A cascade phase change energy storage composite solar energy and ground source heat pump system

Abstract

The present invention discloses a cascade phase change energy storage composite solar energy and ground source heat pump system, which mainly comprises a solar collector (1), a cascade phase change heat storage tank (2), a coil heat exchanger (3), a ground source heat pump (4), a heat exchanger composed of a vertical heat exchanger (5) and a horizontal heat exchanger 6), a hot water storage tank (7), a geothermal coil (8), and first to fourth water pumps (9), (10), (11), (12) and various valves and other components, forming two independent loops, a solar energy loop and a ground source heat pump loop. The present invention makes full use of two renewable resources, geothermal and solar energy, and reduces the consumption of non-renewable energy such as coal. At the same time, the phase change energy storage tank plays a role in peak shaving and valley filling, solving the problems of greenhouse heating energy shortage, serious pollution and high operating costs.

Description

Technical Field

[0001] The invention relates to a heating system, in particular to a cascade phase change energy storage composite solar energy and ground source heat pump system for heating agricultural greenhouses. Background Art

[0002] In northern my country, the construction of greenhouses creates a warm growth environment for plants in winter. However, due to the relatively backward greenhouse heating technology in most parts of my country, greenhouse heating still faces the problems of high cost, serious pollution and poor effect. In addition, in order to reduce the initial investment in greenhouse construction, the enclosure structure of the greenhouse is often simply built with plastic film or glass panels, so the heat load demand in the greenhouse is very large in winter.

[0003] Traditional coal-fired heating has high pollution and hot air heating has uneven temperature. With the implementation of policies and the active response of farmers, the most commonly used heating methods in greenhouses, such as hot air furnaces and coal-fired heating furnaces, will gradually be replaced by new heating systems. The development and utilization of clean energy is a major trend in greenhouse heating in the future.

[0004] Ground source heat pump is an energy-efficient and environmentally friendly energy utilization technology that utilizes shallow underground geothermal resources. It can transfer energy from low-temperature heat sources to high-temperature heat sources by inputting a small amount of high-quality electricity. The winter heat load in northern regions is much higher than the summer cold load, and the soil's thermal recovery capacity is limited. Therefore, a single ground source heat pump will face the problem of soil temperature drop in long-term operation, resulting in a decrease in its evaporation temperature, which in turn affects its COP.

[0005] Solar energy is a world-recognized clean energy source. It is widely used because it can be directly developed and utilized, is easy to collect, and is infinitely renewable. However, single solar energy is greatly affected by the weather, is intermittent and unreliable, and cannot provide continuous, stable, and high-density energy for greenhouses during long periods of continuous rain and at night.

[0006] The Chinese patent with patent number ZL201710830052.5 discloses a solar ground source heat pump combined energy supply system and its operation control method. The system includes a solar heat collection system, a ground source heat pump system, and a buried pipe system, etc. By calculating the parameters of the joint operation of solar energy and ground source heat pump, the heat collection process, heat storage process and heat supplement process of the solar ground source heat pump combined energy supply system are operated and controlled. In the time period when the user needs domestic hot water, the solar energy and ground source heat pump are used to supply energy by controlling the relevant switches and equipment; in the time period when the user does not need domestic hot water, the heat in the solar collector is transferred to the buried pipe heat exchanger through the heat exchanger and transported to the soil, and the soil is heated. The problem with this system is that when the user terminals are relatively scattered, there is no regularity in their heat use, and the regular switching of heat use and heat supplement cannot be achieved. At the same time, if the user's heat use time is much longer than the non-heat use time, the soil temperature still shows a downward trend, and the effect of solar heat supplement is greatly reduced.

[0007] The Chinese patent with patent number ZL201120402886.4 discloses a solar thermal and ground source heat pump combined system. The system includes a solar thermal auxiliary system, a ground source heat pump system, an indoor heating system, a control device, and the like. When the sun is sufficient and the temperature of the solar collector is high, it stores the heat in the hot water storage tank and transfers the heat to the buried pipe system through the heat exchanger, so that the temperature field of the soil can be restored more quickly. When the solar thermal auxiliary system cannot meet the demand of the building, the ground source heat pump system is used to heat it. The problem with this system is that the water tank is used to store heat, which has certain requirements on water quality, so the pipeline design is complicated, and the heat storage capacity is small. Summary of the invention

[0008] In view of the problems existing in the above-mentioned prior art, the present invention proposes a cascade phase change energy storage composite solar energy and ground source heat pump system for heating agricultural greenhouses. The temperature difference between supply and return water is used to increase the temperature of the ground source side inlet, thereby increasing its evaporation temperature, realizing the storage and reuse of solar energy and geothermal energy, and solving the current problem of low COP of ground source heat pumps in northern regions.

[0009] The present invention discloses a cascade phase change energy storage composite solar energy and ground source heat pump system, which comprises two independent loops, a solar energy loop and a ground source heat pump loop; wherein:

[0010] In the independent loop of the solar energy system, the hot water generated by the solar collector 1 is divided into two paths after passing through the first check valve V1 and the first three-way solenoid valve V2. One path flows through the first water pump 9 and the third three-way solenoid valve V7 to enter the coil heat exchanger 3 at the end of the heating for indoor heating; the other path passes through the third solenoid valve V11 and the third check valve V12 to enter the stepped phase change heat storage tank 2 and enters the three energy storage modules from top to bottom to store the excess heat; the two paths merge at the second three-way solenoid valve V3, and the return water with lower temperature enters the hot water storage tank 7 through the second water pump 10 after merging. The low-temperature water from the hot water storage tank 7 passes through the fifth solenoid valve V15 and the second check valve V4 and is mixed with tap water to reduce the water temperature. The replenishment water enters the circulation through the first solenoid valve V5. After merging, the hot water with lower temperature enters the geothermal coil 8 to heat the roots of crops, and then returns to the solar collector 1 through the second solenoid valve V6;

[0011] In the ground source heat pump loop, the ground source heat pump 4 is divided into two paths after passing through the fourth water pump 12 and the fifth three-way solenoid valve V9. One path passes through the third three-way solenoid valve V7 to enter the coil heat exchanger 3 at the end of the heating to provide indoor heating; the other path enters the last energy storage module of the cascade phase change heat storage tank 2 to store heat. Similarly, the two return water paths are merged through the sixth three-way solenoid valve V10 and returned to the ground source heat pump 4.

[0012] The step phase change heat storage tank 2 is directly connected to the coil heat exchanger 3; the third and fourth temperature sensors 15 and 16 are respectively arranged at both ends of the first three-way solenoid valve V2; the fifth to seventh temperature sensors 17, 18, and 19 are respectively arranged in the three modules of the step phase change heat storage tank 2, and the first and second temperature sensors 13 and 14 are respectively arranged on both sides of the first solenoid valve V5;

[0013] The system includes the following three modes:

[0014] Nighttime ground source heat pump heating and energy storage mode: the fifth three-way solenoid valve V9 and the sixth three-way solenoid valve V10 are opened, the third three-way solenoid valve V7 opens interfaces Ⅰ and Ⅱ, the fourth three-way solenoid valve V8 opens interfaces Ⅰ and Ⅱ, the third and fourth water pumps 11 and 12 are opened, and the indoor heating of the greenhouse is provided through the coil heat exchanger 3, and the excess heat is stored in the phase change heat storage tank; when the value of the seventh temperature sensor 19 is higher than the phase change temperature of the phase change material of 35°C, the interfaces Ⅲ of the fifth three-way solenoid valve V9 and the sixth three-way solenoid valve V10 are closed; when the greenhouse ground temperature is too low and the roots of the crops are frozen or frosted, the interfaces Ⅲ of the fourth three-way solenoid valve V8, the interfaces Ⅰ and Ⅱ of the second three-way solenoid valve V3, the second check valve V4, the second solenoid valve V6, the first check valve V1, the interfaces Ⅰ and Ⅱ of the first three-way solenoid valve V2, and the first water pump 9 and the second water pump 10 are opened;

[0015] Solar heating and energy storage mode during the day: the first check valve V1, the first three-way solenoid valve V2, the Ⅰ and Ⅲ interfaces of the third three-way solenoid valve V7, the Ⅰ and Ⅲ interfaces of the fourth three-way solenoid valve V8, the second three-way solenoid valve V3, the second check valve V4, the second solenoid valve V6 and the third solenoid valve V11, the third check valve V12 are opened, and the indoor heating of the greenhouse is provided through the coil heat exchanger 3, and the excess heat is stored in the stepped phase change heat storage tank 2, and flows through the three phase change modules in sequence for heat storage; when the readings of the fifth, sixth and seventh temperature sensors 17, 18 and 19 are all higher than the phase change temperature of their phase change materials, the first three-way solenoid valve V2 and the Ⅲ interface of the second three-way solenoid valve V3, as well as the third solenoid valve V11 and the third check valve V12 are closed, and the energy storage ends; at the same time, according to the reading of the first temperature sensor 13, it is judged whether to open the first solenoid valve V5 for water replenishment, and according to the reading of the second temperature sensor 14, the opening of the first solenoid valve V5 is controlled;

[0016] Phase change energy storage tank heating mode during the day: when it is cloudy or the solar energy is insufficient, the fourth check valve V14, the fourth solenoid valve V13, the Ⅱ and Ⅲ interfaces of the third check valve V2, the Ⅰ and Ⅲ interfaces of the third three-way solenoid valve V7, the Ⅰ and Ⅲ interfaces of the fourth three-way solenoid valve V8, and the Ⅱ and Ⅲ interfaces of the second three-way solenoid valve V3 are opened, so that the high-temperature hot water flows out from the first module of the phase change heat storage tank and enters the coil heat exchanger to heat the greenhouse. The lower temperature return water flows into the third module of the phase change heat storage tank, completing a cycle.

[0017] The ground source side of the ground source heat pump 4 is provided with two types of heat exchangers, namely a vertical heat exchanger 5 and a horizontal heat exchanger 6 .

[0018] The high-temperature hot water flowing out of the step phase change heat storage tank 2 enters the coil heat exchanger 3 through the fourth check valve V14, the fourth solenoid valve V13, the first three-way solenoid valve V2, the third three-way solenoid valve V7 and the first water pump 9 for indoor heating, and then returns to the step phase change heat storage tank 2 through the fourth three-way solenoid valve V8 and the second three-way solenoid valve V3, which is a cycle.

[0019] The stepped phase change heat storage box 2 is formed by combining three phase change materials with different temperatures, namely 55°C phase change material, 45°C phase change material and 35°C phase change material, and the temperature difference does not exceed 10°C.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The present invention makes full use of two renewable resources, geothermal and solar energy, to reduce the consumption of non-renewable energy such as coal. At the same time, the phase change energy storage box plays a role in peak shaving and valley filling, solving the problems of greenhouse heating energy shortage, serious pollution and high operating costs.

[0022] 2. The combined heating system provided by the present invention has a hot water storage tank installed on the return water pipe on the energy-using side and the ground source side of the ground source heat pump to store part of the heat and take into account the role of the heat exchanger. First, the water temperature can be reduced by controlling the flow rate of the water tank outlet and mixing with the replenishing water, thereby avoiding the damage to crops caused by excessive temperature. Second, the return water temperature of solar energy is reduced, the temperature difference is increased, and the heat exchange efficiency of the solar collector is improved; third, the ground source heat pump side can continuously exchange heat, increase the water inlet temperature at the ground source side entrance, thereby increasing the evaporation temperature of the ground source heat pump, and then increasing the COP of the ground source heat pump.

[0023] 3. According to weather conditions, electricity prices and the energy storage conditions in the cascade energy storage box, the operating mode is switched to ensure that the operation of the system of the present invention is high-efficiency, low-cost and has a good heating effect.

[0024] 4. The present invention provides a cascade phase change energy storage composite solar energy and ground source heat pump system for heating agricultural greenhouses. Geothermal coils are laid between crops to increase the ground temperature in the greenhouse, thereby increasing the root temperature of the crops, avoiding the rapid growth and development of the aboveground stems and leaves of vegetable seedlings and the slow growth and development of the underground roots, resulting in thin and weak vegetable seedlings.

[0025] 5. The present invention provides a cascade phase change energy storage composite solar energy and ground source heat pump system for heating agricultural greenhouses, which can be used for heating general greenhouses and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the overall structure of a cascade phase change energy storage composite solar energy and ground source heat pump system of the present invention.

[0027] Reference numerals:

[0028] 1. Solar collector, 2. Step phase change heat storage tank, 3. Coil heat exchanger, 4. Ground source heat pump, 5. Vertical heat exchanger (buried pipe), 6. Horizontal heat exchanger (buried pipe), 7. Hot water storage tank, 8. Geothermal coil, 9, 10, 11, 12, the first to fourth water pumps, 13, 14, 15, 16, 17, 18, 19, the first to seventh temperature sensors, V1, V4, V12, V14, the first to fourth check valves, V5, V6, V11, V13, V15, the first to fifth solenoid valves, V2, V3, V7, V8, V9, V10, the first to sixth three-way solenoid valves. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0030] like Figure 1The figure shows the overall structure of a cascade phase change energy storage composite solar energy and ground source heat pump system of the present invention. The system mainly includes a solar collector 1, a cascade phase change heat storage tank 2, a coil heat exchanger 3, a ground source heat pump 4, a heat exchanger composed of a vertical heat exchanger 5 and a horizontal heat exchanger 6, a hot water storage tank 7, a ground heat coil 8, and the first to fourth water pumps 9, 10, 11, 12 and various valves and other components. The specific structure and the positional relationship of each part are described as follows:

[0031] The solar thermal collector 1 and the ground source heat pump 4 are two independent loops.

[0032] The hot water generated by the solar collector 1 is divided into two paths after passing through the first check valve V1 and the first three-way solenoid valve V2. One path flows through the first water pump 9 and the third three-way solenoid valve V7 to enter the coil heat exchanger 3 at the end of the heating to provide indoor heating; the other path passes through the third solenoid valve V11 and the third check valve V12 to enter the stepped phase change heat storage tank 2 and enter the three energy storage modules from top to bottom to store the excess heat. The low-temperature return water merges with the upper branch at the second three-way solenoid valve V3. After the merger, the return water with a lower temperature enters the geothermal coil 8 through the second three-way solenoid valve V3 and the hot water storage tank 7 to provide heating for the roots of crops, and then returns to the solar collector 1 through the second solenoid valve V6.

[0033] The ground source heat pump 4 is divided into two paths after passing through the fourth water pump 12 and the fifth three-way solenoid valve V9. One path passes through the third three-way solenoid valve V7 and enters the coil heat exchanger 3 at the end of the heating to provide indoor heating; the other path enters the last energy storage module of the stepped phase change heat storage tank 2 to store heat. Similarly, the two return water paths are merged through the sixth three-way solenoid valve V10 and return to the ground source heat pump 4 to complete a cycle.

[0034] Two heat exchangers are arranged on the ground source side of the ground source heat pump 4, including a horizontal heat exchanger 6 and a vertical heat exchanger 5, which operate alternately to improve the soil recovery capacity; at the same time, the geothermal coils 8 laid between crops will also store energy in the soil, thereby increasing the speed of soil temperature recovery.

[0035] The high-temperature hot water flowing out of the phase change energy storage tank 2 enters the coil heat exchanger 3 for indoor heating through the fourth check valve V14, the fourth solenoid valve V13, the first three-way solenoid valve V2, the third three-way solenoid valve V7 and the first water pump 9, and then returns to the cascade phase change heat storage tank 2 through the fourth three-way solenoid valve V8 and the second three-way solenoid valve V3 to complete a cycle.

[0036] The stepped phase change heat storage tank 2 is composed of three phase change materials with different temperatures, namely 55°C phase change material, 45°C phase change material and 35°C phase change material, and the temperature difference does not exceed 10°C. The hot water from the solar collector 1 flows through the 55°C phase change module due to its high temperature, fully exchanges heat with it, and then enters the other two phase change modules in turn. The hot water from the ground source heat pump 4 flows back after directly entering the 35°C phase change module due to its low temperature. At the same time, the three phase change modules are respectively equipped with the fifth, sixth and seventh temperature sensors 17, 18 and 19, which are connected to the external controller to facilitate reading the internal temperature value. When the read temperature is higher than the phase change temperature, it is considered that the heat storage is sufficient, thereby closing the III interface of the first three-way solenoid valve V2 or the III interface of the fifth three-way solenoid valve V9.

[0037] In order to prevent the return water temperature from being too high and being detrimental to crop growth, a heat storage tank 7 is set up in front of the second water pump 10, and the flow is controlled by the fifth solenoid valve V15. When the value of the first temperature sensor 13 is too high, the first solenoid valve V5 is opened to replenish water and lower the water temperature. By judging the reading of the second temperature sensor 14, the opening of the first solenoid valve V5 is controlled to adjust the temperature of the water entering the geothermal coil 8.

[0038] The solar collector 1 is a flat plate collector, a vacuum tube collector or a heat pipe collector, and is installed on the top of the greenhouse through a bracket; the water in the solar collector 1 is still circulating, so as to avoid freezing and cracking of the pipe.

[0039] The user end is a coil heat exchanger 3 and a geothermal coil 8. The hot water first flows through the coil heat exchanger 3 to heat the greenhouse by convection, and then flows through the geothermal coil 8 to maintain the root temperature required for crop growth. A temperature sensor and a water replenishment device are installed between the two to prevent the water temperature from being too high and causing damage to the crops.

[0040] Horizontal buried pipes and vertical buried pipes are respectively set up on the ground source side, and a hot water storage tank is set between the return water on the heating side and the water supply on the ground source side.

[0041] At night, the water in the solar collector is still circulating, which can prevent the pipes from freezing and cracking.

[0042] The cascade phase-change heat storage tank is composed of phase-change materials of three temperatures.

[0043] The working process of the present invention is as follows:

[0044] Nighttime ground source heat pump heating and energy storage mode: The fifth three-way solenoid valve V9 and the sixth three-way solenoid valve V10 are opened, the third three-way solenoid valve V7 opens interfaces Ⅰ and Ⅱ, the fourth three-way solenoid valve V8 opens interfaces Ⅰ and Ⅱ, the third and fourth water pumps 11 and 12 are opened, and the indoor heating of the greenhouse is provided through the coil heat exchanger 3, and the excess heat is stored in the phase change heat storage tank. When the value of the seventh temperature sensor 19 is higher than the phase change temperature of the phase change material of 35°C, the interfaces Ⅲ of the fifth three-way solenoid valve V9 and the sixth three-way solenoid valve V10 are closed. When the greenhouse ground temperature is too low and the roots of crops are frozen or frosted, the interfaces Ⅲ of the fourth three-way solenoid valve V8, the interfaces Ⅰ and Ⅱ of the second three-way solenoid valve V3, the second check valve V4, the second solenoid valve V6, the first check valve V1, the interfaces Ⅰ and Ⅱ of the first three-way solenoid valve V2, and the first water pump 9 and the second water pump 10 are opened.

[0045] Solar heating and energy storage mode during the day: the first check valve V1, the first three-way solenoid valve V2, the I and III interfaces of the third three-way solenoid valve V7, the I and III interfaces of the fourth three-way solenoid valve V8, the second three-way solenoid valve V3, the second check valve V4, the second solenoid valve V6, the third solenoid valve V11, and the third check valve V12 are opened, and the indoor heating of the greenhouse is provided through the coil heat exchanger 3, and the excess heat is stored in the stepped phase change heat storage tank 2, and flows through the three phase change modules in sequence for heat storage. When the readings of the fifth, sixth, and seventh temperature sensors 17, 18, and 19 are all higher than the phase change temperature of their phase change materials, the first three-way solenoid valve V2 and the III interface of the second three-way solenoid valve V3, as well as the third solenoid valve V11 and the third check valve V12 are closed, and the energy storage ends. At the same time, according to the reading of the first temperature sensor 13, it is judged whether to open the first solenoid valve V5 for water replenishment, and according to the reading of the second temperature sensor 14, the opening of the first solenoid valve V5 is controlled.

[0046] Phase change energy storage tank heating mode during the day: when it is cloudy or the solar energy is insufficient, the fourth check valve V14, the fourth solenoid valve V13, the Ⅱ and Ⅲ interfaces of the third check valve V12, the Ⅰ and Ⅲ interfaces of the third three-way solenoid valve V7, the Ⅰ and Ⅲ interfaces of the fourth three-way solenoid valve V8, and the Ⅱ and Ⅲ interfaces of the second three-way solenoid valve V3 are opened, so that the high-temperature hot water flows out from the first module of the phase change heat storage tank and enters the coil heat exchanger to heat the greenhouse. The lower temperature return water flows into the third module of the phase change heat storage tank, completing a cycle.

[0047] Compared with the traditional energy storage tank, the cascade phase change heat storage tank provided by the present invention is composed of three phase change materials. Solar high-temperature hot water flows through 55-degree, 45-degree, and 35-degree phase change materials respectively, which can fully exchange heat and reduce exergy loss. The water temperature on the user side of the ground source heat pump is relatively low, so it is only connected to the 35-degree phase change material. This phase change heat storage tank uses valley-priced electricity to store the heat of the ground source heat pump at night and use it during the day, reducing the operating cost of greenhouse heating.

Claims

1. A cascade phase change energy storage composite solar energy and ground source heat pump system, characterized in that: The system includes two independent loops: a solar loop and a ground source heat pump loop; wherein: In the independent loop of the solar energy system, the hot water generated by the solar collector (1) is divided into two paths after passing through the first check valve (V1) and the first three-way solenoid valve (V2). One path flows through the first water pump (9) and the third three-way solenoid valve (V7) and enters the coil heat exchanger (3) at the heating end to provide indoor heating; the other path passes through the third solenoid valve (V11) and the third check valve (V12) and enters the stepped phase change heat storage tank (2) and enters the three energy storage modules from top to bottom in order to store excess heat. The two paths merge at the second three-way solenoid valve (V3), and after the merger, the return water with a lower temperature enters the hot water storage tank (7) through the second water pump (10), and the low-temperature water from the hot water storage tank (7) passes through the fifth solenoid valve (V15) and the second check valve (V4) to mix with the tap water to reduce the water temperature, wherein the replenishing water enters the circulation through the first solenoid valve (V5), and after the merger, the hot water with a lower temperature enters the geothermal coil (8) to heat the roots of the crops, and then passes through the second solenoid valve (V6) to return to the solar collector (1); In the ground source heat pump loop, the ground source heat pump (4) is divided into two paths after passing through the fourth water pump (12) and the fifth three-way solenoid valve (V9). One path passes through the third three-way solenoid valve (V7) and enters the coil heat exchanger (3) at the end of the heating to provide indoor heating; the other path enters the last energy storage module of the cascade phase change heat storage tank (2) to store heat. Similarly, the two return water paths are combined through the sixth three-way solenoid valve (V10) and return to the ground source heat pump (4). The stepped phase change heat storage tank (2) is directly connected to the coil heat exchanger (3); a third temperature sensor (15) and a fourth temperature sensor (16) are respectively arranged at both ends of the first three-way solenoid valve (V2); a fifth to a seventh temperature sensor (17), (18) and (19) are respectively arranged in the three modules of the stepped phase change heat storage tank (2); a first temperature sensor (13) and a second temperature sensor (14) are respectively arranged on both sides of the first solenoid valve (V5); the stepped phase change heat storage tank (2) is formed by combining three phase change materials with different temperatures, namely, a 55°C phase change material, a 45°C phase change material and a 35°C phase change material, and the temperature difference between the three phase change materials does not exceed 10°C; The system includes the following three modes: Nighttime ground source heat pump heating and energy storage mode: the fifth three-way solenoid valve (V9) and the sixth three-way solenoid valve (V10) are opened, the third three-way solenoid valve (V7) opens interfaces Ⅰ and Ⅱ, the fourth three-way solenoid valve (V8) opens interfaces Ⅰ and Ⅱ, the third and fourth water pumps (11) and (12) are opened, and the greenhouse is heated through the coil heat exchanger (3), and the excess heat is stored in the phase change heat storage tank; when the value of the seventh temperature sensor (19) is higher than the phase change temperature of the phase change material of 35°C, the phase change temperature of the phase change material is increased. When the temperature in the greenhouse is too low and the roots of the crops are frozen or frosted, the third interface of the fourth three-way solenoid valve (V8), the first and second interfaces of the second three-way solenoid valve (V3), the second check valve (V4), the second solenoid valve (V6), the first check valve (V1), the first and second interfaces of the first three-way solenoid valve (V2), and the first water pump (9) and the second water pump (10) are opened. During the day, solar energy heating and energy storage mode: the first check valve (V1), the first three-way solenoid valve (V2), the I and III interfaces of the third three-way solenoid valve (V7), the I and III interfaces of the fourth three-way solenoid valve (V8), the second three-way solenoid valve (V3), the second check valve (V4), the second solenoid valve (V6), the third solenoid valve (V11), and the third check valve (V12) are opened, and the indoor heating of the greenhouse is provided through the coil heat exchanger (3), and the excess heat is stored in the cascade phase change heat storage tank (2), and flows through the three phase change modules in sequence. Heat storage; when the readings of the fifth, sixth and seventh temperature sensors (17), (18) and (19) are all higher than the phase change temperature of the phase change material, the III interface of the first three-way solenoid valve (V2) and the second three-way solenoid valve (V3) as well as the third solenoid valve (V11) and the third check valve (V12) are closed, and energy storage ends; at the same time, according to the reading of the first temperature sensor (13), it is determined whether to open the first solenoid valve (V5) to replenish water, and according to the reading of the second temperature sensor (14), the opening degree of the first solenoid valve (V5) is controlled; Daytime phase change energy storage tank heating mode: When it is cloudy or the solar energy is insufficient, open the fourth check valve (V14), the fourth solenoid valve (V13), the II and III interfaces of the third check valve (V12), the I and III interfaces of the third three-way solenoid valve (V7), the I and III interfaces of the fourth three-way solenoid valve (V8), and the II and III interfaces of the second three-way solenoid valve (V3), so that high-temperature hot water flows out from the first module of the phase change heat storage tank and enters the coil heat exchanger to heat the greenhouse room; the lower temperature return water flows into the third module of the phase change heat storage tank to complete a cycle.

2. A cascade phase change energy storage composite solar energy and ground source heat pump system as claimed in claim 1, characterized in that: Two types of heat exchangers are provided on the ground source side of the ground source heat pump (4), namely a vertical heat exchanger (5) and a horizontal heat exchanger (6).

3. A cascade phase change energy storage composite solar energy and ground source heat pump system as claimed in claim 1, characterized in that: The high-temperature hot water flowing out of the stepped phase-change heat storage tank (2) enters the coil heat exchanger (3) through the fourth check valve (V14), the fourth solenoid valve (V13), the first three-way solenoid valve (V2), the third three-way solenoid valve (V7) and the first water pump (9) to provide indoor heating, and then returns to the stepped phase-change heat storage tank (2) through the fourth three-way solenoid valve (V8) and the second three-way solenoid valve (V3), thus completing a cycle.

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