Retrofitting of Norwegian Office Buildings towards Nearly Zero Energy-Technical, Environmental, and Economic Aspects
Abstract
The increasing proportion of energy use for buildings in urban environments has necessitated energy efficiency and advancement of the sustainable transformation of building stock towards the zero energy/emission level. In cold climate countries, such as Norway, the building energy efficiency is even more challenging due to cold climate conditions and high heating needs, which accounts for 40-60% of the total energy use. Apart from the energy use, the importance of indoor air quality (IAQ) in well-being and productivity of occupants in non-residential buildings, e.g. offices, cannot be ignored since the occupants spend a lot of their time in the indoor environment. Developing efficient approaches of building retrofitting by taking advantage of sustainable retrofitting technologies plays a key role in achieving such transformation. However, critical assessments of sustainable retrofitting interventions and their effectiveness are still restrained by the deficiency in systematic integration of modelling tools. These were addressed in this thesis with respect to retrofitting the Norwegian office buildings.
The thesis aims at facilitating the development of modelling methods to assist the sustainable retrofitting in the Norwegian office buildings towards the nearly zero energy building (nZEB) level.
In the first step towards nZEB level, various retrofitting scenarios were modelled and analyzed for a typical Norwegian office building of 3000 m2 area through two different optimization approaches. In the first approach, the existing building characteristics were selected based on the Norwegian building code TEK 10 (2010 onwards), and small retrofitting measures (small cost-effective retrofit measures recommended in literature studies) were applied. In the second approach, the TEK 87 (1980s) building requirements were considered for the reference case and larger number of renovation measures were included. In this regard, the retrofit alternatives studied include the renovation of building envelope, fenestration, HVAC system and set points, window opening and shading control methods, and shading materials. Combined impacts and interdependencies among retrofits were also investigated. The optimization framework was developed through a Graphical Script module that implements the connection among input, constraints, and outputs through a visualization interface. In addition, a post-processing detailed computational fluid dynamics (CFD) and daylight analysis was conducted for the optimal solution. The results in the first optimization approach showed that, compared to the reference case building, the energy saving potential of the retrofit measures was 43-56% in various cases in the small retrofitting strategy. Furthermore, the results showed that the high-quality window and external wall were always used in the optimized solutions, but the ground floor and the roof retrofitting were the costliest options and were recommended to be used only when the reduction of operational cost due to energy use was higher than the increase of the investment cost. According to the optimization results in the second retrofitting approach, the building energy use could be significantly reduced up to 77%, compared to the reference building case, while satisfying the thermal and visual comfort conditions. The results of second optimization approach also revealed that both optimized cases equipped with the radiator space heating (RSH) and all-air (AA) systems could satisfy the thermal comfort requirements, based on the comfort category II, for longer period of the year compared to the reference case. Additionally, the AA optimized case showed a better performance in terms of both thermal comfort and visual comfort conditions compared to the RSH optimized case. Various ventilation control strategies in AA cases allowed a better selection of optimization design variables, especially window to floor ratio and shading device control methods affecting the daylight conditions significantly.
Lastly, life cycle assessment (LCA) of CO2-eq emissions was performed for the reference case TEK87 and the optimal solutions in the first optimization approach. The results showed that, compared to the reference building, the greenhouse gas (GHG) emissions associated with the operational energy use could be reduced up to 73% for the retrofitting strategies equipped with AA system. In this regard, the reduction of emissions associated with the operational energy use overweighted the produced embodied emissions of extra materials in the optimal solutions.
It is worth mentioning that the optimization approaches proposed in this thesis can be used at any stage of building design process and can help to improve the robustness of the building design to achieve a nZEB in Norway.
Has parts
Paper 1: Rabani, Mehrdad; Madessa, Habtamu Bayera; Mohseni, Omid; Nord, Natasa. Minimizing delivered energy and life cycle cost using Graphical script: An office building retrofitting case. Applied Energy 2020 ;Volum 268. https://doi.org/10.1016/j.apenergy.2020.114929 This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).Paper 2: Rabani, Mehrdad; Madessa, Habtamu Bayera; Nord, Natasa. Achieving zero-energy building performance with thermal and visual comfort enhancement through optimization of fenestration, envelope, shading device, and energy supply system. Sustainable Energy Technologies and Assessments 2021 ;Volum 44. https://doi.org/10.1016/j.seta.2021.101020 This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Paper 3: Rabani, Mehrdad; Madessa, Habtamu Bayera; Nord, Natasa. Building retrofitting through coupling of building energy simulation-optimization tool with cfd and daylight programs. Energies 2021 ;Volum 14.(8) s. 1-23 https://doi.org/10.3390/en14082180 This is an open access article distributed under the Creative Commons Attribution License (CC BY 4.0)
Paper 4: Rabani, Mehrdad; Madessa, Habtamu Bayera; Ljungström, Malin; Aamodt, Lene; Løvvold, Sandra Emilie Aasestrand; Nord, Natasa. Life cycle analysis of GHG emissions from the building retrofitting: The case of a Norwegian office building. Building and Environment 2021 ;Volum 204. https://doi.org/10.1016/j.buildenv.2021.108159 This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).