A ground-air source heat pump combined heating system based on photovoltaic direct drive

Abstract

The application provides a ground-air source heat pump combined heating system based on photovoltaic direct drive, which comprises a photovoltaic array, an MPPT type DC / DC converter, a direct current bus, a direct current driven ground source heat pump unit, a direct current driven air source heat pump unit, a buried pipe heat exchanger, a direct current driven circulating pump group, an electric valve group and a system controller. The photovoltaic array is connected to the direct current bus through the DC / DC converter, directly drives all heat pump compressors and circulating pumps, forms a full direct current direct drive microgrid, and eliminates the energy loss of the inverter link. The ground source heat pump is configured according to the basic heat load of the building, and the air source heat pump is configured according to the maximum value of the peak load and the heat supplement power, which takes into account the operation efficiency and the construction cost. Through valve group switching, the system has three modes of independent ground source heat pump heating, double heat pump combined heating and non-heating season soil heating, the heating circuit and the heating ground source side share the circulating pump group, the structure is compact, the system can guarantee efficient and stable operation in the whole life cycle, and is suitable for clean heating of public buildings in severe cold regions in the north.

Description

Technical Field

[0001] This invention belongs to the field of clean heating and renewable energy utilization technology, specifically relating to a ground-source-air-source heat pump combined heating system based on photovoltaic direct drive, which is particularly suitable for clean heating scenarios in public buildings in frigid northern regions. Background Technology

[0002] The clean heating process in northern my country is progressing steadily, with single clean energy sources and multi-energy coupling heating technologies being iterated and widely applied. However, significant shortcomings have also emerged, limiting the industry's sustainable development.

[0003] (1) Low-temperature energy efficiency degradation problem of air source heat pump Air source heat pumps are currently the most widely used clean heating equipment, but their heating capacity and energy efficiency drop sharply in low-temperature and high-humidity environments. When the ambient temperature is below -15℃, the heating capacity of ordinary units can decrease by more than 40%, and frequent frosting requires a large amount of energy for defrosting. If large-capacity models are configured to meet extreme operating conditions, on the one hand, the initial investment increases, and on the other hand, the equipment operates in the inefficient range most of the time, resulting in poor overall system economy.

[0004] (2) Soil thermal imbalance problem of buried pipe ground source heat pump system Ground source heat pumps utilize the shallow, constant-temperature layer of soil for heat extraction. The soil temperature is typically 10-15℃, higher and more stable than the ambient temperature, resulting in significantly higher energy efficiency than air source heat pumps. However, in areas primarily used for heating, the accumulated heat extracted from the soil in winter far exceeds the heat released to the soil in summer through natural warming and cooling. Long-term operation leads to cold accumulation in the soil (i.e., the soil temperature around the buried pipe decreases year by year). Typically, after 3-5 years, the unit's evaporation temperature drops significantly, causing a substantial decrease in the system's coefficient of performance (COP). In severe cases, evaporator icing protection can cause shutdown. The conventional solution is to add solar collectors for inter-seasonal heat storage and supplementation, but this involves large collector footprints, high initial investment, and significant fluctuations in the power consumption and efficiency of the additional circulating pumps due to weather conditions. Furthermore, drilling for buried pipes requires substantial space, which is often difficult to find for existing public buildings or renovations of old residential areas, severely limiting the application of ground source heat pumps in northern regions.

[0005] (3) Technical bottlenecks of heat pump coupled photovoltaic system Photovoltaic power generation systems require a grid-connected inverter to convert direct current (DC) to alternating current (AC) before supplying the AC heat pump unit. This process involves inverter losses (approximately 3%-8%), and the multiple conversions from DC to AC and then to AC-DC-AC frequency conversion drive reduce overall efficiency. Although photovoltaic direct-drive heat pump technology has emerged, equipment such as circulating pumps still use AC power, and the overall system still relies primarily on mains electricity.

[0006] (4) Shortcomings of multi-heat pump combined heating system Publicly available patent documents (such as CN106766365A and CN109764574A) propose composite systems of solar-air-source-ground-source heat pumps. However, their heat supplementation methods typically involve direct heat supplementation from solar collectors or using surplus photovoltaic power to drive electric heating. The former requires a large footprint and high investment, while the latter is an inefficient electrothermal conversion. Other solutions use air-source heat pumps for heat supplementation, but all of these require drawing electricity from the grid, incurring additional operating costs.

[0007] In summary, none of the existing technologies have proposed a clean heating system structure that efficiently combines features such as photovoltaic DC drive, decoupling of ground-source and air-source capacity, sharing a single circulating pump set for supplementary heating and heating, and zero-cost supplementary heating. They cannot simultaneously solve a series of problems such as system energy efficiency degradation, high initial investment, high operating costs, site constraints, and long-term sustainability. Summary of the Invention

[0008] To address the aforementioned issues, this invention aims to propose a ground-source-air-source heat pump combined heating system based on photovoltaic direct drive. Through innovative designs such as a full DC direct drive architecture, decoupled dual heat pump capacity configuration, valve group switching and reuse of circulating pumps, and zero-cost photovoltaic supplemental heating, the system simultaneously improves energy efficiency, reduces initial investment and land occupation, solves soil thermal imbalance problems, and achieves optimal life-cycle cost of the heating system.

[0009] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A ground-source-air-source heat pump combined heating system based on photovoltaic direct drive includes a photovoltaic power supply unit, a heat pump heat exchange unit, a heat exchange terminal unit, a circulating pump valve group unit, and a system controller. The photovoltaic power supply unit includes a photovoltaic array, an MPPT-type DC / DC converter with maximum power point tracking, a DC bus, an AC grid, and an AC / DC rectifier. The output of the photovoltaic array is connected to the input of the MPPT-type DC / DC converter, and the output of the MPPT-type DC / DC converter is connected to the DC bus. The AC grid is connected to the DC bus via the AC / DC rectifier, forming a full DC power supply architecture with photovoltaic direct drive as the main method and grid supplementation as a secondary method. The heat pump heat exchange unit includes a DC-driven ground source heat pump unit and a DC-driven air source heat pump unit. Both of their compressors use DC-driven motors and are connected in parallel to the DC bus via DC drivers. The heat exchange terminal unit includes a buried pipe heat exchanger embedded in the soil and a heat user terminal heating system that supplies heat to the building. The circulating pump valve group unit includes a ground source side DC-driven circulating pump, a user side DC-driven circulating pump, and an electric valve group composed of electric valves; the ground source side DC-driven circulating pump is connected in series with the ground source side main pipeline, the user side DC-driven circulating pump is connected in series with the user side main pipeline, and both circulating pumps are connected in parallel to the DC bus. On the ground source side main pipeline, the buried pipe heat exchanger, the ground source side DC-driven circulating pump and the evaporator side of the DC-driven ground source heat pump unit are connected in series; on the user side main pipeline, the user terminal heating system, the user side DC-driven circulating pump and the condenser side of the DC-driven ground source heat pump unit are connected in series. The electric valve group is installed on the condenser side branch pipe of the DC-driven air source heat pump unit. By switching the valve group on and off, the condenser side of the DC-driven air source heat pump unit can be selectively connected in parallel to the user side main pipe or connected in series to the ground source side main pipe. The system controller is communicatively connected to the MPPT type DC / DC converter, AC / DC rectifier, DC-driven ground source heat pump unit, DC-driven air source heat pump unit, each DC-driven circulating pump, and electric valve group, respectively, and is used to control the opening and closing of the valve group to switch the operating mode, and to adjust the equipment operating status according to the real-time photovoltaic output and load demand. The system achieves at least three operating modes by switching through electric valve groups: independent heating mode of ground source heat pump, combined heating mode of dual heat pumps, and soil supplementary heating mode during non-heating seasons; wherein, in the soil supplementary heating mode, the ground source side DC-driven circulation pump is reused as a supplementary heating circulation pump, and the supplementary heating circuit shares the circulation pump and main pipeline with the ground source side circuit under heating conditions.

[0010] Furthermore, the MPPT-type DC / DC converter has dual functions of maximum power point tracking and DC voltage regulation: by adjusting the input impedance in real time through the perturbation observation method or the conductance increment method, the photovoltaic array is always operating near the maximum power point; at the same time, the wide range of fluctuating DC power output from the photovoltaic array is converted into constant voltage DC power output to the DC bus, providing a stable power supply voltage for all DC loads.

[0011] Furthermore, the rated heating capacity of the DC-driven ground source heat pump unit is configured according to the building's basic heat load, which is the heat load value that occurs for a proportion exceeding a set percentage during the annual heating season; the rated heating capacity of the DC-driven air source heat pump unit is the larger of the building's peak heat load and the soil heat replenishment power, wherein the peak heat load is the difference between the building's design heat load and the rated heating capacity of the ground source heat pump, and the soil heat replenishment power is calculated and determined by the duration of the non-heating season and the soil heat balance target.

[0012] Furthermore, in the independent heating mode of the ground source heat pump: the DC-driven ground source heat pump unit, the ground source side DC-driven circulation pump, and the user side DC-driven circulation pump are turned on, and the DC-driven air source heat pump unit is turned off; the electric valve group cuts off the two branch pipes of the air source heat pump condenser, and the ground source side main pipe and the user side main pipe operate independently, with the ground source heat pump independently bearing the building heat load.

[0013] Furthermore, in the dual heat pump combined heating mode: the DC-driven ground source heat pump unit, the DC-driven air source heat pump unit, the ground source side DC-driven circulation pump, and the user side DC-driven circulation pump are all turned on; the electric valve group connects the branch pipeline of the air source heat pump condenser to the user side, so that the condenser side of the DC-driven air source heat pump unit is connected in parallel to the user side main pipeline, and together with the ground source heat pump, it outputs heat to the heat user terminal heating system, and the air source heat pump undertakes the peak heat load exceeding the base load.

[0014] Furthermore, in the soil heating mode: the DC-driven air source heat pump unit and the ground-source side DC-driven circulation pump are turned on, and the DC-driven ground source heat pump unit and the user-side DC-driven circulation pump are turned off; the electric valve group connects the branch pipe of the air source heat pump condenser to the ground source side, so that the condenser side of the DC-driven air source heat pump unit is connected in series with the buried pipe heat exchanger and the ground-source side DC-driven circulation pump to form a closed heating circuit, and the air source heat pump extracts heat from the ambient air and stores heat in the soil through the buried pipe heat exchanger to maintain the soil thermal balance.

[0015] Furthermore, in the independent heating mode of the ground source heat pump and the combined heating mode of the dual heat pump, the system controller prioritizes the output power of the photovoltaic array to drive the entire load of the system; when the photovoltaic output is lower than the power required for the current operation of the system, the controller controls the AC / DC rectifier to draw power from the AC grid and rectify it into DC power to supplement the DC bus, ensuring the continuous and stable heating process.

[0016] Furthermore, in the soil heating mode, the system controller monitors the output power of the photovoltaic array in real time; when the photovoltaic output reaches the minimum starting power of the DC-driven air source heat pump unit and can be sustained for a set duration, the heating operation is started; when the photovoltaic output is lower than the minimum starting power, the heating operation is stopped, and the heating process is preferentially driven entirely by photovoltaic power.

[0017] Furthermore, the compressors of the DC-driven ground source heat pump unit and the DC-driven air source heat pump unit, as well as the drive motors of the ground source side DC-driven circulation pump and the user side DC-driven circulation pump, all adopt DC brushless motors or DC inverter motors, which can achieve stepless speed regulation to dynamically match the real-time photovoltaic output and building heat load demand.

[0018] Furthermore, the system controller is also connected to a temperature sensor group, which includes an outdoor temperature sensor, a soil temperature sensor, and a user-side return water temperature sensor. The system controller dynamically adjusts the operating speed of each heat pump and circulation pump based on real-time heat load, outdoor temperature, soil temperature, and photovoltaic output data, and automatically switches between three operating modes.

[0019] Beneficial effects: Compared with existing technologies, this invention balances operational stability and efficiency, and minimizes land occupation and investment, resulting in a higher life-cycle cost advantage, specifically: The system's energy efficiency is significantly improved: Adopting a fully DC direct-drive microgrid eliminates the need for a photovoltaic grid-connected inverter and multi-stage power conversion, reducing energy loss by approximately 5%-10%. Both the heat pump and circulation pump are DC-driven, enabling stepless speed regulation, resulting in higher energy efficiency for individual devices and the overall system at partial loads. Furthermore, the energy efficiency is significantly improved compared to single air-source heat pump systems in frigid regions; based on soil thermal balance, the system ensures long-term operation of ground-source heat pump systems in northern regions.

[0020] Significantly reduced initial investment and land occupation: Ground source heat pumps are configured according to the base load, air source heat pumps are used for peak shaving, and the number of holes for buried pipes is reduced by 20%-40% compared to pure ground source heat pump systems, solving the problems of insufficient space and high initial investment.

[0021] Reduced footprint and operating costs of the supplementary heating system: During the non-heating season, photovoltaic DC power drives an air source heat pump to reinject heat into the soil. The supplementary heating process does not require external power grid supply. Compared with conventional solar collector supplementary heating systems, it occupies less space and has no additional supplementary heating costs.

[0022] Compact structure, multi-purpose pump: The heat replenishment circuit and the ground source heating circuit share the same circulating water pump and most of the pipelines. Functional reuse is achieved only by switching valve groups, which reduces the number of equipment, pipelines and installation space, and the system has a high degree of integration. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the combined ground-source and air-source heat pump heating system based on photovoltaic direct drive as described in an embodiment of the present invention; Figure 2 This is a schematic diagram of the pipeline connection and working fluid flow direction of the ground source heat pump independent heating mode of the ground source heat pump combined heating system based on photovoltaic direct drive, as described in an embodiment of the present invention. Figure 3This is a schematic diagram of the pipeline connection and working fluid flow direction of the dual heat pump combined heating mode of the ground source-air source heat pump combined heating system based on photovoltaic direct drive, as described in an embodiment of the present invention. Figure 4 This is a schematic diagram of the pipeline connection and working fluid flow direction of the heat replenishment mode of the ground source-air source heat pump combined heating system based on photovoltaic direct drive, as described in an embodiment of the present invention. Detailed Implementation

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0025] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] Example 1 1. Overall System Structure like Figure 1 As shown, the photovoltaic direct-drive ground-source-air-source heat pump combined heating system of the present invention mainly consists of a photovoltaic array 1, an MPPT type DC / DC converter 2, a DC bus 3, a DC-driven ground-source heat pump unit 4, a DC-driven air-source heat pump unit 5, a buried pipe heat exchanger 6, an AC power grid 7, an AC / DC rectifier 8, a heat user terminal heating system 9, a system controller 10, a ground-source side DC-driven circulation pump B1, a user-side DC-driven circulation pump B2, and electric valves F1 to F6.

[0027] Electrical Connections: The output of photovoltaic array 1 is combined through a combiner box and connected to the input of MPPT-type DC / DC converter 2. The output of converter 2 is connected to DC bus 3. The MPPT-type DC / DC converter 2 has dual functions of maximum power point tracking and DC voltage regulation: it adjusts the input impedance in real time using the perturbation observation method or the incremental conductance method, ensuring that photovoltaic array 1 always operates near its maximum power point, maximizing photovoltaic utilization; simultaneously, it converts the wide-range fluctuating DC output from the photovoltaic array into a constant voltage DC output, ensuring the voltage stability of DC bus 3. AC grid 7 is connected to the same DC bus 3 via AC / DC rectifier 8 as a supplementary power source, ensuring stable system operation when photovoltaic output is insufficient.

[0028] The compressors of the DC-driven ground source heat pump unit 4 and the DC-driven air source heat pump unit 5, as well as the drive motors of the circulating pumps B1 and B2, all adopt DC brushless or DC inverter motors, enabling stepless speed regulation. Each is connected in parallel to the DC bus 3 via a DC driver, forming a building-grade all-DC microgrid. Photovoltaic power can directly drive all loads without DC / AC inversion, eliminating multi-stage power conversion losses. This architecture is highly compatible with the daytime heating load characteristics of public buildings, maximizing the utilization of photovoltaic power.

[0029] Water-side connection: The system is equipped with two basic loops: a ground source side main pipeline and a user side main pipeline. On the ground source side main pipeline, the buried pipe heat exchanger 6, the ground source side DC-driven circulating pump B1, and the evaporator side of the DC-driven ground source heat pump unit 4 are connected in series. On the user side main pipeline, the user terminal heating system 9, the user side DC-driven circulating pump B2, and the condenser side of the DC-driven ground source heat pump unit 4 are connected in series.

[0030] The valve assembly consisting of electric valves F1 to F6 is installed on the condenser-side branch pipe of the DC-driven air source heat pump unit 5, and is divided into two branches: one branch connects to the user-side main pipe and is controlled by F5 and F6; the other branch connects to the ground source-side main pipe and is controlled by F1 and F2. By switching the valve assembly on and off, the condenser side of the DC-driven air source heat pump unit 5 can be selectively connected in parallel to the user-side main pipe or in series to the ground source-side main pipe, realizing the switching of different operating modes.

[0031] The system controller 10 is connected to all electrical equipment, valve groups, and temperature sensor groups. The temperature sensor groups include outdoor temperature sensors, soil temperature sensors, and user-side supply and return water temperature sensors. The controller 10 acts as the central hub of the system and realizes automatic mode switching, equipment speed adjustment, and operation protection based on the collected photovoltaic output, temperature, and load data.

[0032] 2. Switching between three operating modes and the working process The system achieves three operating modes through the on / off combinations of electric valves F1 to F6. The start / stop status of the equipment and valve group in each mode is shown in the control status table below:

[0033] The pipeline connections and working fluid flow directions for each mode are respectively... Figures 2 to 4 The specific work process is as follows: Pattern ①: See Figure 2 Ground source heat pump independent heating mode The system operates in this mode when the building's heat load does not exceed the basic heat load. The control status table corresponding to the equipment and valve group status is as follows: Line ①: DC-driven ground source heat pump unit 4, circulating pumps B1 and B2 are open; DC-driven air source heat pump unit 5 is closed; electric valves F3 and F4 are open; F1, F2, F5, and F6 are closed; both branch pipes of the air source heat pump are disconnected.

[0034] Ground source side loop: buried pipe heat exchanger 6 → circulating pump B1 → evaporator side of ground source heat pump unit 4 → buried pipe heat exchanger 6, circulating water absorbs heat from the soil and is transported to the heat pump evaporator.

[0035] User-side loop: Ground source heat pump unit 4 condenser side → circulating pump B2 → heat user terminal heating system 9 → ground source heat pump unit 4 condenser side, circulating water carries the heat released by the heat pump to supply heat to the room.

[0036] In this mode, the ground source heat pump operates efficiently by utilizing the constant temperature characteristics of the soil. Electricity is supplied primarily by direct photovoltaic power, and supplemented by AC grid through AC / DC rectification when insufficient. The system controller 10 dynamically adjusts the speed of the heat pump and water pump according to the real-time photovoltaic output and load demand to achieve efficient matching.

[0037] Mode 2: See Figure 3 Dual heat pump combined heating mode When the outdoor temperature is extremely low and the building's heat load exceeds the basic heat load, the system switches to this mode. The equipment status and valve group status correspond to the control status table, line ②: both heat pump units 4 and 5 and both circulating pumps B1 and B2 are open; electric valves F3, F4, F5, and F6 are open, and F1 and F2 are closed.

[0038] The ground source side loop is consistent with mode ①, and the ground source heat pump unit 4 stably undertakes the basic heat load and always operates in the high efficiency range.

[0039] In the user-side circuit, the condenser side of the air source heat pump unit 5 is connected in parallel to the user-side main pipeline through the branches where F5 and F6 are located, and is connected in parallel with the condenser side of the ground source heat pump unit 4, together delivering heat to the heat user terminal heating system 9. The peak-shaving portion exceeding the base load is borne by the air source heat pump.

[0040] This model can cope with extreme cold conditions without expanding the capacity of ground source heat pumps and underground pipes, effectively reducing initial investment and land requirements.

[0041] Pattern ③: See Figure 4 Soil heating mode During the non-heating season, to address the issue of cold accumulation caused by soil heat extraction in winter, the system switches to this mode. The equipment status and valve group status correspond to line ③ of the control status table: Air source heat pump unit 5 and circulating pump B1 are on; ground source heat pump unit 4 and circulating pump B2 are off; electric valves F1 and F2 are on; F3, F4, F5, and F6 are off.

[0042] Heat replenishment circuit: Air source heat pump unit 5 condenser side → circulating pump B1 → buried pipe heat exchanger 6 → air source heat pump unit 5 condenser side, forming a closed loop.

[0043] After the heat replenishment loop is closed, the air source heat pump absorbs heat from the ambient air and transfers it to the buried pipe heat exchanger 6 via circulating water, storing it in the underground soil to replenish the heat removed in winter and maintain soil thermal balance. In this mode, the main pipeline on the ground source side is reused as a whole, and the circulating pump B1 is reused as the heat replenishment circulating pump, eliminating the need for additional heat replenishment pumps and pipelines, achieving dual-purpose pump and pipeline reuse. Heat replenishment operation is triggered by photovoltaic output: heat replenishment starts when the photovoltaic output reaches the minimum starting power of the air source heat pump and remains so for a certain period of time; it automatically stops when the photovoltaic output is insufficient. Photovoltaic power is used preferentially throughout the heat replenishment process, achieving zero operating costs.

[0044] 3. Verification through specific engineering cases A 8000m² building in Zone B of the frigid northern region 2 Taking an office building as an example, the configuration and techno-economic effects of this system will be further explained. The building is designed for a heat load of 480kW, with a heating season of 180 days (October 20th to April 17th of the following year) and a non-heating season of 185 days. The daily heating period is 8:00-18:00 (10 hours). On weekends and holidays, the system operates at 30% of its rated load for low-temperature anti-freezing purposes. Based on load continuity curve analysis, the basic heat load, which occurs for more than 80% of the heating season, is 320kW, with a peak heat load of 160kW. Geotechnical testing indicates a drilling depth of 120m, with a heat extraction of 30W / m and a heat release of 50W / m per unit hole depth.

[0045] (1) Equipment capacity configuration DC-driven ground source heat pump unit 4: Selected based on a basic heat load of 320kW, with a heating COP of approximately 4.0, an input power of 80kW, and a soil heat extraction power of 240kW.

[0046] Buried pipe heat exchanger 6: Based on the heat extraction demand, the total hole depth is 240kW ÷ 30W / m = 8000m. At 120m / hole, a total of 67 holes are required.

[0047] DC-driven air source heat pump unit (5): Selection based on the larger value of dual constraints. Peak shaving constraint: 160kW heat load needs to be met under the design condition of -18℃; Heat replenishment constraint: The cumulative heat taken during the heating season is about 518,400kWh, the target heat balance rate is 80%, and the heat replenishment needs to be 414,720kWh. During the non-heating season, the average daily heat replenishment is 8 hours, the weather utilization coefficient is 0.9, and the heat replenishment power needs to be about 311kW. When the average temperature during the non-heating season is 18℃, the actual heating capacity of the unit can reach more than 320kW, which meets the heat replenishment needs. Finally, a DC-driven air source heat pump with a heating capacity of 320kW was selected to meet both peak shaving and heat replenishment needs. Check the buried pipe heat replenishment constraint: 311kW ÷ 50W / m = 6220m (52 ​​holes), and take the larger value between it and the heat takement requirement of 67 holes, and finally determine 67 holes.

[0048] Photovoltaic array (1): Configured according to the maximum power consumption of the system under the design conditions during the heating season. Under the design conditions, the ground source heat pump consumes 80kW, the air source heat pump consumes 84kW (COP=1.9), the circulating pump consumes about 13kW, and the total power consumption is about 177kW; considering the actual loss, a margin of 1.1 times is taken, and a 200kWp photovoltaic array is configured, which can stably output more than 180kW at noon on a sunny day.

[0049] (2) Operational effectiveness and economy The total heat supply during the heating season is 259,200 kWh, of which ground source heat pumps consume 43,200 kWh, air source heat pumps consume 54,010 kWh for peak shaving, and circulating pumps consume 7,777 kWh, for a total electricity consumption of approximately 104,987 kWh during the heating season. During the supplementary heating season, the total supplementary heat supply is 414,720 kWh, with air source heat pumps consuming 118,491 kWh and circulating pumps consuming 4,740 kWh, for a total electricity consumption of approximately 123,231 kWh, all of which is met by direct photovoltaic power generation. The annual electricity purchase from the grid is approximately 31,496 kWh, with annual operating electricity costs of approximately 22,000 yuan.

[0050] The following table compares the 20-year lifecycle costs of solar thermal-ground source heat pump coupling solutions with those of traditional solar thermal-ground source heat pump solutions:

[0051] The comparative results show that, under the same heat balance target, this solution saves 18.5% on initial investment, 65.1% on annual operating electricity costs, and 33.8% on total life-cycle costs over 20 years. Simultaneously, the number of underground pipe boreholes is reduced by 33%, significantly lowering land requirements; the air source heat pump serves two purposes, reusing the ground-source circulating pump and piping, resulting in high system integration; and the all-DC direct-drive architecture eliminates inverter losses and is highly compatible with the daytime heat load characteristics of public buildings.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A ground-source-air-source heat pump combined heating system based on photovoltaic direct drive, comprising a photovoltaic power supply unit, a heat pump heat exchange unit, a heat exchange terminal unit, a circulating pump valve group unit, and a system controller (10), characterized in that: The photovoltaic power supply unit includes a photovoltaic array (1), an MPPT type DC / DC converter (2) with maximum power point tracking function, a DC bus (3), an AC grid (7), and an AC / DC rectifier (8); the output end of the photovoltaic array (1) is connected to the input end of the MPPT type DC / DC converter (2) after being combined, and the output end of the MPPT type DC / DC converter (2) is connected to the DC bus (3); the AC grid (7) is connected to the DC bus (3) through the AC / DC rectifier (8), forming a full DC power supply architecture with photovoltaic direct drive as the main method and grid supplementation as the auxiliary method; The heat pump heat exchange unit includes a DC-driven ground source heat pump unit (4) and a DC-driven air source heat pump unit (5). Both of their compressors use DC-driven motors and are connected in parallel to the DC bus (3) through DC drivers. The heat exchange terminal unit includes a buried pipe heat exchanger (6) buried in the soil and a heat user terminal heating system (9) that supplies heat to the building. The circulating pump valve group unit includes a ground source side DC-driven circulating pump (B1), a user side DC-driven circulating pump (B2), and an electric valve group composed of electric valves (F1~F6); the ground source side DC-driven circulating pump (B1) is connected in series to the ground source side main pipeline, the user side DC-driven circulating pump (B2) is connected in series to the user side main pipeline, and both circulating pumps are connected in parallel to the DC bus (3). On the ground source side main pipeline, the buried pipe heat exchanger (6), the ground source side DC-driven circulating pump (B1) and the DC-driven ground source heat pump unit (4) are connected in series on the evaporator side; on the user side main pipeline, the user terminal heating system (9), the user side DC-driven circulating pump (B2) and the DC-driven ground source heat pump unit (4) are connected in series on the condenser side. The electric valve group is installed on the condenser side branch pipe of the DC-driven air source heat pump unit (5). By switching the valve group on and off, the condenser side of the DC-driven air source heat pump unit (5) can be selectively connected in parallel to the user side main pipe or connected in series to the ground source side main pipe. The system controller (10) is connected to the MPPT type DC / DC converter (2), AC / DC rectifier (8), DC-driven ground source heat pump unit (4), DC-driven air source heat pump unit (5), each DC-driven circulating pump and electric valve group, respectively, for controlling the valve group to switch the operating mode, and adjusting the equipment operating status according to the real-time photovoltaic output and load demand. The system achieves at least three operating modes by switching through electric valve groups: independent heating mode of ground source heat pump, combined heating mode of dual heat pumps, and soil supplementary heating mode during non-heating season; wherein, in the soil supplementary heating mode, the ground source side DC-driven circulation pump (B1) is reused as a supplementary heating circulation pump, and the supplementary heating circuit shares the circulation pump and main pipeline with the ground source side circuit under heating conditions.

2. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, The MPPT type DC / DC converter (2) has dual functions of maximum power point tracking and DC voltage regulation: by adjusting the input impedance in real time through the perturbation observation method or the conductance increment method, the photovoltaic array (1) is always working near the maximum power point; at the same time, the wide range of fluctuating DC power output by the photovoltaic array (1) is converted into constant voltage DC power output to the DC bus (3), providing a stable power supply voltage for all DC loads.

3. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, The rated heat capacity of the DC-driven ground source heat pump unit (4) is configured according to the basic heat load of the building. The basic heat load is the heat load value that occurs for a longer period than a set proportion during the heating season. The rated heat capacity of the DC-driven air source heat pump unit (5) is the larger of the building peak heat load and the soil heat replenishment power. The peak heat load is the difference between the building design heat load and the rated heat capacity of the ground source heat pump. The soil heat replenishment power is calculated and determined by the duration of the non-heating season and the soil heat balance target.

4. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, In the independent heating mode of the ground source heat pump: the DC-driven ground source heat pump unit (4), the ground source side DC-driven circulation pump (B1), and the user side DC-driven circulation pump (B2) are turned on, and the DC-driven air source heat pump unit (5) is turned off; the electric valve group cuts off the two branch pipes of the air source heat pump condenser, and the ground source side main pipe and the user side main pipe operate independently, and the ground source heat pump independently undertakes the building heat load.

5. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, In the dual heat pump combined heating mode: the DC-driven ground source heat pump unit (4), the DC-driven air source heat pump unit (5), the ground source side DC-driven circulation pump (B1), and the user side DC-driven circulation pump (B2) are all turned on; the electric valve group connects the air source heat pump condenser to the branch pipeline on the user side, so that the condenser side of the DC-driven air source heat pump unit (5) is connected in parallel to the user side main pipeline, and together with the ground source heat pump, outputs heat to the heat user terminal heating system (9), and the air source heat pump undertakes the peak heat load exceeding the base load.

6. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, In the soil heating mode: the DC-driven air source heat pump unit (5) and the ground source side DC-driven circulation pump (B1) are turned on, and the DC-driven ground source heat pump unit (4) and the user side DC-driven circulation pump (B2) are turned off; the electric valve group connects the branch pipe of the air source heat pump condenser to the ground source side, so that the condenser side of the DC-driven air source heat pump unit (5) is connected in series with the buried pipe heat exchanger (6) and the ground source side DC-driven circulation pump (B1) to form a closed heating circuit. The air source heat pump takes heat from the ambient air and stores heat in the soil through the buried pipe heat exchanger (6) to maintain the soil thermal balance.

7. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, In the independent heating mode of ground source heat pump and the combined heating mode of dual heat pump, the system controller (10) prioritizes the output power of the photovoltaic array (1) to drive the entire load of the system to operate; when the photovoltaic output is lower than the power required for the current operation of the system, the AC / DC rectifier (8) is controlled to take power from the AC grid (7) and rectify it into DC power to supplement the DC bus (3) to ensure the continuous and stable heating process.

8. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, In the soil heating mode, the system controller (10) detects the output power of the photovoltaic array (1) in real time; when the photovoltaic output reaches the minimum starting power of the DC-driven air source heat pump unit (5) and can be sustained for a set time, the heating operation is started; when the photovoltaic output is lower than the minimum starting power, the heating operation is stopped, and the heating process is driven entirely by photovoltaic power.

9. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, The compressors of the DC-driven ground source heat pump unit (4) and the DC-driven air source heat pump unit (5), as well as the drive motors of the ground source side DC-driven circulating pump (B1) and the user side DC-driven circulating pump (B2), all adopt DC brushless motors or DC variable frequency motors, which can realize stepless speed regulation to dynamically match the real-time photovoltaic output and building heat load demand.

10. The ground-source-air-source heat pump combined heating system based on photovoltaic direct drive according to claim 1, characterized in that, The system controller (10) is also connected to a temperature sensor group, which includes an outdoor temperature sensor, a soil temperature sensor and a user-side return water temperature sensor. The system controller (10) dynamically adjusts the operating speed of each heat pump and circulation pump according to real-time heat load, outdoor temperature, soil temperature and photovoltaic output data, and automatically switches between three operating modes.

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