A heating system using flat plate collectors to control the inside greenhouse microclimate in Tunisia

Abstract

The continuous increase in the level of greenhouse gas emissions and the rise in fuel prices are the main driving forces behind the efforts for more effectively utilize various sources of renewable energy. In many parts of the world and specifically in Tunisia, the direct solar radiation is considered to be one of the most promising sources of energy. Annual sunshine can reach 3288 kWh/m2/year be 6 kWh/m2/day. A greenhouse using means active conventional heating consumes 1 litter of fuel/m2/year which leads to 10 kWh/m2/year. Tunisia surface of greenhouse crops is about 1000 hectares this corresponds to 107 l of foil and 108 kWh .In order to reduce the cost of heating the agricultural greenhouse we used the vacuum solar collectors .Their efficiency depends at the same time upon the ambient climatic conditions and the thermal performances of vacuum solar collectors. Capillary polypropylene exchangers are used to attenuate the differences between the diurnal and nocturnal air temperatures under the tunnel greenhouses. Water circulates in these exchangers at hydraulic closed circuit. In this work we have realized an experimental study of a solar energy heating system. Two types of studies have been done. During the day the suspended exchangers recover the energy in excess for the plants comfort. This recovered energy is stored into the greenhouse ground through the buried exchangers the first one concern the functioning temperature of the heating system installed near the greenhouse and used to heat the water stocked in a tank of 300 litters. In the second type, the energy stored in the ground will be restored through the underground exchangers during the night; thermal energy already stored in the tanks is brought back by the suspended exchangers to heat the air greenhouse. In order to prove the efficiency of our system, we present thermal results relative to the effect of the heater system on the greenhouse microclimate and the agronomic results of the greenhouse culture of tomato. These results are very interesting compared to an unheated greenhouse and had a high effect on tomato quality.