Unglazed Transpired Solar Collectors: Heat Loss Theory

[+] Author and Article Information
C. F. Kutscher, C. B. Christensen, G. M. Barker

National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401

J. Sol. Energy Eng 115(3), 182-188 (Aug 01, 1993) (7 pages) doi:10.1115/1.2930047 History: Received July 01, 1992; Revised March 16, 1993; Online June 06, 2008


Unglazed transpired solar collectors offer a potentially low cost, high-efficiency option for once-through applications such as preheating air for ventilation, crop drying, and desiccant regeneration. This paper examines the major heat loss mechanisms associated with this concept. Radiation heat loss is determined by considering losses to both the sky and the ground. Convective heat losses are obtained by integrating the product of the temperature and velocity profiles in the boundary layer at the downwind edge of the collector. This convective heat loss is then expressed in terms of the thermal equivalent length of irradiated absorber, and analysis shows that this loss can be very low for large collectors even under windy conditions. These results are incorporated into a simple computer model which predicts collector efficiency as a function of suction velocity, wind speed, ambient temperature, and radiation. Remaining research issues are discussed.

Copyright © 1993 by The American Society of Mechanical Engineers
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