Heat production unit
Heating networks — Principles, strengths and challenges

In most cases, a network comprises a main heat production unit, which operates continuously, and a back-up unit used as a backup during peak periods, or as a replacement during maintenance or breakdowns. Heat can be generated from a number of energy sources - an "energy mix".

The various energy sources can be of the :

• renewable: biomass combustion (wood, agricultural residues, crops, etc.), geothermal heat recovery from deep aquifers (figure 2 );