aebf01: l4 - lth
TRANSCRIPT
AEBF01: L4
Helena Bülow-Hübe 1
Design of the buildingenvelope
Insulation, thermal bridges, thermalmass
Helena Bülow-Hübe
AEBF01: L4
Helena Bülow-Hübe 2
Heat conduction phenomena
RadiationConvectionConduction
A ’pore’ in an thermalinsulation material:
Thermal conductivity
1,7Concrete
0,6Brick
0,10-0,19Light-weight concrete
0,14Wood, wood boards
0,04Mineral wool
0,03-0,04Polystyrene
14Steel, stainless
50-60Steel, galvanised
220Aluminiumλλλλ (W/m,K )Material
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, linnen-fibres, etc.
Paper-based (cellulose)insulation
”Leca”
Mineral wool(glass fibre)
Polystyrene(XPS)
AEBF01: L4
Helena Bülow-Hübe 3
Alternative building materials
• Leca
blocks insulated blocks
AAC - Lättbetong
• blocks or elements
AAC /Lättbetong• Autoclaved Aerated concrete (AAC), or otherwise known as
Autoclave Cellular Concrete (ACC), is a lightweight, precastbuilding 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 concrete-based 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, MalmöYxhult’s low energyhouse
Some manufacturers
• 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
AEBF01: L4
Helena Bülow-Hübe 4
Conductivity of insulatingmaterials - examples
0,07Wood wool cement, blocks
0,037Mineral wool boards for walls
0,037Polystyrene, EPS (expanded)
0,033Polystyrene, XPS (extruded)
0,039Wood wool /cellulose fiber, (loose fill)
0,10 - 0,19Lightweight concrete (various densities
and wall constructions)
0,205Expanded clay (Lättklinker)
0,042Mineral wool, loose fill
λλλλ (W/m,K )Material
Thermal transmittance, U-value
series with electrical resistances:
R1 R2 R3
sesitot RRRRRR ++++= 321
d2
brick brick
min.ull
Wall section:
d3d1
totRU
1=λd
R =d = thickness (m)λ = heat conductance
(W/m,K)
The inverse of R is called the U-value!
totRU
1=
sesitot RRRRRR +++++= ...321
K/Wm04.0
K/Wm13.02
2
=
=
se
si
R
R Internal heat surface resistance
External heat surface resistance
Rtot, Total heat resistance(m²K/W)
U-value or Thermal transmittance(W/m²K) or (W/m²°C)
Modern single-family house –wood stud frame
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 boardor non-woven fabric
• Insulation between load-bearing wood studs or lightweight studs
• Vapour barrier, 0,2 PE-foil• Board, i.e 13 gypsum
AEBF01: L4
Helena Bülow-Hübe 5
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 outsideof stud frame
• Facade board with slightly higherdensity give bothwind-protection and better insulation + reduced thermalbridges
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
Moisture ris
k!!
Do not use stucco on insulation with organic materials behind in un-ventilated
constructions!!
AEBF01: L4
Helena Bülow-Hübe 6
Timber or log-house (1700s)
Plankhus - Wood planks
Standing wood planks from 1920’s. From (Björk et al., 1984).
Brick
AEBF01: L4
Helena Bülow-Hübe 7
Stenstadshus, fram till 1930
Massive brick walls with timber floors. from (Björk et al., 1984).
Lamellhus, 1930-1960
Light-weight concrete walls and concrete slabs cast on site. From (Björk et al, 1984).
Elementhus, 1960-
Example of pre-fabricated multi-family dwellings. From (Björk et al., 1984).
Outer wall: Sandwich-elementconcrete/min wool/concrete
Slabs:Pre-cast concrete elements
Inner wall: Leight-weight concrete
Wood stud walls 1950
• Wood chips insulation • Too little insulation…
Houses with stud framesApproximate insulation thickness
1960: 95-125 mm1960-70: 145 mm
1970-80: 165 mm
1980-90: 195-245 mm2000: 170-200? mm
Passive houses: 400-500 mm
WoodPlankhus
Regelverks-hus
BrickStenstadshus
1920 1930 1940 1950 1960 1970 1980
Load-bearing external walls
Non-load bearing walls
ÄldreLamellhus
Brick and light-weight concrete
Punkthus Brick and light-weight concrete (concrete)
Wood
Cast-on-site concrete
Pre-cast concrete elements
Nyare Lamell-hus, Skivhus, (Punkthus)
Nyare Lamell-hus, Skivhus
AEBF01: L4
Helena Bülow-Hübe 8
Building material use
wood brick
light-weight concrete
concrete other
How are masonry walls builttoday?
• Homogenous walls of insulatingmaterials: Expanded clay, Lightweight concrete, woodwool cement blocks
• Two layers of brick walls with intermediate insulation layer
• ”improved” blocks i.e. Sandwich-blocks (isoblocks)
isoblock
Economical insulation?
• 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
TilläggsisoleringU-värde för tilläggsisolerad av väggU-värde för tilläggsisolerad av väggU-värde för tilläggsisolerad av väggU-värde för tilläggsisolerad av vägg
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 250 300 350 400 450 500 550 600
Tilläggsisoleringens tjocklek d (mm)
U-v
ärde
(W/m
²,K
)
dddd
Thickness of added insulation, d (mm)
U-v
alu
eo
f w
all(
W/m
²K)
U-value of insulated wall
AEBF01: L4
Helena Bülow-Hübe 9
Effect of thermal bridgesThe extra heat flow is decribed by:
ΨΨΨΨ·llll (W/K) where
ΨΨΨΨ is the ”linear thermal transmittancecoefficient” (W/mK)
llll is the length of the thermal bridge (m)ΨΨΨΨ(psi)
Cantilevering balconies
Intermittent insulation
Other problems?Low surface temperature ����
• Poor thermal comfort• Dirt accumulation
Wood-slab detailpoor – good?
ΨΨΨΨ
ΨΨΨΨ
Källa: Värme och Fukt, K Sandin, LTH
How large is the effect of thermalbridges?
• Competition for housing developmentMajrovägen, 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
Without respect to thermal bridges
10086113Total
182419Household elec.
323528Elec. for operation
502767Heating
NCCHSBBPAEnergy use(kWh/m²,a)
AEBF01: L4
Helena Bülow-Hübe 10
With and without thermal bridges
6.221.11.8Increase (%)
106104115With thermal bridges
10086113Without thermalbridges
NCCHSBBPAEnergy use(kWh/m²,a)
Per Levin & Mao Guofeng, Bygg & teknik 3/94
Exam-work regarding the effect of thermal bridges in houses with
concrete structures
Source: Köldbryggors inverkan på energianvändningenJimmy Svensson och Andreas Westberg (2006).
Examples of serious thermalbridges
Wall element
Horisontal cut prefab. wall
Equivalent insulation thickness = 163 mm (compare 220)
Temperatures
Details between prefab. wall and slab at bay window
Vertikcal cut bay window Temperatures
AEBF01: L4
Helena Bülow-Hübe 11
Edge of slab
Bay window
Psi=0,95 W/mK
Psi=0,63 W/mK
Large increase in demand for delivered energy!
Kv. Sutaren
48 55
2023
0
10
20
30
40
50
60
70
80
90
20 grader 22 grader
Inomhustemperatur
kWh
/ kvm
, år
Med köldbryggor
Utan köldbryggor
Increase is over 40 % !!!
Kuldebroer. Tabeller med kuldebroverdier. Del I og II. www.byggforsk.no
http://bks.byggforsk.no/index.asp?docNumber=471017
Thermal storage capacity
min.wool
series of electrical resistancesand capacities:
R1 R2 R3
∑∑ ⋅⋅=⋅= cdcmC ρC = heat capacity (Ws/K)m = mass (kg)c = spec. heat (Ws/kg,K)ρ = density (kg/m3)
d2
brick brick
wall section:
d3d1
C3C1 C2
per m² wall:
1000
800
1700
1000
800
1500
800
2200
900
500
4200
c (J/kg,K)
0.012
0.4
4.8
5.0
7.2
7.5
12
20
22
39
42
ρρρρ·d·c (kJ/m²K/cm)
(1cm thickness)
500Lightweight concrete
1.2Air
15-150Mineral wool
280Wood wool cement
900Gypsum
500Wood
1500Brick
917Ice
2400Concrete
7800Steel
1000Water
ρρρρ (kg/m3 )Material
Effective thermal capacity
Outer wall Inner wall
Temp TTTT1111
TTTT2222
ToutToutToutTout
AEBF01: L4
Helena Bülow-Hübe 12
Effective thermal capacity
Temp
External insulationInternal insulation
TTTT1111
TTTT2222
ToutToutToutTout
Brick wall or stud frame?• About the choice and effect of structure
materials on thermal climate, energy useand costs in schools
– Exam. Work by Holmberg & Landfors (1997),
Avd f installationsteknik, LTH
Heavy or light walls?
Exterior wall: heavy - light Inner wall: heavy - light
årsenergi75.5 77.2
0
20
40
60
80
100
Tegel Regel
Stomalternativ
Vär
meb
ehov
(kW
h/m
²,år
)
Choice of structure system
Hea
tin
gd
eman
d(k
Wh
/m²a
)
Brick Wood
SommarfalletCost comparison
6651243813103Total
-9187Insurance
-13130Maintenance
-12625Operation
6901238113071Production
DifferenceWoodBrickCost(kr/m²BRA)
AEBF01: L4
Helena Bülow-Hübe 13
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– Normally 33 years are used for writing
off costs for school buildings
• How can better comfort be valued?
Life-cycle perspective of energyuse
Energy used for production & transportation of materials used at erection and demolishing
Energy use for operation duringthe entire life-timeof the building
Study of 4 multi-family buildings(SE)
• Erected in 1996, different but yet all typical of the time
• Various choices of foundation, structuresystems, 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 Energyand Sustainable Buildings. Vol 2, 2001-2002 http://bim.ce.kth.se/byte/leas/
LCA-analysis of the following:
• Production of materials for new productionand 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 energysources for the supply
Analysis of the effects on:
• Global warming• Acid rain (försurning)• Eutrophication (Övergödning)• Ground-level ozone production• Toxicity (for humans)• Energy use
Results LCA analysis
• The operation phase accounts for the largest environmental threat, approx 70-90%
• The production phase has littlesignificance, 10-20% of the total environmental load
� the choice of structuresystems have only small environmental effects
AEBF01: L4
Helena Bülow-Hübe 14
Summary
• Use good insulation materials (i.e thosewith a low lamda-value, gives a lower U-value)
• The better the house is insulated, the moreimportant is the design of constructiondetails
• 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 mostimportant!
Användning85%
Tillverkning15%
production
operation