Primary distribution network
Heating networks — Principles, strengths and challenges

Heat from the production unit is transported via a network of insulated, buried pipes to the various delivery stations (substations) of the connected buildings it is to supply. A heating network operates as a closed circuit; the primary network is made up of an "outward" circuit of pipes transporting the heat transfer fluid, and a "return" circuit bringing the fluid, stripped of its calories, back to the production unit, where it is reheated and sent back into the circuit (figure 4).

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