Tracer Gas Test Methods to

Diagnose Ventilation-Related Indoor Environmental Quality Problems

Prepared byRex W. Moore, CIH, CSP

Boelter & Yates, Inc.Presented by

Catherine E. Simmons, CIHPark Ridge, Illinois

847-685-9285rmoore@boelter-yates.com

11

What is Tracer Gas Testing?

The marking of air with a gas

Monitoring for its presence and concentration

Evaluate ventilation parameters

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A Good Tracer Gas?

Non-toxic

Colorless and odorless

Inert

33

Common Tracer Gases Used

Carbon Dioxide

Nitrous Oxide

Freon

Helium

Sulfur Hexafluoride

44

Tracer Gas Technology

Ventilation Applications

Quantification of outside air

Air distribution system efficiency

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Importance of Outside Air Inside a Building

Too little outside air?Odors-sense of stuffiness

Eye irritation, headaches

Too much outside air?Excess energy costs

HVAC overload?

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How Much Outside Air?

Occupancy Category cfm/person* cfm*/ft2

Office space 5 0.06Classroom 10 0.12Dining room 7.5 0.18Shipping/Receiving --- 0.12Health Club 20 0.06

*Quantities at breathing zone -ASHRAE Guidelines 2004

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Volumetric Air Measurements

ASTM Designation: E741-00Standard Test Method for Determining Air

Change in a Single Zone by Means of a Tracer Gas Dilution

Measure Outside Air?

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ASTM E741 Test Method

Three different methods: Concentration Decay

Constant Injection

Constant Concentration

Determines air change rate

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Air Change Rate?

VOLUME of AIR10 m3

ENCLOSED SPACE (10 m3)

AIR VOLUME10 m3

ONE AIR CHANGE PER HOUR = 1 m3/hour of outside air

1 HOUR

Air Change Rate = The number of room or building volumes per hour that are being displaced with outside air.

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Concentration Decay Method

Inject predetermined volume of gas into room

Mix room air to get uniform concentration

Monitor gas concentration decay

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Concentration Decay Method

Air Change Rate, A =ln CT2 - ln CT1

∆T (in hours)

ln = log normalCT1 = Tracer Gas Concentration at start of test

CT2 = Tracer Gas Concentration at end of test

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Concentration Decay Method

0.002.004.006.008.00

10.0012.00

1 4 7 10 13 16 19 22 25 28 31 34 37 40

Time after test start (minutes)

SF6 C

once

ntra

tion

(ppm

)

A = 5.43

A = 2.66

A = 1.32

A = 0.51

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\ \ \ \

SUPPLY FANRETURN FAN

SPILL INTAKE

LOBBY

Sample

Injection

\ \ \ \ \ \

2

3

Whole Building vs. Single Room

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Advantages

Doesn’t require any airflow measurementsNeed volume

Can do whole building/single room

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Distribution System Efficiency?

How well is outside supply airdistributed to breathing zones inoccupied areas?

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Why Worry About Good Mixing?

Poor MixingOccupant complaints

ASHRAE Standard, Ventilation for Acceptable Indoor Air Quality

Based on amounts of outside air getting to breathing zone not to supply air louvers

System balancing done at louvers

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Short – circuiting airflow patterns

Where a significant portion of supply air flows directly to the exhaust, bypassing the occupied portion (breathing zone) of the ventilated space.

Why Worry About Good Mixing?

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How Do You Test for Good Mixing?

ASHRAE Standard 129 – Measuring Air Change Effectiveness

Uses Tracer Gas Techniques

Age-of-Air Measurements

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Air Exchange Effectiveness?

The definition of air-change effectiveness is based on a comparision of the age of air in the occupied portions of the building to the age of air that would exist under conditions of perfect mixing of the ventilation air.

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Age of Air??The age of the air at a give location is the average amount of time that has elapsed since the air molecules at that location entered the building.

Amount of time outside air has been in an area

Two Methods of determinationStep-up constant tracer gas injectionTracer gas concentration decay

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How is This Testing Done?

Air in the room is marked with tracer gas

Ventilation turned on

Age of Air Measurements Locations of interest-A & B

In the exhaust (C)

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How Do You Measure Age of Air?

Age of air at a location = Average tracer gas level during testTracer gas level at beginning of test

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Age of Air Relates toAir Exchange Effectiveness?

E = < 1.0 (less than perfect mixing)E = 1 (perfect mixing)

Air change effectiveness (E)

E = avg age of air – Exhaustavg age of air – bz

bz = breathing zone

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Significance of Results?

ASHRAE Standard 62.1-2004 Ventilation for Acceptable Indoor Air Quality

Outside air requirements = QA/EAs E decreases, OA should increase

US Green Building Council LEED Rating requires an E > 0.9

In all ventilated zones

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Sampling Instrumentation Measuring

Sulfur HexafluorideAnd Carbon Dioxide

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How to Collect Samples?

Sampling Pump and Tedlar® Bag

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INNOVA Multi-Gas Monitor

Weight (~18 lbs)

Quasi direct-reading instrument

Works on photo acoustic principle

2-3 ppb limit of detection

~ $36,000 purchase cost

~ $2,800 rental fee – California Analytical

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2929

3030

TSI Q-Trac

To detect

Carbon Dioxide

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Foxboro Miran Sapphire

Weight (~18 lbs)

Quasi direct-reading instrument

Works on infrared principle (good down to ~ 50 ppb)

~ $12,000 purchase cost

~ $1,200 rental fee

3232

FTIR

Weight (~50-100 lbs)

Reportedly good down to 50 ppt

~$ 50,000+ purchase cost

~$ 5,000 rental fee

Often needs liquid nitrogen as coolant

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Gas Chromatography with Electron Capture

Varying weights

~ $30,000 - $50,000 Purchase Fee

Rental price????

Reportedly down to 50 ppt

Sample collection normally with syringes

Laboratory type device-Not easily transported

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Poor Man’s Way?

Collect sample in bags or syringes.

Send to laboratory for analysis.

Pros and Cons?

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Thank You

Questions?