ArticlePDF Available

Critical values for the temperature factor to assess thermal bridges

Authors:

Abstract and Figures

Climate analysis was conducted to determine the value for the temperature factor to be used for the design and infrared thermography inspections of Estonian dwellings to assess thermal bridges of the building envelope. For this analysis, data about the outdoor climate were retrieved from six weather stations, covering a 31-year period, from 1970 to 2000. For the indoor boundary conditions, the critical values from field measurements in detached houses were used. The aim was to avoid surface condensation and mould growth. Critical values of the temperature factor were calculated for different indoor humidity and temperature conditions. It was found that to avoid the mould growth on the thermal bridges in dwellings with a moisture excess of + 6 g/m3 during the cold period and + 2.5 g/m3 during the warm period (apartments with high occupancy or low ventilation) the spot temperature factor Rsi f should be greater than 0.80. For surf ace condensation, the limit value is Rsi 0.70. f ≥ In dwellings with a moisture excess during the cold period + 4 g/m 3 and during the warm period + 1.5 g/m3 (commonly detached houses: low occupancy and normal ventilation), to avoid the mould growth the Rsi 0.65 f ≥ is needed and for surface c ondensation Rsi 0.55. f ≥
Content may be subject to copyright.
218
Proc. Estonian Acad. Sci. Eng., 2006, 12, 3-1, 218–229
Critical values for the temperature factor
to assess thermal bridges
Targo Kalamees
Chair of Building Physics and Architecture, Tallinn University of Technology, Ehitajate tee 5,
19086 Tallinn, Estonia; kalamees@uninet.ee
Received 8 February 2006
Abstract. Climate analysis was conducted to determine the value for the temperature factor to be used
for the design and infrared thermography inspections of Estonian dwellings to assess thermal bridges
of the building envelope. For this analysis, data about the outdoor climate were retrieved from six
weather stations, covering a 31-year period, from 1970 to 2000. For the indoor boundary conditions,
the critical values from field measurements in detached houses were used. The aim was to avoid
surface condensation and mould growth. Critical values of the temperature factor were calculated for
different indoor humidity and temperature conditions. It was found that to avoid the mould growth on
the thermal bridges in dwellings with a moisture excess of + 6 g/m3 during the cold period and
+ 2.5 g/m3 during the warm period (apartments with high occupancy or low ventilation) the spot
temperature factor
Rsi
f
should be greater than 0.80. For surface condensation, the limit value is
Rsi
0.70.
f In dwellings with a moisture excess during the cold period + 4 g/m3 and during the warm
period + 1.5 g/m3 (commonly detached houses: low occupancy and normal ventilation), to avoid the
mould growth the Rsi
0.65
f is needed and for surface condensation Rsi
0.55.
f
Key words: temperature factor, infrared thermography, thermal bridge.
1. INTRODUCTION
All the building envelopes have thermal bridges, that is locations where the
thermal resistance is locally lower. Thermal bridges are caused mainly by
geometrical or structural reasons. In cold climate, the assessment of thermal
bridges is important for many reasons. Thermal bridges may lead to surface
condensation, mould growth and staining of surfaces. Due to lower temperatures
in the thermal bridge, higher relative humidity
()
R
H occurs. While surface
condensation starts at
100%,
RH = the limit value for
RH
relative to the mould
growth is above 75% and at
80%,
RH = growth conditions for nearly all species
of mould fungi are good. Thermal bridges lead to an increase of heat losses. An
219
increase in the thermal insulation level will increase the relative significance of
the thermal bridges in the energy consumption of buildings. If large poorly
insulated or uninsulated areas of the envelopes exist, the surfaces will be cold in
winter and may cause thermal comfort problems due to cold draughts or radiation
(in particular, asymmetric radiation).
For the inspection of thermal bridges with infrared thermography in real
buildings, knowledge of the critical level of the thermal conductance of the
thermal bridges is required. The International Energy Agency (IEA) [1] has
proposed to use the method of temperature factor to assess thermal bridges. It is
the responsibility of each country to establish the design values of the
temperature factor. The principle of the temperature factor is included also in the
EN ISO 13788:2001 [2] standard. The temperature factor at the internal surface,
R
si
,
f
shows the relation of the total thermal resistance of the building envelope
T
R
(m2K/W) to the thermal resistance of the building envelope without the
internal surface resistance
si
R
(m2K/W). It depends on the indoor and outdoor
air temperatures
i
T
and
e
T
(°C) and on the temperature at the internal surface of
the building envelope
si
.
T
In the literature the temperature factor is also referred
to as the temperature ratio, temperature index, or condensation resistance factor.
It is expressed as
T
si si e
Rsi
T
ie
.
R
RTT
f
R
TT
−−
==
(1)
Constant temperature factor assumes constant thermal resistance of the
internal surface. In reality, the thermal resistance of the surface depends on the
reciprocal value of the sum of convective
c
()
α
and radiation
r
()
α
heat transfer
coefficients. The heat transfer coefficients can be calculated as [3]
0
.25
c21
2( ) ,
TT
α
=− W/(m2K), (2)
44
12
r12
12
()
1
,
11
()
1
TT
TT
ασ
εε
=⋅
++ W/(m2K), (3)
where
σ
is the Stefan–Boltzmann constant, W/(m2K4),
1
ε
and
2
ε
denote
emissivity of surfaces,
1
T
is temperature of the surface and
2
T
is temperature of
the ambient air or the radiating surface, °K.
Using Eqs. (2) and (3), it is possible to calculate the temperature on the
internal surface of the building envelope. Figure 1 shows the dependence of the
temperature factor on the outdoor temperature and on the thermal transmittances
of the building envelope (without surface heat transfer coefficients). Due to the
higher temperature difference and surface heat transfer coefficients, the building
envelope with the same thermal transmittance shows higher temperature factor
values at lower outdoor temperatures. The influence of the outdoor temperature is
higher on the envelopes with higher thermal transmittance.
220
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
-30 -20 -10 0 10
3.78 [W/(m2?K)] 2.80 [W/(m2?K)] 2.00 [W/(m2?K)]
1.35 [W/(m2?K)] 0.80 [W/(m2?K)] 0.36 [W/(m2?K)]
Outdoor temperature Tout, °C
Fig. 1. The dependence of the temperature factor on the outdoor temperature and on thermal
transmittance of the building envelope.
Many countries have set limit values or guidelines for the temperature factor.
In Belgium, a technical note [4] suggests that to evaluate the condensation risk,
the temperature factor should be 0.2
0.7.
f Dutch building regulations [5] set the
requirements for the normalized temperature factor Rsi
0.65
f for new
residential buildings. In France [6], the temperature factor limits are linked with
the moisture excess in a room. To avoid condensation in rooms with the moisture
excess value 2.5–5 g/m3, the temperature factor should be Rsi
0.52
f> (the
reference conditions are: out
0C,
T out
80%
RH = and in
18 C).
T On the basis
of the indoor temperature + 20 °C and relative humidity 50%, outdoor
temperature – 5 °C, and the highest relative humidity at the surface of the building
envelope 80%, the lowest value of the temperature factor 0.7 is determined in the
German DIN standard [7]. The Swiss standard [8] sets the lower limit for the
temperature factor 0.75. In the United Kingdom [9], to avoid the mould growth
and surface condensation in dwellings, Rsi
0.75.
f In Finland [10], recommenda-
tions for the minimum value of the temperature factor for new buildings are for
floors 0.97 and for walls 0.87. Near the junction of the thermal envelope and
separating walls or near the penetration of the thermal envelope, the spot
temperature factor value should be more than 0.65.
In Estonia, no official requirements or guidelines exist for the value of the
critical temperature factor. In many guidelines and regulations [11–14] require-
ments are formulated to avoid moisture damage, surface condensation and mould
growth. In this study, a special climate analysis was conducted to determine the
Temperature factor fRsi
221
design value for the temperature factor for Estonian dwellings by assessing the
thermal bridges of the building envelope.
2. METHODS
2.1. Outdoor climate conditions
The territory of Estonia can be divided into two climatic areas [15–18]: the
coastal area that is directly influenced by the sea and the inland area. The western
islands region, the West-Estonian region and the northern coastal region make up
the coastal area. The North-Estonian and South-Estonian regions constitute the
inland area. The principal territorial differences in climate are due to the adjacent
Baltic Sea. The boundary line between the two main climatic areas is shown in
Fig. 2.
To determine the critical value of the temperature factor, the outdoor climate
was retrieved from six weather stations, covering a 31-year period, from 1970 to
2000. Meteorological stations were chosen according to the climatic areas and
the building density of the towns. Tallinn, Kuressaare and Pärnu represent the
coastal area and Tartu, Väike-Maarja and Võru the inland area. Tallinn and Tartu
have the highest occupancy and building activity. Kuressaare represents the
western islands region, while Pärnu is the West-Estonian region in the coastal
area. Väike-Maarja represents the North-East Estonia and Võru represents the
South-Estonian highland region.
Fig. 2. Climatic areas of the territory of Estonia. Meteorological stations, the data of which were
used in this report, are indicated by large dots.
222
2.2. Indoor climate conditions
The Estonian indoor climate standard [14] sets the temperature values for three
different categories: A, B, C. During summer, the indoor temperature values
must range between + 22 and + 27 °C and during winter, between + 19 and + 25 °C
in the lowest category C. Because air conditioners are rarely used in detached
single-family houses and the heating systems are usually not used during
summer, indoor temperatures during summer are not well controllable in
detached single-family houses. According to the indoor climate measurements in
Estonian dwellings [19], daily average indoor temperature was almost smooth
between + 20 and + 22 °C during the period when the outdoor daily average
temperature is between – 25 and + 15 °C. By the outdoor temperature of + 15 °C,
the indoor temperature started to rise almost linearly from + 22 up to + 27 °C by
the outdoor temperature of + 25 °C.
Values of the temperature factor were calculated for two indoor temperature
models. First, it was calculated for the average indoor temperature model.
Average temperature model with a moisture excess on a 10% higher critical level
corresponded best to the measured indoor RH values on a 10% higher critical
level. Indoor RH is usually the most important factor for mould growth.
Temperature on a 10% lower critical level was 2 °C lower than the average
temperature. There were also rooms where the temperature was on average 2 °C
lower than the average temperature of all the houses. Therefore, factor analysis of
the critical temperature was done also with the indoor temperature on a 10%
lower critical level.
The indoor humidity level depends mainly on the moisture production, the air
change rate and the outdoor humidity. The indoor climate standard [14] sets the
limit values also for the relative humidity: from 25 to 45% during winter and
from 30 to 70% during summer. Because in detached houses, as a rule, the indoor
air is neither humidified nor dried, in this study, the internal moisture excess,
ν
(difference in the air water vapour content of the indoors and outdoors air), was
used to calculate the indoor humidity. According to the indoor climate
measurements in Estonian detached houses (average occupancy 46 m2/pers,
average ventilation air change rate 0.41 ach (13.3 l/(s pers) and 0.28 l/(s m2)), a
moisture excess on a 10% higher level in houses with low occupancy during the
cold period e
(5C)
T≤+ ° was + 4 g/m3, during the warm period e
(15C)
T≥+ °
close to + 1.5 g/m3 and it decreased between these levels linearly. With a 1 g/m3
change in the moisture excess during the cold period, a 0.5 g/m3 change during
the warm period was observed.
The critical temperature factor was calculated for two different indoor
humidity levels. The moisture excess during the cold period was taken + 4 g/m3
and during the warm period + 1.5 g/m3, that represents a 10% higher humidity
load level in houses with low occupancy. According to statistics, the average
living area per person of the overall Estonian housing stock is 28 m2/pers.
Therefore in apartments, where the living density is higher, more severe design
223
Fig. 3. The indoor climate models used to determine the critical value of the temperature factor.
loads should be taken into account. The moisture excess value + 6 g/m3 during the
cold period and + 2 g/m3 during the warm period were chosen for apartments with
higher living density. As suggested in [2], the values of the moisture excess are
multiplied by 1.1. Figure 3 shows the indoor climate models used to select the
critical value of the temperature factor.
2.3. Method for selecting the critical value of the temperature factor
The values of the critical temperature factor
Rsi
f
were selected to avoid the
mould growth and surface condensation. To avoid the mould growth due to the
outdoor temperature and humidity, the average monthly absolute indoor humidity
was calculated using the internal moisture excess models (Fig. 3). With the
maximum acceptable
RH
at the thermal envelope surface 80%, the maximum
acceptable absolute humidity was calculated. Using it, the minimum acceptable
surface temperature was calculated. Using this minimum acceptable surface
temperature, the outdoor temperature and the indoor temperature, the minimum
temperature factor was calculated according to Eq. (1). The calculation procedure
employed for selecting the critical temperature factor to avoid surface condensa-
tion, was the same, only the daily average climate values and the maximum
acceptable
RH
at the surface of the envelopes, si
100%
RH = were used.
Outdoor temperature Tout, °C
224
For each location, each year and each month, the maximum temperature
factor was calculated. To determine the critical value for the temperature factor, a
10% higher level was used, as is suggested for building physics calculations [20].
It means that 10% of the monthly maximum values would be defined as critical,
whereas the remaining 90% of the monthly maximum values would fall below
the critical temperature factor value. The determined design values of the
temperature factor were rounded.
3. RESULTS
Figures 4 and 5 show the influence of the indoor temperature and of the
moisture excess (marked value during the cold period) on the temperature factor
limits to avoid the mould growth and surface condensation. These figures show a
10% higher level from the six stations during the 31-year period.
To avoid the mould growth on the thermal bridges, the design value of the
temperature factor in dwellings should be Rsi
0.80.
f According to the surface
condensation, the limit value for the temperature factor is Rsi
0.70.
f If it is
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec.
Temperature factor fRsi
Mould growth, lower temp., +4g/m3 Mould growth, lower temp., +6g/m3
Mould growth, average temp., +4g/m3 Mould growth, average temp., +6g/m3
Lower temp. model, ν +4g/m3
Average temp. model,
ν +4g/m3Lower temp. model, ν +6g/m3
Average temp. model,
ν +6g/m3
Fig. 4. Dependence of the critical temperature factor on the calculation models, calculated
according to the mould growth criterion.
225
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sep. Oct. Nov. Dec.
Temperature factor fRsi
Mould growth, lower temp., +4g/m3 Mould growth, lower temp., +6g/m3
Mould growth, average temp., +4g/m3 Mould growth, average temp., +6g/m3
Lower temp. model, ν +4g/m3
Average temp. model,
ν +4g/m3Lower temp. model, ν +6g/m3
Average temp. model,
ν +6g/m3
Fig. 5. Dependence of the critical temperature factor on the calculation models, calculated accord-
ing to the surface condensation criterion.
otherwise indicated, lower indoor humidity conditions (based on the designer’s
investigation of the indoor hygrothermal loads, the ventilation system or lower
occupancy), the temperature factor for avoiding the mould growth should be
Rsi
0.65
f and to avoid condensation Rsi
0.55.
f In the most critical cases
(high indoor humidity conditions, low room temperature), mould growth is
possible even at well-insulated surfaces (Fig. 4). It proves the importance of the
role of ventilation and heating in the regulation of the humidity level in rooms
with high moisture production. The temperature factor Rsi
0.70
f is a suitable
value for avoiding condensation also in the case of the lower temperature model.
In the following, the limit values for indoor relative humidity in relation to
surface condensation and mould growth are calculated. The aim was to find the
highest level of indoor relative humidity by which neither the surface condensa-
tion nor mould growth occurs. The highest relative indoor humidity was selected
from the minimum values for each outdoor temperature calculated using the
temperature factor 0.80 and the highest relative humidity at the surface of the
building envelope si
80%
RH = (mould growth criterion) or Rsi
0.70
f= and
si
100%
RH = (condensation criterion). For lower indoor humidity conditions, the
highest indoor relative humidity was calculated using the temperature factor 0.65
and the highest relative humidity at the surface of the building envelope 80%
(mould growth criterion) or Rsi
0.55
f= and si
100%
RH = (condensation
criterion). Figure 6 shows the limiting curves for the indoor relative humidity for
226
Outdoor temperature Tout, ºC
Fig. 6. Limiting curves for indoor RH to avoid the risk of mould growth and surface condensation
according to determined design values for the temperature factor.
the average indoor temperature model (Fig. 3). Design values of the temperature
factor for a lower humidity load level do not cover standardized indoor relative
humidity values [14]. Therefore, these lower values of the temperature factor are
allowed to be used only if the lower indoor humidity conditions are clearly
defined and argued.
4. DISCUSSION
Temperature factors were calculated for two different indoor humidity and
temperature conditions. The critical relative humidity si
80%
RH = was used for
the mould growth criterion. The critical
RH
for mould growth depends also on
many other factors. According to Hukka and Viitanen [21], at the temperature
si
20 C,
T a mathematical relationship between the temperature and the critical
RH
for mould growth exists. By using this dependence, we obtain an about 3%
lower value of the temperature factor. Nevertheless, constant
RH
was used for
safety reasons.
The determined critical temperature factors can be directly used for thermal
bridge investigations (e.g. with infrared thermography) in real buildings. Indoor,
outdoor and internal surface temperatures can all be directly measured. In the
design process, to calculate the correct internal surface temperature, we should
know the thermal resistance
si
R
of the internal surface. The internal surface
0
10
20
30
40
50
60
70
80
90
100
-25 -20 -15 -10 -5 0 5 10 15 20 25
Indoor relative humidity RHin, %
Series2 Series3
fRsi 0.80, RHsi 80%
fRsi 0.70, RHsi 100%
fRsi 0.65, RHsi 80%
fRsi 0.55, RHsi 100%
RH limits for
heating
s
easo
n
25…45%
RH limits
f
or summ
er
30…70%
Outdoor temperature Tout, °C
227
resistance depends on the convection and radiation coefficients: on the air
movement in the room, on the air and surface temperature distribution in the
room and on surface material properties. The thermal resistance of the surface
may vary a great deal. High values can be found in the case of significant thermal
shielding by furniture and low values, for example, in a room with only external
walls and a convective heating system. To calculate the correct internal surface
temperature in the design process,
si
R
should be determined using the thermal
model of the room, taking into account the thermal resistances of the surrounding
envelope, temperature of the environment, the distribution of the air temperature
in the room and its geometry. If that information is not available, simplified
methods or the values recommended by [22] (in most of the cases considered as
safe values) can be used.
To determine the repair works, based on thermographic studies, defective
constructions in dwellings with a temperature factor Rsi
0.65
f< should be
repaired immediately. Envelopes with the temperature factor Rsi
0.80
f< may be
classified as satisfactory from the point of view of surface condensation and
mould growth and have no need for corrective action. To assess the risk and to
determine the need for envelope repairs for the temperature factor
Rsi
0.65 0.80,
f<< different aspects should be taken into account: hygrothermal
behaviour of the building envelope, parameters of indoor climate, thermal
comfort, purpose of use of the building, economic aspects (repair costs, energy
consumption, payback period), service life of the building, etc.
5. CONCLUSIONS
To determine and classify thermal bridges, the acceptable temperature factor
was calculated for the Estonian climate (during 31 years from six different
locations) and the critical indoor hygrothermal load.
In dwellings with a moisture excess + 6 g/m3 during the cold period and
+ 2.5 g/m3 during the warm period (commonly apartments of high occupancy or
low ventilation), to avoid the mould growth on the thermal bridges, the spot
temperature factor should be Rsi
0.80.
f According to the surface condensation,
the limit value for the temperature factor is Rsi
0.70.
f In dwellings with a
moisture excess + 4 g/m3 during the cold period and + 1.5 g/m3 during the warm
period (commonly detached houses of low occupancy and normal ventilation), to
avoid the mould growth, the temperature factor should be Rsi
0.65
f and to
avoid surface condensation Rsi
0.55.
f In the most critical cases (high indoor
humidity conditions, low room temperature), mould growth is possible even on
well-insulated surfaces. It proves the importance of the role of ventilation to
regulate moisture levels in rooms with a high moisture production.
228
ACKNOWLEDGEMENTS
This study has been financed by Estonian Science Foundation (grant
No. 5654). The author wish to thank the Estonian Meteorological and Hydro-
logical Institute for the climatic data, which made this work possible.
REFERENCES
1. Hens, H. (ed.). Condensation and Energy, Guidelines and Practice. Vol. 2, Annex 14,
International Energy Agency, KU Leuven, 1990.
2. EN ISO 13788:2001. Hygrothermal performance of building components and building elements
– Internal surface temperature to avoid critical surface humidity and interstitial condensa-
tion – Calculation methods. International Organization for Standardization, Brussels, 2001.
3. Hagentoft, C.-E. Introduction to Building Physics. Studentlitteratur, Lund, 2001.
4. Uyttenbroeck, J. and Carpentier, G. Vochthuishouding in gebouwen. Wissenschaftliches und
Technisches Bauzentrum. Technische voorlichtingen 153, Brussels, 1984.
5. NEN 2778:1991. Vochtwering in gebouwen, Bepalingsmethoden. Nederlands Normalisatie-
instituut, Delft, 1991.
6. Berthier, J. Diffusion de vapeur au travers des parois – Condensations. C.S.T.B. – REEF
Sciences du Bâtiment, Vol. II, Paris, 1980.
7. DIN 4108-2:2001-03. Wärmeschutz und Energie-Einsparung in Gebäuden. Teil 2: Mindestan-
forderungen an den Wärmeschutz. Deutsches Institut für Normung, Berlin, 2001.
8. SIA-180:1999. Wärme- und Feuchteschutz im Hochbau. Schweizerische Ingenieur- und Archi-
tektenverein, Zürich, 1999.
9. BRE IP 17/01. Assessing the Effects of Thermal Bridging at Junctions and Around Openings.
BRE, Building Research Establishment Ltd, Garston, 2001.
10. Asumisterveysohje. Sosiaali- ja terveysministeriön oppaita 2003:1, Sosiaali- ja terveysminis-
teriö, Helsinki, 2003.
11. Eluruumidele esitatavad nõuded. Kehtestatud Vabariigi Valitsuse 26.01.1999. a määrusega
nr. 38. Riigi Teataja I, 1999, 9, 38.
12. Ehitusseadus. Vastu võetud 15.05.2002. a seadusega. Riigi Teataja I, 2002, 47, 297.
13. EVS 837-1:2003. “Piirdetarindid. Osa 1: Üldnõuded”. Eesti Standardikeskus, Tallinn, 2003.
14. EVS 839:2003. “Sisekliima”. Eesti Standardikeskus, Tallinn, 2003.
15. Kirde, K. Andmeid Eesti kliimast. Tartu Ülikooli Meteoroloogia Observatooriumi Teaduslikud
Väljaanded, 1939, No. 3.
16. Kirde, K. Kliima-valdkonnad Eestis. Tartu Ülikooli Meteoroloogia Observatooriumi
Teaduslikud Väljaanded, 1943, No. 5.
17. Raik, A. Eesti klimaatilisest rajoneerimisest. Eesti Loodus, 1967, 2, 65–70.
18. Karing, P. Õhutemperatuur Eestis. Valgus, Tallinn, 1992.
19. Kalamees, T. Indoor hygrothermal loads in Estonian dwellings. In Proc. 4th European
Conference on Energy Performance and Indoor Climate in Buildings. Lyon, 2006.
20. Sanders, C. (ed.). Heat, Air and Moisture Transfer Through New and Retrofitted Insulated
Envelope Parts, Environmental Conditions, Task 2, Annex 24, International Energy
Agency, KU Leuven, 1996.
21. Hukka, A. and Viitanen, H. A mathematical model of mould growth on wooden material. Wood
Sci. Technol., 1999, 33, 475–485.
22. EN ISO 10211-1:1995. Thermal bridges in building construction – Heat flows and surface
temperatures – Part 1: General calculation methods. International Organization for
Standardization, Brussels, 1995.
229
Kriitilised temperatuuriindeksid Eesti elamute
külmasildade hindamiseks
Targo Kalamees
On määratud temperatuuriindeksi projekteerimisväärtused külmasildade hin-
damiseks Eesti elamute projekteerimisel ja ekspertiiside tegemisel. On kasutatud
kuue linna 31 aasta (1970–2000) kliimaandmeid. Sisekliima osas on kasutatud
Eesti väikemajade sisekliimauuringu mõõtetulemusi. Temperatuuriindeksi mää-
ramise kriteeriumiks on hallituse tekke ja niiskuse kondenseerumise ärahoid-
mine. Et vältida hallituse tekke riski eluruumides, peab temperatuuriindeks olema
suurem kui 0,8 ning niiskuse kondenseerumise vältimiseks suurem kui 0,7.
... Bu kritik sıcaklık faktörü değeri her ülkenin kendi tasarım kriterlerine bırakılmıştır. Bu değer literatürde aynı zamanda sıcaklık oranı, sıcaklık indeksi ve yoğuşma direnci olarak da ifade edilmektedir [17]. Bina yapısı için hesaplanan sıcaklık faktörü değeri o ülke için daha önceden belirlenen kritik sıcaklık faktörü değerinin üzerinde ise iç ortam yüzeyinde nem ve küf oluşumu engellenmiş olur. ...
... Sıcaklık faktörü (f Rsi ) iç yüzey sıcaklığı (T iy ) ile iç (T i ) ve dış (T ∞ ) ortam havası sıcaklıklarına bağlıdır. Bu değer; şeklinde ifade edilebilir [17]. ...
... To avoid mould growth on the thermal bridges, the minimal spot temperature factor should be f Rsi ≥ 0.80 in the Estonian climate (Kalamees 2006). ...
... In Table 3 there are the average LTT values and the minimum f Rsi values for each of the simulated positions for the nZEB version of the reference house. The f Rsi values which meet the minimum requirement in the Estonian climate (Kalamees 2006) are marked with a light green background. In Table 4 there are the corresponding values for the LEB version of the house. ...
Article
Full-text available
One of the largest sources of heat loss in buildings are the windows. However, windows are alsoimportant to increase solar heat gain and provide daylight. It is necessary to understand how windowdetails influence the energy performance of very energy efficient houses. This is valuable informationfor the design decision making process and may lead to further research or product development. Thispaper examines the influence of window frame thermal transmittance, window frame width and windowinstallation depth on the energy demand of the building. A single-family prefabricated timber nZEBlocated in Estonia was used as a reference building for this study. The results show that decreasing thethermal transmittance and width of the window frame have a remarkable effect on the energy demandof the nZEB (a variation of 42% and 25% respectively). The effect of optimising window installation depthis insignificant (ca 3% variation of heat demand on most of the window placement range and up to 10%of increase in heat demand when comparing the optimal placement to the least effective one). However,it can further improve the energy performance.
... The higher the T f coefficient, the lesser the risk of surface condensation. Some countries have set limits for T f , for instance, in France (T f > 0.52 at reference conditions of T out = 0 • C, RH = 80%, and T in = 18 • C), Germany (T f of 0.87), and Estonia (T f of 0.55) [71], and in the UK and Netherlands a T f of 0.50 is reported [60]. Thus, some researchers deduced that the definitive T f value is not solely based on indoor moisture access, building purpose, and ventilation status but also on the prevailing local climate [34]. ...
Article
Full-text available
Almost every major city’s skyline is known for high-rise iconic buildings with some level of curtain wall system (CWS) installed. Although complex, a CWS can be designed for energy efficiency by integrating insulated spandrel components in space-constrained areas, such as slabs/plenums. The main aim of this study was to experimentally examine the thermal performance of an optimized curtain wall spandrel system integrated with vacuum insulation panel (VIP) as spandrel insulation. The study is based on robust experimental evaluations, augmented with appropriate numerical computations. The main study is constituted of six parts: (1) evaluation of VIP specifications and thermal properties; (2) analysis of VIP spandrel configuration, fabrication, and installation in a test building facility; (3) thermal bridge characterization of VIP spandrels; (4) monitoring and assessment of VIP durability within the spandrel cavities; (5) thermal performance analysis; and (6) assessment of related limitations and challenges, along with some further reflections. In all, 22 VIPs (each of size 600 mm2) were used. The effective thermal conductivity of VIPs ranged from 5.1–5.4 (10−3 W/mK) and the average value for initial inner pressure was approximately 4.3–5.9 mbar. Three VIP spandrel cases were fabricated and tested. The results proved that the Case 3 VIP spandrel configuration (composed of a double-layer VIP) was the most improved alternative for integrating VIPs.
... fR si : 0.65-0.75 (Hens 1992;Oreszczyn et al. 2006;Kalamees 2006;Tsongas 2009;ADF 2010;British Standard 2011, 2013Adan and Samson 2011;Dedesko and Siegel 2015;Azevedo et al. 2015). ...
Article
Full-text available
The occurrence of surface condensation and mould can lead to concerns of poor indoor air quality and adverse health implications of occupants. Remedial actions require identification of the root causes, but this can be challenging even for experts. The focus of the research is the development of a diagnostic tool that helps to streamline root cause analysis. The diagnostic method comprises a protocol with guidelines for installation of sensors, easy data collection, and a set of calculations to process environmental information. Environmental parameters collected and calculated from an environmental monitoring exercise of dwellings with and without mould, include physical properties associated with the indoor surface of external walls and surrounding air conditions. The methodology relies on linking specific surface and air environmental parameters together with critical thresholds proposed for the control and avoidance of surface condensation and mould growth in dwellings. These parameters were assessed and used to determine the likely causal factors of a moisture imbalanced environment leading to surface condensation and mould growth; poor thermal building envelope performance, an imbalanced heat-moisture regime, and/or insufficient ventilation. Examples from different scenarios are presented to show the process towards environmental data collection, post-processing to compute and assess pertinent parameters, and the display of environmental conditions in a clear and easy-to-interpret manner. The novel developed system is a time-saving method for processing and represents environmental data. It provides a straightforward building moisture index (BMI) and a systematic diagnostic procedure for environmental assessment and possible causes of mould growth. This helps to support neutral decision making, to identify rectification strategies and direct to more cost-efficient solutions to existing damp and mould problems in buildings.
... Besides the general calculation approach in the EN ISO 13788 provisions, moreover, a series of National guidelines are available in several countries to recommend minimum limit values for fRsi. These are in the range of fRsi ≥ 0.52 (France), or fRsi ≥ 0.65 (Netherlands) and fRsi ≥ 0.7 for Germany (Kalamee, 2006). ...
Article
Full-text available
Facade elements are known to represent a building component with multiple performance parameters to satisfy. Among others, “advanced facades” take advantage from hybrid solutions, like the assemblage of laminated materials. In addition to enhanced mechanical properties that are typical of optimally composed hybrid structural components, these systems are energy efficient, durable and offer lightening comfort and optimal thermal performance. This is the case of the structural solution developed in joint research efforts of University of Zagreb and University of Ljubljana, within the Croatian VETROLIGNUM project. The design concept involves the mechanical interaction of timber and glass load-bearing members, without sealing or glued glass-to-timber surfaces. Laminated glass infilled timber frames are in fact recognized as a new generation of structural members with relevant load-carrying capacity (and especially the enhancement of earthquake resistance of framed systems), but also energy-efficient and cost-effective solutions. In this paper, brief guidelines for the optimal structural design of glass infilled Cross-Laminated Timber (CLT) framed systems are presented. A special focus is then dedicated to the thermal performance assessment of these innovative CLT-glass facade modules under ordinary operational conditions. Finite Element numerical models of single elements are developed to reproduce a full-size mock-up building. The actual thermal performance is thus carried out with the support of continuous ambient records. The numerical results show that the CLT-glass composite facade system can be efficient and offer stable performances, in line with national and European standards requirements.
... Besides the general calculation approach in the EN ISO 13788 provisions, moreover, a series of National guidelines are available in several countries to recommend minimum limit values for fRsi. These are range of fRsi ≥ 0.52 (France), or fRsi ≥ 0.65 (Netherlands) and fRsi ≥ 0.7 for Germany [33]. With the outside climate (temperature and relative humidity), four main parameters control the surface condensation and development of fungi, namely: ...
Preprint
Full-text available
Facade elements are known to represent a building component with multiple performance parameters to satisfy. Among others, “advanced facades” take advantage of hybrid solutions, like the assemblage of laminated materials. In addition to enhanced mechanical properties that are typical of optimally composed hybrid structural components, these systems are energy-efficient, durable, and offer lightening comfort and optimal thermal performance. This is the case of the structural solution developed in joint research efforts of the University of Zagreb and the University of Ljubljana, within the Croatian Science Foundation VETROLIGNUM project. The design concept involves the mechanical interaction of timber and glass load-bearing members, without sealing or bonded glass-to-timber surfaces. Laminated glass infilled timber frames are recognized as a new generation of structural members with relevant load-carrying capacity (and especially the enhancement of earthquake resistance of framed systems), but also energy-efficient and cost-effective solutions.
... Consequently, temperature factor requirements can vary depending on the harshness of the climate and the indoor humidity load dictated by the use of the building. Guidance sources [10] [11] reckon that a temperature factor of fRsi ≥ 0.80 should be sufficient to prevent surface condensation and mould growth over internal surfaces for dwellings of normal use. ...
Article
Full-text available
Ventilated façade systems, incorporating thermal insulation behind a rear-ventilated cladding, constitute a popular renovation solution in warm European climates. For compliance with building regulations, their energy efficiency is usually obtained through simple onedimensional desktop calculations, which do not consider the impact of the support elements of the cladding penetrating the thermal insulation. This study assesses a ventilated façade system anchored over a solid concrete wall with adjustable stainless steel brackets. One-dimensional calculations are compared against three-dimensional numerical thermal modelling, evaluating the effect of insulation thickness (40–100 mm) and potential gaps in the insulation around anchors. Results indicate low risk of condensation and mould growth over internal surfaces. The additional heat flow induced by stainless steel anchors, which is not considered by simplified calculations, appears lower than for aluminium-based systems but can become significant as insulation levels increase. Ensuring the continuity of insulation around anchors is critical for keeping this additional heat flow at reasonable levels (8–13%). If gaps in the insulation are present around anchors, the additional heat flow increases substantially (25–70%) and pushes effective U-values above 0.4 W/m ² K, thus resulting in unforeseen energy consumption and non-compliance with regulatory requirements in many European locations.
Article
Since many buildings in Canada were built prior to the advent of national and provincial energy codes and standards, quantifying building envelope thermal performance is an important step in identifying retrofit opportunities in existing buildings. This study aimed to use external quantitative infrared thermography (IRT) to estimate effective U-value of opaque building envelopes (considering the effect of thermal bridging sources) of a conditioned at-scale structure comprised of four wood-framed wall assemblies commonly used in Canada. Furthermore, the effect of vignetting artefacts on effective U-value measurements was assessed, followed by a practical approach to correcting for it to improve accuracy of U-value estimation and calibration of energy models. Additionally, a comprehensive uncertainty analysis was performed to evaluate the impact of input variables on the accuracy and uncertainty of results. Finally, apart from qualitative and quantitative thermal assessment of the building envelope, a novel relative quantitative infrared index (IRI) methodology was proposed as a means to facilitate rapid evaluation and subsequent ranking of building envelope thermal performance. The results indicated that vignetting effect has an adverse impact on the accuracy of results, in particular for well-insulated walls where deviations of -42.31% to -83.33% were observed. However, when the proposed practical approach was implemented, substantial improvements in accuracy of walls’ U-value were obtained, ranging from -2.33% to -12.50% after correction versus -13.95% to -58.33% without correction. Moreover, the results indicated that the energy model was substantially more accurate when the effect of thermal bridges were accounted for, and the adverse effect of vignetting was addressed in the estimation of U-value. In this case, ASHRAE Guideline 14 criteria were satisfied: Normalized Mean Bias Error (NMBE) < 5%, and Coefficient of Variation of the Root Mean Square Error (CVRMSE) < 15%. The findings of the uncertainty budget demonstrated that the influence of parameters on U-value depends on the type of wall assembly. Ultimately, wall thermal performance rankings based on IRI were consistent with their U-value rankings, implying that IRI can be a reliable metric for relative quantitative comparison of building envelope thermal performance, regardless of boundary conditions.
Conference Paper
Increased occupancy rates, inappropriate ventilation and intermittent heating regimes in dwellings can result in excessive atmospheric moisture levels, potentially leading to mould growth and lower indoor air quality. Identifying the causes associated to mould growth and taking correct remedial actions can be essential in reducing the prevalence of this problem. In practice it is often complex, even for experts, to accurately identify some of these causes and this can lead to costly and unnecessary interventions. Towards development of a novel systematic diagnostic procedure an extensive monitoring exercise has been undertaken involving collection of environmental data from dwellings with and without mould issues. The data has been analysed, considering building characteristics and occupancy's lifestyle features, with the objective to identify thresholds on measurable parameters that are indicative of mould growth risks. The proposed methodology links key parameters to identify factors that contribute to surface condensation and mould growth in buildings. This research presents a process towards environmental data collection, post-processing to compute and interpret pertinent environmental parameters, and displaying them in a clear and easy-to-interpret manner.
Article
Full-text available
Increased occupancy rates, inappropriate ventilation and intermittent heating regimes in dwellings can result in excessive atmospheric moisture levels, potentially leading to mould growth and lower indoor air quality. Identifying the causes associated to mould growth and taking correct remedial actions can be essential in reducing the prevalence of this problem. In practice it is often complex, even for experts, to accurately identify some of these causes and this can lead to costly and unnecessary interventions. Towards development of a novel systematic diagnostic procedure an extensive monitoring exercise has been undertaken involving collection of environmental data from dwellings with and without mould issues. The data has been analysed, considering building characteristics and occupancy’s lifestyle features, with the objective to identify thresholds on measurable parameters that are indicative of mould growth risks. The proposed methodology links key parameters to identify factors that contribute to surface condensation and mould growth in buildings. This research presents a process towards environmental data collection, post-processing to compute and interpret pertinent environmental parameters, and displaying them in a clear and easy-to-interpret manner.
Article
Full-text available
A mathematical model for the simulation of mould fungi growth on wooden material is presented, based on previous regression models for mould growth on sapwood of pine and spruce. Quantification of mould growth in the model is based on the mould index used in the experiments for visual inspection. The model consists of differential equations describing the growth rate of the mould index in different fluctuating conditions including the effect of exposure time, temperature, relative humidity and dry periods. Temperature and humidity conditions favourable for mould growth are presented as a mathematical model. The mould index has an upper limit which depends on temperature and relative humidity. This limiting value can also be interpreted as the critical relative humidity needed for mould growth depending also on the mould growth itself. The model enables to calculate the development of mould growth on the surface of small wooden samples exposed to arbitrary fluctuating temperature and humidity conditions including dry periods. The numerical values of the parameters included in the model are fitted for pine and spruce sapwood, but the functional form of the model can be reasoned to be valid also for other wood-based materials.
Article
This paper reviews the relations between mould, surface condcnsa tion, chmate, building design and occupancy factors and presents a comprehensive overview of the design guidelines in cool, humid chmates. The analysis showed that the mould condition is more severe than the surface condensation condition, that on an average the standard film coefficient for interior surfaces of 8 W/(m2.K) is too high, that the combined air and humidity transfers in dwellings is convection driven and that the hygroscopic inertia dampens the transient hygric response of an enclo sure.
Vastu võetud 15.05.2002. a seadusega
  • Ehitusseadus
Ehitusseadus. Vastu võetud 15.05.2002. a seadusega. Riigi Teataja I, 2002, 47, 297.
Kehtestatud Vabariigi Valitsuse 26.01.1999. a määrusega nr
  • Eluruumidele
Eluruumidele esitatavad nõuded. Kehtestatud Vabariigi Valitsuse 26.01.1999. a määrusega nr. 38. Riigi Teataja I, 1999, 9, 38.
  • A Raik
Raik, A. Eesti klimaatilisest rajoneerimisest. Eesti Loodus, 1967, 2, 65-70.
Indoor hygrothermal loads in Estonian dwellings
  • T Kalamees
Kalamees, T. Indoor hygrothermal loads in Estonian dwellings. In Proc. 4th European Conference on Energy Performance and Indoor Climate in Buildings. Lyon, 2006.
  • P Õhutemperatuur Karing
  • Eestis
Karing, P. Õhutemperatuur Eestis. Valgus, Tallinn, 1992.
Diffusion de vapeur au travers des parois -Condensations
  • J Berthier
Berthier, J. Diffusion de vapeur au travers des parois -Condensations. C.S.T.B. -REEF Sciences du Bâtiment, Vol. II, Paris, 1980.
Hygrothermal performance of building components and building elements -Internal surface temperature to avoid critical surface humidity and interstitial condensation -Calculation methods
EN ISO 13788:2001. Hygrothermal performance of building components and building elements -Internal surface temperature to avoid critical surface humidity and interstitial condensation -Calculation methods. International Organization for Standardization, Brussels, 2001.