Tim Mahoney, TBE Mechanical Test and Balance Corporation SURGERY SUITE SPACE PRESSURIZATION A local hospital recently completed a new surgical wing, which consisted of the upper floor being the surgery suite and the lower level being the sterile processing and the decontamination area. The surgery suite was made up of 11 operating rooms (OR), a sterile core in the middle and a clean corridor around the perimeter (see the diagram below). OR 11 OR 1 OR 10 OR 9 OR 3 OR 8 OR 4 Clean Corridor 2 OR 2 Sterile Clean Core OR 7 OR 6 OR 5 The upper floor was served by a dedicated air handling unit (AHU) consisting of three supply fans and four return fans. Each OR was served by one supply variable air volume (VAV) box and one return VAV box. Each OR was designed to operate with an offset between the supply and return of 300 cubic feet per minute (CFM). The sterile core was served by multiple supply VAV boxes and multiple return VAV boxes, with a neutral offset. These offsets were intended to maintain a minimum positive pressure in each OR of +.020 in. water column (w.c.) to the clean corridor and +.010 in. w.c. to the sterile core. This leaves the sterile core +.010 in. w.c. to the clean corridor. Clean Corridor During the TAB procedures, it was determined that the 300 CFM offset for each OR was not capable of maintaining the required space pressures. An average offset of 700 CFM was required to achieve the desired pressures. This increased offset was due to the excessive leakage under the doors. This increased the minimum outside air (OA) on the AHU by 4,400 CFM (see the schedule on the facing page). This increased OA was determined to be excessive for the cooling and heating coil capacities of the AHU, which would cause temperature and humidity problems in the ORs. TAB Journal Summer 2019