Informing the next generation residential energy assessment tools

06 May 2019

The Nationwide House Energy Rating Scheme, commonly known as NatHERS, which is applied through software tools such as AccuRate Sustainability, has become the predominant pathway for complying with energy efficiency requirements within the National Construction Code of Australia. Current energy efficiency regulations have remained unchanged for a decade and there is an intention to increase these requirements, through mandating a higher minimum star rating for buildings. Furthermore, existing energy efficiency regulations only cover the building envelope, through the energy needed for space heating and cooling, and not the energy efficiency of major appliances. In addition, current regulations do not incorporate sufficient quality assurance processes, in relation to compliance. Finally, the current regime is inconsistent with international best practice. This project aimed to review, analyse and recommend changes, in light of these issues.
Examination of measured energy for heating and cooling across a number of houses confirmed that a higher star rated home constitutes reduced energy needed for heating and cooling. This result confirms the potential for the scheme to reduce energy costs for heating and cooling, at least up to around 7.5-star homes. However, the study recommended that a number of changes to the assumptions used in AccuRate Sustainability, in relation to the building envelope, are needed to ensure continued robustness and to become consistent with international standards.
A whole-of-house energy assessment method was proposed, including major appliances and end-uses. It was found that greater opportunities exist to reduce whole-of-house energy consumption, through increasing energy efficiency requirements of appliances, in comparison to those in regarding the building shell. A novel method to include the impact of rooftop solar PV and battery technology was developed, based on assessed imported energy from the grid. Unlike international schemes, the proposed methodology will only value self-consumption through energy storage and demand management technologies.
In comparison to international schemes, Australia lags far behind. This is attributable to these schemes being used to encourage energy efficiency in housing, well beyond minimum performance standards. As a result, the robustness of the software tools, combined with a strong quality assurance process, adds value, which in turn the market supports. It is recommended that Australia follow this path, and that a process of continuous improvement be applied to the NatHERS software tools to enable it to be used in the design of energy efficient housing, and promotion, beyond minimum performance requirements. A compliance inspection process and associated metrics are also proposed, to ensure that houses perform to their designed specifications and capability.
The original context of NatHERS was to reduce greenhouse gas emissions. With the rapid transition to renewable energy underway in the Australian energy system, this context is no longer valid. It is recommended that a transition towards energy efficiency regulations that exist within a health and well-being assessment framework be set in motion. This framework would consider factors such as indoor air quality, together with enhancing thermal comfort and minimising household energy costs. Ultimately, this shift will enable the building industry to use these regulations and mechanisms to deliver improved householder amenity for future Australian homeowners.

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