Environmental and economic implications of energy efficiency in new residential buildings: A multi-criteria selection approach

The choice of the most appropriate technologies in buildings is often a challenge at the design stage, especially when many different criteria are taken into account. Consequently, the decision process relies often on one criterion only, such as costs or energy savings. We propose a multi-criteria approach based on multi-attribute utility theory to assess alternative energy efficiency measures, explicitly considering both environmental and economic criteria. We apply it to the design of a new residential building in Milan (Italy), with the aim to maximize CO2 emission savings related to electricity and gas consumption, and to minimize embodied energy and investment costs. After modelling the building prototype, alternative energy efficiency measures are assessed and ranked according to the selected criteria. The building optimized through the implementation of the best performing measures showed an overall 90% reduction in operational primary energy compared to the baseline building. The inclusion of the embodied energy altered the energy performance calculations resulting in 55-67% reduction in total energy over a 10-year period, and 77-82% over a 30-year period. Results point to the importance of a comprehensive implementation of measures, such as thermal improvements, high efficiency equipment, appliances, and renewable energy generation. The paper demonstrates the feasibility of this framework to support the decision process from a multi-criteria perspective, proposing a flexible method that can be adapted to other building types, environmental conditions, materials and technologies. It also highlights the importance of considering both environmental and economic criteria when designing a new building. It stresses how the embodied energy should be a criterion for technology selection, as current strategies to reduce operational energy often increase the amount of energy embodied into buildings with environmental consequences.