Economic feasibility of ultra-low temperature district heating systems in newly built areas supplied by renewable energy

Future district heating systems are expected to supply lower temperatures to increase system efficiency and enable exploitation of renewable heat sources. To answer whether it is beneficial to lower district heating temperatures below the level where it is still possible to supply domestic hot water directly, the economic feasibility of three ultra-low temperature district heating (ULTDH) concepts was compared to low temperature district heating (LTDH). The dependency of the economic feasibility on the boundary conditions of the supplied district heating area was assessed systematically and feasible boundary conditions were identified. For this purpose building plot ratio, specific heat demand and central heating unit were varied. The different solutions were compared based on levelised cost of heat, socioeconomic net present value and overall seasonal coefficient of performance. It was found that in most cases LTDH was economically preferred. ULTDH could be feasible if the linear heat demand density (LHDD) was high, if the cost of decentral units could be lowered or if the investment cost of the central heating unit was significantly lower compared to LTDH. Among the ULTDH solutions, apartment units were preferable for low LHDD, while units at building level performed better for larger LHDD.