R&M Data Center Handbook

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The server cabinets in the hot aisle containment on the other side are located in two rows opposite one another,
with their back sides to one another. Air flows through computers from the outside to the inside via an air duct, so
waste heat is then concentrated in the hot aisle between the rows of racks. The raised floor between them is
sealed tight. The warm air is then fed directly into the closed-circuit cooling units. These use a heat exchanger to
cool the warmed air down to the specified supply air temperature, and then blow it into the outer room. The
difference in temperature between supply air and exhaust air can be monitored and controlled better here than in
the cold aisle process. On the other hand, supply air temperature and flow velocity is easier to regulate in the cold
aisle process, because of the smaller volume.
Which advantages and disadvantages prevail in the end must be examined in the overall consideration of the data
center.
No matter what approach is selected for waste heat management, one must always make sure that air circulation
is not obstructed or even entirely blocked when setting up horizontal cabling (in the raised floor or under the
ceiling) and in vertical cable routing (in the 19” cabinet when connecting to active components). In this way,
cabling can also contribute to the energy efficiency of the data center.
3.5.3. Raised Floors and Dropped Ceilings
The raised floor, ideally 80 centimeters in height, also has a great influence in the area of hot and cold aisles.
Among its other functions, the floor is used to house cabling. Since the floor is also the air duct, cables must not
run across the direction of the current and thus block the path of air flow. One must therefore think about running
the cabling in the ceiling and only using the raised floor for cooling, or at least reducing it to the area of the hot
aisle.
Depending upon building conditions, possible solutions for data center cable routing include the raised floor, cable
trays suspended from the ceiling or a combination of these two solutions.
The supply of cold air to server cabinets may not be restricted when cables are routed through the raised floor. It
is recommended that copper and fiber optic cables be laid in separate cable trays. Data and power supply cables
must be separated in accordance with EN 50174-2 standards. The cable trays at the bottom need to remain
accessible when multiple cable routes are arranged on top of one another.
Cold Kaltgang aisle
Warmgang Hot aisle
It is recommended that
racks be connected with
cabling along the aisles.
Data Datenkabel cables
Cold Kaltluft air Korridor corridor
Power supply
Stromversorgung
Data Datenkabel cables
Perforated
Gelochte
base Bodenplatten plates
Power supply
Stromversorgung
By so doing, the smaller
required volume of
power supply cables are
routed under the cold
aisle directly on the
floorbase, and the more
voluminous data cables
are routed under the hot
aisle in the cable trays
mounted on the raised
floor supports.
If air-conditioning units in this arrangement are also arranged within the aisle extension, corridors result under the
raised floor and can route cold air to server cabinets without signficant obstacles.
If there is no raised floor in the data center or if the raised floor should remain clear for the cooling system, the
cabling must be laid in cable trays suspended under the ceiling. One must also make sure that the distances
between power and data cables as prescribed in EN 50174-2 are observed.
Arranging cable routes vertically on top of one another directly above the rows of cabinets is one possible solution.
In this case, the cable routing may not obstruct the lighting provided for server cabinets, cover security sensors, or
obstruct any existing fire extinguishing systems.
The use of metal cable routing systems for power cables and copper data cables improves EMC protection. Cable
routing systems made of plastic, with arcs and cable inlets that delimit the radii, like R&M’s Raceway System, are
ideal for fiber optic cabling.
Page 72 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0