Comparing climate based daylight modelling with daylight factor assessment - implications for architects

This paper investigates two different daylight metrics, the commonly used daylight factor (DF) and the new IES approved climate based daylight modelling method (CBDM) IES LM-83-12 in comparison, with regards to their impact on the overall energy demand for heating, cooling and lighting as well as the optimum resulting window size. The assessment has been performed for a typical cellular office room in the climate of Athens, Greece. Different window to floor areas have been compared and the variations have been tested with and without an external overhang for North and South orientation and with an internal roller blind for the assessment of the Spatial Daylight Autonomy. The daylight factor (DF) assessment gives satisfactory results for almost all configurations. The IES LM-83-12 metric requires two criteria to be met, the Spatial Daylight Autonomy (sDA) and the Annual Sunlight Exposure (ASE). While the requirements for Spatial Daylight Autonomy are met for most configurations, the requirements for the Annual Sunlight Exposure are only met on the North façade.