Relevance of embodied energy on building retrofit
assessment
Manuela Almeida
University of Minho, School of Engineering, Department of Civil Engineering, Guimarães, Portugal
malmeida@civil.uminho.pt
Ricardo Mateus
University of Minho, School of Engineering, Department of Civil Engineering, Guimarães, Portugal
ricardomateus@civil.uminho.pt
Marco Ferreira
University of Minho, School of Engineering, Department of Civil Engineering, Guimarães, Portugal
marcoferreira@civil.uminho.pt
Ana Rodrigues
University of Minho, School of Engineering, Department of Civil Engineering, Guimarães, Portugal
anarocha32846@yahoo.co.uk
ABSTRACT: Many regulations and initiatives to promote the reduction of the energy
consumption and carbon emissions have been implemented in the building sector.
However, they are mostly targeted for new buildings. In order to have an effective impact
and reach the goals that are being established, it is necessary to act in new but especially
in the existing buildings, which correspond to the majority of the European building stock.
Building renovation improves the buildings’ energy performance, reducing the carbon
emissions related to the operation of the building but the renovation involves adding new
materials and technical systems. The production process of these new materials uses
energy (embodied energy) and releases carbon emissions. In this sense, after a certain
level of energy efficiency, the materials added to the building may have more embodied
energy than the energy savings they will lead to. To evaluate the relevance of the
embodied energy in building renovation, IEA EBC project Annex 56, developed a
methodological framework to evaluate the cost-effectiveness of building renovation
solutions which include a life-cycle impact assessment. In this context and using a
particular case study, different renovation solutions are compared with and without
considering the embodied energy. The results have shown that the embodied energy do
not have a major impact on the evaluation of the cost-effectiveness of the renovation
solutions, but as the renovation approach gets closer to zero non-renewable energy level,
its relevance increases.
Keywords LCA, Building renovation, energy efficiency and carbon emissions
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1. GENERAL INSTRUCTIONS
In Europe, buildings are an important target for the reduction of energy consumption and
related carbon emissions. They are responsible for 40% of the final energy consumption,
which leads to 32% of carbon emissions sent to the atmosphere each year. These values
are not stabilized, presenting an increasing trend (BPIE, 2011).
In an attempt to slow down the increase of these values, the European Commission has
released and reviewed many regulations. A turning point was marked by the EPBD recast
in 2010, where new concepts were introduced, namely the cost optimal and nZEB
(European Parliament, 2010). Besides, to promote the energy efficiency in different
sectors including the building sector, strategies like Europe 2020 and Europe 2030 were
also defined (European Commission, 2016). Despite the effort, these legal means are
mainly targeted for new buildings and the majority of the European building stock has
more than 20 years. Given the low rates of replacement of existing buildings by new
efficient ones (1% to 2% per year), the European Union will not achieve its targets unless
there is a focus on the renovation of the existing buildings (European Commission, 2011).
Existing buildings have their own technical, functional and economic constraints, which
may lead to expensive and complex renovation procedures, hardly accepted by the owners
or promoters. This fact may contribute to missing opportunities of improving the
buildings energy performance (IEA EBC, 2016). Building renovation may improve the
energy performance, but it also increases the investment costs and presents
environmental impacts due to new materials and building integrated technical systems
(BITS) that will be added to the building (Almeida & Ferreira, 2015). In this sense, to try
to address these trade-offs and adapt the new concepts to existing buildings, the IEA EBC
launched a project, Annex 56 - Cost-effective energy and carbon emissions optimization in
building renovation (Almeida & Ferreira, 2015).
The aim of the project is to develop a methodology for the cost-effective renovation of
existing buildings combining energy efficiency measures and the use of energy from onsite renewable sources. The methodology intends to be used by private entities to help in
the decision of renovating a building and also by governmental agencies that can use it for
regulatory purposes. The methodology developed within Annex 56, balances the energy
consumption and the global costs of each renovation scenario in order to compare them. It
uses a life cycle approach instead of a payback period method, as established by the
methodology for the cost optimal analysis presented by the Delegated Regulation
nº244/2012 (European Commission, 2012). In addition to the life cycle costs, the Annex
56 methodology also considers a life-cycle impact assessment (LCIA) method, balancing
not only the energy necessary for the operation phase but also the embodied energy and
the carbon emissions related to the products manufacturing (IEA EBC, 2016). In existing
buildings, the environmental performance is related to the materials added to the building,
while in new buildings it is related to the building structure that involves bigger amounts
of materials and consequently the impact is much more noticeable (IEA EBC, 2016).
Concerning the existing buildings, a question on whether the embodied energy of the
renovation materials and related carbon emissions have a significant weight in the final
primary energy use may arise. When the target is a building with a very high energy
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performance, a significant amount of materials is added in order to strongly decrease its
energy needs and beyond a certain level, the additional savings in energy use might be
lower than the embodied energy of the materials being used. When the target is a nearly
zero energy building, where besides the very high energy performance there is a
significant use of energy from renewable sources, the question is even more relevant once
the non-renewable energy that is saved might be very low.
Within Annex 56 methodology and concerning the LCA, the participants in the project
reached an agreement on restricting the number of indicators used in the analysis. Since
the methodology consists in comparing different renovation scenarios, analysing many
indicators could become very time-consuming and useless (IEA EBC, 2016). In this sense,
only the GWP (global warming potential), the CEDNRPE (cumulative non-renewable primary
energy demand) and CEDTOTAL (cumulative total primary energy demand) were assessed.
The choice is related to the fact that these indicators have good correlation with the
remaining environmental indicators considered in the LCA method, as concluded in other
studies (Mateus et al, 2013).
Taking advantage of one of the several case studies of the project (Mørck et al, 2015),
different renovation scenarios were analysed, with and without the embodied energy, in
order to verify its relevance in a renovation process.
2. METHODOLOGY
In this paper, the Annex 56 methodology was applied to a Portuguese case-study. This
methodology has five main steps: calculation of the energy use of the building in a
reference case (building renovation to restore its functionality without improving the
energy performance), the establishment of different renovation scenarios, calculation of
the energy use for these alternative scenarios, calculation of the global costs associated
with each renovation scenario and life-cycle impact assessment.
It starts with the calculation of the primary energy use in the reference scenario. The
primary energy was calculated using the Portuguese thermal regulation (Ministério da
Economia e do Emprego, 2013) which follows the ISO 13790 (ISO, 2008). The calculations
are performed using a quasi-steady method, considering the indoor comfort temperatures
of 18˚C during the winter and 25˚C during the summer. In these first stages of the analysis,
the primary energy is related to the energy necessary for heating, cooling, domestic hot
water (DHW) and lighting.
Regarding the contribution from on-site renewables, the electricity generation from the
photovoltaic panels is calculated using PVGIS (Photovoltaic Geographical Information
System (http://re.jrc.ec.europa.eu/pvgis/) and the solar thermal contributions is
calculated using Solterm (http://www.lneg.pt/iedt/projectos/370/).
After this step, it is necessary to establish different renovation scenarios. These scenarios
include renovation measures for the buildings envelope and for the BITS. For each of the
established renovation scenarios it is calculated the primary energy use, as done for the
reference situation.
Then, the global costs are calculated. The global costs calculations are performed using the
net present value method or annuity values (IEA EBC, 2014). The global costs include
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investment costs, maintenance, replacement costs and energy costs. The investment costs,
maintenance and replacement costs are calculated using CYPE® software that generates
prices for construction works in Portugal (CYPE Ingenieros, 2014). The energy costs for
the first year are retrieved from ERSE, the Portuguese entity that rules the energy prices
(ERSE, 2012, 2013). The future costs of the energy are estimated using the European
Commission’s predictions (European Commission, 2012). The price of the pellets (solution
foreseen in several renovation scenarios) is based on a research of the Portuguese market
with an estimated increase of 3% per year. A discount rate of 6% is assumed and a lifetime
period of 30 years is considered. The described methodology allows comparing the
renovation scenarios balancing the energy during the operation phase and the related
global costs.
To calculate the environmental performance, it is additionally necessary to quantify the
amount of materials and BITS that are added to the building in each renovation scenario.
The methodology used for the environmental life cycle analysis (LCA) is based on the EN
15978:2011 (CEN, 2011) and follows the steps of the EN ISO 14044:2006 (ISO, 2006). One
of the most important stages of the LCA method is the inventory analysis. In the case of
this study, the inventory analysis entails the quantification of the flows for and from each
renovation scenario. There are several sources for the inventory data and in this study, the
background data related to the considered process units was taken from the Ecoinvent 3.1
database (Weidema et al, 2013). To facilitate the quantification of the environmental
indicators, a life cycle analysis software (SimaPro 8.0.5) was used to modulate the life
cycle of the analysed renovation scenarios and to assess the abovementioned life cycle
impact categories.
3. CASE STUDY
The case study consists of a building built in 1950 which belongs to a social
neighbourhood located in Porto, in the north of Portugal. Most buildings in the
neighbourhood presented signs of degradation and inadequacy to the current living
standards, due to small living areas. These facts justified the decision of renovating the
buildings. Figure 1 shows the building before and after the renovation.
a)
b)
Figure 1 General aspect of the buildings a) before the intervention and b) after the intervention
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The selected case study has two floors and four apartments, two in each floor. It had no
insulation on the envelope and there were no BITS for heating and cooling, apart from
portable electric heaters and fan coils. The DHW (domestic hot water) is provided by an
electric heater with a storage tank.
Table 1 Summary of the U-values before the renovation
Element
U-values before
Exterior walls
1.38/1.69
Roof
2.62
Windows
5.10
Concerning the building solutions, the exterior walls consisted of single hollow brick walls
with cement mortar on both sides, the roof was composed of a lightweight concrete slab
and a structure that supports the fibre cement sheets. The floor consisted of a solid ground
floor and the windows were wood framed with single glazing with external shutters. The
U-values of these elements before the renovation process are presented in Table 1.
From the several renovation scenarios analysed, the implemented one included the
increase of the living areas by joining in just one apartment the two apartments per floor
and the improvement of the building’s envelope. In this context, insulation was added to
some of the elements of the envelope, the windows were changed and new BITS were
installed. The implemented solution on the envelope included the application of ETICS
(external thermal insulation composite system) with 6 cm of EPS (expanded polystyrene)
on the external walls. For the roof, the solution consisted in removing the lightweight slab
and introducing a suspended ceiling, introducing between the ceiling and fibre cement
sheets, XPS (extruded polystyrene) with 5cm thickness. Besides the walls and the roof, the
windows were also replaced introducing double glazing. It was decided not to make any
intervention on the floor since the low floor to ceiling height did not allow increasing the
thickness of the floor. These solutions represent the common building renovation scenario
in Portugal.
In order to apply the Annex 56 methodology, two different solutions for the building
envelope, which include different insulation materials, were analysed. One presents
insulation materials that are usually applied in renovation works (expanded polystyrene
and mineral wool) and the other uses cork that, despite being produced in Portugal, is
applied less often due to its higher price. Table 2 shows the analysed solutions for the
building envelope. In the table, EPS stands for expanded polystyrene, XPS is extruded
polystyrene, MW is mineral wool and ICB is insulation cork boards. The analysis always
included intervention in almost all elements. In cases where the energy performance was
not improved, it was considered just maintenance work, such as painting, repairing cracks
and smaller adjustments to solve further malfunction.
Table 2 Summary of the analysed renovation measures for the buildings envelope
Envelope
Wall
Roof
Reference
Floor
Windows
maintenance
maintenance
_
maintenance
A
EPS 10 cm
MW 14cm
MW 8cm
maintenance
B
ICB 8cm
ICB 8cm
ICB 8cm
wood U=2,4
Chosen/applied
EPS 6 cm
XPS 5cm
_
wood U=3,9
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Furthermore, these two envelope solutions were combined with four different
combinations of BITS. Table 3 shows the above-mentioned combinations of the envelope
solutions and the BITS. In total, 8 different combinations were analysed.
Combination
Reference
1
2
3
4
5
6
7
8
Chosen/applied
Table 3 Summary of the analysed renovation solutions
Envelope
Heating
Cooling
DHW
REN
Multi-split
Electric heater w/
air
Reference
Electric heater
_
storage tank
conditioned
Multi-split air
Electric heater w/
A
_
Solar Thermal
conditioned
storage tank
A
Gas boiler
_
Gas Boiler
_
Air-source heat
A
_
Air-source heat pump Photovoltaic
Pump
A
Biomass boiler
_
Biomass boiler
Biomass
Multi-split air
Electric heater w/
B
_
Solar Thermal
conditioned
storage tank
B
Gas boiler
_
Gas Boiler
_
Air-source heat
B
_
Air-source heat pump Photovoltaic
Pump
B
Biomass boiler
_
Biomass boiler
Biomass
Multi-split air
Electric heater w/
Chosen
_
Solar Thermal
conditioned
storage tank
4. RESULTS OF LIFE CYCLE COSTS ANALYSIS
The life cycle costs analysis started with the calculation of the energy needs and primary
energy use of the building for each of the renovation scenarios considered and the
calculation of the related global costs.
The results of each renovation scenario are presented in figure 2.
Reference
Sol A + EH + ST
Sol A + HP + PV
Sol B + EH + ST
Sol B + HP + PV
Global
Costs (€)
1200
1100
Chosen
Sol A + GB
Sol A + BIO
Sol B + GB
Sol B + BIO
1000
900
800
700
600
Cost optimal solution
500
0
100
200
300
400
500
Non-Renewable primary energy (kWh/m².a)
Figure 2 Results of the LCC analysis (non-renewable primary energy values without the embodied
energy)
In Figure 2 there are two curves, each one related to a different solution for the building's
envelope. The lower curve is related to the solution with current insulation materials and
the higher curve considers the cork insulation boards (ICB). Observing Figure 2 it can be
concluded that the solution with lower global costs includes current insulation materials,
which results from the higher price of ICB. In this sense, the cost optimal solution is
achieved with the solution A for the envelope (which consists of 10cm of EPS for the wall,
14cm MW for the roof and 8cm of MW for the floor) and a gas boiler for heating and DHW.
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The solutions that allow reducing significantly the primary energy use are the ones using a
heat pump and photovoltaic panels, followed by the solutions that use a biomass boiler.
It is important to remind that these results do not yet include the embodied energy.
5. RESULTS OF LIFE CYCLE IMPACT ANALYSIS
After calculating the life cycle costs for the operation phase, it is necessary to calculate the
impact of each renovation scenario in terms of GWP, CEDNRPE and CEDTOTAL. Table 4
presents for each material, BITS or energy vector, the potential unitary environmental
impacts for a kilogram of material, one complete BITS system or for a kWh, in the case of
the used materials, considered BITS and consumed energy, respectively. In order to have
the full impact, those unitary values were multiplied by the total amount of material, BITS
or energy.
Table 4 Summary of the SIMAPRO impacts
GWP [kgEP
CO2/(m2y)]
CED NRPE
[kWh/(m2y)]
CED TOTAL
[kWh/(m2y)]
Exterior walls painting
7,36E-04
4,01E-03
4,31E-03
Repairing and painting windows
wood frames
7,36E-04
4,01E-03
4,31E-03
Black agglomerated cork
3,10E-04
1,86E-03
3,90E-03
XPS
2,83E-03
7,44E-03
7,54E-03
Rockwool
2,91E-04
1,42E-03
1,48E-03
EPS
1,12E-03
7,87E-03
7,95E-03
ETICS (without the insulation)
2,21E-05
1,16E-04
1,30E-04
PVC window
6,99E-04
4,46E-03
4,64E-03
Wood window
4,37E-04
2,16E-03
4,41E-03
Aluminium window
2,54E-03
1,07E-02
1,22E-02
Glass (single)
2,63E-04
9,31E-04
9,57E-04
Glass (double)
3,80E-04
1,53E-03
1,60E-03
Windows sills (aluminium)
2,25E-03
8,44E-03
1,02E-02
PVC membrane under floor cork
insulation
7,69E-04
6,98E-03
7,12E-03
Gas boiler
1,02E-01
4,74E-01
5,13E-01
Air-source heat pump
4,26E-01
5,78E-01
6,10E-01
Biomass boiler
7,87E-01
2,45E+00
2,60E+00
Solar thermal
3,59E-01
1,57E+00
1,77E+00
Photovoltaic
1,05E-01
4,79E-01
5,50E-01
Electricity (PT energy mix)
6,91E-01
2,74E+00
3,22E+00
Natural gas
2,62E-01
1,24E+00
1,24E+00
Biomass
4,50E-02
2,42E-01
1,34E+00
Description
Materials
BITS
Energy
Figure 3 shows the results for the GWP analysis. In the figure, bars 1 to 4 are related to
solution A for the building’s envelope combined with four different BITS. Bars 5 to 8
include solution B for the envelope, combined with four different BITS.
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Observing the figure it is noticeable that the renovation solutions with lower GWP are
number 3 and 7, which include the heat pump and photovoltaic panels, followed by the
solutions 4 and 8 that include a biomass boiler. The chosen/applied solution is among the
worse solutions in terms of GWP and the cost optimal solution (solution 2) also has a high
GWP value.
Concerning the CEDNRPE the CEDTOTAL the results are presented in Figure 4.
Global Warming Potential
[kgCO2-eq/m²a]
120
Total GWP
100
80
60
40
20
0
Figure 3 Results of the global warming indicator (GWP)
500
Total NRPE
total Primary Energy [kWh/m²a]
Non Renewable Energy
[kWh/m²a]
These indicators present the same trend as the GWP, where renovation solutions 3 and 7
(that include the heat pump and the PV) are the ones with lower CED NRPE and lower
CEDTOTAL, followed by solutions 4 and 8 (that include a biomass boiler). Both combinations
use renewable energy sources, reducing significantly the non-renewable energy use.
400
300
200
100
0
a)
500
Total PE
400
300
200
100
0
b)
Figure 4 Results of a) the CDENRPE (Non-Renewable energy) indicator and b) CDETOTAL
The results of the comparison between the renovation solutions considering only the
primary energy related with the operation of the building and the total primary energy
(embodied and operation) are presented in Figure 5.
Observing Figure 5 it is possible to verify that generally there are no significant changes in
the results. Solution A for the building envelope combined with a gas boiler is still the cost
optimal solution. The inclusion of the embodied energy leads to a slight dislocation of the
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points. This is more noticeable in solutions 3 and 7 that without the embodied energy
were almost over the vertical axis and with the inclusion of the embodied energy have
moved slightly away from the origin.
Besides this, without the embodied energy, solution 7 presents a value of primary energy
of 2.78 [kWh/m².y] and solution 3 a value of 6.72 [kWh/m².y]. Considering the embodied
energy, the total primary energy reaches 18.01 [kWh/m².y] in solution 7 and 16.33
[kWh/m².y] in solution 3.
1
2
3
4
5
Cost optimal solution
6
7
8
0
70 140 210 280 350 420 490
Primary Energy [kWh/m².a] (without
embodied energy)
a)
chosen
Yearly Life Cycle Costs [€/m²a]
Yearly life cycle costs [€/m².a]
reference
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
Cost optimal solution
0 70 140 210 280 350 420 490
Total Primary Energy [kWh/m²a] (including
embodied energy )
b)
Figure 5 Results of a) primary energy (not including embodied energy) and b) total primary
energy (including embodied energy)
Thus, concerning the total energy value, there is a switch of positions between these two
solutions. After the inclusion of the embodied energy, solution 3 is the one that leads to the
best energy performance while without the embodied energy it was solution 7.
The reference situation presents a high value for the CEDTOTAL mostly related to the energy
used during the operation phase. In solutions 3 and 7, and given the presence of the
renewable energy sources, the CDETOTAL is mostly due to the impact of the embodied
energy of the insulation materials and the BITS (especially the photovoltaic panels).
Unlike other solutions, and when compared to the primary energy (without the embodied
energy), the reference solution presents a slight reduction of total primary energy, due to
differences in the conversion factor used in the LCA and the grid factor used for the LCC
calculations.
6. CONCLUSIONS
Results from the comparison of the life-cycle cost analysis considering only the
operational energy and the operational and embodied energy show that the inclusion of
the last does not change the cost-effective solutions or the cost optimal renovation
packages. On the other hand, in terms of total primary energy, the best renovation package
has changed due to differences in the environmental impact of insulation materials used in
renovation packages with very low operational energy.
The results for the particular case of Portugal were similar to those achieved in the Annex
56 project for other five case-studies, each one in a different European country.
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Embodied energy and embodied carbon emissions were not found very influential in the
project’s building renovation case studies when the focus is towards cost-effective
renovation solutions. However, when the energy performance approaches nearly zero
carbon emissions or nearly-zero energy renovation levels, the relative contribution of the
embodied energy or embodied carbon emissions rises as far as the renovation becomes
significant. In some cases, the renovation packages with the highest energy performance
when considering only the energy use are not the ones with the best environmental
performance.
These results indicate that when the target is nearly zero carbon emissions or nearly-zero
energy renovation levels, the primary energy and carbon emissions optimization for both
new and existing buildings should be done using a life-cycle perspective including the
embodied impacts.
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