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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
2
1 Thermal Bridging Impact1
3
4
Source: Architecture 2030
5
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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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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71
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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
76
p
Accessing Information
http://www.morrisonhershfield.com/ashrae1365research/Pages/Insights-Publications.aspx
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Thank You
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