Evaluation of a hybrid photo-radiometer sky model compared with the Perez sky model

Abstract

Daylight simulation results greatly rely on the accuracy of sky models. When generic CIE sky and Perez all-weather sky simulate daylighting scenes they simplify cloud distributions. The lack of cloud distributions and subtle luminance variations causes simulation result deviations. High Dynamic Range (HDR) image techniques provide a method of generating accurate and actual skies. This paper explores the accuracy of a horizontal hybrid phadiometer (HPR) sky model, which combines modeled physical descriptions of the sun and HDR sky images. The aim was to build on and enrich the findings of a previous study (Humann and McNeil, 2017).In this study, the HDR images within four office spaces were taken. Simultaneously, global horizontal illuminance and HDR sky images were recorded outside. Simulated luminance maps were generated under both the HPR and Perez skies. Daylight Glare Probability and vertical eye illuminance (Ev) were calculated from 112 groups of luminance maps. The simulated Ev under HPR and Perez skies presented relative RMSE of 21.3% and 23.7%, respectively. The frequencies of accurate glare prediction under HPR and Perez skies were 95.5% and 93.9%, respectively. The results indicated that both the horizontal HPR sky and the Perez sky simulate equally accurate luminance maps.