3. Implications of the Assumptions in Assessing Building Thermal Balance

The assessment of building energy performance in Europe is widely based on standards that usually refer to the simplified method provided for by EN ISO 13790 (2008). In this simplified method, the estimation of heat transfer is steady-state based, and the building energy balance takes into account the behaviour of the building when interacting with the unsteady parameters by introducing a corrector factor related to the thermal mass effect (i.e. utilization factor). Nevertheless, this method, called “quasi-steady-state”, is often unreliable compared to the results provided by a detailed dynamic simulation, in particular concerning the assessment of the thermal need in warmer climates. This chapter highlights this critical point through case studies applications. Additionally, since the common goal of the building energy assessment is to depict a building with an average usage pattern, the implications concerning the assumptions of the main input parameters to be adopted in the building heat balance assessment are also investigated, showing their very high importance in influencing the final climatization need.