Option 1 - Whole Building Energy Simulation (1-10 Points)
Demonstrate a percentage improvement in the proposed building performance rating compared to the baseline building performance rating per ASHRAE/IESNA Standard 90.1-2004 by a whole building project simulation using the Building Performance Rating Method in Appendix G of the Standard.

Option 2 - Prescriptive Compliance Path: ASHRAE Advanced Energy Design Guide for Small Office Buildings 2004 (4 Points)
Comply with the prescriptive measures of the ASHRAE Advanced Energy Design Guide for Small Office Buildings 2004.

Option 3 - Prescriptive Compliance Path: Advanced Building™ Core Performance™ Guide (2-5 Points) Comply with the prescriptive measures identified in the Advanced Buildings™ Core Performance™ Guide developed by the New Buildings Institute.

The windows in the Portland AIA building are actually sliding patio doors and helped earn LEED points for materials and resources and product innovation. Photo courtesy of Michael Mathers

For Portland AIA, the chapter incorporated Option 1 and implemented several energy efficiency strategies to reduce energy consumption in its drive to achieve a Platinum rating. The first decision the chapter made was to incorporate a 100 percent electric power philosophy.

"Our goal was to make the building utilize only electric power and capitalize on the clean energy sources, such as hydro-electric and wind-power, that are available on the local electrical grid in the Northwest," said Alan Scott, AIA, a principal with Portland-based Green Building Services and a member of the Center's LEED certification team.

Other energy saving measures include natural ventilation with roof-mounted turbines and dampers with displacement ventilation, thermal destratification fans that move heated air back to the occupied zone, basement duct work that allow for diffused air heating and cooling, and energy-efficient windows and doors to conserve energy all year long and leverage natural heating and cooling opportunities. Using argon filled, double paned Low-E glass in windows and doors took advantage of today's advanced glass technology that has progressed significantly the past 30 years and is changing the way heating and cooling plans are designed in today's structures.

Low-E and Other Glass Technology

Advances in glass coating technology and stronger regional energy code requirements have helped create a new generation and more sophisticated array of Low-E glass options. The windows and doors in the Portland AIA chapter's new headquarters feature Low-E coatings that contributed to LEED certification points.

To know which Low-E is best suited for a project, it's important to understand just what Low-E is, and how it works. Low-E, meaning "Low-Emissivity," is an extremely thin layer, or more commonly several layers, of metallic particles applied to the glass which, in simple terms, allows the glass to act like a sieve. Long wavelengths, or heat, are filtered out, while short wavelengths (the visible light spectrum) are allowed to pass through.

However, today Low-E means much more. By changing the types of materials used in the "stack" or layers of Low-E, or by increasing or decreasing the number of layers, it is possible to get more specific in designing glass that will meet exact project needs. Need high visible light but low U values? There's a Low-E for that. Need greater protection from fading? There's a Low-E for that. And it can get even more precise. Adding argon gas to the captive air space between glass panes will improve insulating value. Adding various tinting agents to the glass itself will allow for even further refinement of the glass' performance.

Low-E is not the same as tinted glass. Tinting is the adding of alloying materials to the glass itself. The depth of color of tinted glass will change with glass thickness, so that a sheet of 3mm glass will have a lighter tint than that of a sheet of 6mm glass. Small windows next to large fixed units or doors can have different tints, since the standard glass thickness of smaller panes is typically thinner than that of larger ones. Low-E, on the other hand, is applied to the glass, and therefore will have a similar appearance regardless of glass thickness. Also, tinted glass tends to absorb sunlight and will get very hot when installed as a single pane, hence tinting does not improve insulating value.

Solar Heat Gain Coefficient (SHGC) is a rating for measuring how much heat gain is admitted through a window. The lower the SHGC rating, the better the ability of the window to block the heat from the sun. SHGC can also be controlled by the use of Low-E coatings combined with the use of tints, and can even be influenced by the glass surface the Low-E coating is placed upon. Additionally, since less than half of the total solar energy spectrum is visible to the human eye, solar performance of glass can be visually deceptive.

Darker tints don't necessarily mean significantly better SHGC values. For instance, green tinted glass will allow 77 percent visible light transmission, while gray glass only allows 45 percent, yet the gray glass only improves SHGC by 2 percent. A better way to improve SHGC, without compromising visible light transmittance, is through SHGC-specific Low-E coatings.

Perhaps one of the least-often discussed elements regarding glass performance is the comfort level of occupants. If the inside glass temperature of an insulated unit is significantly lower than the room temperature, it can give the occupants a feeling that the room is colder than it actually is. For example, at 0 degrees Fahrenheit outside, the inside surface of double pane glass can be as much as 30 degrees warmer than single pane glass, but still 25 degrees cooler than the same assembly with Low-E coated glass. The converse can be true during hot summer months. Since the Portland AIA building does experience some days of extreme heat and cold throughout the year, this factor was important for keeping occupants comfortable all year long and during those extreme temperature swings. Low-E has the ability to keep the temperature of the surface of the glass facing the interior very near that of the room itself, regardless of outside temperatures.