The knock against net-zero-energy buildings, including homes, is that they’re too expensive and too difficult to get past the fringe. Maybe if there’s a mandate someday, or the price of a solar array drops to the level of a clothes dryer. Maybe.
That’s just not good enough for Tom Hootman, director of sustainability for RNL, a Denver-based global design firm. An architect with an expertise in net-zero-energy buildings, Hootman is convinced that achieving net zero at scale is not only possible now, but at a competitive cost. “It’s the next step beyond the boutique examples we’ve seen so far,” he says. “Not just more buildings, but for larger buildings and more complex programs.”
In fact, Hootman codified his tactics in the book “Net Zero Energy Design,” due for release in November, which he describes as a technical guide for architects. “I want to expose the gap between current practices and new processes that might lead to different results, and how architects can make that shift,” he says.
Though written for the commercial building sector, Hootman’s 10 “best practices” logically translate to the residential realm. For instance, he advocates that building (or home) owners put specific performance requirements in the project contract. “The key is to be specific and help ensure that decisions balance schedule, cost, and performance on equal footing,” he says.
In the case of a homeowner, that might mean performance standards from the latest version of the IECC, a target HERS rating, or requiring a collaborative design-build process instead of a conventional linear, low-bid approach.
Hootman also advocates a continual energy modeling process that extends from design (where it is most common, if still relatively rare) through construction as even slight change orders to a glazing spec or equipment model made in the field can impact energy use—even more so when that spec is repeated in a high-rise or across a community.
“Every design decision, no matter when it’s made, has an energy implication,” he says. “The more you model and measure throughout the project, the better you can deliver the results you want. And, it provides a road map for the building operations team, as well.”
Hootman’s best practices also include a “passive-first” approach, specifically designing, orienting, and building a structure that will self-manage heat gain, daylighting, cooling, and ventilation. In short, he says, “The things we did before air conditioning.”
Of course, achieving net-zero energy will likely require a renewable energy component—most likely solar—an element Hootman says is best integrated from the beginning of the design process instead of tacked on the building at the end. “There are so many implications in terms of massing, roof elements, building orientation, and shading,” he says, that if addressed early can optimize and perhaps downsize an effective array.
Most progressively, Hootman promotes the transition from air-based space conditioning systems to water-based deliver schemes. “Moving energy by air is very inefficient,” he says, noting that the volumetric heat capacity of water is 4,000 times greater than air. “If you first control the envelope, radiated energy is less expensive and more reliable.”
While much of his advice hits the cutting-room floor of a housing industry nearly devoid of any direct or regular architectural involvement, Hootman applied his practices to a feasibility study for a net-zero-energy, mixed-use community in Denver.
In that process, he realized opportunities for developers to initiate energy districts for or within communities that share the up-front cost burden of a solar array or geothermal system serving several homes and buildings while reaping the long-term benefits. “The cost of a geothermal system might be $5,000 to a homeowner in the district,” he speculates, instead of perhaps $20,000 for an individual system installation, making it competitive with traditional HVAC equipment that’s far less efficient and more costly on a monthly basis.
For solar, the district model extends to creating “micro-grids” that supplement or perhaps even supplant (albeit still tied to) the municipal grid and deliver clean and independent energy to homeowners and businesses. “It also allows you to implement smart-grid technology for the district, which isn’t yet available from utilities yet,” says Hootman, thus extending the efficiency of a renewable energy system. “It’s a different way to develop a project.”
Hootman will present his practices at Greenbuild 2012, Nov. 14-16 in San Francisco. For more information and to register, go to www.greenbuildexpo.org.
