Partially dynamic life cycle assessment of windows indicates potential thermal over-optimization

Abstract

To reach the environmental goals set by EU, Energy Performance of Buildings Directive (EPBD) and national building regulations will demand reductions in building’s energy consumption. Energy consumption goals for buildings are pursued through high thermal performance building components (HTPBC). Paradoxically, building regulations have no requirements regarding the embodied energy of buildings and components. To meet the requirements set by governments, HTPBCs in most cases require an increasing embodied energy (from insulation), assumed to be paid back during the service-life of HTPBCs. Accounting for decarbonization of the future energy supply, the expected payback might not be feasible in terms of total environmental footprint, since the future energy supplies are expected to be greener than the building’s embodied energy. Using roof windows as a case study, we assess if strict demands for building’s energy consumption, will lead to more sustainable buildings if all temporal variations in terms of global warming impacts across the service-life are taken into account. A comparison of double and tripple glazed windows reveals that the expected net energy savings obtained during the use phase are compromised by relatively higher impacts induced in the production stage. The case study indicates requirements of building’s energy performance might compromise the overall sustainability of building component solutions, as the additional embodied energy required to produce triple glazed windows most likely will not be compensated for by saved operational energy, when taking into account the forecasted decarbonatization of the building energy future supply.