Operational tool for selecting energy systems for small buildings based on useful energy needs

The European Union is constantly improving the energy performance of buildings directive (EPBD), one of its main objectives being to offer a methodological framework that allows identifying the cost-optimal of energy conservation measures, now with a very strong focus on retrofitting. The share of new buildings is very low, from 1 to 2% of the built stock, and it has become clear that the low renewal rate can jeopardize the assumed goals of reducing energy consumption and, consequently, mitigating the climate changes. There are countless barriers to the energy retrofitting of buildings with an eco-efficiency approach, highlighting the lack of clarity in the strategy of policy makers at national level, complicated regulations of minimum requirements for intervention in the building envelope and renovation of energy systems, lack of information for building owners, corroborated by low quality energy performance certificates and need of simple decision-making support tools. The complexity of analysing scenarios of possible interventions comes from the fact that the economic and environmental impact of a specific measure is influenced by other measures of the same package, which affect the cost optimality. For this reason, the best intervention option may not be a simple combination of individual retrofitting measures. Faced with this complexity, building owners are limited to replacing energy systems at the end of their life cycle. This work proposes an operational tool for selecting energy systems for small buildings based on useful energy needs for domestic hot water preparation, space heating and cooling. Few input parameters are required: energy needs and costs, primary energy and greenhouse gas conversion factors, initial investment, efficiency and embodied impact of energy systems. The methodology applied in this article is aligned with an eco-efficiency approach for the pre-selection of energy systems, integrating cost optimality and life cycle assessment to support decision-making on energy conservation measures. In order to demonstrate its applicability also in the pre-study of the competitiveness of new technologies, an example of an innovative heat pump is presented, in comparison with conventional energy systems in the Portuguese market, to meet useful energy needs in the consumption range of dwellings.