Influence of thermal expansion in district heating network on initiation of leakage points

Abstract

Leakages in Espoo district heating network have increased significantly during the year 2022. The aim of the thesis was to study if a correlation can be found between network operation and leakages. Thesis was limited to study only supply temperature gradients in Espoo area district heating network. Interviews of specialists from other district heating networks were performed. Operational and leakage data analysis started from identifying and collecting relevant data. By experience, specialists indicated limit for acceptable temperature gradient. This limit was utilized in the Espoo network operational data analysis. During the year 2022, a significant increase on the amount of temperature gradients exceeding the limit was noticed. In the leakage data analysis differences in pipe properties, each year, were compared. Leakage analysis includes years 2019, 2020 and 2022 data, until May 2022. The year 2021 was excluded from the leakage analysis due to missing data. Development of year 2022 leakages was assumed to stay constant throughout the year. A possible correlation between network operation conditions and leakages was found. Specialist interviews and literature review support this finding. During the thesis a limit of 2 °C/h for temperature gradient was set to Espoo district heating operation system. This value is significantly lower than Finnish Energy 1–2 °C/ 6 min guideline, thus, Finnish Energy have not determined how long period of stable operation is required after the temperature gradient.