| In China,solar greenhouse of soil wall is used widely because of the good characteristic of heat storage and heat release,convenient soil material and low cost.At present,the soil wall of greenhouse is constructed with super thickness in some district,which will lead to waste land resources.Solar greenhouse as unique greenhouse type in the world can provide the heat for crop in night via the heat storage of wall during the day.Therefore the study on the some characteristic of soil wall is important for the soil wall optimization and simplification,such as the heat storage,the heat release,the heat solar radiation gain and the heat transfer quantity.In the paper,the 1#(the top width is 2m,bottom width is 6m)and 2#(the top width is 1.3m,bottom width is 3m)are selected as research object in Taian,Shandong Province,China.Two greenhouses have the same structure,and five testing layers are arranged at the same location of north wall.The temperature changes of wall interior,solar radiation distribution of wall surface and heat transfer quantity of every testing layer are analyzed based on the testing data.The results are as follows:1.The analysis on temperature changes of wall interior and the evaluation on the heat release efficiency of wallThe temperature changes of wall interior are analyzed based on the testing data of five testing layers of the 2# greenhouse.The results showed that the testing point temperature of wall surface and interior wall(0.1-0.6 m)presented periodicity variation regularity with the indoor temperature variation of greenhouse,and temperature fluctuation amplitude reduced gradually,at the same time the phase was lags obviously along the wall thickness direction.Besides that,the temperature fluctuation of testing point behind 0.7 m tended to the stabilization,which was in the process of the steady-state heat transfer from the soil wall surface to outdoors.In order to evaluate the performance of the heat storage and the heat release of soil wall better,the weighted average values of heat storage of all five testing layers were calculated.On the basis of the heat storage and the heat release results,the average efficiency of heat release for the soil wall during the coldest season period was calculated.The result showed that the average efficiency of heat release was 43% for solar greenhouse of the soil wall,which could release 43% of the heat storage of soil wall during the day to improve the thermal environment of the greenhouse nighttime.2.The study on heat storage and release characteristic of the different thickness wall under sunny and cloudy day conditionThe heat storage and release characteristic of the 1# and 2# greenhouse are analyzed based on the testing data of continous sunny day(from Dec.30 th,2015 to Jan.2th,2016)and cloudy day(Jan.4-6th,2016).The results showed that the heat release of two greenhouses is increasing gradually from first layer to fifth layer,and the temperature change trend is similar for every testing layer.Under the sunny day conditions,the average heat storage of the 1# and 2# greenhouse is 1971.2 k J and 1888.9 kJ respectively,the average heat release of the 1# and 2# greenhouse is 808.1 k J and 763.1 k J respectively.The difference of heat storage and release for two greenhouses is 82.3 kJ and 45.0 kJ respectively.Under the sunny day conditions,the the average heat release of the 1# and 2# greenhouse is 1551.4 k J and 935.5kJ respectively,the average heat release difference of two greenhouse is 615.9 kJ.Although the average heat release of the 1# greenhouse is higher than that of 2# greenhouse,the air temperature of the 1 # greenhouse is only 0.6?higher than the 2 # greenhouse during the cloudy day.It showed that the indoor thermal environment of greenhouse can barely be improved via the increasing wall thickness.3.The study on the solar radiation gain distribution and heat transfer quantity of five testing layers of wallThe solar radiation gain distribution and heat transfer quantity of five testing layers of the 2# greenhouse is analyzed based on the testing data under different weather conditions.The results showed that the solar radiation gain at the second testing layer of wall is largest,followed by the third testing layer,and the value of the second and third testing layer is close.According to the analysis of the heat transfer quantity of five testing layers and north roof,the proportions of the heat transfer quantity of five testing layers are 21%,19%,17%,14% and 12% respectively,and north roof is 17%.It showed that the first and second testing layers are main heat transfer position of wall,which should be arranged for the heat insulating material.4.Temperature field simulation modle of soil wall of greenhouse be establishedTemperature field simulation modle of soil wall of greenhouse be established via the ANSYS software.The temperature changes of soil wall interior under sunny and cloudy day condition are analyzed based on the mothod of steady heat transfer,and the simulated results are verified via the experimental testing data.The results showed that the simulated value is good agree with the experimental value,and the simulated average deviation is ±1.0?.The emperature field simulation modle can predict the temperature changes of soil wall interior,which can provide theoretical reference for the heat transfer characteristic of soil wall in taian region. |
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