Chapter 5:
Overhead or Under-Floor Installation?
What You Will Learn?
• Benefits and drawbacks between ceiling and raised floor to run
power, data connection and cooling system
• Detailed overview of components involved in both options
• Common problems associated with both options
• Overhead installation
Use of false ceiling in which cabling, electrical conduits are
Termination are done above the servers rows
• Under-Floor installation
Flat panels are placed in an elevated grid of horizontal and
vertical bars, electrical conduits, cabling and cooling system
are routed under this raised floor.
Termination are done in a subfloor or into patch panel and
power receptacles within the DC cabinets
Overhead Installation
• Advantages
– Less expensive (Cable try ladder racks and raceways are less expensive
than a complete raised floor system)
– More suitable for limited spaces
– Requires less floor spaces (no entrance ramp)
– Reduce chances to snagging or damaging data cables
• Disadvantages
– Challenges for air circulation within the DC and servers cooling system
– Unplugged power cable or patch cord due to gravity and cord weight
Under-Floor Installation
• Advantages
– Better cooling capabilities
– Protecting infrastructure (patch cords, power cables) against
accidental damage or unplugs
– Easier to support and access infrastructure
• Disadvantages
– More expensive
• Most Data Centers are built with a raised floor
Deciding on whether to go with overhead Or Under Floor installation depends
The needs for the data center
The size of the data center
• If the Data Center is small— In round numbers, generally less than 1000
square feet (100 square meters)—or is being constructed in a building that
has limited space from floor to ceiling, I design it with overhead
infrastructure. The ramp needed for a raised floor and the height it
occupies simply take up too much space in such a small room.
• If the Data Center is larger— I design it with a raised floor and place its
various infrastructure down below. I find the raised floor system essential
for controlling airflow and neatly routing infrastructure. I've also learned
that it is much simpler to lift a floor tile and plug in to or disconnect from
infrastructure components than to climb a stepladder and stretch above a
server cabinet to make connections.
Separation of power & Data
• Separation is a must, EMI may distort information on data cable
• No standards available for the separation distance
Separation of power & Data (Cont.)
• It is not recommended to use overhead & under-floor for
separation (exposed to disadvantages from both scenarios)
• Precautions with using fluorescents lights specially with copper
cables (at least 5 inches distance is recommended)
Plenum and Non-Plenum Spaces
• Plenum: cavities above false ceiling or below raised floor, used for
air distribution in the server environment, such spaces are more
vulnerable to fire
• Certain regulations and building codes have been put in place that
permit only specially rated cables to be used in the plenum to
reduce the chance or effect of a fire
• Chose the right type of cables according to building codes to rout in
a data center
Ceiling Components
• Cable tray (shallow basket), Ladder racks (narrow ladder frame
installed horizontally), both are made of crossed metal bars secured
to the true ceiling and configured to align with infrastructure path
to be followed.
• Raceways: help in organizing the infrastructure to be clustered over
each server cabinet.
• Fire codes are applied on raceways, ladder racks, server cabinets, or
infrastructure equipments which in most of them requires around
50 cm distance between automatic sprinkler and any solid objects
Ceiling Components
Cable Tray
Ladder racks
Ceiling Components (Cont.)
Raceway overhead Termination Example—Front View
Raceway overhead Termination Example—Back View
Having the data ports above the back of the server cabinet in the raceways
would help in connecting them easily while it is not the case with plugging
power cables at the front of the raceways
Raised Floor Components
• During design phase, we need to identify:
- Floor height
- Mechanisms for bringing in equipment
- Weight-bearing capacity
- Types and numbers of floor tiles
- Termination infrastructure
- Other subfloor details
Raised Floor Components (Cont.)
• Floor Height:
some evaluation factors are tide to cooling issues (server
environment size and shape, number of equipment, and how much
cold air needs to be channeled in the space) while others are tide to
infrastructure (how much infrastructure is routed under the floor)
The simple rule is that the more height you have the more air you
can circulate within that space the more effect it has above the
floor, and the more infrastructure can be routed under the raised
Raised Floor Components (Cont.)
• Elevated floor vs. sunken floor
Deciding whether to go with either option should be made early in
the design phase
Raised Floor Components (Cont.)
Mechanisms for bringing in equipment
• Ramps:
- More popular
- Raised floor height and slop determine the ramps length
- Ideal ramps, 1.8 M wide with 1.8m of landings at both ends
- Many building codes requires handrail on both side
- It is recommended to install slip-resistance tread on the ramp
- More than one ramp may be required depending on the DC size
and approved building codes
• Lifts
- Occupies less space
- More expensive
Weight Bearing Ability
• Considered by many as the most important element of any DC floor
• Ideally, DC floor should support 2000 pounds or more per cabinet
• Overall weight bearing ability depends on structure of the building
that entail
Thickness & integrity of the concrete slab with bottom floor
steel skeleton with above the ground DC
• Weight bearing ability should be specified during the design phase
Weight Bearing Ability (Cont.)
• Other type of loads that needs to be specified:
- Static Loads
1. Concentrated or point load: weight applied on small area, area
where pegs or casters for fully loaded cabinets touches the floor
2. Uniform or static load: weight distributed over large area, as in
case of heavy boxes or large equipment sits on the ground
- Dynamic loads
1. Rolling Load(weight rolled over an area from passing
2. Affect load (force generated by dropped objects – item weight
& falling distance)
3. Ultimate load (breaking point of the floor panel)
• It is recommended to apply weight load on ramps or lifts equipped wit
the room
Types and Numbers of Floor Tiles
• Floor tiles comes with standard size (2 feet)
• Typically made of steel with either wood, concrete or steel at the
• Types of floor tiles:
Types and Numbers of Floor Tiles (Cont.)
• It is recommended to review the planed floor tiles deployment with
the person responsible for room cooling as the more use of
perforated and notched panels the harder it is to maintain air
• Use static control tiles to reduce voltage generated by walking people
Types of static floor tiles
Termination Details
• Too many methods are available to terminate electrical outlets and
structured cables (end of flexible conduit, stationary raceways,
server cabinet…etc)
• The goal is to be flexible, not to restrict access, prepare for growth,
and can be reassembled else where
Common Problems
• Poor sizing of tile cut-outs, or placing them in wrong location
causing air to escape from notches
• Mistakes with relation to cable type installation (plenum, nonplenum or low smoke/zero halogen)
• Problems with relation to the strength of the raised floor
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