干旱区生态环境知识资源中心

The aim of this work is to analyze the thermal performance of a greenhouse exposed to semi-arid conditions by investigating experimentally the heat transfers occurring through the walls and ground. A closed unheated Venlo greenhouse without crop in the area of Batna (southern Mediterranean basin) was considered. The study focuses on the effects of (i) the thermal inertia of the soil, (ii) the radiative losses through the cover, and (iii) the convection mode and flow regime on the heat transfer coefficients. Experiments were conducted from January to March 2008 under clear or cloudy skies, and low or high wind velocities. From the results, it is concluded that the heat stored in the ground of the greenhouse represents a significant heat source which can compensate the energy losses through the walls, especially during a night preceded by a high diurnal insulation. This process can maintain an average inside - outside temperature difference during the night within the range [1.59-2.81] K. Results also show that the radiation losses are the main component of the energy losses of the greenhouse, mainly through the outside wall surface of the cover. Conversely, the radiative heat exchange along the inner wall represents the main heat supply to this wall. The convection mode inside the greenhouse induced by the air movement seems to play a significant role on the convective exchange coefficient inside the greenhouse. These coefficients both inside and outside the greenhouse were estimated and analyzed, and a good agreement with the models reported in the literature was found. This study could help growers define and adapt their heating strategy to avoid undesired low temperatures which may damage their crops at night.