TEMPERATURE GRADIENTS IN A SWEET COLOURED PEPPER COMMERCIAL GRENHOUSES EQUIPPED WITH SOLAR HEATING AND EVAPORATIVE COOLING SYSTEMS

The study presents an experimental investigation of solar heating and evaporative cooling systems for heating and cooling sweet coloured pepper greenhouse during Agriculture season of 2010-2011. The use of solar energy system for greenhouse heating in winter and cold days helps to save fossil fuels and conserve green farm environment on the one hand, and on the other, enhances the quality of greenhouse products, reduces production costs and limits the release of greenhouse gases. To predict the air temperature gradients inside a commercial greenhouse, a simple climate model that incorporates the effect of heating cycle and ventilation rate, is functioned. In order to validate the proposed model, different measurements (included indoor and outdoor air temperatures, air relative humidity, and solar radiation flux incident) were measured and recorded in a computer fill. The commercial greenhouse was equipped with a complete solar heating system (six solar panels, storage tank and heat distributing system) for heating 750 litres of water and evaporative cooling system for ventilating and cooling 851.04 m³ total volume. The daily average overall thermal efficiencies of the solar panels and the storage system during the experimental period, respectively, were 67.51% and 75.46%. Over 181 days heating season the solar heating system provided 37.725 kWh (66.61%) of the daily total heat energy required (56.640 kWh). This percentage could be increased by reducing heat losses from the greenhouse. The measured air temperatures held generally above the predicted one by about 1 to 2ºC, during the experimental period. Due to the microclimatic conditions of the greenhouse were at or around the desired level, the sweet coloured pepper had have optimal vegetative growth rate, stem length, number of fruits being seated, and fresh yield.  The total annual costs per square meter of greenhouse were L.E. 35.722.The fresh yield of sweet coloured pepper was 5.563 kg/m², which sold by L.E. 55.63, consequently, the estimated return on capital was 55.73% per annum.