Fifth-generation district heating and cooling systems: A review of recent advancements and implementation barriers

As global urbanisation levels continue to rise, supplying urban areas with low emissions energy becomes imperative in the fight against climate change. In areas with high demand density, district heating and cooling systems are generally a more efficient alternative compared to individual solutions, but current systems are mainly powered by fossil fuels and suffer from significant thermal losses due to high operating temperatures. Fifth-generation district heating and cooling systems (5GDHC) is a promising technology, able to address these drawbacks. 5GDHC systems operate at near ambient temperature, ensuring efficient integration of renewable energy sources and waste heat recovery potential. Their ability to provide simultaneous heating and cooling through the same pipeline and bidirectional energy flows allow for load balancing through the harvesting of demand synergies between different users. 5GDHC systems can play an important role in the energy transition but not much is known about their environmental performance over their life cycle and the novelty of the concept means that planning and design guidelines are scarcely present in the literature, hindering their development and further adoption. This study critically reviews recent advancements in the relevant literature as the 5GDHC technology transitions from research and development to the demonstration phase. Moreover, the paper addresses the design parameters and methodologies encountered in the literature for the modelling and operation of 5GDHC systems. Finally, the economic and environmental performance are discussed while pre-senting an overview of future developments and challenges related to full-scale deployment.