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Network generations (1G–5G)

District heating and cooling (DHC) networks are grouped into generations based on their operating temperatures. The generation determines what kinds of heat source are feasible, how much heat the pipes lose in transit, and what equipment buildings need at their substations. TESSA supports designing and simulating networks of any generation, including 5G anergy networks.

The five generations at a glance

flowchart LR G1["1G<br/>Steam<br/>≥ 200 °C"] G2["2G<br/>Pressurised<br/>hot water<br/>90–120 °C"] G3["3G<br/>Hot water<br/>70–90 °C"] G4["4G<br/>Low-temp<br/>30–70 °C"] G5["5G<br/>Ambient /<br/>anergy<br/>5–25 °C"] G1 --> G2 --> G3 --> G4 --> G5 classDef gen fill:#fff3e0,stroke:#ED6000,stroke-width:1.5px,color:#bf360c class G1,G2,G3,G4,G5 gen
Generation Typical supply temp. Notes
1G ≥ 200 °C Steam; now obsolete; extremely high heat losses
2G 90–120 °C Pressurised water; widespread in older city networks
3G 70–90 °C Hot water; most common current-generation district heating
4G 30–70 °C Low-temperature; suited to low-energy buildings and heat pumps
5G 5–25 °C Ambient loop; buildings extract/inject via heat pumps

1G to 4G: centralised heat distribution

In networks of the first to fourth generation, heat is produced centrally and transported to buildings. The fluid is hotter than the buildings need, so heat flows out of the network at every substation. The key trade-off is supply temperature vs heat loss:

  • Higher supply temperature → larger temperature spread → smaller pipes for the same power, but more heat lost to the ground per metre of pipe.
  • Lower supply temperature → less pipe loss, but buildings may need retrofitting (larger radiators or floor heating) to work with the cooler supply, and central heat pumps become more efficient.

As supply temperature drops from 3G to 4G, central heat pumps become more attractive (higher COP at lower lift), solar thermal and waste heat become easier to integrate, and heat losses drop significantly.

5G: ambient loops and anergy networks

Fifth-generation networks operate at roughly ground temperature — close enough to the ground that pipe heat losses are negligible. Instead of transporting heat centrally, the pipe carries a thermal potential: buildings with heating demand extract heat from the loop via a heat pump; buildings with cooling demand reject heat into the same loop.

This makes cooling a free thermal resource. Waste heat from cooling (which would otherwise be rejected to air) is redistributed to buildings that need heating. In mixed-use districts with simultaneous heating and cooling loads, 5G can significantly reduce total primary energy use.

Key design implications of 5G

  • Every building substation needs a heat pump — the network is too cold to meet building demand directly. This shifts investment from the energy center to the substations.
  • Freeze protection — the fluid may run below 0 °C at peak extraction in cold climates, so a glycol mix is often used.
  • Thermal balance — if the district is heating-dominated, extraction from the loop will cool the ground over time and heat pump COP will decline. Regeneration sources (solar thermal, dry coolers, waste heat) help maintain the ground temperature. See Geothermal borehole fields.
  • Heat loss model — TESSA sets pipe heat loss to zero for cooling-mode and combined networks, because operating temperatures are close to ambient.

Choosing a generation in TESSA

The network generation is determined implicitly by the supply and return temperatures you set on the network's working fluid configuration, and by the substation type you assign to each building connection:

  • Supply temperature ≥ 60 °C + heat exchanger or direct substations → 3G/4G heating network.
  • Supply temperature 10–20 °C + booster heat pump substations → 5G anergy network.

TESSA does not require you to declare a generation number — the simulation adapts based on the temperatures and substation types you configure.

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