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Life cycle primary energy use and carbon emission of residential buildings
Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development. (Ecotechnology)
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: urn:nbn:se:miun:diva-14942ISBN: 978-91-86694-57-9 (print)OAI: oai:DiVA.org:miun-14942DiVA: diva2:459741
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
List of papers
1. Primary energy implications of ventilation heat recovery in residential buildings
Open this publication in new window or tab >>Primary energy implications of ventilation heat recovery in residential buildings
2011 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 43, no 7, 1566-1572 p.Article in journal (Refereed) Published
Abstract [en]

In this study, we analyze the impact of ventilation heat recovery (VHR) on the operation primary energy use in residential buildings. We calculate the operation primary energy use of a case-study apartment building built to conventional and passive house standard, both with and without VHR, and using different end-use heating systems including electric resistance heating, bedrock heat pump and district heating based on combined heat and power (CHP) production. VHR increases the electrical energy used for ventilation and reduces the heat energy used for space heating. Significantly greater primary energy savings is achieved when VHR is used in resistance heated buildings than in district heated buildings. For district heated buildings the primary energy savings are small. VHR systems can give substantial final energy reduction, but the primary energy benefit depends strongly on the type of heat supply system, and also on the amount of electricity used for VHR and the airtightness of buildings. This study shows the importance of considering the interactions between heat supply systems and VHR systems to reduce primary energy use in buildings.

Keyword
Mechanical ventilation; Heat recovery; Heat supply systems; Electric resistance heating; Heat pump; District heating; CHP plant; Primary energy
National Category
Environmental Biotechnology Civil Engineering
Identifiers
urn:nbn:se:miun:diva-13330 (URN)10.1016/j.enbuild.2011.02.019 (DOI)000292231600008 ()2-s2.0-79956354126 (Scopus ID)
Available from: 2011-03-01 Created: 2011-03-01 Last updated: 2017-12-11Bibliographically approved
2. Building energy-efficiency standards in a life cycle primary energy perspective
Open this publication in new window or tab >>Building energy-efficiency standards in a life cycle primary energy perspective
2011 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 43, no 7, 1589-1597 p.Article in journal (Refereed) Published
Abstract [en]

In this study we analyze the life cycle primary energy use of a wood-frame apartment building designed to meet the current Swedish building code, the Swedish building code of 1994 or the passive house standard, and heated with district heat or electric resistance heating. The analysis includes the primary energy use during the production, operation and end-of-life phases. We find that an electric heated building built to the current building code has greater life cycle primary energy use relative to a district heated building, although the standard for electric heating is more stringent. Also, the primary energy use for an electric heated building constructed to meet the passive house standard is substantially higher than for a district heated building built to the Swedish building code of 1994. The primary energy for material production constitutes 5% of the primary energy for production and space heating and ventilation of an electric heated building built to meet the 1994 code. The share of production energy increases as the energy-efficiency standard of the building improves and when efficient energy supply is used, and reaches 30% for a district heated passive house. This study shows the significance of a life cycle primary energy perspective and the choice of heating system in reducing energy use in the built environment.

Keyword
Building code; District heating; Electric heating; Life cycle primary energy; Passive house
National Category
Civil Engineering
Identifiers
urn:nbn:se:miun:diva-13352 (URN)10.1016/j.enbuild.2011.03.002 (DOI)000292231600011 ()2-s2.0-79956371037 (Scopus ID)
Available from: 2011-03-07 Created: 2011-03-07 Last updated: 2017-12-11Bibliographically approved
3. Carbon implications of end-of-life management of building materials
Open this publication in new window or tab >>Carbon implications of end-of-life management of building materials
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.

National Category
Construction Management Other Environmental Engineering
Identifiers
urn:nbn:se:miun:diva-8582 (URN)10.1016/j.resconrec.2008.12.007 (DOI)000264650400006 ()2-s2.0-63749083154 (Scopus ID)
Available from: 2009-02-17 Created: 2009-02-17 Last updated: 2017-12-13Bibliographically approved
4. Life cycle primary energy implication of retrofitting a wood-framed apartment building to passive house standard
Open this publication in new window or tab >>Life cycle primary energy implication of retrofitting a wood-framed apartment building to passive house standard
2010 (English)In: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 54, no 12, 1152-1160 p.Article in journal (Refereed) Published
Abstract [en]

Here we analyze the life cycle primary energy implication of retrofitting a four-storey wood-frame apartment building to the energy use of a passive house. The initial building has an annual final energy use of 110 kWh/m(2) for space and tap water heating. We model improved thermal envelope insulation, ventilation heat recovery, and efficient hot water taps. We follow the building life cycle to analyze the primary energy reduction achieved by the retrofitting, considering different energy supply systems. 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. The primary energy use for material production increases when the operating energy is reduced but this increase is more than offset by greater primary energy reduction during the operation phase of the building, resulting in significant life cycle primary energy savings. Still, the type of heat supply system has greater impact on primary energy use than the final heat reduction measures.

Place, publisher, year, edition, pages
Elsevier, 2010
Keyword
Retrofitting; Passive house; Existing building; Life cycle; Primary energy; Heat supply systems
National Category
Construction Management Other Environmental Engineering
Identifiers
urn:nbn:se:miun:diva-11446 (URN)10.1016/j.resconrec.2010.03.010 (DOI)000281752400015 ()2-s2.0-77955850346 (Scopus ID)
Available from: 2009-02-17 Created: 2009-02-17 Last updated: 2017-12-12Bibliographically approved
5. Primary energy implications of end-use energy efficiency measures in district heated buildings
Open this publication in new window or tab >>Primary energy implications of end-use energy efficiency measures in district heated buildings
2011 (English)In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 43, no 1, 38-48 p.Article in journal (Refereed) Published
Abstract [en]

In this study we explore the effects of end-use energy efficiency measures on different district heat production systems with combined heat and power (CHP) plants for base load production and heat-only boilers for peak and medium load productions. We model four minimum cost district heat production systems based on four environmental taxation scenarios, plus a reference district heat system used in Östersund, Sweden. We analyze the primary energy use and the cost of district heat production for each system. We then analyze the primary energy implications of end-use energy efficiency measures applied to a case-study apartment building, taking into account the reduced district heat demand, reduced cogenerated electricity and increased electricity use due to ventilation heat recovery. We find that district heat production cost in optimally-designed production systems is not sensitive to environmental taxation. The primary energy savings of end-use energy efficiency measures depend on the characteristics of the district heat production system and the type of end-use energy efficiency measures. Energy efficiency measures that reduce more of peak load than base load production give higher primary energy savings, because the primary energy efficiency is higher for CHP plants than for boilers. This study shows the importance of analyzing both the demand and supply sides as well as their interaction in order to minimize the primary energy use of district heated buildings.

Keyword
CHP plant; District heat production; Energy efficiency; Environmental taxations; Primary energy; Buildings
National Category
Construction Management Other Environmental Engineering
Identifiers
urn:nbn:se:miun:diva-11899 (URN)10.1016/j.enbuild.2010.07.029 (DOI)000284682700005 ()2-s2.0-78049480263 (Scopus ID)
Available from: 2010-08-06 Created: 2010-08-06 Last updated: 2017-12-12Bibliographically approved
6. Effect of thermal mass on life cycle primary energy balances of a concrete- and a wood-frame building
Open this publication in new window or tab >>Effect of thermal mass on life cycle primary energy balances of a concrete- and a wood-frame building
2012 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 92, no 1, 462-472 p.Article in journal (Refereed) Published
Abstract [en]

In this study we analyze the effect of thermal mass on space heating energy use and life cycle primary energy balances of a concrete- and a wood-frame building. The analysis includes primary energy use during the production, operation and end-of-life phases. Based on hourby- hour dynamic modeling of heat flows in building mass configurations we calculate the energy saving benefits of thermal mass during the operation phase of the buildings. Our results indicate that the energy savings due to thermal mass is small and varies with the climatic location and energy efficiency levels of the buildings. A concrete-frame building has slightly lower space heating demand than a wood-frame alternative, due to the benefit of thermal mass inherent in concrete-based materials. Still, a wood-frame building has a lower life cycle primary energy balance than a concrete-frame alternative. This is due primarily to the lower production primary energy use and greater bioenergy recovery benefits of the wood-frame buildings. These advantages outweigh the energy saving benefits of thermal mass. We conclude that the influence of thermal mass on space heating energy use for buildings located in Nordic climate is small and that wood-frame buildings with CHP-based district heating would be an effective means of reducing primary energy use in the built environment.

Keyword
Buildings; Concrete; Wood; Thermal mass; Dynamic modeling; Life cycle primary energy
National Category
Civil Engineering Environmental Sciences
Identifiers
urn:nbn:se:miun:diva-14944 (URN)10.1016/j.apenergy.2011.11.017 (DOI)000300463800052 ()2-s2.0-83455260407 (Scopus ID)
Available from: 2011-11-28 Created: 2011-11-28 Last updated: 2017-12-08Bibliographically approved

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Citation style
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  • nn-NO
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  • Other locale
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Output format
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