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Exploring the trade-off in life cycle energy of building retrofit through optimization
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction. Urban Design Group at IVL Swedish Environmental Research Institute, Sweden.ORCID iD: 0000-0003-0907-1270
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.ORCID iD: 0000-0001-9279-2233
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.ORCID iD: 0000-0003-0974-2142
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.ORCID iD: 0000-0003-4843-8936
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2020 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 269, article id 115083Article in journal (Refereed) Published
Abstract [en]

Building retrofit is considered as a vital step to achieve energy and climate goals in both Europe and Sweden. Nevertheless, retrofitting solutions based merely on reducing operational energy use can increase embodied energy use, mainly due to altering the existing trade-off between the two. Considering this trade-off is vitally important, especially for retrofitting buildings located in cold climate regions, as reduction of operational energy use to meet standards of energy-efficient buildings may require a deep retrofitting that can considerably increase the embodied energy and thus be unfavorable from a Life Cycle Energy (LCE) perspective. This article presents a case study in which multi-objective optimization was used to explore the impact of a wide range of retrofitting measures on the aforementioned trade-off for a building in Sweden located in a subarctic climatic zone. The studied building was a typical 1980s multi-family residence. The goal was to explore and compare the optimal retrofitting solution(s) for the building, aiming to achieve Swedish energy-efficient building standards (i.e. new-build and near-zero energy standards). The results of the optimization indicated that (1) use of additional insulation in walls and roof, (2) replacement of existing windows with more energy-efficient ones, and (3) change of traditional mechanical extract ventilation to heat recovery ventilation are the primary and optimal retrofitting measures to fulfill the new-build Swedish energy standard and achieve highest LCE savings. However, to fulfill more far-reaching operational energy savings, application of additional retrofitting measures was required, increasing the embodied energy use considerably and resulting in lower LCE savings compared to the optimal retrofitting solution that only reached the Swedish new-build energy standard. The LCE difference between the optimal retrofitting solutions that fulfilled the new-build standard and the strictest near-zero (passive house) standard was 1862 GJ, which is equivalent to almost four years of operational energy use for the original building. This indicates that there is a limit to the reduction of operational energy use when retrofitting existing buildings, beyond which additional reductions can considerably increase the embodied energy and thus be unfavorable in terms of LCE use.

Place, publisher, year, edition, pages
Elsevier, 2020. Vol. 269, article id 115083
Keywords [en]
Building retrofit, Embodied energy, Life cycle energy, Multi-objective optimization, Operational energy, Retrofitting measures
National Category
Construction Management
Research subject
Construction Management and Building Technology
Identifiers
URN: urn:nbn:se:ltu:diva-78989DOI: 10.1016/j.apenergy.2020.115083ISI: 000537619800048Scopus ID: 2-s2.0-85084475658OAI: oai:DiVA.org:ltu-78989DiVA, id: diva2:1432097
Note

Validerad;2020;Nivå 2;2020-05-26 (johcin)

Available from: 2020-05-26 Created: 2020-05-26 Last updated: 2023-03-10Bibliographically approved
In thesis
1. Energy efficiency strategies for residential buildings in a subarctic climate: Impacts on energy use and indoor thermal climate
Open this publication in new window or tab >>Energy efficiency strategies for residential buildings in a subarctic climate: Impacts on energy use and indoor thermal climate
2023 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Adopting energy efficiency strategies in residential buildings are beneficial as these not only improve the energy performance but also improves the indoor thermal climate and minimizes the greenhouse gas emissions. There exist numerous studies on energy efficiency strategies and their influence on indoor thermal climate in residential buildings in cold climates. However, there is a lack of documented and systematic studies that explicitly investigated the selection of appropriate energy efficiency strategies and their impact on the indoor thermal climate in residential buildings in a subarctic climate. Moreover, the impact of such energy efficiency strategies on the life cycle energy use of buildings has not been given appropriate attention in the existing literature. Due to the extreme climate conditions in a subarctic climate – severe cold and dark winter with heavy snow and mild short summer – buildings require a considerable amount of heating energy to maintain a comfortable temperature indoors. Therefore, it is important to adopt energy efficiency strategies that can help obtain operational and life cycle energy savings along with a better indoor thermal climate.

The aim of this study is to evaluate the impact of different energy efficiency strategies on energy use and thermal indoor climate of three selected case study residential buildings in a subarctic climate. Three research questions were formulated: (1) What is the impact of evaluated energy‐efficiency strategies on the operational energy use?, (2) What is the impact of evaluated energy‐efficiency strategies on the life‐cycle energy use?, and (3) What is the impact of evaluated energy‐efficiency strategies on the thermal indoor climate? To address research questions 1 and 3, implemented energy‐efficiency strategies in two low‐energy buildings were evaluated using measured energy data and dynamic building energy and indoor climate simulations. To address research question 2, different combinations of energy efficiency strategies were explored using a multiobjective optimization method to identify optimal retrofitting solutions in terms of life cycle energy savings for a 1980s building.

Results show that besides an airtight and highly insulated building envelope, a well‐functioning heating system is important to achieve low operational energy use. Findings highlight that the role of occupants is vital both in regard to the proper functioning of the heating system and to reduce the need for active heating in an airtight and highly insulated building. The occupants are also important in terms of maintaining a comfortable indoor thermal climate, especially during summer since manual airing and shading can help moderate temperatures indoors. Furthermore, findings show that applying glazed balconies is not necessarily a favorable strategy in terms of operational energy use and indoor thermal climate for a building in a subarctic climate. In comparison, using double instead of single pane balcony glazing and lowering the window to wall ratio improved the operational energy and indoor thermal climate performance. A combination of energy efficiency strategies including the addition of insulation on walls and roofs, there placement of windows from double pane to triple pane ones and the installation of heat recovery ventilation were found optimal to achieve considerable savings in both operational and life cycle energy use. In many cases, the fundamental aim of adopting energy efficiency strategies is to reduce operational energy use, while impacts on life cycle energy use and indoor thermal climate are less prioritized. The findings illustrate the importance of considering impacts on operational energy use, life cycle energy use and indoor thermal climate simultaneously to select energy efficiency strategies that ensure a better and more sustainable built environment.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Building Technologies
Research subject
Construction Management and Building Technology
Identifiers
urn:nbn:se:ltu:diva-95833 (URN)978-91-8048-284-4 (ISBN)978-91-8048-285-1 (ISBN)
Presentation
2023-04-25, T3109, Luleå tekniska universitet, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2023-03-10 Created: 2023-03-10 Last updated: 2023-09-05Bibliographically approved

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Shadram, FarshidBhattacharjee, ShimantikaLidelöw, SofiaMukkavaara, JaniOlofsson, Thomas

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