MIRROR ENCLOSURES FOR DOUBLE-EXPOSURE SOLAR COLLECTORS

A conventional flat-plate collector panel can be employed in a double-exposure configuration when the panel is glazed on both sides and when mirrors are provided to reflect solar radiation onto the back side of the panel. In this paper, several flat-mirror configurations are evaluated and optimal configurations are determined for different solar energy applications at lat. 35, 40 and 45°. The various mirror configurations are evaluated theoretically by calculating direct-beam and diffuse solar radiation enhancement factors. The enhancement factors are defined as the ratio of the solar flux absorbed by both sides of a double-exposure panel to that absorbed by an identical single-exposure panel tilted at the latitude angle from the horizontal. The enhancement factors are calculated using the method of images and take account of the variation of glazing transmittance with incident angle. Optimal mirror configurations were determined for direct-beam solar radiation for both fixed-mirror configurations and adjustable-mirror configurations with semi-annual mirror rotations. Optimal fixed-mirror configurations were obtained for both winter space-heating and year-round applications. An adjustable-mirror configuration, however, was determined to be optimal for year-round solar collection and overall to be most adaptable to a variety of solar energy applications. The same adjustable-mirror configuration was determined to be optimal at all three latitudes and therefore a single design can be employed at diverse locations. © 1979.