Solar air preheaters

Four different simple low cost solar air preheaters have been investigated. Experimental tests and analytical models indicated that this type of collector has an efficiency which is very sensitive to the air coolant flow rate, solar irradiation and its distribution, ambient temperature and wind speed over the collector. Variations in efficiency due to changes in these terms are so large that it is somewhat misleading to present the performance of such collectors by a single efficiency curve. The glazing material and absorber plate radiation properties could play an important role in determining the useful heat output, especially if selective surfaces are used, however, cost considerations will usually mean that low cost construction materials will be used on applications such as building ventilation systems or agricultural crop drying.