New insights into the scientific configuration of a sheet heating system applied in Chinese solar greenhouse

Abstract

• The shadow range on the north wall were analyzed though the perspective of solar radiation. • Theoretical basis for the solar collector size and installation position was proposed. • Daily average heat collection per unit collector area is 5.6 MJ/m 2 . • The control system can be regulated flexibly according to the indoor microclimate. • The solar water heating system is cost effective in terms of investment and energy saving. The traditional Chinese solar greenhouse (CSG) cannot meet the overwinter production of warm-season plants in the cold north of China. At present, a sheet heating system on the north wall is often used to solve the problem of low temperature in the CSG. However, there is a lack of a theoretical basis for the design of collectors in current research. To address this problem, a theoretical basis for the collector size and installation position of the system from the perspective of solar radiation was proposed in this study. A sheet heating system on the north wall was installed in a CSG in Beijing, which is a solar water recycling system (SWRS). To evaluate the thermal performance of the SWRS, field tests and theoretical verification were carried out. The results indicated that the minimum nighttime indoor temperature increased by 3.1 ℃ on average. The duration of nighttime indoor temperatures greater than 8.0 ℃ accounts for 80.0% in cold January. When the indoor temperature was the minimum, the indoor, north wall, north roof, south roof and ground temperatures increased by 3.4 °C, 2.0 °C, 1.8 °C, 1.0 °C and 1.9 °C, respectively. The indoor temperature could be maintained above 6.0 °C on continuous overcast days. The tomato yield increased by 34%, and the plant morphological parameters were better than those in the control greenhouse. The results of the economic analysis indicated that the SWRS is cost-effective in terms of investment and energy savings.