Optimering av framledningstemperatur i Umeå fjärrvärmesystem

Sammanfattning

This thesis investigates how the supply temperature affects the heat losses and transport times in the district heating network of Umeå city, operated by Umeå Energi. The study was based on analyses of production and operational data from customer stations located in outer areas of Umeå during winter periods under year 2024, 2025 and 2026. The purpose of the study was to examine how operating conditions and supply temperature affects the district heating network, with focus on how heat losses are affected by supply temperature and how long time it takes for a temperature change from the production plant to reach outer areas of the network. The results show that several factors besides supply temperature affects the transport time from the production plant to customer stations, such as flow rate, network load, geographical structure of the area and operating conditions. The lowest transport times occurred during periods of high network load and low outdoor temperatures, which indicates that increased flow rate in the network results in lower transport times. The transport times were also affected by network constraints and by the geographical location of the outer area in relation to the production plants within the network. The results also show that higher supply temperatures and higher network loads led to greater variations in network heat losses. At the same time, the results indicated that the supply temperature alone cannot explain the heat losses, and that several factors influence the network heat loss, including thermal lag, network load, control strategy and flow rate. The network heat loss analysis indicates that operational data from the previous 12–24 hours should be included in control system to counteract network heat losses caused by stored energy and lag. Finally, this study shows that supply temperature is a significant factor with great influence on both heat losses and transport times in the district heating network. However, district heating systems are complex and several other important factors besides supply temperature affect the results and are therefore important to analyze.