Launching LEAFF

The National Fenestration Rating Council’s Linear Energy Analysis for Fenestration (LEAFF) new simulation methodology aims to reduce the amount of time required to conduct simulation testing, streamline the certification process and empower manufacturers to advance the continuous improvement of fenestration products.

NFRC estimates LEAFF will roll out in the next six months. Manufacturers do not need to be NFRC members to use the tool; it is available for everyone. As with any new process, there’s often a learning curve, and NFRC plans to offer a training session in late May.

How it Works – Trendlines

Formerly known as Residential Component-Based Calculation, the LEAFF methodology leverages the simulation process that NFRC has relied on for more than 30 years.  

The LEAFF method establishes a fenestration product’s energy performance with various glazing and frame types using product-line characteristics to determine trendlines. This replaces the need to run multiple simulations separately.

Current simulating procedures for residential products allow manufacturers to produce the matrix of performance data they need, but as these matrices grow and new options for improving thermal performance enter the market, these procedures have become time consuming and costly.

Furthermore, these current procedures often require simulating numerous individual product options for a product line. A product line with 100 individual product options, for instance, could require modeling 20 individual options or possibly all 100. 

Seeking a Solution

The LEAFF methodology provides a more efficient alternative by using a regression line (trendline) approach based on the center-of-glass (COG) U-factor value. 

The trendline is calculated by plotting three product options that generates a slope intercept formula (y=mx+b). Generally, there will be multiple trendlines for each product line. To calculate the whole product U-factor rating, the LEAFF Certified Simulator places the COG value for a specific glazing option in the formula. Going back to the example of the product line with 100 options, if there are three trendlines when using LEAFF, the simulator is required to model just nine options. 

While investigating the viability of a component methodology for NFRC’s residential certification program, staff experienced two “ah-ha” moments. 

The first occurred when they uncovered how to categorize all the components to determine the number of trendlines. When comparing LEAFF whole product ratings to the current methodology, research showed that the LEAFF methodology’s ratings were a maximum of +/- 0.003 Btu/h·ft2·ºF different. 

The second came when they realized modeling can be reduced 80 to 99 percent when adding options to a product line that is certified using LEAFF. Today, if you add an option, in most cases, you have to model it to generate the whole product ratings. LEAFF, however, eliminates the modeling when the options can use an already established trendline. The simulator creates the glazing option, applies the COG U-factor to the trendline formula, and you have the whole product rating. 

Once users become acclimated with the new methodology, LEAFF has the potential to reduce the time required for performing certain simulations. Simplifying the certification process and decreasing the manufacturer’s time to market are the two potential benefits that could come from this.