• Energy Research

Abstract Forests can help mitigate climate change in different ways, such as by storing carbon in forest ecosystems, and by producing a renewable supply of material and energy products. We analyse the climate implications of different scenarios for forestry, bioenergy and wood construction. We consider three main forestry scenarios for Kronoberg County in Sweden, over a 201-year period. The Business-as-usual scenario mirrors today's forestry while in the Production scenario the forest productivity is increased by 40% through more intensive forestry. In the Set-aside scenario 50% of forest land is set-aside for conservation. The Production scenario results in less net carbon dioxide emissions and cumulative radiative forcing compared to the other scenarios, after an initial period of 30–35 years during which the Set-aside scenario has less emissions. In the end of the analysed period, the Production scenario yields strong emission reductions, about ten times greater than the initial reduction in the Set-aside scenario. Also, the Set-aside scenario has higher emissions than Business-as-usual after about 80 years. Increasing the harvest level of slash and stumps results in climate benefits, due to replacement of more fossil fuel. Greatest emission reduction is achieved when biomass replaces coal, and when modular timber buildings are used. In the long run, active forestry with high harvest and efficient utilisation of biomass for replacement of carbon-intensive non-wood products and fuels provides significant climate mitigation, in contrast to setting aside forest land to store more carbon in the forest and reduce the harvest of biomass.

Abstract In this study we present a method for analysis of cost-effectiveness of end-use energy efficiency measures and demonstrate its application for modelling a wide range of energy renovation measures for a typical 1970s multi-family building in Sweden. The method integrates energy balance and bottom-up economic calculations considering total and marginal investment costs of energy efficiency measures as well as net present value of total and marginal savings of the measures. The energy renovation measures explored include additional insulation to basement walls, exterior walls, and attic floor, improved new windows, efficient electric appliances and lighting, efficient water taps, glazed enclosed balcony systems, and exhaust air ventilation heat recovery systems. The measures are analysed first individually and then designed to form economic packages. Our results show that improved windows give the biggest single final energy savings while resource-efficient taps is the most cost-effective measure for the building. We find that the cost-effectiveness of the energy renovation measures is sensitive to real discount rates and energy price increases. Cost-optimal final heat savings varies between 34% and 51%, depending on the choice of real discount rate and energy price increase. The corresponding electricity savings varies between 35% and 43%. This study shows a method and the significance of various technical and economic-related parameters in achieving deep energy savings cost-efficiently.

Abstract In this study, we analyse and compare the primary energy use and carbon dioxide (CO2) emissions associated with different insulation, cladding and frame materials for a constructed concrete frame multi-storey residential building in Sweden. Our approach consists of identifying individual materials giving the lowest primary energy use and CO2 emissions for each building envelope part and based on that, modelling different material combinations to achieve improved alternatives of the concrete frame building with the same operation energy use based on the Swedish building code or passive house criteria. We analyse the complete materials and energy chains, including material losses as well as conversion and fuel cycle losses. The analysis covers the primary energy use to extract, process, transport, and assemble the materials and the resulting CO2 emissions to the atmosphere. The results show wide variations in primary energy and CO2 emissions depending on the choice of building envelope materials. The materials for external walls contribute most to the primary energy and CO2 emissions, followed by foundation, roof and external cladding materials. The improved building alternatives with wood construction frames, wood external cladding, expanded polystyrene as foundation insulation and cellulose insulation in the external walls and roof result in about 36 - 40% lower production primary energy use and 42 – 49% lower CO2 emissions than the improved concrete alternative when achieving the same thermal performance. This study suggests that strategies for low-energy buildings should be combined with resource-efficient and low carbon materials in the production phase to mitigate climate change and achieve a sustainable built environment.

Abstract In this study we use dynamic simulation to explore the interactive impacts of different uncertain parameter values in energy balance modelling of existing and improved variants of a Swedish multi-storey residential building. We modelled variations as well as interactive influence of different simulation assumptions and parameters encompassing outdoor microclimate, building thermal envelope and technical installations including household equipment. The results indicate that the interactive influence of the parameters on calculated space heating of buildings seems to be small and relatively more evident for a low-energy building than for a conventional building. The influence of the interactions between the parameter combinations becomes more evident as several parameters are varied simultaneously. The results also indicate that calculated space heating demand of a building is noticeably influenced by how heat gains from household equipment and technical installations are modelled. The calculated final energy for space heating for the analysed building versions varied between 13-43% depending on the energy efficiency levels for household equipment and technical installations as well as their interactions with other parameter values variations. This study shows the importance of appropriate input parameters and assumptions for building energy balance calculation.

Abstract Primary energy implications over the life cycle of a multi storey residential building with different building systems are explored here. The main structural materials of the buildings include precast concrete, cross laminated timber (CLT) and prefabricated timber modules (modular). The analysis covers energy and material flows from different life cycle phases of the building versions, designed to meet the energy performance of the Swedish building code (BBR) and passive house criteria. The CLT and modular buildings were found to result in lower production primary energy use and higher biomass residues compared to the concrete alternative. The heating value of the recoverable biomass residues from the production phase of the CLT building is significantly larger than the primary energy required for its production. Primary energy use for production and construction constitutes 20–30% and 36–47% of the total primary energy use for production, construction, space heating, ventilation and demolition for the BBR and passive buildings, respectively. Space heating with combined heat and power (CHP) and ventilation electricity for the BBR and passive building versions form 70–79% and 52–63%, respectively, of the total primary energy use for production, construction, space heating, ventilation and demolition for a lifespan of 80 years. The CLT and modular buildings give 20–37% and 9–17% lower total life cycle primary energy use, respectively, than the concrete alternative when space heating is from CHP.

Abstract We analyse the life cycle carbon implications of a building, with structural frame of prefabricated concrete, prefabricated modular timber or cross laminated timber (CLT) elements, designed to meet the Swedish passive house criteria. The analysis covers non-biogenic carbon flows related to the building alternatives, over an assumed life time of 80 years. The building alternatives are all modelled to have the same housing service and operation energy demand. Substitution factors, showing the efficiency of CO2 emissions reductions when wood alternatives are used instead of non-wood alternatives, are calculated for the CLT and modular alternatives with reference to the concrete alternative. The results show that the CLT and modular buildings give less carbon emissions to the atmosphere during production and when the buildings are demolished at the end-of-life. Moreover, the wood residues from the production and end-of-life activities for the timber alternatives far exceed that for the concrete alternative. The substitution factors differ slightly between the CLT and the modular alternatives, and are significantly lower when fossil gas is substituted by wood residues instead of fossil coal. In summary, the life cycle carbon emissions are significantly lower for the timber alternatives.

In this study we explore key parameter values, methods and assumptions used for energy balance modelling of residential buildings in the Swedish context and analyse their effects on calculated ener ...

In this study, we explored the effects of different design strategies on final and primary energy use for production and operation of a newly constructed apartment building. We analysed alternatives of the building “As built” as well as to energy efficiency levels of the Swedish building code and passive house criteria. Our approach is based on achieving improved versions of the building alternatives from combination of design strategies giving the lowest space heating and cooling demand and primary energy use, respectively. We found that the combination of design strategies resulting in the improved building alternatives varies depending on the approach. The improved building alternatives gave up to 19–34% reduction in operation primary energy use compared to the initial alternatives. The share of production primary energy use of the improved building alternatives was 39–54% of the total primary energy use for production, space heating, space cooling and ventilation over 50-year lifespan, compared to 31–42% for the initial alternatives. This study emphasises the importance of incorporating appropriate design strategies to reduce primary energy use for building operation and suggests that combining such strategies with careful choice of building frame materials could result in significant primary energy savings in the built environment.

Abstract Here, we analyse final and primary energy savings and overheating risk of deep energy renovation of a Swedish multi-storey residential building of the 1970s under climate change and consider overheating control measures to reduce cooling demand and risk of overheating. The energy-efficiency measures include additional insulation to basement walls, exterior walls, and attic floor as well as improved energy-efficient windows and doors, balanced ventilation with heat recovery (VHR), lighting, household appliances as well as water taps and shower heads. The future climates are based on the representative concentration pathways scenarios. We find that implementing improved energy-efficient windows and doors, VHR and additional insulation to external walls give significant final and primary energy savings for space heating. The total operation final and primary energy use decrease averagely by 58% and 54%, respectively when all the measures are cumulatively applied under both current and future climate scenarios. Efficient household appliances and lighting as well as appropriate overheating control measures significantly reduce cooling demand and risk of overheating. The indoor air temperature and overheating risk as well as the final energy savings are influenced by the considered climate scenarios.