Investigation of Retrofit Solutions of Window-Wall Assembly Based on FMEA, Energy Performance and Indoor Environment

Multi-storey buildings built before the 1960s have a large energy saving potential. The windows and facades are the two components with largest saving potentials. Many buildings from the period before the 1960s have windows and facades worth preserving from an architectural point of view and therefore outside insulation is not possible. Development of new retrofit solutions should be longlasting and not cause collateral damage to the existing structures. This paper describes a rational optimisation approach for analysing retrofit solutions based on durability, energy savings and indoor environment. The failure mode and effect analysis is used for assessing the durability. The energy saving is calculated as the heat loss through the structure. Daylight simulations are performed to evaluate the indoor environment. In the paper a window with a secondary glazing and a box window, both with internal insulated walls, are investigated. The thermal result shows that a box window has the lowest heat loss and heat loss transmittance. The daylight for the two window-wall assemblies performs equally, but worse than the existing window-wall assembly. The durability of the assemblies is most critical to moisture from the inside. The box window has the lowest temperatures on the cavity surface and is therefore more vulnerable toward condensation. The basis of the rational optimisation approach is the total economy considering the initial, operational and maintenance costs over the lifetime of the building. The maintenance costs can be found from the durability assessment as the indoor environment and energy calculations cover the operational costs. These investigations are needed to analysis the retrofit solution.