Research on a One-Dimensional Unsteady Energy Transfer Model for Greenhouse Soil: Acquisition Considering Initial and Boundary Conditions

Abstract

Soil temperature (ST) is one of the most crucial factors influencing crop growth and greenhouse thermal environments. In order to accurately predict ST, this study has established a one-dimensional unsteady energy transfer model (OUETM) for greenhouse soil. This model can be used to predict ST at depths from 0.02m to 1.0m. To address the difficulty of obtaining boundary conditions, the top boundary is set as the first type of boundary condition, and is measured by an ST sensor. Two solutions (1.05m and 10.15m below ground) are proposed for the location of the bottom boundary. The energy flux density at the bottom boundary is set to zero. The accuracy verification test shows that the maximum values of mean absolute error and mean absolute percentage error between measured and calculated ST were 1.13℃ and 4.49%, respectively. To obtain initial values without sensors, this study proposes an initial value condition acquisition scheme that exploits the correction effect of real-time boundary conditions and OUETM, allowing ST to approach real value over time. The average prediction deviation between measured and calculated initial values was 0.94℃. In conclusion, OUETM is a highly accurate tool for predicting greenhouse soil temperature. With the initial value and boundary condition acquisition methods, OUETM can obtain ST at different depths using only the ground surface temperature as input. This is a more practical method, but it can also be applied to the greenhouse energy management and the use of geothermal energy in creating a more sustainable future.

Keywords: Greenhouse, soil temperature, One-dimensional unsteady energy transfer model, Boundary condition, Initial value condition