Analysis of overheating risk in Passivhaus dwellings during warm season and the night natural ventilation strategies to mitigate it

Resumen

During the last decade, energy consumption in the European Union related to buildings accounts for 40% of the total consumption. In consequence, some strategies and goals have been set up to reduce it, mainly with 2020, 2030 and 2050 targets. In order to achieve them, one of the main instruments have been the Energy Performance of Building Directive that promotes Nearly Zero Energy Building (nZEB) constructions. According to this directive, many strategies have been adopted in order to reduce energy demand. A certificate that has been popular it´s the Passivhaus Certificate, creating extremely low-energy demand consumption and airtight buildings. Different norms define the limit of indoor comfort for these constructions (ISO 7730, ASHRAE 55-1992, EN 15251, CIBSE Guide A, CIBSE TM52, CIBSE TM59 and Passivhaus standards). They will be taken into account in this study. As a result of the actual climate change predictions towards a warmer world, multiple studies have focused on the exploration of the actual overheating risk in this type of buildings, especially in multifamily dwellings. They recommend strategies to mitigate it as, for example, solar protection, low insolation materials thickness (roof and wall), hybrid or natural ventilation, passive and low-energy solutions during cooling and intermediate period, active solutions along the heating season, verification of occupancy, shape, activity and orientation, etc. As shown in previous studies, night ventilation has a positive contribution to the cooling effect of indoor spaces during the warm period, reducing daytime ventilation. Nevertheless, its efficiency is strongly related to three parameters: temperature difference indoor-outdoor, air flow rate and thermal capacity of the building. The study will be focus on applying night natural ventilation measures in order to provide the best solutions to the case study, a high-rise residential building in Bolueta, Bilbao, which has already a Passivhaus certificate. It will be carried out with different simulations and calculations with the help of software as Design-Builder and Computational Fluid Dynamics simulations. Comparing the different solutions and taken the best combination of them and adding other measures, a shading measure, in order to mitigate the overheating risk during warm season.