sustainability
Article
Environmental Performance of a Cost-Effective Energy
Renovation at the Neighbourhood Scale—The Case for Social
Housing in Braga, Portugal
Ricardo Barbosa 1,2, * , Manuela Almeida 1 , Raúl Briones-Llorente 3
1
2
3
*
Citation: Barbosa, R.; Almeida, M.;
Briones-Llorente, R.; Mateus, R.
Environmental Performance of a
and Ricardo Mateus 1
Department of Civil Engineering, ISISE, University of Minho, 4800-058 Guimarães, Portugal;
malmeida@civil.uminho.pt (M.A.); ricardomateus@civil.uminho.pt (R.M.)
Low Carbon & Resource Efficiency Unit, R&Di, Instituto de Soldadura e Qualidade, 4415-491 Grijó, Portugal
Department of Electromechanical Engineering, University of Burgos, 09006 Burgos, Spain; rbriones@ubu.es
Correspondence: rmbarbosa@isq.pt
Abstract: It is increasingly recognised that the energy renovation of the existing building stock will
be determinant for achieving 2030 and 2050 decarbonisation targets in Europe. As operational energy
is being dramatically reduced through regulatory efforts and funding from the European Union, the
relevance of the environmental performance of these interventions becomes higher, namely regarding
embodied energy and carbon emissions associated with the materials that compose the renovation
solutions. Although some studies address these impacts in buildings, the range of studies focusing on
the neighbourhood scale is limited. This article presents a methodological framework combining a life
cycle cost assessment (LCC) and a life cycle assessment (LCA). The purpose is to assess the relevance
of embodied energy and carbon emissions on the cost-effectiveness of building renovation solutions
towards nZEB at the neighbourhood scale by comparing an operational energy approach and a whole
life cycle approach in a case study of a social housing neighbourhood in Braga, Portugal. The results
suggest an increase in indicators values demonstrating a negative impact on the achievable reduction
of both energy and emissions when the whole life cycle approach is considered, which can constitute
a critical point for policy formulation in the decarbonisation of the built environment.
Cost-Effective Energy Renovation at
the Neighbourhood Scale—The Case
for Social Housing in Braga, Portugal.
Keywords: cost-effectiveness; neighbourhood scale; LCA; embodied energy; energy renovation;
social housing; whole life cycle
Sustainability 2022, 14, 1947.
https://doi.org/10.3390/su14041947
Academic Editor: Helena Corvacho
Received: 29 November 2021
Accepted: 4 February 2022
Published: 9 February 2022
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4.0/).
1. Introduction
The building sector is at the centre of the discussion for the decarbonisation objectives
set for 2030 and 2050, and existing scientific knowledge points in the direction that increasing the energy performance of the already existing building stock is a cost-effective path to
get there [1]. Importantly, in this regard, the Energy Performance of Buildings Directive
(EPBD) from 2010 introduced determinant new concepts, namely the nearly zero-energy
buildings (nZEB) [2], and is considered one of the most significant turning points in terms
of legislation. Nearly zero-energy buildings are characterised by presenting high levels of
energy efficiency. Moreover, according to the general concept, as defined in the EPBD, the
energy required to operate such buildings should be provided to a significant extent by
renewable sources produced on-site or nearby [2]. The timeline defined in the EPBD indicates that all new buildings (and major renovations) should be nZEB from December 2020.
Despite its importance for achieving the objectives mentioned above, most current policies
still focus too much on new buildings. According to some studies, the vast majority of
the existing building stock, which is more than twenty years old, is not being properly
addressed [3]. Most countries have important improvements in energy efficiency, driven by
increasingly demanding regulatory requirements and available funding from the European
Union. However, taking into consideration that cost-effective energy renovations can lead
Sustainability 2022, 14, 1947. https://doi.org/10.3390/su14041947
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to significant energy savings and that the existing buildings are only being replaced by
new constructions at a rate of 1–2% per year [4], it is considered that there is still immense
potential for decarbonisation of the existing stock to be realised. In consequence, several
strategies are being proposed and tested to accelerate the building renovation rate. In this
context, implementing interventions at the district or neighbourhood scale is considered
one of the avenues that would allow speeding up the process of reducing greenhouse
gas emissions of the building sector. This upper scale would allow taking advantage of
potential economies of scale and interactions and synergies available at this scale, including
integrating and optimising renewable energy sources [5].
On the other hand, as operational energy is being dramatically reduced, the relevance
of the environmental performance of these interventions becomes significantly higher [6],
namely regarding the embodied energy and carbon emissions of the measures and equipment that renovations rely on. The environmental performance of an energy renovation,
when evaluated according to a life cycle assessment (LCA), is directly related to the materials and energy spent in the process. Therefore, the impact of materials and equipment
that are going to be added in the renovation procedure must be balanced with its effect
concerning energy savings during operation. Research already identified that, as the level
of ambition of an energy renovation rises, its investments costs and environmental impacts
also increases, but the operation costs and impacts associated with using the buildings are
less significant [7]. In this sense, it can be considered that the relevance of the embodied
parcel regarding energy and carbon emissions associated with an energy renovation is
directly related to the objective outlined for the intervention. Within the renovation process,
reducing primary energy by minimising demand or using renewable energy sources can
lead to an increase of the embodied energy associated with the added materials, both on
the envelope and the technical systems. This was already identified in research, namely
regarding interventions with a nearly zero target, where using renewable energy systems is
considered to be crucial [8].
The use of LCA in the building sector is not new. This type of assessment has been used
since the 1990s [9], including studies addressing renovation interventions (e.g., [10,11]).
However, LCA studies focusing on the analysis of cost-optimal renovation solutions are
limited and geographically dispersed. Nevertheless, Almeida et al. [8] compared costeffective calculations in several national contexts across Europe with interesting results
in terms of the prioritisation of measures towards the nearly zero energy level of the
renovated buildings and the demonstration of a decreasing effect of the achievable energy
reduction when the embodied energy and emissions are considered in the calculations. In
addition, the knowledge that supports LCA and cost-effective energy renovation at the
neighbourhood or district scale is still dispersed and lacks diversity, particularly considering
different pre-existing situations and contexts. Examples of existing studies at this scale
include research addressing environmental performance in district heating contexts, e.g.,
the study from Feofilvos et al. [12], where low-temperature district heating coupled with
renewable sources is analysed. A very recent study from Milic et al. performed an economic
and environmental performance analysis of a district heating system in Sweden and
investigated the interaction between the implementation of energy efficiency measures and
the operation of district heating. Results suggest that there are significant environmental
benefits from implementing energy efficiency measures, but the revenue of the district
heating decreases [13]. Similar results were also found by another study [14], which showed
that this question can constitute a significant barrier for energy renovation implementation
at this scale in northern Europe. Other studies approached the problem from the urban
scale using multi-objective optimisation techniques and simplified archetypes and found
out that for decarbonisation of the building stock, the use of efficient technical systems
is crucial [15]. Existing studies also include exploratory approaches to building stocks
whose results suggest offsetting a considerable amount (about 65%) of greenhouse gas
emissions, taking into account the materials used in the renovation [16] and also that
in some contexts, the trade-off between resource efficiency and environmental impacts
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could be necessary [17]. Following the identification of this gap, the IEA-EBC Programme
launched in 2017 a project entitled “Annex 75: Cost-Effective Building Renovation at
District Level Combining Energy Efficiency and Renewables” (https://annex75.iea-ebc.
org/, accessed on 22 November 2021). One of its main objectives is the development of a life
cycle cost (LCC) assessment methodology to analyse the cost-effectiveness of interventions
that combine measures to increase energy efficiency and measures implementing on-site
renewable energy sources in different national contexts. This project involves 30 institutions
of 13 different countries and builds on the findings of the previous IEA EBC Annex 56
project (http://www.iea-annex56.org/ accessed on 22 November 2021) [18], upscaling
the study to groups of buildings and also districts. The methodology, which is already
published [5], intends to analyse and compare primary energy and the (global) costs
of several renovation scenarios, taking into account a life cycle approach, following EU
regulations [19]. In addition to the LCC, the work being developed also investigates the
possibility of LCC/LCA integration, looking into the balance of the energy needed for the
operation of the building and the embodied parcel regarding energy and emissions implied
in the materials used in a renovation intervention. In that context, this paper reports a study
of the integration of the cost-effectiveness calculations and LCA at the neighbourhood
scale, using a case study from a social housing context located in Braga, Portugal, and
comparing two different approaches: the operational energy approach and the whole life
cycle approach.
Section 2 presents the methodology pursued in this study, and in Section 3, the case
study is described. The results of the study are discussed in Section 4. In the final section,
the conclusions are presented.
2. Methodology
The study follows a methodological framework comprising two steps: (1) a costoptimal methodology using LCC and (2) a life cycle assessment (LCA), whose results
would be integrated. The two steps are described in detail in the following subsections.
2.1. Life Cycle Cost Assessment
The methodology used in this study for the life cycle cost assessment is in line with the
cost-optimal calculation procedure designed explicitly for neighbourhoods and districts in
the scope of the Annex 75 project, already detailed in another publication [5]. The methodology is based on comparing several renovation scenarios. The cost-effectiveness threshold
is constituted by what is normally designated as a reference case, where it is considered
that there is no improvement in energy performance. The reference case is composed
of “anyway renovation” measures that focus on maintaining the building and revolving
around aesthetical, functional and structural issues. Using this approach, a renovation
scenario will be considered cost-effective if it presents better energy performance or lower
costs during the life cycle of the building than the reference case. In this study, renovation
scenarios are packages of measures that can integrate building envelope improvements
(e.g., increased insulation) and more efficient technical systems, which can be centralised
or decentralised. The renovation scenarios can also include renewable energy sources
(RES). For comparison purposes, three main indicators are computed: energy use, carbon
emissions and global costs.
2.1.1. Energy Demand Calculation
Energy use was computed through numerical simulation. According to the methodology defined in the Annex 75 project, the method used in the analysis should be consistent
with regulations in the national context being analysed. As such, calculations regarding
energy use were performed using dynamic numerical simulations in an hourly time step by
Energy Plus [20] software and an OpenStudio graphical interface for modelling purposes.
Energy Plus is widely used for energy calculations in buildings, and it is considered to
present the level of detail and customisable configurations for the analysis being made in
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this study. In particular, it allows to model several different buildings and assumptions and
simulate the group of buildings as one entity. It also provides several options for graphical
modelling, which was also considered a key point for the choice of the software since it
facilitates the geometrical data input in a complex model. Hourly energy consumption
data are not available in Portugal. As such, the calculations rely on assumptions explained
in the case study section (Section 3).
Computations for renewable energy systems used SCE.ER [21] and PVGIS [22]. SCE.ER
is mainly used for national regulation compliance of renewable energy systems and possess
an extensive database of equipment’s used in the Portuguese context. In this study, it was
used for simple calculations of solar thermal systems sizing for each house. It is a simple
Excel-based tool that allows obtaining verifiable and robust results. The PVGIS was used
for photovoltaic calculations. It is a tool developed by the European Commission Joint
Research Council that allows for calculations for sizing of PV systems with impressive
accuracy due to the extensive number of solar radiation data with high spatial and temporal
resolution. Both tools are widely used in the Portuguese context for renewable energy
sizing calculations and are therefore considered suitable for the context of this study.
2.1.2. Global Costs Calculation
Regarding costs, the approach of this study uses the concept of “global costs”, which is
meant to include all costs which occur in the life cycle of the materials used in construction,
as well the systems included in the renovation intervention. Therefore, the calculation
of the costs includes investment costs, maintenance costs, energy costs and replacement
costs. Importantly, it also includes the costs associated with materials disposal when its life
cycle is considered to be over. Costs assessment was based on a market-based information
tool [23]. To assure comprehensiveness, it included costs of preparation for the intervention,
such as the use of scaffoldings and the cost of labour (in terms of man-hours).
The calculations generally follow the EU Delegated Regulation methodology [15] and
consider 30 years as the life cycle of the building. The methodology uses the global cost
method. According to this method, the present value of the costs during the life cycle of the
building is discounted to the first year in the calculations (Equation (1)) [18]. In the case that
the renovation measure lasts more than the period considered for the analysis, a residual
value is considered and applied a linear depreciation. The application of the method
implies the projection of energy costs, which were retrieved from different documentation
sources (e.g., [24]). For this study, following indications from a widely used report [25] and
previous research [26]), a discount rate of 3% was considered.
"
#
j !
t
1
Global cost Cg (t) = Cl + ∑ ∑ Ca,j (k) ×
(1)
− Vf ,t (k)
r
1 + 100
k j =1
t: Calculation period
Cg (t): Global cost (referred to starting year t0 ) over the calculation period
Cl : Initial investment costs for a measure or set of measures k
Ca, j (k) : Annual cost during year j for a measure or set of measures k
Vf,t (k) : Residual value of a measure or set of measures k at the end of the calculation period
(discounted to the starting year t0 )
r: Discount rate
2.2. Life Cycle Assessment
To consider the integration of the embodied portion in the whole life cycle approach,
this study investigated the integration of a life cycle assessment (LCA) approach in the costeffectiveness calculations (using LCC) for an energy renovation at a neighbourhood scale.
The LCA analysis in this study is based on the methods defined in the IEA EBC Annex
56 LCA report [7] and was used and tested in other studies in different scales of analysis
(i.e., [8,27]). The LCA methodology is an established approach for quantifying the embodied
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parcel regarding primary energy and carbon emissions. In the LCA methodology used
in this study, two types of system boundaries were defined: a temporal boundary (which
defines important phases during the life cycle of the building), which was defined taking
into account the EN 15978 standard [28]. It also establishes a physical boundary in order to
define both materials and energy flows. Regarding the temporal boundary (Figure 1), the
different life cycle phases are the following: (1) the production phase—which encompasses
the processes from cradle to gate regarding the production of materials and technical
systems, including extraction of raw materials to final products; (2) the construction phase—
the boundary in this phase includes the processes needed for the construction and or the
installation of materials and technical systems, as well as equipment such as scaffolding;
(3) the operation phase—this phase is comprised by the period of time in which the building
is used and operated by the occupant. It starts at the end of renovation intervention and goes
until the end of the life stage. It includes processes such as maintenance and replacement
of components. Importantly, it also includes the operational energy; (4) the end of life
phase—it considers processes for demolition, transport and appropriate disposal of waste,
which depends on the material or component. Regarding the physical boundary, this
analysis is focused on measures applied in the buildings located in the neighbourhood
with the purpose of improving energy efficiency. Therefore, the assessment performed
in terms of LCA is restricted to measures that will affect the energy performance, such
as improvements in the thermal envelope, in more efficient (including renewable-based)
building-integrated technical systems (BITS).
Figure 1. Life cycle main stages considered in the LCA analysis (adapted from EN 15978).
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This study uses two indicators commonly used in LCA for the evaluation of environmental impacts and resource use: (1) carbon emissions, which is represented by the
global warming potential (GWP), which allows for the quantification of the amount of
CO2 involved over the life cycle of a product—in this case, the materials and systems
in each renovation package) and (2) non-renewable primary energy (NRPE) demand [7].
The assessment used data from the EcoInvent database [29] retrieved through SimaPro.
Computation involved calculation of the materials involved in each renovation scenario
and multiplication by impacts per energy carrier. Finally, the assessment results (computed
as unit of surface area) are divided by the calculation period. Equation (2) exemplifies the
calculation for primary energy [7], and the same rationale is used for carbon emissions.
PEbuilding = PEmaterials + PEBITS + PEop energy use
(2)
where
PEbuilding is the primary energy of the building renovation;
PEmaterials is the primary energy connected with materials used in the neighbourhood
energy renovation;
PEBITS is the primary energy linked with the BITS;
PEop energy use is the calculated primary energy for the energy spent in the operation of
the building.
In order to differentiate the primary energy demand (and carbon emissions) used in
the operational approach, the terms “embodied primary energy” and “embodied carbon
emissions” are used in this study.
2.3. LCC/LCA Integration and Results Presentation
The methodology used in this study proposes that results from the calculations performed for LCC and LCA can be integrated and the two approaches considered in this
study—Operational Energy approach and Whole Life Cycle approach—can be compared.
For the operational approach, non-renewable primary energy (NRPE) and carbon emissions (represented by GWP) were calculated from the energy demand calculations detailed
in Section 2.1.1 for every building in the neighbourhood, taking into account adequate
distinctive assumptions such as specific constructive characteristics, occupancy and solar
orientation in order to compute the total energy demand per square metre of the group
of buildings. Only the energy demand that must be provided by non-renewable energy
sources was considered. To obtain the primary energy and corresponding greenhouse emissions, conversion factors consistent with the national context being studied were applied. In
the operational energy approach, cost-optimal calculations concerned the strict application
of the LCC methodology as detailed in Section 2.1. It takes into account calculated energy
required during the operation of the building for the reference case and as a result of the
implementation of the renovation measures being studied and their calculated global cost
(using Equation (1)) during the 30-year life cycle. On the other hand, in the whole life
cycle approach, in addition to the energy spent in the operation of the buildings (and the
corresponding generated emissions), the results from the LCA (detailed in Section 2.2) were
integrated. This means that the embodied parcel is considered in the calculation of both
the NRPE and GWP for the reference case and each of the renovation measures considered
in the analysis, according to the rationale explained in Section 2.2, and in particular using
Equation (2).
The results from these calculations regarding different renovation measures and
scenarios can be compared by plotting the two indicators using scatter diagrams, such as
the one presented in Figure 2. In the graph, the x-axis indicates the non-renewable primary
energy use, and the y-axis presents the global costs. As explained in Section 2.1, results
from calculating the two approaches are compared with the corresponding reference case,
which also determines the cost-effectiveness threshold. Graphs in Section 4 are generated
using this rationale.
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Figure 2. Generic representation of cost-effectiveness of different renovation scenarios. Source:
adapted from [26].
3. Case Study
3.1. The Neighbourhood
This work focuses on the assessment of the relevance of the embodied portion of
energy and carbon emissions in cost-optimal renovations at the neighbourhood scale. For
this purpose, the Picoto neighbourhood in Braga (Portugal) was used as a case study
to investigate the methodological framework proposed in this article. According to the
Koppen and Geiger climate system, Braga is considered as Csb (Mediterranean warm/cool
summer climates) [30]. The highest temperature in Braga is found in June (average of
20.3 ◦ C) and the lowest in January (average temperature of 8.4 ◦ C). The average annual
temperature is 14.2 ◦ C [31].
The Picoto neighbourhood was originally built in the 1990s for social housing purposes. It is currently managed by Bragahabit, which is the municipal company in charge
of managing the public building stock of the city. The neighbourhood also represents the
type of construction of the most prolific time in the promotion of adequate housing in
low-income households in Portugal in the last century, which corresponds to the implementation of the PER (Special Resettlement Programme) in 1993. However, as in many
built social infrastructures, the Picoto neighbourhood presents construction characteristics
that prioritise affordability over performance. Consequently, most of the social housing
stock—representing about 2% of the total national stock of buildings—presents low quality
in terms of construction, with insufficient energy performance and inadequate thermal
indoor conditions. In the case of the Picoto neighbourhood, there is also a noticeable
lack of maintenance interventions throughout the years. The presence of informal selfconstructions attached to the houses also contributed to the overall degradation of the
neighbourhood. An aerial view of Picoto neighbourhood is shown in Figure 3.
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Figure 3. Aerial view of Picoto neighbourhood.
The Picoto neighbourhood consists of fifty single-family houses of two stories. They are
grouped into five rows of six dwellings each and two other rows of ten dwellings each. The
orientations are approximately North–South and East–West. Buildings totalise 1767.10 m2
of heated area. As stated, all buildings are similar from the constructive perspective, and
the same materials are used. Each building is composed of two types of exterior walls. The
designated “facade type 1”—F1—is constituted by a non-insulated wall with two plastered
layers of hollow bricks (9 cm + 9 cm) and a U-value of 1.1 W/m2 K. On the other hand, the
“facade type 2”—F2—which composes the lower part of the facade (closer to the ground) is
constructed from concrete blocks (U-value of 1.9 W/m2 K) and the roof is covered by panels
of undulating asbestos cement (U-value of 3.8 W/m2 K). The aluminium framed windows
present only single glazing and a U-value of 5.70 W/m2 K. Materials were analysed in situ,
whereas thermal properties were retrieved from a database used for informing national
regulation [32]. Each house has a gas boiler powered by natural gas, with a performance of
80%, for domestic hot water supply. Space heating is guaranteed with individual electric
heaters. These are common conditions in Portuguese households, which have no tradition
of centralised approaches to heating the entire building, neighbourhood or district.
Considering these characteristics, the energy needs of the reference case were simulated using Energy Plus (Table 1). Typical user behaviour and occupancy profiles (including
an average of 4 W/m2 regarding internal gains) were considered [26]. Domestic hot water
(DHW) needs were estimated according to national thermal regulations procedures, which
considers a fixed value per person (40 L/person with a temperature increase of 35 ◦ C).
Temperature set points for thermal comfort were considered 18 ◦ C in the heating season
and 25 ◦ C in the cooling season, and conversion factors for primary energy and greenhouse
emissions also followed national thermal regulations requirements [33].
Table 1. Calculated energy demand for the neighbourhood.
Heating
Total neighbourhood load
(kWh/m2 year)
164.31
(kWh/year)
290,335
Cooling
DHW
(kWh/m2 year)
7.33
(kWh/m2 year)
W26.16
3.2. The Renovation Scenarios
Fifteen measures were evaluated to improve the thermal performance of the envelope
based on passive strategies and in accordance with the objectives and technologies proposed
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in the aforementioned IEA EBC Annex 75 project. In the first phase, a preliminary analysis of
individual measures for improving the building envelope was performed. A comprehensive
set of measures (considering different types of materials and thicknesses) were chosen to
take into account common use in the Portuguese construction market and the consistency
with the type of buildings found in the case study. Thermal properties for this analysis
were collected from ITE50 [32]. The best results from the individual measures—according
to various criteria: cost-effectiveness, best energy performance and cost—were then used
for aggregating packages presented in Table 2.
Table 2. Proposed envelope renovation packages.
Renovation Packages for Improving the Buildings’ Envelope
Facade
P1
P2
Renovation packages
P3
P4
P5
Roof
ETICS MW 80 mm
(F1* and F2**)
ETICS EPS 80 mm
(F1* and F2**)
ETICS EPS 80 mm
(F1* and F2**)
ETICS EPS 80 (F1*)
ETICS EPS 120 (F2**)
ETICS MW 160 mm (F1*)
ETICS MW 200 mm (F2**)
Windows
Sandwich panel PUR 30 mm
Sandwich Panel MW 30 mm
Sandwich panel PUR 30 mm
Sandwich Panel MW 100 mm
Sandwich Panel MW 100 mm
PVC frame with double low emissivity
glazing (U = 1.40 W/(m2 K)) with solar
protection (g = 0.20)
Aluminium frame with double glazing
(U = 3.30 W/(m2 K) and g = 0.76)
Aluminium frame with double glazing
(U = 3.30 W/(m2 K) and g = 0.76)
Aluminium frame with double glazing
(U = 3.30 W/(m2 K) and g = 0.76)
PVC frame with double low emissivity
glazing (U = 1.40 W/(m2 K)) with solar
protection (g = 0.20)
ETICS—external thermal insulation composite system; MW—mineral wool; EPS—expanded polystyrene; PUR—
polyurethane foam; PVC—polyvinyl chloride; *F1—facade type 1; **F2—facade type 2.
The measures considered interventions in the following elements: (i) facades; (ii)
sloped roofs; (iii) thermal bridges; (iv) windows. Table 2 shows the renovation packages
that were prepared for dynamic simulation.
In addition, five new systems were designed to meet the need for hot water and space
heating, as well as for space cooling. The first energy supply system (ESS1) is decentralised
and considers individual equipment (per dwelling), which is representative of the solutions
typically adopted for housing. The other four solutions represent options for centralised
systems designed to meet all the neighbourhood needs, except for ESS3, the biomass boilerbased solution, which cannot meet cooling needs. This solution can be considered because
the risk of having overheating in summer is low due to the specific characteristics of the
building together with Braga’s climate. Solutions 2, 4 and 5 are based on the use of heat
pumps. In addition, the implementation of renewable energy, such as solar thermal and
solar photovoltaic, was studied. Table 3 shows the proposed energy supply systems.
Table 3. Proposed energy supply systems.
Energy Supply System (ESS)
1: Conventional Decentralised
2: Centralised heat pump
System Solutions
3: Centralised biomass boiler
4: Centralised heat pump +ST
5: Centralised heat pump +PV
Heating
Cooling
Electric heater
H=1
Heat pump
COP/SCOP = 4.06/3.77
Biomass boiler
H = 1.07
Heat pump
COP/SCOP = 4.06/3.77
Heat pump
COP/SCOP = 4.06/3.77
Multi-split
EER = 3
Heat pump
EER/SEER = 3.97/8.41
DHW
RES
Natural gas heater h = 0.71
-
Heat pump
COP = 4.10
-
(zero)
Biomass boiler h = 1.07
-
Heat pump
EER/SEER = 3.97/8.41
Heat pump
EER/SEER = 3.97/8.41
Heat pump
COP = 4.10
Heat pump
COP = 4.10
ST (DHW)
PV (zero)
RES—renewable energy sources; ST—solar thermal; PV—photovoltaic system.
Finally, the twenty-five combinations resulting from combining each package of thermal envelope renovation measures with each proposed new energy supply system were
studied and compared with the reference case with the help of a spreadsheet developed for
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this purpose. Results were plotted in scatter diagrams for comparison between the two
indicators analysed.
4. Results
Figures 4 and 5 present the results for the cost-effectiveness calculations concerning
the NRPE and GWP, respectively. The figures present the results for the two different
approaches considered in this study. The operational energy approach (OE) results are
represented by the outlined markers, while results from the whole life cycle approach
(WLC) where embodied values are considered are represented by opaque markers. The
different colours stand for the five energy supply systems, and the geometry of markers
corresponds to each of the five renovation packages considered.
Figure 4. Cost-effectiveness non-renewable primary energy.
Except for the ESS1 (decentralised conventional systems), the results for the operational
energy approach (without taking into account embodied values) indicate that the remaining
four energy supply systems are cost-effective. In particular, the cost-optimal energy supply
system is ESS2 (centralised heat pump), which present the lowest global costs. The global
cost of the package of measures associated with this energy supply system ranges from
655.14 EUR/m2 to 861.47 EUR/m2 , depending on the specific measures being implemented.
For ESS2, the lowest value (655.14 EUR/m2 ) for the global cost is associated with P2 (ETICS
EPS 80 mm F1 and F2 + Sandwich Panel MW 30 mm+ AL Frame with double glazing).
It should be highlighted that ESS5 (centralised heat pump + PV) and ESS3 (centralised
biomass boiler) are the energy supply systems presenting the best performance by costeffectively allowing a zero-emission neighbourhood independently of the chosen envelope
renovation package. The renovation package P5 (ETICS MW160 + MW200+ Sandwich
MW100 + PVC Window Solar Protection) is the one that consistently presents higher
reductions both in terms of NRPE (an average of 82.21 kWh/m2 ·y) and emissions (an
average of 37.16 Kg CO2eq ) in all of the five energy supply systems. However, these
significant reductions are also directly related to the highest cost of all renovation packages
considered in this analysis.
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Figure 5. Cost-effectiveness global warming potential.
Results suggest that the cost-optimality of the renovation packages is related to the
energy supply system that is considered in the renovation scenario. For the energy supply
systems ESS1 (decentralised conventional systems), ESS3 (centralised biomass boiler) and
ESS5 (centralised heat pump and PV), the cost-optimal renovation package is P3 (ETICS EPS
80 mm + Sandwich Panel PUR 30 mm + AL Frame with double glazing), which presents
global costs of 1112.51 EUR/m2 , 951.08 EUR/m2 and 832.39 EUR/m2 , respectively. For ESS2
(centralised heat pump) and ESS4 (centralised heat pump with a solar thermal system), the
cost-optimal renovation package is P2 (ETICS EPS 80 mm + Sandwich Panel MW 30 mm
+ AL Frame with double glazing), which presents global costs of 665.14 EUR/m2 and
777.05 EUR/m2 , respectively.
Regarding the whole life cycle approach, results from this study suggest that considering the embodied parcel both in energy and emissions does not affect the relative
positioning between the analysed renovation packages and systems, although there is an expected overall increase in the value of the indicators. This increase is noticeable in the cases
of the ESS3 (centralised biomass boiler) and ESS5 (centralised heat pump + PV), which led
to zero energy and zero emissions. When the embodied values are considered, in terms of
energy, the main differences could be found in ESS5 (centralised heat pump + PV), where
the embodied values increased, on average, 80.64 kWh/m2 ·y throughout all the renovation
packages. ESS1 (decentralized conventional systems) also computed a relevant difference
(average of 57.4 kWh/m2 ·y). A particularly significant difference was found regarding
the results on this energy supply system when associated with the renovation package P3
(ETICS EPS 80 mm F1 and F2, Sandwich Panel PUR 30 mm, Aluminium frame with double
glazing), which presents a difference of 83.3 kWh/m2 ·y. In the same direction, P4 (ETICS
EPS80 EPS120, Sandwich Panel MW 100 mm, Aluminium frame with double glazing) also
computed a relevant difference of 61.15 kWh/m2 ·y, when compared with the operational
energy approach. Not surprisingly, concerning embodied emissions, ESS1 (conventional decentralised systems) and ESS5 (centralised heat pump + PV) energy supply systems present
the highest difference between the operational energy and the whole life cycle approaches.
When embodied emissions are considered, ESS5 (centralised heat pump + PV) presents an
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average increase of 38.15 Kg CO2 and ESS1 (decentralised conventional systems) 41.18 Kg
CO2 throughout all the renovation packages.
Concerning the carbon emissions associated with the renovation packages, the most
significant difference between the two approaches was found in P3, which is composed
of ETICS EPS 80 mm in both facades, Sandwich Panel PUR 30 mm in the roof and a new
aluminium frame with double glazing windows. This renovation package is the one presenting higher difference when embodied emissions are considered in ESS1 (decentralised
conventional systems), ESS2 (centralised heat pump), ESS3 (centralised biomass boiler) and
ESS4 (centralised heat pump + ST). Results also found that P2—the package considering
ETICS EPS 80 mm in both facades, a Sandwich Panel MW 30 mm in the sloping roof and
new aluminium frame with double glazing windows—is the renovation package where
the difference between considering embodied values and not considering these values is
most notable (39.29 Kg CO2 ) in ESS5 (centralised heat pump + PV).
Importantly, results highlight a negative effect on the achievable energy reduction
of considering a whole life cycle approach. Results from this study suggest that, when
embodied values are considered, they significantly impact the reductions promoted by
the energy renovation interventions. Figure 6 shows the comparison between the two
approaches in terms of average reductions achieved by the energy renovation interventions by the energy supply system. For operational energy approach, it uses the results
from the energy demand calculations. Results regarding the whole life cycle approach in
Figure 6 considers both the energy demand from the buildings and the embodied energy
calculated by the LCA (as a result of Equation (2)). Although the decrease in the achievable
reductions is relevant in all the studied energy supply systems, the effect is evident in ESS5
(centralised heat pump + PV). Here, the results indicate a reduction in the operational
energy approach of 100% in terms of NRPE and carbon emissions. However, when the
whole life cycle approach is analysed, it shows 84% and 69% reductions for NRPE and
emissions, respectively. It should also be highlighted that in terms of individual package of
measures, P3 (ETICS EPS 80 mm F1 and F2, Sandwich Panel PUR 30 mm, Aluminium frame
with double glazing) is the one presenting the highest impact in terms of the difference
between the two approaches. For instance, in terms of NRPE, it presents a difference in
values averaging 10%. For emissions, the average difference in this package is 14%.
Figure 6. Comparison between achievable energy and emissions reductions. NRPE—non-renewable
primary energy; GWP—global warming potential; OE—operational energy; WLC—whole life cycle.
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5. Discussion
Addressing the whole life cycle of the building from an environmental assessment perspective is becoming increasingly important regarding the decarbonisation of the building
stock. Buildings, both new and existing ones, are becoming progressively more energyefficient. At the same time, the European Union is continuously pushing for more demanding regulations that would allow the necessary cuts in emissions by 2030 and 2050.
As the operational energy (and corresponding carbon emissions) is being minimised, the
embodied energy and embodied emissions remain mostly untreated, which is considered
to be the next level on tackling “building performance levels” [6]. In this context, there is
also an opportunity arising from the next revisions planned of the most important policy
instruments concerning the field of energy efficiency in buildings, namely the EPBD and
the Energy Efficiency Directive.
Considering life cycle emissions and energy from all phases of building materials is
a complex task. It presents some significant challenges, such as the lack of available data
and different boundary conditions. However, there is already evidence that embodied
values can be determinant for achieving energy and emissions objectives. While some
studies address the subject at the building scale level [8,27,34], research results point out
that in interventions at a larger scale, such as the ones needed to achieve such ambitious
results, the consideration of embodied values can offset reductions considerably [13].
However, results from this study suggest that there are some advantages in intervening
at the neighbourhood scale using a centralised approach. These advantages are notable
concerning, for example, the cost-effectiveness of a heat pump and the emissions in relation
to decentralised systems (commonly used in Portugal). However, the results suggest that
some caution is advised for interventions associated with renewable energy sources, such
as solar thermal and PV panels. These interventions are beneficial when an operational
energy approach is considered but can negatively impact the achieved reductions in energy
and emissions when the whole life cycle of the intervention is considered. These results are
in line with previous studies, such as [35,36], which also drew attention to the importance
of the different energy mixes in the different contexts under analysis.
6. Conclusions
There is growing evidence that as the operational energy is being reduced in existing
buildings—partially due to successful energy renovations—the relevance of the environmental performance of these interventions is becoming more significant. In this context,
embodied energy and emissions are entering the realm of policy discussions, and their
central place is becoming evident.
This study intends to contribute to the ongoing discussions by investigating the
integration of life cycle assessment in cost-effectiveness calculations at the neighbourhood
scale by comparing the operational energy approach and the whole life cycle approach and
using a social housing neighbourhood located in Braga, Portugal, as a case study. For this
study, the non-renewable primary energy and the global warming potential were used as
main indicators.
Results suggest that the consideration of the embodied values (in the whole life cycle
approach) does not affect the relative positioning of the renovation measures in costeffectiveness analysis when compared with the operational energy approach (which does
not consider the embodied values). However, there is an expected increase in the values of
the indicators analysed. This is particularly visible in the results of renovation measures
calculated under ESS3 (centralised biomass boiler) and ESS5 (centralised heat pump + PV)
systems. When using the ESS5 system (centralised heat pump + PV), the difference in
primary energy values, whether considering or not the embodied energy of the materials
used in the renovation intervention, is, on average, 80.64 kWh/m2 ·y. On the other hand, the
results also show that the difference between considering or not the emissions embodied in
the materials used in the renovation packages simulated in the ESS5 is, on average, 38.15 Kg
CO2 . Still, concerning carbon emissions associated with ESS1 (conventional decentralized
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systems) and the different renovation packages simulated under this system, the difference
between the two approaches is, on average, 41.18 Kg CO2 .
Notably, the consideration of embodied values has a negative impact on the potential
achievable reduction both in terms of energy and emissions. The decrease in the reduction
achieved is noticeable in almost every renovation package and energy supply system, with
particular relevance in the case of ESS5 (centralised heat pump + PV). For this energy supply
system, results suggest that there is a significant negative effect in the achievable energy
and emissions reduction when the whole life cycle approach is considered. The calculations
concerning this energy supply system show that energy and emissions reductions are, on
average, 16% and 31% lower when the embodied values are considered.
Although results are related to the Portuguese context, the study is useful for demonstrating the applicability of the approach and offering insights into the implications at the
neighbourhood level. With very few adaptations, the integration between LCC and LCA
as used in this study can easily be applied to different national contexts. The most critical
point for the application of the methodology would be data availability and accessible
inventories, namely regarding environmental impacts. This study, which aimed to test the
methodology, used a very limited number of renovation packages. In terms of future studies, including a broader range of renovation measures can also provide useful information
for performing cost-effectiveness calculations and informing policy decision making and
formulation, such as the integration of embodied values in building energy regulations. In
this regard, results from studies such as this one can be helpful to inform policy regarding
the impact of considering a whole life cycle approach in decarbonisation plans of the built
environment, which can constitute a critical point for policy formulation in the energy
efficiency field.
Author Contributions: Conceptualisation, R.B. and M.A.; methodology, R.B. and M.A.; formal
analysis, R.B., R.M. and R.B.-L.; investigation, R.B. and R.B.-L.; writing—original draft preparation,
R.B. and R.B.-L.; writing—review and editing, R.B. and M.A.; visualisation, R.B.; supervision, M.A.
All authors have read and agreed to the published version of the manuscript.
Funding: This work was partly financed by FCT / MCTES through national funds (PIDDAC) under
the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under
reference UIDB/04029/2020. Currently, Raúl Briones-Llorente is a Research Teaching Staff at the
University of Burgos, thanks to a postdoctoral contract co-financed by the Consejería de Educación de la
Junta de Castilla y León and the Operational Programme of the European Social Fund.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Acknowledgments: The work presented in this paper has been developed by the authors as a con
tribution to the IEA EBC Annex 75 project. The authors would like to acknowledge all the project
participants and all national funding organisations. The authors want to thank Jesús Marcos García
Alonso of the Department of Electromechanical Engineering of the University of Burgos for his
collaboration in the calculations of centralised systems.
Conflicts of Interest: The authors declare no conflict of interest.
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