Abstract
Designing buildings retrofit is not an easy task because a wide selection of energy-efficiency measures are technically available on the market, each of which can be applied to a different extent. In a range of different levels, from policy makers to energy service companies, owners, or conductors, there is a need to find the way to plan interventions, depending on the economic resources available and on some additional performance requisites, such as comfort levels, environmental impact, and so on. This means that some guidance is necessary to decide which would be the most effective combination of retrofit solutions among different packages. In other words, the final goal of a retrofit design is typically the optimization of a set of different aspects, not only the minimization of energy needs, with the consequent reduction of CO2 emissions, but also the maximization of the economic efficiency, dealing with either subsidies or proper investments, depending on the specific perspective, the preservation or improvement of the indoor environmental quality, and ultimately the long term sustainability of the intervention.On the one hand, most of these goals have a competing nature and optimizing just one of them could compromise the achievement of the others. On the other hand, the analysis of all the possible alternatives of interventions requires the application of techniques able to investigate the entire size of the problem, without excluding some of the possibilities, and to find a trade-off among the objectives, at the same time. The research of the attainment of multiple objectives by means of the exploration of all the possible solutions can be solved applying some mathematical techniques known as multicriteria or multiobjective optimization analysis. In this chapter an overview of different methodologies to deal with multiobjective projects and methods to assist and to define the retrofit interventions is described. The techniques are there, but only research institutions really have demonstrated the capability to implement them. There's not a lack of algorithms for building retrofit or management, but there is still a lack of dedicated software tools, specifically developed for guiding retrofit decisions and using the most promising algorithms, user-friendly enough to support the designer and decision-maker in defining the best alternatives to be considered. For larger applications, on the other hand, practitioners and energy service companies can find useful support in new entrepreneurship initiatives and start-ups focused on providing calculation and optimization services, with an in-depth knowledge of building physics, economics and finance, and fiscal aspects. High initial investments and entering barriers, both cultural and technical, are overcome thanks to an externalization strategy that can justify the settlement of new companies.