Transition towards carbon neutral district heating by utilising low-temperature heat

Pauli Hiltunen

Research output: ThesisDoctoral ThesisCollection of Articles


Heating and cooling sector accounts for more than half of the total energy demand in European Union. Traditionally, fossil fuels have had a large share in producing heat to buildings and domestic hot water. Therefore, to mitigate the climate change and achieve European Union's climate goals, decarbonisation of the sector is essential. The war in Ukraine and energy crisis in 2022 increased the pressure to reduce the dependency of imported fossil fuels in heating even more. The transition of old infrastructure to low-carbon heat sources will take decades and will likely happen step-by-step. In this thesis, the transition to carbon-neutral production in Espoo district heating system was investigated. Especially, the role of low-temperature waste heat from the data centres in Espoo during the transition and feasibility of electrified district heating during electricity price shocks were studied. Utilising heat from district heating network's return water to provide heating and improve the energy efficiency were investigated in the campus of Tallinn Technical University was studied in this thesis as well. Utilising the return water of district heating in low-temperature energy cascades has been discussed as an option to reduce distribution losses in newly built or refurbished areas during the transition to low-temperature district heating. Use of heat from return water reduces the return temperature of the district heating network, which has a positive impact on the energy efficiency of the entire system. Electrification of district heating reduces the consumption of combustible fuels and can help balancing the electricity markets with high share of intermittent power production such as wind or solar power. Furthermore, digitalisation of the society will increase the already high energy demand of IT sector. Cooling of data centres produces large quantities of waste heat, which can be utilised in district heating. The results of this thesis show that district heating can provide environmentally sustainable alternative to the university campus heated by a natural gas-fired boiler reducing carbon emissions and primary energy consumption. Implementing a sub-network utilising low-temperature heat from the city's district heating network could reduce the emissions and primary energy consumption even more by lowering the heat losses and improving the efficiency of power and heat production in the combined heat-and-power plants. Waste heat from data centres can provide economical heat source for base load production in district heating systems, but it suits poorly for peak demand production during the heating season due to the mismatch between waste heat load and heat demand. Increasing electricity price hinders the profitability of heat pumps priming the low-temperature waste heat. However, heat pumps proved to produce economically viable heat even with high electricity prices, if the costs of fossil fuels are high as well, as it happened in 2021.
Translated title of the contributionSiirtymä hiilineutraaliin kaukolämpöön hyödyntämällä matala lämpötilaista lämpöä
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Syri, Sanna, Supervising Professor
  • Syri, Sanna, Thesis Advisor
  • Volkova, Anna, Thesis Advisor, External person
Print ISBNs978-952-64-1749-3
Electronic ISBNs978-952-64-1750-9
Publication statusPublished - 2024
MoE publication typeG5 Doctoral dissertation (article)


  • district heating
  • heat pumps
  • waste heat
  • data centre
  • heat efficiency


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