporating temperature will not cause the first compressor 11 to stop due to the high intake air temperature and thus cause the high-pressure refrigerant circulation circuit 1 to not operate, then the controller controls the bypass branch 4 to not operate, so as to improve the overlap efficiency of the heat pump system.

It should be noted that the present invention does not impose any restrictions on the specific set value of the first preset difference. Those skilled in the art can set it according to the actual operation of the cascade heat pump system, or set it according to the user's The acquisition of actual use requirements is not limiting; preferably, the first preset difference is 1° C. to ensure the efficient operation of the high-pressure refrigerant circulation loop 1 to the greatest extent.

In addition, it should be noted that the present invention does not impose any restrictions on the specific execution order of step S101 and step S104, and can be executed simultaneously or sequentially without any order, and those skilled in the art can set it according to the actual situation.

Next, referring to FIG. 4 , FIG. 4 is a flow chart of the specific steps of the second preferred embodiment of the control method of the present invention. As shown in FIG. 4 , based on the cascade heat pump system described in the above embodiments, the control method of the second preferred embodiment of the present invention includes the following steps:

S201: Obtain the ambient temperature where the cascade heat pump system is located;

S202: if the ambient temperature is greater than or equal to the preset ambient temperature, control the first low-pressure refrigerant circulation circuit to not operate, and control the second low-pressure refrigerant circulation circuit to operate;

S203: if the ambient temperature is lower than the preset ambient temperature, control the first low-pressure refrigerant circulation loop to operate, and control the second low-pressure refrigerant circulation loop to not operate;

S204: Obtain the current suction pressure and the maximum suction pressure of the first compressor;

S205: Calculate the difference between the maximum suction pressure and the current suction pressure, and record it as the second difference;

S206: if the second difference is less than the second preset difference, control the bypass branch to operate;

S207: If the second difference is greater than or equal to the second preset difference, control the bypass branch to not operate.

First, in step S201, the controller acquires the ambient temperature of the cascade heat pump system detected by the temperature sensor; of course, the present invention does not make any specific acquisition timing and acquisition method of the ambient temperature. Restriction, the controller may acquire in real time, or acquire in a certain period of time, which is not restrictive, and those skilled in the art can set by themselves according to the actual situation. Preferably, the controller acquires the ambient temperature in real time, so as to be able to adjust the operating state of the cascade heat pump system in a timely and effective manner, thereby effectively improving the operating energy efficiency of the cascade heat pump system and expanding the The operating range of the cascade heat pump system.

Next, the controller controls the operating states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature.

It should be noted that the present invention does not impose any restrictions on the specific control logic of the above steps, and the controller can control the on-off state of the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 according to the ambient temperature, and also The operating speeds of the refrigerants in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 can be controlled, which are not limiting, and can be set by those skilled in the art according to actual conditions.

Preferably, in step S202, if the ambient temperature is greater than or equal to the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation circuit 2 to not operate, and controls the second low-pressure refrigerant circulation circuit 3 to operate, In order to effectively reduce the operating energy consumption of the cascade heat pump system.

Further, in step S203, if the ambient temperature is lower than the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation circuit 2 to operate, and controls the second low-pressure refrigerant circulation circuit 3 to not operate, so as to effectively It is ensured that the heat exchange of the intermediate heat exchanger 14 can make the high-pressure refrigerant circulation circuit 1 operate normally, so as to meet the user's use requirements.

It should be noted that the present invention does not impose any restrictions on the specific set value of the preset ambient temperature. Those skilled in the art can set it according to the actual operation of the cascade heat pump system, or according to the actual use of the user. Demand acquisition, which is not restrictive.

Further preferably, in step S204, the controller acquires the current suction pressure and the maximum suction pressure of the first compressor 11 detected by the pressure sensor. It should be noted that the present invention does not impose any restrictions on the specific acquisition timing and acquisition method of the current inspiratory pressure, and those skilled in the art can set it according to the actual situation.

Next, the controller controls the operating state of the bypass branch 4 according to the current suction pressure and the maximum suction pressure; of course, the present invention does not limit the specific control logic of this step, for example, the The controller may compare the current suction pressure with the maximum suction pressure, and control the operating state of the bypass branch 4 according to the result of the magnitude comparison.

Preferably, in step S205, the controller calculates the difference between the maximum suction pressure and the current suction pressure, which is recorded as a second difference.

Next, the controller controls the operating state of the bypass branch 4 according to the second difference. Specifically, in step S206, if the second difference is smaller than the second preset difference, it means that the current suction pressure is close to the maximum suction pressure at this time, and the first compressor 11 has suction due to suction. If the gas pressure is too high and shut down, resulting in the risk that the high-pressure refrigerant circulation circuit 1 does not operate, the controller controls the operation of the bypass branch 4 to reduce the condensation temperature of the intermediate heat exchanger 14 by reducing the refrigerant condensation temperature of the intermediate heat exchanger 14. The evaporation temperature of the refrigerant, thereby reducing the suction pressure of the first compressor 11, ensures that the high-pressure refrigerant circulation circuit 1 can operate normally.

Further, in step S207, if the second difference is greater than or equal to the second preset difference, it means that the difference between the current suction pressure and the maximum suction pressure is large, and the first compressor 11 can operate normally, the controller controls the bypass branch 4 to not operate, so as to improve the operation efficiency of the cascade heat pump system.

It should be noted that the present invention does not impose any restrictions on the specific set value of the second preset difference. Those skilled in the art can set it according to the actual operation of the cascade heat pump system, or set it according to the user's The actual use needs to be obtained, which are not restrictive.

In addition, it should be noted that the present invention does not impose any restrictions on the specific execution order of step S201 and step S204, and can be executed simultaneously or sequentially without any order, and those skilled in the art can set it according to the actual situation.

In addition, in the case where the first low-pressure refrigerant circulation circuit 1 operates and the bypass branch 4 does not operate, that is, when the first low-pressure refrigerant circulation circuit 1 operates and the first difference value is greater than or equal to the first preset When the difference or the second difference is greater than or equal to the second preset difference, the control method of the present invention further includes acquiring the temperature of the refrigerant at the outlet of the second heat exchanger The temperature of the refrigerant at the outlet of the heat exchanger 23 is further controlled to further control the operation state of the bypass branch 4, so as to effectively avoid the problem of frosting or even cracking of the second heat exchanger 23.

It should be noted that the present invention does not impose any restrictions on the specific acquisition timing and acquisition method of the refrigerant temperature at the outlet of the second heat exchanger 23, nor does it impose any restrictions on the specific control logic of the above steps. Set by yourself.

Preferably, if the temperature of the refrigerant at the outlet of the second heat exchanger 23 is less than or equal to the preset refrigerant temperature, the controller controls the bypass branch 4 to operate so that the discharge port of the second compressor 21 flows out The refrigerant directly enters the second heat exchanger 23 through the bypass branch 4, thereby effectively avoiding the problem that the second heat exchanger 23 is frosted or even cracked due to the low temperature.

Further, if the refrigerant temperature at the outlet of the second heat exchanger 23 is greater than the preset refrigerant temperature, the controller controls the bypass branch 4 to not operate, so as to effectively ensure the operating energy efficiency of the cascade heat pump system. .

It should be noted that the present invention does not impose any restrictions on the specific set value of the preset refrigerant temperature, and those skilled in the art can set it by themselves according to the actual operation of the cascade heat pump system.

So far, the technical solutions of the present invention have been described with reference to the preferred embodiments shown in the accompanying drawings, however, those skilled in the art can easily understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims (10)

1. A control method of a cascade heat pump system is characterized in that the cascade heat pump system comprises a high-pressure refrigerant circulation loop, a first low-pressure refrigerant circulation loop, a second low-pressure refrigerant circulation loop and a bypass branch,

the high-pressure refrigerant circulating loop is provided with a first compressor, a first heat exchanger, a first throttling component and an intermediate heat exchanger, the first low-pressure refrigerant circulating loop is provided with a second compressor, the intermediate heat exchanger, a second throttling component and a second heat exchanger, the second low-pressure refrigerant circulating loop is provided with a fluorine pump, a second heat exchanger and the intermediate heat exchanger, two ends of the fluorine pump are connected with the first low-pressure refrigerant circulating loop, two ends of the second compressor are connected with the second low-pressure refrigerant circulating loop, the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop are arranged to be capable of selectively exchanging heat with the high-pressure refrigerant circulating loop through the intermediate heat exchanger,

a first end of the bypass branch is connected between a connection point of the fluorine pump and the first low-pressure refrigerant circulation loop and the second heat exchanger, a second end of the bypass branch is connected between the second compressor and the intermediate heat exchanger, a control valve is arranged on the bypass branch and can control the on-off state of the bypass branch,

the control method comprises the following steps:

acquiring the ambient temperature of the cascade heat pump system;

controlling the running states of the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop according to the environment temperature;

acquiring operation parameters of the high-pressure refrigerant circulation loop;

and controlling the running state of the bypass branch according to the running parameters of the high-pressure refrigerant circulating loop.

2. The control method according to claim 1, wherein the step of controlling the operation states of the first and second low-pressure refrigerant circulation circuits according to the ambient temperature includes:

and if the ambient temperature is greater than or equal to a preset ambient temperature, controlling the first low-pressure refrigerant circulation loop not to operate, and controlling the second low-pressure refrigerant circulation loop to operate.

3. The control method as claimed in claim 2, wherein the step of controlling the operation states of the first and second low-pressure refrigerant circulation circuits according to the ambient temperature further comprises:

and if the environment temperature is lower than the preset environment temperature, controlling the first low-pressure refrigerant circulation loop to operate, and controlling the second low-pressure refrigerant circulation loop not to operate.

4. The control method according to claim 3, wherein the step of obtaining the operating parameters of the high-pressure refrigerant circulation circuit specifically comprises:

acquiring the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger;

the step of controlling the operation state of the bypass branch according to the operation parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:

and controlling the running state of the bypass branch according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature.

5. The control method according to claim 4, wherein the step of controlling the operation state of the bypass branch according to the current refrigerant evaporating temperature and the maximum refrigerant evaporating temperature specifically comprises:

calculating the difference value between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, and recording the difference value as a first difference value;

if the first difference is smaller than a first preset difference, controlling the bypass branch to operate; and/or the like and/or,

and if the first difference value is greater than or equal to the first preset difference value, controlling the bypass branch circuit not to operate.

6. The control method according to claim 3, wherein the step of obtaining the operation parameter of the high-pressure refrigerant circulation loop comprises:

acquiring the current suction pressure and the maximum suction pressure of the first compressor;

the step of controlling the operation state of the bypass branch according to the operation parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:

and controlling the running state of the bypass branch according to the current suction pressure and the maximum suction pressure.

7. The control method according to claim 6, wherein the step of controlling the operating state of the bypass branch according to the current suction pressure and the maximum suction pressure specifically comprises:

calculating the difference value between the maximum suction pressure and the current suction pressure, and recording as a second difference value;

if the second difference is smaller than a second preset difference, controlling the bypass branch to operate; and/or the like, and/or,

and if the second difference is greater than or equal to the second preset difference, controlling the bypass branch not to operate.

8. The control method according to any one of claims 5 or 7, wherein in a case where the first low-pressure refrigerant circulation circuit is operated and the bypass branch is not operated, the control method further comprises:

acquiring the temperature of a refrigerant at an outlet of the second heat exchanger;

and further controlling the running state of the bypass branch according to the temperature of the refrigerant at the outlet of the second heat exchanger.

9. The control method according to claim 8, wherein the step of further controlling the operating state of the bypass branch according to the temperature of the refrigerant at the outlet of the second heat exchanger specifically comprises:

if the temperature of the refrigerant at the outlet of the second heat exchanger is less than or equal to the preset temperature of the refrigerant, controlling the bypass branch to operate; and/or the like and/or,

and if the temperature of the refrigerant at the outlet of the second heat exchanger is greater than the preset temperature of the refrigerant, controlling the bypass branch not to operate.

10. A cascade heat pump system characterized in that it comprises a controller capable of performing the control method of any one of claims 1 to 9.

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