Computation of IR sky temperature and comparison with surface temperature

The effects of atmospheric IR radiation must be accounted for in energy budget computations of solar collectors. IR radiation is often parameterized by determining an equivalent sky temperature dependent on surface temperature. Hourly values of IR radiation were computed at eleven stations in the United States in 1971 and 1972 and the equivalent sky temperature obtained. The model used for these computations was verified by comparison with special observations in the Lake Ontario region taken during the International Field Year of the Great Lakes (IFYGL) in 1972. Differences between surface temperature and sky temperature ranged between 5 and 20°C and are a complex function of season (specifically of cloudiness, humidity, and surface temperature) and geographical location.