Numerical Simulation Analysis Of Heat Storage And Insulation Performance Of Chinese Solar Greenhouse Wall In Non-cultivated Land

Chinese solar greenhouse is a type of agricultural facilities developed by China independently,its unique building envelope provides proper growth environment for vegetables.Hexi Corridor is located in Gansu Province with plenty of light,heat,and non-cultivated land resources,thus,solar greenhouse production in non-cultivated land has a good prospect for development.To reduce costs and enhance the utilization of land,dinas,aerated concrete block,hollow brick,concrete and other materials are applied in construction of solar greenhouse envelope widely.The lack of comprehensive study on heat transfer performance of solar greenhouse wall in non-cultivated land,therefore,there has not been standard in this field now,which leads to nonstandard structure,expensive cost and unsatisfactory heat storage and insulation performance.According to heat transfer theory,based on geographical position and climate of Hexi corridor,a temperature dynamic model was established for solar greenhouse wall,to numerical simulate and analyze heat storage and insulation performance of 5 solar greenhouse walls in Hexi Corridor non-cultivated land quantitatively.Based on the temperature dynamic model,the thermal performance of greenhouse wall with air enclosures covered with aluminum foil was studied,which supplied theoretical basis for solar greenhouse wall insulation design in non-cultivated land.The main studies and results were as follows:1)Based on one-dimensional conduction differential equation,adopted finite volume method,built temperature dynamic model of solar greenhouse wall to numerical simulate and analyze heat transfer performance in the wall and wrote MATLAB procedure.Then a simulated heat transfer experiment was conducted in a solar greenhouse in Jiu Quan,which north wall was composed by aerated concrete block and dinas.The results showed that the simulation results of the model was identical.2)This study suggested the evaluation indicators for heat storage and insulation performance of solar greenhouse wall,which included net heat storage of wall inner surface at daytime,net heat release of wall inner surface at nighttime,and net heat dissipate of wall outer surface at all day.There were 5 types of solar greenhouse walls in Hexi Corridor non-cultivated land,the first was composed by flanged wall and dinas,the second was composed by concrete wall and dinas,the third was composed by stone wall and dinas,the fourth was composed by aerated concrete blocks and dinas,the fifth was composed by hollow bricks and dinas.In sunny day,compared with solid clay wall,the net heat storage of wall inner surface at daytime of the first and third wall rose of 15.4% and 9.4% respectively,while the second,fourth,and fifth reduced by 2.7%,92.8%,and 61.5% respectively.The net heat release of wall inner surface at nighttime of the first,second,and third wall rose of 42.9%,16.6%,and 31.3% respectively,while the fourth and fifth reduced by 92.3% and 65.3% respectively.The net heat dissipate of wall outer surface at all day of this 5 walls reduced by 40.3%,36.7%,43.4%,57.5%,and 26.2% respectively.Heat storage and insulation performance of the first wall was excellent,the third wall was the next,the second wall followed,the fourth and fifth wall were unsatisfactory.Thus,the last two greenhouse walls were not suggested further wide application in Hexi corridor in future.3)The wall surface covered with aluminum foil could effectively reduce radiation heat in the air enclosure.In wall insulation design of solar greenhouse,the suitable height and thickness of air enclosure covered with aluminum foil were 1.5 m and 0.03 m respectively.When temperature difference between inside and outside surface of the enclosure was 2-20 K in the simulation of heat preservation layer,thermal resistance was 0.70-0.55 K·m2/W in the air enclosure,heat preservation and heat insulation effect was equivalent to 0.81-0.64 m thickness of solid clay wall,or 0.55-0.43 m thickness of red brick wall,or 0.20-0.16 m thickness of coal cinder,or 0.06-0.05 m thickness of pearlite,or 0.03-0.02 m thickness of polystyrene board.4)There are two types of solar greenhouse wall structures: 360 mm thickness of red brick wall + three 30 mm air enclosures covered with aluminum foil + 120 mm thickness of red brick wall,240 mm thickness of red brick wall + three 30 mm air enclosures covered with aluminum foil + 240 mm thickness of red brick wall.The heat released to inside greenhouse form the two walls greatly increased than 480 mm thickness of red brick wall,but was not significantly different from the wall of the same structure composed by red brick wall and polystyrene board.Polystyrene board can be replaced with enclosure of this suitable structure in solar greenhouse wall design.