Development and experimental validation of a hydraulic design and control philosophies for 5th generation district heating and cooling networks

Sector coupling and energy sharing are key elements in effectively decarbonising the thermal grid. 5th Gener- ation District Heating and Cooling (5GDHC) provides a system for combining heating and cooling via an ambient temperature network. A main design challenge for 5GDHC is establishing a control regime that allows flow bidirectionality and energy synergies between heating and cooling. This work develops and experimentally validates a 5GDHC system wide hydraulic design and two fitting control strategies on a small scale. One has fixed grid return temperatures (TGridFix) while the other free floating grid temperatures (TGridFloat). Both feature decentralised variable speed pumping and a centralised passive balancing unit aimed at alleviating control in- stabilities arising from pump hunting. Experiments showed that TGridFix demonstrates slightly higher electrical consumption for the booster heat pump (Seasonal Coefficient of Performance of 3.84 compared to 4.16 for 20 h of operation) due to a mismatch between the evaporator and the grid temperature difference. Overall, TGridFix can lead to low prosumer interaction and better system wide predictability. Further considerations on general- isability of findings and full-scale implementations are highlighted. This works presents a set of detailed and experimentally validated control philosophies for 5GDHC systems, elucidating a key system implementation challenge.