aebf01: l4 - lth

AEBF01: L4

Helena Bülow-Hübe 1

Design of the buildingenvelope

Insulation, thermal bridges, thermalmass

Helena Bülow-Hübe

AEBF01: L4


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


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


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


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


Timber or log-house (1700s)

Plankhus - Wood planks

Standing wood planks from 1920’s. From (Björk et al., 1984).

Brick

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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


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


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


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


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


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


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


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

aebf01: l4 - lth

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