Step 3 of Restarting your HVAC

BY Burns Mechanical IN Maintenance, Service

Written By Dan Kerr, P.E. (President, Burns Mechanical, Inc.)


As the Philadelphia region begins the process of re-opening commercial facilities, significant questions arise regarding the capabilities of HVAC systems to reduce the risk of viral infection. We’ve spent a significant amount of time synthesizing the latest engineering and scientific evidence against the backdrop of what we’ve learned from decades of engineering, building, commissioning, and maintaining HVAC systems.

Our first post in this series focused on the primary importance of introducing proper outside ventilation air into your building. The second article tackled the often-overlooked practice of continuous commissioning. Today we’ll address air cleaning and sterilization devices; a space in which product claims and business opportunists abound.


Step 3: Air Cleaning Devices


We saved this topic as the last in our three-part series for good reason. Due to a lack of external form of indoor environmental enforcement, there are many inadequately ventilated and maintained commercial facilities. Proper ventilation, commissioning and maintenance are invisible to building occupants, yet absolutely fundamental in diluting the build-up of contaminants. It’s tempting, and far too easy, to substitute a device – something to point at to make everyone feel safer – for the more difficult processes described in our earlier posts. HVAC air cleaning devices like those described below do not prevent person-to-person viral transmission. Further, there’s no known scientific evidence that recirculated building “return” air, which passes over cleaning devices, has caused spread of viral infection.


This topic is worthy of much elaboration. Let’s briefly address it in three broad subtopics:

Filtration – Max your MERV: Despite their small size as illustrated, COVID-19 particles apparently glom onto larger particles, and HVAC filters rated MERV-13 and higher have been shown to be effective at capturing airborne viruses. HEPA filters are even more efficient than MERV-16. So, in general, we recommend installing the highest MERV rating possible within your system’s filter racks without inducing too much pressure drop across the fan(s). Stand-alone fan filter units, particularly commercial and consumer grade HEPA units, provide a good way to increase total filtered airflow beyond what the HVAC can provide. This method of super-filtration is proven and used successfully in pharma and other applications.

Illustration by Daniel Overby


UVGI: Ultraviolet light in the C-spectrum is effective at inactivating viral, bacterial and fungal organisms, and has been used successfully in commercial applications for many years. We have had good success installing UVGI lamps within hospital air handling units, but they can also be implemented within HVAC ducts or directly in the occupied space – primarily for surface disinfection. Note that UV light of this wavelength is quite harmful to the eyes and skin. Proper PPE must be worn while maintaining these relatively inexpensive devices. UVGI wasn’t always widely accepted as a legitimate means of infection control. Strong empirical data on effectiveness came about only as the market pushed its implementation as the result of a wave of hospital-stay related secondary infections, which leads us to discuss other methods of infection control.


All the Rest: There are many additional air disinfection products available in the market, among them bipolar ionizers and sorbents. They are in various stages of testing and development to back claims of effectiveness. ASHRAE’s most recent position statement (referenced below) wants more empirical evidence prior to full-on endorsement of additional technologies. This has caused a fair amount of outspoken indignation, particularly by advocates of one specific manufacturer of bipolar ionizers. We are presently integrating three alternative air cleaning technologies into projects of significant scale. In each case our client is willing to embrace some calculated risk: and they are all already executing on the fundamentals of ventilation and continuous commissioning – not relying solely on a new product to potentially compensate for pre-existing problems. My advice to those who choose to be outraged at ASHRAE is to play an active role rather than throwing stones. ASHRAE is a volunteer, consensus-based organization made up of similar-minded folks.


When implemented with the fundamentals of proper distancing and hygiene, we’re confident that executing our 3-step approach to HVAC will provide the safest possible environment as your buildings re-populate.



*Helpful Independent Links:

ASHRAE Epidemic Task Force, Useful Resources

ASHRAE Position Document on Filtration and Air Cleaning

How can airborne transmission of COVID-19 indoors be minimized?