Building energy performance analysis: A case study

International standards, in particular the Italian one, evaluate buildings energy performance assuming steady-state working conditions: currently, the study of the energy performance of buildings is based on a simplified calculation that estimates the energy demand using monthly or seasonal average outdoor temperatures. For this reason we have conducted a comparative analysis of the energy performances of an old building using a semi-stationary software and a dynamic one. The studied building is placed in the peripheral part of an historical city located in the center of Italy. We have performed three simulations considering transparent elements characterized by progressively improved properties of thermal transmittance and solar gain factor. A comparison between the outputs of the two codes, in order to highlight the different ways of evaluating the energy contributions to annual energy demand, has been performed. Finally, the models were validated by means of an in-situ measurement campaign using a heat flow meter – in order to measure the thermal transmittance of the opaque walls – and a thermographic camera. This modus operandi allowed us to appreciate how the use of a dynamic software is essential to deal with the inertial properties of the structure and to calculate in an accurate way the annual energy demand.