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

2. 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 …

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

4. 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

5. 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

6. 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

7. 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)

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

9. 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)

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

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

12. Thank you for your attention Questions? Remarks?

13. 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