Solar collectors for pre-heating of air for drying grain and hay in Norway

摘要

A brief analysis of crop drying with ambient air in a temperate humid climate is given as an introduction. The significant increase in drying potential that can be achieved with a slight warming of the air makes up the background for the analysis of solar collectors. The bare plate collector built with corrugated metal sheets is the most widely used collector for pre-heating of air for crop drying in Norway. An analysis of the major variables that determine the collectors performance is made, and an equation that can be used to estimate efficiency is suggested. In order to evaluate the potential of other widely used building materials as solar air collectors, black concrete roof tiles and wooden wall boards have been tested as permeable collectors. Measurements of the performance of solar collectors in several farm buildings have been made. Due to several factors that can be hard to determine with good accuracy, the results from such measurements will always be associated with a high uncertainty. Very often, with the flow rates used in pre-heating of air for crop drying, efficiencies are found in the range 0.4 to 0.6. The extra costs associated with the construction of a solar collector can vary from NOK 20 to NOK 100 per m(sup 2), depending on conditions, material costs and labour costs. If the system is used in a way that it will produce 40 kWh per m(sup 2) and year, the energy price will be less than NOK 0.40 per kWh, with 15% capital costs and depreciation on an investment of NOK 100 per m(sup 2). 92 refs., 80 figs., 13 tabs.