Quantcast Guidelines for HVAC System Design

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be energized during winter only via a summer/winter switch in series with the
control thermostat. Humidity shall be limited to 90 percent by energizing the
unit heater at any time without the limitation of the summer/winter switch but
with the limitation of a differential temperature limit thermostat set for 5
degrees F (3 degrees C) over the outside ambient temperature.
Emergency Generator Rooms.  Refer NAVFAC DM-3 Series Mechanical
Engineering, for interior design requirements.
Transportables.  Inside conditions for transportables are the same
as for permanent facilities depending on the needs of the equipment therein as
outlined in the BESEP.  This includes temperature limits and humidity high
limit.  Humidification is normally not provided unless a water supply is
Guidelines for HVAC System Design.  In addition to the specific
requirements in the BESEP, the following guidelines apply to all projects.
Simplicity.  Naval electronic facilities are located worldwide,
often in harsh environments.  In many locations maintenance is a problem
because of the lack of skilled labor and the difficulty in obtaining spare
parts.  Systems that are straightforward in concept and design are preferred
to complicated systems that are difficult to operate and maintain.
Equipment Selection.  NAVFAC DM-3.03 provides information
applicable to a variety of system designs.  The following should be noted
a)  Sensible-to-total-heat ratios. Electronic facilities differ
greatly from comfort cooling applications.  The cooling load in electronic
equipment spaces is predominantly sensible; sensible-to-total-heat ratios
approaching one are common.  Cooling coils designed for comfort applications
are inappropriate since they excessively dehumidify equipment spaces to
satisfy the sensible load.  Conversely, air handlers serving electronic
equipment spaces should not serve comfort-cooled areas as well, since they may
not satisfy the latent load in those areas.
b) Fan-coil units.  NAVFAC DM-3.03 notes that fan-coil units
should not be used for comfort cooling in humid climate zones.  Properly
designed, however, they are suitable for electronic equipment spaces.  Vapor
barrier protection should be adequate and outside ventilation air should be
c)  Economizer cycle. NAVFAC DM-3.03 restricts the use of
economizer cycle controls, mainly in relation to the economics of operation.
For electronic equipment areas, however, economizer cycles make precise
control of humidity difficult.  For those applications where no backup cooling
is provided, an economizer cycle does offer a valid means of emergency
cooling, even in warm climates, if no other means are available.
Fuel Selection. In electronic facilities, cooling or waste heat
removal is the predominant mode of operation and heating requirements may be
nonexistent or minimal.  For those applications where additional heating is


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