Is NatHERS Right for Australia? 8

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Monday, March 30th, 2015
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Sustainability advocates have raised concerns that Australia’s green building criteria are unsuited to the climate zones of many parts of the country, and will thus hamper efforts to raise the energy efficiency of the built environment.

Problems with Australia’s building efficiency criteria were brought to light last year by the winners of the 2014 Australian Institute of Architects Gold Medal, Adrian Welke and Phil Harris of the Northern Territory’s Troppo Architects.

The pair made the point that current criteria are based upon the premise that maximizing the energy efficiency of houses requires sealing them up and stuffing them with insulation instead of exploiting nature design features or enhanced ventilation to achieve more efficient temperature modulation.

Harris noted that many of Troppo’s early houses had received low or zero-star energy ratings despite not spending a single watt of electricity on cooling over the past few decades, and referred to these poor appraisals as being almost a “badge of honour.”

The complaints voiced by Welke and Harris have been at least partially vindicated by a recent CSIRO report for the Department of Industry, which investigated whether or not residential buildings with 5-star energy efficiency ratings under the Nationwide House Energy Rating Scheme (NatHERS) achieved higher levels of efficiency performance.

The CSIRO’s Evaluation of the 5-Star Energy Efficiency Standard for Residential Buildings found that while the 5-star standard did signify a reduction in the level of energy needed to maintain home temperatures in winter, it was also accompanied by higher cooling costs.

This disparity in performance bodes poorly for the application of NatHERS tools to many parts of Australia, given the torrid nature of the country’s climate zones.

“Heating costs were reduced and cooling costs increased in higher-rated houses,” said the report. “The net annual impact was that Brisbane costs were greater in higher-rated houses, whereas Adelaide and Melbourne costs were lower for the higher-rated houses.”

The report also noted that greenhouse gas emissions of higher-rated houses increased in the summer across all cities included in the study, although emission nonetheless fell by seven per cent for the full year.

The reason for the inability of the NatHERS criteria to reflect this disparity in efficiency performance across the seasons is the use of a single rating that is created by adding together both heating and cooling loads.

As a result of this process, a higher rating may not necessarily ensure greater energy efficiency for cooling purposes, which is more important in many parts of Australia due the country’s balmy weather.

If this shortcoming isn’t remedied, then rating systems like NatHERS are likely to become even more disingenuous in future as global climate change results in hotter summers and higher year-round average temperatures and indoor cooling assumes an even greater share of home energy consumption.

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8
  1. Adrian Rosse

    Different rating tools, with relevant building envelope assessment, for different climate zones would be a good start. One example would be the preferred use of reflective insulation and higher % of floor area ventilation levels in warmer (especially tropical) climates.
    This would make a lot more sense rather than the 'one-size fits all' rating system currently in use that encourages the use of bulk insulation and starts from the assumption that dwellings need to be air conditioned in warmer climates to be comfortable.

  2. Peter Hickson, President EBAA

    Australia needs healthy and efficient naturally conditioned buildings with appropriate climate specific responsive designs. Designs focused on maximising gains rather than minimising losses. Avoiding cooling loads is the greatest challenge in Australia with our climates, global warming and a carbon intensive power grid. Avoiding or minimising cooling needs to be rewarded. Cooling is carbon intensive though heating can be carbon neutral. NatHERS simply rewards designs that minimise losses through the building envelope. This strategy for conditioned buildings doesn't suit naturally conditioned buildings. So they rate poorly in predictions though can actually be more efficient when audited. The sad reality is that NatHERS aims at a very modest 10% reduction in terms of total LCD. NSW BASIX aims at 50 – 60%. My old home rates 113% in eTool LCA tool so is beyond carbon neutral and only rates 3.1 stars in NatHERS. In terms of where we need to be in building sustainability NatHERS is irrelevant. In terms of energy efficiency assessment it is limited to rating conditioned buildings poorly. This is a missed opportunity.

  3. Alex Bruce

    If you are looking to get some very basic level of thermal performance (and only thermal performance) for a house then NatHERS is useful.
    To use it as your only measure of total building energy performance or as your primary metric for quantifying the "sustainability" of a house is totally misunderstanding the purpose and limitations of NatHERS.
    It synonymous with saying your new building design will be affordable but only providing the predicted air-conditioning load.
    Again NatHERS is good at what it is meant to be used for. It's a bit unfortunate and unfair on NatHERS that it has been now totally taken and used outside of it's original purpose and context.
    Ask yourself if you were tasked and designing genuinely affordable housing how you would go about modelling and quantifying your designs. Then just just swap the word "affordable" with "sustainable" and you've got a pretty good design philosophy.

  4. Darren O'Dea

    The engine used for NatHERS ratings is certainly raising a few questions. Recent updates for high rise apartments in Melbourne are restricting design to the point where glass selection is limited to very few options. The transfer of heat between apartments is not a factor while u-values are way to sensitive. I personally find it incredible that the csiro don't allow us insight into the engines calculations considering they are employed by tax payers. The engine and thus the rating are not fit for design…. Only black box ratings.

  5. Rob Lord

    I went to a simulation conference in 2001 where this topic was raised and debated so it has rumbled around for a while. Obviously we would all like a program simple enough for any user, which is accurate but also it should allow good or clever design to be rewarded.

    I think we will find that the only improvements to accuracy will come at the expense of the chenath engine and there has been too much investment in that software to let that go easily. the connection to legislation is necessary for the exercise to have any power. As a process, the NCC does allow performance alternatives which could permit "clever design".

    In providing a more accurate software, the industry will lose some current benefits – the cost of assessment will go up, the turnaround time will get worse and the number of practitioners with sufficient skills will diminish. Is that what is the best for the industry?

    Personally, whilst I am conflicted, I think "the glass is half full".

  6. Mike Purtell

    The introduction of the NatHERS system has made huge improvements into the science of housing -vastly improving the energy efficiency of the building envelope.Before the introduction of NatHERS -houses were performing to a pathetic 2 stars or less, with many houses lacking insulation in ceiling spaces and walls -thus making them freezing in winter(high heating bills ) and hot houses in summer(high cooling loads.
    It is laughable to claim that the NatHERs system has not improved the performance of the building envelope.The real problem is that new houses can have a 6 star rated building envelope but if the sailor (occupants) dosent know how to sail the ship then occupant usage of energy will remain high.
    The introduction of the NatHERs system has laid the foundation of good thermal performance science in housing -sure there needs to be refinement but the overall direction has been important for improving the thermal performance of the building envelope in an industry that was continually obsessed with aesthetics (and continues to be so) and the choice of "cheap" building solutions for the building envelope.NatHERs is a good system -we just needs to refine & improve the system.

  7. Joan Day

    I am wondering if a Proposal for Change has been sent to NatHERS and the NCC to mandate energy ratings be based on mid summer rather than July temperatures. For buildings to be more energy efficient, environmentally sustainable and minimise the need for engineered solutions for heating and cooling they need to be light coloured, well insulated roofs.
    Dark roofs are known to contribute to the UIHE and this is related directly and indirectly to heat wave mortalities which number more than annual road tolls.
    I am proposing that cool roofs be mandated for the many health and environmental reasons. I would appreciate that everyone else do the same.

  8. Joan Day

    I have been told by a roofing manufacturer that the ERatings are based on July temperatures and make no concessions for summer heat. This is why roofing colours are heavily based around large choices of dark colours for steel sheeting and both concrete and clay tiles. How can we get NatHERS and the NCC to consider light coloured roofs as 'the required strategy for energy efficient buildings' which also 'require minimal engineered solutions for heating and cooling'? There is a 'Proposal for Change' form on the NCC site which anyone can use to submit ideas for improving building standards in Australia. I suggest anyone who works in the industry or is involved in research should be using their voice to promote change. The http://www.standards.org.au – state that any standard should have a NET benefit to all and should not cost more than the benefit, which is exactly what cool roofs do.
    http://www.yourhome.gov.au recommends light coloured roofs for all homes in climate zones 1 to 6.
    It is time for the professionals to speak up where they will be heard most, in creating change at point of legislative laws.