1. K124 BPH Thermal Protection of Buildings
Zbyněk Svoboda
K124, A529

2. Building Physics General parts: building acoustics natural lighting
thermal protection of buildings
General goals:
to create optimal internal
environment with low external
environmental impacts
to secure long-time durability of buildings

3. Building Physics BPH Used symbols: additional information
important information necessary for exam
information for self-learning
definitions

4. Energy performance of buildings

5. Energy performance of buildings
EU 2004
USA 2007
One of important contemporary issues.
Energy use in buildings makes up to 40 % from total energy use in industrial countries.
Building industry: large savings are possible, solutions exist, realization can be immediate.

6. Energy performance of buildings
Specific energy need for heating
„Zero-energy building“: under 5 kWh/m2
„Energy plus building”: under 0 kWh/m2 : net production of energy
Building industry: large savings are possible, solutions exist, realization can be immediate.

7. Energy performance of buildings
Low-energy buildings

8. Low-energy buildings
controversial in the past, a kind of fashion today,
normal standard in the future
without any considerable restriction for architecture design

9. Low-energy buildings Condition: well-thought-out project!
realistic… or sophisticated solution
The first passive office building in Czechia
Ostrava (arch. R. Václavík)

10. Low-energy buildings Strategies of solution:
building must be designed as a complex with specialists from the beginning
minimalisation of energy consumption (heating/cooling) by means of building design:
insulations above standard
perfect details
perfect realisation
air-tightness

11. Low-energy buildings Strategies of solution:
using of zones (eg. unheated spaces towards North)
considering orientation and location of building

12. Low-energy buildings Strategies of solution:
using of zones (eg. unheated spaces towards North)
considering orientation and location of building
Window energy
balance
(A=1,5 m2):
U = 1,1 m2K/W & g = 0,5
optimum for heating mode: low U-value, high g-value
for cooling mode: shading necessary!

13. Low-energy buildings Strategies of solution:
well-thought-out HVAC design:
efficient heat sources
efficient lighting and appliances
regulation!
usage of renewable sources of energy (collectors, heat pumps, ground heat exchangers…)
everything must be connected and operation modes must be carefully designed

14. Low-energy buildings Strategies of solution:
usage of already presented energy (heat recovery, gains)

15. Low-energy buildings Strategies of solution:
usage of already presented energy (heat recovery, gains)
e.g. Trombe walls

16. Low-energy buildings Strategies of solution:
usage of energy accumulation within building
Heavy weight constructions optimal for heat accumulation
Partitions from unburned clay bricks in timber houses
Accumulation of heat from solar collector to the soil (gravel bed)

17. Low-energy buildings Strategies of solution:
usage of recycled and natural materials
unburned clay
paper
wood
sheep wool
straw
cork

18. Low-energy buildings Strategies of solution:
energy production in buildings
PV systems
cogeneration

19. Energy performance of buildings
EC: support of low-e building by means of legislation, demonstrative and pilot projects and structural funds.
EPBD I and II: European directives about EPofB
National directives and laws:
law no. 318/2012 Sb. and directive no. 78/2013 Sb.
Other documents:
ČSN
TNI
TNI

20. Principles of calculation
Energy performance of buildings
Principles of calculation

21. Principles of EPB calculation
Basic calculation principles for heat transfer in buildings
Newton law (law of cooling)
heat loss
of solid
area
temp. difference surface - air
Published 1701
(Newton is a member of Parliament for 2nd time.
Not very active.)
History context
Beg. 18. cent.: all materials have the same conductivity. Temperature differences are caused by different thermal capacity.
1777: discovery of radiative heat transfer (C. W. Scheele)
: first measurements of thermal conductivity.
I. Newton according to W. Blake

22. Definitions Heat transfer coefficient [W/(m2K)]
Ratio coefficient between heat flow density and temperature difference,
which causes the heat flow.
It specifies how much heat in W is transferred from surface of 1 m2 to ambient fluid (e.g. air) or in opposite direction when temperature difference between surface and fluid is 1 K.
Very unstable quantity, depends on air velocity, shape and size of construction, temperature… Exact values are measured. More empiric equations exist.
heat flow density
It consists of two parts:
Definition – not usable in practical calculations.
More usable equations in following lectures.
convection
heat transfer coefficient:
radiation
Usage: in the cases of heat transfer between solid body and fluid
Typical values hi = 8 W/(m2K) (internal surface of walls),
he = 25 W/(m2K) (external surface of walls).

23. Definitions Surface thermal resistance [m2K/W]
Inverse value to heat transfer coefficient :
Usage: in the cases of heat transfer between solid body and fluid
Typical values Rsi = 0,13 m2K/W (internal surface of walls),
Rse = 0,04 m2K/W (external surface of walls).
Thermal transmittance, U-value [W/(m2K)]
Basic property expressing thermal insulation quality of construction.
It specifies how much heat in W is transferred through construction of 1 m2
(orthogonally to surface) when temperature difference between interior and exterior is 1 K.
Requirements are in ČSN (details in following lectures).
Calculation method is in EN ISO 6946 (details in following lectures).

24. Principles of EPB calculation
Basic calculation principles for heat transfer in buildings
1. Heat transfer through construction (modified Newton law):
heat loss or gain
temperature difference on both sides of construction
thermal transmittance
time (duration of calculated period)
area
Result: heat in J = Ws (Wh are usually used)
Eq. could be also without time: then loss/power output in W
Alternative notation:
transmission heat transfer coefficient [W/K]

25. Definitions Transmission heat transfer coefficient [W/K]
Heat flow by transmission through building envelope related to unitary
temperature difference.
It specifies how much heat in W is transferred through building envelope when temperature difference between interior and exterior is 1 K.
Calculation procedure in EN ISO and EN ISO (details later).
It contains 3 parts:
through
constructions
between
internal and
external air
transmission heat transfer coefficient:
adjacent
to ground
adjacent to
unconditioned
spaces
Alternative according to ČSN :
construction area
thermal transmittance
temperature reduction
factor (influence of
temperature difference
loading the construction)

26. Principles of EPB calculation
Basic calculation principles for heat transfer in buildings
2. Heat for the ventilation:
air density
specific heat capacity of air
time
temperature difference
interior-exterior
volume flow of external (fresh) air
necessary for ventilation [m3/s]
Alternative notation:
ventilation heat transfer coefficient [W/K]

27. Definitions Ventilation heat transfer coefficient [W/K]
Heat necessary for warming of external air entering the interior by
ventilation or through leakages. It is related to unitary temperature
difference between internal and external air.
It specifies how much heat in W is necessary for warming of the whole amount of ventilation air when temperature difference between interior and exterior is 1 K.
Calculation procedure in EN ISO (details later).
General formula:
volume flow of ventilation air
[m3/s]
air density
[kg/m3]
air heat capacity
[J/(kg.K)]

28. Principles of EPB calculation
Basic calculation principles for heat transfer in buildings
3. Energy balance of a space:
heat loss by transmission
heat loss by ventilation
internal gain
transmission heat transfer coefficient through thermal joints

29. Principles of EPB calculation
Basic calculation principles for heat transfer in buildings
Thermal bridges + joints: parts of constructions with increased
heat flow caused by presence of other
materials or by geometry (shape of detail)
parts of constructions
joints between constructions
included in thermal transmittances of constructions
expressed as stand-alone factor

30. Principles of EPB calculation
Basic calculation principles for heat transfer in buildings
Thermal bridges + joints: spots in constructions with increased
heat flow caused by presence of other
materials or by geometry (shape of detail)
correction factor for thermal joints (0 to 0,2 W/(m2K))
approximately:
exactly:
point thermal transmittance (3D details)
length of 2D thermal joint
linear thermal transmittance (EN ISO 10211)

31. Definitions Linear thermal transmittance [W/(m.K)]
Basic parameter expressing thermal-insulation quality of linear (2D) thermal joint.
It specifies how much heat in W is transferred through thermal joint of 1 m
length when temperature difference between interior and exterior is 1 K.
Requirements in ČSN , calculation procedure in EN ISO
Point thermal transmittance [W/K]
Basic parameter expressing thermal-insulation quality of point (3D) thermal
joint.
It specifies how much heat in W is transferred through point thermal joint when temperature difference between interior and exterior is 1 K.
Requirements in ČSN , calculation procedure in EN ISO

32. Principles of EPB calculation
Basic calculation principles for heat transfer in buildings
3. Energy balance of space:
gains = losses („conservation of energy“ law)
2 basic tasks:
calculation of necessary power output of heating (cooling) to maintain desired internal temperature θi
b) calculation
of temperature θi when
heat gains Qg (persons,
boiler, Sun…) are known

33. Energy performance of buildings
Model of building

34. Model of the building
Only conditioned part of building is evaluated. It can be divided to zones.
Zone includes all spaces:
with internal design temperature different not more than 4 C
with the same heating (and cooling) system
with the same ventilation system on at least 80 % of floor area (natural/forced/heat recovery)
with air change rate max. 4-times different within at least 80 % of floor area

35. Model of the building Typical 1 zone buildings:
family and residential houses
common other buildings (offices)
Typical multizone buildings:
multifunctional buildings
factories with administrative units
Boundaries between zones:
1. not taken into account
- if zones have the same heat/cold source
- if the aim of calculation is to evaluate the building as a whole
2. taken into account
- in other cases

36. Model of the building system boundary of zone (building)
Zone boundary:
can be specified generally from:
internal
overall internal
and external dimensions
- according to (not only) Czech regulations: external dimensions
system boundary
of zone (building)
- roof parapets: according to roof
zone boundary is located on external surfaces
special cases:
- ventilated constructions (ext.
surface of therm. insulation)
- floors on ground (dtto)
- floors above basement (accord. to type of basement)

37. (+ detailed calculation)
Model of the building
System boundary:
examples (TNI ):
Small internal unconditioned spaces (stairs, corridors) :
- depend on location
possibilities:
- unheated space
(outside zone)
- part of the zone
edge cases:
In case of doubt:
unheated space
(+ detailed calculation)
Areas of constructions on the zone boundary:
from design dimensions for windows and doors (in plans: dimensions of the openings in walls)
from external dimensions for other constructions

38. Mean thermal transmittance
Energy performance of buildings
Mean thermal transmittance

39. Definitions Mean thermal transmittance of the building [W/(m2K)]
Basic parameter expressing thermal-insulation quality of building
envelope.
It specifies how much heat in W is transferred through 1 m2 of building envelope (i.e. envelope of heated part) when temperature difference between interior and exterior is 1 K.
Requirements in ČSN (details later).
Calculation procedure in ČSN (details later).
The value shows the influence of the building constructions design.

40. Mean therm. transmittance
Requirement of ČSN :
For new buildings and for newly created parts
of refurbished buildings,
it is reaquired:
Only heated part of the building is evaluated.
Requirement is derived by calculation of reference building. It is
the same as evaluated building with some differences:
envelope constructions have U-value on the required level by ČSN
area of windows is taken as max. 50% of the whole wall area (if larger, windows are taken as walls)

41. Mean therm. transmittance
Requirement of ČSN :
calculation:
Requirement for buildings
with prevailing set-point (internal) temperature θim below 18 C or above 22 C:
where Uem,N,20 is basic required value
according to equation on this slide.
required U-value for j construction (details
in next lectures)
temperature
reduction factor
(details following)
sum over envelope constr.
ratio between total envelope area and volume of evaluted part
accepted values: from 0,2 to 1,0
correction for thermal joints
area of j envelope construction
result cannot be higher than:
for new residential b.: 0,5 W/(m2.K)
for other buildings:

42. Definitions Set-point temperature (design internal temperature) [ ̊C]
Required internal temperature guaranteed by heating or cooling (generally different for both modes).
Approximately mean value calculated from air temperature and mean radiant temperature. Usually lower than air temperature.
Usage: energy performance of buildings calculation
Source: ČSN , ČSN EN 12831, investor.
Typical value for heating mode θi = 20 C.
Prevailing set-point temperature (prevailing design internal temperature) [ ̊C]
Set-point temperature of most spaces in evaluated building or its part
(zone).
Typical value for heating mode θi = 20 C.

43. Mean therm. transmittance
Requirement of ČSN :
fullfilment of requirements is expressed
by means of envelope energy certificate:
level corresponding to exact
fullfilment, i.e. Uem = Uem,N
ratio of Uem / Uem,N
(percentage of Uem from Uem,N)
required value Uem,N

44. Mean therm. transmittance
Calculation (ČSN ):
based on principles of EN ISO standards
transmission heat transfer coeff.
total envelope area
typical values: 0,1 (standard); 0,02 (optimalised solution);
0,2 (poor solution)
temp. reduction factor [-]
approx.:
exact:
linear thermal transmittance
[W/(mK)]
point thermal transmittance [W/K]

45. Mean therm. transmittance
Calculation (ČSN ):
temperature reduction factor b:
it expresses influence of real temperature difference
tables in ČSN – not usable for low-e buildings, too old
calculation for constructions adjacent to external air:
design internal temperature adjacent to construction
design outdoor air temperature in winter period
prevailing design internal temperature (prevailing set-point temperature)

46. Definitions Design outdoor air temperature in winter period [ ̊C]
Maximum value from lowest 2-days’ mean values calculated from
minimum daily temperatures during last 20 years.
Defined in ČSN :
Rounded down to nearest WHOLE number (e.g. -13,1 to -14 C)!
Usage: evaluation of constructions and derivation of requirements
Typical values θe from -13 C (e.g. Praha) to -17 C (e.g. Bruntál), extreme -21 C (highest mountain Sněžka).
height above sea level of 1st floor
basic design external temperature in 100 m a.s.l.
CR divided to 4 areas with values:
-12/-14/-16/-18 C
temperature gradient
For 4 areas:
-0,5/-0,2/-0,2/-0,2 C

47. Mean therm. transmittance
Výpočet (ČSN ):
činitel teplotní redukce:
tabulky v ČSN – nepříliš vhodné, částečně zastaralé, pro NED zcela nepoužitelné
Calculation (ČSN ):
temperature reduction factor:
construction adjacent
to unconditioned spaces
temperature in uncondi-tioned space
EN ISO 13789
uncond. space

48. Mean therm. transmittance
Calculation (ČSN ):
temperature reduction factor:
constructions adjacent to ground
ground temperature
EN ISO 13370
steady-state heat transfer coeff. via the ground
without ground
incl. ground

49. Mean therm. transmittance
Calculation (EN ISO 13789):
similar approach, only without factors b
Transmission heat transfer coefficient
Trans. heat transfer coeff. through constructions between internal and external air
Calculation accord. to EN ISO 13789:
steady heat transfer coeff. via ground
calculation accord. to EN ISO 13370:
area of floor
on ground
floor perimeter
U-value of floor including influence of ground
linear thermal transmittance in joint between floor and wall
construc-tions
2D th.
joints
3D th. joints
Heat transfer through:

50. Mean therm. transmittance
Calculation (EN ISO 13789):
similar approach, only without factors b
Transmission heat transfer coefficient
Trans. heat transfer coeff. through constructions between internal and external air
Calculation accord. to EN ISO 13789:
trans. heat transfer coeff. via unconditioned spaces
calculation accord. to EN ISO 13789:
construc-tions
2D th.
joints
3D th. joints
Heat transfer through:
total specific heat flow from interior to unconditioned space
total specific heat flow from unconditioned space to exterior