Investigation of applicability of ashrae clear-sky model to Izmir, Turkey

Since the ASHRAE clear-sky model gives maximum radiation level on the surface, this model is used for solar heat load calculation of air conditioning systems and building designs. This study deals with the solar-radiation variation over a horizontal surface calculated by the ASHRAE clear-sky model with measurements for Izmir, Turkey (latitude:39°24' N; longitude: 27° 15', altitude: 30m). In the past, various empirical correlations have been developed in order to estimate the global clear sky solar radiation around the world. In this study, a new correlation is also developed to establish a relationship between hourly global solar radiation and zenith angle. The new model is then compared with ASHRAE clear-sky model through correlations available in the literature in terms of the widely used statistical indicators, namely; the mean bias error (MBE), root mean square error (RMSE) and t-statistic (t-stat) tests. The new model predicts the hourly global clear sky solar radiation values as a function of zenith angle better than other available models for Izmir in Turkey. ©2008 TIBTD Printed in Turkey