...tight, urban environments. David Dwyer, president of American Renewable Energy and author of “Green Power Blue Collar,” helped local physician Toni Bark design their green home in Evanston, Ill. The 4,700-sq-ft home has 16 wells drilled to 125 ft and two heat pumps that play a part in holding their utility bills under $100 per month.
Dwyer has built what he calls the first geothermal drill designed for urban jobsites. While reluctant to showcase his system yet, he describes it as a three-wheeled machine weighing about 2,500 lb, or 10 times less than a typical, truck-mounted rig. “Our cost of drilling is about half of what our competitors’ are,” Dwyer says.
On a recent Walmart project, Stantec’s Bererton used an innovative rig called a SpiderPlow (see sidebar, below). As more of the world goes geothermal, advancements will continue to drive down the cost of these systems, experts say.
Retrofits, Too
Geothermal HVAC is not just for new buildings. It also can be an effective way to transform an older building into a greener structure. The market for green-building retrofits is expected to grow more than fourfold to as much as $15.1 billion by 2013, according to McGraw-Hill Construction Research & Analytics, which, like ENR, is a unit of The McGraw-Hill Cos. “I would not consider a retrofit without considering geo-source,” says Mark Nussbaum, a principal of Oak Park, Ill.-based Architectural Consulting Engineers. He is working on a $25-million rehabilitation of the Frank Lloyd Wright-designed Unity Temple in Oak Park, targeted to go geothermal.
The renovation is moving into its first phase, a $7.5-million project focused on strengthening the building envelope. Energy-efficient HVAC is part of the second phase, a $2-million project. The final phase—the most expensive portion—is a restoration of interior finishes. When it opened 100 years ago, Unity Temple used a coal-fired boiler that forced warm air into concrete ducts underneath the building. Since the concrete did a better job of absorbing heat than conveying it, the building quickly was retrofitted with steam radiators. It still has no air-conditioning, but Nussbaum has designed a hydronic system of nine, 650-ft-deep, 6-in.-dia. geothermal wells that will feed a water-to-water heat pump.
Under the plan, the system would convey hot and chilled water. Supplementing the heat pump for extreme Chicago weather is a gas-fired boiler to supply water at up to 180°F—as heat pumps can only deliver up to 120°. An energy-recovery ventilator also will temper incoming air. In an earlier design, Nussbaum planned for about 20 wells drilled to 300 ft and thermal-ice storage.
Making fewer wells deeper will help squeeze more energy out of the loop. “I get more capacity per linear foot of pipe in the ground on a deep hole than I do on a shallow one,” says Nussbaum. “You have to do everything you can to make these systems cheaper.” In central Illinois, he notes, the cost to drill a vertical well is about $1,000 per ton. In Chicago, that cost triples. Ice storage eventually was dropped from the plan because it would have required more boreholes, taking up valuable real estate on the historic site.
When installed (the congregation is still seeking financing), the system will provide air-conditioning for the first time and recycle waste heat before it leaves the building. It also will feature a CO2 sensor that measures how many people are breathing in the space—and cycle on the HVAC equipment as needed. “I see a time when that will be a standard design versus a special design,” says Nussbaum. “It is a huge savings because most spaces are unoccupied most of the time, so you do not want to overventilate.”
Though the $1.2-million geothermal retrofit carries large up-front costs—about $24,000 per ton and more than double Chicago’s typical costs—today it would pay back in five to seven years. “We chose it because it was a green solution,” says Emily Roth, executive director of Unity Temple Restoration Foundation. “It was something that was done with an eye to the long term.” Overall, the congregation expects to pay 40% to 50% less on its heating and cooling bills.
Seeking Water
Water-source heat pumps (WSHPs) are a far cheaper way to heat and cool a building, but the trick is finding a nearby source to tap and doing so responsibly. Examples of open-loop water systems are being scattered across the...
