Overview of Hygrothermal Modeling and Demonstration of WUFI ®

1. Overview of Hygrothermal Modeling and Demonstration of WUFI® Presented to: The Atlanta Building Enclosure Council July 11th, 2012 Bryce McQueen

2. Continuing Education Quality Assurance “Wiss, Janney, Elstner Associates” is a Registered Provider with The American Institute of Architects Continuing Education System (AIA/CES). Credit(s) earned on completion of this program will be reported to AIA/CES for AIA members. Certificates of Completion for both AIA members and non-AIA members are available upon request. This program is registered with AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

3. Learning Objectives This presentation will provide an introductory level discussion of concepts associated with heat and moisture transfer through building enclosure assemblies and provide a demonstration of the use of one-dimensional hygrothermal analysis software known as WUFI® (Wärme und Feuchteinstationär). After attending this presentation participants will be able to: • Discuss the basics of hygrothermal modeling concepts and techniques • Discuss moisture transport and storage fundamentals and hygrothermal phenomena in building materials and assemblies • Discuss moisture control performance criteria for building facades, including ASHRAE Standard 160-2009 Criteria for Moisture Control Design Analysis in Buildings. • Describe a case study demonstration of WUFI® • Discuss the basic general capabilities and limitations of hygrothermal modeling software such as WUFI®

4. Hygrothermal Modeling HygrothermalChange in properties due to moisture absorption and temperature change Hygrothermal Modeling Dynamic simulation of moisture and heat transport through multi-layer building components over a period of time Benefits • Provides opportunity to simulate exterior wall hygrothermal performance (without air flow) for comparative purposes • Can be used as a tool to confirm design decisions (within the limits of the software) for wall assemblies in various climatic conditions • Does not require destructive investigation or significant resources to perform, however, confirmation of simulation results are recommended

5. Environmental Data Monitoring Actual hygrothermal conditions of an assembly using environmental data loggers

6. Environmental Data Analysis Analysis of hygrothermal conditions using environmental data loggers Benefits • Actual results (not predicted) that can be verified • Continual wireless monitoring Drawbacks • Significant Cost • Time for Analysis • Interruption of facility operations • Destructive methods required for installation • Possible equipment failure • Sudden environment changes (i.e. opening windows or ceiling tiles) can affect results

7. Hygrothermal Analysis Benefits • Dynamic view of modeled results depicting temperature, relative humidity, dew point, and water content values over time • Analysis time is relatively short • Non-destructive analysis (except in instances of as-built verification) Drawbacks • Results are not actual • Numerous limitations apply (discussed later) • Verification of as-built conditions and results is still recommended in most instances

8. Hygrothermal Model Inputs Assembly Data • Materials • Material Data • Hygrothermal Functions • Additional Data • Heat Sources • Moisture Sources • Air Changes Surface Transfer Properties • Orientation • Inclination • Height • Permeance • Absorptivity • Heat Resistance • Initial Moisture Content Exterior Macro Climate • Historical Climate Data • Air temperature • Air humidity • Short wave radiation • Long wave radiation • Precipitation • Wind velocity and direction • Optional: measured data Interior Climate • Air temperature • Air humidity Time • Simulation Duration

9. Fundamentals of Moisture Transport/Storage • Moisture is present in the air both inside and outside the building envelope and may be in the form of solid ice, liquid, or vapor • Moisture is driven through the building envelope by natural forces such as: • Temperature • Partial vapor pressures (sometimes expressed in terms of relative humidity) • Liquid pressure (suction forces) caused by rain water, water leaks, or surface condensation. • If moisture accumulates above a critical material-dependent threshold, the building components begin to: • Stain • Rot or degrade • Crack or spall • Corrode • Accumulate mold Damage is in many cases related to the inability of the building owner to control moisture within acceptable limits

10. Fundamentals of Moisture Transport/Storage Basic Material Properties • Bulk Density (lb/ft3) • Easy to Measure, known for most materials • Needed for internal conversions (heat capacity, water content) • Porosity (ft3/ft3) • Describes the maximum water content of the material • Needed when a material can absorb vapor or water in its pore structure • Permeability (Perm in) • Specific Heat Capacity (BTU/lb degF) • Sum of the dry material and the amount of bounded water • Thermal Conductivity (BTU/h ft degF) • Dependent on density, temperature, and moisture

11. Hygrothermal Phenomena in Building Practice Optical degradation Soiling, Staining Microbial Growth Efflorescence

12. Hygrothermal Phenomena in Building Practice Damage caused by elevated water content and/or condensation • Freeze-Thaw Cycle • Trapped Moisture • Corrosion • Rust Jacking

13. Hygrothermal Phenomena in Building Practice Damage by hygrothermal stress Shrinkage cracking Damage from hygrothermal dilatation (i.e. spalling , delamination, etc.) Coating failures

14. Hygrothermal Phenomena in Building Practice Health aspects Hygrothermal comfort Air quality Mold growth caused by elevated surface humidity

15. ASHRAE Standard 160-2009 Criteria for Moisture Control Design Analysis in Buildings Design Criteria for Moisture Control in Buildings • Purpose To specify performance-based design criteria for predicting, mitigating or reducing moisture damage to the building envelope, materials, components, systems and furnishings, depending on climate, construction type, and HVAC system operation • Scope • Design of new buildings and retrofit and renovation of existing buildings • All types of buildings, building components and materials • All interior and exterior zones and building envelope cavities • Does not address thermal comfort, acceptable indoor air quality, or the design of building components to resist liquid water leakage (reference ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy

16. Moisture Performance Criteria Mold (according to ASHRAE Standard 160-2009, with 2011 Addendum) 30-day running average surface RH > 80% or 7-day running average surface RH > 98% or 24 hours at 100% and Surface temperature between 50° and 104°F Surface Condensation Determined using Dew Point Analysis (which can be calculated through WUFI)

17. What is WUFI? WUFI-ORNL/IBP is a menu-driven PC program which allows realistic calculation of the transient coupled one-dimensional heat and moisture transport in multi-layer building components exposed to natural weather. It is based on the newest findings regarding vapor diffusion and liquid transport in building materials and has been validated by detailed comparison with measurements obtained in the laboratory and on outdoor testing fields.

18. WUFI Case Study Wall Assembly Case Study Atlanta, Georgia Building Background • Building operates as a hotel • Construction completed in 1987 • Building contains 12 stories above grade • Typical construction consists of cold-formed metal stud infill walls and brick veneer with aluminum storefront windows in punched openings • Water leakage and interior mold growth reported prior to project Initial Investigation • Exterior and Interior Visual Surveys • Roof Condition Assessment • Water Leakage Testing • Exterior and Interior Inspection Openings Supplemental Analysis • Exterior Wall Vapor and Heat Transmission Analysis

19. WUFI Case Study Original Wall Assembly • 3-5/8” red modular brick veneer • 1-1/2” air cavity (non-ventilated) • 1/2“ exterior gypsum sheathing • 6” cellulose fiber insulation • 5/8” interior gypsum wallboard • Vinyl wall covering Interior Design Conditions • Summer • 72 degrees F • 60% R.H. • Winter • 68 degrees F • 40% R.H.

20. WUFI Limitations Some Limitations • WUFI is most commonly one-dimensional. Two-dimensional WUFI software is available but requires significantly more setup and processing time. Three-dimensional simulations using WUFI are not available • Simulations do not account for additional materials or thermal bridges that may be present in an assembly (i.e. metal studs, structural framing, etc.) or material discontinuities (i.e. vapor or air barriers) • WUFI assumes an ideal wall construction. Factors that may introduce additional moisture and/or air movement into the assembly (open sealant joints, open penetrations, deteriorated mortar joints, spalled brickwork, etc.) may change the performance of the wall assembly • Moisture laden air flow cannot be simulated. Significant building problems may exist due solely to air leakage problems, and WUFI does not account for this • Better simulations require accurate material data (certain materials may not be available in the database and some materials may not contain detailed material properties). Composite materials (i.e. OSB, Stucco) may require some manipulation or simplification. Additionally, accurate interior conditions may be hard to determine if design conditions are not provided

21. WUFI Limitations Additional Limitations • WUFI does not take into account liquid transport via seepage flow through gravitation or hydraulic flow through pressure differentials (exacerbated through air leakage sources) • WUFI is a good tool for studying the use of vapor barriers within an assembly, but introducing a double vapor barrier may not give accurate results • Accuracy when introducing large air cavities is decreased due to the limitations of the software in dealing with convective vapor transport • Modeling vertical and horizontal surfaces is fairly straightforward, but modeling soffit conditions can be tricky (must eliminate wind driven rain, solar exposure, and other conditions) • Studying the application of coatings on exterior surfaces is useful and popular, but detailed material data for proprietary coatings can be difficult to come by and are not readily available in the database • Air changes within air cavities and additional heat or moisture sources can be introduced into the model, but can be hard to accurately determine.

22. Questions / Discussion