The Next Frontier of Building Science: Air Leakage · 2019-06-27 · The Next Frontier of Building...
Transcript of The Next Frontier of Building Science: Air Leakage · 2019-06-27 · The Next Frontier of Building...
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The Next Frontier of Building Science: Air Leakage
Achilles Karagiozis
Global Director Building Science, Sustainability Owens Corning
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Acknowledgements
• Mikael Salonvaara, Owens Corning
• Andre Desjarlais, Oak Ridge National Laboratory
• Laverne Dagleish, ABAA
• Dave Wolf, Owens Corning
• Department of Energy, DOE
• Diana Hun, Oak Ridge National Laboratory
• Hartwig Kuenzel, Fraunhofer Institute of Building Physics
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Presentation Layout
• Objectives (Short Term and Long Term)
• Simplification of the Physics
• Air Leakage performance structure
• Passive House wall Heat-Air-Moisture analysis
• Implementation of a approach for Design
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Air flow
JStraube
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Motivations
• My Motivation – Owens Corning wants to provide higher performance level analysis (quantification) to building community
• ORNL/DOE Motivation – Increase awareness and upgrade in performance goals for USA building stock
• ABAA/Industry Motivation- Increase air tightness, understand impact and create a design approach
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6
Question :
How much air
Leakage does
this woodpecker
cause ?
Current Status
Building science is lacking…. Need Quantification
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Air Flow
JStraube
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Actual Measurements
Fresh off the press… Mika’s House Atlanta Aug 1-3
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Actual Measurements
4.142.761.38-0.00-1.38-2.76-4.14
Median
Mean
-0.14-0.16-0.18-0.20-0.22-0.24
1st Q uartile -0.36740
Median -0.14630
3rd Q uartile -0.01300
Maximum 4.84400
-0.23455 -0.22985
-0.14630 -0.14300
0.44625 0.44958
A -Squared 4720.30
P-V alue < 0.005
Mean -0.23220
StDev 0.44791
V ariance 0.20062
Skewness -1.53985
Kurtosis 7.32402
N 139131
Minimum -5.10400
A nderson-Darling Normality Test
95% C onfidence Interv al for Mean
95% C onfidence Interv al for Median
95% C onfidence Interv al for StDev
95% Confidence Intervals
Summary for Out
3.152.101.05-0.00-1.05-2.10-3.15-4.20
Median
Mean
-0.322-0.324-0.326-0.328-0.330
1st Q uartile -0.42250
Median -0.32410
3rd Q uartile -0.24190
Maximum 3.21880
-0.32918 -0.32676
-0.32580 -0.32250
0.22938 0.23109
A -Squared 3235.72
P-V alue < 0.005
Mean -0.32797
StDev 0.23023
V ariance 0.05301
Skewness -0.3569
Kurtosis 12.2600
N 139131
Minimum -4.48640
A nderson-Darling Normality Test
95% C onfidence Interv al for Mean
95% C onfidence Interv al for Median
95% C onfidence Interv al for StDev
95% Confidence Intervals
Summary for Attic
S
T
A
T
I
S
T
I
C
S
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Air Leakage Path
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Attention to all construction Details are a Must !!
Specifying the details…and then training
our contractors to do-it-right!
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Exterior Air Sealing Strategies
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Interior Air Sealing Strategies
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Systems Approach to Air Leakage
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Objectives
Short-Term
• Include air leakage thermal losses in envelope calculations
• Include the impact of air leakage in moisture flow calculations
• Be able to address durability design analysis
Long-Term
• Include 2-D, 3-D capability
• Full building leakage
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16
Create the basic understanding
X(m)
Y(m
)
-0.1 0 0.1
0
0.5
1
1.5
2
2.5 T(C)
20.00
17.86
15.71
13.57
11.43
9.29
7.14
5.00
2.86
0.71
-1.43
-3.57
-5.71
-7.86
-10.00
3 PaWALL 1
OSB
Frame 001 31 Jan 2002 INSTANTANEOUS VALUESFrame 001 31 Jan 2002 INSTANTANEOUS VALUES
X(m)
Y(m
)
-0.1 0 0.1
0
0.5
1
1.5
2
2.5 RH(-)
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
3 PaWALL 1
OSB
Frame 001 31 Jan 2002 INSTANTANEOUS VALUESFrame 001 31 Jan 2002 INSTANTANEOUS VALUESTemperature Relative Humidity
Minneapolis: Study by ORNL and BSC
Intentionally Leaky… added holes
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Air leaks through walls
• Explain the basics needed to be captured in WUFI model
• Show the process
• Take science data to the field (From an academic exercise to reality)
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What is future ?
2 Storey
Building
For a
particular
joint
Air Barrier
system
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Air leakage modes
• Air flow through the wall
– Through insulated wall cavity
– Between components (where the majority of the leakage flow happens)
• Wind-washing
– No flow through – flow in and out (insulation)
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Roles of Air Barriers
• Wind barrier
– Prevent “wind-washing” of insulated cavity
• Air barrier
– Prevent air flows through the wall
or
Terminology Session: Where is Professor Eric Burnett ?
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Forces causing airflow through envelope parts
Infiltration/Exfiltration is the unwanted air movement
through a building and is caused by a pressure difference (air
moves from high pressure to a lower pressure).
Stack Wind + mechanical ventilation
(+/- DP)
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Multi-dimensional flows to 1D
• Add heat and moisture source to – Exterior cavity (air from
outdoors/ins. cavity)
– Insulated cavity (air from ext. cavity/indoors)
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Linear Transport Laws
• Fourier’s Law – Heat is transferred from a region of higher temperature to a region of lower temperature
• Fick's law – Mass is transferred from a region of higher concentration to a region of lower concentration
dx
dTkAQ
dx
dCDAJ
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31
Governing Equations
Mass Balance
0.
aa
a Tt
T
(2)
Momentum Balance
gT
K
TPT
t
Taa
a
aaaaa
aa
D
;
(3)
Where aK = the air permeability (m2).
Energy balance
onCondensati
l
mice
nEvaporatio
vpv
ConductionConvection
apapm
t
TfuTuL
PTuLTTukTVTCt
TTuCTu
D
,.
,.,..,,
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Mesh containing 590 elements Mesh containing 2360 elements
Solve each equation/element
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Flow balance
• Air can leak one-dimensionally all the way through, or some of the air may be lost (or added!)
• Initially, let’s assume that all flow will go through and there are no leaks – Flow direction
would cause problems in assigning the source (attic, etc.)
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Procedure to Calculate Sources and Sinks
• Calculate pressures P – Wind
• Wind pressure coefficients and locations
• Wind speed and direction
– Stack • Neutral pressure plane
– Mechanical ventilation and building pressure balance
• Calculate flow through – Air leakage characteristics
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Wind pressure on buildings
• ASHRAE Fundamentals 2005
– Bernoulli’s equation
• Wind pressure coefficient on the wall Cp
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Wind speed at the building (wall) height
• Location affects the wind speed
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Local wind pressure coefficient Cp – need to simplify
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Simplified wind pressure coefficients
• Default value: assume average wall coefficient (tall buildings)
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Simplified wind pressure coefficients
• Default value: assume average wall coefficient (low-rise)
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Stack pressure
inin RTpM /
• Buoyancy effect: Density difference of air outdoors and indoors
HgTTR
pMP
inout
D )11
(
Dense, cold,
heavy air
Light, warm
air
Neutral pressure plane
H
Wall level
outout RTpM /
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Zone pressures
• Building pressure calculations
• Building zones
– Room to room balance
– Stratification (bottom to top) • Location of the leak in the building and in the element matters!
• Have an attic zone, and a crawlspace zone
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Total pressure difference
Mechanical
inout
p
MechanicalStackwind
PHgTTR
pMUCP
PPPP
D
DD
DDDD
112
21
P_zone
P_crawl
P_attic
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Climate Effects
Hourly
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Climate Stack Pressure
Hourly
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• In addition to exterior cavity, we have now air leaks in and through insulation layer
• Wind Pressure Difference and Thermal Buoyancy result in a pressure difference across the wall.
• Heat source:
• Moisture source:
Equations for sinks/sources
)(, TTCQS inAirpinh
)( ccQS sourcew
Q = CDpn Wall assembly air leakage
characteristics
Q[m³/h-m2] Volume Flow Rate through the
wall per m2
Dp[Pa] Pressure difference across the wall
Sh: Heat Source [W/m²] in: Density of the incoming Air [kg/m³]
Q: Air Flow Rate through the Wall [m3/h-m2]
Cp,Air: Spec. Heat Capacity of Air [J/kg K]
Tin: Temperature; Incoming air [K]
T: Temperature in the Layer [K]
Sw: Moisture Source [kg/m²s]
csource: Water Vapor Concentration in the incoming Air;
[kg/m³]
c: Water Vapor Concentration in the air in Layer [kg/m³]
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• Characterize and identify major air leakage paths in walls
• Assess methods to seal significant sources of leakage
Top plates and sheathing joints
Bottom plate interface to studs, sheathing and foundation
x
x
Electrical outlets
Penetrations for conduits
Sub-Assembly Tests
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Joints/Openings
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Joints/Openings
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DOE/ORNL/Tremco’s ABAA
ASTM 2357 Cycling Pressures
Tim
Maddox
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Phase 3 (2012 – 2013): Critical Tests
Interior Spray-applied foam Mechanically fastened
Non-insulating board stock
Sealers w/ backup structure
Fluid-applied non-foaming
Self-adhered Insulating board stock
• Each of the 8 Air Barrier Systems will be tested at least
5 to 15 different attachments each !
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0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 5 10 15 20 25
Flo
w, cfm
/ft2
Pressure, Pa
Wood frames
Steel frames
CMUs
Example of
Component leakage
Zoom in this
region
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Wolf ,Salonvaara & Tyler; Owens Corning 2012
Residential Application
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Wolf ,Salonvaara & Tyler; Owens Corning 2012
Interior Air Sealing
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Ranking for Particular Air Barrier & Housing Project
Really nice to have blower door data
But what does ACH50 mean ?
We need the actual loading between
Housing Zones
At Minimum ATTIC-MAIN-BASEMENT
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Equations for sinks/sources… cont’d
• Remember the serial order of sources/sinks
– Insulated cavity gets air from exterior cavity or indoors (light weight wood frame wall, for example)
– Relate to three leakage classes (Envelope):
1 ACH50 3 ACH50 5 ACH50
0.2 L/s m2 0.6 L/s m2 1 L/s m2
Good Acceptable High
No air sealing
Band Joist
Top Plate to sheathing
Bottom Plate to Sheathing
Bottom Plate to Slab
Corners
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Example: One to Two sources
• Q = CDpn
• No diffuse seeping flow through materials
– Only sources and sinks • Exterior cavity (maybe,
depends on flow path def.)
• Insulated cavity
Source assigned to this layer.
No sources to ‘impermeable’ that
are bypassed by airflow.
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Wind washing - sources/sinks
• Add heat and moisture source to – Insulated cavity (air from outdoors)
– Flow mostly on the interior side of the insulated cavity (natural convection as a force)
– Air tightness to be defined for cavity
– Force for flow is stack (wind can be added with Cbottom, Ctop)
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Capture and understand
Double stud
Walls
With cellulose
insulation
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Work in Progress
Passive House Air Leakage Study Independent of Insulation Type
Passive House Technical Committee
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Air Leakage Paths
• Short Direct Paths
– By-pass insulated cavity
– Most of whole house BE leakage
– Effects: Thermal > Moisture • If any air moves into the insulated cavity, moisture effects are
multiplied
• Long Indirect Paths
– Flow through insulated cavity
– Less flow than through direct paths
– Effects: Moisture > Thermal
Direct
Indirect
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Air Leakage Rated at 75Pa
• Air barrier
– Materials 0.02 L/sm2 @75Pa
– Assemblies 0.2 L/sm2 @75Pa
– Systems 2.0 L/sm2 @75Pa
• Exponent n=?
– Needed for estimating the flow at building pressures
• These simulations used n=0.5 which gives the highest flow rates at low pressures (safety factor for design)
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Flow Characteristic: Exponent n
Q=C*dpn
n=
Worst Case used
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Assembly Leakage to Whole Building
• Assume
– 30ft x 40ft two story building
– Average ceiling height 8.5ft
– Walls and roofs leak the same 0.2 L/sm2@75Pa
– Flow characteristic n=0.65 or n=0.5 (Q=C*dpn)
L/sm2 @75 0.2 0.4 0.6
cfm/ft2 @75 0.04 0.08 0.16
n=0.65
cfm/ft2 @50 0.031 0.061 0.123
L/sm2 @50 0.154 0.307 0.461
ach50 0.32 0.64 0.95
n=0.50
cfm/ft2 @50 0.033 0.065 0.131
L/sm2 @50 0.163 0.327 0.490
ach50 0.34 0.68 1.01
For all the worldy units
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Airflow Paths
Vinyl
19 mm cavity
WRB
OSB
10 in Insulation
Gypsum
Paint 10 perms
North Orientation… mostly exfitration
Start Time 1 Oct. 2075
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Indoor Moisture Loads
• Loads were calculated assuming
– 9 L/d moisture production (20 lb/d) (SPC160, 2 bdr)
– 500 m3 house volume (17553 cf)
– ach=0.25 (leakage and occupancy effects)
• These result in moisture load of +3 g/m3 when no dehumidification by cooling system
Old and new
SPC160 moisture
loads.
Average house size
f(#bdr) considered.
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Atlanta - Indoors
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Baltimore - Indoors
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Boston - Indoors
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Houston - Indoors
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Minneapolis - Indoors
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Seattle - Indoors
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Mold Growth Estimates
• Predicted maximum Mold Growth Index after exposure to indoor/outdoor weather
– Layers included: WRB and everything inwards
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Results – Atlanta – Max Mold
• Flow rate (rating at 75Pa): 0, 0.2, 0.4, 0.6 L/sm2
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Results – Baltimore – Max Mold
• Flow rate (rating at 75Pa): 0, 0.2, 0.4, 0.6 L/sm2
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Results – Boston – Max Mold
• Flow rate (rating at 75Pa): 0, 0.2, 0.4, 0.6 L/sm2
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Results – Houston – Max Mold
• Flow rate (rating at 75Pa): 0, 0.2, 0.4, 0.6 L/sm2 Peak,
then:
More
air,
lower
Mold
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Results – Houston (-5Pa) – Max Mold
• Flow rate (rating at 75Pa): 0, 0.2, 0.4, 0.6 L/sm2
• Mechanical underpressure 5 Pa
– Note: No vapor retarder in Houston More air, higher Mold
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Results – Houston (-5Pa) – Max Mold
• Flow rate (rating at 75Pa): 0.6 L/sm2
• Mold growth mostly not at the flow path
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Results – Minneapolis – Max Mold
• Flow rate (rating at 75Pa): 0, 0.2, 0.4, 0.6 L/sm2
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Results – Seattle – Max Mold
• Flow rate (rating at 75Pa): 0, 0.2, 0.4, 0.6 L/sm2
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Results - RH
• Examples of airflow effect on relative humidity inside the wall
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Results – Minneapolis - RH
Full wall (left) and top only (right)
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Results - Minneapolis - RH
Full wall (left) and top only (right)
0.2 rated air leakage
through interior
surface
(interior air ‘flushing’
at rim joist)
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Results - Minneapolis - RH
Full wall (left) and top only (right)
0.4 rated air leakage
through interior
surface
(interior air ‘flushing’
at rim joist)
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Results - Minneapolis - RH
Full wall (left) and top only (right)
0.6 rated air leakage
through interior
surface
(interior air ‘flushing’
at rim joist)
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Results - Minneapolis
Stack neutral plane at the bottom of the wall below rim joist
Air leakage
comparison
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Total Moisture Minneapolis
Time starting
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Results – Minneapolis Movie
Minneapolis
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Results – Minneapolis Movie
Minneapolis
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Results – Minneapolis Movie
Minneapolis
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Energy Impact - Assumptions
• Airflow exfiltrates or infiltrates through the wall
• Heat loss due to air flow
– E=Qv*rho*cp*DT where • DT = Tin-Tout, if exfiltrating
• DT = Tin-Tair@surface, if infiltrating
– Tair@surface = air temperature at entrance to indoors at the wall surface
– Airflow affect the conduction heat loss by exchanging heat with the wall
• Yearly sum of conduction heat loss and air heat loss
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Atlanta
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Baltimore
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Boston
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Houston
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Minneapolis
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Seattle
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Air Heat Recovery
– Air flow through the wall gives a small heat recovery
• Compare total heat loss
1. Walls with air leakage
2. Airtight walls with the same air flow rate taken directly from outside
• No HRV
• With HRV (efficiency=?)
• The wall is a heat exchanger
• What air heat recovery efficiency does case (2) need in order to provide the same heat loss as case (1)?
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Filtrating Air Heat Recovery
• More airflow means more heat flow
– The question is whether the air flow is part of designed ventilation or uncontrolled (unwanted) air exchange
• Uncontrolled flow not wanted and causes extra heat loss
• If considered part of the house ventilation: Does the house have a HRV/ERV?
• Air that filtrates slowly through the insulating parts provides heat recovery benefits
• The higher the airflow rate per wall U-value, the lower the relative benefits (heat recovery)
• Air flow going through short cracks or openings provides low heat recovery effects
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Total Moisture in Walls
• All layers included
• Only difference is the air leakage rate
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Atlanta
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Baltimore
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Boston
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Houston
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Minneapolis
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Seattle
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Conclusions
• Moisture performance (mold)
– Standard walls (OSB exterior sheathing) have to be airtight at or below current assembly air tightness requirements (0.2 L/sm2 / 0.04 cfm/sqft @ 75Pa) to reduce risk for mold growth
• Energy performance
– At 0.2 L/sm2@75Pa rating the airflow through the walls increases the heat loss (combined conduction plus air) by roughly 25%
– Flow through insulated cavities can provide some heat recovery, however
• Flow path cannot be controlled, short circuiting will not provide heat recovery
Disclaimer: Results are not to be generalized and are valid only for the simulated structures
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Next Steps
• Study the impact of low air leakage rates on the moisture performance of alternative wall structures such as with exterior continuous insulation
– Risk reduction factors
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Conclusions
• A big step forward in our analysis capability for air flow. Never done before to this level.
• Component air leakage testing with STATISTICS (mean values and spread) would be very useful to create libraries were each air sealing system would be documented.
• New testing apparatus like Owens Corning, TREMCO, ORNL and BSC can provide hard core data to create series and parallel resistance models for airflow calculations in envelopes.
• Revisit the analysis with OC measured data.
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Final Thought
Just think about what
we can do !!!