What do you get when you cross a national administrator, state governments, a scientific agency, non-profit industry organisations, software developers and house builders? NatHERS - an energy modeller’s nightmare.

Section J of the National Construction Code sets the minimum standards for energy efficiency, with residential developments requiring a rating under the Nationwide House Energy Rating Scheme (NatHERS). Using accredited software, this is a star rating system which simulates proposed developments based on the dwelling dimensions, location, orientation and approximate occupancy patterns. It is a fabric-based assessment for heating and cooling loads, and does not consider the energy consumption from appliances, lighting or services.

There are three options for accredited modelling software: AccuRate, First Rate and BERS Pro. They all utilise the same calculation engine that has been developed by the CSIRO. This calculation engine, Chenath, is a closed black box which we don’t have access to, and in October last year, there was a rather large shake-up.

As with all software, updates are to be expected as bugs are fixed and errors corrected. However, in October last year, the release of the new calculation engine, Chenath version 3.13, fundamentally changed the modelling methodology and has had a large (typically negative) impact on many of our projects.

The three different software providers had different dates for incorporation of the new calculation procedure, with AccuRate being the first. The initial release of the new engine was due to be on October 1, 2014, but then this got delayed until November. FirstRate incorporated Chenath v3.13 in February of this year, and BERS Pro is yet to incorporate it. How can you have three accredited pieces of software with different calculation engines?

Now, I am all for improving software to make it more accurate, encouraging more efficient building stock and removing easy compliance due to loopholes or incorrect calculation assumptions. However, the release of this software update fundamentally moved the goal-posts of compliance. The new software requires additional inputs and changes the window types that are available, not to mention the illogical fact that an individual certificate for each apartment now needs to be created, even with repeating floor plates. All of this contributes to a vast increase in computation time for energy modellers.

For large multi-residential towers, the original analyses can be carried out more than two years prior to the final construction design. If this takes place using one version of software, surely the design should continue to be assessed throughout its lifetime using this version? BASIX (the NSW pathway for assessing compliance against Section J) has confirmed that the original version used for the development application can currently be used for the final certification, so surely we should allow the same in the other states?

A large part of the problem is the fact there are so many stakeholders in this process, leading to inconsistent advice. They include: the NatHERS Administrator (Department of Industry and Science), the calculation engine developer (CSIRO), the software providers (AccuRate, First Rate, BERS Pro), assessor accrediting organisations (Association of Building Sustainability Assessors [ABSA] and Building Designers Association of Victoria [BDAV]), energy assessors, house builders and developers, the Australian Fenestration Rating Council (AFRC), the Window Energy Rating Scheme (WERS) and of course the surveyors. No wonder the result is a disjointed, badly reported methodology with minimal industry engagement.

energy modelling

The communication of the changes to the Chenath engine has been limited, with so much wavering around release dates, certification costs (did I mention the certification costs are now roughly double what they were?) and windows data, it was enough to pull your hair out. The release seems to have been rushed through, as since then there have already been two additional updates to the AccuRate software, as bugs have been found and (I am assuming) complaints from assessors are flooding in.

Improving and refining the NCC is part of a progressive strategy on energy efficiency across the building stock, and it’s undoubtedly a lot easier to target those new-build developments rather than existing buildings. However, the process of changing regulation needs to be discussed with industry, stakeholder engagement is paramount to successful incorporation, and it is essential that any changes are presented in a succinct, joined-up approach after sufficient testing.

As the multi-residential market in Australia is booming, maybe it’s time to re-think the NatHERS process.