DG 1110-3-146
Design Guide: Military Police Facilities
December 1979
General Planning and Design Guidance: Environmental Service Sub-Systems
acoustic lining in all ducts serving operational
units with low velocity control as a means of providing
spaces, such as on-duty desk areas, interview and
variable air volume systems.
investigation areas and briefing/conference rooms.
(b) Multi-Zone In a central unit, some of the air
Noise generated by air outlets should be controlled
is cooled while the remainder is heated. The various
by the proper selection and location of these outlets,
spaces to air condition are grouped in zones, and a
both for noise and for draft-free operation. However,
separate low-pressure duct runs from the central unit
in corridors and in administrative office areas it may
to each zone. The cooling required by each zone can
be necessary for the air outlets to create some noise.
thus be varied by adjusting the proportion of heated
This is necessary in order to raise the ambient noise
and cooled air going to that zone.
level to a level which achieves the overall confi-
(c) High-Pressure, Single Duct Air is cooled in a
dentiality and acoustic security required of law en-
central air unit distributed through high-pressure
forcement activities. Too low an ambient noise level
ducts, reduced in pressure by air pressure-reducing
encourages improper and unintentional eavesdrop-
boxes, and delivered to the various spaces through
ping. The installed system should be tuned to the
low-pressure ducts. The cooling provided to any
desirable ambient noise level within a design range
particular space can be varied by adjusting the
that is still protective of acoustically sensitive police
volume of air delivered to the space and/or by heat-
operations. Reference TM 5-805-4 and ASHRAE
ing this cooled air.
Guide.
(d) High-Pressure, Dual Duct In a central unit,
(3) Temperature Control Generally, HVAC sys-
some of the air is cooled while the remainder is
tems require that some means be provided for auto-
heated. This air is then carried in separate high-
matically regulating the heating and/or cooling
pressure ducts to dual-duct air pressure-reducing
requirements of individual spaces. This can be
boxes called mixing boxes, where the hot and cold
achieved by pneumatic, electric, or electronic sys-
air streams are reduced in pressure and mixed to
tems. or a combination of these. A control system
meet the cooling requirements of the space served
will function only within the limitations of the system
by that particular box.
it serves. Thus, in a fan-coil unit system, if the north
and east units are combined into one zone, the auto-
f. OPERATIONAL REQUIREMENTS Where certain
matic temperature controls cannot provide cooling
buildings are not to be air conditioned (cooled) based
of the east units and heating of the north units.
on the weather zone criteria comfort, cooling criteria
should be superceded by operational requirements.
(4) Humidity Control The process of cooling air is
Generally, the on-duty operations area of the facility
always accompanied by dehumidification, thus dur-
will require air conditioning or mechanical ventilation
ing the cooling season humidity control is not a
in order to maintain maximum operational effective-
major problem However. reducing the amount of air
ness, The following factors should be considered in
delivered to rooms. as in a variable volume system,
determining the operational requirements of HVAC
will result in a decrease in its dehumidification capa-
systems.
bility. Too great a reduction of air may cause a
humidity problem. For this reason, in spaces where
(1) Noise Any air conditioning system must be de-
evidence or records are stored or where groups of
signed so that the nose generated by the system is
people work or gather, some form of reheat is always
not objectionable. Noise is produced by the opera-
used. Reheating allows humidity to decrease. During
tion of the equipment, by the movement of air and
the heating season. relative humidity inside a building
water through ducts and pipes respectively, and by
can get too low due to the heating of the air. At
the passage of air through air outlets. Where auditory
this time, moisture must be added to the air to raise
disturbances or physical vibrations can affect the
the humidity level for two reasons first, because a
quality of operations, such as in the communications
too low humidity dries the skin and causes discom-
room undesirable equipment noise should be mini-
fort: second, because a higher humidity enables the
mized by selecting well-Insulated equipment that is
room temperature to be maintained at a lower level
quiet in operation. In addition, residual noise dis-
for the same degree of comfort, thus saving fuel
turbance can be eliminated by requiring that equip-
costs.
ment should be Installed on spring or rubber vibra-
tion isolators. In some cases, such as with fans and
g. SYSTEM SELECTION In selecting an HVAC sys-
pumps, it may be necessary to mount the equipment
tem for military police facilities, consider each of the
on thick concrete pads and then mount the entire
systems discussed above in terms of the needed indi-
assembly on vibration Isolators. In addition, piping
vidual functional activities and the operational require-
that may vibrate should be Isolated from the equip-
ments of spaces served by perimeter and interior sys-
ment and from the building structure.
tems. Tables 3-5 and 3-6 provide general guidance in
selecting an appropriate HVAC system. In general,
select the least costly and most efficient system in terms
movement of air through ducts should be controlled
of energy consumption and required maintanance.
by the use of acoustic lining in the ductwork and/or
3-21
Previous Page
