This is the last in a three-part blog series exploring the impact of building code stringency and the rate of thermal zone technology adoption in fenestration systems used in typical construction across the globe. To date, we have reviewed Europe and North America. In this last part, we focus on China and Australia, and summarize the correlation between code stringency and technology adoption.
China is split into five climate zones with maximum fenestration U-factor requirements governed by the national design standard for energy efficiency for commercial (GB-50189 – 2015) and high-rise residential buildings as follows:
- Severe cold (Inner Mongolia, Jilin) ≤ 2.0 W/m2K [JGJ 26-2018]
- Cold (Beijing, Tianjin) ≤ 2.5 W/m2K [JGJ 26-2018]
- Hot summer/cold winter (Shanghai, Jiangsu) ≤ 3.2 W/m2K [JGJ 134-2018]
- Temperate (Yunnan) ≤ 3.8 W/m2K [JGJ 475-2019]
- Hot summer/warm winter (Guangdong, Fujian) ≤ 3.2 W/m2K. [JGJ 75-2021]
China is moving quickly to mandate higher performance fenestration, with some local jurisdictions driving more stringent performance requirements with their provincial and local codes as illustrated in Figure 1. Although the national design standards allow U-factors from 2.0-3.8 W/m2K, as of 2021, local provinces will mandate equal or lower U-factors than the national design standard for high-rise residential buildings.
For example, Beijing (cold) and the province of Jiangsu (hot summer/cold winter) require fenestration U-factors of 1.1 W/m2K and 2.4 W/m2K, respectively (see Figure 1). The latter requirement in Jiangsu is expected to reduce further to 1.8 W/m2K in 2022. The national design standards for commercial buildings are generally tighter than the high-rise residential requirement. In Guangdong and Shanghai, the commercial requirements are 2.5 W/m2K and 1.8 W/m2K respectively. China’s U-factor requirements for cold climate regions are more stringent than the current requirements in the cold climate northern U.S.
Figure 2 shows example fenestration configurations that meet Window U-factors (Chinese methodology) from 1.1 W/m2K to 3.1 W/m2K to enable comparison to other regions.
In addition to a U-factor requirement, the Chinese provincial codes give a recommendation and, in some cases, a mandate for the size of the thermal barrier to ensure that the fenestration hits the target U-factor. Beijing recommends at least a 39mm thermal barrier to hit the 1.1 W/m2K target. Shanghai’s provincial code requirement mandates the use of a thermal barrier larger than 24mm to ensure achieving the 2.2 W/m2K target.
The low maximum U-factor requirements, coupled with this call for thermal barrier width, is leading to wider and more complex thermal barrier technology becoming mainstream in northern China before it is in the northern U.S. (See Figure 3.) A focus on improving the frame performance first also reduces the tendency for over-reliance on centre of glass U-factor to achieve the assembly performance, delivering more balanced performance and better condensation resistance.
Australia is split into eight climate zones ranging from snowy “alpine” to tropical “high humidity, summer, warm winter”. The major population areas lie in the cool, mild and warm temperate, and warm humid summer/mild winter climate zones. Melbourne is in the mild temperate zone with a climate akin to northern California. Brisbane is in the warm humid summer/mild winter zone, with a climate similar to Florida. Likewise, cooler Canberra has a climate like northern Spain.
Australian building codes set a maximum area weighted U-factor and minimum area-weighted solar heat gain coefficient for the whole wall assembly, averaging opaque and transparent areas. Like in the U.S, use of the performance compliance path allows poorer envelope performance to be traded off with increased efficiency of internal systems.
Until recently, these requirements resulted in installed fenestration with a relatively poor U-factor of 3.0 to 3.5 W/m2K in the temperate climate zones, with even lower performance installed in hotter zones (Figure 5). This performance has been typically achieved by just focusing on improving the centre of glass performance by adopting dual-pane, low-e coated IGU with air, or sometimes argon, depending on the performance needed in that range. Non-thermally broken frames and aluminium IGU spacer have been typical.
In Brisbane and farther north, non-thermally broken frames and single-pane glass have been the norm. Unlike in the similar climates of Miami and Guangdong, IGUs have not traditionally been used even to improve solar heat gain control in Australia. However, this has changed dramatically with a recent new code – NCC 2019. Designers are finding that they can now only achieve compliance with solar heat gain requirements by using triple silver low-e IGUs. The code also requires thermal comfort requirements to be applied to the performance path reference building, and introduces considerations for thermal bridging, both of which reduce the ability to use lower performing fenestration.
This new code, which came into effect in 2020, is also expected to improve the U-factor of installed fenestration to 2.5 to 3.0 W/m2K for the temperate regions, including Melbourne and Canberra. Achieving this performance requires no more than a small 12-15mm thermal barrier in the frame, along with a dual-pane low-e IGU and aluminium spacer. However, the backlog of projects designed to the old standard will delay the impact on business-as-usual for some time.
Glazing performance in Australia is really driven by regulation. Early adoption of new glazing technologies has only really occurred over the past 10 years. Still yet to get a foothold, this is putting Australia realistically 30 years behind the leaders in the world from a glazing performance perspective (Figure 3).
Adoption is determined by the codes
The data from across the globe illustrates clearly that widespread adoption of existing thermal zone technology for fenestration is driven primarily by a jurisdiction’s appetite for building energy efficiency. This, coupled with how prescriptive the code language is for minimum expected fenestration assembly and component level performance, appears to drive typical fenestration design – not the availability of technologies.
We see that climate type plays a role – colder climates will generally have lower U-factors prescribed than hotter climate zones to achieve a similar level of stringency. But when we compare typical fenestration in similar climates, the code stringency, and the way it is implemented, appear to be the most important factors driving installed window performance (Table 1).
Those energy codes that also specified maximum allowable U-factor and/or minimum thermal barrier dimensions (such as in China and Germany), even when following performance compliance paths, cause higher performance fenestration (and higher performance frames and edge of glass) to be adopted as business-as-usual.
In a similar vein, some U.S. states and cities – such as Washington, Massachusetts, and New York City – recently have adopted a maximum area weighted U-factor requirement for the entire envelope, or what is called an envelope backstop. As a result of the reduced ability to trade off lower performing fenestration for higher performing internal systems, higher performance fenestration is starting to be used more. This further demonstrates the power of setting minimum fenestration performance requirements to limit trade-offs, even when following performance compliance paths using whole building simulations.
The momentum for higher stringency codes to close the gap to those in much of Europe is rising in North America, China, and Australia. Thanks to northern Europe’s early drive, the technology to create high-performance fenestration to support higher building efficiency is both available and proven – it is just a matter of adopting it globally. As a result, adoption in other regions can move significantly faster than the 50-year evolution in Europe, which was gated by technology availability. For example, it took some provinces in China a much shorter time (e.g., 20-years) to catch up to the current fenestration “business-as-usual” status of Europe. The rate of adoption is just a function of code stringency and the willingness of the jurisdiction to change more rapidly business-as-usual.
With the equivalent of one New York City being added to the planet every 34 days for the next 40 years (Architecture 2030), stringent energy codes implemented globally are the key to creating more comfortable, healthy, and energy-efficient buildings, and, crucially, addressing the climate crisis.
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