Assessing low temperature waste heat integration in 5th generation district heating and cooling: a case study evaluation

• 5GDHC with WWTP heat recovery offers low LCOE and crucial electrical capacity demand reduction in urban settings. • Novel holistic techno-economic-environmental assessment of STES-free 5GDHC integrating WWTPs as dual source/sink. • Provides evidence for optimal waste heat integration strategies enabling 5GDHC viability despite low demand co-occurrence. Decarbonising urban heating and cooling necessitates innovative solutions that can cost-effectively integrate low-temperature waste heat, such as from Wastewater Treatment Plants (WWTPs). While 5th Generation District Heating and Cooling (5GDHC) offers promising pathways for energy reuse and sector coupling, its techno-economic-environmental performance, particularly when leveraging WWTPs as a dual heat source/sink without Seasonal Thermal Energy Storage (STES), and its precise impact on the electricity grid, remain underexplored. This study investigates the feasibility of 5GDHC in Glasgow’s Clyde Gateway, a large-scale urban regeneration. It critically analyses two WWTP-integrated 5GDHC configurations (direct heat exchanger vs. sewer water source heat pump) and compares their techno-economic-environmental performance against established alternatives: 4th Generation District Heating with individual Air Condition units (4GDH&AC) and building-level reversible Air-Source Heat Pumps (ASHPs). Results demonstrate that even with low heating and cooling demand co-occurrence (3.4% DOC), the direct heat exchanger 5GDHC configuration (5GDHC-1) proved most economically viable, achieving the lowest Levelised Cost of Energy (£227/MWh) compared to 4GDH&AC (£257/MWh). Crucially, 5GDHC solutions exhibited a significantly lower electrical capacity demand (0.7 MVA) than 4GDH&AC (1.5 MVA) and ASHPs (3.0 MVA), offering substantial benefits for grid infrastructure and broader electrification. While 4GDH&AC showed lower overall energy consumption, 5GDHC’s ability to minimise peak electrical load is a distinct advantage. This research highlights that strategic waste heat integration, particularly through direct exchange with the WWTP leveraging ambient network temperature profiles, enables economically viable 5GDHC without STES in low demand co-occurrence scenarios. It provides critical insights for developing resilient, low-carbon urban thermal systems with reduced electricity grid impact. Abbreviations: 4GDH, 4th Generation District Heating; 5GDHC, 5th Generation District Heating and Cooling; AC, Air Condition; ASHP, Air Source Heat Pump; BHP, Booster Heat Pump; BU, Balancing Unit; CAPEX, Capital Expenditure; CO 2e , Carbon Dioxide Equivalent; COP, Coefficient of Performance; DHW, Domestic Hot Water; DOC, Demand Overlap Coefficient; EC, Energy Centre; EER, Energy Efficiency Rating; EHV, Extra High Voltage; HEX, Heat Exchanger; HV, High Voltage; LCOE, Levelised Cost of Energy; OHL, Overhead Lines; OPEX, Operational Expenditure; REPEX, Replacement Expenditure; SCOP, Seasonal Coefficient of Performance; SPF, Seasonal Performance Factor; STES, Seasonal Thermal Energy Storage; SWSHP, Sewer Water Source Heat Pump; TES, Thermal Energy Store; WWHR, Waste Water Heat Recovery; WWTP, Waste Water Treatment Plant; ΔT, Temperature Difference.