Low-Temperature District Heating: Advantages and Disadvantages

Low-temperature district heating networks (5GDHC) achieve heat losses below 3 % (compared to 10—25 % in conventional systems) and can provide heating and cooling simultaneously within the same network using inexpensive plastic pipes. On the other hand, every building needs its own heat pump (SPF 3.5—5.0), and the planning effort is higher due to ground coupling simulation requirements.

Advantages of low-temperature district heating

Minimal heat losses

The greatest advantage of low-temperature district heating networks is their extremely low heat losses. Because the network temperatures are close to the ground temperature (typically 5–20 °C), the temperature difference between the medium and the surroundings is minimal. Whereas conventional district heating networks exhibit heat losses of 10–25 %, losses in low-temperature district heating are typically below 3 %.

With longer trench lengths and low heat line densities — situations in which conventional networks often become uneconomical — low-temperature district heating remains efficient.

Simultaneous heating and cooling supply

Low-temperature district heating networks can provide heating and cooling energy simultaneously within the same network. Buildings with cooling demand feed their waste heat into the network, where it can be used by buildings with heating demand. This synergy significantly improves the overall efficiency of the system.

In mixed-use districts combining residential, office and commercial areas, this effect can be particularly pronounced.

Easy integration of renewable heat sources

Because the network operates at low-temperature levels, many renewable and waste heat sources can be integrated directly:

• Borehole heat exchangers and ground heat collectors
• Solar thermal (including non-high-temperature collectors)
• Waste heat from commerce and industry (including at low temperature)
• Wastewater and river heat

Lower investment costs for pipework

Thanks to the low temperatures, uninsulated or lightly insulated plastic pipes (PE-Xa, PE 100) can be used. These are significantly cheaper than the pre-insulated steel pipes of conventional district heating:

High operational reliability and longevity

Plastic pipes are corrosion-resistant and have an expected service life of more than 50 years. The low temperatures and pressures reduce material stress and maintenance effort.

No danger in the event of leaks

Unlike high-temperature district heating, leaks pose no scalding hazard. The escaping medium is at close to ambient temperature.

Disadvantages of low-temperature district heating

Decentralized heat pumps are required

Every consumer needs their own heat pump to raise the low-temperature level to the usable temperature. This means:

• Higher building-side investment costs (one heat pump per building)
• Electricity costs for heat pump operation
• Maintenance of the decentralized units
• Noise protection must be considered

The seasonal performance factor (SPF) of the heat pumps is typically 3.5–5.0 and depends strongly on the source temperature and the required supply temperature.

Electricity demand

Unlike conventional district heating, where heat arrives at the building ready for use, low-temperature district heating requires significant amounts of electricity for the decentralized heat pumps. With an SPF of 4, around 25 % of the heating energy is needed as electricity.

This requires:

• Sufficient electrical grid capacity within the district
• Economically viable electricity procurement conditions
• Ideally, coupling with local PV power generation

Limited supply temperature

The achievable supply temperature depends on the heat pump. For domestic hot water preparation, at least 60 °C is required (legionella protection). At very low network temperatures in winter, heat pump efficiency drops.

Buildings with high-temperature heating systems (old radiators, >70 °C supply) are only suitable to a limited extent. Surface heating systems (underfloor, wall) with low supply temperatures are ideal.

More complex planning and simulation

The design of low-temperature district heating networks is more demanding than that of conventional systems:

• Ground coupling must be evaluated through annual simulations
• Thermal regeneration of the ground needs to be verified
• Hydraulics differ fundamentally (passive vs. active networks)
• Simultaneity of heating and cooling has to be modeled

Dependence on ground conditions

Performance depends strongly on the local soil conditions:

• Soil thermal conductivity: dry sand (~0.4 W/mK) vs. water-saturated clay (~1.8 W/mK)
• Groundwater level: a high groundwater level improves heat transfer
• Available area: ground heat collectors require 1.5–2.5 m² per kW of extraction capacity

Regulatory uncertainties

The legal classification of low-temperature district heating networks has not yet been conclusively settled in some areas:

• Permitting procedures for geothermal use (water law)
• Delineation from conventional district heating under the German AVBFernwärmeV
• Eligibility for funding (BEW funding is, in principle, available)

When is low-temperature district heating suitable?

Low-temperature district heating is particularly well suited to:

• New-build districts with surface heating systems and low temperature levels
• Mixed-use districts (with both heating and cooling demand)
• Areas with low heat line density, where conventional networks would be uneconomical
• Sites with good ground conditions or available ambient heat sources

The concept is less suitable for:

• Existing districts with high-temperature heating systems
• Areas with very high heat density (conventional district heating is often more economical here)
• Sites without sufficient electrical grid capacity

Conclusion

Low-temperature district heating is not a silver bullet, but it is a powerful concept for the right application. Its minimal heat losses, the ability to supply heating and cooling at the same time and the straightforward integration of renewable sources are compelling advantages. These have to be weighed against the electricity demand of the decentralized heat pumps and the more complex planning effort. A solid simulation with a coupled thermo-hydraulic annual calculation — as enabled, for example, by VICUS Districts — is decisive for demonstrating the economic viability reliably.

Further reading: Low-Temperature District Heating: Fundamentals — basic concepts and operating principles, Dimensioning Low-Temperature District Heating Networks — practical design of 5GDHC systems, Prosumers in District Heating Networks — bidirectional operation and feed-in concepts, BEW Funding — financial incentives for low-temperature networks.

References and Standards

• Buffa, S. et al. (2019): 5th generation district heating and cooling systems: A review of existing cases in Europe. Renewable and Sustainable Energy Reviews, 104, pp. 504–522.
• Lund, H. et al. (2014): 4th Generation District Heating (4GDH). Energy, 68, pp. 1–11.
• IEA DHC Annex TS2 — Implementation of Low-Temperature District Heating Systems