Research On The Design And Application Of Plate Solar-phase Change Heat Storage System In Greenhouse

As an important facility in agricultural production, greenhouse provides a suitable environment for the cultivation of horticultural crops in North China in winter. But, when heating the greenhouse there are many problems, such as high energy consumption, high pollution and high cost. So, develop clean energy has been a hot topic in the field of protected horticulture. In recent years, the study on the phase change energy storage technology has got rapid development in the field of energy, construction and aviation. It is significant to solve the energy crisis and utilization of new energy. There are abundant light and heat resources in China more than 2/3 of the area, the use of phase change energy storage technology to utilize solar energy for greenhouse heating prospects.In this study, I design a solar-phase change heat storage combine the phase change energy storage technology and solar energy collection technology. The solar-phase change heat storage united the auxiliary equipment formed a solar-phase change heat storage system,and used the system in a solar greenhouse. The system uses solar panel to absorb solar radiation during the day and convert it into heat energy and then stored into phase change material. At night, the heat stored in the phase change material is transferred to the greenhouse use air for greenhouse heating. The main research as follows:(1) In the previous basis, choose out and test the phase change material, which is suitable for solar energy storage and greenhouse production. By contrast, Na2HPO4?12H2O is chosen as the phase change material for this experiment. The study found that: the material which mixed the Na2HPO4 ? 12H2 O, Al2O3 and CMC as the ratio of 20:1:1, is stable and its supercooling phenomenon is not obvious. The mixed material’s melting point is 34.6℃ and its latent heat is 214.5J/g. The mixed phase change materials can well meet the requirements of this study.(2) Design and manufacture a solar phase change heat storage, which is composed of atransparent cover, a heat absorbing plate, heat storage units, a frame and the heat insulating material. The lighting area of the heat storage is 1200 mm × 800 mm, and the frame is made of steel plate. The heat absorbing plate covered with titanium oxy-nitride selective absorption coating, and 35 kg phase change material encapsulated in the storage. Solar-phase change heat storage and ventilation pipe, fan, temperature control switch and valves components of solar-phase change heat storage system.(3) Applied the solar-phase change heat storage system in the greenhouse, the following conclusions are obtained through monitored the environmental parameters in the greenhouse and the related parameters of the heat storage system : In sunny days, the greenhouse’s average temperature at night(18:00-8:00) is increased by 2.0 ℃ and the minimum temperature at night increased by 3.1 ℃; Under different weather conditions, the greenhouse’s average minimum temperature is increased by 2.5 ℃ at night, the underground soil’s temperature at 20 cm depth in the average is increased by 1.4 ℃, the greenhouse’s average air relative humidity decreased by 4%; In sunny days, About 70% of the phase change material in the heat storage is completely melted, through calculation, the system’s average radiation collecting efficiency reached 59.2%, the heat release quantity at night is4.05 MJ/m2. In sunny days, cloudy days and under different weather conditions, the night temperature difference is small, the temperature distribution is more uniform than that in the control.Solar-phase change heat storage system, storage the solar energy during the day and used for night heating, provides a new method for greenhouse heating. When using the system, it can be chosen the corresponding area of the storage according to required of greenhouse heating quantity, flexible application; The system set heat / thermal storage device integration, thermal efficiency is high; The system using air as heat transfer fluids can be directly heated greenhouse air, easy to use.