ABSTRACT
Over the last years a big effort has been carried out, mostly within national and international standardization committees, in order to set up common simplified calculation methods to be used by the professionals for the design and evaluation of thermal performance of buildings. Each method has its validity conditions and its simplifying assumptions, concerning thermal modeling of physical phenomena, or the definition of fixed values and special boundary conditions. Both research work and field application show that some aspects are modeled with excessive detail if compared with the uncertainty of some factors, such as thermal properties of materials, climatic conditions, occupancy and ventilation profiles. In this paper, starting from an overview on the latest European standards, different common simplifying hypotheses are analyzed and classified. Using a simple case study, the effect of different assumptions is investigated by means of numerical simulation. The errors produced by different assumptions are then compared with the effects of stochastic input data.
