Energy retrofit alternatives and cost-optimal analysis for large public housing stocks

The study of cost effective solutions for the energy retrofitting of existing buildings is of capital importance for building asset owners, since high up-front investments are required and long payback times are encountered in building renovation projects. The aim of the work is to propose a decision support system (DSS) for the assessment of different renovation strategies through the measure of their economic sustainability in relation to the achieved energy efficiency. The cost optimal analysis of energy retrofit alternatives is performed in the case of a large housing stock owned by a semi-public real estate company, with the goal of meeting nearly zero energy building standards. Energy performances as well as related energy and construction costs are analysed for different retrofit options, adopting Italian laws and regulations. The proposed DSS evaluates the economic sustainability of various design alternatives with the net present value (NPV) and the global cost (GC), as suggested by the EPBD recast EU directive. These indicators are finally compared with the building energy performance index (EP), providing the most efficient design alternatives for each building typology and the most advantageous renovation project among the considered ones.