Exergy analysis of district-heated buildings at different ages : Identification of exergy efficiency and improvement potential for offices with district heating

Sammanfattning

This thesis investigates where major exergy destruction occurs in districtheated buildings and how the exergy performance of heating systems differs between buildings from different construction periods. Three district-heated buildings with varying ages, ventilation systems and thermal demand profiles were analyzed using operational data from building management systems combined with thermodynamic calculations performed in MATLAB. The analysis included district heating substations, secondary heating systems, radiator systems, ventilation heating, heat recovery systems and building climate processes. The results show that the largest exergy destruction occurs where hightemperature district heating is used to satisfy low-temperature heating demands. Temperature mismatch between supplied energy and actual heating demand was identified as the most significant factor effecting exergy performance. The analyses further demonstrate that newer buildings do not necessarily achieve better exergy performance despite reduced energy demand. Building configuration, thermal zoning and temperature levels in the system had greater influence on exergy performance than building age alone. The study concludes that reducing supply and return temperatures, improving temperature matching and implementing low-temperature district heating principles can improve overall exergy performance a lot. These findings highlight the importance of considering energy quality, not only energy quantity, when evaluating and developing future heating systems.