Marta Piñeiro _ Master Thesis by Marta Piñeiro Lago

Aiming for Zero Emissions in a high-rise building Methodological analysis of an Integrated Design Process Marta PiĂąeiro Lago

Masterâ&#x20AC;&#x2122;s thesis in Sustainable Architecture Supervisors: Luca Finocchiaro and Gabriele Lobaccaro Trondheim. June 2018

Acknowledgements I would like to express my special thanks and appreciation to my supervisors, Luca Finocchiaro and Gabriele Lobaccaro, for their patience and constant support throughout the whole process. This master thesis would not have been possible without your advice. I would also like to thank to the rest of the teachers in the Master in Sustainable Architecture for their implication and all the priceless knowledge. I want to express my gratitude to Kristian Edwards and Snøhetta, for providing me with all the information that I needed from the case study building. Thanks to Nils Erik Anders Rønnquist and Bendik Manum for your advice regarding the implementation of the structural system. I am also especially thankful to Aitor Almaraz, for his highly appreciated help with the structural calculation and honest advice. I would like to give a heartfelt thanks to my parents, Carlos and Josefa, for their education, support and understanding. Thanks to you I have been able to experience this unique opportunity not only to study, but to grow surrounded by such an amazing international group of people. I am also veru thankful to my second family here in Trondheim: Raquel, Anxo, Borja, Rubén, Mi Chi, Roberto, Giorgia, Juan, Luca, Camilo, Marilú, Carmen, María and Alexis, for all the dinners, parties, ski trips and so much fun together. Home does not fell so far away when I am surrounded by all of you. Special mention to my awesome classmates from the Master in Sustainable Architecture at NTNU. I could not have been luckier to share these two years with all of you. Special thanks to my inseparable colleagues, Juanma Cruz, Irene Hutami and Nikita Chhajer, for all the moments shared together and friendships that do not care about cultural differences. Finally, I could not end this work without thanking my companion in life, Jairo Rúa, for your patience in reviewing this thesis and the constant jokes to make me laugh during stressful moments.

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Abstract The majority of the population lives in cities, which have been steadily growing due to the continuous increase of inhabitants. In this socio-economic context, population condensation has proven to be the most sustainable urbanism approach,and high-rise buildings emerge as the architectural typology that has been most utilized in order to achieve a sustainable urban model of development. In the current global situation, 32 % of total global ďŹ nal energy use and 19 % of energy-related GHG emissions are due to the building sector. Thus, ďŹ nding a way to build more sustainably is not a possibility, but an urgent need. This thesis develops a methodology that will allow to design high-rise buildings aiming to achieve the Zero Emission Building Standard (ZEB). The methodology is developed through a Case Study High-Rise Building with a climate-adapted design. Parametric tools are implemented towards optimizing the shape and structure of the building and maximising on-site energy production. In addition, Life Cycle Assessment preliminary data and the use of passive strategies are taken into consideration in order to assure a sustainable design.

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Index

Introduction Motivation _ 10

Climate-adapted built form Optimisation parameters _ 30 Design of the geometries to be tested _ 30 Wind optimisation _ 32

State of the art _ 1 1

Solar optimisation _ 38

Aim of the thesis _ 12

Selected geometry _ 42

Methodology _ 13

References _ 49

References _ 15

Case study analysis _ 1 1 Climate analysis _ 12 References _ 27

Preliminary analyses

-6 -

Envelope design Envelope characteristics _ 64 Perforation _ 65 Transparency_ 66 Insulation _ 70 Environmental impact _ 72 Final envelope design _ 73 Variability _ 76 References _ 79

Preliminary considerations _ 52 Structural core _ 53

Structural system selection _ 55 Design and calculation of the deiagrid system _ 58 References _ 61

Structural system

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Process overview _ 82 Adopted design solutions: Findings and conclusions _ 82 Methodology implemented: Findings and conclusions _ 84 Further work _ 84

Conclusion & discussion

Introduction

Aiming for ZEB in a High Rise Building

1. Introduction

1.1. Motivation Urban densiﬁcation has motivated the development of tall building structures as a socio-economic solution for the population growth. Large amounts of greenhouse gas emissions are associated to the construction increase of this architectural typology. Hence, designing sustainable yet functional high-rise buildings has become a major need in the last decades. According to the Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), in 2010 alone, the building sector accounted for 32 % of the total global energy use and 19 % of energy-related greenhouse gas (GHG) emissions. Those emissions added up a total of 49 gigatonnes of CO2 equivalent (Gt CO2 eq) released to the atmosphere (Fig. 1) [1], meaning that 9.31 Gt CO2 eq were directly related to the building sector. In the case of the United States of America, the third most populated country in the world behind China and India [2], 39 % of the total

In China, the biggest pollutant country in the world, the building sector is becoming the second largest carbon emitter [4]. In 2012, China building sector’s emissions of CO2 equivalent raised up to 1600 million tonnes of carbon dioxide, 1200 millions of them due to indirect emissions and 400 million tonnes to direct emission [5]. When it comes to Norway, the building sector consumes around 50% of the total electricity production. The GHG emissions depend on the primary energy source for electricity and heat, which is hydropower in the case of Norway. Thus, embodied emissions related to this sector are lower than in most industrialised countries [6]. Despite its low GHG emissions in the building sector, Norway’s greenhouse gas emissions accounted for 52.8 million tonnes of CO2 equivalent in 2013, meaning that in order

50%

2050

75%

to fulﬁl the Paris Agreement, Norwegian overall emissions must be further reduced to 45-47 million tonnes of CO2 equivalent in 2020 [7]. In this international agreement, 195 United Nations member states agreed to limit the global temperature rise below 2 degrees’ Celsius in respect to pre-industrial levels by 2100. According to scientiﬁc consensus documented by the IPCC, this implied to decrease the emissions in 1000 billion tons of CO2 equivalent worldwide starting in 2011 [8].

32% Industry 25% Emissions CO2 eq

2017

Fig. 2: Global population distribution (data from the Food and Agriculture Organisation of the United Nations -FAO-, 2016).

In 2010, a total of 49 Gt CO2 eq were emitted to the atmosphere

19%

Urban population

Rural population

emissions of GHG are due to this building activity, followed by the 33% of transportation and 29% of industry [3].

In the particular case of Norway, the creation of the Norwegian Climate Act constitutes a commitment to reduce GHG emissions by 40% from pre-industrial levels by 2030, and aims for a further reduction targeting 80-95 % by 2050, in line with EU aspirations [8]. In light of the Food and Agriculture Organisation of the United Nations (FAO) statistics, in 25 years, 75 % of the population will live in cities, while the rural population will be decreased up to a 25 % (Fig. 2) [9]. Moreover, 100 billion people are currently homeless, and 1 billion

AFOLU*

Buildings

3 billion people in the next 20 years

40%

Economic sectors

of the current population

*Agriculture, forestree and other land use

Fig. 1: Emissions of CO2 eq by economic sector (data form the IPCC, 2014).

Fig. 3: Future global population scenario.

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Aiming for ZEB in a High Rise Building

1. Introduction

The role of high-density development for a more sustainable growth

Low density

vs.

High density

Fig. 4: Comparison between high and low development models.

live in slums [10]. It is expected that in the next 50 years a considerable percentage of people in developing countries will have access to adequate housing, electricity, and improved cooking facilities. According to the IPCC “The ways in which these energy-related needs will be provided will signiﬁcantly determine trends in building energy use and related emissions” [1]. Furthermore, as stated by the Canadian architect Michael Green [11], in the next 20 years, world population is expected to be increased by 3 billion people, which represents the 40% of the current global population (Fig. 3). When thinking about such a large number, a highdensity urban model of development seems like the only feasible solution (Fig. 4). High-rise buildings are deﬁned as the architectural typology in which the dimension on its vertical axis (height) is dominant over the horizontal dimension [12]. This implies a reduction on the footprint and therefore, a higher

embodied emissions may double or potentially triple by the next half of the century” [1]. In either case, the new construction activity in developing countries has promising mitigation opportunities albeit the associated signiﬁcant risk [1].

most common candidates to replace concrete or steel. This tendency relies on the fact that , due to their carbon sequestration capacity, massive wood products combine the advantages of a sustainable material with those of industrialised processes.

Recent improvements in building’s technology and know-how have enabled construction and retrofit of very low or even zero energy buildings in developed countries. These retrofitting works have sometimes a high initial investment cost but are cost-effective within the building’s lifetime. In existing buildings, energy savings between the 50 to 90 % of the initial energy consumption have been achieved through deep retrofits [1]. Besides, the use of energy-efficient appliances in lighting and information communication can reduce the substantial increases in electricity use that is expected due to the proliferation of different types of equipment and electronic gadgets used in every day’s contemporary lifestyles.

As an illustration, the carbon storage capacity of a single tree can reach up to 150 Kg of CO2 during its lifetime [15], just by the simple process of photosynthesis. It is estimated that forests could potentially globally sequester up to 2000 million tonnes per year [16]. When using a negative accounting method for the carbon stored in the material, this storage capacity allows compensating the CO2 embodied emissions of the end of life phase. The actual rate of carbon sequestration may vary among the different species. However, younger and fastergrowing trees have higher annual sequestration rates [16]. These are precisely the most suitable kind of species for the fabrication of massive timber products since they allow to increase the production while maintaining a sustainable forest exploitation.

Cities, as we know them nowadays, are predominantly made from steel and concrete. These main construction and structural materials have great embodied emissions due to fabrication and production processes. For instance, in a cradle to gate scope (A1 to A3 according to the System Boundary EN 15804:2012), one cubic meter of in-situ concrete may account for up to 188,23 kg CO2 eq [13], while the embodied emissions for a single cubic meter of structural steel may account for up to 10.68 kg of CO2 eq [14].

density ratio. Due to a lower per capita energy use, which is mainly caused by a reduction in transportation energy, compact or high-density urban models are identiﬁed by the IPCC as an important sectoral climate mitigation measure [1]. In this kind of development models, highrises play an important role. However, there is no international agreement on a minimum height for this architectural typology, as if a building might be considered or not a high-rise depends on its urban context. In Norway, buildings higher than six storeys may already be considered as high-rise buildings in most urban fabrics.

Accordingly, research in the architectural ﬁeld is being oriented towards more energy efﬁcient buildings and the use of more sustainable materials. There is a clear tendency in the current architectural scenario in developing structural prototypes and alternative solutions to conventional structural materials using timber-based products. Industrialized massive wood products such as cross-laminated timber (CLT), laminated veneer lumber (LVL) or glued laminated timber (glulam) are nowadays the

1.2. State of the art According to this aforementioned report, “the key trends that constitute population growth, migration to cities, household size changes, and increasing levels of wealth and lifestyle changes will contribute to signiﬁcant increases in the building‘s energy use. This energy use and its

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In a cradle to gate scope, the use of CLT can suppose up to -601.77 kg CO2 eq per cubic meter of material [17], while a cubic meter of Glulam can suppose up to -629.76 kg CO2 eq [18]. Nevertheless, the embodied emissions in an A1 to A3 phase (production of the materials) for timber-based products can widely vary depending on the Environmental Product Declaration (EPD) database utilised and the accounting method. As a common practice, timber products from sustainably grown forests tend to be considered as carbon neutral since the CO2 emissions released during its combustion at the end-of-life stage are assumed to be resequestered in the growing phase [19]. Due to their minimum footprint and high compactness, high-rise buildings are the most common architectural typology in contemporary cities. The reduction of CO2 embodied emissions due to materials in a high-rise building can be specially noticed in the case of its structure, since

Aiming for ZEB in a High Rise Building

it represents the highest percentage of material in a building. This fact can make a net difference of thousands of kg CO2 eq per structure built. In order to measure the carbon footprint of a building, the life cycle assessment (LCA) was introduced in the architecture field in the ‘60s. This concept emerged as a consequence of the increasing concerns over the limitations of raw materials and energy resources. There was an increase of interest in finding ways to cumulatively account for energy use and to project future resource supplies and use [20]. Today, this method is utilised in the architecture field as a tool for decision-making support to assess the environmental impact of a building through its lifetime [19]. In order to encourage the reduction of GHG emissions due to the building sector activities, official certifications for sustainable and energy efficient buildings were introduced in the ‘90s. Widely known examples of these certifications are the Building Research Establishment’s Environmental Assessment Method (BREEAM) or the Leadership in Energy and Environmental Design (LEED) [21].

1. Introduction

When considering the LCA of a building from a cradle to cradle scope (which means through all the stages of a building’s lifespan within the system boundary EN 15804:2012), operational energy use has traditionally been identified as the main contributor to the GHG emissions [26]. Nevertheless, due to the increase in the regulations’ requirements regarding buildings’ energy efficiency, this stage of the LCA has considerably reduced its environmental impact during the past years [26, 27]. As a result, embodied emissions related to materials from the production and replacement stages are gaining significance [28]. A careful choice of materials can significantly help to achieve a Zero Emission Building standard and consequently, an active reduction in the embodied emissions. However, this approach is not enough if it is not combined with additional energy saving measures such as passive strategies or a climateadapted building design.

Within the Zero Emission Building concept, ﬁve different ambition levels are deﬁned. The lowest ambition level is ZEB-O-EQ, which is achieved when the building’s energy production through renewable energy sources compensates for the embodied emissions of the building’s operation (O), excluding the energy use for appliances and equipment (EQ). The second level, ZEB-O, is similar to the previous one but including

nmental pe viro rfo n E r

e ac m

Moreover, in order to prevent an increase of the global warming effect, national and international initiatives and regulations play an important role. For instance, at the European level, the revised directive on Energy Performance of Buildings (EPBD) of 2010 establishes the nearly Zero Energy Building (nZEB) as the building target from 2018 for all public buildings, and from 2020 for all new buildings [22].

A holistic approach to the architectural design process for high-performance building design and construction is called Integrated Design Process (IDP). It relies on the idea that every decision on the initial stages of the design will have an impact on the performance of the final architectural result (Fig. 5). In order to do that, every member of the team is supposed to shear a common vision of sustainability and work collaboratively to implement the sustainable goals. To apply this complex design process, wide multidisciplinary teams are often required. Since its first application in the 1990’, IDP has been proved to produce more significant results than investing in capital equipment upgrades at

Envir on m

and inte gra sign de ti

ct impa tal en

Energy s yst e

During the past decades, the concept of ZEB has also been widely spread. However, this acronym is linked to a certain degree of confusion since it has two possible signiﬁcances. The ﬁrst one is Zero Energy Building, which is probably the most popular interpretation. This term makes reference to the total building’s energy balance which is supposed to be equal to zero, meaning that the energy demand is balanced with the energy production of the building by means of renewable energy sources.

the energy use for appliances and equipment. The third level, ZEB-OM, compensates for the emissions due to the operation and materials (M). In the fourth level, ZEB-COM, construction (C), operation and embodied emissions due to materials are taken into consideration. Lastly, the highest ambition level is ZEB–COMPLETE, which takes into account all the previous stages, with the addition of the demolition and recycling phases [24, 25].

The second one makes reference to the Research Centre on Zero Emission Buildings (ZEB), which was funded by the Norwegian Research Council in 2009 [6]. The scope of this deﬁnition for the Zero Emission Buildings goes beyond the conventional deﬁnition of Zero Energy Buildings since the research carried out by the ZEB Centre is mainly focus on the overall CO2 eq emissions, minimising the building’s global warming potential through the assessment of its life cycle analysis (LCA). In other words, the aim of this research centre is to create buildings with zero GHG embodied emissions related to their production, operation and demolition [23].

Fig. 5: Integrated energy system concept.

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later stages [29].

1.3. Aim of the thesis In this master thesis, an Integrated Design Process will be applied to the design of a highrise building, creating a methodology that may allow achieving a Zero Emission Building. Departing from the assumption that massive timber products have lower embodied emissions than any other frequently used structural material, the possibilities of timberbased structural systems will be explored within the case of a high-rise building. Rather than focus on the ﬁnal optimal solution, the main purpose of this master thesis will be to design a methodology for the integrated design process of this building typology in a cold climate with the support of parametric design tools and available simulation software. Thus, of the whole integrated design process of a Zero Emission Building, this thesis will only focus on the stages previous to the balance of the CO2 emissions with renewable energy sources, which would later allow achieving this zero emission standard. Henceforth, the direction of this thesis will be towards the reduction of the energy consumption and embodied emissions by the implementation of a climate-adapted built form, passive strategies and optimisation of materials.

Research question According to the previously explained, the research question of this master thesis will be: what methodology should be followed and which parameters should be selected for an Integrated Design Process to minimise the environmental impact of a high-rise building?

Aiming for ZEB in a High Rise Building

1.4. Methodology The recent diffusion of advanced simulation software has modiﬁed the creative process through which architecture is conceived. This software offers an estimation of the environmental behaviour of different built forms, conditioning the canons on which the aesthetics of the project is based. This simulation and computational software can be utilised throughout the design process, ensuring a meaningful basis for the production of sustainable forms. In an ordinary building design process, the task ﬂow has been traditionally a linear and sequential set of activities [30]. However, the Zero Emission objective requires an iterative process that embraces the integration of sustainable goals early in the design process through energy performance and emissions accounting calculations (Fig. 6) [31]. Experience

1. Introduction

and materials of the building, the parameters addressed in this case will be: maximise energy efﬁciency, ensure an optimal production of on-site renewable energy, and minimise the embodied emissions due to materials.

with constructed nearly Zero Energy Buildings, shows that their design process is based on cyclic iterations and simulation-based decision making that effectively integrates, in early stages of the process, all aspects of building design, energy efﬁciency, daylight autonomy, comfort levels, and innovative solutions related to energy production and technical equipment [32].

A possible approach that would allow solving this complex optimisation problem is a multiobjective optimisation through parametric design [25]. In comparison with a conventional approach where alternative design solutions are modelled and tested, parametric models made it possible to generate forms where the solution to a speciﬁc numerical problem is already embedded [34]. However, the results of these machine-driven optimisations are usually far from a rational design in terms of conventional standardised elements for construction. Thus, instead of relying solely on the machines’ mathematical capacity to solve this complex optimisation problem, a balance between a scientiﬁc method and an intuitive approach will be implemented throughout the design of this proposal, combining numerical analysis and literature review with the intuition of the educated architect. The manual optimisation of these three parameters will be achieved by conducting trial-and-error analysis with the help of parametric tools and simulation software to analyse the environmental behaviour of the proposed solution.

As a matter of fact, 80% of all design decisions taken subsequently are inﬂuenced by the 20% of design decisions in early design phases [33]. Henceforth, choosing the key parameters to consider in order to achieve a sustainable highrise, as well as the methodology implemented to analyse those parameters, are decisive factors towards achieving a Zero Emission Building. Assuming that the main drivers on the GHG emissions will be those related to the operation

In order to create a precise design based on a particular location, Snøhetta’s Gullhaug Torg project in Nydalen, Oslo, is selected as a case study in order to set the boundary conditions that will serve as the starting point for a new design. The methodology that will be implemented is divided in four stages. Firstly, the method departs from a preliminary analysis of this case study building and the climate analysis from its location (Chapter 2). Secondly, it is followed by the design of a climate-adapted built form (Chapter 3). Thirdly, the analysis and decision on the structural system (Chapter 4). Lastly, the design of the exterior envelope of the

Fig. 6: Iterative design process.

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building (Chapter 5). As a consequence of the whole design process, an energy demand and embodied CO2 emissions would be obtained (Fig.7). This data would be used to achieve a Zero Emission standard in a further development of the design, which will not be assessed in this thesis. For the case of the climate-adapted built form, the main drivers towards the selection of the building’s shape will be the wind pressure due to prevailing winds and solar radiation. The former aims to minimise the drag force over the building´s envelope, while the study of the latter will allow maximising both solar exposure and solar heat gains. The design of the structural system will rely on the selection of construction and structural materials with lower embodied emissions and the minimisation of those materials. Lastly, the main objectives of the envelope design phase will be to achieve good daylight levels and a satisfactory natural ventilation inside the living spaces of the building. As previously mentioned, since these kind of design processes are iterative, some considerations that otherwise would not be addressed until the next chapter must be taking into account when dealing with the previous parameter. As an example, when addressing the issue of the location for the structural cores, daylight and natural ventilation strategies that will be addressed in the following step of the design will be affected by this decision. Therefore, some previous considerations on these passive strategies must be applied in this phase of the process. This reciprocity during the design process is what makes this kind of projects both complex and interesting.

Aiming for ZEB in a High Rise Building

1. Introduction

4. Envelope Daylight & Natural ventilation

3. Structural system Environmental performance & program distribution

2. Climate-based built form Wind pressure & Solar radiation

1. Preliminary analysis Case study & Climate

5. Energy Energy production & Energy demand

Fig. 7: Scheme of the methodological process and software that will be implemented in this master thesis.

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Aiming for ZEB in a High Rise Building

1. Introduction

References eprint/13467/1/WorldEnergyOutlookSpecialReport2016EnergyandAirPollution.pdf. [6] T. R. C. f. Z. E. B. (ZEB), C. f. E.-F. E. R. (CEER/FME), Ed., ed. Beijing, 2009, p. 21. [7] A. A. Are Lindegaard, Andreas Andersen, Stian Rein Andresen, Torgrim Asphjell, Ellen Bruzelius Backer, Kenneth Birkeli, Katja Ekroll, Helene Frigstad, Henrik Gade, Eilev Gjerald, Hege Haugland, Britta Maria Hoem, Nina Holmengen, Isabella Kasin, Hans Kolshus, Maria Malene Kvalevåg, Hanne Birgitte Laird, Christine Maass, Elisabeth Møyland, Hege Rooth Olbergsveen, Tone Sejnæs Pettersen, Simen Helgesen Ramberg, Bente Rikheim, Audun Rosland, Sissel Sandgrind, Odd Kristian Selboe, Svein Grotli Skogen, Fredrik Weidemann, Elin Økstad, “Knowledge base for low-carbon transition in Norway. Summary,” Norwegian Environment Agency2014, Available: http://www.miljodirektoratet.no/Documents/ publikasjoner/M287/M287.pdf. [8] E. S.F., “Towards a low-emission Norwegian industry,” Enova S.F.ISBN 978-8292502-99-9, 2017, vol. Enova report 2017:5. [9] U. Fao, “How to Feed the World in 2050,” in Rome: High-Level Expert Forum, 2009. [10] F. Magrinyà Torner, “The Challenge of Slums. Global Report on Human Settlements 2003,” Cuadernos Internacionales de Tecnología para el Desarrollo Humano, 2005, núm. 3, no. United Nations Human Settlements Programme, p. 345, 2005. [11] M. Green, “Why we should build wooden skyscrapers,” T. Talks, Ed., ed. Youtube, 2013. [12] Z. Strelitz, Tall Buildings: a strategic design guide. RIBA, 2005. [13] N. AS, “B20 M90 D22, 205000, Vibrerbar betong. Environmental Product Declaration,” ed: The Norwegian EPD Foundation, 2014, p. 6.

[14] S. P. SIA, “Steel Structure. Environmental Product Declaration,” ed: The Norwegian EPD Foundation, 2014, p. 7.

and K. B. Lindberg, “A Norwegian zero emission building deﬁnition,” Passivhus Norden, 2013. [24] A. H. Wiberg et al., “A net zero emission concept analysis of a single-family house,” Energy and buildings, vol. 74, pp. 101-110, 2014.

[15] K. R. Richards and C. Stokes, “A review of forest carbon sequestration cost studies: a dozen years of research,” Climatic change, vol. 63, no. 1-2, pp. 1-48, 2004. [16] N. Y. S. D. o. E. Conservation. (9 May 2018). Trees: The Carbon Storage Experts. Available: https://www.dec.ny.gov/lands/47481. html

[25] G. Lobaccaro, A. H. Wiberg, G. Ceci, M. Manni, N. Lolli, and U. Berardi, “Parametric design to minimize the embodied GHG emissions in a ZEB,” Energy and Buildings, vol. 167, pp. 106-123, 2018.

[17] S. H. e.V., “Cross-laminated timber (X-Lam). Environmental Product Declaration,” ed: Institut Bauen und Umwelt (IBU), 2016, p. 10.

[26] I. Sartori and A. G. Hestnes, “Energy use in the life cycle of conventional and lowenergy buildings: A review article,” Energy and buildings, vol. 39, no. 3, pp. 249-257, 2007.

[18] S. AS, “Standard limtrebjelke,” ed: The Norwegian EPD Foundation, 2014, p. 7. [19] M. De Rosa, M. Pizzol, and J. H. Schmidt, “A comparison of LCA approaches accounting for CO2 emission and sink of forestry products: The case of Timber as a construction material,” 2013.

[27] A. Rønning and A. Brekke, “Life cycle assessment (LCA) of the building sector: strengths and weaknesses,” in Eco-Efﬁcient Construction and Building Materials: Elsevier, 2014, pp. 63-83. [28] M. K. Wiik, S. M. Fufa, T. Kristjansdottir, and I. Andresen, “Lessons learnt from embodied GHG emission calculations in zero emission buildings (ZEBs) from the Norwegian ZEB research centre,” Energy and Buildings, vol. 165, pp. 25-34, 2018.

[20] S. A. I. C. (SAIC), “A Brief History of Life Cycle Assessment,” in Life Cycle Assessment: Principles and Practice, M. A. Curran, Ed., ed. Cincinnati, Ohio: National Risk Management Research Laboratory. Ofﬁce of Research and Development. U.S. Environmental Protection Agency., 2006 p. 3.

[29] A. Zimmerman and P. Eng, “Integrated design process guide,” Canada Mortgage and Housing Corporation, Ottawa, 2006.

[21] A. A. Stephanie Vierra, LEED AP BD+C. Vierra Design & Education Services, LLC. (9 May). Green Building Standards and Certiﬁcation Systems. Available: https://www. wbdg.org/resources/green-building-standardsand-certiﬁcation-systems

[30] A. Mahdavi, “Computational decision support and the building delivery process: a necessary dialogue,” Automation in Construction, vol. 7, no. 2-3, pp. 205-211, 1998. [31] S. Attia and A. De Herde, “Early design simulation tools for net zero energy buildings: a comparison of ten tools,” in Conference Proceedings of 12th International Building Performance Simulation Association, 2011, 2011.

[22] A. J. Marszal et al., “Zero Energy Building–A review of deﬁnitions and calculation methodologies,” Energy and buildings, vol. 43, no. 4, pp. 971-979, 2011. [23]

T. Dokka, I. Sartori, M. Thyholt, K. Lien,

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[32] S. Hayter, P. Torcellini, R. B. Hayter, and R. Judkoff, “The energy design process for designing and constructing high-performance buildings,” 2000: Citeseer. [33] U. Bogenstätter, “Prediction and optimization of life-cycle costs in early design,” Building Research & Information, vol. 28, no. 5-6, pp. 376-386, 2000. [34] L. Finocchiaro and G. Lobaccaro, “Bioclimatic Design of Green Buildings,” Handbook of Energy Systems in Green Buildings, 2017.

Preliminary analyses

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

2.1. Case study analysis As mentioned in the previous chapter, the project developed by Snøhetta for the current parking slot in Gullhaug Square 2A (Nydalen, Oslo) has been selected as a case study. Moreover, its boundary conditions have been used for the design of a new project in this location. These boundary conditions are the urban context, architectural program and local climate.

Urban approach The area of Nydalen (Oslo) was established as an industrial area around the middle of the 19th century. Today, about 30000 people live and study in Nydalen. The scale and density of the building structure has evolved from an industrial area into an urban environment [1]. This area is located in the intersection of the transversal axis given by the Akre river and the belt around the centre of Oslo. In this suburbia area is where the city possesses the biggest potential for growth and expansion. Nydalen district is well connected

Fig. 8: Nydalen Plus master plan. MAD Arkitekter. 2015.

with the city centre and surrounding areas by bus, subway and train, having an excellent potential for accommodating more people without compromising the environmental impact resulting from increased trafﬁc. In addition, the area is also very well suited for cyclists. The Gullhaug Torg project, also called Nydalen Vy, is the “hub” of the master plan Nydalen Plus developed by Avantor towards the horizon of 2030 (Fig. 8). This master plan is based on the implementation of three strategies: connect, activate and densify. By their implementation, Nydalen Plus aims to unify the area of Nordre Aker district with the rest of the city, focusing on the user rather than the infrastructures in order to create a greener Oslo [2]. Avantor assures that all trafﬁc increase in Nydalen will come from cycling, walking and public transport. Moreover, a separated master plan for converting large areas of the city centre car-free has been developed.

Fig. 9: Gullhaug Torg. Snøhetta and MIR. 2015 (available at: https://snohetta.com/projects/269-gullhaug-torg).

Program analysis

In a local context scale, the proposal developed by Snøhetta is based on the plot uniﬁcation, including the bridge as part of the square, as well as on the reinforcement of important connecting lines between different city spaces and service functions in the area. Gullhaug Square will be the district’s most important public space and central meeting point. In this space, different user groups’ needs will be taken care of, and several opportunities to experience and move throughout the plaza at all times of the day during the four seasons of the year will be provided. In this proposal, the Aker river is considered as the focal point and central element of attraction by treating both banks of the river and transforming them into an attractive public space. Moreover, it proposes low parking coverage to promote public transport and ensure efﬁcient utilization of the urban spaces. In Gullhaug Torg, additional parking spaces will be included through underground facilities to release outdoor areas for public use [2]. This urban context developed by Snøhetta will be preserved in the new design proposed in this master thesis (Fig. 11).

Normal

Terrase

Basement

Totals

Housing

4674

280

451

5405

Ofﬁces

4280

351

4635

Commercial

1115

Technical services

343

10416

631

451

11498

Totals

total m2 without basement and terrases total m2 with basement and terrases

10416 m2 / 16 storeys = 651 m2 / storey

Fig. 10: Program analysis of functions and square meters (data from “Gullhaug Torg. Sluttrapport skisseprosjekt”, 2015).

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Architectural principles The shape and expression of the building is the result of the interaction between several parameters, considering the importance of the urban level, ground ﬂoor in terms of footprint, as well as building volume and height. In addition to optimise the needs of daylight and solar gains, the interdisciplinary cooperation around the climatization concept has been of crucial importance for geometry and façade’s design. Lastly, the architecture is characterized by choices related to the goal of reducing greenhouse gas emissions from materials. The project will contain a mix-program of housing, ofﬁces and commercial spaces with a total surface of more than 10000 m2 (Fig. 10). The building volume, with a tall and a low tower combined with a “glass bridge”, comes from the desire to take care of sight lines across the square and the different needs of the façade area (Fig. 9).

Gullhaug Square 2A

On the ground level there will be commercial activities with a café and restaurant with a direct visual connection to the river, as well as a public square oriented to the southwest. This commercial area will have large rooms that extend over two storeys with high openable windows facing the “sun wall” and the public areas. On the east side, towards the main street Nydalen Allé, there will be a lobby for the ofﬁce section as well as shared bicycle facilities. The residential entrance is added in the northwest corner.

Fig. 11: Situation plan. Nydalen area. Snøhetta’s urban proposal. Own elaboration.

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Design according to wind directions

The “glass bridge”, which ﬁlls the space between the two towers, is arranged for a cross-sectional passage where the ﬂooring between the towers extends uninterruptedly. At the ground level, the passage offers a shortcut for people in the area, while serving as an entrance and dining area for the restaurants.

“Triple - Z “ concept: zero energy purchased for ventilation, heating and cooling

The differentiation in height between the two towers is made to create variation in the built shape, customize program and circulation, create better views for the apartments and relate to two different heights: existing buildings and the newly planned altitude of the towers in Nydalen Plus (Fig.13). The 42 apartment units are assembled on the 12 upper floors and organized around a compact core. The tower’s faceted and tapered shape provides a slim volume with a lot of window area and good sun and daylight conditions (Fig. 12), while the lower housing levels are relatively large and area-efficient. The office program requires large, coherent and flexible areas. They are located on the floor plans where the tower volumes meet in the “glass joint”. Here the slabs are interconnected from north to south with two communication cores, the main access being via the low southern tower. In the new building’s proposal developed in this master thesis, the same program distribution will be implemented.

Fig. 12: Wind analysis over the building’s geometry. Snøhetta. 2015 (available at: https://www.futurebuilt. no/content/download/11951/85065).

Energy concept Gullhaug Torg will use innovative environmental technology and, as one of the FutureBuilt pilot projects and part of the “Natural Climatization of Office Buildings” research project, it will become the first building in Norway to be naturally ventilated. It applies a Triple-Z energy concept that has been inspired by the natural climatization strategy of the “22-26” office building in Austria [3]. This triple-Z concept means zero energy purchase for ventilation,

Fig. 13: Gullhaug Torg west elevation with the new towers as part of the future development plan. Snøhetta. 2015.

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heating or cooling. The project’s Triple-Z ambition is groundbreaking in the Norwegian context and challenges many established truths around energy-efficient environmental buildings, that have been assumed by today’s construction industry. This focus has required a thorough understanding of principles and strategies and a solid interdisciplinary project team. The team integrates members with different backgrounds and across disciplines, such as architecture, interior architecture and landscape, construction and geotechnics, building physics, plumbing and electrical, acoustics and fire technicians. It also included experts in the field of natural ventilation, energy efficient heating and cooling systems, daylight and materials. In addition, FutureBuilt has also contributed with expertise in area development in terms of climate-friendly transport and other parameters that ensure a reduction in overall greenhouse gas emissions from the project as a whole [2]. The building’s geometry, material use and programming are optimised for a climatization concept based on natural ventilation with automated façade shutters (Fig. 14) and a highly efficient thermal energy system (LowEx) cast into the slabs (Fig. 15). Relatively small volumes are required to achieve cross-ventilation in the open zones with offices and common areas. Thus, external pressure differences around the building can be utilized to create air flow. This is achieved by opening hatches on opposite façades. Closed volumes, like cellular offices, are added to areas without high solar load where the temperatures are more stable. Features like meeting rooms, with a higher density of people, are added to the corners of the building to get two accessible façades in the room and thus achieve an effective air change rate. This premise has been a driver of the design and led to a building body with many facets [1]. Natural ventilation of indoor environment

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Ventilation concept in the housing

requires a significantly greater factorization of person and equipment load. The load or number of people with associated equipment per m² is important for ventilation, heating and cooling. The ventilation strategy must provide adequate thermal comfort and air quality as in a regular office building with a corresponding m2 per workplace. Future rental terms are intended as an entire or a half floor per tenant. In order to maintain sufficient flexibility, it is considered a one-way cross-ventilation strategy [2].

cross ventilation In summer via vertical openings During the night and winter via top shutters

To ensure a good and stable indoor climate based on natural climatization, the net floor height is set at 3.5 m (gross 3.8 m). Along with the utilization of concrete slabs as thermal mass exposed to the indoor air, the volume helps to equalize temperature fluctuations, as well as provide greater robustness against the accumulation of polluted (used) air. Standard projects need an average of 70-100 cm of room height for technical installations. This project’s strategy reclaims these valuable centimetres which are used in a stratification strategy, increasing light levels in the façade and giving positive results regarding acoustics. The floor height is necessary to allow cold outside air to flow through horizontal hatches up under the deck and allow it to mix with the warm interior air in the room. In zones with higher density of people, this strategy is supported by the assembly of a chamber that regulates the thermal air jets [1].

Exhaust ventilation through bathrooms and kitchens

Fig. 14: Natural ventilation strategy. Snøhetta. 2015 (available at: https://snohetta.com/projects/269-gullhaugtorg).

Thermal mass effect in the ofﬁces Summer _ night cooling through exposed thermal mass

Horizontal opaque openings are used for ventilation during winter. They are placed high above the external walls to ensure minimal drag in winter and night cooling of exposed thermal mass in summer. Vertical openings are used for ventilation during most of the year. These opening have the possibility of manual override (Fig. 14). Due to potential glare challenges, workplaces are drawn from the façade at a distance of 60-100 cm. This gives an improved transport area around the workplaces and reduces the glare at workplaces near the windows [2].

Winter _ low sun angle heats the exposed thermal mass (solar heat gains) Fig. 15: Thermal mass effect. Snøhetta. 2015 (available at: https://snohetta.com/projects/269-gullhaug-torg).

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For about. 10% of the year, at peak summer and coldest winter days, there is a need for some degree of heating or cooling. The high-efficiency low-energy or exergy (LowEx) solution systems provide low-temperature radiant surfaces. The required areas for radiant surfaces in offices consist on the 25% of the useful floor area (BRA) and are located in both horizontal and vertical elements that serve as zone sections (Fig. 15). For flexibility reasons, horizontal exergy surfaces are laid in a one-meter band in the floor around the façade [2]. Exergy surfaces should transport hot water and function in principle as an active thermal mass that circulates low-temperature water (3 degrees above the room temperature). Exergy surfaces have a constant temperature as opposed to a classic thermostat-controlled system. In the housing program, the heating surface area is increased to 50% of the useful floor area due to lower personal heat loads. In this part of the program, the system is considered more robust with an increased proportion of vertical active surfaces. A 60-80 cm band in the longitudinal direction of the façade ensures a gentle atmosphere in the living area, giving a special aesthetic quality to the floor of the home. Placement of furniture and carpets has an impact on the effectiveness of this system. In the remaining period of the year where no radiant cooling or heating is required, these surfaces act as exposed thermal mass (Fig. 15) [2]. In order to achieve this building’s zero heating or cooling standard, the building is dependent on exposed surfaces with high thermal inertia. Vertical and horizontal exposed surfaces are positioned to utilize solar heat gains in winter, and a night cooling strategy ensures that the daytime temperature does not exceed the comfortable levels in summer. Temperature fluctuations on a 24-hour basis are highly smoothed by a lightweight construction system. Exposed thermal mass that does not require additional heavy masses with associated negative LCA is an essential component of the building strategy (Fig. 15) [2].

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

2.2. Climate analysis Climate adaptation of buildings is probably the oldest and most effective energy-saving measure. Since the ancient times, regional climatic adaptation has always play an important role as an essential principle of architecture [4]. According to I. Andersen, of all the design measures that must be implemented in the design process of a Zero Emission Building, the location, orientation and form of the building are within the most efficient ones. This is due to the fact that they do not involve any extra investment cost, yet they have highly significant effects on the final result [5]. The Three-tier Approach to the Sustainability Design established by N. Lechner, enunciates the importance of basic building design as the base of the pyramid for the design of sustainable buildings, emphasizing the importance of building’s climate adaptation [6]. This same idea is also illustrated in the Trias Energetica pyramid,

Psychrometric chart in Nydalen, Oslo

developed by the ZEB centre as a crucial strategy for the Integrated Design Process (IDP) [5]. Thus, the importance of a thorough climate analysis is crucial in order to implement the most efﬁcient passive strategies and an adequate building’s shape climate adaptation. In this master thesis, the climate analysis has been carried out by means of Ladybug, a parametric tool for Rhinoceros that allows to easily visualize the different climatic parameters and their possible impact on the architectural form.

Comfort zone

Temperature ranges As previously mentioned, the location of the project is to be set in Nydalen, located in the Nordre Aker district of Oslo. According to the Köppen climate classiﬁcation [7], the climate in the Norwegian capital belongs to the subtype Cfb (Warm Summer Continental Climate).

Fig. 17: Psychrometric chart from Nydalen area (weather data analysed with Ladybug).

Psychrometric chart with passive strategies

Monthly diurnal averages in Nydalen, Oslo Köppen climate classiﬁcation _ Cfd Warm Summer Continental Climate

Thermal mass + night ventilation

Comfort thermal neutrality Temperatures range

Direct solar radiation

Diffuse solar radiation Internal heat gains

Fig. 16: Monthly diurnal averages values for temperatures range, direct and diffuse solar radiation. (data extracted from local weather ﬁle and analysed with Weather Tool).

Fig. 18: Psychrometric chart from Nydalen area (weather data analysed with Ladybug).

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Comfortable hours with no passive strategies

Comfortable hours due to internal heat gains

Total comfortable hours with internal heat gains

Fig. 19: Yearly comfortable hours for three different scenarios (weather data analysed with Ladybug).

Tempered by the proximity of the Atlantic Ocean and the Gulf Stream, the average temperature in Oslo is 6.9 °C. Winters are cold, with temperatures below 0 °C from September to April, with an average temperature of -4.3 °C in December and January, the coldest months of the year. As shown in Fig. 16, only a small percentage of the temperature ranges of the months from

Passive strategies implementation

April to August are inside the temperature ranges considered as comfort thermal neutrality. Moreover, due to the continental character of this climate, hot temperatures above the comfort thermal neutrality range can also be registered during the summer months of June, July and August. Henceforth, the application of passive or active systems for heating and cooling will be necessary to achieve the thermal comfort condition.

In order to assess the importance of the implementation of passive strategies, the psychrometric chart has been utilised. This chart is a graphic representation of the air properties in a speciﬁc climate such as relative humidity, wet bulb temperature, dry bulb temperature and dew point temperature. It allows to graphically analyse different types of psychrometric

Monthly average precipitations. Oslo airport observation site Data for 2017 (mm) 208.4

125.6 100.6

102.3 82.7 38.5 MAR

47.2

APR

50.0

MAY

JUN

79.6

63.7

JUL

54.3

AUG

SEP

OCT

NOV

DEC

37.5 JAN

17.9

FEB

Fig. 20: Monthly average precipitations. Oslo Airport observation site, Ullensaker. 2017 (data available at: https://www.yr.no/place/Norway/Akershus/Ullensaker/Oslo_Airport_ observation_site/statistics.html).

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processes in order to find solutions related to temperature and humidity problems, avoiding the architect to carry out long and tedious mathematical calculations. In Fig. 17 and 18 it is possible to observe that the majority of temperatures throughout the year are quite cold and close to the saturation limit, which also means that the annual precipitations are quite abundant. In Fig. 17, the comfort zone is marked inside a black polygon. It can be observed that only a few temperature ranges are within this comfort zone. In order to improve the temperature and humidity conditions of the air, the effectiveness of different passive strategies has been assessed. The strategies tested are Evaporative cooling, thermal mass + night ventilation, internal heat gains, dehumidification, desiccant dehumidification and humidification. In Fig.18, the effect of the most effective passive strategies for this climatic conditions are illustrated with grey polygons. These resulted to be the use of internal heat gains and thermal mass combined with night ventilation strategies, from which the crucial one is the use of internal heat gains. The improvement consequences of using this passive strategy can be clearly observed in Fig. 19, where a comparison between the yearly hours inside the comfort zone (marked in yellow) with and without the use of internal heat gains

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Wind rose for the whole year

Wind rose for the hot season

(Each closed polyline shows frequency of 1.7% = 151 hours)

Frequency (%) Average wind velocity (m/s)

Fig. 21: Wind rose with frequencies and average wind velocities for the whole year (weather data analysed with Ladybug).

has been carried out. Nevertheless, in this same ﬁgure it can also be observed that this measure alone is not enough to situate the whole set of annual temperatures inside the comfort zone. Therefore, during the months of January, February, March, April, October, November and December (marked with a predominantly greenish blue

Fig. 22: Wind rose with frequencies and average wind velocities for the hot season (from June to September) (weather data analysed with Ladybug).

colour), additional heating systems must be implemented.

months with higher amount of precipitations in 2017 were August (with an average of 208 mm), October (with an average of 125 mm), and September and January (with an average of 100 mm). In contrast, the months with less amount of precipitations were February and March, with an average of less than 40 mm (Fig. 20).

Precipitations As mentioned before, the amount of annual precipitations in the city of Oslo is quite signiﬁcant. According to data from the Oslo Airport observation site in Ullensaker [8], the

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Prevailing winds Due to the increase of pressure over the building associated with the height, the wind is a highly signiﬁcant factor when designing a high-rise building. As can be observed in Fig. 21, 22 and 23, for the case of Oslo, the prevailing wind directions can reach signiﬁcant values of over 10 m/s throughout the year.

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

Wind rose for the cold season

Wind proďŹ le. Prevailing wind average velocity

(Each closed polyline shows frequency of 1.7% = 151 hours)

Fig. 23: Wind rose with frequencies and average wind velocities for the cold season (from October to May) (weather data analysed with Ladybug).

The prevailing wind directions for the entire year (Fig. 21) are from the south, with an average wind velocity of 2.82 m/s and a frequency of 11.23 % of the year; south-southwest, blowing during 10.13 % of the year with 2.93 m/s as average velocity; and the north-northwest during 9.97 % of the year with an average wind velocity of 3.13 m/s. Fig. 22 shows the prevailing winds for the hot months of the year (from June to September),

where the north-northwest direction is the prevailing with an average wind velocity of 2.87 m/s and a frequency of 13.66 % of the time. Regarding the cold part of the year (which in the case of Oslo can be considered from October to May), the two prevailing directions for the wind are south-southwest (with an average speed of 2.95 m/s and a frequency of 12.33 %), and south (with a frequency of 12.33 % and an average

Fig. 24: Wind proďŹ le for prevailing wind average velocity (weather data analysed with Ladybug).

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Aiming for ZEB in a High Rise Building

2. Preliminary analyses

speed of 2.95 m/s).

Prevailing winds in the context of Nydalen

Despite the prevailing wind speeds being very low with respect to the maximum wind velocity, a maximum wind speed of 20 m/s is too signiﬁcant to be ignored. Thus, the new proposal for this high-rise building must take the pressure associated with this maximum wind speed into consideration, at least for the prevailing wind directions.

Solar radiation Due to its location in the north hemisphere, the orientation with a higher exposure in Oslo will be towards the south. This fact can be clearly appreciated in Fig. 26 and 27.

In Fig. 26, the annual mean values for the total radiation in every direction are depicted. When referring to the total solar radiation, both the diffuse and direct radiation are included in the definition. It is observed that the maximum value corresponds to 700 kWh/m2 for the south orientation, while surfaces oriented to the north can received up to 100 kWh/m2 due to diffuse radiation caused by the reflection of the solar rays in the clouds and other surfaces. The last figure (Fig. 27) shows the mean values for the direct and diffuse solar radiation. The values for the direct radiation refer to the energy transfer by the solar rays reaching the earth surface on a straight line. In the case of the orientation with higher solar exposure (towards the south), this values can reach up to 500 kWh/ m2, whereas for the northwest and northeast directions the mean values are less tan 100 kWh/m2. Due to the natural sun path, surfaces oriented towards the north will not receive direct solar radiation.

Fig. 25: Yearly wind rose overlapped with the context for the intervention (weather data analysed with Ladybug).

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Regarding the diffuse solar radiation, also shown in Fig. 27, this term refers to the energy transferred by the solar rays that have been scattered by molecules and particles in the atmosphere and reached the ground after being deviated of their initial trajectory. For orientations

Aiming for ZEB in a High Rise Building

2. Preliminary analyses

References Radiation rose

towards the south, this values can reach up to 400 kWh/m2, while for the north orientation the mean values are around 150 kWh/m2.

Total solar radiation for the whole year

The values for the total solar radiation will be used to analyse the solar heat gains of the building proposed.

[1] Naturligvis, “Passiv klimatisering av fremtidens. Energieffektive bygg. Erfaringsrapport,” 2018, Available: https://www. futurebuilt.no/content/download/11951/85065. [2] A. Danielsberg et al., “Gullhaug Torg sluttrapport skisseprosjekt 2015,” Oslo: Avantor. 2015. [3] B. Eberle, “2226 building Lustenau (Austria) 2013: Climatización natural mediante regulación de ﬂujos,” A+ T: revista trimestral de Arquitectura y Tecnología, no. 44, pp. 96-101, 2014. [4] K. Yeang, A. Balfour, and I. Richards, Bioclimatic skyscrapers. Ellipsis London, Limited, 1994. [5] A. G. Hestnes and N. L. Eik-Nes, Zero Emission Buildings. Fagbokforlaget, 2017. [6] N. Lechner, Heating, cooling, lighting: Sustainable design methods for architects. John wiley & sons, 2014. [7] M. Kottek, J. Grieser, C. Beck, B. Rudolf, and F. Rubel, “World map of the KöppenGeiger climate classiﬁcation updated,” Meteorologische Zeitschrift, vol. 15, no. 3, pp. 259-263, 2006.

Fig. 26: Radiation rose for the total solar radiation throughout the year (weather data analysed with Ladybug).

Radiation rose

Direct solar radiation for the whole year

Radiation rose

Diffuse solar radiation for the whole year

[8] Oslo Airport Observatory Site. (2017). Weather statistics for Oslo Airport. Available: https://www.yr.no/place/Norway/Akershus/ Ullensaker/Oslo_Airport_observation_site/ statistics.html

Fig. 27: Radiation rose for the direct and diffuse solar radiation throughout the year (weather data analysed with Ladybug).

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Climate-adapted built form

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3.1. Optimisation parameters

3.2. Design of geometries to be tested

According to the aforementioned Threetier Approach to the Sustainability Design developed by N. Lechner, decisions on the initial design stages can reduce the energy consumption of buildings up to 80 %. This approach sets the basic building design on the base of the three-tier pyramid as the main contributor to the effectiveness of the ﬁnal result, with passive systems on the middle of the pyramid, and mechanical equipment on the top [1]. In this basic building design, the decision on the building’s shape can be considered a crucial stage.

It is important to point out that the optimisation of the building’s shape to minimise wind pressure loads may seem to be in contradiction with the fact that wind is one of the main driving forces for natural ventilation. According to T. Kleiven, the two passive strategies associated with natural ventilation are thermal buoyancy and wind. As explained by this author, “thermal buoyancy will typically be the driving force on a calm cold day with practically no wind, whereas pressure differentials created by wind will typically be the dominating driving force on a windy hot day” [6].

Besides, in his book “Bioclimatic Skyscrapers”, K. Yeang points out the importance of building’s climate adaptation in order to reduce its energy consumption [2]. In “Design with Climate”, V. Olgyay understands this climate adaptation as a consequence of the natural forces acting on the shape of living organisms. Thus, every natural form can be read as a balance of forces [3], which may be also applicable to architectural forms.

These passive strategies are commonly utilised in combination but they can also occur separately [6]. The aforementioned scenario of a calm cold day will be the prevailing situation for Nydalen throughout the year, as shown in the previous climate analysis. Accordingly, for this particular location, the optimisation of the building’s shape to be exposed to a minimum wind pressure will not be detrimental for the implementation of an efﬁcient natural ventilation system.

In order to achieve the harmony between shape and natural forces, the climatic parameters previously analysed will be implemented in a geometry study to ﬁnd out the most suitable shape to this particular climate and architectural typology.

In addition to this, in a cold climate like the one in Norway, taking maximum advantage of the solar heat gains during winter can make a signiﬁcant difference on the overall energy consumption for heating. Such approach becomes specially relevant if today´s construction systems are considered, as they are mainly focused on the air-tighness of buildings in order to reduce their thermal losses.

At this step of the design, it is important to remember that the biggest driver on the overall GHG emissions of a high-rise building is the amount and type of materials utilised on its structure, representing the largest amount of materials in the whole building [4]. Moreover, the main factor that drives the amount of materials needed in a high-rise building typology is the stress on the structure due to the wind pressure [5]. Thus, optimising the building’s shape in order to bear the minimum wind pressure seems like the most logical approach, in order to pursue the goal of reducing the GHG embodied emissions from materials to the minimum, as established in the introduction of this thesis.

In order to select the geometry that will be developed further on the next chapters of this thesis, a sensitivity analysis of the previously mentioned parameters has been carried out. This approach is based on the simulation of several geometries under different wind and solar radiation conditions. As a result of the broad range of possible combinations, a trade off between wind and solar performance is selected as ultimate design. Six different geometries have been chosen to be analysed in relation to the selected parameters. Three of them are four-sided polyhedrons, while the other three have rounded shapes (Fig. 28). The four-sided polyhedrons have been designed in a way that they have the maximum possible area exposed to the south. This has been done in order to maximise both its solar heat gains and its potential for energy production through a photovoltaic system, which will be important in order to achieve the Zero Emissions balance. The shape shown in Fig. 29 is a combination of two simple rectangles. One aligned with the main street Nydalen Allé, and the second one aligned with the bank of the river. The second shape is a simple offset of the plot perimeter (Fig. 30). Finally, the third one has been designed with the optimum angle for maximising the solar radiation that the south-oriented façades are receiving (Fig. 31). This angle is 67.5º with the

Fig. 28: Selected geometries to be tested

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The round shapes have been designed in order to create minimum resistance to the wind pressure and therefore to minimise the horizontal forces over their envelopes. Shape number 4 has a circular footprint (Fig. 32). This is to create a geometry that reacts in an equal manner to wind blowing from every direction. Shape number 5 is an elliptical shape (Fig. 33). The base ellipse of this geometry has been aligned with the natural directionality of the plot which, as a matter of fact, coincides with the prevailing wind directions. Lastly, geometry number 6 has the shape of a water drop (Fig. 34). To make a precise comparison of these six geometries, all of them have been scaled to have the same ﬂoor area (650 m2) and the same height (65 m). The selection criteria utilised for the election of the most adequate geometry will be the following, enunciated in this order of priority: 1. Minimum force on the envelope due to prevailing winds. 2. Maximum mean power per exposed area during the cold season.

Selected geometries

As a conclusion, wind pressure and solar radiation will be the selected natural forces to be analysed as driving parameters for the design of the built form.

horizon line according to the research published in “Boosting solar accessibility and potential of urban districts in the Nordic climate: A case study in Trondheim” [7].

3. Maximum energy production potential for the future installation of photovoltaic solar panels.

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3. Solar angle shape

1. Combined shape

650 m2

67.5º

Fig. 29: Roof plan and axonometry of the ﬁrst selected geometry.

67.5º

Fig. 31: Roof plan and axonometry of the third selected geometry.

2. Plot shape

4. Circular shape

650 m 2

650 m2

Fig. 30: Roof plan and axonometry of the second selected geometry.

Fig. 32: Roof plan and axonometry of the fourth selected geometry.

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Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

3.3. Wind optimisation 5. Elliptical shape

650

The load on a surface due to the wind action is directly proportional to the wind pressure over the surface integrated over the affected area (Fig. 35). This force due to the wind action is called drag force. The drag force is a horizontal force, perpendicular to the envelope of the building. This horizontal force multiplied by the distance from the base of the building cause a bending moment applied at the base. Therefore, the higher the distance, the greater the moment. Wind speed increases with the height.This behaviour arises from the viscous forces that the ďŹ&#x201A;uid, in this case air, experiences against the Earth surface, other buildings, trees and other elements. These facts explain why wind force is detrimental when designing a high-rise building.

force consequence of the combination of these individual pressures. The vortexes on the back faĂ§ade have signiďŹ cant importance, as they are created alternately in a clockwise and counter clockwise direction due to the variation on the ďŹ&#x201A;ow speed on the side faĂ§ades. This produces vibrations in a cross-wind direction, that the structure of the building will have to handle. In order to reduce the vortexes on the back side it is important to reduce the distance between both wind ďŹ&#x201A;ows from the side faĂ§ades (distance between dashed lines in Fig. 36) , so-called separation area [5].

Drag force Fig. 33: Roof plan and axonometry of the ďŹ fth selected geometry.

6. Water drop shape

đ??šđ??š =

đ?&#x2018;&#x192;đ?&#x2018;&#x192; â&#x2C6;&#x2014; đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ??´đ??´

đ?&#x2018;&#x192;đ?&#x2018;&#x192; â&#x2C6;&#x2014; đ?&#x2018;&#x2018;đ?&#x2018;&#x2018;đ??´đ??´ đ??šđ??š đ??´đ??´

Drag coefďŹ cient Cd = * , â&#x2C6;&#x2014; - + +

đ??šđ??š đ??´đ??´ Cd = * + , â&#x2C6;&#x2014; -

Fig. 35: Formulas for the drag force and drag coefďŹ cient.

65 0m

According to the Eurocode-1, there are 5 terrain categories associated with different roughness degrees. For the case of Nydalen, category 4 applies, belonging to an area in which at least 15 % of the surface is covered by buildings with an average height of more than 15 m [8]. Wind does not affect uniformly to the different faĂ§ades of a building (Fig. 35). As a general rule, the faĂ§ade facing the wind direction will receive a positive pressure, while the side and back faĂ§ades will handle vortexes and underpressures (Fig. 36). The drag force is the overall

Fig. 34: YRoof plan and axonometry of the sixth selected geometry.

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Fig. 36: Common wind ďŹ&#x201A;ow in a rectangular building.

An efďŹ cient way to reduce the separation area is by creating elongated geometries. The optimal geometry is the shape of an airfoil [5]. However, this kind of shapes may be optimal for one prevailing wind direction but detrimental for others. The behaviour against the wind is measured by the drag coefďŹ cient, which is directly proportional to the drag force divided by the area, and indirectly proportional to the product of the air density divided by two and the squared wind speed. In other words, the drag coefďŹ cient shows us how aerodynamic a geometry is. The smaller the number, the more aerodynamic the geometry will be. In order to test which geometries better behaves with respect to the prevailing wind directions, the six geometries designed on the previous chapter have been tested in a virtual wind tunnel. This wind tunnel has been simulated by means of Flow Design, a user-friendly simulation tool that helps to test ideas in early design stages of

Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Wind analyses with Flow Design (wind coming from the south)

1. Combined shape

2. Plot shape

3. Solar angle shape

4. Circular shape

5. Elliptical shape

6. Water drop shape

Fig. 37: Wind tunnel simulations with Flow Design for the six geometries designed.

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Aiming for ZEB in a High Rise Building

3. Climate-adapted built form

Summary of analyses (wind coming the south) Summary of from analysis

Summary of analyses Summary oftheanalysis (wind coming from north-northwest)

(wind coming from the south)

Shape

1. Rectangular shape

2. Plot shape

3. Solar angle shape

4. Circular shape

5. Elliptical shape

6. Water drop shape

Wind direction

(wind coming from the north-northwest)

2 / Climate-based build form

Testing time (minutes)

Positive peak pressure (Pa)

Negative peak pressure (Pa)

Highest wind velocity (m/s)