Upload
dinhlien
View
222
Download
0
Embed Size (px)
Citation preview
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
11
What is Tracer Gas Testing?
The marking of air with a gas
Monitoring for its presence and concentration
Evaluate ventilation parameters
44
Tracer Gas Technology
Ventilation Applications
Quantification of outside air
Air distribution system efficiency
55
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?
66
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
77
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?
88
ASTM E741 Test Method
Three different methods: Concentration Decay
Constant Injection
Constant Concentration
Determines air change rate
99
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.
1010
Concentration Decay Method
Inject predetermined volume of gas into room
Mix room air to get uniform concentration
Monitor gas concentration decay
1111
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
1212
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
1313
\ \ \ \
SUPPLY FANRETURN FAN
SPILL INTAKE
LOBBY
Sample
Injection
\ \ \ \ \ \
2
3
Whole Building vs. Single Room
1414
Advantages
Doesn’t require any airflow measurementsNeed volume
Can do whole building/single room
1515
Distribution System Efficiency?
How well is outside supply airdistributed to breathing zones inoccupied areas?
1616
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
1717
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?
1818
How Do You Test for Good Mixing?
ASHRAE Standard 129 – Measuring Air Change Effectiveness
Uses Tracer Gas Techniques
Age-of-Air Measurements
1919
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.
2020
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
2121
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)
2222
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
2323
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
2424
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
2727
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
3131
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
3333
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
3434
Poor Man’s Way?
Collect sample in bags or syringes.
Send to laboratory for analysis.
Pros and Cons?