Geothermal heating and cooling: Renewable energy’s hidden gem


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This is a& re-post from Yale Climate Connections by Philip Warburg

Often described as a giant tower of Jenga blocks, Boston University’s Center for Computing and Data Sciences shows no outward signs of leading the race to sustainable energy design. No rooftop wind turbines grace its heights; no solar panels are mounted on the multiple roof decks jutting out from the building’s core.

What makes this building unique lies deep underground, where water circulating through 31 geothermal boreholes will supply 90 percent of its heating and cooling needs when the building opens, as scheduled for later this year. Through a process called geothermal heat exchange, water pumped from 1,500 feet underground will draw upon the near-constant temperature that prevails beneath the earth’s surface &- 50 to 60 degrees Fahrenheit year-round. Even on the coldest New England days, water prewarmed by the earth will be circulated through& heat pumps& that will further raise its temperature to deliver heat where needed. On warmer days or in heavily occupied spaces where heat builds up even in winter, the heat exchangers will draw on the earth’s cooler temperature to provide air conditioning.

Heat pump flowIn the summer, heat is extracted from the home, and is discharged into the earth. In the winter, the process is reversed. (Source:& Solar Review)

Dennis Carlberg, associate vice president for university sustainability, was a key player in preparing& BU’s Climate Action Plan, which set 2040 as the target date for achieving net carbon neutrality. That goal is to be met by phasing out gas-fueled heating systems, stepping-up energy efficiency, and investing in on-campus renewable energy sources like the data center’s geothermal plant. The university already draws its electricity from renewable energy, via a& power purchase agreement& with a South Dakota wind farm.

Carlberg acknowledges that transforming a largely built campus in a dense urban setting is a tough challenge, but he credits the data center with opening people’s minds to new technology solutions. “The center has been a fabulous exercise in understanding what we can do,” he says. “It’s given our campus planning and operations folks a deep understanding of how this works. You’re always afraid of what you don’t know, right? You’re going to come up with excuses for not doing it, but we’re doing it!”

Campus-wide geo-exchange

Smith College in Northampton, Massachusetts, does not face the space limitations of an urban university, but it is burdened by a decades-old steam heating system fueled by natural gas, backed up by oil, that serves 79 of the campus’s 104 buildings.& In 2010, the college announced an ambitious goal: campus-wide carbon neutrality by 2030.& “We thought we were at the cusp of a cellulosic ethanol revolution,” says Dano Weisbord, who is in charge of campus planning and sustainability.& “That really didn’t pan out.” Though many higher education institutions& substantially rely on biofuels and biomass& to meet their climate goals, Weisbord warns that they can be significant sources of carbon pollution.&

More recently, Smith has adopted a district energy master plan with geothermal at its core. About 90 percent of Smith’s heating and cooling load is to be met by three separate geothermal subdistricts, each fed by its own field of geothermal boreholes.& In the first phase, 80 boreholes will be drilled to a depth of 850 feet in the college’s Davis Lawn, home turf to the Quidditch (aka “Quadball”) team.& A high-density polyethylene (HDPE) pipe six inches in diameter will be inserted into each borehole, and within that enclosure, a pair of narrower-gauge pipes encased in thermally conductive grout will circulate water in a& closed-loop system, absorbing the relatively constant temperature of the surrounding rock, soils, and groundwater.

Much of Northampton’s subterranean geology is characterized by& arkose& &- a mid-brown sedimentary rock that appears on many Smith buildings including the newly updated Neilson Library, designed by Maya Lin.& While denser rock formations &- granite for example &- tend to be more effective in conducting and storing thermal energy, Weisbord describes arkose as a moderately effective geothermal battery.

Each of Smith’s geothermal districts will have its own energy plant where heat pumps will be used to raise or lower the temperature of water after it has circulated through the district’s borehole loops.& The water will then be fed into a network of heating and cooling pipes that deliver thermal comfort to individual buildings before being returned to the borehole field for recharging.

Distribution linesHeating and cooling distribution lines being laid outside the Lamont House dormitory for phase 1 of the geo-exchange network at Smith College. (Photo credit: Dano Weisbord)

While geo-exchange will substantially reduce Smith’s use of natural gas, electricity will be needed to operate the heat pumps and water-circulating equipment. To ensure that this electricity comes from renewable sources, Smith has led a five-college consortium that is purchasing a third of the power generated by a 76.5-megawatt solar farm in Farmington, Maine. Students from the participating colleges have responded enthusiastically to this shared initiative.

All three phases of Smith’s geo-exchange network are scheduled for completion by 2028, at a cost of $210 million. If the college’s estimates are on target, the 30-year discounted lifecycle cost of this investment will be $279 million, about $60 million less than it would spend during the same period if it were to continue operating and maintaining its current, fossil fuel-dependent heating and cooling systems.

According to research carried out by Weisbord and colleagues in the Smith engineering department, roughly 100 U.S. colleges and universities have installed geothermal systems on their campuses.& Yet geothermal’s reach extends well beyond academia.

‘Doing the right thing’ in a corporate setting

Epic Systems,& a healthcare software giant& that handles medical records for 250 million patients, has made geothermal energy a centerpiece of its thousand-acre headquarters site in Verona, Wisconsin. Nearly 11,000 employees occupy some eight million square feet of indoor space, including offices and meeting rooms, two large-capacity auditoriums, multiple restaurants,& and a large data center. All are heated and cooled by geothermal energy.

“It’s part of an energy portfolio that is all centered around doing the right thing,” says facilities director Derek Schnabel. He acknowledges that being 100% reliant on geothermal for heating and cooling is a challenge. “We’ve found it just makes us better operators and owners because we don’t have natural gas as a backup. Once you have [conventional] boilers, you use them. And then they become a crutch and you don’t get the peak efficiency out of the system that was promised.”

Despite Wisconsin’s northern climate, Epic spends about nine-and-a-half months per year cooling its buildings. Yet when it’s needed, heating demands about 25 percent more electricity. “To raise 50-degree water to 130 degrees is 80 degrees of work,” Schnabel explains. Cooling a building requires just a modest drop to 44 degrees from the ambient temperature of water coming out of Epic’s 6,000-plus geothermal boreholes. Much of the electricity that powers the campus comes from renewable energy: a wind turbine array twelve miles from campus and eighteen acres of on-campus solar panels.

Though less demanding of electricity, cooling Epic’s buildings poses a different challenge: maintaining a stable temperature underground over a multi-year period. A system that relies heavily on geo-exchange for cooling month after month, year after year, can gradually cause the ambient earth temperature to rise, making it harder for the system to efficiently meet air-conditioning needs. Epic has two “geo-exchange water features” that help correct this imbalance.& One is a 5.4-acre stormwater detention pond where water is circulated through nearly 150 miles of tightly coiled plastic piping called “slinky loops,” supplementing the cooling capacity of Epic’s geothermal wells. Water drawn from the chilly depths of a 21-acre artificial lake further helps keep the geo-exchange system in balance.

Building by building

New residential and mixed-use real estate projects offer another promising direction for geothermal entrepreneurship. In Toronto, a pioneering company called Subterra Renewables is bringing geothermal heating and cooling to a growing number of condominium complexes in and around the city.& Twenty-one buildings& equipped with Subterra geo-exchange systems are already operational; a half-dozen more are in development.&

Matthew Tokarik, Subterra’s president, describes his company’s model as helping customers avoid the “pain point” of high capital outlays while still saving on operating costs. Instead of selling geothermal systems to condominium associations, Subterra retains ownership of the systems it installs and sells thermal comfort as a service. “We’ll basically sell you the energy as an operating cost for less than a comparative fossil fuel burning system,” he says.&

In addition to freeing its clients from upfront costs, Subterra eases the anxiety of building owners and operators “who don’t really understand the fundamentals of how [geothermal] is working.” Preserving a balance between cooling and heating loads is as important to long-term geothermal performance in individual buildings as it is on college and corporate campuses.&

“Part of our service is guaranteeing that the system is going to stay within certain temperature bounds, which in turn indicates proper system operation for tenants,” Tokarik explains. “Every couple of months, usually after a heating or cooling season, we’ll go and deep dive the data, just to make sure it’s within our ranges.” & & &

To streamline its geothermal pipeline and broaden its geographical reach, Subterra has added vertically integrated drilling services in multiple locations, allowing it to set its own drilling schedule rather than adapting to the timeline of an outside driller. Particularly in confined urban settings, drilling boreholes for geothermal systems must precede all other phases of building construction. “When we become the driller, the installer, the designers, we really will have start-to-finish knowledge of how the system is going to work and operate,” Tokarik predicts.

Neighborhood geo-exchange

While& economies of scale& generally favor geothermal in large, multi-unit buildings, advocacy for street-scale “geo micro districts” has recently gained significant momentum in Massachusetts. Protesting a& rash of methane leaks& in gas distribution lines across the state, activists with a group called HEET &- Home Energy Efficiency Team &- questioned the wisdom of simply replacing old gas lines.&

“We were about to spend& at least $9 billion& on new fossil fuel infrastructure,” recalls HEET co-founder Audrey Schulman. “I thought that was a waste so I started trying to figure out what we could do instead.” She turned to the group’s co-founder, Zeyneb Magavi, who asked, “Why don’t we do networked ground source heat pumps instead?”& &

HEET commissioned a& feasibility study& which laid out the technical and economic arguments for linking clusters of homes and small businesses into micro districts with geothermal boreholes and connector pipes running along public rights of way, much like the gas distribution lines that now run under our streets. Eventually, Schulman and Magavi argued, these micro districts could aggregate into citywide geothermal grids.&

Schulman and Magavi immediately recognized the need to persuade gas utility executives that repurposing their companies as purveyors of thermal comfort, rather than suppliers of a particular fuel, could be in their long-term interest. They succeeded with the state’s two largest gas distributors.& In October 2020, Eversource won the Massachusetts Department of Public Utilities’ approval for a& demonstration project& looping 45 buildings in Framingham. In December 2021,& National Grid received that department’s green light& for a pilot involving as many as four shared geothermal loops, each connecting 20 to 40 residential and/or commercial customers. Its& implementation plan, filed in May 2022, is now out for public comment.&

(Photo credit: Philip Warburg)

More than meets the eye

Ever since President Jimmy Carter heralded renewable energy as an alternative to fossil fuel reliance in the 1970s, above-ground clean energy resources such as solar and wind have captured the lion’s share of public attention and policymakers’ zeal.& Their contribution to decarbonizing electricity is critical.

At the same time, geothermal energy needs to be embraced as a key element in transitioning to a more sustainable energy future. A& recent U.S. government study& estimates that geothermal heat exchange could supply about 23 percent of total U.S. residential heating and cooling demand by mid-century. Commercial and public buildings offer huge added potential for harvesting the earth’s thermal energy.

With the planet’s building stock expected to& double by 2060, the need to transform how we heat and cool our indoor built environment has never been more urgent.& Vastly under-utilized today, geothermal energy has a central role to play.

Philip Warburg, former president of the Conservation Law Foundation, is a senior fellow at Boston University’s Institute for Global Sustainability.