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The suitable design is the most important key to a cost-effective solar air heater. Although, there are many techniques that have been proposed to improve the solar air heaters' performance by means of different turbulence promoters, they cannot ensure a compromise between the cost and the effectiveness. The aim of this study is to find simple and tolerable solution to get rid of the inconvenience resulting from the widely adopted heat transfer enhancement techniques by providing an optimized solar air heater design. The proposed design consists of a slightly curved smooth flow channel with an absorber plate of convex shape. A prototype of a curved solar air heater of 1.28 m 2 collector area was built and tested under summer outdoor conditions in Biskra (Algeria). The performance was evaluated in terms of thermal and effective efficiency for mass flow rates of 0.0172, 0.029 and 0.0472 kg/sm 2 . It is observed that the overall efficiency of this solar air heater is considerably higher in comparison with the efficiency range of the conventional smooth flat plate heaters reported in the literature for similar operating conditions.

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Abstract. Geothermal energy uses an air ground exchanger to cool buildings with minimum of energy. The outlet air coming from this exchanger can be directly used for space cooling if its temperature is low enough. In this study we try to evaluate the profile of ground temperature to decide of the depth to bury the exchanger. Through modeling and experimentation, we try to evaluate the performance of a horizontal pipe used for cooling, for this finite differential method which consists on dividing the length of the exchanger on multiple equal segments and by the knowledge of initial and boundary conditions the profile of the air temperature is that carry out. The authors conclude that many parameters influence the performance of earth to air exchanger such as the nature of the ground, the ground depth diameter of the duct and the throughput flow.