Connection methods in district heating networks Kevin Sartor Thermodynamics Laboratory, University of Liège, Belgium

Substation Link between (group of) buildings and heating plant(s) Could be composed of Piping and insulation Isolation valves Heat exchangers Tank (domestic hot water) Heat metering …

Connection methods Open connection method No hydraulic separation Direct connection method Indirect connection method Hydraulic separation Various Connection Alternatives [1]

Open connection method Simple No heat exchanger, no pump No extra investment Same water in primary and “secondary” network No hydraulic separation Some water is used to DHW

Open connection method Temperature between 70 and 135°C Disadvantages Could be dangerous for inhabitants DH water could be too high due to pressure and temperature ranges Difficult to control the temperature network Higher return temperature (higher heat losses) No hydraulic separation (Higher risk of leakages) Consumption of water Extra money for water treatment Reduce service time of DHN

Direct connection method Simple No heat exchanger, No pump if buildings is not too tall Same water in primary and secondary network No hydraulic separation

When using them? Direct connection method Disadvantages Water temperature < 90°C Water pressure < 6 bar No loss of temperature (no intermediate HX) Disadvantages No hydraulic separation (Higher risk of leakages)

Indirect connection method Heat exchanger in each (group of) buildings Hydraulic separation

When using them? Indirect connection method But Water temperature over 110°C Water pressure up to 16 bar Hilly locations But Extra cost (HX, pumps) Extra pumping cost (in the secondary side) Loss of temperature (HX operation)

Control strategy DH Supply temperature DH water flow rate Determined by weather conditions DH water flow rate Determined by differential pressure at critical point

Conclusions Each method has its (dis)advantages Proposal: Indirect connection method More complete DH Supply DH Return HX

Thank you for your attention Questions? Remarks?

Sources [1] Guidelines for district heating substations, Europower, 2008 [2] Background Report on EU-27 District Heating and Cooling Potentials, Barriers, Best Practice and Measures of Promotion, JRC scientific and policy reports, 2012 [3] Evaluation of systems and products – Chapter 4, Danfoss [4] District heating systems in Finland and Russia, Kirill Eliseev 2011