The drilling rig set up shop on a grass patch in downtown Carbondale, facing the community center and not far from a community garden, but this rig wasn’t searching for oil and gas — it was looking for heat.
The 500-foot bore hole the rig drilled was the first step in determining the viability of heating and cooling a section of the town with geothermal energy.
Using a $716,000 grant from the U.S. Department of Energy, a coalition of local government and community groups, with the help of the National Renewable Energy Laboratory, is looking to design a system to serve a 16-acre area.
The geothermal system would provide at least 50% of the heating and cooling for the area, which includes the community center, a town administration building, the high school, a library, 20 townhouses and 20 condominiums.
“This is a chance to tie together the heating and cooling of a variety of types of buildings in one district,” said Jon Fox-Rubin, innovation manager for Clean Energy Economy for the Region, a Carbondale-based nonprofit promoting rural clean energy projects.
CLEER is overseeing the project for the Carbondale Geothermal Coalition, which includes the Garfield County Library District, the Roaring Fork School District, and the town of Carbondale and the Third Street Center, a hub for community activities.
“Carbondale has a goal of being carbon neutral by 2040,” said Ben Bohmfalk, the town’s mayor. “A project like this fits right in with our plans.”
While Carbondale is seeking to be an early adopter of new geothermal technology, Colorado through $12 million in grants is looking to promote geothermal — from heating homes to making electricity — across the state.
“We are technology agnostic,” said Bryce Carter, geothermal emerging markets program manager at the Colorado Energy Office, which is administering the grant program. “We are excited to see what comes out of the woodwork. What developers think will work in Colorado.”
The Carbondale project combines two long-standing heating ideas with a newer one — heat pumps.
“This is the fifth generation of district heating and it is really efficient compared to previous generations,” said Xin Jin, a National Renewable Energy Laboratory researcher advising the Carbondale project.
District heating, using a central source to heat an area, dates to the Roman Empire, while tapping into a geothermal source was first done in the French village of Chaudes-Aigues in 1332. The town, its name meaning “hot water” in the regional language of Occitan, still claims some fame for its therapeutic hot springs.
The first district heating system in the U.S. was launched in 1877 and the Denver City Steam Heating Co. started operations in 1880. Xcel Energy still operates the steam system today.
The first geothermal system was the Boise Warm Springs Water District in 1892. Today, the district heats about one-third of downtown Boise.
There are about 19 geothermal district heating systems in the U.S. and most, like Boise or Pagosa Springs, depend on geothermally heated water. The Pagosa Springs Geothermal Utility heats businesses and homes and keeps the town’s sidewalk snow-free.
How it might work
Carbondale has no hot springs and while existing systems provide only heat, the town’s “fifth generation” system will also provide cooling.
The temperature a few hundred feet below the surface remains a relatively constant 50 degrees Fahrenheit and that is plenty warm enough for a heat pump.
“We create an ambient temperature loop with water coming out 50 degrees, from 500 to 600 feet below ground, then going through heat pumps and returning to the ground at about 45 degrees,” Fox-Rubin said.
The heat pumps pull the heat out of the water using a refrigerant with a very low boiling point, a compressor condenses the vapor raising the temperature and then moves it indoors. The heat pump uses electricity, but nothing is burned to make heat.
During the summer the heat pump works in reverse pulling heat out of the home or building, warming the water by about 2 degrees and sending it back into the ground.
Most heat pumps being installed in homes and businesses are “air source,” which means they are pulling heat from the air, not the subsurface.
“Air-source efficiency goes down when it gets cold,” Jin said. “The ground temperature is more or less constant so the geothermal heat pump is more efficient.”
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Drilling geothermal wells, however, is expensive, as much as $20,000 for a bore hole, and requires space large enough for a rig.
“It is very expensive for a single home,” Jin said, “but when we can do it at scale it becomes more economically efficient.”
And unlike the districts in Chaudes-Aigues or Pagosa Springs, the fifth-generation systems do not need an active geothermal spring as a heating source.
The goal for Carbondale is to provide half the heating and cooling for its district, Fox-Rubin said, as it isn’t economical to shift all buildings to heat pumps for some have relatively new and efficient heating systems.
In buildings and homes where the heating systems are old enough to merit being replaced with new heat pumps the system would provide 100% of the heating and cooling.
After the bore hole was drilled, high density polyethylene tubing was placed down the hole and water was run through it to test the thermal conductivity.
This thermal response test will give the coalition a better idea of the viability of the project.. The tests found the ambient earth temperature was 58 degrees Fahrenheit, which Fox-Rubin said is “a promising number” and that the ground is sufficient for a geothermal system. It will, however, be another week for the full analysis to be completed.
“We don’t know the cost yet. That is one of things we have to determine,” Fox-Rubin said. “We don’t know how many bore holes will be needed to heat the district.”
Once that information is in hand the team will design a system and submit an application to the DOE for a second grant, which would cover 80% of the cost of construction, with a 20% local match.
In the first round the DOE gave $13 million in planning and development grants to 11 towns and cities. Four of those were to rural communities — Middlebury, Vermont; Seward, Alaska; Shawnee, Oklahoma; and Carbondale.
“That’s who we are competing against,” Fox-Rubin said. “It’s a friendly competition.”
The National Renewable Energy Laboratory is also advising the Middlebury and Seward projects, as well as a district system for an even more remote Alaska site 60 miles from Nome.
“If we can do this, if we can do a district heat system for a small community in Alaska, then bigger communities can also follow suit and learn from our experience,” Robbin Garber-Slaght, a researcher at the laboratory’s Alaska campus and co-lead for the Seward the project, said in a statement.
One way or another, Fox-Rubin said the project may move forward. “Once the economics are there and the payback is reasonable, I hope we can go ahead even without federal support.”
Carbondale might get some help at the state level. In 2022, the legislature passed House Bill 1381, which created the $12 million grant program to support geothermal energy for heating and cooling for homes, businesses and communities and for the generation of electricity.
Geothermal for electricity production requires seeking greater heat at great depths. “When you start going really deep, 10,000 to 20,000 feet you can access heat in any part of the state,” the state energy office’s Carter said. “This is where we want to leverage oil and gas expertise.”
The grants run from $10,000 for a single home to 50% match of $500,000 for the first $1 million in constructing a district or industrial system. The bigger electricity generation projects could be eligible for additional funding, Carter said.
“We have to think of the ground as a big thermal battery,” Carter said.
An industrial geothermal system would also be eligible for tax credits under a program established this year by House Bill 1272.The DOE began accepting applications for the first round of funding Nov. 14 and will continue to do so until Jan. 19.