passive air cavity convection on the wetting and drying ...passive air cavity convection on the...
TRANSCRIPT
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Passive Air Cavity Convection on the Wetting
and Drying Behavior of Building Envelopes
Dr. Achilles Karagiozis Owens Corning Global Director, Building Science
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Thank you
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• All Students from Penn State, UofW
• All Technical staff from ORNL
• All Collaborators (FhG/IBP), VTT,WSU
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Presentation Roadmap/Deliverables
• Why is it important ?
• Recent History…Past Literature
• Research
– Development of CFD Analysis
– Validation & Analysis of Laboratory Wetting/Redistribution/Drying
– Validation with “Real Life” Field Conditions
– Simulation Parametric Evaluation
• New Cavity Ventilation Approach in WUFI
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Why is it important ?
• With the 2009 & 2012 IECC code enhancement for higher efficiency requirements for envelopes means we need to increase drying capability of these envelopes.
• Requirement: Building Envelope Assemblies need to be hygrothermally designed for moisture control
• Passive drying provided by air cavity ventilation would be a most welcomed means of providing free drying.
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• Burnett, Straube and Karagiozis [2005] (Positive)
• Straube and Burnett [1995] (Positive)
• Popp [1980] (Positive)
• Kuenzel [1983] (No effect)
• TenWolde [1985] (Negative effect)
• Hansen [2002] (Negative effect)
• Bassett & McNeil [2006] (Positive effect)
• Kristin Nore [2009] (Positive)
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Past Literature on Cavity Ventilation
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Kuenzel and Mayer 1983
• The most important characteristics found was the size of the vent openings and the presence of an unobstructed cavity.
• The three most important forces affecting ventilation drying were found to be 1) wind induced pressure differences, 2) solar-induced buoyancy (stack effect), and 3) solar heating.
• Solar heating increased the air temperature of the cavity air and thus allowed the transport of a much larger volume of water vapor.
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Field measurement of ventilation behind large cladding panels on a three-storey building
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Kuenzel and Mayer 1983
• Hourly average air velocities of 0.05 to 0.15 m/s (0.16 to 0.49 ft/s) were measured in the wall cavities when the windspeed was between 1 to 3 m/s (3.28 to 9.8 ft/s). Wind direction influenced the ventilation air velocity more than windspeed.
• Walls with non-airtight joints (e.g., slate, shingles) were also shown to be ventilated (using tracer gas techniques), albeit less than intentionally vented walls.
• The greater the number of joints and the leakier the joint, the more ventilated the cavity.
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Kuenzel and Mayer 1983
• The pumping action of the wind was postulated as the ventilation mechanism in these walls.
• It was observed that with sufficient ventilation, condensation on the backside of the cladding rarely occurred.
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Kuenzel 1984 (Fraunhofer)
• 100 gravimetric measurements were made of several different walls assemblies built in accordance with the German DIN 1053 masonry standard
• The authors concluded that the presence of an air space had no noticeable effect on the moisture content of the brick veneer or insulation.
• Another study by The German Institut für Ziegelforschung (Institute for Brick Research) conducted a unique field study of the effect of ventilation on the drying of brickwork [Jung 1985].
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Brick veneers in walls with and without (the cavity was filled with insulation) an air space
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More Studies
• This ventilation velocity was deemed to be slow enough that the insulation value of the air space was not significantly affected and yet resulted in an average of 100 air exchanges per hour. Measurements of the moisture content of the brickwork immediately after construction showed that drying occurred faster on the cavity side than on the outside. Within three weeks the brickwork dropped from 12% moisture content by volume to about 1.5%.
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Laboratorium voor Bouwfysica in Belgium (Field Study)
• Ventilation behind brick veneers study showed that ventilation has practically no effect on the heat transmission values of the air space, but it is was also found to be difficult to quantify the benefit of ventilation to moisture removal rates.
• Recommended that ventilation continue to be used in veneer walls with air spaces, only drain openings are required in cavities filled with insulation because the ventilation rates would be very low in any case.
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Masonry Walls
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Akoestisch Advies Bureau Peutz & Associes BV [Anon 1984]
• Analysis/Measurements with large vent areas could, on average, have ventilation velocities of 0.5 to 3 m/s.
• For Dutch conditions, such large velocities result in enough ventilation to ensure that condensation would not occur on the backside of panels for typical backup wall assemblies.
• The panel sizes examined ranged from 200 to 800 mm in height, were installed over a 20 mm cavity, and had full-length open joints 20 mm wide.
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Theoretical and wind tunnel study of the potential for ventilation in an open-jointed, small-panel cladding product.
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CMHC Building Engineering Group at the Uof W [Straube and Burnett 1995]
• Ventilation of enclosure walls study on theoretical analysis of the flow mechanics and drying physics of ventilation and an experimental study of the flow resistance of vents and detailed field measurement of wind driving pressures
• Investigated the role of air spaces in ventilation drying and pressure moderation. This study demonstrated that ventilation could be useful as a means to control inward vapor drives behind brick veneers
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Kenneth Sandin [1991] of Lund University, Sweden
• Extensive study of ventilation behind brick veneer by the Swedish Building Research Council. (0.3 to 8 ACH (20-50mm)
• When an entire brick was removed every 1200 mm were substantial ventilation rates of 3 to 25 ACH measured.
• In other published work [Sandin 1993, 1990], Sandin questioned the effectiveness of ventilation in a climate (similar to Canada) where ventilation drying might remove 3 kg of moisture per month and driving rain could deposit 20 to 50 kg/month.
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Lawton, Brown and Lang, Lab drying study for CMHC
• Full-scale wall samples, 1.2x2.4 m, with stucco cladding where built and wetted by simply injecting 4 liters of water over 4 days.
• Water simply leaked out since little was absorbed.
• The walls were exposed to 10 °C exterior conditions with no wind and no solar radiation.
• Authors state that these factors would have no significant effect on drying.
• The major conclusions of this study were that drying process for all specimens was very slow and took months to achieve any significant effect.
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Lab climate chamber studies, Envelope Drying Rate Analysis
• CMHC EDRA Test panels submersion in water prior to being assembled complete walls. In Phase 1 steady conditions at 5 C and 70% relative humidity were simulated. In Phase 2 the panels exposed to simulated daily radiation peaking at 120 W/m2 (equivalent to diffuse radiation on the North side of a high latitude building) and a simulated wind pressure difference of 1-5 Pa between the top and bottom to the assemblies.
• The sample walls included stucco and vinyl cladding, vented, and ventilated designs, polymer and paper based sheet sheathing membranes, and OSB and plywood sheathing. 16
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Phase I:
Phase II:
Panels with ventilation spaces dried faster than comparable panels without such spaces, wider ventilation spaces dried faster than narrow ventilation spaces, top and bottom vented ventilation spaces dried faster than comparable panels with bottom-only vented spaces. A second series tests that simulated low levels of solar radiation, solar radiation had little or no effect on panels without ventilation spaces, solar radiation caused an increase in the panels’ drying rate, bottom venting performed similarly to panels with top and bottom venting.
Lab climate chamber studies, Envelope Drying Rate Analysis
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Hansen, Nicolajsen, and Stang [2002] field ventilating cavities in timber frame wall
• Ventilation with dry air removes moisture from the construction whereas ventilating with humid air could add moisture to the construction.
• They conducted an experiment with 12 different wall assemblies with various types of cladding and wind barriers and ventilated/non-ventilated spaces and space/no space combinations
• The walls were not wetted in any way. All walls remained below critical wood moisture content levels (below 20% MC) and seasonal variations were observed.
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• It was concluded that ventilation had no significant effect on wood framed wall systems.
• The authors concluded, “the behavior of wood frame walls with non-ventilated cavities, in terms of the moisture content behind the wind barrier, was not found to be inferior to the behavior of wood frame walls with a ventilated cavity”.
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Hansen, Nicolajsen, and Stang [2002] field ventilating cavities in timber frame wall
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Kristin Nore: Hygrothermal performance of ventilated wooden cladding 2009
• The cavity reduces the risk of moisture problems in wall assemblies
• It serves as a safety valve, discharging excess moisture by drainage and ventilation.
• Fields shows only a few millimetre cavity operates sufficiently.
• Although the four year study shows some results, the service life of a wooden cladding might exceed a hundred years with correct design and maintenance.
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Pressnail et al (climate chamber drying study)
• Small wall assemblies with soaked wood cladding under conditions conducive to solar driven inward vapor flow. One test set had an exterior air cavity behind the cladding.
• Ventilation was definitively shown to significantly reduce or eliminate solar-driven inward condensation.
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Bassett & McNeil (Field) Measured ventilation rates in water managed wall cavities
Ventilation rates driven by “realworld” fluctuating wind and stack pressures using a duel wavelength infra-red sensor was calibrated in the 0 to 3% range and assembled, together with gas lines and solenoid valves, to deliver tracer and sample air from the wall cavity. 2 to 12 cc/s, and the CO2 dosing rate was 0.3 and 4 cc/s.
CO2 Tracer absorption in building materials was studied.
• The tracer method has a long time constant (at least 10 minutes) not to be used to measure ventilation changes on a short time scale.
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Bassett & McNeil (Field) Measured ventilation rates in water managed wall cavities
• Vented: The high average measured ventilation rate (0.4 l/s.m) indicates that infiltration paths are likely to play an important role.
• Ventilated: In drained and ventilated cavities the average ventilation rates (over 60 days of measurement) was 1.4 l/s.m compared with 1.5 l/s.m predicted from climate data.
• Drainage : were an order of magnitude lower than those in the open rainscreen walls, averaging 0.04 l/s.m.
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Past Work/Conclusions
• Although ventilation has been studied by a range of researchers, it is difficult to develop a consensus from the research.
• It can be said that field research tends to support the concept that ventilation airflow can be significant and that this airflow causes drying when clear open spaces exist.
• Results from laboratory and climate chamber studies tend to show less or no drying.
• Theoretical studies tend to show that ventilation has the potential for significant drying
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The light has arrived……
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Penn State University
Oak Ridge National
Laboratory
University of
Waterloo
ASHRAE TC 4.4
TRP 1091
How many pages is it ?
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Three Institutions (2001-2004)
• Three institutions were involved in this project, namely, the Pennsylvania Housing Research/Resource Center at Penn State (PHRC/PSU), the Building Engineering Group at the University of Waterloo (BEG/UW), and the Building Technology Center at Oak Ridge National Laboratory (BTC/ORNL).
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Approach
WUFI
Advanced
Hygrothermal
Field
&
Lab
Theory
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Interrelated Work Segments
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Objectives
• Understand of the nature and potential for ventilation drying, study, the contribution of sheathing membrane and the type of cladding to the overall performance of residential wall systems.
• To generate experimental data on the performance of ventilation strategies and their effect on the overall performance of wood-framed, screened wall systems
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Objectives
• To benchmark and validate computer-based simulation procedures. A comprehensive program of advanced, state-of-the-art hygrothermal modeling was envisaged, mainly to extend the knowledge to other wall systems for at least six representative climatic areas. These data were then to be used to provide the basis for the development of air cavity design guidelines.
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Theory
• Air Cavity Configuration
• Geometry considerations
• Vent opening types
• Duct air flow theory
• Vent Air Flow Forces
• Pressure Dynamics
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Wall System- Terminology
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5 Critical Air Cavity Compartments
Ventilation Cavity Compartments
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Vent types
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Ventilation Options
Continuous Slot Discrete Slot
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Ventilation Cavity Physics
• Flow velocity
• Roughness of the sides
• The size (depth) and shape of the cavity
• Number and size of obstructions and degree of baffling
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Air Cavity Ventilation Systems
Ventilated Vented Unvented
Open: Top & Bottom Open: Bottom Open: No Opening
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Ventilation Cavity Physics
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Darcy-Weisbach Equations: Frictional Shear (Velocity profile)
ASHRAE 2001 H2.8
Idelchik : Friction factor for rectangular conduit with any roughness in laminar flow
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• Local disturbances of the flow, • Separation of flow from surfaces, and • Formation of vortices and strong turbulent agitation of the flow.
Exit and Entrance Resistances
Ventilation Cavity Physics
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Elbow & Turns Resistances
Ventilation Cavity Physics
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Ventilation Cavity Physics
Exterior pressure coefficients for low-rise buildings
Stack Pressure
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exitcavityinTotal PPPP
2
2
2 5.032
5.0 vCD
LkvCP exit
h
f
inTotal
stackwindTotal PPP
Ventilation Cavity Physics
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Ventilation Cavity Physics
Climate Conditions
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Theory Predictions
Windward wall: 0.20 Pa – 0.60 Pa = -0.40 Pa (upward flow – wind minus stack for 5 oC)
• - 0.40 Pa would drive 0.50 l/s (0.61 m3/(m2•hr) or 26.3ACH
Windward wall: 0.20 Pa – 3 Pa = -2.7 Pa (upward flow – wind minus stack for 30 oC)
• - 2.7 Pa would drive 1.3 l/s (1.57 m3/(m2•hr) or 68.4 ACH
Leeward walls and sidewalls: 0.60 Pa (upward flow due to stack for 5 oC)
• - 0.60 Pa would drive 0.62 l/s (0.75 m3/(m2•hr) or 32.6ACH 44
Brick veneers with chamber depths of 3/4 in. (19 mm)
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Climate: Stack Pressure (Pa) Brick Cladding South Facing
Stack pressure potential (Pa) (hourly data) for airflows behind the brick cladding facing South-West in seven locations in the US.
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46
Climate: Stack Pressure (Pa) Brick Cladding South-West
Stack pressure potential (Pa) (hourly data) for airflows behind the brick cladding facing South-West in seven locations in the US.
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47
Climate: Wind Pressure (Pa) Brick Cladding South Facing
Wind pressure potential (Pa) (hourly data) for airflows behind the brick cladding facing South-West in eight locations in the US. Difference between wind pressure coefficients (Cp) in the top and in the bottom of the wall (height = 2.5 m) is 0.1
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48
Climate: Wind Pressure (Pa) Brick Cladding South Facing
Wind pressure potential (Pa) (hourly data) for airflows behind the brick cladding facing South-West in eight locations in the US. Difference between wind pressure coefficients (Cp) in the top and in the bottom of the wall (height = 2.5 m) is 0.1
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Advance Analysis
TC4.4: Project 1091-TRP
Development of Design Strategies for Rainscreen and Sheathing Membrane
Performance in Wood-framed Walls
49
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Three critical competencies
Modeling Field Lab
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51
But the real question is where to get the
Air Cavity Ventilation Numbers ?
Some Engineering Magic
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Modeling
Model Inputs: • Accurate representation of components/materials • System/sub-systems characterization • Physics • Appropriate loads (Boundary Conditions) Promised: • be as complex and comprehensive as possible when accuracy is needed • be as complex and comprehensive as needed when relative accuracy is sufficient
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Project Objectives:
Two Main Objectives
• Nature and relevance of air cavity ventilation • Performance and contribution of sheathing membrane
How was work proposed:
a) Generate laboratory data (benchmark model + understanding)
b) Generate field data (realistic input to model + performance data)
c) Use modeling to extend understanding to other walls and climates (supplemented by 3-D CFD)
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Numerical Modeling
CFD
• Turbulent 3-D air flows
• Acceleration/Deceleration forces, Shear stress at boundaries
• Entry and Exit pressure drops
• Real dynamic wind pressures
• Air flow movement
A series of 3-D Simulations were performed:
Conjugated Heat and Mass transfer were performed 54
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Goal – Quantify Internal Convection Effects for Wall Cavities
• Heat and Moisture Transport
• Computational Models
• Experimental Benchmarks
55
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CFD Tool Used – CFX 5.5
• Tetrahedral/prism mesh
• Locally refined mesh (near edges and high velocity
gradients)
• Scaleable wall functions
• Multiple turbulence models
• Permits multiple fluids
56 T. Stovall (ORNL)
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Geometric Model Considerations
• Brick/mortar roughness
• Depth of cavity
• Openings
• Physical phenomena/time scales
57
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Initial Model – 3D
• 50 mm depth
• 2.43 m height
• 0.61 m width (between symmetry)
• Bottom and top openings
58
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Parameters Varied for Model of Brick Rainscreen Wall:
• Wind speed: 0, 1, 4, 7, 10 m/s (normal)
• Solar radiation: 0, 629, 903 W/m2
• External air temperature: 250 and 305 K
• Cavity depth: 19 and 50 mm
• Ventilation slot height: 79 and 158 mm (10 mm wide)
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Parametric Analysis
60
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CFD Wall Analysis: Two Walls
61
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CFD Geometry
62
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CFD Geometry
63
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Results (Center of cavity ) 50mm, with 4 m/s wind speed
Summer Winter Summer Winter
64
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65
Side view of velocity field at bottom bisecting the ventilation slots.
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Air Flowed From Bottom
to Top
With Some Recirculation Areas
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Slight Differences in Velocity Profiles 5 mm From Rough Wall Surface
67 Smooth 3 mm ks
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Flow Separation and Recirculation Apparent at Top Opening in Applied 2 Pa Pressure Differential, Cold Winter
68
Top
Bottom
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69
Velocity Profiles, Bottom Section, Winter, 2 Pa
Pressure Gradient, Smooth Walls
Near bricks center of gap near interior wall
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Multivariate Regression Used with CFD Results from 22 Cases
• Examine:
– Total Ventilation Flow Through Cavity
– Vertical Cavity Pressure Change
– Pressure Drop in Ventilation Slot
• As a function of :
– Wind Speed
– Outdoor Air Temperature
– Solar Radiation
– Cavity Depth and Ventilation Slot Height
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Multivariate regression analysis
71
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Equation
72
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Comparison between Eqn 1 & CFD Summer
73
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74
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Vinyl
75
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What have we learned
Approach 1:
• Develop flow equations based on Duct analogy flow (Simple Theory)
• We can determine Pressure forces from stack, mechanical pressure and wind by simple correlations.
Approach 2:
• Develop flow equations based on CFD (True resistances)
• Superimpose pressures from stack and mechanical pressures with CFD wind (or use simple CFD derived correlation)
76
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How do I deploy cavity ventilation in
Hygrothermal modeling ?
Let’s look at the transport.. 77
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[K/s] Change of Temperature in Time (solution)
Heat Transport
[W/m³]
External Heat Source
New in Ver. 4.1
Transport Equations in WUFI®
Change of the Heat Flux in Depth Change of the Diffusion Flux gv In Depth => Heat Source due to sorption
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[1/s] Change of RH in Time (solution)
Moisture Transport
[kg/m³] Moisture Storage Capacity of the material
[kg/sm³]
external Moisture Source
neu ab Ver. 4.1
Change of he total Moisture Flux in Depth
Transport Equations in WUFI®
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Heat Sources
sh • x=Sh
[W/m³] External Heat Source Density
[W/m²] External Heat Source
x [m] Element Thickness
Sh= f • Is
f [-] Fraction
Is [W/m²] Solar Radiation on the Surface
0
10
20
30
40
0 6 12 18 24 30 36
Time from Begin of Calc. [h]
He
at
So
urc
e S
h [
W/m
²]
Sources/Sinks
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Moisture Sources
sw x=Sw
[kg/sm³] External Moisture Source Density
[kg/sm²] Ext. Moisture Source
x [m] Element Thickness
f [-] Fraction
R [mm/h] Driving Rain on the Surface
[l/hm²]; [kg/hm²]
3600
R f
ehS Sw
0,0E+00
2,0E-06
4,0E-06
6,0E-06
0 6 12 18 24 30 36
Time from Begin of Calc. [h]M
ois
ture
So
urc
e S
w
[kg
/sm
²]
Sources/Sinks
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Calculation of the Source Term due to Ventilation
0
10
20
30
0 6 12 18 24 30 36
Time from Begin of Calc [h]
Air
Ch
an
ge
Ra
te [
1/h
]
Sh: Heat Source [W/m²] out: Density of the exterior Air [kg/m³]
ACH: Air Change Rate in the ventilated Layer [1/h]
dVent: Thickness of the ventilated Layer [m]
Cp,Air: Spec. Heat Capacity of Air [J/kg K]
Tout: Temperature; Outdoor [K]
TVent: Temperature in the ventilated Layer [K] (mean value of all Elements)
Heat Source: )TT(Cd3600
ACHS
VentOutAir,pVentouth
Moisture Source:
Sw: Moisture Source [kg/m²s]
cout: Water Vapor Concentration in the Air; Outdoor [kg/m³]
cVent: Water Vapor Concentration in ventilated Layer [kg/m³] (mean value
of all Elements)
)cc(d3600
ACHS
VentOutVentw
Sources/Sinks for Ventilation
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Question 1:
Ok… we can sort get a reasonable estimate for air flow in exterior claddings..
But
How well can we model the moisture transport ??
83
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Laboratory and Field Measurements
• Let’s start with Laboratory measurement… see if we can predict the same transport phenomena
• If successful let’s move to the field.. !!
• If not successful let’s go to the beach …
84
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Panel ventilation drying study
Variables Studied
• sheathing membrane (A)
• Airspace (B) volume
• induced flow rate (E)
• Cladding (C)
• Vents (D)
85
B (A
irspa
ce)
A (S
hthg
Mem
bran
e)
C (C
ladd
ing)
D (Vents)E (Induced Flow)
OSB
Foil-
face
d P
olyi
soW
ettin
g S
yste
mH
omas
ote
Penn State
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86
Panel ventilation drying apparatus
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Test Panel Assembly: Laboratory
87
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Wetting Mechanism
88 Van Straaten, MscE
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Drying rates (None to 1.6 L/s)
89
-200
0
200
400
600
800
1000
1200
1400
1600
0 24 48 72 96 120 144 168 192 216 240 264 288 312 336
Time (h)
We
igh
t C
ha
ng
e f
rom
Sta
rt (
g)
No Flow
0.2 L/s
0.4 L/s0.8 L/s1.6 L/s
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Summary table
90
Flow Rate(L/s)
Air Change Rate(ACH)
Approx. Drying Rate(g/h)
Drying Time(days)
1.6 40 17 4.4
0.8 20 9 6.9
0.4 10 8 8.5
0.2 5 5 12.6
No Ventilation Airflow
0 1 Did not dry completely
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Advanced Hygrothermal Modeling to predict drying in this 2D case
91
1-D or 2-D Vapor Air Flow Vapor and Liquid Diffusion Solar and Sky Radiation Wind-Driven Rain Moisture-Thermal Sources and Sinks Dynamic Stack and HVAC Effects Liquid Transport as a function of process
Model Features
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Well……
92
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First never done before….
93
Problem…. ASHRAE data for Wood fiber board were Asphalt Coated. The Penn State Homosote were not Asphalt Coated. ORNL performed Hygrothermal Material Properties And these were used…. Let’s see if this helped ??
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ASHRAE Homosote
94
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Laboratory Validation (0.8 Lps)
95
Panel 8 - Weight Change
-200
0
200
400
600
800
1000
1200
1400
1600
7/3/02 12:00 AM 7/4/02 12:00 AM 7/5/02 12:00 AM 7/6/02 12:00 AM 7/7/02 12:00 AM 7/8/02 12:00 AM 7/9/02 12:00 AM 7/10/02 12:00 AM
Date
Weig
ht
(g)
Weight changeMoisture Expert
0.7 % (E-S)/E <0.35 %>
2.6 % (E-S)/E <0.4 %>
4.6 % (E-S)/E < 0.5 %>
6.2 % (E-S)/E <1%>
20.0 % (E-S)/E < 4% >
Figure 3. Airflow manifolds connected to test panel on counterbalance system (Burnett et al [2004])
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Laboratory Validation (1.6 Lps)
96
Panel 9 - Weight & Relative Humidity
0
200
400
600
800
1000
1200
1400
1600
7/11/02 12:00 AM 7/13/02 12:00 AM 7/15/02 12:00 AM 7/17/02 12:00 AM 7/19/02 12:00 AM 7/21/02 12:00 AM 7/23/02 12:00 AM 7/25/02 12:00 AM
Date
We
igh
t (g
)
Weight changeMoisture Expert
Figure 3. Airflow manifolds connected to test panel on counterbalance system (Burnett et al [2004])
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Relative Humidity Comparison
97 Nov 1, 2007
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Spatial T & RH Distributions
98
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Experimental Drying rates
99
-200
0
200
400
600
800
1000
1200
1400
1600
0 24 48 72 96 120 144 168 192 216 240 264 288 312 336
Time (h)
We
igh
t C
ha
ng
e f
rom
Sta
rt (
g)
No Flow
0.2 L/s
0.4 L/s0.8 L/s1.6 L/s
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Fix the Experiments…..
100
When
Interior
conditions
are
Kept
constant
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Expand the experiments (Go Crazy)
101
What happens when
RHin is 10 %, 20 %
Lower ? or higher ?
0.2 lps
Case 1.6 lps W
eig
ht
kg
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Got arrogant with modeling !!
Even corrected the laboratory data… This could mean trouble..!
102
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Field Monitoring
103
Vinyl Wall Brick Wall
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104 Nov 1, 2007
U N I V E R S I T Y W A T E R L O O
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Field Validation at BEGHUT
105
Brick SBPO Ventilated
0
5
10
15
20
25
30
02/01/02 05/12/02 08/20/02 11/28/02 03/08/03 06/16/03
Date
Ho
mo
so
te M
C,
weig
ht-
%
MeasuredCalc
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Field Validation
106
Vinyl SBPO Ventilated
0
5
10
15
20
25
30
02/01/02 05/12/02 08/20/02 11/28/02 03/08/03 06/16/03
Date
MC
, w
eig
ht-
%
MeasuredCalc
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Validation (LAB + FIELD)
• ME has been validated for Brick & Vinyl Walls
• Excellent Agreement was found
• Complex Processes Involved:
● Liquid Penetration (Incidental Water)
● Redistribution of Water
● Ventilation drying
● Diffusion Transport
107
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Validation for another site..
108
C
A
S
C
A
D
E
S
O
L
Y
M
P
I
C
S
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Validation in Puyallup WA
109 Nov 1, 2007
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Validation with WUFI
110 Nov 1, 2007
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Parametric Analysis
111
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Interior conditions
112
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Parametric Analysis
113
Acronyms
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Fitting Loss Coefficient
114
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Results
115
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Results
116
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Air Exchange per Hour (ACH) (Outputs) Seattle
Ventilated Brick Histogram
0
1000
2000
3000
4000
5000
5 15 25 50 75 100More
Air Changes/hr Bin
Fre
qu
en
cy
(h
r)
0%
20%
40%
60%
80%
100%
FrequencyCumulative %
117
Vented Brick Histogram
0100020003000400050006000
5 15 25 50 75 100More
Air Changes/hr Bin
Fre
qu
en
cy
(h
r)
0%20%40%60%80%100%
FrequencyCumulative %
Non-Ventilated Vinyl Histogram
0
1000
2000
3000
4000
5 15 25 50 75 100More
Air Changes/hr Bin
Fre
qu
en
cy (
hr)
0%20%40%60%80%100%
FrequencyCumulative %
Ventilated Vinyl Histogram
0
1000
2000
3000
4000
5 15 25 50 75 100More
Air Changes/hr Bin
Fre
qu
en
cy
(h
r)
0%20%40%60%80%100%
FrequencyCumulative %
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Air Exchange per Hour (ACH) (Outputs) Minneapolis
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Concept of Safety Factor
119
Mo
istu
re C
on
ten
t kg
/kg
SF= 1 % Water Penetration Ventilation reduces MC_max load by 41 % Venting reduces MC_max load by 28 %
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120
Risk Assessment/Safety Factor
Safety
Factor of safety of 1 implies no safety at all. Hence some engineers prefer to use a related term, Margin of Safety (MoS) to describe the design parameters. The relation between MoS and FoS is
MoS = FoS - 1.
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121
Concept of Safety Factor
Ventilation can tolerate wetting loads for WDR 2% For Seattle
Seattle
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122
Concept of Safety Factor
Ventilation can tolerate wetting loads for WDR 3% For Charlotte
Charlotte
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Summary
• Presented a simplified resistance network model that
was shown to be sufficient for prediction of air cavity ventilation. Good moisture transport predictions.
• WUFI has included the capability as a design tool to prediction this phenomena
• Two independent field test confirm applicability of new approach
• Mass flows in a cavity are more sensitive to vent dimensions than cavity depth in the 20 to 50 mm range.
• Ventilation is a safety factor close to 2% of current ASHRAE SPC 160 loads (2013) 123
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Conclusions
Implementation of the ventilation air cavity strategy enhanced the overall drying performance of absorptive cladding wall systems (brick veneer) in all five climates examined in this study.
In some climates, early fall conditions showed a net increase in moisture accumulation due to the presence of cladding ventilation, but the sheathing was below 10 % moisture content (i.e, well within the safe zone).
Vented cavity wall systems had substantially less drying potential for the absorptive cladding wall systems when compared to ventilated systems, this was due to less ventilation air flow.
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125
Non-absorptive wall systems were found to benefit from ventilation , but at a much lesser extent due to inherit leaky structure of the vinyl siding.
From the parallel simulation activity with two different initial construction moisture conditions, all absorptive cladding wall systems that started with a moisture content of the OSB at 32 %, had difficulty in drying within (4 weeks to below 80 %).
Problems did exist for the location of Seattle to dry within an acceptable time for the vented system for brick clad walls.
Conclusions
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126
The effective ventilation rate behind the cladding depended on both the wall system and the exterior climate. In Miami and Minneapolis, high winds and temperature gradients allowed large ventilation air changes in the walls. Cladding ventilation rates ranged between 0 to 150 air changes per hour.
The results showed that sheathing membranes for climates like Minneapolis (cold) did show some influence even though this was secondary to the choice of the ventilation strategy.
Conclusions
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The higher the IC moisture, the more influence of the choice of the sheathing membranes. In most climates, in some period of year the 15 # felt performed better and in other period the SBPO membrane. These conclusions are based on using the OSB as the sheathing of the wall.
Additional analysis has conclusively demonstrated the superior performance of cladding ventilation versus vented and unvented strategies.
The beneficial effects of air cavity ventilation seem to be directly dependent on climate.
Conclusions
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Call to Professors/Farmers
UnKnowns: Limited Understanding air flows in cases with fluctuating wind pressures and infiltration paths.
The ventilation rates need to be measured and reported that at least driven by “realworld” fluctuating wind and stack pressures.
Simple software apps for a wide range of geometries to produce ACH in air cavities..
128
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Smart Air Cavity Designs
In 2007 approached by Manufacturer of innovative product… a dimpled sheet of polyethylene (John & I)
“ Let’s use it as a ventilated Rainscreen and yes in Cold Climates and why not everywhere else ?”
129
• Understand drainage, air flow resistance of wall system
with Dimple PE sheet and Drying tests performed by J.
Straube
• Calibrated model for flow and Validated drying model
with good results
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130
Smart Air Cavity Designs
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Modeling Analysis
131
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132 Time(d)
To
talM
ois
ture
inW
all
(kg
)
0 100 200 300 400 500 600 7001
1.2
1.4
1.6
1.8
2
July 1
Felt Wrap
Delta Drainwrap System
Frame 001 21 Apr 2005 Layer moisture contents | Layer moisture contents Modeling Analysis
Toronto
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133 Time(d)
OS
BM
ois
ture
Co
nte
nt
inW
all
(kg
/kg
)
0 100 200 300 400 500 600 700
1
1.5
2
2.5
3
3.5
July 1
Felt Paper
Delta Drainwrap System
Delta Drainwrap (50 % blockage)
Delta Drainwrap (85 % blockage)
SEATTLE
Frame 001 24 Apr 2005 Layer moisture contents | Layer moisture contents Modeling Analysis
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Time(d)
To
talO
SB
Mo
istu
reC
on
ten
tin
Wa
ll(k
g)
0 100 200 300 400 500 600 700
1
1.5
2
July 1
Felt Paper
Delta Drainwrap System
Delta Drainwrap (50 % blockage)
Delta Drainwrap (85 % blockage)
Norfolk
Frame 001 08 Oct 2005 Layer moisture contents | Layer moisture contents Modeling Analysis
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Modeling Analysis
0 200 400 600 800
Time (Days)
0.5
0.6
0.7
0.8
0.9
1
Rel
ativ
e H
umid
ity (
- )
15 # Felt Paper
Delta Drain Wrap
RH in Insulation(Exterior Most Location)
July 1
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136
Experimental Set-up
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Experimental Set-up
ORNL Test Facility: Charleston SC
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138
Exterior & Interior Conditions
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Measurements (Month of June)
139
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Measurements (Month of June)
140
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Measurements (Month of June)
141
Exterior Gypsum
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Measurements (Month of Feb)
142
Monthly Average Relative Humidity RH 2
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Measurements (Month of Feb)
143
Monthly Average Relative Humidity RH 3
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Measurements (Month of Feb)
144
OSB
0
10
20
30
40
50
60
70
80
1 28 55 82 109 136 163 190 217 244 271 298 325 352
Wall11-RH3Wall13-RH3
Wall
Winter Period Hourly
Synthetic Membrane
Dimple
Sheet
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Measurements (Yearly)
145
OSB
J.F. Straube BSC Field Study
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Air Flow Dynamics
146
Horizontal Test
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Air Flow Dynamics
147
Horizontal Test
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Air Flow Dynamics
148
Horizontal Test
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Air Flow Dynamics
149
Horizontal Test - 1 storey
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Air Flow Dynamics
150
Horizontal Test -3 Storey
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151
Three Venting Options
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Air flow in Front & Back Air Spaces
152
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Air flow in Front & Back Air Spaces
153
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154
Air flow in Front & Back Air Spaces
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155
Effect of Height for Brick wall with 2 top and 2 bottom openings
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Air Flow Dynamics
156
Vertical Test-3 Storey
Measure Solar, Wind speed,
Velocity, Tracer gas, T, RH,
Pressure
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6/19/200- 6/20/2008
05
101520
2530354045
0 6 12 18 24 30 36 42 48
Time (hr)
Te
mp
era
ture
( o
C)
1st Storey2nd Storey3rd Storey
Front Air SpaceJune 19,20
Field Monitoring
157
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Field Monitoring
158
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Field Monitoring
159
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Field Monitoring
161
7/15/2008-7/16/2008
0
10
20
30
40
50
60
0 4 8 12 16 20 24 28 32 36 40 44 48
Time
Air
Ch
an
ges (
1/h
r), T
( o
C)
0
200
400
600
800
1000
1200
So
lar
Ra
dia
tio
n (
W/m
2)
Front Air Space
Back Air Space
Temperature
Horizontal SolarRadiation
3 Storey Brick
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Field Monitoring
162
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Air Changes per hour
Top & Bottom ACH
05
101520253035404550
0.25
1.77
3.28 4.
8
6.31
7.83
9.34
10.9
12.4
13.9
15.4
16.9
18.4 20
21.5 23
Time (hr)
Air
Ch
an
ge
Ra
te
bottomtop
Pressure Distribution
-2
-1.5
-1
-0.5
0
0.5
1
1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91
Time (0= Midnite, 47.5=Noon) = 24 hr
Pre
ss
ure
(P
a)
Pressure 1Pressure 2Pressure 3Pressure 4Pressure 5
5:00 PM2:00 PM
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Front Air Cavity
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165
Conclusions
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Brick (Interior/Exterior ACH)
166
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CO2 as Tracer Gas
167
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168
Cladding Ventilation QUANTIFIED
0
5000
10000
15000
20000
25000
0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140
Time
Co
ncen
trati
on
Ventilated Brick (20-120 ACH) for 1 to 4 m/s)
Vented Brick (5 - 45 ACH) for 1 to 4 m/s)
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169
Cladding Ventilation QUANTIFIED
Ventilated ( 10 - 20 ACH) for 0 to 2 m/s)
Vented (1.5 - 10 ACH) for 0 to 2 m/s)
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170
Drainage
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171
Test Conventional Approach
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172
Test Conventional Approach
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173
Drainage
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Conclusions
• The first series of tests allowed the characterization of the flow in both front and back spaces for the three ventilation strategies.
• The result indicated that the highest resistance is due to the entry and exits in these air cavities at higher velocities.
• At low velocities (low air exchange rates) the inlet and outlet resistances diminish significantly.
• The conventional brick openings recorded a higher resistance than the slotted arrangement
174
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• The flow along the length of the wall in either front or back air space is only slightly reduced by the height of the application of the Delta-Dry weather resistive barrier (8ft versus 16 ft versus 24 ft).
• At lower pressures, both front and bottom cavities became well ventilated (higher than 5 air changes per hour).
• The field tests show that the driving force is primarily due to solar radiation inducing buoyancy in the air space cavities.
175
Conclusions
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• The buoyancy was present while the wall is directly within the solar path and a few hours after the direct sun impinging on the wall.
• The cavity ventilation flow seems to reduce rapidly, and is close to zero for at least 8 to 10 hours per day.
• This observation is true for the summer periods and may be different during other periods of the year, and at other climatic locations, and orientations.
• The effect of wind was not found to be significant driver for air flow through either front or back cavities.
176
Conclusions
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• However, wind pressures may vary a lot on the building shell depending on the building, its design and surrounding structures and therefore definite conclusions can not be made based on this individual study.
• To understand the moisture performance, simulations can be performed using the results generated in this project, to address these issues.
177
Conclusions
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Validation work for Solar Driven Moisture
178
Brick/Stucco Air Space-B SPBO OSB FIB GYP Vinyl Wall
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APPARATUS
Weighing Cups
Balance
Drying Ovens
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APPARATUS (CONTINUED)
Environmental Chambers
Temperature and Humidity controlled
Use Salt Solutions (ASTM E 104)
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Water Vapor Permeance of Wall Materials
0
5
10
15
20
25
30
35
40
0 10 20 30 40 50 60 70 80 90 100
Average Relative Humidity, %
Perm
s
Oriented Strand Board
15 # Felt
Brick, 5/8"
WVP of some materials
Brick 1st Year
ASHRAE 1325
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Sorption Isotherm
of some materials
Fortifiber Ashpalt Saturated Kraft Sheathing
Dried at 23°C, 0.2% RH
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80 90 100
Relative Humidity, %
Mo
istu
re C
on
ten
t, %
Jumbo TexJumbo Tex HDSuper Jumbo Tex
ASHRAE 1325
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Liquid Uptake
• Avalue Old Brick (2005-2006) A= 0.1 kg/m2
• Avalue New Brick (2006-2007) A= 0.8 kg/m2
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New Results
0 20 40 60 80 100Relative Humidity (%)
0
0.04
0.08
0.12
0.16
Mo
istu
re C
on
ten
t (k
g/k
g)
Brick Material DataBrick Phase IBrick Phase II
Sorption IsothermNew Data
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Sorption Isotherm: Wall Paper
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0 20 40 60 80 100
RH
Mo
istu
re C
on
ten
t (k
g/k
g)
Sample 1Sample 2Sample 3Sample 4
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y = 1.73E-05x4 - 1.20E-04x3 - 2.25E-01x2 + 3.27E+01x - 4.86E-08R2 = 1.00E+00
y = 0.2216x2 - 5.5884x + 14.626R2 = 0.9879
y = 0.0573x2 - 1.7851x + 7.5399R2 = 0.9168-2000
0
2000
4000
6000
8000
10000
12000
0 20 40 60 80 100 120
Brick1Brick2TyvekJumboTexLinear (Tyvek)Poly. (JumboTex)Poly. (Brick2)Poly. (Brick1)
Kirchoff’s Potential for Vapor Flux Analysis
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Validation Data: Moisture Content MC1
MC 1: 10 mm depth
u- m
oist
ure
cont
ent (
kg/k
g)
Time (days)
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Validation Data: Moisture Content RH3
Plywood RH3
RH
(-)
Time (days)
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0 4000 8000 12000Time (hr)
0
10
20
30
40
Tem
pera
ture
( oC
)
ME Simulation
Experimental-Field data
Fit 1: ME Simulation
Fit 1: Experimental-Field Data
Jan. 1
OSB exterior location (2 mm from surface)OSB
Validation Data:
Temperature T11
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Observations from Modeling vs Field
Good agreement (ME and Field)
Agreement with RH, T and Moisture Content
Validation requires full material properties
Needed to include effects of cladding venting potential
Solar radiation important
Wind driven rain important
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New Validation: ASHRAE 1235
Wall 1: Validation
Brick Cladding
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Brick Cladding Validation
Material Properties were measured
Issues with rain loads + Weather data completeness + testing
Water Penetration ?
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0 100 200 300 400 500
0
0.2
0.4
0.6
0.8
1
50E-10,New weath WDRwall + Roof (Unvented)
Measurements
Vented
Ventilated
Fit 1: Running average:Measurements
Fit 1: Running average
Very Permeable inside 50E-10No Water Penetration
RH1
0
10
20
30
40
50
0 4000 8000 12000
0
5
10
15
20
25
0 100 200 300 400 500
0
0.2
0.4
0.6
0.8
1
50E-10,New weath WDRwall + Roof (Unvented)
Measurements
Vented
Ventilated
Fit 1: Running average:Measurements
Very Permeable inside 50E-10
No Water Penetration
RH3
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0 100 200 300 400 500
0
0.2
0.4
0.6
0.8
1
50E-10,New weath WDRwall + Roof
Measurements
50E-10,Old Weath (Calc WDR)
Very Permeable inside 50E-10
No Water Penetration
No VCVENT
RH4
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Deconstruction
196
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The issues
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The issues
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The issues
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The issues
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Conclusion
Workmanship in buildings can alter the performance in a major way. Critical to the validation of models.
Measured material properties are very important in validation analysis.
Low absorptive claddings are favorable in wet and hot climates.
Results demonstrate confidence in hygrothermal models for simulations.
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Another BIG CONCLUSION
• Leave the model validation to the EXPERTS-developers… Very few of you can even use a model correctly.
• Do not say you validated a model…. By using material properties from the database, weather data from the database, and ASHRAE SPC 160 interior conditions…..
• You may say you calibrated your model…
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Thank you
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Questions ?