How a heat network works

A heat network functions like a large-scale central heating system. It consists of underground circulation pipes that deliver heat from a heat source to consumers. These consumers can vary widely and often include combinations such as residential buildings, offices, schools, hospitals, and swimming pools. Each consumer has a delivery station, mainly composed of a heat exchanger, that provides space heating and domestic hot water, replacing individual heating systems like boilers.

Heat networks are not tied to any specific technology. They can use renewable heat or residual heat (e.g.: from industry or data centres) that otherwise would be released it in the atmosphere. Renewable heat sources can include:

• Biomass
• Solar boilers
• Heat pumps extracting heat from water:
  • Aquafer water (geothermal)
  • Sewage water (riothermal)
  • Surface water (aquathermal)

In an aquathermal district heating project a heat exchanger and heat pump extracts heat from the water of a river, a lake or the sea at a central point and distributes it to various consumers.

An employee of Brugg Pipes coats the shell of a heat pipe.

The evolution of district heat networks is often categorised into different generations, reflecting advances in technology, efficiency, and environmental considerations:

• 3rd Generation: Traditional district heat networks using high-temperature systems (e.g., 70–90°C) that deliver heat primarily from fossil fuels or centralised biomass sources. These systems are effective but less energy-efficient and require robust insulation to minimise losses.
• 4th Generation: Modern systems that use lower temperatures (e.g., 50–70°C), often leveraging renewable energy sources and waste heat. These networks are more efficient and align better with energy-saving building standards.
• 5th Generation: The latest approach, emphasising ultra-low temperatures (e.g., 10–30°C) combined with localised heat pumps. These systems operate very efficiently and allow for bidirectional energy flows, enabling heat sharing and integration with decentralised renewable sources. They are highly adaptable and ideal for new sustainable urban developments.

This progression demonstrates the increasing focus on energy efficiency, sustainability, and flexibility in district heat network design.

Advantages of heat networks

Compared to individual heating systems, heat networks consume less energy for the same amount of heat due to:

• Higher energy efficiency in the central heat source.
• Reduced standby losses.
• Beneficial use of residual heat that would otherwise be wasted.
• A collective system needs less overall heat capacity than the sum of individual systems because of a diversity factor in heat usage when a lot of consumers are connected to the same system. For example not all people will heat their house at the same time or shower at the same time. Because of that, building a central heat system that is the sum of all individual peak demands does not make sense because they never occur at the same time.

Additionally, the centralised supply of heat is reliable and convenient for users. It requires minimal on-site infrastructure, is fire-safe, and eliminates the need for exhaust systems or periodic maintenance of individual systems.

In neighbourhoods or cities with high heat demand density, collective renewable heat sources can be more cost-effective than installing individual renewable heat solutions.

Is a heat network suitable everywhere?

• European cities and municipalities with a focus on sustainability are creating heat zoning plans. These plans identify which areas will have district heat networks and where individuals will need to manage their own heating systems.
• Densely populated areas are more likely to be eligible for connection. However, some buildings may not be able to connect due to their location.
• The European STRATEGO study estimates that district heat networks can meet 40–65% of the heat demand in various European countries.
• Outside prioritised zones, heat decarbonisation will rely on individual solutions like heat pumps (air/air, air/water or water/water), biomass boilers, or solar thermal energy.