Modelling and optimal design of an electric substrate heating system for greenhouse crops

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 h eating 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. Different configurations in the design and operating methods for the elect ric substrate heating were examined over a period of two years. The temperatures of the substrate were estimated by the model within an ave rage value of 0.47 degrees C and the energy consumption associated with the different experimental localized heating configurations was predicted with in an average deviation from the experimental results of under 7%. In the experimental installation, the use of thermal insulation and heat ac cumulators produced energy savings from 14 to 20%. For energy conservation, the best configuration for localized electric heating systems with heating cables placed in the substrate and buried at a depth of 0.2 m, comprised t hermal insulation and heat resistant brick under the substrate as a heat ac cumulator. The combination of using a heat accumulator plus energy consumpt ion only during the night when electricity is cheaper produced a total cost saving of 27%, (C) 1999 Silsoe Research Institute.