One of the challenges in using free cooling is that fresh air can contain particulates that, over time, could affect the working and longevity of servers. At the Wynyard facility, HP uses bag filters (pictured above) to filter the outside air before it enters the equipment area.
Once the air is filtered, it moves into the sub-floor plenum (which is pressurized, just like a smaller raised floor) and flows upward through slotted vents directly into the cold aisles of the data center, which are fully-enclosed by a cold-aisle containment system. Capping the cold aisles in a "cool cubes" design allows the system to operate with lower airflow rate than typical raised floors in an open hot aisle/cold aisle configuration.
Louver systems (shown below) are used in multiple areas of the facility, opening and closing vents to manage the movement of air throughout the facility.