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Ventilation rates in recently constructed U.S. school classrooms.
S Batterman1, F-C Su1, A Wald1
1University of Michigan, Ann Arbor, MI, USA.
Indoor Air
|April 4, 2017
Summary
Many US schools have inadequate ventilation, impacting student health and academic performance. This study reveals most classrooms fail to meet recommended ventilation rates, necessitating improvements for better indoor air quality.
Area of Science:
- Environmental Health
- Building Science
- Indoor Air Quality
Background:
- Low ventilation rates (VRs) in schools are linked to increased absenteeism, decreased academic performance, and teacher dissatisfaction.
- Mechanically ventilated schools, including those with LEED and EnergyStar certifications, may still suffer from insufficient air exchange.
- Concerns exist that energy-saving and comfort-focused measures might compromise essential ventilation and indoor air quality (IAQ).
Purpose of the Study:
- To measure ventilation rates in recently constructed or renovated U.S. schools.
- To compare the accuracy and applicability of different ventilation measurement methods (CO2, steady-state, build-up, decay, transient mass balance).
- To identify factors influencing ventilation rates and their impact on IAQ.
Main Methods:
- Ventilation rates were measured in 37 U.S. schools using CO2 and four mass balance techniques.
- The transient mass balance method was identified as superior for accurately reflecting dynamic occupancy changes.
- Data were collected during school hours and after closure to assess diurnal variations in ventilation.
Main Results:
- Average air change rates (ACRs) during the school day were 2.0±1.3 hour⁻¹, with only 22% of classrooms meeting recommended minimums.
- ACRs significantly decreased to 0.21±0.19 hour⁻¹ when HVAC systems were shut off after school hours.
- Ventilation rates were not significantly different by building type but were lower in schools using unit ventilators or radiant heating, smaller schools, and larger classrooms.
Conclusions:
- Most surveyed schools exhibit inadequate ventilation, potentially impairing indoor air quality and negatively affecting occupants.
- The transient mass balance method is recommended for accurate VR measurement in dynamic environments.
- There is a critical need to enhance ventilation standards in schools and ensure energy efficiency measures do not compromise IAQ.
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