THESE days, environmental friendliness often translates to "greenness," which focuses on two primary aspects: (1) the lifecycle of the product-energy use, resource sustainability, and pollution contribution inherent in the product's manufacturing and ultimate disposal, and (2) the ability of the product to enhance the greenness of the building in which it is used-lower energy consumption and a more healthful or pleasant environment for the occupants.
In the case of windows, lifecycle considerations differ according to the materials used in the final product. The various framing materials each have positives and negatives that sometimes give rise to confusing competing claims among various suppliers, as well as misconceptions among consumers. Trying to sort these out can be a daunting chore. However, in terms of environmental compatibility or greenness, all materials have positive contributions to make. Some examples:
• Wood is considered renewable and sustainable, and is low in "embodied energy"-the energy needed to manufacture the material or fabricate the product.
• Aluminum has well-established recyclability. Products made with recycled aluminum embody only about 5% of the energy needed to make primary aluminum, and the raw material for aluminum (bauxite) is plentiful. Aluminum is also high in strength while low in weight, all desirable qualities for fabrication, transportation and installation.
• Vinyl, being a thermoplastic material, can be recycled into new window frames and other products. While little post-consumer recycling is being done at present, owing to the fact that the vast majority of inherently durable vinyl windows are still in service, groundwork is being laid for a recycling infrastructure. Although some environmental groups have crusaded against vinyl of all types, unbiased life-cycle analysis readily refutes the myths ranging from lead content to dioxin releases during manufacturing.
• Fiberglass is chemically inert, strong and has good thermal properties. It is currently used in about 3% of the windows sold for new construction or remodeling/replace-ment in North America, with the percentage projected to increase as manufacturing costs trend downward.
In general, fenestration products of all types are becoming recognized as essential for meeting green/sustainable building criteria by providing daylighting, views, ventilation, and thermal comfort. Wood, vinyl and fiberglass naturally insulate against heat flow, while aluminum frames are engineered with effective thermal barriers between the inner and outer frame elements.
Today's well-designed windows can reduce energy consumption for heating and cooling by reducing heat transmission between the interior and the exterior and by regulating solar heat gain. Several factors can maximize the energy-savings aspect:
• Insulating (double-pane) glazing with inert gas infill and low-emission, low-E coatings that feature a microscopically thin coating of silver or tin oxide that reflects radiant solar heat rather than absorbing and conducting it through the glass.
• Warm edge spacers that separate the two panes of a double-glazed insulating glass unit.
• Use of framing with inherent or engineered energy-saving features.
Windows are rated and labeled for thermal performance (in terms of heat transmission measured by U-factor, solar heat gain measured by the Solar Heat Gain Co-efficient, and air infiltration) by the National Fenestration Rating Council (NFRC). These factors should be as low as economically practical, although SHGC should be higher in northern climates so that solar heating can supplement artificial heating. AAMA is the NFRC's largest licensed independent certification and inspection agency for testing and labeling windows for these thermal performance factors.
Greenness doesn't end with energy efficiency considerations, however. The use and placement of windows should be evaluated holistically as a system, in interaction with other building systems. A prime example of this is maximizing daylighting as a means to reduce dependency on electric lighting. Not only is daylighting being rediscovered as a means to enhance human well-being and productivity, it reduces energy demand for lighting itself, as well as the heat load that electric lighting places on air conditioning systems.
Obviously, the degree of energy saving measures to be employed and the benefits of interactive considerations like daylighting depend heavily on the climate in which the building is located. The International Energy Conservation Code adopted by many local jurisdictions sets energy performance targets for specific climate zones, as does the U.S. Department of Energy's more stringent Energy Star for Windows program.
As a building component, windows must serve other purposes besides greenness or energy efficiency. Depending on their placement, use, and applicable code requirements, they must variously provide means of emergency egress, defense against forced entry, resistance to water leakage, and protection from high winds and impact from wind-borne debris in locations subject to hurricanes. Meet-ing these requirements often means tradeoffs. For example, making the window tight enough to shut out the last puff of drafty air could render it too hard to operate in case of emergency.
Finally, note that the performance of the window product and the installed window system is the key, not some pre-conceived notion as to what material is "better" than another. For this reason, the North American fenestration standard for windows, doors and skylights is material-neutral, as is the AAMA certification program that offers independent, third-party verification of compliance with the standard. Laboratory tests determine structural strength, air infiltration, water resistance, wind resistance, and thermal performance, as well as other factors. The AAMA Gold Label bears witness to continued conformance of the product line, backed by twice-annual, third-party unannounced inspections of the manufacturers' production facilities. For vinyl and fiberglass windows, this is backed by a profile certification program that tests for conformance with applicable standards, ranging from UV weathering to lead content.
In addition, AAMA is developing a green certification program to rate the green credentials of products. All of these programs allow products of any material to be evaluated on a level playing field for what really counts-performance.
Of course, it has long been recognized that a window product's performance is only as good as its installation, which can vary in quality depending on the experience and expertise of the installer. Following the manufacturer's approved instructions to the letter, and/or using certified installers, will ensure the best solution to structurally sound, environmentally friendly, and energy efficient window performance.
Today's highly engineered windows are manufactured with advanced processes that render them environmentally acceptable on the basis of a complete, unbiased life-cycle analysis. More to the point, their use brings beneficial daylighting and views to green-conscious buildings, while offering improved thermal performance. Realizing all of these benefits in practice means selecting products proven to meet material-neutral performance standards, and then ensuring they are properly installed.
- Rich Walker is president and c.e.o. of the American Architectural Manufacturers Association. He can be reached at (847) 303-5664 or www.aamanet.org.