Keeping Cool (or Warm)

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-By Jen Hocken

The cost of heating and cooling homes is often unnecessarily high. Inefficiencies at every step along the chain can easily add up to waste and added expense. The good news is that the energy that is needed to keep warm in the winter and cool in the summer can be dramatically reduced with a plan of good design and high quality construction of the home, with the twin benefits of lowering costs for residents and reducing greenhouse gas emissions into the atmosphere.

The purpose of NatHERS is to aid Australian Governments in reducing the energy and greenhouse gas impact of residential buildings. NatHERS stands for Nationwide House Energy Rating Scheme, and it allows for the design and construction of homes to be assessed by professionals using computer modeling programmes. Assessing a home’s thermal performance at the design stage can establish simple, economical ways to save energy. This helps lower energy bills and is beneficial for the environment as well.

NatHERS began in 1993; it was created by the Australian and New Zealand Minerals and Energy Council in order to establish one standard rating system for thermal performance in Australian homes. The intent was to “assist the public and the building industry in identifying the extent to which any house (new or existing) has the potential, through its design and construction, to be of high efficiency in its use of energy for heating and cooling purposes,” according to Angelo Delsante of the CSIRO Division of Building, Construction and Engineering. NatHERS was then used to support the regulation of new building standards by some State and Territory Governments. This began with introducing a minimum of four star rating requirements for new home designs in 1995 in the ACT. The NSW Government’s Energy Smart Homes Program from 1997-1999 also used the NatHERS rating system.

According to the NatHERS website, computer simulations are used to identify the potential thermal comfort of homes in Australia on a scale from zero to 10 stars, with zero representing a high need for cooling and heating to be comfortable. Zero stars means that the building does not help reduce the need for energy use to stay warm or keep cool. A five star rating represents an acceptable amount of thermal performance, but not outstanding. The full 10 star rating means that homes will most likely not have to use any artificial cooling or heating. Most houses that were built in 1990 rated only one star on the NatHERS scale, and before the national energy efficiency regulations for houses came into effect in 2003, less than one per cent of homes in Australia received a five star rating.

The Building Code of Australia states the regulations for most jurisdictions. Some parts of the regulations concern the building shell; the roof, the walls, the windows and the floor, and other parts of the regulations are for parts that are built into the home – hot water systems and ducts and pipes for cooling and heating systems.

Assessors for NatHERS use the tools and software to predict the thermal performance of planned residential buildings on the scale from zero to 10. This prediction is based on the building plans and drawings at the design stage; however as energy efficiency becomes more popular, assessors can also provide ratings for existing buildings and suggest possible improvements that can be made. These assessors must have expertise in building residential homes and in-depth knowledge of construction materials. Other qualities and skills of an assessor are compliance with regulation, customer service, computer literacy, occupational health and safety compliance and ethical behaviour. Presently, the only recognised course for NatHERS assessors is the NSW accredited Vocational Education and Training Accreditation Board (VETAB) Short Course in Building Thermal Performance Assessment.

Any given household employs different rooms for different purposes, and the desired level of comfort for each varies. Desired levels of thermal comfort even vary throughout the day. Therefore, thermal comfort must be distributed appropriately throughout the home. For purposes of “fair comparisons between buildings” the NatHERS scheme sets out some standards for acceptable comfort levels within the home. According to the NatHERS website, for living spaces, including the kitchen, thermal comfort of around 20 degrees C is maintained from 0700 to 2400. For sleeping spaces, such as the bedroom and surrounding areas, thermal comfort is maintained from 1600 to 0900. The heat setting is set to 18 degrees C from 0700 to 0900 and from 1600 to 2400, but then it drops to 15 degrees C from 2400 to 0700, when most people are already asleep. The temperature setting must vary for the expected function of the room, and the amount of clothing that will most likely be worn. In a bedroom, sheets and blankets are used; therefore the temperature can be lower. The level of comfort can also be changed through natural means. NatHERS requires that all openings/windows are able to function at all hours, although of course it may be necessary at times to keep them closed. There are also ways to circulate the air naturally, such as with ceiling fans.

The software responsible for assessing energy ratings has evolved over the years. According to the NatHERS website, the development of the first generation of NatHERS by CSIRO started in the early 1990s. It was based on years of research about simulating heat flows in residential homes. This was the basis of the national rating scheme that was ultimately implemented in 2003. In 1993, Sustainability Victoria (previously known as Energy Victoria) released the first version of FirstRate. The second generation of NatHERS software was improved in 2006 to assess thermal comfort across all Australian climates. The improvements made include: more realistic modelling of the benefits of natural ventilation and the cooling effects of ceiling fans; heat flows in underfloor, roof spaces and between attached dwellings; and the inclusion of a greatly expanded base of climate data. The outdated and more limited software tools were gradually eliminated after 2007.

Currently, there are three NatHERS software tools used for energy rating that have all been approved under the “Procedure for Accrediting Software under the Nationwide House Energy Rating Scheme.” AccuRate is the recent and the most improved software tool; it was designed by the CSIRO based on years of research in the way that buildings handle Australian conditions. However, the software tools FirstRate and BERS Professional, which was designed by Solar Logic, both offer versions that are also accredited for use in NatHERS. The software accreditation procedure is updated often, with the most recent update in 2011. All three of these software tools use the same calculation engine that was designed by the CSIRO, called Chenath Engine.

The star rating in the NatHERS does not include hot water systems or other appliances such as washing machines and refrigerators because they usually have a shorter working life than the actual house. The rating is based on the parts of the house that are not usually replaced, like the roofs, walls, windows and floors; therefore a home’s rating will not change each time an appliance is replaced.

According to the NatHERS website, on the 2nd of July 2009, the Council of Australian Governments signed the National Partnership Agreement on Energy Efficiency, which delivers a nationally consistent and cooperative approach to energy efficiency, including: assisting homes to reduce energy use by giving information and advice, financial assistance and demonstration programs, as well as assistance to businesses and industries. Nationally consistent energy efficiency standards for appliances and equipment were also included, and in 2010 new standards were introduced for the energy performance of air conditioners. Governments are working together to improve the energy efficiency of their own buildings and operations, and significantly contribute to emissions reductions. People and governments are coming together to strive for the goal of energy efficiency because the benefits are so great.

The Nationwide House Energy Rating Scheme provides a standardised way to rate the amount of energy used in a house across Australia, and how to decrease this amount. NatHERS is essential for the sustainability of the environment, and is also beneficial for reducing the cost of energy bills. Thermal assessment software is necessary to test the quality of building design, or to test compliance with building or planning standards. The NatHERS is not mandated, but the star rating system can be used to demonstrate compliance with the BCA requirements for energy efficiency. Going forward, the Australian Government hopes to further improve dwelling thermal performance and continue to build upon the quality of residential energy rating software.

Home Automation

Call it ‘domotics,’ and you are likely to receive a blank stare, but refer to it as ‘smart home’ or ‘home automation,’ and you will get a nod of acknowledgement. For the past few years, consumers have heard the word ‘smart’ attached to countless products and services, from food and drink to snacks like popcorn and mobile phones, which no one seems to refer to as a ‘cellphone’ anymore. Yet what, exactly, constitutes ‘smart’?

July 27, 2021, 3:41 PM AEST