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.