needed on an occasional basis only, when equipment is off or when unseasonable
its low first cost, low maintenance, simplicity, and reliability. If a fuel
selection analysis is prepared for areas not containing electronic equipment,
life-cycle costing techniques should be in accordance with NAVFAC P-442,
Economic Analysis Handbook.
Humidification. Electronic equipment areas generally require less
humidification per thousand BTU per hour (MBH) of heating than comfort
applications. Humidification needs are higher if a proper vapor barrier is
not provided, if excessive fresh air is admitted to the space, if
dehumidification during the cooling process is excessive, or if the humidity
ratio of the outside ventilation air is less than the humidity ratio desired.
The following methods of humidification are suitable:
a) Steam grid. This method is the simplest and provides the
quickest response. It is preferred when steam (devoid of chemicals) is
available. This process will add to the cooling load.
b) Atomized water. Atomized water provided by air-assist,
mechanical, or water spray methods provides fast response and reduces the
cooling load. It requires in-line demineralizers to avoid mineral dust in the
air, however, this can be expensive if the water is high in mineral content
(hard) or if large quantities of outside ventilating air are admitted.
c) Evaporative. Humidification, by pan-type humidifiers, gives a
slow response, possible overshoot and may add to the cooling load.
Maintenance requirements are high in areas with hard water although an
automatic flush cycle helps to reduce maintenance.
d) Steam injection. Steam injection by electric package units
provides medium to fast response, requires large amounts of electrical power
and adds to the cooling load. Scaling problems are the same as with the
evaporative pan method.
Dehumidification. Electronic equipment areas also require less
dehumidification per ton of cooling than comfort applications. Less
dehumidification is required in properly designed electronic facilities.
Cooling coils, therefore, should be designed for higher sensible-to-total load
ratios. Occasional higher latent loads can be handled by small separate
dehumidifiers located in the space and controlled by a humidistat if
necessary. Reheat should be avoided where possible and, if required, should
utilize waste heat.
Air Distribution. Where floors are raised, underfloor distribution
of conditioned supply air is convenient. Unless the equipment is specifically
designed to receive raw supply air, direct connection between the air plenum
and the equipment should be avoided. Instead, relocatable floor panels should
supply air to the room and the equipment should take tempered air from the
room. If overhead distribution is provided, low-velocity/low-pressure duct-
work is desirable. Both with overhead and underfloor air distribution, air
terminal devices must be located to allow the air to reach the area of the
loads. If the electronic equipment is in a high-bay area with an overhead