WINDOW

A computer program for calculating total window thermal performance indices

 

WINDOW

Berkeley Lab WINDOW is a publicly available computer program for calculating total window thermal performance indices (i.e. U-values, solar heat gain coefficients, shading coefficients, and visible transmittances). Berkeley Lab WINDOW provides a versatile heat transfer analysis method consistent with the updated rating procedure developed by the National Fenestration Rating Council (NFRC) that is consistent with the ISO 15099 standard. The program can be used to design and develop new products, to assist educators in teaching heat transfer through windows, and to help public officials in developing building energy codes.

For more information or user support, email WINDOWHelp@lbl.gov

Program Updates: 

The main change from Berkeley Lab WINDOW 5 to Berkeley Lab WINDOW 6 and 7 is the ability to model complex glazing systems, such as venetian blinds and roller shades. In addition, many bugs have been fixed.

Program Features: 

WINDOW features include:

  • updated algorithms for the calculation of total fenestration product U-values and Solar Heat Gain Coefficient consistent with ASHRAE SPC142, ISO15099, and the National Fenestration Rating Council
  • a Condensation Resistance Index in accordance with the NFRC 500 Standard
  • a surface temperature map
  • an integrated database of properties
  • links to other LBNL window analysis software:
    • THERM, for calculating 2-D frame and edge effects
    • RESFEN, for calculating the energy effects of windows in typical houses throughout the United States
    • Optics for the optical properties of all coated and uncoated glazings, laminates, and applied films.
Program Capabilities: 

WINDOW offers the following features:

  • The ability to analyze products made from any combination of glazing layers, gas layers, frames, spacers, and dividers under any environmental conditions and at any tilt;
  • updated algorithms for the calculation of total fenestration product U-values and Solar Heat Gain Coefficient consistent with ASHRAE The ability to model complex glazing systems such as venetian blinds and roller shades;
  • Directly accessible libraries of window system components, (glazing systems, glazing layers, gas fills, frame and divider elements), and environmental conditions;
  • The choice of working in English (IP), or Systeme International (SI) units;
  • Help Screens and a manual;
  • A print feature which generates detailed results for a window, window component, or library;
  • The ability to specify the dimensions and thermal properties of each frame element (header, sills, jamb, mullion) in a window;
  • A multi-band (wavelength-by-wavelength) spectral model;
  • A Glass Library which can access spectral data files for many common glazing materials from the Optics5 database;
  • A night-sky radiative model;
  • A link with the DOE-2.1E and EnergyPlus building energy analysis program.
Program Indices and Other Results: 

For a user-defined fenestration system and user-defined environmental conditions, WINDOW calculates:

  • The U-value, solar heat gain coefficient, shading coefficient, and visible transmittance for the complete window system;
  • The U-value, solar heat gain coefficient, shading coefficient, and visible transmittance for the glazing system (center-of-glass values);
  • The U-values of the frame and divider elements and corresponding edge-of-glass areas (based on generic correlations);
  • The total solar and visible transmittance and reflectances of the glazing system;
  • Color properties, i.e. L*, a*, and b* color coordinates, dominant wavelength, and purity for transmitted and reflected (outdoor) solar radiation;
  • The damage-weighted transmittance of the glazing system between 0.3 and 0.38 microns;
  • The angular dependence of the solar and visible transmittances, solar and visible reflectances, solar absorptance, and solar heat gain coefficient of the glazing system;
  • The percent relative humidity of the inside and outside air for which condensation will occur on the interior and exterior glazing surfaces respectively;
  • The center-of-glass temperature distribution.