California Center for Sustainable Energy

Passive design concepts achieve energy efficiency

When designing new commercial construction or remodeling an existing building, you can achieve tremendous energy savings by employing relatively simple technologies integrated into the building envelope. Speaking at a recent workshop at CCSE, architect Greg Sharp of Covina, Calif., explained how a building’s exterior can passively promote sustainability by controlling energy losses and gains.

Sharp outlined four areas passive building measures can help to create high-performance green buildings: advanced walls, glazing, cool roofs and building-integrated solar photovoltaic ( PV) systems. While such measures will cost more up front, the energy savings will yield a solid return on investment, Sharp said, sometimes more quickly than traditional building approaches.

Advanced Walls

Trombe walls and double-skin facades take advantage of differences in exterior and interior air temperatures. Particularly effective in colder climates, a trombe wall is a sun-facing glass wall built a few inches to a few feet from a building’s exterior, creating an air gap that absorbs solar energy and releases it toward the interior spaces. In moderate climates, a double-skin façade may be similarly constructed, creating a glass box which may be either naturally or mechanically ventilated. The effectiveness of both systems is highly dependent on outdoor conditions and must be individually designed for specific buildings and locations otherwise their performance will not be satisfactory, Sharp said.

Two types of prefabricated wall systems can be employed to greatly increase building envelope efficiency.  Insulated concrete forms (ICFs) and structural insulated panels (SIPs) both offer incredibly high levels of thermal resistance (R-value) as well as great soundproofing and can aid protection from fire and other hazards.

Similar to oversized Lego bricks, ICFs are lightweight foam blocks with hollow cores reinforced with steel or plastic bracing into which concrete is poured and left to cure. The foam remains on the concrete, and wiring and plumbing are installed in channels cut into the foam with interior and exterior materials added on top.

Looking much like foam sandwiches, SIPs are 4- to 6-inch-thick foam core sheets covered on both sides with laminated plywood, drywall sheets or other surface materials. SIPs can be assembled up to three times more quickly than wood framing and come in standard-sized sheets as well as factory prepared custom sizes that have precut doorways, windows and wiring outlets.

High-Performance Glazing

Glazing, or glass, such as in windows or doors, is the area of the highest degree of heat gain and loss. Forming the indoor-outdoor connection, glazing controls what gets in and what gets out and plays a key role in building energy performance, overall aesthetics and interior comfort.

For most commercial buildings, interior cooling is the most important factor in glazing, with a perfect window being one that lets light in, but little heat. This can be accomplished with window tints, reflective coatings and spectrally selective glazings that pass much of the visible daylight but block infrared heat. For buildings where the concern is heat loss, there is low-emissive (low-e) glazing that traps heat inside.

The newest glazing technology is electrochromic glass that dynamically changes from clear to opaque and back again with the click of a switch. These “smart” windows have ultra-thin layers of metal-oxide coatings that can change the glass to be clear or dark when a small voltage is applied. Currently, you have to buy such glazing as a self-contained unit, however, work is under way to develop a smart window film that could be retrofitted to existing windows, Sharp said.

Cool Your Roof

If you haven’t noticed, most roofs are dark-colored, which on a hot, summer days can heat rooftops 50 to 90 degrees hotter than ambient temperatures. Not only does this result in significant heat gain in the building, but also greatly intensifies the “heat island effect” in urban areas. The solution is simply changing the roof’s solar reflectance with a cool white surface.

For new construction, the best cool roof is a single-ply reinforced membrane made of a polyvinyl chloride or synthetic rubber. For retrofits with roofs in good condition, a liquid applied coating can be sprayed or brushed on. According to Sharp, a single-ply installation runs about $3.00-4.50 per square foot, and a coating costs around $1.50-2.00 a square foot. Incentives for cool roofs are often available from local utilities.

Building Integrated PV

We’re all familiar with solar photovoltaic ( PV) panels that are rack mounted on a rooftop or the ground, but a new trend is to integrate solar materials into the building’s surface. Building integrated PV materials may replace a standard roof tile or be built into façades, awnings and other shading systems – also reducing heat gain and controlling glare. There are also solar shingles and other roofing materials. A new technology that should become really popular is transparent solar power-producing windows, Sharp said.

Continue reading May's newsletter.