A photovoltaic photo-thermal heat pump system based on reverse brayton cycle and a control method thereof

Abstract

This invention discloses a photovoltaic thermal heat pump system and its control method based on a reverse Brayton cycle, relating to the field of heat pump technology. The system includes a photovoltaic thermal air collector, a regenerator, a compressor mechanism, a heat exchanger, a power turbine mechanism, and a thermal storage heating system connected by pipelines. The photovoltaic thermal air collector uses photovoltaic waste heat to heat the air, raising the base temperature of the cycle. The preheated air, after being heated by the regenerator, enters the compressor mechanism, where it is compressed and heated between each stage of the compressor. Heat is released to the outside through the user-side heat exchanger between stages, achieving tiered heating and intermediate cooling effects. Finally, the air expands to perform work. This invention improves the energy quality of the air by preheating it with a photovoltaic thermal air collector, while simultaneously increasing photovoltaic power generation efficiency; it also improves the heating efficiency ratio (COP) of the air circulation heat pump in extremely cold environments by using staged compression to reduce the compression specific work.

Description

Technical Field

[0001] This invention relates to the field of new energy utilization and heat pump technology, and in particular to a reverse Brayton cycle heat pump system and equipment that combines solar photovoltaic and photothermal technology, staged regeneration and a free rotor-assisted two-stage compression architecture, as well as a supporting operation control method. Background Technology

[0002] With the increasing global demand for clean heating, heat pump technology has been widely adopted. However, traditional air source heat pumps mostly use vapor compression cycles (using phase change refrigerants such as Freon). In extremely cold regions (such as outdoor ambient temperatures below -30°C), traditional heat pumps face severe failure problems: during low-temperature startup, defrosting, and operation mode switching, compressor lubricating oil is prone to stagnation in the throttling device and heat exchanger, affecting the stability of system oil return; the extremely low evaporation pressure of the refrigerant leads to an exponential increase in the suction specific volume, resulting in a precipitous decrease in heating capacity (even less than 40% of the nominal value); at the same time, in order to produce 50°C heating hot water at -30°C, the system pressure ratio is extremely high, which can easily cause the compressor discharge temperature to exceed the limit or even burn out.

[0003] Reverse Brayton cycle (air circulation) heat pumps use air as the working fluid, eliminating phase change and the risk of frost formation, and theoretically possess extremely strong low-temperature adaptability. However, ordinary single-stage air circulation heat pumps also face the problem of excessively high compression ratio under low temperature and large temperature differences, resulting in lower efficiency.

[0004] Introducing solar photovoltaic (PV) thermal modules into heat pump systems to preheat the working fluid is a way to improve energy efficiency. However, most existing PV thermal module heat pumps are coupled with fluorine systems, and directly introducing PV thermal modules into the air circulation often faces the problem of heat quality mismatch (if introduced directly after reheating, the temperature of the reheated air may be higher than the temperature of the PV thermal modules, resulting in heat backflow). In addition, there is a serious time mismatch between the peak of power generation and heat production (daytime) and the peak of heating demand (cold nights with no sunlight). Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a photovoltaic-thermal heat pump system based on the reverse Brayton cycle and its control method, which solves the defects of the prior art in cold regions such as heating attenuation, high compressor power consumption, mismatch of photovoltaic-thermal heat quality and supply-demand time mismatch.

[0006] The present invention provides a photovoltaic-thermal heat pump system based on the reverse Brayton cycle, comprising: a first regenerator, an air-liquid heat exchanger, a photovoltaic collector, a second regenerator, a second user heat exchanger, an electric compressor, a drive motor, a first user heat exchanger, a second compressor, and a power turbine.

[0007] In the direction of the working gas flow:

[0008] The cold-side inlet of the first regenerator is connected to the environment, and its cold-side outlet is connected to the heated-side inlet of the air-liquid heat exchanger. The heated-side outlet of the air-liquid heat exchanger is connected to the cold-side inlet of the second regenerator. The cold-side outlet of the second regenerator is connected to the intake port of the electric compressor via a pipeline. The exhaust port of the electric compressor is connected to the hot-side inlet of the first user heat exchanger. The hot-side outlet of the first user heat exchanger is connected to the intake port of the second-stage compressor. The exhaust port of the second-stage compressor is connected to the hot-side inlet of the second user heat exchanger. The hot-side outlet of the second user heat exchanger is connected to the hot-side inlet of the second regenerator. The hot-side outlet of the second regenerator is connected to the hot-side inlet of the first regenerator. The hot-side outlet of the first regenerator is connected to the intake port of the power turbine, and the exhaust port of the power turbine is connected to the environment. The photovoltaic collector is connected to the heating side of the air-liquid heat exchanger via a closed pipeline, and a pump drives the internal antifreeze for heat exchange.

[0009] Optionally, the working gas absorbs low-grade heat from the photovoltaic collector in the air-liquid heat exchanger.

[0010] Optionally, the electric compressor is driven by the drive motor on a single shaft; the secondary compressor is coaxially and directly connected to the power turbine, and the expansion work generated by the power turbine is directly used to drive the secondary compressor.

[0011] Optionally, the first regenerator, the air-liquid heat exchanger, and the second regenerator together constitute a staged regenerative preheating mechanism.

[0012] Optionally, the system further includes a heat storage heating subsystem; the first user heat exchanger and the second user heat exchanger are configured as gas-liquid heat exchangers, and their heated side water circuits are connected in parallel or in series, and then connected to a heat storage device for supplying heating to the user terminal or for time-shifted storage of thermal energy.

[0013] Optionally, the working gas flowing inside the system is air, and it is an open-loop system.

[0014] Optionally, the photovoltaic-thermal heat pump system also includes a control unit, which is electrically connected to the circulation pump on the photovoltaic collector side, the drive motor, and the environmental sensor, respectively.

[0015] The control unit is configured to: acquire the current solar irradiance and ambient temperature; execute a time-sharing control strategy according to a preset solar thermal energy storage scheduling algorithm; adjust the operating power and working fluid flow of the drive motor; and control the system according to the control method of the heat pump system to minimize the overall operating cost of the system.

[0016] 1. On the other hand, the present invention also provides a control method for a photovoltaic-thermal heat pump system as described in any of the above technical solutions, which utilizes a time-sharing control strategy to control the photovoltaic-thermal heat pump system, the time-sharing control strategy including:

[0017] Daytime heat storage mode: When the solar irradiance is detected to be higher than the preset threshold and it is during a period of low electricity prices, the drive motor is controlled to run at high frequency and high power; the heat generated by the first user heat exchanger and the second user heat exchanger, after meeting the immediate heat load of the building, is transferred to the heat storage device for storage; at the same time, the maximum convective heat exchange of the photovoltaic collector is maintained to cool the photovoltaic module.

[0018] Nighttime heat release mode: When the solar irradiance is detected to be lower than the preset threshold or during peak electricity price periods, the heat storage device is turned on first to supply heat to the user terminal; the drive motor is controlled to operate at a lower frequency or power than the preset value or to be shut down and standby.

[0019] Off-peak electricity pricing: During off-peak electricity pricing periods, the power of the motor is increased to a value greater than or equal to a preset value to generate more heat for heating or heat storage.

[0020] Beneficial effects:

[0021] 1. Breakthrough in extreme cold adaptability: Using air as the circulating working fluid eliminates the limitations of evaporation pressure in traditional refrigerant systems, removing the risk of freezing and frost. Combined with a two-stage compression architecture, it can stably output high-quality heating hot water above 50℃ even in outdoor environments of -30℃, without any reduction in heating capacity.

[0022] 2. Photovoltaic-thermal coupled reverse Brayton cycle heat pump achieves "double increase in heat and electricity": Photovoltaic-thermal components increase the compressor suction temperature and reduce compression power consumption; at the same time, they remove the waste heat from the photovoltaic panel, ensuring its photoelectric conversion efficiency.

[0023] 3. Maximize economic benefits: By combining heat storage and strategic control, we can achieve "low-cost heating and storage with solar thermal assistance during the day, and release stored heat at night to avoid extremely cold and inefficient areas"; make efficient use of off-peak electricity prices at midday; and minimize the operating cost of all-weather heating for buildings. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments 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.

[0025] Figure 1 This is a schematic diagram of the heat pump system structure provided in an embodiment of the present invention.

[0026] The components include: 1. First regenerator; 2. Air-liquid heat exchanger; 3. Photovoltaic collector; 4. Second regenerator; 5. Second user heat exchanger; 6. Electric compressor; 7. Drive motor; 8. First user heat exchanger; 9. Second compressor; 10. Power turbine; 11. Pipeline. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments.

[0028] Reference Figure 1 This embodiment provides a photovoltaic-thermal heat pump system based on the reverse Brayton cycle, including: a first regenerator 1, an air-liquid heat exchanger 2, a photovoltaic collector 3, a second regenerator 4, a second user heat exchanger 5, an electric compressor 6, a drive motor 7, a first user heat exchanger 8, a second-stage compressor 9, and a power turbine 10. The connection relationships of each component are described in detail below:

[0029] In the flow direction of the working gas: the cold-side inlet of the first regenerator 1 is connected to the environment, and the cold-side outlet is connected to the heated-side inlet of the air-liquid heat exchanger 2; the heated-side outlet of the air-liquid heat exchanger 2 is connected to the cold-side inlet of the second regenerator 4; the cold-side outlet of the second regenerator 4 is connected to the suction port of the electric compressor 6 via pipe 11; the exhaust port of the electric compressor 6 is connected to the hot-side inlet of the first user heat exchanger 8; the hot-side outlet of the first user heat exchanger 8 is connected to the suction port of the secondary compressor 9; The exhaust port of the secondary compressor 9 is connected to the hot-side inlet of the second user heat exchanger 5; the hot-side outlet of the second user heat exchanger 5 is connected to the hot-side inlet of the second regenerator 4; the hot-side outlet of the second regenerator 4 is connected to the hot-side inlet of the first regenerator 1; the hot-side outlet of the first regenerator 1 is connected to the air inlet of the power turbine 10, and the exhaust port of the power turbine 10 is in communication with the environment; wherein, the photovoltaic collector 3 is connected to the heating side of the air-liquid heat exchanger 2 through a closed pipeline, and a pump is set to drive the built-in antifreeze for heat exchange.

[0030] In this embodiment, ambient air flows sequentially through the cold side of the first regenerator 1, the heated side of the air-liquid heat exchanger 2, and the cold side of the second regenerator 4, and is connected to the electric compressor 6 via pipeline 11; the exhaust port of the electric compressor 6 is sequentially connected to the hot side of the first user heat exchanger 8, the secondary compressor 9, the hot side of the second user heat exchanger 5, the hot side of the second regenerator 4, and the hot side of the first regenerator 1, and is finally discharged to the power turbine 10.

[0031] It should be understood that, in this embodiment, the working gas absorbs low-grade heat from the photovoltaic collector 3 in the air-liquid heat exchanger 2.

[0032] In addition, in this embodiment, the electric compressor 6 is driven by the drive motor 7 on a single shaft; the secondary compressor 9 is coaxially and directly connected to the power turbine 10, and the expansion work generated by the power turbine 10 is directly used to drive the secondary compressor 9.

[0033] In this embodiment, the photovoltaic-thermal heat pump system also includes a control unit, which is electrically connected to the circulation pump on the photovoltaic collector 3 side, the drive motor 7, and the environmental sensor. The control unit is configured to: acquire the current solar irradiance and ambient temperature; execute a time-sharing control strategy according to a preset solar thermal energy storage scheduling algorithm; adjust the operating power and working fluid flow of the drive motor 7; and control the system according to the heat pump system control method to minimize the overall operating cost of the system.

[0034] This embodiment also provides a reverse Brayton cycle photovoltaic thermal heat pump system and its control method as described in the above embodiments, the complete thermodynamic cycle process of its working fluid is as follows:

[0035] Staged heat absorption and preheating process: Ambient air (e.g., -30℃) first enters the cold side of the first regenerator 1, absorbing the residual heat from the exhaust gas, resulting in an initial temperature increase. Subsequently, the air enters the air-liquid heat exchanger 2, where it absorbs waste heat from the photovoltaic panels collected and transported by the photovoltaic collector 3, undergoing a second stage of heating. The heated medium-temperature air then enters the cold side of the second regenerator 4, where it is further heated to the highest intake temperature by the high-temperature return gas inside the system, and finally drawn into the electric compressor 6 through pipeline 11. This staged regeneration can match the heating temperature range of the photovoltaic thermal modules.

[0036] The two-stage compression and cascade heat release process: Under grid power supply, drive motor 7 drives electric compressor 6 to perform the first-stage adiabatic compression of air, increasing its temperature and pressure. The air then enters the first user heat exchanger 8, where its high-grade sensible heat is transferred to the external heating circulating water or heat storage tank. This process not only provides heating for users but also acts as "interstage cooling," lowering the air temperature. The cooled air then enters the second-stage compressor 9 for the second-stage compression, reaching the system's maximum design pressure. It then enters the second user heat exchanger 5 for secondary heat release, reheating the heating water.

[0037] Deep reheating and expansion work recovery process: High-pressure, medium-temperature air exiting the second user heat exchanger 5 passes sequentially through the hot side of the second regenerator 4 and the first regenerator 1, transferring its heat to the intake air in a stepped manner, while its own temperature decreases. Finally, the high-pressure air enters the power turbine 10, expands, and performs work before being discharged outdoors. In particular, the mechanical work recovered by the power turbine 10 in this process is directly transmitted to the second-stage compressor 9 via a coaxial connection, forming a closed-loop self-driven supercharging system.

[0038] Furthermore, considering the trend in my country's new power system where "the rapid development of photovoltaics leads to off-peak electricity prices during midday and peak electricity prices at night," the system in this embodiment is equipped with a thermal storage tank and performs the following controls:

[0039] During the day (when solar energy is available, typically during off-peak / peak electricity prices): The control unit detects high solar irradiance, at which time the photovoltaic collector 3 has the highest thermal efficiency, the electric compressor 6 has a high intake temperature, and the system COP is at its peak. The controller commands the motor 7 to operate at full power for efficient heating, and the large amount of hot water produced, in addition to meeting the current heating needs, is all stored in the thermal storage tank.

[0040] At night (no solar energy, extremely cold, usually peak electricity price period): the controller instructs the system to shut down or maintain operation at a low speed. The heating system switches to primarily releasing heat from the heat storage tank. This strategy "shifts" the high-energy-consuming operation of the heat pump to the period with the most favorable weather and electricity prices, maximizing economic benefits.

[0041] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A photovoltaic photothermal heat pump system based on reverse Brayton cycle, characterized in that, include: The system comprises a first regenerator (1), an air-liquid heat exchanger (2), a photovoltaic collector (3), a second regenerator (4), a second user heat exchanger (5), an electric compressor (6), a drive motor (7), a first user heat exchanger (8), a second-stage compressor (9), and a power turbine (10). In the direction of the working gas flow: The cold-side inlet of the first regenerator (1) is connected to the environment, and the cold-side outlet is connected to the heated-side inlet of the air-liquid heat exchanger (2); the heated-side outlet of the air-liquid heat exchanger (2) is connected to the cold-side inlet of the second regenerator (4); the cold-side outlet of the second regenerator (4) is connected to the suction port of the electric compressor (6) through a pipe (11); the exhaust port of the electric compressor (6) is connected to the hot-side inlet of the first user heat exchanger (8); the hot-side outlet of the first user heat exchanger (8) is connected to the suction port of the secondary compressor (9); the secondary compressor... The exhaust port of (9) is connected to the hot side inlet of the second user heat exchanger (5); the hot side outlet of the second user heat exchanger (5) is connected to the hot side inlet of the second regenerator (4); the hot side outlet of the second regenerator (4) is connected to the hot side inlet of the first regenerator (1); the hot side outlet of the first regenerator (1) is connected to the air inlet of the power turbine (10), and the exhaust port of the power turbine (10) is connected to the environment; wherein, the photovoltaic collector (3) is connected to the heating side of the air-liquid heat exchanger (2) through a closed pipeline, and a pump is set to drive the built-in antifreeze for heat exchange.

2. The photovoltaic-thermal heat pump system according to claim 1, characterized in that, The working gas absorbs low-grade heat from the photovoltaic collector (3) in the air-liquid heat exchanger (2).

3. The photovoltaic-thermal heat pump system according to claim 1, characterized in that, The electric compressor (6) is driven by the drive motor (7) on a single shaft; the secondary compressor (9) is coaxially and directly connected to the power turbine (10), and the expansion work generated by the power turbine (10) is directly used to drive the secondary compressor (9).

4. The photovoltaic-thermal heat pump system according to claim 1, characterized in that, The first regenerator (1), the air-liquid heat exchanger (2), and the second regenerator (4) together constitute a staged regenerating preheating mechanism.

5. The photovoltaic-thermal heat pump system according to claim 1, characterized in that, The system also includes a heat storage heating subsystem; the first user heat exchanger (8) and the second user heat exchanger (5) are configured as gas-liquid heat exchangers, and their heated side water circuits are connected in parallel or in series and then connected to a heat storage device for supplying heating to the user terminal or for time-shifting storage of thermal energy.

6. The photovoltaic-thermal heat pump system according to any one of claims 1 to 4, characterized in that, The working gas flowing inside the system is air, and it is an open-loop system.

7. The photovoltaic-thermal heat pump system according to claim 1, characterized in that, It also includes a control unit, which is electrically connected to the circulation pump on the photovoltaic collector (3) side, the drive motor (7) and the environmental sensor respectively; The control unit is configured to: acquire the solar irradiance and ambient temperature of the current environment; execute a time-sharing control strategy according to a preset solar thermal energy storage scheduling algorithm; adjust the operating power and working fluid flow of the drive motor (7); and control the system according to the control method of the heat pump system to minimize the overall operating cost of the system.

8. A control method for a photovoltaic thermal heat pump system as described in any one of claims 1-7, characterized in that, The photovoltaic-thermal heat pump system is controlled using a time-sharing control strategy, which includes: Daytime heat storage mode: When the solar irradiance is detected to be higher than the preset threshold and it is during the off-peak electricity price period, the drive motor (7) is controlled to run in a high-frequency and high-power state; the heat generated by the first user heat exchanger (8) and the second user heat exchanger (5) is stored in the heat storage device after the heat load of the building is met; at the same time, the maximum convective heat exchange of the photovoltaic collector (3) is maintained to cool the photovoltaic module; Nighttime heat release mode: When the solar irradiance is detected to be lower than the preset threshold or during the peak electricity price period, the heat storage device is turned on first to supply heat to the user terminal; the drive motor (7) is controlled to run at a lower frequency or power than the preset value or to be shut down and standby. Off-peak electricity pricing: During off-peak electricity pricing periods, the power of the motor is increased to a value greater than or equal to a preset value to generate more heat for heating or heat storage.

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