Clearview National November 2014 - Issue 156 | Page 84
glass&sealedunits
BFRC and
Measured
Thermal
Conductivity Values
»»BFRC 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 100772 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 BundesverbandFlachglas (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/bfdata-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?
BFRC license holders can of
course 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. Yet,
under certain circumstances, it
is possible to substitute certain
components without requiring a
re-simulation.
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 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 better thermal
performance is only permissible
providing the type and depth of
secondary sealant is unchanged.
If, when changing a spacer
bar, a modification to the type
or depth of secondary sealant
is necessary, then re-simulation
would be needed, as under these
circumstances 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 reevaluation 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
84 » N OV 2014 » CL EARVI E W- UK . C O M
Image courtesy of the
Thermoseal Group
replacement
has an equal or lower
effective thermal conductivity
(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.”
I’ve been told that my BFRC
license is valid for 5 years. Is
this true?
BFRC licenses are created as a
result of a BFRC simulation being
undertaken for a given set of
components i.e. Frame sections,
reinforcement (if applicable),
Glass types, spacer bars and
sealants. The existing BFRC
license is valid for five years
provided the component parts
remain commercially available.
If a given component has been
superseded by a replacement
with equivalent or better thermal
performance then simple
substitution may be possible
without full re-simulation.
However, in cases where the
replacement part has an inferior
thermal performance, simple
substitution is not permitted and
a new license will be required
(supported by updated simulation
data).
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.
Does using the BF 2 box models
prevent changing the type of
secondary sealant?
The BF website lists test reports
in two categories.
At the top of the page are
results for spacer bars which can
be simulated with both PU / PS
and Hot Melt sealants, as they
have demonstrated the ability to
Pass EN 1279 parts 2 and 3 with
all secondary sealant types.
At the bottom of the page is
a list of spacer bars that have
only been tested with Hot Melt
sealant and can therefore only
be simulated with this type of
sealant. BFRC will only accept
simulation reports that have a
listed combination of spacer bar
and sealant.
For further information
contact BFRC direct by
calling 020 7403 9200 or
email [email protected]