Exhaustive overview of advances in integrating renewable energy sources into district heating systems

This study offers a comprehensive overview of the recent advances in various aspects of district heating systems (DHSs), focusing on the fourth and fifth generations of heat distribution networks integrated with different renewable energy sources (RES). The study highlights the integrated approach of various advanced renewable technologies applied to DHSs, such as solar and geothermal energy, biomass, industrial waste heat, and especially the implementation of conventional heat pumps (HPs) and solar-assisted HPs with solar thermal (ST), photovoltaic (PV), or PV-thermal (PV/T) panels in resilient and sustainable buildings and DHSs to increase energy and environmental performances. The ineffectiveness of refrigerant can be used to evaluate quickly the HP energy efficiency only with the values of the operating temperatures, and to evaluate the energy performance of the HP-PV/T hybrid system, the use of the global seasonal performance factor ((SPF_HP-PV) is also considered. Additionally, it shows the possibility of recovering excessive pressure from DHSs using pumps working as turbines. The study also describes the major components and evolution of DHSs, briefly reviews low and ultra-low temperature DHSs, and implementation of borehole and hot water TES technology into DHS. It also discusses the main optimisation techniques, simulation tools, control methods, and maintenance for DHSs, as well as alternative connection modes of RES to DHS. Finally, some original research and a literature review are included on several applications of implementing various RES in resilient and sustainable buildings and DHS.