ENERGY MODELLING FOR HEATED CONCRETE FLOORS IN GREENHOUSES

A simple time-dependent model, with one-hour time steps, was used to calculate the energy balance of a simulated greenhouse with a heated concrete floor. Outside climate data and greenhouse parameters (thermal loss coefficient, transmissivity of the cover, setpoint temperatures) were the input values required by the programme. Greenhouse soil, air temperature and the energy supplied were obtained by means of the programme. The experimental greenhouse used (130 m², single layer of methacrylate) had a concrete floor heated from an electric boiler. Electrically driven air heaters were used for comparison.

The experimental results produced a thermal loss coefficient of 10.1 W/m²K for the heated concrete floor and of 15.8 W/m²K for the air heaters, taking the crop temperature as the setpoint (0.5 m height). With the setpoint at 1.5 m, there were no significant differences between both systems (13.7 and 12.6 W/m²°C, respectively). Simulations with the energy model showed that annual energy saving was about 20%, with the setpoint at 0.5 m. This means a cost saving of about $2.5/m² year (2 ECU/m² year). The system showed to be economically feasible in ornamental crops with low canopy. The energy model can predict the energy consumption of a heated concrete floor in any location.