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Networked geothermal

Illustration of a networked geothermal system along a street. Water circulates through boreholes and a shared loop of pipe to deliver temperature to ground source heat pumps in connected buildings. Source: HEET

Networked geothermal is a system of networked ground source heat pumps that delivers heating and cooling to connected buildings. Networked geothermal systems have been used for decades on college campuses, and are currently being installed by gas utilities and others across the country as a safe and affordable way to deliver heating and cooling without emissions.

How it works

One or more water pumps circulate water along a shared loop of pipe and into boreholes in the street. The temperature of the water is maintained partly through boreholes a few hundred feet deep, allowing the water to pick up the stable ground temperature of the earth via geothermal heat exchange. In temperate climates, the design temperature ranges from approximately 40-90°F, though different system designs have different ranges. The temperature of the water can also be regulated by connecting to local thermal sources and sinks—eg. a body of water, municipal sewage lines, waste water facilities—to stay between 40-90°F, the temperature range where heat pumps work most efficiently. A supplemental backup heater, chiller or air source heat pumps on the shared loop of water can help maintain the temperature within the desired temperature range during unusual heating or cooling events, if needed.

Water is then delivered to buildings, where a ground source heat pump pulls heat inside or rejects heat back into the loop to raise or lower the indoor temperature, and distributes temperature through its normal distribution system (i.e. radiators, vents, etc.). The system connects buildings with different heating needs, so energy is not wasted, but is exchanged or stored in the ground until it is needed.

Heat pumps

The first heat pump was created in 1856, for the use of drying salt from salt marshes. The first ground-source heat pump was created in the 1940s. The oil crisis of the 1970s increased interest in heat pump technology and significant improvements have been made to the design over the last 50 years. In recent years, the desire to move away from fossil fuels, along with advances in refrigerants, have led to much greater use of heat pumps, especially in Nordic countries. In Sweden, one in five homes use ground-source heat pumps.

Sharing and storing energy

The system works most efficiently when it includes buildings that use heating and cooling in different ways. Even in a temperate climate, an office building will tend to use cooling throughout the year because of all the warm computers inside of it. Thus even when the temperature is cold outside, that office building will be “rejecting” heat, returning the water into the system hotter than it was before. Homes down the street can then use that heat. The shared loop essentially transfers thermal energy from one building to another. This “synchronous load cancellation” results in a more efficient overall system by reusing thermal energy shed by other buildings that would be wasted otherwise.

If the other buildings on the system’s shared loop do not require that thermal energy, excess heat can be stored in the bedrock through the boreholes until it is needed. This storage results in “asynchronous” load cancellation, increasing the efficiency of the system further and over longer periods of time.

Ownership model

The system can be owned by municipalities, developers, utilities, or others.

Thermal networks should be deployed everywhere and anywhere, owned by anyone, however, most of this wiki focuses on the gas utility ownership model, because gas utilities transitioning from gas to geo will leverage already existing utility companies’ expertise, workforce and business model. Instead of networked geothermal competing with existing gas utilities, it provides them an avenue to use their workers and experience to aid the clean energy transition necessary in order to cut emissions fast, moving away from fossil fuels.

Equity considerations of utility ownership model

The utility of a utility is to pay the upfront cost of shared expensive long-lived infrastructure, maintain and operate it, and socialize the cost across all customers over decades. Utility companies already have the right of way in the street and expertise with pumping thermal energy underground. They also have the financing expertise to spread the cost of the system across all of us customers and over decades.

The utility ownership model provides clean, affordable, safer energy to everyone on the street, not just those who have disposable income or good financing (as happens too often with solar). Additionally, it reduces stranded assets from increased gas infrastructure investment. In order to maintain safe operation of the current gas system billions of dollars are required to repair leak-prone aging infrastructure, and since this cost is spread over all gas customers (rate-base), customers would be paying for assets in the ground for many decades. These assets or infrastructure will have to be retired before they are done being paid off due to the nation’s aggressive climate targets.

Having utilities spend the customer money on non-emitting infrastructure that can meet any decarbonization mandate and make the area a little more energy independent, might be a better way to spend that money than gas infrastructure.

However much of it is also applicable to other ownership models as well.

Case studies

Networked geothermal, or networked ground source heat pumps, has been used for decades on campuses to heat and cool multiple buildings. From Texas to Toronto, networked geothermal systems have been shown to reduce energy use and cut cost and emissions in a variety of climate zones.

Colorado Mesa University (Grand Junction, Colorado)

Weber State University (Ogden, Utah)
Green Streetscapes (West Union, Iowa)
Springwater Mattamy Homes (Markham, Ontario)
Whisper Valley (Austin, Texas)
Skidmore College (Saratoga Springs, NY)

Gas utility installations

Map from Eversource Gas showing where the Framingham networked geothermal loop will be located. Source: https://www.eversource.com/content/residential/about/transmission-distribution/projects/massachusetts-projects/geothermal-pilot-project

Eversource Gas

In the fall of 2022, Eversource Gas broke ground on the first gas utility-installed networked geothermal system in the nation. The system will provide heating and cooling to 37 buildings–32 residential and five commercial–for a total of 140 customers. Test well borehole drilling and thermal capacity testing has already been completed.

The utility, along with the City of Framinghamn and HEET have been selected as one of 11 recipients of the Department of Energy’s Community Geothermal funding initiative. The award of $715,000 will go towards planning the expansion of an in-of the Framingham geothermal network, adding an additional loop.

Construction timeline and updates are available on Eversource's website.

National Grid Gas

National Grid Gas has selected Lowell, Massachusetts as the site for its first networked geothermal demonstration installation. The utility has a test borehole in the ground as of May 2023. See National Grid's video for more information.

Selecting a site

The ideal site would supply energy to more than one building, with the total heating and cooling use of around 300 tons (this is the equivalent thermal energy use of between 75 to 100 homes). The greater diversity in the heating and cooling loads, the more efficient the overall system will be and the fewer linear feet of boreholes needed to provide the needed temperature. Other good items to look for include:

The ability to expand the system in the future
Sources of thermal energy such as surface water, solar heating or waste water
How many owners would beed to be consulted
Major technical challenges or expensive retrofits such as steam heat

Additional documents

Interconnection and sizing

Networked geothermal systems are designed to interconnect to each other. Over time, a system can expand from serving a few buildings to serving an entire municipality or territory.

It is highly unlikely that a large group of mixed-energy-use buildings (i.e. office buildings, ice rinks, homes, supermarkets, and schools) will need the maximum amount of heating or cooling at the same time. Networked geothermal systems are thus sized for the likely peak heating and cooling load of the connected buildings, rather than for the sum of all the maximum heating or cooling loads of the individual buildings. This is possible due to the interconnectedness of the system, and the inherent energy sharing and load canceling.

The larger the system and the more diverse the energy needs of the connected buildings, the more efficient the system will be and the easier it will be to balance the thermal loads.

Naming

Networked geothermal synonyms

Networked ground-source heat pumps, geothermal micro districts, GeoMicroDistricts, geothermal networks, community-style heat pump systems, community heat pumps

Similar technology

Thermal Networks/Thermal Energy Networks (TENs): A shared loop of water with or without boreholes attached. Water temperature is maintained through energy load cancellation (some buildings using heating at the same time others are using cooling) and through backup heating and cooling "assets" attached to the shared loop. These networks can include combustion heating systems (such as a gas boiler attached to the shared loop) or not. Thermal energy networks can also include boreholes and can have no combustion. Networked geothermal and Clean Thermal Networks are a subset of Thermal networks and Thermal Energy Networks.
Clean Thermal Networks (CTENs): A thermal network without any combustion. Networked geothermal without any supplemental backup boiler is one example.
5th generation district heating and cooling systems (5GDHC) or 5th Generation district energy: Systems are decentralized, bi-directional, close to ground temperature networks that use direct exchange of warm and cold return flows and thermal storage to balance thermal demand as much as possible. 5th gen includes all of the above but is not synonymous because although the bidirectional pipes allow for buildings with different needs to exchange thermal energy so that energy losses are reduced and efficiency enhanced, they sometimes use 2-pipe or 4-pipe distribution which achieves lower efficiencies than a single-pipe system.

What it's NOT

Geothermal Electric Power: Electric generation plant from boreholes that are deep enough (generally more than a mile deep) to access temperatures high enough to create steam or hot water to spin turbines to generate electricity.
Geothermal District Energy: A central heating plant uses steam or hot water from deep geothermal boreholes. The distribution pipes must be insulated to reduce temperature losses with distance and the system cannot grow beyond the size of the central plant's capacity. Additionally this system does not provide cooling.
Geothermal Building: A single building with a heat pump in the building which takes temperature (both heating and cooling) from water moved through shallow boreholes.

Outcomes

Safety: Networked geothermal systems use water to move temperature and require no combustion. In contrast to natural gas, there is no risk of explosion and no risk of leaking greenhouse gasses.
Efficiency: Networked geothermal systems improve on the efficiency of an individual ground source heat pump by connecting many together. When one building requires a lot of cold, like an office building, it returns water into the system hotter, providing heating for other buildings on the loop that need it. Reusing this shed thermal energy is known as synchronous load cancellation. Additionally, heat can be stored in the bedrock through boreholes until it is needed, allowing for thermal storage (AKA asynchronous load cancellation). Together, this synchronous and asynchronous load cancellation makes networked geothermal the most efficient thermal energy system known.
Emissions: Networked geothermal uses only electricity to power heat pumps in the buildings and to pump water through the shared loop. Because the system is so efficient, electricity use is minimal and will always have lower emissions than a combustion system such as a gas boiler or oil furnace. The actual emissions will always depend on the fuel mix of the local electric grid. In Massachusetts, for example, any building that transitions from natural gas heating to a networked geothermal system would reduce its emissions 60%, given the local electric grid fuel mix. As state and regional commitments to sourcing electricity from renewable sources are met, these emissions will continue to drop.
Indoor air quality: Combustion in a building is associated with lower indoor air quality, which exacerbates conditions such as asthma and heart disease. Heat pumps do not involve any combustion on site, so no indoor air pollution is created.
Cooling: Networked geothermal provides cooling in addition to heating. As the climate heats up and heat waves become more common, access to reliable indoor cooling will become critical. Heat waves are already more deadly than any other severe weather event.
Reduced water use: The pipes for the system need to be filled only once. Because commercial buildings connected can be cooled by the networked geothermal system, rather than by chillers (which cool through evaporation), the system can save significant amounts of water. The Colorado Mesa University networked geothermal installation reduced the college's water use by 60% per square foot of conditioned space.
Reduced customer energy bills: Applied Economics Clinic predicts that residential heating bills for customers connected to a networked geothermal system are likely to be significantly lower than gas heating bills. This scenario is based on networked geothermal installed by utilities, with the infrastructure amortized over decades and across all customers, the same way gas infrastructure is currently paid for. Currently, about 50% of gas bills in Massachusetts pay for fuel itself. The remaining 50% of the bill pays for the operation and maintenance of the gas infrastructure. With networked geothermal systems, the only fuel needed is a relatively small amount of electricity, greatly reducing the cost. Networked geothermal system installations on campuses have shown significant energy savings, along with reduced water use and emissions reductions (see case studies).
Local energy independence & reduced price volatility: Networked geothermal systems are not dependent on fuel deliveries from distant states or countries since the energy is sourced from the local ground. Changes in supply and demand of fuels are difficult to predict and can result in dramatic changes in the price of fuel. Networked geothermal combined with local electric generation can achieve 100% energy independence for entire communities.
Reliability: With the gas system, natural gas has to travel hundreds or thousands of miles from wellhead to end use. This distance can result in single point failures, like in January, 2019 when a gas pipe malfunction in Ohio cut off the gas supply for Newport, Rhode Island during a historic cold stretch. Since the source for networked geothermal’s energy is the local ground, as long as you have access to electricity, you will have access to that heating and cooling. While networked geothermal systems can be interconnected to cover entire cities, each networked geothermal system can be as small as a single block and function independently, if needed. If the system has batteries to power it in case of an electrical outage, a networked geothermal system can serve as an island of resilience for a neighborhood.
Reduced impact on the electric grid:
To meet local, state and federal building decarbonization mandates, we must meet the energy needs of buildings with electricity and then produce that electricity from renewable sources. However, moving all of our needs to electricity will significantly increase the strain on the electric grid. If the grid does not have adequate generation sources or transmission needed to meet supply, this could lead to higher costs and increased risk of brownouts and blackouts. In a paper published in Scientific Reports, researchers from HEET, Harvard University and Boston University use a model called the Falcon Curve to illustrate how technology efficiency is a key factor that will affect the affordability, speed and equity of emissions reductions. Inefficient electrification will add a huge burden to the electric grid, creating a peak energy need in the winter that will require a costly buildout of the electric grid, driving up costs. Adding networked geothermal into the picture for heating and cooling buildings greatly reduces this energy peak because it is so efficient and requires minimal energy compared to any other electric method of delivering thermal energy to buildings.
Thermal storage: One of the main issues with significantly increasing renewable electricity generation is variability based on weather or solar conditions. Networked geothermal boreholes can store thermal energy in the bedrock to be used months later. During the shoulder months, heat can be stored to be used the following season. This energy storage increases the overall efficiency of the system further by allowing the excess heat in the summer to be stored until it’s needed in the winter.

Policy changes needed

To allow and incentivize networked geothermal, policy changes (both legislative and regulatory) will be needed. What should be changed and when will depend on the specific policies of each state and what the aligned stakeholders want. Below is a list of the policy areas that might need to be addressed. These changes are likely to go through several stages as networked geothermal becomes increasingly understood, trusted and normalized.

Stage 1- Pilot

Fund a feasibility or scoping study through ratepayers or the state. A feasibility study examines the overall potential in the area given its climate, geology, energy use intensity, etc. A scoping study searches for sites that would be financially attractive.
Fund demonstration installations thought ratepayers or the state or other funding. The installations would benefit the ratepayers through exploring a model that can meet the state's emission mandates while reducing the likelihood of the gas utility assets becoming stranded as the customers defect to air source heat pumps. Examples of rate cases:
- Eversource Gas Rate Case
  - Approval Order (DPU 19-120)
  - HEET's Brief
- National Grid

Ensure maximum learning and trust from the installations. The point of any installation or study is increased understanding and trust. Thus it is critical to ensure the results are studied by independent experts trusted by all sides, and to ensure the maximum transparency of data. One example of this is Massachusetts funded a research team to study the first installations and create a databank, including best practices.
Experiment with customer billing and metering. Networked geothermal can be billed via gallons of water entering a unit, or through BTUs (British Thermal Units), or through a monthly customer service charge based on expected peak load.

Stage 2 - Permit Scaling

Define networked geothermal as non-combusting and utility-scaled.
Allow gas utilities to install and fund networked geothermal. Most gas utilities are currently only legally allowed to sell gas. This must be changed for utilities to install networked geothermal widely.
Allow gas infrastructure funding to go to networked geothermal installations instead along street segments where the gas infrastructure would otherwise have to be upgraded.
Merge the gas/networked geothermal rate base to avoid reduced gas customer base creating rising gas customer heating bills (since there will be fewer customers paying for the same sized system with the same operations and maintenance cost). Rising gas customer bills can make customers leave the gas system faster, resulting in a vicious cycle that will result in stranded assets. Merging the gas and geothermal rate base allows the gas system (and customers and workers) to transition from one system to another all within the same rate base, avoiding the reduction of customers that leads to rising energy bills and stranded assets.
Allow for thermal service & infrastructure to be installed, for thermal service to be equivalent to gas, for the”obligation to serve” new customers to be met with thermal service, rather than with gas. Ensure that the gas utility franchise in each municipality is modified to include the ability to install thermal infrastructure also.
Disincentivize investment in new gas infrastructure at a speed that meets the local emission mandates and reduces the potential for customer price shocks.
Use Performance Based Incentives to give gas utilities more profit for non-combusting infrastructure, such as networked geothermal, and less profit for combustion infrastructure.
Examine regulations around borehole drilling to ensure they are sensible. In some states, boreholes are considered water wells and therefore are regulated under the jurisdiction of the local board of health. If a networked geothermal system contains just water with no glycol or other harmful chemical in it, and any slurry and environmental impact from the drilling is properly controlled, health and environmental impacts would be minimal or nonexistent.
Examine regional driller certifications to ensure they allow for the workforce to scale and work in the street. If the certification can be as similar as possible to nearby states, drillers will have a regional zone within which to work, attracting more of them.

Step 3 - Equitable Transition

Consider changing electric rates for heat pump owners to reward customers for helping the state meet its emission reductions. Reducing electric rates for heat pumps will also help low-income customers to transition to electricity, and to enjoy improved indoor air quality in their homes without being financially penalized. Ground source heat pump customers in particular should be rewarded for the benefits to the electric grid of reducing electric peaks in comparison to other methods for electric heat, while increasing the overall amount of electricity being sold ("load factor").
Examine the potential for electric utilities to pay for a portion of the building retrofits based on those benefits to the electric grid.
Use a special purpose vehicle through section 1706 of the Inflation Reduction Act to get a large loan ($500 million or more) from the Department of Energy’s Loan Program Office. Loans from the LPO are backed by the federal government and have significantly lower interest rates than the rates most utilities can get. As a requirement of the loan, direct the cost savings from the lower interest rate to be spent on customer retrofits and/or worker retraining. In Massachusetts, using 2021 data, the cost savings were roughly equivalent to $16,000 per unit (home or business).
Allow current gas workers to transition in their jobs, keeping their salary and benefits. Gas and water pipes (used for the shared horizontal loop with networked geothermal) are made of the same material. Gas workers are already certified to operate and maintain this part of the system.
Create a tactical thermal transition tool mapping future investments into gas infrastructure, electric grid constraints, building stock, geology, energy use intensity, and any other data layers necessary to find the fastest and least expensive method to transition.
Experiment with methods of customer acquisition. Publish all the street segments where gas infrastructure will have to be upgraded (whether replacing vintage pipe or upgrading for gas constraints). Try out having gas utilities or independent vendors contact the customers to explain options.
Stage the customer retrofits using multi-modal heat pumps. There are now heat pumps that can pull temperature off of either the air or the ground, depending on what equipment they are connected to. This means that as the combustion HVAC in the buildings reach end of life, they can be transitioned to heat pumps and connected to an outside air source compressor. When networked geothermal reaches that street the heat pumps in the building can easily be connected to the system. The outdoor air source compressor can then be moved to wherever it is needed by another customer.
Allow for neighborhood electrification with avoided costs. Where networked geothermal is not financially viable, allow the gas utility to move the customers to electric heat, using the avoided costs to replace all gas appliances with electric or propane appliances.

Relevant legislation

New York - Utility Thermal Energy Network and Jobs Act, HB23-1252 (passed)
Massachusetts - An Act Driving Clean Energy and Offshore Wind, H5060 (passed)
Colorado - Concerning the implementation of measures to advance thermal energy service, HB23-1252 (Passed)
MA - Future of Clean Heat, H.3202, S.2105 (submitted)
VT - An Act Relating to Affordable Community Energy Solutions H.56 (submitted)

Maryland - Geothermal Heating & Cooling Systems, HB 1007, (submitted)
Minnesota - Natural Gas Innovation Act, 216B.2427 (passed)
Washington - Incentivizing development and acquisition of renewable energy resources, HB.1619 (submitted)
Washington - Supporting Washington's clean energy economy and transitioning to a clean, affordable, and reliable energy future, HB. 1619, (submitted)

Associations to contact for more information

To get connected to organizations listed below, email wiki@heet.org.

Thermal Utility Reform Initiative (TURI) - A national coalition of climate advocacy organizations pushing for networked geothermal.
International Ground Source Heat Pump Association (IGSHPA) -An international organization works to advance ground source heat pump (GSHP) technology on local, state, national, and international levels.
GeoExchange Organization (GEO) - The voice of the geothermal heat pump industry in the US.
NY-GEO (New York Geothermal Energy Organization) - A nonprofit dedicated to promoting geothermal heating and cooling. To get connected, email wiki@heet.org
Utility Networked Geothermal Coalition (UNGC) - A national coalition of gas utilities learning and working actively toward networked geothermal.
Geothermal Rising - Primarily deeper geothermal (aka hot rock) used to create electricity, but also includes networked geothermal.