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Carbon implications of end-of-life management of building materials
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
2009 (English)In: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 53, no 5, 276-286 p.Article in journal (Refereed) Published
Abstract [en]

In this study we investigate the effects of post-use material management on the life cycle carbon balance of buildings, and compare the carbon balance of a concrete-frame building to that of a wood-frame building. The demolished concrete is either landfilled, or is crushed into aggregate followed by exposure to air for periods ranging from 4 months to 30 years to increase carbonation uptake of CO2. The demolished wood is assumed to be used for energy to replace fossil fuels. We calculate the carbon flows associated with fossil fuel used for material production, calcination emission from cement manufacture, carbonation of concrete during and after its service life, substitution of fossil fuels by recovered wood residues, recycling of steel, and fossil fuel used for post-use material management. We find that carbonation of crushed concrete results in significant uptake of CO2. However, the CO2 emission from fossil fuel used to crush the concrete significantly reduces the carbon benefits obtained from the increased carbonation due to crushing. Stockpiling crushed concrete for a longer time will increase the carbonation uptake, but may not be practical due to space constraints. Overall, the effect of carbonation of post-use concrete is small. The post-use energy recovery of wood and the recycling of reinforcing steel both give higher carbon benefit than the post-use carbonation. We conclude that carbonation of concrete in the post-use phase does not affect the validity of earlier studies reporting that wood-frame buildings have substantially lower carbon emission than concrete-frame buildings.

Place, publisher, year, edition, pages
2009. Vol. 53, no 5, 276-286 p.
National Category
Construction Management Other Environmental Engineering
Identifiers
URN: urn:nbn:se:miun:diva-8582DOI: 10.1016/j.resconrec.2008.12.007ISI: 000264650400006Scopus ID: 2-s2.0-63749083154OAI: oai:DiVA.org:miun-8582DiVA: diva2:173813
Available from: 2009-02-17 Created: 2009-02-17 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Life cycle primary energy use and carbon emission of residential buildings
Open this publication in new window or tab >>Life cycle primary energy use and carbon emission of residential buildings
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the primary energy use and carbon emissions of residential buildings are studied using a system analysis methodology with a life cycle perspective. The analysis includes production, operation, retrofitting and end-of-life phases and encompasses the entire natural resource chain. The analysis  focuses, in particular, on to the choice of building frame material; the energy savings potential of building thermal mass; the choice of energy supply systems and their interactions with different energy-efficiency measures, including ventilation heat recovery systems; and the effectiveness of current energy-efficiency standards to reduce energy use in buildings. The results show that a wood-frame building has a lower primary energy balance than a concrete-frame alternative. This result is primarily due to the lower production primary energy use and greater bioenergy recovery benefits of wood-frame buildings. Hour-by-hour dynamic modeling of building mass configuration shows that the energy savings due to the benefit of thermal mass are minimal within the Nordic climate but varies with climatic location and the energy efficiency of the building. A concrete-frame building has slightly lower space heating demand than a wood-frame alternative, because of the benefit of thermal mass. However, the production and end-of-life advantages of using wood framing materials outweigh the energy saving benefits of thermal mass with concrete framing materials.

A system-wide analysis of the implications of different building energy-efficiency standards indicates that improved standards greatly reduce final energy use for heating. Nevertheless, a passive house standard building with electric heating may not perform better than a conventional building with district heating, from a primary energy perspective. Wood-frame passive house buildings with energy-efficient heat supply systems reduce life cycle primary energy use.

An important complementary strategy to reduce primary energy use in the building sector is energy efficiency improvement of existing buildings, as the rate of addition of new buildings to the building stock is low. Different energy efficiency retrofit measures for buildings are studied, focusing on the energy demand and supply sides, as well as their interactions. The results show that significantly greater life cycle primary energy reduction is achieved when an electric resistance heated building is retrofitted than when a district heated building is retrofitted. For district heated buildings, the primary energy savings of energy efficiency measures depend on the characteristics of the heat production system and the type of energy efficiency measures. Ventilation heat recovery (VHR) systems provide low primary energy savings where district heating is based largely on combined heat and power (CHP) production. VHR systems can produce substantial final energy reduction, but the primary energy benefit largely depends on the type of heat supply system, the amount of electricity used for VHR and the airtightness of buildings.

Wood-framed buildings have substantially lower life cycle carbon emissions than concrete-framed buildings, even if the carbon benefit of post-use concrete management is included. The carbon sequestered by crushed concrete leads to a significant decrease in CO2 emission. However, CO2 emissions from fossil fuels used to crush the concrete significantly reduce the carbon benefits obtained from the increased carbonation due to crushing. Overall, the effect of carbonation of post-use concrete is small. The post-use energy recovery of wood and the recycling of reinforcing steel both provide higher carbon benefits than post-use carbonation.

In summary, wood buildings with CHP-based district heating are an effective means of reducing primary energy use and carbon emission in the built environment.

Place, publisher, year, edition, pages
Östersund: Mittuniversitetet, 2011. 165 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 115
National Category
Civil Engineering Environmental Sciences
Identifiers
urn:nbn:se:miun:diva-14942 (URN)978-91-86694-57-9 (ISBN)
Public defence
2011-11-08, Q221, Campus Östersund, Östersund, 12:00 (English)
Opponent
Supervisors
Available from: 2011-11-28 Created: 2011-11-28 Last updated: 2012-07-30Bibliographically approved

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Dodoo, AmbroseGustavsson, LeifSathre, Roger

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