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.
“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,” said 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.
On the basis of the values determined by ift Rosenheim, Bundesverband Flachglas produces objective data sheets for each of eight representative Psi values per warm edge spacer bar system. These can be found here.
The explanations on the data sheets refer to the principles of the values shown: The equivalent thermal conductivity was determined in accordance with ift guideline WA-17/1 “Thermally improved spacer bars – Determining the equivalent thermal conductivity through measurement”. This confirms that the indicated values – in comparison to the merely “declared” values – are based on measurements and calculations. The basis for this is ift guideline WA-08/3 “Thermally improved spacer bars – Part 1: Determination of representative Psi values for profile sections of windows”.
The only recommendation, therefore, is to opt for spacer bars from manufacturers that have gone through this independent testing procedure and are able to present a data sheet from Bundesverband Flachglas.