1. Minimum internal surface temperature
Properties of constructions
Minimum internal surface temperature

2. Min. internal surf. temperature
It is used for evaluation of the risk of vapor condensation on internal surface and of the risk of mould growth.
When does surface
condensation occur?
Surface temperature is lower than dew point temperature of
ambient air.

3. Definitions Dew point temperature [˚C] humidity of air is 100 %).
Temperature with the maximum saturation of air by water vapor (relative
humidity of air is 100 %).
It depends on temperature and relative humidity of air.
E.g. for air with temperature
20 ˚C and rel. humidity 50%,
dew point temperature is
9,3 ˚C.
If we cool the air with temperature
20 ˚C and rel. humidity 50%
to 9,3 ˚C, it will be saturated by
water vapor.

4. Surface humidity above 80% and…
Min. internal surf. temperature
It is used for evaluation of the risk of vapor condensation on internal surface and of the risk of mould growth.
When does mould
growth start?
- oxygen
air RH optimally over 60%
temperature opt C
nutrients: dust, organic scraps, C+N from air, trace nutrients (rain, breath, fingerprints…)
Surface humidity above 80% and…

5. Min. internal surf. temperature
It is used for evaluation of the risk of vapor condensation on internal surface and of the risk of mould growth.
Internal surface condensation has no connection with vapor transfer through constructions! (it cannot be influenced by vapor barrier etc.)
It depends only on thermal-insulating properties of constructions (R, U, details…) and on boundary conditions.

6. Min. internal surf. temperature
Surface vapor condensation could be eliminated by:
1) increase of surface temperature of construction
Possibilities: - improvement of thermal insulation (larger thickness, continuity of insulation in details,
thermal breaks…)
- warming of construction’s internal surface
2) decrease of dew point temperature of internal air
Possibilities: - decrease of internal air humidity (dehumidification, ventilation, limitation of sources)

7. Temperature factor at internal surface
Properties of constructions
Temperature factor at internal surface

8. Temperature factor at internal surface
Alternative expression of internal surface temperature – independent on boundary conditions – it is parameter of construction or detail.
Internal surface temperature calc.
START
variable for various boundary conditions
Temperature factor at int. surface
STOP
constant, parameter of construction
It is used in catalogues of details…
… and for evaluation of requirement
(from 2007).

9. Calculation: Temperature factor at internal surface
design temperature of external air in winter period
design temperature of internal air
(or generally: the same temperature which was used to calculate internal surface temperature θsi )

10. Calculation: Temperature factor at internal surface
surface temperatures calculation:
opaque constr.: 0,25 m2K/W
windows, doors: 0,13 m2K/W
behind furniture: 0,50 m2K/W
min. internal surface temperature
details:
numerical solution necessary, no formulas for direct calculation
planar constructions:

11. Calculation: Temperature factor at internal surface
surface temperatures calculation:
opaque constr.: 0,25 m2K/W
windows, doors: 0,13 m2K/W
behind furniture: 0,50 m2K/W
min. internal surface temperature
details:
numerical solution necessary, no formulas for direct calculation
Int. surface temperature
and temperature factor:
problem of critical details,
(temp. factor is satisfactory for every
planar construction with satisfactory
U-value), it is necessary
to solve th. bridges
planar constructions:

12. Requirement of ČSN 730540-2: Temperature factor at internal surface
dependent on type of construction:
windows + doors – elimination of surface condensation
other – elimination of mould growth
derived from max. acceptable surface RH:
100 %
80 %
for interiors with RH  60 %:

13. and φi=50% (for -5 C in exterior):
Temperature factor at internal surface
Requirement of ČSN :
dependent on type of construction:
windows + doors – elimination of surface condensation
other – elimination of mould growth
derived from max. acceptable surface RH:
Typical values
for θe=-15 C, θai=20,6 C
and φi=50% (for -5 C in exterior):
windows: fRsi,cr = 0,653
other: fRsi,cr = 0,747
100 %
80 %
for interiors with RH  60 %:

14. for ventilated constructions:
Temperature factor at internal surface
Requirement of ČSN :
for interiors with RH > 60 %:
requirement does not have to be fulfilled but following must be ensured:
satisfactory thermal transmittance
excellent function during surface condensation
adjacent constructions without defects from moisture
elimination of mould growth in some other way than high surface temperature
RH near surface can be also decreased using AC
for ventilated constructions:
temp. factor at internal surface of external deck:
variable in direction of air flow
usually evaluated only at outlet

15. Thermal bridges and joints: calculations and design recommendation
Properties of constructions
Thermal bridges and joints: calculations and design recommendation

16. parts of constructions between constructions
Thermal bridges and joints
Terminology:
Thermal bridges and joints: parts of construction with increased heat
flow caused by more conductive
materials or geometry
parts of constructions
between constructions
Types of bridges and joints:
geometrical
(due to shape)
constructional
(due to load bearing
structure)
systematic
(regularly repeating)
convective
(due to convection through leakages)

17. The most common appearance
Thermal bridges:
slope roofs with insulation
timber buildings
curtain walling
sandwich panels
anchors, fasteners
etc. etc.
Thermal joints:
all connections wall-window
connection wall-roof, wall-ceiling
and wall-floor on ground
cantilevers (balconies, overhangs)
any local disruption of thermal insulation
etc. etc.

18. Thermal bridges and joints
Governing equations:
part. diff. equation for heat conduction
3D steady state
conduction
in general, numerical solution necessary (FEM, FDM)
2D steady state conduction

19. Thermal bridges and joints
Numerical solutions:
using software (e.g. COMSOL, ANSYS, FLIXO,AREA…)
specific steps are dependent on SW
generally:
identification of th. bridge
model selection (2D, 3D)
simplification
specification of materials and conditions
model creation
calculation
interpretation and evaluation of results
quality of model
depends on purpose:
windows x
common details
correct Rsi necessary (0,25 a 0,13)!
specified for surfaces in contact with air
sections = adiabatic boundaries (without heat flow over boundary)
condition in ground (mean annual temperature, usually 5 C)
in 3 m (1 m) under the floor

20. Thermal bridges and joints
Numerical solutions:
using software (e.g. COMSOL, ANSYS, AREA, CUBE3D)
specific steps are dependent on SW
generally:
identification of th. bridge
model selection (2D, 3D)
simplification
specification of materials and conditions
model creation
calculation
interpretation and evaluation of results
quality of model
depends on purpose:
windows x
common details
procedures in EN ISO 10211, EN ISO and EN ISO 13947
It is necessary to include also a part of construction around th. bridge, boundary = min. 1 m or 3 * bridge thickness or symmetry axis.

21. Thermal bridges and joints
Example of calculation:
input information
calculation results
geometry of the model
fRsi = 0,881

22. Thermal bridges and joints
What are the effects of thermal bridge?
decreased internal surface temperature
increased external surface temperature
increased heat flow
visually: higher density of isotherms

23. Elimination of bridges and joints
Possibilities:
basic rule: decrease the number of thermal bridges and joints
(mainly of balconies, overhangs, cantilevers…)
if not possible, try to change static scheme
(use separate columns instead of cantilever etc.)
always continuous insulation!
„iso – beam“

24. …preferably from external side
Elimination of bridges and joints
Possibilities:
basic rule: decrease the number of thermal bridges and joints
(mainly of balconies, overhangs, cantilevers…)
if not possible, try to change static scheme
(use separate columns instead of cantilever etc.)
always continuous insulation!
…preferably from external side
and in max. thickness!

25. Elimination of bridges and joints
Possibilities:
- simple shapes are better
think about real possibilities
of building process!
the simpliest shapes
with smallest problems

26. Elimination of bridges and joints
Possibilities:
- decrease the area of external
surfaces
(beware of high roof parapets!)
- optimalisation of the shape
Extremely disadvantageous:
large external surface
smal internal surface
Spittelau Viadukt
Zaha Hadid,
Vídeň

27. Elimination of bridges and joints
use up-to-date technologies
insulation fasteners (basalt) in sandwich walls
insulation pads
under anchors
insulatiuon of wall footing
(here Wienerberger)
hardened plastics:
Purenit,
Compacfoam

28. Elimination of bridges and joints
eliminate even „small“ thermal bridges
hidden screw
EPS plug
injection anchors Spiral Anksys up to 300 mm

29. Elimination of bridges and joints
eliminate even „small“ thermal bridges
Importance of thermal
bridges and joints rises.
The better the primary construction,
the worse problem the bridge is.
Heat loss through thermal joints:
formerly units of %
today even tens of %
from the building
total heat loss.
Fixing blocks Dosteba – various types, even for high load