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A building’s HVAC system is designed to perform several tasks: filter, cool, heat, humidify, dehumidify, pressurize, and/or exhaust. Each of these tasks affects indoor air quality. For example, if incom­ing air is not properly filtered, excessive dust from the outdoors is drawn into the building. If supplied air is not conditioned or heated satisfactorily, occupants may experience thermal discomfort. If supplied air is not dehumidified appropriately, excessive relative humidity levels may promote microbial growth.

Positive vs Negative Operating room and protective isolation = Positive Airborne isolation = Negative When the total CFM from supply air (1&2) > than the return air (3), the room is under positive pressure and the air will flow out of the room. When the CFM from the return air (3) > than the supply air (1&2), the room is under negative pressure and the air will flow into the room

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Two principles for air-conditioning operating rooms are that air should be supplied at the ceiling, in a unidirectional or laminar air pattern, and that higher air change rates result in lower bacte­rial counts within the room. However, these principles are applied along a wide spectrum, and ongoing research is being conducted to optimize air distribution airflow patterns and quantities.