AEBF01: L4
Design of the building
envelope
Insulation, thermal bridges, thermal
mass
Helena Bülow-Hübe
Helena Bülow-Hübe
1
AEBF01: L4
Heat conduction phenomena
Radiation
Convection
Conduction
A ’pore’ in an thermal
insulation material:
Thermal conductivity
Material
Aluminium
Steel, galvanised
Steel, stainless
Concrete
Brick
Light-weight concrete
Wood, wood boards
Mineral wool
Polystyrene
Helena Bülow-Hübe
λ (W/m,K )
220
50-60
14
1,7
0,6
0,10-0,19
0,14
0,04
0,03-0,04
Insulating building materials
• Mineral wool
– Glassfibre – Isover
– Rock wool – Paroc
• Polystyrene
– Extruded – XPS
– Expanded – EPS
• Light expanded clay
(Lättklinker) – Leca
• Lightweight concrete
(Lättbetong) – Yxhult
• Wood wool – (Holzwolle)
Träullit
• Insulation of wood wool,
cellulose, wool, linnenfibres, etc.
Mineral wool
(glass fibre)
Polystyrene
(XPS)
Paper-based (cellulose)
insulation
”Leca”
2
AEBF01: L4
Alternative building materials
• Leca
AAC - Lättbetong
• blocks or elements
blocks
insulated blocks
AAC /Lättbetong
• Autoclaved Aerated concrete (AAC), or otherwise known as
Autoclave Cellular Concrete (ACC), is a lightweight, precast
building material. AAC provides structure, insulation and fire
resistance in a single material. AAC products include blocks, wall
panels, floor and roof panels, and lintels.
• It has since been refined into a high thermally insulating concretebased material used for construction both internally and externally.
Besides insulating capability, one of AAC's advantages in
construction is its quick and easy installation since the material can
be routed, sanded and cut to size on site using standard carbon tip
band saws, hand saws and drills.
• Even though regular cement mortar can be used, 98% of the
buildings erected with AAC materials uses thin bed mortar, which
comes to deployment in a thickness of 1/8 inch. This varies on
national building codes and creates solid and compact building
members. AAC material can be coated with a stucco compound or
plaster against the elements. Siding materials such as brick or vinyl
siding can also be used to cover the outside of AAC materials.
Brick buildings
• Lightweight concrete (AAC)
blocks with stucco
Bo 01, Malmö
Yxhult’s low energy
house
Some manufacturers
•
•
•
•
•
•
•
Helena Bülow-Hübe
http://www.isover.se
http://www.paroc.se
http://www.termotra.se
http://www.ekofiber.se
http://www.traullit.se
http://www.leca.se
http://www.yxhult.se
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AEBF01: L4
Conductivity of insulating
materials - examples
Material
λ (W/m,K )
Polystyrene, XPS (extruded)
0,033
Polystyrene, EPS (expanded)
0,037
Mineral wool boards for walls
0,037
Mineral wool, loose fill
0,042
Wood wool /cellulose fiber, (loose fill)
Wood wool cement, blocks
Lightweight concrete (various densities
0,039
0,07
0,10 - 0,19
0,205
The inverse of R is called the U-value!
Rsi = 0.13 m 2 K/W
Internal heat surface resistance
Rse = 0.04 m 2 K/W
External heat surface resistance
Rtot = Rsi + R1 + R2 + R3 + ... + Rse
U=
1
R tot
Wall section:
d2
d1
and wall constructions)
Expanded clay (Lättklinker)
Thermal transmittance, U-value
d3
brick
brick
min.ull
R=
d
λ
series with electrical resistances:
R1
R2
R3
Rtot = Rsi + R1 + R2 + R3 + Rse
d = thickness (m)
λ = heat conductance
(W/m,K)
U=
1
Rtot
Modern single-family house –
wood stud frame
Rtot, Total
heat resistance
(m²K/W)
U-value or
Thermal transmittance
(W/m²K) or (W/m²°C)
Single-layer external wall –
principle
• Rain-coat, i.e. wood panel,
brick etc
• Ventilated air cavity
• Ext. wind-barrier, i.e. 9
gypsum, fibre cement board
or non-woven fabric
• Insulation between loadbearing wood studs or
lightweight studs
• Vapour barrier, 0,2 PE-foil
• Board, i.e 13 gypsum
Helena Bülow-Hübe
4
AEBF01: L4
Double-layer stud frame
• Insulation in two layers
with studs in perpendicular
directions give fewer
thermal bridges and less
air-gaps (cracks)
–-> better craftsmanship,
better U-value
Homogenous insulation layer outside
of stud frame
• Facade board with
slightly higher
density give both
wind-protection and
better insulation +
reduced thermal
bridges
In the case with brick wall (skalmur):
Better protection against moisture problems
caused by excessive mortar behind the brick.
Exterior insulation of load-bearing
concrete wall
• Light-weight
concrete and
concrete walls
are air-tight and
are insulated
with an exterior
homogenous
layer
Stucco on insulation layer
is
Mo
Helena Bülow-Hübe
Do not use stucco on insulation with
organic materials behind in un-ventilated
constructions!!
k!!
ris
e
tur
5
AEBF01: L4
Timber or log-house (1700s)
Plankhus - Wood planks
Brick
Standing wood planks from 1920’s.
From (Björk et al., 1984).
Helena Bülow-Hübe
6
AEBF01: L4
Stenstadshus, fram till 1930
Lamellhus, 1930-1960
Light-weight concrete walls and concrete slabs cast on site.
From (Björk et al, 1984).
Massive brick walls with timber floors.
from (Björk et al., 1984).
Elementhus, 1960-
Wood stud walls 1950
• Wood chips insulation
• Too little insulation…
Outer wall: Sandwich-element
concrete/min wool/concrete
Slabs:
Pre-cast concrete elements
Inner wall:
Leight-weight concrete
Example of pre-fabricated multi-family dwellings.
From (Björk et al., 1984).
Houses with stud frames
Approximate insulation thickness
Plankhus
Wood
Wood
Regelverkshus
Stenstadshus
Brick
Äldre
Lamellhus
1960: 95-125 mm
1960-70: 145 mm
1970-80: 165 mm
1980-90: 195-245 mm
2000: 170-200? mm
Passive houses: 400-500 mm
Helena Bülow-Hübe
Brick and light-weight concrete
Brick and light-weight concrete (concrete)
Punkthus
Load-bearing
external walls
Non-load 1920
bearing walls
Nyare Lamellhus, Skivhus,
(Punkthus)
Nyare Lamellhus, Skivhus
1930
1940
1950
1960
1970
1980
Cast-on-site concrete
Pre-cast concrete elements
7
AEBF01: L4
Building material use
wood
brick
concrete
How are masonry walls built
today?
other
• Homogenous walls of insulating
materials: Expanded clay,
Lightweight concrete, wood
wool cement blocks
• Two layers of brick walls with
intermediate insulation layer
• ”improved” blocks i.e. Sandwichblocks (isoblocks)
isoblock
light-weight concrete
U-value of insulated wall
U-värde för tilläggsisolerad av vägg
1.4
U-värde (W/m²,K)
• Consider the system border (=the
exerior of the wall?)
• In a super-insulated building, the
extra insulation in a passive house
can be financed by a simpler, or no
traditional heating system
Tilläggsisolering
1.6
U-value of wall (W/m²K)
Economical insulation?
1.2
1
0.8
d
0.6
0.4
0.2
0
0
50 100 150 200 250 300 350 400 450 500 550 600
Tilläggsisoleringens tjocklek d (mm)
Thickness of added insulation, d (mm)
Helena Bülow-Hübe
8
AEBF01: L4
Effect of thermal bridges
Cantilevering balconies
The extra heat flow is decribed by:
Ψ·ll (W/K) where
Ψ
(psi) Ψ
l
Intermittent insulation
is the ”linear thermal transmittance
coefficient” (W/mK)
is the length of the thermal bridge (m)
Other problems?
Low surface temperature • Poor thermal comfort
• Dirt accumulation
Wood-slab detail
poor – good?
Ψ
Ψ
Källa: Värme och Fukt, K Sandin, LTH
How large is the effect of thermal
bridges?
• Competition for housing development
Majrovägen, Stockholm, 1990
• Aim to stimulate development of buildings with
low energy use and good indoor climate
• Three winners:
– Svenska bostäder/BPA
– HSB/Ohlsson & Skarne
– NCC-Stockholm
Helena Bülow-Hübe
Without respect to thermal bridges
Energy use
(kWh/m²,a)
Heating
BPA
HSB
NCC
67
27
50
Elec. for operation
28
35
32
Household elec.
19
24
18
Total
113
86
100
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AEBF01: L4
With and without thermal bridges
Energy use
(kWh/m²,a)
BPA
HSB
NCC
Without thermal
bridges
113
86
100
With thermal bridges
115
104
106
Increase (%)
1.8
21.1
6.2
Per Levin & Mao Guofeng, Bygg & teknik 3/94
Exam-work regarding the effect of
thermal bridges in houses with
concrete structures
Examples of serious thermal
bridges
Source: Köldbryggors inverkan på energianvändningen
Jimmy Svensson och Andreas Westberg (2006).
Wall element
Horisontal cut prefab. wall
Temperatures
Details between prefab. wall and
slab at bay window
Vertikcal cut bay window
Temperatures
Equivalent insulation thickness = 163 mm (compare 220)
Helena Bülow-Hübe
10
AEBF01: L4
Psi=0,63 W/mK
Large increase in demand for
delivered energy!
Kv. Sutaren
90
Edge of slab
kWh / kvm, år
80
Psi=0,95 W/mK
70
23
60
20
50
Med köldbryggor
40
Utan köldbryggor
30
55
48
20
10
0
20 grader
22 grader
Inomhustemperatur
Increase is over 40 % !!!
Bay window
Kuldebroer. Tabeller med kuldebroverdier. Del I
og II. www.byggforsk.no
Thermal storage capacity
wall section:
d1
d2
series of electrical resistances
and capacities:
d3
brick
brick
min.wool
C = heat capacity (Ws/K)
m = mass (kg)
c = spec. heat (Ws/kg,K)
ρ = density (kg/m3)
http://bks.byggforsk.no/index.asp?docNumber=471017
Material
ρ (kg/m3 ) c (J/kg,K)
1000
4200
(1cm thickness)
42
Steel
7800
500
39
Concrete
2400
900
22
Ice
917
2200
20
Brick
1500
800
12
Wood
500
1500
7.5
Gypsum
900
800
7.2
Lightweight concrete
500
1000
5.0
4.8
Mineral wool
Air
280
1700
15-150
800
0.4
1.2
1000
0.012
Helena Bülow-Hübe
R2
C1
C2
R3
C3
per m² wall:
C = ∑m⋅ c = ∑ρ ⋅ d ⋅ c
ρ·d·c (kJ/m²K/cm)
Water
Wood wool cement
R1
Effective thermal capacity
Outer wall
Temp
Inner wall
T1
T2
Tout
11
AEBF01: L4
Brick wall or stud frame?
Effective thermal capacity
Internal insulation
• About the choice and effect of structure
materials on thermal climate, energy use
and costs in schools
External insulation
Temp
T1
T2
Tout
Exterior wall: heavy - light
Värmebehov (kWh/m²,år)
Heavy or light walls?
Heating demand (kWh/m²a)
– Exam. Work by Holmberg & Landfors (1997),
Avd f installationsteknik, LTH
100
årsenergi
80
75.5
77.2
Brick
Wood
Tegel
Regel
60
40
20
0
Inner wall: heavy - light
Stomalternativ
Choice of structure system
Sommarfallet
Cost comparison
Cost
(kr/m²BRA)
Production
Brick
Wood
Difference
13071
12381
690
Operation
25
26
-1
Maintenance
0
13
-13
Insurance
7
18
-9
13103
12438
665
Total
Helena Bülow-Hübe
12
AEBF01: L4
Rather brick than wood!
• The heavy structure system has a
higher initial cost (production cost)
• It is paid-back in 28 years, i.e. it is
cost effective if used longer than 28
years
Life-cycle perspective of energy
use
Energy used for
production &
transportation of
materials used at
erection and
demolishing
Energy use for
operation during
the entire life-time
of the building
– Normally 33 years are used for writing
off costs for school buildings
• How can better comfort be valued?
Study of 4 multi-family buildings
(SE)
• Erected in 1996, different but yet all typical of
the time
• Various choices of foundation, structure
systems, size, insulation levels (Uavg=0.26-0.44)
and ventilation systems
– Adalberth, K, m fl (2001). Life Cycle Assessment of
four Multi-Family Buildings. Int. J of Low Energy
and Sustainable Buildings. Vol 2, 2001-2002
http://bim.ce.kth.se/byte/leas/
Analysis of the effects on:
•
•
•
•
•
•
Global warming
Acid rain (försurning)
Eutrophication (Övergödning)
Ground-level ozone production
Toxicity (for humans)
Energy use
Helena Bülow-Hübe
LCA-analysis of the following:
• Production of materials for new production
and renovation
• Transports during building phase, renovation,
and demolishment
• Erection and demolishment
• The building’s use (assumed to 50 years)
– The energy use of the building with a mix of energy
sources for the supply
Results LCA analysis
• The operation phase accounts for
the largest environmental threat,
approx 70-90%
• The production phase has little
significance, 10-20% of the total
environmental load
the
choice of structure
systems have only small
environmental effects
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AEBF01: L4
Summary
• Use good insulation materials (i.e those
with a low lamda-value, gives a lower Uvalue)
• The better the house is insulated, the more
important is the design of construction
details
• Thermal bridges must be included in the
total energy balance of the building
Tung stomme ger jämnare inneklimat
men sparar inte mycket energi
• Störst påverkan på operativ temperatur,
dvs upplevt inneklimat
• Årsenergibehovet för tung stomme kan
förväntas vara något lägre, ca 85-95% av
behovet för lätta stommar (100%)
• Även trä har relativt stor värmekapacitet,
och kan utnyttjas för värmelagring (massiv
träkonstruktion)
The operation phase is the most
important!
Tillverkning
15%
production
operation
Användning
85%
Helena Bülow-Hübe
14
