Unravelling the relationship between energy and indoor environmental quality in Australian office buildings.

• The indoor environment quality in office buildings has an impact on energy consumption. • One unit increase in NABERS Energy and IE rating score can reduce normalized energy use intensity by 21.98 kWh/m2 and 9.88 kWh/m2 per annum, respectively. • High-performing NABERS buildings can deliver 13% better IEQ with 36% less energy consumption than their low-performing counterparts. • Government regulations should request both Energy and IEQ certificates for commercial buildings. Green building studies generally focus on singular performance aspects (e.g., energy, waste, water, indoor environment) with few tackling the relationships between each other, particularly the relationship between indoor environmental quality (IEQ) and building energy consumption. This study aims to explore the relationship between IEQ performance and energy consumption in National Australian Built Environment Rating System (NABERS) certified buildings. A verified climate normalization factor was localized to standardize energy use intensity in buildings from different climate zones of Australia. The normalized energy use intensity (NEUI) was calculated for all office buildings and correlated with their NABERS Energy and IE rating scores. Multivariate linear regression results reveal that one unit increase in NABERS Energy rating score and IE score can reduce NEUI by 21.98 kWh/m2 and 9.88 kWh/m2 per annum, respectively. Also, this study develops an Energy and Indoor Environment Index to benchmark the energy and IEQ performance of Australian office building. Buildings with excellent NABERS Energy and IE ratings (scores equal to/higher than 5) have been classified as high-performance NABERS buildings (HNBs) and the rest as low-performance NABERS buildings (LNBs). A comparison between 49 HNBs and 48 LNBs demonstrates that, on average, HNBs can deliver 12.6% better indoor environment quality with 35.9% less energy consumption than LNBs. In contrast, many LNBs either use excessive energy to provide a sufficient IEQ, or sacrifice IEQ to reduce energy costs and/or achieve a high NABERS Energy rating. [ABSTRACT FROM AUTHOR]