From Indoor Air Quality
“HVAC” refers to the system that supplies heating or air conditioning to the occupied spaces of the building—whether office, factory, warehouse, or residence (HVAC stands for Heating, Ventilating, Air Conditioning).
I want to focus on HVAC systems in commercial buildings. No matter what type of air filtration is used in the system, it is not perfect. Some smaller particulates will get through the filter. Also, did you know that very few HVAC systems filter the recirculated air? This is important because doors and windows can bring in dust which predictably bypasses the filters. Also, internal activities where paper dust, or packaging, or some production activity generate and add more dust to the air.
Maybe the occupied spaces are cleaned regularly but not the ductwork which is an inseparable part of the air inside the building!
Remember seeing the black soot on the ceiling’s diffusers that supply air to the office. Even more of that dust is inside the ductwork. Most building’s HVAC’s ductwork and fan systems are 1.) never cleaned, 2.) only cleaned when they become so dust-loaded and airflow is impeded, 3.) every 5, 10, 20 years. At least, every 3 to 5 years, the interior of the HVAC systems including ductwork, fans, air intakes, drip pans, and inside filter banks need to be inspected. Not an easy task.
Special equipment and knowledge of HVAC systems are required to access the important parts of that system. Boroscope cameras are used to inspect and record the accumulated dust/debris inside the system (Of course, plugs are needed to close the holes after inspection). Sometimes, it’s even necessary to cut—or access—hatchways into ducts, fan housings, and filter banks. Sampling/testing and analysis of collected system debris may also be important—especially after a fire or material release (this was a major issue near Ground Zero when the Twin Towers collapsed and hazardous dust entered the Lower Manhattan Buildings’ HVAC systems. When the power went down, that debris settled in the buildings’ ductwork).
This issue also applies to production facilities that use local exhaust ventilation to carry contaminants away from the work area. I have seen instances where the dust accumulated in the ductwork so much that eventually, the ductwork collapsed due to the weight of the debris!
Regular inspection and regular internal system cleaning are critical in maintaining air quality in the occupied spaces. There is no difference between the air in the ductwork and the air breathed by the building’s occupants.