SE--Structure and Environment Temperature Control and Energy Conservation in a Plastic Greenhouse

The existence of computer control systems for environmental management in greenhouses provides the opportunity for better productivity and energy saving. The choice of a proper control algorithm and strategy adjusted to local conditions and requirements is also a matter of great importance. In this study, a model for environmental control in greenhouses suitable for Mediterranean conditions was developed. This model was based on a temperature control algorithm adapted to local needs and climatic conditions with the appropriate modifications. It was tested for its efficiency in a plastic greenhouse cultivated with gerbera. The algorithm allowed indoor temperatures to cycle in phase with the external temperature by means of a solar clock instead of a computer clock. Besides, the desired temperature was modulated as a function of global radiation. Hourly and daily corrections maintained the short and long term temperature averages within the desired levels. Furthermore, stable, weather related night set points, combined with higher daily temperature regimes, could reduce greenhouse heat losses and meet the physiological requirements for growth and development of the plants. The control algorithm was found effective in applying control strategies for optimum energy saving: A 16% energy saving was achieved without any reduction of the yield during two consecutive growing years, by using an elevated nightly temperature set point during cold and windy weather and a reduced one during warmer and calm conditions.