DG 1110-3-146
Design Guide: Military Police Facilities
December 1979
General Planning and Design Guidance: Environmental Service Sub-Systems
are on; how much equipment is in the space, and how
(2) Snow Removal In areas where heavy snow
many people are in it. Since all the functional and
accumulations are anticipated, consider the use of
operational requirements and environmental factors
a snow-melting system for all major visitor/staff and
contributing to the heat gain of a space vary with the
on-duty entrances and operational areas and for
time of day and with the use and orientation of the
overhangs above covered guard mount areas.
space, the main problem in air conditioning system
decision is to match the amount of cooling delivered to
d. VENTILATION The ventilation system for a build-
a space to its heat gain and comfort requirements.
ing can be achieved either by natural ventilation or by
This may also Involve reheating of cooled air, however
mechanical ventilation While natural ventilation (oper-
reheating is not permitted where personnel comfort
able windows) is always preferable, it leads to such great
is the only consideration. Reheating may be permitted
restrictions in the efficient use of space that it is not a
where operational effectiveness depends on pre-
significant factor in the design of the building. Mechan-
scribed comfort conditions (e.g., prisoner holding,
ical ventilation Includes the supply, exhaust, and re-
communications center, on-duty operations areas,
circulation of air either by separate or combined sys-
etc.). Air conditioning systems that meet the opera-
tems or both. Typically, an air-handling unit will pull
tional requirements of military police activities must
in fresh outside air, filter, cool or heat it, and deliver it
be designed to set both solar and Internal heat gains.
via ductwork to various spaces. The suction power of
the air-handling unit, aided by the pressure buildup
(1) Room Units lndividual units contain a heating/
in the various spaces, also acts to draw air out of the
cooling coil, air filter and a small fan or induced air
various spaces and, through modulating dampers, ex-
nozzle and provide all the heating and cooling re-
haust all or part of this air to the outside and return
quirements of the space. These units are most com-
the rest to the unit. Return air mixes with fresh air,
monly used in perimeter systems, however, they can
the mixture is filtered and heated, and the mechanical
also be used in interior systems. It is comparatively
ventilation cycle continues. The mixture of fresh and
easy to control the quantity of water to each unit
returned air is normally closer to the desired room
thus, each unit can be made into a separate zone
condition than 100% fresh air, requires less heating,
relatively inexpensively. Another advantage of room
and, therefore, saves energy and costs. Where exhaust
units is that the initial installed cost is less than that
quantities are small, replacement air can be "borrowed"
of an all-air system. The main disadvantage of the
from adjacent spaces, where significant quantities of
room unit system is that no `free cooling is possible
exhaust air are involved (e.g., interior briefing rooms),
as with the all-air system.
a system must be provided to supply makeup air.
(2) Central Air Systems The air conditioning sys-
(1) Requirements Odor removal is the main pur-
tems currently in use represent different methods of
pose of providing fresh air in a ventilation system.
utilizing two basic ways of cooling a space: one is
Hence, exhaust outlets should be located above or
to cool air in a central unit with the refrigeration
close to odor sources and the quantity of air ex-
equipment, and then deliver this air to spaces to be
hausted should be related to the source of the odor.
air conditioned; the other is to cool water and deliver
Thus, the quantity of air exhausted from a toilet or
the water to room units where room air can be blown
detention area is usually 2 cfm per square foot of
past a water coil and be cooled. The requirement of
area, while from a briefing or operations room it is
a good air conditioning system is that it should pro-
usually only 1 cfm per square foot. In the on-duty
vide, in the most economical way possible, the cool-
operations area, some air is exhausted through vents
ing, dehumidification and ventilation requirements
above heat-producing equipment and some from the
of all the various and different spaces in a building.
room in general.
The following four basic central air systems have
possible application to military police facilities.
(2) Special Conditions In air conditioned build-
ings, separate exhaust systems may also be required
(a) Low-Pressure Air is cooled in a central unit
for conference/briefing rooms (smoking, comfort, or
and distributed to various spaces through low-pres-
function) and for odor and heat-producing areas
sure ducts, with a constant air quantity being sup-
such as detention areas and communications rooms.
plied. The amount of cooling provided to any particu-
These exhaust systems may be set up to be in use
lar space can be controlled by varying the volume of
only when the space is occupied. If the area is large
supply air or the temperature difference between the
enough to require a separate supply air system, then
room and the supply air. The different spaces are
the associated return air system can be arranged to
grouped in zones for similar geographic orientation
function as an exhaust system when desired.
and similar use, and the cooled air going to any
particular zone is tempered to match the zone re-
e. AIR CONDITIONING The heat gain of any space,
quirements. A space will be under or over-cooled to
and hence the amount of cooling it needs, depends
the extent that it differs from the average for that
not only on outside temperature conditions and on
zone. Where individual control is essential, con-
how much direct sunlight it gets (solar heat gain),
sideration should also be given to the use of terminal
but also on functional requirements; how many lights
3-20
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