Humidity Control in School Facilities

Consulting engineers who design school facilities are challenged with controlling space humidity while also providing continuous ventilation as required by ASHRAE Standard 62-1999, now part of most major building codes. What would appear to be a simple design process is complicated by various logistical and operational factors. Schools, by nature, have a high occupant density which results in large outdoor air quantities being handled by the heating, ventilating and air conditioning (HVAC) system. The vast majority of schools, particularly those located in hot and humid climates, incorporate packaged cooling equipment, often incapable of effectively managing space humidity when delivering a high percentage of outdoor air. Maintenance departments at many schools are understaffed, which can limit equipment options available. School facilities are constructed on a tight budget, and capital allocations for mechanical equipment must compete with more visual items such as architectural details, computer labs and maximizing the number of classrooms. For these reasons, it should not be surprising that the U.S. Government’s General Accounting Office reported that 20% of the schools surveyed suffer from poor indoor air quality (IAQ) (GAO 1995, 1996). More than one third (36%) of the schools surveyed considered the HVAC systems “less than adequate”.