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ESTABLISHING THE LIFE CYCLE PRIMARY ENERGY BALANCE FOR
POWERHOUSE KJØRBO
Henning Fjeldheim1,*, Torhildur Kristjansdottir2,3 and Kari Sørnes3
1
Skanska Norge, Norway
The Norwegian University of Science and Technology, Norway
3
Sintef, Norway
*
Corresponding email: [email protected]
2
SUMMARY
Powerhouse Kjørbo is a refurbished commercial building in Sandvika, Norway which was completed in
2014. The goal of the project was to make an energy positive building by compensating the energy
demand for the production of materials and components, the construction installation process, energy
for operation and end-of-life treatment with onsite production of renewable energy.
LCA-methodology was used to establish the primary energy balance and was used actively throughout
the interdisciplinary and iterative design process to ensure decision making based on a lifecycle
perspective.
The results show a net positive primary energy balance over the lifecycle for Powerhouse Kjørbo. This
shows a huge potential for developing the existing building stock to become, not only much more
energy efficient, but also energy positive.
Key words:
Zero energy building, nZEB, ZEB, LCA, energy positive, embodied energy, greenhouse gas emissions
INTRODUCTION
The background for this work was the establishment of the Powerhouse alliance and their goal to
create buildings in though Nordic climates that have a positive lifecycle primary energy balance. The
Powerhouse alliance consists of the real estate company Entra, the construction company Skanska,
Snøhetta architects, the environmental non-governmental organization ZERO, the aluminium company
Hydro, the aluminium profile company Sapa and the consulting firm Asplan Viak.
Powerhouse buildings have to comply with an ambitious set of criteria regarding the design and
production of energy. In general the term Powerhouse is similar to a life cycle zero energy building as
introduced in Hernandez and Kenny (2010), Voss and Musall (2011), Berggren et al. (2013) and
Cellura et al. (2014). Even though the life cycle zero energy balance has been introduced, there are to
the authors’ knowledge no previous studies of life cycle zero primary energy office buildings in the
Nordic climate. Also, there is no scientific consensus on how to calculate a life cycle primary energy
balance for a zero energy building.
Powerhouse Kjørbo is a pilot building within the Research Centre on Zero Emission Buildings (ZEB).
The balance indicator used for Zero Emission Buildings is measured in carbon dioxide equivalents,
thus parallel calculations were performed also for this metric.
The building analysed and descried in this paper is the refurbishment of two office building blocks
connected by a common stairway. The building is located in Sandvika, Norway and was originally
finished in 1980. This is the first Powerhouse to be built and was completed in 2014. This paper
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presents the efforts made and calculation methods applied for establishing the lifecycle primary energy
balance for the building.
The objective of this paper is to present the experiences that were made from this pilot building with
focus on documenting the efforts for reducing the environmental loads as well as the calculations
method applied. Furthermore the objective is to establish the initial calculation scenarios for which
future performance studies can be compared to.
The Powerhouse Definition
The main definition of a Powerhouse is a building that shall produce at least the same amount of
energy from on-site renewables as the energy used for production and transport of materials, the
construction installation process, maintenance and replacement, demolition and operation (excluding
plug-loads), demolition and end-of-life treatment. In addition, the exported energy shall in average not
be of less quality than the imported energy. This implies that produced and exported electricity can
offset corresponding amount of imported energy for both electricity and thermal purposes, while
produced and exported thermal energy cannot offset imported electricity. The building shall also as a
minimum fulfil all the requirements of the Passive House standard.
Design process
To meet the requirements of the definition, the work on the energy balance was started at the very
beginning of the design process. The key to success was the multidisciplinary design process
involving all participants and the very clear common goal. Experts in LCA defined the criteria for the
calculation method for the materials, transportation and construction. The design team completed an
iterative process of establishing alternative solutions, creating inventories and assessing these
according to the defined method. The results were used as input to further design of the building.
Energy designers worked with the design team to bring the energy demand in operation to a minimum.
Case description
Powerhouse Kjørbo is two office buildings of 3 or 4 floors respectively connected by a shared stairway.
The building was originally completed in 1980. The heated useful floor area is about 5.180 m2. Energy
efficiency measures and materials with low embodied energy have been crucial for obtaining the
energy goal. A very efficient ventilation concept has been developed. This has to a great extent
reduced the over all energy demand for operation.
Sandvika is located at approximately 60 degrees north latitude. The annual mean outdoor temperature
at the location is about 5,9°C and the annual mean horizontal irradiation is about 110 W/m² (955
kWh/m²a). The design occupancy schedule is 12 hours a day, 5 days a week, 52 weeks a year.
The energy concept is based on the principle of first reducing the lifecycle primary energy demand,
including both operational and embodied energy. Secondly the remaining energy demand is balanced
by locally produced renewable energy.
Due to the fact that the energy need for ventilation normally comprises a large share of the energy
budget in office buildings, there has particularly been a high focus on reducing the energy need for
ventilation for Powerhouse Kjørbo. This includes both using low emitting materials to reduce the
ventilation demand, demand control, displacement ventilation, low pressure design to minimize fan
energy, and highly efficient heat recovery. During normal operation, the average ventilation air volume
is about 3 m3/m2h wintertime, and about 6 m3/m2h summertime (on warm days).
Furthermore the very energy efficient building envelope summarized in Table 1 combined with daylight
utilization, a lighting control system suiting the different user needs, energy efficient fixtures and a
ground source heat pump reduces the electricity demand for operation.
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Table 1 Thermal properties of the building envelope after refurbishment
Properties
After renovation
U-value external walls
0,13 W/m²K
U-value roof
0,08 W/m²K
U-value floor on ground
0,14 W/m²K
U-value windows and doors
0,80 W/m²
“Normalized” thermal bridge value, (per m²
heated floor area)
0,02 W/m²K
Air tightness, air changes per hour (at 50 Pa)
0,24
To reduce the embodied energy of the materials and components all existing reinforcing steel and
concrete constructions is utilized in the refurbished building. In addition, the existing glass facade
panels are reused as interior office fronts in the refurbished buildings. The new façade cladding is
made of charred wood, with long lifetime and marginal need for maintenance. The photovoltaic
modules generating locally produced renewable energy have been selected based on an evaluation of
the overall balance between embodied energy and efficiency.
METHOD
This chapter describes the method that was applied to establish the balance for primary energy and
greenhouse gas (GHG) emissions for Powerhouse Kjørbo.
Life cycle approach
According to the definition of Powerhouse, all life cycles of the building should be accounted for when
establishing the primary energy balance. Thus, the method for the calculations is based on the method
presented in the standard for life cycle analysis of buildings, EN 15978:2011 (CEN, 2011). Our
analysis included the environmental impact categories global warming potential based on the IPCC
100 year perspective (Solomon et al., 2007) and primary energy use, based on the cumulative energy
demand method (Frischknecht et al., 2007). The standard terminology used in the ecoinvent report for
the cumulative energy is as follows: "The cumulative energy demand (CED) states the entire demand
valued as primary energy, which arises in connection with the production, use and disposal of an
economic good (product or service) or which may be attributed respectively to it in a causal relation."
(Althaus et al., 2010) Biogenic CO2 for the timber used in the construction is not accounted for in the
analysis. Absorption of CO2 by carbonatisation of the concrete is also not considered. Furthermore the
production of energy from the incineration of wood in C3 is not included.
The functional unit of the analysis is one square meter (1 m2) of the refurbished heated floor area of
2
5180 m over an estimated service lifetime of 60 years. From the standard EN15978:2011, the
following life cycle stages are included: the product phase Raw material supply (A1), Transport (A2),
Manufacturing (A3) the construction phase (Transport to the construction site (A4), construction and
installations (A5) process, the use phase, replacement of components (B4), operational energy use
and production of energy (B6) and the entire end of life phase (C1-C4).
Inventory analysis
The following sections describe the inventory gathered for the different life cycle phases and scenarios
used for the calculation. The structure of the inventory analysis for the construction materials is
according to the Norwegian standard, Table of building elements: NS 3451:2009 (Standard Norway,
2009).
The product phase
The material inventory analysis included the following construction parts based on the inventory
suggested by Wittstock et al. (2011): Foundation and load bearing structure, basement walls, exterior
walls, structural vertical elements, surface coating, floor structure and slabs, coverings and tightness
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elements, roof framework, partitioning walls, internal doors, suspended sealing, windows and joinery
work, exterior doors, floors, painting and wallpaper coverings, heating and ventilations systems,
electricity wiring (high and low voltage), communication and network, elevator and photovoltaic
systems with inverters. The amounts of materials have been gathered by using material takeoffs from
the Revit BIM (Building information model) for the construction materials and MagiCad for the
ventilation system. During the construction phase quantities have been updated if changes were made
to the design. The primary energy and GHG emissions are based on data gathered and analysed
directly from producers, type III environmental product declarations (EPDs), ecoinvent database v2.2
(Swiss Center for Life Cycle Inventories, 2010) and scientific articles. The analysis by (Fthenakis, 2012
) provided inputs into the embodied energy in the PV modules.
The construction installation process
For the design phase an estimate was made for the energy demand in the construction installation
process based on registered data from previous construction projects and adjusted based on known
differences. During the construction phase the estimates were updated with actual registered transport
distances as well as electricity and fuel consumption.
Replacement scenarios
The replacement scenarios were based on service lifetimes available from the product category rules
(PCR) from the relevant building material type when available, like presented in EPD-Norway (2007)
for insulations materials. When PCR where not available, guidelines for service lifetime of building
components, SINTEF Building and Infrastructure's guidelines Byggforskserien 700.320 was used.The
calculations equations presented in EN15978 (CEN, 2011) were applied for the number of
replacements necessary. In general the replaced components are based on the same inventory as
the initial inventory, assuming no change in technical performance or production. The service lifetime
for the PV modules was based on Fthenakis (2011).
Scenario for technical developments for PV modules
It was assumed that the embodied energy and emissions from the production of the PV modules will
be reduced with 50% in 30 years. This is of course uncertain, however analysis presented by
Frischknecht et al. (2015), Bergesen et al. (2014) and Mann et al. (2014) support that there is a
continuous improvement in the in the production of PV modules. The improvements are mainly
connected to increased material efficiency, improved production processes and the transition to
increased use of renewable energy in the production process. It is also assumed that the efficiency of
the PV modules installed after 30 years will have an increased efficiency by about 40 % from 20 % to
28%. This is based on the average historic development of Single Junction GaAs - Single crystal cells
and Thin film crystal cells recorded by Wilson (2014) (NREL 2014). This is also in accordance to the
optimistic scenario presented in (Frischknecht, 2015).
Operational energy demand
The simulations of operational energy demand are done using the dynamic energy simulation tool
SIMIEN (Programbyggerne 2012) and are in accordance with the Norwegian Standard NS
3031:2007+A1:2011 (Standard Norway 2007). However, energy demand for lighting and equipment is
in accordance with expected real use, but for a normalized operation period.
Development of grid based electricity mix
The primary energy factor for grid based European electricity mix has been assumed to decrease
linearly from 3,43 in 2010 to 2,38 (kWh primary energy/ kWh energy consumed) in 2050 according to
Kindem Thyholt et. al. (2015). This results in an average primary energy factor of 2,55 for the service
life of Powerhouse Kjørbo. This scenario is in accordance with the guidelines from the ZEB centre and
is based on the technological development scenario to meet the 2-degree target. Correspondingly the
CO2-factor for the electricity mix has been assumed to decrease linearly from 0,53 kg CO2 eq./kWh in
2010 to 0 g CO2 eq./kWh in 2054 with an average of 0,17 kg CO2 eq./kWh for the service life of
Powerhouse Kjørbo.
th
According to guidelines for the Norwegian EPD foundation, EPD-Norge, prior to the 12 of June 2014
EPDs for products in Norway should be based on the nordic grid electricity mix including imports for
the last three documented years (The Norwegian EPD Foundation 2012). EPDs providing static
information have been used in the calculations. Thus a nordic grid electricity mix has been applied for
the calculation of embodied energy to maintain coherent system boundaries for the calculations.
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On-site energy production
The onsite production of renewable energy from photovoltaic modules was calculated using the
program PVsyst and the NASA-SSE (Power 2013) database as the source for irradiation data.
Deconstruction
In lack of good data, the deconstruction phase is assumed to be equal to the construction installation
process. Less heating will be needed as the duration will be shorter, but deconstruction of concrete
structure will require more fuel for machinery. These differences are assumed to balance each other.
End-of-life treatment
The scenarios for the end-of-life treatment of the various materials are based on the average
distribution of recycling, incineration and landfill of concrete, aluminium, glass, gypsum, insulation,
plastic, steel, wood, textile, bitumen and generic waste between 2006 and 2011 (Statistisk Sentralbyrå
2013).
The transport of waste from site to treatment facility and disposal were based on Erlandsen (2009) and
supplemented with generic distances from Wittstock et. al. (2011) where necessary due to lack of
data.
Limitations and simplifications
As the Powerhouse Kjørbo is a refurbishment project, there were possibilities to reuse a selection of
the building materials on site. As an example: The loadbearing structure from the previous building
has been adjusted and reused in the new building. According to section 7.3 in EN15978:2011,
environmental loads from components shall be allocated based on the remaining service life. Analyses
concluded that based on the calculation rules of the standard, the impacts of demolishing the old
structure and rebuilding it with todays materials would result in a 50% reduced environmental impact.
This was decided to be counter intuitive and it was chosen to disregard the environmental loads of the
existing structure which is not in line with the standard. This decision was made to encourage reuse of
materials and because the reused components were older than 30 years.
Transport of materials and components to the site was registered and accounted for. The tonnage for
each transport of materials and components is not known and the total tonnage of the building has
therefore been evenly distributed over the total number of transports distances.
Due to the static information of the EPDs, there is an inconsistency between the primary energy
factors and CO2 factors used for the operational energy demand and the production of materials and
components.
RESULTS
The overall balance for primary energy and GHG emissions are presented in Table 2. The negative
sum for primary energy indicates an overall surplus of produced local renewable energy. The positive
sum for GHG emissions shows that the ZEB balance related to GHG emissions is not fulfilled. Figure 1
and Figure 2 show the distribution of the embodied energy and GHG emissions in materials and
components according to NS 3451:2009 and the major categories of materials respectively.
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Table 2 The overall balance for primary energy and GHG emissions
Life cycle stages
A1-A3
Raw materials supply, Transport and Manufacturing
A4
Primary energy
GHG emissions
(kWh primary
(kg CO2 eq/m2
year)
2
energy/m year)
20,11
3,77
Transport to site
0,11
0,02
A5
Construction and installation on site
2,67
0,23
B4
Replacements
10,34
1,82
B6
Operational Energy Use - Energy demand
58,10
3,89
B6
Operational Energy Use - Energy production
-121,80
-7,03
C1
Deconstruction
2,67
0,23
C2
Transport
0,27
0,06
C3
Waste treatment processes for reuse, recovery or/
and recycling
0,11
0,02
C4
Disposal
0,47
0,43
-26,96
3,44
Sum
Figure 1 Embodied primary energy in materials and components distributed on the major categories of
materials
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Figure 2 Embodied GHG emissions in materials and components distributed on the major categories
of materials
DISCUSSION
The finalized energy balance shows a positive margin for the production of local renewable energy
from photovoltaic modules relative to the lifecycle energy demand. It must be pointed out that the
primary energy balance presented is based on the energy demand calculated in the design phase and
not the resulting energy budget with updated numbers after monitoring and verification of the actual
energy demand in operation. However raw data measurements from the first year of operation show
that the actual energy consumption is slightly lower than the calculated results from the design
process. 2014 was an especially sunny summer in Oslo giving great solar energy output but should at
the same time increase the demand for cooling.
The results also interestingly show that materials, transport, construction, deconstruction and end-oflife treatment make up 39 % of the total lifecycle primary energy demand and 63% of the lifecycle
GHG emissions of which the production of materials and components make up about 85% in both
cases. This shows the increasing importance of addressing these aspects when designing buildings
with low energy demand. Efficient resource use, transport logistics, construction and end-of-life
treatment should be considered in an integrated way. It is important to keep in mind the exclusion of
the existing load carrying system of concrete and the inclusion of the photovoltaic modules in the
results when comparing with other calculations as both have significant impact on the overall results.
An inclusion of the embodied energy for a load carrying system would or example increase the primary
energy demand over the lifecycle by approximately 5%.
There are always significant uncertainty issues related to lifecycle counting of primary energy and
GHG emissions. Scenarios are set based on probable outcomes, emission factors related to material,
energy and transport inputs are based on databases giving average production values and scenarios
for waste treatment is made on the basis of todays practice.
The method of lifecycle accounting is always developing and the practice for how to account for
energy and carbons related to materials such as wood is something that has been a large discussion
since the work related to Powerhouse Kjørbo started. In the calculations presented the energy related
to energy feedstock and carbon uptake is not taken into account.
Low energy efficient and low carbon housing is often associated to new buildings where fewer
constraints are given. Having in mind that Powerhouse Kjørbo is a refurbishment project shows the
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great potential in the existing building stock. There is a huge need for upgrading the standard of
buildings already built, both in Norway and internationally. If the renovation processes happens in the
right way, the gain is double – we are reusing the resources already extracted and are at the same
time making an energy efficient building for the future.
CONCLUSIONS
The primary energy balance presented for the project Powerhouse Kjørbo is net positive. The results
show that the energy demand for the production of materials and components, the construction
installation process and transport impacts the overall energy demand significantly. This proves the
importance of expanding the focus from operational energy demand to considering the whole lifecycle
when designing sustainable buildings.
ACKNOWLEDGEMENT
The Powerhouse Kjørbo project received funding from Enova, a Norwegian public enterprise with the
aim to facilitate the transition to a more sustainable consumption and production of energy. The
authors gratefully acknowledge the support from the Research Council of Norway and several partners
through the Research Centre on Zero Emission Buildings (ZEB) [4] as well as the close cooperation
with the Powerhouse alliance partners and the design team to make this project a reality.
REFERENCES
ALTHAUS, H.-J., BAUER, C., GABOR DOKA, ROBERTO DONES, ROLF FRISCHKNECHT,
STEFANIE HELLWEG, SÉBASTIEN HUMBERT, NIELS JUNGBLUTH, THOMAS KÖLLNER,
YVES LOERINCIK, MANUELE MARGNI & NEMECEK, T. 2010. Implementation of Life Cycle
Impact Assessment Methods. In: HISCHIER, R. & WEIDEMA, B. (eds.) Data v2.2 (2010).
St.Gallen: ecoinvent centre.
BERGESEN, J. D., HEATH, G. A., GIBON, T. & SUH, S. 2014. Thin-Film Photovoltaic Power
Generation Offers Decreasing Greenhouse Gas Emissions and Increasing Environmental Cobenefits in the Long Term. Environmental science & technology, 48, 9834-9843.
BERGGREN, B., HALL, M. & WALL, M. 2013. LCE analysis of buildings – Taking the step towards Net
Zero Energy Buildings. Energy and Buildings, 62, 381-391.
CELLURA, M., GUARINO, F., LONGO, S. & MISTRETTA, M. 2014. Energy life-cycle approach in Net
zero energy buildings balance: Operation and embodied energy of an Italian case study.
Energy and Buildings, 72, 371-381.
CEN 2011. EN 15978: Sustainability of construction works. Assessment of environmental
performance of buildings. Calculation method.
DOKKA, T. H., SARTORI, I., TYHOLT, M., LIEN, K. & BYSKOV LINDBERG, K. 2013. A Norwegian
zero emission building definition. Passivhus Norden. Gothenburg, Sweden.
EPD-NORWAY 2007. Product-category rules (PCR) For preparing an environmental declaration
(EPD) for Product Group Insulation materials In: NORWEGIAN EPD FOUNDATION (ed.).
ERLANDSEN, L. M., 2009. System Analysis of Commercial Waste Recovery Options.
FRISCHKNECHT, R., ITTEN, R., WYSS, F., BLANC, I., HEATH, G., RAUGEI, M., SINHA, P. &
WADE, A. 2015. Life cycle assessment of future photovoltaic electricity production from
residential-scale systems operated in Europe, Subtask 2.0 "LCA", IEA-PVPS Task 12.
FRISCHKNECHT, R., JUNGBLUTH, N., ALTHAUS, H.-J., BAUER, C., DOKA, G., DONES, R.,
HISCHIER, R., HELLWEG, S., HUMBERT, S., KÖLLNER, T., LOERINCIK, Y., MARGNI, M. &
NEMECEK, T. 2007. Implementation of Life Cycle Impact Assessment Methods Data v2.0
(2007) ecoinvent report No. 3. Dübendorf: Swiss Centre for Life Cycle Inventories.
FTHENAKIS, V. 2011. Methodology Guidelines on Life Cycle Assessment of Photovoltaic Electricity:
IEA PVPS Task 12.: International Energy Agency.
GRAABAK, I. & FEILBERG, N. 2011. CO2 emission in different scenarios of electricity generation in
Europe. SINTEF Energy Research.
HERNANDEZ, P. & KENNY, P. 2010. From net energy to zero energy buildings: Defining life cycle
zero energy buildings (LC-ZEB). Energy and Buildings, 42, 815-821.
THE NORWEGIAN EPD FOUNDATION. 2012. Vekting av CO2 ved bruk av elektrisitet i
produksjonsfasen (A3) uttrykt i EPD. http://www.epdnorge.no/article.php?articleID=1592&categoryID=657
MANN, S. A., DE WILD-SCHOLTEN, M. J., FTHENAKIS, V. M., VAN SARK, W. G. J. H. M. & SINKE,
W. C. 2014. The energy payback time of advanced crystalline silicon PV modules in 2020: a
prospective study. Progress in Photovoltaics: Research and Applications, 22, 1180-1194.
www.7phn.org
Page 8/9
7. Passivhus Norden | Sustainable Cities and Buildings | Copenhagen, 20-21 August 2015
NATIONAL RENEWABLE ENERGY LABORATORY. 2014. Best Research-Cell Efficiencies.
http://www.nrel.gov/ncpv/images/efficiency_chart.jpg
PROGRAMBYGGERNE. 2012. SIMIEN - Simulering av energibruk og inneklima i Bygninger. v.5.010.
www.programbyggerne.no
POWER. 2013. Surface meteorology and Solar Energy. https://eosweb.larc.nasa.gov/sse/
SOLOMON, S., QIN, D., MANNING, M., MARQUIS, M., AVERYT, K., M., M., TIGNOR, B., LEROY
MILLER, HENRY, J. & Z. CHEN 2007. Climate Change, 2007. The Physical Science Basis,
Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).
Cambridge University Press; Cambridge (United Kingdom): IPCC.
STATISTISK SENTRALBYRÅ. 2013. Statistikkbanken. http://statbank.ssb.no/statistikkbanken/
STANDARD NORWAY 2007. NS 3031:2007+A1:2011, Beregning av bygningers energiytelse. Metode
og data.
STANDARD NORWAY 2009. NS 3451, Bygningsdelstabellen (Table of building elements).
SWISS CENTER FOR LIFE CYCLE INVENTORIES 2010. Ecoinvent version 2.2.
THYHOLT, M. K., FJELDHEIM, H., BUIJS, A., DOKKA, T. 2015. Primærenergifaktorer for Powerhouse
- Med revisjon av primærenergifaktoren for elektrisitet
VOSS, K. & MUSALL, E. 2011. Net Zero Energy Buildings, Germany, Detail
WITTSTOCK, LENZ, SAUNDERS, ANDERSON, CARTER, GYETVAI, KREISSIG, BRAUNE,
LASVAUX, BOSDEVIGIE, BAZZANA, SCHIOPU, JAYR, NIBEL, CHEVALIER, HANS,
FULANA-I-PALMER, GAZULLA, M., BARROW-WILLIAMS & SJOSTROM 2011. EeB
Guidance Document. Part B: Buildings. Operational guidance for life cycle assessment studies
of the Energy-Efficient Buildings Initiative. European union, 7th Framework Programme.
www.7phn.org
Page 9/9