Estimation of Daylight Availability and Illuminance on Vertical South Facing Surfaces in Tehran

To effectively design daylight in buildings, daylight availability data are necessary. Although there is a great potential of daylight energy in Iran, its use is hindered by absence of measured data. In this paper the illuminance data on vertical south facing surfaces of Tehran were estimated using IESNA model. For this propose an illuminance measuring set was used for measuring vertical illuminances for standard times over 20 days at one minute intervals from 9 a.m. to 4 p.m. Then the measured data were compared with IESNA model calculated data. A regression model between measured and calculated data was developed which showed an acceptable linear correlation (r2=0.9535). Also mean hourly and monthly vertical illuminance was obtained from the new equation between measured and calculated data for a whole working year. To estimate daylight availability, frequency curves for vertical illuminance on south facing surfaces were created.