17
PRO INSTALLER NOVEMBER 2014
PRO NEWS
@proinstaller1
BFRC, SPACER BARS &
MEASURED THERMAL
CONDUCTIVITY VALUES
The BFRC is the UK’s national system for rating Energy Efficient Windows and is responding to questions raised
following its statement clarifying the situation regarding measured thermal conductivity values for spacer bars.
Why has BFRC
changed the
way it deals
with simulating
spacer bars?
BFRC has adapted its
requirements to reflect
the changes to BS EN ISO
10077-2 2012. This standard
requires measured thermal conductivity values to
be derived according to a
very specific set of criteria.
BFRC investigations have
determined that the only
way to currently satisfy the
standard is to use a measured conductivity value
obtained from Bundesverband-Flachglas (BF) 2 box
model (currently this is the
only item of data taken from
the datasheet). Only datasheets currently available
on the BF website (www.
bundesverband-flachglas.
de/shop/kostenfreie-downloads/bf-data-sheets-english)
are deemed to be acceptable for new BFRC rating
applications or for product
substitutions.
These changes came into
place following numerous
discussions with industry.
Can BFRC license
holders substitute
components within
a licensed window?
Answer: BFRC license
holders can change the
components within a licensed window. However,
as these changes are likely
to have a substantial effect
on the window’s energy
rating performance, in
most cases a full re-simulation and re-evaluation
of the window in question
is required. Under certain
circumstances, it is possible
to substitute certain components without requiring a
re-simulation.
Image courtesy of
Thermoseal Group
components does
not result in a
lowering of the window’s
energy rating performance.
It is important to bear in
mind that simple substitution (without re-simulation)
is only permissible for
one component at a time.
For instance, substituting
a spacer bar of equal or
‘BFRC’s rules on substitution
without re-simulation are designed
to safeguard the homeowner’
The BFRC substitution
rules, which were created
in 2010 following consultation with the fenestration
industry, are still applicable and available, and are
designed to ensure that
any simple substitution of
better thermal performance
is only permissible providing the type and depth of
secondary sealant is unchanged. However, it is not
possible to guarantee that
the window’s energy rating
will not decrease slightly.
BFRC’s
rules on substitution without re-simulation are designed to
safeguard the homeowner in
that the WER performance
of a window will be the
same (or slightly better)
using these rules. Where
the performance cannot be
guaranteed to be the same
or better, a full re-simulation
and re-evaluation needs to
take place.
Clause 4 of the BFRC
Substitution Rules for Glazed
Units states that: “Spacer
bars (including the primary
sealant and desiccant) may
be substituted when the
replacement has an equal or
lower effective thermal con-
ductivity (measured to 3 decimal places)
than the spacer bar specified
in the original license.
Effective thermal conductivity of the spacer bar
(including the primary
sealant and desiccant) shall
be determined either by tabulated value from BS EN ISO
10077:2 2012 or if a measured value is required, thermal conductivity values shall
be obtained from a currently
listed 2 box model datasheet
from the BF website.” (Web
address as above)
What depth of
secondary seal
is used for rating
purposes?
All spacer bars are simulating as being positioned
with the top of the bar inset 12mm from the edge of
the glass, as this is how the
vast majority of IGU’s are
manufactured in the UK.
Deviation from this depth
is permitted provided
documentary evidence to
support the compliant manufacture is supplied and is
deemed to be acceptable
by BFRC’s technical committee. BFRC is consulting
with industry via the GGF
Technical Committee which
is currently reviewing the
sealant depth issue. More
information will be made
available in due course.
‘BFRC is consulting
with industry’
For further information
contact BFRC direct by
calling 020 7403 9200 or
email [email protected]