Facilities (Learning Spaces)

FRESH AIR: The Impact of HVAC Systems on Indoor Air Quality

classroom fresh air


We all learned in high school biology that we inhale oxygen and exhale carbon dioxide (CO2). Both are natural gases along with others that make up the air we breathe. Nature does a great job of maintaining the proper balance for all of us to live healthy lives. However, when we load a classroom space with 20 to 30 children for several hours each day, CO2 levels will invariably begin to rise.

Depending on the level of natural ventilation (windows and doors) and the mechanical systems used to condition the space, the amount of carbon dioxide in the classroom can increase significantly by the end of the school day. While higher than normal CO2 levels do not present an inherent safety issue, numerous studies have shown attendance and academic performance are negatively impacted. Students exposed to high CO2 levels become drowsy, inattentive, easily confused, and their capacity for learning is diminished when CO2 levels are high. Obviously, this is in direct opposition to the very reason we send our children to school.

To some degree, this is a problem of our own making, an unintended outcome of everyday facilities practices. Safety and security concerns can also contribute to higher CO2 levels in classrooms. The new standards require exterior doors and windows to be secured during the school day and often include keeping interior doors closed as well. The days of propping open a door or opening windows in classrooms to let in a little fresh air are all but over.

Unfortunately, in many school districts, providing fresh air in the classroom is often a low, or practically non-existent concern for maintenance staff. For many of them, the day begins and ends with hot or cold complaints and simply trying to keep equipment running. There is never enough time or money, and honestly, no one complains about excessive levels of CO2. In fact, for the savvy HVAC tech, life is much simpler if the default position for fresh air louvers is effectively shut off, eliminating almost all fresh air to the classroom. Introducing sub-freezing air combined with moisture from snow and rain can spell disaster for exposed coils and piping systems. Conversely, bringing in outside air during the summer months when most schools are unoccupied and do not require fresh air, subjects buildings to high humidity, mold and mildew, and higher energy costs. With the exception of computer-controlled outdoor air louvers, which have their own special brand of issues, manually regulated fresh air intake louvers are not always easy to access, let alone adjust properly. Rather than climbing up a ladder to the roof and wrestling with louver systems that once opened may not close when the time comes, it makes sense to leave well enough alone. The result could be subjecting occupants of classroom spaces to less than optimal air quality to support the learning environment.

Concentrations of carbon dioxide in outside air average around 400 parts per million (ppm). Building codes require mechanical systems in schools to provide fresh air ventilation. ASHRAE standard 62.1 specifies a ventilation rate of 15 cubic feet per person (ages 5-8) in classrooms. The recommended level is reduced to 13 cfm/p for ages 9 plus. A normal level of CO2 gas inside of the classroom ranges between 750 to1,250 ppm. A fully loaded space without adequate ventilation can register CO2 concentrations as high as 2,500 to 5,000 ppm.

Fortunately, once understood, it’s a problem that can be solved. Brian Caffrel, Energy manager with Building Clarity states, “ASHRAE 62.1 has two main methods for ventilation design: First is the VRP (ventilation rate procedure) method, which is more prescriptive in nature. Second is the IAQ (indoor air quality) method that is more of a calculation-based approach.” In the design of HVAC systems for schools, his company takes a proactive approach to complying with code requirements and insuring optimal air quality for students. Caffrel explains, “Using Dynamic air cleaners we utilize the IAQ approach since we are actively removing contaminants from the air stream. This allows us to bring in less outdoor air for direct displacement, resulting in a system providing superior indoor air quality and higher efficiency due to the lower amount of outside air required.”

School facilities, particularly older, less energy-efficient buildings require maintenance and operations technicians to pay greater attention to fresh air ventilation. They are faced with an enormous variety of equipment ranging from outdated HVAC systems with literally no provision for fresh air exchange to state-of-the-art equipment that automatically maintains a balance between energy efficiency and air quality. It is not a simple task to balance best practices for energy efficiency with indoor air quality standards. The incorporation of outdoor air often requires more energy to condition to comfort levels and few systems use Dynamic air cleaners reducing the need for outside air. In a perfect world, HVAC technicians should not only be well trained on the mechanical equipment controls that regulate fresh air, particularly inside of classrooms, but also the IAQ standards that require technicians to maintain a balance between thermal comfort, energy efficiency, and indoor air quality.

However, even under the best of circumstances expecting maintenance technicians to know when equipment has been adjusted properly in order to provide adequate indoor air quality is a game of chance. This is especially true in the absence of monitoring or data analysis of the breathing air in each classroom space. With modern technology, measuring CO2 levels in the classroom is as simple as measuring temperature or humidity. For example, CO2Meter.com out of Ormond Beach, Fla., has developed an easy to read sensor that can be mounted on the wall in every classroom for a little more than $100 per unit. Along with temperature and humidity, it shows current readings for CO2 in parts per million. Better yet, the unit is designed to log data over a period of time, allowing facility managers to make adjustments and balance energy management with optimal indoor air quality. In certain cases, when it is determined that existing equipment settings are incapable of providing adequate fresh air for all students and staff, monitoring data can be used at a higher administrative level to support more costly capital improvements within the district. It is relatively common for schools to report classroom conditions involving temperature, humidity, unusual smells, etc. These concerns are associated with conditions teachers can easily detect by their senses. Without actually taking an accurate measurement, it is nearly impossible for teachers to recognize when CO2 levels are elevated and request adjustments to HVAC controls regulating fresh air ventilation.

All teachers and building staff should be made aware of the impact fresh air ventilation has on student performance. Morgan Morris, director of Marketing for CO2Meter. com emphasized, “Elevated CO2 levels in schools is a topic deserving more training and awareness. With education, school officials would be more likely to monitor spaces and use their analysis to improve classroom conditions for students and teachers.”

Managing the levels of carbon dioxide in the classroom on a routine basis along with adjustments to mechanical equipment when necessary can improve student achievement. With emphasis on test scores playing a significant role in the perceived effectiveness of public education, it would seem any advantage should be worthy of consideration.

This article originally appeared in the School Planning & Management January/February 2019 issue of Spaces4Learning.