Adaptive ventilation for climate control in a medieval church

International Journal of Ventilation
ISSN: 1473-3315 (Print) 2044-4044 (Online) Journal homepage: http://www.tandfonline.com/loi/tjov20
Adaptive ventilation for climate control in a
medieval church in cold climate
Margus Napp, Magnus Wessberg, Targo Kalamees & Tor Broström
To cite this article: Margus Napp, Magnus Wessberg, Targo Kalamees & Tor Broström (2016)
Adaptive ventilation for climate control in a medieval church in cold climate, International
Journal of Ventilation, 15:1, 1-14
To link to this article: http://dx.doi.org/10.1080/14733315.2016.1173289
Published online: 18 May 2016.
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Date: 18 May 2016, At: 04:36
INTERNATIONAL JOURNAL OF VENTILATION, 2016
VOL. 15, NO. 1, 1 14
http://dx.doi.org/10.1080/14733315.2016.1173289
Adaptive ventilation for climate control in a medieval church
in cold climate
€mb
Margus Nappa, Magnus Wessbergb, Targo Kalameesa and Tor Brostro
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a
Chair of Building Physics and Energy Efficiency, Tallinn University of Technology, Tallinn, Estonia; bDepartment of
Art History, Conservation, Campus Gotland, Uppsala University, Uppsala, Sweden
ABSTRACT
ARTICLE HISTORY
Old medieval churches hold objects of great historical and cultural value:
organs, altars, paintings. But they have no systems for indoor climate
control or the church may be heated only at services. These conditions are
inadequate for the preservation of cultural heritage. The objective of this
paper is to assess an adaptive ventilation (AV) solution in a church for
reduction of the relative humidity (RH) in an unheated church to prevent
mould growth and disintegration of wooden parts. The operation
principle of the system is to ensure ventilation in the church when water
vapour content in the outdoor air is lower than that indoors, to lower the
RH in the church. A case study in Hangvar Church in Gotland, Sweden, was
conducted to test the performance of AV to reduce the RH in the church.
Field measurements showed that AV has a positive impact on the indoor
RH of the church. During the measurement period without climate
control, the RH in the church was higher than 70% of 98% of the time;
with AV, the indoor RH was higher than 70% only 78% of the time.
Building simulation was carried out to test the performance and energy
consumption of AV under different conditions. The simulations showed
that auxiliary heating and airflow rate both have high impact on the
system performance. The higher the heating power, the more effective
the system is; thus, lower airflow rates are needed. Infiltration has also
high impact on the system performance: the lower the infiltration rate, the
better the AV performance is.
Received 15 November 2015
Accepted 1 March 2016
KEYWORDS
Adaptive ventilation; indoor
climate; climate control;
energy performance; historic
building; church
1. Introduction
1.1. Climate control in historic churches
The indoor climate is one of the most important factors in the preservation of medieval churches and
their interior. Most rural churches have no climate control or very simple systems when heated only
at services. In between services, the building is left unheated or at a background temperature. Thus,
the indoor climate challenge for these churches is twofold: to provide comfort for visitors during services and to maintain a good preservation climate when the church is not in use. This paper deals
mainly with the latter.
With none or very low heating between services, the indoor climate in medieval churches is dictated by the outdoor climate and the hygrothermal inertia of the massive structures. As a result, the
indoor climate is generally quite stable with slow seasonal changes in temperature and humidity.
CONTACT Targo Kalamees
targo.kalamees@ttu.ee
© 2016 Informa UK Limited, trading as Taylor & Francis Group
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M. NAPP ET AL.
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During winter, the relatively low thermal resistance of the building envelope causes low wall surface
temperatures (which increases relative humidity (RH)) and high energy costs for heating. Moisture
transport into the building from driving rain and ground sources often results in a considerably
higher moisture ratio (MR, g/kg) inside.
Many churches face problems related to high RH, increasing risk of damages of fungi, mould and
rot and insects (Kalamees et al., 2015; Scheiding, Plaschkies, & Weiß, 2008). Strong RH fluctuations
may cause flaking of paint and wood cracking (Mecklenburg, Tumosa, & Erhardt, 1998).
The conventional way to reduce RH is through conservation heating or dehumidification
€m & Larsen, 2012), (Kurabuchi, Ogasawara, Ochiai, & Lee, 2013). However, these solutions are
(Brostro
quite costly both in terms of investments and energy demand. A cost-efficient method for climate
control is needed to lower the humidity in the church for reduction of biological activity and condensation on the surfaces.
1.2. Adaptive ventilation
Ventilation may seem as an obvious and simple solution to reduce humidity levels. However, air
exchange in a historic building through infiltration or ventilation has a complex effect on the indoor
climate in general and on humidity in particular. Depending on the outdoor and indoor climate conditions, air exchange can either increase or decrease the RH in a building. A classic example is an
unheated church where doors and windows are opened in the spring to warm the building up. Inside
the building, the warm outside air is cooled off and the RH increases. Hygroscopic materials, such as
plaster and wood, are saturated and condensation may occur on cold surfaces. On the other hand,
when the outdoor climate is drier than that inside, ventilation can have a significant positive effect
by decreasing the humidity level in a church. The controlling principle of adaptive ventilation (AV) is
to ventilate only when the MR inside the building is higher than that outside. It is equally important
not to ventilate when the MR outside is higher. Thus, both air tightness and ventilation must be controlled and adapted through the use of mechanical fans and dampers controlled by indoor and outdoor climate sensors.
A recent development is adaptive or controlled ventilation, a potentially low-energy and low
impact option, which has been tested in case studies. Adaptive ventilation was implemented in the
Torhalle in Lorsch, Germany, where condensation on the wall paintings was avoided by mechanical
fans controlled by indoor and outdoor climate sensors (Reiss & Kiessl, 1986). Its seasonal use was
tested in the Antikentempel in Potsdam-Sanssouci Park to prevent mould growth on the walls and
ceiling. From May to September, a fan mounted in the skylight provided AV (Brockmann, 2010). A
€m, Hagentoft, & Wessberg, 2011), concase study in a historical house in Gotland, Sweden (Brostro
firmed that AV is particularly useful when there are internal moisture sources in the building, resulting in absolute humidity levels higher than those outside and the system produced a significant
drying effect. In addition, mould risk was kept at an acceptable level for most of the time. Antretter
et al. (2013) have investigated AV by means of computer simulations. AV has been implemented and
€m, 2013).
assessed in a number of churches in Denmark and Sweden (Larsen, Wessberg, & Brostro
In the cases above, the control systems were custom designed for each building. However, due to
the covariance of temperature and absolute humidity in the outside air, the effect on RH inside a
building is limited in a short term. In a typical diurnal cycle, the temperature will be lower outside
when the moisture ratio (MR, g/kg) is higher inside and the fan is running. This means that the ventilation has a cooling effect that tends to increase RH, even though at the same time, moisture is
removed from the building. In this paper, a commercial solution intended for cold attics and crawl
spaces under houses (Hagentoft & Kalagasidis, 2010) is used to assess AV performance in Hangvar
Church on the island of Gotland. In order to allow for parameter studies and to explore the potential,
additional simulations were carried out to find out how different airflow rates, heating powers and
infiltration affect AV performance in a medieval church.
INTERNATIONAL JOURNAL OF VENTILATION
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2. Methods
2.1. Hangvar Church
Hangvar Church on North Gotland, Sweden (Figures 1 and 2), was built in the thirteenth century. The
construction is typical of Gotland churches, with outer walls and vaults made of lime stone in
lime mortar and a wooden roof construction with tiles. The total volume of the church is 1000 m3
and the total floor area 144 m2. The church is used on an average once a month, mainly for weddings
and funerals. The church is intermittently heated for services and unheated in between.
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2.2. Measurements
RH and temperature were measured in the middle of the church hall (Figure 2) with a Testo data logger at a one-hour interval. Measurements were taken over two time periods:
Period 1: one full year before installation of AV; from September 2010 to August 2011
Period 2: one full year with the AV system running; from September 2012 to August 2013
Outdoor temperature, RH and solar radiation for the same periods were obtained from the Swedish Meteorological and Hydrological Institute (SMHI) in Visby Airport.
Infiltration measurements were conducted in the church (Mattsson, 2013) by the fan pressurisation method (EN 13829, 2000) and by the low pressure pulse technique (Cooper, Etheridge, & Smith,
2007).
The AV system (see Figure 3) was installed in July 2012. The system used is a control system mainly
intended for ventilation of attics (Hagentoft & Kalagasidis, 2010), consisting of a ventilator set-up, a
control unit and two sensors; an indoor sensor and an outdoor sensor for temperature and RH measurements. The system calculates and compares the moisture ratio both indoors and outdoors in real
Figure 1. Hangvar Church, exterior (a) and interior (b).
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M. NAPP ET AL.
Figure 2. Plan of the church and positions of indoor climate sensors and loggers.
time and activates the fan if the outdoor moisture ratio is 10% lower than the indoor value. The system is located in the tower staircase and the inlet air is taken from an opening in the tower wall. The
inlet air is supplied to the church via the fan through a duct in a temporary tower door.
From September 2012 to December 2012, the speed of the ventilator was set to run proportional
to the difference between the indoor and the outdoor moisture ratio, starting at 50% of max speed.
From January 2013, the speed of the ventilator was set to run at 100% any time the moisture ratio
was 10% lower outdoors than indoors.
Figure 3. Adaptive ventilation principle (left) and its installation in Hangvar Church (right).
INTERNATIONAL JOURNAL OF VENTILATION
5
The system composed of two electric heaters with a total power of 1800 W is also equipped with
photovoltaics (PV) panels (Figure 1a). Electricity collected in the daytime is sold to the grid and at
night-time when the outdoor moisture content is usually lower than that indoors and the system is
operational, the collected energy is bought back and used for the heaters.
Mould risk is assessed in relation to the isopleth curve RHLIM I (Sedlebauer, 2001) which is the temperature-dependent lowest limit in RH where mould growth can occur on biological recyclable materials.
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2.3. Simulation
The envelope of the church has high hygrothermal inertia; therefore, it is essential to use dynamic
computer simulation of heat, air and moisture of the whole building to calculate the church’s indoor
€rsell et al., 1999; Sahlin, 1996) was used for indoor
climate and energy usage. The software IDA-ICE (Bjo
climate and energy analysis. This software has been meticulously validated (Achermann, 2000; Achermann & Zweifel, 2003; Kropf & Zweifel, 2001; Travesi, Maxwell, Klaassen & Holtz, 2001) and allows the
modelling of a multi-zone building, internal and solar loads, outdoor climate, heating, ventilation and
air conditioning (HVAC) systems, dynamic simulation of heat transfer and air flows. It is widely applied
in energy performance and indoor climate calculations as well as in those of renovation of indoor climate, and energy performance of buildings (Alev et al., 2014; Arum€agi & Kalamees, 2014; Jokisalo
et al., 2008; Kuusk, Kalamees & Maivel, 2014; Napp & Kalamees, 2015; Pavlovas, 2004; Woloszyn, Kalamees, Olivier Abadie, Steeman, & Sasic Kalagasidis, 2009).
The indoor climate and energy simulation model for Hangvar Church enabled simulation of the performance of indoor temperature and humidity, energy use for heating and ventilation, flow of air, heat
and moisture through the external walls and humidity generation indoors. The simulation model consists of six zones: hall, choir, sacristy, porch, tower and the well-ventilated attic. Thermal and hygric
properties for heat, air and moisture (HAM) simulation are shown in Tables 1 and 2. In the simulation
model of the church’s hall, for four external walls, the common thermal wall model was replaced with
the hygrothermal (HamWall) model (Kurnitski & Vuolle, 2000) to calculate the moisture flow through
the building envelope. The walls were divided into 18 layers (Table 3) to calculate the flow of moisture
in the walls. The wooden interior parts, furniture and structures in the church were taken into account
by an additional 100 m2 wooden surface. The simulation model was calibrated based on indoor and
outdoor measurements between September 2012 and September 2013 (Figure 10).
One-pane clear glazing was used with a solar factor of 0.85 and heat transmittance of 5.8 W/(m2K).
3. Results
3.1. Field measurements of AV performance
Figure 4 shows the indoor climate during one-year periods before (left) and after (right) the installation of AV. A significant decrease in RH was achieved. The average RH decreased from 81% to 75%.
See Table 4 for further details.
Table 1. Structures, materials and their thermal properties.
Materials (from inside
Structure
to outside)
Thickness d (m)
External wall
Render
0.025
Lime stone masonry
1.45
Render
0.025
Render
0.025
Attic floor
Limestone arch
0.4
Render
0.025
Floor
Lime stone slab
0.25
Soil
1.0
Door and furniture
Wood
0.05
Thermal conductivity λ
(W/(m¢K))
0.8
1.2
0.8
0.8
1.2
0.8
1.2
2.0
0.13
Specific heat c
(J/(kg¢K))
790
880
790
790
880
790
880
1000
1.0
Density r
(kg/m3)
1800
2300
1800
1800
2300
1800
2300
2000
510
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M. NAPP ET AL.
Table 2. Hygric properties of materials.
Water vapour transmission1
2
Material
d0 (m /s)
B
6.4 £ 10¡7
Limestone
1.89 £ 10¡7
3.8 £ 10¡6
Render
2.929 £ 10¡6
2.9 £ 10¡6
Wood
7.3 £ 10¡7
C
4.7
10
4.75
RH1 (%)
82
20
84
Sorption isotherm2
w1 (kg/m3)
RH2 (%)
80
100
57
100
72
100
w2 (kg/m3)
100
82
100
Water vapour dv D d0 C B(RH/100)C, m2/s, where d0, m2/s, is if RH D 0%, B and C are constants and RH, %.
Water vapour capacity relation to RH is given with three lines: start: w D 0kg/m3, RH D 0%, first breakpoint: w1; RH1, second
breakpoint: w2; RH2 D 100%
1
2
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Table 3. Discretisation of the external wall.
Number of layer
Thickness (mm)
C
C
Render
1 2 3 4
1 2 5 6
5
6
6
6
7
10
8
100
External wall
Limestone
9
10 11 12
614 614 100 10
13
6
14
6
15
6
Render
16 17
5 2
P
P 18
1500
18
1
The use of a ventilation system can increase RH fluctuations. Both Figures 4 and 5 indicate that the
fluctuations have increased in Period 2 compared to Period 1. The standard deviation on the fluctuations has increased from 3.5 to 5.2. According to the European standard (EN 15757, 2010), fast RH
fluctuations less than §10% RH from the 30-day running average are considered safe. Figure 4 shows
that the number of events where RH is outside the §10% limits has increased in Period 2.
Figure 4. Left, measurements from Period 1, September 2010 to August 2011, no climate control by AV. Right, measurements from
Period 2, September 2012 to August 2013, with AV. In addition to hourly values also 30 days running average and §10% limits
according to EN15757 (2010).
Table 4. Field measurements statistics.
Average moisture Average
Percentage of time
Average
over 70% RH
temperature ( C) ratio DMR (g/kg) RH (%) Max RH Min RH (%)
Autumn: September, October, November
Period 1
11.1
82
93
74
100
Period 2
11.3
1.19
77
90
63
89
Winter: December, January, February
Period 1
3.4
80
91
66
93
Period 2
3.3
1.27
75
96
54
78
Spring: March, April, May
Period 1
6.8
80
90
63
100
Period 2
5.3
1.09
73
99
54
68
Summer: June, July, August
Period 1
17.0
83
93
68
100
Period 2
17.0
1.03
74
92
56
79
Annual average
Period 1
9.6
81
96
63
98
Period 2
9.3
1.20
75
99
54
78
Percentage of time
over RHLIM
52
19
1
0
0
1
68
19
31
8
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Figure 5. Mould risk without (left) and with (right) AV assessed with the isopleth curve LIM I (Sedlebauer, 2001).
Figure 6. Duration graph of critical limit for mould growth RH/RHLIM I for Period 1 (red) and Period 2 (black), left. Seven-day
running average of the difference between indoor MR and outdoor MR, right.
Figure 5 shows that with AV, though significantly reduced, mould risk is not eliminated. The time
over the critical limit was reduced from 31% to 8% of the time over one year.
As can be seen from Figure 6, even a small reduction in RH can be important. Suppose the objective is to keep RH below RHLIM I, the duration graph shows that AV reduced operational time for an
auxiliary active humidity control, i.e. a dehumidifier, from 3750 hours to 1450 hours.
Figure 7. Occasions when RH is above the critical limit RH/RHLIM. Without (left) and with (right) climate control by AV.
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M. NAPP ET AL.
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Table 5. Infiltration measurements in the church.
Q50 Q50/Aenvelope
(l/s) (l/(s∙m2))
Fan pressurisation method, higher indoors 707
0.92
Fan pressurisation method, lower indoors 654
0.85
Low pressure pulse
Combined
Q4 Adaption-constant Adaption constant, Equivalent leakage
(L/s)
(L/(s∙Pan))
CL (n [-])
area (with 4 Pa) (m2)
143
59.7
0.632
139
59.2
0.614
131
0.051
54.4
0.648
RH must be over the critical limit for a number of days for mould to grow (Sedlebauer, 2001). Without climate control by AV, the average duration above the critical limit was 72 hours (3 days) and the
longest period was 826 hours (34.4 days). With AV in operation, the average duration was 32 hours
(1.3 days) and the longest period as 134 hours (5.6 days), see Figure 6. This is probably the most
important effect of AV, see Figure 7.
In addition to the measurable effects shown above, visitors and people working in the church felt
that the indoor air quality had improved, mainly due to the elimination of bad smell.
The infiltration measurements with the fan pressurisation method (EN 13829, 2000) and the low
pressure pulse technique (Cooper et al., 2007) are presented in Table 5. The average q50 in the church
is 0.89 l/(s∙m2) and the equivalent leakage area at 4 Pa is 0.051 m2.
Figure 8 shows the moisture ratio inside and outside the building with and without AV. It can be
seen that the moisture excess is reduced due to AV. The data in Table 4 show that the reduction of
RH levels is mainly due to a reduction of MR since the difference in average temperature for the two
periods is relatively small. The yearly average of MR sank from 6.5 g/kg to 5.9 g/kg, which is a reduction of moisture by 9%. During Period 2, September 2012 to August 2013, 1100 kg of water was
removed from the church. This means that in addition to the short-term effects discussed above,
there is a possible long-term effect of drying out the massive building envelope.
The energy needed to run the fan is marginal. During one year, the fan itself used only 250 kWh
electricity. This gives a drying efficiency of 0.22 kWh per kg.
Figure 9 shows the energy generated by the PV panels and the energy used by the inlet air heaters. During Period 2, the PV panels generated sufficient energy to preheat the inlet air 9 of the
12 months. When the fan was operating at full speed and solar energy was available, the heaters
gave the inlet air a temperature increase of 11 C, which was generally sufficient to mitigate the cooling effect that can counteract the positive effect of removing moisture from the building. The total
amount of energy used for preheating of the inlet air during Period 2 was 2066 kWh (Wessberg,
€m, 2014).
Larsen, & Brostro
Figure 8. Seven-day moving average of both indoor and outdoor MR. Without AV to the left and with AV to the right.
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INTERNATIONAL JOURNAL OF VENTILATION
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Figure 9. Energy produced and consumed during the period with AV.
The case study has shown that AV is potentially an energy-efficient method to reduce RH in
unheated historic buildings. In order to facilitate proper design and operation of adaptive systems, it
is necessary to know the capacity of the fan, air tightness of the building and how heat input affects
the overall performance. This will be addressed by indoor climate and energy simulation.
3.2. Simulation
3.2.1. Calibration of the indoor climate and energy simulation model
IDA-ICE simulation program was used for a parameter study to show the influence of different AV
parameters on the indoor climate and energy performance. The simulation model of the indoor climate and energy performance of Hangvar Church was calibrated for the AV test period from September 2012 to August 2013. In general, good agreement was found between the measured and
simulated climate for the period (Figure 10). The simulated temperature shows coincidence with the
measured temperature. The higher peaks in the measured temperature resulted from an additional
heater in the church, which was used during services, weddings and funerals. Also, the simulated
moisture content shows high similarity with the measured moisture content.
During the simulation, the heating unit added to the system was assumed to be in operation all
the time when AV was working. In the AV simulation, the inlet air temperature was limited to <30 C
to avoid too high inlet temperatures and excessive dryness of the inlet air. The higher the heating
Figure 10. Comparison of measured and calculated temperature (left) and moisture ratio (right) in Hangvar Church with adaptive
ventilation.
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M. NAPP ET AL.
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Figure 11. Left, efficiency of AV with different airflows and heating powers. Right, energy use of AV per year with different air
flows and heating.
power, the higher the effect of AV is. At the maximum tested heating power of 20 W/m2, the simulation showed the highest effect of drying the church (Figure 11, left). The efficiency of AV also
depends on the airflows. With increasing airflows, the temperature of the inlet air decreases. At very
low airflows, AV is not sufficient to ensure lower RH levels. With no heating or low heating power, AV
is most effective in the range of 1.2 1.6 l/(s∙m2). Lower airflow rates are more efficient when more
heating is applied. At a heat input of 10 W/m2, the most effective airflow rate is 0.8 l/(s∙m2) and for
20 W/m2 it is 0.7 l/(s∙m2). The highest heating power of 20 W/m2 (Figure 11, left) is most effective, as
it decreases the RH most. In Figure 11 (right), the bottom axis shows the time in percentiles when the
RH is higher than 70%.
The most effective airflows are also the most energy consuming, as they use more power to heat up
the church, thus decreasing the indoor RH. With a heating power of 20 W/m2, the most power consuming and effective airflow rate is 0.8 l/(s∙m2), at RH over 70% for 6.5% of the year (Figure 11, right).
Figure 11 presents only the heating capacity for the AV. With the highest heating power of
20 W/m2 and airflow of 0.8 l/(s∙m2) and the fan SFP of 1.5 the energy needed for the fan operation would be 12% of the total heating consumption.
The dependence of AV performance on infiltration is presented in Figure 12. Both an effective
leakage area and an air leakage rate q50 are given. AV is very dependent on infiltration, especially
Figure 12. Adaptive ventilation with different infiltration rates.
INTERNATIONAL JOURNAL OF VENTILATION
11
near lower infiltration values. Thus, the AV performance can be improved by lowering the air infiltration rate.
With AV, the fluctuation of temperature and RH tends to increase. With the system turned off, the
maximum hourly temperature fluctuation was 0.5 Ch. With AV and 1.2 l/(s∙m2), the maximum hourly
temperature fluctuation was 1.2 C∙h. Additional heating increases the temperature fluctuations even
more. At 0.8 l/(s∙m2) and 10 W/m2, maximum hourly temperature fluctuation was 1.6 C∙h and at
0.8 l/(s∙m2) and 20 W/m2, it was 2.4 C∙h. The maximum hourly RH fluctuation without the system
was 4.1% with AV, 1.2 l/(s∙m2) and with no heating, it was 6.5%. Additional heating of 20 W/m2 and
0.8 l/(s∙m2) increases the hourly RH fluctuation to 9.8%.
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4. Discussion
This case study shows that AV improved the indoor climate in the church. The time over the critical
mould limit was reduced from 31% to 8% (Table 4) and the time needed for active climate control
was reduced by 60%. Most importantly, the continuous time periods over the critical limit were
reduced substantially. Even considering that measurements were made in different years and under
different outdoor climate conditions, the improvements in the indoor climate are significant.
During one year, around 1100 kg of water has been removed from the building, which indicates
that, in addition to the diurnal effects, there may also be a long-term effect where the building envelope slowly dries out. Continued monitoring over several years is needed for further investigations.
The case study shows that AV can be a low-cost and low-energy option as compared to other
types of humidity control, such as humidification and conservation heating. However, in the case
study, even AV combined with auxiliary heating was not sufficient to eliminate mould risk
completely.
The parameter study by use of simulations for AV showed a potential to enhance the performance
by making the building more air tight and by controlling the airflow rate.
The higher the heating unit, the better the AV performs; however, even a small heat input gives a
significant improvement (Figure 11, left).
The most effective airflow rate under heating not applied is 1.5 l/(s∙m2), under heating applied, the
optimal airflow rates decrease (Figure 11). The reason is that with higher heating power applied, the
system would start working more as a heater just to heat up the church and larger airflow rates
would import too much cold outside air to the church. With the largest heating power, 20 W/m2, the
optimal airflow rate is 0.7 l/(s∙m2). At higher airflow rates, the inlet air is not sufficiently heated. In
terms of RH control, the most effective solutions are also the most energy consuming.
Adaptive ventilation is also influenced highly by infiltration (Figure 12). The lower the infiltration
rate, the better the AV performance is. With infiltration rates lower than 2.0 l/(s∙m2), the performance
of AV is very highly influenced by small changes in infiltration rates.
Infiltration field measurements with the fan pressurisation method (Table 5) show the infiltration
of 0.89 l/(s∙m2) in the church which is low enough to see the results of the AV performance (Figure 12).
However, even small improvements in the infiltration would increase AV performance.
Both the case study and the simulations showed that the performance of AV has limitations.
Mould risk levels can be reduced significantly, but even with an optimal design, they cannot be
completely eliminated. The remaining load for climate control is small and of short duration. Since it
is limited to the warmer part of the year, it can be managed with a small condensing dehumidifier.
The study of AV in Hangvar Church, as well as the studies in two churches in Germany (Antretter et al., 2013) and in a church in Estonia (Napp & Kalamees, 2015), showed that the system can
increase the fluctuation of temperature and RH in the church. Thus, in the AV design, it is necessary to take into account that the system may increase RH fluctuations. However, the RH fluctuations caused by the AV system are small as compared to the variation of RH during intermittent
heating for services.
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M. NAPP ET AL.
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5. Conclusion
The aim of the study was to improve the indoor climate in the unheated church by the use of an AV
system. In the non-climate control period, our measurements showed high RH rates, which could
damage the church artwork and valuables. We tested the AV starting from September 2012 until
August 2013. The test period showed large improvements over the RH rates in the church, by lowering the annual average RH of 81% measured in the non-climate control period to 69% measured during the AV test period.
In addition to the test in the church, simulations done with the IDA-ICE program for Hangvar
Church showed that heating power and airflow have impact on the AV performance. The larger the
heating unit, the better the AV performance is. The most efficient airflow rate at heating applied is
0.7 0.8 l/(s∙m2). The relatively low amount of used energy for preheating of the inlet air does not justify the investment of PV panels (Wessberg, 2014). As AV is largely influenced by the infiltration rate,
the performance of AV depends on air tightness, which in turn can be improved to some extent for
most churches.
Acknowledgments
This study utilises the measurements collected in the project ‘Sustainable Management of Historic Rural Churches in the
Baltic Sea Region’ financed by the Central Baltic Interreg IV A and simulations made in the project IUT1¡15 ‘Nearly-zero
energy solutions and their implementation on deep renovation of buildings’ financed by the Estonian Ministry of Education and Research.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by Central Baltic Interreg IV A [grant Sustainable Management of Historic Rural Churches in the
Baltic Sea Region], Estonian Centre of Excellence in Zero Energy and Resource Efficient Smart Buildings and Districts,
ZEBE [grant number TK146] funded by the European Regional Development Fund, and by the Estonian Research Council,
with Institutional research funding [grant number IUT1-15].
Notes on contributors
Margus Napp is a researcher in Chair of Building Physics and Energy Efficiency, Tallinn University of Technology, Tallinn,
€ His research focuses on energy efficiency in providing indoor cliEstonia and an engineer in design agency IB Aksiaal OU.
mate of historically buildings.
Magnus Wessberg is a lecturer at Department of Art History, Conservation at Uppsala University, Campus Gotland, Sweden. With a background in engineering, his research focuses on energy efficient way to control temperature and humidity to create a good indoor climate for preservation of historically important buildings.
Targo Kalamees is a professor of Building Physics and head of Chair of Building Physics and Energy Efficiency, Tallinn
University of Technology, Tallinn, Estonia. His research focuses on building physics, renovation of buildings, energy performance and indoor climate of buildings.
Tor Brostr€
om is a professor in Conservation at Uppsala University, Campus Gotland, Sweden. With a background in engineering, his research focuses on indoor climate and energy conservation in historic buildings. He is coordinator of the
Swedish national research programme on energy efficiency in historic buildings.
INTERNATIONAL JOURNAL OF VENTILATION
13
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