What is Thermonet Europe?
Thermonet Europe is an independent non-profit association aimed at promoting the adoption of thermonet systems, which contribute to transitioning to more climate-friendly solutions. Its members include municipalities, regional authorities, government entities, knowledge institutions, and private companies such as consultants, manufacturers, contractors, installers, and utility companies.

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What is a thermonet?
A thermonet is a distribution grid of – typically – uninsulated pipes that transport thermal energy across properties at a temperature close to ground temperature. The network consists of uninsulated plastic pipes, similar to those used for water and gas supply, with both supply and return lines. The term “thermonet” is a newly coined word used since 2016 and successfully promoted in Denmark by the association Termonet Danmark since 2020. It refers solely to the pipe network connecting energy sources and heat pumps. The term is a noun written with a lowercase initial letter. Thermonet is part of what is internationally known as 4GDH (4th Generation District Heating, defined by smart control) and 5GDHC (5th Generation District Heating and Cooling, defined by a distribution network that can provide both heating and cooling).

What is collective heating and cooling based on thermonet?
To provide collective heating and cooling via a thermonet, thermal energy is collected from or delivered to the ground and/or other sources, and decentralized heat pumps are placed close to consumption points, either on individual properties or in the neighborhood. The thermonet refers to the pipes connecting these heat pumps, typically located on individual properties. Collective heating and cooling based on thermonet as a comprehensive solution, is sometimes referred to as “cold district heating.” Ownership of thermonet can be organized through energy communities, utility companies, private companies or a more informal setup among residents. It depends on rules and regulations of in the country in question.

Does a thermonet provide district heating?
Not in itself, but it can be part of a district heating solution. The thermonet consists of the pipes connecting multiple larger heat pumps on the cold side in a district heating system. On the warm side of the heat pumps, insulated pipes distribute heat to consumers.

How can it be efficient to move heat through a thermonet when the pipes are uninsulated?
Thermal energy can be transported at various temperatures. In conventional district heating systems with large heat pumps, heat is distributed through insulated pipes, typically resulting in about 20% heat loss. In collective heating and cooling based on thermonet, decentralized heat pumps allow geothermal and other thermal energy to be transported at ground temperature to the heat pump’s location. There is no heat loss in a thermonet; instead, the network contributes to collecting additional geothermal energy.

What is the difference between decentralized and individual heat pumps?
Decentralized heat pumps are owned by an energy community or district heating company and are part of a collective production and distribution system across multiple properties. Individual heat pumps serve a single property and are owned or leased by the property owner.

How does collective heating and cooling based on thermonet differ from individual air-to-water heat pumps?
A collective heating and cooling system based on thermonet is more energy-efficient than individual air-to-water heat pumps with equivalent capacity. This is primarily because ground temperatures in winter are higher than air temperatures, and temperatures in the summer as lower, resulting in lower annual electricity consumption for water-to-water heat pumps. Thermonet systems can utilize local waste heat, which is not possible with air-to-water heat pumps. Collective heating and cooling based on thermonet also places less strain on the electricity grid, especially during peak loads on very cold days or very hot days, which is a key factor in grid design. Large-scale use of thermonet can reduce the need for electricity grid expansion.

How does the financing of collective heating and cooling based on thermonet differ from individual geothermal or air-to-water heat pumps?
Collective heating and cooling based on thermonet spans multiple properties, with the supply network and thermal energy extraction systems can be owned by an operating company, similar to consumer-owned or municipal heating companies. Loan financing can be secured against the entire system. Collective ownership and long-term financing avoid large upfront costs for consumers, promoting the green transition. Individual geothermal systems with water-to-water heat pumps or air-to-water heat pumps are tied to a single property, and financing is arranged by the property owner.

How long does a collective heating and cooling system based on thermonet last?
The oldest known thermonet, established in Germany in 1979, is still operational, including some of the original heat pumps. Plastic pipes used in thermonet systems typically have a 50-year warranty, and experience from water supply systems using similar pipes suggests an economic depreciation period of 75 years, with an industry-estimated lifespan of 100+ years. Decentralized heat pumps connected to a thermonet are typically depreciated over 20 years but have been known to be able to last up to 40 years. In comparison, air-to-water heat pumps are depreciated over 15 years and have a typical expected lifespan of up to 20 years.

Can villages access collective heating and cooling via thermonet if conventional district heating is not available?
It depends on specific calculations. Collective heating and cooling based on thermonet can often reach less densely populated areas than conventional district heating. Uninsulated plastic pipes are cheaper than insulated steel pipes, easier to weld, can be plowed into agricultural land (allowing continued crop use), and can be laid using directional drilling if needed. Overall, establishing a thermonet is less expensive than a comparable district heating network, requiring fewer connected consumers.

Where are heat pumps placed in collective heating and cooling via thermonet?
The most efficient placement is within the connected properties, where a district heating unit would typically be installed. They can also be placed outside the property, e.g., in a well, shed, or nearby building in the neighborhood. Large heat pumps at existing district heating companies can also be connected via a thermonet, with insulated pipes used from the heat pump to the point of use.

Who owns the thermonet and heat pumps?
Ownership can be organized through an energy community, a utility company or a private company. Operation and maintenance are more efficient and cost-effective when using the same or a few types of heat pumps across all consumption points. If conditions allow, the energy community may limit its role to the thermonet and thermal energy extraction, with consumers responsible for purchasing, installing, and operating their own heat pumps, possibly through a subscription model. In district heating solutions, the district heating company owns and operates the thermal energy extraction system, thermonet, and large heat pumps.

What is the difference between conventional district heating, ultra-low-temperature district heating, and collective heating and cooling based on thermonet?

• Conventional district heating (4th generation): Uses insulated supply networks with flow temperatures of 60-70°C, sufficient to heat domestic water. Central heat pumps, often air-to-water, are increasingly used.
• Ultra-low-temperature district heating: Uses insulated pipes with flow temperatures of 30-40°C, suitable for floor heating in modern, well-insulated homes. Decentralized heat pumps raise the temperature for domestic hot water.
• Collective heating and cooling based on thermonet (previously called cold district heating): Uses uninsulated pipes with flow temperatures around ground temperature (0-10°C, depending on the season). Decentralized heat pumps raise temperatures for both heating and domestic hot water. In summer, thermonet can provide passive cooling via circulation pumps without using heat pumps.

How is heat collected, and how much electricity is used?
Heat is typically collected from shallow geothermal sources, such as horizontal pipes in a field at 1-2 meters depth, heat spirals, or vertical closed-loop geothermal boreholes (5-500 meters deep). Local excess heat sources, such as industry, wastewater treatment plants, or relief wells, can also be used. The thermonet itself contributes 10-50% of the thermal energy. Approximately 75% of the delivered heat is collected thermally, with the remaining 25% from electricity used by decentralized heat pumps.

Is thermonet a purely Danish phenomenon?
No, similar developments are occurring in many countries and on several continents. In January 2024, the EU Parliament adopted a resolution on geothermal energy, urging the EU Commission to promote public loan guarantees for collective heating based on geothermal energy, similar to those for conventional district heating in Denmark, and to increase focus on shallow geothermal energy as an underutilized resource for the green transition.

Why haven’t I heard about thermonet and its possibilities for district heating and reducing electricity grid expansion?
There is a lack of awareness among state and local authorities and actors in conventional district heating and electricity supply. The opportunity to establish collective heating and cooling based on thermonet should be considered when a public body is doing energy planning, but often it is not even considered.