Lowering the level in DH networks is a crucial issue allowing the transition from fossil to renewable heat supply. Today in Switzerland most networks operate with supply temperatures ranging from 70 to 110 °C making the use of heat pumps and/or geothermal heat difficult. Lowering both supply and return temperatures show high benefit in terms of technical and economic performance.

In Danemark a lot of optimisation work was done, showing that operation at lower temperature levels is feasible. However, optimizing an existing DH network is challenging and the reasons that act as a barrier can be: (i) inappropriate design of the sub-station; (ii) regulations issues; (iii) poor insulated buildings requiring high supply temperature in radiators and (iv) inefficient heat exchangers.

To tackle this wide subject this talk will:

• Show the benefits of lowering temperature in the context or renewable heat
• Present a benchmark on several DH networks in Switzerland
• Show a diagnostic tool allowing to identify the connected substations contributing most to high return temperatures
• Show some examples of good and bad practices
• Apply the presented concepts to a case-study of a low temperature DH network being heated by a centralized heat pump of 5MW.