Indoor Air Quality - Tools for Schools Action Kit for Canadian Schools

Chapter 7: Air Handling Checklist (Continued)

Exhaust Systems

Exhaust systems are used to remove air that contains contaminants, including odours. Some HVAC designs also rely on the operation of exhaust fans to create negative pressure that draws outdoor air into the building through windows and gaps in the building envelope.

19. Confirm that exhaust fans are operating

Use chemical smoke to confirm that air is flowing into the exhaust grille(s).

20. Verify that local exhaust fans remove enough air to eliminate odours and chemical fumes

If the fan is intended to exhaust the entire room, stand outside the room with the door slightly open and use chemical smoke to confirm that air is being drawn into the room from locations both high and low in the door opening.

If the fan is running, but air isn't flowing toward the exhaust intake (or not enough air is moving to do the job), check for the following possibilities:

• the backdraft damper at the exhaust outlet does not open;
• obstructions in the ductwork;
• leaky or disconnected ductwork;
• broken fan belt;
• motor running backwards; or
• design problems (e.g., undersized fan).

21. If the exhaust fan is located close to the contaminant source, rather than on the roof, and exhaust air is ducted through the building under positive pressure

Confirm that the exhaust ductwork is sealed and in good condition. Make any repairs permanent and take any other measures that help ensure there will be adequate outdoor air in the future.

How to Measure Airflow - Reference Information

This section provides basic guidance and options for determining air movement and measuring outdoor air supply. It is divided into three sections:

• using chemical smoke to determine air flow direction;
• measuring airflow to determine outdoor air supply quantity; and
• estimating outdoor air quantity using carbon dioxide measurements.

Deciding which Equipment to Use for Measuring Airflow

Both flow hoods and pitot tubes can be used to measure airflow. Flow hoods are designed to measure flow at grilles and diffusers. Pitot tubes and anemometers are designed to measure air velocity in ducts, which is then used to calculate airflow. While flow hoods are more expensive to purchase, they are quicker and easier to use. Flow hoods can be used to measure airflow in ducts by adding the airflows from all vents connected to a given duct.

Often, the amount of duct leakage is significant. By comparing the total airflow at the fan to the sum of all vents connected to the fan, an estimate of the duct leakage can be determined. If the variation is large or the sum of the vents is greater than the fan capacity, further investigation should be undertaken.

22. Using Chemical Smoke to Determine Air Flow Direction

Chemical smoke can help with evaluation of HVAC systems, tracking air and pollutant movement, and identifying pressure differentials. Chemical smoke moves from areas of higher pressure to areas of lower pressure if there is an opening between them (e.g., door, utility penetration).

Because chemical smoke is the same temperature as the surrounding air, it is extremely sensitive to air currents. Investigators can learn about airflow patterns by observing the direction and speed of smoke movement. Smoke released near outdoor air intakes will indicate whether air is being drawn into the intake. Puffs of smoke released at the shell of the building (by doors, windows, or gaps) will indicate whether the HVAC systems are maintaining interior spaces under positive or negative pressure relative to the outdoors.

Chemical smoke is available with various dispensing mechanisms, including smoke "bottles," "guns," "pencils," or "tubes". The dispensers allow smoke to be released in controlled quantities and directed at specific locations. It is often more informative to release several small puffs of smoke as you move along an air pathway rather than a large amount in a single puff.

Caution: Read the equipment manufacturer's information. Chemical smoke devices may use titanium tetrachloride to produce smoke. Although the small amounts of chemicals produced during testing are normally not hazardous, you should avoid inhaling smoke from these devices. The concentrated fumes from smoke devices can be very corrosive.

Determining Air Movement from Diffusers and Grilles

Puffs of smoke released near HVAC vents give a general idea of airflow. (Is it in or out? Vigorous? Sluggish? No flow?) This is helpful in evaluating the supply and return system and determining whether ventilation air actually reaches the breathing zone. For a variable air volume system, be sure to take into account how the system is designed to modulate. The system could be on during the test, but off for most of the rest of the day. "Short-circuiting" occurs when air moves directly from supply diffusers to return grilles, instead of mixing with room air in the breathing zone. If a substantial amount of air short-circuits, school occupants may not receive adequate supplies of outdoor air and pollutant emissions may not be diluted sufficiently.

Chemical smoke can also be used to assess the performance of fume hoods and exhaust fans. If the smoke released at a certain point is not captured, neither will any other contaminant.

23. Measuring Outdoor Air Supply Quantity

This section describes methods for determining the amount of outdoor air supplied by a single ventilation unit, using either a flowhood or air velocity measurement device. These are general instructions for measuring airflow. You should also follow the instructions provided by the manufacturer of your measuring equipment.

Step 1. Determine Airflow Quantity

Using a flowhood
Flowhoods measure airflow in cubic feet per minute (CFM) or litres per second (Lps) at a diffuser or grille. To measure airflow, hold the flowhood up to the diffuser and read the airflow value. Follow the instructions supplied with the flowhood regarding its use, care, and calibration.

Using Velocity Measurements
For information on measuring air velocity using a pitot tube or anemometer, and calculating outdoor air supply, see the instructions supplied with the equipment.

Airflow in ductwork can be estimated by measuring air velocity at various positions in the duct cross-sections. The airflow instrument should have instructions for conducting this procedure (airflow traverse).

Measure the air velocity in the duct and calculate the airflow by multiplying the area-averaged velocity times the cross sectional area of the duct.

Systems with No Mechanically Supplied Outdoor Air
If the ventilation system does not use mechanically supplied outdoor air, the amount of outdoor air infiltrating the area can be estimated. Estimate air infiltration by measuring the quantity of air exhausted by exhaust fans serving the area.

Using a small floor plan, such as a fire escape map, mark the areas served by each exhaust fan.

Measure airflow at grilles or exhaust outlets using a flowhood. Determine the airflow in ductwork by conducting an airflow traverse.

Add the airflows from all exhaust fans serving the area to determine the total air exhaust.

24. Estimating Outdoor Air Using Carbon Dioxide Measurements

Carbon dioxide (CO₂) is a normal part of the atmosphere. Exhaled breath from building occupants and other sources increase indoor CO₂ levels above the levels found in outdoor air. CO₂ should be measured with a direct-reading meter. Use the meter according to manufacturer's instructions. Indoor CO₂ concentrations can, under some test conditions, be used to assess outdoor air ventilation. A comparison of peak CO₂ readings between rooms and between air handler zones may help to identify and diagnose various building ventilation deficiencies.

Estimating the quantity of outdoor air supply for mechanical systems

Take CO₂ readings, with minimal delays between readings, at supply outlets or air handlers to estimate the percentage of outdoor air in the supply airstream.

The percentage or quantity of outdoor air is calculated using CO₂ measurements as shown below:

Outdoor air (%) = (CR-CS) divided by (CR-CO) x 100

Where: CS = CO₂ parts per million (ppm) in the supply air (if measured in a room), or in the mixed air (if measured at an air handler)

CR = ppm of CO₂ in the return air

CO = ppm of CO₂ in the outdoor air (Typical range is 300-450 ppm.)

All these concentrations must be measured, not assumed.

To convert the outdoor air percentage to a volume of outdoor air in litres per second, use the following calculation:

Outdoor air (Lps) = Outdoor air (percent) / 100 x total airflow (Lps)

The number used for total airflow may be the air quantity supplied to a room or zone, the capacity of an air handler, or the total airflow of the HVAC system. However, the actual amount of airflow in an air handler is often different from the quantity stated in design documents. Only the measured airflow is accurate.

Interpreting Indoor CO₂ Concentration Measurements

Record the number of school occupants, time of day, position of windows and doors, and weather for each period of CO₂ testing.

• Take measurements to evaluate the adequacy of ventilation when CO₂ concentrations are expected to peak. It may be helpful to compare measurements taken at different times of day. Classroom CO₂ levels will typically rise during the morning, fall during the lunch period, then rise again, reaching a peak in mid-afternoon.
  
  
• Take several CO₂ measurements in the area under consideration. Collect CO₂ ventilation measurements away from any source that could directly influence the reading (e.g., hold the sampling device well away from exhaled breath, preferably at a point of well-mixed air within the room such as an exhaust fan inlet).
  
  
• Take several measurements outdoors.
  
  
• For systems with mechanically supplied outdoor air, take one or more readings at the following locations:
  
  
  • at the supply air vent;
  • in the mixed air (if measured at an air handler);
  • in the return air.

Note locations where CO₂ concentrations are 1,000 ppm or higher. Short-term conditions where CO₂ levels exceed 1000 ppm may indicate temporary ventilation problems caused by increased occupancy or ventilation system changes. Chronic conditions where CO₂ levels exceed 1000 ppm (for several hours on each of several days) may indicate the need for increased ventilation, or a modification in the space occupancy or use.

Note that there may still be under-ventilation problems in rooms with peak CO₂ concentrations below 1,000 ppm. CO₂ is produced by human respiration (breathing), and concentrations can change rapidly as people move in and out of a room. Four to six hours of continuous occupancy are often required for CO₂ to approach peak levels.

Problem Summary

All activities on this checklist have been completed and no help is required.

OR

A list of problems and/or assistance required is attached.

Air Handling Log - DRAFT

Instructions:

• Make one copy of this Log for each ventilation unit in the
  school
• Perform the activities in the Ventilation Checklist for each
  ventilation unit and use this Log to record results
• A "No" response requires further attention

Name
Room or Area
School
Date Completed
Signature

Activity

1. Outdoor air intake not obstructed
   • Needs Attention If "No" Yes/No
   • OK (Date)
2. Outdoor air intake clear of nearby pollutant sources
   • Needs Attention If "No" Yes/No
   • OK (Date)
3. Outdoor air moving into intake
4. Filters in good condition, properly installed, and no major air leaks
   • Needs Attention If "No" Yes/No
   • OK (Date)
5. Drain pan clean and no standing water
   • Needs Attention If "No" Yes/No
   • OK (Date)
6. Heating and cooling coil(s) clean
   • Needs Attention If "No" Yes/No
   • OK (Date)
7. Interior of air handling unit and ductwork clean
   • Needs Attention If "No" Yes/No
   • OK (Date)
8. Mechanical room free of trash and chemicals
   • Needs Attention If "No" Yes/No
   • OK (Date)
9. Controls information on hand
   • Needs Attention If "No" Yes/No
   • OK (Date)
10. Clocks, timers, and switches set properly
    • Needs Attention If "No" Yes/No
    • OK (Date)
11. Pneumatic controls okay
    • Needs Attention If "No" Yes/No
    • OK (Date)
12. Outdoor air damper operating properly
    • Needs Attention If "No" Yes/No
    • OK (Date)
13. Freeze-stat reset
    • Needs Attention If "No" Yes/No
    • OK (Date)
14. Mixed air thermostat set properly
    • Needs Attention If "No" Yes/No
    • OK (Date)
15. Economizer set per specifications
    • Needs Attention If "No" Yes/No
    • OK (Date)
16. Fans supplying outdoor air operate continuously during occupied periods
    • Needs Attention If "No" Yes/No
    • OK (Date)
17. Air distributions functioning per design
    • Needs Attention If "No" Yes/No
    • OK (Date)
18. Air flow direction (relative pressures) okay
    • Needs Attention If "No" Yes/No
    • OK (Date)
19. Exhaust fan(s) operating
    • Needs Attention If "No" Yes/No
    • OK (Date)
20. Local exhaust fan(s) remove enough air to eliminate odours and chemical fumes
    • Needs Attention If "No" Yes/No
    • OK (Date)
21. Exhaust ductwork sealed and in good condition
    • Needs Attention If "No" Yes/No
    • OK (Date)
22. Use of chemical smoke to determine air flow direction
    • Needs Attention If "No" Yes/No
    • OK (Date)
23. Outdoor air supply quantity measured
    • Needs Attention If "No" Yes/No
    • OK (Date)
24. Outdoor air using carbon dioxide measurements estimated
    • Needs Attention If "No" Yes/No
    • OK (Date)

Activity Number
Notes and Comments

Comments Form

Indoor Air Quality Tools for Schools Action Kit for Canadian Schools

We anticipate revising the Tools for Schools Action Kit in the future. To help us ensure that the Kit meets the needs of those who are using it, please send us your comments about how easy or difficult you found the Kit to use. Suggestions for how to make the Kit more useful are especially welcome. If a reply is requested, please provide your name, address and phone number along with the completed sheet and mail it to:

• Health Canada
  Healthy Environments and Consumer Safety Branch
  Indoor Environments Division
  Room 120, Environmental Health Centre (P.L. 0801D)
  Tunney's Pasture, Ottawa, Ontario K1A 0L2

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