Draft is the enemy of energy efficiency. Drafts or air leakages are year-round issues: in winter, they allow valuable warm air to escape and unwanted external cold air to enter; in summer, the reverse occurs.
Seal your building and you will save money on annual heating and cooling costs, and the size of your heating and cooling system, while improving the health and comfort of occupants.
Air leakages occur in many parts of the building envelope but we are taking a look here specifically at windows. Air leakage of windows is measured in litres of air per second per square meter of window area (L/s.m2). WERS-rated windows must satisfy Australian Standard AS 2047 ‘Windows in Buildings — selection and installation’ which allows a maximum infiltration rate of 5.0L/s.m2 at a positive pressure difference of 75Pa but this is inadequate in cool and cold climates, particularly in high wind areas.
The Australian Government writes in Your Home Guide to ‘Choose well-made windows and doors with tight air seals. Window manufacturers are required to have their products tested to this standard and register them with the Windows Energy Rating Scheme (WERS)’. Many manufacturers exceed the minimum standard, with Paarhammer air infiltration ratings from of 0.05L/s.m2 to 0.31L/s.m2, depending on the actual product. The lower the air infiltration figure, the less air will pass through cracks in the window assembly, improving the energy rating.
Incorrect window installation can also cause problems including poor air sealing between window and wall which results in reduced energy efficiency. A new initiative the AWA has planned for 2016 is educating window installers through video creation, online training module and NATA accredited installers program.
Increasing the air tightness of a home generally increases temperature and humidity differentials and can increase condensation risk. The government’s Your Home Guide explains ‘showers, clothes dryers, stoves, etc. should be vented to the outside if possible, and that double glazing helps significantly for windows’. Should condensation issues arise, they can be overcome by simply opening a window for a short time - e.g. while brushing your teeth - and are far outweighed by the energy savings.
South Australia consulting firm Sustainability House points out that new homes in Australia may be as much as three times as leaky as commonly assumed, leading to unexpectedly poor performance and high energy bills. The Australian National Construction Code Section J calls for draught sealing, but it has no mention at all of performance testing or even inspection. Contrast this with Passivhaus design, which calls for verification of the building’s airtightness at a level more than 20 times tighter than many typical new Australian homes.
Will Australian homeowners embrace performance testing and demand draft proof, energy efficient and comfortable homes? The right choice of tested windows without air leakage could be a start in this direction.
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