Commercial HVAC Contractors: How to Address IAQ

by Jim Rosenthal

The following identifies where to begin your assessment of Commercial Buildings.

Common Indoor Air Quality Problems in Commercial Buildings

Lack of Outdoor Air

Thanks to a wide range of deferred maintenance issues—from broken fan belts to control failures—the amount of outdoor/ventilation air in buildings often falls well below code, design specifications, and best practices. Properly diluting indoor air with outdoor air is highly effective for reducing concentrations of infectious aerosols. Filtration issues—HVAC filters are often misaligned, damaged, or missing. Without proper filtration, infectious aerosols can travel in the return air from one room to the entire facility through the supply air distribution system.

Improper Fan Operation.

Supply and return fans may run at less than design speed—and therefore do not supply enough air to the space. This can affect building pressurization, allowing infectious aerosols to move from room to room. Bathroom exhaust fans turned off. This not only reduces ventilation but detracts from the desired negative pressurization in the bathroom. Why is negative pressure important? Because toilet flushing can expel high concentrations of infectious aerosols into the air, and negative pressure keeps them from flowing to adjoining rooms.  Bathrooms should be maintained at negative air pressure when compared with surrounding spaces. This prevents the spread of infectious aerosols from toilet flushes.

Effective Solutions

1. Improve current systems via repair/commissioning,

Retro- and continuous commissioning can yield fast improvements with limited investment. 

  • Ensure all control elements are in working order. 
  • Inspect/repair filters.
  • Seal ducts. This simple steps can vastly improve a fan’s ability to move the air it was designed to move, from and to the correct places.
  • Seal building envelope. With too much air leakage, proper space pressurization may not be possible. Consider sealing all gaps through doors, walls, and roofs.

2. Improve current systems via modifications/operational change.

  • Increase outside air quantities strategically. This typically requires use of air-to-air heat recovery systems to mitigate the energy impact of higher outdoor air levels.
  • Implement demand-controlled ventilation. Another mature tactic to ensure adequate outdoor air. Monitors detect CO2 concentrations; as concentrations increase, the outdoor air damper is opened to allow more fresh air.
  • Improve humidity control. Best practice, at least when respiratory illnesses are prevalent, is to maintain 40-60% relative humidity, at which the human body is best able to ward off infectious disease.
  • Improve air distribution. Turbulent airflow can spread infectious aerosols. Review the relationship between supply diffusers and exhaust grilles to ensure smooth, uniform flow, and direct flow from “clean” to “dirty” areas.
  • Upgrade filtration. Evaluate your filtration to implement the best available technology. Consider HEPA filtration (which may be a costly retrofit) for high- risk environments, lower-cost properly designed filters for lower-risk environments.
  • Improve room pressurization control.
  • Install no-touch features, including infrared operators for faucets, toilets, paper towel dispensers, and building entrance doors.

3. Use HVAC disinfection tactics.

  • Ultraviolet germicidal irradiation (UVGI). A simple retrofit can incorporate this technology into air handling cooling coils to supplement filtration. The UV light kills viruses and other pathogens by damaging the structure of their nucleic acids and proteins.
  • Air ionizers. Ions also disrupt the structure of microbes without harm to human occupants. Unlike many chemical disinfectants, then, air ionizers can be deployed in occupied rooms.

4. Use in-room disinfection.

  • Ozone/vaporized hydrogen peroxide. Unlike UVGI, these chemicals can disinfect an entire room, both air and surfaces. For safety reasons, however, they should only be used in unoccupied rooms.
  • Disinfection UV lighting. Germicidal infection control lighting systems come in two varieties: in-duct/upper room GUV (germicidal ultraviolet), which is proven effective but carries safety risks to occupants, and a visible-spectrum surface disinfecting system, which uses room light fixtures to provide continuous disinfection even in occupied rooms.

Other Articles in this Series

This article appeared as part of a feature story in the October / November 2020 print issue of Southern PHC. Featured alongside was Poor IAQ & Low Humidity COVID-19  Catalysts.

Jeremy McDonald, PE

Jeremy McDonald, PE, is vice president of Guth Deconzo Consulting Engineers.


Jeremy McDonald is vice president of Guth Deconzo Consulting Engineers. McDonald is a professional engineer with more than 25 years of experience in HVAC design, energy services, commissioning and the construction management industry. His expertise includes indoor air quality assessments, with a focus on higher education and healthcare (hospitals/nursing homes) facilities.

McDonald is LEED certified, CCP commissioning certified, a certified energy manager (CEM) and a Professional Engineer (NYS). He is also an adjunct professor for Rensselaer Polytechnic Institute (RPI) in Troy, N.Y. He holds a master’s in Environmental Management & Policy and a bachelor’s in Mechanical Engineering, both from RPI.


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