Evaluation of solar hay drying and collector efficiency

Two solar collectors were constructed and adapted for hay drying. Instrumentation was adapted to obtain data adequate for collector and drying efficiency. A south facing metal barn roof (3.90 m by 12.19 m) was adapted for solar collection by placing plywood under the rafters, forming 55.88 cm by 10.16 cm ducts. A comparison was made between a black painted and a badly weathered surface. In addition, a 1.52 m by 18.29 m suspended plate collector was constructed so that the heated air was paralleled into the same drying system, so that it could be used with or separated from the roof collector. The open construction drying chamber was sufficient for five 500 kg roll bales. Instrumentation and measurement was provided for temperature, relative humidity, air velocity, system air pressure and solar radiation, along with periodic hay moisture content values. A special lithium chloride, heated electrical hygrometer was designed, constructed and calibrated which was used to determine drying conditions of the air within the large bale. Drying experiments conducted in late fall, 1976, showed that, even under the adverse conditions of very low seasonal temperatures and high relative humidities, the solar collectors increased drying potential of the air adequate for moisture removal from the hay bale. Solar collector efficiencies compared favorably to those obtained by earlier researchers, with efficiencies of 65.5 percent for the suspended-plate collector and 45.4 percent for the roof collector. In addition, an increased efficiency of 5.8 percent was found for the painted roof as compared to the weathered roof.