Modeling - A tool to assess the moisture response of walls

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Modeling - A tool to assess the moisture response of walls

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Modeling – a tool to assess the moisture response of walls

Mukhopadhyaya, P.; Maref, W.

ORAL-626

A version of this document is published in / Une version de ce document se trouve dans : Building Science Insight 2003, (15 Cities across Canada), Oct. 7, 2003, pp. 1-56

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Building Science Insight 2003

Modeling – A Tool to Assess

the Moisture Response of Walls

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Presentation Outline

Why Modeling? Modeling the wall

Computer aided modeling tool Analysis of moisture response Parametric study

Effect of water leakage

Effect of material properties Concluding remarks

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Presentation Outline

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Why Modeling - Remember this slide?

Modeling – as used to simulate wall performance

• “Hygrothermal analysis” – Dr P. Mukhopadhyaya

• Overview of results derived from response of

various wood-frame wall assemblies to different climate loads

• Performance assessment of walls to inadvertent

moisture entry

Modeling – as used to simulate wall performance

• “Hygrothermal analysis” – Dr P. Mukhopadhyaya

• Overview of results derived from response of

various wood-frame wall assemblies to different climate loads

• Performance assessment of walls to inadvertent

moisture entry Estimate Long-term Performance Testing Experience Modeling

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Why Modeling?

Can Identify components that stay 'too wet' for 'too long’.

Helps to assess relative risk

of moisture mismanagement associated with climates and wall assemblies.

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Presentation Outline

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Modeling the Wall

T,WV

T,WV,P

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Modeling the Wall

T, WV, P T, WV, P

T, WV, P

T,

WV,

P

T ,WV

T

,

WV

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Mimicking Exposure in Fast Forward Motion

Wall characteristics:

• With and without deficiency allowing water leakage into the stud cavity

•Material Properties

T, WV,P

T,

WV

,

P

T, WV

T,

WV

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Modeling the Wall

Modeling – performance assessment by simulation

Indoor climate •Temperature •Water vapour (RH) •Air pressure Outdoor climate •Temperature •Wind pressure •Rain •Water vapour (RH) •Solar radiation

Inter-related System

?

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Presentation Outline

Why Modeling?

Modeling of the wall

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Computer Aided Modeling Tool

hygIRC 2D

– hygrothermal modeling tool

Accounts for heat, air and moisture transport Fast

Flexible Validated Reliable

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Presentation Outline

Why Modeling?

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The Latest Approach for Analysis of

Moisture Response

The Latest Approach for Analysis of

Moisture Response

Developed from a Consortium Project

at IRC/NRC

M

oisture

M

anagement

I

n

E

xterior

W

all

S

ystems

MEWS

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MEWS Methodology at a Glance

Climate characterization Model Simulation hygIRC Output Full-scale tests DWTF Material properties Benchmarking MEWS Curve Building practice

Moisture Load Due to Climate Severity

R e sp o n se

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Applications

Five Wall Types: – Stucco cladding – Masonry cladding – EIFS cladding

– Composite hardboard siding (HS) – Vinyl siding (VS)

Seven Geographic Locations:

Ottawa, Winnipeg, Seattle, Wilmington (NC), Phoenix, Fresno, San Diego

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hygIRC Outputs and Moisture Response

Two sets of output from hygIRC

•

Relative humidity

•

Temperature

At any selected location in the wall at any desired time

MEWS methodology uses these two outputs to assess the “MOISTURE RESPONSE”.

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hygIRC Outputs

0.5 Snapshot X Y 0.05 0.1 1 1.5 2 T 20.0000 17.1429 14.2857 11.4286 8.5714 5.7143 2.8571 0.0000 -2.8571 -5.7143 -8.5714 -11.4286 -14.2857 -17.1429 -20.0000 Tem perat ure C onto ur Stucco Wall Wall Height (m)

Wall Width (m) - Expanded

Sheathing Board

Exterior Cladding

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hygIRC Outputs

X Y 0 .0 5 0 .1 0 .5 1 1 .5 2 R H 0 .9 2 3 0 0 .8 6 1 5 0 .8 0 0 0 0 .7 3 8 4 0 .6 7 6 9 0 .6 1 5 4 0 .5 5 3 8 0 .4 9 2 3 0 .4 3 0 7 0 .3 6 9 2 0 .3 0 7 7 0 .2 4 6 1 0 .1 8 4 6 0 .1 2 3 1 0 .0 6 1 5 O T O S 1 0 0 .0 4 4 5 m 0.6 m Exterior face

OSB layer facing stud cavity Bottom Plate; Top layer; Half-width 0.00494 m 0.00143 m Stucco Wall Relat ive Hu midit y Con tour Wall Height (m)

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hygIRC Outputs – Region of Focus

X Y 0. 0 5 0. 1 0.5 1 1. 5 2 R H 0. 9 2 3 0 0. 8 6 1 5 0. 8 0 0 0 0. 7 3 8 4 0. 6 7 6 9 0. 6 1 5 4 0. 5 5 3 8 0. 4 9 2 3 0. 4 3 0 7 0. 3 6 9 2 0. 3 0 7 7 0. 2 4 6 1 0. 1 8 4 6 0. 1 2 3 1 0. 0 6 1 5 0.0445 m 0.6 m Exterior face Regions of Focus 0.00494 m 0.00143 m Wall Height (m)

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Assessing Excessive Risk of Deterioration

0 10 20 30 40 50 0 200 400 600 800 Time (days) T e m p er at u re ( °C ) 0% 20% 40% 60% 80% 100% Re la ti ve Hu m id it y Tem perature

Relative Hum idity

Threshold

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A New Moisture Response Index

The RHT Index

Combines three major factors influencing

the moisture response –

• Relative Humidity

• Temperature

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A Measure of Too Much for Too Long

The RHT Index

Where to calculate RHT Index?

– Location most susceptible to detrimental effects of moisture

accumulation, i.e., Region of Focus

Characteristics

– Captures duration of coexistence of RH and T conditions above set threshold levels

– Threshold levels depend on selected deterioration processes for material of interest

• 95% RH: relevance to growth of wood decay fungi • 80% RH: relevance to corrosion processes

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A New Moisture Response Index

RHT Index

RHT = 0

when RH ≤ RHx % and/or T ≤ Tx°C

RHT = (RH-RHx)×(T-Tx)

when RH > RHx % and T >Tx°C

Cumulative 2yr RHT Index* =∑ (RH-RHx) × (T-Tx)

for RH > RHx% and T > Tx°C Threshold

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A Measure of Too Much for Too Long

Observed RH = 98% T = 15°C Threshold RH = 95% T = 5°C

RHT(95) = (98 - 95)

×

(15 - 5)

RHT(95) = 30

RHT Index

=

∑

RHT(95)

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Analysis of Output – Cumulative RHT Index

Relative Humid ity (RH-95) Temperature (T-5) Every 10 da ys 2 Y ea rs 30 35 42.7 0 0 0 0 78.3 35 15 0 RHT Index = 30+35+42.7+78.3+35+15 = 236

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Presentation Outline

Why Modeling?

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Water Leakage

Modeling – performance assessment by simulation

, WV

,

WV

T

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Field Observations – Water Leakage

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Field Observations - Deterioration

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No Water Leakage

0,0

No leakage in stud cavity

Moisture Response

Moisture Index (MI)

RH

T Index

Case II

Case I

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Effect of Water Leakage

0,0

Water leakage into stud cavity

RH

T Index

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Effect of Water Leakage

BLUE - no leakage into

0,0

Water leakage into stud cavity

RH

T Index

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Water Leakage & Moisture Management

M o is tu re Re s pons e

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Effect of Water Leakage

RH

T

Ottawa - No Water Leakage

70% 75% 80% 85% 90% 95% 100% 0 100 200 300 400 500 600 700 800 Time (days) RH -25 -20 -15 -10 -5 0 5 10 15 20 25 T ( °C ) Relative Humidity (RH) Temperature (T)

Ottawa – RHT Index = 0; Moisture Index (MI) = 0.93

T

RH

RH threshold

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Effect of Water Leakage

Ottawa – RHT Index = 652; Moisture Index (MI) = 0.93

T

Q

Ottawa - Water Leakage

70% 75% 80% 85% 90% 95% 100% 0 100 200 300 400 500 600 700 800 Time (days) RH -25 -20 -15 -10 -5 0 5 10 15 20 25 T ( °C )/ Q ( d ec i-L /m 3 .s ) Relative Humidity (RH) Temperature(T) Water Leakage (Q) T RH RH threshold T threshold

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Effect of Water Leakage

Ottawa - No Water Leakage

70% 75% 80% 85% 90% 95% 100% 0 100 200 300 400 500 600 700 800 Time (days) RH -25 -20 -15 -10 -5 0 5 10 15 20 25 T ( ° C ) Relative Humidity (RH) Temperature (T) T RH RH threshold T threshold T Q

Ottawa - Water Leakage

70% 75% 80% 85% 90% 95% 100% 0 100 200 300 400 500 600 700 800 Time (days) RH -25 -20 -15 -10 -5 0 5 10 15 20 25 T ( ° C )/ Q (d e c i-L /m 3 .s ) Relative Humidity (RH) Temperature(T) Water Leakage (Q) T RH RH threshold T threshold

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To Benefit from Evaporative Drying, Control Wetting

Goal: to reduce the magnitude of the RHT response reducing Q

0 500 1000 1500 2000 2500 0 0.2 0.4 0.6 0.8 1 1.2 1.4

Q Q/2 Q/4

Moisture Response (RHT Index)

M o is tur e Re s pons e Phoenix Winnipeg Ottawa Seattle Wilmington, NC Saskatoon

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What Came Out of the Modeling Results?

Reduction of water leakage into the wall

leads to better moisture management.

• Importance of detailing the junctions.

• Strategies to reduce/prevent deficiencies.

• Ensure rapid drainage of the leaked water out of

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Presentation Outline

Why Modeling?

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Effect of Cladding Material Properties

Gypsum (12 mm) Vapour barrier (0.152 mm) Insulation space (89 mm) Sheathing board (11 mm) Sheathing membrane (0.23 mm) Stucco cladding (19 mm) Bottom plate ht. (76 mm) Top plate ht. (76 mm) 2400 mm

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Effect of Cladding Material Properties: Stucco Walls

A designer has:

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Effect of Cladding Material Properties: Stucco Walls

0 500 1000 1500 2000 2500 0 0.2 0.4 0.6 0.8 1 1.2

Moisture index (MI)

RH T i nde x I II Phoenix Wilmington Winnipeg Ottawa Seattle

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The Reason

What Brings About the Difference?

STUCCO II has liquid diffusivity that is one

order of magnitude less than STUCCO I.

dr op_s R ain Stucco I Liquid water Stucco II Time = t₁ Time = t₁ Liquid water

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Effect of Sheathing Material Properties: Masonry Walls Effect of Sheathing Material Properties: Masonry Walls

Gypsum (12 mm)

Vapour barrier (6 MIL) Insulation space (89 mm) Wood Sheathing (11 mm) Sheathing membrane (0.2 mm) Air cavity (25 mm) Bottom plate ht. (76 mm) Top plate ht. (76 mm) Brick veneer (90 mm) 2400 mm

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A designer has:

Two Types of Sheathing Boards –

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0 500 1000 1500 2000 2500 3000 0 0.2 0.4 0.6 0.8 1 1.2 Moisture index (MI)

RHT in d e x Phoenix Wilmington Winnipeg Ottawa Seattle I II

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Material Selection – Board I and Board II

0 200 400 600 800 1000 1 2 RHT I n d e x I _II

Vancouver

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The Reason

What Brings About the Difference?

BOARD II has water vapour permeance that is

one or two orders of magnitude higher than BOARD I

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Presentation Outline

Why Modeling?

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Concluding Remarks , cont’d

Climate characterization Model Simulation hygIRC Output Full-scale tests DWTF Material properties Benchmarking MEWS Curve Building practice