required by the equipment. When the plenum supplies air to the room,
relocatable floor panels with registers or perforated flush panels are used.
The perforated panels are suitable for high-traffic areas and may be located
close to the equipment, since they produce a high degree of mixing with room
air. Floor registers are not flush and should not be located in areas of
heavy traffic or where wheeled carts are expected to operate. They are
capable of longer throw and better directional control and may be appropriate
for use in certain locations.
b) Above-ceiling Systems. Overhead supply systems through ceiling
plenums with perforated panels as diffusers are occasionally used for computer
rooms. This can cause hot spots in high-load areas, however, and generally is
not as flexible as diffuser grille distribution. An advantage of ceiling
systems is that they do not collect dirt from the floor area. Best conditions
are usually achieved by distribution ductwork, with the air discharged into
the space through diffusers in the ceiling. Perforated ceiling tiles are
usually inadequate as air outlets for final distribution to a computer room,
since they normally are incapable of handling the large quantities of air
required in these applications.
Return air may also be ducted from ceiling-mounted return air
registers in an overhead system. Short-circuiting between supply and return
may occur if care is not exercised in locating the supply and return
terminals. Overhead ducted supply usually serves normal building loads for
lights, occupancy, and the structure, while under-floor systems normally serve
to augment the central system in removing heat from the computers. Either can
be used, but both may create drafts, especially when ceilings are low. With
both systems, provisions must be made to maintain room relative humidity.
18.104.22.168 Computer Equipment Cooling. Some computer equipment requires
distilled water for cooling. This requirement will be indicated in the BESEP.
Normally, when this requirement exists, the cooling system is provided by the
manufacturer as part of the computer equipment, and is connected to a heat
exchanger, which in turn can be connected to the chilled-water systems as a
final heat sink. Chiller water piping, therefore, is often required in the
computer room. Careful installation of the piping and proper insulation,
where necessary, should minimize the possibility of leaks and condensation. A
separate refrigeration system for the computer equipment is desirable because
of the need for continuous year-round operation, the need for higher
reliability than with comfort applications, and the need for some components
(in critical applications) to be on the UPS circuit. Heavy loads such as
chillers or compressors are never to be placed on the UPS output circuit.
Some installations require the chilled water system to be sized for growth so
that it can be expanded to accommodate future additions to the data processing
22.214.171.124 Condensing Methods. In some locations, cooling towers may be
acceptable; in others, the need for winterization and excessive water
treatment may preclude their use. Air-cooled refrigeration condensers with
head pressure controls and separate hot gas and liquid lines for each,
refrigeration circuit are widely used. In installations where multiple
refrigeration systems are involved and/or the units are remote from the point
of heat rejection, air-cooled heat exchanger systems tend to simplify the