Using Carbon Dioxide as a Tracer
Gas to Measure Air Change Rate in a
Single Zone
C. Simmons, F. Boelter, G. Crawford, Boelter & Yates,
Inc., Park Ridge, IL
Presented by:
Catherine E. Simmons, CIH
Boelter & Yates, Inc. 2004
Situation
Ventilation information was needed to
perform a retrospective exposure
assessment.
Procedure was needed to determine the
ventilation rate in air changes per hour
(ACH) for representative boiler rooms and
an isolation test chamber.
Boelter & Yates, Inc. 2004
Research
Boiler Room Ventilation
z Published Information on Boiler Room Air
Change Rates
z ASHRAE, BOCA and NFPA reviewed for
ventilation requirements in ACH
Ventilation Models Using Tracer Gas
z Published Ventilation Models using Tracer Gas
z Standard Test Method for Determining Air
Change in a Single Zone by Means of a Tracer
Gas Dilution – ASTM E 741 – 00
Boelter & Yates, Inc. 2004
Problem
z
Existing methods allow for the use of a variety of tracer
gases to be used.
z
Each has advantages and disadvantages.
z
Selected method
z
z
z
z
z
highly portable
easily measured
non-toxic or very low toxicity
inexpensive
Tracer gas acceptable to school district personnel.
Boelter & Yates, Inc. 2004
Research
z
Standard Test Method for Determining Air Change in a
Single Zone by Means of a Tracer Gas Dilution – ASTM E
741 – 00
z Tracer gases (examples)
z
z
z
z
CO2 – PEL 5000 ppm
SF6 – PEL 1000 ppm
CO – PEL 50 ppm
Selection of test method
z
z
z
Concentration Decay
Constant Injection
Constant Concentration
Boelter & Yates, Inc. 2004
Resolution
z
z
Selection of tracer gas
z Carbon dioxide
ƒ Relatively high PEL
ƒ Inexpensive
ƒ Easy to obtain and measure
ƒ Acceptable to School personnel
Selection of method
z Concentration Decay Test Method
z Measures the decay rate of carbon dioxide over
time to calculate the air exchange rate.
z Regression Analysis
InC(t) = -At + C(0)
ƒ
Boelter & Yates, Inc. 2004
Sample Time
Air Change Rate (1/hr)
Minimum Duration (hour)
0.25
4
0.5
2
1
1
2
.5
4
.25
Minimum sample duration based on 10% uncertainty at the 95%
confidence level in the detection of air change rate, a tracer gas
concentration measurement precision error of 5% of reading and
various air change rate. Using the regression method reduces the
minimum test duration due to more than 2 data points.
Boelter & Yates, Inc. 2004
Boiler Room Ventilation
Testing Using Tracer Gas
z
Representative Boiler Rooms
z Elementary School - IN
z Elementary School - IL
z Middle School - IL
Boelter & Yates, Inc. 2004
Gas Injection and Distribution
Boelter & Yates, Inc. 2004
Direct Reading Equipment
TSI Q-Trak
Log Data
Boelter & Yates, Inc. 2004
School
Indiana
• 5500 ft3 Boiler Room
• Volume of gas needed
• Calculated based on room
size and target
concentration of 4000 ppm
Vtracer = Ctarget X Vzone
• 2 boilers
– Input BTU/hr. - 117,000
– Input BTU/hr. – 156,000
• Both boilers operating
during the testing
• No mechanical ventilation
Boelter & Yates, Inc. 2004
Carbon Dioxide
Concentration in Parts Per
Million (PPM)
Average CO2 Concentration vs Time
Indiana Boiler Room - 2 Boilers Operating
March 26, 2003
4500
4000
3500
3000
2500
2000
1500
1000
500
0
Trial 1 - Average
CO2 Concentration
(PPM) 5.2 Air
Changes Per Hour
Trial 2 - Average
CO2 Concentration
(PPM) 5.3 Air
Changes Per Hour
1 7 13 19 25 31 37 43 49 55 61 67 73
Time in Minutes
Trial 1 – 5.2 ACH
Trial 2 – 5.3 ACH
Average 5.2 ACH
Boelter & Yates, Inc. 2004
Elementary School
Illinois
• Measured Volume –
24,322 ft3.
• 2 Boilers
• Ventilation tracer
gas testing
conducted with
boilers on and off.
Boelter & Yates, Inc. 2004
Elementary School
Average CO2 Concentration vs Time
Ventilation Rate - Boilers Off
1.8 Air Changes Per Hour
March 27, 2003
3000
Carbon Dioxide
Concentration
(ppm)
2000
1000
0
0
18.75
37.5
56.25
5000
4000
3000
2000
1000
0
Trial 2 - Average Carbon
Dioxide Concentrations
with 2 Boilers Operating
0
2 .2 5
4 .5
6 .7 5
9
1 1 .3
1 3 .5
1 5 .8
18
2 0 .3
2 2 .5
2 4 .8
27
2 9 .3
3 1 .5
4000
C a rb o n D io x id e
C o n c e n tra tio n
(p p m )
March 27, 2003
Trial 3 - Average Carbon
Dioxide Concentrations
with 2 Boilers Operating
Time in Minutes
Time in Minutes
Trial 1
Boilers On
Boilers Off - 1.8 ACH
Trial 2 – 3.5 ACH
Trial 3 – 3.9 ACH
Average 3.7 ACH
Boelter & Yates, Inc. 2004
Middle School
Illinois
z
16,372 ft3
Boiler
Room
z
2 Identical
Boilers
Boelter & Yates, Inc. 2004
Middle School
Average CO2 Concentration vs Time
Boiler Room - 2 Boilers
March 31, 2003
Average Carbon Dioxide Concentration (ppm) vs
Time
Middle School
March 21, 2003
4000
Carbon Dioxide
Concentration (ppm)
3000
2000
1000
Carbon Dioxide
Concentration (PPM)
5000
5000
Boilers On (1 boiler on part
time): Trial 2 - Average CO2
Concentration 4.4 Air
Changes Per Hour,
GlenCrest School March 31,
2003
4000
3000
2000
1000
0
0
0
25
50
75
1 11 21 31 41 51 61 71 81 91
Time in Minutes
Boilers On: Trial 3 - Average
CO2 Concentration 5.3 Air
Changes Per Hour,
GlenCrest School March 31,
2003
Time in Minutes
Boilers Off
Boilers On
1.2 ACH
Trial 2 - 4.4 ACH
Trial 3 - 5.3 ACH
Average – 4.9 ACH
Boelter & Yates, Inc. 2004
Measured Range of Boiler Room
Ventilation
z
Summary
z
Boilers Off
Range: 1.2 to 1.8 ACH
z
Boilers On
Range: 3.7 to 4.9 ACH
Boelter & Yates, Inc. 2004
Isolation Test Chamber
•
•
•
• 2 viewing windows
Approximately 20’ x 20’ x 9’
(3600 ft3)
• Entrance airlock
• Decontamination Shower (if
Wood Frame
needed)
Polyethylene sheeting on
• HEPA filtered exhaust
walls and floors
Boelter & Yates, Inc. 2004
machines for ventilation
HEPA Filtered Exhaust Machines
for Chamber Ventilation System
Note: Using various configurations, both machines operated
as exhaust (tubing was attached to machines to exhaust
outside the building). Boelter & Yates, Inc. 2004
Installation and Measurement of
Ventilation System
z
z
z
z
Various configurations to achieve
approximately 1, 3, 5 and 10 ACH
Carbon dioxide tracer gas used to
measure ventilation rate.
Each rate tested twice to assure
repeatability.
Final ventilation rates were: 1.2, 2.9, 5.7,
10.7 ACH.
Boelter & Yates, Inc. 2004
6000
5000
4000
Trial 1 - high
3000
Trial 1 - low
2000
Trial 2 - high
1000
Trial 2 - low
16:50
16:48
16:46
16:44
16:42
16:40
16:38
16:36
16:34
16:32
16:30
0
16:28
Carbon Dioxide
Concentration (ppm)
Carbon Dioxide Concentration (ppm) vs Time
B & Y Test Chamber
5.7 Air Changes Per Hour
April 29, 2003
Time
Trial 1 – 5.8 ACH
Trial 2 – 5.8 ACH
Trial 1 – 5.8 ACH
Trial 2 – 5.5 ACH
Boelter & Yates, Inc. 2004
Average 5.7
Conclusions
z
Ventilation rates for representative boiler
rooms were between 1 and 5 ACH.
z
Using carbon dioxide as a tracer gas and
following ASTM E 741 – 00, Standard Test
Method for Determining Air Change in a
Single Zone by Means of a Tracer Gas
Dilution met the objectives and goals of the
project.
Boelter & Yates, Inc. 2004
Benefits
z
Carbon Dioxide as a tracer gas
z
Inexpensive, reliable procedure for IH’s to determine
ventilation rates.
z
Measuring Equipment is readily available
z
The method provides an additional tool for
industrial hygienists to better characterize
workplace conditions during the initial stages of
an exposure assessment.
z
Ventilation information is critical to the ability to
perform and validate mathematical modeling for
exposure estimation.
Boelter & Yates, Inc. 2004
Well Mixed Room Model - Constant
Contaminant Emission Rate
G + C ⋅Q ⎡
Q + k ⋅ V ⎞⎤
Q+ k ⋅V ⎞
⎛
⎛
IN
L
L
⎢1 − exp ⎜ −
C(t) =
t ⎟⎥ + C 0 exp ⎜ −
t⎟
⎜
⎟⎥
⎜
⎟
Q + k ⋅V ⎢
V
V
⎝
⎠⎦
⎝
⎠
⎣
L
Input Variables
CIN
mg/m3
Concentration in incoming air
G
mg/min
Generation Rate
Q
m3/min
Exhaust air flow
V
m3
Volume of Room
KL
per min
Loss Pathway (sinks)
C0
mg/m3
Initial concentration
Boelter & Yates, Inc. 2004
Effect of Ventilation Rate on
Concentration of Contaminant
Predicted Concentration at 0.01, 0.1, 1, 3, 4, 5 and 10
Air Changes Per Hour
0.7
0.6
0.5
0.01
ACH
0.1
ACH
1 ACH
0.4
3 ACH
0.3
4 ACH
0.2
5 ACH
0.1
Boelter & Yates, Inc. 2004
45
42
39
36
33
30
27
24
21
18
15
12
9
6
3
0
0
10
ACH
Thank you!
Questions?
Speaker Contact Information:
Catherine E. Simmons, CIH
Boelter & Yates, Inc.
Park Ridge, IL
[email protected]
Boelter & Yates, Inc. 2004