Simulating the prediction of moisture movement and related risk within building envelopes has gained momentum with the increased use of thicker walls, new materials and assemblies. One such simulation software used widely across North America for hygrothermal analysis is WUFI 5.1. As with any other simulator, WUFI 5.1 requires a few basic inputs such as location, orientation, climate and construction. But hygrothermal modeling is not a clear-cut task. The interactions between the macro level inputs and the dependency on molecular make-up and characteristics of materials makes prediction of hygrothermal performance very volatile. This volatility could lead to under or over predicting moisture related risk in building elements. As a part of an ongoing research and monitoring project, the authors’ team evaluated and intends to monitor several different configurations of wall assemblies in multiple climate and moisture zones to determine the accuracy of moisture modeling. The goal is to make recommendations to ensure durable, efficient assemblies. Based on this research, this paper presents a systematic approach to hygrothermal modeling with WUFI 5.1. Methods to determine compliance with existing failure criteria using results from WUFI 5.1 are discussed. General software observations and possible future improvements are suggested

1. A Systematic Approach to
SimBuild
2012 Hygrothermal Modeling and
Compliance With Failure Criteria
Using WUFI
Pallavi Mantha
© 2011 Steven Winter Associates, Inc. All rights reserved.
StevenWinter Associates Inc.
pmantha@swinter.com
www.swinter.com

2. SWA
RESEARCH
500 WUFI Simulations
78 Hybrid Insulation
Variations Of IECC Walls +
16 [R-40 and R-60]
Variations of High R-value Walls
© 2011 Steven Winter Associates, Inc. All rights reserved.
06 Interior Insulation
Variations of Brick Walls With
04 [4, 5, 6 and 7]
Climate Zones
03 [A-moist, B-dry and C-marine]
Moisture Regimes

3. ASHRAE
• Sets the performance criteria to minimize
STANDARD problems associated with moisture in
160 building envelope assemblies
• 30–day running average surface RH<80%
when the 30-day running average surface
temperature is between 41°F and 104°F
• Applies to all materials and surfaces in the
© 2011 Steven Winter Associates, Inc. All rights reserved.
building envelope except :
• the exterior surface & materials that are
naturally resistant to mold
• or have been chemically treated to resist
mold growth.

4. • Developed by Fraunhofer / ORNL
WUFI • Widely used in USA
• WUFI –Pro [1D], WUFI 2D and WUFI
Plus
• Predicts moisture transfer by diffusion
and capillary flow
© 2011 Steven Winter Associates, Inc. All rights reserved.

5. © 2011 Steven Winter Associates, Inc. All rights reserved.
INPUT
WUFI workflow
OUTPUT
POST-
ANALYZE
PROCESS +CONCLUDE

6. • Understand your assembly!
INPUT • Get tested material data for existing
buildings (esp. masonry)
Construction
Assembly
© 2011 Steven Winter Associates, Inc. All rights reserved.

7. • Choose as-is orientation or the worst
INPUT case
• Set driving rain coefficients (per
Orientation ASHRAE 160 if showing compliance)
© 2011 Steven Winter Associates, Inc. All rights reserved.

8. • Define exterior and interior surface
INPUT properties
Surface
Transfer
Coefficients
© 2011 Steven Winter Associates, Inc. All rights reserved.

9. • Define initial Temperature [ T ] and
INPUT Relative Humidity [RH]
• ASHRAE 160 requires 2x 80%RH
Initial (2x90% for concrete) for NC with wet
Conditions construction materials
© 2011 Steven Winter Associates, Inc. All rights reserved.

10. • Set simulation length
INPUT • Varies with type of analysis. Minimum
recommended is 3 years
Calculation
Period
© 2011 Steven Winter Associates, Inc. All rights reserved.

11. • Choose from weather data (MRY) library
INPUT • Accepts many other file formats or user
defined
Outdoor
Climate
© 2011 Steven Winter Associates, Inc. All rights reserved.

12. • Quick climate analysis
INPUT • Helps choose worst case orientation based
on driving rain and solar exposure
Outdoor
Climate
© 2011 Steven Winter Associates, Inc. All rights reserved.

13. • Input custom sine curves if you know the
INPUT interior conditions
Indoor
Climate
© 2011 Steven Winter Associates, Inc. All rights reserved.

14. • Use ASHRAE 160 indoor climate if
INPUT complying against that Standard
Indoor
Climate
© 2011 Steven Winter Associates, Inc. All rights reserved.

15. • Export data to post-process
OUTPUT • Two main methods of export
• Keep track of units!
© 2011 Steven Winter Associates, Inc. All rights reserved.

16. • Export data to post-process
OUTPUT • Two main methods of export
• Keep track of units!
© 2011 Steven Winter Associates, Inc. All rights reserved.

17. • WUFI gives multiple outputs
OUTPUT • Essential outputs to comply against
failure criteria:
Failure Criteria WUFI Output Files
Rot/Decay in Moisture content
OSB/plywood in Plywood/OSB
© 2011 Steven Winter Associates, Inc. All rights reserved.
Mold growth T and RH at potential
Potential (ASHRAE) condensation surfaces
Condensation potential Interior T and RH
Assembly water content Assembly water content
Frost damage Moisture content in brick

18. © 2011 Steven Winter Associates, Inc. All rights reserved.
Moisture Content
0%
5%
10%
15%
20%
25%
POST-
4A-1
4A-3
ANALYZE
PROCESS/
4A-5
ROT/DECAY
4A-7
4A-9
4A-11
•
•
4B-1
4B-3
4B-5
4B-7
4B-9
4B-11
4C-1
4C-3
4C-5
4C-7
1st Year Max
4C-9
4C-11
5A-1
5A-3
5A-5
5A-7
20% threshold.
5A-9
Wall ID
5A-11
3rd Year Max
5B-1
5B-3
Predicted MC in OSB
5B-5
Mass-Percent M- %.
5B-7
5B-9
5B-11
Average
6A-1
6A-3
6A-5
6A-7
6A-9
6B-2
6B-4
6B-6
6B-8
Convert water content in lb/ft3 to
7-1
7-3
7-5
7-7
The M-% value should not exceed the
7-9

19. POST- • Calculate 30 day running average of
PROCESS/ surface RH and surface T
ANALYZE
• Fails if surface RH<80% when surface
MOLD 41oF >T<104oF
GROWTH - 4A - Wall 1: 30 Day Moving Average
ASHRAE 160
120 120
CRITERIA 100 100
Relative Humidity (%)
© 2011 Steven Winter Associates, Inc. All rights reserved.
Temperature (F)
80 80
60 60
40 40
20 20
Temperature
Relative Humidity
0 0
Jun 12
Jun 13
Jun 14
Oct 11
Apr 12
Oct 12
Apr 13
Oct 13
Apr 14
Oct 14
Dec 11
Feb 12
Aug 12
Dec 12
Feb 13
Aug 13
Dec 13
Feb 14
Aug 14

20. POST- • Isopleths indicate mold germination
PROCESS/ time and growth rate based on T & RH
ANALYZE
• Check the isopleths for dots crossing
MOLD the LIM B I and LIM B II lines
GROWTH -
ISOPLETHS
© 2011 Steven Winter Associates, Inc. All rights reserved.

21. POST- • WUFI-Bio compares measured/
PROCESS/ simulated transient ambient and fungi
ANALYZE
growth conditions
MOLD • Check color of signal light
GROWTH -
CRITICAL
WATER
CONTENT
© 2011 Steven Winter Associates, Inc. All rights reserved.
METHOD

22. POST- • WUFI-Bio compares measured/
PROCESS/ simulated transient ambient and fungi
ANALYZE
growth conditions
MOLD Check color of signal light
• • mold growth > 7.87 in/yr
GROWTH -
CRITICAL • 7.87 in/yr > mold growth < 1.96 in/yr
WATER
CONTENT • mold growth < 1.96 in/yr
© 2011 Steven Winter Associates, Inc. All rights reserved.
METHOD

23. POST- • Calculate total water content in lb/ft2
PROCESS/ of building envelope
ANALYZE
• Assembly water content should
ASSEMBLY decrease over time
WATER
CONTENT
© 2011 Steven Winter Associates, Inc. All rights reserved.

24. POST- • Can be calculated more than one way
PROCESS/ • Recommend running a THERM model
ANALYZE
• Assess in combination with other
CONDENSA results
-TION
POTENTIAL
© 2011 Steven Winter Associates, Inc. All rights reserved.
Avg. Dew Point [51 F]
Due To Air Leakage
Avg. Dew Point [28 F]
Due To Diffusion

25. POST- • Identify free saturation in lb/ft3 of the
PROCESS/ brick used
ANALYZE
• Calculate critical saturation threshold
FROST (90% of free saturation)
DAMAGE • Count freeze-thaw [FT] cycles
• One FT cycle = T at hour [h] < freezing
limit and T at hour [h+1] > thawing limit
© 2011 Steven Winter Associates, Inc. All rights reserved.
• Count FT cycles when water content in
brick > critical saturation limit

26. POST- • Identify free saturation in lb/ft3 of the
PROCESS/ brick used
Water Content [lb/ft 3 ]
25
ANALYZE
• Calculate critical saturation threshold
20
Critical
Saturation
15 [90% of free
FROST (90% of free saturation)
10
saturation]
WC @ Wythe 1
DAMAGE • Count freeze-thaw [FT] cycles
5
0
• One FT cycle = T at hour [h] < freezing
limit and T at hour [h+1] > thawing limit
120
Freezing
© 2011 Steven Winter Associates, Inc. All rights reserved.
100 Temp. [23F]
• Count FT cycles when water content in
Temperature [oF]
80 Thawing
brick > critical saturation limit [32F]
60
Temp.
Temp. @
40 Wythe 1
Freeze Thaw
20
Cycles
0
Oct-12 Oct-13 Oct-14 Oct-15
Time

27. CONTACT
THANK YOU
Pallavi Mantha
© 2011 Steven Winter Associates, Inc. All rights reserved.
Steven Winter Associates, Inc.
pmantha@swinter.com
www.swinter.com