Developing Low-conductance Window Frames: Capabilities and Limitations of Current Window Heat Transfer Design Tools — State-of-the-Art Review

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 that incorporate very low-conductance glazing. 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 2D 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. Asses 3D 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 2D and 3D 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 3D 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]  W. P. Goss,et al.  Two-dimensional finite-element model of heat transfer in complete fenestration systems , 1994 .

[2]  Yie Zhao.  Investigation of heat transfer performance in fenestration system based on finite element methods , 1998 .

[3]  Kuan-chao Chen,et al.  Natural convection in an air layer enclosed within rectangular cavities , 1978 .

[4]  Arild Gustavsen.  Heat transfer in window frames with internal cavities , 2001 .

[5]  Seppo A. Korpela,et al.  Multicellular natural convection in a vertical slot , 1983, Journal of Fluid Mechanics.

[6]  Sylvie Lorente,et al.  Multicellular natural convection in a high aspect ratio cavity: experimental and numerical results , 2000 .

[7]  T. Unny,et al.  Free convective heat transfer across inclined air layers , 1976 .

[8]  Dragan Curcija,et al.  Guidelines for modeling projecting fenestration products , 1998 .

[9]  Christian Kohler,et al.  Two-Dimensional Computational Fluid Dynamics and Conduction Simulations of Heat Transfer in Horizontal Window Frames with Internal Cavities , 2008 .

[10]  Roydon A. Fraser,et al.  Local heat transfer coefficients for a flush-mounted glazing unit , 1998 .

[11]  Svend Svendsen,et al.  Calculating the heat transfer coefficient of frame profiles with internal cavities , 2004 .

[12]  Arild Gustavsen,et al.  Two-Dimension Conduction and CFD Simulations for Heat Transfer inHorizontal Window Frame Cavities , 2005 .

[13]  W. P. Goss,et al.  Prediction of the multicellular flow regime of natural convection in fenestration glazing cavities , 1997 .

[14]  Viktor Polevikov,et al.  Numerical study of problems on high-intensive free convection , 1977 .

[15]  A. H. Elmahdy,et al.  Thermal performance of complex fenestration systems , 1994 .

[16]  Iso Tc,et al.  Thermal Performance of Windows, Doors and Shading Devices — Detailed Calculations , 2000 .

[17]  D. Arasteh,et al.  The Significance of Bolts in the Thermal Performance of Curtain-Wall Frames for Glazed Facades , 1997 .

[18]  Seppo A. Korpela,et al.  Heat Transfer Through a Double Pane Window , 1982 .

[19]  John L. Wright,et al.  A two-dimensional numerical model for natural convection in a vertical, rectangular window cavity , 1994 .

[20]  Arild Gustavsen,et al.  Natural Convection Effects in Three-Dimensional Windows Frames with Internal Cavities , 2001 .

[21]  E.R.G. Eckertf,et al.  Natural convection in an air layer enclosed between two vertical plates with different temperatures , 1961 .

[22]  K.G.T. Hollands,et al.  Heat Transfer by Natural Convection Across a Vertical Air Cavity of Large Aspect Ratio , 1996 .

[23]  Arild Gustavsen,et al.  Numerical Simulation of Natural Convection in Three-dimensional Cavities with a High Vertical Aspect Ratio and a Low Horizontal Aspect Ratio , 2007 .

[24]  Arild Gustavsen,et al.  Three-Dimensional Conjugate Computational Fluid Dynamics Simulations of Internal Window Frame Cavities Validated Using Infrared Thermography , 2001 .

[25]  K. Hollands,et al.  Heat Transfer by Natural Convection Across Vertical and Inclined Air Layers , 1982 .

[26]  K.G.T. Hollands,et al.  Analysis of Heat Transfer by Natural Convection Across Vertical Fluid Layers , 1977 .

[27]  G. Batchelor,et al.  Heat transfer by free convection across a closed cavity between vertical boundaries at different temperatures , 1954 .

[28]  John L. Wright,et al.  A Correlation to Quantify Convective Heat Transfer Between Vertical Window Glazings , 1996 .