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Evanston buildings install ground source heat pumps, attempt to boost energy efficiency 

Jul 21, 2023

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This summer hasn’t been normal. The hottest days in the last 100,000 years were recorded on four consecutive days in early July. Toxic smoke from Canadian wildfires traveled thousands of miles, poisoning the air in Chicago, New York City and elsewhere. People, especially those with health problems, were instructed to stay inside – a measure not dissimilar to the pandemic that killed hundreds of thousands of Americans in 2020. However, unlike COVID-19, which for many was addressed with vaccines and an N95 mask, climate change is here to stay.

Many people – from homeowners and condo developers to consultants and architects – have started thinking about what they can do to reduce their carbon footprint. In Evanston, one innovative solution is installing a geothermal heating and cooling system. Geothermal technology has been around since the 1950s but has only recently started to gain traction as a viable renewable energy source. Four locations in Evanston – two residential and two institutional – are a few of the many places that are turning to geothermal energy.

True geothermal energy, commonly used in places such as Iceland, New Zealand and the Philippines, takes advantage of reservoirs of hot water at varying depths below the earth’s surface. Temperatures can range from 300 degrees to over 700 degrees Fahrenheit.

However, this level of geothermal energy cannot be found in Evanston. Here, the heat of the ground five feet down is a constant 55 degrees Fahrenheit. This necessitates a different type of geothermal energy: ground source heat pumps (GSHP). They can be installed a few different ways, but in Evanston, designers typically use a vertical loop system.

“For a vertical system, holes (approximately four inches in diameter) are drilled about 20 feet apart and 100 to 400 feet deep,” explains the U.S Department of Energy’s website. “Two pipes, connected at the bottom with a U-bend to form a loop, are inserted into the hole and grouted to improve performance. The vertical loops are connected with horizontal pipe, placed in trenches, and connected to the electric heat pump in the building.”

In the winter, the antifreeze fluid in the underground pipes transfers the warmer underground heat to the heat exchanger of the heat pump in the building, which warms the building air. In the summer, the reverse happens and the heat pump removes heat from the building air and transfers it underground through the fluid in the pipes, thus cooling the building.

GSHPs are becoming more common globally, with the International Energy Agency reporting that global sales of heat pumps grew 11% in 2022, which was the second straight year of double-digit growth. Furthermore, the Department of Energy states that approximately 50,000 geothermal heat pumps are installed in the U.S each year.

One of those new heat pumps belongs to longtime Evanston residents Bill and Eleanor Revelle. Although they built their remarkable energy-efficient lakeside home in 2002, it was not until this year that they decided to invest in a GSHP.

The Revelles’ house overlooks Lake Michigan through triple-pane windows, with vibrant native plants flourishing in the yard. With everything from solar hot water collectors in their driveway to photovoltaic shingles on the roof and dual-flush toilets in their bathrooms, this property reflects a balance of nature, engineering and architecture. It is built on sustainability. The photovoltaic roof shingles produce 85% of the electricity used in the house and help power the new heat pump.

“[Architect Ellen Galland, Eleanor and I] wanted to build the most energy-efficient house we could build at the time,” says Bill Revelle.

The Revelles – Second Ward City Council Member Eleanor and Northwestern University Psychology Professor William – spared no expense building their house sustainably. However, for 20 years, they used gas as a supplement to their solar energy. This was because they felt a GSHP would not be environmentally beneficial to install when the house was built in 2002.

“We didn’t do [ground source heating] because at the time, we penciled it out and the amount of carbon it takes to produce electricity to do the ground source heat pump at the time was more than using gas to do it,” Bill explained.

So, why did they decide to install the GSHP now?

“The main reason to do it is because we want to get off natural gas,” said Eleanor. Her husband added, “Heat pumps have been around for quite a while, but they’ve become much more efficient over the last 10 years.”

Despite the recent improvements in heat pump design, installing a GSHP is not easy. The Revelles explained that workers had to drill through 110 feet of clay, then through limestone, shale and sand. Drilling through sand is especially difficult because the sand fills in the vacated space when a hole is dug.

The system has been a success for the Revelles.

“So far, we have only been using the air conditioning part of the system, which seems to be very efficient and [is] producing cooling and dehumidification very quietly and efficiently,” said Bill.

While the Revelles’ house is an exceptional feat of sustainable technology, the Revelles had the financial resources to fund their geothermal system. At the town houses at Lake Street and Ashland Avenue, the cost to install GSHPs was spread among the seven units.

The development is dubbed “Homes That Work.” Tom Engel, one of the developers of the 2009 project, explains why these town houses are unique.

“It was a B1 district, so you could have a business in the storefront on the ground floor and a home with three bedrooms above it,” Engel says.

The buildings were not only designed to combine business with housing, they were also built for sustainability. The designers used energy-efficient appliances that prioritize insulation and energy savings. And they opted to install GSHPs which, Engel explains, were intended to save money in the long run.

“In this climate, geothermal is very successful for air conditioning,” Engel says. “Basically, the cost is very minimal [once the system is installed]. The only cost for air conditioning really is running a fan, which is equivalent to a light bulb.”

Another advantage to the use of ground source heat pumps for cooling is the elimination of noisy outdoor condensing units, said Marian Tweedie, one of the architects of Homes That Work.

However, in the roughly 14 years that have passed since GSHPs were put in place, some limitations have emerged. Engel says that ground source heating’s restrictions in the winter make it a much-less feasible energy option in cold weather than other renewables like wind and solar. Electricity is needed to provide supplemental heat in very cold weather.

“In the spring and the fall, [a GSHP] is very effective for heating and very economical. In the middle of winter, temperatures get freezing. It’s still used, but it’s supplemental, and the supplemental heat that it requires is very expensive,” said Engel.

Nate Kipnis, known for his sustainable practices as an architect in the Chicago area, shared Engel’s view on geothermal’s challenges in the Midwest.

“Ground source is way too expensive, too invasive on many sites and has way too much equipment,” Kipnis wrote in an email to the RoundTable. “They also use a lot more power for the pumps that are required to circulate the fluid through the underground piping system.”

Kipnis said he prefers to use air-source heat pumps (ASHPs), which extract heat from the outside air, compress it, and move it indoors. Kipnis says that ASHPs are cheaper and easier to install, using less equipment and space.

However, similar to its counterpart in the ground, there is one glaring problem with air source heating: cold weather.

“The only advantage of ground source [heat pumps] is in fact that they are slightly better in ultra-cold weather compared to air-source systems,” said Kipnis.

Bill Revelle added that air-source heating is simply much less efficient than geothermal heating.

“We had considered air-source heat pumps vs. ground-source,” Revelle wrote in an email. “A simple comparison suggests that air source is cheaper but less efficient than ground source.” He pointed out that, according to an article in Energy Sage, “the efficiency of a ground source system is roughly 50% higher than air source. Our goal was to cut the use of C02 producing power sources by as much as possible. Thus, the choice of the ground source system.”

While Engel highlights the struggles of GSHPs in cold weather at Lake and Ashland, low temperatures only scratch the surface of the problems at a second lakefront geothermal location.

In 2010, administrators at Garrett-Evangelical Theological Seminary – a graduate school of theology of the United Methodist Church located on the Northwestern campus – opted to install geothermal in two of their buildings with the help of Indie Energy Systems Company. The company had trademarked a “smart geothermal” technology that was meant to be affordable and reliable. Unfortunately, their technology proved to be neither affordable nor reliable for the seminary.

A few years after the installation of the 27-well GSHP system, Grumman|Butkus Associates (GBA) – an Evanston-based consulting firm – was hired to evaluate the problematic system. Steve Zehr was the project manager at GBA, and he explained in an email to the RoundTable what went wrong with Garrett Evangelical’s GSHPs.

“The GSHP system which was installed at Garrett did not work as intended during the first years of operation,” he wrote. “The heat pumps could not provide adequate cooling during the summer and during the winter they were using campus steam to heat the loop rather than heat sourced from the ground.”

Grumman|Butkus found that this happened because there were not enough geothermal wells to supply heating and cooling to the building. Additionally, the two valve vaults which fed the underground piping were constructed with the wrong materials and were rapidly corroding–even leaking at times.

Indie Energy went out of business in 2012, and the substantial cost of fixing the geothermal system meant that the Garrett buildings could only partially rely on the company’s “smart geothermal” energy.

“Ground-source heat pump technology has proven to be reliable and will be a key part of our decarbonization efforts, but it does require careful engineering design to work as intended,”

Zehr concludes. “Unfortunately, the system which was installed at Garrett was deficient.”

Geothermal technology has proven to be imperfect, but it is improving. MIT Technology Review reports that heat pumps are getting better, with new models being “more efficient and better able to handle cold weather.” This is proven at another lakeside location: the Evanston History Center.

The EHC lives at the onetime home of Charles Gates Dawes, a former U.S. Vice President and Nobel Peace Prize winner. The Dawes House was constructed in 1894 and currently serves as a well-preserved museum and repository of archives, with a 2013 geothermal installation providing heating.

“Just because [the house] is old, doesn’t mean it can’t function in today’s world with today’s technology,” says EHC Director of Facilities Kris Hartzell. “So I think that part of our mission is to showcase the fact that as a historic building, we’re absolutely adaptable to the current technologies.”

Hartzell says she believes that a successful geothermal installation must be personalized and well-thought out.

“I think you need to not have an ego. I think you need to understand and work with the system, [and] the parameters or the constraints that you’re given and not just be like, ‘Well, this should work.’” Hartzell voices. “You need to have an understanding of how the materials and the construction are going to affect the efficacy of your system.”

The seven GSHPs located at the towering lakeside mansion have been a success since they were installed nearly a decade ago, with the help of supplemental electric heat on the colder winter days.

“The heating has been working fine. It’s just great. Never had a problem, never been chilly,” Hartzell emphasizes.

When designed correctly, GSHPs save Evanstonians money because of their efficiency and longevity. And while the technology is still improving, these examples in Evanston show that people across professions and backgrounds are investing in renewable energy, hoping to create a greener planet for future generations.

“We have to eliminate our carbon footprint. It’s that simple,” concludes Bill Revelle.

For Garrett-Evangelical Theological Seminary:

For Homes that Work:


For Evanston History Center:

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Milo Slevin is a 2023 summer intern for the Evanston RoundTable. He is a senior at Evanston Township High School and the feature editor for the school newspaper, The Evanstonian. Milo enjoys playing soccer,... More by Milo Slevin

Sign up for our free newsletterfour consecutive days in early JulyU.S Department of Energy’s website.House of sustainabilityaccording to an article in Energy SageGarrett-Evangelical Theological SeminaryEvanston History Center Please consider making an additional gift!Donate Now