This is part two of a three-part blog series analysing the correlation between building energy code stringency and technology adoption, using fenestration thermal zone technology – polyamide thermal barriers and warm-edge spacer – as an example. Part one reviewed the current state of the art in thermal barrier and insulating glass unit (IGU) warm-edge spacer technology and the leadership role northern European countries have played in driving innovation in this area, in large part due to stringent code U-factor requirements.
In case you missed it, you can read part 1 HERE
Part two will review the current state of technology adoption and related code stringency in North America – the U.S. and Canada. To support climate comparisons with countries in Europe, figure 1 shows a climate zone map of the world.
Cover Image: Photo by Steve LeBlanc, Contract Glaziers
The United States
In the U.S., code adoption is fragmented and slow, with individual states determining their own building energy codes. Some states have no state-wide building energy code at all, leaving it to local towns and cities to create requirements. Most states adopt a version (sometimes modified) of one of two national model codes: 1) The International Energy Conservation Code (IECC) or 2) the ANSI/ASHRAE/IES Standard 90.1 (ASHRAE 90.1) which is an American National Standards Institute (ANSI) standard, published by the ASHRAE, and co-sponsored by Illuminating Engineering Society (IES). Both are revised on a three-year cycle.
All codes have a prescriptive and a performance compliance path. The performance path uses building energy simulation to demonstrate the building design performs as well or better than the reference building. The reference building is defined using the specified component requirements of the prescriptive compliance path.
Figure 2 shows a map of the prescriptive U-factor requirements (NFRC) for U.S. commercial buildings. As expected, the warmer southern climate zones typically have higher maximum U-factors than those in the colder northern zones. The maximum U-factors are a function of the version of the IECC or ASHRAE 90.1 adopted and the climate zone, and represent a best case for actual installed fenestration performance in new construction.
Typically, installed fenestration has higher U-factors because of the use of the performance path. This approach allows designers to trade off lower envelope thermal performance with increases in the efficiency of internal systems if the overall energy performance meets the target. This is typically the lowest cost route. However, Massachusetts, Washington state, and New York City have recently implemented a maximum total envelope U-factor limit (envelope backstop) to reduce the extent of this trade-off. The positive impact on fenestration performance is most noticeable in Massachusetts where the backstop is more limiting.
Also, many states are still referencing the IECC 2012 and 2015 versions, which allow the performance path of the equivalent 2010 and 2013 versions of the ASHRAE Standard 90.1 to be used. The window U-factors in these versions were significantly higher than those in the IECC.
Considering the differences in U-factor calculation, the U.S. requirements, even in the central and northern climate zones – including cities like Chicago, Boston, New York, Seattle, Minneapolis, San Francisco, and Washington, D.C. – are less stringent than in similar climates in northern Europe. For example, the climate of Minneapolis has been compared to that of Moscow (or colder), Chicago to Kiev, Philadelphia to Salzburg, Boston to Berlin.
Only in a very small northern part of the U.S. does the requirement fall below 2.0 W/m2K (NFRC). A maximum prescriptive U-factor of 2.2-2.7 W/m2K is more typical in the more populated central and northern areas, which can be achieved in an aluminium window by using a standard argon-filled low-e dual pane IGU, aluminium spacer, and small (</=15mm), simple thermal breaks (Figure 3).
With no separate requirements for centre of glass, frame, and edge of glass, North American windows are typically designed with narrow frames to maximize the impact of the glass performance on the assembly U-factor. As a result, the business-as-usual commercial window systems installed in the U.S. use thermal break technology introduced more than three decades ago (see Figure 4) and the penetration of warm-edge spacer remains low, at 10-20%, but dual-pane insulating glass with high-performance low-e coatings and argon fill is common.
Many U.S. fabricators do offer aluminium windows performing at 1.1 W/m2K (NFRC) and better (Figure 5), and warm-edge spacer is available from most glass fabricators. They are just not widely used in commercial buildings – at least not yet.
Interestingly, the adoption of warm-edge spacer is much higher in U.S. residential windows. This has been, in part, driven by compliance to the above code EnergyStar program, which has become a market norm. Also, the residential-style warm-edge spacer and sealant system combinations – such as foam and u-channel with hotmelt butyl – support low-cost, high-volume production capability, but are typically not suitable for commercial applications.
Although much of Canada is much colder than the U.S., many of Canada’s population centres – such as Vancouver, Toronto, and Ottawa – are in the same climate zones as those of northern U.S. states. Typically, the standard fenestration installed in these Canadian cities have higher thermal performance than those in the northern U.S. This is because of more stringent code requirements, which are rapidly growing more stringent aligned with the Pan-Canadian Framework on Clean Growth and Climate Change. The maximum U-factor for commercial fenestration prescribed by Canada’s National Energy Code for Buildings (NECB) is currently 1.4 to 2.4 W/m2K depending on climate zone and province, with large reductions coming in 2022.
Several Canadian cities and provinces – such as Toronto, Vancouver, and British Columbia – already have adopted more stringent requirements. In fact, British Columbia (including Vancouver) borrowed measured envelope air-tightness and thermal performance requirements from the Passive House International standard.
British Columbia’s Step Code creates tiers of increasing performance levels, charting a path to net-zero energy readiness by 2032 and signaling to the market exactly what performance will be needed and when. The province has built incentive programs to drive adoption of higher tier performance prior to when each will be mandated to drive innovation and performance. This tiered format is likely to be adopted by the NECB in future revisions.
Consequently, the typical thermal barrier size is currently 24 to 38mm in Canada, moving to 44 to 48mm next year (Figure 4). Some complex polyamide thermal barrier systems with fins are also used in colder regions, such as Quebec. Additionally, low conductivity polyamide materials are being used in new fenestration designs where system depth is limited, such as in sliding doors. The adoption of warm-edge spacer in commercial applications is also high, estimated at over 80%.
In part three of this blog series, we will conclude with a review of the status of code stringency and thermal zone technology adoption in China and Australia. Comparisons will be made across all the regions we have reviewed, connecting code requirements, and the specifics of language around fenestration and fenestration component minimum performance, with the extent of technology adoption.
In case you missed it, you can read part 1 HERE. Part 3 of this blog series will be published on 2nd July 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