Carbondale geothermal project wins US Dept. of Energy design grant

A local team has kicked off the design phase of an innovative geothermal demonstration project in Carbondale, with test drilling likely to begin in early November. 

The US Department of Energy gave the official go-ahead to the Carbondale Community Geothermal Coalition to begin work on the project this month. A $716,000 DOE grant will fund feasibility, modeling, design and planning of a large-scale system to heat and cool a 16-acre section of Carbondale comprising a mix of institutional and residential buildings.

The Carbondale Community Geothermal Coalition includes Clean Energy Economy for the Region (CLEER), the Town of Carbondale, the Third Street Center, the National Renewable Energy Laboratory, Garfield County Library District, Roaring Fork School District and national geothermal consulting firm GreyEdge Group.

CLEER – which also runs the programs of Garfield Clean Energy – assembled the coalition and will serve as project lead.

Additionally, the coalition plans to collaborate with Colorado Mountain College to explore how the project could be an opportunity for workforce training and development, according to CLEER executive director Alice Laird.

The project is one of only 11 nationwide to receive an initial design grant through the DOE Geothermal Technologies Office’s Community Geothermal Heating and Cooling Design and Deployment Initiative. It’s one of four recipients located in rural areas, Laird added.

“This is such an exciting opportunity to showcase a really innovative, impactful clean-energy solution right here in Carbondale. This will enable us to explore another approach to reduce or eliminate our dependence on natural gas for heat,” said Carbondale Mayor Ben Bohmfalk. He said the concepts being tested here could be replicated widely and become one of the key tactics to driving down greenhouse gas emissions in other rural communities. 

The project’s origins go back to a conference held in 2018 at the Third Street Center, where internationally recognized architect Ed Mazria presented the concept of “zero-energy districts” that eliminate fossil fuel use and emissions not just in individual buildings but at a neighborhood – or district – scale. This approach can support Carbondale’s efforts to meet countywide clean energy and emissions goals set by Garfield Clean Energy, which the town adopted earlier this year. 

The DOE grant will fund the design of a shared geothermal system to serve a proposed district that extends from the Third Street Center to the Carbondale Library and east to include the Second Street Townhomes. The district was selected because of its range of building types and its highly visible location, according to CLEER innovation manager Dr. Jon Fox-Rubin.

The Third Street Center is an indispensable part of the proposed district, Fox-Rubin said, because it illustrates both the progress that the town has already made on clean energy and the opportunity for further improvement. The building is “net zero” in terms of its electricity consumption – its solar panels generate more electricity than the building uses – but at the same time, it is the biggest consumer of energy within the proposed district and it’s heated with natural gas.

Technically known as an ambient-temperature loop, the proposed system consists of a field of dozens of narrow boreholes, a horizontal loop making a circuit of the district, and heat pumps replacing furnaces or boilers in each building. Unlike geothermal projects that tap into very hot water or steam, an ambient system harnesses the low-grade heat found underground almost everywhere.

Fluid circulating through the system draws heat from the ground in the cold months and sends waste heat down into it in hot weather. The heat pumps function like reversible air conditioners, concentrating heat and moving it either into or out of the buildings. The entire system is powered by electricity, thus eliminating natural gas and its emissions. Geothermal heat pump systems like this are five to eight times more efficient than direct electric heating.

A similar system, designed by the GreyEdge Group, operates on the campus of Colorado Mesa University in Grand Junction. Fox-Rubin said, “Carbondale’s project is a big deal for the region, because it will be the first multi-building geo-exchange system designed for a small rural community.”

The work funded by the DOE design grant will take place over the next year. After the design phase, the DOE will open up a competitive second phase that could provide additional funding to build the system.

Work will start with the drilling of one or two test wells on town property adjacent to the Third Street Center. A drilling company has been contracted, and Fox-Rubin said it will start in early November. The drilling and thermal conductivity testing should be completed in about a week.

The operation will be much like drilling a water well, although Fox-Rubin stressed that no water will be taken out of the ground. The purpose of the test well is to enable the team to measure the thermal properties of the ground under the site.

Over the course of the next year, the design team will analyze the site’s geothermal potential, model and design the geothermal system, design heating-system retrofits for some of the buildings, and develop a budget and a funding proposal to DOE to actually build the system.

Fox-Rubin said that the majority of the DOE funding will go to the team of engineering, geothermal and building experts, as well as the test site drilling.

Fox-Rubin said that the Carbondale system will be designed to initially supply about a half of the district’s heating and cooling needs, with the ability to scale up to 100 percent over time. The team’s goal is to demonstrate that a geothermal district heating system can be economically feasible even with older existing buildings, he explained, and one of the keys to that will be to retrofit the buildings’ heating systems based on lifecycle economics and payback considerations. Thus, it may take five or more years to complete the transition for the entire neighborhood.