Influences of HVAC (heating, ventilating, and air conditioning) design and operation on radon mitigation of existing school buildings. Report for December 1987-March 1989

This paper discusses various school building characteristics identified as influencing radon entry, the design and operation of installed mitigation systems in four Maryland schools, and the success of these systems in reducing school radon levels. Results indicate that one of the most significant factors contributing to elevated radon levels in schools is room depressurization caused by the HVAC system exhausting more air from a room than the supply fan is furnishing to the room. Conversely, if the HVAC system pressurizes the room, radon entry can often be prevented as long as the fan is operating. Four Maryland schools with varying types of HVAC systems have had mitigation systems installed to reduce elevated levels of indoor radon. Mitigation techniques include depressurization of the area under the slab, sometimes accompanied by the sealing of cracks and holes, and the temporary reduction of radon levels by pressure control through the HVAC system. These systems were effectively reducing radon levels following their installation during the summer of 1988.