P. Francisco Duct Leakage Testing

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



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?



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?



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



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



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



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



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



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



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



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



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



Ramping Accuracy – follow-up project


• 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





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?


- 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




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


CONCLUSION

Blower Door Side



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


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


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




• 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



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



Comparison to Duct Blaster – follow-up project

Comparison to Pressure Pan – Wisconsin study

Comparison to Pressure Pan – follow-up study



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



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

P. Francisco Duct Leakage Testing

Documents

Transcript of P. Francisco Duct Leakage Testing