High School Air Quality/Odor Investigation

November 2021

 

Due to reported noxious odors, Indoor Environmental Concepts (IEC) was engaged to perform an assessment of the air quality at a local high school, specifically evaluating office space serviced by a forced air heating, ventilation and air conditioning (HVAC) system. Initial inspection of the system and ceiling space by the HVAC service provider did not identify any unusual conditions.

 

IEC’s review of the HVAC system design, which services the area of concern, revealed the Air Handler Unit (AHU-2) is in the boiler room with the fresh air intake located in the west wall adjacent to an exterior courtyard. The gas fueled  boilers were ruled out  as the source of the odor by visual inspection and measurements from a photoionization detector for VOCs. 

 

Interviews with staff indicated odors had been experienced several times in the area and odors had been reported in the auditorium on various occasions. Further discussion with the facility personnel indicated continuous HVAC system operation based on normal occupancy on weekends and increased percentage of fresh air to mitigate the spread of COVID-19 by dilution ventilation.

 

From the roof, IEC inspected the boiler exhaust stack, immediately adjacent to the courtyard where the AHU fresh air intake is located.  The smoke stack housing is a brick structure which elevates approximately 5 feet above the roof membrane. Two (2) individual exhaust pipes protrude up above the brick structure approximately 3 feet. Both of the individual exhaust pipes are covered by “cone caps.” The two (2) roof-top AHUs that service the auditorium are approximately 25 feet to the northeast of the stack.

 

In accordance with the ASHRAE Standards, “the goal of stack design is to specify the minimum flow of the exhaust, exhaust velocity, and stack height that ensure acceptable air quality at all locations of concern.” In other words, the goal is to exhaust the contaminants at a height and velocity sufficient to allow atmospheric dilution ventilation which will not be re-entrained into the building via nearby fresh air intakes or cause detrimental effects to the community. Exhaust velocity of approximately 2600 feet per minute (fpm) prevents rain from entering the stack. Exhaust above 2000 fpm is the goal to provide sufficient plume rise and dilution. With these considerations, ASHRAE does not recommend installing cone caps or hinged covers over discharges since these can minimize exhaust velocity and dilution.