Numerical Simulation Of The Thermal Performances Of Greenhouse Wall With Phase Change Materials By Active-Passive Heat Storage

Solar Greenhouse is a facility for agricultural construction that use of solar energy as a heat source to carry out anti-seasonal cultivation,which made a great contribution for the supply of fresh vegetables in China.But the solar greenhouses display a certain degree of limitations in the progress of application under complex climatic conditions.In order to improve the performance of the greenhouse,explore the ability to use the solar energy and reduce dependence and impact on outdoor conditions,this paper had done some research on the basis of the previous research.Based on the previous research of the research group,this paper carried out the following research work around the construction of the north wall,evaluation of winter night thermal environment in greenhouse,optimization of active-passive phase change heat storage wall and other aspects by means of combining theoretical analysis,numerical analysis and experiments from the view of enhancing heat preservation wall was developed to control the thermal environment of solar greenhouse.First of all,this paper analysis the solar greenhouse north wall on temperature distribution,heat storage,indoor temperature and other aspects,and then get conclusion of the main problems from the passive heat storage wall.The results show that there are subcooled areas inside the passive wall,which cannot contribute heating to the greenhouse.There is "value insulation,contempt for heat storage,heat transfer and heat storage fuzzy" problem in the way of wall construction.Saving more heat at the expense of increasing the thickness of the wall will made land utilization reduced.Passive thermal storage greenhouse was easy to be affected by outdoor environment and had low temperature at night,so it cannot meet thermal environment requirements under the complex climate change.Secondly,by summarizing the shortcomings of the typical passive greenhouse wall,a new type of active-passive phase change heat storage wall model of solar greenhouse was put forward on the basis of experimental verification.The heat storage layer composed of inner greenhouse wall is made of steel drums with phase change materials,which was used to absorb and storage heat.The heat storage coil layer is set in the middle to improve the temperature of the wall and realize the purpose of heat insulation by circulating hot air.The Outer wall is insulation layer to set insulation of the brick wall.The new type of solar greenhouse wall in line with the ideal wall structure of the building concept,and strive to serve as the load bearing,insulation and heat storage of the overall performance.Thirdly,according to the theory of heat transfer,hydrodynamics and the engineering examples,Fluent software was used to establish the three-dimensional model of the active-passive phase change thermal storage solar greenhouse.The results show that the temperature of the north wall is higher than the temperature of the indoor air and the wall release heat to the air in greenhouse.The wall heating system allows the greenhouse air to circulate regularly and make the air evenly which improves the utilization of heat.The mean temperature is 10.2 ? in active-passive phase change greenhouse and 10.5 ? higher than the compared greenhouse before opening insulation in the next morning.The indoor temperature and mean air temperature in active-passive phase change greenhouse were also improved than the compared greenhouse.Fourthly,the optimal analysis of the active-passive phase change thermal storage solar greenhouse was carried out,including the optimum thickness of the brick and the insulation layer.In order to determine suitable thickness of the brick layer and insulation layer,the thickness of the brick layer and insulation layer are changed to analyze and calculate the suitable thickness by researching thermal resistance,heat storage coefficient,thermal inertia and other parameters of the solar greenhouse.The results show that the thicker the insulation and the brick layer,the smaller the heat loss of the greenhouse envelope,which also contribute to the higher temperature in the greenhouse.The superior insulation thickness of active-passive phase change heat storage north wall is 50 mm,and the brick is 600 mm in Beijing area.The thermal environment model of solar greenhouse in the active-passive phase change heat storage wall proposed by the research group has reduced dependency on solar radiation to a certain extent,and solved the low temperature problem in winter night and temperature distribution uniform problem,to ensure the continuous growth of greenhouse crops demand,and enhance the greenhouse on the outdoor complex climate conditions of adaptability.The active-passive phase change heat storage greenhouse is especially suitable for the north heating greenhouse and winter nursery greenhouse,which also can make the greenhouse temperature stability and make more heat contribution to ensure the continuous growth of crops in winter.The construction of active-passive phase change heat storage greenhouse widened the scope of application of new greenhouse wall to a certain extent,which provides a reference for the construction of the heat storage greenhouse.