030 GGP 1213

GGP December 2013

Energy Efficiency 30 December 2013 A level playing field In relation to the BFRC’s recent clarification of validated conductivity values for warm edge spacers, Mark Hickox, sales director at Thermoseal Group, discusses the current requirements for spacer bar conductivity values. As members of the GGF and Bundesverband Flachglass (BF), we, like other spacer bar manufacturers, have been involved in many of the discussions leading to the current proposed route for establishing a fair and accepted method to calculate conductivity values. As outlined by the BFRC, future guidelines have not yet been set, but current requirements are that data from accredited sources is permitted providing it is fully compliant with BS EN 10077-2:2012. Therefore, reports such as those published by IFT Rosenheim or an equivalent test are accepted, but you should check with the BFRC that the particular report that you are given is both valid and accepted. Reports carried out by IFT Rosenheim are conducted using 15.5mm spacer bar (with PIB applied this gives an airspace of 16mm) and measure the thermal transmittance through the spacer bar (desiccant filled) sandwiched between two panes of glass. The actual result of this test is an average value rather than the ‘best’ result. We can provide a copy of this test method on request which can be used in Window Energy Rating (WER) simulations for any airspace. Please note that if you receive a test report for a spacer bar carried out on 20mm airspace, results can only be applied to glazing simulations of 20mm airspace and above. Improved energy efficiency Of course, for Thermobar warm edge spacer tube and Thermoflex warm edge foam spacer we have a full and valid IFT report which we can provide as required. As a warm edge spacer bar manufacturer we are continually striving for the best thermal values on the market and Thermobar and Thermoflex are both one of the best. However, when it comes to WERs, it’s important to remember that it is the thermal transmittance at the edge of the unit and not just about spacer bar value. In fact, the sealant can affect the overall edge value to a greater extent. That is why we are in favour of the proposed ‘Two Box Model’ for substitution which we put to the BFRC back in April. This takes into account the value of the whole edge of the unit and shows a comparison of the thermal performance through the edge of insulated glass, including spacer bar, desiccant, PIB and sealant. This is particularly important when you look at single seal systems such as foam spacer which currently use a minimum sealant depth of 5mm “as a warm edge spacer bar manufacturer, we are continually striving for the best” as opposed to an average depth of seal. If the average depth of seal were used in the calculations then sealant type would have more influence than spacer type. Back in April, we commissioned an independent consultant to produce a report showing thermal calculations using the ‘Two Box Model’. As per the drawings above which have been extracted from the report, the heat flow is calculated including box 1 (the secondary sealant) and box 2 (the spacer, PIB and desiccant combination). The Window Energy Rating’s scheme itself is also changing to strive for improved energy efficiency, hence the introduction of the new ‘A+’ rating from the BFRC and the ‘A*’ rating from CERTASS. These are new bands which effectively mean that they have a plus value rather than a zero or negative value which means that there is actual energy gain on the window. The two box model for substitution will mean that customers who opt for a Simple Energy Licence whether a band ‘C’, ‘B’, ‘A’, ‘A*’ or ‘A+’ will be able to swap spacer bar and sealant as long as the edge value is the same or better than the allowance within that rating. For a standard WER label which includes a published ‘U’ value we advise customers to select the rating that they require and then choose the products that have the lowest thermal performance that will achieve that rating to allow for substitution of any better performing product. For example, if they can achieve a ‘C’ rating using an aluminium spacer bar in a gas filled unit, then this is advised as they can then choose to exchange for any warm edge spacer bar tube to comply with guidelines for substitution – that substitution is allowed for any product that is considered the ‘same’ or ‘better’ in terms of performance within the unit. It’s worth noting that the BFRC will soon launch an online tool for substitution and registering simulations.


GGP December 2013
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