Cascade heat pump system

Abstract

The utility model discloses a cascade heat pump system which comprises a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a first compressor and a second compressor. The first heat exchanger is arranged in an outdoor environment and exchanges heat through an outdoor fan; the second heat exchanger comprises a first passage and a second passage and is used for heat exchange between a refrigerant in the first passage and a refrigerant in the second passage; the first compressor, the first heat exchanger and the first passage form a first cycle; the third heat exchanger exchanges heat with the liquid heat exchange medium; the second compressor, the second passage and the third heat exchanger form a second cycle; the fourth heat exchanger exchanges heat with the liquid heat exchange medium and forms a third cycle with the first heat exchanger and the first compressor; the first cycle and the second cycle are in linkage heating operation or the third cycle is in linkage operation; and the third cycle can be used for refrigerating or heating. According to the utility model, high-efficiency operation and high-efficiency defrosting of the system are realized when the compression ratio is medium and small, the power of an outdoor fan is not increased, and energy and cost are saved.

Description

Technical Field

[0001] The utility model relates to the technical field of air conditioning, in particular to a cascade heat pump system. Background Art

[0002] In order to achieve efficient heating or cooling of air source heat pumps under a larger ratio of condensing pressure to evaporating pressure, the prior art adopts cascade heat pump cycle technology to improve the operating performance of air source heat pumps under a large compression ratio. Specifically, the heat produced by the air source heat pump unit comes from the condenser of the high-temperature section heat pump unit, and the low-temperature section air source heat pump is only associated with the high-temperature section heat pump evaporator to provide heat source to the high-temperature section.

[0003] The existing technology adds pipes and heat exchangers in the low-temperature section that can be directly connected to the high-temperature section condenser, so that when the ambient temperature is high, the heat exchanger added in the low-temperature section can directly form a heat pump circulation system with the high-temperature section condenser to perform efficient heating operation with medium or small compression ratios.

[0004] When the cascade air source heat pump with the above structure defrosts, the high temperature section cycle and the low temperature section cycle run simultaneously to defrost the low temperature section evaporator, which makes the system control complex and inefficient; or the added low temperature section heat exchanger is directly connected to the high temperature section condenser for single cycle refrigeration operation; the added low temperature section heat exchanger defrosts the low temperature section heat exchanger and provides heat, which has the problems of unsynchronized defrosting and low efficiency; that is, the added low temperature section heat exchanger needs special installation to make the low temperature section heat exchanger defrost evenly. In addition, the addition of the low temperature section heat exchanger increases the volume of the outdoor heat exchanger, and the fan power needs to be increased to adapt, which occupies a large space and increases the cost.

[0005] The above information disclosed in the background technology is only used to increase the understanding of the background technology of the present application, and therefore, it may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] In view of the problems of low efficiency and low defrosting efficiency of the cascade heat pump system proposed in the background technology at small and medium compression ratios, the utility model proposes a cascade heat pump system to achieve efficient operation at small and medium compression ratios, efficient defrosting, reduced costs and energy saving.

[0007] In order to achieve the above-mentioned utility model purpose, the utility model adopts the following technical solutions:

[0008] A cascade heat pump system comprises a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, a first compressor, and a second compressor;

[0009] The first heat exchanger is arranged in an outdoor environment and exchanges heat with the outdoor environment through an outdoor fan;

[0010] The second heat exchanger comprises a first passage and a second passage, and is used for heat exchange between the refrigerant in the first passage and the refrigerant in the second passage;

[0011] The first compressor is connected with the first heat exchanger and the first passage through a pipeline to form a first cycle;

[0012] The third heat exchanger is arranged to exchange heat with the liquid heat exchange medium;

[0013] The second compressor is connected with the second passage and the third heat exchanger through a pipeline to form a second cycle;

[0014] The fourth heat exchanger is arranged to exchange heat with the liquid heat exchange medium, and is connected to the first heat exchanger and the first compressor through pipelines to form a third cycle; the first cycle and the second cycle are linked to heat operation or the third cycle is operated; the third cycle operation can be cooling or heating.

[0015] In some specific embodiments, it further includes a first controllable valve, a second controllable valve, a third controllable valve, a fourth controllable valve, a fifth controllable valve, and a first throttling element; the first compressor includes a first exhaust port and a first intake port;

[0016] The first exhaust port is connected to one end of the first passage through the first controllable valve, connected to one end of the fourth heat exchanger through the second controllable valve, and connected to one end of the first heat exchanger through the third controllable valve; the first air intake port is connected to one end of the first heat exchanger through the fourth controllable valve, and connected to one end of the fourth heat exchanger through the fifth controllable valve;

[0017] The other end of the first heat exchanger is connected to the other end of the first passage and the other end of the fourth heat exchanger through the first throttling member.

[0018] In some specific embodiments, a first one-way valve is further included, which is connected in series to the pipeline between the other end of the first heat exchanger and the other end of the first passage, and the first passage is connected to the first heat exchanger.

[0019] In some specific embodiments, a refrigerant circulation pump is further included, which is connected in parallel with the first throttling member, and two ends of the refrigerant circulation pump are respectively connected with two ends of the first throttling member through pipelines;

[0020] The refrigerant circulation pump, the first heat exchanger, the third controllable valve, the first controllable valve, and the first passage form a fourth cycle, which operates in conjunction with the second cycle.

[0021] In some specific embodiments, a second one-way valve is further included, which is connected in series with the refrigerant circulation pump through a pipeline, and its two ends are respectively connected to the two ends of the first throttling member;

[0022] The refrigerant circulation pump includes a liquid inlet and a liquid outlet; the second one-way valve is located between the refrigerant circulation pump and the first heat exchanger, connected to the liquid outlet, and communicated with the first heat exchanger from the liquid outlet.

[0023] In some specific embodiments, a gas-liquid separator is further included, which includes an inlet and an outlet;

[0024] The inlet is connected to an end of the fourth controllable valve away from the first heat exchanger and an end of the fifth controllable valve away from the fourth heat exchanger; the outlet is connected to the first air intake port.

[0025] In some specific embodiments, it further includes a four-way valve, a first controllable valve, a second controllable valve, and a first throttle; the four-way valve includes a first port, a second port, a third port, and a fourth port; the first compressor includes a first exhaust port and a first suction port;

[0026] The first port is connected to the first exhaust port; the second port is connected to the first air intake port; the third port is connected to one end of the first passage through the first controllable valve and to one end of the fourth heat exchanger through the second controllable valve; the fourth port is connected to one end of the first heat exchanger;

[0027] The other end of the first heat exchanger is connected to the other end of the first passage and the other end of the fourth heat exchanger through the first throttling member.

[0028] In some specific embodiments, a first one-way valve is further included, which is connected in series to the pipeline between the other end of the first heat exchanger and the other end of the first passage, and is connected from the first passage to the first heat exchanger.

[0029] In some specific embodiments, a second throttling device is further included; the second compressor includes a second exhaust port and a second intake port, which are respectively connected to one end of the third heat exchanger and one end of the second passage; the other end of the second passage is connected to the other end of the third heat exchanger through the second throttling device;

[0030] The first throttling element is a two-way throttling valve; the second throttling element is a one-way throttling valve, and throttling is performed from the third heat exchanger to the second passage.

[0031] In some specific embodiments, the third heat exchanger and the fourth heat exchanger are integrally configured as a fifth heat exchanger;

[0032] The fifth heat exchanger includes a third passage and a fourth passage, which are used for the second cycle and the third cycle respectively.

[0033] The cascade heat pump system of the utility model adds a fourth heat exchanger on the high-temperature condenser side to form a third cycle with the first compressor and the first heat exchanger; when the first heat exchanger needs to be defrosted, the third cycle is operated in a refrigeration state to form a single-stage compression refrigeration to defrost the first heat exchanger; first, the fourth heat exchanger exchanges heat with the liquid heat exchange medium, with high heat exchange efficiency and high evaporation efficiency, thereby improving the defrosting efficiency of the first heat exchanger; secondly, through the refrigeration of the third cycle, the first heat exchanger directly defrosts itself as a condenser, with balanced defrosting and high efficiency; high defrosting efficiency reduces the impact of frosting on the heating of the system. Thirdly, the fourth heat exchanger is set to exchange heat with the liquid heat exchange medium, and the volume of the heat exchanger is relatively small compared to the air-cooled heat exchanger, which reduces the occupied space, and does not need to increase the power of the outdoor fan, thereby reducing costs.

[0034] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0036] Figure 1 is a schematic diagram of a system structure according to an embodiment;

[0037] Figure 2 is a schematic diagram of a system structure according to an embodiment;

[0038] Figure 3 is a schematic diagram of a system structure according to an embodiment;

[0039] Figure 4 is a schematic diagram of a system structure according to an embodiment;

[0040] Figure 5 is a schematic diagram of a system structure according to an embodiment;

[0041] Figure 6 is a schematic diagram of a system structure according to an embodiment;

[0042] Figure 7 is a schematic diagram of a system structure according to an embodiment;

[0043] Figure 8 is a control flow diagram according to an embodiment;

[0044] Fig. 9 is a control flow diagram according to an embodiment;

[0045] Fig.10 Schematic diagram of a control flow according to an embodiment.

[0046] Reference numerals,

[0047] F, outdoor fan; H1, first heat exchanger; H2, second heat exchanger; H21, first passage; H22, second passage; H3, third heat exchanger; H4, fourth heat exchanger; H5, fifth heat exchanger; H51, third passage; H52, fourth passage; S1, first controllable valve; S2, second controllable valve; S3, third controllable valve; S4, fourth controllable valve; S5, fifth controllable valve; C1, first compressor; C2, second compressor; Y, gas-liquid separator; V1, first throttling device; V2, second throttling device; V3, first non-return valve; V4, second non-return valve; V5, non-return valve group; P, refrigerant circulation pump; V, four-way valve; 1, first port; 2, second port; 3, third port; 4, fourth port. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0049] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the feature. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0050] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0051] The disclosure below provides many different embodiments or examples for realizing different structures of the utility model. In order to simplify the disclosure of the utility model, the components and settings of specific examples are described below. Of course, they are merely examples, and the purpose is not to limit the utility model. In addition, the utility model may repeat reference numbers and / or reference letters in different examples, and such repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the utility model provides various specific examples of processes and materials, but those of ordinary skill in the art may be aware of the application of other processes and / or the use of other materials.

[0052]

Principle of air conditioner

[0053] The air conditioner performs the air conditioner's refrigeration cycle by using a compressor, condenser, expansion valve, and evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0054] The low-temperature and low-pressure refrigerant enters the compressor, which compresses it into high-temperature and high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0055] The expansion valve expands the high-temperature and high-pressure liquid refrigerant condensed in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the refrigerant expanded in the expansion valve and returns the low-temperature and low-pressure refrigerant gas to the compressor. The evaporator can achieve a cooling effect by utilizing the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. In the entire cycle, the air conditioner can adjust the temperature of the indoor space.

[0056] The outdoor unit of the air conditioner refers to a portion of a refrigeration cycle including a compressor and an outdoor heat exchanger, the indoor unit of the air conditioner includes an indoor heat exchanger, and an expansion valve may be provided in the indoor unit or the outdoor unit.

[0057] The indoor heat exchanger and the outdoor heat exchanger function as a condenser or an evaporator. When the indoor heat exchanger functions as a condenser, the air conditioner functions as a heater in a heating mode, and when the indoor heat exchanger functions as an evaporator, the air conditioner functions as a cooler in a cooling mode.

[0058]

This application

[0059] In some specific embodiments, reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 6 , Figure 7 , Figure 8 The cascade heat pump system includes a first heat exchanger H1, a second heat exchanger H2, a third heat exchanger H3, a fourth heat exchanger H4, a first compressor C1, a second compressor C2, a first temperature sensor, and a controller.

[0060] The first heat exchanger H1 is of fin type, disposed in the outdoor environment, and exchanges heat with the outdoor environment through the outdoor fan F.

[0061] The second heat exchanger H2 includes a first passage H21 and a second passage H22, and realizes heat exchange between the refrigerant in the first passage H21 and the refrigerant in the second passage H22, and simultaneously completes condensation or evaporation of the refrigerant in the first passage H21 and evaporation or condensation of the refrigerant in the second passage H22.

[0062] The first compressor C1 is connected to the first heat exchanger H1 and the first passage H21 of the second heat exchanger H2 through a pipeline to form a first cycle, which can realize the heating operation of the first passage H21 as a condenser. That is, during the first cycle operation, the first passage H21 acts as a condenser and the first heat exchanger H1 acts as an evaporator.

[0063] The third heat exchanger H3 is arranged to exchange heat with a liquid heat exchange medium; for example, if the liquid heat exchange medium is water, the third heat exchanger H3 is arranged in a water tank to exchange heat with the water in the water tank.

[0064] The second compressor C2 is connected to the second passage H22 of the second heat exchanger H2 and the third heat exchanger H3 through a pipeline to form a second cycle, which can realize the heating operation of the third heat exchanger H3 as a condenser. That is, the third heat exchanger H3 acts as a condenser and the second passage H22 acts as an evaporator when the second cycle is running. That is, the third heat exchanger H3 realizes water heating provided to users; that is, it provides a heating heat source for hot water for users.

[0065] The fourth heat exchanger H4 is arranged to exchange heat with a liquid heat exchange medium; for example, if the liquid heat exchange medium is water, the fourth heat exchanger H4 is arranged in a water tank to exchange heat with the water in the water tank. The fourth heat exchanger H4 is connected to the first heat exchanger H1 and the first compressor C1 through a pipeline to form a third cycle, which can realize the heating operation of the fourth heat exchanger H4 as a condenser. That is, when the third cycle is in heating operation, the fourth heat exchanger H4 acts as a condenser and the first heat exchanger H1 acts as an evaporator.

[0066] The first cycle and the second cycle are linked to heat the first operation mode, that is, two-stage compression heating; the third cycle heating operation is the second operation mode.

[0067] The first temperature sensor is used to detect the ambient temperature.

[0068] The controller is connected to the first temperature sensor for obtaining the ambient temperature.

[0069] The controller of the system is configured to set a target temperature for heating S100; cyclically obtain the ambient temperature, calculate the difference between the target temperature and the ambient temperature S200, and determine whether to operate in the first operation mode or the second operation mode S300 according to the difference between the target temperature and the ambient temperature.

[0070] The cascade heat pump system of this embodiment determines the heating capacity required by the system by the difference between the target temperature and the ambient temperature, and selects the first operation mode with high heating capacity or the second operation mode with low heating capacity according to the required heating capacity, so that the heating load of the system matches the required heating capacity, which not only improves the stability of the system operation but also improves the energy efficiency of the system.

[0071] In addition, the third heat exchanger H3 and the fourth heat exchanger H4 are both set to exchange heat with the liquid heat exchange medium, and can be set to a smaller volume relative to the air-cooled fin heat exchanger; that is, the cascade heat pump system reduces the volume of the heat exchanger of the cascade heat pump system when realizing the second operating mode of single-stage compression heating compared to the prior art, reduces the occupied area and does not need to increase the power of the outdoor fan F, thereby reducing costs.

[0072] Of course, the first cycle and the second cycle can also be linked for refrigeration to achieve two-stage compression refrigeration with a high compression ratio; the third cycle can also be operated for refrigeration.

[0073] In some specific embodiments, reference Figure 1 , Figure 8 The cascade heat pump system further includes a first controllable valve S1, a second controllable valve S2, and a first throttle V1; the first compressor C1 includes a first exhaust port and a first intake port.

[0074] The first exhaust port is connected to one end of the first passage H21 through the first controllable valve S1, and is connected to one end of the fourth heat exchanger H4 through the second controllable valve S2; the first air intake port is connected to one end of the first heat exchanger H1.

[0075] The other end of the first heat exchanger H1 is connected to the other end of the first passage H21 and the other end of the fourth heat exchanger H4 via the first throttle V1.

[0076] The system operates in the first operation mode by controlling the first controllable valve S1 to be connected, the second controllable valve S2 to be cut off, the first compressor C1 to operate, and the second compressor C2 to operate; that is, when the system determines that the first operation mode needs to be operated, the first controllable valve S1 is controlled to be connected, the second controllable valve S2 to be cut off, and the first compressor C1 and the second compressor C2 to operate.

[0077] The system operates in the second operation mode by controlling the second controllable valve S2 to be connected, the first controllable valve S1 to be cut off, the first compressor C1 to operate, and the second compressor C2 to stop operating; that is, when the system determines that the second operation mode needs to be operated, the second controllable valve S2 is controlled to be connected, the first controllable valve S1 is controlled to be cut off, the first compressor C1 to operate, and the second compressor C2 to stop operating.

[0078] The cascade heat pump system of this embodiment realizes the switching between the first operation mode and the second operation mode by providing the first controllable valve S1 and the second controllable valve S2, which is simple, reliable and efficient.

[0079] In some specific embodiments, reference Figure 3 , Figure 7 , Figure 8 , Fig. 9 The cascade heat pump system also includes a refrigerant circulation pump P and a third controllable valve S3.

[0080] The two ends of the refrigerant circulation pump P are respectively connected to the two ends of the first throttling member V1 through pipelines; the two ends of the third controllable valve S3 are respectively connected to the first exhaust port and one end of the first heat exchanger H1, forming a fourth cycle consisting of the first heat exchanger H1, the first passage H21, and the refrigerant circulation pump P; the refrigerant in the fourth cycle is not compressed by the compressor and is only used as a heat exchange medium.

[0081] The fourth cycle and the second cycle are linked to operate in the third operation mode. That is, when the third operation mode is in operation, the refrigerant circulation pump P is controlled to operate, the third controllable valve S3 and the first controllable valve S1 are connected, and the second controllable valve is controlled to be cut off, so that the refrigerant in the fourth cycle circulates; the refrigerant that does not pass through the compressor exchanges heat with the external environment in the first heat exchanger H1, and exchanges heat with the refrigerant in the second passage H22 in the first passage H21. The second cycle is in heating operation; the second passage H22 acts as an evaporator; and the third heat exchanger H3 acts as a condenser.

[0082] The first operation mode, the second operation mode or the third operation mode is determined according to the difference between the target temperature and the ambient temperature.

[0083] Specifically, when the system determines to operate in the third operation mode, the first controllable valve S1 and the third controllable valve S3 are controlled to be connected, the second controllable valve S2 is controlled to be closed, the first compressor C1 is controlled to stop running, and the refrigerant circulation pump P and the second compressor C2 are controlled to run.

[0084] The cascade heat pump system of this embodiment realizes the control operation of the third operation mode when the refrigeration capacity is between the first operation mode and the second operation mode by setting the third controllable valve S3 and the refrigerant circulation pump P. The operation mode to be executed is determined by judging the difference between the target temperature and the ambient temperature, thereby improving the degree of automation of the system operation.

[0085] In some specific embodiments, reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 The liquid heat exchange medium is water, which is used to provide hot water to users or use hot water to heat the target object or space; the target temperature is the target water temperature, which can be automatically obtained according to the ambient temperature.

[0086] The target temperature is linearly related to the ambient temperature. That is, the target temperature is equal to the sum of the product of the first coefficient and the ambient temperature and the second coefficient. The first coefficient and the second coefficient can be set according to different needs of different application scenarios.

[0087] The cascade heat pump system of this embodiment improves the automation and intelligence of system operation by automatically generating the target temperature.

[0088] In some specific embodiments, reference Figure 8 , Fig. 9 , a first temperature threshold and a second temperature threshold which is smaller than the first temperature threshold are set, and a target temperature is obtained S101; the ambient temperature is obtained cyclically, and the difference between the target temperature and the ambient temperature is calculated S200; the difference between the target temperature and the ambient temperature is compared with the first temperature threshold and the second temperature threshold; when the difference between the target temperature and the ambient temperature is not smaller than the first temperature threshold S301, the first operation mode S401 is operated; when the difference between the target temperature and the ambient temperature is not greater than the second temperature threshold S302, the second operation mode S402 is operated; when the difference between the target temperature and the ambient temperature is between the second temperature threshold and the first temperature threshold, the third operation mode S403 is operated.

[0089] In some specific embodiments, the first temperature threshold and the second temperature threshold are range values, and the switching from the first operation mode to the third operation mode and the switching from the third operation mode to the second operation mode are performed at the minimum values ​​of the first temperature threshold and the second temperature threshold, respectively; the switching from the second operation mode to the third operation mode and the switching from the third operation mode to the first operation mode are performed at the maximum values ​​of the first temperature threshold and the second temperature threshold, respectively.

[0090] That is, when the system operates in the first operating mode and the difference between the target temperature and the ambient temperature is not greater than the minimum value of the first temperature threshold, the system switches to the third operating mode; if the difference between the target temperature and the ambient temperature is not greater than the minimum value of the second temperature threshold, the system switches to the second operating mode.

[0091] When the system operates in the third operating mode and the difference between the target temperature and the ambient temperature is not greater than the minimum value of the second temperature threshold, the system switches to the second operating mode; if the difference between the target temperature and the ambient temperature is not less than the maximum value of the first temperature threshold, the system switches to the first operating mode.

[0092] When the system operates in the second operating mode and the difference between the target temperature and the ambient temperature is not less than the maximum value of the second temperature threshold, the system switches to the third operating mode; when the difference between the target temperature and the ambient temperature is not less than the maximum value of the first temperature threshold, the system switches to the first operating mode.

[0093] The cascade heat pump system of this embodiment realizes hysteresis control of switching between system operation modes by setting the first temperature threshold and the second temperature threshold as range values, thereby reducing the frequency of switching between system operation modes and improving the stability and reliability of system operation.

[0094] In some specific embodiments, the first temperature threshold and the second temperature threshold are point values; the conversion between the first operation mode and the third operation mode, and the switching between the second operation mode and the third operation mode are controlled by fixed hysteresis.

[0095] That is, the hysteresis of the first temperature threshold and the hysteresis of the second temperature threshold are set; when the difference between the target temperature and the ambient temperature is not less than the sum of the first temperature threshold, the second temperature threshold and the hysteresis, the first operation mode is switched to the third operation mode, and the third operation mode is switched to the second operation mode; when the difference between the target temperature and the ambient temperature is not greater than the difference between the first temperature threshold, the second temperature threshold and the hysteresis, the second operation mode is switched to the third operation mode, and the third operation mode is switched to the first operation mode.

[0096] The cascade heat pump system of this embodiment reduces the frequency of system operation mode switching by setting the hysteresis to control the hysteresis of the operation mode switching, thereby improving the stability and reliability of the system operation.

[0097] In some specific embodiments, the hysteresis of the first temperature threshold is equal to the hysteresis of the second temperature threshold.

[0098] In some specific embodiments, the first temperature threshold is equal to the difference between the target temperature and the ambient temperature when the unit energy efficiency in the first operating mode is equal to the unit energy efficiency in the third operating mode; the second temperature threshold is equal to the difference between the target temperature and the ambient temperature when the unit energy efficiency in the second operating mode is equal to the unit energy efficiency in the third operating mode.

[0099] That is, the unit energy efficiency of the first operating mode is equal to the ratio of the unit heating capacity to the sum of the power of the outdoor fan F and the power of the first compressor C1 and the power of the second compressor C2; the unit energy efficiency of the second operating mode is equal to the ratio of the unit heating capacity to the sum of the power of the outdoor fan F and the power of the first compressor C1; the unit energy efficiency of the third operating mode is equal to the ratio of the unit heating capacity to the sum of the power of the second compressor C2 and the power of the refrigerant circulation pump P.

[0100] The first temperature threshold and the second temperature threshold can be obtained by an experimental method. Specifically, the system runs the first operation mode, the second operation mode, and the third operation mode of the set parameters respectively, and respectively calculates the unit energy efficiency and the corresponding target temperature and the difference between the ambient temperature; obtains the difference between the target temperature and the ambient temperature when the unit energy efficiency of the first operation mode is equal to the unit energy efficiency of the third operation mode, and the difference between the target temperature and the ambient temperature when the unit energy efficiency of the second operation mode is equal to the unit energy efficiency of the third operation mode.

[0101] In some specific embodiments, reference Figure 2 , Figure 3 , Figure 6 , Figure 7 , Fig.10 The cascade heat pump system also includes a second temperature sensor, a fourth controllable valve S4, and a fifth controllable valve S5.

[0102] The second temperature sensor is disposed on the first heat exchanger H1 and is used to detect the evaporation temperature.

[0103] The first air intake port is connected to one end of the first heat exchanger H1 through a fourth controllable valve S4, and is connected to one end of the fourth heat exchanger H4 through a fifth controllable valve S5.

[0104] A defrost temperature threshold S500 is preset; during the heating operation of the first operation mode and the second operation mode, the ambient temperature and the evaporation temperature are cyclically obtained, and the difference between the ambient temperature and the evaporation temperature is calculated S600; when the difference between the ambient temperature and the evaporation temperature is not less than the defrost temperature threshold S700, the third controllable valve S3 and the fifth controllable valve S5 are controlled to be connected, the first controllable valve S1, the second controllable valve S2, and the fourth controllable valve S4 are controlled to be cut off, the first compressor C1 is controlled to operate, and the second compressor C2 is controlled to stop operating, and the fourth operation mode S800 of the third cycle is operated to defrost the first heat exchanger H1.

[0105] When the first cycle and the third cycle are in heating operation, the first controllable valve S1 and the fourth controllable valve S4 are controlled to be connected, the second controllable valve S2, the third controllable valve S3 and the fifth controllable valve S5 are controlled to be cut off, and the first compressor C1 and the second compressor C2 are controlled to operate; or the second controllable valve S2 and the fourth controllable valve S4 are controlled to be connected, the first controllable valve S1, the third controllable valve S3 and the fifth controllable valve S5 are controlled to be cut off, and the first compressor C1 is controlled to operate and the second compressor C2 is stopped.

[0106] The cascade heat pump system of this embodiment controls the first controllable valve S1, the second controllable valve S2, the third controllable valve S3, the fourth controllable valve S4, and the fifth controllable valve S5 to make the third cycle of the cascade heat pump system work in the refrigeration state, that is, the fourth operation mode, forming a single-stage compression refrigeration to defrost the first heat exchanger H1; first, the fourth heat exchanger H4 exchanges heat with the liquid heat exchange medium, with high heat exchange efficiency and high evaporation efficiency, thereby improving the defrosting efficiency of the first heat exchanger; second, through the refrigeration of the third cycle, the first heat exchanger H1 directly defrosts itself as a condenser, with balanced defrosting and high efficiency; high defrosting efficiency can further reduce the impact of frost on the heating of the system. Thirdly, the fourth heat exchanger H4 is set to exchange heat with the liquid heat exchange medium, and the volume of the heat exchanger is relatively small compared to the volume of the air-cooled heat exchanger, which reduces the occupied space, and does not need to increase the power of the outdoor fan F, thereby reducing costs and saving energy.

[0107] In some specific embodiments, reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 The cascade heat pump system also includes a first one-way valve V3.

[0108] The first one-way valve V3 is connected in series to the pipeline connecting the other end of the first heat exchanger H1 and the other end of the first passage H21, and is communicated from the first passage H21 to the first heat exchanger H1. That is, the other end of the first heat exchanger H1 is connected to the other end of the first passage H21 through the first one-way valve V3 and the pipeline; the first one-way valve V3 is communicated from the other end of the first passage H21 to the other end of the first heat exchanger H1. That is, the other end of the first heat exchanger H1 is connected to one end of the first one-way valve V3 through the pipeline; the other end of the first one-way valve V3 is connected to the other end of the first passage H21 through the pipeline, and the first one-way valve V3 is communicated from the other end of the first passage H21 to the other end of the first heat exchanger H1.

[0109] When the cascade heat pump system of this embodiment operates in the fourth operation mode, the first one-way valve V3 prevents the refrigerant flowing out from the other end of the first heat exchanger H1 or the other end of the fourth heat exchanger H4 from entering the first passage H21, thereby reducing the mass of the circulating refrigerant, ensuring the quality of the refrigerant in the third cycle, and improving the heating and defrosting efficiency.

[0110] In some specific embodiments, reference Figure 3 , Figure 6 , Figure 7 The cascade heat pump system further includes a second one-way valve V4. The refrigerant circulation pump P includes a liquid inlet and a liquid outlet.

[0111] The second one-way valve V4 is connected in series with the refrigerant circulation pump P through a pipeline, and its two ends are respectively connected to the two ends of the first throttling member V1. It is located between the refrigerant circulation pump P and the first heat exchanger H1, and is connected from the refrigerant circulation pump P to the first heat exchanger H1.

[0112] That is, one end of the second one-way valve V4 is connected to the other end of the first heat exchanger H1 through a pipeline, and the other end is connected to the liquid outlet of the refrigerant circulation pump P; the liquid inlet of the refrigerant circulation pump P is connected to the other end of the first passage H21, or is connected to the other end of the first passage H21 through the first one-way valve V3; the second one-way valve V4 is connected from the liquid outlet of the refrigerant circulation pump P to the other end of the first heat exchanger H1.

[0113] The cascade heat pump system of this embodiment is provided with a second one-way valve V4 to prevent the refrigerant from entering from the liquid outlet of the refrigerant circulation pump P and flowing out from the liquid inlet to reversely drive the refrigerant circulation pump P, thereby ensuring the stability, reliability and safety of the system operation.

[0114] In some specific embodiments, reference Figure 2 , Figure 3 , Figure 5 , Figure 6 , Figure 7 On the basis of the above-mentioned cascade heat pump system, it also includes a gas-liquid separator Y, which includes an inlet and an outlet.

[0115] The inlet is connected to one end of the fourth controllable valve S4 away from the first heat exchanger H1 and one end of the fifth controllable valve S5 away from the fourth heat exchanger H4; the outlet is connected to the first air intake port.

[0116] That is, the inlet is connected to one end of the first heat exchanger H1 through the fourth controllable valve S4, and is connected to one end of the fourth heat exchanger H4 through the fifth controllable valve S5; and the outlet is connected to the first air intake port.

[0117] That is, the first air intake port is connected to one end of the fourth controllable valve S4 and one end of the fifth valve through the gas-liquid separator Y; the other end of the fourth controllable valve S4 is connected to one end of the first heat exchanger H1; the other end of the fifth controllable valve S5 is connected to one end of the fourth heat exchanger H4.

[0118] In some specific embodiments, reference Figure 4 The cascade heat pump system includes a first heat exchanger H1, a second heat exchanger H2, a third heat exchanger H3, a fourth heat exchanger H4, a first compressor C1, a second compressor C2, a four-way valve V, a first controllable valve S1, a second controllable valve S2, and a first throttling element V1.

[0119] The first heat exchanger H1 is arranged in the outdoor environment and exchanges heat with the outdoor environment through the outdoor fan F.

[0120] The second heat exchanger H2 includes a first passage H21 and a second passage H22, and is used for heat exchange between the refrigerant in the first passage H21 and the refrigerant in the second passage H22.

[0121] The first compressor C1 is connected to the first heat exchanger H1 and the first passage H21 through pipelines to form a first cycle.

[0122] The third heat exchanger H3 is configured to exchange heat with the liquid heat exchange medium.

[0123] The second compressor C2 is connected to the second passage H22 and the third heat exchanger H3 through pipelines to form a second cycle.

[0124] The fourth heat exchanger H4 is configured to exchange heat with the liquid heat exchange medium, and is connected to the first heat exchanger H1 and the first compressor C1 through pipelines to form a third cycle; the first cycle and the second cycle are linked to heat operation or the third cycle operation; the third cycle operation can be cooling or heating.

[0125] The four-way valve V includes a first port 1, a second port 2, a third port 3, and a fourth port 4; the first compressor C1 includes a first exhaust port and a first intake port.

[0126] The first exhaust port is connected to the first port 1; the second port 2 is connected to the first intake port; the third port 3 is connected to one end of the first passage H21 through the first controllable valve S1 and to one end of the fourth heat exchanger H4 through the second controllable valve S2; the fourth port 4 is connected to one end of the first heat exchanger H1.

[0127] The other end of the first heat exchanger H1 is connected to the other end of the first passage H21 and the other end of the fourth heat exchanger H4 via the first throttle V1.

[0128] The cascade heat pump system of this embodiment realizes the heating operation of the first cycle or the heating operation of the third cycle or the cooling operation of the third cycle through the four-way valve V and the first controllable valve S1 and the second controllable valve S2.

[0129] In some specific embodiments, the controller of the cascade heat pump system is connected to the first temperature sensor and the second temperature sensor to obtain the ambient temperature and the evaporation temperature; the controller is connected to the outdoor fan F, the first compressor C1, the second compressor C2, the first controllable valve S1, the second controllable valve S2, the third controllable valve S3, the fourth controllable valve S4, the fifth controllable valve S5, the first throttling device V1, the second throttling device V2, and the refrigerant circulation pump P to control their actions according to the control logic.

[0130] In some specific embodiments, the controller of the cascade heat pump system is connected to the first temperature sensor and the second temperature sensor to obtain the ambient temperature and the evaporation temperature; the controller is connected to the outdoor fan F, the first compressor C1, the second compressor C2, the first controllable valve S1, the second controllable valve S2, the four-way valve V, the first throttle V1, and the second throttle V2 to control their actions according to the control logic.

[0131] In some specific embodiments, reference Figure 4 The cascade heat pump system also includes a gas-liquid separator Y, which includes an inlet and an outlet.

[0132] The second port 2 is connected to the first air intake port through the gas-liquid separator Y. That is, the inlet is connected to the second port 2; and the outlet is connected to the first air intake port.

[0133] In some specific embodiments, reference Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 The cascade heat pump system also includes a second throttling device V2; the second compressor C2 includes a second exhaust port and a second intake port, which are respectively connected to one end of the third heat exchanger H3 and one end of the second passage H22; the other end of the second passage H22 is connected to the other end of the third heat exchanger H3 through the second throttling device V2.

[0134] The first throttle member V1 is a two-way throttle valve; the second throttle member V2 is a one-way throttle valve, which throttles from the third heat exchanger H3 to the second passage H22.

[0135] In some specific embodiments, reference Figure 6 , Figure 7 The first throttle member V1 can be connected to a one-way valve group V5 composed of four one-way valves to form a bridge type, and the one-way throttle valve is arranged on the bridge to realize a two-way throttling function.

[0136] In some specific embodiments, reference Figure 3 , Figure 4 , Figure 5 , Figure 6 The third heat exchanger H3 and the fourth heat exchanger H4 are integrated into a fifth heat exchanger H5.

[0137] The fifth heat exchanger H5 includes a third passage H51 and a fourth passage H52, which are used for the second cycle and the third cycle respectively.

[0138] The cascade heat pump system of this embodiment further reduces the volume of the heat exchanger of the cascade heat pump system by integrating the third heat exchanger H3 and the fourth heat exchanger H4, thereby reducing the occupied space and further reducing the cost.

[0139] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0140] The above is only a specific implementation of the utility model, but the protection scope of the utility model is not limited to this. Any changes or substitutions that can be easily thought of by technicians familiar with the technical field within the technical scope disclosed by the utility model should be included in the protection scope of the utility model. Therefore, the protection scope of the utility model should be based on the protection scope of the claims.

Claims

1. A cascade heat pump system, characterized in that: include: A first heat exchanger is arranged in an outdoor environment and exchanges heat with the outdoor environment through an outdoor fan; A second heat exchanger comprising a first passage and a second passage, and configured to exchange heat between the refrigerant in the first passage and the refrigerant in the second passage; A first compressor, which is connected to the first heat exchanger and the first passage through a pipeline to form a first cycle; A third heat exchanger, which is arranged to exchange heat with the liquid heat exchange medium; a second compressor connected to the second passage and the third heat exchanger through a pipeline to form a second cycle; The fourth heat exchanger is arranged for heat exchange with the liquid heat exchange medium, and is connected to the first heat exchanger and the first compressor through pipelines to form a third cycle; the first cycle and the second cycle are linked to heat operation or the third cycle is operated; the third cycle operation can be cooling or heating.

2. The cascade heat pump system according to claim 1, characterized in that: It also includes a first controllable valve, a second controllable valve, a third controllable valve, a fourth controllable valve, a fifth controllable valve, and a first throttling element; the first compressor includes a first exhaust port and a first intake port; The first exhaust port is connected to one end of the first passage through the first controllable valve, connected to one end of the fourth heat exchanger through the second controllable valve, and connected to one end of the first heat exchanger through the third controllable valve; the first air intake port is connected to one end of the first heat exchanger through the fourth controllable valve, and connected to one end of the fourth heat exchanger through the fifth controllable valve; The other end of the first heat exchanger is connected to the other end of the first passage and the other end of the fourth heat exchanger through the first throttling member.

3. The cascade heat pump system according to claim 2, characterized in that: It also includes a first one-way valve, which is connected in series to the pipeline between the other end of the first heat exchanger and the other end of the first passage, and is connected from the first passage to the first heat exchanger.

4. The cascade heat pump system according to claim 3, characterized in that: It also includes a refrigerant circulation pump, which is connected in parallel with the first throttling member, and two ends of which are respectively connected to two ends of the first throttling member through pipelines; The refrigerant circulation pump, the first heat exchanger, the third controllable valve, the first controllable valve, and the first passage form a fourth cycle, which operates in conjunction with the second cycle.

5. The cascade heat pump system according to claim 4, characterized in that: It also includes a second one-way valve, which is connected in series with the refrigerant circulation pump through a pipeline, and its two ends are respectively connected to the two ends of the first throttling member; The refrigerant circulation pump includes a liquid inlet and a liquid outlet; the second one-way valve is located between the refrigerant circulation pump and the first heat exchanger, connected to the liquid outlet, and communicated with the first heat exchanger from the liquid outlet.

6. The cascade heat pump system according to claim 2, characterized in that: Also included is a gas-liquid separator, which includes an inlet and an outlet; The inlet is connected to an end of the fourth controllable valve away from the first heat exchanger and an end of the fifth controllable valve away from the fourth heat exchanger; the outlet is connected to the first air intake port.

7. The cascade heat pump system according to claim 1, characterized in that: It also includes a four-way valve, a first controllable valve, a second controllable valve, and a first throttle; the four-way valve includes a first port, a second port, a third port, and a fourth port; the first compressor includes a first exhaust port and a first intake port; The first port is connected to the first exhaust port; the second port is connected to the first air intake port; the third port is connected to one end of the first passage through the first controllable valve and to one end of the fourth heat exchanger through the second controllable valve; the fourth port is connected to one end of the first heat exchanger; The other end of the first heat exchanger is connected to the other end of the first passage and the other end of the fourth heat exchanger through the first throttling member.

8. The cascade heat pump system according to claim 7, characterized in that: It also includes a first one-way valve, which is connected in series to the pipeline between the other end of the first heat exchanger and the other end of the first passage, and is connected from the first passage to the first heat exchanger.

9. The cascade heat pump system according to any one of claims 2 to 8, characterized in that: The second compressor further comprises a second throttling device; the second compressor comprises a second exhaust port and a second intake port, which are respectively connected to one end of the third heat exchanger and one end of the second passage; the other end of the second passage is connected to the other end of the third heat exchanger through the second throttling device; The first throttling element is a two-way throttling valve; the second throttling element is a one-way throttling valve, and throttling is performed from the third heat exchanger to the second passage.

10. The cascade heat pump system according to any one of claims 1 to 8, characterized in that: The third heat exchanger and the fourth heat exchanger are integrally configured as a fifth heat exchanger; The fifth heat exchanger includes a third passage and a fourth passage, which are used for the second cycle and the third cycle respectively.

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