The First Step to Restarting Your HVAC

2Jun2020
BY Burns Mechanical IN Maintenance, Service

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

 

As the Philadelphia region prepares to re-open commercial facilities, significant questions arise regarding the capabilities of HVAC systems to reduce the risk of viral infection. Product claims and business opportunists abound in an environment of fear. It can be overwhelming.

Of course we have to caveat that each building and circumstance is unique. There is no single silver bullet answer. We hope that it’s also clear that you can’t HVAC your way out of sound social distancing and hygiene practices. Common sense needs to prevail.

Those points made, 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. Though no “one size fits all,” we’ve attempted to break a large problem into a 3-step process, focusing on un-biased fundamentals.

 

STEP 1: Ventilation Air

Chart demonstrates poor ventilation control by measuring CO2 concentration

First and foremost, does your building have an adequate supply of outside ventilation air? Providing adequate and effective outside ventilation air is the single most important factor for infection control.* At the time your building was constructed the HVAC systems needed to meet the indoor air quality standards of the day, which included introducing a minimum volume of ventilation air. However, we observe that systems quickly fall out of commission if not maintained properly. The attached chart illustrates this problem in classrooms at a client’s high school.

Present building energy codes in Philadelphia require the implementation of demand-controlled ventilation (DCV) cycles, which is a control strategy that monitors and adjusts the volume of outside ventilation air based on real-time occupancy. Now would be a good time to disable those control cycles, ensuring that the indoor air is continuously flushed. While there will be an energy cost penalty for doing so, the HVAC system likely has the capacity to satisfy the increased load.

The prevailing wisdom among independent thinkers in the HVAC industry is that, if feasible, unoccupied control cycles should be disabled as we re-open for business. During an unoccupied cycle, the outside ventilation air dampers are closed, building air is recirculated, and temperatures are reset since nobody is in the building. Disabling this control strategy has the benefit of super-flushing the building of airborne contaminants. But beware that simply opening your outside air dampers during unoccupied periods can induce significant humidity problems. Lacking additional engineering advice, your best bet is to leave the facility in occupied mode 24/7, regardless of building operations.

Stay tuned for our next posts, which will cover steps 2: Continuous Commissioning and Maintenance, and 3: Air Cleaning Devices!

 

 

*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?