Indoor Air Quality in Office Buildings: A Technical Guide

5. Detailed Assessment

5.3 Assessing the HVAC System

The HVAC system should be providing adequate amounts of out-door air based on occupancy rates and activities (ASHRAE Standards). The minimum ventilation rate should be maintained continuously during the occupancy period: the amount of outdoor air volume should never drop below 7.5 L/s per person, and offices should receive 10 L/s per person.

IAQ complaints can often be linked to insufficient ventilation. Ventilation systems can also introduce outdoor contaminants and trans-port pollutants within the building. Every component of the HVAC system is of interest, either as a source of contamination or as a compo-nent that fails to provide a necessary air handling or air conditioning function. The procedures described below constitute current good practice.

5.3.1 Collecting Background Information

• Talk to facilities staff. Find out about equipment operating and maintenance schedules. Maintenance that dislodges or generates pollutants should be performed outside the usual building occu-pancy periods. Discussions may reveal patterns that relate the timing of complaints to cycles of operation or to other events. A log of maintenance activities and system operations can be helpful.
• Review documentation on HVAC design, installation, and operation.
  Consider:
  
  
  • the design capacity, supply and exhaust air volume
  • the existing and planned use of each building area
  • the location of internal AHUs and supply and return diffusers serving the complaint area.
• Compare actual flow rates, distribution, and outdoor air rates with design values.

5.3.2 Inspecting the HVAC System

• Inspect outside air dampers, noting their position, the type of control mechanism, and its condition.
• Note the distance and direction of combustion sources, building exhausts, cooling towers, and other potential sources of pollutants in relation to the outside air intake.
• Examine the garage and loading dock for proper ventilation and pollution migration.
• Check supply air fans for operational problems, including defective belts, missing blades, build-up of particulates, and microbial growth.
• Check the interior of the mixing chambers for signs of failing insulation, debris, rust, or microbial growth.
• Ensure that air ducts and ceiling plenums are being maintained and cleaned to prevent dust from providing a substrate for mould growth.
• Verify the existence of a proper maintenance schedule for ceiling AHUs and perimeter fan coil units, induction units, and unit ventilators.
• Check that all combustion sources are being exhausted.
• Ensure that the efficiency rate of the filter bank is at least 30% (dust spot). In large office buildings, a primary filter - usually a panel or roll type - is used in conjunction with a higher efficiency (up to 85%, dust spot) bag filter. A maintenance schedule should be in place. Examine the system filters for proper fit. Verify that they are replaced often enough to prevent build-up of particulate matter. Filters should be replaced when the specified maximum pressure drop is reached.
• Check the system for microbial growth:
  
  
  • Note the presence of stagnant water. Condensate pans under cooling coils should have drain lines and sufficient pitch so that water drains completely.
  • Verify the existence of a maintenance program to prevent the build-up of microbial slime on HVAC system components that become wet. Contaminated surfaces should be disinfected while the building is vacant. Approved biocides should be used in water spray humidifiers as a decontamination procedure only if proper cleaning cannot be done.
  • Monitor the general bacterial population in humidifier reser-voirs and water towers by taking samples using test strips or slides (heterotrophic plate counts) and comparing the results with a colour chart to determine concentration.
    
    
    • Examine the humidifier for the presence of microbial growth, particulates, or chalky deposits and note any use of treatment chemicals. Water quality is best maintained by adding potable water to the reservoir so that the level of total dissolved solids does not exceed 2-3 times its normal concentration.
    • Central boiler steam should not be injected directly into the supply air by a steam humidifier because of the potentially harmful volatile chemicals used to treat the boiler supply water. A steam-to-steam converter or a separate steam generator should be used.