This article looks at the rules governing the use of the 3 software tools and some of limitations embedded within the software tools that assessors should be aware of when undertaking an assessment.

What buildings can be assessed using the software tools?

To most assessors, the answer to this question is straight forward. Under the National Construction Code - Building Code of Australia Volumes 1 and 2, only Class 1, 2, 4 and attached 10 buildings may be assessed using a software tool accredited under NatHERS.  

Amazingly, examples of class 3 buildings and other building types assessed with NatHERS accredited software tools still surface from time to time.

What limitations exist within the NatHERS accredited software tools themselves??

All 3 software tools are accredited under NatHERS but BERS Pro and FirstRate5 have limitations nominated as a condition of the accreditation. Assessors who use either of these tools must take these limitations into account when rating a building and consider using an alternative tool if the tool of first choice cannot be used as a result of the limitations.

In summary, BERS Pro cannot be used to model buildings that contain “tilted roof windows with blinds” and  FirstRate5 cannot be used to model buildings that require “slab edge insulation”.

There are no limitations on Accurate as the NatHERS benchmark tool.

Are there any limitations on the data that assessors enter into the software tools??

Yes, there are a limitations on data entry set by the rules and limits of what the underlying Chenath engine can model and all 3 software tools are designed so that assessor enter data that meets these rules.

What are these limitations??

Each tool will permit up to 150 zones to be modelled. Remember that the software tools create zones as part of the simulation process that reduces the number of zones available to the assessor to actually use. In practice, most buildings will contain far fewer than 150 zones so this limitation is usually not a problem. The greater the number of zones, the longer the simulation time.

Within a zone, assessors can generally enter 10 of anything, 10 ceiling fans, 10 lights, 10 windows in a wall and so on. Some of the tools will warn the user that they have exceeded this limit, some don’t so be careful if the simulation does not appear to work as it should.

External walls - the software tools only permit a maximum of 10 external wall types. Additionally, doors and openings modelled in external walls are included as part of this total. If all 4 door types are used this reduces the available number of wall types to 6. Furthermore, the wall type used as part of the highlight/clerestory window element is also counted so it is possible in some complex buildings to only be allowed to have a maximum of 5 external wall types modelled that requires the assessor to rationalise the range of wall types modelled in the tool prior to simulating.

Internal doors/openings - the width of the element must not exceed its height. For large wide openings, divide the element into a series of smaller narrower elements. For BERS Pro users, permanent openings must be modelled as doors until the existing ventilation bug in the Chenath engine is resolved.

Voids to double height spaces in two zones, one above the other, need to be modelled carefully. The simulation process will not work if ALL of the floor shared between two zones is removed. Assessors need to ensure that a minimum of 0.1 m² remains for the simulation to work correctly.

Ventilation - it is worth noting that nominating the number of exhaust fans or unsealed downlights within a zone does NOT automatically adjust any added insulation value. Loss in the average R-Value in ceiling insulation due to penetrations (downlights, exhaust fans etc.) must be calculated separately or adjusted in accordance with the BCA.

Windows - if using Custom Values be aware that the values embedded within the tools are quite old and in some cases, windows cannot be supplied with the SHGC and U-Values nominated. This limitation is being addressed by DCCEE with new window data being prepared for inclusion in the tools and new assessor procedures for their use are being drafted.

Acknowledging all of the above limitations, it is important to remember that assessor only model the building in accordance with the plans and specifications supplied by the client.