IAQ Solutions to Improve Schools, Now and in the Future

1. No Mechanical Ventilation System: Many currently operating schools were built during a time that predates a code requirement for outside air. These “leaky” buildings with operable windows were expected to “breathe” on their own. Over time, many districts have replaced the operable windows with fixed windows or secured them shut. And, of course, opening a window in winter isn’t practical in many climates.

2. Design Deficiencies: These are common in many schools and in particular those with variable air volume (VAV) systems, one of the most common mechanical systems used in K-12 environments. These systems often fail to provide sufficient outside air in some areas (particularly in the more densely occupied areas such as classrooms) while simultaneously providing excessive outside air in other areas, resulting in a double penalty of poor IAQ and unnecessary energy use.

3. System Degradation: Over time, a system can develop issues that compromise IAQ, even if installed correctly. This is exacerbated by a lack of adequate maintenance capacity and training that afflicts many school districts.

4. Energy Efficiency: There is a lack of emphasis on the connection between IAQ and occupant performance. Even in school districts with more robust facilities staff, the emphasis is typically on energy efficiency rather than IAQ. In many cases, we have even seen operational measures put in place that cause harm to IAQ in pursuit of energy savings.   

IAQ monitoring.

Once systems have been commissioned/retro-commissioned and are working properly, it is important to know that they are working to perform their intended function. IAQ monitoring is one measure that provides better insight into the health of a space. The sensors and monitors that are currently available range from low cost with limited detection capabilities, to expensive lab-grade units. Basic consumer units that detect CO2 can be found online for less than $100, and we have even seen teachers bring these into their classroom as they now understand the correlation between CO2 rates and viral transmission.

The sweet spot for school districts seems to be in the $500–$700 range for “Grade B” sensors. These are more robust than consumer models, reasonably accurate, but far less costly than lab-grade equipment. In addition to CO2, these units typically detect other contaminants such as particulate matter (PM2.5,10), VOCs, ozone, or formaldehyde in addition to basic criteria like temperature and humidity. More advanced units can integrate into the building automation system, but even standalone systems can provide a district with more insight into the state of their air quality.

When deployment of these sensors is combined with on-going monitoring, a school district can proactively address issues that occur. In the example previously provided of a failed outside air damper, this zone of the school would have experienced high CO2 levels, along with potentially high levels of total volatile organic compounds (TVOCs) and particulate matter. Had IAQ sensors been deployed and monitored, the district would have realized that an issue was occurring that required further investigation. This likely would have led them to discover the source of the issue and resolve it in short order, eliminating a much longer exposure to poor air quality.

Modeling for viral transmission.

In response to the pandemic, several tools have been developed that allow for modeling of viral transmission in buildings. One such tool developed by BranchPattern is called the Facility Infection Risk Estimator™,8 which can currently model both SARS-CoV2 and Influenza A. It allows the user to create a representative model of an environment, such as a classroom, gym or cafeteria. By changing the parameters such as ventilation, filtration, relative humidity, exposure time, and vaccination rates, the user can predict the likelihood of viral transmission over a day, or in the case of the Influenza A, over an entire flu season, which can then be aggregated over the whole building to show the impact of the environment on things such as total teacher and student days lost.

One of the primary reasons for developing this tool was to allow users to make smarter decisions about where to invest in strategies that reduce viral transmission. Some of these strategies often require additional energy use to function. For example, both increasing the amount of outside air used for ventilation and selecting higher rated filters will typically have energy penalties associated with them. The questions of “how much outside air should I bring in?” and “what level of filtration should I use?” can then be answered for the specific building and environment through modeling.

When used in concert with energy modeling tools, a number of strategies can then be evaluated from the standpoint of health benefits, cost, and energy impact. This approach provides a more holistic view of the strategies being considered and makes for more informed decisions.

Balancing IAQ with energy consumption.

As school districts have implemented improvements to ventilation related to COVID-19, they have generally experienced increases in energy use and utility costs. This has reinforced the incorrect impression that good IAQ implies higher energy use. Both can be achieved in the same building using smart design combined with effective maintenance.

HVAC system overhauls are good opportunities to realize excellent IAQ and high energy efficiency. A strategy we recommend to our clients is Dedicated Outside Air Supply (DOAS) in which heating and cooling systems are decoupled from ventilation and energy recovery. This approach delivers the promised combination of good IAQ and high energy efficiency. This principle can be applied to new construction and existing school HVAC system renovations.