Welcome to our FAQ.
We’re collecting questions about Thermal Energy Networks and networked geothermal systems with a focus on how we can implement them in Vermont.
We’re developing this resource and value your input.
Send your questions to info@vctn.org We’ll do our best to answer and post them here.
Thank you to Jake Marin at Efficiency Vermont for his expert review.
For questions about geothermal systems for an individual home, visit one of these national resources:
GeoExchange, “The Voice of the Geothermal Heat Pump Industry in the United States,” a non-profit trade association
International Ground Source Heat Pump Association, IGSHPA, a non-profit organization advancing ground source heat pump technology and training ground source heat pump technicians and inspectors
FREQUENTLY ASKED QUESTIONS
A RESOURCE FOR VERMONTERS
WHAT ARE “NETWORKED GEOTHERMAL” AND “THERMAL ENERGY NETWORKS”?
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Networked geothermal systems are a local energy solution that uses thermal energy from underground and shares it between buildings in a neighborhood, around a town center, or on a campus. As with individual geothermal systems, water-filled pipes in shallow boreholes access the constant temperature of the earth and deliver it to heat pumps inside buildings, where it’s compressed into warm or cool air as needed. In a networked system, buildings are also linked by horizontal pipes that share temperatures between buildings and exchange thermal energy between them. These networks often result in efficiency gains as well as reduced costs for individual buildings.
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Thermal Energy Networks share heating and cooling between buildings just like a geothermal network, but can also include other thermal sources, such as excess heating created by data centers, large-scale refrigeration in grocery stores, or ice rinks. They can also harness heat from or reject cold into wastewater systems. These networks are closed loops of water-filled pipes underground that collect, deliver, and optimize sharing of thermal energy.
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We can use both individual and networked geothermal energy to meet our energy needs and our climate goals in Vermont. While geothermal for a large building or a single house is an important clean energy option, it can be too costly for many Vermont homeowners or an individual business to install.
Thermal Energy Networks help maximize efficiency and increase the affordability of heating and cooling for entire communities or neighborhoods. They can also make use of waste heat, balance thermal loads between buildings, and reduce electric peaks. As a rural state with a blend of close-knit towns and far-flung homes, we have an opportunity to advance both individual and networked thermal solutions.
WHAT ARE SOME POSSIBLE SOURCES OF THERMAL ENERGY?
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In Vermont, heat is a precious resource, yet we waste a lot of it every day. All the hot or warm water we use for washing—whether in our homes, laundromats, hotels, restaurants, etc.—goes down the drain.
Refrigeration and air conditioning reject heat into the air, especially from grocery stores, ice rinks, and large buildings. Industrial processes often generate heat that’s vented outside or hot water that’s flushed away.Think of the large cheese or maple syrup making, food production, resort areas, and brewery or distillery operations in Vermont. Where are there wastewater treatment plants or town wastewater systems? What buildings or neighborhoods are nearby that could use that heat?
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Wastewater can be a perpetual source of heat. Thermal systems that use wastewater are closed and sealed. They divert wastewater in order to extract heat before returning the stream to the wastewater system. An explanatory video by one of the leading companies installing these systems can be found here, with more information on their website.
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Yes. Surface water thermal systems are working in many places, both for community-scale projects and as pond loop systems for individual homes. They can be closed loop, extracting only temperature from the water, or open loop, using the water as part of the system.
In Vermont, we need to know a lot more about the impact of using our rivers and lakes to heat and cool buildings before considering surface water systems. Our waterways are critical resources and integral to our ecosystems. They’re also part of what many of us value about living in Vermont. There are other key thermal sources to tap—ones we create ourselves, often waste, and should fully explore first.
VERMONT’S GEOLOGY & NATURAL LANDSCAPE
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Yes. Bedrock is an excellent conductor of thermal energy, much better than sand or loose soil. A borehole drilled through bedrock also doesn’t require steel casing to prevent cave-ins as needed in sand or soil. Drilling through bedrock can be more expensive, but can be offset by savings on casing.
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Geothermal loops can be installed in most locations. Open loop systems require access to large volumes of water, but closed loop is possible in nearly all subsurface types. Varying soil conductivity and access to water makes each project unique, but this is often not known until a test bore is drilled. Limited mapping exists which gives drillers a sense of the subsurface geology, but this can vary dramatically, even in a small area.
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Underground pipes are made of durable but flexible plastic. Boreholes go deep underground, so are unlikely to be damaged during extreme weather. Horizontal pipes in a network are buried about six feet deep, so are more protected from floods or storms than power lines and similar to gas pipes. While no system is entirely safe, geothermal and Thermal Energy Networks are one of the most resilient energy systems. Should damage occur, there are no dangerous consequences from the pipes or fluid.
IS OUR GEOLOGY SUITABLE FOR GEOTHERMAL SYSTEMS?
HOW WOULD THESE SYSTEMS IMPACT LAND OR LANDSCAPES IN VERMONT?
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No. Networked systems are closed loops, meaning that they don’t use or interact with water in the environment. When the system is constructed, pipes are filled with water that continuously circulates to carry temperature. Ground loops can contain an antifreeze additive, though this is most commonly propylene glycol, which is non-toxic and food grade.
Ensuring the health of our ecosystems is critical as we develop solutions to heat and cool our buildings. Thermal Energy Networks have minimal impact on our land and water systems. Drilling boreholes and creating trenches for horizontal pipes can be done away from sensitive areas and can be managed to minimize impact.
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A properly designed geothermal system does not impact soil or ground temperatures and is fully renewable. The heat stored in the ground is inexhaustible, being constantly replenished by the sun and the core of the earth. Improperly designed/installed systems can cause a temporary and localized heating/cooling condition, but this self-corrects rapidly and can be avoided by good loop design.
In our colder climate, we can consider what sources to add to a thermal network rather than relying solely on geothermal for heating larger, particularly residential areas. Wastewater is a thermal source often already on site that can supplement geothermal in heating-dominant Vermont.
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Geothermal and other Thermal Energy Networks often include a chemical added to the water in pipes to prevent freezing. The antifreeze used in these systems is propylene glycol. This fluid is a food grade additive “generally recognized as safe” by the U.S. Food and Drug Administration (FDA) (FDA 2017). It can be confused with ethylene glycol, previously used in antifreeze, which is toxic if consumed. Even with this chemical added, the system uses mainly water, a much safer way to deliver thermal energy than with explosive, corrosive gasses.
Any pipe can leak. However, plastic pipes are the most durable material available and are produced in much longer segments than metal pipes. A borehole or a section between buildings could have just one section of pipe, meaning no joints and less chance of leaking. Because propylene glycol is non-toxic and food safe, rare leaks that do occur have very minimal environmental impact.
HOW DO THEY WORK IN VERMONT’S CLIMATE?
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In Vermont and even farther north, the temperature of the earth is a constant 45-50ºF about 4-5 feet underground. This provides a reliable, consistent energy source for ground source heat pumps in our buildings.
A geothermal network functions best when it includes mixed-use buildings with a diversity of heating and cooling needs. Systems connecting buildings that can share heating and cooling require fewer boreholes and can be more efficient and cost-effective.
Although our climate in Vermont is heating dominant—requiring more heating than cooling—a properly designed system can deliver enough heat to keep us comfortable year-round.
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Vermonters know how to put our available resources to work. When we can recover waste heat and pipe it to where it’s needed, we can create even more efficient thermal networks as well as fewer boreholes and lower installation costs. Waste heat comes from a variety of sources such as office buildings, commercial refrigeration, wastewater, or even breweries and other industrial facilities. Diversifying our thermal sources optimizes our capacity to heat buildings even on the coldest days.
ABOUT THE SYSTEMS
INSIDE
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Distribution infrastructure for ground source heat pump (GSHP) heating and cooling is often very similar or even identical to conventional HVAC systems. Piping or ductwork distributes heating or cooling throughout a building. When the heat pump creates warm or cool air, one or more fans push this air through ductwork to registers in rooms. If the distribution system is water-based, such as for baseboard, radiator, or in-floor radiant systems, the GSHP-conditioned water is piped to those “emitters” throughout the building.
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A ground source heat pump (GSHP), about the size of a conventional boiler, is most commonly located in a basement or mechanical room and connects to piping or ductwork throughout a building to distribute heating or cooling, as with any HVAC system.
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Yes, and it depends. Although distribution systems for geothermal and other Thermal Energy Networks are often very similar to that of conventional ones, there are added considerations.
For forced air systems, the condition and size of ductwork is very important. Delivered air temperatures from geothermal or other Thermal Energy Networks are lower than air heated by fossil fired furnaces. Undersized and/or leaky ductwork can result in efficiency losses as well as reduced ability to provide adequate heating or cooling. Existing ductwork should be evaluated before switching to a (geo)thermal system.
A similar issue exists for buildings that use heated water in radiators or baseboards. Due to the lower delivered water temperatures in a geothermal or other Thermal Energy Network, conventional distribution systems are often incapable of providing adequate heat. Heating systems designed for low temperature water such as radiant floors are generally geothermal ready, but older style radiators or hot water baseboards generally require more involved modifications.
For more information on compatible indoor distribution systems, please see our Compatible HVAC Systems fact sheet.
OUTSIDE
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While research and testing is underway to line existing gas distribution pipes for thermal energy distribution using water, these horizontal pipes are not currently being used for thermal energy networks. Where there is already a gas system, metal or plastic pipes need to be replaced with insulated plastic pipes for geothermal or other thermal energy distribution.
In Vermont, there are just three counties with gas systems—Chittenden, Franklin, and Addison—so we have significant opportunities to install geothermal or Thermal Energy Networks in places that rely on oil or propane. We can also identify older, leakier sections of the gas system to replace with Thermal Energy Networks rather than new gas pipes.
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While the vertical pipes that access underground temperatures are not insulated, the plastic distribution pipes are. Metal pipes are used for parts of the system inside a building where corrosion from exposure to the elements isn’t an issue.
SYSTEM MANAGEMENT & MAINTENANCE
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The components of a geothermal or other Thermal Energy Network are durable, reliable, and long-lasting. All are protected either underground or inside of buildings, which adds to their lifespan. A ground source heat pump can be expected to last for approximately 25 years, while the pipes underground have up to a 50-year warranty and are likely to last longer.
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The pipes themselves generally don’t require any maintenance. However, the glycol concentration inside the piping is important to maintain to prevent freezing and should be checked annually to ensure the levels remain consistent. The heat pump itself should be serviced annually, just like a boiler.
INSTALLATION
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Each system is specifically designed for the location and the buildings it serves, so the number and depth of boreholes—and therefore the amount of drilling required—will vary substantially from one project to another.
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Buildings that are heated with hot air or hot water in any form can connect easily to a geothermal or other Thermal Energy Network. Buildings heated with steam radiators would need new internal distribution systems.
For more information, please see: Indoor heating and cooling systems that connect to geothermal and Thermal Energy Networks
COSTS
Understanding costs for geothermal and other Thermal Energy Networks can be challenging. “It depends” is a frequent answer. In addition, many of the existing systems are owned by private companies that have not shared information about their costs.
Thermal Energy Networks are designed to fit a particular location, geology, and cluster of buildings. The customized nature of these systems contributes to their overall efficiency, but also makes it difficult to determine average costs. Most projects include a feasibility study that evaluates opportunities to access and move heat. Based on those findings, engineers can tailor the design and select technologies to maximize efficiency and cost-effectiveness.
Vermont Community Thermal Networks and our partners are researching financing opportunities that can make these systems affordable for Vermonters. We’re also identifying ownership models that contribute to local economic development, maximizing community benefits and yielding cost savings over time.
Learn more in the Understanding Ownership section of our toolkit.
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As a long-term investment in shared infrastructure, similar to a town water or wastewater system, upfront costs to install Thermal Energy Networks are high. While the cost of the ground source heat pumps (GSHPs) that move heat within and among buildings is comparable to air source heat pumps (ASHPs), installation and drilling costs are significant and can vary widely depending on the region and site geology.
The upfront costs of Thermal Energy Networks are balanced by low operational and minimal maintenance costs, making low customer bills possible and creating cost savings over time.
To further understand the financial benefits of Thermal Energy Networks, please see our 1-pager “Thermal Energy Networks Highlights”. In addition, our fact sheet on benefits to the electric grid describes how Thermal Energy Networks can keep electricity costs low by balancing loads and shaving peaks.
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Operational costs are low, in part, because the initial investment essentially buys all the “fuel”—or the ability to access and compress temperature from the ground or from waste heat sources—upfront. The system accesses heat that consistently replenishes itself and that can even be stored in the thermal network for later use, so there’s no need to add more “fuel” over time.
Unlike fossil fuels or other combustible materials, the temperature from geothermal boreholes and waste heat is readily available locally and doesn’t fluctuate in price depending on markets and supply.
The main operational cost is the electricity needed to run GSHPs, which is about ⅕ of the electricity that other kinds of heat pumps require. If that electricity is provided by on-site solar, operational costs can be even lower. Because GSHPs use so much less electricity, they can help to reduce peaks in energy demand which, in turn, lowers electric rates.
The components of thermal networks last longer than conventional boilers or air-source heat pumps, so maintenance is infrequent and costs are low.
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Not yet! Since systems are unique to the opportunities and needs of each location, this information is typically determined as part of a feasibility study for a particular project.
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One source of financing is the 2022 Inflation Reduction Act. IRA incentives last through 2032 and offer 40% off of the system: 30% off of components, plus an additional 10% when the components are manufactured domestically (which most if not all are). Other sources of financing can come from unprecedented levels of federal funding in the form of grants and low-interest loans.
The Vermont Bond Bank, Vermont Economic Development Authority (VEDA), and Vermont Housing Finance Agency (VHFA) are part of the Vermont Public Financing Climate Collaborative. They have partnered together to help Vermont access greenhouse gas reduction funds and can work with towns, developers, and businesses to create a financing package for projects.
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Thermal Energy Networks can be financed as cost-effective, affordable local projects in the same way that Vermont towns install and run municipal water or wastewater systems. As shared infrastructure, these networks can be financed using a utility model to access capital for the upfront costs, then recover that investment in rates over time.
Acting as a utility, a municipality or other community entity can issue bonds, borrow capital, and/or create public-private partnerships to fund project development and installation. Once the Thermal Energy Network is built, that entity can establish and collect rates from customers connected to the system, spreading costs over a longer term to keep monthly bills affordable. A community ownership model that uses this longer-term framework can make Thermal Energy Networks accessible in more Vermont towns, ensure affordability for all Vermonters, and direct any revenue into improving or expanding the system.