Ventilation Rates Determined by IAQ Studies

case_env_mzaconductsA large school district in a hot humid part of the country had a number of school buildings where high humidity had been caused by improper operation of aging air conditioning equipment.  This resulted in mold growth and other indoor air quality issues.  Repairs needed by the air conditioning equipment were sufficient to trigger compliance with current building codes, that required much higher ventilation rates than the equipment had been designed for.  The air conditioning equipment had been installed decades earlier when ventilation requirements were much lower.  The air conditioning units did not have the capacity to deal with the increased ventilation rates, and would have to be replaced.  In addition, the central chilled water plant, and distribution piping did not have capacity and would also have to be replaced.  This put the school district on the horns of a dilemma, they had a number of schools with humidity, and hence mold problems, and a limited budget.  If they had to replace all air conditioning units and the central chilled water plant, they would only be able to correct the mold problems in a few of the affected schools.

We were able to solve this dilemma by application of the ASHRAE IAQ Procedure, which allows ventilation rates to be determined by measuring contaminant levels in the building.  The only reason we were able to do this is because we approach ventilation studies as a collaboration between our certified industrial hygienists and mechanical engineers.  The industrial hygienists measured the contaminant levels in the buildings, and determined the ventilation rate each building needed to meet code requirements.  This rate slightly exceeded the original design capacity of the equipment.  The mechanical engineers designed modifications to the existing equipment that allowed it to handle this ventilation rate.

Collaboration between our industrial hygiene and engineering staff allowed the existing air conditioning equipment to be modified to provide proper dehumidification.  Reusing the existing equipment and central chilled water plants substantially reduced costs at each school.  This permitted the humidity problems to be corrected in many more schools, providing a greatly improved educational environment for the students and faculty.