Inconsistencies are shown to exist in the presentation and formulation of the ASHRAE solar radiation model. To remove them, it is proposed:

1. to include in the Fundamentals Handbook the clearness number in the expressions for the direct and, in particular, the sky diffuse irradiation under cloudless conditions, and
2. to rewrite the expressions for cloudy sky conditions so that they reduce to the cloudless formulation when the cloud cover is zero and they do not give rise to negative values o£ the sky diffuse irradiation as is presently the case under certain conditions.

Units: SI