Carbon dioxide cascade heat pump system

Abstract

This invention discloses a carbon dioxide cascade heat pump system, comprising a carbon dioxide heat pump system, an intermediate heat exchange system, and a user-side heat exchange system. The carbon dioxide heat pump system includes a first compressor, a first heat exchanger for heat exchange between the carbon dioxide heat pump system and the user side, a second heat exchanger for heat exchange between the carbon dioxide heat pump system and the intermediate heat exchange system, a first expansion valve, an evaporator, a first valve, a second valve, a third valve, and a fourth valve. The intermediate heat exchange system includes a third heat exchanger for heat exchange between the intermediate heat exchange system and the user-side heat exchange system. By designing the connection and position relationships of each component, this invention's carbon dioxide cascade heat pump system can solve the problem of reduced reliability of the intermediate heat exchanger caused by excessively high exhaust temperature when the conventional carbon dioxide heat pump system operates in low-temperature environments. It also solves the problems of low defrosting efficiency, long defrosting time, and poor defrosting effect of conventional carbon dioxide cascade systems.

Description

Technical Field

[0001] This invention relates to the field of heat pump technology, and specifically to a carbon dioxide cascade heat pump system. Background Technology

[0002] Cascade heat pump systems generally include a high-temperature stage circulation loop and a low-temperature stage circulation loop. The high-temperature stage circulation loop and the low-temperature stage circulation loop exchange heat through a shared intermediate heat exchanger. The low-temperature stage circulation loop absorbs heat from the low-temperature environment and supplies heat to the high-temperature stage circulation loop through the intermediate heat exchanger. However, the low-temperature stage circulation loop of a carbon dioxide cascade heat pump system uses carbon dioxide as the refrigerant. However, in practice, it has been found that the exhaust temperature of the low-temperature stage circulation loop is too high when operating in a low-temperature environment, which can easily lead to a decrease in the reliability of the intermediate heat exchanger. Moreover, frost is easily formed on the evaporator surface, and the defrosting time is long and the defrosting effect is poor. Summary of the Invention

[0003] The purpose of this invention is to overcome one or more shortcomings of the prior art and provide an improved carbon dioxide cascade heat pump system, which can solve the problem of reduced reliability of intermediate heat exchangers caused by excessively high exhaust temperature when the low-temperature carbon dioxide heat pump system is running in a low-temperature environment. At the same time, it solves the problems of low defrosting efficiency, long defrosting time and poor defrosting effect of conventional carbon dioxide cascade systems.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A carbon dioxide cascade heat pump system, comprising a carbon dioxide heat pump system, an intermediate heat exchange system, and a user-side heat exchange system.

[0006] The carbon dioxide heat pump system includes a first compressor, a first heat exchanger, a second heat exchanger, a first expansion valve, an evaporator, a first valve, a second valve, a third valve, and a fourth valve; the outlet of the first compressor, the second valve, the first heat exchanger, the second heat exchanger, the first expansion valve, the evaporator, the fourth valve, and the inlet of the first compressor are connected in sequence.

[0007] One end of the first valve is connected to the refrigerant inlet of the first heat exchanger, and the other end is connected to the air inlet of the first compressor; one end of the third valve is connected to the air outlet of the first compressor, and the other end is connected to the refrigerant inlet of the evaporator.

[0008] The first heat exchanger is used for heat exchange between the carbon dioxide heat pump system and the user-side heat exchange system; the second heat exchanger is used for heat exchange between the carbon dioxide heat pump system and the intermediate heat exchange system; the intermediate heat exchange system includes a third heat exchanger, which is used for heat exchange between the intermediate heat exchange system and the user-side heat exchange system.

[0009] According to the present invention, the carbon dioxide cascade heat pump system includes a heating state and a defrosting state;

[0010] When the carbon dioxide cascade heat pump system is in the heating state, the first valve and the third valve are both closed, and the second valve and the fourth valve are both open. The outlet of the first compressor, the second valve, the first heat exchanger, the second heat exchanger, the first expansion valve, the evaporator, the fourth valve, and the inlet of the first compressor sequentially form a circulation loop. The first heat exchanger and the intermediate heat exchange system are both used to supply heat to the user-side heat exchange system, and the second heat exchanger is used to supply heat to the intermediate heat exchange system.

[0011] When the carbon dioxide cascade heat pump system is in the defrosting state, the second valve and the fourth valve are both closed, and the first valve and the third valve are both open. The outlet of the first compressor, the third valve, the evaporator, the first expansion valve, the second heat exchanger, the first heat exchanger, the first valve, and the inlet of the first compressor sequentially form a circulation loop. The first heat exchanger is used to absorb heat from the user-side heat exchange system, and the intermediate heat exchange system stops operating.

[0012] According to some specific aspects of the present invention, the intermediate heat exchange system further includes a second compressor, a fourth heat exchanger, and a second expansion valve, wherein the third heat exchanger and the fourth heat exchanger each independently include two heat exchange pipelines that exchange heat with each other.

[0013] The outlet of the second compressor, one heat exchange pipeline of the third heat exchanger, one heat exchange pipeline of the fourth heat exchanger, the second expansion valve, the second heat exchanger, the other heat exchange pipeline of the fourth heat exchanger, and the inlet of the second compressor are connected in sequence.

[0014] According to some specific aspects of the present invention, the user-side heat exchange system includes a water pump, a proportional valve, and a fifth heat exchanger capable of exchanging heat with the user environment. The outlet of the water pump, the proportional valve, the first heat exchanger, the fifth heat exchanger, and the inlet of the water pump are connected in sequence. The two ends of another heat exchange pipeline of the third heat exchanger are connected to the outlet of the water pump and the inlet of the fifth heat exchanger, respectively.

[0015] According to some specific aspects of the present invention, the user-side heat exchange system further includes a flow meter disposed between the outlet of the fifth heat exchanger and the inlet of the water pump, and is used to monitor the flow rate of water flowing to the water pump.

[0016] According to some preferred aspects of the invention, the surface temperature of the evaporator is Ta, and the ambient temperature is Tb;

[0017] When Ta≤0℃ for 40 to 50 minutes and Tb-Ta≥3 to 5℃, the carbon dioxide cascade heat pump system enters the defrosting state, the second compressor stops, and the proportional valve is opened to 100%.

[0018] When Ta ≥ 10~15℃, the carbon dioxide cascade heat pump system exits the defrosting state, closes the first valve and the third valve, and opens the second valve and the fourth valve.

[0019] According to some preferred aspects of the present invention, when the carbon dioxide cascade heat pump system is in the heating state, the exhaust pressure Ph of the first compressor is detected and the saturation temperature Tc is calculated.

[0020] Detect the outlet temperature Th of the first heat exchanger;

[0021] dT = Th - Tc, adjust the opening of the proportional valve to make dT 35-45°C.

[0022] According to some preferred aspects of the present invention, the hot water flow rate is qm obtained from the flow meter;

[0023] The carbon dioxide cascade heat pump system also includes a power meter connected to the main power supply circuit, through which the real-time power consumption w of the carbon dioxide cascade heat pump system is obtained;

[0024] The outlet temperature of the water pump is T1, the inlet temperature of the fifth heat exchanger is T2, and the first compressor is a variable frequency compressor.

[0025] The real-time energy efficiency ratio (COP) of the carbon dioxide cascade heat pump system is calculated using the following formula:

[0026] COP = qm × 4.18 × (T2 - T1) / w, adjust the operating frequency of the first compressor (Hz) to make the COP reach its maximum value;

[0027] The operating frequency HZ of the first compressor that maximizes the COP varies at each ambient temperature Tb and each outlet temperature T1. An optimal operating frequency HZ under the current conditions is obtained based on each ambient temperature Tb and the required outlet temperature T1 of the water pump. Tb，T1 Record the optimal operating frequency (Hz). Tb，T1 And the corresponding ambient temperature Tb and the outlet temperature T1 of the water pump are used to obtain a statistical array;

[0028] During operation, based on the ambient temperature Tb and the outlet temperature T1 of the water pump, the value of HZ is searched in the statistical array.Tb，T1 That is, controlling the operating frequency of the first compressor to be Hz. Tb，T1 .

[0029] According to some specific and preferred aspects of the invention, the second compressor is a fixed-frequency compressor.

[0030] According to some specific and preferred aspects of the invention, the refrigerant used in the intermediate heat exchange system includes refrigerant R134a.

[0031] According to some specific and preferred aspects of the invention, the evaporator is a finned tube evaporator, and preferably may be equipped with a fan.

[0032] According to some specific and preferred aspects of the present invention, the first valve, the second valve, the third valve and the fourth valve are all solenoid valves.

[0033] According to some specific aspects of the present invention, the carbon dioxide heat pump system further includes a gas-liquid separator, the inlet of which is connected to the first valve and the fourth valve respectively, and the outlet of which is connected to the air inlet of the first compressor.

[0034] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0035] This invention redesigns the structure of a carbon dioxide cascade heat pump system by adding a first heat exchanger before the second heat exchanger between the carbon dioxide heat pump system and the intermediate heat exchange system. This first heat exchanger pre-cools the high-temperature exhaust gas, and this heat can then be transferred to the user side. This not only improves energy utilization but also controls the temperature of the high-temperature exhaust gas entering the second heat exchanger, preventing the intermediate heat exchanger (corresponding to the second heat exchanger) from becoming unreliable due to excessively high exhaust temperatures during the operation of the first compressor of the carbon dioxide heat pump system. Furthermore, through the design of multiple valves, this invention allows the carbon dioxide heat pump to directly guide the high-temperature exhaust gas from the first compressor to the evaporator, thereby achieving rapid defrosting with high efficiency and good defrosting effect. In particular, the presence of the first heat exchanger also allows it to act as an evaporator, absorbing heat from the user's environment, ensuring a smooth defrosting process. This solves the problems of low defrosting efficiency, long defrosting time, and poor defrosting effect in conventional carbon dioxide cascade systems. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of the carbon dioxide cascade heat pump system in heating mode in an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the carbon dioxide cascade heat pump system in defrost mode in an embodiment of the present invention;

[0039] In the attached diagram, the following are the reference numerals: 1. First compressor; 2. Gas-liquid separator; 3. Evaporator; 4. Fan; 5. First expansion valve; 6. First heat exchanger; 7. Second heat exchanger; 8. Second expansion valve; 9. Fourth heat exchanger; 10. Second compressor; 11. Third heat exchanger; 12. Water pump; 13. Fifth heat exchanger; 14. Proportional valve; 15. First valve; 16. Second valve; 17. Third valve; 18. Fourth valve; 19. Flow meter. Detailed Implementation

[0040] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0042] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] In this invention, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0044] It should be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component.

[0045] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0046] like Figures 1 to 2 As shown, this example provides a carbon dioxide cascade heat pump system, which includes a carbon dioxide heat pump system, an intermediate heat exchange system, and a user-side heat exchange system. The carbon dioxide heat pump system includes a first compressor 1, a first heat exchanger 6, a second heat exchanger 7, a first expansion valve 5, an evaporator 3, a first valve 15, a second valve 16, a third valve 17, and a fourth valve 18. The outlet of the first compressor 1, the second valve 16, the first heat exchanger 6, the second heat exchanger 7, the first expansion valve 5, the evaporator 3, the fourth valve 18, and the inlet of the first compressor 1 are sequentially connected. One end of the first valve 15 is connected to the refrigerant inlet of the first heat exchanger 6, and the other end is connected to the inlet of the first compressor 1. One end of the third valve 17 is connected to the outlet of the first compressor 1, and the other end is connected to the refrigerant inlet of the evaporator 3.

[0047] The intermediate heat exchange system also includes a second compressor 10, a third heat exchanger 11, a fourth heat exchanger 9, and a second expansion valve 8. The third heat exchanger 11 and the fourth heat exchanger 9 each independently include two heat exchange pipelines that exchange heat with each other. The outlet of the second compressor 10, one heat exchange pipeline of the third heat exchanger 11, one heat exchange pipeline of the fourth heat exchanger 9, the second expansion valve 8, the second heat exchanger 7, the other heat exchange pipeline of the fourth heat exchanger 9, and the inlet of the second compressor 10 are connected in sequence.

[0048] The user-side heat exchange system includes a water pump 12, a proportional valve 14, and a fifth heat exchanger 13 capable of exchanging heat with the user environment. The outlet of the water pump 12, the proportional valve 14, the first heat exchanger 6, the fifth heat exchanger 13, and the inlet of the water pump 12 are connected in sequence. The two ends of another heat exchange pipeline of the third heat exchanger 11 are connected to the outlet of the water pump 12 and the inlet of the fifth heat exchanger 13, respectively.

[0049] The first heat exchanger 6 is used for heat exchange between the carbon dioxide heat pump system and the user-side heat exchange system, the second heat exchanger 7 is used for heat exchange between the carbon dioxide heat pump system and the intermediate heat exchange system, and the third heat exchanger 11 is used for heat exchange between the intermediate heat exchange system and the user-side heat exchange system.

[0050] In this example, the carbon dioxide cascade heat pump system includes a heating state and a defrosting state;

[0051] When the carbon dioxide cascade heat pump system is in heating mode, the first valve 15 and the third valve 17 are both closed, and the second valve 16 and the fourth valve 18 are both open. The outlet of the first compressor 1, the second valve 16, the first heat exchanger 6, the second heat exchanger 7, the first expansion valve 5, the evaporator 3, the fourth valve 18, and the inlet of the first compressor 1 form a circulation loop in sequence. The first heat exchanger 6 and the intermediate heat exchange system are used to supply heat to the user-side heat exchange system, and the second heat exchanger 7 is used to supply heat to the intermediate heat exchange system.

[0052] When the carbon dioxide cascade heat pump system is in defrost mode, the second valve 16 and the fourth valve 18 are both closed, and the first valve 15 and the third valve 17 are both open. The outlet of the first compressor 1, the third valve 17, the evaporator 3, the first expansion valve 5, the second heat exchanger 7, the first heat exchanger 6, the first valve 15, and the inlet of the first compressor 1 form a circulation loop in sequence. The first heat exchanger 6 is used to absorb heat from the user-side heat exchange system, and the intermediate heat exchange system stops operating.

[0053] In this example, the user-side heat exchange system also includes a flow meter 19, which is installed between the outlet of the fifth heat exchanger 13 and the inlet of the water pump 12, for example, on the pipeline connecting the outlet of the fifth heat exchanger 13 and the inlet of the water pump 12, and is used to monitor the flow rate of water flowing to the water pump 12.

[0054] In this example, the surface temperature of evaporator 3 is Ta, and the ambient temperature is Tb. When Ta ≤ 0℃ for 40 to 50 minutes and Tb - Ta ≥ 3 to 5℃, the carbon dioxide cascade heat pump system enters the defrosting state, the second compressor 10 stops, and the opening degree of proportional valve 14 is 100%. When Ta ≥ 10 to 15℃, the carbon dioxide cascade heat pump system exits the defrosting state, the first valve 15 and the third valve 17 are closed, and the second valve 16 and the fourth valve 18 are opened.

[0055] In this example, when the carbon dioxide cascade heat pump system is in heating mode, the exhaust pressure Ph of the first compressor 1 is detected and the saturation temperature Tc is calculated; the outlet temperature Th of the first heat exchanger 6 is detected; dT = Th - Tc, and the opening of the proportional valve 14 is adjusted to make dT 35-45℃.

[0056] In this example, the hot water flow rate is qm according to flow meter 19; the carbon dioxide cascade heat pump system also includes a power meter connected to the main power supply circuit, through which the real-time power consumption w of the carbon dioxide cascade heat pump system is obtained; the outlet temperature of water pump 12 is T1, the inlet temperature of the fifth heat exchanger 13 is T2, and the first compressor 1 is a variable frequency compressor; the real-time energy efficiency ratio (COP) of the carbon dioxide cascade heat pump system is calculated using the following formula:

[0057] COP = qm × 4.18 × (T2 - T1) / w, adjust the operating frequency of the first compressor 1 (Hz) to make COP reach its maximum value;

[0058] At each ambient temperature Tb and each outlet temperature T1, the operating frequency HZ of the first compressor 1 that maximizes the COP varies, and an optimal operating frequency HZ under the current conditions is obtained based on each ambient temperature Tb and the required outlet temperature T1 of the water pump 12. Tb，T1 Record the optimal operating frequency (Hz). Tb，T1 And the corresponding ambient temperature Tb and the outlet temperature T1 of water pump 12, to obtain a statistical array;

[0059] During operation, based on the ambient temperature Tb and the outlet temperature T1 of water pump 12, the value of HZ is searched in the statistical array. Tb，T1 That is, controlling the operating frequency of the first compressor 1 to be Hz. Tb，T1 .

[0060] In this example, the second compressor 10 is a fixed-frequency compressor, and the refrigerant used in the intermediate heat exchange system may include, but is not limited to, refrigerant R134a.

[0061] In this example, the evaporator 3 is a finned tube evaporator, preferably equipped with a fan 4; the first valve 15, the second valve 16, the third valve 17 and the fourth valve 18 are all solenoid valves.

[0062] In this example, the carbon dioxide heat pump system also includes a gas-liquid separator 2. The inlet of the gas-liquid separator 2 is connected to the first valve 15 and the fourth valve 18, respectively, and the outlet of the gas-liquid separator 2 is connected to the air inlet of the first compressor 1.

[0063] See Figure 1As shown, it provides an exemplary schematic diagram of the operation of a carbon dioxide cascade heat pump system in heating mode. When heating is applied to the user side, both the first valve 15 and the third valve 17 are in the closed state. Figure 1 (The dashed lines in the text indicate that they are not connected). At this time, the second valve 16 and the fourth valve 18 are in the open state. That is, the high-temperature carbon dioxide gas from the first compressor 1 is introduced into the first heat exchanger 6 (also known as the precooler) through the second valve 16. It exchanges heat with the circulating water on the user side at the precooler to provide heat to the user side. At this time, the cooled carbon dioxide refrigerant enters the second heat exchanger 7. The second heat exchanger 7 is the intermediate heat exchanger for heat exchange between the carbon dioxide heat pump system (usually called the low-temperature stage system in the cascade heat pump system) and the intermediate heat exchange system (usually called the high-temperature stage system in the cascade heat pump system). If the inlet gas temperature is too high, it will reduce the reliability of the second heat exchanger 7 and the heat exchange efficiency will not be ideal. However, the present invention cools the gas first through the precooler before it is introduced into the intermediate heat exchanger, which can significantly improve its heat exchange efficiency. After cooling down again at the intermediate heat exchanger, the carbon dioxide refrigerant absorbs heat from the environment at the evaporator 3 after being throttled by the first expansion valve 5. Then it flows to the gas-liquid separator 2 through the fourth valve 18 and is circulated back to the first compressor 1.

[0064] As for the intermediate heat exchange system, during the operation of the aforementioned carbon dioxide heat pump system, the second compressor 10 is always in the start state. The refrigerant of the system (e.g., R134a) is compressed by the second compressor 10 and then supplied to the user side at the third heat exchanger 11. It then flows to one of the heat exchange pipes of the fourth heat exchanger 9. The fourth heat exchanger 9 can be called a regenerator. Its purpose is to facilitate heat exchange between the refrigerants themselves. Specifically, the refrigerant from the third heat exchanger 11 enters the fourth heat exchanger 9 and is throttled by the second expansion valve 8. It then absorbs heat at the second heat exchanger 7 and flows back to the other heat exchange pipe of the regenerator, realizing the heat exchange of the refrigerant itself. After that, it circulates to the air inlet of the second compressor 10.

[0065] For the user-side heat exchange system, during the operation of the aforementioned carbon dioxide heat pump system and intermediate heat exchange system, the water pump 12 pumps the portion of circulating water that needs to be heated to the third heat exchanger 11 for heat exchange and absorption, and pumps the remaining circulating water to the first heat exchanger 6 after flowing through the proportional valve 14 for heat exchange and absorption, and finally collects it into the fifth heat exchanger 13 (i.e., the user-side heat exchanger) to supply heat to the user. Finally, the circulating water is pumped back to the water pump 12 to continue circulating.

[0066] See Figure 2 As shown, it provides an exemplary schematic diagram of a carbon dioxide cascade heat pump system in defrost mode. Defrosting is required because frost has formed at evaporator 3, affecting operation. During defrosting, the second valve 16 and the fourth valve 18 are closed (e.g., Figure 2The dashed lines indicate that they are disconnected and not connected to the system, and the second compressor 10 is shut down. Its shutdown means that the heat exchange function of the third heat exchanger 11 and the second heat exchanger 7 is temporarily inactive. That is, only the carbon dioxide heat pump system and the user-side heat exchange system are running, and the proportional valve 14 is open at 100%.

[0067] In the carbon dioxide heat pump system, the high-temperature carbon dioxide from the first compressor 1 flows to the evaporator 3 through the third valve 17. At this time, the high-temperature carbon dioxide refrigerant can heat and defrost the frost on the surface of the evaporator 3. Then, after the refrigerant is cooled by heat exchange, it flows through the first expansion valve 5 through the second heat exchanger 7 (at this time, the second heat exchanger 7 only serves as a flow channel), and then flows to the first heat exchanger 6. At this time, the first heat exchanger 6 acts as a conventional evaporator, absorbing the heat from the user side. Then, it flows back to the gas-liquid separator 2 through the first valve 15, and then circulates back to the first compressor 1.

[0068] For the user-side heat exchange system, during the operation of the carbon dioxide heat pump system, the circulating water is cooled down because heat is absorbed at the first heat exchanger 6. When it flows to the user-side heat exchanger, i.e. the fifth heat exchanger 13, it absorbs heat from the user-side environment (equivalent to cooling the user side). Finally, the circulating water is pumped back to the water pump 12 to continue circulating.

[0069] In summary, this invention, through structural design of the carbon dioxide cascade heat pump system, further adds a first heat exchanger before the second heat exchanger between the carbon dioxide heat pump system and the intermediate heat exchange system. This first heat exchanger can pre-cool the high-temperature exhaust gas, and this heat can then be exchanged to the user side. This not only improves energy utilization but also controls the temperature of the high-temperature exhaust gas entering the second heat exchanger, avoiding the problem of reduced reliability of the intermediate heat exchanger (corresponding to the second heat exchanger) due to excessively high exhaust temperature during the operation of the first compressor of the carbon dioxide heat pump system. In addition, through the design of multiple valves, this invention allows the carbon dioxide heat pump to directly guide the high-temperature exhaust gas from the first compressor to the evaporator, thereby achieving rapid defrosting with high efficiency and good defrosting effect. In particular, the presence of the first heat exchanger also allows it to act as an evaporator, absorbing heat from the user-side environment, ensuring a smooth defrosting process. This solves the problems of low defrosting efficiency, long defrosting time, and poor defrosting effect in conventional carbon dioxide cascade systems.

[0070] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A carbon dioxide cascade heat pump system, characterized in that, The carbon dioxide cascade heat pump system includes a carbon dioxide heat pump system, an intermediate heat exchange system, and a user-side heat exchange system. The carbon dioxide heat pump system includes a first compressor, a first heat exchanger, a second heat exchanger, a first expansion valve, an evaporator, a first valve, a second valve, a third valve, and a fourth valve; the outlet of the first compressor, the second valve, the first heat exchanger, the second heat exchanger, the first expansion valve, the evaporator, the fourth valve, and the inlet of the first compressor are connected in sequence. One end of the first valve is connected to the refrigerant inlet of the first heat exchanger, and the other end is connected to the air inlet of the first compressor; one end of the third valve is connected to the air outlet of the first compressor, and the other end is connected to the refrigerant inlet of the evaporator. The first heat exchanger is used for heat exchange between the carbon dioxide heat pump system and the user-side heat exchange system; the second heat exchanger is used for heat exchange between the carbon dioxide heat pump system and the intermediate heat exchange system; the intermediate heat exchange system includes a third heat exchanger, which is used for heat exchange between the intermediate heat exchange system and the user-side heat exchange system. The carbon dioxide cascade heat pump system includes a heating state and a defrosting state; When the carbon dioxide cascade heat pump system is in the heating state, the first valve and the third valve are both closed, and the second valve and the fourth valve are both open. The outlet of the first compressor, the second valve, the first heat exchanger, the second heat exchanger, the first expansion valve, the evaporator, the fourth valve, and the inlet of the first compressor sequentially form a circulation loop. The first heat exchanger and the intermediate heat exchange system are both used to supply heat to the user-side heat exchange system, and the second heat exchanger is used to supply heat to the intermediate heat exchange system. When the carbon dioxide cascade heat pump system is in the defrosting state, the second valve and the fourth valve are both closed, and the first valve and the third valve are both open. The outlet of the first compressor, the third valve, the evaporator, the first expansion valve, the second heat exchanger, the first heat exchanger, the first valve, and the inlet of the first compressor sequentially form a circulation loop. The first heat exchanger is used to absorb heat from the user-side heat exchange system, and the intermediate heat exchange system stops operating.

2. The carbon dioxide cascade heat pump system according to claim 1, characterized in that, The intermediate heat exchange system also includes a second compressor, a fourth heat exchanger, and a second expansion valve. The third heat exchanger and the fourth heat exchanger each independently include two heat exchange pipelines that exchange heat with each other. The outlet of the second compressor, one heat exchange pipeline of the third heat exchanger, one heat exchange pipeline of the fourth heat exchanger, the second expansion valve, the second heat exchanger, the other heat exchange pipeline of the fourth heat exchanger, and the inlet of the second compressor are connected in sequence.

3. The carbon dioxide cascade heat pump system according to claim 2, characterized in that, The user-side heat exchange system includes a water pump, a proportional valve, and a fifth heat exchanger capable of exchanging heat with the user environment. The outlet of the water pump, the proportional valve, the first heat exchanger, the fifth heat exchanger, and the inlet of the water pump are connected in sequence. The two ends of another heat exchange pipeline of the third heat exchanger are connected to the outlet of the water pump and the inlet of the fifth heat exchanger, respectively.

4. The carbon dioxide cascade heat pump system according to claim 3, characterized in that, The user-side heat exchange system also includes a flow meter, which is installed between the outlet of the fifth heat exchanger and the inlet of the water pump, and is used to monitor the flow rate of water flowing to the water pump.

5. The carbon dioxide cascade heat pump system according to claim 3, characterized in that, The surface temperature of the evaporator is Ta, and the ambient temperature is Tb; When Ta ≤ 0℃ for 40~50 minutes and Tb-Ta ≥ 3~5℃, the carbon dioxide cascade heat pump system enters the defrosting state, the second compressor stops, and the proportional valve opens to 100%. When Ta ≥ 10~15℃, the carbon dioxide cascade heat pump system exits the defrosting state, closes the first valve and the third valve, and opens the second valve and the fourth valve.

6. The carbon dioxide cascade heat pump system according to claim 3, characterized in that, When the carbon dioxide cascade heat pump system is in the heating state, the exhaust pressure Ph of the first compressor is detected, and the saturation temperature Tc is calculated. Detect the outlet temperature Th of the first heat exchanger; dT = Th - Tc, adjust the opening of the proportional valve to make dT 35~45℃.

7. The carbon dioxide cascade heat pump system according to claim 4, characterized in that, The hot water flow rate is qm according to the flow meter. The carbon dioxide cascade heat pump system also includes a power meter connected to the main power supply circuit, through which the real-time power consumption w of the carbon dioxide cascade heat pump system is obtained; The outlet temperature of the water pump is T1, the inlet temperature of the fifth heat exchanger is T2, and the first compressor is a variable frequency compressor. The real-time energy efficiency ratio (COP) of the carbon dioxide cascade heat pump system is calculated using the following formula: COP = qm × 4.18 × (T2 - T1) / w, adjust the operating frequency of the first compressor (Hz) to make the COP reach its maximum value; At each environmental temperature Tb, at each outlet temperature Tl, the operating frequency HZ of the first compressor is varied so that the COP reaches a maximum value, and the optimum operating frequency HZ is obtained for each environmental temperature Tb and for the outlet temperature Tl of the water pump required Tb，T1 The optimum operating frequency HZ is recorded Tb，T1 and the corresponding environmental temperature Tb and outlet temperature Tl of the water pump, obtaining a statistical array; During operation, based on the ambient temperature Tb and the outlet temperature T1 of the water pump, the value of HZ is searched in the statistical array. Tb，T1 That is, controlling the operating frequency of the first compressor to be Hz. Tb，T1 .

8. The carbon dioxide cascade heat pump system according to claim 2, characterized in that, The second compressor is a fixed-frequency compressor.

9. The carbon dioxide cascade heat pump system according to claim 1, characterized in that, The intermediate heat exchange system uses refrigerant R134a, and the evaporator is a finned tube evaporator.

10. The carbon dioxide cascade heat pump system according to claim 1, characterized in that, The first valve, the second valve, the third valve, and the fourth valve are all solenoid valves; and / or, the carbon dioxide heat pump system further includes a gas-liquid separator, the inlet of which is connected to the first valve and the fourth valve respectively, and the outlet of which is connected to the air inlet of the first compressor.

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