Evaluation systems for energy efficiency in historical buildings

The evaluation of energy behaviour of historic buildings is a complex and not yet fully resolved theme, because currently the criteria and the tools available for designers are mainly designed for modern buildings. In ancient buildings, the lack of energy supply plants requires the conscious exploitation of local renewable energy resources and the optimization of the thermal performance of the building envelope. However, the fast change of the user’s comfort requirements, the introduction of new preservation criteria for cultural heritage, the mandatory requirements to reduce GHG emissions and the energy production from renewable sources required a very careful design of building envelope and HVAC system. This paper presents the comparative results of energy evaluation of two historical churches having similar function. The thermal performance are evaluated by means of static (currently used for energy certification in Italy) and dynamic computer simulations. The experimental data serve as verification of the thermo-physical parameters of the building envelope components for carrying out energy performance simulations: energy bills, temperature and relative humidity of air. In particular, the simulations are performed using the thermal transmittance values, actually measured in situ, as suggested in the Italian standard UNI 11300-1:2008 and calculated according to the European standard UNI EN ISO 6946:2008 on several ancient buildings with different wall thicknesses and construction techniques. The present study aims to understand which energy audit schemes, more or less evolved, simulate better the real energy performances of the historic buildings and identify the strengths and the limits of each software for static and dynamic energy simulations. The final goal includes the need of intervening on a “particular” types of heritage to optimize the requirements of energy efficiency and effectiveness together with the preservation of their cultural values. An accurate diagnosis is the first step to identify the suitable intervention. Finally, the evaluation of energy retrofit obtained by dynamic simulation permitted to assess the real energy performance improvement and demonstrate that, in some cases, the conservative interventions have a proven effectiveness