Central Heating Plants. Refer to MIL-HDBK-1003/6.
Base the total heating system capacity on normal demand rather
than total connected load.
Snow Melting Systems. Provide snow melting systems to
maintain an access area free of snow and ice for such areas as
hospital entrances and hangar doors.
All-Air Systems. Refer to ASHRAE Systems Handbook. In
humid climates, provide all-air systems for air conditioning.
These systems are central systems which provide complete sensible
and latent heating and cooling of the air supply. These systems
are either single path or dual path. Single-path systems have
heating and cooling elements in a series configuration. Dual-
system components at a central location provides increased
opportunity for energy conservation.
Constant-Volume Systems. Use where room conditions are
to be maintained by supplying a constant volume of air to the
space and varying supply air temperature in response to demands
for net space heating or cooling.
a) Applications. In addition to multi-zone systems,
this includes single-zone or single-space applications in
auditoriums, meeting rooms, cafeterias, restaurants, and small
b) Multi-zone Systems. Use these systems to provide
individual temperature control of a small number of zones,
maximum 10 zones, from a central air handler. For normal comfort
cooling applications, place cooling and heating coils in the air
handler. For applications where humidity control is critical,
place coils in series so that air is conditioned by the cooling
coil prior to passing to the hot deck. Provide cooling by
direct-expansion or chilled-water coils. Provide heating by
steam coils, hot water coils, or electric coils.
c) Terminal Reheat Systems. These systems
zoning limitations by adding individual heating coils
zone's branch duct to compensate for areas of unequal
load. Heat, whether in the form of hot water, steam,
electrical resistance heaters, is applied to either
preconditioned primary air or recirculated room air.
(1) These systems waste energy because supply air
is cooled to a low enough temperature to serve the zone needing
the coolest air, but then supply air must be reheated for other
zones to avoid overcooling. Where constant volume is maintained,