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Old buildings that represent and maintain historic values often have poor indoor conditions and energy efficiency. The aim of this work was to evaluate the influence of building structures on airtightness and energy performance of certain historic building types. In this study on-site measurements, dynamic simulation and questionnaires were used. Significant differences between the levels of the airtightness of the historic houses exist in the studied region. No statistically significant correlation was found between the structure types and the envelope tightness. The typical air leakage places of the studied houses were at the junctions of the envelope structures. Measured air exchange rates indicated that the level of ventilation is insufficient in some of the houses while some are too leaky. If the airtightness of the naturally ventilated house is improved, the acceptable ventilation rate has to be guaranteed. Tightening the envelope and moving from natural to mechanical ventilation was the most effective way to improve the indoor conditions and energy performance.
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International Journal of Ventilation ISSN 1473-3315 Volume 14 No 1 June 2015
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Airtightness, Air Exchange and Energy Performance in Historic
Residential Buildings with Different Structures
Lari Eskola1, Ûllar Alev2, Endrik Arumägi3,2, Juha Jokisalo1, Anna Donarelli3, Kai Sirén1
and Targo Kalamees2
1Aalto University, Finland
2Tallinn University of Technology, Estonia
3Uppsala University, Sweden
Abstract
Old buildings that represent and maintain historic values often have poor indoor conditions and energy
efficiency. The aim of this work was to evaluate the influence of building structures on airtightness and energy
performance of certain historic building types. In this study on-site measurements, dynamic simulation and
questionnaires were used. Significant differences between the levels of the airtightness of the historic houses
exist in the studied region. No statistically significant correlation was found between the structure types and the
envelope tightness. The typical air leakage places of the studied houses were at the junctions of the envelope
structures. Measured air exchange rates indicated that the level of ventilation is insufficient in some of the
houses while some are too leaky. If the airtightness of the naturally ventilated house is improved, the acceptable
ventilation rate has to be guaranteed. Tightening the envelope and moving from natural to mechanical
ventilation was the most effective way to improve the indoor conditions and energy performance.
Key words: airtightness, air exchange, dynamic simulation, energy performance, historic buildings.
1. Introduction
The Energy Performance of Buildings Directive
(EPBD) of the European Union requires the energy
performance of buildings to be enhanced (Council
Directive 2010/31/EU of 19 May 2010). At the
moment European countries are developing national
regulations to comply. However the requirements set
may be incongruent to the requirements for
traditional and historic buildings although officially
protected buildings can be excluded from energy
performance requirements.
In the Baltic Sea area, national boards of antiquities,
open air museums and cultural heritage societies are
making efforts to preserve old buildings and
construction methods (National Board of Antiquities,
2012; Cultural Heritage, 2013). Old buildings often
have problems with air leakage and indoor conditions
(Saı
̈d et al., 1999; Papadopoulos et al., 2003; Yardim
and Tuncoku, 2008) and they need professional
maintenance and renovation if they are to be
preserved. It can be concluded from previous studies
(Cantin et al., 2010; Avdelidis et al., 2004; Vissilia
and Villi, 2010; Ascione et al., 2011) that
multifaceted approaches are required to study historic
buildings. As structures and building typology differ
in historic buildings, special analyses of airtightness
and energy performance are needed.
The airtightness of structures and energy efficiency
of buildings has been reported in many studies
(Desmarais et al., 2000; Orme et al., 1998;
Ruotsalainen et al., 1992; Sherman and Dickerhoff,
1998; Hamlin and Gusdorf, 1997; Janssens and
Hens, 2003; Younes et al., 2011). However, in the
investigations of historic residential buildings in the
Baltic area these features remain unknown.
The aim of this study was to determine the influence
of a building structure on the airtightness and energy
performance of certain historic building types in the
Baltic region. In this context a house built before
1940 is qualified as “historic”. The houses under
consideration are located in the Baltic Sea region:
Estonia, Finland and Sweden where the climate
conditions are quite similar but clearly the buildings
are country specific.
2. Houses
A total of 68 historic houses were investigated
which were built between the years 1650 to 1938
(Figure 1). Some of the houses are unheated and
unused during the winter season.
The building material used in traditional rural houses
in Estonia and Southern Finland is wood. Walls are
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L Eskola, Û Alev, E Arumägi, J Jokisalo, A Donarelli, K Sirén and T Kalamees
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mostly built of logs. In Gotland the investigated
houses are mainly built of stone (Figure 2).
2.1 Estonian Houses
Twenty four wooden houses were investigated in
Estonia. Ten houses are inhabited permanently, six
are used occasionally during winter and
permanently in the summer and eight are used only
in the summer. Major or minor renovations have
been undertaken in all the investigated houses.
In Estonia the predominant historic farmhouse is a
barn-dwelling (Figure 3). This has one storey with
an attic and a high roof. It serves both as a living
and husbandry building and consists of three main
parts i.e. a kiln-room, a threshing room and
bedrooms. The kiln-room serves as a living and
working room all year round, although in autumn it
was used to dry grain.
2.2 Finnish Houses
Twenty wooden houses were investigated in Finland
(Figure 4). Four of them serve as open air museums.
Both small single-family houses and houses with
three apartments were included. Fifteen of the
investigated houses are inhabited permanently, one
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Figure 1. Construction time and heated floor area of the investigated houses.
Figure 2. Typical structures in a) Estonia, b) Finland, and c) Sweden.
International Journal of Ventilation ISSN 1473-3315 Volume 14 No 1 June 2015
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is used occasionally during winter and permanently
in the summer and four are used only in the summer.
2.3 Swedish Houses
Out of the 24 houses investigated, 22 were built
of stone and 2 of wood between the middle of the
17th century and 1929 (Figure 5). Both small
farmsteads and larger mansions were studied. Six
houses are inhabited permanently, nine are used
occasionally during winter and permanently in
the summer and nine are used only in the
summer.
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Figure 3. Estonian example house and floor plan.
Figure 4. Finnish example house and floor plan.
Figure 5. Swedish example house and floor plan.
L Eskola, Û Alev, E Arumägi, J Jokisalo, A Donarelli, K Sirén and T Kalamees
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3. Methodology
3.1 Measurements
The purpose of the measurements was to determine
the airtightness and typical leakage locations of
historic buildings. Airtightness was measured in all
buildings. Other airtightness related properties were
investigated in selected buildings, mainly to support
energy simulations. Measurements were made
during the years 2010-2012. The construction types,
systems and use of the houses were investigated
using a questionnaire.
3.1.1 Airtightness
The airtightness of each building was measured
according to a standardized (EN 13829, 2001) fan
pressurization method with an automated
performance testing system. To compare the
tightness of different houses, the airflow rate at a
pressure difference of 50 Pa was divided by the
building’s total envelope area, resulting in the air
leakage rate q50, (m3/h.m2).
3.1.2 Location of Leakages
To determine air leakage locations and their
distribution around the building envelope, internal
surface temperatures were measured during winter
using an infrared camera (Kauppinen, 2001).
First, to find thermal bridges, imaging was
undertaken without pressurization and then to
induce leakage, thermal imaging was undertaken
in conjunction with pressurization. By comparing
the two thermal images it was possible to find the
leakage paths.
3.1.3 Air Exchange Rate
All selected houses were naturally ventilated. The
air change rate was measured using a passive
tracer gas method (Sandberg, 1989) (accuracy
± 5%), which gives an average value of the supply
airflow during the measurement period. The
method is based on passive sources and sampling
tubes.
The indoor-outdoor temperature difference is an
important driving force for air exchange. Indoor air
temperatures were measured in different rooms with
temperature loggers and outdoor air temperature
was measured close to each house. The
measurement period for each house was at least a
year.
To compare different tracer gas measurement results
between different countries and different climate
conditions, a climate correction was made. This was
based on the assumption that the difference between
the measured air change rate in different climatic
conditions is equal to the difference between the
simulated air change rate in the corresponding
climatic conditions. Thus, the following equation
was used to correct the air change rate:
ACHmref = ACHmlocACHsloc + ACHsref (1)
where:
ACHmref is the corrected air change rate value
corresponding to reference climatic
conditions [1/h],
ACHmloc is the measured air change rate value in
local climatic conditions [1/h],
ACHsloc is the simulated air change rate using local
climate data [1/h], and
ACHsref is the simulated air change rate using
reference climate data [1/h].
The reference climate conditions were selected from
a weather station close to an average of Estonian
weather during the tracer gas measurement period.
The indoor temperature used for the reference
simulation was calculated as an average temperature
from all Estonian houses. The simulated total air
change rates were composed from hourly simulation
results.
3.1.4 Structures, Systems and Use of Buildings
Information about the structures, heating systems,
ventilation and sanitary systems was gathered from
occupants using a questionnaire. The survey also
contained questions about energy consumption and
use of systems and buildings in general as well as
occupants’ habits, typical perceptions, complaints,
and symptoms related to the indoor climate.
Additionally, some structures, such as foundation,
roof, crawl space, external walls, floors, and
windows, were studied more closely with material
non-destructive methods.
3.2 Simulations
The objective of the simulations was to determine
the effect of airtightness on the air exchange rate
and the energy performance of the buildings.
Simulation models were based on real buildings but
the energy technical features, such as insulation,
window type and heating system, were chosen to
represent all studied buildings from each country.
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International Journal of Ventilation ISSN 1473-3315 Volume 14 No 1 June 2015
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Simulations were made using the IDA Indoor
Climate and Energy 4.2 (IDA-ICE) dynamic
building simulation tool (Sahlin et al., 2004). This
software allows the modelling of multi-zone
buildings, HVAC systems, internal and solar loads,
and outdoor climate and provides simultaneous
dynamic simulation of heat transfer and air flows
with variable time step. IDA-ICE has been validated
in different case studies, for example by Achermann
and Zweifel (2003) and Woloszyn and Rode (2008).
Three simulation models were constructed for the
air exchange and energy simulations, one for each
example house. The simulation model of the Finnish
example house was based on an old two-floor log
house (Figure 4). Only the first floor is heated. The
house has five rooms, a kitchen, a bathroom and a
cold porch on the first floor. In the cold attic there
are two bedrooms to be used in the summer time.
Similar models were created for the Estonian and
Swedish example houses. Table 1 shows details of
the properties of an average house based on all the
houses investigated in each country. Leakage routes
in the simulation models were distributed according
to the results of the infrared imaging.
The simulation model was validated by comparing
simulated indoor air temperature and air exchange
rate against the measured values. The properties of
the example houses and hourly weather data of the
validation periods were used. Outdoor temperature
and relative humidity measured next to the example
houses and other weather quantities (wind speed,
solar radiation etc.) measured at the closest weather
station were used in the validation simulations. The
behaviour of the occupants (presence of the
occupants, use of lighting and equipment, etc.)
during the validation periods was simulated in
accordance with the occupants’ survey. A four-
person family was used as a user profile for internal
heat gains. Annual internal heat gains were
10.5 kWh/m2 from occupants, 12.6 kWh/m2 from
equipment and 7 kWh/m2 from lighting.
Weather data for these simulations were acquired
from the Finnish and Estonian Test Reference Years
(Kalamees et al., 2012; Kalamees et al., 2006).
Swedish weather data were acquired from the data
measured at the weather station in Gotland, Visby in
2000. The annual average outdoor temperatures are
5.7 °C in Estonia, 5.6 °C in Finland and 6.2 °C in
Sweden. Average wind velocities are 3.8 m/s in
Estonia, 4.1 m/s in Finland and 6.1 m/s on the
Gotland island of Sweden.
3.3 Statistical Analysis
The aim of the statistical analysis was to find out if
different structures have significant influence on the
airtightness of the selected buildings. The difference
was tested with the ANOVA analysis method
(Lehmann, 1959). When the ANOVA test leads to
significant results, then at least one of the samples is
different from the other samples. The hypothesis of
the test was that there is no difference between the
structural features and they have no influence on the
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Table 1. Structures, areas and q50 of original validated simulation models and average.
Estonia Finland Sweden
Average Example Average Example Average Example
house house house house house house
Area, m2
I Floor 75 75 181 181 120 120
II Floor 124 124
U-value, W/(m2,K)
External wall 0.61 0.61 0.57 0.52 1.82 1.82
Roof/attic floor 0.41 0.41 0.37 0.37 0.68 0.33
Base floor 0.48 0.41 0.37 0.37 0.32 0.32
Window 2.9 2.9 2.8 2.8 2.9 2.7
Air leakage rate, q50
m3/(h m2) 15.8 6.4 13 8.6 17.4 14.8
L Eskola, Û Alev, E Arumägi, J Jokisalo, A Donarelli, K Sirén and T Kalamees
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level of airtightness. This was tested using a
confidence level α = 0.05.
Because of the wide range of q
50 measurement
results, different structural factors should exist to
explain variations in airtightness. In the following
analysis, the structures are categorized and analyzed
by their characteristics to find out if different
structural features have an effect on airtightness in
the investigated houses. Several assumptions are
necessary to use the ANOVA test:
the samples are independent and random;
the response variable is normally distributed
within each population;
the different populations may have different
means;
all populations have the same standard deviation.
4. Results and Analysis
4.1 Airtightness
The measured values of the airtightness of the
studied buildings are presented and discussed
below. Building airtightness is expressed by the
average air leakage rate q50 (m3/h.m2) at a pressure
difference of ±50 Pa. Figure 6 shows all the
resulting q50 values and their average values
measured in each country.
The range of the measured q50 values was large,
from 3.9 to 35.2 m3/h.m2 (Figure 6). The q50 values
were analyzed with the questionnaire results and
the collected information on the building structures
in order to find out the factors that affect
airtightness.
First, the analysis showed some common
characteristics of the influencing factors. It was
found that in the four houses of q50 less than
8 m3/h.m2, a major renovation of the envelope
structures (for example, external wall, ceiling or
base floor structures) had been made. Additionally,
the Estonian houses with q50 less than 8 m3/h.m2 had
all internal surfaces, except floors, covered with
plaster and paint or wallpaper. However, 8 houses
with a q50 between 9 and 16 m3/h.m2 had also been
renovated. This showed that most of the renovated
houses were still quite leaky even after renovation.
It was also found that the leakiest 8 houses with q50
greater than 21 m3/h.m2 are either museum
buildings, usually moved and rebuilt, or under major
renovation during measurements, or used only in the
summer time.
The ANOVA test was used to study if there was a
statistically significant relation between the
measured q50 values and the structural properties of
the houses. The measured q50 values were classified
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Figure 6. Airtightness measurement results of the studied houses.
International Journal of Ventilation ISSN 1473-3315 Volume 14 No 1 June 2015
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according to the foundation type, the wind barrier of
the base and the attic floor, the type of external wall
structure, internal plastering of the external walls,
and the type of renovations made.
The foundation structures of the investigated houses
had a slab on the ground, a ventilated crawl space
and a non-ventilated crawl space. In Estonia the
traditional foundation structure is a closed crawl
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Table 2. The effect of structural properties and renovations on the airtightness of the studied houses
analyzed with the ANOVA test.
Factor\Country Estonia Finland Sweden
n q
50 Avg q50 SD n q50 Avg q50 SD n q50 Avg q50 SD
(m3/h)/
m2)
(m3/h)/
m2)
(m3/h)/
m2)
(m3/h)/
m2)
(m3/h)/
m2)
(m3/h)/
m2)
Foundations
Slab on ground 7 17.2 11.9 1a8.8 3.1 - - -
Ventilated crawl space 6 14.2 6.9 14 10.6 3.1 2a12.4 2.3
Non-ventilated crawl space 8 14 7.9 1a12.2 3.1 6 14.2 2.3
p-value 0.71 0.75 0.18
Wind barrier on base floor
Yes 3 25.3 10.7 5 9 3 8 14.7 3.4
No 21 14.4 7.5 11 11.3 2.8 1a13.3 3.4
p-value 0.02 0.15 0.71
Wind barrier on attic floor
Yes 4 17 11.1 13 12.2 6 4 22.5 10
No 20 15.5 8.3 8 14.4 7.5 9 15.5 5.4
p-value 0.68 0.5 0.16
External wall structure
Log 24 15.8 8.5 14 10.4 2.9 - - -
Timber frame ---2a12.12.91
a12 2.2
Stone ------7142.2
p-value - 0.06 0.18
Internal plaster of external wall
Yes 7 12.5 5.2 1a8.6 3 11 17.4 7.1
No 17 17.2 7.3 14 11.1 3 0 - -
p-value 0.23 0.52 -
Renovation
Major 7 11.4 4.6 9 10.4 3.4 0 - -
Minor 7 12.9 3.9 7 10.9 2.7 11 17.4 7.1
No renovation 6 13.2 4.6 0 - - 0 - -
p-value 0.72 0.55 -
a standard deviation is the same as in the compared selection
L Eskola, Û Alev, E Arumägi, J Jokisalo, A Donarelli, K Sirén and T Kalamees
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space. This is non-ventilated and the inner surface of
the foundation wall is sealed with a thick soil layer.
A similar foundation type can be found in Swedish
and Finnish houses too. In Finland the most
common foundation structure is a ventilated crawl
space.
In 16 of the houses, a wind barrier was used on the
ground floor. A wind shield board was used as a
wind barrier in 9 houses and building paper in 7
houses. Twenty one of the houses were equipped
with a wind barrier on the attic floor and a wood
fibre board was used in 6 and building paper in 13
of the houses.
Three kinds of external wall structures were used in
the investigated houses. The most common is a log
wall mostly used in Estonia and Finland. A
limestone structure was most common in Sweden.
There were also two houses in Finland and one in
Sweden consisting of a timber frame wall structure.
Moss was used as a sealant between the logs in 75%
of the studied log houses and flax was used in 25%
of the log houses. An internal lime or clay plastering
of the external walls had been used in 19 of the
houses. The houses were divided into three groups
depending on the level of renovation undertaken:
major renovation, minor renovation or no
renovation. Major renovation included renovation of
the envelope structure. The minor renovation group
had a minor impact on the envelope structures but
covered for example, renovation of the electricity or
heating system.
Table 2 shows the results of this statistical analysis.
The assumptions shown in Section 3.3 were used in
the ANOVA test and the results are statistically
significant with the chosen confidence level if the p-
value is less than 0.05.
Although the studied structural properties or
renovations showed some effect on airtightness,
there was an insufficient number of houses to show
a statistically significant effect.
The only statistically significant result shows that
the airtightness of the Estonian houses without a
wind barrier on the base floor is 43% smaller than
that of the houses with the wind barrier. However
the wind barriers were retrofitted into these houses
and this could have introduced additional leakage.
In addition leakage differences could be caused by
other constructional factors.
The results of Table 2 indicate that the differences
between the level of airtightness of the historic
buildings cannot be explained by a single factor.
However it is possible that the airtightness of the
connections and junctions of the envelope has a
major influence on the airtightness of the studied
historic buildings although this analysis did not
show it quantitatively.
4.2 Location of Leakages
Thermal imaging was used to examine the location
of thermal bridges and leakage places of the selected
houses. The number of studied houses in Estonia
was 24, in Finland 4 and in Sweden 7.
Figure 7 shows the infrared images of a log house
under the normal (a) and 50 Pa negative internal
pressure across the envelope (b). Figure 7a shows
the location of thermal bridges and Figure 7b the
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International Journal of Ventilation ISSN 1473-3315 Volume 14 No 1 June 2015
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thermal bridges and leakage places. These figures
show that there are some thermal bridges in the
window frames and leakage places between the
window frame and the wall structure even with the
windows sealed for the winter time. Leakage places
can be seen at the junctions of the walls, floor and
the ceiling. There is an old plastic membrane in the
floor while the walls are covered with wallpaper and
there is building paper in the ceiling. These
materials are blocking leakages in the surfaces while
the leakage routes can be found at the junctions.
Thermal imaging shows that the typical location of
leakages is similar in each country. Typical air
leakage places are at the junctions of external and
internal walls, walls and the ground floor or walls
and the ceiling. This indicates that the walls, the
ground floor and the ceiling of the houses are not as
leaky as their junctions.
4.3 Air Exchange
4.3.1 Measured Air Exchange
The air exchange rate of the houses was measured
using the passive tracer gas method during the
heating season. Important elements for the air
exchange of naturally ventilated houses are the
airtightness of the envelope and the air pressure
difference between the indoor and outdoor air across
the building envelope. Because the pressure
difference is climate dependent due to wind and
stack effect, a climate correction was made for air
exchange rates measured in Finnish and Swedish
houses using the method discussed in Section 3.1.3.
The resulting correction factor was 0.14 1/h for
Finland and 0.2 1/h for Sweden. They are positive in
value and are quite high, especially because the
outdoor temperature during the tracer gas
measurements in Estonia was significantly lower
than in the measurement periods in Finland and
Sweden. The corrected air change rate values
(ACHmref) are shown in Figure 8 as a function of the
measured airtightness of the houses.
The range of the measured air exchange rate was
wide, from 0.23 to 1.92 1/h. This indicates that the
level of ventilation is insufficient in some of the
houses while some of the houses are too leaky
(Figure 8). For example, the acceptable range of the
air exchange rate is (0.5 0.7 1/h) in accordance
with the National Building Code of Finland (D2,
2012).
Figure 8 shows a slight correlation between the
measured air exchange rates and the measured
airtightness of the one- and two-storey houses. The
linearly fitted equations shown in the figure
approximate the air exchange rate as a function of
airtightness of the houses. According to these
approximations, the average air exchange rate can
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Figure 8. The corrected air exchange rates and q50 values of the studied houses.
L Eskola, Û Alev, E Arumägi, J Jokisalo, A Donarelli, K Sirén and T Kalamees
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be approximated by dividing the measured q50 value
by 9 for a two-storey house or by 22 for a one-
storey house. A similar rule of thumb for the average
infiltration rate has been reported earlier
(Liddament, 1986; Sherman, 1987).
However, Figure 8 shows that besides the
airtightness and the height of the building, the air
exchange rate depends on other factors because the
correlations between the air exchange rate and the
airtightness are quite weak. Other factors affecting
the air exchange rate are, for example, the location
of the leakages (Jokisalo et al., 2009) and the
behaviour of the occupants (window ventilation, use
of a stove or a fireplace).
The average air change rates of the one- and two-
storey buildings are shown in Table 3. According to
the results, the average ventilation rate of the two-
storey building is about 2.2 times higher than the
average ventilation rate of the one-storey building.
This result is statistically significant (p-value is
0.01) with the confidence level 0.05 according to the
ANOVA test.
4.3.2 Simulated Air Exchange
Simulation models of the example houses were
validated by comparing the simulated and measured
indoor air temperatures and air exchange rates. The
tracer gas measurement periods of each country
were used as a validation period. The local
measured weather data and the behaviour of the
occupants during the validation period were used as
initial data for the simulation (see Section 3.2).
Typical locations of leakages of the houses were
used in the simulation (see Section 4.2).
Table 4 shows the average measured and simulated
indoor air temperatures of the validation periods of
each country. The average difference between the
measured and simulated temperatures was 0.1 °C in
the Estonia case, 0.3 °C in the Finnish case, and
from 0.1 to 0.6 °C in the Swedish case. The average
values of the simulated temperatures were well in
line with the measurement results which indicates
that the simulation models can be used to predict
thermal conditions of the studied example houses.
The simulated air exchange rate was validated in the
Finnish case. Figure 9 shows hourly values of the
simulated air exchange rate of the example house
during the validation period. The range of air
exchange rate varies from 0 to 0.65 1/h due to the
variations in local wind speed and indoor outdoor
temperature difference. The simulated average air
exchange rate of the validation period was
compared against the average air exchange rate
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Table 3. Average air change rates in one-storey (Estonia and Finland) and
two-storey (Sweden) buildings.
1 Storey 2 Storey
Quantity 10 3
ACHmref 0.6 1.3
Standard deviation 0.29 0.54
Table 4. Measured and simulated average indoor temperatures during the validation periods.
Estonia Finland Sweden
(19.1-7.2) (13.4- 4.5) (1.4.-30.4)
Measured Simulated Measured Simulated Measured Simulated
[°C] [°C] [°C] [°C]
2. Floor 14.1 13.5
1. Floor 17.6 17.7 14.2 13.9 19.8 19.7
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measured by the tracer gas method (see Section
3.1.3). Both the simulated and measured values of
the average air exchange rate are 0.19 1/h. This
indicates that the simulation model is capable of
simulating the air exchange rate of the house at
sufficient accuracy. Here the vertical distribution of
leakage places has a significant impact on the
infiltration rate, as shown, for example in Jokisalo et
al. (2009), indicating that the location of air
leakages should be taken into account in the
simulation of infiltration airflows.
The building model was used to study the effect of
airtightness on the air exchange rate. The Finnish
example house was simulated for different q50
values in the sheltered and exposed wind conditions.
The simulation model approximates the local wind
conditions by means of the vertical wind profile
model originally presented in Sherman and
Grimsrud (1980) and the wind pressure coefficients
for single-family buildings (Liddament, 1986).
Figure 10 shows the average air exchange rate as a
function of airtightness in the sheltered and exposed
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Figure 9. Simulated air change rate of the Finnish example house during the validation period.
Figure 10. Average air exchange rate of the Finnish example house during the heating season as a function of the
airtightness of the envelope and the wind conditions. Acceptable level for ventilation rate is 0.5-0.7 1/h.
L Eskola, Û Alev, E Arumägi, J Jokisalo, A Donarelli, K Sirén and T Kalamees
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wind conditions during the heating season when the
outdoor temperature is below +15 °C. The house
was simulated using 21 °C as a set point for heating.
The acceptable range of the air exchange rate in
accordance with the National Building Code of
Finland (D2, 2012) is shown in Figure 10.
Figure 10 shows that the wind conditions have a
strong effect on the air exchange rate of the
naturally ventilated building. According to the linear
fit of the simulated air exchange rate, the average air
exchange rate of the studied naturally ventilated
house fulfills the Finnish guideline if the q50 value
ranges between 7 and 10 m3/h.m2 in the exposed
wind conditions or 15 and 22 m3/h.m2 in the
sheltered wind conditions. However, indoor air
temperature also influences the air change rate.
According to the simulation results, one-degree
temperature reduction from the used heating set
point decreases the air exchange rate of the studied
one-storey house by 3%.
Because the air exchange rate of naturally ventilated
buildings depends on the temperature and wind
conditions, the instantaneous ventilation rate varies
significantly. Although the average air exchange rate
is at an acceptable level, the instantaneous air
exchange rate may be significantly lower. Figure 11
shows the simulated distribution of the air exchange
rate over the heating season if the example house is
located in the sheltered or exposed wind conditions.
The q50 value of the house is 10 m3/h.m2.
Figure 11 shows that the air exchange rate is below
0.5 1/h 90% of the time in the heating season if the
house is located in the sheltered wind conditions or
47% of the time under exposed wind conditions.
These results show that if the airtightness of the
naturally ventilated house is improved, for example,
in order to improve energy efficiency, the acceptable
ventilation rate has to be maintained. Hence the
ventilation system has to be renovated if the proper
ventilation rate is not reached. Installation of a
mechanical supply and exhaust ventilation system
with heat recovery (MVHR) would be an energy
efficient solution. Then the airtightness of the
envelope could be improved as much as possible
without sacrificing indoor air quality.
4.4 Energy Performance
The influence of the airtightness, the ventilation
system and thermal indoor conditions on the energy
performance of the historic houses was studied by
means of the simulation models. The example
houses of each country were simulated q50 values
varying from 0.1 to 30 m3/h.m2 and each case was
simulated using both natural ventilation and MVHR.
Temperature efficiency of the heat recovery was
assumed to be 80%, which corresponds to the value
of modern systems. While the air exchange rate of
the naturally ventilated houses was based only on air
infiltration through the envelope, the total
ventilation rate of the mechanically ventilated
________________________________________________________________________________________________________________________
22
Figure 11. Distribution of the air exchange rate during the heating season.
International Journal of Ventilation ISSN 1473-3315 Volume 14 No 1 June 2015
________________________________________________________________________________________________________________________
houses consisted of both the constant ventilation
rate of the air handling unit (0.5 1/h) and air
infiltration.
The measured average indoor air temperatures of
the studied houses during the three coldest months
(January-March) were used as set points of space
heating in the naturally ventilated cases. These were
21.5 °C for Estonia, 20.5 °C for Finland, and
17.5 °C for Sweden. The Estonian and Finnish set
points are quite high because these values are based
only on the properly heated zones (indoor
temperature above 15 °C) of the continuously
heated houses. All the mechanically ventilated
houses were simulated for 21 °C set point for
heating, as suggested in (D2, 2012). The country
specific average levels of thermal insulation of the
houses (see Table 1) were used in the simulations.
Figure 12 shows the effect of the airtightness, the
ventilation system and thermal conditions on the net
heat demand of the spaces and ventilation. Results
show that the airtightness has a significant effect on
the heat demand of the houses and increases almost
linearly with the air leakage rate. It should be noted
that the ventilation rate of the simulated naturally
ventilated house is within the suggested range (0.5 –
0.7 1/h) (D2, 2012) if the q50 value of the houses is
from 12 to 17 m3/h.m2 in the Estonian case, from 16
to 22 m3/h.m2 in the Finnish case, and from 9 to
12 m3/h.m2 in the Swedish case. The differences of
the acceptable ranges of airtightness between the
countries are caused by the different wind
conditions, indoor and outdoor conditions and
height of the buildings. For example, the acceptable
range is lower in the Swedish example house
because it is higher and located in harsher wind
conditions than the Estonian and the Finnish houses.
The airtightness of the mechanically ventilated
house could be as low as possible without
compromising the level of indoor air quality. The
suggested acceptable level of q50 value for the
mechanically ventilated houses range from 0 to
5 m3/h.m2. Figure 12 shows that the energy
performance of the mechanically ventilated house
with heat recovery is clearly better than that of the
naturally ventilated houses for the suggested level of
airtightness and ventilation rate.
The results show that the level of indoor air
temperature during the heating season has a
significant effect on the energy performance of the
studied poorly insulated historic houses (Figure 12).
For example, the 0.5 °C difference in the set point of
heating in the Estonian case has about the same
effect on the heat demand as the replacement of the
natural ventilation by the energy efficient ventilation
heat recovery system. Also, improved indoor
________________________________________________________________________________________________________________________
23
Figure 12. Annual net heat demand of spaces and ventilation of historic houses with natural (NV)
and mechanical ventilation (MV).
L Eskola, Û Alev, E Arumägi, J Jokisalo, A Donarelli, K Sirén and T Kalamees
________________________________________________________________________________________________________________________
thermal conditions of the Swedish example house
and the installed ventilation heat recovery increase
the net heat demand of the house up to 50%.
Because the thermal comfort of the occupants of the
historic or any other houses should not be sacrificed
for energy performance, the acceptable thermal
conditions and indoor air quality should be
maintained without wasting energy. This could be
achieved in historic houses by increasing thermal
insulation, improving envelope airtightness and
installing MVHR systems.
5. Conclusions
Various historic houses were investigated.
Significant differences between the levels of the
airtightness of these houses exist in the studied
region. The measured q50 value varied from 3.9 to
35.2 m3/h.m2 with an average of 15.8 m3/h.m2 in
Estonia, 13.0 m3/h.m2
in Finland, and 17.4 m3/h m2
in Sweden. The statistical analysis showed no
structural properties or reasons which could explain
the observed differences in airtightness. Thermal
camera imaging showed that the typical air leakage
places of the studied houses are at the junctions of
the envelope structures and the structures (walls,
base floor and ceiling) are minor pathways for air
leakage. Connections and junctions have major
influence on the airtightness of the studied historic
houses but this analysis did not show it
quantitatively.
The validation of the simulated air exchange rate
indicates that the location of leakage places should
be taken into account in the simulation of infiltration
air flows. The simulations show that the distribution
of the air exchange of naturally ventilated buildings
is unacceptable. The measured air exchange rates of
one-storey houses were found to range from 0.2 to
1.2 1/h and in two-storey houses from 0.8 to 1.9 1/h,
indicating that the level of ventilation is insufficient
in some of the houses and some of them are too
leaky. The average measured air exchange rate of
the two-storey houses is about two times higher than
that of the one-storey houses. The airtightness has a
significant effect on the energy performance of the
houses and their heat demand increases almost
linearly with the air leakage rate. When the
airtightness of the naturally ventilated house is
improved, the acceptable ventilation rate has to be
guaranteed. The airtightness of the mechanically
ventilated house could be as low as possible without
compromising the level of indoor air quality.
Because the thermal comfort of the occupants of the
historic or any other houses should not be sacrificed
due to the energy efficiency, the acceptable thermal
conditions and indoor air quality should be
maintained without wasting energy.
Tightening the envelope and moving from natural to
mechanical ventilation with heat recovery are most
effective for improving the indoor conditions and
energy performance of the historic houses. When the
energy performance of the naturally ventilated
historic houses is improved, the functioning of the
whole building should be taken into account.
Acknowledgements
This study has been carried out in HELTH-project
(Healthy and Energy-efficient Living in Traditional
Rural Houses) under the Central Baltic Interreg IV
A programme (2007-2013) funded by the European
Regional Development Fund of the European
Union.
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This paper contains an overview of infrared thermography and its applications relating to the investigation of historic structures. In particular, this state of the art, non-destructive technique was used for the assessment of various traditional–historical materials and structures after they had been conserved, restored or repaired using, depending on the case, different treatments. Non-destructive testing and evaluation was performed on the materials and structures in order to assess the physicochemical behaviour of conservation treatments such as stone cleaning, stone consolidation, repair mortars, as well as to disclose any substrate features, such as tesserae on plastered mosaic surfaces. Wherever necessary, the emissivity values of the investigated materials were taken into account, after their determination in the laboratory on representative samples. The outcome of this work provides strong evidence that infrared thermography is an effective technique for the evaluation of historic buildings and sites.
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A full-scale wood frame test hut with nine wall specimens, typical of low-rise residential construction in the province of Quebec, was built inside an environmental chamber. This test hut was subjected to 66 days of simulated winter and 47 days of late spring climatic conditions to verify the feasibility of different methods of mapping and representing graphically air exfiltration. Through a better understanding of the movement of air through the envelope, the risks related to moisture condensation within the envelope for different wall compositions can be better ascertained. The air leakage pattern characterization methods implemented were two-dimensional grid moisture content monitoring and three-dimensional grid temperature monitoring. The moisture content and temperature data were presented in a graphic form, using isohygrons and isotherms. Temperatures without the impact of air leakage were also calculated using a three-dimensional conductive heat transfer model. The air leakage pattern characterization methods and the resulting moisture and temperature maps are presented and discussed herein.