'A' Energy Rating for Mumford & Wood
The majority of Mumford & Wood’s vertical sliding sash windows manufactured for use in new build, renovation and refurbishment projects are at least 1300mm wide and over 2.15m tall. Window units with this or a greater area, and using the standard Mumford &Wood frame sections, will achieve an indicative energy rating of ‘A’, the highest standard available using BFRC energy analysis tools.
Solar gain is a significant beneficial element in assessing the overall energy rating and this ‘free’ heat increases in relation to the larger glazed surface area available. This heat must be obtained in such a way that reduces its loss back to the environment.
A low ‘U’ value for the combined glazed
unit and frame sections means reduced heat transfer. The overall energy rating is affected more by the solar gain than the ‘U’ value of the IGU. Therefore the more glass area relative to the frame area, the better the result – hence bigger windows will have better energy ratings and smaller windows will have lower energy ratings. (See attached matrix showing the range that could be expected from our standard sash*.)
The BFRC rating process uses software that allows accredited simulators to calculate formal energy ratings. These ratings are established using a window unit of only 1230mm wide and just 1480mm high. With such a small glazed area, energy-rating calculations indicate a C rating for a Mumford & Wood unit if made to this size, which advances to a B rating if non-standard, thinner frame sections were to be used.
The Mumford & Wood standard specification for their range of vertical sliding sash windows includes a 4/14/4 double glazed unit using a Low iron/Low E glass combination with a 90% argon gas fill.
Mike Harris, Technical Director, Mumford & Wood, rightly points out that ratings should apply to window sizes frequently installed in British buildings. “Premium quality developments and prestigious renovations all take VSS units at least 2.150m tall. The ‘A’ rating achieved at this size and above, provides M&W customers with the highest possible combination of thermal performance, operational efficiency and recognised aesthetics.”
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