A large school district in the humid southeast U.S., with over 45 million square feet of conditioned floor space, needed to replace old air-conditioning systems that were unable to maintain comfort conditions and control humidity. Installation of new systems meant that the schools had to be brought into compliance with current building code ventilation requirements. As the chilled water plants in these schools were designed to accommodate ventilation rates that were a fraction of current standards, they did not have capacity for cooling, and dehumidifying the additional humid outside ventilation air.
We recommended to the school district that instead of blindly applying prescriptive ventilation rates from the code, they apply the ASHRAE Indoor Air Quality procedure to determine the ventilation rates needed to control airborne contaminants and provide acceptable indoor air quality for the students and staff.
During the study, carbon dioxide from the student occupants was monitored, and used to determine the actual ventilation rates in the schools. These actual ventilation rates and the corresponding indoor air conditions were determined for schools on 58 school campuses which had high relative humidity problems resulting from failing air conditioning equipment.
Concentrations of hazardous contaminants and respiration byproducts in each campus building were monitored and correlated with ventilation rates. This data was used to determine the amount of fresh air required to maintain contaminant levels below ASHRAE 62-2004 exposure levels. The school district was trying to stretch its limited budget to correct high humidity, and the attendant mold and indoor air quality problems in as many schools as possible.
Ventilation rates determined by this study were low enough that, in most cases, the existing chilled water plants at the schools could be retained. This significantly reduced the cost of the dehumidification retrofit at each school, thus allowing humidity problems in more schools to be corrected within budgetary constraints. As high humidity and attendant mold growth are the primary causes for degraded indoor air quality in hot humid climates, this allowed the district to provide a healthy school environment in the maximum number of schools.