Public defence in Mechanical Engineering, M.Sc. Pauli Hiltunen

How to utilise low-temperature waste heat and return water of district heating networks in district heating production? 

Heating and cooling sector accounts for approximately half of the total energy demand in European Union, and fossil fuels have had a major role in the European heating markets. Decarbonisation of the sector is essential to mitigate the climate change and achieve European Union's climate goals. The war in Ukraine and the energy crisis in 2022 increased the pressure to reduce the use of imported fossil fuels in heating sector even more. District heating is produced centrally and delivered to the customers using a piping network. The heating plants can utilise various renewable and low-carbon heat sources. Therefore, decarbonised district heating can reduce the dependency on fossil fuels in the European heating markets. However, the transition of the existing infrastructure to low-carbon district heating will take decades and will likely happen step-by-step. In this thesis, waste heat utilisation, electrified district heating and low-temperature networks were studied as means to reduce the use of fossil fuels in district heating production. 

The results of this thesis show that district heating can provide environmentally friendly alternative to natural gas heating in a university campus in Tallinn, and utilising heat from the district heating network’s return water can improve the overall efficiency of the entire system. Data centre waste heat can provide constant heat supply in Espoo district heating system but due to the mismatch between the waste heat load and heat demand, meeting the peak demand is difficult during the heating season. Because heat pumps are needed for utilising the low-temperature waste heat, electricity price has a significant impact on the feasibility of waste heat utilisation. However, if fuel prices are also in a high level as they were in the end of 2021, heat pumps proved to maintain their competitiveness even with high electricity prices. Heat pumps and combined heat-and-power plants together can balance the production costs if the electricity price is varying highly. This can also help balancing the electricity markets with high share of intermittent renewable electricity production.

Doctoral Student: Pauli Hiltunen

Opponent: Senior Researcher Dominik Dominkovic, Technical University of Denmark

Custos: Prof. Sanna Syri, Aalto University School of Engineering, Department of Mechanical Engineering

The public defense will be organized as a hybrid event in Lecture Hall R001/M232 M1, Otakaari 1 and on Zoom.

The thesis is publicly displayed 10 days prior to the defense in the publication archive Aaltodoc of Aalto University. 

Contact information of doctoral student:

Doctoral theses in the School of Engineering: https://aaltodoc.aalto.fi/handle/123456789/49