Residential Performance:
Annual Energy Database

Over the past several years, the National Fenestration Rating Council (NFRC) has developed technical procedures for determining the thermal performance properties of fenestration products. These properties document the thermal performance of the product in response to specific physical effects. U-factors define heat transfer as a function of temperature differences, Solar Heat Gain Coefficients are the fraction of incident solar radiation transmitted into the space, and Air Infiltration measures heat transfer as a function of a pressure differential.

For the consumer or lay-person looking to understand the energy (heating and/or cooling) impacts of specific windows in typical residential applications, and to select an appropriate window for their application, they must balance the positive and negative effects of these three parameters. For example, during the heating season, solar gains through a window can often counter heat lost through a window due to temperature differences (U-factor effect) and pressure differences (Air Infiltration effect). During the cooling season, solar heat gains are the dominant source of unwanted heat gain in a typical residential building; U-factors and Air-Infiltration rates play an additional role, typically minor.

Members of the NFRC's Annual Energy Subcommittee are developing a simulation based procedure to evaluate the energy (and associated cost) impacts of windows and other fenestration products.  The (climate dependent) modeling assumptions used in this exercise were intended to represent typical new houses in the United States.  (As part of the accompanying RESFEN software development effort, similar modeling assumptions were developed for typical existing houses.)

The efforts of this NFRC subcommittee to date include several databases of heating and cooling energies, for typical windows, in 52 North American climates. These databasases are downloadable. (Future efforts will address the effects of skylights and existing construction.) This subcommittee is currently exploring how to simplify these database sinto a rating.

Other supporting documentation:

• Initial Review of Impacts of NFRC Board Committee Proposed Changes for Residential Modeling Assumptions
  Joe Huang, Robin Mitchell, Steve Selkowitz; LBNL; December 2003
• Impacts of AEP Modeling Assumptions: An Initial Study
  Steve Selkowitz, Robin Mitchell, Dariush Arasteh; LBNL; July 2007

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