By Matt M. Casey
When the owners of the St. Johnsbury Athenaeum—home to one of the oldest art galleries in the US—needed a new solution for an old lighting problem, they installed one of the newest building envelope technologies available: dynamic glass.
For decades, the administration sent a worker to the roof each year to paint the 240-year-old skylight white. The light-scattering layer prevented unwanted ultraviolet (UV) rays from damaging the artwork inside. Recently, the skylight fell beyond repair, and the board of trustees decided to replace it with remotely tintable, triple-paned glass. The glass, while expensive, presented a better solution than an annual spring coat of paint. In addition to stopping incoming UV rays, it allowed the gallery manager to determine how much solar heat to reflect back into the sky. For a space that resembles a greenhouse affixed to the top of an old library that serves as a significant side benefit.
While the gallery at the St. Johnsbury Athenaeum exists under unique circumstances, the lessons learned from its challenges apply more broadly. Each year, energy prices notch ever-higher, and the public focuses more attention on the dangers of global warming. Both factors compel building owners to reduce energy use. Asking workers and customers to endure less-comfortable temperatures goes only so far. When tinkering with the thermostat reaches its limits, tightening a building’s envelope can significantly improve a structure’s energy efficiency. The current state of the art in tight building envelopes includes uniting long-forgotten lessons with cutting-edge technologies.
Beyond art galleries, dynamic glass gives architects and mechanical engineers a way to selectively reduce solar heat gain across a broad range of projects with minimal aesthetic impact. According to Helen Sanders, vice president of technical business development for SAGE Electrochromics, the product has become particularly popular in all-glass designs reminiscent of the Apple Store cube. Dynamic glass can reject up to 91% of incoming solar heat, she says, while still allowing occupants to see outside through a tinted pane. At its clearest setting, SAGE dynamic glass blocks 47% of incoming solar heat, and building occupants can choose from four settings: complete transparency, maximum dimming, or two settings in between determined during the initial consultation phase. Should occupants choose an intermediary setting, integrated light sensors modulate window tint to assure the correct level of light streams through. Building managers can also connect the glass to smart building systems to centrally automate window tinting.
While such a system may sound complicated or difficult to install, Sanders says the window portion installs like any other double- or triple-paned window. The additional wiring carries little current, and can be installed by anyone certified to work with Ethernet cables and other low-voltage wires. Operating 2,000 square feet of dynamic glass, she says, requires about as much energy as a 60-W lightbulb—a burden significantly outweighed by the associated energy savings. In the near future, the installation will grow easier; SAGE is currently finalizing a new window model that uses both wireless controls and wireless power.
Sanders won’t speak to the specific cost of a SAGE glass installation. However, she says she compares the price of her company’s dynamic glass not to the cost of other windows, but the combined cost of other windows and mechanical light-blocking solutions. In the context of continued mechanical maintenance, she says SAGE customers usually find her company’s electrochromic glass economically attractive.
For a less-expensive and more passive system, building owners may favor thermochromic glass. These panes, which companies such as RavenBrick sell for about 40% less than electrochromic systems, take lighting control out of the occupants’ hands and leave it up to the sun. As solar energy heats thermochromic glass, the glass automatically darkens in a fashion similar to the popular Transitions prescription lenses.
Architects and designers looking for a case of advanced techniques in building envelopes should look no further than Monticello. Eric Bloom, a consultant with Navigant Research, notes that the former home of Thomas Jefferson features double-glazed windows that date back to the founding father’s 18th century time there. Despite the age of the structure, architects have only recently viewed the then cutting-edge technique as an attractive option for modern commercial buildings.
Improved modern multi-pane glass may include an insulating gel or gas between layers. Gasses can be invisibly lost if the glass or a seal cracks—which may necessitate that building managers in charge of such a structure institute annual or semiannual inspections.
The problem, Bloom says, is that multiple-paned glass demands a high price tag—not as high as dynamic glass, but still significantly higher than single-paned glass. He says a typical multi-paned installation will pay for itself, in about a decade. That can be a problem for developers who aim to sell their buildings quickly and won’t realize long-term savings. As a result, they often pursue only those investments with a payoff period no longer than three to four years, which means greater use of single-paned glass.
For existing buildings where the owners discover that solar heat raises cooling costs more than expected, window films provide a versatile and cost-effective retrofit. According to a study by the International Window Film Association, energy savings from rejecting solar energy can repay the cost of a window film installation in as little as two years. While the technology has been around for decades, modern developments offer a variety of options including clear or mirrored window films that can be installed internally or externally for different installation conditions, cosmetic appearances, and overall efficiency.
“We have about 100 different solar control window films,” says Mark Carlson, head of window film business development for Hanitek. “In office buildings, we usually install at night so that it doesn’t affect the tenants at all.”
On one recent project, Carlson says, Hanitek united authorized dealers from several areas to complete the installation of 50,000 square feet of window film during a single weekend.
In addition to blocking solar heat gain, window films can freight a number of other abilities. Carlson says Hanitek specializes in window films that keep glass intact during bomb blasts or rocket attacks. Bill Pettit, a technical service engineer for 3M, says his company can integrate into any window film a coating that keeps glass from shattering and falling during an earthquake. And, Kathryn Giblin, director of global marketing and technical services for Solar Gard, says her company can integrate improved UV protection.
“The majority of our films have been skin cancer recommended,” says Giblin.
In addition to reducing the UV-A and UV-B damage that could lead to skin cancer, she says her company’s films have been particularly popular among hotels where the reduced UV penetration also reduces the fading of curtains, rugs, and furniture. Solar Gard also recently debuted a new low-emissivity film, which mimics the effects of low-E windows. Such windows reflect energy to keep internal heat in and external heat out. If a given building’s design failed to integrate such windows, a low-e film can work as a retrofit.
Despite window film’s static nature, Pettit with 3M suggests them for any climate, north or south. “New York City is one of the largest markets for window film in the world,” he says.
The heat that non-filmed buildings would gain during the winter is mostly useless, Pettit adds. Unless the structure has been built to accommodate for the effect, the portions of the buildings exposed to the sun would get too hot while darker areas remain too cold. Additionally, he says, the ambient solar heat gain would only be useful two or three months each year.
|Photo: Schneider Electric
The US contains a small but growing number of zero- and low-energy buildings.
Raise the Roof
The US contains a small but growing number of zero- and low-energy buildings. One trait they share, according to Bloom with Navigant, is a well-insulated roof. He notes that the Adam Joseph Lewis Center for Environmental Studies at Oberlin College even suffered an unfortunate side effect of low-energy operation; snow piled up atop its R-30 insulated roof and threatened its structural stability. For most buildings, heat leaks through the roof and melts snow. The tight, toasty Lewis Center, meanwhile, kept its heat in and required that men with shovels clear it off manually.
Insulation, says Allen Sopko of Firestone Building Products, is the most important component of any roofing system, but it’s also a difficult area for innovation. If a building needs greater insulation, building owners and architects can simply add additional layers with minimal consequence outside of the initial price. If a project calls for maximum insulation with minimal roof depth, several companies produce high-density roof insulation such as Firestone’s ISO 95. The company has enough confidence in its own product to use it atop the new Bridgestone Americas Technical Center in Akron, OH.
In addition to raw insulation, Sopko says that Firestone and other firms offer a variety of improved air and water-blocking layers that not only help prevent the passage of air from the inside to the outside, but also prevent the water-driven breakdown of insulating materials. Products like Firestone’s V-Force, he said, may cost more than the thin plastic sheets and duct tape that have been the standard for roof air barriers, but can reduce air leaks to “close to nothing.” Installers unite V-Force sheets through peel and stick panels. The product is so tough, he says, that it could function as a temporary roof for up to 45 days in the event of damage that can’t be immediately addressed.
Beyond insulation, roofing companies have moved en-masse to offer white and reflective top layers. The design choice, famously pushed by United States Secretary of Energy Steven Chu, generally works to reduce the urban “heat island” effect, but Sopko says it could also yield benefits for individual structures. The technique works similarly to window films, reflecting the sun’s heat back upward and reducing the amount of energy needed for internal cooling.
California has required that flat-topped commercial buildings use white roofing since 2005, but the practice has been spreading, due in part to Leadership in Energy and Environmental Design (LEED) certifications. Adding a white roof gives the building a point toward qualification, but Sopko says it may not always make sense. In upper latitudes, building owners may want the roof absorb the sun’s rays during the cold winter months. When LEED is not a factor, a roof of another color may be worthwhile for buildings in northern climates. In some cases, the color of the roof may be of no consequence at all.
“There’s a movement to have the roofing system to be more of a substrate rather than just a roofing system,” states Sopko.
On many buildings, that means rooftop gardens, racks of solar panels, or solar cells adhered directly to the roof surface. Sopko has heard anecdotal evidence that vegetative roofs tend to lead to cooler buildings, but he feels that mounting solar cells may be counter-productive; installing heat-absorbing black elements may defeat the purpose of installing a white roof. Racks of solar panels don’t appear to cause much of a problem when it comes to maintaining the building envelope, but “there are some peel and stick products, [and] we’ve found that those have a tendency to heat up quite a bit,” he adds.
No matter which type of photovoltaic system a building owner plans to install, Sopko suggests that they make sure that they install a new roof first. Firestone has seen several projects, he said, where the building manager installed solar panels only to have to rip them up a couple years later to fix a leak or replace a roof.
California has required that flat-topped commercial buildings use white
roofing since 2005.
Beyond the Wall
While single pane windows may be an easy target (they are “little better than an open window” for insulation purposes, according to Bloom), walls make up the largest portion of most commercial structures. Plain suburban office buildings outnumber glass towers, says Christopher Mathis, president of Mathis Consulting. That means lots of cinderblock and steel-box construction—much of which currently has too little insulation.
“One of the fastest-growing areas in design right now is trying to relearn those lessons from the 70s and trying to apply them to commercial spaces,” says Mathis.
Those forgotten lessons include moving insulation to the outside. Right now, he says, builders and architects try to cram the space between the siding and the sheet rock with insulation, but even high-density fiberglass batts only freight a maximum R-value of 5. Mathis, noting that most American buildings stand for at least five decades, would like to see more new structures achieve an R-value closer to 30.
In a typical structure for warmer climates, he suggests a concrete block wall with 1 to 4 inches of insulating board on the outside covered by building paper or housewrap. Any facade would hang outside of that. For northern climates, he suggests a similar approach with metal or wood frame construction. By putting the insulation on the outside, Mathis says, the insulation can stop the heat before it achieves any penetration into the building at all. In addition to granting a higher R-value, such a technique would prevent air and water leakage. That not only saves heating costs (Mathis saw one building where about half of its heating load stemmed from air leakage), but it also makes the wall more durable. He adds that he has sometimes reached his hand into the wall of a two-year old building and found the wooden studs wet and spongy.
While thicker exterior insulation forces certain cosmetic changes such as deeper window sills, Mathis notes that builders have known how to do that for decades. Older buildings in the Northeast frequently include deep window frames.
For some structures, simply using the properties of basic building materials can help reduce cooling costs. When ViaWest—a cloud storage company with a client list that includes Facebook—decided to open a new data center outside of Las Vegas, the firm bought a preexisting warehouse. Ten cooling inches of concrete separated the building’s interior from the outside. Todd Gale, ViaWest’s vice president for data center architecture and innovation, says the structure had no air conditioning on the day he first visited.
“On a typical 115-degree Las Vegas day, it was about 85 or 90 within the building,” he says.
While the concrete provides little as far as R-value, it provides a great deal of thermal mass. The concrete cools overnight and absorbs heat the following day, which delays the heat’s penetration into the building.
The National Renewable Energy Laboratory (NREL) used a similar approach when it built a new office building in Golden Colorado. Building designers included 6 inches of concrete in each wall to slow the daily warming process. The NREL office even performs nightly purges of warmed air to maximize the poured stone’s passive cooling abilities.
No One Solution
The NREL’s facility, like ViaWest’s and others, employed a constellation of approaches to reduce heating and cooling-related energy costs. Before beginning operations, ViaWest added R-22 installation to its concrete walls and doubled the roof insulation from R-19 to R-38. As a result of those and other improvements, Gale says, servers consume nearly 77% of the energy consumed the site. For some less efficient datacenters, non-server needs such as climate control can account for as much as two-thirds of energy consumption.
NREL took more extreme efforts. Its new office facility employs solar cells, lighting louvers, and building orientation, among other things, to achieve an office space that annually produces as much energy as it consumes.
Most building managers have little need for zero-energy facilities; the payoff for such investments can take decades to realize. But using a few envelope-tightening techniques can pay off in just a few years. That payoff may come faster if energy costs continue to rise. According to the Organisation for Economic Co-operation and Development, oil is expected to demand $190 per barrel by the year 2020.
And, as Mathis notes, the typical American building will stand for 50 years or more.
Author’s Bio: Journalist Matt M. Casey writes about science and technology at gistpodcast.com.