title: Ventilation rates in recently constructed U.S. school classrooms.
abstract: Low ventilation rates (VRs) in schools have been associated with absenteeism, poorer academic performance, and teacher dissatisfaction. We measured VRs in 37 recently constructed or renovated and mechanically ventilated U.S. schools, including LEED and EnergyStar-certified buildings, using CO2and the steady-state, build-up, decay, and transient mass balance methods. The transient mass balance method better matched conditions (specifically, changes in occupancy) and minimized biases seen in the other methods. During the school day, air change rates (ACRs) averaged 2.0±1.3 hour-1, and only 22% of classrooms met recommended minimum ventilation rates. HVAC systems were shut off at the school day close, and ACRs dropped to 0.21±0.19 hour-1. VRs did not differ by building type, although cost-cutting and comfort measures resulted in low VRs and potentially impaired IAQ. VRs were lower in schools that used unit ventilators or radiant heating, in smaller schools and in larger classrooms. The steady-state, build-up, and decay methods had significant limitations and biases, showing the need to confirm that these methods are appropriate. Findings highlight the need to increase VRs and to ensure that energy saving and comfort measures do not compromise ventilation and IAQ.
authors.affiliation: University of Michigan, Ann Arbor, MI, USA.
authors.forename: S
authors.identifier: 0000-0001-9894-5325
authors.initials: S
authors.lastname: Batterman
authors.affiliation: University of Michigan, Ann Arbor, MI, USA.
authors.forename: F-C
authors.initials: FC
authors.lastname: Su
authors.affiliation: University of Michigan, Ann Arbor, MI, USA.
authors.forename: A
authors.initials: A
authors.lastname: Wald
authors.affiliation: University of Michigan, Ann Arbor, MI, USA.
authors.forename: F
authors.initials: F
authors.lastname: Watkins
authors.affiliation: University of Michigan, Ann Arbor, MI, USA.
authors.forename: C
authors.initials: C
authors.lastname: Godwin
authors.affiliation: University of Michigan, Ann Arbor, MI, USA.
authors.forename: G
authors.initials: G
authors.lastname: Thun
mesh_terms: D016902:Air Pollution, Indoor / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis; D004784:Environmental Monitoring; D012574:Schools; D014481:United States; D014691:Ventilation / Q000592:standards*
chemical_list: D002245:Carbon Dioxide
keywords: air change; carbon dioxide (CO2); high-performance buildings; ventilation