NFRC in the News

Evolution Toward Energy Ratings

National Fenestration Rating Council approves new technical standards for energy performance of nonresidential fenestration products

By Mike Manteghi and Charlie Curcija

Members of the National Fenestration Rating Council of Silver Spring , Md. , strive to implement a voluntary certification and labeling program to measure the performance of commercial windows and curtain walls. Discussions have been going on for many years, as has the research to back such an ambitious program. Below, a status report.

The National Fenestration Rating Council includes nonresidential products in its rating system within the framework of residential windows and based on 2001 procedures, with one notable exception: site-built products. Site-built products are manufactured by several parties – for instance, frame components are manufactured separately from insulating glass units – and often put together by an independent party, the glazing contractor or glazier. Recognizing this, NFRC has established separate procedures for these products. The council also has developed a separate certification process for buildings with more than 10,000 square feet of fenestration.

Who's Responsible?

This process is still very similar to the one for residential windows in that it requires a single party to take responsibility for certification. This task is often fulfilled by the framing system manufacturer, placing undue burden on one side, as the framing manufacturer's role is limited to selling and delivering frame lineals, then put together at the site. Meanwhile, insulating glass units manufactured by another party, are put into the framing system.

In 2001, a nonresidential group at NFRC started to overhaul the procedures and standards for nonresidential products. The Nonresidential Task Group became the Nonresidential Subcommittee, with Mike Manteghi, research and innovation director from TRACO of Cranberry Township, Pa., appointed as chair. Since then, a radically different methodology has been developed to address issues of importance for nonresidential products, such as:

•  A simple and workable rating system

•  Recognition for the effects of nonresidential fenestration products on building energy performance

•  Recognition for size-specific performance.

But in the end, the new methodology provided solutions to all these issues.

Charlie Curcija, senior research fellow of the University of Massachusetts at Amherst , led the development of technical procedures and helped prepare the NFRC standards, specifically, section 5.6 of NFRC 100 and 200. Theses standards were approved and made final at NFRC's spring meeting last March in Miami and await appropriate certification language and revision of the NFRC database structure before they can become fully implemented standards and procedures.

Component Modeling Procedure

The procedure is called the Component Modeling Procedure because the building blocks are basic fenestration components; glazing, spacers, frame cross sections and so forth. Rating of each component allows for a more flexible system where each component manufacturer can supply ratings. Insulating glass manufacturers will provide “center of glass” performance, spacer manufacturers will provide spacer performance and the frame manufacturers will provide frame-assembly performance indices. A manufacturer or fabricator can also provide all component information from one place, if desired. Instead of fixed-size ratings, the system provides comparison-type ratings with apples-to-apples comparisons. It also provides component performance indices for calculating size-specific performance as well as calculating energy performance of whole buildings. This is especially important for code compliance and accurate heating-ventilating and air conditioning system sizing and balancing. Instead of applying the same fixed-size ratings for all products, it will be possible to calculate the performance of a specific system installed in a specific building. The procedure proves natural solutions for site-built products as well.

In the past, one problem for site-built products was that each component was manufactured by a different entity and later put together by another party. The Component Procedure allows each manufacturer to provide its own component ratings, while the final integrator, the glazier or glazing contractor, can obtain whole product ratings by using component information and an approved integration tool available from NFRC.

Computer Simulations

The NFRC ratings are provided on labels with numbers produced exclusively by computer simulation. Physical testing is used only for validation purposes for products with no approved simulation procedure for products that don't validate. Validation is defined as an agreement between testing and baseline simulation results within specified tolerances. The majority of products are well within these validation limits, so, for all practical purposes, the numbers on a label come from computer simulations.

The new nonresidential procedure does not differ in that regard and goes a step further: Instead of modeling every single option, mainly individual products with different glazing, such as gas filling, coatings and spacer configurations, the nonresidential procedure uses only four base simulations called best-worst options. Namely, two generic glazing systems and two generic spacer configurations – representing opposite ends of the performance spectrum – are used for every product line.

Instead of modeling hundreds of different options, only four are modeled:

•  The best-best option represents the best glazing with the best spacer

•  The best-worst option represents the best glazing with the worst spacer

•  The worst-best option represents the worst glazing with the best spacer

•  The worst-worst option represents the worst glazing with the worst spacer

From these four base simulations, linear and logarithmic interpolations are used to generate any glazing or spacer configuration without further modeling. The method eliminates the need for simulating every option as is the present case. This simplifies a manufacturer's options, while saving money. The tool that will facilitate these interpolations, an advanced database, is under development and will be available by the time the NFRC certification procedures and language are ready.

Timeline

Completion of the nonresidential rating system and tools are planned for the end of 2005, and a pilot project will commence in 2006 with a final rating system implementation date of Jan. 1, 2007 .

Manufacturers of nonresidential products will receive label certificates for their products and projects under the new system and they will benefit by their ability to meet code requirements.

Meanwhile, please keep in mind that NFRC does not set code requirements. NFRC ratings simply reflect product performance and are determined in a fair, accurate and credible manner. These performance indices are put on a label or label certificate and it is up to code bodies to set minimum levels of thermal performance.

The cost to manufacturers will be comparable to the cost of complying with the present residential rating system.

Manufacturers of nonresidential windows and curtain walls have voiced concern that the existing program may be complex and cumbersome, but the new nonresidential procedure has been developed with these concerns in mind and with the participation from members of the industry. Furthermore, NFRC subcommittee members encourage industry participants to continue contributing to the development of these standards and expressing their concerns about it. For more information, contact NFRC at info@nfrc.org or visit www.nfrc.org .

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Manteghi is the research and innovation director for TRACO of Cranberry Township, Pa., and a member of the National Fenestration Rating council Board of Directors; Curcija is a senior research fellow at the University of Massachusetts in Amherst .