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8/2/2019 P. Francisco Duct Leakage Testing
http://slidepdf.com/reader/full/p-francisco-duct-leakage-testing 1/21
Duct Leakage TestingPaul W. Francisco, University of Illinois
Why Test?
• Many duct locations are unpleasant
• Many duct systems do not leak very much
• Those that do can cost a lot of energy
• 10% supply leak corresponds to about 15-20% energy
penalty
8/2/2019 P. Francisco Duct Leakage Testing
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What is the question?
• Are the ducts tight enough for certification (e.g. HERS,
Energy Star)?
• Should air sealing be done by a program (e.g. utility,
weatherization)?
• Where are the leaks?
• Has enough sealing been done?
• How much did we save?
8/2/2019 P. Francisco Duct Leakage Testing
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Very Important…
How often does the test give the
correct feedback?
Duct Leakage Diagnostics
• Pressure Pans
• Duct Blaster
• Delta-Q
Duct Leakage Diagnostics
•What test should be used?
• When should that test be used?
• Why should that test be used?
8/2/2019 P. Francisco Duct Leakage Testing
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Test Comparison
AccessRegisters
Automation Leakage tooutside
TotalLeakage
Leakage atOperating
Conditions
Pressure
Pan √ √
Duct Blaster √ √ √
Delta-Q √ √ √
Nulling Test for Comparison
• Use a Duct Blaster as envelope fan to “null out” change in
envelope pressure caused by unbalanced duct leakage
• First with normal operation – unbalanced leakage
• Second with return isolated and a Duct Blaster assisting the
AH fan so there is no return leakage – supply leakage
• Difference is return leakage
• Measures leakage directly – thought to be accurate
• Very sensitive to wind
Nulling Test
-500
-400
-300
-200
-100
0
10:41:30 10:42:00 10:42:30 10:43:00 10:43:30 10:44:00 10:44:30 10:45:00 10:45:30 10:46:00 10:46:30 10:47:00 10:47:30 10:48:00 10:48:30 10:49:00 10:49:30
PoutBD Ps upplen Pnull
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Nulling Test
- 1
- . 5
0
. 5
1
0 20 40 60 80(mean) meanqenv
95% CI Fitted values
Site 4 Unbalanced
Pressure Pan Test
• Essentially a zone pressure diagnostic for the ducts
• Depressurize house with blower door
• Cover registers, one at a time, with pressure pan andmeasure pressure
• Elevated readings indicate holes in the ducts that areconnected to outdoors
Pressure Pan Test
• Simple to do
• Need to access all registers
• Identifies specific duct runs that have problems
• Robust/Repeatable
8/2/2019 P. Francisco Duct Leakage Testing
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Pressure Pan Test
• Proximity of holes to register impacts reading – closer means higher
• Implication – LOW pressure leaks give HIGHER pressure
pan readings
• Does not indicate actual flow leakage
• Rewards most for leaks that matter least
Pressure Pan Test Example #1
• 8 registers: 2 3 4 3 4 2 3 2
• Two possibilities:
• Modest leaks at boots
• Larger leak at plenum
• Boot leaks are not worth sealing, plenum leak is!
Pressure Pan Test Example #2
• 8 registers: 2 3 4 18 4 2 3 2
• Register 4 has a major leak
• May also be responsible for magnitude of other readings
8/2/2019 P. Francisco Duct Leakage Testing
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Pressure Pan Test – other considerations
• Many can’t be covered by a pressure pan – use anythingthat can fully cover the register/grille, e.g.
• Duct mask tape
• Sweatshirt
• Pillow
Pressure Pan Test – other considerations
• Some ducts lead to registers through each side of a wall
• Seal one off
• Pressure pan the other one
• Failure to seal one off is like leaving half of the register
uncovered
Duct Blaster Test
• Leakage to Outside?
• Seal all registers
• Pressurize house with blower door
• Pressurize ducts with Duct Blaster
until duct-to-house pressure is zero
• Duct Blaster flow is leakage number
8/2/2019 P. Francisco Duct Leakage Testing
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Duct Blaster Test
• More difficult to do than pressure pan• Sealing registers can be time-consuming
• Registers may be inaccessible
• For energy concerns, supply is moreimportant
• To assess supply and return separately,need to isolate the two sides and testthem individually
Duct Blaster Test
• Also does not indicate actual leakage
• Is actually a measure of airtightness
• Counts holes equally regardless of location
• Robust/Repeatable*
* If leakage to inside is low – see next slide
Effect of Interior Leakage and Imprecise House-Duct Pressure Balance
Source: Pigg and Francisco 2008
0
5 0
1 0 0
1 5 0
2 0 0
S u p p l y C F M @ 2
5 E r r o r R e l a t i v e t o
E x a c t M a t c h i n g
0 500 1000 1500Total Supply Leakage, CFM @ 25
0.2 Pa mismatch
0.5 Pa mismatch
1.0 Pa mismatch
8/2/2019 P. Francisco Duct Leakage Testing
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Duct Blaster Test
• Total leakage?
• Don’t need blower door
• Includes leakage to inside – not focused on energy
concerns
• If low total leakage, then certainly low leakage to outside
Delta-Q Test
• Preferably automated
• Do 4 multi-point blower door tests
• Depressurization, air handler off
• Depressurization, air handler on
• Pressurization, air handler off
• Pressurization, air handler on
• Use software to calculate leakage estimates from flow
differences
Delta-Q Test
• Estimates actual leakage
• Requires only a blower door (and a computer)
• Do not need to access registers
• Leakage to outside only
8/2/2019 P. Francisco Duct Leakage Testing
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Delta-Q – “When Last We Met”
• Completed field study performed in conjunction withMidwest weatherization agencies
• Looked at:
• Ramping sampling protocol
• Analysis methods – non-negative least squares (NNLS) and
“scanning”
• Bin size for data processing
• Possibility of using one ring instead of two
Delta-Q – “When Last We Met”
• Conclusions
• NNLS and scanning gave similar results, NNLS ok
• NNLS since dropped for variety of reasons
• Bin size of 5 Pa good, 1 Pa too small
• Possibility of using one ring instead of two was promising,
but not conclusive and needed protocol for choosing ring
• Wind was a significant problem
• How to best minimize impacts
Since then…
• Study on new Wisconsin homes completed (funding Focus
on Energy)
• 19 homes, most for Energy Star or EPACT
• User repeatability experiment conducted (C. Olson)
• 7 homes by volunteers
• Follow-up study in Illinois (funding DOE and ODOD)
• 14 homes with ducts outside conditioned space
8/2/2019 P. Francisco Duct Leakage Testing
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Follow-up Project (concluded March 2009)
• Various options for testing
• Ramping vs. stations
• Two rings vs. one ring
• Feasibility / protocol
• Location of outdoor pressure hose
• To reduce wind noise
• How to put a number on uncertainty?
Field Study
• 14 homes
• Chosen to have ducts outside conditioned space
• Average 1816 ft2 (range 1144 – 3332)
• Average 10.6 ACH50 (range 6.7 – 15.6)
Tests Performed
• At least 5 repeats of each of ramping and stations
• Also 1-3 one-ring, two-ramp tests per home• “Control” tests done when time permitted
• Duct Blaster and pressure pans
• Nulling
8/2/2019 P. Francisco Duct Leakage Testing
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Ramping vs. Stations
Ramping vs. Stations
• Collect data in 5 Pa bins
• Difference between AH on and
AH off
• Software calculates leakage
estimates from best fit –
“scanning”
Delta-Q Accuracy – Wisconsin project
8/2/2019 P. Francisco Duct Leakage Testing
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Ramping Accuracy – follow-up project
Ramping vs. Stations
• Stations provided estimates slightly higher than ramping on
average, about 10 cfm on both supply and return
• Stations takes longer under windy conditions
• Stations more sensitive to sampling rate
- 5 0
0
5 0
1 0 0
1 5 0
D i f f e r e n c e b e t w e e n F u l l a n d R e d u c e d S a m p l i n g , c f m
Ramping, Supply
Ramping Return
Stations, Supply
Stations, Return
Ramping vs. Stations
8/2/2019 P. Francisco Duct Leakage Testing
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Ramping vs. Stations
CONCLUSION
Prefer Ramping
Outdoor Pressure Location
• Three options considered
• Leeward side (expected best)
• 4-side manifold
• Blower door side (sometimes
same as leeward)
• Question: Do you get enough
benefit by running additional
hoses?
Outdoor Pressure Location
- 2 0 0
0
2 0 0
4 0 0
6 0 0
R a m p i n g - S u p p l y E s t i m a t e s , c f m
0 100 200 300 400Nulling Test Supply Leakage, cfm
one-one l ine Leeward
Manifold Blower Door
8/2/2019 P. Francisco Duct Leakage Testing
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Outdoor Pressure Location
0
2 0
4 0
6 0
8 0
1 0
0
S t d . D e v . o f S u p p l y L e a k a g e E s t i m a t e s , c f m
LeewardManifold
Blower Door
Outdoor Pressure Location - Leeward
- 4 0 0 0
- 2 0 0 0
0
2 0 0 0
4 0 0 0
B l o w e r D o o r F l o w , c f m
-50 0 50Leeward Pressure, Pa
AH off
AH on
Outdoor Pressure Location
CONCLUSION
Blower Door Side
8/2/2019 P. Francisco Duct Leakage Testing
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One-Ring vs. Two-Ring
• If one ring was used, choose smallest ring that gets to 30Pa
• One ring tests with only one ramp extracted from normal
test data
• One ring tests with two ramps done as additional tests –
usually only one per house
One-Ring vs. Two-Ring
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0
1 0 0
2 0 0
3 0 0
4 0 0
5 0 0
A v e r a g e O n e - R i n g S u p p l y E s t i m a t e , c f m
0 100 200 300 400 500Average Two-Ring Supply Estimate, cfm
One-Ring vs. Two-Ring
0
2 0
4 0
6 0
8 0
S t a n d a r d D e v i a t i o n o f L e a k a g e E s t i m
a t e , c f m
S up pl y, t wo ri ng s R et ur n, tw o ri ngs
Supply, one ring Return, one ring
8/2/2019 P. Francisco Duct Leakage Testing
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One-Ring vs. Two-Ring
• No statistical difference between one-ring and two-ring testaverages
• Primary benefit of two-ring tests is additional data from two
ramps
• When conditions warrant can do two ramps for a single ring
One Ring vs. Two Rings
CONCLUSION
Can Use One RingUse Smallest Ring that gets to 30 Pa
Use Two Ramps unless calm winds
Uncertainty Estimation for Delta-Q
• Would allow user to determine whether leakage estimate
could be relied upon
• Use variability among repeated tests compared to
individual Delta-Q test data standard error to obtain
multiplier (to standard error) that covers 95% of estimates
• Wisconsin, user repeatability experiment, and Illinois
studies all suggested multiplier between 2 and 3
• Suggest use about 2.5
8/2/2019 P. Francisco Duct Leakage Testing
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Delta-Q Final Recommendations
• Ramping protocol
• Outdoor reference on blower door side of house
• One ring
• Smallest that can reach 30 Pa
• Two ramps unless calm conditions
• Use uncertainty estimate to be built into software
Comparisons to Other Tests
• Duct Blaster test at 25 Pa
• Pressure Pan
• Mean value for Wisconsin
• Mean and median values for Illinois
Comparison to Duct Blaster – Wisconsin project
8/2/2019 P. Francisco Duct Leakage Testing
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Comparison to Duct Blaster – follow-up project
Comparison to Pressure Pan – Wisconsin study
Comparison to Pressure Pan – follow-up study
8/2/2019 P. Francisco Duct Leakage Testing
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Comparison to Other Tests – Conclusions
• All tests show very low leakage or very high leakage
• Duct Blaster
• Tends to overestimate – leakage pressures lower than 25 Pa
• Pressure Pan
• Median tracks leakage reasonably well with regard to
indicating appropriateness of air sealing
Comparison to Other Tests – Conclusions
• Duct Blaster
• Most appropriate for new construction when ducts should be
tight in the first place
• Best done at rough-in when ducts are still easily accessible
• Pressure Pan
• Use median to indicate value of air sealing (suggest 4 Pa)
• Individual readings can highlight specific defects
Conclusions
• No one test appropriate for all conditions
•Use each as needed
• Delta-Q can be useful for weatherization
• Low or high leakage estimates often conclusive, simple test
• Pay attention to uncertainty!
• Pressure pan can also be useful
• Median for overall leakage assessment
• Individual readings to highlight major problems
8/2/2019 P. Francisco Duct Leakage Testing
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Test Usage
• Can be used as screening tools for each other
• Do pressure pan, if sealing needed can do Delta-Q to get
leakage estimate for program-wide savings estimate
• Do Delta-Q (gets blower door CFM50 also), if indicates
possible need for sealing do pressure pan to target leakage
location