Sustainable Built Environment Research

Life cycle and system perspectives

The built environment accounts for a large share of the global total primary energy use and will play a major role in reducing primary energy use and greenhouse gas emissions. The construction of new resource-efficient buildings and infrastructure is important in the longer term, while efficiency improvements to existing buildings and infrastructure is important in the short run as the rate of turnover of existing buildings and systems is low.

Life cycle and system perspectives are needed to develop resource efficient buildings. All the life cycle phases of a building – production, operation, retrofitting and end-of-life – should be considered and optimized as a whole, including the energy and material chains from natural resources to final services. Most existing studies on energy implications of buildings are based on final energy use, while the primary energy use will more accurately reflect the use of energy resources. For the same energy services, different energy supply systems can result in significantly different primary energy use.

Renewable resources

Increased use of renewable resources such as wood-based building materials and fuels produced from sustainably forestry, instead of non-renewable materials and fuels can result in less greenhouse gas emissions. Forest resources, therefore, can play an important role in a long-term strategy to mitigate climate change. In the wood product chain, significant quantities of biomass residues are produced that can be used to replace fossil fuels such as coal. Finally, at the end of its service life the wood product itself could be used to replace fossil fuels.

Time and geographical perspectives are important in a wood-based strategy for mitigating climate change, since different forest management practices yield benefits at different time and geographical scales, and because the benefits of substituting non-wood products and fossil fuels with biomass are typically cumulative. We develop methodologies and tools to quantify and minimise greenhouse gas emissions and primary energy use over the life cycle of wood products, and link these benefits to different forest management practices for different time scales and geographical regions.

Energy efficiency and energy supply

Measures are increasingly being implemented to reduce building envelope heat losses, and buildings have become more airtight. Swedish policy aims to reduce final energy use in buildings by 50% by 2050, and for new buildings to be constructed with very low energy demands. This requires substantial changes to how the built environment is developed and supplied with energy.

District heating systems, which supply about half of the space heating in Sweden, use primary energy very efficiently when the district heat is co-produced with other products such as electricity. The co-production of district heat is expected to increase. The interaction of district heating systems and energy efficiency measures can be complex, depending on the scale and period of the intervention and the energy use profile of buildings. Our research 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.

Primary energy- and carbon-efficient systems

Modern techniques to construct multi-storey wood-framed buildings with low life cycle primary energy use and greenhouse gas emissions have been developed. An example is the four award-winning 8-storey wood-framed apartment buildings (Figure 1) constructed in Växjö.

Figure 1. An award-winning, 8-storey wood-framed building in Växjö, Sweden.
Photo: Martin Johansson.

Our analysis of the life cycle primary energy use and carbon dioxide (CO2) emission of one of the buildings shows that using recovered woody biomass residues to replace fossil coal more than offsets the emissions from production phase fossil fuel use and process emissions associated with the concrete used in the building.

Building passive houses, which are designed for very low operating energy use, is increasingly suggested. Figure 2 shows the primary energy use and CO2 emissions to produce, space heat and ventilate, and finally to demolish a conventional and a passive house with different frame materials in Växjö. The passive house uses more materials thus increasing the production energy use, but the reduced space heating and ventilation energy use is much more significant. The wood frame construction reduces the production primary energy use and carbon emission, compared to the concrete frame construction.

Figure 2. Primary energy use for heating and ventilation of a house with biomass-based district heat mainly from combined heat and power production, (2) primary energy use to produce the house, (3) primary energy benefits which arise at end-of-life, and (4) energy content in the wood residue which is created when the house is built. The house is assumed to be built with a concrete or wood frame in accordance with the Swedish building code (BBR 2012) or passive-house criteria. The assumed life of the house is 50 years and the primary energy use is calculated as annual values per square meter of heated building area. (Adapted from: Dodoo, A., Gustavsson, L., & Sathre, R. 2012)