INOM
EXAMENSARBETE TEKNIK, GRUNDNIVÅ, 15 HP
STOCKHOLM SVERIGE 2020,
Energy efficiency in glass buildings
A study about the energy efficiency of glass
buildings in Stockholm and how related demands are met
EIVIND MYKLEBUST STØVNE ISAK SØGAARD VALLINDER
KTH
SKOLAN FÖR ARKITEKTUR OCH SAMHÄLLSBYGGNAD
TRITA ABE-MBT-20366
www.kth.se
I
Abstract
The building and property sector stands for one third of the final energy usage in Sweden and this should be diminished, in order to reach goals within environmental sustainability. Glass is a poor thermal insulator but nevertheless a popular choice of material when constructing new buildings. The contradiction between need of energy efficiency and the wish for “glass buildings” led to the subject of this report. This Bachelor’s thesis examines how demands on energy efficiency is met in nine glass buildings in Stockholm. Glass buildings and the current legislation is discussed from a perspective of environmental sustainability. This was done by investigating the demands stated by Boverket from a historical perspective, executing
quantitative measurements of heat transfer on elected objects, and interviewing stakeholders linked to the buildings and the Swedish legislation.
The study shows that the construction of glass buildings has been possible due to a
restructuring of the demands on energy efficiency and technical development. It was found, in most cases, that the shares of glass were in fact lower than apparent. A larger share of glass in the building envelope required creative measures to achieve energy solutions, within legislative demands. Nevertheless, the inlet of solar radiation heat is the greatest challenge.
Despite the challenges, the desire for glass is rooted in well-being and aesthetic values, which insinuate that glass buildings will be included in the cityscape henceforth. The conclusions drawn from these results are that the energy performance of glass buildings is still weaker than conventional “solid wall buildings”. Enhancement regarding insulation abilities and improvements of excluding solar radiation must be realized to strengthen the environmental sustainability of this category of buildings.
Keywords: U-factor, Um-factor, energy efficiency, primary energy coefficient, energy certificate, Swedish building legislation, BBR, glass buildings.
II
Sammanfattning
Bygg- och fastighetssektorn står för en tredjedel av den slutliga energianvändningen i Sverige, vilken måste minimeras för att nå miljömässiga hållbarhetsmål. Att bygga i glas är populärt bland moderna byggnader, trots att glas har relativt låg termisk isolationsförmåga.
Motsättningen mellan behovet av energieffektivitet och efterfrågan på “glashus” skapade ämnet för denna rapport. Detta kandidatexamensarbete utforskar hur energieffektivitetskrav möts i nio olika glasbyggnader i Stockholm. Glashus och nuvarande lagstiftning diskuteras ur ett miljömässigt hållbarhetsperspektiv. Detta gjordes genom undersökningar av Boverkets krav ur ett historiskt perspektiv, kvantitativa mätningar av värmeflöden, samt intervjuer med aktörer kopplade till byggnaderna och svensk bygglagstiftning.
Studien visar att byggnation av glashus har blivit möjlig på grund av en omstrukturering av energieffektivitetskraven samt teknisk utveckling. Det visade sig att andelen glas i de
undersökta byggnaderna oftast var lägre än det såg ut. Större andel glas i klimatskalet krävde kreativa åtgärder för att uppnå energilösningar inom lagstiftningen. Det visade sig också att solinstrålning var den största energiutmaningen för glasbyggnaderna. Trots utmaningarna finns värden anknutna till estetik och välmående som skapar en efterfrågan på glashus, och detta leder till att glashus fortfarande kommer inkluderas i stadsmiljön framöver. En slutsats från arbetet är att energiprestandan i glasbyggnader är svagare än för konventionella
“tätväggsbyggnader”. Förbättringar av glaskonstruktionen gällande isolationsförmåga och utestängning av värme från solinstrålning måste realiseras för att stärka den miljömässiga hållbarheten för denna byggnadskategori.
III
Acknowledgements
We would like to thank everyone that contributed to this report by sharing their opinions and inspiring perspectives. We would like to thank, Bo Berggren, Jonny Olsson, Oskar Häger and Anders Liljegren from Vasakronan and Eric Mårtensson from Skanska for their expertise about Sthlm Seaside and Kista Science Tower, Christoffer Haag and Jamal Nouman from Incoord and Tobias Rosberg from AIX Arkitekter for their expertise about the Royal College of Music, Marja Lundgren from White Arkitekter for her expertise about Katsan, Josefin Larsson and Stefan Nilsson from Wingårdhs for their expertise about Scandic Victoria Tower and Clarion Hotel Sign, Peter Gustafsson from Gustafsson Projekt for his knowledge about Aula Medica, Michael Eskils from AMF Fastigheter for his expertise about Gallerian Mall, Daniel Bäcklin from Stockholm Stad for his expertise about Kulturhuset Stadsteatern, and Lin Liljefors from Boverket for her expertise about the Swedish legislation.
Secondly, we would like to thank our supervisor prof. Björn Palm, at KTH Royal Institute of Technology, for his support and guidance during the project. For his feedback and expertise within the field of this thesis. We would also like to thank research engineer Peter Hill for his guidance regarding heat flux instruments.
Stockholm, May 2020
Isak Søgaard Vallinder & Eivind Myklebust Støvne
IV
Table of content
Abstract I
Sammanfattning II
Acknowledgements III
Nomenclature VI
1. Introduction 1
1.1 Aim 2
1.2 Objectives 2
1.3 Methodology 2
1.4 Limitations 2
2. Demands on energy efficiency 4
2.1 Methodology of document study 4
2.2 Historical demands 4
2.3 Current demands 6
3. Buildings subject to inspection 8
4. Heat flux measurement & calculation 11
4.1 Description of heat flux sensors 11
4.2 Methodology of heat flux measurement 11
4.3 Calculated U-factors 13
5. Energy performance 17
6. Interviews with relevant stakeholders 19
6.1 Methodology and interviewees 19
6.2 The choice of glass 21
6.3 How are BBR energy efficiency demands met? 21
6.4 General statements on glass buildings 24
6.5 Environmental certification systems 25
7. Discussion 27
8. Conclusions 31
Bibliography 32
Appendix A: Quantitative measurements and calculations 34
Appendix B: h-factor formula 35
Appendix C: Interview template 36
V
List of tables
Table 1. Energy efficiency demands. 7
Table 2. Elected objects of study. 8
Table 3. Key data extracted from measured U-factors. 14
Table 4. Information about interviews. 20
Table 5. Prominent measures taken to obtain satisfying energy efficiency. 22 Table 6. Environmental certification systems in evaluated objects. 26 Table 7. Quantitative measurements of heat flux and calculated U-factors on
objects. 34
List of figures
Figure 1. Historical development of maximal Um-factors. 5
Figure 2. Objects of study. 9
Figure 3. Reference building, KTH U-building. 10
Figure 4. Pictures of measurements. 12
Figure 5. Measured U-factors for glass walls. 14
Figure 6. Measured U-factors distributed by buildings’ years of completion. 15 Figure 7. Calculated primary energy coefficient (EPET) for corresponding object. 17 Figure 8. Primary energy coefficient distributed by buildings’ years of completion. 18
VI
Nomenclature
BBR “Boverkets byggregler”, Boverket’s building regulations
Boverket The Swedish National Board of Housing, Building and Planning
Building shell/envelope The outer structure of a building (facade)
Climate shell The outer structure of a building (facade)
ECS Environmental certification systems
EPET Primary energy coefficient [kWh/m2 year]
h-factor Combined convective and radiative heat transfer coefficient [W/m2K]
SGBC Sweden Green Building Council
U-factor
The amount of heat transferred through the building shell if the temperature difference between indoors and outdoors is 1 degree Celsius [W/m2K]
Um-factor Building shells average U-factor [W/m2K]
1
1. Introduction
Over the years, the concept of sustainability has been reinterpreted and narrowed down to three pillars, namely social, economic, and environmental sustainability, coined during the 2002 World Summit on Sustainable Development (Fletcher, 2002). The most frequently cited and widely used definition was first presented in the so-called Brundtland Report in 1987,
“To meet the needs and aspirations of the present without compromising the ability to meet those of the future” (World Commission on Environment and Development, 1987).
The built environment is a fundamental part of our daily lives. It offers homes, schools, workplaces, hospitals, theatres, and other public buildings. However, it is the single largest energy consumer in the European Union (EU), responsible for 40% of the total final energy usage and 36% of the greenhouse gas emissions (European Commission, 2020). This is mainly due to a high proportion of old buildings with low energy performance resulting in a large part of used energy going to waste. Up to 90% of the buildings total environmental impact is due to energy consumed during the operational phase (Ochoa et. al. 2005).
Nevertheless, the building sector with its variety of applications and purposes, is essential within sustainable development and a sustainable society.
In order to cope with the statement in the Brundtland Report, and meet the energy and
climate objectives, improvements within energy efficiency must be realized. This can be done by implementing policies and directives. Boverket (the national board of housing, building, and planning) is the responsible authority for setting policies regarding energy efficiency in buildings in Sweden. Energy efficiency can be viewed from two perspectives. Either the aim is to maximize the output, given a certain input or to minimize the input, given a certain output. In the aspect of energy efficiency in buildings the output is a service, for example the level of thermal comfort, and the input is energy in terms of heating, cooling, or electricity.
In 2017, the building and property sector accounted for 32% of the total final energy usage in Sweden, and 19% of Swedish greenhouse gas emissions (Boverket, 2020a, 2020c). Due to these emissions, as well as economic costs, energy efficiency in buildings has become a severe focal point for legislators. In 1945, Boverket published their first public demands on energy efficiency in buildings, in the form of a maximal overall heat transfer coefficient through outer walls (BABS, 1946). However, this paper will supply several examples of new, modern buildings in Stockholm with facades of glass, despite glass being a less efficient thermal insulator than solid, insulated walls (Çengel & Ghajar, 2015, pp 912-917). This apparent contradiction between sustainability goals and actual development is the premise for the topic question of this thesis.
2
1.1 Aim
The aim of this thesis is to identify how Boverket’s demands on energy efficiency (presented in BBR) is achieved in various buildings with climate shells consisting of a large share of glass. Furthermore, strengths and weaknesses regarding glass buildings and the current legislation is investigated, with a focus on environmental sustainability.
1.2 Objectives
One goal of the project is investigating Swedish demands on energy efficiency in buildings from a historical perspective.
Another goal is quantitatively measuring overall heat transfer coefficients (U-factors) through the outer walls of relevant examples of glass buildings in Greater Stockholm, as well as assessing how the demands in BBR are met for these examples.
A third goal is discussing energy efficiency in glass buildings related to relevant legislation, with a focus on environmental perspectives.
1.3 Methodology
Boverket’s current and historical demands were examined as a literature study of their published documents and laws. The same type of study was also used for exploring the concept of sustainable development, with the Brundtland report as the main source.
The process of choosing buildings for examination in this study is described in chapter 3.
Quantitative results were obtained by heat transfer coefficient evaluations based on measurements by two different types of heat flux sensors and a thermometer. Also,
qualitative interviews with stakeholders responsible for the buildings’ energy efficiency were conducted to discuss how the BBR-demands are met for each case, and other relevant topics.
Due to the fact that three different methods were used, concerning different parts of the thesis, it was decided in consultation with the supervisor that more detailed methodology should be described in the corresponding chapters. Chapters 2, 4 and 6 were therefore
structured with individual parts for methodology, results, and some discussions. In chapter 7, topics of discussions from the different chapters were combined as a basis for further
discussions.
1.4 Limitations
The project’s limitations were such that the perspective of energy efficiency was in focus.
Obtaining this was viewed as the ultimate environmental desire through the working process, even if there were other, conflicting environmental desires to consider. Also, the economic and social perspectives of sustainability were mostly neglected in this project. Additionally, building categories that are not relevant for the objects of study (e.g. villas and factories)
3 were disregarded throughout the project. Lastly, no investigation was performed regarding the sources of, and emissions from the electric energy system. It affects the building sector in total and would therefore not reveal any particular aspects of glass buildings.
4
2. Demands on energy efficiency
2.1 Methodology of document study
In the following pages, Sweden's historical demands on energy efficiency in buildings, will be presented, as well as the demands of today. The historical and current demands on energy efficiency were examined as a literature study of the published documents and laws. Swedish building legislation dating back to 1945 is published online, and the energy related sections of these publications were examined thoroughly. The documents in question, is neutral authority sources of building legislation and is therefore viewed as completely reliable.
2.2 Historical demands
Energy efficiency demands in Sweden have developed dramatically from when the oldest available building legislation was published until today. The one criterion which has always existed in this period of time is a form of maximum Um-factor (only the U-factor of solid parts of climate shells was included until 1989) allowed for Swedish buildings. As shown in figure 1, this limit initially fluctuated around 1.00 W/m²K before it dropped in 1975. At the same time, an article stating that no more than 15% of the outer surface could consist of windows was implemented. Such limitations in different forms lasted until 2006. From 1989 to 2006, Um-factor limits depended on the ratio between window area and total external area.
Building legislators also started separating commercial and residential buildings in terms of energy efficiency demands in 1989. From 2006, the total Um-factor of the buildings’ building shell was reviewed and more limitations, especially those regarding energy usage relating to building area were added to the legislation. Energy usage in buildings was introduced to Boverket’s building regulations and has since been combined with limitations on the Um- factor of the building shell. (BABS 1947-1968, SBN 1968-1989, NR 1989-1994, BBR 1-27)
5 Figure 11,2: Historical development of maximal Um-factors for large residential buildings and commercial buildings, heated by other energy sources than electricity in the Stockholm area. Based on BABS 1947-1968, SBN 1968-1989, NR 1989-1994 and BBR 1-27.
Figure 1 shows that despite the fact that Um-factors were calculated on solid walls only, insulation demands were rather lenient until 1975. According to Kaijser & Kander (2013), the oil crisis in 1973 led to a large governmental focus on energy savings and several studies were performed with this purpose. This is a plausible explanation for the sudden sternness regarding Um-factor limitations. As technology advanced and environmental awareness increased, limitations became even stricter before bouncing up again along with the
implementation of limitations regarding energy usage. Also, the maximum window area limit vanished in the same period. This can be interpreted as a shifted focus from maximizing thermal insulation to efficient energy usage in general. What these changes meant to the possibility of building glass buildings will be further discussed in chapter 7.
The indicator first introduced to measure energy usage in buildings in Sweden, was called
“specific energy usage”. Specific energy usage was defined as delivered energy to the building divided by the floor area of tempered spaces. The indicator contains the cumulative energy usage annually. Since 2017, the current way of assessing energy performance is by
1 From 1945 to 1989, Um-factors were not calculated with respect to windows, doors etc., only to the wall itself.
2 From 1989 to 2002, Um-factors depended on the ratio between window area and total external area. The graph is based on a 15% ratio as this was the maximum ratio allowed before 1989.
6 using the indicator “primary energy coefficient” (EPET)3, which differs from specific energy usage by weighting factors for energy carriers and climate zones.
2.3 Current demands
Today, four different limitations are formulated for different types of properties. These apply to a building’s primary energy coefficient, installed electrical power, average heat transfer coefficient, and average air leakage of the building shell. The primary energy coefficient is calculated as follows:
𝐸!"# = ∑ (
!"##$,&
'()* &"+,-,&&".$$,&&"/,&)
0&12 ∗!"&
).)3# (Eq. 2.1)
i denotes the surfaces of the climate shell.
EPET = Primary energy coefficient, [kWh/m2 year]
Euppv = Energy for heating, [kWh/year]
Fgeo = Geographic adjustment factor. Fgeo = 1.0 for every municipality in Greater Stockholm.
Ekyl = Energy for cooling [kWh/year]
Etvv = Energy for domestic hot water [kWh/year]
Ef = Property energy, e.g. lighting, fans, and pumps [kWh/year]
PE = Primary energy factor for energy carrier.
Atemp = The area of space regulated for temperatures over 10 ºC, enclosed by the climate shell.
(BBR 25)
In short, the primary energy coefficient is a summation of all yearly energy necessities for heating, cooling, domestic hot water, and property specific energy (e.g. fans and pumps).
Furthermore, it is multiplied by a factor depending on energy carriers (1.6 for electricity and 1.0 for every other energy carrier) and divided by the total area of heated spaces. One can however steer clear of these limitations, if one can document that inadequate energy
efficiency is compensated for by heat generation from internal industrial processes. (BBR 25, BBR 26)
Three of the limits corresponding to the types of property and locations relevant for this project is shown in table 1. For the objects of study (see chapter 4), there are no specific restrictions on air leakage (BBR 26). The limitation of installed electric power for heating was neglected in this project, as it turned out that all objects of study was heated by district heating (chapter 6.3).
3 “Primärenergital” in Swedish, freely translated by the authors.
7 Table 1: Energy efficiency demands, based on BBR 26.
Type of property EPET [kWh/m2 year] Installed electric power for heating [kW]
Average heat transfer coefficient [W/m2 K]
Large residential buildings
85* 4.5 0.40
Commercial buildings 80** 4.5 0.60
* Addition with 70 * (qavg – 0.35) kWh/m2 year is allowed, where qavg [l/sec m2] represents the average outdoor air flow, under the condition that Atemp ≥ 50 m2, and that more than 50% of the Atemp consists of apartments with a living area of maximum 35 m2 each, and qavg is above 0.35 l/sec per m2 in temperature regulated spaces. The addition is only allowed if requirement of ventilation in specific places, e.g. kitchen, bathroom and toilet, exists. Maximal qavg credited is 0,6 l/sec m2.
** Addition is allowed if for hygienic reasons, the outdoor air flow in heated spaces is above 0.35 l/sec m2. Addition with 70 * (qavg – 0.35) kWh/m2 year, where qavg [l/sec m2] represents the average outdoor air flow during the heating season. Maximal qavg credited is 1,00 l/sec m2.
Having presented the historical and current demands on energy efficiency, the following chapters will discuss and address aspects of the buildings of study and glass buildings in general.
8
3. Buildings subject to inspection
The following chapter contains a description of how the buildings of interest were chosen, and a brief presentation of the objects. The nine buildings in Greater Stockholm listed in table 2 were chosen to be investigated. The identification was rooted in conversations with
property owners, the authors’ own knowledge of Stockholm, and minor research on architect and property firms’ websites. A requirement for being a relevant object of study was that at least one side of the building shell consisted of glass for a greater part, which was assessed visually. Based on the varied applications and age of the objects of study, characteristic challenges with glass buildings were assumed to be highlighted. Pictures of the studied buildings are included in figure 2, while the reference building is shown in figure 3.
Table 2: Elected objects of study.
Property District Application Year of completion
(in current form)
Scandic Victoria Tower Kista Hotel 2011
Kista Science Tower Kista Offices 2002
Aula Medica Solna Academic 2013
Royal College of Music (Main entrance)
Östermalm Academic 2016
Clarion Hotel Sign Norrmalm Hotel 2008
Kulturhuset Stadsteatern Norrmalm Culture 1974
Gallerian Mall Norrmalm Retail 2019
Katsan Södermalm Offices 2003
Sthlm Seaside Hammarby Sjöstad Offices 2017
9 Figure 2: Objects of study. From top left: Scandic Victoria Tower, Clarion Hotel Sign, Kulturhuset Stadsteatern, the Royal College of Music, Kista Science Tower, Aula Medica,
Gallerian Mall, Katsan and Sthlm Seaside.
10 Figure 3: Reference building, KTH U-building.
11
4. Heat flux measurement & calculation
The following part moves on to describe the heat flux sensors used for measurements and the methodology of the heat flux measurement. Furthermore, the calculations of the U-factors is presented as well as the results from the heat flux measurements.
4.1 Description of heat flux sensors
The equipment used for U-factor measurements was provided by KTH’s Department of Energy Technology. Two different sensors were used to approximate the amount of heat flux through the glass facade in the buildings of study. Both sensors are based on the Seebeck effect4. Serially connected thermopiles inside the sensor generates a voltage signal
proportional to the heat that passes through the sensor element. By dividing the voltage value by the sensor sensitivity, it is converted to a heat flux (greenTEG, n.d. a). The sensors are both functioning according to “auxiliary wall principle”, which means that a slab (auxiliary wall) is placed on the wall, of which you want to measure the heat flux in. By directly connecting the slab to the wall, the same heat flux passes through the element of the wall, as through the slab.
The oldest sensor was developed at KTH Royal Institute of Technology, in 1957 and is not a conventional instrument with an established model name, henceforth it will be referred to as
“KTH-sensor”. The newer sensor was obtained by KTH in 2016 and produced by the Swiss company greenTEG and will accordingly, henceforth be referred to as “greenTEG-sensor”.
Its full model name is gSKIN® - XO 67 7C (Heat Flux Sensor) and is approved for measurements that follows the ISO 9869 norm. The sensitivity of the greenTEG-sensor is 16.65 μV/(W/m2). The approximation of heat flux done with these sensors does not require any knowledge of the thermal conductivity or thickness of the subject of measurement.
4.2 Methodology of heat flux measurement
Heat flux measurements were conducted at the objects of study in rooms with relatively steady temperatures and without direct solar radiation on cold winter days, to achieve optimal accuracy. The sensors were placed in the centre of glass wall sections until a steady heat flow was obtained. The ambient inside and outside temperatures were measured close to where the heat flux measurements were performed. The thermometer used for this purpose was a “Fluke 52 II Dual Probe Digital Thermometer” using type T thermocouples. It is important to
emphasize that these measured U-factors differs from the Um-factor mentioned in BBR, as the measurements only applies to a small area of the glass wall while Um-factors is a mean U- factor value of the entire building envelope. Measurements conducted with both types of sensors are illustrated by figure 4.
4 Thermoelectric effect which is a direct conversion of temperature difference to electric voltage.
12 Figure 4: Pictures of measurements. Left: greenTEG-senor measurement at the Royal
College of Music. Right: KTH-sensor measurement at Scandic Victoria Tower.
In addition to the nine objects of study, the U-building (Undervisningshuset) at KTH campus.
was examined as a reference building. The construction of the U-building was finished in 2017, with significantly less glass than the other objects of study and a focus on sustainability and energy efficiency. For the reference U-factor, the measurement was done on solid wall.
A disadvantage with the methodology regarding heat flux sensors is the short measurement time span, which may have resulted in inaccurate data. According to ISO 9869-1:2014, measurements should be performed over the course of 72 hours for results of scientific accuracy (greenTEG, n.d. b). Another source of inaccuracy is that the weather conditions were not the same on the days of measurement. When measuring the U-value of the glass in the Royal College of Music, Aula Medica, and the reference building the weather was snowy which may have resulted in misleading values, since the U-value changes if the glass is wet or covered by snow. This was avoided by measuring on surfaces which were determined dry.
Despite not using a standardized measuring method, the results were considered useful since they provided a basis for comparison between the buildings and the projected U-factor for the glass. The two different sensors did show a consequent relationship between both building age and actual U-factors provided by interviewees, which made it relevant for the study. The measurements were performed on every object of study except Kulturhuset Stadsteatern
13 (under renovation) and Kista Science Tower. For the latter, measurements were postponed because of lack of access and then cancelled due to the Covid-19 pandemic.
Initially, an IR-camera and IR-thermometer were also used for heat transfer coefficient calculation, but this method provided results differing largely from the other measurements in an unreasonable and inconsistent manner. The calculations were based on assumptions
concerning heat transfer coefficients (h-factors) and the measurements themselves were challenging due to radiation reflections on glass surfaces. This challenge was tentatively solved by attaching a piece of heat conductive tape on the surface which made it easier to measure the tape temperature instead of the glass. In several cases, the temperature obtained by the piece of tape was unreasonable, (e.g. it could be higher than the ambient inside temperature even though heat was flowing from inside to outside).
The formula for calculating the h-factor can be found in appendix B. The formula requires the assumption that the glass is only facing interior walls with uniform temperature same as the ambient air temperature, as well as knowledge about the emissivity of the glass. The specific emissivity of the glass in the objects of study were not available. This led to rough
estimations that may have resulted in misleading values. These calculations also resulted in U-factors completely incoherent with the result from both heat flux sensors. Despite of the roughly estimated h-factor value, the main reason for neglecting the U-factor values obtained with this method, was the highly unreasonable surface temperatures obtained by the IR- camera and IR-thermometer.
4.3 Calculated U-factors
The measured heat fluxes and temperatures were converted to U-factors based on the formula, Eq. 4.1, for total heat transfer through windows provided by Çengel & Ghajar (2015, p 552):
𝑞′ = 𝑈 ∗ (𝑇* − 𝑇+) → 𝑈 = ,-
(#&.#*) (Eq. 4.1) q’: Heat flux per square meter of wall (glass facade) [W/m2]
U: Overall heat transfer coefficient [W/m2K]
Ti: Ambient inside temperature [K]
To: Ambient outside temperature [K]
Figure 5 shows the calculated U-factor for every building based on the two different sensors.
For every object of study except one (Clarion Hotel Sign), the U-factors based on the older heat flux sensor surpassed the newer one with approximately 0.2 - 0.3 W/m2K. The
mentioned measurement where the sensors ranked oppositely, led to the by far highest factor measured, and this measurement was deemed untrustworthy. However, it did not affect the key results and trends discussed later in the thesis. All other measured U-factors were deemed trustworthy because the KTH-sensor and greenTEG-sensor measurements correlated
14 smoothly, and the results matched what was expected. Table 3 shows key data extracted from the measurements, and figure 6 shows the U-factors from the KTH-sensor distributed by the buildings’ years of completion.
Figure 5: Measured U-factors for glass walls. Reference value measured on solid wall.
Table 3: Key data extracted from measured U-factors.
U-factor category greenTEG - sensor KTH - sensor
Span [W/m2K] 0.51 - 1.78 0.72 - 1.66
Average [W/m2K] 0.95 1.11
Reference building [W/m2K] 0.10 0.23
Span ratio* 5.1 - 17.8 3.1 - 7.2
Average ratio* 9.5 4.8
* Ratio is defined as the U-factor in question divided by the reference building value.
15 Figure 6: Measured U-factors distributed by buildings’ years of completion, based on KTH-
sensor.
The real U-factors used in the energy calculations for Sthlm Seaside and the Royal College of Music were provided by respective interviewees. According to these, the real center-of-glass U-factors for these facades are 0.7 and 0.86 W/m2 K, respectively. When inspecting the measured values in Appendix A, KTH-sensor measurements states these values as 0.72 and 0.87 (while greenTEG-sensor gives 0.51 and 0.60). Despite the KTH-sensor being 60 years older than its counterpart, these precise results lead to KTH-sensor measurements being the basis for figure 6 and discussions regarding the measured U-factors.
One immediate observation based on the KTH-sensor bars in figure 5 is that none of the buildings would satisfy the Um-factor limitations in BBR if the building shell was made entirely from glass, since all the U-factors is above 0.6 W/m2 K. Some of the building shells are straying far from the limit, especially Clarion Hotel Sign, Katsan, and Scandic Victoria Tower. From figure 5 and table 3, one can also see quite clearly that all the measured glass facades have poor insulation capability compared to the reference building. Even the best climate shells have corresponding U-factors approximately three times larger than the reference, meaning three times as much heat is leaking through the facades on cold days.
From a worst-case point of view, the factor may be as large as seven. A third key observation can be made from figure 6, namely that the newer glass building shells have significantly lower U-factors than the older ones. All these observations are subjects to further discussions in chapter 7.
16 Again, it is important to emphasize that the measurements regarded U-factors, not Um-factors.
In reality, many of the building shells in this study does in fact consist largely of other materials than glass and the reference building does have windows as well. However, the differences between the glass facades and the solid reference wall does highlight the variations in insulation capabilities. Since the measurements were conducted at wintertime and without sunshine, they do not illustrate the material abilities of handling solar radiation, only the abilities regarding insulation. Also, there are as mentioned large uncertainties
regarding the accuracy of the measurements. The trends shown by the results should therefore be the highlighted aspects from this chapter, not the exact, numeral results. However, as explained in chapter 2, the U-factor and Um-factor of a building is not the only aspect relevant for examining energy efficiency in a building. The upcoming chapter presents the main findings regarding the energy performance of the objects of study.
17
5. Energy performance
Most of the objects of study in this project are legally required to have an “energy
certificate”, which is registered by Boverket. An energy certificate is a document containing detailed information about the actual energy usage in a building. This data is measured after the building is put into use, meaning it is more accurate than the simulated energy usage which is obtained in the planning process. Based on data from the energy certificates, figures 7 and 8, which shows primary energy coefficients distributed by the buildings and their respective year of completion, is obtained. Gallerian was recently reopened after renovation and has therefore no available energy certificate as of May 2020. The certificates regarding Clarion Hotel Sign and Scandic Victoria Tower are also unavailable, as hotels are generally not obliged to have this document. (Boverket, 2019)
Figure 7: Calculated primary energy coefficient (EPET) for corresponding object, with data from energy certificates provided by Boverket. (BBR 26)
18 Figure 8: Primary energy coefficient distributed by buildings’ years of completion, based on
energy certificates provided by Boverket (2020b).
Energy certificates are found at Boverkets website and are available up to ten years after execution. The energy performance in the buildings today may therefore alter from the measured value of the time the certificate was done. The certificate for Kulturhuset
Stadsteatern is from 2010 and is the oldest one, and since the building is under renovation, a different result is expected when the renovation is finished. Kulturhuset Stadsteatern is also the oldest building which is a likely reason for the high value of EPET.
Furthermore, figure 8 implies that energy efficiency has improved greatly from the building of Kulturhuset Stadsteatern until the last two decades. However, one can see no clear trend within this last twenty-year period, suggesting a more moderate development. The Royal College of music has got an EPET-value almost as high as Kista Science Tower even though their respective years of completion differs with 14 years. Katsan shows a relatively low value of EPET despite that the building was completed in 2003 and in account of its big share of glass. Reasons for these variations will be discussed later. Only Aula Medica and Sthlm Seaside meet the EPET demand of today. Aula Medica has an average hygienic outdoor airflow qavg of 0.89 l/sec m2 meaning that the building has an EPET-limitation of 117.8
kWh/m2 year. This is 36.8 units more than the actual EPET-value of the building. Additionally, one can observe that the EPET of the reference building was 60 kWh/m2 year, which is only 4 units below Sthlm Seaside.
19
6. Interviews with relevant stakeholders
Thus far, this thesis has focused on historical and current demands on energy efficiency, measurements of U-factors, and energy performance of elected objects of study. The
following chapter will describe the procedure and methods of the interviews performed. It is followed by key findings from these interviews, regarding how energy demands are met in the objects of study.
6.1 Methodology and interviewees
Interviews were included in this project due to the advantage of obtaining useful information about perceptions and opinions, and deepening the understanding of building specific
solutions and data. Interview objects were identified through recommendations made by the buildings’ contact persons and project managers. This resulted in interviewees with varied professions including architects, property managers, project managers, and energy
consultants. A disadvantage with interviewing stakeholders is that they may have self-serving bias towards their own work. For this reason, interview material was used critically with a search for undisputed facts. However, the interviewees own opinions were included and welcomed, as these were deemed as interesting results as well.
One interview (regarding Sthlm Seaside) was conducted in person, while the others were performed digitally, due to the Covid-19 pandemic. In many cases, energy reports and other data sources were provided by the interviewees. Also, an interview with a representative from Boverket was performed for discussing the legislation. A full list of interviewees and
interview formats is shown in table 4. The interviews with the building representatives followed a standardized template created by the authors, to be found in Appendix C. Every interviewee was offered a chance to confirm that they have been quoted correctly upon publication.
20 Table 4: Information about interviews.
Associated property
Interviewee Title Employer Format Date
(2020) [mm- dd]
Scandic Victoria Tower
Josefin Larsson Senior Lead Architect Wingårdhs Video 04-29
Kista Science Tower
Oskar Häger Technical property developer
Vasakronan Video 03-18
Anders Liljegren Technical property developer
Vasakronan Video 03-18
Aula Medica Peter Gustafsson Construction manager Gustafsson Projekt
E-Mail 05-12
Royal College of Music
Christoffer Haag Technical consultant Incoord AB Video 03-24
Jamal Nouman Energy & HVAC consultant
Incoord AB Video 03-24
Tobias Rosberg Architect AIX
Arkitekter
E-Mail 02-13
Clarion Hotel Sign
Josefin Larsson Senior Lead Architect Wingårdhs Video 04-29
Stefan Nilsson Lead engineer Wingårdhs Video 04-29
Kulturhuset Stadsteatern
Daniel Bäcklin Energy Coordinator City of Stockholm
E-mail 04-09
Gallerian Mall Michael Eskils Sustainability manager
AMF Fastigheter
E-Mail 04-02
Katsan Marja Lundgren Sustainability specialist / architect
White Arkitekter
Video 03-27
Sthlm Seaside Bo Berggren Technical property manager
Vasakronan In person
03-09
Jonny Olsson Technical property developer
Vasakronan In person
03-09
Eric Mårtensson Project manager Skanska In person
03-09
Lin Liljefors Project manager / engineer
Boverket Video 04-02
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6.2 The choice of glass
An important objective during the interviews was to determine why glass was chosen as a major component in the respective climate shells. Are there any indoor climate advantages?
Is the choice based on an environmental life cycle assessment on materials? For both
questions, the answer simply was no. Every interviewee answered that the choice of glass as a significant facade material to their knowledge was a pure aesthetic priority. Among these answers, more detailed explanations as to why glass was seen as an aesthetically pleasing material varied.
For office buildings like Kista Science Tower and Sthlm Seaside, creating desirable office spaces for potential tenants was emphasized in the planning process. Companies want spaces with panoramic views, vast daylight inlet, and a sense of connection with the outside world and the developers need to fulfill this demand for commercial viability. For the Royal
College of Music, glass provided a desirable institutional appearance and the architect behind Kulturhuset Stadsteatern wanted the building to showcase the cultural events within it.
Furthermore, several interviewees stated that overarching, architectural area plans by local authorities often includes varied facade materials, and that this was a contributing factor for choosing glass. The general opinion among the interviewees was that the future in our urban areas is likely to include even more glass buildings. Conclusively, glass has many beneficial aesthetic qualities for tenants and different stakeholders, making it desirable in many
situations. However, good energy and environmental performance is also an important demand from these stakeholders, highlighting the conflict between energy efficiency and aesthetics which is the main premise of this thesis.
6.3 How are BBR energy efficiency demands met?
Perhaps the most pressing topic discussed during the interviews concerned how energy efficiency demands are met for each building. First of all, it is important to underline that very differing laws applied at the times of approval for respective building (see chapter 2, and table 2). For instance, Kulturhuset Stadsteatern was built just before Um-factor limitations were tightened and when there were no demands on specific energy usage. This means that meeting the demands were much easier than it would have been today. Also, Katsan and Kista Science Tower were constructed before quantitative limitations on energy usage were implemented. A few measures turned out to be especially prominent, and these are
summarized in table 5. All buildings are heated by district heating, and all besides Katsan is cooled by district cooling (Katsan cooling will be discussed later). Additionally, quite a few of the buildings have either installed or planned solar panels, and solar protection in the form of blinds or window films are implemented in several cases.
22 Table 5: Prominent measures taken to obtain satisfying energy efficiency, stated by the interviewees.
Object District
heating
District cooling
Solar panels
Heat pumps Visible blinds etc.
Scandic Victoria Tower X X - - -
Kista Science Tower X X X X X
Aula Medica X X - X -
Royal College of Music (Main entrance)
X X - - X
Clarion Hotel Sign X X - - -
Kulturhuset Stadsteatern X X X - -
Gallerian Mall X X Planned - -
Katsan X - - - X
Sthlm Seaside X X Planned - X
An additional distinct feature that was made clear upon visiting several objects of study, was that most of them had a lower share of glass in their climate shell than what is apparent from the outside. Both Aula Medica and Scandic Victoria Tower have facades containing a mosaic of glass with different color shades and transparencies. From the inside, it becomes clear that a majority of the pieces are actually just a cover on the outside of a solid wall. This means that what appeared to be a glass building actually has a majorly solid climate shell with glass covering and a large number of windows. In Aula Medica for instance, glass only stands for 25-33% of the climate shell. This may be seen upon as an energy efficient measure that does not affect the scenic expression of the building from the outside, but compromises the desirable characteristics of glass that you experience from the inside.
Clarion Hotel Sign, Kulturhuset Stadsteatern, and Sthlm Seaside, however, have a glass climate shell in only one direction, respectively northeast and north. Gallerian is divided into several parts with completely different facade designs, where only the relatively short north- facing side and less than half of the side facing east is predominantly of glass. In the other orientations, walls are solid with a relatively low share of glass. Both of these measures lead to a significant decrease in the building Um-factor, and interviews confirmed that they were implemented strategically with this purpose. The north-facing glass walls also lead to less solar radiation than a south-facing would have, which reduces the risk of summerly overheating, according to the interviewees. None of the buildings with reduced shares of glass have any particularly creative energy solutions like the ones which will be presented below, besides district heating, district cooling, and blinds. This also apply for the reference building, according to its energy certificate. An additional observation to make, is that the
23 only two buildings which are below today’s EPET-limitations (Sthlm Seaside and Aula
Medica) actually have relatively small shares of glass.
The measures mentioned above means that only three out of nine objects of study really have climate shells consisting majorly of glass. Interviews show that these ones have demanded more creative solutions to obtain desired energy efficiency levels. Katsan is built next to, and partially on top of a channel (Hammarby Kanal), and channel water is pumped in large tubes through the house, for effective and self-produced cooling. An important observation
regarding this system is that the local cooling system does not reduce the total energy usage of the building, but it does reduce the amount of “bought energy” significantly. The latter is the basis of the statistics reported to authorities (like the ones shown in figure 7). Solar panels and other forms of local energy production also have this same effect on statistics. Another interesting aspect with Katsan is that it was built at a time where only Um-factor limitations existed, and this parameter was not affected by the mentioned innovative measures. The measures were done to satisfy the developers’ own demands, while the City of Stockholm decided to make an exception to neglect the actual Um-factor demand in this case, according to Marja Lundgren, architect at White Arkitekter.
This highlights a weakness in the legislation at that time, as well as proves that developers in some cases take initiative to set their own demands higher than those set by Boverket.
According to Lundgren, this is done because the company wants to lay on the forefront of the development, and because they want to build houses that will be loved and thus kept in the future. The claim that developers take their own “green” initiatives is supported by
representatives from Vasakronan who presented that energy efficiency demands in their company policy is stricter than those stated in BBR. They motivated this to some extent with economic profitability, but mainly with a genuine environmental commitment and a similar strategic desire to be in the leading edge. Vasakronan often need to meet requirements from the City of Stockholm as well, and these demands are situated between BBR demands and their own demands in terms of strictness.
Another sheer glass building which has demanded creative solutions is the Royal College of Music. The building is designed as a cluster of solid wall buildings containing concert halls, practice facilities, and study rooms, enclosed by a glass cube. Within these units, heating and cooling is regulated independently, as if they were independent, stand-alone buildings. The glass-enclosed space outside of these units is solely meant for short-time visits (e.g. cafeteria, reception, and transport between units) and this is a key feature for meeting energy efficiency demands, according to the interviewees from Incoord AB. Short visitation periods enables setting a larger acceptable temperature span in these spaces, leading to lowered needs of heating and cooling on respectively cold winter days and sunny summer days. One can also take advantage of the facts that these are education facilities, meaning that visitation will be very low during the summer which enables energy savings, as temperature control can be more lenient in this period.
24 The Royal College of Music stands out from the rest of the buildings since no other objects have such units with independent energy systems inside of the climate shell. This design solution contributed to acceptable energy usage, but the developers also needed to meet Um- factor limit which were 0.7 W/m2 K (BBR 18). According to the buildings’ energy report provided by Incoord AB, the glass used for the facade has a U-factor of 0.86 W/m2 K while the calculated Um-factor was 0.53 W/m2 K. The report shows that this is mainly due to large, insulated concrete surfaces such as the roof and the walls of the basement having very low U- factors (0.08-0.17 W/m2 K). This exemplifies how greatly Um-factors can be manipulated by solid surfaces that do not influence the aesthetic appearance.
The remaining sheer glass building is Kista Science Tower, which was planned at a time where Um-factor demands depended on the share of windows and that this share was limited to 18% of floor area (BBR 1-12). It is not clear how a glassed skyscraper could be built at that time, and what Um-factor demands were applicable, as none of the stakeholders relevant to this building had any explanation to this. However, the building is enclosed with a solar film and automatic blinds to exclude solar radiation, as well as having varied types of glass and composition of the facade in the different cardinal directions to optimize the energy performance. Kista Science Tower is the only object of study with both an installed heat pump system, and solar panels of significance. This confirms a clear trend, that the three buildings that are the closest to being sheer glass buildings are the ones with the most complex and innovative energy efficiency measures.
Interviews also illustrated some examples of aesthetic desires working together with energy efficiency. Wingårdhs Arkitektkontor wanted Scandic Victoria Tower to contain reflective glass to improve its silhouette from a distance. This type of glass reduces det solar radiation inlet. Also, a significant architectural aspect of Aula Medica is that its southern wall is
severely inclined, which also leads to a similar solar heat reduction. These two design aspects are thus leading to a decreased need of cooling in the summer, meaning energy efficiency is enhanced. This shows that design and energy efficiency are not always contradicting aspects.
6.4 General statements on glass buildings
Interviews led to several statements being made, which were deemed relevant for further discussions. Generally, the different stakeholders interviewed all agreed that a glass building undisputedly brings several challenges not provided by solid wall climate shells. These challenges lead to more complex simulations and calculations, and subsequently more intricate solutions. The greatest challenge with glass facades in terms of energy usage is not the poor insulation ability, but the vast inlet of solar radiation heat during sunny summer days, according to the interviewees. A recurring statement was that glass is problematic in the summer due to solar radiation, problematic in the winter due to poor insulation abilities and only advantageous during a few days per year. This claim refers to both indoor climate and energy usage. It is also common that the glass is covered with a film that reduces the amount of incoming solar radiation, which then lessens the benefit from solar radiation during cold days.
