Livelli ottimali di costo per involucri ad alta efficienza energetica

In the last decade, the increasing demand for energy efficient buildings has led the stakeholders to look for technological solutions at the highest level, often with high investment costs. The EPBD recast 2010/31/EU on energy efficiency in buildings for the first time emphasizes the need to make design choices taking into account the cost-benefit assessment during the estimated life cycle of buildings. In this perspective, the “optimal” energy efficiency solution is not the one that achieves the best energy performance ever, because this may involve a higher initial investment cost, non-depreciable during the life cycle of the building. The “optimal” solution is rather the point of balance between investment and depreciation, estimated considering all the cost elements that come into play during the life cycle of the building. The Directive then addresses the stakeholders to choose “balanced” technologies, not necessarily the most efficient. However, the application of the calculation method is quite elaborate and requires a precise definition of all the variables involved: the cost of each building component that influences the energy performance; financial parameters; times of maintenance and replacement of components, time of service life of the building, etc. Consequently, there is a possible risk that the uncertainty in the evaluation of these parameters is so influential to make difficult to identify the “optimal” energy efficiency solution in terms of cost-benefit analysis. The present paper shows the first results of a research on the evaluation of the influence of the uncertainty of the input variables on the results of a cost-benefit evaluation of design choices related to the building envelope. The evaluation was performed on 25 alternatives wall solutions, showing primarily as not necessarily the ones with the lower thermal transmittance are the most convenient, considering the entire life cycle of the building. Indeed, these are characterized by higher costs during construction (investment costs) that are not offset by a reduction in operating costs (energy consumptions). Then applied the Monte Carlo statistical method, by assigning to the variables involved oscillating values within predefined intervals, we obtained that, when considering the possible variability of these quantities, it becomes very difficult for any designer to assess unambiguously the optimal solution in terms of cost-benefit analysis.