Operational and embodied energy analysis of 8 single-occupant dwellings retrofit to nZEB standard

In line with the Energy Performance of Buildings Directive, Irish dwellings are being retrofit to near Zero Energy Building (nZEB) standards - with a number of the deep energy retrofits classified as A-rated. As a result of the low operational energy, the embodied energy share of an nZEB's life cycle energy is significantly increased. Therefore, to obtain a holistic picture of the change in energy profile of buildings, the embodied energy of the material added to achieve that low performance should also be taken into account. This paper presents results from a case study of 8 single-occupant terrace bungalows retrofit to nZEB standard. The pre- and post-retrofit operational performance is first estimated using the Irish Dwelling Energy Assessment Procedure (DEAP). The post-retrofit operational performance of the space heating and domestic hot water heating system is also measured over a year. The embodied energy is estimated by way of embodied carbon/energy calculations. Monitored results of the 8 similar buildings exhibit a wide variance of operational energy consumption while the embodied energy is (by nature of the calculation) consistent. The average estimated primary energy requirement for the buildings was 674 kWh/(m2ᐧyear) pre-retrofit and 38 kWh/(m2ᐧyear) post-retrofit while the average measured primary energy requirement for space heating and hot water alone was 119 kWh/(m2ᐧyear) – ranging from 74 to 167 kWh/(m2ᐧyear) for the 8 houses. The embodied energy of the materials and technologies used to retrofit the buildings was 676 kWh/m2. Despite the building performing worse than expected, desirable primary energy and carbon paybacks of 2.0 and 6.1 years were achieved respectively. These positive payback periods are largely due to the very poor operational performance of the buildings pre-retrofit.