Enhancement of ground radiation in greenhouses by reflection of direct sunlight
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Substantial gains in greenhouse ground illumination/irradiance were obtained with a reflecting wall that was positioned so as to reflect the incoming sunlight from the northern face of the greenhouse to its ground. The effect was particularly significant in winter when the sun was low throughout the day and most of the radiation passed through the greenhouse so that its ground radiant power was reduced. Four types of greenhouse with reflecting walls exhibiting increasing efficiencies of insolation were developed. A theory describing a several-fold enhancement of ground irradiance and radiant energy was developed. Effects of sky (diffuse) radiation on clear and cloudy days were also considered. An experimental model, as well as a full-scale greenhouse with a reflecting wall with provision for measuring ground illumination was constructed and exposed to the sun: Actual measurements were conducted over several days, supporting the theoretical calculations.