Thesis for the degree of Doctoral of Philosophy
in the subject of Ecotechnology and environmental science
Östersund 2016
ENERGY PERFORMANCE OF RESIDENTIAL BUILDINGS
- projecting, monitoring and evaluating
Itai Danielski
Faculty of Science, Technology, and Media
Mid Sweden University, SE-831 25 Östersund, Sweden
ISSN 1652-893X,
Mid Sweden University Doctoral Thesis 238
ISBN 978-91-88025-52-4
Akademisk avhandling som med tillstånd av Mittuniversitetet i Sundsvall
framläggs till offentlig granskning för avläggande av teknologie doktorsexamen
tisdag 23 februari, 2016, klockan 10:15 i sal G1352, Mittuniversitetet Östersund.
Seminariet kommer att hållas på engelska.
ENERGY PERFORMANCE OF RESIDENTIAL BUILDINGS - projecting, monitoring, and evaluating
Itai Danielski
© Itai Danielski, 2016
Department of Ecotechnology and Sustainable Building Engineering,
Faculty of Science, Technology, and Media
Mid Sweden University, SE-831 25 Östersund, Sweden
Telephone: +46 (0)771-975 000
Printed by Mid Sweden University, Östersund, Sweden, 2016
i
ABSTRACT
Energy security and climate change mitigation have been discussed in Sweden
since the oil crisis in the 1970s. Sweden has since then increased its share of
renewable energy resources to reach the highest level among the EU member states,
but is still among the countries with the highest primary energy use per capita. Not
least because of that, increasing energy efficiency is important and it is part of the
Swedish long term environmental objectives. Large potential for improving energy
efficiency can be found in the building sector, mainly in the existing building stock
but also in new constructions.
Buildings hold high costs for construction, service and maintenance. Still, their
energy efficiency and thermal performance are rarely validated after construction or
renovation. As energy efficiency become an important aspects in building design
there is a need for accurate tools for assessing the energy performance both before
and after building construction. In this thesis criteria for energy efficiency in new
residential buildings are studied. Several building design aspects are discussed with
regards to final energy efficiency, energy supply-demand interactions and social
aspects. The results of this thesis are based on energy modelling, energy
measurements and one questionnaire survey. Several existing residential buildings
were used as case studies.
The results show that pre-occupancy calculations of specific final energy demand
in residential buildings is too rough an indicator to explicitly steer towards lower
final energy use in the building sector. Even post occupancy monitoring of specific
final energy demand does not always provide a representative image of the energy
efficiency of buildings and may result with large variation among buildings with
similar thermal efficiency. A post occupancy method of assessing thermal efficiency
of building fabrics using thermography is presented. The thermal efficiency of
buildings can be increased by design with low shape factor. The shape factor was
found to have a significant effect on the final energy demand of buildings and on
the use of primary energy. In Nordic climates, atria in multi-storey apartment
buildings is a design that have a potential to increase both energy efficiency (by
lower shape factor) and enhance social interactions among the occupants.
ii
SAMMANFATTNING
Energiförsörjning och åtgärder för att minimera klimateffekter har diskuterats i
Sverige sedan oljekrisen på 1970-talet. Sverige har sedan dess ökat sin andel
förnyelsebar energi till den högsta nivån bland EU:s medlemsstater. Samtidigt
tillhör Sverige de länder som har störst primärenergianvändning per capita. Detta
gör det viktigt att öka energieffektiviteten i samhället, vilket också är del av de
svenska miljömålen. Byggsektorn har stor potential för energieffektivisering, främst
vad gäller det befintliga byggnadsbeståndet men också i nya byggnader.
Byggnader har förhållandevis höga kostnader för uppförande, drift och
underhåll. Ändå valideras sällan energieffektivitet och termiska prestanda hos
byggnader efter uppförande eller renoveringsåtgärder. Med energieffektivitet som
en allt viktigare aspekt vid design av byggnader uppkommer behov av noggranna
verktyg för att kunna bedöma energiprestanda både före och efter att byggnader har
uppförts. I denna avhandling studeras kriterier för energieffektivitet i nya
bostadshus. Några aspekter av byggnadsdesign diskuteras vad gäller
energieffektivitet, interaktion mellan produktion och efterfrågan i energisystemet
samt rörande sociala aspekter. Resultaten i denna avhandling är baserade på
energimodellering, energimätningar samt en enkätundersökning. Flera befintliga
bostadshus har används för fallstudier.
Resultaten visar att beräkningar av specifik slutlig energianvändning i
bostadshus före deras uppförande är en alltför grov indikator för att uttryckligen
styra byggsektorn mot lägre slutlig energianvändningen. Inte heller mätning av
specifik slutliga energianvändning efter byggnaders uppförande kommer alltid att
ge en representativ bild av byggnadernas energieffektivitet och kan uppvisa stora
variationer för byggnader med liknande prestanda. En metod för att bedöma
termiska prestanda hos befintliga byggnaders klimatskal genom termografering
presenteras. Termiska prestanda hos byggnader kan ökas genom att utforma dem
med låg formfaktor. Värdet på formfaktorn befanns ha betydande effekt på deras
slutliga energianvändning, liksom för primärenergianvändning. I nordiskt klimat är
atrium i flerbostadshus en design med potential att öka både energieffektivitet
(genom lägre formfaktor) och den social interaktion mellan de boende.
iii
PREFACE
This work was carried out within a doctoral research project in the Ecotechnology
research group at Mid Sweden University. It is a part of the interdisciplinary subject
of environmental science. My personal goal was to gain a broad overview of the
interconnection between buildings, energy production and the environment. This
thesis compendium is a summary of a journey. A journey of knowledge and new
discoveries, in which my life perspective has shifted in so many ways, thanks to the
many people whom I have met along the way.
I would like to start by thanking all my supervisors, Professor Morgan Fröling,
Professor Leif Gustavsson and Doctor Anna Joelsson. Your guidance, advice and
contribution to this research are highly appreciated and your signature is apparent
in the entire text. I would like to give special thanks to Professor Inga Carlman for
her support and guidance during this journey.
A special thanks also goes to professor Thomas Olofsson, Magnus Rindberg from
Närhus, Åke Mård from Koljern, Anders Lundström from Glulam and Daniel Köbi
from Jämtkraft, for their engagement and support in my research.
Many thanks go to my colleagues in the Department of Ecotechnology and
Sustainable Building Engineering, and a special thanks to: Ambrose Dodoo, Bishnu
Poudel, Felix Dobslaw, Gireesh Nair, Kerstin Hemström and Truong Nguyen for the
inspiring discussions and many laughs. You made these years a bit lighter.
Finally, but not least, I am thankful to my wife and children who have shared
this journey with me during both good and more difficult periods. And to my
parents, on the other side of the Mediterranean, I hope to make you proud.
iv
v
LIST OF PAPERS
Paper I Leif Gustavsson, Ambrose Dodoo, Nguyen Truong, Itai Danielski
Primary energy implications of end-use energy efficiency measures in
district heated buildings
Energy and Buildings, 43 (1) (2011) 38-48
Paper II Itai Danielski
Large variations in specific final energy use in Swedish apartment buildings:
Causes and solutions
Energy and Buildings, 49 (0) (2012) 276-285
Paper III Itai Danielski, Morgan Fröling, Anna Joelsson
The Impact of the shape factor on final energy demand in residential
buildings in Nordic climates
World Renewable Energy Congress 12-19 May 2012. Denver,
Colorado, USA
Paper IV Itai Danielski, Michelle Svensson, Morgan Fröling
Adaption of the passive house concept in northern Sweden - a case study of
performance
Passivhus Norden. 21-23 October 2012, Göteborg, Sweden.
Paper V Itai Danielski, Gireesh Nair, Anna Joelsson, Morgan Fröling
Heated atrium in multi-storey apartment buildings, a design with potential
to enhance energy efficiency and to facilitate social interactions
Submitted for publication.
Paper VI Itai Danielski, Morgan Fröling
In-situ measurements of thermal properties of building elements using
thermography under non-steady state conditions
Submitted for publication.
vi
Contribution report
The author of this thesis is the main author and responsible for measurements,
analysis and discussions in the Papers II, III, IV and VI. In Paper I the author is
responsible for the energy modelling and involved in discussions and reviewing of
the manuscript. In Paper V the author is the main author, responsible for the final
energy modelling and analysis, construction of and practical implementation of the
survey and for results discussions.
vii
Other publications by the author related to the research in this thesis
Danielski, I., M. Fröling, A. Joelsson
Air source heat pumps and their role in the Swedish energy system
GIN - Greening of Industry Network. 2012. Linköping, Sweden.
Danielski, I., G. Nair, M. Fröling
Heated atrium in multi-story buildings: A design for better energy efficiency and social
interactions
Passivhus Norden. 2013. Göteborg, Sweden.
Danielski, I. M. Fröling
Systems effecting systems when managing energy resources
ISEM - Ecological Modelling for Ecosystem Sustainability in the context of Global
Change. 2013. Toulouse, France.
Danielski, I., M. Svensson, M. Fröling
Adaption of the passive house concept in northern Sweden: a case study of performance
PassivhusNorden. 2013. Göteborg, Sweden.
Jonasson, J., I. Danielski, L.-Å. Mikaelsson, M. Fröling
Approach for sustainable processes for the built environment in triple helix cooperation: the
case of Storsjö strand in Östersund
Linnaeus ECO-TECH. 2014. Kalmar, Sweden.
Jonasson, J., I. Danielski, M. Svensson, and M. Fröling
A two family house built to passive house standard in the north of Sweden – environmental
system performance
Linnaeus ECO-TECH. 2014. Kalmar, Sweden.
Jonasson, J., I. Danielski, M. Fröling
Life cycle assessment of a passive house in northern Sweden.
20th International Sustainable Development Research Conference. 2014. Trondheim.
Danielski, I.
Energy efficiency of new residential buildings in Sweden: Design and Modelling Aspects
Licentiate thesis, The Department of Ecotechnology and Sustainable Building
Engineering, Mid Sweden University, Östersund, Sweden. 2014.
Danielski, I., Fröling, M.
Diagnosis of buildings’ thermal performance - a quantitative method using thermography
under non-steady state heat flow
Energy Procedia, 83, (2015) 320-329.
viii
TABLE OF CONTENTS
ABSTRACT ......................................................................................................................... I
SAMMANFATTNING .................................................................................................... II
PREFACE .......................................................................................................................... III
LIST OF PAPERS ............................................................................................................. V
1. INTRODUCTION ...................................................................................................... 1
1.1. The role of energy in the building sector ........................................................ 2
1.2. Energy and buildings in Sweden ..................................................................... 3
1.3. Energy requirements ......................................................................................... 4
1.4. The aim of the thesis .......................................................................................... 6
2. METHODOLOGY ...................................................................................................... 7
2.1. System analysis of energy demand in buildings ........................................... 7
2.2. Data collection .................................................................................................. 10
2.2.1. External sources of data .................................................................................. 10
2.2.2. Energy monitoring ........................................................................................... 10
2.2.3. Measurements of thermal properties ............................................................ 10
2.2.4. Final energy modelling ................................................................................... 11
2.2.5. Questionnaire survey ...................................................................................... 11
3. CASE STUDY BUILDINGS ................................................................................... 12
3.1. The Wälludden building ................................................................................... 12
3.2. The Stockholm program ................................................................................. 13
3.3. The Röda Lyktan building ................................................................................ 15
3.4. The atrium building......................................................................................... 16
3.5. Wooden cabin ................................................................................................... 17
4. POST OCCUPANCY ENERGY MONITORING ............................................... 18
4.1. The building interior layout design .............................................................. 19
4.2. Time elapse before the start of the energy monitoring ............................... 23
5. ENERGY PERFORMANCE GAP .......................................................................... 25
5.1. Discrepancies between calculated and monitored values .......................... 25
ix
5.2. Causes for discrepancies ................................................................................. 28
5.2.1. Assumptions during final energy calculations ............................................ 28
5.2.2. Systematic errors .............................................................................................. 31
5.2.3. Thermal performance gap .............................................................................. 32
6. POST OCCUPANCY EVALUATION BY THERMOGRAPHY ....................... 33
6.1. Thermography for quantitative analysis ...................................................... 33
6.2. Experiment results ........................................................................................... 35
7. THERMAL EFFICIANCY OF BUILDING ENVELOPE .................................... 38
7.1. The shape factor of buildings ......................................................................... 38
7.2. Glazed area in buildings ................................................................................. 44
8. BUILDING DESIGN IN AN ENERGY SYSTEM PERSPECTIVE .................. 47
8.1. Dynamic energy demand-supply interaction .............................................. 47
8.2. Reference heat and power production plant ................................................ 48
8.3. Energy efficiency measures ............................................................................ 50
9. BUILDING DESIGN AND SOCIAL ENVIRONMENT ................................... 52
9.1. Atrium ............................................................................................................... 52
9.2. Social interactions ............................................................................................ 53
10. DISCUSSION ...................................................................................................... 57
10.1. Indicators for energy efficiency ..................................................................... 57
10.2. Indicators for efficient building design ......................................................... 58
10.3. Thermal properties of buildings in use ......................................................... 59
10.4. Primary energy use .......................................................................................... 59
10.5. Social interactions ............................................................................................ 60
11. CONCLUSIONS .................................................................................................. 61
REFERENCES ................................................................................................................... 63
x
1
1. INTRODUCTION
Through the history of civilization humans have built shelters to practice their
social activities, while having protection against weather, wild animals, and other
human beings. Over the course of time, vernacular dwellings have evolved to
respond to climate challenges, available materials and cultural expectations in a
given location [1]. Such buildings include, e.g. the adobe house [2], the open
courtyard building design [3] and the Inuit igloos in Greenland and northern
Canada [4].
New technologies, new materials, and changes in societal structures have
changed the way buildings have been designed and constructed. With industrialism,
manufacturing enterprises and production of large quantities of inexpensive
industrial goods became the basis of the economy and employment in most western
countries. Employment was concentrated in urban factories, which together with
changes in western societies led to large migration into industrial centers in the 19th
century [5]. When land prices increased in city-centers, the desire to construct high
elevated buildings could be fulfilled partly due to the invention of new materials
and techniques like the Portland cement and the reinforced concrete. Reinforced
materials increased the strength of constructions, and hence played a vital role when
designing buildings. So did also the prices of materials [6].
Modern architecture, which began in the last part of the mid-19th century [7],
arose in the wake of these developments. The term “modern building construction”
or “modernism” was coined after the 2nd world war [8]. It was related to social and
political conditions [9], to the evolution of materials and to technological
advancement, which brought innovations. New materials, such as iron, steel and
sheet-glass and new techniques approved of by building codes and standards, as
well as other political incentives, had not only an impact on building constructions
as such, but also on new housing development.
New building techniques, using reinforce materials and steel structure, changed
the forms of buildings from the heavyset stone architecture – typical before the 19th
century – to a more slender one. Stronger and taller constructions, using less stone,
brick or wood, could be erected and it broke the dependence on walls as the
supporting function. This meant that buildings were no longer treated as bodies,
restricted to less advanced technique and enclosed by massive materials, but rather
as volumes of lights, lines and shapes with simple and functional design. The walls
become subordinate elements more of thermal berries, as the bearing parts were
beams in concrete or steel and pillar constructions. The often rich ornamentation was
more or less banned and in focus was instead the structural elements. [10]. This trend
was captured by the famous words of Mies van der Rohe “Less is more” a principle
2
for minimalist design, i.e. to do the most with as little materials and forms as possible
[10]. Modern architecture can also be characterized by houses taller than 6 floors,
which were rare earlier. With the invention of the elevator and management of water
pressure, the height of buildings could increase significantly.
Reactions against modernism became strong in the last decades of the 20th century
with the movement of postmodern architecture. Postmodern architecture was
represented by a diversity of expressions without restricting principles and by
idolizing unique forms bringing back premodern elements and decorations. This
architecture has in its turn been criticized for being vulgar, populist, extravagant,
and introvert, not engaging itself in contemporary social and environmental issues.
Since the start of the postmodern architecture, in the middle of the 20th century,
the world had reached new heights of population growth rates with about 1 billion
every 12-13 years. Human population, consumption patterns, and economic growth
have increased the demand for natural resources [11]. Modern lifestyle has reached
a stage where ecological services are used faster than nature can regenerate them
[12] and humanity has become more dependent on energy. For example Heating,
Ventilation and Air Conditioning systems (HVAC) in buildings became widely used
to improve indoor comfort.
After the oil-supply crises in the middle of the 1970s, the connection between
building design and the environment changed from just providing sufficient
thermal comfort to promoting energy efficiency due to the awareness of the fact that
natural resources are limited [13, 14]. That was the start of the sustainable
architecture movement. It was during this time building regulations in many
countries started to include aspects of thermal performance of building fabrics [13]
and in recent years also the reduction of greenhouse gases [13]. Today, the
sustainable construction movement is international in scope, with almost 60 national
green building councils establishing ambitious goals for the built environment in
their countries [15].
1.1. The role of energy in the building sector
Buildings affect the environment during their entire life time, which include:
production of material, construction, operation, maintenance, disassembly and
waste management. During these phases natural resources are consumed, land is
used, waste is produced and emissions are released to the environment. The effect
on the environment may remain many years after a building is demolished.
With business as usual, the environmental impact of the building sector will
increase in the future due to increased demand for better indoor comfort, increased
time spent indoors [16] and global population growth. Predictions done by the UN,
3
point at 1.0 to 3.5 billion additional people by 2050, which is equivalent to 15% - 50%
of current world population [17]. It is a challenge to provide a sufficient number of
dwellings for a growing world population while maintaining a high standard of
living and good thermal comfort. Yet, it is a greater challenge to ensure that these
buildings will comply with the principle set by the global society in the WCED-
report Our Common Future to “meet the needs of the present without
compromising the ability of future generations to meet their own needs” [18].
At the same time the building sector holds high potential to reduce energy
demand [19]. As a measure to realize this potential, the European parliament
approved the Directive on the Energy Performance of Buildings [20] in 2010. The
directive requires that by the end of 2020, all newly constructed buildings in the EU
should be “nearly zero-energy buildings”, and member states should stimulate the
transformation of existing buildings under refurbishment into nearly zero-energy
buildings. Although the concept of “nearly zero-energy buildings” is not defined,
the objective of this directive is to promote a building design with improved energy
performance in all EU member states.
1.2. Energy and buildings in Sweden
Sweden is an industrialized country with a high standard of living, high GDP per
capita (USD 40,700) and rich in resources for heat and power production including
hydro, solar, biomass, wind, and uranium (currently not utilized). It is located in the
northern part of Europe between 55° and 70° latitude with temperate to sub-arctic
climate and average annual outdoor temperatures that ranges from 9°C in the south
to below 0°C in the north. In such climatic conditions there is a dependency on
energy resources to obtain sufficient indoor thermal comfort [21].
In 2013, Sweden was ranked third in Energy Sustainability Index by the World
Energy Council [22], which includes three indicators: energy security, social equality
and environmental impact mitigation. At the same time, Sweden was also highly
ranked in terms of primary energy per capita [23]. A significant cause for the high
primary energy demand per capita is the large share of existing dwellings that were
built during the 1960’s and 1970’s [24]. At that period, energy efficiency in buildings
was not prioritized due to low energy prices. As a result, the Swedish residential
and service sector became the most energy intensive sector with about 40% of the
total final energy demand [25].
The Swedish population have increased steadily in recent years by an average of
0.4% per year and is expected to grow by additional 2.1 million citizens by 2060 [26],
which is 23% of today population. This value may be underestimated, as it does not
consider the current and possible future waves of incoming conflict and climate
4
refugees. The annual rate of new constructed residential dwellings for the last 20
years was slightly higher with 0.5% on average [27], and the goal of the Swedish
government is to build additional 250,000 new dwelling units by 2020 [28]. Thus, to
reach the Swedish energy goal of 20% lower total final energy demand by 2020, in
comparison to year 1990 [29], design of new buildings should aim for high energy
efficiency.
1.3. Energy requirements
New residential buildings in Sweden are required by the Swedish building code
(BBR) [30] to fulfil a set of goals concerning safety, energy efficiency and thermal
comfort. These goals, listed in Table 1, include limits for specific final energy
demand of the building for each of the four climate zones, as illustrated in Figure 1.
Stricter energy requirements than the Swedish building codes are encouraged by
different certification schemes with labels issued by a third party. These can be
divided between environmental and energy only certification schemes.
Environmental certification schemes evaluate a range of issues concerning the
building, the installed systems, and in some cases the building site and occupants’
possibilities for sustainable behaviour. International environmental certifications are
BREEAM and LEED. Many countries have their own national schemes such as the
Miljöbyggnad scheme in Sweden, provided by the Sweden Green Building Council [31].
Figure 1. Illustration of the four climate zones (I – IV) used in the Swedish building
code.
5
Table 1. The energy requirements of the Swedish building code for different Swedish
climate zones [30].
Climate zone Unit I II III IV
The specific final energy demand* kWh/(m2 year) 115 (85) 100 (65) 80 (50) 75 (45)
Installed power rating for heating** kW 5.5 5 4.5 4.5
Average thermal transmittance*** W/( m2 K) 0.4 0.4 0.4 0.4
* Household electricity is not included. Values in brackets are for dwellings with electric heating.
** For dwellings with electric heating and a heated floor area up to 130 m2.
For each additional 1 m2 heated floor area, 0.035 kW should be added.
*** Watt per building’s envelope area and degree Kelvin.
The Miljöbyggnad certification system is developed for the Swedish building
sector, and is based on the Swedish construction practice. It includes 16 different
performance indicators, where two of them concern energy demand: the building’s
specific final energy demand and the maximum heat load demand per floor area, as
listed in Table 2. Each indicator is graded by three levels: Bronze, Silver and Gold.
In addition to the environmental certification schemes there are the EU’s
GreenBuilding programme and the Passive house criteria, which only focus on energy.
The EU’s GreenBuilding label is intended for existing buildings that achieve a 25%
reduction in final energy demand by implementing energy efficiency measures or
new buildings with 25% lower calculated energy demand in comparison to the
Swedish building code. It is worth noting that specific final energy demand has large
weight in the different certification schemes and policies.
The requirements for certifying passive houses in Sweden [32] are a modification
of the international passive house criteria [33] to the Swedish climate conditions, and
include requirements concerning thermal resistance and air tightness of the building
envelope. There are two requirements for energy demand: (i) the ratio of heat load
demand to the heated floor area of the building; and (ii) the specific final energy
demand, which are listed in Table 3 for the different climate zones, as illustrated in
Figure 1.
Table 2. The Miljöbyggnad certification scheme for energy demand indicators [31].
Indicators Climate zone Bronze Silver Gold
The specific final energy demand ≤100%* ≤75%* ≤65%*
Heat load demand (W/m2) I** ≤ 84 (≤ 56) ≤ 56 (≤ 42) ≤ 34 (≤ 28)
II** ≤ 72 (≤ 48) ≤ 48 (≤ 36) ≤ 29 (≤ 24)
III+IV** ≤ 60 (≤ 40) ≤ 40 (≤ 30) ≤ 25 (≤ 20)
* % of the energy requirements of the Swedish building code (BBR), see Table 1.
** Values in brackets are for dwellings with electric heating.
6
Table 3. The Swedish energy criteria for passive houses by heating system and
climate zone for building with floor area that is smaller than 400 m2 [32].
Climate zone: I II III+IV
Heat load demand/Floor area W/m2 19 18 17
For non-electric heating systems kWh/(m2 year) 63 59 55
For electric heating systems kWh/(m2 year) 31 29 27
For a combination of different types
of heating systems
kWh/(m2 year) 78 73 68
The variety of building certification schemes and the different concepts of energy
efficient buildings, e.g. mini energy, near zero energy, zero energy, and passive
house indicate that evaluation of building energy efficiency is subjected to different
interpretation.
1.4. The aim of the thesis
The objective of the research presented in this thesis is to evaluate criteria for
energy efficiency in new residential buildings by examining a number of building-
design aspects. It analyses how building-design can affect final energy demand
during the service life time of a building, and explore the connection between energy
demand and supply systems in order to minimize primary energy use. The thesis
includes two main research questions:
What are the difficulties of projecting and evaluating energy performance of
residential buildings? And how could it be improved?
What are the effects of buildings’ exterior and interior design regarding energy
efficiency and social interactions? And which design parameters are important
to consider?
7
2. METHODOLOGY
Modification of existing buildings and energy systems is not always practical or
possible. Instead analytical calculations, modelling and monitoring can be used to
study the effect of different variables on the performance of the whole system in
question. The following sections describe the methods and the analytical tools that
were used in this thesis.
2.1. System analysis of energy demand in buildings
A system can be viewed as “a regularly interacting or interdependent group of
items (components) forming an unified whole” [34]. The exchange of information,
material or energy among the different components is an essential part of the system
in question, which is best described by Aristotle’s argument that the whole is greater
than the sum of its parts.
Energy systems can be analysed by a top-down or a bottom-up approaches. A
top-down model begins with an aggregated description of the system and then sub-
divides it to understand the functioning of the different components of the system.
Truncation errors are avoided, but it provides a limited understanding of how the
different processes can be altered to achieve improvements.
In this thesis the bottom-up approach was used. A bottom-up model can analyse
how small modifications affect the system as a whole and the interactions among its
different components. First, a detailed understanding of the fundamental
components and processes of the system is required. Then aggregate system
behaviour is generated by modelling the relations between the individual
components of the system. The conclusions are determined by the magnitude of the
changes observed under small modifications of a single parameter at a time. The
disadvantage of a bottom-up approach is that the further upstream the analysis
expands the more difficult it becomes to determine all the indirect inputs to the
processes. The exclusion of many small energy inputs may generate a significant
truncation error.
Therefore, it is important to define the boundaries of the modelled system. The
boundaries act as a cut off, in which all the components outside the boundaries are
excluded. The choice of the boundaries may affect the outcome and should therefore
be clearly described. In this thesis the boundaries vary depending on the objective
of the analysis, as illustrated in Figure 2. In Paper VI the system is a single wall and
the boundary is set on the wall surface. The system includes all the heat flows
through these boundaries. In Papers II to V the system is an entire building, in which
the walls are only one of the components. The boundary is set on the exterior side of
8
the thermal envelope of the building and include all energy flows through it and
between the different components of the buildings. In Paper I, the system includes
the entire energy chain from natural resources via heat and power production plants
to energy services in the buildings, i.e. the buildings acts as one of the components
of the whole energy system. To overcome allocation difficulties of heat and power
in district heating plants, the system was expanded to include the marginal power
plant (see Figure 2) and the subtraction method was used. The subtraction method
[35] will be explained in detail in section 7.
Conclusions from system analysis can be obtained if a similar functional unit is
used for all the systems. The functional unit is a quantified performance of a product
(goods or service) of a system [36]. It provides a reference to determine equivalence
between systems. There is a need for similar units also in energy system assessments.
When discussing energy supply and energy demand, a variety of functional units
and related parameters can appear. In this thesis two functional units and two
energy related parameters are used.
Functional units:
One unit of building floor area and year
One unit of apartment floor area and year
Parameters:
Final energy demand denotes the energy supplied to the building in the form
of electricity, or heat for space heating and domestic water heating. In this
thesis the final energy could denote the sum of all these energy flows or
individual energy flows. In the latter, description of the type of energy flow
will be provided.
Primary energy use represents the energy content in the energy resources that
are needed in order to deliver final energy to a building. It hence includes
all the energy losses along the energy chain from natural resources to energy
services.
9
Figure 2. An overview of systems boundaries used in the research described in this thesis.
10
2.2. Data collection
The results of system modelling are only as good as the quality of the data input
and assumptions. This section will describe the data sources that were used in the
research described in this thesis.
2.2.1. External sources of data
Monitored meteorology data for outdoor temperature, wind, solar radiation and
humidity were obtained from different sources. In Papers I and II data was obtained
from the NOAA Earth System Research Laboratory. In Paper III data was obtained
from temperatur.nu. In Paper V data was obtained from the Swedish Meteorological
and Hydrological Institute (SMHI).
The daily district heat production in Paper I was obtained from the local district
heating provider in Östersund, Jämtkraft. Monitored final energy demand for the
Stockholm program buildings was obtained from the Stockholm municipality by
personal communication [37] and from the local district heating network in
Stockholm, Fortum Värme. Architectural drawings of the buildings were obtained
from: the Stockholm city archives, from the Östersund city archive, from the Umeå
city archive and by personal communication [38, 39].
2.2.2. Energy monitoring
One year post occupancy monitoring of all the energy flows of a passive house
was performed and is described in Paper IV. The measurements started in May 2012,
after a period of individual adjustments for the indoor comfort levels for each of the
two residential units, and about two years after the completion of the construction
work. Separate measurements were performed for space heating, domestic water
heating, household electricity and for auxiliary electricity including electricity for
the water pumps and the ventilation system. The measurement equipment was
installed by Jämtkraft and was collected by remote reading. Indoor temperature was
monitored in three locations in each residential unit: the main bed room, the
bathroom and the corridor. Outdoor temperature was measured as well.
2.2.3. Measurements of thermal properties
A quantitative method using thermography and heat flux meters (HFMs) is
described in Paper VI. This method aims to improve existing methods by enabling
to measure thermal properties of building fabrics even during consistently changing
meteorological conditions. The method was tested on a wooden cabin, described in
section 3.5.
11
The measurement period started January 2015 and ended in June the same year.
During the measurement period the wooden cabin was heated by an electric heater
connected to a thermostat, with indoor temperature that fluctuated between 20°C
and 24°C, which is assumed to simulate living conditions. The walls were exposed
to the continuously changing local outdoor weather conditions in the city of
Östersund in Sweden. The temperature differences between the indoor and the
outdoor environment fluctuated over the measurement period between 9°C and
40°C. Outdoor parameters as wind velocity, humidity and precipitation were
fluctuating as well.
2.2.4. Final energy modelling
The final energy balance of a building describes all the energy flows to and from
the building and was conducted with the VIP-Energy energy simulation tool. The
VIP-Energy [40] is a dynamic energy balance simulation program that calculates the
energy performance of buildings hour by hour considering the building’s design,
thermal properties, orientation, heating and ventilation systems, infiltration, indoor
and outdoor metrological conditions, daylighting, shading, and operation schedule.
The VIP-Energy was validated by IEA-BESTEST [41], ASHRAE-BESTEST and CEN-
15265 [42] validation tests.
2.2.5. Questionnaire survey
A survey was used to collect primary data about the social interaction of
occupants living in a multi-storey apartment building design with an atrium. A
questionnaire was sent to all 32 apartments in the building and included a pre-paid
and addressed return envelope for the responses. The choice of which individual
giving the answers for each apartment was left up to the respondents. The objective
was to understand the residents’ experience and perception of the heated atrium in
their building. The questionnaire comprised of three parts: information about the
apartment, experiences of the heated atrium and questions of socio-demographic
interest. The survey was conducted during May-June 2014, and the response rate
after one reminder was 72% (23 apartments). For additional understanding, a
follow-up discussion was held with two representatives of the buildings association
after the responses were collected.
12
3. CASE STUDY BUILDINGS
Case study research can bring understanding of a complex issue by analysing a
number of selected cases. Johansson [43] distinguishes between three types of case
study practices: the “explicative”, which focuses on one unit of analysis but with
many variables and qualities; the “experimental”, which focuses on one or a few
units of analysis and a few isolated variables; and the “reductive”, which focuses on
many units of analysis and a few variables.
The “experimental” and “reductive” types of case study practices were used in
this thesis using different cases (units of analysis) of existing residential buildings.
In Paper I, IV, V and VI “experimental” case studies were used, which include the
Wälludden, the Röda Lyktan project, the heated atrium and the wooden cabin case
studies. In Paper II and III, a “reductive” case study was used, which includes 22
multi-storey apartment buildings located in Stockholm. The following sections
provide descriptions of these case studies.
3.1. The Wälludden building
The Wälludden building, Paper I, is a four-storey apartment building with
wooden-frame foundation. It has 16 apartments and a total heated area of 1190 m2.
It was constructed in 1995 in Växjö, Sweden, but was analysed with the climate data
of Östersund. The roof consists of two layers of asphalt-impregnated felt, wood
panels, 400 mm mineral wool between wooden roof trusses, polythene foils and
gypsum boards, giving an overall U-value of 0.13 W/(m2 K). The windows are
double glazed and have a U-value of 1.90 W/(m2 K). The external doors have a U-
value of 1.19 W/(m2 K) and consist of framing with double glazed window panels.
The external walls have a U-value of 0.20 W/(m2 K) and consist of three layers: 50
mm plaster-compatible mineral wool panels, 120 mm thick timber studs with
mineral wool between the studs, and a wiring and plumbing installation layer
consisting of 70 mm thick timber studs and mineral wool. Two-thirds of the facade
is plastered with stucco, while the facades of the stairwells and the window consist
of wood panelling. The ground floor consists of 15 mm oak boarding on 160 mm
concrete slab laid on 70 mm expanded polystyrene and 150 mm macadam, resulting
in a U-value of 0.23 W/(m2 K). Detailed information, including drawings and thermal
properties can be found in Persson [44].
13
3.2. The Stockholm program
The Stockholm program for environmentally adapted buildings [45] (hereinafter called
the ‘Stockholm program’, see Figure 3) was launched in 1996 and aimed to stimulate
the building industry to construct sustainable buildings. Certain guidelines were
required to be followed during the planning and construction processes. For
example, the program applied higher restrictions for the maximum final energy
demand in comparison to the Swedish building code at that time.
Until the end of the program in 2005, 77 projects of multi-storey apartment
buildings were constructed within the Stockholm municipality. Each project
comprised of one or more multi-storey apartment buildings. Of all construction
projects, ten were used as a case study with a total of 22 multi-storey apartment
buildings. Eight of them were analysed in Paper II (the buildings in locations 1-8 in
Table 4) and five of them in Paper III (the buildings in locations 2, 4, 6, 9, 10 in Table 4
and illustrated in Figure 3). These multi-storey apartment buildings were chosen
because of the similarities in thermal properties, energy systems and the absence of
areas for commercial purposes. All buildings are connected to the local district
heating network in Stockholm operated by Fortum Värme, which supplies the heat
for space and domestic water heating. All buildings have forced ventilation air flow.
The buildings’ final energy demand over one year was monitored both by the
buildings’ proprietors after settling and by Fortum Värme during 2005 and 2006. The
monitored values and the design of the buildings were used to analyse the impact
of the interior design and the exterior design on the final energy demand (Paper II
and Paper III).
Table 4. Description of the residential building that participate in the Stockholm program.
Location name Floor area
(m2)
No. of
buildings
No. of
storeys
No. of
apartments
1 Sundet 4,900 2 5 39
2 Fladen 3,200 2 5 31
3 Fjärden 3,200 2 5 31
4 Spinnsidan 1,613 2 3, 4 16
5 Tjärnen 5,895 3 5-7 60
6 Installation & Hologrammet 6,571 3 5-7 62
7 Polygripen 4,146 2 3 38
8 Tjockan 9,700 4 4 91
9 Följetongen 567 1 3 6
10 Tjoget 975 1 4 12
14
Figure 3. Example of five multi-storey apartment building that participated in the
Stockholm program. The design of these buildings was analysed in Paper II
and Paper III.
The project Fladen, within the Stockholm program includes two identical but
mirrored buildings. One of the buildings (bottom right in Figure 3) was used as a
reference example to study the effects of the shape factor and the relative size of the
common area on the specific final energy demand (Papers II and III).
It is a five-storey apartment building with a total floor area of 1600 m2. The roof
consists of two layers of asphalt-impregnated felt over 25 mm plywood sheet, with
300 mm of mineral wool between the wooden roof trusses and 150 mm of concrete,
providing an overall U-value of 0.13 W/(m2 K). The external walls have a U-value of
0.25 W/(m2 K) and consist of 8 mm of plaster, 150 mm of mineral wool between
wooden studs and 150 mm of brick. The facade consists of 33% triple-glazed
windows and doors with an overall U-value of 1.20 W/(m2 K). The ground floor
consists of 20 mm oak boarding on a 180 mm concrete slab laid on 150 mm of
expanded polystyrene and 100 mm of asphalt, resulting in a U-value of 0.24
W/(m2 K).
15
3.3. The Röda Lyktan building
The Röda Lyktan building is a semidetached house with two identical dwellings
located in Östersund. It was constructed during 2010 with a design that meets the
requirements for Swedish passive houses as published by the Centre for zero energy
buildings (SCNH) and reported in the Forum for energy efficiency buildings (FEBY)
[32]. It was the first building that met the passive house criteria in Northern Sweden
(latitude 63°N), climate zone I (see Figure 1 in section 1.3). To date, the number of
passive houses in the region of climate zone I is still less than 1% of the total passive
houses in Sweden [46, 47].
The two dwellings were inhabited by families with different characteristics: a
couple with no children in one unit and a couple with two children in the other. Each
residential unit has two storeys and a total floor area of 160 m2, which includes: a
cloakroom, hall, a kitchen, a living room, a toilet, a bathroom, a laundry room, a
storage room and four bedrooms, as illustrated in Figure 4. In addition, a wooden
terrace, a balcony, an adjacent garage and a garbage room are located outside the
thermal envelope of the building and therefore not considered as part of the floor
area.
The Röda Lyktan building has a wooden frame on concrete slab with steel mesh
on foam sheets (cellular plastics). The outer walls are made of several layers
including: gypsum board, 175 mm stone wool, 240 mm cellulose fibres and wood
panel at the exterior. The roof is made of metal sheets on top of composite wood
board, cellulose fibres, stone wool and a gypsum board at the interior. The ratio
between the building’s thermal envelope and its floor area, i.e. the shape factor of
the building, is about 2, which indicates a relatively compact building. The thermal
properties of the different elements are listed in Table 5.
Figure 4. Drawing of the first floor (left) and the second floor of the Röda Lyktan.
16
Table 5. The thermal properties of the Röda Lyktan building (Paper IV).
Building component Area
m2
U-average
W/(m2 K)
U · Area
W/K
Roof 168.0 0.078 13.1
External wall 242.5 0.093 22.6
Windows 57.6 0.750 43.2
Doors 4.2 0.800 3.4
Slab on ground 163.3 0.110 18.0
Cold bridges - total - - 8.9
Thermal envelope total 635.6 0.172 109.2
The heating system includes a water-based pre-heater coil in the ventilation
system and floor heating in the bathroom and in the entrance hall. The main source
for heat is the local district heating plant for both space and domestic water heating.
A secondary heat source is a wood-fuel stove installed in the living room. The stove
can be used by the occupants according to their wishes. A balance ventilation unit
with a rotary heat exchanger is installed in each of the dwellings to reduce
ventilation heat losses.
3.4. The atrium building
The atrium building was constructed during 2006 in the northern part of Sweden
and comprises of two identical five-storey apartment buildings that are joined by an
enclosed and heated linear atrium in between them, as illustrated in Figure 5. Each
of the buildings has a total floor area of 1915 m2 and accommodates 16 apartments
with two, three, and four rooms. The fifth floor is used entirely as a common area
for the purpose of services and storage. The entrance to each of the apartments is
through an indoor balcony facing towards the atrium. All balconies on each floor
are connected by suspended corridors as illustrated in Figure 5. A staircase and an
elevator are located in the middle of the atrium and serve both buildings. The total
floor area in the atrium space is 1376 m2, of that 484 m2 at the ground level and
additional 892 m2 of indoor balconies, corridors, staircase and an elevator. The
atrium is heated during the cold season, and thus can be used by the residents for
different activities all year around.
17
Figure 5. An indoor photo of the atrium (left figure) and an outdoor photo of the atrium
building (right figure). The red lines mark the location of the atrium.
3.5. Wooden cabin
The wooden cabin is a single-room test facility with 15 m2 floor area, as illustrated
in Figure 6. It was located at Mid Sweden University in Östersund, Sweden and was
designed and constructed for the purpose of testing a new method to evaluate
thermal properties of building fabrics by using thermography. The walls of the
wooden cabin were constructed with glued laminated spruce timbers which are kiln
dried and joined together with dowel mouldings, a technique developed by Glulam
[48]. The thermal properties of the north, east and west walls were analysed. The
walls were constructed with different thicknesses: 140 mm, 165 mm and 190 mm,
respectively to represent walls with different thermal properties.
Figure 6. Scematic drawing of the wooden cabin. The test objects are the west, north
and east facing external walls.
18
4. POST OCCUPANCY ENERGY MONITORING
In the age of increasing environmental awareness and a growing demand for
energy efficient buildings, the construction industry is faced with the challenge to
ensure that the energy efficiency and the thermal performance projected during the
design stage are achieved once a building is in use [49]. Still, energy efficiency and
thermal performance seems to rarely be validated after construction or renovation.
There are different methods that could be used to evaluate the energy efficiency
and thermal performance of buildings after construction (post occupancy
evaluation). These can be divided in qualitative methods such as airtightness test,
cavity inspection and thermography [50]; and quantitative methods such as energy
monitoring, co-heating test [51] and the use of measurement tools, e.g. heat flux
sensors (HFM) [52] and thermal cameras. A co-heating test provides an average
value of the thermal efficiency of a whole building but not for a specific element of
the building fabric [53], while HFMs provide a point measurement and may fail to
represent the thermal performance of complete building elements. Thermography
can be used both for qualitative and quantitative analysis of building fabrics and its
advantages will be discussed further in section 6.
Energy monitoring can be used for evaluating energy efficiency. It requires at
least one year of continues monitoring to obtain representative annual final energy
demand. During the measurement period all energy flows, indoor and outdoor
thermal conditions need to be monitored. At the end of the measurement period the
specific final energy demand is calculated by dividing the total monitored final
energy demand of a building by the functional unit of the total floor area. The
specific final energy demand is commonly used as an indicator for the energy
efficiency of buildings in different energy certification schemes and building code.
It is used to evaluate energy efficiency of buildings with different sizes of floor area
and to compare to reference values.
However, the indicator has some difficulties when used before the building is
constructed, e.g. for building certification, as will be discussed in section 5. And also
if it is used with post occupancy energy monitoring, as will be discussed in this
section regarding the building interior design and the time period of measurements.
19
4.1. The building interior layout design
The measured floor area of a building can vary by 20% depending on its
definition [54]. In Sweden, the “floor area” is defined by the National Board of
Housing, Building and Planning (Boverket) [55] and is measured according to the SS
021054 standard [56]. The Swedish definition is equivalent to the European “overall
internal dimension” [54], with the exception that it excludes adjacent garages and
areas with indoor temperature that is lower than 10ºC during the heating season.
The reason is that such low-heated areas will reduce the value of the specific final
energy demand [57], and thus may misrepresent the energy efficiency of the
building in comparison to other buildings.
In multi-storey apartment buildings the definition of “floor area” can be divided
further into three types of sub-areas: apartment areas, common areas and
commercial areas. The specific final energy demand of a building is the weighted
arithmetic average of the specific final energy demand of its sub-areas. Common
areas, hereinafter, are defined as all the areas within a building’s thermal envelope
that are not within the apartments, e.g. corridors, staircases and basements and atria.
Commercial areas, e.g. offices and small shops, are out of the scope of this thesis.
Similar to adjacent garages, the common areas in multi-storey apartment
buildings may have lower specific final energy demand in comparison to apartment
areas. Probable reasons are: (i) lower indoor temperature [30], which results in lower
heat losses [58, 59]; (ii) lower ventilation air-flow [30], which results in both lower
ventilation heat losses and a lower amount of electricity consumed by the ventilation
system; (iii) lower demand for domestic water heating in common areas; and (iv)
lower electricity consumption in the common areas by occupants. The reasons for
the lower use of electricity can, for example, be the use of efficient lightning and the
absence of white goods and multimedia devices, which together comprise about 70%
of the demand for household electricity in Sweden [60].
The specific final energy demand in multi-storey apartment buildings was in
Paper II and Paper V found to depend on the building interior layout design. The
results were confirmed both by energy simulation, using the Stockholm program
and the atrium case studies and will be describe in the following sections.
Results (Stockholm program)
In Paper II, the final energy demand of one of the two buildings in the project
Fladen was modelled with five different ratios of apartment area to total floor area.
The ground floor was first modelled with four apartments. In each subsequent
model an area of a single apartment was allocated to the common area, which
increases the relative size of the common area by 5%, until the common area
20
occupied the entire ground floor. The Fladen project is one of the ten construction
projects in the Stockholm program described in section 3.2.
The following parameters were calculated from the model: (i) the specific final
energy demand in the apartment area, i.e. the final energy demand in the apartment
area divided by the apartment floor area; (ii) the specific final energy demand in the
common areas, i.e. the final energy demand in the common area divided by the
common area; and (iii) the specific final energy demand of the building, which was
calculated by two methods: method I, the final energy demand was divided by the
total floor area of the building, which is the method that is currently used in the
building sector; and method II, the final energy demand was divided by the
apartment area only. The results from the model were compared with post
occupancy energy monitoring of eight multi-storey apartment buildings projects
with different ratio of apartment to total floor area), as illustrated in Figure 7. The
building are part of the Stockholm program, which described in section 3.
The modelled specific final energy demand in the apartment areas (red line in
Figure 7) was found to be 3 to 6 fold higher in comparison to the common areas (blue
line in Figure 7). As a result, the value of the specific final energy demand of the
building increases as the relative size of apartment areas increases. The results from
the model were confirmed by post occupancy energy monitoring of the multi-storey
apartment buildings (circles in Figure 7).
Figure 7. A comparison between energy modelling and post occupancy energy
monitoring of multi-storey buildings with different ratios of apartment area to
total floor-area.
0
40
80
120
160
200
240
0.65 0.70 0.75 0.80 0.85 0.90 0.95
Spe
cifi
c fi
nal
en
erg
y d
em
and
kWh
/(m
2ye
ar)
The ratio of apartment area to total floor area
SimulatedWhole building - method II
MeasuredWhole building - method II
SimulatedApartment area
SimulatedWhole building method I
MeasuredWhole building - method I
SimulatedCommon area
21
Reducing the relative size of apartment areas from 90% to 70% was found to
reduce the value of the specific final energy demand by 30 kWh/(m2 year). However,
designing buildings with a lower share of apartment areas does not increase the
energy performance of buildings. On the contrary, the heating demand per unit of
apartment floor area (method II) may even increase, as larger common areas may
result in additional heat losses, e.g. through ventilation and by conduction through
the building fabric. This is illustrated in Figure 7 by the dashed line and confirmed
with post occupancy energy monitoring (squares).
Results (Atrium building)
Multi-story apartment buildings with atria is a special case of building design
with low ratio of apartment area to total floor area. The atrium in the atrium case
study building, analysed in Paper V, was constructed within the thermal envelope
of the building. It is heated during the heating season and therefore, according to
the Swedish building code [30], can be counted as part of the floor area of the
building. The share of apartment area in the atrium case study is 59% of the total
floor area of the building.
Figure 8 illustrates a model of the specific final energy demand by type of area,
i.e. apartment, common and atrium areas and by different climate scenarios for the
atrium building. Similar to the results in Figure 7, the specific final energy demand
in the apartment areas is higher in comparison to the specific final energy demand
in the common and atrium areas.
Figure 8. The specific final energy demand for different zones in the atrium building: the
apartment area, common area and for the atrium area. For each building zone
the final energy demand in that zone divided by the size of its floor area.
0
20
40
60
80
100
120
140
0 1 2 3 4 5 6 7 8 9 10Spe
cifi
c fi
nal
en
erg
y d
em
and
kWh
/(m
2ye
ar)
Avrage annual outdoor temperature C°Climate scenarios
Apartment area
Atrium area
Common area
22
Due to the low ratio of apartment to total floor area, the modelled specific final
energy demand of the atrium building was 25% lower in comparison to a similar
building without an atrium, as illustrated in Figure 9A. The non-atrium building is
existing multi-story apartment building with similar dimensions like each of the two
adjacent buildings to the atrium case study building, and it was modelled with
similar thermal properties. The modelled specific final energy demand of the atrium
building was found to be below the requirement for passive houses in Sweden [32].
The modelled specific energy demand for space heating was found to range from 36
kWh/(m2 year) in the north (Jokkmokk) to 12 kWh/(m2 year) in the south (Malmö) of
Sweden.
Small differences in specific final energy demand were calculated between the
atrium and non-atrium buildings using the apartment area as functional unit, as
illustrated in Figure 9B. However, unlike the results in Figure 7, the atrium building
was still found to have better overall energy efficiency by 2% to 3% and less energy
demand for space heating by 9% to 15%. The reason for that will be explained in
section 7 with regard to the thermal efficiency of the building envelope.
Figure 9. The modelled specific final energy demand of the atrium and the non-atrium
buildings in different climate scenarios. Figure 9A (left) and Figure 9B (right)
represent the specific final energy demand normalised with the total floor area
as defined according to Boverket [30] and by the apartment area only,
respectively.
23
4.2. Time elapse before the start of the energy monitoring
The time period of post occupancy energy monitoring was found in Paper II to
effect the measurement results. Energy monitoring conducted shortly after the
completion of construction may not provide representative values and may
contribute to the energy performance gap between the projected values and post
occupancy energy monitoring. The energy performance gap will be further
discussed in section 5. Probable reasons are:
High moisture levels, originating from the construction work, may still remain
in the building structure after completion. The evaporation of the excess moisture
may take up to two years and requires additional energy [61].
High moisture levels in the building fabrics may reduce the effectiveness of the
building’s insulation [61]. As a consequence, higher final energy demand may be
measured during the early service period of buildings.
Energy systems in newly constructed buildings require a period of adjustment to
meet the desired energy demands. As the complexity of the energy system in
buildings increases, maintenance and system control become more difficult and
may require a longer time to adjust [62]. The length of the adjustment period
depends on the knowledge and skill of the operator. During this period, the final
energy demand may be higher or lower than the demand during “normal
operation” conditions. Torcellini et al. [63] concluded that post occupancy
monitoring of energy performance is essential to ensure that the goals of the
design are met. This should be done under “normal operation” conditions, while
the system is optimized for the energy demand and outdoor conditions.
Buildings may not be occupied instantaneously. Unoccupied apartments have no
demand for domestic hot water and indoor temperature may be lower than
thermal comfort levels [64]. Therefore, energy monitoring during a period with
partial occupancy will result in lower values.
Results - Multi-storey apartment buildings (the Stockholm program)
The effect of the monitoring time-period is illustrated in Figure 10, using multi-
storey apartment buildings from the Stockholm program. The results show that post
occupancy energy monitoring started less than two years after the completion of the
building had 15%-34% differences in comparison to posterior measurements from
later periods. The energy demand was found to either increase or decrease with
time. The final energy demand in buildings, monitored two years or more after
completion, had less than 7% differences in comparison to posterior measurements.
This change in final energy demand can be regarded as a normal variation, for
example due to variations meteorological conditions among different years.
24
Figure 10. Post occupancy energy monitoring for space and domestic water heating in
three different years and for eight projects from the Stockholm program, see
section 3.2 for case study description. The 1st measurement, after building
completion, was conducted by the building proprietors. The 2nd and 3rd
measurements were conducted by the local district heating provider for years
2005 and 2006, respectively. The time elapsed since the building completion
and start of the first energy monitoring is indicated above the X-axis.
Results - Detached houses (Röda Lyktan)
Post occupancy energy monitoring in the Röda Lyktan case study started about
two years after the completion of the construction work and after a period of system
adjustment to the individual thermal comfort preferences of each family. During the
energy monitoring period, both families reported that they were satisfied with their
indoor thermal comfort conditions. It is most likely that, prior to the system
adjustment, different final energy demand would have been measured, as the
homeowners of Apartment I and Apartment II experienced too high, respective too
low indoor temperatures during that period (Paper IV).
0
50
100
150
200
250
Spe
cifi
c fi
nal
en
erg
y d
em
and
kWh
/(m
2ye
ar)
Less than two years More than two years
1st measurement 2nd measurement 3rd measurement
Location
25
5. ENERGY PERFORMANCE GAP
Specific final energy modelling of buildings are commonly used to meet local
environmental targets, building code requirements and voluntary goals such as
passive house certificates. The compliance of the energy models to energy targets is
usually performed during the design stage of the building, before it is built or
renovated. Discrepancy between the modelled energy demand and post occupancy
energy monitoring are commonly referred to as the energy ‘performance gap’ [65].
According to Menezes at el. [49] the performance gap could be reduced by
knowledge acquired from post occupancy evaluation of constructed buildings,
which will produce more accurate models of final energy demand for new designed
buildings. One such example is the Forum for Energy Efficient Buildings (FEBY) report
[32]. The FEBY report tries to define specific values that aim to represent the average
final energy demand for different energy flows in Swedish buildings. It includes
energy demand for residents’ activities like domestic water heating and household
electricity. The values are based on monitored data from several studies and are
currently suggested to be used for certifying zero-energy- /mini-energy-/ and
passive houses. The following sections will discuss the energy performance gap
more in detail with examples from Sweden based on the results from Paper II, Paper
IV and Paper VI.
5.1. Discrepancies between calculated and monitored values
Two examples of energy performance gap between projected and monitored
values of final energy demand have been analysed. These include the Röda Lyktan
case study (Paper IV), a semi-detached house that was built according to the passive
house standard, and the Stockholm project case study, which includes multi-storey
apartment buildings (Paper II).
Results - Detached houses (Röda Lyktan)
Figure 11 illustrates the energy performance gap found between the projected
and monitored final energy demand of the Röda Lyktan case study (Paper IV).
Differences were found in all energy flows: (i) space heating was underestimated by
22% - 37%; (ii) domestic water heating was overestimated by 40% - 170%; (iii)
household electricity was overestimated by more than twofold; and (iv) auxiliary
electricity was overestimated by 50%. In total, the annual final energy demand was
28% and 33% higher than the calculated values for Apartment I and Apartment II,
respectively. The measured final energy demand is just below the requirements for
passive house in climate zone I, as listed in Table 3.
26
Figure 11. The projected and monitored final energy demand by energy type of the two
apartments in the Röda Lyktan project (Paper IV).
Results - Multi-storey apartment buildings (Stockholm program)
The Stockholm program tried to implement more ambitious energy goals in
comparison to the national building code during that time, as listed in Table 6. As a
control mechanism to achieve its energy goals, the Stockholm program required that
the specific final energy demand of all buildings that participated in the program
had to be modelled before they were built. The building proprietors were also
required to conduct one year post occupancy energy monitoring, as a feedback
mechanism to evaluate the success of the program to achieve its energy goals.
Table 6. Monitored and required specific final energy demand in kWh/(m2 year) [37].
Heating system
Monitored values
kWh/(m2 year)
Projected values
kWh/(m2 year)
Minimum Maximum
DH1 111 242 140
DH + VHR2 109 334 125
Electric heating 70 121 90
1 DH - District Heating
2 VHR - Balance Ventilation with Heat Recovery
31 29.5 42.6
10
6.7
15.511.1
5.810.7 6.97.4
18.7
39.338.3
0
10
20
30
40
50
60
70
80
90
100
110
Calculated values Household I Household II
Spe
cifi
c fi
nal
en
erg
y d
em
and
kWh
/(m
2ye
ar)
Household electricity
Auxilary electricity
Domestic water heating
Wood stove
Space heating
27
A comparison between the projected and monitored values was presented in Paper
II and is illustrated in Figure 12. A significant energy performance gap was found
between the projected and the post occupancy energy monitoring among all the
buildings that participated in the Stockholm program. According to the projected
values, buildings constructed in 86% of the projects should have achieved the energy
requirements of the Stockholm program, while post occupancy energy monitoring
revealed that buildings in only 18% of the projects actually did. Variations in final
energy demand and energy performance gap were also found in the Bo1
construction project [66] in the city of Malmö Sweden, and the Lindås passive house
project [64] in Göteborg Sweden. Post occupancy energy monitoring revealed large
variation in specific final energy demand among the buildings, which could partly
be explained by the interior design of the building, as discussed in section 4 and by
the thermal efficiency as will be discussed in section 7.
Figure 12. The modelled and monitored specific final energy demand of apartment
buildings in 77 construction projects that participated in the Stockholm program.
Each value represents an average value of all the apartment buildings from the
same construction project.
0
50
100
150
200
250
300
350
400
Spe
cifi
c fi
nal
en
erg
y d
em
and
kWh
/(m
2ye
ar)
Construction projects
Monitored values in buildings with forced ventilation
Monitored values in buildings with ventilation heat recovery (VHR)
Monitored values in buildings heated with heat-pump
Calculated values
28
5.2. Causes for discrepancies
This section addresses different reasons for the energy performance gap between
the calculated and monitored final energy demand. Four main causes were
identified. Three are described in Paper II and the fourth in Paper III: (i) the time
elapsed between construction completion and the beginning of energy monitoring,
as discussed in section 4.1.2; (ii) assumptions made during final energy calculations;
(iii) systematic errors in calculations; and (iv) the thermal performance gap,
5.2.1. Assumptions during final energy calculations
Energy efficiency in newly constructed buildings in Sweden is generally
evaluated based on the architectural drawings together with assumptions regarding
local weather conditions, performance of energy systems, occupants’ behaviour and
thermal comfort. According to Menezes et al [49], final energy demand calculations
seldom agree with post occupancy energy measurements due to the high
uncertainty in energy models of buildings. According to Pettersen [67], it is
impossible to predict the energy demand with better accuracy than ±15–20%, if the
behaviour of the residents is unknown. According to Kalema et al. [68] assumptions
may lead to larger energy performance gap than the use of different calculation and
simulation methods. The Röda Lyktan case study and the apartment buildings that
participated in the Stockholm program are examples of semidetached and multi-
storey apartment buildings, in which fault assumptions were used.
Results - Detached houses (Röda Lyktan)
The monitored final energy of the two dwellings in the Röda Lyktan case study
revealed two main differences in the occupants’ behaviour. The first is the
occupants’ preferences for indoor thermal comfort. The average indoor temperature
in Apartment II (a family with two children) was found to be 2.5ºC higher in
comparison to Apartment I (two adults) during the heating season, as illustrated in
Figure 13. As mentioned before, both families were satisfied with their indoor
thermal comfort during the monitoring period, which indicates that the temperature
differences were purely due to diversity in preference of thermal comfort between
the families. These differences were found to be the main cause for the 25% higher
demand for space heating in Apartment II in comparison to Apartment I, as illustrated
in Figure 11.
The second difference is the time spent indoors. Apartment I was unoccupied for
two weeks during the winter, and Apartment II was unoccupied for four months
during the summer. In both periods relatively low indoor temperatures were
monitored. The long unoccupied period in Apartment II is the cause for the lower
yearly energy demand for domestic water heating in comparison to Apartment I.
29
Higher values for domestic hot water and household electricity would be expected
in Apartment II if it was occupied the entire year, which would also result in larger
differences in final energy demand between the two apartments.
Using average values, as suggested by FEBY, may not be representative for one
or two apartment units in detached houses as the behaviour of the residents can vary
significantly and have large impact on the result. For example, the annual energy
demand for domestic hot water in the two apartment of the Röda Lyktan case study,
was found to be 11.1 kWh/(m2 year) and 5.8 kWh/(m2 year) in comparison to the
FEBY’s average value of 20 kWh/(m2 year). That could be explained by the long
period in which the dwelling of Apartment II was unoccupied and the low
population density in Apartment I, i.e. 80 m2 per person in comparison to the Swedish
average value of 44 m2 per person [69]. On the other hand, household electricity was
39.3 kWh/(m2 year) and 38.3 kWh/(m2 year) for Apartment I respective Apartment II
in comparison to 30 kWh/(m2 year) as proposed by FEBY.
Both the relative high consumption of household electricity and the lower value
of energy demand for domestic water heating have nothing to do with the building
design. They depend solely on tenants’ activities and preferences, but still have large
effect on the ability to certify these buildings as passive houses. About 40% of the
heat demand is covered by household electricity, which results in lower energy
demand for heating. The low energy demand for domestic hot water also contributes
to lower total heating demand.
Results - Multi-storey apartment buildings (Stockholm program)
Figure 14 illustrates the distribution of the discrepancies between the projected
values and post occupancy energy measurements among the multi-storey
apartment buildings that participated in the Stockholm project (see Figure 12). It is
a normal distribution with standard deviation of 15%, i.e. about 32% of the
calculated energy demand deviated from the expectation values by more than 15%.
Normal distribution is, among others, a distribution of errors, which suggest that
the large standard deviation is likely to be due to errors in assumptions for unknown
variables, for example variables concerning occupants’ behaviour, outdoor
conditions, etc.
30
Figure 13. The outdoor temperature and the indoor temperatures monitored in different
rooms in the two apartments in the Röda Lyktan case study.
15
17
19
21
23
25
27
Ap
artm
en
t II
Ind
oo
r te
mp
ratu
re °
CMain bedroom Corridor Bathroom
15
17
19
21
23
25
27
Ap
artm
en
t I
Ind
oo
r te
mp
ratu
re °
C
-30
-20
-10
0
10
20
30
40
Ou
tdo
or
tem
pra
ture
°C
31
Nu
mb
er o
f co
nst
ruct
ion
pro
ject
s
Figure 14. The X-axis represents the deviation of the modelled values from the monitored
specific final energy demand (in percent). The Y-axis represents the number of
construction projects in each interval among the 77 projects that participated in
the Stockholm program.
5.2.2. Systematic errors
It is important that the algorithm used to model energy demand in buildings
should be empirically validated to reduce the magnitude of errors. A validation test
can assess the program’s performance of real design problems [70]. Examples of
validation tests are: the IEA-BESTEST [41] by the International Energy Agency, the
ASHRAE-BESTEST by the American Society of Heating and Air-Conditioning
Engineers and the CEN-15265 [42] by the European Committee for Standardization.
Results - Multi-storey apartment buildings (the Stockholm program)
The expectation value of the normal distribution illustrated in Figure 14 was
found to be equal to -19%, which implies that the projected values of the buildings
were on average 19% lower than the post occupancy energy monitoring values. Such
a result could be obtained by a similar error done in all simulations or by a similar
error within the calculation algorithm.
The Stockholm program recommended the Enorm 2004 simulation program [71],
as the calculation method, which was also used by the majority of the buildings’
proprietors. The program is not validated and according to its developer, the Enorm
2004 includes a simplified model of solar radiation and excludes the effects of heat
accumulation in the building and overheating [71], which could be the reasons for
the low expectation value.
32
5.2.3. Thermal performance gap
The energy performance gap can also partly be explained by discrepancies
between the projected and actual values of the thermal transmittance of building
fabrics (also known as the overall heat transfer coefficient or U-value). Such
differences were found by Johnston at el. [53] after in situ measurements in 25 new
constructed buildings in the UK. Similar results were also found using co-heating
test to measure the heat losses of 16 newly constructed apartments in the UK [72].
Results (wooden cabin)
Thermography measurements of the walls of the wooden cabin in Paper VI
indicated that the thermal transmittance, in particular of wooden walls, can be
effected by quality of materials and weather conditions. The thermal properties of
building fabrics may not be a constant value but may change over time. And thus,
could contribute to the energy performance gap. More detailed results will be
presented in section 6.
33
6. POST OCCUPANCY EVALUATION BY THERMOGRAPHY
Thermography is a non-destructive testing method that can provide quick and
accurate readings and could also be used for post occupancy evaluation of thermal
performance of building fabrics. Since the introduction of infrared cameras in 1929,
thermography is used to address an increasing range of applications [73] and
gaining extensive popularity among methods for building diagnostics [73]. The IEA
has considered thermography for detecting defects in buildings in both annex 40 [74]
and annex 46 [75]. The European standard EN 13187-1998 specifies a qualitative
method using thermography for detecting thermal irregularities in building fabrics.
Thermography has large potential for detection of thermal bridges [76], high moister
levels [77, 78] and defects in building fabrics [79-82]. It can be used both for quality
control during construction of new buildings [83] and for investigating the condition
of existing buildings, e.g. listed buildings [84, 85].
6.1. Thermography for quantitative analysis
Several studies have also used thermography for quantitative analysis of thermal
performance of building fabrics. Ohlsson and Olofsson [86] developed a method to
measure the heat flux through a wall element by a single thermal image. They
achieved less than 10% uncertainty under the conditions of natural convection. But,
during forced convection (modelling wind) less reliable results were obtained. Their
experiment was performed in a controlled environment with steady-state heat flow
conditions.
According to Lehmann et al. [87], steady-state heat flow through building fabrics
is seldom, if ever, met since buildings are exposed to consistently changing
meteorological conditions. To obtain more accurate results Albatici et al. [88]
recommended to use thermography on walls facing north and east before sunrise
and with overcast sky. Albatici et al. [88] also recommended that the following
conditions should be reached during a survey:
Wind speed near the building façade should be lower than 0.5 m/s.
The difference between indoor and outdoor ambient air temperature should be
at least 15°C.
The outdoor temperature should have less than 6 °C temperature swing during
the 12 h prior to the measurement.
In similarity to steady-state heat flow, such requirements are not always possible
to obtain on demand. Fokaides and Kalogirou [89] used thermography during near
steady-state conditions, in which measurement periods with relatively stable
thermal conditions were selected. In their study they evaluated the thermal
34
transmittance of different envelope elements of five buildings in Cyprus. Their
results deviated by 10% to 20% in comparison to the theoretical values. Albatici et
al. [88] also used thermography during near steady-state conditions to calculate the
U-value of five different walls form light to heavy constructions. In average the
results deviated by 26% from the theoretical values and by 22% from measurements
done by heat flow meters (HFMs). Higher uncertainty in results were obtained for
light weight constructions like wooden fabrics in comparison to concrete fabrics.
Sham et al. [90] used thermography during varying weather conditions with no
demand for steady-state heat flow. They monitored the exterior surface temperature
of buildings in Hong Kong and calculated the heat flow over time from building
fabrics to the outdoor environment. However, no uncertainty analysis or validation
of the results were reported.
From the above mentioned studies [86-90] it appears that uncertainty increases
as the condition of the survey deviate from steady state. It was also apparent that
the above mentioned studies are strongly relying on the temperature difference in
the boundary layer between the examined object and ambient air. The conductivity
of the boundary layer is described by the convection heat transfer coefficient [50].
Still, none of the above mentioned studies measured the convection heat transfer
coefficient but relied on values from the literature. According to Defraeye et al. [91],
values of convection heat transfer coefficient (hconv) can differ significantly and were
found to differ among the above studies as well. For example, for wind velocities (v)
below 5 m·sec-1, Ohlsson and Olofsson [86] assumed hconv=4· v +5.6, Sham et al. [90]
assumed hconv=3.9· v +5.62, Albatici et al. [88] assumed hconv=3.8054· v and Fokaides
and Kalogirou [89] assumed a constant value of hconv=7.7 W·m-2·K-1. Not knowing the
exact value of the convection heat transfer coefficient may impose errors in the
calculations.
In Paper VI, a method is described to measure thermal properties of building fabrics
during normal meteorological outdoor conditions, in which steady state heat flow is
seldom achieved. The method includes two stages. The measurements in both stages
are performed simultaneously.
Stage 1, the convection heat transfer coefficient (hconv) is determined using both
thermography and HFMs on a small segment of the examined building fabric, as
illustrated in Figure 15. The convection heat transfer coefficient (hconv) is determined
by a linear regression of the convection heat flow (QConv) against the difference
between the indoor temperature and the interior surface temperature of a small
building fabric segment area Δ(TIndoor - TSmall wall). The convection heat transfer (QConv)
was calculated according to Eq.1. The conduction heat flow through the wall (QCond)
is measured by HFMs. The interior surface temperature on the small wall segment
35
(TSmall wall) is measured by thermography. The emissivity (ɛ) of the building fabric was
determined by thermography according to the method describe in [92].
QConv = QCond − ε ∙ σ ∙ (TReflection4 − TSmall wall
4 ) Eq.1
Stage 2, the thermal transmittance of the examined building fabric (ULarge) is
determined by a linear regression of the conduction heat flow through the large wall
segment (QCond,Large wall) against the difference between the indoor and outdoor
temperatures Δ(TIndoor – TOutdoorl). The parameter, QCond,Large wall, was calculated
according to Eq.2 using infra-red camera and indoor temperature sensors.
QCond, Large wall = hconv ∙ (TIndoor − TLarge wall) + ϵ ∙ σ ∙ (TReflected4 − TLarge wall
4 ) Eq.2
6.2. Experiment results
In Paper VI, thermal properties measurements by thermography were found to
have high precision and were validated with measurements done by HFM and
theoretical values from the literature. The convection heat transfer coefficient was
found to be a key factor for obtaining accurate results. It was calculated by using
both HFM and thermography on a small wall segment and was found to be 2.47
W/(m-2 K) for the north wall and 2.46 W/(m-2 K) for the east wall with ±3% and ±6%
uncertainty, respectively, as illustrated in Figure 16. Due to the effect of solar
radiation the value of the convection heat transfer coefficient of the west wall was
12%-14% higher.
Figure 15. Representative examples of thermal images of the three walls of the wooden
cabin, taken 1st of February. The indoor and outdoor temperatures at the time
were 21.2°C and -7.5°C, respectively. The temperature scale in each image
ranges from 15°C to 19°C. The darker colours represent colder surface
temperatures. The small wall segment and large wall segment are marked by
small and large black rectangles. Source: Paper VI.
36
Figure 16. The convection heat transfer coefficient of the west wall (left figure), north wall
(centre figure) and east wall (right figure) with confidence interval of 95% certainty
(red lines). The Y-axis represent the convection heat transfer (QConv) calculated.
The X-axis represent the temperature difference between the indoor temperature
and the interior wall surface ΔT = (TIndoor - TSmall wall). The dashed lines represent
95% certainty for measurements to disperse around the mean (black trend-line).
Figure 17 illustrates the measurement results of the thermal transmittance and
conductivity of the three measured walls, using thermography. The values are
compared with point measurements by HFMs. The values of thermal transmittance
obtained by thermography on a small wall area with uniform temperature were
found to differ by less than 1%, which suggest that the two measurement methods
are compatible on areas with high temperature uniformity. However, values of
thermal transmittance measured on a large wall segment using thermography, were
found to be 3% to 5% higher in comparison to the thermal transmittance measured
on a small wall area. The reason was thermal inhomogeneities like wood checks and
knots and the contact areas between the wood beams. The results demonstrate the
ability of thermography to measure average values of large areas of building fabrics,
thus accounting for thermal inhomogeneities, which are characterised by different
thermal properties.
The results from thermography measurements were compared with values of
thermal transmittance measured by HFMs during near steady-state heat flow
conditions. The difference was found to be 2%. Near steady-state measurements
were performed during a period with warmer weather conditions; 7°C higher in
average both indoor and outdoor. According to Glass and Zelinka [93] the
conductivity of wood increases with about 2% to 3% with a temperature increase of
10°C due to the absorption of moisture in the wood, which could be the reason for
the 2% difference in values.
y = 2.741x
0
5
10
15
20
25
30
35
0 2 4 6 8 10
He
at f
lux
W
·m-2
ΔT [K]
West wall
y = 2.471x
0 2 4 6 8 10ΔT [K]
North wall
y = 2.460x
0 2 4 6 8 10ΔT [K]
East wall
37
The conductivity of the small wall segment of the west, north and east walls were
found to deviate by 9%, 5% and 2%, respectively in comparison to measured
conductivity values of Spruce wood stated in the literature (0.11 W/(m K)) [93].
According to Glass and Zelinka [93] literature values of wood conductivity can vary
as much as 20%. The conductivity of the large wall segment could not be determined
since the temperature of the exterior surface of the large wall segment were not
measured. But the values are expected to be higher by 3%-5% in comparison to the
conductivity of the small wall segment due to the inhomogeneities, as illustrated in
Figure 15. Thus, the conductivity values of the large wall segment are expected to be
0.106 W W/(m-2 K), 0.108 W/(m-2 K) and 0.113 W/(m-2 K) for the west, north and east
walls with 6%, 2% and 3% deviation from the theoretical values, respectively.
Figure 17. Summary of the main results: the thermal transmittance and the conductivity of
the west, north and east walls. The error bars represent the confidence interval
with 95% certainty.
0.40
0.45
0.50
0.55
0.60
0.65
0.70
HFM
: Sm
all w
all
The
rmo
grap
hy:
Sm
all w
all
The
rmo
grap
hy:
Lar
ge w
all
HFM
: Sm
all w
all
The
rmo
grap
hy:
Sm
all w
all
HFN
nea
r st
ead
y st
ate
: Sm
all w
all
The
rmo
grap
hy:
Lar
ge w
all
HFM
: Sm
all w
all
The
rmo
grap
hy:
Sm
all w
all
The
rmo
grap
hy:
Lar
ge w
all
The
rmal
tran
smit
tan
ce
W/(
m2
K)
West wall North wall East wall0.05
0.07
0.09
0.11
0.13
0.15
0.17
The
ore
tica
l val
ues
of
Spru
ce w
oo
d [
33
]
East
wal
l
No
rth
wal
l
We
st w
all
Co
nd
uctivity W
/(m K
)
Small wall
38
7. THERMAL EFFICIANCY OF BUILDING ENVELOPES
The thermal envelope of a building is the area that separates the conditioned and
unconditioned spaces of a building, or alternatively, the indoor and the outdoor
environment, and is the cause for a large part of the heat losses. The effect of the
design of the thermal envelope on the final energy demand was analysed in Paper
II, Paper III and Paper V using multi-story apartment buildings from the Stockholm
program and the atrium building case study.
7.1. The shape factor of buildings
Conduction heat losses can be reduced by designing buildings with better
thermal efficiency, which suggests that the thermal envelope could be used as an
indicator for energy performance of buildings. Such an attempt was made by
Jinghua et al. [94]. They developed a heat transfer rate index for thermal envelope
performance of residential buildings and used the ratio of thermal envelope area to
building volume as one of the parameters. This ratio is called the shape factor of the
building and is a measure of the building’s compactness. Buildings with lower shape
factors have a smaller thermal envelope area in proportion to their volume and are
therefore more compact.
The shape factor could also be defined as the ratio between thermal envelope
area to floor area (Paper II), instead of building’s volume. The envelope to volume
definition describes the geometrical compactness efficiency of a given building
shape, while the envelope to floor area definition can be considered as the
architectural volume efficiency [95]. The advantage of the latter definition is the
dependency of the shape factor on the floor height, or on the number of storeys for
a given building volume, and thus reflecting better on how efficient the volume of
the building is used. Figure 18 illustrates the concept of the shape factor and explains
the four factors that influence its value.
(i) The floor height. Buildings with lower floor height will have lower ratio of
thermal envelope to floor area, as compared between building ˈAˈ and ˈBˈ.
(ii) The shape of the building for a given volume, as compared between building
ˈAˈ and ˈCˈ.
(iii) Irregular façades with trenches and bulges, e.g. balconies that extend beyond
the façade, may increase the shape factor of a building, as compared between
building ˈAˈ and ˈEˈ.
(iv) The size of the building. Buildings with similar shape and larger volume will
have lower shape factor, as compared between building ˈAˈ and ˈDˈ. Larger
building volume can be achieved by increasing the height and the length of a
building.
39
Figure 18. Factors affecting the shape factor of buildings: the shape of the building, its
size and irregular façades. The parameter ˈaˈ symbolizes one unit of length.
The thermal envelope of a building may include both opaque (e.g. walls) and
transparent areas (e.g. windows). Transparent areas enable free heat from solar
radiation to enter the building, resulting in lower heating demand during the cold
periods. In climates with high intensity of solar radiation during the heating seasons,
the effect of the size of the transparent area may be stronger than the effect of the
shape factor. Catalina et al. [96] performed energy simulations for different building
shapes with climate data from Nice and Lyon in France and found lower heating
demand with a higher shape factor. Parasonis et al. [97] obtained similar results by
calculating the optimum shape for a multi dwelling residential building with 900 m2
of floor area in Kaunas, Lithuania.
In climates dominated by cooling demand, the optimal ratio between the external
walls and the volume of buildings is uncertain and further studies are needed.
Ourghi et al. [98] analysed the impact of the shape factor on the cooling demand of
an office building in Tunis and Kuwait. They compared rectangular and ‘L’ shaped
buildings and found a strong correlation between the shape factor, the window size
and the cooling demand. Florides et al. [99] compared buildings with similar
volumes but different shape factors, using the climate conditions of Nicosia in
Cyprus. The impact of the shape factor on the cooling demand was minor in
comparison to the change in heating demand. Depecker et al. [100] conclude that
there is no correlation between the final energy demand and the shape factor of
buildings in climates with predominate cooling demand. In their study they used
the climate conditions in Paris and Carpentras in France.
A B C D E
Volume a3 a3 a3 8a3 a3
Floor area 2a2 a2 2a2 16a2 2a2
Thermal envelope 6a2 6a2 7a2 24a2 7a2
Shape
factor
(envelope to volume) 6/a 6/a 7/a 3/a 7/a
(envelope to floor area) 3 6 3.5 1.5 3.5
40
Several studies have reported that in climates with heating demand, buildings
designed with lower shape factors have lower conduction heat losses per floor area,
resulting in lower specific heating demand. Aksoy and Inalli [101] studied the
difference in final energy demand between three buildings in the climate in Elaziğ
in Turkey, with building length to building depth ratios of: 1:1, 2:1 and 1:2
respectively. They found that the rectangular shape (1:1) had the lowest heating
demand. Ratti at el. [102] calculated a 10% difference in specific final energy demand
between buildings in Toulouse and Berlin only due to differences in their buildings’
morphology. Depecker et al. [100] arrived at a similar conclusion by calculating the
final energy demand of 16 identical dwelling units that were arranged in different
configurations and thus, with different shape factors. Both Ratti et al. [102] and
Depecker et al. [100] suggested that colder climate conditions may increase the
impact of the shape factor on the final energy demand.
The size of the building is one of the parameters that affects the building
compactness, i.e. the shape factor. However, the maximum possible width of
residential buildings is limited due to requirements of natural light and visual
comfort. According to the Swedish building regulations: “Rooms in buildings, where
people are present other than occasionally shall be designed and oriented to ensure adequate
access to direct daylight” [30]. Baker and Steemers [103] defined spaces that benefit
from daylight as the “passive zone”. They approximated the maximum width of the
passive zone to twice the floor height, or about 5.5 m in a typical residential building.
Beyond that depth artificial light during daytime and forced ventilation are needed
[103].
The dichotomy between compact form, the building’s volume and the
requirements for daylight in residential buildings could potentially be addressed by
a building design with an atrium. It enables to increase the building size in three
directions enabling: compact design, low shape factor and inlet of natural light to
interior spaces. The feasibility of atrium design with respect to daylight is described
by Sharples and Lash [104] and by Samant [105]. The effect of the shape factor on the
energy efficiency of buildings is demonstrated regarding the Stockholm program
and atrium building in the following sections.
41
Figure 19. Post occupancy energy monitoring of multi-storey apartment buildings with
different shape factors (listed above the X-axis) and the modelled specific final
energy demand for the same buildings when their size of the thermal envelope
is modified so that all buildings have a shape factor of 1.23.
Results (Stockholm program)
During winter time, the average outdoor temperatures in Sweden varies from
about 0ºC in the south to about -20ºC in the north and solar irradiance is week. These
climate conditions stress the importance of the shape factor in new designed
buildings. According to Paper II, the differences in shape factors among multi-storey
apartment buildings were one of the reasons for the variation in specific final energy
demand. This is illustrated in Figure 19 by comparison between post occupancy
energy monitoring and modelled values and the final energy demand of the
buildings modelled with similar shape factor.
The effect of the shape factor on the specific final energy demand for space
heating in multi-storey apartment buildings for different Swedish climate scenarios
and different buildings thermal envelope properties is modelled in Paper III. The
result showed up to a 55 kWh/(m2 year) difference in specific final energy demand
per unit change of shape factor, as illustrated in Figure 20. The value was found to
be lower for buildings with improved thermal envelope efficiency and for building
locations with higher outdoor temperature during the heating period.
100
130
160
190
220
250
Sp
ecif
ic f
inal en
erg
y d
em
an
dkW
h/(
m2
year)
Construction projects
Monitored value
Calculated values with similar shape factor
1.57 1.41 1.23 1.23 1.17 1.11 1.1 1.01
Shape factor
42
Figure 20. The change in specific heat demand per unit difference in shape factor (Y-axis)
for different climate scenarios (X-axis) and thermal envelope efficiencies. The
trend line does not include the red points, representing climate with 60% higher
wind velocity.
The impact of the shape factor increases with higher wind velocity (Paper III).
The effect of the wind is shown by the red coloured symbols in comparison with the
trend lines, in Figure 20. These points represent the climate conditions in Malmö,
Sweden, with 7.7°C average outdoor temperature. Malmö is a coastal city with an
average of 60% higher wind velocity than the three other locations in the model. The
effect of the shape factor on the specific heating demand is expected to nullify in
climates with average outdoor temperatures between 10°C and 14°C depending on
the properties of the thermal envelope of the buildings.
Results (Atrium building)
Section 4.1.1 showed that the atrium case has higher energy efficiency in
comparison to a building with similar dimensions without an atrium; 2% to 3%
lower specific final energy demand and 9% to 15% less energy demand for space
heating. This was illustrated in Figure 9B in section 4.1. The higher energy efficiency
of the atrium building when it comes to space heating is explained in Paper V by the
shape factor and illustrated in Figure 21. A linear correlation was found between the
final energy demand for space heating and the shape factor, independent of thermal
envelope and climate scenarios. The atrium building was compared to two buildings
with higher shape factor and was found to have the lowest specific final energy for
space heating. The effect of the shape factor is stronger in colder climates and for
buildings with lower thermal efficiency, which is illustrated in Figure 21 by the
tangent of the trend-line in each scenario.
0
10
20
30
40
50
60
70
80
-3 -1 1 3 5 7 9 11 13 15
kWh
/(m
2ye
ar· S
F)
Annual average outdoor temperature
Low thermal envelope
Medium thermal envelope
High thermal envelope
43
Shape factor
Figure 21. The specific final energy demand for space heating vs. the shape factor for
different thermal envelope and climate scenarios. The climate scenarios are
represented by city name and yearly average outdoor temperature.
The atrium building design also has the lowest average daily peak demand for space
heating during the coldest day of the year when solar intensity is minor, as
illustrated in Figure 22. The effect of the peak load demand will be further discussed
in section 8.
Shape factor
Figure 22. The specific peak load demand (per apartment area) vs. the shape factor with
different thermal envelope scenarios and climate scenarios, as listed in Table 2.
The climate scenarios are represented by city name and yearly average outdoor
temperature.
0
20
40
60
80
100
120
1.4 1.6 1.8 2 2.2
Spe
cifi
c sp
ace
he
atin
gkW
h/(
m2
year
)
Malmö (8.8°C)
1.4 1.6 1.8 2 2.2
Växjö (6.4°C)
1.4 1.6 1.8 2 2.2
Umeå (3.3°C)
1.4 1.6 1.8 2 2.2
Jokkmokk (1.1°C)
0
10
20
30
40
50
60
1.4 1.6 1.8 2 2.2
Spe
cifi
c p
ow
er
W/m
2
Malmö (8.8°C)
1.4 1.6 1.8 2 2.2
Växjö (6.4°C)
1.4 1.6 1.8 2 2.2
Umeå (3.3°C)
1.4 1.6 1.8 2 2.2
Jokkmokk (1.1°C)
44
7.2. Glazed area in buildings
The effect of the amount of glazed area on the final energy demand depends on
latitude, cloud formation, the outdoor thermal conditions and the properties of the
thermal envelope, both for external walls and windows. Sweden is an elongated
country stretched over 15º latitude with variations of both intensity of solar radiation
and outdoor temperature.
Results (the Stockholm program)
Figure 23 illustrates the effect of the size of glazed area on the final energy
demand of buildings with two thermal envelope scenarios. The effect of glazed area
in Swedish climates found to be minor in comparison to the effect of the shape factor
(Figure 22). The results is based on the assumption that the thermal performance of
external walls correspond to the thermal performance of windows, i.e. buildings that
are design with low overall heat transfer coefficient of external walls will also have
energy efficient glazed area. Under these assumptions, the size of glazed area will
have no significant effect on the heating demand as long as the heat gains from solar
radiation through one unit area is equal to the difference in heat losses through one
unit of glazed area and one unit area of opaque walls. The results in Figure 23
represent an average for all building orientations. It provides a general rule of thumb
as orientation of glazed areas toward a specific direction is not always possible.
Figure 23. The effect of the relative size of glazed area on the specific heat demand of
buildings with different thermal and climate scenarios.
45
Results (atrium building)
Figure 24 illustrates the effect of the external glazed area in the atrium on the
specific final energy demand for space heating in the building. In all scenarios larger
glazing area in the atrium found to increase the demand for space heating. To reduce
the effect of glazed area, more energy efficient glazing should have been used in the
model. The thermal envelope scenarios were determined in relation to the actual
thermal properties of the atrium building.
Atrium’s glazed area of total atrium’s envelope area
Figure 24. The specific final energy for space heating of the atrium building for three thermal
envelope scenarios and four climate scenarios represented by city name. The X-
axis represents the percentage of atrium’s external glazed area of its total
envelope area (both opaque and glazed areas including the atrium’s roof, ground
floor and the façades toward the adjacent buildings). The percentage value of the
actual atrium building is 13.3%.
Figure 25 illustrates the effect of the size of glazed area on the demand for
cooling, i.e. the energy that needs to be removed from the atrium to maintain thermal
comfort with indoor temperature below 25°C during the warm season. The demand
for cooling was found to be reduced with lower glazed area but was not affected by
the thermal efficiency of the atrium’s envelope. The effect of the glazed area can be
reduce with solar shading devices, Paper V.
0
20
40
60
80
100
120
6% 8% 10% 12% 14%
Spe
cifi
c sp
ace
he
atin
gkW
h/(
m2
year
)
Malmö 8.8°C
6% 8% 10%12%14%
Växjö 6.4°C
6% 8% 10%12%14%
Umeå 3.3°C
6% 8% 10%12%14%
Jokkmokk 1.1°C
46
Atrium’s glazed area of total atrium’s envelope area
Figure 25. Specific cooling demand vs. the size of the glazed area in the atrium for different
climate and thermal envelope scenarios. The Y-axis represent the cooling
demand divided by apartment area. The X-axis represents the percentage of
atrium’s external glazed area of its total envelope area (both opaque and glazed
areas including the atrium’s roof, ground floor and the façades toward the
adjacent buildings). The percentage value of the actual atrium building is 13.3%.
0
20
40
60
80
100
120
6% 8% 10% 12% 14%
Spe
cifi
c co
olin
g d
em
and
kWh
/(m
2ye
ar)
Malmö 8.8°C
6% 8% 10% 12% 14%
Växjö 6.4°C
6% 8% 10%12%14%
Umeå 3.3°C
6% 8% 10%12%14%
Jokkmok 1.1°C
47
8. BUILDING DESIGN IN AN ENERGY SYSTEM PERSPECTIVE
This section highlights the importance of analysing the final energy demand in
buildings with respect to the energy supply. The choice of supply system and type
of fuels have significant impact on the primary energy [106]. The change in primary
energy due to differences in design depends on the characteristics of the energy
production system. Therefore, demand and supply sides and their interaction need
to be analysed in order to minimize the primary energy. In Sweden, these
interactions are of interest as 90% of the multi-storey apartment buildings and 12%
of the detached houses are connected to district heating [25, 107]. Thus, the demands
of heat and power are interconnected. The importance of such interactions and
system dynamics was studied by Joelsson et al. [108], Difs et al. [109] and in Paper I.
8.1. Dynamic energy demand-supply interaction
In Paper I, a dynamic model was developed that calculate the effect of change in
final energy demand, e.g. by energy efficiency measures in buildings, on energy
production. The model include the following steps: The heat load duration of the
heat demand in a building is modelled and matched to the heat load duration of heat
production in the district heating for each day of the year, as illustrated in Figure 26.
Daily changes in heat demand in the buildings are assumed to effect the marginal
heat production technology in the district heating plant. The marginal technology is
not constant in time and may shift between base load and peak load demand within
the same district heating network (Paper I). For periods when the marginal plant is
the combined heat and power (CHP) plant, changes in heat production will result in
changes in co-generated electricity.
Co-generation of heat and power in district heating is a multi-functional process,
which induces allocation difficulties. That is, how much of the inputs and outputs
of the process are attributable to each of the products or services under assessment.
Different allocation methods can be used [110], but according to the ISO14040
standard [36], “Allocation should be avoided, wherever possible, either through subdivision
of the multifunction process into sub-processes, and collection of separate data for each sub-
process, or through expansion of the systems investigated until the same functions are
delivered by all systems compared.”
System expansion is an adequate method for avoiding allocation [110]. It can be
used with the subtraction method [35] assuming that the secondary product (e.g.
cogenerated electricity in a CHP plant) would replace a similar product that instead
would have been produced in a standalone power plant. The total amount of
primary energy used in the district heating plant is then credited with the amount
48
of primary energy that would have been used to produce the avoided electricity in
a standalone power plant. The standalone power plant is assume to be the marginal
power production technology.
When it comes to power production, Sweden is part of the Nordic electricity
trading market, the NordPool. The Swedish electricity grid is connected by high
voltage cables to Norway, Finland, Denmark, Poland and Germany, via the latter
also to the Baltic States, the Netherlands, Luxembourg, Belgium, France, Austria and
Switzerland. As a result, the Swedish electricity system is not a closed system but
part of larger system that extends beyond the physical borders of the country. Small
changes in electricity demand in Sweden may affect electricity production in other
parts of Europe, i.e. the marginal power production. Considering long term effects,
the marginal power plant assumes to have the highest variable costs. Currently, coal-
fired condensing plants (CST) are considered as the current marginal electricity
production technology in the Nordic region [111]. However, this may change in the
future due to factors including investments, greenhouse gas reduction policies,
strategic and security reasons [112].
8.2. Reference heat and power production plant
The district heating system analyzed in this thesis is confined to the city of
Östersund, Sweden, with its local climate condition and local heat demand. In Paper
I, the heat production during the 12-month period from 1st May 2008 to 30th April
2009, was used as illustrated in Figure 26. During that period, the total production
was 210 GWh of electricity and 612 GWh of heat. The heat and electricity production
system consists of CHP with 80 MW heat and 40 MW electricity, a flue gas condenser
with 30 MW of heat and two heat only boilers (HOB) with 25 MW of heat each. A
water accumulator tank with a total capacity of 26,000 m3 reduces the daily variation
in heat production, and thus increases the total efficiency of the heat and electricity
production. The CHP plant and the HOB are fueled by peat (~10%) and biomass
residues (~90%) such as bark, sawdust, logging residues, and recovered wood.
49
Figure 26. Supply - demand interaction. The upper figure represent changes in heat load
demand in the building. The lower figure represent the production heat load in
the district heating system and the affected marginal heat production technology
for each day of the year. It is assumed that both heat demand and heat production
are affected by the outdoor weather conditions.
50
8.3. Energy efficiency measures
Paper I analyses how the energy system is affected by implementing energy
efficiency measures in residential buildings. The Wälludden case study, described
in section 2.2.1, was analysed with different energy efficiency measures including:
water savings taps, energy efficient windows and doors, an additional 100 mm and
250 mm mineral wool insulation in the roof and walls respectively, and a balance
ventilation with heat recovery instead of forced ventilation. The changes in thermal
properties due to the energy efficiency measures are listed in Table 7.
Results (Wälludden)
Reducing heating demand during periods in which the CHP unit is the marginal
heat production technology in the district heating plant will simultaneously reduce
production of cogenerated electricity. The electricity deficit is assumed to be covered
by the marginal power production. As a result, the primary energy savings at the
district heating plant will be offset by the added primary energy at the marginal
power plant, resulting in minor primary energy savings.
According to Paper I, a significant primary energy saving can be obtained by
reducing heat demand during periods, in which peak load production units are in
operation, even if these units only cover a small share of the total heat supply. As a
result, a building design that provides the lowest peak load demand may result in
the largest primary energy savings. Peak load heating demand can be reduced, e.g.
by design with more efficient thermal envelope, i.e. low shape factor and high
thermal resistance, as illustrated in Figure 22.
Table 7. Energy efficiency measures.
Energy efficiency measures U-value W/(m2 K)
Before After
Energy efficient windows 1.90 0.85
Energy efficient doors 1.19 0.85
Additional 100 mm mineral wool insulation in the roof 0.13 0.11
Additional 250 mm mineral wool insulation in the facade 0.20 0.11
51
Preliminary results (the Stockholm program)
In an ongoing study of the effect of the shape factor in an energy system
perspective, the total specific primary energy use, which include the annual amount
of primary energy to operate the building and the annualized embodied energy for
constructing the building (assuming 50 years life time), was found to increase
linearly with higher shape factor regardless of the building frame, climate and
thermal envelope scenarios, as illustrated in Figure 27. The difference in specific
primary energy use due to the variation in shape factor (from 1 to 1.9, see Figure 3)
was found to be similar to the difference in specific primary energy due to variation
in thermal envelope (from common practice buildings to passive house standard).
The effect of the shape factor on the annual primary energy, i.e. the slope of the
trend-line in each thermal scenario in Figure 27, includes contributions from both
the embodied energy in the construction materials and from the production of
energy carriers for building operation. The contribution from building operation
was found to be between 50% and 83% of the total effect, with higher percentage
values for buildings with lower thermal envelope efficiency and for buildings
located in colder climates.
Shape factor
Figure 27. Preliminary results from an ongoing study regarding the total annual specific
primary energy, i.e. energy production + embodied energy in construction
materials (per year of building life-time) vs. the shape factor of multi-storey
apartment buildings (Stockholm program) with different building frames, thermal
envelopes and climate scenarios.
0
50
100
150
200
250
0.9 1.1 1.3 1.5 1.7 1.9
Spe
cifi
c p
rim
ary
en
erg
y d
em
and
kWh
/(m
2ye
ar)
Malmö
0.9 1.1 1.3 1.5 1.7 1.9
Karlstad
0.9 1.1 1.3 1.5 1.7 1.9
Östersund
0.9 1.1 1.3 1.5 1.7 1.9
Jokkmokk
0.981 < R2 < 0.999 16.5 < m < 34.9
52
9. BUILDING DESIGN AND SOCIAL ENVIRONMENT
Sustainable development can be expressed as stable societies where people are
able to satisfy their basic needs and thereby live good lives, within the limits of
planetary boundaries [113]. The built environment hold a major challenge for
sustainable development as it impacts both environment and society. In Nordic
countries it is responsible for one-third of the final energy demand [114] and at the
same time have an important role regarding social issues like interactions among
people and sense of community [115].
While there are both environmental and social aspects to consider when working
for technical solutions to stir society in the direction of sustainable development,
projects often tend to focus solely on one of these aspects, and the prospects of their
interlinkage are rarely explored. For a development that effectively leads to
sustainable results it is desirable to plan each function to fulfil as many
environmental and social goals as possible at the same time. The previous sections
described the environmental advantages (through primary energy) of compact
building design with atrium in multi-storey building as an example. This section
discusses the effect of building design on social interactions, with regard to the
atrium space.
9.1. Atrium
An atria or open courtyard is an old design concept that can be found in the
architecture of ancient civilisations based in warmer climates such as the Romans,
Greeks, Chinese and Arab cultures [116]. The courtyards from those periods were
not fully enclosed [117] and where important for social life through a protected
outdoor environment for the purpose of working, gardening, sleeping and for
variety of social activities. The courtyard also brought environmental benefits as it
had an effect on the indoor thermal and visual comfort within the adjacent buildings.
It provided daylight, passive solar gains [103] and was part of the natural ventilation
system as it acted as an air channel to enhance convective airflow through and
around the adjacent buildings [118].
In Nordic climates, an open courtyard design within buildings may not entail
large benefits as a place for social interaction. That is due to shorter daylight hours
and poorer outdoor thermal comfort during the cold season. A design with an
enclosed and heated courtyard within a residential building (henceforth: “heated
atrium”) may be utilized better throughout the year. However, enclosed and heated
atrium design in multi-story apartment buildings is not common in the Nordic
regions, and indoor common areas in multi-story apartment buildings are usually
53
not designed in a way that becomes an integral part of the residents’ day-to-day
activities or to encourage social interactions among occupants.
9.2. Social interactions
Social interactions provide opportunities for social ties, which in turn is reported
to be beneficial, at least to some extent, for the psychological well-being of
individuals [119]. It facilitates a community feeling or sense of pride and attachment
among people living in a specific area [120]. A sense of community is a feeling that
provides the individuals with a belief on the “right to belong” [121], a sense of
security, emotional safety [122] and improved subjective wellbeing [123]. Putnam
[124] suggests that the integration of individual to the community is achieved partly
through interactions of residents and by getting to know the neighbours.
Neighbourhoods offer different type of localities: public, semi-privet and private
spaces [115]. Accordimg to Kearney [125], outdoor public space has a strong positive
impact on sense of community. The location of the common space is important for
social interaction and if the place is centrally located and accessible then more
dwellers will use it [126]. Access to public spaces like pedestrian [127-129], parks
[130], main streets [131, 132] were also reported to effect social interaction.
Furthermore, the ability of the residents to see and hear others using the common
place will encourage social interaction [126]. Semi-privet spaces like terrace house’s
front yards and front porches were reported to encourage social life and sense of
community in residential neighbourhoods [133, 134]. In private spaces, factors such
as proximity of apartments in multi-storey buildings, its orientation towards other
apartments, position and quality of common place within the building were found
to affect the social interactions among dwellers [135-137].
The studied heated atrium building incorporate all the above three localities:
apartments as private spaces orientated towards each other, indoor balconies and
corridors facing the courtyard acting as a semi-private spaces, and the courtyard, as
a public or common space in the “middle” of the residential building.
The following sections will discuss the survey results about the perceptions of
the residents of the heated atrium case study regarding the impact of building design
on their social/neighbourly everyday interactions.
Results - Post purchase assessment
Figure 28 illustrates the respondents’ reply to three questions related to post
purchase assessment. All agreed that the heated atrium was one of the reasons for
buying the apartment followed by the architectural design (95%). Location was
named as a purchase reason by 71% of the respondents, while price by only 24%.
54
All the respondents were satisfied with their apartment and the majority had a
positive attitude towards the heated atrium and indoor balconies, including the
daytime lighting during summer. However, 17% of the respondents believed that
the daylight during winter was insufficient, which may be due to the short daylight
hours and low solar intensity during that time of year. Only one responder was
dissatisfied with the thermal comfort in the atrium.
83% of the respondents reported that during winter they can come out from their
apartment without wearing any bulky warm clothes. Approximately, 90% of them
agreed to the statement that the heated atrium gives them a sense of
“neighbourliness and belongingness, and 65% agreed that the atrium makes them
feel safe and secure. The ability to be present in the atrium without the need for
outdoor clothes (when it is cold outside) was valued by 83% of the respondents. On
a separate question 96% stated that they definitely recommend to their friends or
relatives to purchase an apartment in a building with an atrium.
Figure 28. Post purchase assessments questions.
0
3
6
9
12
15
18
21
24
Atr
ium
Arc
hit
ectu
re a
nd
des
ign
Loca
tio
n
Att
ract
ive
pu
rch
ase
pri
ce
No
. o
f re
spo
nd
ers
What were the reasons for purchasing your apartment?Agree Neither nor Disagree
Atr
ium
sp
ace
Co
rrid
ors
& b
alco
nie
s
Day
ligh
t -
Sum
mer
Day
ligh
t -
Win
ter
Ther
mal
co
mp
fort
What is your attitudetorward the atrium?
Positive Neither nor Negative
Feel
ing
of
har
mo
ny
and
be
lon
gin
g
No
ne
ed f
or
ou
tdo
or
clo
thes
Hig
her
fee
ling
of
safe
ty
What do you like about the atrium?
Agree Neither nor Disagree
55
Results - Social aspects
Figure 29 illustrates the respondents’ reply to three questions about their social
life in the building. Both the heated atrium and the indoor balconies were found to
be used by more than 85% of them for social activities involving family, friends or
neighbours. The atrium space was found to be the locations, in which 87% of the
respondents often meet each other. 78% often meet in the indoor balconies and 70%
in the staircase. The apartments are places, in which least of the respondents meet
each other (43%).
The indoor balconies are used for relaxation by 61% of the respondents and for
storage by 43%. 35% of them stated that the heated atrium is used by kids for
playing. A few of them also noted that they use the indoor balconies for dining and
cultivation.
Of the respondents 96% agreed that the heated atrium facilitate them to talk more
often with their neighbours. 75% stated that they know a person well in more than
eight of the apartments. More than 80% agreed that if they would be in need of help
with different services, like buying groceries, watering the plants, collecting post
and car driving, their neighbours would come forward.
Figure 29. Questions concerning social aspects.
0
3
6
9
12
15
18
21
24
Atr
ium
Ind
oo
r b
alco
nie
s
Stai
rcas
e
Bu
ildin
g ex
it
Ap
artm
en
t
No
. o
f re
spo
nd
ers
How often do you meet and talk with your neighbours in the:
Often Sometimes Never
Occ
asio
nal
so
cial
even
ts
Fam
ily a
nd
fri
end
sga
ther
ing
Co
ffe
e w
ith
nei
ghb
ou
rs
Ch
ildre
n t
o p
lay
Which activities does the atrium is used for?
Often Sometimes Never
Mee
tin
g p
lace
wit
h n
eig
hb
ou
rs
For
rela
xati
on
As
a st
ora
ge p
lace
Which activities does the balconies are used for?
Often Sometimes Never
56
Results - Energy aspects
Figure 30 illustrates the reply to four questions about energy use. 13% of the
respondents believe that the atrium significantly increase the demand for space
heating in the building, while 50% disagree. 67% and 48% think that it is important
to reduce the demand for space heating and electricity, respectively. 50% of the
respondents stated that they are already undertaking enough measures to reduce
household’s energy use. And only one respondent reported that he/she was
influenced by neighbours to reduce household energy use.
Figure 30. Questions concerning energy demand aspects.
0
3
6
9
12
15
18
21
24
No
. o
f re
spo
nd
ers
The atrium increase heating significantly
Agree Neither nor Disagree
Spac
e h
eat
ing
Ho
use
ho
ldel
ectr
icit
y
How important it is to reduce the energy for:
Not important Neither nor Important
Par
tne
r
Ne
igh
bo
urs
Frin
ds
Co
llegu
es
How much are you influenced to reduce energy by:
Much Neither nor Not at all
57
10. DISCUSSION
The sustainable construction movement that started after the oil crises in the
middle of the 1970s aimed to reduce the environmental impact of buildings by
finding answers to two important questions [15]: What is a high-performance
building? And how to determine if a building meets the requirements of this
definition? To answer such questions there is a need for indicators that will
accurately evaluate the energy performance of buildings.
10.1. Indicators for energy efficiency
The Swedish building code uses the specific final energy demand as an energy
indicator. This indicator is also used in building certification schemes. It uses the
total floor area of the building as the functional unit, which enables it to compare
buildings with different sizes. However, as has been indicated by the results section
and in the appended Papers II and V, there are difficulties when the indicator,
specific final energy, is used to steer toward energy efficient buildings.
First, the specific final energy demand, as indicator, is often used already during
the design stage to ensure meeting the energy requirements. The specific final
energy demand take into account the building design, climate conditions, energy
systems and also the occupants’ behaviour. Hence, it requires validated algorithms
that could be applied on a large variety of buildings. Flexible algorithms that provide
the ability to modify many variables are complex and require sufficient competence.
The Stockholm program for environmental adapted buildings was the first in
Sweden to demand energy modelling in the design stage. However, there was no
demand regarding the quality of the modelling and a relative simple and non-
validated algorithm was used by most of the proprietors. As a result, the projected
values of specific final energy demand were in average underestimated by 19%, and
thus post occupancy energy monitoring of the majority of the building projects
exceeded the energy goals of the program (Paper II).
Second, even with validated algorithm and sufficient competence, some
variables needed for modelling of specific final energy demand are unknown, or at
least hard to determine exactly, before buildings are constructed, for example,
variables concerning future weather and performance of systems to be installed.
Variables concerning occupants’ indoor activities and preferences, e.g. indoor
temperature and household electricity, are especially difficult to predict and can
vary considerably among different households (se e.g. Paper IV). Such variables
cannot be ignored and need to be assumed instead. Assumptions are subjective to
the knowledge and the experience of the modeller and are one of the causes for the
energy performance gap between modelled and post occupancy energy monitoring
58
(Paper II and IV). By assuming standardized values, as suggested by FEBY [32],
different design solutions can be compared but the model results will probably still
differ from post occupancy energy monitoring. Underestimated modelled values in
comparison to post occupancy energy monitoring make it harder to steer society
toward less environmental impacts from energy use in buildings. It may also lead to
dissatisfaction among homeowners regarding their building’s performance. That
may be a greater concern in low energy buildings due to higher investment costs
and higher expectations. After the building is built it is difficult to put the finger on
the cause without proper post occupancy evaluation. The fault could be in the
building design, in the quality of work and materials, in the energy system installed
or due to the behaviour of the occupants.
Third, post occupancy evaluation of the specific final energy demand, e.g. by
energy monitoring, depends on the monitoring period (Paper II) and on the interior
design of the building (Paper II and V), and thus may not accurately represent the
energy efficiency of the building. The specific final energy demand represents the
average final energy demand per unit of a building’s floor area. It presumes that the
different zones in a building have equal contribution to the total final energy
demand, which is not always correct. For example, apartment areas in multi-storey
apartment buildings in Sweden have higher final energy demand per unit of area
compared to, e.g. corridors, staircases, basements, attics etc. (Paper II and V). As a
result, buildings that are designed with lower relative size of apartment area will
have lower value of specific final energy demand in comparison to buildings with
similar thermal efficiency but higher ratio. It should be noted that low ratio of
apartment to total floor area could be an advantage in some cases, e.g. in buildings
with atrium design. An alternative choice, which would steer more strongly toward
better energy performance, would be to use the apartment area as the reference area
for specific energy use instead of the total floor area in multi-story apartment
buildings.
10.2. Indicators for efficient building design
Another alternative, which could be explored for use in building codes and
certification schemes for energy efficiency in residential buildings, could be an
indicator based on the intrinsic properties of buildings, e.g. the shape factor and the
average thermal transmittance of the building. Both the shape factor and the average
thermal resistance of the thermal envelope can be derived directly from the
building’s drawings, even before it is built.
The shape factor of a building is a measure of building compactness. Buildings
with lower shape factor will have smaller size of thermal envelope, and thus lower
heat losses. The energy demand for space heating increase linearly with the shape
59
factor (Paper III and V). The results of this thesis indicate that from energy
perspective buildings in Nordic climates preferably should be built with low shape
factor. This is more important for regions with colder outdoor climate
10.3. Thermal properties of buildings in use
Post occupancy measurement using thermography has a potential to evaluate
thermal properties of buildings fabrics after construction. Thermography has the
potential to provide both qualitative and quantitative inspections. Qualitatively, it
can inspect the building for imperfections, and quantitatively, it can potentially
measure the average thermal properties of building fabrics. The proposed
quantitative method, described in Paper VI, seems to have the potential to be applied
directly on building fabrics, even when subjected to varying meteorological
conditions, and account for all thermal inhomogeneities.
10.4. Primary energy use
Heating systems within buildings and energy supply systems have very little to
do with the energy efficiency of the building design. Heating systems usually have
much shorter life time than the life time of buildings. For example, many of the
houses constructed during the 50s and 60s in Sweden are still in use today, but their
installed heating systems have been replaced at least ones; from oil boilers to
biomass boilers, resistance electric heating, district heating, and in recent years to
heat pumps of different types. In contrast, once the building is constructed it is less
adaptable to changes.
The amount of primary energy resources that are used by a building cannot be
assessed solely by the final energy demand or thermal efficiency as indicators. The
choice of heating system, the energy supply system and type of fuel has significant
impact on the use of energy resources [106]. Reducing final energy demand is not in
itself a guarantee for reducing the use of primary energy resources (Paper I), [138].
For example, installation of ventilation heat recovery or heat pumps in buildings
that are connected to district heating will reduce the final energy demand. Such
measures will reduce production of cogenerated electricity, which is an efficient
method to produce electricity (in Sweden, about 50% of the energy for space and
domestic water heating is supplied by district heating utilities [25]). At the same time
it will increase the demand for electricity, the demand for peak power capacity, and
result in lower use of existing heat supply capacities [139].
Energy supply systems are also affected by energy demand patterns. Building
designs that aims to reduce peak load demand were found to have the largest
savings in primary energy (Paper I). To quantify the impact of building design on
60
primary energy, a model needs to include the building, the energy supply system
and the dynamic interaction between them. One such model is described in Paper I.
10.5. Social interactions
The built environment holds both environmental and social challenges. In the EU
and the US people spend about 90% of their time indoor [140, 141], but still indoor
common areas in multi-story apartment buildings are usually not designed in a way
to enhance social interactions. The atrium building, studied in Paper V, seems to be
a design concept that in Nordic climates has the possibility to enhance both final
energy efficiency and social interactions. The studied building was designed to have
semi-private spaces as indoor balconies and indoor public spaces, which seems to
become an integral part of the residents’ day to day activities. The atrium, indoor
balconies and indoor corridors are the locations in the atrium building, which have
high level of social interactions among the residents and appears to facilitate a sense
of “neighbourliness and belongingness” among the residents. The atrium building
is an example that innovative design can fulfil several environmental and social
goals at the same time.
61
11. CONCLUSIONS
Pre-occupancy calculations of specific final energy demand in residential
buildings are too rough an indicator to explicitly steer toward lower final energy
demand in the building sector. Among the reasons are unknown variables before
the building is constructed, wrong assumptions during calculations and algorithm
faults.
The specific final energy demand as indicator for post occupancy energy
monitoring may not provide a representative image of the energy efficiency of a
building if the energy measurements are performed too early. The specific final
energy demand is also affected by the interior design of the building. A building
with lower ratio of apartment to total floor area has lower values of specific final
energy demand, but not necessarily better energy efficiency.
The shape factor of buildings has significant effect on the final energy demand of
buildings and the use of primary energy. From energy perspective, newly
constructed buildings in Nordic climates should be designed with as low shape
factor as possible.
Atrium design in residential buildings located in Nordic climates have a potential
to obtain high energy efficiency by compact design (low shape factor). From a social
point of view, an atrium space may provide the residents with a sense of
“neighbourliness and belongingness” and facilitates social interactions during the
day to day activities. Thus, new building projects or restoration of existing buildings
should consider social factors already at an early stage of the design.
Thermography have a potential in evaluation of thermal performance of building
fabrics. It could be applied directly on building fabrics even if subjected to varying
meteorological conditions and be applied on building fabrics with different sizes
and account for all thermal inhomogeneities.
Energy efficiency measures should be evaluated in a relevant energy system
context. For example, significant primary energy savings in district-heated buildings
can be obtained by reducing peak load demand, even if peak load production units
cover only a small share the of total heat load.
62
Future research
Two areas for future research that have become especially clear during the work
with this thesis are:
The need to find good indicators for building performance, including energy,
environmental and social aspects of building design. There is also a need to
explore how such indicators should be combined to best describe the overall
performance of buildings.
Methods like thermography for post occupancy evaluation of building energy
performance need to be developed, improved and standardised. The aim
should be to ensure that the projected thermal properties are obtained, but also
to evaluate new construction materials and technologies.
63
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