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Why NatHERS should be open source

··424 words
Felix Andrews
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For transparency, progress and accountability of a model that is central to the Australian residential building sector affecting millions of people. (Ownership and control can remain with CSIRO.)

When I say NatHERS here, I really mean the simulation engine used in all accredited NatHERS software, known as Chenath.

The NatHERS simulation engine has been developed by CSIRO since the scheme started in the 1990s. I am proposing that the source code be publicly released.


NatHERS software implements a complex model of heat transfer in buildings. Some of the underlying sub-models have been described in broad terms in published papers. But many of the hundreds of assumptions and details inherent in such a model are not visible.

As the Australian building code targets higher performance building standards, it is exposing some limitations of our models. If left unchecked these can cause perverse outcomes. It is essential that we can have an open conversation about appropriate assumptions. And that starts with a full knowledge of the current system.

The NatHERS software has a special status in that:

  • it is specified in the building code, which directly affects millions of people;
  • it was developed with public funding.

A cornerstone of science is openness. There would be greater trust in a model that can be scrutinised and analysed.

Wouldn’t this create chaos?


The governance of NatHERS software would not be affected by releasing the source code. The current custodians (CSIRO and the NatHERS Administrator) would retain full control of their codebase, and that is the only one that can be used for certification to the National Construction Code. License fees would be unaffected.

One of the most successful building energy models internationally is Energy Plus, developed by the US Department of Energy. It is open source software. In fact, this is sometimes used in Australia to prove compliance of commercial buildings.

Does the Australian Government do open source?


CSIRO has already released software under an open licence, such as for example an energy system model.

An online repository of open source software, Github, lists 43 Australian Government agencies having code on its platform.

One element of the Digital Transformation Agency’s Digital Service Standard v1 is: Make source code open. One of the key benefits being to “increase transparency”.

Who makes this decision?

I don’t know. But change is more likely if more people support it.