Thermal performance of solar greenhouse with composite wall using wheat shell-mortar block filling with heat storage material in north Xinjiang

The greenhouse in the Gobi Desert region of Xinjiang is under severe conditions in winter. The problem is that the traditional wall can not meet the demand of thermal environment for crop growth at night. The main structure of the wall is made of wheat shell and mortar block. The main factors affecting the compressive strength and thermal conductivity of the block are cement content, binder content and wheat shell content. Three-element and three-level orthogonal test is designed to determine the ratio of wheat shell to mortar block. Finally, it is determined that the reasonable level is 35% cement, 4% adhesive, 2.5% wheat shell, fine sand and moderate amount of water. The wheat shell-mortar block sample was prepared and the tests of compressive strength and thermal conductivity were carried out. Solar greenhouse was built with composite wall of wheat shell-mortar block and filling material. A solar greenhouse was 37 cm ordinary brick wall together with 10 cm benzene panel. Each greenhouse has 24 measuring points, and the mean temperature and ground temperature were measured. The thermal insulation and heat storage performance of 2 kinds of solar greenhouses with different walls at winter night were compared, and the middle space of the block was filled with slag and quicklime which both have small thermal conductivity and are stable. The data in the coldest 8 days from January 14 to January 21, 2017 were selected as the comparative study object. The results show that: In the same external environment, when the minimum temperature at winter night is -12.8 ℃, the indoor temperature of wheat shell-mortar block composite wall is 9.5 ℃, while the temperature of brick wall in solar greenhouse is 4.4 ℃. The temperature of the greenhouse of compound wall is 5.1 ℃ higher than that of brick wall. When the temperature at winter night is -20.8 ℃, the indoor temperature of wheat shell-mortar block composite wall is 7.5 ℃, while the temperature of brick wall in solar greenhouse is 3.2 ℃. The temperature of the greenhouse of compound wall is 4.3 ℃ higher than that of brick wall. The minimum room temperature at night in the solar greenhouse of masonry compound wall occurs 42 min later than normal brick masonry wall. For the tomato planted under the same conditions in 2 kinds of wall greenhouses, the flowering time of tomato in compound wall greenhouse is 7 d earlier, and the harvest time of tomato was 16 d earlier. The tomato yield during the first month in composite wall solar greenhouse is 1 768 kg, and the yield in brick wall solar greenhouse is 1 493 kg. The yield of single shed in composite wall solar greenhouse is increased by 18.4%. It is verified that the thermal insulation and heat storage performance of the composite wall solar greenhouse with wheat shell-mortar block and filling material are obviously superior to brick wall solar greenhouse. It can accumulate more heat energy and the rate of heat dissipation is stable. The compound wall solar greenhouse can effectively improve the growing environment of crops in the greenhouse, which meets the growth requirement of the fruits and vegetables for good temperature and good light. And it is suitable for the accumulation of dry matter in fruits and vegetables, so crops can be harvested in advance and production increases. The research provides a theoretical reference for the design and application of mortar block composite wall in solar greenhouse