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The building design process is crucial in efforts to implement energy-efficient practices by adopting Energy Efficiency Measures (EEMs). However, design choices based solely on reducing operational energy use can significantly increase a building's embodied energy and Life Cycle Energy (LCE) use, because there is a trade-off between embodied and operational energy. This article presents a case study in which multi-objective optimization was used to explore the effects of various EEMs on the aforementioned trade-off. Optimal solution(s) for six different building shapes (rectangular, H-, U-, l -, T- and cross-shaped) based on two sets of EEMs were investigated and compared. The first set of EEMs consisted of EEMs that can be implemented or modified during the early design phase, such as the building's shape, orientation, Window to Wall Ratio (WWR), and constituent materials. The second set comprised EEMs that can be implemented later in the design phase (i.e. EEMs relating to the constituent materials). The LCE reductions achieved by finding optimal solutions for EEMs in the first set (ranged from 2175.2 to 3803.8 GJ) were significantly (over 5 times) higher than those achieved for the second set (ranged from 418.6 to 625.6 GJ) for all building shapes. Moreover, LCE use for pre-optimization building designs varied significantly with building shape. However, after optimization, the differences in LCE use between the optimal solutions of different building shapes were modest. This means that designers and construction companies can select building shapes based on customer requirements, but also highlights the importance of using multi-objective optimization during early design process to identify optimal combinations of EEMs that minimize LCE use.

The building design process plays a central role in efforts to implement energy-efficient practices. However, unilateral design choices based solely on reducing operational energy use can significantly increase a building’s embodied energy and life cycle energy use as there is a trade-off between embodied and operational energy. To support such trade-off problems, multi-objective optimization represents a useful approach that produces a set of optimal solutions from where a solution can then be selected and progressed within the design process. Selecting one solution from the set of optimal solutions can however be a challenging task as each solution has the potential to be chosen as the optimum. Therefore, the purpose of this study was to explore how solutions from a multi-objective optimization approach can be analyzed further to provide information to decision-makers when selecting the optimal design solution. An approach is proposed where the integration of post-optimization sensitivity analysis into a multi-objective optimization approach aims to support decision-makers in analyzing the optimal solutions provided by the optimization process. The applicability of approach is demonstrated using a case of a multifamily apartment building located in Sweden, where the aforementioned trade-off is explored for a set of energy efficiency measures. Thereby, a diverse range of optimal solutions that could result in up to 4520 GJ life cycle energy (LCE) savings relative to the case building’s initial design was initially identified using the multi-objective optimization. These solutions were then subjected to a sensitivity analysis where the results indicated that in general the lowest and highest sensitivity in terms of LCE use belonged to the insulation thicknesses in roof and walls, respectively. Furthermore, the thickness of exterior floor insulation yielded the greatest variation in the sensitivity. The findings of case study indicate that the post-optimization sensitivity analysis can add valuable information that complements the results obtained using a multi-objective optimization approach. Consequently, it can support decision-making on how to progress with the design in terms of what design parameters have a negligible or significant impact on the objectives when they are varied, thus facilitating prioritization.

Design choices with a unilateral focus on the reduction of operational energy for developing energy-efficient and near-zero energy building practices can increase the impact of the embodied energy, ...

Assessment of the embodied energy associated with the production and transportation of materials during the design phase of building provides great potential to profoundly affect the building’s energy use and sustainability performance. While Building Information Modeling (BIM) gives opportunities to incorporate sustainability performance indicators in the building design process, it lacks interoperability with the conventional Life Cycle Assessment (LCA) tools used to analyse the environmental footprints of materials in building design. Additionally, many LCA tools use databases based on industry-average values and thus cannot account for differences in the embodied impacts of specific materials from individual suppliers. To address these issues, this paper presents a framework that supports design decisions and enables assessment of the embodied energy associated with building materials supply chain based on suppliers’ Environmental Product Declarations (EPDs). The framework also integrates Extract Transform Load (ETL) technology into the BIM to ensure BIM-LCA interoperability, enabling an automated or semi-automated assessment process. The applicability of the framework is tested by developing a prototype and using it in a case study, which shows that a building’s energy use and carbon footprint can be significantly reduced during the design phase by accounting the impact of individual material in the supply chain.

A bottom-up dynamic modeling framework aiming to incorporate realities of the decision-making process when implementing energy-saving building renovations is proposed and applied to a case study of all multifamily buildings in Gothenburg, Sweden. The developed model is based on real conditions of existing buildings, from the national Energy Performance Certificate database, building and property registers, and cadastral maps from the city planning office. Although explorative, the framework accounts for the reaction capacity in terms of (i) investments by all property owners and (ii) total workmanship capacity in the city. Two scenarios were considered to account for renovations driven solely by technical renovation needs (end-of-life of building components) and by cost efficiency; further, both scenarios were investigated at different levels of reaction capacity. The developed framework is easily replicable to other regions and cities. The retrofitting includes, as individual measures as well as in packages, increased insulation levels, increased efficiency of lighting and appliances, and the installation of heat recovery systems and photovoltaic panels. Whereas implementation of energy-efficient measures dictated solely by technical renovation needs led to a very low energy demand, with some buildings becoming energy producers by 2050, implementation strictly driven by cost-efficiency (from the perspective of the property owners) only reduced the energy demand by 5% during this time and would not fully utilize the investment capacity of the property owners. Furthermore, the current limitations of reaction capacity for the market shares allowed for a reduction of the energy demand by only 15% during the same period. Workmanship capacity was more constraining than investment capacity and is thus identified as a local imperative need and suggests co-benefits related to job creation within the construction sector.

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.

Green roofs are complex technology systems, adopting a vegetation layer on the outermost surface of the building shell. A proper design implement environmental and energy benefits. Green roof are aimed to reduce roof temperature and thus the summer solar gains, without worsening the winter energy performance. Most studies evaluating green roof performance have been conducted in warmer climates. There are very limited studies of green roofs in cold climate. Some research has investigated the thermal effect of the snow layer on green roof. But no study has so far evaluated the energy performance of green roof in sub-arctic climate. This study evaluates the heat flow and thermal effect on a green roof situated on a passive house building in the sub-arctic town Kiruna, Sweden for a period from 25th of October—4th of January. The ongoing measurements of temperature and heat flux is done on an extensive green roof and compared to the same roof covered solely by a roofing felt layer. The fluctuation in temperature was consistently higher for the roof with the roofing felt layer than for the green roof. But the surface temperature of both roofs was getting more and more align as the roofs are covered by snow during November and December. However during December month the green roof had a higher heat flux out of the building compared to the black roof.

Evaluation of carbon impacts during building design has for too long unilaterally focused on the operational carbon impacts through the application of Energy Efficiency Measures (EEMs), e.g. enhancing the thermal resistance of the building envelope by using additional insulations, Window to Wall Ratio (WWR) etc. Research indicates that there is a need to also include the embodied carbon impacts and optimizing the trade-off between embodied and operational carbon impacts. Multi-objective optimization approaches can be a solution for handling this trade-off. Therefore, a previously developed BIM-based multi-objective optimization approach has been extended to also cover the impact of the carbon footprint. The extended optimization approach was then tested in a case study of a multifamily residential building located in Stockholm to find the optimal design solutions of the embodied versus operational carbon impact trade-off. The results of the case study demonstrate the applicability of the extended approach in handling the trade-off problem and aiding in more environmentally friendly decisions during the design process.

Research indicates that the operational energy and the embodied energy caused by production of building materials off-site (i.e., "cradle-to-gate" embodied energy) contribute to the major part of a ...

The building sector contributes significantly to the energy use and related greenhouse gas (GHG) emissions. Prior research has mainly focused on the impacts associated with material selection and b ...

The construction and operation of buildings account for a significant part of the energy use and greenhouse gas emissions. Most design approaches to reduce the use of energy are focusing on the ope ...

Construction and operation of buildings and infrastructure is a main contributor to emissions of greenhouse gases (GHG) in Sweden. The embodied energy of construction, meaning all the energy that is used until the completion of the construction project, cause roughly 10 million tones of CO₂ equivalent emissions each year which equals to the emissions from all cars in Sweden (IVA 2014). About 6 million tones of CO₂ equivalent emissions are attributed to the embodied energy of roads, railroads and other civil works while the remaining 4 million tones are attributed to the embodied energy of buildings (IVA 2014). Although reducing energy use and associated GHG-emissions in road and railroad construction is prioritized by the Swedish Transport Administration (Trafikverket 2012), the GHG-emissions from such construction projects have increased in recent years (Boverket 2014). Many of the existing efforts to reduce energy use and associated GHG-emissions focus on individual phases of the life cycle and don’t take into consideration the effects at other stages during the whole life cycle of a project (Boverket 2011). A crucial step in the assessment of energy use and associated GHG-emissions is to clarify and categorize the different phases of a life cycle. Figure 1 shows a proposed categorization of life cycles phases and use of energy based on previous research (Davies et al. 2014). Buildings’ main use of energy happens during its operational phase from e.g. heating, lighting and use of electrical appliances (Sartori and Hestnes 2007). In infrastructure projects such as road construction the embodied energy is roughly equal to the operational energy for roads with lighting, or in fact considerably higher if the road lacks lighting (Stripple 2001).