Life-cycle design and multi-objective optimization of residential building envelope and systems

Abstract

The building sector is undergoing a transition, where the aim is to build energy efficient, cost-optimal and carbon-optimal buildings. One such example in terms of regulation is European performance of buildings directive (EPBD), where EU member states agreed that by the end of 2020 all new buildings are to be nearly zero energy building. Here, the focus is to reduce the operational energy (heating, electricity, cooling etc.) needs of a building, although at the same time there is a rise in energy demand in building elements production and construction phase (i.e, embodied energy). Thereby, the present dissertation argues with the conventional design approach based on only operational energy. This dissertation uses simulation, life cycle analysis and life cycle optimization as methods to design life cycle energy efficient, cost-optimal and carbon-optimal building envelope and services through case studies for residential building in Finland. For building envelope, the life cycle energy balance of different structural alternatives is shown. It is found that energy differences between considered structural concepts are rather visible in the production stage of building and energy benefit from material recycling. Among the considered advanced window technologies, in general vacuum window and in some conditions PV window provide maximum life cycle cost savings for the case study building in Finland. The energy-cost optimization study shows that many of the non-dominated optimal solutions shows higher U-value or, thinner insulation obtained from life cycle optimization compared to conventional operational phase optimization. Moreover, the pareto fronts obtained from life cycle optimization are steeper in nature towards the head, compared to the pareto fronts obtained from operational optimization. In carbon-cost optimization study, the results shows that heating system is a dominant design variable, which results in clearly separated pareto fronts for each systems. The embodied carbon is 39% and 28% of life cycle carbon footprint for a carbon-optimal and cost-optimal solution respectively obtained in the case study. The results obtained from the early building design optimization case study are rather obvious, but it shows the power of multi-objective optimization for aiding early design decisions. Finally, the results of this dissertation can contribute towards the design of life cycle low energy or low carbon cost effective optimized building.