The question of whether innovation is needed in glass and glazing was explored in the Spring 2021 issue of IGS. We identified a lack of adoption of current energy-saving technologies in the U.S., positing that significant impact could be made on building performance if the current state-of-the-art envelope technologies were fully adopted as business-as-usual.
Cover image (left to right): Leeza SOHO in Beijing, image courtesy of Hufton+Crow; Space Needle in Seattle, photo by Oakie on Unsplash; and 707 Fifth in Calgary, photo by Steve LeBlanc, Contractor Glaziers
The article hypothesized that a key reason for lack of existing technology adoption was due to lack of stringency in energy codes. To assess the correlation between code stringency and technology adoption, we have gathered the current business-as-usual in fenestration performance in several regions across the globe along with their corresponding code trajectories.
Sharing our assessment, we begin a three-part blog series:
Fenestration U-factor calculations across the globe
Before diving into the regional details, differences in calculation methodologies must be understood since fenestration U-factor procedures differ across the globe (Table 1). Disparities in calculation (simulation) methods, film coefficients, exterior temperature conditions, and standard sizes on which the calculations are made, create complexity of comparison between regions.
An excellent summary of the differences between U.S. and European standards was presented at the 14th Canadian Conference on Building Science and Technology. Variations in thermal performance of up to 25% have been reported between U.S. and European assembly U-factors! As we review different thermal performance requirements across the globe, please remember: A window with a U-factor of 2.0 W/m2K in Europe does not have equivalent performance to window with a 2.0 W/m2K in China nor to a window with a U-factor of 2.0 W/m2K in the U.S. However, within each region, the “lower is better” rule still applies for U-factor.
Current status of technology for fenestration thermal performance
Polyamide (PA) thermal barrier technology has evolved substantially during the past 50 years (Figure 1) to address all elements of heat transfer through a range of strategies: Increasing widths to over 100mm, creating additional shape complexity, and foam inserts to manage convection, implementing lower conductivity materials, and adding low-emittance films to reduce radiation. Customized systems have also been developed to support specialized applications like curtain wall pressure plates and sliding doors, and providing anti-bimetal functionality.
Warm-edge spacer, such as plastic hybrid stainless steel spacer (PHSS), has also been used in both residential and commercial applications for over 20 years. The widely used PHSS spacer typically can reduce the fenestration U-factor (National Fenestration Rating Council [NFRC] method) by about 0.1-0.2 W/m2K, and up to 0.3 W/m2K when used in structurally glazed systems.
Countries of western Europe – in particular, Germany, Poland, Switzerland, and Scandinavia – have been the engines driving the development of thermal break and warm-edge spacer technology. This is because of the stringency of their code requirements, and their colder climates compared to southern Europe (Figure 2).
In Germany, from 2002 to 2009, the maximum fenestration U-factor (European standard) was 1.7 W/m2K. (This is still more stringent than most places in the U.S. require in 2021). Since 2009, when the German performance-based code, EnEV, was made significantly more stringent, the requirement has been a very low 1.3 W/m2K. The EnEV includes low maximum U-factors, air-tightness and thermal bridging requirements, incentive schemes, and a target for a zero-energy standard for 2020.
A building design must show energy use of 75% or less than a reference building in which the default fenestration U-factor of 1.3 W/m2K is used. This approach supports the adoption of high thermal performance fenestration. Although the maximum fenestration U-factors have remained constant since 2009, the energy consumption targets for the buildings have continued to decrease since 2009, with 15% reductions in EnEV 2014 and EnEV 2016 versions, driving the use of yet lower fenestration U-factors.
As a result, the business-as-usual aluminium window installed in Germany is 75mm deep and uses a thermal barrier technology of around 40mm wide, incorporating a variety of sophisticated barrier types (Figure 3), and has a U-factor of 1.3 W/m2K or less. Triple pane use is widespread, and the penetration of warm-edge spacer technology is 70%-75%.
Warm-edge spacer penetration is even higher in Scandinavia at over 80%, and in Switzerland and Austria at around 90%.
Europe has been the global driver of innovation in thermal barrier and warm-edge spacer technology (Figure 4). Non-mandatory stretch standards like the Passive House Institute’s and those for net-zero energy buildings continue to drive further innovation in this area, charting a path for mandatory codes to follow, and supporting further technology adoption. Other areas of the globe are following Europe’s adoption path, some faster than others.
In parts two and three of this blog series, we will explore the fenestration thermal zone technology adoption in North America, China, and Australia, and their corresponding code structures that drive it.
Part 2 of this blog series will be published on 18th June 2021, to be notified of its release and other world class thought leadership, sign up to our newsletter HERE
Article courtesy of Technoform North America
Technoform North America: Helen Sanders, PhD, Helen.Sanders@technoform.com; Alex Blakeslee, Alexandra.Blakeslee@technoform.com
Technoform Asia-Pacific: Amos Seah, Amos.Seah@ap.technoform.com; Vincent Wardill, Vincent.Wardill@technoform.com
Technoform Europe, Middle East, and Africa: Jose Del Toro, Jose.DelToro@technoform.com