Development of a meteorological illuminance model for daylight computations

Building simulation programmes need detailed hour-by-hour weather data. In the absence of measured irradiation and illuminance data, validated meteorological radiation and illuminance models may be used. These models are primarily based on the estimation of solar-beam attenuation through the terrestrial atmosphere. Broadly speaking, there are two strands of such computations. One of these strands is based on sunshine, temperature and humidity data and takes into consideration the attenuation due to mixed gases (such as oxygen, nitrogen and carbon dioxide), water vapour, ozone and aerosols. The other procedure requires cloud-cover data to obtain the degree of attenuation of clear-sky beam irradiance due to clouds. The authors have extended the application of the above models to obtain hourly and sub-hourly values of solar illuminance, via an interface with a luminous efficacy model. An account of the physical basis of the presently-proposed models and their validation is presented herein.©