Matt Stringfellow, LEED® Green Associate, Mechanical & Electrical Systems Group Manager, Kraus-Anderson Construction Company
COVID-19 has changed the world. Pandemics have a way of doing that. We behave differently, we play differently, and we work and learn differently. Health experts also remind us that a COVID-19 vaccine will not be the end to pandemics, as the next one may be right around the corner. So, how do construction, engineering, and design firms work with their clients to build in strategies for adapting to COVID-19 and beyond?
Understanding how COVID-19 is transmitted is central to its mitigation. COVID-19 is a contagious disease caused by the SARS family virus that spreads primarily through droplets of saliva or discharge from the nose. Coughing and sneezing as well as simply talking and breathing can release the droplets into the air, to the ground, and on other surfaces, which can be touched and redistributed.
While public health officials insist masks, social distancing, surface cleaning, and hand washing are unquestionably the most important measures to be taken, building owners are also looking to other experts to reduce or prevent the spread. The American Society for Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has made recommendations that list several steps to build resiliency into existing buildings.
• Increase disinfection of frequently touched surfaces;
• Install more hand sanitation dispensers;
• Supervise or shut down food preparation and warming areas, including the office pantry and coffee station;
• Close water fountains and encourage employees to bring their water from home;
• Change air filters on a regular basis;
• And, if possible, install hands-free control devices to reduce physical contact, including power door operators or manual “foot” door pulls at bathrooms; and automatic touchless water flush valves for toilets/urinals, sink faucets, soap and paper towel dispensers, and bottle water filling stations.
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Once these basics are covered, additional actions related to HVAC systems can prevent the spread of the virus, beginning with increasing outdoor fresh air ventilation. Outdoor fresh air is required to help dilute indoor airborne contaminants such as carbon dioxide CO2, which people exhale when they breathe. Buildings are typically-designed to meet the minimum code requirement for the quantity of outdoor fresh air ventilation, which is based on building type and occupant density. In most cases, this minimum amount is in the range of ±15 percent of the total supply airflow for the building.
In addition, many buildings in temperate climates are designed for a “free-cooling” control cycle in the spring and fall, whereby the quantity of outdoor fresh air is automatically increased to 100 percent to take advantage of free cooling provided by the temperature of the outdoor air, typically in the range of ±50 deg. F. A design engineer should be consulted to examine the building’s heating and cooling equipment to determine if the outdoor fresh air ventilation quantity can be increased without detrimental effects on the comfort of the building occupants during the extreme seasons. At a minimum, an air balancing contractor should be consulted to measure the current quantity of outdoor fresh air ventilation for all building systems to confirm that the quantities meet the original design specifications and/or code minimum requirements.
It is also important for each building to have supply air and return air ductwork systems that promote effective ventilation airflow. This means that every room should have supply and return air grilles placed strategically in the room to prevent dead air pockets where airborne contaminants can linger.
• Disable demand-controlled ventilation (DCV) to keep the outdoor fresh air ventilation quantity as high as possible;
• Increase relative humidity to between 40-60 percent (this may require significant design changes to the building envelope);
• Improve central air filtration efficiency to at least MERV13 or the highest level compatible with the filter rack, and seal the edges of the filter to limit bypass;
• Keep systems running longer hours, 24/7 if possible;
• Install bypass HEPA filtration or portable room air cleaners with HEPA filters;
• Install needlepoint bi-polar ionization air cleaning.
COVID-19 is not like other viruses, and much more research needs to be done to learn why it behaves differently. Therefore it is premature to make definitive statements about potential risk mitigation efforts. We all are wise to follow the science and be open to learning more facts and new information.
In the meantime, there are many ideas that can enhance and improve indoor air quality for building occupants as well as improve building interior environmental conditions that will help to mitigate virus transmission. For this reason, it is critical to develop a comprehensive plan to evaluate existing building conditions. Then, from a cost and logistic standpoint, define and understand the implications for any and all improvements to make fully informed decisions on which improvements to undertake.
Furthermore, anything a building owner does to build resiliency into its HVAC system should in no way eliminate constant diligence in wearing masks, maintaining social distancing, cleaning surfaces, and washing hands. That simple science remains the most effective means for reducing the spread of COVID-19.