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British Fenestration Rating Council
The British Fenestration Rating Council (BFRC) is
an independent UK body that emerged from Government funded research
with trade associations, laboratories, analysts and universities.
The aim of the BFRC is to operate a ‘fair, accurate and credible’
uniform national UK rating system for the thermal performance of fenestration
products.
The BFRC rating applies to domestic windows only
and can be a way of complying with ADL-1B, Conservation of fuel
and power in existing dwellings. The rating is a comparison,
not an absolute scale. It is designed to provide an easy to understand
way for consumers and specifiers to compare competing products.
For this reason all BFRC ratings are calculated for windows that are
1430mm by 1230mm (as set out in GGF Data Sheet 2.2).
The BFRC Rating Equation
The BFRC Rating equation is;
BFRC Rating =
218.6 x Window Solar Factor
– 68.5
x (Window U-value + Effective Air Infiltration Factor)
The units
are kWh/m2/year.
The window solar factor (g-value) is a measure of
the amount of heat gain from sunlight. The solar factor
is expressed as a number between 0 and 1. A lower solar factor
means less heat gain.
It is important that the correct g-value is used
for the calculation. In most cases the g-value of the glass
is available from the glass supplier. Usually the g-value
perpendicular to the glass surface is given which needs to be converted
into a time-averaged g-value. The actual g-value used in the
calculation is that for the window which can be found from the time-averaged
glass value by knowing the window sightlines (including all gaskets etc).
The window thermal transmittance (U-value) measures
how good a product is at preventing heat from escaping.
The lower the U-value the better the product is at preventing heat
escaping. The U-value used for the BFRC rating equation is that
of the whole window and not that of the glass. The U-value of
the window should be provided from detailed simulations carried out
by BFRC Certified Simulators to BS EN ISO 10077-2.
A lower number for the window air leakage means
less uncontrolled air leakage and heat loss. Air leakage
rates for buildings and building components are measured with a pressure
difference of 50 Pa between the internal and external air pressures.
This air leakage rate is not suitable for use in energy calculations
and has to be scaled back to more accurately represent the true value.
Existing air leakage results may be used if the test was performed by
a UKAS laboratory according to BS 6375 Part 1.
The BFRC Rating number is calculated using the BFRC
Rating equation. This gives the numerical BFRC Rating (generally
a negative number) that can be converted to an A-G band.
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BFRC Rating Scale
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BFRC Rating
[kWh/m2/year]
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A
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0 or greater
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B
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-10 to < 0
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C
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-20 to < -10
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D
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-30 to < -20
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E
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-50 to < -30
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F
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-70 to < -50
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G
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Less than -70
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BFRC
Label
A BFRC
label refers to a specified and defined window configuration and
size manufactured from specified and defined parts. The label
consists of a graphical representation of the energy rating band,
the actual Rating number and the individual values for the thermal transmittance,
solar factor and air leakage. The climate zone is also included
as this will dictate the actual BFRC rating. For example in some
cold climates it may be beneficial to higher solar factor, so this
would have to be taken into account when deciding the rating boundaries.
An example of a BFRC label is shown below.
How to obtain a BFRC rating
Full
details on how to obtain a BFRC rating, and the fees involved, are given
in the
BFRC
website. Manufacturers are required to have a recognised
quality management system in place (BS EN ISO 9001 or similar approval).
The main steps are as follows:
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Appoint an Independent Agency (IA) – they are the managers
of the BFRC process;
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IA verifies all window simulations. Those
carried out by a BFRC Certified Simulator are automatically accepted.
If window simulations have not previously been carried out, the IA
will do these;
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Approval of suitable quality management system.
If one is not in place the IA will assist with the setting up of
one;
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After successful completion of the verification
process the IA informs the manufacturer and requests authorisation
to release the results to the BFRC for formal recognition and listing.
After release of results and payment of the BFRC fees,
the BFRC will:
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List the product on the BFRC web based database;
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List the products on the Energy Efficient Window database;
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Authorise the manufacturer to use the BFRC Window Energy
Label on BFRC Certified products;
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Authorise the manufacturer to use the BFRC Window Energy
Label and information in appropriate publications.
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