buildings
Article
Nearly Zero Energy Buildings: An Overview of the
Main Construction Features across Europe
Giulia Paoletti *, Ramón Pascual Pascuas, Roberta Pernetti and Roberto Lollini
EURAC Research, Institute for Renewable Energy, Viale Druso 1, 39100 Bolzano, Italy;
[email protected] (R.P.P.); [email protected] (R.P.); [email protected] (R.L.)
* Correspondence: [email protected]; Tel.: +39-0471-055-661
Academic Editors: Francesco Guarino and Sonia Longo
Received: 28 March 2017; Accepted: 23 May 2017; Published: 31 May 2017
Abstract: Nearly Zero Energy Buildings (nZEBs) represent the backbone to achieve ambitious
European goals in terms of energy efficiency and CO2 emissions reduction. As defined in the EPBD, by
31 December 2020, all of the new buildings will have to reach a target of nearly zero energy. This target
encourages the adoption of innovative business models as well as the technology development in the
building sector, aimed at reducing energy demand and exploiting local renewable energy sources (RES).
Assessing the share of implementation and the performance of technologies in new or renovated
nZEBs is strategic to identify the market trends and to define design guidelines with the most effective
solutions according to the context. In this regard, this paper analyses the construction features of a set
of nZEBs, collected in 17 European countries within the EU IEE ZEBRA2020 project, with a special
focus on the influence of the boundary conditions on the technologies adopted. The results show
a general high insulation level of the envelope and recurrent specific technologies in the Heating
Ventilation Air Conditioning (HVAC) system (i.e., heat pumps and mechanical ventilation), while the
climatic conditions do not drive significantly the design approach and the nZEB features.
Keywords: nearly Zero Energy Buildings; construction features; technology solution sets
1. Introduction
The Energy Performance of Buildings Directive (EPBD 2010/31/EU) [1] established that all of
the new constructions, from 31st December 2020, will have to reach the standard nearly Zero Energy
Buildings (nZEBs), which implies a large scale deployment of this kind of buildings. As defined
in the art.2, a ‘nearly Zero-Energy Building’ is a building with very high-energy performance that
should cover the nearly zero energy (or at least a very low amount of it) required by on site or nearby
energy production from Renewable Energy Source (RES). Such qualitative definition leaves a lot of
space for national interpretation and for the adoption of the quantitative indices to be considered (i.e.,
performance targets, amount of renewables to be integrated, CO2 emissions, etc.). Due to this reason
and to specific local conditions as well as construction practice, European countries have adopted their
own definition, and there are some relevant inconsistencies across Europe [2–4].
In France, for example, an nZEB has to accomplish the “RT2012” (national law), which requires
a primary energy consumption lower than 60 kWh/(m2 ·year) in new residential buildings (including
heating, DHW, cooling, ventilation, lighting and auxiliary systems) and variable value limits for
new non-residential buildings, as lower than 110 kWh/(m2 ·year) in office buildings (including
heating, DHW, cooling, ventilation, lighting and auxiliary systems). Whereas in Austria, the “OIB
Directive 6” (national law) establishes that a building is an nZEB when the primary energy is
less than 160 kWh/(m2 ·year) in new residential (including heating, DHW, cooling, ventilation and
electric appliances) and less than 170 kWh/(m2 ·year) in non-residential (including heating, DHW,
cooling, ventilation, electric appliances and lighting). On the other hand, in Italy, the “DM 20 of
Buildings 2017, 7, 43; doi:10.3390/buildings7020043
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June 2015” (national law) defines the primary energy limits of nZEBs using a calculation process
based on reference buildings and introduces a minimum rate of renewables (including heating, DHW,
cooling, ventilation in residential buildings and also lighting and mobility of persons (e.g., elevator) in
non-residential ones).
Further than the comparative analysis of the European nZEB definitions, the project EU IEE
ZEBRA2020 aims to assess the current state of transition of the building stock towards the nZEB target
and to define solutions to overcome the identified market barriers. In fact, the project highlighted
that, despite the technologies for nZEBs are ready and proven, the average EU rate of new nZEB
construction is low and is increasing slowly, and thus targeted national countermeasures should
be adopted.
In this regard, the identification of best practices, performance targets, technology solution sets
and the definition of design guideline represent strategic actions that can support the designers in
planning new nZEBs. These issues represent the key factors to foster the uptake of nZEB across
Europe; in fact, there are a large number of European projects and an extensive literature in this
field. In fact, there are several papers dealing with the definition of the general effective design
approach based on cost-optimal principles [5,6], and that analyzes specific technologies influencing
the nZEB performances. In particular, the focus is on the envelope features [7,8], the HVAC system
components [9–11] and the integration of renewable energies [12].
Nevertheless, although the large number of papers dealing with the topic, currently, the impact
of the technologies as well as the final performances are evaluated or by simulation activities or by
monitoring a reduced number of real buildings. Currently, an evaluation of the nZEB features and
related performances based on a large sample of buildings is missing. The main reason is the lack of
structured and populated databases including nZEB data across Europe. In fact, in the past recent
years, several European projects dealt with the setup of building databases, that represent an important
starting point for this work, but none of them is specifically focused on nZEBs.
Among all, the main databases considered are: “EU IEE TABULA-EPISCOPE” [13], aimed
at classifying the building stock in representative typologies, “EU H2020 ODYSSE-MURE” [14]
that includes data to assess the general trends at country level and effectiveness of energy related
implemented policies, “EU IEE ENTRANZE Data Tool” [15] and “EU IEE ENTRANZE Cost Tool” [16],
that include detailed information on a set of buildings but are not specifically focused on nZEB.
Moreover, in the report “A harmonized database to share nZEBs good practices” [17] is described
the framework and the main information to be collected for setting up a database for nZEBs in
the Mediterranean-climate zone; nevertheless, it is not yet populated with a significant number
of buildings.
Finally, it is under development the new release of the “EU Building Stock Observatory”
(https://ec.europa.eu/energy/en/eubuildings), an online database that monitors the energy
performance of buildings across Europe and collects the building stock characteristics, the costs
and state of implementation of relevant EU Directives across the Member States. “EU Building Stock
Observatory” is an online database developed for the European Commission by Building Performance
Institute Europe (BPIE) in collaboration with Ecofys, Energy Research Centre of the Netherlands (ECN),
Enerdata, Seven and many national partners. The next developments will be focused on building
renovation and nZEB.
The development of the database in EU IEE ZEBRA 2020 started from the structure and the
indicators of these available tools. It is specifically focused on nZEBs, including buildings features,
technical systems, passive and active solutions adopted, and it was populated with a significant
number of cases that allows for carrying out analyses on the performances and on the features of
nZEBs buildings across Europe.
The analysis reported in this paper represents a first step for the elaboration of an nZEB design
guideline, and aims to identify the recurrent technology solutions, and the related performances in the
nZEB building stock across Europe. The main nZEB features were identified by analyzing the solutions
Buildings 2017, 7, 43
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implemented in nZEB, considering both residential and non-residential buildings, new and renovated
ones. The analysis is conducted in 17 European countries presenting different climatic conditions,
building regulations and local nZEB definitions.
2. Methodology
In order to identify the nZEBs’ features, we performed an investigation in 17 European countries
(Austria, Belgium, Czech Republic, Denmark, France, Germany, Italy, Lithuania, Luxemburg, Norway,
Poland, Romania, Slovakia, Spain, Sweden, Netherlands and United Kingdom) on design strategies and
technologies implemented on a sample of 411 residential and non-residential buildings. The analyzed
buildings were identified in reports and Energy Performance Certificate (EPC) databases within the
project EU IEE ZEBRA2020. In addition, the data collection was focused on buildings constructed
or renovated after 2010, in order to represent the picture after the EPBD recast. Each country data
elaboration was based on different sample size according to the availability of information.
It is estimated that most of the collected buildings fulfill the nZEBs target as defined at national
and regional level. Nevertheless, when the data collection was taking place, some countries (e.g.,
Germany and Spain) involved in the analysis lacked of an official nZEB definition [3,4]. In these cases,
we included in the sample a set of exemplary cases of high energy-efficient constructions.
European Climatic Zone
Local climate conditions are defined as “the weather conditions prevailing in an area in general or over
a long period” (https://en.oxforddictionaries.com/definition/climate). As the history of architecture
shows, the local climatic conditions have been one of the most significant factors that influence the
building features. In the last century, the technology improvement changed the design approach
and the impact of the climate boundaries on the architectural features decreased; thus, the buildings
present homogeneous features across Europe. Currently, the introduction of the nZEB target increased
the importance of reducing the energy needs, and the ‘passive design’ according to the local climate
conditions becomes a recurrent practice. The main reason is that the implementation of passive design
strategies allows for taking advantage of the local energy sources and reducing the energy needs for
heating or cooling, also influencing the aesthetics and the functional building features.
In most of the cases, the energy performance indicators are based on climatic zones identified
by external temperatures. Nevertheless, other factors like humidity, atmospheric pressure, wind,
precipitation or solar radiation also play an important role in the energy needs of a building. A common
standard for the classification of European climatic zones and for the consequent performance target
normalization are still missing and in several studies, analysis or projects, a different classification
is being used (e.g., MORE-CONNECT (http://www.more-connect.eu/the-project/concept-andapproach/), GE20 (http://geoclusters.eu/), iNSPiRe (http://inspirefp7.eu/), TABULA and EPISCOPE
(http://episcope.eu/iee-project/tabula/), 4RinEU (http://www.4rineu.eu/), etc.). Moreover, each
country has defined its own national climatic zone classification in relation to the specific climatic
characteristics, and according to them, also the variable limits of energy performance indicators [18].
Within EU IEE ZEBRA2020 project, each nZEB included in the analysis was associated to the related
Heating Degree Days (HDD) and Cooling Degree Days (CDD) using the same calculation method [18].
In order to determine the values of HDD and CDD, we assumed identical reference temperatures for all
nZEBs’ location (15 ◦ C for HDD and 18.5 ◦ C for CDD), and we adopted average daily temperature values
of the last 36 months (the data were gathered from http://www.degreedays.net) [2]. Nevertheless,
the level of accuracy of the climatic data for describing the conditions of the selected nZEBs can be
affected by the distance between the building and the nearest weather station. In fact, different case
studies, although located in different microclimates areas with different environment features (e.g.,
altitude, slope, orientation, soil type, solar irradiation), present the same HDD and CDD, due to the
lack of more detailed data.
Buildings 2017, 7, x FOR PEER REVIEW 4 of 22 Buildings 2017, 7, 43
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Buildings 2017, 7, x FOR PEER REVIEW 4 of 22 In order to classify the buildings, we adopted three winter climates (warm, mild and cold) according to HDD, as shown Figure 1. In order
order to
to classify
classify the
the buildings,
buildings, we
we adopted
adopted three
three winter
winter climates
climates (warm,
(warm, mild
mild and
and cold)
cold) In
according to HDD, as shown Figure 1. according
to HDD, as shown Figure 1.
Figure 1. Classification of nZEBs by countries, according to HDD (15 °C) and CDD (18.5 °C). Definition of three winter rigidity levels (warm HDD15 < 1000; mild 1000 ≤ HDD15 < 2000 and cold ◦ C) and CDD (18.5 ◦ C). Definition
Figure
Classification
of nZEBs
by countries,
according
to HDDto (15
Figure 1.1. Classification of nZEBs by countries, according HDD (15 °C) and CDD (18.5 °C). HDD ≥ 2000). Note: one point can include more than one building, because one point represents a of
three winter rigidity levels (warm HDD15 < 1000; mild 1000 ≤ HDD15 < 2000 and cold HDD ≥ 2000).
Definition of three winter rigidity levels (warm HDD15 < 1000; mild 1000 ≤ HDD15 < 2000 and cold location. Note:
one point can include more than one building, because one point represents a location.
HDD ≥ 2000). Note: one point can include more than one building, because one point represents a location. It is possible to point out that the buildings located in Norway, United Kingdom, Belgium, It
is
possible to point out that the buildings located in Norway, United Kingdom, Belgium,
Denmark and Austria present a reduced climate variability, while those in Italy and Spain have larger Denmark
and
Austria
a reduced
variability,
those inUnited Italy and
Spain have
larger
It is possible to present
point out that the climate
buildings located while
in Norway, Kingdom, Belgium, ranges of HDD and CDD, according to the different climate zones in the countries. ranges
of
HDD
and
CDD,
according
to
the
different
climate
zones
in
the
countries.
Denmark and Austria present a reduced climate variability, while those in Italy and Spain have larger It is important to point out that, due to the reduced number of buildings available in the sample, It
is important
out that, due
to thein reduced
number
of buildings
available
the
ranges of HDD and CDD, according to the different climate zones in the countries. as shown in Figure to2, point
the technology analysis the warm climatic zone could have a in
lower sample,
as
shown
in
Figure
2,
the
technology
analysis
in
the
warm
climatic
zone
could
have
a
lower
It is important to point out that, due to the reduced number of buildings available in the sample, representativeness than the analysis in the mild and cold climates. representativeness
than2, the
analysis
in theanalysis mild andin cold
as shown in Figure the technology the climates.
warm climatic zone could have a lower representativeness than the analysis in the mild and cold climates. Figure 2. Share of nZEBs collected in relation to the climatic zones.
Figure 2. Share of nZEBs collected in relation to the climatic zones. 3.
Data Collection Figure 2. Share of nZEBs collected in relation to the climatic zones. 3. Data Collection As showed in Table 1, the analysis is based on 411 nZEBs (recently constructed or renovated)
3. Data Collection located in 17 European countries.
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Table 1. Number of nZEBs collected in each European country.
Country
Number of nZEBs
Austria (AT)
Belgium (BE)
Czech Republic (CZ)
Denmark (DK)
France (FR)
Germany (DE)
Italy (IT)
Lithuania (LT)
Luxemburg (LU)
Netherlands (NL)
Norway (NO)
Poland (PO)
Romania (RO)
Slovakia (SK)
Spain (ES)
Sweden (SE)
United Kingdom (UK)
Total
30
15
9
9
30
31
100
8
8
15
31
23
29
9
32
15
17
411
The collected data were deduced from EPCs, building databases and reports on energy efficiency
buildings, providing information on:
•
•
•
•
•
•
•
•
•
•
type of building: residential and non-residential;
type of construction: new and renovated;
year of construction or renovation;
location and climate conditions (HDD and CDD);
energy performance: heating demand, understood as energy need (heat to be delivered to, or
extracted from, a conditioned space to maintain the intended temperature conditions during
a given period of time [19]) and primary energy demand (energy that has not been subjected to
any conversion or transformation process [20]) according to national standards;
envelope features: thermal transmittance (U-values) and insulating materials;
windows features: thermal transmittance (Uwin -value), type of glass, solar gain (g-value) and
frame material;
passive strategies implemented: sunshade, natural ventilation, night cooling, evaporative cooling,
sunspaces, thermal mass or green roof;
HVAC systems: typology of heating, cooling, Domestic Hot Water (DHW) and mechanical
ventilation systems;
Renewable Energy Systems (RES) installed: photovoltaic or solar thermal systems.
All of the above-mentioned information for the building samples is available in the ‘Data tool
nZEB buildings’, an online tool elaborated within EU IEE ZEBRA2020 project (www.zebra2020.eu),
where main nZEB features are shown by use (residential and non-residential), by country and by
climatic zone.
4. Data Analysis
The sample is composed by 64% “residential” and 36% “non-residential” buildings, in line with the
rates of the European building stock [21]. In addition, 81% of the selected nZEBs are “new buildings”,
while the “renovated buildings” represent the 19%.
Due to the different existing definitions and calculation approaches developed in Europe,
a direct comparison among the level of global energy performance indicators cannot be performed.
In particular, one of the most critical parameters is the primary energy demand, since it is calculated
The sample is composed by 64% “residential” and 36% “non‐residential” buildings, in line with the rates of the European building stock [21]. In addition, 81% of the selected nZEBs are “new buildings”, while the “renovated buildings” represent the 19%. Due to the different existing definitions and calculation approaches developed in Europe, a Buildings
2017, 7, 43
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direct comparison among the level of global energy performance indicators cannot be performed. In particular, one of the most critical parameters is the primary energy demand, since it is calculated through different energy balance methods, with different boundary conditions, primary energy through different energy balance methods, with different boundary conditions, primary energy factors,
factors, CO2 equivalent emissions, and with different contributions of active and passive systems (i.e., CO2 equivalent emissions, and with different contributions of active and passive systems (i.e., heating,
heating, cooling, lighting, ventilation). cooling, lighting, ventilation).
Consequently, we focused the analysis on the heating demand, since the discrepancies between Consequently, we focused the analysis on the heating demand, since the discrepancies between
countries in the calculation approach are reduced due to the common standard for the energy balance countries in the calculation approach are reduced due to the common standard for the energy balance
calculation provided by the EN ISO 13790 [19]. calculation provided by the EN ISO 13790 [19].
Moreover, within this work, in order to reduce the inconsistencies due to the calculation method, Moreover, within this work, in order to reduce the inconsistencies due to the calculation method,
we analyzed quantitative parameters calculated through EU standards (i.e., thermal transmittance), we analyzed quantitative parameters calculated through EU standards (i.e., thermal transmittance),
values coming from the technical sheets (i.e., efficiency of the HVAC devices), as well as qualitative values coming from the technical sheets (i.e., efficiency of the HVAC devices), as well as qualitative
data (i.e., the typology of technological systems installed). data (i.e., the typology of technological systems installed).
4.1. Heating Demand 4.1. Heating Demand
The analysis on the nZEBs “heating demand” were made according their HDD and in relation The analysis on the nZEBs “heating demand” were made according their HDD and in relation to
to the use of the buildings and construction typology, as shown in Figure 3. the use of the buildings and construction typology, as shown in Figure 3.
(a) (b) Figure 3. Heating demand of nZEBs in relation to the use of the buildings, as well as the construction Figure 3. Heating demand of nZEBs in relation to the use of the buildings, as well as the construction
type, new buildings (a) and renovated buildings (b) according to HDD (15 °C). type, new buildings (a) and renovated buildings (b) according to HDD (15 ◦ C).
It can be pointed out that the coefficient of determination of the regression (R2) is very low in all It can be pointed out that the coefficient of determination of the regression (R2 ) is very low in
cases (new or renovated and residential or non‐residential buildings). Accordingly, there is no all cases (new or renovated and residential or non-residential buildings). Accordingly, there is no
significant relation between the nZEB heating demand and HDD and the analyzed buildings present significant relation between the nZEB heating demand and HDD and the analyzed buildings present
high performance levels despite the climate conditions. Furthermore, it could be deduced that the high performance levels despite the climate conditions. Furthermore, it could be deduced that the
adoption of the energy efficiency technology is not strongly affected by the climate condition, with adoption of the energy efficiency technology is not strongly affected by the climate condition, with
different levels of effort in design solutions. In fact, in the 93% of the buildings, the “heating demand” different levels of effort in design solutions. In fact, in the 93% of the buildings, the “heating demand”
is lower than 40 kWh/(m2∙year). is lower than 40 kWh/(m2 ·year).
Going into more detail for each climatic zone, the boxplots of Figure 4 show the median value Going into more detail for each climatic zone, the boxplots of Figure 4 show the median value of
of heating demand of nZEBs according to use of the building (residential and non‐residential) and heating demand of nZEBs according to use of the building (residential and non-residential) and type
type of construction (new and renovated). of construction (new and renovated).
It can be noticed that the median values of the heating demand tend to grow according to the HDD,
for all the building typologies and uses, as shown in Figure 4. Nonetheless, in each climate rigidity, the
interquartile ranges (i.e., central rectangle that includes the 50% of the “heating demand” values) of new
buildings result in being more compact and lower than the renovated ones. This outcome highlights
Buildings 2017, 7, x FOR PEER REVIEW 7 of 22 It can be noticed that the median values of the heating demand tend to grow according to the HDD, for all the building typologies and uses, as shown in Figure 4. Nonetheless, in each climate rigidity, the interquartile ranges (i.e., central rectangle that includes the 50% of the “heating demand” Buildings 2017, 7, 43
7 of 22
values) of new buildings result in being more compact and lower than the renovated ones. This outcome highlights the difficult implementation in existing buildings of energy efficient measures like installation of insulating materials, improvement of the airtightness, and reduction of thermal the difficult implementation in existing buildings of energy efficient measures like installation of
bridges. insulating materials, improvement of the airtightness, and reduction of thermal bridges.
Figure 4. Heating demand of nZEBs according to use (residential and non-residential) and type of
Figure 4. Heating demand of nZEBs according to use (residential and non‐residential) and type of construction (new (new and and renovated) renovated) for for different different climate climate condition. condition. Note: Note: in in warm warm climates climates for for both both
construction renovated residential and new non-residential buildings, the limits of the interquartile ranges (central
renovated residential and new non‐residential buildings, the limits of the interquartile ranges (central rectangle) correspond to the only two values of Heating Demands of the collected nZEBs.
rectangle) correspond to the only two values of Heating Demands of the collected nZEBs. 4.2. Features of the Thermal Envelope 4.2. Features of the Thermal Envelope
The history of the architecture shows that, until the 19th century, building materials and features The history of the architecture shows that, until the 19th century, building materials and features
were strictly connected to the context, typical construction techniques and climate conditions. were strictly connected to the context, typical construction techniques and climate conditions.
The of the building building
stock characteristics (e.g., dimensional, The analysis analysis
of European the European
stock characteristics
(e.g., technological, dimensional,
functional, performed within EU FP7‐iNSPiRE project (FP7‐iNSPiRE technological,etc.), functional,
etc.), performed
within
EU FP7-iNSPiRE
project
(FP7-iNSPiRE project: project:
www.inspirefp7.eu) [22], highlighted that the thermal envelope features of existing buildings change www.inspirefp7.eu) [22], highlighted that the thermal envelope features of existing buildings change
according to the rigidity of the climate. In particular, the HDD strongly affect the envelope thermal according to the rigidity of the climate. In particular, the HDD strongly affect the envelope thermal
transmittance: buildings located in cold winters (high value of HDD) present reduced envelope “U‐
transmittance: buildings located in cold winters (high value of HDD) present reduced envelope
value” in both opaque and transparent parts, as shown in Figure 5. “U-value” in both opaque and transparent parts, as shown in Figure 5.
On the contrary, as shown in Figure 6–8, the thermal transmittance of the envelope components On the contrary, as shown in Figures 6–8, the thermal transmittance of the envelope components
in nZEBs result in being very similar in different climate zones. In addition, no remarkable variations in nZEBs result in being very similar in different climate zones. In addition, no remarkable variations
between new or renovated and residential or non‐residential buildings can be highlighted. This result between new or renovated and residential or non-residential buildings can be highlighted. This result is
2 ·K). is the minimum requirements set legislation,
by national which usually duedue to theto minimum
requirements
set by national
whichlegislation, is usually around
0.30is W/(m
2
around 0.30 W/(m
∙K). Figure 6 shows
the average nZEB thermal transmittance of the external envelope according to
Figure 6 shows the average nZEB thermal transmittance of the external envelope according to HDD:
Figure 6a reports U-values highlighting the use of the building (residential or non-residential),
HDD: Figure 6a reports U‐values highlighting the use of the building (residential or non‐residential), while Figure 6b highlights the kind of intervention (new or renovated building). As both graphics show,
while Figure 6b highlights the kind of intervention (new or renovated building). As both graphics no significant differences can be observed between the type of use and the type of the intervention.
show, significant differences can ofbe wall
observed between the type use and the type of the Inno general,
the medium
values
thermal
transmittance
areof always
very
low:
between
2
2
intervention. 0.12 W/(m ·K) in places with high HDD to 0.20 W/(m ·K) in zones with low HDD. In some cases, the
thermal transmittance of external walls are higher than 0.35 W/(m2 ·K), most of all in buildings located
in ‘warm climates’ (HDD < 1000), where the minimum requirements for U-values are less restrictive.
Higher wall thermal transmittance values have been observed in renovated historic buildings or in
buildings with a particular interest located in the three climate zones, where the envelope performance
improvements, (i.e., installation of insulating materials), are limited due to the conservation constraints.
Buildings 2017, 7, 43
Buildings 2017, 7, x FOR PEER REVIEW Buildings 2017, 7, x FOR PEER REVIEW 8 of 22
8 of 22 8 of 22 Figure 5.
5. U‐values U‐values of of external external walls walls of of the the building building stock stock before before renovation renovation in in different
different European
European Figure
U-values
of
external
walls
of
the
building
stock
before
renovation
in
Figure 5. different European climate areas with respect to HDD. Source: EU FP7‐iNSPiRe project. D6.5‐Position Paper on Systemic climate areas with respect to HDD. Source: EU FP7-iNSPiRe project. D6.5-Position Paper on Systemic
climate areas with respect to HDD. Source: EU FP7‐iNSPiRe project. D6.5‐Position Paper on Systemic Energy Renovation [22]. Energy
Renovation [22].
Energy Renovation [22]. (a) (a) (b)
(b)
Figure 6. (a) Thermal transmittances of walls of nZEB according to HDD, and in relation to the use of Figure 6. (a) Thermal transmittances of walls of nZEB according to HDD, and in relation to the use of Figure
6. (a) Thermal transmittances of walls of nZEB according to HDD, and in relation to the use of
the buildings (residential and non‐residential); (b) type of intervention (new and renovated buildings). the buildings (residential and non‐residential); (b) type of intervention (new and renovated buildings). the buildings (residential and non-residential); (b) type of intervention (new and renovated buildings).
In general, the medium values of wall thermal transmittance are always very low: between 0.12 In general, the medium values of wall thermal transmittance are always very low: between 0.12 A2 similar analysis was carried out for all the2building components (i.e., wall, roof, floor, and
W/(m2∙K) ∙K) in in places places with high high HDD HDD to to 0.20 0.20 W/(m
W/(m2∙K) ∙K) in in zones zones with with low low HDD. HDD. In In some some cases, cases, the the W/(m
windows),
as shownwith in Figure 7.
2∙K), most of all in buildings located thermal transmittance of external walls are higher than 0.35 W/(m
2
thermal transmittance of external walls are higher than 0.35 W/(m
∙K), most of all in buildings located The breakdown for the building elements confirms the general
trend identified for the average
in ‘warm climates’ (HDD < 1000), where the minimum requirements for U‐values are less restrictive. in ‘warm climates’ (HDD < 1000), where the minimum requirements for U‐values are less restrictive. envelope U-value; in fact, the performances of the building components present a weak correlation
Higher wall thermal transmittance values have been observed in renovated historic buildings or in Higher wall thermal transmittance values have been observed in renovated historic buildings or in with
the external climate conditions, as highlights by coefficient of determination (R2 ). The box plots
buildings with a a particular particular interest interest located located in in the the three three climate climate zones, zones, where where the the envelope envelope buildings in Figure 8with show the
interquartile ranges
(central rectangle)
that include
the 50% of the
“U-values”
performance improvements, improvements, (i.e., (i.e., installation installation of of insulating insulating materials), materials), are limited limited due to to the the performance of each building
components. The interquartile
ranges
of opaque envelopeare (walls, roofs,due and floors)
conservation constraints. conservation constraints. result in being very compact, with median values ranging from 0.12 W/(m2 ·K) to 0.16 W/(m2 ·K):
A similar analysis similar analysis was was carried carried out out for all for all the the building building components (i.e., components (i.e., wall, wall, roof, roof, floor, floor, and and A windows), as shown in Figure 7. •windows), as shown in Figure 7. Walls between 0.11 W/(m2 ·K) and 0.17 W/(m2 ·K) (median U
at 0.14 W/(m2 ·K));
W-value
•
•
•
Roofs between 0.09 W/(m2 ·K) and 0.15 W/(m2 ·K) (median UR-value at 0.12 W/(m2 ·K));
Floors between 0.12 W/(m2 ·K) and 0.23 W/(m2 ·K) (median UF-value at 0.16 W/(m2 ·K));
Windows between 0.85 W/(m2 ·K) and 1.04 W/(m2 ·K) (median UWin-value at 0.96 W/(m2 ·K)).
This analysis confirms that he thermal transmittance of the nZEBs’ components is homogeneous
across the three climatic zones.
Buildings 2017, 7, x FOR PEER REVIEW Buildings
2017, 7, 43
9 of 22 9 of 22
(a)
(b)
(c)
(d)
Figure 7. Thermal transmittances of walls (a); roofs (b); ground floors (c) and windows (d) of nZEB Figure
7. Thermal transmittances of walls (a); roofs (b); ground floors (c) and windows (d) of nZEB in
in relation of the use of the buildings (residential and non‐residential) according to HDD. relation of the use of the buildings (residential and non-residential) according to HDD.
The breakdown for the building elements confirms the general trend identified for the average envelope U‐value; in fact, the performances of the building components present a weak correlation with the external climate conditions, as highlights by coefficient of determination (R2). The box plots 2∙K) to 0.16 W/(m
2∙K): 2∙K)); result in being very compact, with median values ranging from 0.12 W/(m

Walls between 0.11 W/(m2∙K) and 0.17 W/(m2∙K) (median UW‐value at 0.14 W/(m
2∙K) and 0.15 W/(m2∙K) (median UR‐value at 0.12 W/(m2∙K)); Roofs between 0.09 W/(m2∙K) and 0.17 W/(m
2∙K) (median UW‐value at 0.14 W/(m2∙K));  Walls between 0.11 W/(m
2∙K) and 0.23 W/(m2∙K) (median UF‐value at 0.16 W/(m2∙K)); 
Floors between 0.12 W/(m
2

Roofs between 0.09 W/(m ∙K) and 0.15 W/(m2∙K) (median UR‐value at 0.12 W/(m2∙K)); 2∙K) and 1.04 W/(m2∙K) (median UWin‐value at 0.96 W/(m2∙K)). 
Windows between 0.85 W/(m
2∙K) and 0.23 W/(m
2∙K) (median UF‐value at 0.16 W/(m2∙K)); 
Floors between 0.12 W/(m
2∙K) and 1.04 W/(m2∙K) (median UWin‐value at 0.96 W/(m2∙K)). 2017, 7, 43
Buildings
Windows between 0.85 W/(m
(a) 10 of 22
(b)
(a) (b)
Figure 8. Thermal transmittance of walls, roofs, floors (a) and windows (b). Figure 8. Thermal transmittance of walls, roofs, floors (a) and windows (b). Figure 8. Thermal transmittance of walls, roofs, floors (a) and windows (b).
This analysis confirms that he thermal transmittance of the nZEBs’ components is homogeneous across the three climatic zones. This analysis confirms that he thermal transmittance of the nZEBs’ components is homogeneous Figure
9 reports the share of insulating materials of walls and roofs. It is remarkable that “EPS” is
Figure 9 reports the share of insulating materials of walls and roofs. It is remarkable that “EPS” across the three climatic zones. the
most
common
material used in walls, while “stone wool” is the preferred option for roofs.
is the most common material used in walls, while “stone wool” is the preferred option for roofs. Figure 9 reports the share of insulating materials of walls and roofs. It is remarkable that “EPS” is the most common material used in walls, while “stone wool” is the preferred option for roofs. (a) (b)
(a) (b)
Figure 9. Share of insulating materials used in walls (a) and roofs (b). Note: the charts include the Figure
9. Share of insulating materials used in walls (a) and roofs (b). Note: the charts include the
buildings according to the collected information. buildings
according to the collected information.
Figure 9. Share of insulating materials used in walls (a) and roofs (b). Note: the charts include the buildings according to the collected information. It can be noticed that the “EPS” is used in 30% of the building for the wall insulation walls and It can be noticed that the “EPS” is used in 30% of the building for the wall insulation walls and
only for the 15% for the roofs. On the contrary, the use of “wood fiber” for roof insulation increases onlyIt can be noticed that the “EPS” is used in 30% of the building for the wall insulation walls and for the 15% for the roofs. On the contrary, the use of “wood fiber” for roof insulation increases
around 10% in comparison to the wall application. only for the 15% for the roofs. On the contrary, the use of “wood fiber” for roof insulation increases around 10% in comparison to the wall application.
In this regard, insulating materials with higher thermal capacity offer better performance during around 10% in comparison to the wall application. In this regard, insulating materials with higher thermal capacity offer better performance
during
the summer time, affecting positively the periodic thermal transmittance Y
mn (W/(m2∙K)) and thermal In this regard, insulating materials with higher thermal capacity offer better performance during 2
the summer time, affecting positively the periodic thermal transmittance Ymn (W/(m ·K)) and thermal
time shift (h) of the building envelope components. Although no information about these two the summer time, affecting positively the periodic thermal transmittance Y
mn (W/(m2∙K)) and thermal time shift (h) of the building envelope components. Although no information
about these two
parameters have been collected for the nZEB sample, we investigated which materials are used in time shift (h) of the components. Although no information about are
these two parameters
have
beenbuilding collectedenvelope for the nZEB
sample, we
investigated
which materials
used
in
parameters have been collected for the nZEB sample, we investigated which materials are used in 3
different climatic conditions, according to the mass (kg) and density (kg/m ) of the insulating materials.
Figure 10 shows the use of low and high density insulating materials in walls and roofs according to
the HDD and CDD.
Buildings 2017, 7, x FOR PEER REVIEW 11 of 22 different climatic conditions, according to the mass (kg) and density (kg/m3) of the insulating materials. Figure 10 shows the use of low and high density insulating materials in walls and roofs Buildings 2017, 7, 43
11 of 22
according to the HDD and CDD. (a)
(b)
Figure 10. Typology of the most common insulating material used in the walls (a) and in the roofs (b) Figure 10. Typology of the most common insulating material used in the walls (a) and in the roofs
of noted data nZEBs collected, in relation to the HDD and CDD and according to low and high density (b) of noted data nZEBs collected, in relation to the HDD and CDD and according to low and high
of insulating materials. density of insulating materials.
From a technical point of view, we expected a higher use of insulating materials with high Frommass a technical
point
of view, we expected a higher
use of insulating
with high
thermal
thermal in warm climates [23]. Nevertheless, the insulation adopted materials
in both cold and warm mass
inresults warm climates
[23]. Nevertheless,
adopted inno both
cold andinfluences warm zones
results
zones in being quite homogeneous the
in insulation
walls and roofs, and significant of the inclimate being quite
homogeneous
in walls and roofs,
and
no significant
climate
conditions
conditions on the insulation density can be observed. It is influences
important of
to the
point out that the building envelopes are composed by various layers of different materials that play together a relevant on
the insulation density can be observed. It is important to point out that the building envelopes are
role, and, by
in most of layers
the cases, the higher contribution to the thermal inertia from composed
various
of different
materials
that play
together
a relevantcomes role, and,
inmassive most of the
layers (e.g., bricks, stone, etc.). Therefore, choice of an insulating seems to be more etc.).
cases,
the
higher
contribution
to the
thermalthe inertia
comes
from
massivematerial layers (e.g.,
bricks,
stone,
influenced by other factors than by their performance in the cooling period. Therefore, the choice of an insulating material seems to be more influenced by other factors than by
Considering the characteristics of the windows, despite the expectations, we observed that their performance
in the
cooling period.
“triple glazing” systems are also applied on buildings located in cooling dominated climates, as Considering
the characteristics
of the windows,
despite
the expectations,
we observed
that “triple
shown in Figure 11. glazing” systems are also applied on buildings located in cooling dominated climates, as shown in
Figure 11.
Buildings 2017, 7, x FOR PEER REVIEW Buildings 2017, 7, x FOR PEER REVIEW Buildings
2017, 7, 43
12 of 22 12 of 22 12
of 22
Figure
11. Typology of the most common glass typologies of windows in nZEBs collected, in relation
Figure 11. Typology of the most common glass typologies of windows in nZEBs collected, in relation Figure 11. Typology of the most common glass typologies of windows in nZEBs collected, in relation to
the
HDD
and CDD.
to the HDD and CDD. to the HDD and CDD. Due to to the the lack lack of of more more specific specific information information concerning concerning the the double double glass glass coating coating (e.g., (e.g., low low Due Due
to
the
lack
of
more
specific
information
concerning
the
double
glass
coating
(e.g.,
low
emission, selective…), it is difficult to add further considerations. In fact, these glazing systems have emission, selective…), it is difficult to add further considerations. In fact, these glazing systems have emission, selective . . . ), it is difficult to add further considerations. In fact, these glazing systems
similar thermal transmittance, but but
different windows’ proprieties (e.g., glass emissivity) that can can similar thermal transmittance, but different windows’ proprieties (e.g., glass have
similar
thermal
transmittance,
different
windows’
proprieties
(e.g.,
glassemissivity) emissivity)that that
can
influence the choice of one or other glass according to the building context (orientation, dimension of influence the choice of one or other glass according to the building context (orientation, dimension of influence the choice of one or other glass according to the building context (orientation, dimension of
the windows, building use, etc.). In addition, the lack of reliability of the specific data hinders a more the windows, building use, etc.). In addition, the lack of reliability of the specific data hinders a more the
windows, building use, etc.). In addition, the lack of reliability of the specific data hinders a more
detailed analysis. As it can be seen in Figure 12, the thermal transmittances of triple glass windows detailed analysis. As it can be seen in Figure 12, the thermal transmittances of triple glass windows detailed
analysis. As it can be seen in Figure 12, the thermal transmittances of triple glass windows
are clearly lower in comparison to double and low‐e glazing typologies. However, in the case of low are clearly lower in comparison to double and low‐e glazing typologies. However, in the case of low are clearly lower in comparison to double and low-e glazing typologies. However, in the case of low
emission double
double glasses, the median of the the thermal thermal transmittance is just slightly slightly lower than the emission double glasses, the median of transmittance just lower the emission
glasses,
the
median
of the
thermal
transmittance
is justis slightly
lower than
thethan median
median in the simple double glass. For this reason, it can be deduced that, during the data collection, median in the simple double glass. For this reason, it can be deduced that, during the data collection, in
the simple double glass. For this reason, it can be deduced that, during the data collection, some
some double‐glazing with low emissivity properties were wrongly identified as a simple double glass. some double‐glazing with low emissivity properties were wrongly identified as a simple double glass. double-glazing with low emissivity properties were wrongly identified as a simple double glass.
Figure 12. Thermal transmittance according to the type of window glass. Figure 12. Thermal transmittance according to the type of window glass. Figure
12. Thermal transmittance according to the type of window glass.
4.3. Mechanical Ventilation 4.3. Mechanical Ventilation Buildings 2017, 7, 43
Buildings 2017, 7, x FOR PEER REVIEW 13 of 22
13 of 22 Buildings 2017, 7, x FOR PEER REVIEW 13 of 22 4.3. Mechanical
Ventilation
The use of mechanical ventilation in buildings ensure air exchange at a certain rate. It reduces the indoor carbon dioxide concertation, moisture, smoke or other possible contaminants. In addition, The use of mechanical ventilation in buildings ensure air exchange at a certain rate. It reduces The
use of mechanical ventilation in buildings ensure air exchange at a certain rate. It reduces the
the air‐movement improves the comfort of the occupants. the indoor carbon dioxide concertation, moisture, smoke or other possible contaminants. In addition, indoor
carbon dioxide concertation, moisture, smoke or other possible contaminants. In addition, the
From the improves
results of the
the comfort
analysis, be noticed that mechanical ventilation is a recurrent the air‐movement improves the comfort of the occupants. air-movement
of it thecan occupants.
technical solution in new and renovated nZEBs (share of 89%), as shown in Figure 13. This technology From the
the results
results of
of the
the analysis,
analysis, it
it can
can be
be noticed
noticed that
that mechanical
mechanical ventilation
ventilation is recurrent From
is aa recurrent
is used without any relevant difference in warm, mild and cold climates. Only in 11% of the selected technical solution in new and renovated nZEBs (share of 89%), as shown in Figure 13. This technology technical
solution in new and renovated nZEBs (share of 89%), as shown in Figure 13. This technology
nZEBs, the data any
information was not declared not and
defined during the data collection, for this is used without any relevant difference in warm, mild and cold climates. Only in 11% of the selected is used without
relevant difference
in warm,or mild
cold climates.
Only
in 11%
of the selected
reason in these cases the results are defined as “unknown”. nZEBs, the data information was not declared or not defined during the data collection, this nZEBs, the data information was not declared or not defined during the data collection, for thisfor reason
reason in these cases the results are defined as “unknown”. in
these cases the results are defined as “unknown”.
Figure 13. Mechanical ventilation systems declared. Figure 13. Mechanical ventilation systems declared.
Figure 13. Mechanical ventilation systems declared. In order to reduce the increasing heating and cooling demands due to the replacement of the indoor air with the outside air, most of the mechanical ventilation systems include heat recovery. In order to reduce the increasing heating and cooling demands due to the replacement of the In
order to reduce the increasing heating and cooling demands due to the replacement of the
These permit recovering heat or cold from the outgoing air to pre‐heat or pre‐cool the indoor systems air most of indoor
air with with the the outside air, outside air, most
of the the mechanical mechanical ventilation ventilation systems systems include include heat heat recovery. recovery.
incoming fresh air. The high efficiencies of the heat recovery systems (over 80%), as declared in data These systems
systems permit
permit recovering heat or cold the outgoing air to pre‐heat or the
pre‐cool the These
recovering
heat
or cold
fromfrom the outgoing
air to pre-heat
or pre-cool
incoming
collected, make their use very frequent in ventilation systems in new and renovated buildings, and incoming fresh air. The high efficiencies of the heat recovery systems (over 80%), as declared in data fresh air. The high efficiencies of the heat recovery systems (over 80%), as declared in data collected, make
they are commonly used (84%), as the Figure 13. This is also in line with the results of the survey collected, make their use very frequent in ventilation systems in new and renovated buildings, and their
use very frequent in ventilation systems in new and renovated buildings, and they are commonly
carried out within EU IEE ZEBRA2020 project to building professionals, in which 92% of the they are commonly used (84%), as the Figure 13. This is also in line with the results of the survey used (84%), as the Figure 13. This is also in line with the results of the survey carried out within EU IEE
respondents adopt “sometimes” or “often” heat recovery systems in ventilation when constructing carried out project
within to
EU IEE ZEBRA2020 project to building professionals, which 92% of the ZEBRA2020
building
professionals,
in which
92% of the
respondents in adopt
“sometimes”
or
high‐energy efficient buildings [2]. respondents adopt “sometimes” or “often” heat recovery systems in ventilation when constructing “often” heat recovery systems in ventilation when constructing high-energy efficient buildings [2].
high‐energy efficient buildings [2]. 4.4. Heating System 4.4. Heating System
4.4. Heating System Concerning the different boiler configurations (i.e., combined and separate generation of heating Concerning the different boiler configurations (i.e., combined and separate generation of heating
and DHW), around 60% of analyzed nZEBs use one single system for both needs (heating + DHW). Concerning the different boiler configurations (i.e., combined and separate generation of heating and DHW),
around 60% of analyzed nZEBs use one single system for both needs (heating + DHW).
On the other hand, 26% use separated thermal systems for heating and DHW, and, for the rest of the and DHW), around 60% of analyzed nZEBs use one single system for both needs (heating + DHW). On the other hand, 26% use separated thermal systems for heating and DHW, and, for the rest of the
sample (14%), there is no information about the used systems (i.e., unknown), as shown in Figure 14. On the other hand, 26% use separated thermal systems for heating and DHW, and, for the rest of the sample
(14%), there is no information about the used systems (i.e., unknown), as shown in Figure 14.
sample (14%), there is no information about the used systems (i.e., unknown), as shown in Figure 14. Figure 14. Heating and DHW systems used in nZEBs collected.
Figure 14. Heating and DHW systems used in nZEBs collected. Figure 14. Heating and DHW systems used in nZEBs collected. Buildings 2017, 7, 43
Buildings 2017, 7, x FOR PEER REVIEW Buildings 2017, 7, x FOR PEER REVIEW 14 of 22
14 of 22 14 of 22 The most commonly used
used system
system to to produce heating and DHW is the the the
“heat pump”, with with
a The most commonly used system DHW is “heat pump”, with a The
most
commonly
to produce produceheating heatingand and
DHW
is
“heat
pump”,
presence of 32%, followed by “boiler” (23%) and “district heating” (14%), as shown in Figure 15. presence of 32%, followed by “boiler” (23%) and “district heating” (14%), as shown in Figure 15. a presence
of 32%, followed by “boiler” (23%) and “district heating” (14%), as shown in Figure 15.
Figure 15. Share of systems to produce heating and DHW in the selected nZEBs.
Figure 15. Share of systems to produce heating and DHW in the selected nZEBs. Figure 15. Share of systems to produce heating and DHW in the selected nZEBs. Figure
16 shows the share of the most used heating systems according to the climatic zone.
Figure 16 shows the share of the most used heating systems according to the climatic zone. The Figure 16 shows the share of the most used heating systems according to the climatic zone. The reduced number of buildings in the sample could affect the representativeness of the technologies The
reduced
number of buildings in the sample could affect the representativeness of the technologies
reduced number of buildings in the sample could affect the representativeness of the technologies used for the warm climates. Nevertheless, Figure 16 reports the share of heating systems of the three used
for the warm climates. Nevertheless, Figure 16 reports the share of heating systems of the three
used for the warm climates. Nevertheless, Figure 16 reports the share of heating systems of the three climatic zones. The “heat
“heat pump”
pump” is
is the
the most
most used used technology, technology, with a alower lower penetration in in
a cold cold climatic zones. The “heat pump” is the most in a climatic
zones.
The
used
technology,with witha lowerpenetration penetration
a cold
climatic zone (31%). This technology is widely adopted in warm‐mild climates (42%), since it allow climatic zone (31%). This technology is widely adopted in warm‐mild climates (42%), since it allow climatic
zone (31%). This technology is widely adopted in warm-mild climates (42%), since it allow for
for achieving high performance levels with mild external temperature, and it is commonly used to for achieving high performance levels with mild external temperature, and it is commonly used to achieving
high performance levels with mild external temperature, and it is commonly used to also
also satisfy the cooling needs in summer periods. also satisfy the cooling needs in summer periods. satisfy
the cooling needs in summer periods.
Figure 16. Share of heating systems according to climatic zones.
Figure 16. Share of heating systems according to climatic zones. Figure 16. Share of heating systems according to climatic zones. The
survey implemented within EU IEE ZEBRA2020 project to building professionals confirmed
The survey implemented within EU IEE ZEBRA2020 project to building professionals confirmed The survey implemented within EU IEE ZEBRA2020 project to building professionals confirmed that
“heat pumps” and “condensing boilers” are the most used heating systems, as shown in Figure 17.
that “heat pumps” and “condensing boilers” are the most used heating systems, as shown in Figure that “heat pumps” and “condensing boilers” are the most used heating systems, as shown in Figure 17. 17. Buildings 2017, 7, 43
Buildings 2017, 7, x FOR PEER REVIEW Buildings 2017, 7, x FOR PEER REVIEW 15 of 22
15 of 22 15 of 22 Figure
17.
Percentage
of
active
solutions
used
Source:
survey
implemented
to
building
Figure in nZEBs. Figure 17. 17. Percentage Percentage of of active active solutions solutions used used in
in nZEBs.
nZEBs. Source: Source: survey survey implemented implemented to to building building professionals
[2].
professionals [2]. professionals [2]. By analyzing the technology adopted during the last years, the trends for the heating systems in By analyzing the technology adopted during the last years, the trends for the heating systems in By
analyzing the technology adopted during the last years, the trends for the heating systems in
different climates highlight a constant use of heat pump systems in mild climates, and a reduction of different climates highlight a constant use of heat pump systems in mild climates, and a reduction of different
climates highlight a constant use of heat pump systems in mild climates, and a reduction
a boiler system with an increment of stove systems (Figure 18). In addition, it can be noticed that a boiler system with an increment of stove systems (Figure 18). In addition, it can be noticed that of
a boiler system with an increment of stove systems (Figure 18). In addition, it can be noticed that
“district heating” is very common in cold climates (normally in North and East Europe), probably “district heating” is very common in cold climates (normally in North and East Europe), probably “district
heating” is very common in cold climates (normally in North and East Europe), probably
because of the longer period, thus investing in this type of infrastructure is more profitable [24,25]. because of the longer period, thus investing in this type of infrastructure is more profitable [24,25]. because
of the longer period, thus investing in this type of infrastructure is more profitable [24,25].
Nevertheless, political reasons and national strategies could be also behind the high use of district Nevertheless, political reasons and national strategies could be also behind the high use of district Nevertheless,
political reasons and national strategies could be also behind the high use of district
heating in these countries. heating in these countries. heating
in these countries. Figure 18. Heating systems technologies trend according to climatic zones. Note: the heating systems
Figure 18. Heating systems technologies trend according to climatic zones. Note: the heating systems Figure 18. Heating systems technologies trend according to climatic zones. Note: the heating systems technology trend in warm climates has too few nZEBs to be presented.
technology trend in warm climates has too few nZEBs to be presented. technology trend in warm climates has too few nZEBs to be presented. The
energy carriers used by thermal systems in the collected buildings can be gathered in four
The energy carriers used by thermal systems in the collected buildings can be gathered in four The energy carriers used by thermal systems in the collected buildings can be gathered in four groups:
“natural
gas”, “district heating”, “electricity” and “RES” (e.g., firewood, wood pellets, wood
groups: “natural gas”, “district heating”, “electricity” and “RES” (e.g., firewood, wood pellets, wood groups: “natural gas”, “district heating”, “electricity” and “RES” (e.g., firewood, wood pellets, wood chips,
solar thermal . . . ), as shown in Figure 19.
chips, solar thermal…), as shown in Figure 19. chips, solar thermal…), as shown in Figure 19. Electricity
is the most used source for thermal systems (share of 28%) such as air, water, soil heat
Electricity is the most used source for thermal systems (share of 28%) such as air, water, soil heat Electricity is the most used source for thermal systems (share of 28%) such as air, water, soil heat pumps
and direct electric technologies.
pumps and direct electric technologies. pumps and direct electric technologies. Buildings 2017, 7, 43
Buildings 2017, 7, x FOR PEER REVIEW Buildings 2017, 7, x FOR PEER REVIEW 16 of 22
16 of 22 16 of 22 Figure 19. Share of energy carriers used by thermal plants. Figure 19. Share of energy carriers used by thermal plants. Figure
19. Share of energy carriers used by thermal plants.
4.5. Cooling System 4.5. Cooling System 4.5.
Cooling System
As previously said, the cooling needs to depend on several aspects like external climate As previously said,
said, the
the cooling
cooling needs
needs to
to depend
depend on
on several
several aspects
aspects like
like external
external climate
climate As
previously
conditions, use of the building (use profile, internal gains, etc.), building construction features (such conditions, use of the building (use profile, internal gains, etc.), building construction features (such conditions,
use of the building (use profile, internal gains, etc.), building construction features (such as
as window‐to‐wall ratio, etc.) and shading system, among others. as window‐to‐wall ratio, etc.) and shading system, among others. window-to-wall
ratio, etc.) and shading system, among others.
In addition, 25% of the selected nZEBs use a cooling system, divided between residential (46.5%) In addition, 25% of the selected nZEBs use a cooling system, divided between residential (46.5%) and non‐residential The box plot diagrams in system,
Figure 20 shows the CDD values of the In
addition, 25% of(53.5%). the selected
nZEBs
use
a cooling
divided
between
residential
(46.5%)
and non‐residential (53.5%). The box plot diagrams in Figure 20 shows the CDD values of the locations where the cooling system is installed both for residential and non‐residential buildings in and non-residential (53.5%). The box plot diagrams in Figure 20 shows the CDD values of the locations
locations where the cooling system is installed both for residential and non‐residential buildings in the sample. where
the cooling system is installed both for residential and non-residential buildings in the sample.
the sample. Figure
20. Distribution of CDD of residential and non-residential buildings with cooling systems.
Figure 20. Distribution of CDD of residential and non‐residential buildings with cooling systems. In In 75% of the residential buildings collected, the CDD results are equal to or higher than 510 CDD, while, 75% of the residential buildings collected, the CDD results are equal to or higher than 510 CDD,
in the non‐residential buildings, results are equal to or higher than 240 CDD. Figure 20. Distribution of CDD of residential and non‐residential buildings with cooling systems. In while,
in the non-residential buildings, results are equal to or higher than 240 CDD.
75% of the residential buildings collected, the CDD results are equal to or higher than 510 CDD, while, The results showed in Figure 20 highlights in most the cases (75%—first quartile), a in the non‐residential buildings, results are equal to or higher than 240 CDD. The
results
showed
in Figure
20 highlights
that,that, in most
of theof cases
(75%—first
quartile),
a cooling
cooling system in new nZEB is installed if the CDD are higher than 238 for non‐residential buildings system
in new nZEB is installed if the CDD are higher than 238 for non-residential buildings and for
and for CDD higher than 507 for residential buildings. The results in Figure 20 highlights that, in most of the cases (75%—first quartile), a CDD higher
thanshowed 507 for residential
buildings.
This difference confirms that the cooling energy consumption in non‐residential buildings is cooling system in new nZEB is installed if the CDD are higher than 238 for non‐residential buildings This difference confirms that the cooling energy consumption in non-residential buildings is
higher than in residential ones [26]. In fact, non‐residential buildings have higher internal loads due and for CDD higher than 507 for residential buildings. higher
than in residential ones [26]. In fact, non-residential buildings have higher internal loads due to
to the considerable use of appliances and lighting [27], and they are mainly occupied during daytime This difference that and
the cooling consumption in non‐residential buildings is the considerable
use confirms of appliances
lightingenergy [27], and
they are mainly
occupied during
daytime
hours, i.e., when the radiation and temperatures are higher. Missed information, like wall‐window higher than in residential ones [26]. In fact, non‐residential buildings have higher internal loads due hours,
i.e., when the radiation and temperatures are higher. Missed information, like wall-window
ratio (WWR) or orientation, reduce the possibility to go deeply in the nZEB features’ analysis of their to the considerable use of appliances and lighting [27], and they are mainly occupied during daytime ratio
(WWR)
influence. or orientation, reduce the possibility to go deeply in the nZEB features’ analysis of
hours, i.e., when the radiation and temperatures are higher. Missed information, like wall‐window their influence.
ratio (WWR) or orientation, reduce the possibility to go deeply in the nZEB features’ analysis of their influence. Buildings 2017, 7, 43
Buildings 2017, 7, x FOR PEER REVIEW 17 of 22
17 of 22 The most used cooling systems are “heat pumps” with a share of 75% and in particular the “heat The
most used cooling systems are “heat pumps” with a share of 75% and in particular the “heat
pumps using the outside air as heat source” (share of 13%), as shown in Figure 21. The advantages pumps
using the outside air as heat source” (share of 13%), as shown in Figure 21. The advantages
originated from this kind of technology, such as the satisfaction of the heating and cooling demands, originated
from this kind of technology, such as the satisfaction of the heating and cooling demands, the
the energy
low energy costs the environmental friendliness of this system (for the reduced carbon low
costs and
theand environmental
friendliness
of this system
(for
the reduced
carbon
emissions),
emissions), foster their implementation in nZEBs. foster
their implementation in nZEBs.
Figure 21. Share of cooling system typologies used in selected nZEBs (a total of 101 buildings with
Figure 21. Share of cooling system typologies used in selected nZEBs (a total of 101 buildings with cooling systems).
cooling systems). 4.6.
Passive Solutions
4.6. Passive Solutions Passive
Passive solutions
solutions in
in buildings
buildings are
are climate-based
climate‐based design
design measures
measures used
used to
to reduce
reduce the
the energy
energy demand
of
the
building
by
exploiting
the
natural
resources
available
in
the
context
(e.g.,
daylighting,
demand of the building by exploiting the natural resources available in the context (e.g., daylighting, natural
ventilation, night cooling, etc.).
natural ventilation, night cooling, etc.). The
use of these strategies result in being very important in high-energy efficient buildings, as their
The use of these strategies result in being very important in high‐energy efficient buildings, as implementation
can produce
an important
decreasedecrease of the energy
demand.
potential
their implementation can produce an important of the energy This
demand. This reduction
potential depends
on
the
set
of
passive
solutions
applied
and
on
the
climate
context.
In
cold
climates,
highly
reduction depends on the set of passive solutions applied and on the climate context. In cold climates, insulated
and airtight
have to face
high
risk [28], which
bewhich significantly
highly insulated and buildings
airtight buildings have to overheating
face high overheating risk can
[28], can be reduced
by
means
of
natural
ventilation
[29].
In
warm
climates,
a
reduction
of
internal
and
solar loads
significantly reduced by means of natural ventilation [29]. In warm climates, a reduction of internal implies
energy savings due to a reduction in the utilization of air conditioning.
and solar loads implies energy savings due to a reduction in the utilization of air conditioning. In
this regard, the lack of information concerning the usage of passive strategies in the collected
In this regard, the lack of information concerning the usage of passive strategies in the collected nZEBs
is
a weak point of this investigation. From one side, the missing data depend on the lack of
nZEBs is a weak point of this investigation. From one side, the missing data depend on the lack of answers
due
to the
answers due to the open
open questions
questions used
used to
to outline
outline the
the passive
passive solutions.
solutions. On
On the
the other
other side,
side, some
some passive
are
mandatory
in some
countries,
suchsuch as shading
systems
or green
hence,
passive strategies
strategies are mandatory in some countries, as shading systems or roofs,
green and,
roofs, and, they
could not be identified as additional passive solutions in the data sources. Although the high
hence, they could not be identified as additional passive solutions in the data sources. Although the importance
for the reduction of the energy demand, only 36% of the collected buildings (150 nZBEs)
high importance for the reduction of the energy demand, only 36% of the collected buildings (150 declared
the
use of passive strategies, as shown in Figure 22.
nZBEs) declared the use of passive strategies, as shown in Figure 22. Nevertheless, we can also deduce significant results from the reduced sample: in particular, the
most mentioned passive strategies are the sunshade (80%), natural ventilation (63%), night cooling
(59%) and thermal mass (57%).
Buildings 2017, 7, x FOR PEER REVIEW 18 of 22 Buildings
2017, 7, 43
Buildings 2017, 7, x FOR PEER REVIEW 18
of 22
18 of 22 Figure 22. Share of known passive strategies used in nZEBs. Nevertheless, we can also deduce significant results from the reduced sample: in particular, the most mentioned passive strategies are the sunshade (80%), natural ventilation (63%), night cooling (59%) and thermal mass (57%). Figure
22. Share of known passive strategies used in nZEBs.
Figure 22. Share of known passive strategies used in nZEBs. 4.7. Renewable Energy 4.7. Renewable
Energy
Nevertheless, we can also deduce significant results from the reduced sample: in particular, the In this part, the RE production systems were analyzed. In particular, the focus of the most mentioned passive strategies are the sunshade (80%), natural ventilation (63%), night cooling In this part, the RE production systems were analyzed. In particular, the focus of the investigation
investigation was on Solar Thermal (ST) and Photovoltaic (PV) Systems installed. (59%) and thermal mass (57%). was on Solar Thermal (ST) and Photovoltaic (PV) Systems installed.
It is apparent that the integration of renewables is crucial in an nZEB; in fact, it occurs in 81% of It is apparent that the integration of renewables is crucial in an nZEB; in fact, it occurs in 81% of
4.7. Renewable Energy the cases in the sample, since most of the national definitions require a minimum amount of energy the cases in the sample, since most of the national definitions require a minimum amount of energy
produced from RES according to the indications of the EPBD. In particular, the installation of PV In this part, RE production systems of
were In particular, the focus of the produced
from
RESthe according
to the indications
the analyzed. EPBD. In particular,
the installation
of PV
accounts for 29% of the sample, and ST systems is around 28%, as shown in Error! Reference source investigation was on Solar Thermal (ST) and Photovoltaic (PV) Systems installed. accounts
for 29% of the sample, and ST systems is around 28%, as shown in Figure 23. Finally, the 24%
not found.. Finally, the 24% of nZEBs collected uses both systems (PV and ST systems), while, in 19% It is apparent that the integration of renewables is crucial in an nZEB; in fact, it occurs in 81% of of nZEBs
collected uses both systems (PV and ST systems), while, in 19% of the cases, the detailed
of the cases, the detailed information is missed. the cases in the sample, since most of the national definitions require a minimum amount of energy information
is missed.
produced from RES according to the indications of the EPBD. In particular, the installation of PV accounts for 29% of the sample, and ST systems is around 28%, as shown in Error! Reference source not found.. Finally, the 24% of nZEBs collected uses both systems (PV and ST systems), while, in 19% of the cases, the detailed information is missed. Figure
23. Share of installation of PV and solar thermal systems.
Figure 23. Share of installation of PV and solar thermal systems. Error! 24
Reference not the share of exploitation
different technologies RES Figure
presents source the share
of found. differentpresents technologies
for RES
in the three for defined
exploitation in the three defined climatic zones. It is possible to underline a reduced integration of climatic
zones. It is possible to underline a reduced integration of PV and ST in nZEBs located in
PV and ST in nZEBs located in cold climates zone than in mild climates (44% vs. 60%), mainly due to cold
climates zone than
in mild climates (44% vs. 60%), mainly due to less sunlight availability in
Figure 23. Share of installation of PV and solar thermal systems. less sunlight availability in higher latitudes. In particular, the cold climate zone does not higher
latitudes.
In particular,
while the
cold climate
zone doeswhile not present
a significant
wide diffusion
present a significant wide diffusion of a specific technology, the mild climate zone shows a high share of
a specific
technology,source the mild
climate
zone
shows the a high
share
photovoltaic
system installed
Error! Reference not found. presents share of ofdifferent technologies for RES of photovoltaic system installed with
(45% considering plants coupled with ST). Finally, the
in number
the warm (45%
considering
plants
coupled
ST).
Finally,
in
the
warm
climate
zone,
although
of
exploitation in the three defined climatic zones. It is possible to underline a reduced integration of buildings
in the sample reduced and the representativeness of the sample is lower, a higher share of
PV and ST in nZEBs located in cold climates zone than in mild climates (44% vs. 60%), mainly due to nZEBs
with STavailability is observedin (41%
considering
plants
coupled with
PV).
less sunlight higher latitudes. In particular, while the cold climate zone does not present a significant wide diffusion of a specific technology, the mild climate zone shows a high share of photovoltaic system installed (45% considering plants coupled with ST). Finally, in the warm Buildings 2017, 7, x FOR PEER REVIEW Buildings 2017, 7, x FOR PEER REVIEW 19 of 22 19 of 22 climate zone, although the number of buildings in the sample reduced and the representativeness of climate zone, although the number of buildings in the sample reduced and the representativeness of the sample is lower, a higher share of nZEBs with ST is observed (41% considering plants coupled the sample is lower, a higher share of nZEBs with ST is observed (41% considering plants coupled Buildings
2017, 7, 43
19 of 22
with PV). with PV). Figure 24. Share of PV and ST systems installed according to climatic zones.
Figure 24. Share of PV and ST systems installed according to climatic zones. Figure 24. Share of PV and ST systems installed according to climatic zones. Figure
25 shows the share of buildings with one or more renewable energy systems installed, also
Figure 25 shows the share of buildings with one or more renewable energy systems installed, Figure 25 shows the share of buildings with one or more renewable energy systems installed, also including the heat pumps in the considered technologies. also including the heat pumps in the considered technologies. including the heat pumps in the considered technologies.
Figure 25. Share of renewable energy systems installed (heat pumps, PV and ST) in the nZEBs analyzed.
Figure 25. 25. Share Share of of renewable renewable energy energy systems systems installed installed (heat (heat pumps, pumps, PV PV and and ST) ST) in in the the nZEBs nZEBs Figure analyzed. analyzed. It is important also to point out that, for cold climates, six percent of the buildings (26 buildings)
It is important also to point out that, for cold climates, six percent of the buildings (26 buildings) It is important also to point out that, for cold climates, six percent of the buildings (26 buildings) declared
no renewable energy system (heat pumps, PV or ST) installed. This share results in being
declared no renewable energy system (heat pumps, PV or ST) installed. This share results in being declared no renewable energy system (heat pumps, PV or ST) installed. This share results in being very
low in relation to the previous outcome of Figure 24, where 41% of cases declared no PV or ST
very low in relation to the previous outcome of Error! Reference source not found., where 41% of very low in relation to the previous outcome of Error! Reference source not found., where 41% of systems
installed. This information further highlights the large use of heat pumps in cold climates.
cases declared no PV or ST systems installed. This information further highlights the large use of heat cases declared no PV or ST systems installed. This information further highlights the large use of heat Similar
considerations are valuable also for mild and warm climates. The thermal system used in all
pumps in cold climates. Similar considerations are valuable also for mild and warm climates. The pumps in cold climates. Similar considerations are valuable also for mild and warm climates. The these
buildings for heating and DHW are traditional or condensing boiler fuelled mainly by natural
thermal system used in all these buildings for heating and DHW are traditional or condensing boiler gasthermal system used in all these buildings for heating and DHW are traditional or condensing boiler (96%) and direct electric technologies (4%), without any photovoltaic, thermal panels, heat pumps
fuelled mainly by natural gas (96%) and direct electric technologies (4%), without any photovoltaic, or fuelled mainly by natural gas (96%) and direct electric technologies (4%), without any photovoltaic, other
bio-fuel system installed. Furthermore, these buildings are located in mild-cold climates
where heating during the winter is necessary. The lack of use of renewable energy systems in some
nZEBs is mainly due to the construction period of these buildings, since, in some cases, they were built
before the EPBD implementation at the national level, and due to the lack of information during the
data collection.
Buildings 2017, 7, 43
20 of 22
5. Conclusions
This paper aims to identify the main technologies adopted across Europe in the construction as
well as in the renovation of buildings towards the target nZEBs. In particular, we evaluated to which
extent the adoption of the technologies is influenced by the climate conditions.
The analysis was based on a sample of 411 representative European high energy performance
buildings (new and renovated, residential and non-residential) mainly located in mild-cold climates,
whose features have been collected within the EU IEE ZEBRA2020 project.
As a general outcome, we can deduce that the climate conditions do not represent the main
parameter affecting the definition of the technology package to achieve the nZEB target. Nevertheless,
we can highlight that the availability of natural sources in the zones (i.e., solar irradiation) affects the
use of renewable technologies. In fact, we observed a reduced share of PV and ST in cold climates and
an increased share in mild and warm climates, due to the higher irradiation and production potential
that enhance the cost-effectiveness of the technologies.
This result was confirmed by the survey to building professionals carried out within EU IEE
ZEBRA2020 project [2]. In fact, only 3.5% of the respondents selected “the adaptability to climatic
context” as an important criteria for adopting a specific technology, while the “investment costs” (27%),
“energy performance” (16%) and “operational cost” (14%) were the preferred ones.
The heating demand analysis shows that energy efficiency technological solutions are selected
independently to the climate condition. The heating demand values of the buildings are similar in
all climates, as well as the thermal transmittance of the envelope components (both transparent and
opaque). This is mainly influenced by the similar national envelope minimum requirements defined
across Europe. Moreover, the HDD and CDD do not even influence so strongly the choice of the
insulating materials and their associated properties (high or low thermal inertia).
Concerning the active solutions, the recurrent technologies are the mechanical ventilation, with
a share of 89% in the sample and a high penetration of heat recovery systems (able to supply heating,
DHW and cooling demand). In cold climate zones, the district heating systems is widely used,
accounting for 25%.
Within the analyzed sample, the cooling system is installed in 25% of the buildings, and we
identified the thresholds for the installation of such systems around 240 CDD for non-residential
buildings, and 510 CDD for residential ones.
As a general remark, it is important to point out that the building data collection was carried out
from EPCs, building databases and reports on energy efficiency buildings. The size of the analyzed
buildings sample is relatively small (411 buildings) due to the reduced amount of available data, and
the lack of existing nZEB information; moreover, it has different levels of accuracy as a result of the
heterogeneous collection process (EPCs, building databases and reports on energy efficiency buildings).
In some cases, the limited level of detail of the data reduced the possibilities to investigate deeply the
technology market penetration and its relation to the climate conditions.
Moreover, one of the most critical issues across Europe is the heterogeneous calculation approach
for the energy performance indicators. The EPBD introduced the general nZEB concept to the European
Member States, while national and regional regulations defined tailored calculation methods and
targets in terms of both primary energy and share of renewable energy. This means that performance
indicators are evaluated with different calculation methods, boundary conditions (i.e., base internal
temperature), and conversion factors. At the European level, more efforts should be made to harmonize
the calculation methods and the boundary conditions, and to make building energy consumption data
available. Moreover, an open accessible European EPC cadaster, also including construction costs and
actual energy consumption data, would represent a strategic tool to define the nZEB learning curve,
assess the relative rate of penetration in the building stock, and give meaningful information to manage
decision process of relevant stakeholders (developers, designers, builders, and manufacturers).
Further analysis should be performed increasing the number of case studies, especially in warm
climates, and investing more efforts during the data collection phase, raising the detail level and
Buildings 2017, 7, 43
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taking into account the local specificities, as well as the minimum requirements provided by law
and incentives as the main drivers for the technologies. Future studies should include the analysis
of the costs and the influence on the adoption of the technologies, also considering that the nZEB
requirements should be set according to cost-optimal levels and Life Cycle Assessment (LCA) as
requested in the EPBD recast.
Nevertheless, this work is a pioneering study on European nZEB stock and the results of the
analysis present an overview of the main technologies adopted in new and renovated nZEBs in
Europe, and represent an important step for the definition of design guidelines with the most effective
solutions. Furthermore, the identification of the most used technology solutions in relation to the
climate condition should be used from building manufactories in order to identify the building market
needs and address the efforts.
Acknowledgments: This work was supported by EU IEE ZEBRA2020 project that has financed the investigation.
We thank to the efforts invested by the EU IEE ZEBRA2020 project partners, especially to the project coordinator
Raphael Bointner, who recently passed away, and to our colleagues Annamaria Belleri, Giuseppe De Michele and
Sofia Rioli for the feedback during the works.
Author Contributions: Ramón Pascual Pascuas contributed with the collection of nZEBs data, Giulia Paoletti
carried out the analysis concept, and together interpreted the data and wrote the paper. Roberta Pernetti
supervised the data analysis and composition of the paper. Roberto Lollini revised the article.
Conflicts of Interest: The authors declare no conflict of interest.
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© 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
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