| The wall of the existing active heat storage solar greenhouse(AHSSG)has good heat storage effect,which plays an important role in improving the indoor thermal environment at night.However,there are still some problems,such as large heat loss of front roof,high construction cost,small heat storage capacity,low heat transfer efficiency,unreasonable air flow movement mode,etc.And thus the heat storage potential of the back wall and soil is still not well explored.It is urgent to study the structure optimization and heat transfer characteristics of the wall and soil in the active thermal storage cycle system.Therefore,based on the previous research results of the research group,this paper focuses on structure optimization and heat transfer characteristics of solar greenhouse active heat storage cycle system.First of all,the study starts from the front roof thermal insulation and optimize the insulation measurements to reduce the heat loss.Secondly,the study focus on optimization of the wall and structure by adopting new materials and new forms to improve the wall heat storage and temperature preservation.Finally,the study focus on the active thermal storage air flow movement to optimize the motion path,improve the active heat storage efficiency.The main results are as follows:(1)The existence of thermal disfigurements will lead to the increase of heat transfer coefficient,the acceleration of heat loss and the decrease of temperature.The larger the ratio of thermal disfigurements area,the more obvious the influence on the increasing trend of heat transfer coefficient and heat flux,and the more obvious temperature drop.When the indoor temperature is the same and there are no thermal disfigurements,the heat flux density through the envelope is different.And the temperature decreased in the order of front roof > back roof > back wall,indicating the front roof is the main channel of indoor heat loss.Compared with the front roof and back roof,the wall is more sensitive to thermal disfigurements.Based on the analysis of heat transfer theory and test results,comprehensive considering factors of the greenhouse structure,crop demand,outdoor minimum temperature,and insulation quilt properties,the expression of the thickness and thermal conductivity of thermal insulation quilt under different outdoor minimum temperatures is given.(2)Under the same weather conditions,the temperature retention of greenhouse with back wall made by sand filled cement pipe(W3)and light weight aggregate concrete block(W2)is better than that of ordinary clay brick(W1).Under typical weather conditions,the indoor highest temperature of W2 and W3 is nearly the same,which is higher than that of W1;the indoor temperature of W2 is slightly higher than that of W3,and W1 is the lowest.The temperature distribution of W3 is more uniform than that of W2.The heat storage capacity and heat release rate of the W3 are much higher than those of W1 and W2.The comprehensive performance of heat insulation and heat storage of W3 is better than that of W2 and W1.(3)When the heat transfer tube is the same,the transferred heat amount in clay loam soil is the smallest,and that in sand soil is the largest.When the mulch is the same,the heat transfer per unit time of the PVC whole tube is the minimum,while that of the PVC porous tube is the largest.The transferred heat amount of the ground heat exchange system can be improved by changing the form of heat transfer tube,and the improvement degree is independent on the soil.The transferred heat amount can be significantly improved by setting large number of holes on heat transfer tube.(4)In the same period of time,the transferred heat amount in the back wall with the top in bottom out distribution duct(DF)is the largest,while that in the back wall with top in side out distribution duct(CF)is slightly greater than that of the back wall with top in bottom out with straight up and down duct(Z).The temperature of the active heat storage wall is higher than that of the passive heat storage wall,and the back wall with the top in bottom out distribution duct(DF)showed the highest the overall temperature and the most uniform temperature distribution.The distribution duct is favorable to improving the heat storage range of the wall.The optimum duct is top in bottom out distribution duct(DF)among the three kinds of active heat storage duct layout,which makes the indoor average temperature increased most obviously,showed the highest temperature at night,and more uniform of temperature.(5)The temperature characteristics of active heat storage greenhouse with three different layout schemes of stereoscopic cycle system were analyzed,including the back wall top in straight up and down directly connected to the ground single tube out(L1),the back wall top in bottom out with 4 distributed tubes directly connected to the ground 4 distributed tubes out(L2),and the back wall top in bottom out with single straight up and down tube,then connected to the ground 4 distributed tubes(L3).It is found that the L2 scheme is the optimized duct layout,with which the greenhouse showed the highest heat storage amount and indoor temperature.Compared with the merely back wall active heat storage,the stereoscopic cycle active heat storage can significantly improve the indoor and soil temperature at night.Compared with the optimized back wall active heat storage greenhouse(DF),the lowest and average indoor temperature of the stereoscopic cycle active heat storage greenhouse with L2 scheme at the time of the lowest indoor temperature are increased by 0.72 °C and 1.75 °C,respectively.Compared with the passive heat storage back wall greenhouse,the lowest and average indoor temperature at the time of the lowest indoor temperature are increased 3.28 °C and 3.49 °C,respectively.The experimental verification shows that,compared with the traditional passive heat storage greenhouse,under continuous cloudy(snow)days in winter,the lowest indoor and soil temperature of stereoscopic cycle active heat storage greenhouse with(L2)scheme are respectively increased by 1.85 °C and 1.46?1.5 °C when the indoor temperature is the lowest.The results of this study provide technical reference and theoretical basis for envelope optimization,wall materials optimization,and heat transfer tube form and layout optimization of active solar greenhouse,which has certain theoretical and application value. |
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