New design concept and thermal performance of a composite wall applied in solar greenhouse

Traditional solar greenhouse wall combines the functions of heat preservation and heating. It cannot accommodate both heat storage and insulation that the heat stored in the wall is uncontrollably lost as the temperature difference between the interior and exterior increases. This study proposed a novel composite wall (NCW) with an independent modular wall made of expanded polystyrene board and reinforced concrete (EPCW), and a solar water heating system (SWHS). The thermal properties of traditional brick walls and novel composite walls were assessed through field tests. Numerical simulations were utilized to analyze the heat transfer processes occurring within the wall, enabling determination of the magnitude of heat transfer towards both the interior and exterior. The thermal resistance of the ECPW with the same thickness is 1.5 times higher than that of clay bricks. Meanwhile, the heat loss from the exterior wall is reduced by 44% through the EPCW. The SWHS installed on the greenhouse north wall increases heat storage by 89% and heat release by 256%. The greenhouse annual input cost for using NCW is 2.5 USD m-2 year-1 in 20-year life. It is 32.4% lower than that of a conventional clay brick greenhouse, and has some promotional and application value.