Holistic renovation strategies for cold climate buildings: simulation-based insights into decarbonization and cost-effectiveness

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2025-10-10
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Date

2025

Department

Sähkötekniikan ja automaation laitos
Department of Electrical Engineering and Automation

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Mcode

Degree programme

Language

en

Pages

97 + app. 83

Series

Aalto University publication series Doctoral Theses, 167/2025

Abstract

The building sector is a major contributor to global energy use and CO2 emissions, accounting for approximately 40% of total energy use in the European Union, and 21% in China. In cold climate regions, where space heating dominates end-use demand, renovating existing buildings serves as a critical strategy for achieving long-term decarbonization goals. Despite growing interest in this area, there remains a need for systematic and transferable frameworks to assess holistic renovation strategies under various building types and energy contexts. This thesis proposed a simulation-based multi-objective optimization framework to identify cost-effective and low-carbon renovation solutions. Two case studies demonstrated its applicability: a rural residential building in northern China and a public kindergarten in Finland, which were evaluated using life-cycle cost (LCC) and annual CO2 emissions as key performance indicators. Given the local heating practices in rural China, the first phase assessed the impact of heating operation modes on the performance of individual envelope renovation. Compared to the prerenovation baseline, cost-optimal solutions achieve a 30−40% emission reduction. Under intermittent heating, LCC increases by 7%, while continuous heating leads to an 8% decrease. To improve indoor air quality during heating season, the second phase evaluated the technoeconomic and environmental performance of four mechanical ventilation systems. Exhaust ventilation system is identified as the most cost-effective option in life-cycle terms, while balanced ventilation system incorporating heat recovery and earth-air heat exchanger achieves the lowest CO2 emissions. The inclusion of earth-air heat exchangers reduces reheater capacity and defrost operations, with enhanced performance under colder conditions. The optimization method was then extended to holistic renovation packages that integrate envelope upgrades, ventilation improvements, and decentralized energy systems. Biomass-based system and photovoltaic (PV)-combined heat pump system achieve annual 53−90% emission reduction and 6−18% LCC savings compared to pre-renovation. Their cost-optimal configurations offer comparable LCCs to envelope-only solutions, with additional emission reductions of 15−52%. The method was further applied to a Finnish hybrid energy system combining renewable-powered heat pumps, PV generation, and district heating (DH). PV-combined ground-source heat pump with zero-emission DH from hydrogen waste heat achieves the lowest LCC, reducing costs by up to 23% compared to DH-only cases. This lower DH pricing scheme also reduces heat pump capacity by 10% points. Both decentralized and hybrid renewable-powered electrification strategies offer resilient, cost-effective solutions for decarbonizing cold climate buildings, with increasing benefits as the grid continues to decarbonize. This thesis presents a comprehensive, adaptable framework for identifying renovation strategies and offers practical guidance for carbon-neutral, economically viable building systems in cold climates.

Description

Supervising professor

Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering and Automation, Finland

Thesis advisor

Kosonen, Risto, Prof., Aalto University, Department of Energy and Mechanical Engineering, Finland

Keywords

building renovation, cold climate, simulation-based optimization, life-cycle cost, renewable energy, ventilation, heat pumps, electrification

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Parts

  • [Publication 1]: Hu, X.; Jokisalo, J.; Kosonen, R.; Lehtonen, M.; Shao, T. (2023). Cost-Optimal Renovation Solutions for Detached Rural Houses in Severe Cold Regions of China. Buildings, 13, 771.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202303222498
    DOI: 10.3390/buildings13030771 View at publisher
  • [Publication 2]: Hu, X.; Jokisalo, J.; Kosonen, R.; Lehtonen, M. (2025). Economic and environmental impacts of different ventilation systems in detached rural houses in severe cold climate. Journal of Building Engineering, 99, 111689.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202501101127
    DOI: 10.1016/j.jobe.2024.111689 View at publisher
  • [Publication 3]: Hu, X.; Jokisalo, J.; Kosonen, R.; Lehtonen, M. (2025). Cost-effective and Low-carbon Solutions for Holistic Rural Building Renovation in Severe Cold Climate. Energy and Buildings, 336, 115609.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202504093123
    DOI: 10.1016/j.enbuild.2025.115609 View at publisher
  • [Publication 4]: Ju, Y.; Hu, X.; Jokisalo, J.; Kosonen, R.; Xue, T.; Meriläinen, A.; Kosonen, A. (2025). Cost-optimal dimensioning of hybrid heat pump systems utilizing waste heat from hydrogen production for a kindergarten in cold climate. Energy and Buildings, 332, 115430.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202502242479
    DOI: 10.1016/j.enbuild.2025.115430 View at publisher

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https://urn.fi/URN:ISBN:978-952-64-2704-1

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[diss] Sähkötekniikan korkeakoulu / ELEC