The building industry currently accounts for approximately one fifth of the total greenhouse gas emissions in Australia. With the expected rise in population as well as the combination of smaller family sizes and the demand for larger more comfortable houses the impact of the building industry will continue to increase. Many different mandatory and voluntary rating tools have been developed around the world to ensure buildings move to become more sustainable, however studies have shown that these sustainable homes often underperform as they consume more energy than expected. Under the Nationwide House Energy Rating Scheme (NatHERS), Australia has targeted the operational energy reduction for heating and cooling. It has been found that there is a gap between the rating and the actual operational output of the houses as poor build quality, inaccuracy of the assessment tools and the occupants lack the knowledge on how to operate and maintain their homes efficiently all contributing to higher than expected operational energy. A broader outlook on sustainability outside of the operational energy demand of a house, Life cycle assessment tools are becoming increasingly more common. A life cycle assessment tool provides a complete evaluation of the carbon footprint in terms of the greenhouse gas emissions for the entire embodied and operational energy of a house which can be used in combination with the existing NatHERS to increase the understanding of sustainability in the Australian building industry. A life cycle assessment also has the potential to be used as a decision making tool to identify and influence the products or processes that would optimise the sustainability of the building.
This study includes monitoring the energy and water used in each home in addition to the photovoltaic solar production observed during the first year of the two year monitoring period for ten existing houses. The houses consist of both new six star rated homes as well as older retrofitted homes with different occupancies. The houses were all assessed with life cycle assessment software called eTool which measured the full lifecycle global warming impact of the existing houses. The operational data was then compared with the eTool prediction to investigate the house efficiency comparing the two ratings to identify specific areas of operational reduction improvements. Further analysis of the houses operational monitored data occurred via the process of an audit to further investigate how the occupant’s behaviours and house inefficiencies influence the performance of the house in terms of energy and water efficiency and whether there were any common trends identified among the houses.
The results of the study found that the eTool life cycle assessment provides an accurate representation of the actual energy and water usage based of the ten houses when compared with the 2015 measured values. The variations that did occur through the eTool assessment were identified further via the audits and were found to be associated with behaviour choices of the occupants, inefficiency with build quality, design or problems with technologies employed. Some technology problems encountered during the audit was that solar hot water systems were underperforming for some houses due to shading occurring during winter. An insight into the house inefficiencies was achieved by investigating the thermal performance of the building during the audit. The tool used was a thermal imaging camera. This identified that the major areas of heat gain were through missing insulation and unshaded east and west facing windows. From the life cycle assessment inefficiencies with solar photovoltaic production were detected at three of the houses due to the systems being shaded, dusty and located on a southern facing roof. The Life cycle assessment report also helps identify that the older houses which consist of lightweight construction have a lower embodied energy than the newer double brick houses. Interestingly the embodied energy of a retrofitted house with the old section being double brick and the new section being lightweight bulk insulated cladding has its highest impacting materials being brick and concrete. Another finding was that most of the houses had a higher portion of the solar production exported to the grid rather than utilised by the house which indicates that perhaps the PV systems are not being used to their full potential
