Net lifecycle operational and embodied energy associated with window replacement and maintenance: A case study of an institutional building in Ireland

Maintenance strategies that sustain low energy use need to consider both the operational and embodied energy associated with refurbishment decisions. This study investigates window replacement in a representative highly-glazed building in Ireland. Thermal imaging, in-situ U-value sensors, and smart meters were deployed to evaluate façade heat losses and envelope efficiency, followed by the development of a calibrated building energy simulation model. Three scenarios for window replacement were considered: periodic maintenance only, replacement with maintenance, and replacement without maintenance. The cost of net lifecycle operational and embodied energy was calculated for each of these scenarios over a 60-year reference period assuming differing rates of U-value degradation. The results show that window replacement combined with scheduled maintenance achieves up to a 46% reduction in heating energy and nearly halves the lifecycle heating cost compared with only scheduled maintenance. In this case study, the illustrative embodied energy assessment showed approximate values of 42, 372, and 660 kWh/m² of floor area for the three scenarios, indicating the balance of upfront material impacts when compared with long-term operational savings.