Optimisation of multi-residential building retrofit, cost-optimal and net-zero emission targets

The European Union's (EU) building stock is characterised by low energy efficiency and slow growth rates. To achieve EU's greenhouse gas (GHG) emission targets, doubling building retrofit rates is one of the focuses of the European Green Deal. In this article, a real-world retrofit study was conducted, testing the limits towards carbon neutrality. A multi-objective optimisation process was developed, aiming to minimise the operating GHG emissions and the life-cycle cost. The process was applied to a typical multi-residential building and was tested in the four Greek climate zones. It was found that the cost optimal retrofit agrees with the observed market trends (envelope insulation, double-glazed windows, air-to-air heat pumps (HP) and solar thermal collectors), leading to more than 60% reduction in GHG emissions. A maximum of 87% to 96% reduction was achieved by applying thicker envelope insulation, low-carbon (biomass boiler) or high-efficiency (gas-condensing boiler, air-to-air or air-to-water HPs) heating and cooling systems, photovoltaic-thermal and facade-integrated photovoltaic systems. A net zero GHG emission retrofit could not be achieved within the building premises without considering the future decarbonisation of the electricity grid and the installation of efficient electricity-driven systems. Crown Copyright (c) 2021 Published by Elsevier B.V. All rights reserved.