02372nas a2200181 4500008004100000050001500041245012000056210006900176300001200245490000700257520173300264100002101997700002502018700002602043700002402069700002202093856007502115 2008 eng d aLBNL-1022E00aDeveloping Low-Conductance Window Frames: Capabilities and Limitations of Current Window Heat Transfer Design Tools0 aDeveloping LowConductance Window Frames Capabilities and Limitat a131-1530 v323 a

While window frames typically represent 20-30% of the overall window area, their impact on the total window heat transfer rates may be much larger. This effect is even greater in low-conductance (highly insulating) windows which incorporate very low conductance glazings. Developing low-conductance window frames requires accurate simulation tools for product research and development. Based on a literature review and an evaluation of current methods of modeling heat transfer through window frames, we conclude that current procedures specified in ISO standards are not sufficiently adequate for accurately evaluating heat transfer through the low-conductance frames.

We conclude that the near-term priorities for improving the modeling of heat transfer through low-conductance frames are:

  1. Add 2-D view-factor radiation to standard modeling and examine the current practice of averaging surface emissivity based on area weighting and the process of making an equivalent rectangular frame cavity.
  2. Assess 3-D radiation effects in frame cavities and develop recommendation for inclusion into the design fenestration tools.
  3. Assess existing correlations for convection in vertical cavities using CFD.
  4. Study 2-D and 3-D natural convection heat transfer in frame cavities for cavities that are proven to be deficient from item 3 above. Recommend improved correlations or full CFD modeling into ISO standards and design fenestration tools, if appropriate.
  5. Study 3 D hardware short-circuits and propose methods to ensure that these effects are incorporated into ratings.
  6. Study the heat transfer effects of ventilated frame cavities and propose updated correlations.
1 aGustavsen, Arlid1 aArasteh, Dariush, K.1 aJelle, Bjørn, Petter1 aCurcija, Dragan, C.1 aKohler, Christian uhttps://facades.lbl.gov/publications/developing-low-conductance-window01246nas a2200169 4500008004100000050001500041245006200056210006100118260002500179520069000204100001900894700002000913700002700933700002500960700002200985856006901007 2004 eng d aLBNL-5551700aDevelopment of Trade-Off Equations for EnergyStar Windows0 aDevelopment of TradeOff Equations for EnergyStar Windows aBoulder, COc08/20043 a

The authors explore the feasibility of adding a performance option to DOE's EnergyStar© Windows program whereby windows of differing U-factors and SHGCs can qualify so long as they have equivalent annual energy performance. An iterative simulation procedure is used to calculate trade-off equations giving the change in SHGC needed to compensate for a change in U-factor. Of the four EnergyStar© Window climate zones, trade-off equations are possible only in the Northern and Southern zones. In the North/Central and South/Central zones, equations are not possible either because of large intrazone climate variations or the current SHGC requirements are already near optimum.

1 aHuang, Yu, Joe1 aMitchell, Robin1 aSelkowitz, Stephen, E.1 aArasteh, Dariush, K.1 aClear, Robert, D. uhttps://facades.lbl.gov/publications/development-trade-equations01238nas a2200169 4500008004100000050001500041245008000056210006900136260002700205520065300232100002500885700001900910700002000929700002200949700002200971856007500993 1999 eng d aLBNL-4402000aA Database of Window Annual Energy Use in Typical North American Residences0 aDatabase of Window Annual Energy Use in Typical North American R aDallas, Texasc02/20003 a

This paper documents efforts by the National Fenestration Rating Council to develop a database on annual energy impacts of windows in a typical new, single family, single story residence in various U.S. and Canadian climates. The result is a database of space heating and space cooling energies for 14 typical windows in 52 North American climates. (Future efforts will address the effects of skylights.) This paper describes how this database was created, documents the assumptions used in creating this database, elaborates on assumptions, which need further research, examines the results, and describes the possible uses of the database.

1 aArasteh, Dariush, K.1 aHuang, Yu, Joe1 aMitchell, Robin1 aClear, Robert, D.1 aKohler, Christian uhttps://facades.lbl.gov/publications/database-window-annual-energy-use