title: The effects of building-related factors on classroom relative humidity among North Carolina schools participating in the 'Free to Breathe, Free to Teach' study.
abstract: Both high and low indoor relative humidity (RH) directly impact Indoor Air Quality (IAQ), an important school health concern. Prior school studies reported a high prevalence of mold, roaches, and water damage; however, few examined associations between modifiable classroom factors and RH, a quantitative indicator of dampness. We recorded RH longitudinally in 134 North Carolina classrooms (n = 9066 classroom-days) to quantify the relationships between modifiable classroom factors and average daily RH below, within, or above levels recommended to improve school IAQ (30-50% or 30-60% RH). The odds of having high RH (>60%) were 5.8 [95% Confidence Interval (CI): 2.9, 11.3] times higher in classrooms with annual compared to quarterly heating, ventilating, and air-conditioning (HVAC) system maintenance and 2.5 (95% CI: 1.5, 4.2) times higher in classrooms with HVAC economizers compared to those without economizers. Classrooms with direct-expansion split systems compared to chilled water systems had 2.7 (95% CI: 1.7, 4.4) times higher odds of low RH (<30%). When unoccupied, classrooms with thermostat setbacks had 3.7 (95% CI: 1.7, 8.3) times the odds of high RH (>60%) of those without setbacks. This research suggests actionable decision points for school design and maintenance to prevent high or low classroom RH.
  
  
  CONCLUSIONS
  This study combines longitudinal measurements of classroom relative humidity with school inspection data from several schools to describe the problem of relative humidity control in schools. Our findings on how maintenance and mechanical factors affect classroom humidity provide suggestions on building operations policies and heating, ventilating, and air-conditioning (HVAC) design considerations that may improve classroom relative humidity control.
authors.affiliation: Epidemiology Department, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: K A
authors.identifier: http://orcid.org/0000-0002-8530-0066
authors.initials: KA
authors.lastname: Angelon-Gaetz
authors.affiliation: Epidemiology Department, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Richardson
authors.affiliation: North Carolina Division of Public Health, Department of Health and Human Services, Raleigh, NC, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Lipton
authors.affiliation: Epidemiology Department, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: S W
authors.initials: SW
authors.lastname: Marshall
authors.affiliation: Maintenance Operations Department, New Hanover County Schools, Wilmington, NC, USA.
authors.forename: B
authors.initials: B
authors.lastname: Lamb
authors.affiliation: Support Services, Chapel Hill-Carrboro City Schools, Chapel Hill, NC, USA.
authors.forename: T
authors.initials: T
authors.lastname: LoFrese
mesh_terms: D000389:Air Conditioning; D016902:Air Pollution, Indoor / Q000032:analysis*; D015331:Cohort Studies; D006361:Heating; D006801:Humans; D006813:Humidity; D008137:Longitudinal Studies; D009657:North Carolina; D012574:Schools; D014691:Ventilation
keywords: Building-related factors; Classrooms; Indoor air quality; Longitudinal study; Relative humidity; Schools