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Other window energy rating schemes
National Fenestration Rating Council (NFRC) – USA
To address concerns about energy consumption the fenestration
industry developed many new technologies in order to become more energy
efficient, such as low-e coatings on glass, gas filling of glazing
unit cavities and warm edge spacers.
Manufacturers started to make unrealistic claims about the
thermal performance of these new technologies. The NFRC was
set up in 1989 to prevent confusion, and in their own words “…by providing
fair, accurate and credible, user-friendly information on fenestration
product performance.” Today more than 300 manufacturers rate
and label approximately 100000 products through the NFRC.
As with the BFRC rating, the NFRC bases its rating on 3 criteria:
•
U-value (called the U-factor);
• Solar heat gain
coefficient (equivalent to the g-value);
• Air leakage.
Further information
can also be given such as the visible transmission and the condensation
resistance.
As the climate in the USA is so varied a single nationwide
scale for the rating boundaries can not be used. The above
factors are combined differently depending on the environment.
There are four climatic regions:
•
Northern climate region – more extremely cold days
than hot and homeowners spend more on energy bills for heating than
on cooling. Requirements are to allow sunlight to help warm the
home and to minimise heat transfer from inside to outside.
•
North/central climate region – characterised by hot
and often humid summer weather and cold, although not usually extreme,
winter weather. Homeowners spend more to heat their homes than
on cooling them. Requirements for fenestration products would
be to limit the amount of heat transferred through the window to the
outside when it is cold out, and also limit the amount of heat that can
build up from the sun during the hotter months.
•
Southern/central climate region – characterised by
hot and often long summers, but typically require heating to stay comfortable
in the winter. Homeowners use more energy to cool their homes
than to heat them. Required to balance both the heating and cooling
needs by limiting both the heat lost from the home when it’s cold outside,
and the heat that can build up from the sun in hotter weather.
•
Southern climate region – characterised by long periods
of hot and humid weather and mild winters. Requirements for
fenestration products are to minimize the heat build up from the sun,
to keep a home cooler and more comfortable without reducing the amount
of light coming through the window.
Window Energy Rating Scheme (WERS) – Australia
Established in 1995 the WERS is managed by the Australian
Window Association and acts as a fair, rigorous and credible system
for testing performance claims. The ratings are designed to ‘plug-in’
to NatHERS, Australia’s Nationwide House Energy Rating Software.
The WERS also applies in New Zealand.
As with the NFRC the climate in Australia is split into zones,
depending on the properties the windows need to have. The three
zones are:
•
Heating zone where the priority is to retain heat
in the home and maximise the use of solar energy (i.e. a low U-value
and high solar heat gain coefficient);
•
Mixed zones – the priority here is to keep heat out of the
home except during the mild winters where solar gain and keeping heat
in the house becomes important (low U-value and a mixture of high (for
north) and low (east and west facing windows) solar heat gain coefficients);
•
Cooling zone – the priority in these climates is to
keep unwanted heat out of the home (low U-value and low solar heat
gain coefficient).
Windows have their heating and cooling performance rated
separately on a scale of 0 (poor performance) to 5 (best performance)
stars. Each star gives an indicative improvement of the performance
when compared to a clear single glazed aluminium window. As
an example 2 stars give an improvement of 18 per cent when considering
heating, and 24 per cent when considering cooling.
In addition to the star rating the actual energy performance
of the window is given which includes the U-value, solar heat gain
coefficient, visible transmission, fabric fading transmittance and
air infiltration.
Energy Rating (ER) – Canada
Canada’s Energy Rating (ER) scheme is similar to the NFRC.
As before the rating is based on the thermal performance (U-value),
solar performance (total solar transmittance, g-value) and air infiltration.
The Annual rating is expressed in terms of whether the window is
a net energy gain or loser for the home, taken over the whole heating
season. Canada is overwhelmingly heating dominated so the rating
system is less complex than America where there are huge differences
in the climate across the country.
For most windows physical testing is not required and results
from computer simulations can be used. For complex products the
ER does offer the option to test.
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