MODELING WINDOWS IN DOE-2.1E

The most recent version of the DOE-2 building energy simulation progra m, DOE-2.1E, provides for more detailed modeling of the thermal and op tical properties of windows. The window calculations account for the t emperature effects on U-value, and update the incident angle correlati ons for the solar heat gain properties and visible transmittance. Init ial studies show up to a 35% difference in calculating peak solar heat gain between the detailed approach and a constant shading-coefficient approach. The modeling approach is adapted from Lawrence Berkeley Lab oratory's WINDOW 4 computer program, which is used in the National Fen estration Rating Council (NFRC) U-value rating procedure 100-91. This gives DOE-2.1E the capability to assess the annual and peak energy per formance of windows consistent with the NFRC procedure. The program ha s an extensive window library and algorithms for simulating switchable glazings. The program also accounts for the influence of framing elem ents on the heat transfer and solar heat gain through the window.