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Written By: Robert E. Sheriff, MS, CIH, CSP, President
November 27, 2018, Updated September 2019
Inspecting your Ventilation (HVAC) System
“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 generates and adds 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 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. Borescope 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.
For most systems, every 3 to 5 years an inspection of the interior of the HVAC should be performed. A schedule of cleaning can then be established. Atlantic Environmental can perform such internal HVAC system inspections.
There are a variety of methods for testing of ventilation systems depending on the building’s configuration and use.
In-office buildings, the best method is to measure the air intake volumes at the air intakes. From there the calculation can be made to obtain an Air Changes Per Hour (ACH) and compared to recommended air change rates for similar occupancies.
In industrial buildings, measuring exhaust volumes of both the General Ventilation (wall fans, roof fans, and local exhaust ventilation).
If it is important to ensure the proper balance between supply and exhaust air, then the supply air volume must also be measured.
This is critical in a production building where there is often a lack of adequate make-up air to balance the amount of exhaust air creating a “negative pressure” in the building (ex. hard to open the exterior doors due to negative pressure).
When addressing air contaminant control ventilation, the approaches become much more complex. There is too much information to be addressed in this presentation. Issues of capture velocity, transport velocity, static pressure, type of fans, ductwork and filtration must be addressed—as well as supply/exhaust air balance.
There are many technical references discussing Local Exhaust Ventilation. One of the best—and most current is the Industrial Ventilation Manual published by the American Conference of Industrial Hygienists (ACGIH). The 29th edition published in 2016 is now two (2) separate tests: 1. Design and 2. Operation and Maintenance.
For further details on Ventilation, please refer to the other “Ventilation” subjects on our website https://www.atlenv.com/. or simply fill out our online contact form to learn more. We will be happy to help you.
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