Determining economic feasibility of supply temperature reduction in existing district heating system through thermohydraulic modelling

District heating systems are traditionally designed to operate with fossil fuel energy sources, and the supply temperature levels must be reduced to enable the usage of sustainable low temperature heat sources. In this study, the economic effects of different supply temperature reductions were examined through thermohydraulic modelling. The case study was the district heating system of Kangasala, Finland. The simulations were conducted with existing substation equipment and upgraded substations. The objective was to determine the economic feasibility of a supply temperature reduction by examining the decreased heat losses and the increased pumping energy usage. The generated savings from a reduced supply temperature from 115 °C to 90 °C in the studied system are insignificant, only 0.50 ‰ with existing equipment and 2.37 % with upgraded substations. With existing equipment, the increase in pumping energy use decreases the generated savings, and with the upgraded customer substations the investment costs are not reasonable compared to the savings. The conclusion is that a supply temperature reduction in an outdoor temperature compensated system, like in Kangasala, results in limited savings. A supply temperature reduction needs to be accompanied by a change in the production portfolio to be economically feasible.