A methodology for selecting a sustainable development strategy for connecting low heat density consumers to a district heating system by cascading of heat carriers

The paper presents a methodology for supporting the decision making on how to sustainably develop an existing district heating system when consumers located in a remote, low-heat consumption density area are connected to the system. Several scenarios are proposed where a multi-generative system is assessed by implementation of industrial heat pumps (HP), solar photovoltaic (PV) system, and low-temperature regime into an existing district heating system in various combinations. The methodology is based on multi-criteria analysis allowing for energy, economic, exergy, and environmental (4E) assessment. The research is based on a case study of an autonomous district heating system in a medium-sized urban settlement with an average heat generation of 8.3 GWh/year. The primary heat consumers are apartments and industrial buildings. In the system, the power-to-heat concept is realized, and solar PVs serve as a price-balancing instrument of power. The results show that in such a system, the most sustainable scenario for connecting the consumers located in the low-heat consumption density area is to transition from the use of natural gas to biomass as a fuel in addition to installing booster HP coupled with solar PV panels and implementation of energy efficiency measures. That allows reducing primary energy factor, increasing the avoided CO₂ emissions, and decreasing the levelized cost of heat.