Improving indoor air quality is a critical measure building operators can take to ensure safe reopening amidst the coronavirus pandemic.
Improving indoor air quality is a critical item among the menu of measures building operators can take to ensure safe reopening amidst the coronavirus pandemic. Given the likelihood of airborne viral exposure indoors, high-occupancy facilities have to consider changes to their HVAC systems and building operations to minimize the risk of transmission.
While a full ventilation system replacement is an unlikely short-term solution, an evaluation of existing HVAC systems might reveal immediate opportunities for maintenance and interim upgrades. To help reduce the spread of contagions through ventilation systems, we’ve outlined proactive steps facilities teams can take over the next few months, followed by long-term strategies to consider. These measures are applicable to several building types, including K-12 schools, colleges, and offices.
Assess and Maintain Existing HVAC Systems
Facilities operations and maintenance teams should conduct a detailed assessment of existing HVAC systems. At a minimum, this should include checking outside air and exhaust dampers or fans for proper operation and set-points. All systems and equipment should undergo preventative maintenance, including air filter changes, proper filter sealing, as well as any necessary cleaning. Bringing more outside air into buildings is one of the most effective ways to reduce the risk of pathogen spread through recirculated indoor air. A comprehensive engineering analysis can identify to what extent a system’s outside air ventilation rate can be increased without compromising proper filtration, temperature, and humidity control. Engaging a professional engineering consultant may be necessary at this stage and will provide an objective perspective as well as insight into local and industry trends.
Improve System Efficiency Through Retro-Commissioning
Depending on the age of the systems and the level of confidence in their operational parameters, Retro-Commissioning may be recommended as a next step to ensure all systems are performing as intended. Retro-commissioning is a systematic process of investigating, testing, and verifying how systems work individually and together with the goal of identifying operational improvements. The findings will determine if any system needs to be optimized or brought back in line with the original design intent. This process often re-establishes efficiencies, improves occupant comfort, and gains energy savings all while ensuring proper ventilation and environmental controls to improve indoor air quality.
Sufficiently Purge Indoor Air
It is highly recommended to purge buildings at maximum outside air rates for 2 hours prior to and after occupancy. This includes operating exhaust fans as well as opening the outside air dampers. Opening all windows can also serve this function for buildings without the capacity to treat large quantities of outside air and when outside air conditions allow. In addition, operating HVAC systems full-time (24/7) is recommended to maintain continuous air circulation, filtration, and ventilation even during non- occupied hours.
Control Relative Humidity
The control of relative humidity has been shown to have a significant impact on the viability of viruses in the air. Research has shown that the most unfavorable relative humidity for survival of microorganisms is between 40% and 60%. Maintaining this level of humidity requires active de-humidification in the summer and active humidification in the winter. This can be achieved by retrofitting central air handling systems or duct distribution with humidifiers and dehumidifiers. While these technologies are well understood and readily available, they often require significant retrofits to HVAC systems. Alternatively, local in-room equipment could be considered to control humidity, though these systems will typically not achieve the same effectiveness of distribution and capacity as a central system. Whenever humidification is added to a structure, building envelope conditions should be reviewed for vapor barriers and, in some cases, retrofits may be required to prevent moisture migration into walls.
Explore New Technologies
We’ve discussed increasing ventilation rates and filtration, improving air distribution, and controlling relative humidity as long-term strategies for improving air quality. To validate the investment in these strategies and ensure their effectiveness, we recommend verifying system performance regularly by implementing supplemental automatic sensing and monitoring technologies to confirm flow rates, filter pressure drops, and contaminant levels. In addition to using this data to maintain systems, it can be used as a tool in education and community outreach.
Other technologies for consideration include Ultraviolet (UVC) Irradiation and Bi-Polar Ionization, both of which continue to be studied as a means of reducing the spread of infectious disease through air systems. Additional research is required to validate their efficacy and understand any risks involved. However, these technologies currently look promising and may become part of a longer-term strategy.
These risk-reduction measures to improve indoor air quality represent one layer of defense and are most effective in concert with other strategies such as physical distancing, face masks, and heightened cleaning and hygiene protocols. For more detailed information and strategies on managing indoor air quality, we’ve compiled the below list of articles and resources: