The Effects of Thermal The Effects of Thermal Bridging on Building

Envelope Performance

A Whole Building Energy Perspective

Dave André P EngDave André, P.Eng.January 2014

Thermal Bridging Impact1 g g p

Thermal Bridging Overview2

Thermal Bridging Prioritization3

Building Envelope Thermal Performance4

Best Practice Design Approach5

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1 Thermal Bridging Impact1

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Source: Architecture 2030

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Source: http://www.energycodes.gov/adoption/states

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Source: http://www.energycodes.gov/adoption/states

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Source: http://www.energycodes.gov/adoption/states

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PerspectivePerspective

Compliance – Energy Codes

Performance -Heat Loss, Condensation and Durability

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Thermal Bridging Overview2

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Thermal BridgingWhat is a Thermal Bridge?

• Highly conductive material that by-passes insulation layer• Areas of high heat transfer• Can greatly affect the thermal performance of assembliesg y p

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• ASHRAE 90.1

• Uvalues (max.)

• Continuous Insulation

• Wall framing heat loss

• 2013 Handbook Fundamental

i i i• Multidimensional Construction

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ASHRAE Standard 90.1ASHRAE Standard 90.1

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ASHRAE Standard 90.1ASHRAE 90.1 & thermal bridging

TABLE A3 3 A bl U F f S l F W llTABLE A3.3 Assembly U-Factors for Steel-Frame Walls

Overall U-Factor for Assembly of Base Wall Plus Continuous Insulation (Uninterrupted by Framing)Continuous Insulation (Uninterrupted by Framing)

Rated R-Value of Continuous Insulation

= R-8

= R 8 + R 8

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= R-8 + R-8

How is Thermal Bridging Typically Evaluated?

Hand Calculations

Computer ModelingLab Measurement

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The Real World is Complicated!

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ASHRAE Research ProjectDetails Catalogue

• 40 building assemblies and details common to North American construction

• Focus on opaque assemblies, but also includes some glazing g gtransitions

• Details not already addressed in ASHRAE publicationsp

• Highest priority on details with thermal bridges in 3D

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• Exterior Insulated Steel Stud

• Concrete Mass Wall

• Curtain Walls

• Precast Panels

• Brick Veneers

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Overall Heat Loss

oQQ slabQ

Additional heat loss due to the slab

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Overall Heat Loss

/ LQslab /=Ψ Ψ×= LQslabOR

The linear transmittance represents the additional heat flow because of the heat flow because of the slab, but with area set to zero

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Overall Heat LossTypes of Transmittances

Clear Field Linear Point

oQ χΨoUor

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Overall Heat Loss

Total Heat loss Heat loss due to anomalies

heat loss due to clear field +=

( ) ( )nLAUQ Totalo ⋅Σ+⋅ΨΣ+⋅= χ)(

oQ

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Overall Heat Loss

( ) ( ) UnLU +⋅Σ+⋅ΨΣ

=χ

oTotal

UA

U +

h bl f i h l fi ld f The assembly U-factor is the clear field U-factor, plus all the linear and point transmittances

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Living Building ChallengeLiving Building Challenge

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2Thermal Bridging Prioritization3

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High Rise Residential• Inverted roof assemblies

• Window wall glazing (vision

High Rise Residential

Window wall glazing (vision and metal panel areas)

• Punched windows

• Select portions of opaque wall (brick veneer, EIFS, etc.)

• Slab edges (cantilevered Slab edges (cantilevered balcony slabs and window wall bypasses)

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• Vision AreaPriority 1

• Slab Edges (cantilevered balcony slab, shelf angles, etc.)

• Window TransitionPriority 2

Window Transition

• Opaque Wall Framing (sub Priority • Opaque Wall Framing (sub girts)

Priority 3

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30

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32

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SI (W/m∙K)

IP (BTU/hr∙ftoF)(W/m K) (BTU/hr ft F)

Ψ 0.59 0.3434

SI (W/m∙K)

IP (BTU/hr∙ftoF)

Ψ 0.21 0.1235

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SI (W/m∙K)

IP (BTU/hr∙ftoF)(W/m K) (BTU/hr ft F)

Ψ 0.47 0.2737

SI (W/m∙K)

IP (BTU/hr∙ftoF)

Ψ 0 31 0 18Ψ 0.31 0.18

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Slab Edges

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40

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Ψ ≈ 0.263 BTU/ft·hroF

(0.454 W/m·K)

Flashing extends past thermal break to frame

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Heat Flow through Window Transition

Heat Flow through 4’ x 8’ Window

Q = 24 x 0.263 = 6.3 BTU/ft∙hroF

Q = 32 x 0.35 = 11.2 BTU/ft·hroF

Ψ = 0.028 BTU/ft·hroF

(0.048 W/m·K)

Flashing stops at th l b kthermal break

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Heat Flow through Window Transition

Heat Flow through 4’ x 8’ Window Window Transition

Q = 24 x 0.028 = 0.67BTU/ft∙hroF

4 x 8 WindowQ = 32 x 0.35 = 11.2 BTU/ft∙hroF

Vertical Z-Girts Horizontal Z-Girts Mixed Z-Girts Intermittent Z-Girts

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Continuous Insulation Systems

• IMP• EIFS • Continuous

insulation ’ systems can’t

escape the poor details poor details problem

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• IMP Panel Example – effectively continuous insulation but…

• Potentially 40% (plus) heat flow attributed to y (p )window transition

• Panel assembly of U-0.048 is only U-0.127 (effective R-21 to R-8) when considering thermally inefficient details

• Improved to U-0.065 (R-15) without much difficulty (no continuous metal flashing)

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Insulated Metal Panels

Insulated Metal Panels

Direct heat flow path from interior to exterior through fl hi d t dflashing and studs

P t ti ll 40% ( l ) h t fl tt ib t d t i d t iti• Potentially 40% (plus) heat flow attributed to window transition• Improved to U-0.065 (R-15) without much difficulty (no continuous

metal flashing)

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Office• Inverted roof assemblies

• Curtain wall glazing

Office

Curtain wall glazing

• Specialty glazing

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•Vision AreaPriority 1

•SpandrelPriority 2

S i lt Gl iP i it 3 •Specialty GlazingPriority 3

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Area of circle represents Area of circle represents total envelope heat loss

Fenestration heat loss, UA, Btu/hr-FOpaque wall heat loss UA, Btu/hr-F

2,592 2,98

10,984

81%

,19%

8,244

73%

,3

27%

5,504

62%

3,373

38%2,76442%

3,76458%

Ration = 40%Glazing U=0.40

Ratio = 30%Glazing U=0.40

62%

Ration = 20%Glazing U=0.40

Ratio 10%, Glazing U=0.40

Opaque Wall U=0.059Total Heat Loss = 13576 Btu208% increase

Opaque Wall U=0.059Total Heat Loss 11227 Btu72% increase

Opaque Wall U=0.059Total Heat Loss = 887736% increase

Glazing U 0.40Opaque Wall U=0.059 (R=17)Total Heat Loss = 6528 Btu

575757

Glazing Spandrel Areasg p

No Spray Foam58

Glazing Spandrel Areasg p

S F59

Spray Foam

Glazing Spandrel Areasg p

8 28.8 9.1

9

10

7.48.2

6

7

8

n R

Val

ue

3.44.2

4.8 5.0

3

4

5

6

ndre

l Sec

tion

0

1

2

3

Span

00 5 10 15 20 25 30

Back Pan Insulation

Detail 22 (Air in Stud Cavity) Detail 23 (Spray Foam in Stud Cavity)

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Glazing Spandrel Areas

N S F S FNo Spray Foam Spray Foam61

Glazing Spandrel Areas

• Provide R-15 insulation in the back panthe back pan

• Provide continuous insulation inboard of the back pan in an airtight back pan in an airtight fashion

• Maximize area with floor to ceiling spandrel to further improve performance

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3Building Envelope Thermal Performance4

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How to Use Data Sheets - Sample Projectp j

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How to evaluate relative contribution of details

Wall Parameter Wall Parameter Values

Wall Width 30 ft (9 1m)Wall Width 30 ft (9.1m)Wall Height 100 ft (30.5m)# of floors 10Glazing % 40%

Steel stud with R-20 exterior

gWindow Perimeter

Length 28 ft (8.5m)

# of Windows 25Opaque Wall 1800 sqft (167 2m2)Steel stud with R 20 exterior

insulation and horizontal girts and R-12 in the stud cavity;

U-0.049 Btu/hrft2oF

Opaque Wall 1800 sqft (167.2m2)

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Shelf angle Parapet

CornerS g Parapet

Window Transition

Slab

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Calculations Sample Example 1Calculations Sample – Example 1

H t l d heat loss due Total Heat loss

( ) ( )

Heat loss due to anomalies

heat loss due to clear field

+=

( ) ( )nLAUQ Totalo ⋅Σ+⋅ΨΣ+⋅= χ)(

Q = 0 049 Btu/hrft2oF * 30 ft (width) * 100ft (height) * %60 (area) oQ 0.049 Btu/hrft F 30 ft (width) 100ft (height) %60 (area) = 88 Btu/hroF

( )slabL⋅Ψ = 0.445 Btu/hrft2oF * 30 ft (width) * 10 (# floors)( )slabLΨ= 134 Btu/hroF

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Clear Wall Only Including Poor Details Including Efficient Details

0.12

0.14

0.16

R‐3.9

R‐4.5

R‐5.0 R‐5.3R‐5.2

sem

bly

to E

nerg

y

Clear Wall Only Including Poor Details Including Efficient Details

0.08

0.10

man

ce o

f Wal

l Ass

of F

loor

Are

a)

0.02

0.04

0.06 R‐10.2

R‐14.3R‐16.7

of T

herm

al P

erfo

rmU

se(G

J/m

2o

0.00

Con

trib

utio

n o

Additional building energy use based on thermal performance of the building wall assembly for varying amounts of nominal exterior insulation for a mid-rise MURB in

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Edmonton (overall assembly thermal resistance in ft2·ºF·h/Btu also given)

Key Point Whole Building Energy

• Approaches

Key Point – Whole Building Energy

• Efficient details, thin insulation

• Thick insulation, poor details

• At low effective R-values, increases = big energy savings

• High effective R-value = thermally efficient details and some insulation insulation.

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4Best Practice Approach5

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Closing Remarks

• Shift from nominal R-value thinking to effective R-value

• Move beyond simply adding “more insulation”. Examine cost effectiveness

f i l ti th b ildi of insulating the building envelope through better details

• Look to building envelope to provide opportunity to achieve energy gains

• Be prepared to modify details and evaluate new products

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p

Accessing Information

http://www.morrisonhershfield.com/ashrae1365research/Pages/Insights-Publications.aspx

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Thank You