Dell PowerEdge Rack Enclosure 4820 - Manual (Page 5)

Dell Data Center Site Planning Guide
Page 3
Ceiling Clearance
Before a recommended ceiling height can be provided, there are several things that first must be
considered. First and foremost is compliance with the National Fire Protection Association (NFPA),
which provides guidance for adequate clearance around fire detection and suppression
devices. Typically this is 46 centimeters (cm) (18 inches [in]) minimum above the top of the rack
enclosure. Dell recommends additional clearance of at least 30 cm (12 in). There are several reasons to
allow a minimum of 76 cm (30 in) clearance above the rack:
 Airflow management
 Overhead cabling and/or power
 Sprinkler system/fire suppression
 Lighting placement and room for light spectrum to work
The data center cooling strategy needs to be taken into account; specifically how the supply air is
delivered from (and how exhaust air is returned to) the cooling system(s). Any ducting positioned above
the rack should be accounted for in the site planning.
Likewise, any overhead cabling or power in place or planned should be incorporated into the floor plan
design. Suspended tracks for cabling or power may affect the placement of racks. Fire suppression
systems must also be accounted for, to ensure they can operate effectively after the racks and
equipment are deployed.
Consideration should be given to overhead lighting fixture arrangement to ensure that planned
cabinet(s) placement does not interfere with the fixtures’ ability to provide adequate lighting in the
space. Lighting should be adequate for servicing the equipment. A lower ceiling can cause dark areas
which make it more difficult to see, especially at the back of racks
Generally, for a 42U rack, Dell suggests that the ceiling height should be at least 2.74 meters (m) (9
feet [ft]) high. Similarly, for a 24U rack, the ceiling should be at least 1.83 m (6 ft) high, and for a 48U
rack, the ceiling should be at least 3.05 m (10 ft) high.
Aisle Clearance
Aisle spacing should also be taken into consideration. Dell recommends a minimum of 91 cm (36 in)
continuous clearance in the front of the rack to allow for installation of equipment and in the rear of
the rack for service access. This will also allow sufficient space for wheelchairs or carts. Deeper
equipment may require additional space for installation or servicing in the rack. 81 cm (32 in) should
be the minimum clearance around any obstruction.
Other Considerations
If the rack is intended to be used on a raised flooring system, the raised flooring system’s stated load
capacity for both rolling loads and static loads should be reviewed against the anticipated load of the
rack. Other considerations for a raised-floor deployment include proper grounding, anti-static, and
non-magnetic conditions.
Rack height, rack placement, and door swings should comply with all local codes ensuring proper
spatial clearances around electrical enclosures, fire and smoke detection/suppression systems (under-
floor and overhead), defined emergency egress pathways, and so forth.