Residential Heating and Cooling Energy Cost Implications Associated with Window Types

We present a comparative study in which residential heating and cooling energy costs aresanalyzed as a function of window glazing type, with a particular emphasis on the performancesof windows having low-emittance coatings. The DOE-2.1B energy analysis simulationsprogram was used to generate a data base of the heating and cooling energy requirementssof a prototypical single-family ranch-style house. Algebraic expressions derived bysmultiple regression techniques permitted a direct comparison of those parameters thatscharacterize window performance: orientation, size, conductance, and solar transmissionsproperties. We use these equations to discuss the energy implications of conventionalsdouble- and triple-pane window designs and newer designs in which number and type ofssubstrate, low-emittance coating type and location and gas fill are varied. Results arespresented for the heating-dominated climate of Madison, WI, and cooling-dominated locationssof Lake Charles, LA, and Phoenix, AZ. The analysis shows the potential for substantialssavings but suggests that both heating and cooling energy should be examinedswhen evaluating the performance of different fenestration systems. Coating and substratesproperties and the location of the coating in the glazing system are shown to havesmoderate effects as a function of orientation and climate. In addition, with the low-conductancesglazing units, the window frame becomes a contributor to overall residentialsenergy efficiency.