Window design strategies to conserve energy

Abstract

A multitude of design strategies are available to achieve energyefficient windows. Opportunities for improving window performance fall into six groups: site, exterior appendages, frame, glazing, interior accessories, and building interior. Design strategies within these groups can improve one or more of the six energy functions of windows: solar heating, daylighting, shading, insulation, air tightness, and ventilation. Included in this report are 33 strategies; an explanation of the physical phenomena responsible for each strategy's energy performance, summarized energy and non-energy advantages and disadvantages; aesthetic considerations; cost approximations; example installations, laboratory studies, or calculations by the authors; and references. Intended readers include professional designers, lessees and owners of commercial space, home buyers and owners, window component manufacturers, and researchers. The report's purpose is to draw attention to the wide range of options currently available to conserve energy with windows.

A regional economic assessment of selected window systems

“…The thermal model used to compute energy gains and losses through windows is described in Simplified Analysis of Thermal and Lighting Characteristics of Windows; Two Case Studies [ 2 ] . The window systems examined in this report, as well as many additional window systems not examined here, are described in Window Design Strategies to Conserve Energy [3]. An overview of findings from the interdisciplinary project was reported in A New Look at Windows [4], An earlier NBS report, Retrofitting Existing Housing for Energy Conservation: An Economic Analysis [5], applied an economic optimization model to a group of energy conservation techniques, and identified the minimum sizes of storm windows which would be cost effective for a variety of climates and a range of current energy prices.…”

“…a Life-cycle costs include the present value costs of (1) purchasing and installing the windows (in excess of the costs of a brick wall section of equal size), (2) purchasing the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows on a regular basis, and (4) (In either case, however, single glazing is only slightly preferred to double glazing.) It is estimated that if energy prices escalate rapidly, the savings in lighting and cooling costs will allow the window system to pay for itself in three to four years.…”

“…3 Life-cycle costs include the present value costs of (1) purchasing and installing the windows (in excess of the costs of a brick wall section of equal size), (2) purchasing the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows on a regular basis, and (4) …”

“…3 Life-cycle <:osts include the present value costs of (1) purchasing and installing the windows (in excess of the costs of a brick wall section of equal size), (2) purchasing the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows on a regular basis, and (4) of 12 percent compounded annually, net losses for single-glazed windows are more than double those experienced with constant real energy prices, rising higher than $1500 for northerly exposures. With double glazing, the net losses are about 50 percent higher than those experienced at constant energy prices.…”

“…•21 a Life-cycle costs include the present value costs of (1) purchasing and installing the windows (in excess of the costs of a brick wall section of equal size), (2) purchasing the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows on a regular basis, and (4) 3 Life-cycle costs include the present value costs of (1) purchasing and installing the windows (in excess of the costs of a brick wall section of equal size), (2) purchasing the Venetian blinds and shutters, (3) cleaning, recaulking and repainting the windows on a regular basis, and (4) • It does become cost effective, however, for north-facing windows and for large window areas if energy prices escalate rapidly. For smaller windows facing south, east, or west, the thermal shutters are estimated to provide an adequate substitute for double glazing.…”