Formal Interpretations Guidelines for Design and Construction of Health Care Facilities, 2006 edition
“Question 2: Is it the intent of Guidelines Section 2.1-10.2.2.4 to prohibit ceiling-mounted returns (low-level returns are, of course, required) in lieu of returns mounted high on the wall to increase the air mixing in the room and aid in the reduction of particulates?
Response: The intent is not to prohibit the use of ceiling-mounted return/exhausts as long as they are used in addition to the required low wall grilles. (However, care must be taken that the location of ceiling grilles does not disrupt the primary airflow over the sterile area.) This arrangement is supported by the above-referenced studies, which concluded the following: “In a room that provides a laminar flow regime, a mixture of exhaust location levels works better than either low or high level locations only. However, the difference is not significant enough that the low or high level location systems are not viable options.” This conclusion makes no reference to the exhaust location being high on the wall or located in the ceiling. Therefore, if the proper exhaust mixture can be achieved by an exhaust grille located in the ceiling, this would be considered to meet the intent of Section 2.1-10-2.2.4.”