Energy and GHG reductions considering embodied impacts of retrofitting existing dwelling stock in Greater Melbourne

Abstract

Energy retrofits of buildings usually ignore the amount of embodied energy and greenhouse gas (GHG) emissions needed to reduce the operating energy and related emissions. Focusing on the Greater Melbourne Area (GMA), the fastest growing capital city in Australia, this paper analyses the embodied impacts of different dwelling stock retrofit programs using a combination of a top-down and a bottom-up approach. We look at dwelling stocks that have been built before 2005 (i.e., before a minimum 5-star rating in energy performance was introduced in Australia) because these are expected to consume, without any retrofit or upgrade, about 34.9 TWh of energy or emit 8.57 × 106 t-CO2eq GHG for heating and cooling every year. Retrofit options to improve their energy star rating range from relatively cheap and easy options (e.g., draught sealing) to relatively expensive options (e.g. double glazing of windows). If all these buildings' energy efficiency is improved to the level of a 6-energy rated dwelling across the metropolitan region, we can save about 25.5 TWh per year in heating and cooling energy (or 6.25 × 106t-CO2eq GHG each year). However, the retrofit program is estimated to consume 4.75 TWh of embodied energy, or have 1.89 × 106t-CO2eq embodied GHG emissions. This is equivalent to 50% of the annual heating and cooling energy for the stock, or 81% of operational GHG emissions due to heating and cooling of existing dwellings. Considering the total life cycle energy and GHG emissions over the life of the buildings, although reducing the operational heating and cooling energy will remain to be the primary driver for action, the proportion of the embodied impacts’ contribution is expected to increase in the coming years especially as the implementation of net-zero energy/emissions concepts become more commonplace.