Aperture-based daylight modelling: evaluating the airmass refinement for the sunlight beam index

Aperture-based daylight modelling (ABDM) is a new building simulation paradigm founded on measures of an aperture's 'connectedness' to the sun and the external environment. At the planning level, there currently does not exist anywhere an evaluative schema which is equally applicable to measures of solar energy potential (for PV performance, overheating risk, etc) and measures of sunlight/daylight amenity (for daylight, well-being, connectivity/view, etc). ABDM addresses that shortcoming. This paper describes the latest development of ABDM which is the addition of an airmass factor in the computation of the sunlight beam index (SBI). This enhancement preserves the 'geometrical purity' of ABDM, but now airmass SBI can serve as a reliable proxy for direct sun irradiation totals derived from weather files.