A model is devised of a substrate heating system for greenhouse crops. The object is to predict the temperature of the substrate and to estimate the energy consumption. The model was validated experimentally in a localized heating installation of the substrate by using an electric cable and applied to a crop of gerbera (Gerbera jamesonii H. Bolus ex Hook) in a greenhouse. Di!erent con"gurations in the design and operating methods for the electric substrate heating were examined over a period of two years.
The temperatures of the substrate were estimated by the model within an average value of 0)473C and the energy consumption associated with the di!erent experimental localized heating con"gurations was predicted within an average deviation from the experimental results of under 7%.
In the experimental installation, the use of thermal insulation and heat accumulators produced energy savings from 14 to 20%. For energy conservation, the best con"guration for localized electric heating systems with heating cables placed in the substrate and buried at a depth of 0)2 m, comprised thermal insulation and heat resistant brick under the substrate as a heat accumulator. The combination of using a heat accumulator plus energy consumption only during the night when electricity is cheaper produced a total cost saving of 27%.