A multi-objective evaluation for envelope refurbishments with electrochromic glazing

The main aim of this paper is a multi-objective evaluation of electrochromic (EC) glazing with consideration of operational and embodied energy including the impact of switchable glazing on visual and thermal comfort. Different criteria were evaluated for the refurbishment of a prototypical 30 m2 office room in Mannheim, Germany. The room prototype was assumed as lightweight and heavyweight construction, where refurbishment strategies such as the addition of thermal insulation and the exchange of windows were investigated. For the window exchange, EC-glazing was compared to a high-performance glazing with solar coating. The EC-glazing was automated via a rule-based (incident radiation) and a penalty-based (multi-objective prediction) control strategy. Regarding operational energy, the EC-glazing performed slightly better than the glazing with solar coating. However, the results showed that the high amount of embodied energy in EC-glazings could not be justified by the rather small savings of the operational energy. On the other hand, with the penalty-based control, the EC-glazing improved visual comfort significantly in comparison to the static glazing with solar coating. The decision to replace the original glazing with an EC-glazing as opposed to a glazing with solar coating would have to be based on the improvement of occupants’ comfort, due to an unjustifiable increase of embodied energy and marginal savings of operational energy.