Retrofit ready : redefining energy and carbon life cycle methods

Abstract

Retrofits are a necessity for reducing the UK’s energy demand and carbon emissions. However, with 26 million homes to treat and massive implications for material consumption, life cycle energy and carbon impacts demand close attention; this refers to the operating impacts, as well as the embodied impacts, i.e. those expended in products for resource extraction, manufacture, and end-of-life waste treatment and disposal. Sparse data on retrofits and inconsistency in life cycle methods confounds the relationship between operating and embodied impacts at a population-level, meaning that identification of the dominant factor, and hence retrofit’s overall benefit, remains ambiguous. Variability of embodied impact data, and underrepresentation of prominent retrofit materials were found to present further barriers to robust analysis. A redefined approach for a “retrofit life cycle analysis” (RLCA) is proposed, alleviating inconsistencies present in previous studies, and pinpointing the focus on the life cycle performance of thermal measures. This enables the derivation of an operating savings and embodied expenditure balance (O:E), which facilitates better evaluation of the life cycle performance than simply describing the resulting operating or embodied impacts. Through RLCA and the O:E balance, quantifiable parameters for proceeding, redesigning, or discontinuing the retrofit may be established, described as the “Retrofit Tipping Point”. The approach is tested with two archetypal UK case study houses and proposed retrofits, plus variants. Operating impact savings were found to dominate the O:E balance in all variants, demonstrating that the retrofits achieved operating savings in excess of the embodied expenditure, indicative of a favourable energy and carbon life cycle impact. Insulation materials made the largest embodied contribution in most cases. Case study data was comparable in magnitude to other literature studies; linear regressions relating operating and embodied impacts revealed line gradients close to zero, indicating very minimal change in embodied impacts as operating energies reduce. This suggests that even extensive retrofits can be beneficial over their life cycle.EPSRC Doctoral Training Partnership fundin