Using Carbon Dioxide as a Tracer Gas to Measure Air Change … · 2019. 5. 28. · Boelter & Yates,...

Boelter & Yates, Inc. 2004

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


Situation

Procedure was needed to determine the ventilation rate in air changes per hour (ACH) for representative boiler rooms and an isolation test chamber.

Ventilation information was needed to perform a retrospective exposure assessment.


ResearchBoiler Room Ventilation

Published Information on Boiler Room Air Change Rates

ASHRAE, BOCA and NFPA reviewed for ventilation requirements in ACH

Ventilation Models Using Tracer GasPublished Ventilation Models using Tracer GasStandard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution – ASTM E 741 – 00


ProblemExisting methods allow for the use of a variety of tracer gases to be used.

Each has advantages and disadvantages.

Selected method highly portableeasily measurednon-toxic or very low toxicityinexpensive

Tracer gas acceptable to school district personnel.


Research

Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution – ASTM E 741 – 00

Tracer gases (examples)CO2 – PEL 5000 ppmSF6 – PEL 1000 ppmCO – PEL 50 ppm

Selection of test methodConcentration Decay Constant InjectionConstant Concentration


Resolution

Selection of tracer gasCarbon dioxide

Relatively high PELInexpensiveEasy to obtain and measureAcceptable to School personnel

Selection of methodConcentration Decay Test MethodMeasures the decay rate of carbon dioxide over time to calculate the air exchange rate.Regression AnalysisInC(t) = -At + C(0)


Sample Time

20.5

.254.5211

40.25Minimum Duration (hour)Air Change Rate (1/hr)

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.


Boiler Room Ventilation Testing Using Tracer Gas

Representative Boiler RoomsElementary School - INElementary School - ILMiddle School - IL


Gas Injection and Distribution


Direct Reading Equipment

TSI Q-Trak

Log Data


SchoolIndiana

• 5500 ft3 Boiler Room• Volume of gas needed• Calculated based on room

size and target concentration of 4000 ppmVtracer = Ctarget X Vzone

• 2 boilers– Input BTU/hr. - 117,000– Input BTU/hr. – 156,000

• Both boilers operating during the testing

• No mechanical ventilation


Average CO2 Concentration vs Time Indiana Boiler Room - 2 Boilers Operating

March 26, 2003

0500

10001500200025003000350040004500

1 7 13 19 25 31 37 43 49 55 61 67 73Time in Minutes

Carb

on D

ioxi

de

Conc

entra

tion

in P

arts

Per

M

illio

n (P

PM)

Trial 1 - AverageCO2 Concentration(PPM) 5.2 AirChanges Per Hour

Trial 2 - AverageCO2 Concentration(PPM) 5.3 AirChanges Per Hour

Trial 1 – 5.2 ACH Trial 2 – 5.3 ACHAverage 5.2 ACH


Elementary SchoolIllinois

• Measured Volume –24,322 ft3.

• 2 Boilers • Ventilation tracer

gas testing conducted with boilers on and off.


Ventilation Rate - Boilers Off1.8 Air Changes Per Hour

March 27, 2003

0

1000

2000

3000

4000

0 18.75 37.5 56.25Time in Minutes

Carbon DioxideConcentration(ppm)

Trial 1

Boilers Off - 1.8 ACH

Average CO2 Concentration vs Time

March 27, 2003

010002000300040005000

02.

25 4.5

6.75 9

11.3

13.5

15.8 18

20.3

22.5

24.8 27

29.3

31.5

Time in Minutes

Car

bon

Dio

xide

C

once

ntra

tion

(ppm

) Trial 2 - Average CarbonDioxide Concentrationswith 2 Boilers OperatingTrial 3 - Average CarbonDioxide Concentrationswith 2 Boilers Operating

Boilers On

Trial 2 – 3.5 ACH

Trial 3 – 3.9 ACH

Average 3.7 ACH

Elementary SchoolElementary School


Middle SchoolIllinois

16,372 ft3

Boiler Room

2 Identical Boilers


Average Carbon Dioxide Concentration (ppm) vs Time

Middle SchoolMarch 21, 2003

0

1000

2000

3000

4000

5000

0 25 50 75

Time in Minutes

Carbon DioxideConcentration (ppm)

Boilers Off

1.2 ACH

Average CO2 Concentration vs Time Boiler Room - 2 Boilers

March 31, 2003

010002000300040005000

1 11 21 31 41 51 61 71 81 91Time in Minutes

Carb

on D

ioxi

de

Conc

entra

tion

(PPM

) Boilers On (1 boiler on parttime): Trial 2 - Average CO2Concentration 4.4 AirChanges Per Hour,GlenCrest School March 31,2003

Boilers On: Trial 3 - AverageCO2 Concentration 5.3 AirChanges Per Hour,GlenCrest School March 31,2003

Boilers On

Trial 2 - 4.4 ACH

Trial 3 - 5.3 ACH

Average – 4.9 ACH

Middle School


Measured Range of Boiler Room Ventilation

SummaryBoilers Off

Range: 1.2 to 1.8 ACH

Boilers On

Range: 3.7 to 4.9 ACH


Isolation Test Chamber

• Approximately 20’ x 20’ x 9’(3600 ft3)

• Wood Frame• Polyethylene sheeting on

walls and floors

• 2 viewing windows• Entrance airlock• Decontamination Shower (if

needed)• HEPA filtered exhaust

machines for ventilation


HEPA Filtered Exhaust Machinesfor Chamber Ventilation System

Note: Using various configurations, both machines operated as exhaust (tubing was attached to machines to exhaust outside the building).


Installation and Measurement of Ventilation System

Various configurations to achieve approximately 1, 3, 5 and 10 ACHCarbon 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.


Carbon Dioxide Concentration (ppm) vs Time B & Y Test Chamber

5.7 Air Changes Per Hour April 29, 2003

0

1000

2000

3000

4000

5000

6000

16:2

8

16:3

0

16:3

2

16:3

4

16:3

6

16:3

8

16:4

0

16:4

2

16:4

4

16:4

6

16:4

8

16:5

0

Time

Car

bon

Diox

ide

Conc

entra

tion

(ppm

)

Trial 1 - high

Trial 1 - low

Trial 2 - high

Trial 2 - low

Trial 1 – 5.8 ACH Trial 2 – 5.8 ACH

Trial 1 – 5.8 ACH Trial 2 – 5.5 ACH

Average 5.7


Conclusions

Ventilation rates for representative boiler rooms were between 1 and 5 ACH.

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.


BenefitsCarbon Dioxide as a tracer gas

Inexpensive, reliable procedure for IH’s to determine ventilation rates.

Measuring Equipment is readily available

The method provides an additional tool for industrial hygienists to better characterize workplace conditions during the initial stages of an exposure assessment.

Ventilation information is critical to the ability to perform and validate mathematical modeling for exposure estimation.


⎟⎟⎠

⎞⎜⎜⎝

⎛ ⋅+−+

⎥⎥⎦

⎤

⎢⎢⎣

⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛ ⋅+−−

⋅+

⋅+= t

V

Vk Q exp C t

V

Vk Q exp 1

Vk Q

QC G C(t) LL

L

IN0

Well Mixed Room Model Well Mixed Room Model -- Constant Constant Contaminant Emission RateContaminant Emission Rate

Initial concentrationC0 mg/m3

Loss Pathway (sinks)KL per minVolume of RoomV m3

Exhaust air flowQ m3/min

Generation RateG mg/min

Concentration in incoming airCIN mg/m3

Input Variables


Predicted Concentration at 0.01, 0.1, 1, 3, 4, 5 and 10 Air Changes Per Hour

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45

0.01ACH0.1ACH 1 ACH

3 ACH

4 ACH

5 ACH

10ACH

Effect of Ventilation Rate on Concentration of Contaminant


Thank you!

Questions?Speaker Contact Information:

Catherine E. Simmons, CIHBoelter & Yates, Inc.

Park Ridge, [email protected]

Using Carbon Dioxide as a Tracer Gas to Measure Air Change … · 2019. 5. 28. · Boelter & Yates,...

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