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 Generation 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 (T_GridFix) while the other free floating grid temperatures (T_GridFloat). Both feature decentralised variable speed pumping and a centralised passive balancing unit aimed at alleviating control instabilities arising from pump hunting. Experiments showed that T_GridFix 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, T_GridFix can lead to low prosumer interaction and better system wide predictability. Further considerations on generalisability 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.