A Carbon Footprint of an Office Building

Abstract

Current office buildings are becoming more and more energy efficient. In particular the importance of heating is decreasing, but the share of electricity use is increasing. When the CO 2 equivalent emissions are considered, the CO 2 emissions from embodied energy make up an important share of the total, indicating that the building materials have a high importance which is often ignored when only the energy efficiency of running the building is considered. This paper studies a new office building in design phase and offers different alternatives to influence building energy consumption, CO 2 equivalent emissions from embodied energy from building materials and CO 2 equivalent emissions from energy use and how their relationships should be treated. In addition this paper studies how we should weight the primary energy use and the CO 2 equivalent emissions of different design options. The results showed that the reduction of energy use reduces both the primary energy use and CO 2 equivalent emissions. Especially the reduction of electricity use has a high importance for both primary energy use and CO 2 emissions when fossil fuels are used. The lowest CO 2 equivalent emissions were achieved when bio-based, renewable energies or nuclear power was used to supply energy for the office building. Evidently then the share of CO 2 equivalent emissions from the embodied energy of building materials and products became the dominant source of CO 2 equivalent emissions. The lowest primary energy was achieved when bio-based local heating or renewable energies, in addition to district cooling, were used. The highest primary energy was for the nuclear power option.

Full text

Energies 2011, 4, 1197-1210; doi:10.3390/en4081197
energies
ISSN 1996-1073
www.mdpi.com/journal/energies
Article
A Carbon Footprint of an Office Building
Miimu Airaksinen 1,* and Pellervo Matilainen 2
1 VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, Finland
2 Skanska M&E Finland Oy, P.O. Box 114, FI-00101 Helsinki, Finland;
E-Mail: pellervo.matilainen@skanska.fi
* Author to whom correspondence should be addressed; E-Mail: miimu.airaksinen@vtt.fi;
Tel.: +358-40-770-4832; Fax: +358-20-722-7009.
Received: 4 May 2011; in revised form: 10 August 2011 / Accepted: 17 August 2011 /
Published: 19 August 2011
Abstract: Current office buildings are becoming more and more energy efficient. In
particular the importance of heating is decreasing, but the share of electricity use is
increasing. When the CO2 equivalent emissions are considered, the CO2 emissions from
embodied energy make up an important share of the total, indicating that the building
materials have a high importance which is often ignored when only the energy efficiency
of running the building is considered. This paper studies a new office building in design
phase and offers different alternatives to influence building energy consumption, CO2
equivalent emissions from embodied energy from building materials and CO2 equivalent
emissions from energy use and how their relationships should be treated. In addition this
paper studies how we should weight the primary energy use and the CO2 equivalent
emissions of different design options. The results showed that the reduction of energy use
reduces both the primary energy use and CO2 equivalent emissions. Especially the
reduction of electricity use has a high importance for both primary energy use and CO2
emissions when fossil fuels are used. The lowest CO2 equivalent emissions were achieved
when bio-based, renewable energies or nuclear power was used to supply energy for the
office building. Evidently then the share of CO2 equivalent emissions from the embodied
energy of building materials and products became the dominant source of CO2 equivalent
emissions. The lowest primary energy was achieved when bio-based local heating or
renewable energies, in addition to district cooling, were used. The highest primary energy
was for the nuclear power option.
OPEN ACCESS

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Keywords: energy efficiency; CO2 emissions from energy use and materials;
primary energy
1. Introduction
Buildings account for circa 40% of the total energy use in Europe [1], and for about 36% of the
EU’s total CO2 emissions [2,3]. Even though energy saving measures at the building level have been
proposed, the net energy use at the city/district levels is still increasing. Buildings are important in
achieving the EU’s energy savings target and to combat climate change, while contributing to energy
security [4]. The building industry and the built environment are one of the largest contributors to
energy and materials use worldwide. In the northern part of the European Union, 41% of the total final
energy use comes from buildings, with 30% being used in residential buildings [5]. According to the
EuroACE report [6], 57% of the energy used in buildings is for space heating, 25% for hot water, 11%
for lighting and electrical appliances, and 7% for cooking.
Buildings are an exceedingly complex industrial product with a lifetime of decades. While there
have been certain on-going efforts to control and manage individual aspects of the environmental
aspects of buildings (i.e., energy codes, automation and control schemes, thermal comfort),
comprehensive approaches have been lacking [7,8], particularly in the design stages of a building’s life
span. Unfortunately, it is in the design stage when the greatest opportunities to affect changes whose
benefits can last for decades are available.
In Finland, residential and commercial buildings account for 40% of all energy use; in addition
commercial and apartment buildings have a notable influence on the peak demand in some periods.
Energy and electric intensity in commercial buildings has clearly increased, and residential energy use
continues to increase (mainly due to electricity use).
Key features of the Finnish energy policy are improved energy efficiency and increased use of
renewable energy sources [9]. To achieve a sustainable shift in the energy system, a target set by the
authorities, both energy savings and increased use of low-pollution energy sources are therefore high
priority areas. Building low-energy buildings, characterized by lower thermal energy demand than new
buildings with ordinary energy standards, is in accordance with the declared national aim of reducing
energy use. However, in the future the use of electricity will be of more importance in respect to CO2
emissions and primary energy use.
The space heating demand of buildings has decreased by improved insulation, reduced air leakage
and by heat recovery from ventilation air. However, these measures result in an increased use of
materials. As the energy for building operation decreases, the relative importance of the energy used in
the production phase increases and influences optimization aimed at minimizing the life cycle energy
use. The life cycle primary energy use of buildings also depends on the energy supply systems.
Presently, the share of renewable energy used in the built environment is very modest; the
renewable energy accounted for 10.3% of gross final energy consumption in the EU-27 in the year
2010 [10]. Both at national and international level, the targets for energy efficiency and share of
renewable energy production imply a steep increase of intermittent renewable energy.

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The use of a larger share of renewable energy compared to today’s levels with present day
technology presents a number of challenges. Renewable energy supplies such as solar or wind energy
have a fluctuating character, which is obviously problematic to the demand side: energy needs are
usually rather constant or often not in the same temporal cycle as the supply. In addition the peak
supply from renewable energies can be much higher than demand and the excess renewable energy
cannot be stored. Especially in northern climates, the space needed for local renewable production
(area of collectors, etc.) might become disproportionately large. Furthermore, the location of the
buildings/districts is not always suitable for utilization of some renewable sources.
The ambition in sustainable development of the built environment is to reduce the harmful impact
of the nature of materials and building energy use. Often the building energy use and the minimization
of its CO2 equivalent emissions are considered to be the desired goal. However, as the energy use
decreases the importance of CO2 equivalent emissions originating from building materials and
products increases. Thus, what kind of materials and building products are used becomes more
important. In addition, the minimization of CO2 equivalent emissions is perhaps not the only desired
target, but we need to consider also the minimization of primary energy use, since it highlights rather
well the use of natural resources. The aim of the study is therefore to:
1. Find out the different available options in the design phase in order to minimize the
energy consumption;
2. Consider how the CO2 equivalent emissions from the embodied energy from building materials
and CO2 equivalent emissions from energy use in the building should be treated;
3. Consider how we should weight the primary energy use and the CO2 equivalent emissions of
different design options.
In this study is a real office building was studied. The building already had a rather compact
quadratic shape, therefore the geometry is not a variable in this study, which is a limitation of
this approach.
2. Methods and Studied Building
2.1. Studied Building
The studied building is an office building located in Helsinki developed by Skanska Commercial
Development Finland. The building was under design phase and the aim was to study different
alternatives in order to choose the most energy and environmental efficient way to erect the building.
The gross floor area of the nine storey building is 26,000 m2. The geometry of the building is
quadratic. The studied properties are shown in Table 1.

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Table 1. Studied design alternatives. The control systems include ventilation and lightning.
Feature Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
Building envelope excl.
windows
Building
Code 2010
Building
Code 2010
Building
Code 2010
Building
Code 2010
Building
Code 2010
Passive
house
Windows (W/m2K) 1.0 1.0 1.0 1.0 0.7 0.7
Ventilation heat recovery 70% 70% 80% 80% 90% 90%
LED lighting in garage in garage in garage in garage in all spaces in all spaces
Systems control level building room room building room room
In the 2010 Building Code the U-values for external walls is 0.17 W/m2K, base floors 0.16 W/m2K,
roofs 0.09 W/m2K and doors 1.0 W/m2K. The ventilation heat recovery requirement in the 2010
Building Code is 45%, which was not used in calculations, since that was not an option in the design
phase. In the so called passive house level the U-values for external walls is 0.08 W/m2K, base floors
0.15 W/m2K, roofs 0.08 W/m2K and doors 0.7 W/m2K.
2.2. Calculation Tool
The buildings were modelled in a dynamic IDA simulation environment [11], where a RC-network
(resistance-capacitance network) model of a building was used. IDA is a modular simulation
environment, which consists of a translator, solver, and modeler. The solver and physical models are
separated, which makes it possible to change the mathematical formula of any component without
changing the model description file. The modules are written in Neural Model Format (NMF), which
serves at the same time as a readable document and a computer code. Via the translator, the modules
can be used in several modular simulation environments [12–14].
2.3. Building Model
The building model was the architect’s real 3D model but the building spaces were simplified to
43 different zone models each representing typical uses of the space type, such as office rooms,
meeting rooms, cafeteria, etc. In each space the occupants were assumed to be present between 8–16 h
and the lightning and equipment were on between 7–17 h. The different profiles for internal loads and
lightning are those typically used in Finnish simulations. The main information is shown in Table 2.
Table 2. Modelled spaces and their internal loads, air flows, heating and cooling set points
as well as room area and height.
Zone Name Number
of Zones
Room
Height
(m)
Area
(m2)
Setpoint (°C) Air (L/s m2) Occup.
(No./m2)
Lights
(W/m2)
Equip.
(W/m2)
Heat Cool Supply Return
Open office 1 1 3.3 360.4 21 25 1.5 1.5 0.06 12 30
Service 7 5.3 64.43 21 25 0.5 0.5 0 8 0
Storage 3 5.3 16.61 18 25 0 0.35 0 8 0
Kabinets 1 5.3 12.71 21 25 1.5 1.5 0.06 12 30
Meeting BIM 2 5.3 36.26 21 25 5 5 0.1 12 30
Meeting 1 2 5.3 27.34 21 25 5 5 0.1 12 30

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Table 2. Cont.
Zone Name Number
of Zones
Room
Height
(m)
Area
(m2)
Setpoint (°C) Air (L/s m2) Occup.
(No./m2)
Lights
(W/m2)
Equip.
(W/m2)
Heat Cool Supply Return
Post office 7 5.3 43.46 21 25 0.5 0.5 0 8 0
Storage 3 5.3 15.72 18 25 0 0.35 0 8 0
Restaurant 6 5.3 211.3 21 25 6 6 0.06 12 0
Kitchen 6 5.3 100.6 21 25 10 10 0.06 20 50
Lifts 8 5.3 16.25 21 25 8 8 0 8 0
WC 4 5.3 34.08 21 25 0 1.5 0 8 0
Client service 1 5.3 162.3 21 25 1.5 1.5 0.06 12 30
Atrium 5 35 142.4 21 25 2 2 0 20 0
Group meeting 2 3.3 20.74 21 25 5 5 0.1 12 30
Meeting 2 2 3.3 19.81 21 25 5 5 0.1 12 30
Storage 3 3.3 16.61 18 25 0 0.35 0 8 0
WC 4 3.3 31.94 21 25 0 1.5 0 8 0
Open office 2 1 3.3 382.6 21 25 1.5 1.5 0.06 12 30
Lobby 1 3.3 34.2 21 25 1.5 1.5 0.06 12 30
Storage 3 3.3 12.47 18 25 0 0.35 0 8 0
Meeting 3 2 3.3 22.57 21 25 5 5 0.1 12 30
WC 4 3.3 19.35 21 25 0 1.5 0 8 0
Atrium corridor 1 5 3.3 74.8 21 25 1 1 0 8 0
Atrium corridor 2 5 3.3 61.79 21 25 1 1 0 8 0
kabinett 1 5.4 56.8 21 25 1.5 1.5 0.06 12 30
Sauna 9 5.4 125.9 21 25 1 1 0 12 0
HVAC room 10 5.4 440.4 20 25 0 0.35 0 8 0
Storage 3 5.4 16.61 18 25 0 0.35 0 8 0
Office 1 5.4 104.2 21 25 1.5 1.5 0.06 12 30
Meeting 4 2 5.4 22.18 21 25 5 5 0.1 12 30
Storage 3 5.4 26.23 18 25 0 0.35 0 8 0
Library 1 5.4 33.37 21 25 1.5 1.5 0.06 12 30
WC 4 5.4 23.73 21 25 0 1.5 0 8 0
Atrium corridor 3 5 5.4 99.7 21 25 1 1 0 8 0
Cafeteria 6 5.3 198.6 21 25 1.5 1.5 0.06 8 0
Corridor 5 5.3 56.7 21 25 1 1 0 8 0
Service 12 3.9 238.9 21 25 0.5 0.5 0 5 0
Cellar 1 11 3.9 1527 15 25 1 1 0 5 0
Storage 1 12 3 506.2 21 25 0.5 0.5 0 5 0
Cellar 2 11 3 1426 15 25 1 1 0 5 0
Storage 2 12 3.1 506.2 21 25 0.5 0.5 0 5 0
Cellar 3 11 3.1 1426 15 25 1 1 0 5 0

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2.4. Embodied Carbon in Materials
The embodied carbon in materials and material production process was calculated according to
ISO 14020 and ISO14040, as well as ISO 14025. In addition the National Method for Building
Products and Components were used [15]. Material specific environmental certificates and
declarations were used. The embodied CO2 includes energy consumption of building materials and
products, the use of raw materials and greenhouse gases. The most important greenhouse gases are
fossil fuel derived CO2, CH4 and N2O. In the calculations the greenhouse gases are transformed to CO2
equivalents by using IPCC’s characteristic factors, in which the corresponding factors for CO2 are 1,
CH4 corresponds 25 and N2O 298. The sum of these is the CO2 emissions from embodied energy of
building materials and products.
2.5. Energy Sources and Their CO2 Equivalent Emissions and Primary Energy
The studied alternatives for energy sources and their CO2 equivalent emissions are shown in
Table 3. The average values in district heating and electricity refer to average values in Finland for
2008. In Finland 75% of the district heating is produced in electricity co-generation power plants. The
primary energy factors for district heating systems are less than zero, due to the co-generation of heat
and power. The factors are calculated by applying the benefit allocation method in co-generation. In
the district cooling the production is 40% from free cooling (sea water), 30% from absorption heat
pumps and 30% from heat pumps. In green electricity 80% of the power comes from wind and 20%
from bio-based fuels.
Table 3. Primary energy factors and CO2 equivalent emissions used.
Primary Energy Factor CO2 equivalent *
District heating average 1.87 0.22
District heating bio 0.4 0.12
Electricity average 1.87 0.38
Electricity from district heating average 1.87 0.38
Peak electricity from nuclear power 2.8 0
Peak electricity from coal 2.0 0.928
District cooling 0.25 0.12
Green electricity 0.2 0
* Unit: kg CO2/kWh.
The service life for building was assumed to be 50 years. The embodied CO2 emissions from
building materials and process were estimated according to design drawings.
3. Results
The energy consumption was highest in the case 1 and lowest in the case 6. But the energy
consumption in case 4 was also really high, being nearly the same as in the case 1 and showing that the
building level control is inefficient with respect to energy saving. In particular the heating energy
consumption is the highest when the control is at the building level. The energy consumption was 20%

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lower in case 6 compared to case 1. The only difference between cases 3 and 4 was the temperature
control. In case 3 the control was at the room level, while in the case 4 the control was at the building
level. That resulted in a 7% difference in total energy consumption and a 20% difference in space
heating, in addition the difference in cooling was also 20% between those two cases (Figure 1). Since
in office buildings the electricity use has higher importance than heating, case 6 does not have that
much difference in consumption, even though the insulation values are much better (equal to passive
house). The major difference between cases 3 and 5 was the LED lightning, in case 5 all lightning was
done by LEDs, which clearly resulted in a lower energy consumption. The use of lower U-values in
windows (from 1.0 to 0.7 W/m2K) did not afford that much energy consumption savings. This was due
to the rather high internal loads (typical office equipment and people) thus, the heating demand was
already rather low.
Figure 1. Yearly energy consumption in different cases. Electricity AC represents for
electricity for air conditioning systems.
0
20
40
60
80
100
120
Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
Energy consumption (kWh/m
2
)
Equipment
Indoor lightning
Electricity AC
Cooling
Domestic hot water
Space heating
The shares of the total energy consumption are shown in Figure 2. Due to the rather cold Finnish
climate, space heating still represents a rather high share of the whole energy consumption, but it is not
dominant as it used to be in older buildings (e.g., office buildings from 1970s). The shares of
equipment and cooling are rather big. If all electricity use is added (equipment, indoor lightning, and
AC electricity) the share is close to 50% of the total consumption. If the cooling is done with
electricity the share is between 65–70%, evidently highlighting the importance of saving electricity. In
office buildings the use of domestic hot water is typically very low, as can be seen in Figure 2.

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Figure 2. The share of different energy use in different cases.
0 %
10 %
20 %
30 %
40 %
50 %
60 %
70 %
80 %
90 %
100 %
Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
The share of energy consumption
Equipment
Indoor lightning
Electricity AC
Cooling
Domestic hot water
Space heating
3.1. CO2 Equivalent Emissions
The Finnish Building code is very advanced with respect to reducing heat losses from buildings;
e.g., the U-values and ventilation heat recovery, as well as air tightness of the building envelope, are
required to be rather good. This can be clearly seen from the energy consumptions (Figure 1). The CO2
equivalent emissions of heating are also rather low due to the low energy consumption when average
Finnish district heating, cooling and electricity are used as energy sources (Figure 3). In Figure 3
heating includes both space heating and domestic hot water.
Figure 3. The share of each energy consumption and embodied CO2 in different cases
when average district heating, cooling and electricity are used. The heating includes both
space heating and domestic hot water heating.
-
5 000 000
10 000 000
15 000 000
20 000 000
25 000 000
Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
kg CO2 eq
CO2 embodied
Electricity
Cooling
Heating

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Due to the low heating energy consumption the embodied CO2 emissions and electricity are
dominant components in the CO2 emissions. That is actually rather surprising, since case 1 is the
typical building code level in new office buildings, and only ventilation heat recovery is clearly better
than the average in new buildings. In this study the embodied CO2 includes energy consumption of
building materials and products, and the use of raw materials and greenhouse gases, see Section 2.4.
Evidently, if all the electricity used is generated from renewable energy sources and for district
heating and cooling bio-fuels are used, the embodied CO2 emissions have the highest share and the
over all CO2 equivalent emissions decrease dramatically (Figure 4). However, the problem with
renewable electricity is that the power plants produce renewable energy on a yearly basis. Thus,
sometimes the electricity might originate from fossil fuels for a short period of a time if not enough
electricity from renewable sources is available. The electricity produced by fossil fuels is substituted
by renewable energy on a yearly basis to get the balance. Usually this means excess energy, e.g., from
wind power.
Figure 4. The share of each energy consumption and embodied CO2 equivalent in different
cases when district heating, cooling from bio-fuels is used and electricity is from renewable
energy sources.
-
5 000 000
10 000 000
15 000 000
20 000 000
25 000 000
Case 1 Case 2 Case 3 Case 4 Case 5 Case 6
kg CO2 eq
CO2 embodied
Electricity
Cooling
Heating
Figure 5 shows the primary energy consumption as a function of the relation between embodied and
energy-derived CO2 equivalent emissions. The CO2 equivalent embodied corresponds to the CO2
equivalent emissions from materials during their lifetime and CO2 energy corresponds the CO2
emissions from energy use in the building (heating, cooling and electricity). When all different options
for heating, cooling and electricity sources were compared it can be clearly seen that the nuclear-based
energy alternatives all ended up with rather high primary energy consumption and since the building
energy use is carbon neutral, the embodied CO2 emissions become dominant (Figure 5).
If low primary energy is the target, then bio-based district heating systems seems to be effective as
well as the use of electricity from renewable energy sources. Ground heat or the average local heating
performed rather similarly in respect to primary energy use. This is because the ground heating

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systems use electricity but they can utilize the “free” thermal energy obtained from the ground. It can
be seen that the local variations do have an effect on both primary energy use and CO2 emission
(Figures 3–5); in some parts the average Finnish values do have a good correlation to local energy
production, but in some places the local production is closer to biomass-based production and in other
locations closer to peak conditions (see Table 3). The lowest primary energy use is in alternatives
based on bio local heating, cooling and green electricity. The lowest relation between CO2 embodied
and CO2 energy in addition to low primary energy use was with the cases based on bio local heating,
cooling and average electricity. When average electricity or nuclear energy based electricity was used,
there was a clear trend in that energy saving gave the highest primary energy use savings.
The lowest primary energy was achieved when bio-based or renewable energies were used in
addition to local heating and cooling. Obviously the highest primary energy was when nuclear power
was used. When the primary energy use and CO2 equivalent emissions are minimized the
CO2 equivalent emissions originated from materials become rather dominant. In this study the
CO2 equivalent emissions originated from building materials and products is between 2.4 to 3.1 higher
compared to CO2 equivalent emissions originated from building energy use during running time when
the building façade was non-wooden and the service life was 50 years.
Figure 5. Primary energy consumption as a function of the relation between embodied and
energy derivated CO2 equivalent emissions. The CO2 embodied corresponds to the
CO2 emissions from materials during their life time and CO2 energy corresponds the
CO2 emissions from energy use in the building (heating, cooling and electricity). The time
period used in calculations is 50 years.
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,00,51,01,52,02,53,03,5
CO2 embodied / CO2 ener
gy
Primary energy use (10^7 kWh)
Average district heating, cooling and
electricity
Bio district heating, cooling and green
electricity
Bio district heating, cooling and electricity
average
Ground heat and cool, electricity average
Ground heat and cool peak from coal,
electricity average
Ground heat and cool peak from nuclear,
electricity average
All electricity nuclear
∞

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4. Discussion
Finland is committed to the EU’s 2020 targets which correspond to a 20% reduction in CO2
emissions compared to 1990 levels [16]. In addition, the Finnish Government has committed to cut
down CO2 emissions by 80% by the year 2050 compared to the levels of 1990 [17].
The question is where we should target efforts to achieve these goals? At low CO2 emission levels
or low primary energy levels? The advantage of targeting low CO2 levels, especially in energy
consumption, is the fact that the CO2 emissions are minimized, which is of course one of our major
targets. However, considering only low CO2 emissions in energy consumption still allows us consume
rather high amounts of low CO2 emitting energy [18]. Many low polluting energy sources, e.g., wood,
are natural resources which we shouldn’t waste. In addition the renewal period and the life cycle of the
renewable energy source, must be considered as well. Hence low primary energy use should also be
one of the priority targets since it reduces the use of natural resources.
Choosing the right energy source is a tricky question and is dependant on the location of the
building. When only CO2 emissions are considered, nuclear power has a strong position, but when
primary energy considerations are taken into account nuclear power loses its advantage. Renewable
energies are obviously strong alternatives. However, especially with wind and solar energy, the supply
and demand of energy do not always match. Therefore both daily and seasonal storage are often
needed. Bio-fuel based local heating and cooling seem to perform well, both in respect to primary
energy use and CO2 equivalent emissions, but there are big differences between average Finnish
energy production and single power plants, e.g., the CO2 equivalent emissions might nearly double
depending on the energy source and power plant type.
According to this study a building with efficient local heating as a heat source, and a building with
ground heat (nuclear power used for complimentary electricity source) performed very similarly in
respect to CO2 equivalent emissions. However, conclude from this that which alternative we choose is
not important is dangerous. Hypothetically, if the use of local heating were to drop dramatically, the
primary energy factor and CO2 equivalent emissions from electricity would rise, leading to an increase
of the emissions from the ground heat system.
When all different options were compared the nuclear-based energy alternatives all ended up with
rather high primary energy consumption and since the building energy use is carbon neutral, the
embodied CO2 emissions become dominant. If low primary energy is the target then bio-based local
heating systems seems to be effective as well as the use of electricity from renewable energy sources.
Ground heat or the average local heating performed rather similarly in respect to primary energy use.
This is because ground heating systems use electricity, but they can utilize the “free” thermal energy
from the ground.
To target low CO2 levels, especially in energy consumption, is obviously one of our major
objectives, but considering only low CO2 equivalent emissions in energy consumption might lead us to
a wrong path; it does not limit our consumption of low CO2 emitting energy. That is naturally not our
target since low polluting energy sources such as wood, pellets and nuclear power energy are also
natural resources which we should use with care. Setting low primary energy use as a target reduces
the use of natural resources.

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Problems in the yearly calculations arise due to the fact that we always excluded when energy is
needed, which is also very important, sometimes even crucial, to consider. An example of that might
be under dimensioned ground heat solutions used in buildings, which cannot be used on very cold days
and need typically supportive power in those days. In respect to emissions, this can be problematic if
the extra power supplied to markets is produced with a polluting energy source. On the other hand, in
the buildings where cooling is needed, ground heat has the advantage that it can be used during cooling
periods as well.
This paper was based on a real building with already had a rather compact quadratic form, therefore
the building geometry was not a variable in this study even though it is well known, as found in
several studies (e.g., [19,20]), that the geometry of the building has a high impact on building
energy consumption.
5. Conclusions
Current office buildings are becoming more and more energy efficient. Especially, while the
importance of heating is decreasing, the share of electricity use is still increasing. When the CO2
equivalent emissions are considered, the CO2 equivalent emissions from embodied energy have an
important share, indicating that the building materials have a high importance which is often ignored
when only the energy efficiency of running a building is considered.
The reduction of energy use reduces both the primary energy use and CO2 emissions. The reduction
of electricity use has a specially high importance for both primary energy use and CO2 equivalent
emissions when fossil fuels are used. Often energy originated from fossil fuels is also used as a
complimentary source of energy, thus the importance of reducing energy use and especially electricity
originated from fossil sources has a high priority.
The lowest CO2 equivalent emissions were achieved when bio-based, renewable energies or nuclear
power was used to supply energy for the office building. Evidently then the share of CO2 equivalent
emissions from embodied energy from building materials and products became the dominant source
for CO2 emissions.
The lowest primary energy was achieved when bio-based local heating or renewable energies were
used in addition to local cooling. Obviously the highest primary energy was when nuclear power was
used. When the primary energy use and CO2 equivalent emissions are minimized the
CO2 equivalent emissions originated from materials become rather dominant. In this study the
CO2 equivalent emissions originated from building materials and products is between 2.4 to 3.1 higher
compared to CO2 equivalent emissions originated from building energy use during running time when
the building façade was non-wooden and the service life was 50 years. This paper did not study the
effect of building geometry.
Acknowledgements
This study was funded by Skanska M&E which is greatly acknowledged for this very interesting
opportunity to study in depth different energy alternatives at the design phase.

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