Glass & Sealed Units Extra
PROUD SPONSOR OF GLASS & SEALED UNITS EXTRA
Identifying certified spacer bars
Independent test methods guarantee objective data
» WHILE HARDLY ANYONE HAD HEARD OF THE TERM “ warm edge ” just 10 short years ago , statutory requirements and increasing environmental awareness have ensured a gradual decline in the use of spacer bars made from aluminium or stainless steel . The number of providers of warm edge spacer bars has since grown accordingly – which makes it all the more important to know the differences between the products . Especially when it comes to the thermal values of the spacer bars , objective and comparable data are vital . Because these values support one of the most critical sales arguments for windows as the final product .
Generally speaking , it must be in the interest of providers to create transparency about the properties of a product , and in doing so make their customers feel confident about its quality . Just how important this is can be seen in the diesel emissions scandal in the automotive industry . “ Stringent tests for insulating glass units have long been prescribed by the RAL Quality Association . Our top priority as far as our customers are concerned is to be totally transparent and to comply with uniform guidelines for spacer bars . Everything else is to the detriment of our credibility ,” says Victoria Renz-Kiefel , Managing Director of SWISSPACER .
In the “ warm edge ” working group of Bundesverband Flachglas , the company is bracing itself for the regular verification of the thermal conductivity of warm edge spacer bars by ift Rosenheim ( German Window Technology Institute Rosenheim ). The working group also developed the new ift guideline VE-17 / 1 ” Product characteristics and test procedures for proving the usability of spacer bar systems in the glazing edge of insulating glass units ”. The guideline ’ s objective is to describe uniform test procedures that demonstrate the usability of the products in the glazing edge of insulating glass units .
The independent procedure for evaluating different spacer bars
The performance of the glazing edge flows into the calculation of the heat transfer coefficient for a window ( Uw ) via the length-related Psi value . This Psi value of the window or the façade describes the heat losses along the edge of the glass . The value takes into consideration the interaction of frame profile , glass , spacer bars and sealants , and is essentially determined by the thermal conductivity of the spacer bar . It can therefore be determined for the glazing edge overall only with specific information on the frame and glass .
But how is the Psi value arrived at ? And what exactly does an independent certificate look like for the important components of the spacer bar ? First , the thermal conductivity of the spacer bar , the
Influence of the areas on the Uw value . © SWISSPACER
so-called lambda value ( λ ), is determined by an independent institute ( ift Rosenheim ). This is done using a standardised measuring method established in the “ warm edge ” working group ( ift guideline WA- 17 / 1 “ Thermally improved spacer bars – Determining the equivalent thermal conductivity through measurement ”). The lambda value ( W / mK ) represents the thermal conductivity of a material and is one of the elementary values for assessing and determining that material ’ s suitability for construction or refurbishment purposes .
Moreover , each spacer bar achieves a very specific value . This is because both the precise composition of the material and the structure of the spacer bars vary from provider to provider and influence the thermal conductivity – for example , through the additional metalcoated foils that prevent the escape of the gas filling and the penetration of water vapour .
The exact values can be determined through measurements taken by independent institutes such as ift Rosenheim . We therefore speak of a lambda value that has been measured or determined using measuring equipment . In contrast to this , some providers supply data sheets or certificates with Psi values calculated in accordance with EN ISO 10077-2 . In the case of such certificates , it can be assumed that the spacer bar provider does not belong to the “ warm edge ” working group and is not in possession of a comparable data sheet with measured values , but instead indicates calculated values .
In order for the information on the thermal conductivity of the various spacer bar systems to be comparable , despite all the complexity , Bundesverband Flachglas carried out a research project and then transferred the results to a guideline ( ift guideline WA-08 / 3 “ Thermally improved spacer bars – Part 1 : Determination of representative Psi values for profile sections of windows ”). With this guideline , so-called representative Psi values can now be determined under exactly the same constraints for a uniform presentation of the results . In doing so , the representative Psi values are based on four common frame materials and two common glazing types – and thus provide an objective basis for comparison .
76 » SEP 2021 » CLEARVIEW-UK . COM