Systemoptimering av fjärrvärmeproduktion med värmepumpar för sänkning av returtemperatur : En teknisk-, ekonomisk- och miljömässig analys av returtemperatursänkning i Umeås fjärrvärmesystem med värmepumpar

Sammanfattning

This study investigates the optimization of Umeå’s district heating (DH) network by strategically integrating heat pumps to lower return temperatures, improve system efficiency, and reduce dependency on expensive peak load production. A detailed model of the DH network was developed using NetSim, an advanced simulation tool, and calibrated with one year of temperature data from Umeå Energi. The simulations covered the entire network and associated heat production facilities, with three scenarios evaluated based on heat pump installations at Backen, Olofsdal, and Röbäck. The simulations show that reduced return temperatures improve the temperature differential, increase system capacity, reduce flow and pressure requirements, and enable greater energy recovery through flue gas condensing at the CHP plant Dåva. This resulted in a capacity increase of up to 17 MW at Dåva, and the average return temperature decreased by 5.7°C at outdoor temperatures of –20°C. The analysis revealed clear differences in profitability across scenarios from an economic perspective. Olofsdal achieved the highest net present value (NPV) of approximately 135 MSEK and a payback time of 12.4 years at an electricity price of 0.15 SEK/kWh. Röbäck also showed positive financial performance with an NPV of about 40 MSEK and a payback time of 5.2 years. However, Backen had a negative NPV of around –30 MSEK and was not profitable under any of the analyzed conditions. These results underline the importance of correct system sizing, strategic placement, and replacing expensive peak load generation. The integration of heat pumps contributes to a significant reduction in CO2 emissions, up to 9,700 tons per year, primarily by displacing fossil-intensive peak load production and improving flue gas condensing efficiency. The findings also emphasize the importance of complementary technologies such as waste heat recovery, customer-side optimization, and low-temperature network solutions in supporting the transition toward sustainable district heating. In conclusion, properly sized and strategically located heat pumps can deliver substantial technical, economic, and environmental benefits. Combined with other innovative technologies, this approach strengthens the resilience and sustainability of future district heating systems.