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AIR LEAKAGE: DIFFICULTIES IN

MEASUREMENT, QUANTIFICATION AND

ENERGY SIMULATION

BEST2 Conference, Portland, OR

Session WB6-1

13 April 2010

Michael Waite, P.E., LEED AP

Simpson Gumpertz & Heger Inc.

Co-Author: Sean O’Brien, P.E., LEED AP

Outline

• Air Barrier Definitions

• Performance Criteria

• Testing

• Energy Analysis

2

Outline



• Testing

• Energy Analysis

3

Air Barriers

• Material: A single component of the building

enclosure with a specific air resistance

– Examples: Self-adhering membranes, spray-applied foam

insulation, gypsum wallboard, sheet metal

4

Air Barrier Materials

5

Air Barriers

• Material: A single component of the building

enclosure with a specific air resistance

– Examples: Self-adhering membranes, spray-applied foam

insulation, gypsum wallboard, sheet metal

• Assembly: A collection of air barrier materials or

transitions between air barrier materials

– Examples: Roof-to-wall transitions, wall assemblies (sometimes

including fenestration, penetrations, etc.)

• System or (“Continuous Air Barrier”): Integrated air

barrier materials, assemblies and seals continuous

across the entire building enclosure

6

Outline



• Testing

• Energy Analysis

7

Performance Criteria

• Historically few quantitative requirements for air

leakage/barriers in the U.S.

• U.S. building codes have contained qualitative

language, with some exceptions

– “seal joints”, “weather-stripping”, etc.

– ASHRAE 90.1

– IECC

• Where progress has been made, mostly limited to

“air barrier materials”

8

Performance Criteria – Materials

• 0.004 cfm/sf at 75 Pa pressure differential

• National Building Code of Canada

• Massachusetts State Building Code

• Air Barrier Association of America (ABAA)

• Proposed addendum to ASHRAE 90.1

9

Performance Criteria – Assemblies

• Air Barrier Association of America (ABAA)

– 0.04 cfm/sf at 75 Pa

– Also in proposed addendum to ASHRAE 90.1

• National Building Code of Canada

– Recommended performance for buildings with typical interior

relative humidity levels


• Fenestration

– Ranges from 0.06 cfm/sf (curtain-wall/storefront) to 0.3 cfm/sf

(operable and other types) at 75 Pa – AAMA

10

Performance Criteria – Whole Envelope

• Most representative of actual continuous air barrier

performance

• Until recently, common references did not reflect

actual performance

11


• ASHRAE Handbook–Fundamentals

– Several contradictory values included

– “Tight”: 0.1 cfm/sf at 75 Pa

– “Average”: 0.3 cfm/sf at 75 Pa

– “Leaky”: 0.6 cfm/sf at 75 Pa

– Based on an “arbitrary” classification in 1976 study of 8 glazed

aluminum curtain wall buildings (Tamura and Shaw 1976)

• More recent studies have shown higher leakage rates


– Average of 200 buildings (Emmerich and Persily 2005)

– Also now included in ASHRAE Fundamentals (2009)

12


• ASHRAE Handbook–Fundamentals

– Several contradictory values included

– “Tight”: 0.1 cfm/sf at 75 Pa

– “Average”: 0.3 cfm/sf at 75 Pa

– “Leaky”: 0.6 cfm/sf at 75 Pa

– Based on an “arbitrary” classification in 1976 study of 8 glazed

aluminum curtain wall buildings (Tamura and Shaw 1976)

• More recent studies have shown higher leakage rates


– Average of 200 buildings (Emmerich and Persily 2005)

– Also now included in ASHRAE Fundamentals (2009)

13

Performance Criteria – Continuous Air Barrier

• Air Barrier Association of America

– 0.4 cfm/sf under a pressure differential of 0.3 in. water (75 Pa)

• Some individual stricter criteria

– U.S. Army Corps of Engineers: 0.25 cfm/sf at 75 Pa

– Individual project specifications

• 2006 United Kingdom Building Regulations

– Requires whole building test for buildings over 500 m2

– 0.547 cfm/sf at 50 Pa (equivalent to ~0.7 cfm/sf at 75 Pa)

14

Outline



• Testing

– Quantitative

– Qualitative

• Energy Analysis

15

Quantitative Testing - Materials

• ASTM E2178 - Standard Test Method for Air

Permeance of Building Materials

• Laboratory test for material properties only

– Air leakage measured at various static pressures

Quantitative Testing - Materials

Quantitative Testing – Components

• ASTM E283 - Standard Test Method for Determining

Rate of Air Leakage Through Exterior Windows,

Curtain Walls, and Doors Under Specified Pressure

Differences Across the Specimen

• Laboratory test for component performance

– Air leakage measured at a single specified test pressure

– ASTM E783: Field equivalent

Field Testing – ASTM E783


Differential

pressure

Temp / RH

Laminar flow

element (airflow

measurement)

Fan/blower

not shown

Quantitative Testing – Assemblies

• ASTM E2357 - Standard Test Method for Determining

Air Leakage of Air Barrier Assemblies

• Laboratory test for air barrier assembly performance

(can be applied to field conditions as well)

– Initial air leakage measured at various static pressures

– Specimen is “conditioned” by exposure to dynamic pressure

loads, then re-tested

Quantitative Testing – Assemblies

Field Testing of Air Barrier Assemblies

• Field testing of free-standing mockups is similar to

laboratory test procedure

• Field testing of in-place assemblies can be extremely

difficult

Quantification Difficulties

• Testing a 5 ft x 5 ft area to 0.04 cfm/sf requires

measurement of just 1 cfm

Assembly Test – Interior Chamber

Interior chamber

Air barrier

Leakage through

surrounding walls

may bypass air

barrier

“Seal” on exterior

for measurement of

chamber leakage

Quantification Difficulties

• Testing a 5 ft x 5 ft area to 0.04 cfm/sf requires

measurement of just 1 cfm

• Uncontrolled air leakage through CMU walls could

easily exceed 1 cfm, creating a “false negative” test

result

Assembly Test – Exterior Chamber

Exterior chamber

Air barrier

“Seal” on exterior

for measurement of

chamber leakage

Extraneous leakage path is

now on interior side of air

barrier

Chamber Construction

Difficult Details

Quantitative Testing – Air Barrier Systems

ASTM E779: Standard Test Method for

Determining Air Leakage Rate by Fan

Pressurization

Quantitative Testing - Systems

• “Blower Door” testing

– Quantifies air leakage on a whole-building scale

– Results normalized to building surface area

• Typically use air barrier surface area

• No established definition for “building surface area”

• Most recent studies use “above grade surface area of the building

envelope”

– ASTM E779 designed for simple detached buildings

Performing an E779 Test

• Create a single “zone” in the building by opening

doors, partitions, etc.

• Close off ductwork, air intakes, vents, etc. that do

not typically contribute to air leakage into the

conditioned space

• Take airflow and corresponding pressure

measurements during pressurization and

depressurization of the building

Air Leakage Testing of Large Buildings

Air Leakage Testing in Multi-Unit Buildings

Outline



• Testing

– Quantitative

– Qualitative

• Energy Analysis

36

Qualitative Testing

• Location of air leakage sites in a building enclosure

– Certification of qualitative performance (“no visible air

leakage…”)

– Identify leakage paths to remediate during construction

– Failure analysis / forensics

Qualitative Testing

• ASTM E1186 - Standard Practices for Air Leakage

Site Detection in Building Envelopes and Air Barrier

Systems

• Basic methodology

– Impose differential pressure on component/building

– Use visualization aids to locate air leakage

• Tracer smoke

• Infrared

• Detection liquid (i.e., soapy water)

Blower Door Pressurization

• Option 1: Use a blower door (or HVAC system) to

pressurize/depressurize an entire room

– Useful for testing multiple

windows, doors, etc. in a

single space

– May not be practical for large

spaces with high leakage

rates (limited test pressures)

– Requires enclosed spaces; may

not be practical during

construction

Test Chambers

• Option 2: Use localized chambers for testing of

specific areas / components

– Can be performed during

construction or in partially

enclosed spaces

– Can typically test at high pressure

(75 pa / 0.3 in. H20 +)

– May be less efficient than

blower door for testing

multiple areas/components

Handheld Test Device

41

• Calibrated device generates

pre-set pressure differential

– Highly localized, useful for

fasteners and masonry ties but

not large components

Lab Testing of Fasteners with Handheld Device

Detection Methods - Liquid

Detection Methods - Liquid

• Liquid must be applied directly to the point of

leakage

• Can be messy

• Difficult on vertical surfaces

Detection Methods – Tracer Smoke

Detection Methods – Tracer Smoke

• Paths can be difficult to distinguish under low or

variable pressure conditions

• Smoke can be difficult to see / document

• More effective with negative pressure

• Difficult to perform in windy conditions

• Smoke may be acrid

Detection Methods - Infrared

Detection Methods - Infrared

• Can be extremely efficient

– Locate multiple air leaks in short time

– Minimize the need for sample openings / investigation

• Requires temperature differential

– Ideally 30º to 40ºF

• Results may be subject to interpretation

– Secondary verification (smoke, etc.) should be used

• May not locate small or concealed leaks

– Fully surveying a building can take a long time

Outline



• Testing

• Energy Analysis

55

Energy Analysis

• EnergyPlus building energy simulations of DOE’s

“Medium Office” Benchmark Building

56

Energy Analysis – Envelope Parameters

57

Location SHGCRoof

InsulationWall

Insulation

Miami 0.25 R-15 R-13

Las Vegas 0.25 R-15 R-13

Chicago 0.39 R-15 R-13 + R-3.8 c.i.

Baseline Parameters

Location SHGCRoof

Insulation1Wall

Insulation2

Miami 0.20 R-20 R-13 + R-3.8 c.i.

Las Vegas 0.20 R-20 R-13 + R-3.8 c.i.

Chicago 0.34 R-20 R-13 + R-7.6 c.i.

Adjusted Parameters

Energy Analysis – Air Leakage Parameters

• 1.55 cfm/sf at 75 Pa

– Average from recent study


– Representative of UK code requirement


– Well-detailed and constructed tight building

• Air leakage varied with exterior wind speed

58

Results – Miami

Air Leakage

(cfm/sf)SHGC

Roof

InsulationWall Insulation

Total (Source)

MMBtu % Reduction

1.55 0.25 R-15 R-13 6778 N/A

1.55 0.20 R-15 R-13 6698 1.2%

1.55 0.25 R-20 R-13 6764 0.2%

1.55 0.25 R-15 R-13 + R-3.8c.i. 6736 0.6%

0.70 0.25 R-15 R-13 6714 0.9%

0.15 0.25 R-15 R-13 6669 1.6%

59

• Energy use effect of significant air leakage reduction

is comparable to reduced solar heat gain coefficient

• Additional insulation has lesser effect on energy use

Results – Las Vegas

Air Leakage

(cfm/sf)SHGC

Roof


Total (Source)

MMBtu % Reduction

1.55 0.25 R-15 R-13 7104 N/A

1.55 0.20 R-15 R-13 7074 0.4%

1.55 0.25 R-20 R-13 7084 0.3%

1.55 0.25 R-15 R-13 + R-3.8c.i. 7034 1.0%

0.70 0.25 R-15 R-13 6896 2.9%

0.15 0.25 R-15 R-13 6746 5.0%

60

• Large potential savings in “balanced” climate

• Heating savings significant in all but the warmest

U.S. climates

Results – Chicago

Air Leakage

(cfm/sf)SHGC

Roof


Total (Source)

MMBtu % Reduction

1.55 0.39 R-15 R-13 + R-3.8c.i. 7454 N/A

1.55 0.34 R-15 R-13 + R-3.8c.i. 7424 0.4%

1.55 0.39 R-20 R-13 + R-3.8c.i. 7428 0.4%

1.55 0.39 R-15 R-13 + R-7.6c.i. 7396 0.8%

0.70 0.39 R-15 R-13 + R-3.8c.i. 7060 5.3%

0.15 0.39 R-15 R-13 + R-3.8c.i. 6751 9.4%

61

• Energy savings very significant in cold climate

• Expect savings to increase further moving north

Results – Peak Heating

62

CityAir Leakage

(cfm/sf)

Peak Heating (Site)

MBtu/h % Reduction

Miami 1.55 293.5 --

Miami 0.15 218.5 25.6%

Las Vegas 1.55 505.4 --

Las Vegas 0.15 407.9 19.3%

Chicago 1.55 814.6 --

Chicago 0.15 502.0 38.4%

Recap/Conclusion

• Establish quantitative criteria.

• Select correct test protocols to evaluate compliance

for specific scenario/construction

• Use qualitative testing to identify deficient areas and

remediate those areas, if possible

• Inaccurate air leakage values can have significant

impact on predicted energy use

– Less significant in cooling climates than in heating climates

– Energy simulations likely underpredict energy use due to

widespread use of low assumed air leakage values

• Peak heating demand very dependent on air leakage63

Questions?

Michael Waite, P.E., LEED AP

Simpson Gumpertz & Heger Inc.

[email protected]

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