The importance of service life for IGUs
Why design-related decisions are crucial for reducing environmental impact
An article in Glass Magazine® by Helen Sanders
Architectural and design firms, as well as some regulatory bodies, increasingly require environmental impact data for building systems. While designers are requesting carbon footprint metrics to quantify the embodied carbon of insu-lating glass units, the design community should also consider IGU service life—the estimated time an IGU can function be-fore needing to be repaired or replaced.
An understanding of service life, and how it relates to environmental impact, is crucial to capture the full carbon reduction potential of high performance IGUs.
Operational carbon and embodied carbon Carbon emissions for glazing systems are often measured through two metrics: operational carbon and embodied carbon. Both metrics are important to understand with regard to reducing building emissions.
Operational carbon, or OC, is the carbon emissions caused by operating a building. For most buildings, the improved energy efficiency of building materials results in reduced OC. Howev-er, this is not always the case—for example, when a building’s power is sourced from clean ener-gy, such as on-site renewables or a low-carbon electric grid, even an energy inefficient building could have low OC.
Embodied carbon, or EC, is the carbon emitted during a product’s raw material extraction and manufacturing. Approximately 75% of an IGU’s EC is from energy-intensive flat glass production (see Figure-1). Only 10% is due to the insulating glass process itself—approximately half from the electricity to run the IG line and half from the edge seal materials (spacer, sealants, desiccant).
Most factors that impact an IGU’s EC are those that glass fabricators cannot change. The project-specific IGU design itself determines the EC—the number and thickness of the lites, the heat treat-ment, as well as the edge seal materials specified. The fabricator’s location also impacts the product’s EC, depending on the electric grid’s carbon intensity. In addition, the dual seal polyisobutylene, or PIB, and silicone edge seal system is ubiquitous in commercial IGU applica-tions. The quantities used are deter-mined by durability needs and similar for all fabricators.
For IGUs, service life matters IGUs have an important role to play in reducing both the OC and EC of a building. High-performance fenestration can play a significant role in reducing OC by reducing a building’s lifetime heating and cooling loads, assuming the fenestration’s efficiency performance does not degrade. These emissions reductions accrue through the building’s service life. Maximizing fenestration service life is therefore critical to maximizing accrued emissions reductions.
Extending the service life of an IGU assembly also plays a critical role in reducing a building’s EC. Securing a long service life for an assembly also pre-serves the large upfront EC investment in the flat glass used to make the IGU. For example, selecting an alternative product that halves the upfront EC, but also halves the service life, is not a better choice. Due to its shorter service life, the IGU will need to be replaced sooner, which then increases the overall EC for the building. EC per year of service life is an important (but not yet widely utilized) metric that should be used to support product selection.
Best practices for managing IGU service life
For these reasons, asking for the carbon footprint of IGUs from different fabrica-tors to make supply chain decisions is not meaningful for project-level carbon reduction decision-making.
While the impact of IGU manufacturing on EC seems minor, the edge seal selection details and manufacturing quality have an oversized impact on service life, which is a driver of long-term embodied and operational carbon emissions.
An IGU’s service life is maximized if:
- Its edge seal is carefully designed to manage the environmental conditions and climate loads;
- Its edge seal uses high-quality spacer, desiccant and sealants in sufficient quantity, and if those materials are appropriate to the application and work effectively together as a system;
- It is manufactured with consistent and effective quality control; and
- It is carefully installed to effectively manage water, material compatibility and edge pressure, and provide suf-ficient edge support to manage shear and deflection.
Fabricator and installer certification programs—such as the IGCC/IGMA and IGMAC programs for IGU fabricators and the NACC and AGMT programs for installers—support quality fenestration designs, fabrication and installation. Choosing certified fabricators, IGU de-signs and installers can reduce service life risk, supporting improved perfor-mance and longevity.