Research Of Temperature In Soil Wall And Solar Greenhouse

Solar greenhouse with soil wall as the enclosure structure is an original greenhouse type of China. This type of greenhouse is suitable for our national conditions and energy efficiency requirement, for it is simple, low cost and better heat preservation, there wasn't supplementary heating equipment in greenhouse which could provide the temperature for normal growth of the plant only by own structure. In this condition, it can avoid the consumption of sources of energy, and reduce the pollution of environment from supplementary heat. The wide application of this type of greenhouse in China has produced fine economical and social benefits.Up until now, the study of greenhouse back-wall focused on the heterogeneous compound wall, the thermal-keeping effect of which is better but the cost is high. The promotion became difficult in the rural areas. There were many existing many problems, for example the bad thermal effect, the back-wall thicker or not. All of which caused the high cost or wasting of arable land. The way of study nowadays concentrates on testing the thermal performance and improving the structure according to the testing result but was short of complete theory. Study of the variation of greenhouse temperature, the variation of the back-wall inside temperature and the variation trends annual need further research.This experiment studied the temperature of the greenhouse made of soil comprehensively, made sure the suitable thickness of the back-wall. The experiment paved the way for stimulating the constant temperature layer, suitable thickness and exploring the variation of the temperature and provided the statistics of how to improve arable land using rate, and a preferential structure, by measuring the temperature of north wall and processing the statistics.Took the soil-walled greenhouse in Xing yang, Zhengzhou as example, experimental test and theoretical analysis as a combination of methods was adopted to carry on the study of the soil temperature of it, the concrete results were as follows:The experiment focused on the inside temperature of the soil made greenhouse, basing on the assumption that the thickness was able to keep the temperature requirement of vegetables and there was a constant temperature layer. We found the boundary point between constant temperature layer and various temperature layer by the research of much experimental test. Boundary between temperature-change layer and temperature-constant layer changes in different season: at the beginning, the inside point was 1.4m to the inside wall surface, the outside point was 1.1m to the outside surface, this showed there was a temperature-constant layer there, but In January, the two points were 50cm away, which showed the temperature-constant layer increased to some extent and the thickness of the wall complied with the thermal-keeping standard. In winter, there was no apparent variation of the boundary between temperature-change layer and temperature-constant layer.In spring, boundary between temperature-change layer and temperature-constant layer changes with the temperature rising. during the late ten days of March ,the inside point was 1.5m to the inside wall surface, the outside was 1.1m to the outside wall surface, the distance between the two points was 40cm.two sides of the back wall begins to absorb heat with the temperature rising ,which lead to the variation of the temperature-constant layer and the variation of the two points. In middle April, the distance of the two points was, but the inside point was 1.6m to the inside wall surface, the outside point was 0.9m to the outside wall surface. The concept of the temperature-constant layer was different in spring and winter .the two sides of the temperature-constant layer did not changed heat ,but in spring ,each side of the temperature-constant layer absorbs heat ,which lead the temperature rising and the change of the two points.The wall and indoor temperatures of soil-walled greenhouse were tested on the spots through reasonable test scheme. The results showed that the thermal insulation effect of soil wall was fine, and it could satisfy the basic temperature requirement of crops in a non-supplementary heating weather condition in winter. We had a comprehensive rule on the variation of the inside temperature of back-wall and the variation of temperature in different seasons.In winter, the inside temperature of the soil-made wall reduces with the thickness increasing and the temperature of the wall reducing. The temperature between 1.4m and 1.9m was nearly constant even in different time, which showed the existence of the temperature-constant layer in winter. the temperature from inside to temperature-constant layer was a little higher than that of other time. In day time, with the room temperature rising, the inside wall began to absorb heat and temperature rose. With the winter ending, the inside wall could absorb heat more time in day time. During late February, the inside wall could absorb heat all the afternoon in sunny days. From 0.4m to the inside of the wall, the temperature-changing trends were exactly the same, reducing gently until the temperature-constant layer reduces gently. From temperature-constant layer to outside, the temperature-changing trends was nearly the same, reducing slowly.In spring ,the temperature of the wall rises apparently ,which showed the wall the whole wall was absorbing heat .the average temperature-changing trends of different depths was the same , the inside wall temperature rising apparently in the middle of the day .with the outside temperature rising ,the wall kept more heat. Early spring, the wall emitted heat to greenhouse the first half-night. Late spring, the wall emitted heat to greenhouse to keep the temperature after evening .the temperature of two sides of the wall rises because of the outside temperature rising, which leads to the temperature rising of temperature-constant layer. From temperature-constant layer to outside temperature-changing trends was slowly. Two points away from each other 1.7m, the temperature changed only 3℃.The experiment result stimulated the constant temperature layer, various temperature layer, and thermal-absorbing layer.The experiment result showed that : the heat-absorbing layer was 0.3m in winter ,heat-reserving layer was 1.1m, temperature-constant layer was 0.5m.The suitable thickness range of the soil wall is 2.6m and the thermal insulation effect is not obvious with the increasing thickness when over 2.6m.