Decision matrix methodology for retrofitting techniques of existing buildings

Abstract The building sector is the highest energy consumer (38.1%) in the European Union. This consumption has to be reduced in both new and existing buildings. Respect to the existing ones, they need an effective energy renovation as the current European Directives reflect. Specifically, according to these Directives, all countries have had to retrofit 3% of their public buildings per year since 2014. There are dozens of retrofitting measures that can be applied to each building, and selecting the most appropriate ones is not an easy task. In this paper, a decision matrix is proposed as a tool to identify the most appropriate retrofit measures of an existing building. This decision matrix is calculated using dynamic simulation tools. Furthermore, a sensitivity analysis is carried out and the energy deviations produced modifying the input variables are quantified. The outputs obtained by this decision matrix are the building loads of each retrofit measure and the associated cost. After obtaining this decision matrix, a multi-variable optimization has been made considering different cost functions. This methodology has been applied to an educational building at Oviedo University, located in Gijon (Spain). According to the climate classification of Gijon, the Spanish normative and the building layout, three upgrading measures have been studied: addition of insulation on the envelope, windows renovation and shading devices. It has been observed that the influence of the cost function selected is relevant, and for the educational building, the case with the best glazing but only intermediate facade insulation is the best retrofitting choice according to the majority of cost functions compared.