Is NaTHERS Holding Back Sustainable Best Practice? 13

By
Tuesday, May 12th, 2015
liked this article
Embed
Autodesk – 300 X 250 (expire December 31)
advertisement
stop
FavoriteLoadingsave article

One of the biggest challenges for the built environment is reducing greenhouse gas emissions. Earth building has been around for centuries, houses nearly half of the world’s population and is arguably the pinnacle of sustainable best practice. But not according to NaTHERS.

“The best approach to heating and cooling is about maximizing gains through harnessing natural conditions like solar gain, breezes and the cool of night in naturally conditioned ventilated buildings,” said Peter Hickson, president of the Earth Building Association of Australia (EBAA).

“This recommended design paradigm differs significantly from the sealed and insulated box model supported by the Energy Efficiency Provisions in the National Construction Code (NCC), which concentrates on minimizing losses from conditioned spaces through the building envelope.”

Hickson argued that this best practice approach is more suited to Australian climates and climate change predictions, unlike the singular focus on a well-insulated and sealed envelope. In addition, energy efficiency isn’t implemented at the expense of indoor air quality and occupant health and safety when using this method.

Other Earth Building Advantages

  • The techniques have been developed for different climates
  • Wall densities can be varied to maximise performance in any climate
  • Earth is approved in BAL Flame Zone
  • Earth is non-toxic, non-allergenic, doesn’t rot, and isn’t attacked by vermin and termites
  • It can be load-bearing and is durable
  • It has the best embodied energy figures and, being dense, it has excellent sound isolation
  • Earth balances and stores temperature and humidity
  • Earth is abundant and available everywhere locally
  • Earth protects and preserves timber
  • Earth walls block electromagnetic radiation

But earth building is continually being challenged by new legislation and requirements to comply with statutory regulations. The most challenging recent legislation involves finding ways of complying with tightening energy efficiency in the area of space heating and cooling.

“Earth builders believe existing earth buildings already comply,” Hickson said. “But passing House Energy Rating assessment tools has been a challenge in colder climates for earth buildings. Difficulty in gaining approval has led to a serious contraction of our industry in Victoria and the problem may well spread to cold regions in other states as they adopt the Nationwide House Energy Rating Scheme, NatHERS.”

Hickson argued that a singular focus on building envelope is not the answer to building energy efficiency.

“NatHERS is focussed on improving the performance of the external envelope of brick veneer project homes fitted with air conditioners, buildings mostly built without regard for simple climate responsive design principles and without ‘effective’ mass,” he said. “Why the focus on the envelope? Because poorly designed, effective lightweight project homes are the reality and the problem.”

Hickson pointed out that the great majority of postwar housing in Australia uses lightweight construction and doesn’t follow even basic climate design principles. Two-thirds of new homes are fitted with at least one refrigerated air-conditioner. Western Australia (WA) is the exception to this preference for lightweight building.

In WA, the building stock is predominantly full brick masonry and rammed earth, though this is changing through the introduction of energy efficiency measures. So recently, lightweight construction is gaining a foothold in WA.

Once a proposed building plan is presented to the NatHERS assessment process, all that can be done to these buildings to make them more energy efficient is to seal them tightly, insulate them well and control ill-placed windows with shading and/or double glazing.

“It is remedial action, not best practice,” said Hickson. “It is like spending the entire health budget on giving sick patients triple bypasses rather than spending something on preventative measures like promoting a healthy diet and exercise.”

In her book House Rating Schemes: From Energy to Comfort Base (Green Energy and Technology), Maria Kordjamshidi states that House Energy Rating Schemes (HERs) from around the world are unable to adequately model anything but sealed insulated conditioned buildings. In line with this, Hickson says NatHERS does not have even basic ventilation logic.

“It doesn’t model these buildings as they are operated in reality or as they need to be operated for the health and safety of occupants with minimum air changes,” he said. “It doesn’t allow for modelling using appropriate ventilation logic to maximise efficiency.”

The problem, he added, is made worse because, due to its design limitations and protocol, NatHERS is discouraging and disallowing naturally conditioned buildings with more effective energy efficiency outcomes.

“It is actively promoting poor building outcomes,” he argued. “This may be unintentional but it is a real consequence. If it cannot model earth buildings that are in effect mass-linked ventilated buildings then to use it to model these buildings gives erroneous results.”

This, Hickson said, sends the wrong message to designers, architects, building assessors and certifiers, builders and clients. He is at a loss as to why bureaucrats and politicians worldwide have legislated the industry down this path and counter to the intentions of professional thermal modelling experts.

So what is the reason? According to the NatHERS administrator, major project builders constructing those ubiquitous lightweight buildings support NatHERS because they can use the same design in any climate, on any site, in any orientation and still easily comply with NatHERS.

“To me, this is an indication of failure of the scheme to improve design and that it simply about mitigating problems with poor designs,” said Hickson.

“The CSIRO Chenath engine is sound and there is no doubt that thermal modelling can be useful in optimising design. We need NatHERS to be capable of modelling naturally conditioned buildings, all buildings with minimum air changes and building designs not just building envelopes.

“Buildings proposed for tropical Darwin with a latitude just 12.5 degrees south of the equator should look totally different to buildings proposed for a much colder Hobart, 42 degrees south of the equator. The age-old approach of designing buildings to suit climates is the one I support.”

Embed
FavoriteLoadingsave article

Comments

 characters available
*Please refer to our comment policy before submitting
Discussions
13
  1. Lawrence

    All NatHERs software takes into account of natural ventilation based on the following factors:
    – The local weather file
    – The terrain of the location
    – The building orientation
    – The building footprint
    – The height of the building above ground level
    – The types of ventilation opening (like whether it is an awning or louvre window)
    – The size of ventilation openings
    – The size of infiltration gaps around openings
    – The location of openings in relation to the building and each other
    – The number and type of obstructions between the ventilation openings; and
    – Whether the openings are obstructed by flyscreens
    Indeed this has been the major focus of the software development from 1st generation till today. Any accredited assessor would know this and we use it to our advantage in our designs.

    I agree the system could be improved but let's do so constructively from an informed position.

    • Peter Hickson, President EBAA

      Lawrence, The Chenath engine is sound and the tools are capable of complex analysis as you point out. The AccuRate software (at least) can model in free running mode and in regulation mode. Regulation mode must be used for rating purposes. I am familiar with the simple ventilation logic that was encoded in version two and I know it was never used. When using Regulation Mode (in version three) what ventilation logic is encoded, is it variable and are 1 to 2 minimum air changes required for healthy indoor air quality included in modelling? I haven't invested in NatHERS software and training however I have invested considerable time in research and delved deeply into NatHERS, worked with assessors, consulted with members of the Technical Advisory Committee for NatHERS, its Head, the man in charge of the CSIRO's engine, thermal modelling researchers and professionals from around the world. My criticism is written from this informed position and is not limited to that which is found in this brief article. I am willing to listen and open to fair criticism. I'm informed NatHERS isn't capable of modelling mass-linked ventilated buildings in Regulation Mode. Has something changed?

    • Lawrence

      @ Peter

      Poor ventilation modelling was a known issue with 1st generation software.

      The modelling of natural ventilation was THE major upgrade when 2nd generation software was introduced back around 2007.

      Regardless of mode, the software automatically and dynamically works out when it is preferable to use natural ventilation. You can notice a difference by changing the operable areas of the openings, their orientations or even the relative heights of the openings. Today the only real difference between rating mode and non-rating mode is you can change whether a zone is conditioned or not.

      From NatHERS website:
      "NatHERS software considers whether spaces can achieve thermal comfort through three means:
      • by natural means (e.g. open windows)
      • cooling via mechanical air movement (e.g. ceiling fans)
      • by adding or extracting an amount of energy to that space via heating and cooling appliances and equipment.

      All external openings (e.g. windows) are considered to be operable at all hours, although a factor has been incorporated to limit the number of operations to one per each three hour period."

  2. Daryl Hargreaves

    Building designers are more than aware of the deficiencies of the NatHERS approach. As an accredited energy rater I am continually flummoxed at how First Rate 5 flies in the face of conventional building efficiency knowledge. Explaining to my clients that they need to spend more on insulation only to have it all fly out the windows when they are opened is a frustrating thing. Now we are being forced by NatHERS to complete a CERT IV course to learn what we already know so that accreditation can be standardised across the nation. Red tape bureaucracy at it's best.

    • Peter Hickson

      I sympathise with you Daryl. The focus of NatHERS is on the external fabric and not design. These are not my words. This is the government line. There is no doubt that occupants require indoor air quality be maintained for health and safety. Before energy efficiency measures were introduced 1 to 2 air changes per hour were recommended for homes. A well sealed and insulated light weight building stores nothing but air at a conditioned temperature. With minimum air changes this efficiency is simply lost out the window. As you point out the value of the insulation is diminished. It is more possible to achieve both minimum air changes and energy efficiency with mass because mass reconditions air changes. The trick is to get natural conditions like shade, cool of night, breezes or solar access to prepare the mass for this work. This is what climate responsive design is about. Mass also banks energy used in heating (or cooling though seldom required) so it is released slowly and not lost through the external fabric or so easily through ventilation. We hope to see things improve. Small business suffers most from legislative and bureaucratic demands.

  3. tristan

    I disagree that lightweight building rates better in NatHERS, and that WA is shifting to lightweight construction to achieve compliance with energy regulations. You can increase the efficiency of cavity masonry by introducing cavity insulation. In my experience, insulated cavity walls rate almost as well as reverse brick veneer – the widely accepted 'best practice' wall type.
    In Perth and the SW, it has always been my experience that introducing mass will increase a NatHERS rating. I find it can be very difficult to achieve compliance with a lightweight home in a cooler climate. NatHERS really loves mass, but it needs resistance as well. Have you tried modelling your earth walls with added insulation? The rating will sky rocket.

    Earth construction provides plenty of mass, but very little insulation. Un-insulated mass walls are only really suitable to arid climates – when it is very hot in the day, and cold at night, earth will be very good at stabilising the extremes and providing a constant indoor temperature. In temperate areas (where most of us live) – it will do the same, but often this 'average' temperature will be outside of a comfortable level.

    • Peter Hickson

      Thanks Tristan. WA has the best building stock in Australia. Yes we have looked at adding insulation within walls and varying density depending on earth building technique. Both are possible though cost and practical problems arise as they would do insulating cavity brick. We have achieved much better star ratings in colder climates with medium and low density earth wall values though NatHERS doesn't have an option in the library of materials for this yet and they won't accept values established by German research. There is a reasonable direct correlation between density and resistivity rising with lower density and capacitance falling at the same time. Total R value can be readily and reliably estimated for any earthwall density and thickness of course. NatHERS won't accept this. We have also been advocating appropriate climate responsive design. Mass has be used in all climates successfully. Design principles lead to dramatically different looking designs. Adaptive Comfort levels proven acceptable in naturally conditioned buildings often equate to the "averages" you mention. More appropriate heating thermostat settings would help rating in all mass buildings.

  4. Tony Isaacs

    Recent research that I conducted for the NatHERS administrator allowed me to 'pop the hood' on the NatHERS simulation engine and find out exactly how often windows were opened to provide comfort as opposed to how often they air condition. And just how much more comfortable houses would feel when windows were opened. This research showed that NatHERS tools do not simulate sealed boxes e.g. in Darwin windows opened to provide comfort 65% of the time, air conditioned 15% of the time with a maximum comfort benefit of 5 degrees in a house with good cross ventilated design, less than 3 in a (not too bad) spec house. In Brisbane, windows were opened around 50%, air conditioning used less than 1%. This doesn't mean that all outcomes from using NatHERS software are ideal, nor does it mean that the simulation shouldn't be improved. But, if there are problems they don't arise from simulating a sealed box. This is a myth that has been around from the days of 1st generation NatHERS tools. 2nd generation tools, developed 10 years ago, just don't have this problem anymore.

    • Peter Hickson

      Thanks Tony. A recent study. A very old magazine article written by you claims the same and yet this totally contradicts what we were told just last year by a well-credentialed scientist expert in thermal modelling. 2nd generation tools included a very simple ventilation logic in REGULATION Mode – never switched on! NatHERS won't answer questions. Perhaps in this forum we can work through them. To clarify, are these homes in tropical climates comfortable (65% D & 50% B) of the year through ventilating according to Programmed Ventilation Logic during modelling within REGULATION Mode? Could be fragments of day or night? In most climates outdoor and indoor conditions are favourable a large percentage of the time if you piece together the hours of comfort. FREE RUNNING Mode simulates this. Thermal mass greatly extends and connects these periods. Did the recent study include other climates? Are at least minimum air changes modelled 100% of the time in all homes in all climates? If so what is the rate? What is the current ventilation logic in REGULATION Mode, is it VARIABLE and is it definitely switched ON? Is a ventilation logic used in all three NatHERS software options?

    • Tony Isaacs

      Hi Peter, to clarify, the figures I gave were all in regulation mode i.e. in regulation mode in Darwin the windows were opened 65% of the time to achieve comfort and cooling was only activated to achieve comfort 15% of the time. Brisbane figures were also in regulation mode. In Darwin the 65% represents the number of hours per year where opening windows will either cool down the house (i.e. cooler outside than inside) or provide sufficient air movement to make you feel cooler up to the point of activating cooling. The expert you refer to may well be very well credentialed, but these figures are taken directly from the the output of AccuRate. So regardless of opinion, this is how the software actually works.

  5. Harold Lee

    Nathers is in urgent need of overhaul – it fails to cater to the diversity of a country as large and with as much climactic variability as Australia.

    • Peter Hickson

      Harold thanks for your thoughts. We have a number of problems with NatHERS though using climate files it should be able to cope with simulating buildings in a diverse range of climates. Thermal Modelling engineers have told us it doesn't have a ventilation logic able to model naturally conditioned buildings and Lawrence and Tony disagree although I await clarification on minimum air changes and ventilation logic in Regulation Mode. A number of things are certain though. In most Australian climates cooling is the greater challenge. Heating can be carbon neutral and cooling is carbon intensive and has major peak load implications. Global warming is real and colder climates are becoming warmer climates. BRANZ predicts Melbourne will go from a climate requiring four times heating to cooling to one requiring twice the cooling to heating. Generally, mass building require little cooling and some heating. You could argue they are more climate change ready. The CSIRO has found an increase in cooling loads across the country in newer star rated buildings. My 23 yr old high mass home doesn't need cooling and NatHERS modelling also agrees the requirement would be very low.

  6. WillTurner

    L.Daniel & T.Williamson's (Uni of Adelaide) excellent 2015 paper on
    "House energy rating schemes and low energy dwellings: The impact of occupant behaviours in Australia"

    – It is clear from the investigation presented above that current static occupant related settings within the Nationwide house energy rating scheme thermal performance simulation software don't adequately reflect actual practices within a cohort of low energy house holds in Australia.
    – The regulatory provisions in the NCC, aimed at making buildings more energy efficient, are based assumptions on generic occupant use patterns and behaviours. The results presented above demonstrate that, at least for earth constructed dwellings, the assumptions do not represent the actual situation.
    – This mismatch disadvantages people wishing to construct such dwellings by “imposing” upon them design solutions which potentially result in an unnecessary cost burden.
    – If a more realistic assumption of user pattern and behaviour is used, it is likely that this house design can achieve higher than 6 Star rating without requiring such improvements that will increase the construction cost.
    – These NatHERS issues were acknowledged in a report for the Australian Government in 2010. This report stated that a number of the assumptions within NatHERS did not adequately reflect user behaviour and recommended that adjustments be made to occupancy and thermostat settings to better reflect actual practices
    – in some cases a building design that fails to meet regulation does not necessarily diminish its ability to perform as a low-energy building. Regulations and standards can actually ‘fail’ people's attempts to be more energy efficient