Analysis on the practice of underground heat stora

2022-08-10
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Analysis on the practice of using solar energy for underground heat storage in vegetable greenhouses

Abstract: in order to comprehensively promote solar energy, our department has tested, analyzed and studied the use of solar energy to increase temperature in vegetable greenhouses. The project is carried out in the vegetable planting demonstration base of the Academy of Agricultural Sciences in Yulong Town, Daxing District, Beijing. Two greenhouses were randomly selected to install the solar heat collection module produced by our company. The results show that the monthly average temperature of soil temperature in the greenhouse with 12 temperature measuring points is higher than that without solar collector module. The rise of soil temperature is conducive to the growth of vegetables and improves the economic benefits of greenhouse

key words: vegetable greenhouse; solar energy; Principle of solar water heating system; Soil heat storage

geographical location of Beijing: 39 ° 57 north latitude, temperature: the average temperature of the coldest month in Beijing in the past 10 years is -13.4 ℃. Cold water temperature: according to table 5.1.4 recommended minimum water temperature in the coldest month of code for design of building water supply and drainage GB50015-2003, the average temperature of cold water in Beijing is 10-15 ℃. Solar energy: Beijing is an area rich in solar energy resources. The annual sunshine hours 5. Pay attention to the number of parts that are easy to rust or are not used for a long time is 3000-3200 hours; The amount of solar radiation on the horizontal plane is 5400-6700mj/㎡ a. (1) This temperature limits the open-air growth of vegetables and greatly reduces the yield of vegetables. How to obtain higher soil temperature in colder seasons has always been the core issue of the Academy of Agricultural Sciences. Although plastic film covered greenhouses were built, and the room temperature was increased by sunlight or fire heating, it was difficult to increase the soil temperature (2). The surface temperature is only slightly higher, which is still far from meeting the temperature conditions required for the growth of vegetables

in order to improve the greenhouse temperature, our department has built two sets of soil accumulation solar energy systems for the vegetable greenhouse on the basis of early scientific research

I. equipment and principle

Beijing Daxing Yulong Academy of Agricultural Sciences is located in the south of the road 1 km south of the Yulong exit of Beijing Kaifeng expressway, facing south, with a brick wall foundation. The North brick wall is 3M high; Connect to the north wall and cover the 3M wide room top at an angle of 15 degrees to the South; The brick walls on the East and west sides are high in the north and low in the South; The sloping top of the greenhouse to the south is covered with polyethylene plastic film. 17 solar energy heat collection modules (produced by Beijing Yinghao Sunshine Solar Energy Industry Co., Ltd.) with a heat collection area of 3.4m2 are installed on the roof along the North brick wall. A layer of heat dissipation PEX pipes are laid 40cm and 80cm away from the soil surface in the vegetable greenhouse, with a pipe spacing of 40cm. In the greenhouse, Moldex3D, the global leader of plastic mold flow analysis software along the wall above the ground, announced on September 11 that Moldex3D dimimat RP (reinforced plastics) was officially released. 80cm of the table was paved with 50cm of polystyrene board for insulation

operation schematic diagram

the system is fully automatic. It adopts the hot water engineering control system in the solar energy industry, and the CPU programmable control. The specific operation principle is as follows:

the system uses a floating ball to replenish water. A 100L insulation water tank is installed on the upper part of the heat collection module, and the floating ball is used to control the replenishment of water (connected with tap water). In order to improve the health and rapid development of the aluminum based new material industry, the system will replenish water when there is water loss. Connect automatic exhaust valves at both ends of the system

when the temperature sensor T1 detects that the temperature of the make-up water pipe is lower than the set value (generally 3 degrees), the system is set at 5 degrees. Start the anti freezing heat tracing belt to prevent the pipeline from cracking

when the temperature sensor T3 detects that the difference between the water outlet temperature of the heat collection module and the temperature sensor T2 detects that the temperature of the water return port of the heat collection module is greater than the set value (generally set at 5 degrees), the system is set at 10 degrees. Start the circulating water pump P1 to pump the high-temperature hot water in the heat collection module into the underground coil for circulation

the temperature sensor T2 detects that the return water temperature of the heat collection module is generally set at 35 ℃. It can be set at will (0-99 degrees). The temperature sensor T2 detects that the outlet water temperature of the heat collection module is generally set at 46 degrees. It can be set at will (0-99 degrees)

PEX coil at 40cm underground is used for heat exchange of underground soil in winter, and PEX coil at 80cm underground is used for heat exchange of underground soil in summer

II. Economic analysis

the initial investment of this system is 45000 yuan, including (heat collection module, control system, pipeline, angle iron, water demand drying pump, labor, etc.) operation cost: water pump 250W, flow: 2.4t/h, annual average daily operation: 4 ± 2 h. Average daily operation cost: 0.25 × 4=1KWh。 Agricultural electricity: 0.42 yuan/kWh. Total electricity charge: 1 kWh × 0.42 yuan/degree =0.42 yuan. The average monthly electricity charge is 0.42 yuan × 30 days =12.6 yuan/month. Investment comparison between underground solar energy storage and coal-fired heating

III. safety and environment of independent solar energy storage system

(I) safety

1, bearing capacity

(1) pressure of independent solar water heater on roof: 50 kgf/m2

(2) roof bearing capacity: kgf/m2. The roof can withstand the pressure of solar collector module

2. Lightning protection

3. The solar hot water heat collection module is set on the north side of the greenhouse. According to the regulations, the solar collector module support is connected with the lightning wire on the north wall

4. The solar collector module is set on the north side of the greenhouse. Add lightning arrester on the roof as required

(II) environmental independent solar heating system saves land (built on the roof), does not affect the indoor and outdoor environment, and saves energy. The adoption of this technology meets the requirements of the whole society to promote "green building"

IV. social and economic benefits of the greenhouse underground heat storage solar energy project

the solar energy heat storage engineering system is the utilization of clean energy, and the carbon dioxide emission reduction of the above project is:

according to the formula: qco2= (△ qsave) × n × Fco2 × 44)/(W × Eff × 12) , then the emission reduction of carbon dioxide in 15 years qco2=227t

while a large number of renewable energy are developed, solar energy has been widely used. The production and sales of solar collector modules are increasing year by year, and the annual sales volume has exceeded sevenoreight million units. How much economic value solar energy can create depends on the comprehensive ability of decision makers

at present, there are 20million users of solar water heaters in China, and the annual growth rate is 20-30%. From this group of figures, it can be seen that solar energy will replace conventional energy in the future

v. policy support

today, when the country vigorously develops renewable energy, it has also given a large number of preferential policies to encourage the development and application of renewable energy projects and supporting equipment

1. In 2006, Ma Kai, director of the national development and Reform Commission, said at the meeting of six ministries and commissions including the Propaganda Department of the CPC Central Committee: "the government will formulate the catalogue of energy-saving products." We will implement the mandatory government procurement policy for energy-saving products, and specifically include energy conservation in the government procurement catalogue

2. If you choose to live in the suburbs or rural areas, you can apply for low interest loans for new rural construction

VI. conclusion and discussion

through the underground storage of solar heat energy, the energy in the greenhouse can be increased. The new heat also realizes the dynamic balance. It verifies the relevant articles published by Professor Xiong peigui (3), and the relevant temperature analysis is not emphasized here. This paper focuses on the engineering control and economic analysis of underground solar energy accumulation in greenhouse

this project adopts the solar hot water engineering control g-control cabinet (gz-c CPU control system (4) produced by Beijing Yinghao Sunshine Solar Energy Industry Co., Ltd.), which has the functions of temperature difference cycle, antifreeze cycle, antifreeze heat tracing, low cost, easy installation and debugging, etc. At present, PLC programming control is widely used in the market (relatively high cost), and this project can also use PLC programming control system

after installing the solar heat collection module, the solar heat energy is directly stored in the underground soil for the growth of vegetables, which not only saves energy and emissions, but also increases the economic income of vegetables. It is the inevitable way for the development of ecological agriculture

References:

1 code for design of building water supply and drainage GB50015-2003 table 5.1.4

2 Han Baihua Pay country Mao Xiujie Liu Yan Fu Lifan Overview of soil problems in protected vegetable cultivation Jilin agriculture 2007.04

3 Zhang Hailian Xiong peigui Zhao Limin Xuhaiqin Study on the effect of solar thermal energy stored underground in greenhouse. Northwest Agricultural Journal 1997.6 (1): 54~57

4 internal data of Beijing Yinghao Sunshine Solar Energy Industry Co., Ltd. (end)

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