Fenestration is the most significant envelope design determinant of energy use in nonresidential buildings.sThis paper presents our assessment of energy use effects of low-emissivity (low-E) versus conventional glazing for a range of window-to-wall ratios in a daylighted office building, in representative hot and cold climates.sLow-E glazings transmit cooler daylight than their conventional counterparts because, for asgiven visible transmittance, they reflect a much larger fraction of incident solar infrared radiation. Westhus use the ratio of visible transmittance to shading coefficient, which we define as Ke, to compare theseffect of representative glazing characteristics on component and total-building energy use, peak electricalsdemand, and required cooling equipment sizes.

We conclude that insulated glazings with low-E coatings can provide lighting and cooling energy savingssin both hot and cold climates. The most dramatic lighting, cooling, and total electricity energy savingssare achieved for increases of Ke within the range of 0.5 to 1.0; higher Kes provide diminishing savings.sThe increased R-value of low-E insulated glass units provides significant benefits in cold climates and issnot a liability in hot climates.

Low-E glazings also help increase the mean radiant temperature of interior environments in wintersand reduce it in summer, and provide greater architectural design freedom without adverse energy consequences.sFurther, the higher first costs of these glazings may be more than offset by savings from smallerscooling equipment, energy and peak-demand cost savings, long-term financial gains from better rentals,sand increased productivity due to improved occupant comfort.