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

Chapter 7: Air Handling Checklist

Introduction

The IAQ Action Kit is a practical tool to help school boards and school employees understand and address indoor air quality (IAQ) problems. The kit provides clear and easily applied information that can be used to improve the indoor environment of schools, help prevent indoor air quality problems, and resolve problems promptly if they do arise.

This checklist provides instructions to help school maintenance staff, facilities staff, and contract service providers identify and prevent potential IAQ problems resulting from inadequate school ventilation.

The tasks identified in this checklist should only be performed by or with the assistance of a trained professional in that field. In performing tasks in this checklist, applicable federal, provincial, territorial and municipal regulations and guidelines should be respected including local fire regulations, building codes and occupational health and safety codes.

Overview

Supplying an adequate amount of outdoor air to an occupied area (ventilation) is necessary for good indoor air quality. Schools use a variety of methods for ventilating the building with outdoor air: 1) mechanically based systems such as unit ventilators; central heating, ventilation, and air conditioning (HVAC) systems; and central exhaust systems, and 2) passive systems that rely on operable windows, air leaks, wind, and the stack effect (the tendency of warm air to rise).

Not all school buildings can supply and distribute the same quantity of outdoor air as a modern, mechanically vented building. This does not mean that the school cannot meet acceptable IAQ standards. All buildings require an integrated plan to manage IAQ, with ventilation being only one component.

The Air Handling Checklist is designed to ensure that the school ventilation is suitable for the school's current requirements.

Most of the checklist activities apply mainly to mechanical ventilation systems, and are designed to accomplish several functions:

• Ensure that the ventilation system is clean.
• Ensure that an adequate amount of outdoor air is reliably supplied to occupied areas.
• Ensure that the system design, operation and maintenance are appropriate for its current use.

Many of the following activities should be performed by individuals with appropriate training in mechanical systems and safety procedures. Most activities can be performed with basic maintenance tools. If any problems or deficiencies are identified, a ventilation system specialist should be consulted.

Measuring airflow can only be done correctly with reliable equipment. A visual inspection or test for air movement can indicate basic airflow, but cannot determine how much air is actually moving.

Activities 17-21 can be applied to passive ventilation systems. For those activities that do not apply, write "NA" in the date column of the Air Handling Log.

A school may have multiple ventilation units and systems. Perform the following activities and complete the Air Handling Log for each unit. The activities are listed in a specific order to avoid needing to repeat any activities as the inspection of a unit progresses. The following process is recommended in order to save time when performing the activities:

Activities 1-3

Perform these activities for all outdoor air intakes while outside the building, and mark the results on the Air Handling Log for each unit.

Activities 4-12

Perform these activities as a set on each ventilation unit while in the room and the unit is open.

Activities 13-16

Perform these ventilation control system activities as required in specific situations.

Activities 17-21

Perform these air distribution and exhaust system activities as required in specific situations.

Activities 22-24

Perform these airflow measurement activities on all units when airflow measurement equipment is available.

Outdoor Air Intakes

If outdoor air intakes are deliberately blocked, become clogged with dirt or debris, or are contaminated, they are unlikely to supply sufficient outdoor air.

	On a small floor plan (e.g., a fire escape floor plan), mark the locations of outdoor air intakes, based on mechanical plans (if available) and observations made while performing these activities.
	Obtain chemical smoke (or a small piece of tissue paper or light plastic) before performing Activity 3. For more information on chemical smoke, see "How to Measure Air Flow", at the end of this checklist.
	Ensure that the ventilation system is on and operating in the "occupied" mode.

1. Ensure that the outdoor air intakes are unobstructed
   
   

   	From outside the school building, check the intakes for obstructions, such as debris, clogged screens, damage, or makeshift covers (e.g., boards or plastic).
   	Remove any obstructions.
   	Install corrective devices if snowdrifts or leaves often block an intake.

   
    
2. Ensure that outdoor air intakes are clear of nearby pollutant sources
   
   

   Check the intakes from outside the school building to confirm that pollutant sources are not located near outdoor air intakes.

   • At ground level, look for dumpsters, loading docks, parking lots, and areas where buses idle.
   • At roof level, look for plumbing vents, exhaust outlets (such as kitchen, toilet, or laboratory exhaust fans), puddles on the roof, and mist from air-conditioning cooling towers.
     
     

   	Ensure that birds and other pests do not roost or inhabit the areas around the air intakes.
   	Resolve problems due to pollutants near intakes:

   • Remove sources, where possible (e.g., move a dumpster to another location).
   • Separate the source from the intake (e.g., add another pipe section to raise a nearby exhaust outlet above the intake).
   • Change operating procedures (e.g., turn off vehicles instead of idling them at loading docks and bus stands).
     
     

   Designated outdoor smoking areas should not be near an intake.

   
   
3. Confirm that outdoor air is entering the system intake (visual indication)
   
   

   	Use chemical smoke (or a small piece of tissue paper or light plastic) to test whether air is flowing into the intake grille.
   	Confirm the operation and positions of intake dampers during all operating cycles.

System Cleanliness

Accumulated dirt can prevent the ventilation system from operating properly, causing under-ventilation, uncomfortable temperatures, a reduction in operating efficiency (higher utility bills), more maintenance, and shorter equipment life spans.

Air filters are intended primarily to prevent dirt and dust from accumulating in the HVAC system. If filters are not properly selected and maintained, built-up dirt in coils and ducts can encourage the growth of microorganisms. Filters that are clogged with dirt restrict the flow of air through the HVAC system. If filters "blow out" or do not fit properly, they can allow the passage of unfiltered air. Dirt can accumulate on coils, creating a need for more frequent cleaning and reducing the efficiency of the heating and/or cooling plant. It is much less expensive to trap dirt with properly maintained filters than to remove it from ductwork, coils, fan blades, and other HVAC system components or the building interior.

4. Inspect air filters on ventilation equipment
   
   

   	Review ventilation system filter components and specifications to ensure that the proper filters are being used.
   	Install new filters as needed. Shut off ventilation system fans when replacing filters so that dirt will not blow downstream. Vacuum the filter area before installing the new filter.
   	Confirm that filters fit properly in their tracks, with no air leaks around the air filter.
   	Confirm that filters are installed in the proper direction for airflow.

   
   
5. Ensure that condensate (condensed water, frost, or "fog") drain pans are clean and drain properly
   
   

   	Drain pans should slant toward the drain so they do not collect and hold water.
   	Check for traps and drains within the plenums and ducts. Ensure that they are flushed and filled with clean water on a regular basis.

   
   
6. Ensure that heating and cooling coils are clean
   
   
7. Ensure that air handling units (air mixing chambers, coils, and fan blades) and duct interiors are clean
   
   

   	Visually inspect the interior and exterior of all system components.
   	Note that crawlspaces, tunnels, and other areas may be used as ducts, or may be in contact with the ventilation airstream. Understand the system layout and inspect all areas.
   	Properly decommission and remove any unused system components.

   
   
8. Ensure that mechanical rooms are free of trash and chemicals
   
   

   	Check mechanical rooms for unsanitary conditions, leaks, or spills.
   	Confirm that mechanical rooms and air mixing chambers are not used to store trash or chemical products and supplies.

System Controls

Various controls are used to adjust ventilation systems to ensure that they provide acceptable and reliable performance. The main objectives of outdoor air controls are:

• to ensure that air dampers are always at least partially open (minimum position) during occupied hours; and
• to ensure that the minimum position provides an adequate amount of outdoor air for the occupants.

These activities apply to most ventilation systems.

Activities 9-11 generally serve multiple ventilation units, while activities 12-16 are related to and performed at each individual ventilation unit. Based on the equipment and your experience, perform as many of the activities, and make as many indicated repairs, as possible. Discuss the need for additional help to complete any activities or repairs with the maintenance supervisor.

9. Gather controls information
   
   Ventilation controls may be unique. Since there are many different types and brands of control components, you should:
    

   	Gather and read any controls specifications, as-built mechanical drawings, and controls operations manuals (check with the maintenance supervisor).
   	Contact the system installer or HVAC maintenance contractor to obtain controls information that is missing.

   
   
10. Check clocks, timers, and seasonal switches
    
    

    	Confirm that summer-winter switches are in the right position.
    	Confirm that time clocks read the correct time.
    	Confirm that time clock settings fit the actual schedule of building use (night/weekend set-back and set-up).

    
    
11. Check pneumatic control system components
    
    

    	Test the line pressure at both the occupied (day) setting and the unoccupied (night) setting to determine whether the overall system pressure is appropriate.
    	Confirm that the line dryer is preventing moisture buildup.
    	Check the control system filters. The filter at the compressor inlet should be changed periodically in keeping with the compressor manufacturer's recommendation (for example, when you blow down the tank).
    	Ensure that the line pressure at each thermostat and damper actuator is at the proper level (no leakage or obstructions).
    	Repair or replace defective components.

    
    
12. Check outdoor air damper operation
    
    Before continuing, the air temperature in the indoor area(s) served by an outdoor air damper must be within the normal operating range. Ensure that the outdoor air damper is visible for your inspection.
    
    

    	Turn off the air handler connected to the outdoor air damper and confirm that the damper fully closes within a few minutes.
    	Turn on the air handler and confirm that the outdoor air damper opens (at least partially) with little or no delay.
    	Set the room thermostat to a temperature at least 5°C above and then below the current room temperature. Observe the damper for movement (damper should go to its design set-point position).

    • Confirm that the damper actuator is linked to the damper shaft and that any linkage set screws and bolts are tight.
    • Confirm that rust or corrosion is not preventing free movement.
    • Confirm that either electrical wires or pneumatic tubing is connected to the damper actuator.
       

    	Reset thermostat(s) to appropriate temperature(s).
    	Proceed to Activities 13-16 if the damper seems to operate properly.

    Note: The minimum damper setting may need to be adjusted, using a nut or a knob, to create a larger damper opening.
     
13. Confirm freeze-stat condition
    
    HVAC systems with water coils need protection from freezing. The freeze stat may close the outdoor air damper and disconnect the supply air when tripped. (The typical trip range is 2 to 5°C).
     

    	If the freeze-stat has a manual reset button (usually red), depress the button. If a click is heard, the freeze-stat was probably tripped. Consider replacing manual reset freeze-stats with automatic reset freeze-stats.
    	If the freeze-stat has an automatic reset, disconnect power to the controls and test for continuity across the terminals.

    
    
14. Check mixed air thermostat
    
    

    	The mixed air stat for heating mode should be set no higher than 18°C (typically 13 to 18°C).
    	The mixed air stat for cooling mode should be set no lower than the room thermostat setting.

    
    
15. Check air economizer setting
    
    Economizers use varying amounts of cool outdoor air to assist with the cooling load of a room or rooms. The airflow will vary but should not be less than the minimum ventilation rate.
    
    There are two types of economizers, dry-bulb and enthalpy. Dry-bulb economizers vary the amount of outdoor air based on the outdoor air temperatures, and enthalpy economizers vary the amount of outdoor air based on the outdoor air temperature and humidity level.
     

    	Confirm proper settings based on design specifications or local practices (dry-bulb setting is typically 18°C or lower).
    	Check the sensor to make sure that it is shielded from direct sunlight.

    
    
16. Confirm that fans operate continuously during occupied periods
    
    Any fan that helps move air from outdoors to indoors must operate continuously during occupied hours, even though the room thermostat is satisfied.
     

    	If the fan shuts off when the thermostat is satisfied, change the control cycle to prevent under-ventilation.
    	Note any complaints of drafts or cold temperatures. Some equipment such as a gas-fired furnace has a limited capability for controlling the supply air temperature. As the outdoor air temperature decreases, the amount of supply temperature variation with the burners on or off increases.

Air Distribution

Even if enough outdoor air is brought into a building, IAQ problems can develop if the outdoor air is not properly distributed. In such cases, under-ventilation occurs in particular areas of the building rather than being widespread. Problems with air distribution are most likely to occur in areas where:

• ventilation equipment is malfunctioning;
• room layouts have been altered without adjusting the HVAC system; and
• the population of a room or zone has grown without adjustment to the HVAC system.

Air pressure differences move air contaminants from outdoors to indoors and transport them within buildings. In schools with mechanical ventilation equipment, fans are the dominant influence on pressure differences and airflow. In schools that lack mechanical ventilation equipment, natural forces (wind and stack effect) primarily influence airflow.

To prevent infiltration of outdoor air and soil gas (e.g., radon), mechanically ventilated buildings are often designed to maintain a higher air pressure indoors than outdoors. This is known as positive pressurization. (See "Exhaust Systems" and "How to Measure Airflow" for a description of building pressurization.) At the same time, exhaust fans control indoor contaminants by keeping rooms such as smoking lounges, bathrooms, kitchens, and laboratories under negative pressure compared to surrounding rooms. "Negative pressure" and "positive pressure" describe pressure relationships. A room can operate under negative pressure compared to neighbouring rooms, but at the same time it may be positive compared to outdoors.

17. Check air distribution
    
    Verify that the air pathways in the original ventilation system design continue to function.
     

    	Check to see whether operable windows have been replaced by windows that cannot be opened.
    	Check to see whether passive gravity relief ventilation systems and transfer grilles between rooms and corridors are functioning. If they are closed off or blocked to meet modern fire codes, consult with a professional engineer for remedies.
    Caution: Consult with your local fire department for more information on fire regulations and prevention.
    	Verify that every occupied space has a supply of outdoor air (mechanical system or operable windows). If the building relies on passive ventilation, ensure that the occupants are aware of the need for ventilation and how ventilation can be provided.
    	Confirm that supplies and returns are open and unblocked. If outlets have been blocked intentionally to correct drafts or discomfort, investigate and correct the cause of the discomfort and re-open the vents.
    	In areas with no source of outside air, modify the HVAC system to correct the problem.
    	Check for barriers, such as room dividers, large freestanding blackboards or displays, or bookshelves that could block the movement of air in the room, especially obstacles that block air vents.

    
    
18. Check air flow direction - building pressure
    
    Conduct this activity after ensuring the following conditions:
    
    
    • Confirm that the system, including any exhaust fans, is operating on the occupied cycle.
    • Confirm that outdoor conditions are calm (wind less than 10 km/hour), since wind forces can cause large pressure differences within buildings.
       

    	Use chemical smoke to determine whether air flows out of the building through leaks in nearby windows, doors, or other cracks and holes in exterior walls (pressurized interior).
    	Use chemical smoke to determine whether air flows out of the building through below-grade cracks and holes such as floor joints or pipe openings (pressurized interior).