Cost-effective renovation of Nordic old apartment heating systems with hydrogen-production-based low-temperature district heating

Integrating waste heat from hydrogen production into low-temperature district heating (LTDH) can improve hydrogen production profitability and the renewable energy usage of building heating. However, cost-effectiveness evidence for such applications on the demand side of old buildings remains limited. This study evaluates the potential of hydrogen-production-based waste heat in an LTDH context for two old Finnish apartment buildings with commonly used high-temperature radiators (80/50 °C and 70/40 °C). Based on these buildings, LTDH solutions are proposed to address the temperature mismatch between LTDH supply and existing space heating systems: retaining the existing radiators with the backup heater (an electric heater or a heat pump), and retrofitting low-temperature radiators (60/30 °C) compatible with LTDH. IDA ICE was used for energy simulations for representative weather years and a future climate scenario of 2050, and indoor temperature simulation during the cold event. The economic feasibility of each solution is evaluated. The findings indicate that LTDH meets at least 93% of total heat demand with 80/50 °C radiators and about 99% with 70/40 °C radiators. Backup electric heaters and heat pumps raise peak electricity demand by up to 169% and 38%, respectively, relative to the references. Resilience analysis indicates that backup heating is required to maintain indoor temperatures for the old building with 80/50 °C radiators. Economically, all proposed LTDH solutions are feasible with lower life-cycle costs (LCC) than the reference cases. Electric heater yields the shortest discounted payback period, whereas the heat pump solution offers the lowest cost over the full life cycle.