Abstract
The Italian law sets minimum performance requirements for the building envelope in order to limit the summer energy need. Since the cooling demand is strongly affected by the external climate conditions, a collection of weather data representative of the climate features of the site (i.e. a test reference year) is needed to perform realistic dynamic simulations. Usually, the test reference years are known only for the main cities. Unfortunately, due to the orography, especially in northern Italy, and to the particular shape of the Italian cities, a considerable part of buildings belongs to areas with climate conditions differing from those of the main cities. Consequently, even if in principle it is possible to adjust data trends to account for the differences, such data will always be affected by uncertainties. Furthermore, weather data have an intrinsic uncertainty caused by the sensitivity and accuracy of instruments and the particular measurements conditions. In this paper, the influence of several parameters on the energy performance and the reliability of a quasi steady state approach for the prediction of cooling loads are analyzed. In particular, the sensitivity of the energy performance of the envelope (EPe,inv) to weather data, both for light and massive buildings, is investigated. In this sensitivity analysis, the real trends and periodic variation of the main external weather variables, such as dry bulb temperature and solar radiation, are used. Several simulations with different levels of mean value and amplitude of each external forcing factor and various combinations of weather variables are performed, in order to study the influence of each parameter. From these results, some considerations are presented on the reliability of the quasi steady methods applied to energy need calculations for the summer season, in particular in Mediterranean region.