As More Buildings Go Geothermal, Project Teams Are Thinking Outside the Borehole
An article titled the “Fireless Furnace” appeared in the Oct. 25, 1948, issue of LIFE magazine. There, postwar America witnessed the emergence of a futuristic technology that Lord Kelvin, the king of cold, only dreamed about a century earlier. The fireless furnace avoided burning fossil fuels by piping water through coils in the ground and then through a heat pump. But the technology was too expensive—about $3,000 installed—and too new to gain acceptance. “However, as the efficiency of getting heat from the earth improves, it is almost certain that eventually the heat pump will be able to compete successfully with conventional heaters in most localities,” said the story.
Sixty years later, geothermal-heat pumps (GHPs) and related systems are competing. If designed to be efficient, these systems can produce more energy than they consume—three to five times as much on average—yielding a positive coefficient of performance (COP). But a system’s ability to save the owner money still remains a huge question, considering manufacturers’ equipment labels do not always match real-life performance due to loose regulations; engineers are still struggling with design complexities; contractors are demanding a wide range of drilling, trenching and fit-up fees; the varying geology and climate across the U.S.; and fluctuating energy prices.
“With renewable and alternative energy, you have to think outside the box,” says Jim Bererton, who heads Edmonton, Alberta-based Stantec Consulting’s sustainability practice. “If you try to do [projects] conventionally, you will fail.”
Bererton’s recent experience with geothermal heating, ventilating and air conditioning (HVAC) led him to try some unusual approaches, such as using foundation piles as heat sinks, a fairly common approach in Europe but virtually nonexistent in North America. He also used a special off-road tractor that simultaneously can cut a trench and lay piping. Both methods saved building owners thousands of dollars in installation costs, shortening the payback time by years. Bererton and others say getting the most out of alternative energy forces owners, designers and contractors to break down jobsite barriers and become creative.
As more professionals gain experience with geothermal heat exchange, the technology is maturing. “It has got its driver’s license, but at night, we are still worried about it coming home,” explains Paul Ormond, who heads up the geothermal practice at Manchester, N.H.-based consultant Haley & Aldrich.
Geothermal systems also are becoming larger in size, pushing designers’ old rules of thumb into obsolescence. “Geothermal grew up 30 years ago, making small systems for residential homes,” says Ormond. Now, the technology “is growing up to big buildings…and that is where we see problems in the industry.” Shortcuts, such as sizing a heat pump without conducting an energy audit or considering other factors, may work for homes but do not work on larger buildings, which are more complicated structures. “Engineers do not design residential, three-ton heat-pump systems,” says Warren Lloyd, vice president of Rock Island, Ill.-based KJWW Engineering Consultants. “Contractors do.”
Despite those who feel hot, cold or lukewarm about geothermal, the market for ground-source heat pumps (GSHPs) is on the rise, lately growing at double-digit rates due to high energy prices, green design and pressure on the building sector to cut its carbon emissions. In 2007, shipments of GSHPs surged 36% to 86,396 units, while capacity grew 19% to 291,300 tons of air-handling over the prior year, according to the Energy Information Administration. Ground- and water-source heat pumps (WSHPs) are expected to be a prime strategy in future green building and decarbonization.
The U.S. Dept. of Energy estimates “aggressive deployment” of GHPs could save up to $38 billion annually in...
...reduced energy bills, put a significant dent in greenhouse gases and reduce the need to build 105 GW of electrical capacity by 2030. If not designed well, GHPs can have unintended consequences, such as astronomical costs, increased energy use and polluted groundwater. The devil, as they say, is in the details.
Fundamentally, GSHP technology benefits from ground temperatures, which are a relatively constant 50°F to 60°F, requiring less “lift” to pump heat to and from a building. WSHPs used in underwater applications rely less on constant temperatures and more on evaporative or deepwater cooling; they also can run summer to winter. Combined with high-grade insulation, windows, ducts and climate controls, GHPs make sense in many buildings.
Although geothermal heat exchange grew up in the Midwest, where seasonal changes make it easier to predict performance in small homes, it now is being implemented in all corners of North America on a wide variety of projects. Designers also are learning how to use the earth or a nearby water source as a storage device to reject heat during the cooling season and extract it later. That gives geothermal a “cool” factor, but not everyone is fully unlocking the potential.
Changing Seasons
The key, experts say, is figuring out how to balance the load to keep the pump’s compressors working as little as possible over the year. Installation is a big factor in predicting performance, as well as cost. All GSHPs are closed loops, arranged in a vertical or horizontal fashion. They generally do not cost more than conventional furnaces; laying the ground loops is the added cost. The wells require expensive, shallow trenches, more expensive boreholes or a combination of both. Installation equates to a few dollars per foot up to $25 per foot, according to U.S. government statistics.
Nonetheless, heat pumps are infinitely flexible inside a building. Users can tailor them to regional needs, and some even are designing “hybrid” systems to take advantage of local power, geology and climate. One such system, designed for Canadian airline company WestJet’s headquarters in Calgary, Alberta, incorporates heat sinks in the six-story, 314,000-sq-ft building’s foundations. By looping tubes inside 105 bored piles, “we reduced the capital cost,” says Bererton. This method is more mature in Europe, where foundations commonly double as heat exchangers.
Because geothermal systems still are relatively new to the many players on a project team, the unexpected easily can arise during installation. Completed last January at a cost of about $100 million, the WestJet corporate building lost 30% of its ground loop due to pier-construction problems, requiring workers to drill 20 additional, small-diameter boreholes at 350 ft deep.
Normally, the building’s water-to- water heat pumps would need 200 boreholes, so the owner still saved more than $700,000 and expects to save $200,000 per year in energy while emitting about 2,000 fewer tons of carbon dioxide. Part of the savings is due to the unusual addition of a conventional chiller and condensing boiler. The secret sauce, Bererton says, is a computer controller that takes into account daily costs of electricity and natural gas and accordingly cycles the systems on and off to deliver the best bang for the buck. “We are targeting that the COP is better than the price ratio of electricity and natural gas,” says Bererton. “We only run the heat pumps when it is going to save us money.”
Drilling equipment is another low-hanging fruit ripe for innovation. In Chicago, a homebuilder whose friend, and now wife, convinced him to build her a greener home is leading the charge to cut costs for vertical-well construction in...
...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...
...campus of Harvard University, where units currently installed on seven buildings use “standing-column wells,” about 6 in. dia and drilled as deep as 1,500 ft. These wells—an average of three per building—use a pump that extracts water from the bottom of the well where the water is cooler, exchanges it with heat pumps and returns it to the top of the well, where the water is warmer.
Like ground wells that are left to heat up after summer, COP drops when water wells heat up. Well-designed and -constructed wells promote heat dissipation, while poor ones require users to “pump and dump,” or bleed, water. Wells that are not drilled deep enough, or “short-drilled,” by an inexperienced contractor also may lack the capacity to allow heat to escape, warns Nathan Gauthier, assistant director of Harvard’s sustainability office and a member of the U.S. Green Building Council’s Energy and Atmosphere Technical Advisory Group.
Another environmental problem is the cross-linking of aquifers. Since drilling exposes soil strata, underground water that may not naturally come into contact with other sources suddenly is introduced. “If there is an aquifer at 100 ft and another one at 300 ft, a gas station may have contaminated the one at 100 ft,” Gauthier explains. While geotechnical consultants can help identify the risks, the construction industry as a whole has not solved this potential problem yet, experts say.
All heat pumps depend on compressors and refrigerants to transfer energy to and from the ground loop. Savings come from a lower head pressure that geothermal “recycling” affords. However, not all geothermal systems rely on heat pumps. One such system, popular in Europe and quickly gaining traction in North America, is deepwater source cooling (DWSC).
Cornell University uses DWSC to cool its classrooms in Ithaca, N.Y. A 2-milelong intake pipe located about 250 ft below the surface of nearby Lake Cayuga delivers 39°F water into onshore heat exchangers. A second, closed loop brings chilled water to campus at about 47°F. Warmer water is rejected through a 500-ft-long diffuser pipe close to the lake’s surface. The chilled water flows directly through the classrooms, eliminating the school’s previous chillers, which ran on ozone-depleting refrigerants.
Cornell’s system, designed for 20,000 tons, allows the $58-million investment to surge to a COP of 25 and reduce overall cooling energy by 86%. Cornell estimates savings are on track to repay the cost premium over conventional methods in 10 to 13 years from the 2000 completion date, a payback that now is approaching. “The savings is on the order of 25 million kWh,” says William S. “Lanny” Joyce, Cornell’s senior manager of engineering, planning and energy. “That is almost 10% of our campus electrical use.” He notes that the local community also benefits from reduced peak loading on the electrical grid.
Because the loops never mix, Cornell’s approach is a closed-loop geothermal system that does not rely on heat pumps. A more typical closed-loop system that uses heat pumps can be found in Elgin, Ill., where Sherman Health, the owner of a new, 255-bed hospital almost finished in the Chicago suburb, plans to save more than $1 million a year by tapping into a 15-acre, 17-ft-deep geothermal pond—one of the world’s largest—that is heating and cooling the 650,000-sq-ft facility. The owner knew that it needed to build a 5-acre stormwater-detention pond on its 154-acre site, so it tripled the size to accommodate a geothermal, closed water loop.
Shades of Green
All geothermal systems require electricity; heat pumps require even more. The “greenness” is determined by the efficiency of the overall design and the type of electricity going in. There is no shortage of strong opinions here.
Before designers even consider adding a geothermal system, it is critical to reduce building energy loads by upgrading the envelope and, if appropriate, HVAC ductwork. “The technology is fundamentally sound,” explains Joe Lstiburek, principal of forensic consultant Building Science Corp., Somerville, Mass. “But a lot of people are using them for really, really poor buildings.” For every dollar spent on conservation—better windows, insulation, ductwork—two dollars can be saved on the size of the geothermal system. But as many buildings are designed inefficiently, geothermal has become the “greenie-weenie technology du jour,” he says.
Another issue is whether or not GHPs are a renewable source of energy. Gauthier and Lstiburek say the “geothermal” moniker is nothing more than smart marketing. Others, such as Bererton, think it “should be considered the same as solar,” he says. “If you look at a COP of four for a heat pump in heating mode, one unit of electricity gives you four units of heat, so where did those three units of heat come from? They came from the sun, so you really are 75% solar.”
With these systems, energy use likely drops, but it never goes away. Nor does it return. As such, USGBC’s LEED rating system does not identify GHPs as renewable. The Internal Revenue Service does, and it provides special tax credits. The debate rages on, but experts unanimously agree: These systems are green so long as they are intelligently planned, executed and maintained. Says Dwyer, “I think it has got a long, healthy future.”
