In the emergence of the global pandemic, COVID-19, many offices found themselves sending employees home and allowing for remote work as everyone tried to understand the virus. As we move back into the very same buildings that we left months before, we are faced with new steps being taken to maximize employee safety. Social distancing, face masks, new hand sanitizer dispensaries, and extra surface cleaning throughout the building are being implemented, but what about the air we breathe? As we learn more about infectious diseases and how they can spread, we need to consider how Heating, Ventilation, and Air-Conditioning (HVAC) systems are affecting the spaces we work in.
All buildings are designed using the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) and International Mechanical Code (IMC) minimum ventilation rates in breathing zones. These rates are based on the space type, number of people in and the square footage of the space. This is already incorporated into your HVAC ventilation system. Research has shown that fresh, outside air in your building can help reduce the risk of transmission of diseases through the air. So, the question must be asked - how can we improve the air quality to further reduce the spread of infectious Bacteria and Viral diseases?
ASHRAE released a position document on infectious aerosols that suggested HVAC modification options based on Center for Disease Control (CDC) guidelines. These options can be summed up by air dilution, temperature and humidity control, and air cleaning as described below:
Increasing your outside air ventilation can decrease the amount of recirculated air in your building. This can be accomplished with changes to your building HVAC controls to increase minimum ventilation (Assuming your Cooling and Heating Coils can accommodate the added outside air load) or night purging with fresh air of your building.
Provide tighter control of temperature and humidity in the building. ASHRAE Data (Taylor and Tasi 2018) suggests that controlling relative humidity reduces transmission of certain airborne infectious organisms.
Increasing your ability to clean the air by increasing your air filter efficiency (MERV) rating to minimum Merv 13 (Assuming your System Fan can accommodate the added resistance of a more efficient filter), adding portable room air cleaners, or adding duct mounted devices can help clean the air that is recirculated in your building. Other possible air cleaning strategies include installing an Ultra-Violet Germicidal Irradiation (UVGI) on the discharge side of a cooling coil kills bacteria that tend to form on coils. However, UVGI lights are not effective on Virus’s. A Bi-Polar Ionization device in your system inserts a positive ion onto small dust particles and causes them to cling onto other dust particle, thus forming large enough particles for the MERV 13 filter to effectively capture. In addition, they have been proven to effectively sterilize Virus (including Covid-19) rendering them unable to reproduce.
Which option is best for you? What are the costs to implement the above? This depends on what system you have, what is applicable, and what works best for the way your office operates. When designing future workspaces, these same options above can be implemented at the beginning of the design process for approximately $350/ton of HVAC cooling. Including multiple options early on and having the equipment that will have the capabilities to respond to emerging situations will only help to better protect you and the people you work with. We would suggest clients speak to a trusted Professional Engineer to determine the costs and system modifications that would bring the most value for their conditions.
In summary, there is not a one size fits all, but your HVAC system can play a critical role in providing a healthy building for everyone that occupies the space, ultimately creating a safer environment to work in.
Associate, Mechanical Engineer