Application of Perez Daylight Efficacy Model for Kolkata

The availability of daylight on any plane of a building and the passive heat gain due to the corresponding incident solar radiation is correlated by daylight luminous efficacy. The present study was carried out to evaluate daylight efficacy on exterior horizontal plane for Kolkata using Perez Model an established analytical model and Indian measured solar radiation database. The analytical model was selected according to the sky conditions throughout the year. The estimated efficacy models were used to predict horizontal global and diffuse illuminances. The predicted global and diffuse illuminance was validated with the measured illuminance values using standard statistical tools. The estimated Root Mean Square Deviation (RMSD) and Mean Bias Deviation (MBD) between experimental and simulated values of illuminance are +7 % and ±4.5 % respectively. An analytical model of luminous efficacy for Kolkata was also developed from the measured values. From the study, it has been found that diffuse luminous efficacy varies from 114–138 lm/W whereas global luminous efficacy varies from 98–112 lm/W in a year. It is also observed that sky clearness index and diffuse irradiance ratio have significant effect on the variations of luminous efficacy in different seasons. © 2014, The Institution of Engineers (India).