Measurement of apparent solar constant and apparent extinction coefficient at Edmonton (Alberta) Canada

Abstract

The annual variation at Edmonton, Alberta, Canada (latitude 53° 34′N, longitude 113° 31′W), of the apparent solar insolation at air mass zero I ∗ , the apparent extinction coefficient a ∗ , and the ratio B of the sky-scattered insolation on a horizontal surface (i.e. diffuse radiation) to the direct normal insolation, were calculated using the equations I dn = I ∗ exp( −a ∗ sinα) and ( I hor I dn ) = sinα+B . The range of I ∗ was 325–375 B.t.u. ft −2 hr −1, the range for a ∗ was 0·075–0·23, and a variation from 0·05 to 0·12 was found for B. Periodic curves were determined and the results compared with the values published by ASHRAE. In general, there was agreement between the values for a ∗ and B. But considerable disagreement resulted for I ∗ , with the measurements giving low values during the months of November to January instead of the anticipated higher values quoted in ASHRAE.