Refurbishment design through cost-optimal methodology: the case study of a social housing in the northern Italy

The theme of the energy retrofit on social housing in Italy is still an unsolved problem, due especially to lack of funds; a solid methodological base to achieve optimal energy levels, considering the best balance with the costs, can be useful to face this emergency and can be replicated in similar cases widely spread in Italy. The European Directive 2010/31/UE establishes a comparative methodology for calculating cost-optimal levels of minimum energy performance requirements for buildings and building elements. The cost-optimal methodology is addressed to the National Authorities in order to give guidelines to compare energy efficiency measures in relation to their energy performance and the relative costs; this methodology is here applied on a social housing building consisting in 30 units located in Pavia, in the northern Italy, in order to demonstrate how this methodology can be used as a supporting decision tool for refurbishment interventions on existing residential buildings, when investments from Public Authorities or privates are involved. The research is developed according to the methodology described by the Guideline that integrates the Directive 2010/31/EU. The building of the case study is defined and characterized through a field investigation aimed at detecting the characteristics of the building related to geometry and morphology, envelope and plant properties, use profile, etc. A series of energy efficiency measures are defined in order to identify different improvement scenarios, related both to the envelope and the technical systems (as an example, opaque envelope insulation, replacement of doors and windows and the heat generator). The energy evaluation is conducted to predict the overall energy consumption for the case study in the hypothesized scenarios while the economic evaluation is performed in accordance with the EN 15459: 2007 to calculate the overall cost in the context of a total renovation, considering the cost of the initial investment, maintenance, eventual replacement, dismantling and residual cost, in a financial perspective. Finally, the optimal cost level for the case study is evaluated through calculations that bring to define the best energy saving measures, corresponding to the group of energy-saving measures that, if implemented, would lead to the best ratio costs / energy benefits. The energy calculation is supported by dynamic simulations, with the aim to provide a better evaluation accuracy of the different energy saving "packages" thought for the refurbishment. The work is expected to be a stimulus for the definition of specific refurbishment plans for the energy efficiency increase of the social housing buildings.