Predicting the energy consumption of heated plastic greenhouses in south-eastern Spain

Measurements of heat consumption in a parral type greenhouse, equipped with an air-heating system, were carried out in south-eastern Spain (Almería) during the 1998/99 winter. From the daily values of heat consumption (Qd, MJ m d) recorded in five identical greenhouses heated to different night temperature set-points (Tc), and data of minimum outside air temperature (Te,min), relationships between Qd and the temperature difference (∆Tmin = Tc – Te,min) were established. Linear regressions between Qd and ∆Tmin gave satisfactory fits (R ranging from 0.75 to 0.83), considering that Te,min was the only input data for the model. When all data were pooled, the correlation was curvilinear, the best fit to a 2 order polynomial being Qd = 0.049 ∆Tmin – 0.001 ∆Tmin + 1.107 (R = 0.89). Validation of this model was performed using data obtained during other years, giving a fair agreement at the daily (R = 0.86), 10-day (R = 0.95) and yearly (R = 0.99) time scales. This simple model could be of interest to growers for decision-making related to the choice of set-point temperature and crop planning in heated greenhouses. Additional key words: air heating, energy use model, Phaseolus vulgaris, temperature.