The textbook on bacterial transmission includes a surprising chapter or two.
Whether kids like school or not, attendance is mandatory for many years. Academic performance during this time often influences eventual jobs, income, and life satisfaction. During the formative years, parents mandate adequate sleep and good eating habits to improve their children’s concentration. Architects endeavor to design new school buildings to optimize student alertness with colorful interiors and an abundance of natural light.
In addition to parents, teachers, and architects, HVAC engineers have a critical role in improving student performance and helping to make school a positive experience. Abundant research shows that ventilation design choices clearly influence our health and productivity. Indoor air pollutants such as carbon dioxide and volatile organic compounds diminish cognitive functioning and, therefore, academic performance.
Despite a known relationship between ventilation and health, traditional HVAC designs focus on managing energy consumption rather than occupant wellbeing. Building ventilation in the United States consumed approximately 1.75 exajoule, or 4% of total building energy use in 2010, which increased tenfold when heating and cooling were included (U.S. Department of Energy). Understandably, this clear and measurable relationship between energy consumption and HVAC choices affects ventilation design.
Conversely, there is less data on ventilation design and on another important health concern — communicable viral and bacterial illnesses. While many people are aware of the airborne spread of tiny cold and flu viruses, transmission of bacteria through bio-aerosols has been more difficult to track. This is now changing, thanks to new genetic analysis techniques that identify the DNA “fingerprints” of specific bacterial strains. These tests identify and map large microbial communities in the built environment through air, surface, and liquid sampling.
What has been discovered about HVAC design and the spread of bacterial bio-aerosols in schools? Are the micro-organisms in on-site classrooms friends or foes to students?
The movement of bacteria from students, building dust, and outdoor soil in classrooms is fascinating, and the travel routes are surprisingly related to indoor ventilation. While bacteria found in human skin and oral samples were most prevalent on seats and desk surfaces, walls and floors were more strongly populated by species found in soils. These microbial communities were significantly different from each other in ways not predicted by spatial distances, indicating that indirect transmission on airborne particles had a greater impact than spread through surface touching!
We know that inhalation of infectious aerosols is a critical route of exposure to bacteria, fungi, and viruses that can make students sick. Understanding that both human occupancy and ventilation determine the microbial community in buildings, engineers can design HVAC systems to truly keep student health and education the number one priority in schools by keeping the following points in mind.
- While most bacteria found in classrooms are harmless, some can cause serious infections.
- Outdoor geography, building and ventilation designs, indoor air temperature, relative humidity, and occupants determine indoor microbial communities.
- Indirect transmission through bio-aerosols and dust suspension is as important as direct contact in the spread of bacteria.
- Natural ventilation, appropriate indoor air humidification (40-60%), and moisture management through proper building envelope insulation are essential to student health. ES