Simulation and Experiments of Active Greenhouse Heating System
This paper proposed an active greenhouse heating system which focused on the problem of crop growth under extreme cold weather. At the beginning, heat transfer process of heating system was analysed based on thermal equilibrium theory. Radial and axial heat conduction mathematical analysis model of temperature control system were established respectively. Then, numerical simulation of temperature distribution was carried out by means of finite element method (FEM) software. When the effective operation range (later referred to as Qf) was defined with soil temperature more than 15 °C at 20 cm underground, opening temperature of heating system should be no less than 28 °C. Simulation results show that an increase of air inlet temperature by 2 °C could extend axial effective operating range by 2.4 m–2.8 m. Later, field test was implemented in greenhouses which located in Changping district, Beijing. Finally, compared with simulation data, the field testing data shows that the perturbation law of heating system heat transfer process on shallow and deep layer soil temperature is consistent with theoretical analysis. The numerical simulation could help to guide the temperature control of greenhouse.