Using Carbon Dioxide as a Tracer Gas to Measure Air Change Rate in a Single Zone

Transcription

1 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

2 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.

3 Boiler Room Ventilation Research Published Information on Boiler Room Air Change Rates ASHRAE, BOCA and NFPA reviewed for ventilation requirements in ACH Ventilation Models Using Tracer Gas Published Ventilation Models using Tracer Gas Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution ASTM E

4 Problem Existing methods allow for the use of a variety of tracer gases to be used. Each has advantages and disadvantages. Selected method highly portable easily measured non-toxic or very low toxicity inexpensive Tracer gas acceptable to school district personnel.

5 Research Standard Test Method for Determining Air Change in a Single Zone by Means of a Tracer Gas Dilution ASTM E Tracer gases (examples) CO 2 PEL 5000 ppm SF 6 PEL 1000 ppm CO PEL 50 ppm Selection of test method Concentration Decay Constant Injection Constant Concentration

6 Resolution Selection of tracer gas Carbon dioxide Relatively high PEL Inexpensive Easy to obtain and measure Acceptable to School personnel Selection of method Concentration Decay Test Method Measures the decay rate of carbon dioxide over time to calculate the air exchange rate. Regression Analysis InC(t) = -At + C(0)

7 Sample Time Air Change Rate (1/hr) Minimum Duration (hour) 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.

8 Boiler Room Ventilation Testing Using Tracer Gas Representative Boiler Rooms Elementary School - IN Elementary School - IL Middle School - IL

9 Gas Injection and Distribution

10 Direct Reading Equipment TSI Q-Trak Log Data

11 School Indiana 5500 ft 3 Boiler Room Volume of gas needed Calculated based on room size and target concentration of 4000 ppm V tracer = C target X V zone 2 boilers Input BTU/hr ,000 Input BTU/hr. 156,000 Both boilers operating during the testing No mechanical ventilation

12 Average CO2 Concentration vs Time Indiana Boiler Room - 2 Boilers Operating March 26, 2003 Carbon Dioxide Concentration in Parts Per Million (PPM) Trial 1 - Average CO2 Concentration (PPM) 5.2 Air Changes Per Hour Trial 2 - Average CO2 Concentration (PPM) 5.3 Air Changes Per Hour Time in Minutes Trial ACH Trial ACH Average 5.2 ACH

13 Elementary School Illinois Measured Volume 24,322 ft 3. 2 Boilers Ventilation tracer gas testing conducted with boilers on and off.

14 Elementary School Ventilation Rate - Boilers Off 1.8 Air Changes Per Hour March 27, 2003 Average CO2 Concentration vs Time March 27, Time in Minutes Carbon Dioxide Concentration (ppm) Carbon Dioxide Concentration (ppm) Time in Minutes Trial 2 - Average Carbon Dioxide Concentrations with 2 Boilers Operating Trial 3 - Average Carbon Dioxide Concentrations with 2 Boilers Operating Trial 1 Boilers On Boilers Off ACH Trial ACH Trial ACH Average 3.7 ACH

15 Middle School Illinois 16,372 ft 3 Boiler Room 2 Identical Boilers

16 Middle School Average Carbon Dioxide Concentration (ppm) vs Time Middle School March 21, Time in Minutes Carbon Dioxide Concentration (ppm) Carbon Dioxide Concentration (PPM) Average CO2 Concentration vs Time Boiler Room - 2 Boilers March 31, Time in Minutes Boilers On (1 boiler on part time): Trial 2 - Average CO2 Concentration 4.4 Air Changes Per Hour, GlenCrest School March 31, 2003 Boilers On: Trial 3 - Average CO2 Concentration 5.3 Air Changes Per Hour, GlenCrest School March 31, 2003 Boilers Off Boilers On 1.2 ACH Trial ACH Trial ACH Average 4.9 ACH

17 Measured Range of Boiler Room Ventilation Summary Boilers Off Range: 1.2 to 1.8 ACH Boilers On Range: 3.7 to 4.9 ACH

18 Isolation Test Chamber Approximately 20 x 20 x 9 (3600 ft 3 ) Wood Frame Polyethylene sheeting on walls and floors 2 viewing windows Entrance airlock Decontamination Shower (if needed) HEPA filtered exhaust machines for ventilation

19 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).

20 Installation and Measurement of Ventilation System 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.

21 Carbon Dioxide Concentration (ppm) vs Time B & Y Test Chamber 5.7 Air Changes Per Hour April 29, :28 16:30 16:32 16:34 16:36 16:38 16:40 16:42 16:44 16:46 16:48 16:50 Carbon Dioxide Concentration (ppm) Trial 1 - high Trial 1 - low Trial 2 - high Trial 2 - low Time Trial ACH Trial ACH Average 5.7 Trial ACH Trial ACH

22 Conclusions Ventilation rates for representative boiler rooms were between 1 and 5 ACH. Using carbon dioxide as a tracer gas and following ASTM E , 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.

23 Benefits Carbon 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.

24 C(t) Well Mixed Room Model - Constant Contaminant Emission Rate G + C Q Q + k V Q + k V IN L + L = 1 exp t C exp t Q + k V V 0 V L Input Variables C IN mg/m 3 Concentration in incoming air G mg/min Q m 3 /min Generation Rate Exhaust air flow V m 3 Volume of Room K L per min Loss Pathway (sinks) C 0 mg/m 3 Initial concentration

25 Predicted Concentration at 0.01, 0.1, 1, 3, 4, 5 and 10 Air Changes Per Hour 12 Effect of Ventilation Rate on Concentration of Contaminant ACH 0.1 ACH 1 ACH 3 ACH 4 ACH 5 ACH 10 ACH

26 Thank you! Questions? Speaker Contact Information: Catherine E. Simmons, CIH Boelter & Yates, Inc. Park Ridge, IL