The importance of energy efficient building products is growing, driven in part by the increased stringency of local codes and standards. The Attachments Energy Rating Council (AERC) and Northwest Energy Efficiency Alliance (NEEA) suggest that window attachment products such as secondary glazing could provide a cost-effective retrofit solution to increase a building envelope’s energy efficiency and occupant comfort. In the session, “Pushing the (Building) Envelope with Commercial Secondary Window Field Tests,” hosted during the Association of Energy Services Professionals’ Annual Conference, panelists discussed the benefits of secondary glazing products.
Secondary Glazing Explained
Shannon Christie, program manager for AERC, explained that while building envelopes are a significant contributor to energy performance they often aren’t prioritized during energy retrofits. Poor building envelope performance can lead to occupant comfort issues and increased energy use.
“The Department of Energy has identified window attachments as a way to address this issue,” said Christie. “They are available at relatively lower price points compared to full window replacements.”
While common window attachment products such as blinds, storm windows or cellular shades are often thought of as aesthetic, they can also provide insulation and create energy savings of 3-30%, according to Christie. In addition to increased energy efficiency, window attachment products can provide added thermal comfort, reduced glare and noise reduction. AERC has a rating system for these types of products, which also include secondary glazing.
Secondary glazing can be affixed to the interior or exterior of a building’s existing windows and consists of glass, polymer or acrylic materials with aluminum or other types of frames. These products can consists of one or multiple glass lites, low-E coatings and even vacuum insulating glazing or photovoltaic coatings.
The NEEA Field Test
NEEA program manager Natalie Hatheway explains that adding secondary glazing can result in similar performance compared to a complete window replacement but with approximately 50% less cost, even more if a window replacement project would require cranes, large amounts of scaffolding or a tenant move out.
“Sometimes it can be more like 80% savings,” she said. “There are situations where the cost of secondary glazing is much less than a replacement.”
Hatheway said secondary glazing can lead to a 5-15% reduction in heating/cooling energy use and a reduction of $32 per square foot compared to window replacement, though the price depends on the extent of product customization. She said that, in an older building, if a baseline single-lite window’s U-value is 1.12, then with a single-lite secondary window it could be lowered to a U-value of 0.53. With a double-lite secondary window the U-value could be as low as 0.27. Secondary glazing products can create lower peak heating and cooling demand which means the HVAC system won’t have to work as hard to moderate building temperatures.
She looked at a case study of 195 Church Street in New Haven, Conn. The building was built in 1974 and still had its original windows. With a secondary glazing product from Wausau, the building experienced energy savings of 19% and annual cost savings of $203,000.
NEEA currently is conducting a commercial field test in the Northwest on commercial offices, schools and hospitality buildings. The organization has partnered with six secondary glazing manufacturers (Alpen, Larson, Allied Window, Maine Glass, Inovues and QuantaPanel) to offer a 12-30% discount on materials. NEEA also is offering an incentive of $1 per square foot up to $10,000. The organization will offer free energy modeling, installation support and in-depth technical support. The monitoring will last for nine months with pre- and post-installation thermal modeling. The study will begin in the spring.
Con Edison Program
Moshfiq Islam, senior specialist, energy efficiency and demand management at Con Edison, spoke about his company’s program for secondary glazing in the commercial, industrial and multifamily markets. He explained that New York City’s Local Law 97 will lead to upgrades on pre-1980s buildings with single glazing in the near future. Con Edison has identified secondary glazing as a viable and cost-effective solution.
Islam said that 20% of estimated incentives will be disbursed after the products’ installation with the remaining 80% disbursed after post-installation measurement and verification.