Use of solar energy for the agricultural greenhouses autonomous conditioning

Abstract

Capillary polypropylene exchangers are used to attenuate the differences between the diurnal and nocturnal air temperatures under the tunnel greenhouses. The climate conditioning system tested is composed of exchangers buried into a greenhouse and others suspended in its internal air. Water circulates in these exchangers in a hydraulic closed circuit. During the day, the suspended exchangers recover the energy in excess for the plant comfort. This recovered energy is stored into the greenhouse ground through the buried exchangers. During the night, thermal energy already stored is brought back by the suspended exchangers to heat the air in the greenhouse. A theoretical approach was elaborated to size thermal energy storage and restore system. The necessary exchange surfaces for the greenhouse conditioning depend on the required values of diurnal and nocturnal temperatures. The autonomous greenhouse conditioning was possible only for low temperatures. Temperatures of 20°C in the day and 12°C at night were reached in winter. More favorable temperatures for the plant growth of 25°C during the day and 18°C at night were reached during the other months. This conditioning system allowed a heat quantity extraction of 150 W.m −2/d. This energy quantity is sufficient to provide the needs of the tunnel greenhouse with polyethylene covers that is very common in Tunisia. The system cost is appropriate for agricultural applications. In addition, a surface quality and a constituting matter of this exchanger prevent the tartar formation and therefore its obstruction.