Energy Losses or Savings Due to Air Infiltration and Envelope Sealing Costs in the Passivhaus Standard: A Review on the Mediterranean Coast

Abstract

To obtain the Passivhaus Certificate or Passivhaus Standard (PHS), requirements regarding building envelope air tightness must be met: according to the n50 parameter, at a pressure of 50 Pa, air leakage must be below 0.6 air changes per hour (ACH). This condition is verified by following the blower door test protocol and is regulated by the ISO 9972 standard, or UNE-EN-13829. Some construction techniques make it easier to comply with these regulations, and in most cases, construction joints and material joints must be sealed in a complex way, both on façades and roofs and at ground contact points. Performing rigorous quality control of these processes during the construction phase allows achieving a value below 0.6 ACH and obtaining the PHS certification. Yet, the value can increase substantially with the passage of time: as windows and doors are used, opened, or closed; as envelope materials expand; with humidity; etc. This could result in significant energy consumption increases and losing the PHS when selling the house at a later point in time. It is therefore important to carefully supervise the quality of the construction and its execution. In this study, we focused on a house located in Sitges (Barcelona). The envelope air tightness quality was measured during four construction phases, together with the sealing of the joints and service ducts. The blower door test was performed in each phase, and the n50 value obtained decreased each time. The execution costs of each phase were also determined, as were the investment amortisation rates based on the consequent annual energy demand reductions. Air infiltration dropped by 43.81%, with the final n50 value resulting in 0.59 ACH. However, the execution costs—EUR 3827—were high compared to the energy savings made, and the investment amortisation period rose to a 15- to 30-year range. To conclude, these airtightness improvements are necessary in cold continental climates but are not applicable on the Spanish Mediterranean coast.

Full text

Citation: Echarri-Iribarren, V.;
Gómez-Val, R.; Ugalde-Blázquez, I.
Energy Losses or Savings Due to Air
Infiltration and Envelope Sealing
Costs in the Passivhaus Standard: A
Review on the Mediterranean Coast.
Buildings 2024,14, 2158. https://
doi.org/10.3390/buildings14072158
Academic Editors: Alberto Meiss
and Irene Poza Casado
Received: 18 May 2024
Revised: 15 June 2024
Accepted: 18 June 2024
Published: 13 July 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
buildings
Article
Energy Losses or Savings Due to Air Infiltration and Envelope
Sealing Costs in the Passivhaus Standard: A Review on the
Mediterranean Coast
Víctor Echarri-Iribarren 1, 2, * , Ricardo Gómez-Val 1and Iñigo Ugalde-Blázquez 1
1
Department of Architecture, International University of Catalunya, Carrer Iradier 22, 08017 Barcelona, Spain;
rjgomez@uic.es (R.G.-V.); iugalde@uic.es (I.U.-B.)
2Department of Building Construction, University of Alicante, Carretera de San Vicente s/n, San Vicente del
Raspeig, 03690 Alicante, Spain
*Correspondence: vecharri@uic.es; Tel.: +34-93-254-18-00
Abstract: To obtain the Passivhaus Certificate or Passivhaus Standard (PHS), requirements regarding
building envelope air tightness must be met: according to the n
50
parameter, at a pressure of
50 Pa, air leakage must be below 0.6 air changes per hour (ACH). This condition is verified by
following the blower door test protocol and is regulated by the ISO 9972 standard, or UNE-EN-13829.
Some construction techniques make it easier to comply with these regulations, and in most cases,
construction joints and material joints must be sealed in a complex way, both on façades and roofs
and at ground contact points. Performing rigorous quality control of these processes during the
construction phase allows achieving a value below 0.6 ACH and obtaining the PHS certification.
Yet, the value can increase substantially with the passage of time: as windows and doors are used,
opened, or closed; as envelope materials expand; with humidity; etc. This could result in significant
energy consumption increases and losing the PHS when selling the house at a later point in time.
It is therefore important to carefully supervise the quality of the construction and its execution. In
this study, we focused on a house located in Sitges (Barcelona). The envelope air tightness quality
was measured during four construction phases, together with the sealing of the joints and service
ducts. The blower door test was performed in each phase, and the n
50
value obtained decreased each
time. The execution costs of each phase were also determined, as were the investment amortisation
rates based on the consequent annual energy demand reductions. Air infiltration dropped by 43.81%,
with the final n
50
value resulting in 0.59 ACH. However, the execution costs—EUR 3827—were high
compared to the energy savings made, and the investment amortisation period rose to a 15- to 30-year
range. To conclude, these airtightness improvements are necessary in cold continental climates but
are not applicable on the Spanish Mediterranean coast.
Keywords: Passivhaus Standard; airtightness; energy efficiency; building overheating; construction
quality; investment amortization; air infiltration; blower door test; envelope sealing;
Mediterranean climate
1. Introduction
According to EUROSTAT’s latest available publication, the real estate sector, especially
the residential sector, is responsible for 27.9% of energy consumption. This is why it is nec-
essary to reduce the energy consumption of buildings. It is also a regulatory obligation [
1
].
In recent years, the European Commission has issued a number of directives to reduce
energy consumption in housing construction [
2
,
3
]. These directives have been transposed
into various member countries’ regulatory frameworks, including in southern Europe.
However, in southern European countries, a shift of mindset needs to occur towards de-
signing more energy-efficient homes [
4
]. These changes have already been introduced in
Spain at the regulatory level in the country’s Technical Building Code (CTE), which encom-
passes all applicable construction regulations and includes energy consumption reduction
Buildings 2024,14, 2158. https://doi.org/10.3390/buildings14072158 https://www.mdpi.com/journal/buildings

Buildings 2024,14, 2158 2 of 20
as an essential parameter [
5
–
7
]. Passivhaus certification (PHS) is set to gain ground as
a housing
construction option, owing mainly to the low operational energy consumption
of Passivhaus buildings [
8
]. The certification requires that newly built homes follow an
envelope airtightness standard below 0.6 ACH at 50 pascals (Pa) of pressure (n
50
). This
requirement entails additional efforts for construction companies and property developers,
as they need to implement a series of controls and repairs until the n
50
requirement is
fulfilled, making it possible to obtain PHS certification.
In recent years, several studies have been conducted on the performance of these
buildings in terms of comfort [
9
] and energy efficiency. A substantial number of detailed
analyses have been conducted on the functioning of these homes in cold climates, both
in public buildings [
10
] and in private ones [
11
]. These analyses have demonstrated
that energy consumption related to heating uses represents more than 50% in several
Western countries. Optimal results have been obtained regarding the climatic behaviour
of the houses studied. For example, the geometry of the façades helps to minimise the
overheating of housing, such as the 115
◦
inclination of the south façades in London [
12
].
The cost of incorporating the Passivhaus standard into buildings varies between 8% and
15% [
13
]. There have also been related studies in Mediterranean climate conditions showing
that comfort requirements account for 72% of the total energy use [
14
], as is the case in
other warm climates [
15
]. In this case, no unanimous results or conclusions have been
reached, generating debates in the scientific community about the suitability of the PH
Standard and the need to adapt it [
16
]. This aspect depends very much on the location.
For example, in Ireland, the simulation estimated an overheating rate of 0%. The main
problem detected in the research is the risk of overheating in buildings [
17
,
18
]. To this
end, building shapes have been examined, as well as sun protection features and the
dimensions of the openings [
19
], leading to an optimal window-to-façade ratio of 30%.
Building shapes and distribution plans are also directly related to climatic behaviour, with
an ideal ratio of 1:1.44 [
20
]. Analyses have even been conducted on the types of rooms in
which the greatest overheating occurs, with bedrooms presenting the highest risks [
21
].
For all these reasons, the human factor has proven to have a direct impact on the risk of
overheating in these homes, with confirmation from more than 20% of the inhabitants [
22
].
To improve this aspect in Passivhaus buildings, it is necessary to adopt solutions that
incorporate passive natural ventilation and sunlight systems [
23
]. These conditions are
especially suitable for warm or temperate climates, in which the architectural characteristics
of the building directly influence how these buildings will function climatically in the most
adverse summer months [24].
Another interesting dimension of analysis and improvement regarding Passivhaus
houses is the increase in air infiltration through envelopes. It is important to observe how
this latter parameter evolves by taking measurements in Passivhaus homes that have been
in use for a long period of time. In this regard, it is notable that, due to the increase in
recent years in the size of building openings, infiltration studies of existing buildings have
detected lower air infiltration rates in older and less insulated buildings than in more
modern buildings. With respect to the measurements conducted through case studies over
a long period of time, such as a full year, optimistic estimates of previous energy demand
simulations have been compared with actual consumption [
25
,
26
]. The real data obtained
after the Passivhaus building is in operation has been shown to present higher values than
those estimated through simulation.
To date, studies have focused on indoor air quality [
27
] and on how to improve indoor
air quality and performance [
28
]. The ventilation demand also influences thermal comfort,
resulting in an optimal relationship between a mix of natural and mechanical ventilation
during 82% of the annual occupancy [
29
]. The interior comfort parameter is regarded as key,
given that it is among the objectives of a range of current regulations. It has been found that
this objective is not always met and that the measures implemented to improve comfort
and indoor air quality are in fact doing the opposite. Despite comfort improvements
observed in most modern buildings, which have even obtained a Passivhaus (PHS)-type

Buildings 2024,14, 2158 3 of 20
certification, it is necessary to ask whether the required efforts of Passivhaus compliance
do have
an effective
impact on the parameters [
30
]. Studies have concluded that nZEBs are
more likely to overheat than older and conventional buildings. These different kinds of
buildings even maintain similar CO2concentrations.
In relation to air infiltration through windows, various analyses have been conducted
to improve airtightness [
31
,
32
]. However, it has been shown that studies are lacking on
how to homogenise the controls that allow for evaluating Passivhaus house behaviour and
their operation over time [
33
,
34
]. It is particularly important to evaluate the extra cost of
obtaining the PHS in hot and temperate climates, although it has been shown to perform
well regarding energy demands and CO2emissions [11].
Yet, no studies have been found on both the technical and financial costs of the leak
checks that must be performed in succession using the blower door test until fulfilling the
Passivhaus standard requirement. For its part, the financial effort required to obtain PHS
certification has been evaluated. Taking into account the various current administrative
subsidies [
35
] and construction cost increases, it has been found to amount to approximately
30%. This extra cost is amortised over an average period of around 10 years, so the extra
effort is generally considered acceptable. However, if such solutions and certifications are
to be globally implemented within the country—and not restricted to luxury housing—the
focus must be on low-cost or social housing scenarios [
36
]. Affordable social housing
construction costs can be reduced by up to 22% of the build cost, even while maintaining
the PHS. No studies have been performed on the additional costs and time required to
achieve an n
50
parameter below 0.6 ACH once optimal climate conditioning solutions have
been applied. It is worth noting that to comply with the certification procedure, the leak
detection procedure and sealing need to be performed repeatedly until fulfilling the PHS
certification requirement. The punctual air infiltrations detected have a major impact on the
building’s overall tightness and, therefore, on its climatic conditioning and energy demands.
These infiltrations usually occur through the window joinery [
37
]. In Passivhaus homes,
these leaks are reduced to a minimum, unlike in traditional construction [
38
]. In the case of
existing buildings, the PHS requirement of n
50
is not as demanding as it is below 1 ACH.
Despite this, the difficulty of achieving this parameter in these constructions makes such
renovations even more costly, and it is not certain that the outcome
will be successful [39]
.
Regarding home construction systems, few studies have applied modular prefabri-
cated systems. In theory, these systems are ideal for building Passivhaus homes, but they
must be optimised to ensure adequate climatic operation as well as easy and effective joint
sealing produced by the system [
40
]. In this study, just four connection details fulfil the
PHS requirements.
The Passivhaus certification requires the commitment of all agents involved, including
in the design phase, the project technical drafting process, all construction phases, and sub-
sequent use and maintenance. Insufficient production and management of these measures,
commitment, and system knowledge would seriously jeopardise the expected beneficial
results or lead to unforeseen negative outcomes [
41
]. The present work is
an in-depth
study of the latest requirements necessary to obtain the Passivhaus certification for a home.
It highlights the measurements and work evaluation necessary to guarantee adequate
envelope airtightness and the obtention of the certification, as well as the investment amor-
tisation periods within the framework of the Mediterranean climate. A comparison with
cold Central European climates is also provided.
This study’s objective was to quantify the energy savings achieved during the var-
ious phases of the Passivhaus home envelope sealing and analyse the subsequent cost-
effectiveness. The aim was to analyse the standard’s applicability to homes located on
the Spanish Mediterranean coast and to conduct a comparison with the Central European
continental climate. To do this, we performed a case study analysis.

Buildings 2024,14, 2158 4 of 20
2. Description of the Case Study
The property under study was a newly built detached single-family house located in
the municipality of Sitges (on street 30–32 Camídel Coll) in the province of Barcelona. The
house has a basement, a ground floor, and a first floor (Figure 1). The basement was built
with a perimeter wall and a reinforced concrete slab. The upper floors were constructed
using a system of prefabricated panels made by the Evowall company. Their system of
massive panels with a metal lattice was approved by the European Technical Assessment.
The panels are made of a metal framework of S275 hot-rolled steel, with 5 cm of EPS thermal
insulation, 8 cm of PIR thermal insulation, a mortar coating using a mixture of cement and
EPS insulation, and gypsum on the inner face. The outer face consists of a mortar coating
applied with a cement and insulation mix, finished with a lime mortar layer (Figure 2).
The windows are made of PVC with rolling shutters. According to tests conducted by the
Technological Institute of Construction (ITEC), the U of the façade panels is
0.214 W/(m2K)
,
and that of the roof panels is 0.475 W/(m
2
K). The exterior carpentry—profiles, tracks, and
shutters—was made by the Weru group.
Buildings 2024, 14, 2158 4 of 20
Spanish Mediterranean coast and to conduct a comparison with the Central European
continental climate. To do this, we performed a case study analysis.
2. Description of the Case Study
The property under study was a newly built detached single-family house located in
the municipality of Sitges (on street 30–32 Camí del Coll) in the province of Barcelona. The
house has a basement, a ground floor, and a first floor (Figure 1). The basement was built
with a perimeter wall and a reinforced concrete slab. The upper floors were constructed
using a system of prefabricated panels made by the Evowall company. Their system of
massive panels with a metal laice was approved by the European Technical Assessment.
The panels are made of a metal framework of S275 hot-rolled steel, with 5 cm of EPS ther-
mal insulation, 8 cm of PIR thermal insulation, a mortar coating using a mixture of cement
and EPS insulation, and gypsum on the inner face. The outer face consists of a mortar
coating applied with a cement and insulation mix, finished with a lime mortar layer (Fig-
ure 2). The windows are made of PVC with rolling shuers. According to tests conducted
by the Technological Institute of Construction (ITEC), the U of the façade panels is 0.214
W/(m2 K), and that of the roof panels is 0.475 W/(m2 K). The exterior carpentry—profiles,
tracks, and shuers—was made by the Weru group.
(a) (b)
Figure 1. (a) Floor plan with dimensions; (b) Exterior view of south façade.
This house was built in view of achieving the Passivhaus certification, which sets an
n50 < 0.6 ACH for newly-built single-family homes. The building section for which the PHS
certification studies were conducted was the housing area itself, located on the ground
floor and the first floor (Figure 3). The garage and the machine room in the basement were,
therefore, not built according to Passivhaus standards.
Figure 1. (a) Floor plan with dimensions; (b) Exterior view of south façade.
Buildings 2024, 14, 2158 5 of 20
Figure 2. Construction details of the typical envelopes.
Figure 2. Cont.

Buildings 2024,14, 2158 5 of 20
Buildings 2024, 14, 2158 5 of 20
Figure 2. Construction details of the typical envelopes.
Figure 2. Construction details of the typical envelopes.
This house was built in view of achieving the Passivhaus certification, which sets
an n50 < 0.6
ACH for newly-built single-family homes. The building section for which the
PHS certification studies were conducted was the housing area itself, located on the ground
floor and the first floor (Figure 3). The garage and the machine room in the basement were,
therefore, not built according to Passivhaus standards.
The layout is shown in Figure 4. To ensure appropriate sealing and to comply with the
PHS requirements, different measurements were taken by the construction company using
the blower door test. Measurements were taken by the construction company on several
occasions, specifically on 3 October 2023 and 21 November 2023. On 5 December 2023,
the Praxis company, specialising in Passivhaus certification, was required to perform the
blower door test. Measurements were also made using a digital anemometer and smoke
machine to detect air leaks during these tests.
Buildings 2024, 14, 2158 5 of 20
Figure 2. Construction details of the typical envelopes.
Figure 3. Cont.

Buildings 2024,14, 2158 6 of 20
Buildings 2024, 14, 2158 6 of 20
Figure 3. Furnished and delimited ground floor and first floor.
The layout is shown in Figure 4. To ensure appropriate sealing and to comply with
the PHS requirements, different measurements were taken by the construction company
using the blower door test. Measurements were taken by the construction company on
several occasions, specifically on 3 October 2023 and 21 November 2023. On 5 December
2023, the Praxis company, specialising in Passivhaus certification, was required to perform
the blower door test. Measurements were also made using a digital anemometer and
smoke machine to detect air leaks during these tests.
Figure 4. Cross-section of the kitchen and first-floor master bedroom.
The conducted tests led the construction company to carry out a series of additional
seals, especially in the service ducts, which presented the greatest number of detected air
leaks (Figure 5). Plastic tape and elastic amorphous seals were used for the sealing.
Figure 3. Furnished and delimited ground floor and first floor.
Buildings 2024, 14, 2158 6 of 20
Figure 3. Furnished and delimited ground floor and first floor.
The layout is shown in Figure 4. To ensure appropriate sealing and to comply with
the PHS requirements, different measurements were taken by the construction company
using the blower door test. Measurements were taken by the construction company on
several occasions, specifically on 3 October 2023 and 21 November 2023. On 5 December
2023, the Praxis company, specialising in Passivhaus certification, was required to perform
the blower door test. Measurements were also made using a digital anemometer and
smoke machine to detect air leaks during these tests.
Figure 4. Cross-section of the kitchen and first-floor master bedroom.
The conducted tests led the construction company to carry out a series of additional
seals, especially in the service ducts, which presented the greatest number of detected air
leaks (Figure 5). Plastic tape and elastic amorphous seals were used for the sealing.
Figure 4. Cross-section of the kitchen and first-floor master bedroom.
The conducted tests led the construction company to carry out a series of additional
seals, especially in the service ducts, which presented the greatest number of detected air
leaks (Figure 5). Plastic tape and elastic amorphous seals were used for the sealing.

Buildings 2024,14, 2158 7 of 20
Buildings 2024, 14, 2158 7 of 20
(a) (b)
Figure 5. (a) Detection of air infiltration after phase P1; (b) Details of sealing using adhesive tape.
3. Materials and Methods
A building’s annual energy demand depends on various factors, some of which are
highly complex, such as the orientation, local climate, materials used, and the technical
characteristics of the envelopes [42]. Assessing the actual heat flow through envelopes
over the cycle of a week, a month, or a full year is a truly complex task [43]. It requires
simulation tools that consider the envelope thermal inertia and ground contact, the ther-
mal bridges of the construction systems used, as well as the solar radiation on the exterior
surfaces or the air conditioning systems used. In addition, factors relating to the construc-
tion’s inherent deficiencies must be considered, such as contacts between different mate-
rials, joineries, intrinsic humidity variations, expansion effects during the material execu-
tion of the project, etc. Envelope airtightness varies according to climatic conditions, out-
side air pressure at any given time, and the maintenance and usage by the home’s users
of mobile elements such as carpentry, adjustable slats, or grids [44]. This makes it difficult
to estimate or quantify the real energy impact of air infiltration, which is also subject to
unforeseen events and imbalances. Constant variations in outdoor air pressure make it
even harder, although this point can be solved by obtaining annual statistical averages per
season or at specific times of the year [45]. Despite the above, designing a suitable meth-
odology and strategy to extract data from methodology-adapted parameters allows for
approaching the problem with the necessary level of quality assurance.
3.1. Envelope Airtightness
The main study objective was to quantify the energy impacts of envelope airtightness
under various scenarios and to estimate the corresponding investment amortisation. To
this end, we present below the case study of a house whose envelope airtightness value
was expected to be low owing to the quality of the construction company and the prefab-
rication system used, as well as the applied sealing, carpentry quality, and air tightness.
The execution of the envelope sealing took place over four phases at four- and six-
week intervals. We performed the blower door test four times, immediately after each
phase. This allowed for making on-site decisions regarding the technique to be used in
Figure 5. (a) Detection of air infiltration after phase P1; (b) Details of sealing using adhesive tape.
3. Materials and Methods
A building’s annual energy demand depends on various factors, some of which are
highly complex, such as the orientation, local climate, materials used, and the technical
characteristics of the envelopes [
42
]. Assessing the actual heat flow through envelopes over
the cycle of a week, a month, or a full year is a truly complex task [
43
]. It requires simulation
tools that consider the envelope thermal inertia and ground contact, the thermal bridges
of the construction systems used, as well as the solar radiation on the exterior surfaces
or the air conditioning systems used. In addition, factors relating to the construction’s
inherent deficiencies must be considered, such as contacts between different materials,
joineries, intrinsic humidity variations, expansion effects during the material execution of
the project, etc. Envelope airtightness varies according to climatic conditions, outside air
pressure at any given time, and the maintenance and usage by the home’s users of mobile
elements such as carpentry, adjustable slats, or grids [
44
]. This makes it difficult to estimate
or quantify the real energy impact of air infiltration, which is also subject to unforeseen
events and imbalances. Constant variations in outdoor air pressure make it even harder,
although this point can be solved by obtaining annual statistical averages per season or at
specific times of the year [
45
]. Despite the above, designing a suitable methodology and
strategy to extract data from methodology-adapted parameters allows for approaching the
problem with the necessary level of quality assurance.
3.1. Envelope Airtightness
The main study objective was to quantify the energy impacts of envelope airtightness
under various scenarios and to estimate the corresponding investment amortisation. To this
end, we present below the case study of a house whose envelope airtightness value was

Buildings 2024,14, 2158 8 of 20
expected to be low owing to the quality of the construction company and the prefabrication
system used, as well as the applied sealing, carpentry quality, and air tightness.
The execution of the envelope sealing took place over four phases at four- and six-week
intervals. We performed the blower door test four times, immediately after each phase.
This allowed for making on-site decisions regarding the technique to be used in phases P2,
P3, and P4, and whether or not to carry them out. This was performed according to the n
50
value obtained, the expected execution costs for each phase, and the amortisation of these
seals according to the energy savings made.
Phase P1
Sealing of construction joints using a hermetic liquid membrane. Application of
expanding polyurethane foam in joinery together with the façade envelope manufacturers.
Plastic adhesive tape and amorphous seals. Completed in September 2023.
Phase P2
Detection of critical points. Sealing of joints of materials and plane contacts using
polyurethane expanding foam. Contact between carpentry and shutter units with ISO3
polyurethane-based adhesive plastic tapes. Amorphous seals.
Phase P3
Sealing of joints between plane contacts and materials using polyurethane expand-
ing foam. Seals in installation passageways, mainly electrical ones, are based on ISO3
polyurethane-based adhesive plastic tapes and elastic amorphous ISO-TOP seals.
Phase P4
Detection of insufficiently airtight spots. Joints are sealed using techniques similar to
those in P3.
To evaluate the envelope airtightness value, the blower door test was conducted in the
various construction phases. It was executed in accordance with European
Standard EN 13829
(
Thermal performance of buildings—Determination of air permeability of buildings—Fan
pressurization method
) using the blower door GMBH MessSysteme für Luftdichtheit
equipment. Corresponding graphs were obtained for pressurisation and depressurisation
at 10–70 pascals (Pa) of air pressure and an n
50
airtightness value of 50 Pa. A specific sheet
developed for the research group “Architecture & Energy” of the University of Valladolid
was used to characterise the resulting information [
46
]. This tool was developed specifically
to characterise 140 parameters that can intervene in infiltration [
46
]. The parameters were
collected in a database, which was then used for the overall result evaluation.
To obtain the average building envelope airtightness value—a parameter that is always
difficult to quantify—we followed the protocol established in the UNE-EN-ISO 13790:2008
standard. This method allows for converting the n
50
value to a rate of changes/hour
under normal pressure conditions and as an average value over a time interval via the
following expression:
nwinter = 2·n50·ei·εi, (1)
n50—air changes/hour at 50 Pascals;
ei—wind protection coefficient = 0.05;
εi—height correction factor = 1.
In this way, using the DesignBuilder version 7 tool and the mathematical corpus
described in Section 3.2.1, it was possible to simulate the energy impact. We obtained
global annual energy demand values and partial ones exclusively due to the envelope
airtightness value.
We used the blower door test tool to detect thermal bridges through images from
Flyr’s ThermaCam P25 thermal imaging camera. The quantification was conducted using
the AnTherm programme, and we estimated a thermal bridge gain or loss of pressure of
3.5% of the total thermal loads due to the envelope thermal transmittance U-values, which
were close to those obtained in previous studies [47,48].

Buildings 2024,14, 2158 9 of 20
3.2. Assessment of the Energy Impact of Air Infiltration
Estimating the energy impact of air infiltration is an arduous task. It cannot be entirely
accurate, as it depends not only on the airtightness of the building envelope but also on
weather conditions, which are usually difficult to predict [
49
]. No common criterion exists
regarding which model is suitable to assess the energy impact of air infiltration through
the envelope [
50
]. So far, different calculation models have been developed to varying
degrees of complexity and reliability [
51
]. The simplest models are based on a uniform
distribution of leak pathways and constant average leaks over time. In this study, the
impact was evaluated using two different tools and methodologies: a simplified calculation
model (Equations (1)–(8)), and DesignBuilder simulation software.
3.2.1. Application of the Simplified Calculation Model
The first simplified calculation model used applies the degree-day concept, which
links the average temperature outside the tested home to the indoor comfort temperature
(21
◦
C for heating and 24
◦
C for cooling) [
7
]. This estimate is theoretical: real energy
consumption depends on each household’s specific indoor air temperature T
i
setpoint
conditions. This calculation procedure makes it possible to assess the Q
inf
energy impact
considering specific climatic data of the house location. The calculation considers the air
infiltration flow obtained through the blower door test n
50
, the specific capacity of the V
inf
air in the area under study, and the temperature differences between the home’s indoor air
Tiand outdoor air Te[52].
Qinf =Cp·Gt·Vinf, (2)
Here,
Q
inf
is the annual energy loss (kWh/year) due to air infiltration. Q
inf-H
is considered
for heating and Q
inf-C
for cooling. Annual energy losses are expressed per surface area unit.
Cpis the specific air heat capacity, which is 0,34 Wh/m3K.
G
t
is the number of annual degree-days (kKh/year), both for heating (G
t-C
), with
a basic
comfort temperature of 21
◦
C, and for cooling (G
t-R
), with a basic comfort tempera-
ture of 25 ◦C.
V
inf
is the air leakage rate (m
3
/h). V
inf
must be obtained from the values obtained
in the test, which are expressed with a pressure difference of 50 Pa and do not reflect the
actual filtration process to which the house is subjected.
The Persily–Kronvall estimation (Equation (3)) is a simple and widespread model in
the scientific community, and it was adopted in this first model [
53
]. It assumes a linear
relationship between permeability at 50 Pa and the average annual infiltration:
qinf =q50/20, (3)
where
qinf is the air permeability (m3/(h m2)].
q50 is the air permeability at 50 Pa (m3/(h m2)).
This linear relationship between tightness and infiltration was subsequently evolved [
53
],
incorporating some parameters and coefficients based on the house location characteristics
according to Equations (4) and (5):
qinf =q50/N, (4)
N=C·cf 1·cf 2·cf 3,(5)
where
N is a constant.
C is the climate factor, calculated in the model using hourly climate data for over
200 points in the U.S. and Canada. The value ranges from 15 to 30.
cf
1
is the building height correction factor, applicable to buildings in which the tested
spaces are on one floor (cf 1= 1) up to three floors (cf 1= 0.7).

Buildings 2024,14, 2158 10 of 20
cf
2
is the site shielding correction factor, for well-shielded cases (cf
2
= 1,2), (cf
2
= 1) or
exposed houses (cf 2= 1), (cf 2= 0.9).
cf
3
is the leak correction factor, which depends on the value of the leakage exponent
n. Buildings with small cracks receive a correction factor cf
3
= 1.4 while leaking buildings
with large cracks or holes have a correction factor cf3= 0.7.
This extended simplified model was adopted to calculate the average infiltration
flow in the Spanish Mediterranean region, obtaining the climatic factor C value through
assimilation with US climates as a function of the average temperature and wind speed. For
the coefficients cf
1
,cf
2,
and cf
3
, a value equal to 1 was adopted in all three cases, since the
small cracks detected in the envelope of the dwelling reached an average value. The type
of infiltration opening was obtained from the mean value of the flow exponent,
n = 0.59
.
The V
inf
, or air leakage rate, required to determine the energy impact was calculated based
on the air permeability rate and the envelope surface area (Equation (6):
Vinf =qinf −AE, (6)
where
AEis the envelope area (m2).
Once we obtained the value of the envelope air infiltration volume or air leak-
age rate V
inf
to calculate the energy impact according to the annual average corrected
through Equations (1)–(6), we quantified the sensible heat Q
s
and latent heat Q
l
using the
following equations:
Qs=Vinf·Ce·ρ·(Te−Ti), (7)
Here,
Q
s
is the value of the energy impact of the sensible heat of the air leakage rate V
inf
(W).
Vinf is the air leakage rate (m3/h).
Ceis the specific air heat under normal conditions (0.349 Wh/kgK).
ρis the air density (kg/m3).
T
e
is the outside air temperature in degrees Kelvin (K), taken as an annual
average value
.
Tiis the inside air temperature (21 K in winter and 24 K in summer).
Ql=Vinf·Cv·ρ·(We−Wi), (8)
Here,
Qlis the energy impact value of the latent heat of the air leakage rate Vinf (W).
Vinf is the air leakage rate (m3/h).
Cvis the water vaporisation heat (0.628 W/gvapour).
ρis the specific air volume (kg/m3).
W
e
is the specific outside air humidity taken as the annual average value (g
vapour
/kg).
Wiis the specific indoor air humidity (gvapour/kg).
3.2.2. Obtaining Annual Energy Demand Using DesignBuilder
The second quantitative approximation method was executed through DesignBuilder.
To quantify the energy impact, the U-value transmittance values of all envelopes [
54
]
obtained in
situ using the TESTO 635-2 [
55
,
56
] equipment were entered into the Design-
Builder model. To simulate the building’s behaviour in terms of energy demand and
interior comfort parameters, the data and parameter values described next were intro-
duced into the tool. The winter period ran from 1 December to 30 April, and the summer
period from 1 May to 30 November. This decision was based on the results obtained in
previous studies and according to the various model calibrations performed in the same
geographical location. The indoor air temperatures were set at 21
◦
C in winter and
24 ◦C
in summer. Maintenance temperatures of 17
◦
C in winter and 27
◦
C in summer were
selected for night-time. For the regulatory calculation of air renewal, the occupancy was
5 people. To comply with regulations, a value of 0.63 ACH was established according to

Buildings 2024,14, 2158 11 of 20
Spain’s current Technical Building Code (CTE). The model was applied by eliminating the
existing basement of the dwelling, considering a very airtight access door, and calculating
the energy loss values with the U-value, as if the ground floor were in contact with the
ground. The air infiltration values entered in the tool were those obtained by the blower
door test. All parameters related to the outdoor climate, including the solar radiation
values, setpoint temperatures, air change rate according to the CTE regulations, etc., were
entered into the DesignBuilder tool. The calculation model used in DesignBuilder was that
of the total demand for all energy necessary to establish the set temperature conditions.
Therefore, the energy efficiency of the heat recovery unit was not taken into account. The
infiltration values obtained in the n
50
were applied in the four construction phases P1, P2,
P3, and P4, with the calculated air infiltration value average of the building envelope being
transformed according to expression (1).
A thermoflowmetric study of the opaque envelopes was conducted for the two south
façade rooms (kitchen at a height of 0.70 m and living room), the north façade (multipurpose
room), and the north and south façade first-floor bedrooms. The ground contact U-value
transmittance was also calculated in accordance with ISO 9869-1:2014 [
57
]. The tests
lasted at least one week for each U-value transmittance measurement. The data were
analysed using AMR WinControl software (https://www.ahlborn.com/en/products/amr-
win-control-software-for-data-acquisition-and-measured-data-processing) developed by
Ahlborn for ALMEMO measuring equipment. The method used was the “average method”,
i.e., the thermal transmittance was calculated by dividing the thermal flow average density
by the difference in average temperature [58,59].
3.3. Air Infiltration and Its Energy Impact: Investment Amortisation Approach
Having established a method to quantify the air infiltration energy impact and com-
pare it using DesignBuilder, it was possible to pursue the study objectives. To this end, four
phases of the construction and sealing process, P1, P2, P3, and P4, were technically defined,
and the execution cost of each was quantified. The investment amortisation period was
estimated according to the methodology shown in Figure 6.
Buildings 2024, 14, 2158 11 of 20
existing basement of the dwelling, considering a very airtight access door, and calculating
the energy loss values with the U-value, as if the ground floor were in contact with the
ground. The air infiltration values entered in the tool were those obtained by the blower
door test. All parameters related to the outdoor climate, including the solar radiation val-
ues, setpoint temperatures, air change rate according to the CTE regulations, etc., were
entered into the DesignBuilder tool. The calculation model used in DesignBuilder was that
of the total demand for all energy necessary to establish the set temperature conditions.
Therefore, the energy efficiency of the heat recovery unit was not taken into account. The
infiltration values obtained in the n
50
were applied in the four construction phases P1, P2,
P3, and P4, with the calculated air infiltration value average of the building envelope being
transformed according to expression (1).
A thermoflowmetric study of the opaque envelopes was conducted for the two south
façade rooms (kitchen at a height of 0.70 m and living room), the north façade (multipur-
pose room), and the north and south façade first-floor bedrooms. The ground contact U-
value transmiance was also calculated in accordance with ISO 9869-1:2014 [57]. The tests
lasted at least one week for each U-value transmiance measurement. The data were an-
alysed using AMR WinControl software (https://www.ahlborn.com/en/products/amr-
win-control-software-for-data-acquisition-and-measured-data-processing) developed by
Ahlborn for ALMEMO measuring equipment. The method used was the “average
method”, i.e., the thermal transmiance was calculated by dividing the thermal flow av-
erage density by the difference in average temperature [58,59].
3.3. Air Infiltration and Its Energy Impact: Investment Amortisation Approach
Having established a method to quantify the air infiltration energy impact and com-
pare it using DesignBuilder, it was possible to pursue the study objectives. To this end,
four phases of the construction and sealing process, P1, P2, P3, and P4, were technically
defined, and the execution cost of each was quantified. The investment amortisation pe-
riod was estimated according to the methodology shown in Figure 6.
Figure 6. Methodology to assess energy and investment amortisation in the 4 scenarios under study.
The n
50
value and the actual building envelope airtightness over the entire one-year
cycle were progressively analysed over the 4 phases, together with the energy impact due
to these air infiltrations. Finally, the home’s life cycle cost (LCC) was applied in the 4 sce-
narios or designed phases. To this end, the UNE-EN 15459-1:2018 [60] standard was ap-
plied to the house CCL in the 4 scenarios, P1, P2, P3, and P4. The overall cost was calcu-
lated using the following expressions:
Figure 6. Methodology to assess energy and investment amortisation in the 4 scenarios under study.
The n
50
value and the actual building envelope airtightness over the entire one-year
cycle were progressively analysed over the 4 phases, together with the energy impact due to
these air infiltrations. Finally, the home’s life cycle cost (LCC) was applied in the 4 scenarios
or designed phases. To this end, the UNE-EN 15459-1:2018 [
60
] standard was applied to

Buildings 2024,14, 2158 12 of 20
the house CCL in the 4 scenarios, P1, P2, P3, and P4. The overall cost was calculated using
the following expressions:
Cg(t) = Cl+∑jh∑t
i=1(Ca,i(j)·Rdisc (i)) −ValF,t(j)i, (9)
RR=Rint −Ri
1+Ri/100 , (10)
Rdisc (i) = 1
1+RR/100 i
, (11)
where
Cg—overall cost.
Cl—initial investment costs.
Ca—recurring costs.
Rdisc—discount rate.
i—years.
Valf—residual value (EUR).
RR—real interest rate.
Ri—inflation rate.
Rint—interest rate.
The investment costs, recurring costs, and maintenance costs for a period of
30 years
were obtained from various databases of companies in the sector in Barcelona. The
costs of the energy consumed over 30 years were determined using expressions (7) and
(8), adjusted to the DesignBuilder simulation estimates, and an electricity mix cost of
0.242 EUR/kWh [61].
This quantification of overall execution costs and the savings achieved by reducing the
actual envelope airtightness in each phase allowed us to address the study hypothesis. By
subsequently determining the market value of the Passivhaus certification and comparing
it with non-certified housing values, we could establish whether it would be advisable
or not to adopt the sealing requirements of phases P2, P3, and P4 to reduce the n
50
value
below 0.6 ACH.
4. Results
Table 1shows the n
50
results obtained from the blower door test in each of the
4 phases
,
as well as the estimation of the energy loss calculation due to air infiltration according to
expression (1). As can be observed, the initial value was above 0.6 ACH, and a substantial
reduction was achieved in phases P2 (Figure 7), P3, and P4, dropping below the maximum
value allowed by the Passivhaus standard. The techniques for detecting the largest infil-
tration points, in addition to those applied for sealing, were satisfactory, and the desired
objective was met. Since similar results have been obtained in previous publications, we
were able to conclude that the work was technically valid [32,37].
Table 1. Results of n50 and average winter and summer infiltration in the three phases.
Envelope Air Infiltration eiεiP1 P2 P3 P4 % Reduction
n50 (blower door test) ACH 1.05 0.95 0.75 0.59 43.81
nwinter and nsummer 0.05 1 ACH 0.105 0.095 0.075 0.059 43.81

Buildings 2024,14, 2158 13 of 20
Buildings 2024, 14, 2158 13 of 20
Figure 7. Results from n
50
and the blower door test in phase P2.
Table 2. Calculation of annual energy demands due to air infiltration in the four phases.
Parameter Material Execution and Sealing Phases
Phase P1 P2 P3 P4
q
inf
m
3
/hm
2
0.289 0.262 0.207 0.164
V
inf
m
3
/h 73.87 66.97 52.79 41.92
Q
s
kWh/y 319.15 288.75 227.96 179.33
Ql kWh/y 2632.28 2381.58 1880.20 1479.09
Annual energy demand due to infiltration kWh/m
2
y 6.55 5.74 4.46 3.73
Annual energy demand (expressions (1) to (8)) kWh/y 10,203.60 9989.37 9560.18 9191.32
Percentage % 100.00 97.79 93.69 90.08
As illustrated in Table 3, the results of the DesignBuilder simulations (Figure 8) are
visibly close to those obtained through the mathematical expressions (1 to 8), with a max-
imum deviation of 2.2%. They were both conducted to obtain the annual energy demand.
For the ideal load method to achieve annual energy consumption, a recuperator efficiency
(Siber DF Excellen 400 Plus) value of 0.85 was taken into account in terms of air renewal.
Table 3. Calculation of energy loads and demands of the four phases, using DesignBuilder.
Parameter P1 P2 P3 P4
Total surface area 255.62 m
2
Total volume 703.8 m
3
Envelope airtightness (n
50
)
ACH 1.05 0.95 0.75 0.59
Lighting load kWh 1693.14 1693.14 1693.14 1693.14
Ventilation load (0.63 ACH) kWh 982.85 984.18 985.79 988.86
Envelope infiltration load kWh 1632.65 1435.93 1137.92 932.57
Occupancy load kWh 1618.82 1616.98 1613.21 1610.34
Envelope U load kWh 5103.92 5111.30 5126.22 5137.67
Windows U load kWh 2302.07 2266.72 2315.77 2282.63
Annual energy demand due to infiltration kWh/m
2
y 6.38 5.62 4.36 3.64
Total winter demand kWh/y 5546.4 5433.30 5221.12 5040.88
Total winter energy demand kWh/m
2
y 21.197 20.830 20.115 19.506
Figure 7. Results from n50 and the blower door test in phase P2.
Regarding the translation of these values into energy consumption quantifications, Ta-
ble 2breaks down the methodological process in Section 3.2.1., in which C = 18,
cf
1
= 1, cf
2
= 0.9, and cf
3
= 1.4. This air infiltration energy demand is also given with
respect to the energy demand of air changes of 0.63 ACH and the annual energy demand
due to air conditioning. These values are similar to those obtained in previous publica-
tions [
30
]. The energy demand due to envelope air infiltration accounted for 16.41% of
the annual energy demand in P1 and dropped to 11.93% in P3. These values are high
for conventional homes but not for Passivhaus Certificate housing, where thermal load
reduction and the heat recovery system substantially reduce annual energy demands [
62
].
Table 2. Calculation of annual energy demands due to air infiltration in the four phases.
Parameter Material Execution and Sealing Phases
Phase P1 P2 P3 P4
qinf m3/hm20.289 0.262 0.207 0.164
Vinf m3/h 73.87 66.97 52.79 41.92
QskWh/y 319.15 288.75 227.96 179.33
Ql kWh/y 2632.28 2381.58 1880.20 1479.09
Annual energy demand due to infiltration kWh/m2y6.55 5.74 4.46 3.73
Annual energy demand (expressions (1) to (8))
kWh/y 10,203.60 9989.37 9560.18 9191.32
Percentage % 100.00 97.79 93.69 90.08
As illustrated in Table 3, the results of the DesignBuilder simulations (Figure 8) are vis-
ibly close to those obtained through the mathematical expressions (1 to 8), with
a maximum
deviation of 2.2%. They were both conducted to obtain the annual energy demand. For the
ideal load method to achieve annual energy consumption, a recuperator efficiency (Siber
DF Excellen 400 Plus) value of 0.85 was taken into account in terms of air renewal.

Buildings 2024,14, 2158 14 of 20
Table 3. Calculation of energy loads and demands of the four phases, using DesignBuilder.
Parameter P1 P2 P3 P4
Total surface area 255.62 m2
Total volume 703.8 m3
Envelope airtightness (n50) ACH 1.05 0.95 0.75 0.59
Lighting load kWh 1693.14 1693.14 1693.14 1693.14
Ventilation load (0.63 ACH) kWh 982.85 984.18 985.79 988.86
Envelope infiltration load kWh 1632.65 1435.93 1137.92 932.57
Occupancy load kWh 1618.82 1616.98 1613.21 1610.34
Envelope Uload kWh 5103.92 5111.30 5126.22 5137.67
Windows Uload kWh 2302.07 2266.72 2315.77 2282.63
Annual energy demand due to infiltration kWh/m2y6.38 5.62 4.36 3.64
Total winter demand kWh/y 5546.4 5433.30 5221.12 5040.88
Total winter energy demand kWh/m2y21.197 20.830 20.115 19.506
Total summer demand kWh/y 4661.40 4555.62 4338.97 4150.43
Total summer energy demand kWh/m2y17.739 17.404 16.665 16.016
Solar gains through the glass in winter kWh −2701.90 −2701.90 −2701.90 −2701.90
Annual energy demand (DesignBuilder) kWh/y 9983.60 9772.09 9401.70 9081.41
Total annual energy demand kWh/m2y28.367 27.659 26.210 24.957
Buildings 2024, 14, 2158 14 of 20
Total summer demand kWh/y 4661.40 4555.62 4338.97 4150.43
Total summer energy demand kWh/m2y 17.739 17.404 16.665 16.016
Solar gains through the glass in winter kWh −2701.90 −2701.90 −2701.90 −2701.90
Annual energy demand (DesignBuilder) kWh/y 9983.60 9772.09 9401.70 9081.41
Total annual energy demand kWh/m2y 28.367 27.659 26.210 24.957
Figure 8. DesignBuilder simulation model.
As can be observed, glazing solar gains lead to significant heating savings in winter,
with a free gain of 10.57 kWh/m2 y. This can occur thanks to the automated regulation
system of opening and closing blinds or shuers depending on the solar radiation condi-
tions and the Ti, if allowed. In this way, the winter energy demand is 10.63 kWh/m2 y in
Phase 1 and 8936 kWh/m2 y in Phase 4.
Table 4 shows the results obtained for the execution costs, maintenance costs, overall
costs, annual energy savings due to infiltration reduction, and construction investment
amortisation periods. These amortisation periods were estimated based on experiences
reported in other studies [63,64]. The databases of companies in the sector were used to
calculate the installation costs. The cost of plastic adhesive jointing tape was based on a
ratio of 30.59 EUR/mL, including the costs of the operating technicians. Elastic amorphous
seals were valued according to previous experience and average construction company
costs. The total considered cost, including labour, was 16.59 EUR/mL.
Table 4. Calculation of the investment amortisation period of the four phases.
Sealing Type Cost
(EUR/mL)
Measurement
(mL)
Total Cost
(EUR/m) P1 (EUR) P2 (EUR) P3 (EUR) P4 (EUR)
Hermetic liquid membrane 44.38 192.5 8542.80 8.542.81
Expanding polyurethane foam 22.75 127.8 2907.45 2049.60 563.22 294.77
Plastic adhesive joint tape 30.59 127.8 3909.36 2189.63 657.16 901.6 160.44
Elastic amorphous seals 16.59 111.7 1853.25 584.08 421.61 297.92 549.64
Initial investment costs EUR 17,193.40 13,365.90 1641.99 1494.29 691.18
Maintenance costs (30 years) EUR 2096 1437.0 325.0 237.0 97.2
Overall Cost (Cg) EUR 19,289.4 14,802.9 1966.99 1731,29 788.38
Annual energy consumption kWh/year 9983.60 9772.09 9401.70 9081.41
Annual savings (0.242 EUR/kWh) EUR 51.74 155.61 244.90
Amortisation Period Years 31.73 20.15 15.63
Figure 8. DesignBuilder simulation model.
As can be observed, glazing solar gains lead to significant heating savings in winter,
with a free gain of 10.57 kWh/m
2
y. This can occur thanks to the automated regulation sys-
tem of opening and closing blinds or shutters depending on the solar radiation conditions
and the Ti, if allowed. In this way, the winter energy demand is 10.63 kWh/m
2
y in Phase 1
and 8936 kWh/m2y in Phase 4.
Table 4shows the results obtained for the execution costs, maintenance costs, overall
costs, annual energy savings due to infiltration reduction, and construction investment
amortisation periods. These amortisation periods were estimated based on experiences

Buildings 2024,14, 2158 15 of 20
reported in other studies [
63
,
64
]. The databases of companies in the sector were used
to calculate the installation costs. The cost of plastic adhesive jointing tape was based
on
a ratio
of 30.59 EUR/mL, including the costs of the operating technicians. Elastic
amorphous seals were valued according to previous experience and average construction
company costs. The total considered cost, including labour, was 16.59 EUR/mL.
Table 4. Calculation of the investment amortisation period of the four phases.
Sealing Type Cost
(EUR/mL)
Measurement
(mL) Total Cost
(EUR/m)
P1
(EUR)
P2
(EUR)
P3
(EUR)
P4
(EUR)
Hermetic liquid membrane 44.38 192.5 8542.80 8.542.81
Expanding polyurethane foam 22.75 127.8 2907.45 2049.60 563.22 294.77
Plastic adhesive joint tape 30.59 127.8 3909.36 2189.63 657.16 901.6 160.44
Elastic amorphous seals 16.59 111.7 1853.25 584.08 421.61 297.92 549.64
Initial investment costs EUR 17,193.40
13,365.90
1641.99 1494.29 691.18
Maintenance costs (30 years) EUR 2096 1437.0 325.0 237.0 97.2
Overall Cost (Cg)EUR 19,289.4 14,802.9 1966.99 1731,29 788.38
Annual energy consumption kWh/year 9983.60 9772.09 9401.70 9081.41
Annual savings (0.242 EUR/kWh)
EUR 51.74 155.61 244.90
Amortisation Period Years 31.73 20.15 15.63
As can be observed, the amortisation periods of investments in the detection work
and subsequent joinery sealing in the various phases were too long; they amounted to
over
30 years
for P2 and more than 15 years for P4. These values are well above those
required for an adequate operation, which would be around 5–10 years. In addition, the
electricity mix cost was higher in those years than in 2020, which would have led to even
less favourable rates. A comparison of the four scenarios is shown in Figure 9.
Buildings 2024, 14, 2158 15 of 20
As can be observed, the amortisation periods of investments in the detection work
and subsequent joinery sealing in the various phases were too long; they amounted to
over 30 years for P2 and more than 15 years for P4. These values are well above those
required for an adequate operation, which would be around 5–10 years. In addition, the
electricity mix cost was higher in those years than in 2020, which would have led to even
less favourable rates. A comparison of the four scenarios is shown in Figure 9.
Figure 9. Results of the global cost for 30 years, energy due to infiltration, annual energy demand,
and investment amortisation period in the four scenarios under study.
Lastly, we analysed the infiltration energy impact and investment amortisation in
colder climate zones, in this case, in Central Europe [36,65], and compared the data with
those of the Spanish Mediterranean region. To do this, we used the same case study, the
house in Sitges, and simulated its location in Prague using DesignBuilder. The conditions
of construction culture, execution costs, and per capita income, which do not differ sub-
stantially from those of Spain, support the validity of the comparison. The most notable
difference was the electricity mix cost per kWh: it was EUR 0.3212 in Prague and EUR
0.242 in Sitges (Barcelona).
Table 5 and Figure 10 show the results obtained. One can see that the energy impact
due to infiltration was around 217–228% higher than that of Sitges. The annual energy
demand was 51,981 kWh/m
2
compared to 28,367 kWh/m
2
in Sitges, i.e., 183.25% higher.
The PHS requirements would not be met in that case. On the other hand, the amortisation
periods of the investments made to seal the envelopes, in all their phases, would be highly
recommended, as they reduce the annual energy demand to a value of 46,087 kWh/m
2
y,
allowing for amortisation of the investments in less than 5 years.
Table 5. Calculation of energy demand and investment amortisation period in Prague.
PRAGUE
Parameter P1 P2 P3 P4
Overall cost (C
g
) 94.1% per capita EUR 13,929.5 1850.93 1629,14 741.87
Annual energy demand due to infiltration kWh/y −1153.89 −1045.44 −587.83 −651.70
Annual energy demand due to infiltration kWh/m
2
y 13.84 12.72 10.93 8.33
Total winter energy demand kWh/y 7035.30 6963.39 6813.58 6707.65
Total winter energy demand kWh/m
2
y 46.43 44.99 43.27 40.82
Total summer energy demand kWh/y 913.15 924.89 941.16 962.38
Total summer energy demand kWh/m
2
y 5.555 5.430 5.339 5.270
Total annual energy demand kWh/y 13,287.38 12,890.15 12,425.68 10,433.64
Total annual energy demand kWh/m
2
y 51,981 50,427 48,610 46,087
Annual savings (0.3212 EUR/kWh) EUR 127.56 276.72 916.44
Amortisation Period Years 14.51 12.58 4.61
Figure 9. Results of the global cost for 30 years, energy due to infiltration, annual energy demand,
and investment amortisation period in the four scenarios under study.
Lastly, we analysed the infiltration energy impact and investment amortisation in
colder climate zones, in this case, in Central Europe [
36
,
65
], and compared the data with
those of the Spanish Mediterranean region. To do this, we used the same case study, the
house in Sitges, and simulated its location in Prague using DesignBuilder. The conditions
of construction culture, execution costs, and per capita income, which do not differ sub-
stantially from those of Spain, support the validity of the comparison. The most notable
difference was the electricity mix cost per kWh: it was EUR 0.3212 in Prague and EUR 0.242
in Sitges (Barcelona).

Buildings 2024,14, 2158 16 of 20
Table 5and Figure 10 show the results obtained. One can see that the energy impact
due to infiltration was around 217–228% higher than that of Sitges. The annual energy
demand was 51,981 kWh/m
2
compared to 28,367 kWh/m
2
in Sitges, i.e., 183.25% higher.
The PHS requirements would not be met in that case. On the other hand, the amortisation
periods of the investments made to seal the envelopes, in all their phases, would be highly
recommended, as they reduce the annual energy demand to a value of 46,087 kWh/m
2
y,
allowing for amortisation of the investments in less than 5 years.
Table 5. Calculation of energy demand and investment amortisation period in Prague.
PRAGUE
Parameter P1 P2 P3 P4
Overall cost (Cg) 94.1% per capita EUR 13,929.5 1850.93 1629,14 741.87
Annual energy demand due to infiltration kWh/y −1153.89 −1045.44 −587.83 −651.70
Annual energy demand due to infiltration kWh/m2y13.84 12.72 10.93 8.33
Total winter energy demand kWh/y 7035.30 6963.39 6813.58 6707.65
Total winter energy demand kWh/m2y46.43 44.99 43.27 40.82
Total summer energy demand kWh/y 913.15 924.89 941.16 962.38
Total summer energy demand kWh/m2y5.555 5.430 5.339 5.270
Total annual energy demand kWh/y 13,287.38 12,890.15 12,425.68 10,433.64
Total annual energy demand kWh/m2y51,981 50,427 48,610 46,087
Annual savings (0.3212 EUR/kWh) EUR 127.56 276.72 916.44
Amortisation Period Years 14.51 12.58 4.61
Buildings 2024, 14, 2158 16 of 20
Figure 10. Comparative results of the global cost for 30 years, energy due to infiltration, annual
energy demand, and investment amortisation period between P1 and P4 in Sitges and Prague.
5. Discussion
The application of the Passivhaus standard to housing on the Mediterranean coast
has been the subject of ongoing debate. The most controversial factor is the overheating
of the air and interior walls in summer, which leads to significant comfort loss and high
air conditioning energy consumption.
Yet, to date, there has been lile discussion on the need to build an envelope that
would be as airtight as that required in Central Europe. As established by Wolfgang Feist,
the current director of the Darmstadt Passivhaus Institut, and by Bo Adamson in the late
1980s, achieving an n
50
value below 0.6 ACH seems to be an obvious condition to fulfil in
that area. However, this requirement is not so justifiable on the Mediterranean coast,
where the outside air rarely drops below 0 °C. It would therefore be relevant to conduct
further research and establish reasonable n
50
value parameters taking into account con-
struction execution costs and an amortisation period of less than 5 years for construction
and sealing cost overruns. Another decisive factor in this issue is the market value that
Passivhaus certification would give to the property in terms of capital gains. This variable
would undoubtedly make it advisable to adopt n
50
values below 0.6 ACH since the addi-
tional construction and sealing costs are usually much lower than the market value in-
crease of the property.
It is also necessary to incorporate the variable of overall material implementation
costs, which differ greatly from one country to another in the Mediterranean region and
Central Europe. In Germany, they account for approximately 1600–2800 EUR/m
2
, while in
Spain, they are in the range of 1400–2200 EUR/m
2
. Currently, the Passivhaus standard
involves an additional cost that ranges from 3% to 8% of the total construction budget,
with the average additional cost in Germany being 6%, though there have been cases
where the extra cost is nil. In the Spanish Mediterranean area, the average cost overrun is
around 27%, due to overall lower carpentry quality, poor airtightness, and the absence of
heat recovery systems in conventional construction.
6. Conclusions
The requirement to apply a maximum value of n
50
of 0.6 ACH in Passivhaus homes
on the Spanish Mediterranean coast is subject to debate. Given the values found in this
study for a PH house located in Sitges (Barcelona), it would seem more reasonable to ap-
ply the construction and sealing techniques of the Phase 1 envelope only. If successive
phases of seal improvement were applied—P2, P3, and P4—to reduce the n
50
value to 0.6
ACH with a higher material execution cost, the investment amortisation period would be
too long, as it would range from 15 to 30 years. The resulting n
50
value in P1 is 1.05, which
is far above the PHS limit. However, the energy losses due to this value increase annual
energy demand by only 13.66%, that is, 3.41 kWh/m
2
y, accounting for an annual energy
cost increase of EUR 244.90. Compared to the execution costs of EUR 3827 for the three
phases—the total costs applied in P4—the investment amortisation period would be over
Figure 10. Comparative results of the global cost for 30 years, energy due to infiltration, annual
energy demand, and investment amortisation period between P1 and P4 in Sitges and Prague.
5. Discussion
The application of the Passivhaus standard to housing on the Mediterranean coast
has been the subject of ongoing debate. The most controversial factor is the overheating of
the air and interior walls in summer, which leads to significant comfort loss and high air
conditioning energy consumption.
Yet, to date, there has been little discussion on the need to build an envelope that
would be as airtight as that required in Central Europe. As established by Wolfgang Feist,
the current director of the Darmstadt Passivhaus Institut, and by Bo Adamson in the late
1980s, achieving an n
50
value below 0.6 ACH seems to be an obvious condition to fulfil in
that area. However, this requirement is not so justifiable on the Mediterranean coast, where
the outside air rarely drops below 0
◦
C. It would therefore be relevant to conduct further

Buildings 2024,14, 2158 17 of 20
research and establish reasonable n
50
value parameters taking into account construction
execution costs and an amortisation period of less than 5 years for construction and sealing
cost overruns. Another decisive factor in this issue is the market value that Passivhaus
certification would give to the property in terms of capital gains. This variable would
undoubtedly make it advisable to adopt n
50
values below 0.6 ACH since the additional
construction and sealing costs are usually much lower than the market value increase
of the property.
It is also necessary to incorporate the variable of overall material implementation costs,
which differ greatly from one country to another in the Mediterranean region and Central
Europe. In Germany, they account for approximately 1600–2800 EUR/m
2
, while in Spain,
they are in the range of 1400–2200 EUR/m
2
. Currently, the Passivhaus standard involves
an additional cost that ranges from 3% to 8% of the total construction budget, with the
average additional cost in Germany being 6%, though there have been cases where the
extra cost is nil. In the Spanish Mediterranean area, the average cost overrun is around 27%,
due to overall lower carpentry quality, poor airtightness, and the absence of heat recovery
systems in conventional construction.
6. Conclusions
The requirement to apply a maximum value of n
50
of 0.6 ACH in Passivhaus homes on
the Spanish Mediterranean coast is subject to debate. Given the values found in this study
for a PH house located in Sitges (Barcelona), it would seem more reasonable to apply the
construction and sealing techniques of the Phase 1 envelope only. If successive phases of
seal improvement were applied—P2, P3, and P4—to reduce the n
50
value to 0.6 ACH with
a higher material execution cost, the investment amortisation period would be too long, as
it would range from 15 to 30 years. The resulting n
50
value in P1 is 1.05, which is far above
the PHS limit. However, the energy losses due to this value increase annual energy demand
by only 13.66%, that is, 3.41 kWh/m
2
y, accounting for an annual energy cost increase
of EUR 244.90. Compared to the execution costs of EUR 3827 for the three phases—the
total costs applied in P4—the investment amortisation period would be over 15 years. The
same would be true for phases F2 and F3, where the implementation costs would be EUR
1641.99 and EUR 3136.28, respectively, and the amortisation periods would be 31 years
and
20 years
. It would therefore be advisable not to undertake phases P2, P3, and P4. The
property could not obtain the PHS with an n
50
value of 1.05 ACH, but given that the PHS
does not contribute to market value in the Spanish real estate valuation system, there is no
need to continue improving envelope tightness with phases P2, P3, and P4.
When the same house is subjected to a DesignBuilder simulation in Prague, i.e.,
in
a colder
Central European climate, the scenario is entirely different. Severe winter
conditions imply that reducing the air infiltration through the envelope to the n
50
value of
0.59 ACH entails significant annual energy savings of 2853.74 kWh/y. The electricity mix
costs EUR 0.324/kWh, and a substantial annual saving of EUR 916.44 is achieved. In this
case, the amortisation period of the investments required to improve the construction is
less than 5 years. We can thus conclude, in this specific case study, that the execution of
phases P2, P3, and P4 would be feasible in cold continental climates, but in mild conditions,
such as the Mediterranean climate, it would be more appropriate, in terms of energy and
investments, to maintain the initial building construction solution of phase P1. To draw
any concrete conclusions from an environmental perspective, it would first be necessary to
conduct the arduous task of completing a whole life cycle assessment (LCA), including the
P2, P3, and P4 sealing techniques.
To summarise, we are facing a complex problem that requires successive examinations
and a detailed analysis of case studies in order to determine an n
50
infiltration value ad-
justed to the climatic conditions and the energy and execution cost requirements according
to each region or geographical area.

Buildings 2024,14, 2158 18 of 20
Author Contributions: Conceptualization, V.E.-I. and R.G.-V.; methodology, V.E.-I.; software, I.U.-B.;
validation, V.E.-I., I.U.-B. and R.G.-V.; investigation, V.E.-I., I.U.-B. and R.G.-V.; resources, R.G.-V. and
I.U.-B.; data curation, V.E.-I. and I.U.-B.; writing—original draft preparation, V.E.-I.; writing—review
and editing, V.E.-I.; funding acquisition, R.G.-V. All authors have read and agreed to the published
version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement: There is not data available publicly.
Acknowledgments: The authors gratefully acknowledge the technical help provided by EVOWALL
TECHNOLOGY S.L. and the RV4 architect’s office in order to carry out the different tests needed for
this paper.
Conflicts of Interest: The authors declare no conflicts of interest. The company and the architect’s
office had no role in the design of the study; in the collection, analyses, or interpretation of data; in
the writing of the manuscript; or in the decision to publish the results.
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