MIL-HDBK-1003/3
8.2.5
Operation of Freeze Protection. A freezestat with an
extended surface sensing element, located ahead of the chilled
water coil, shall stop the supply fan, return system components
to their fail-safe position, and initiate a low-temperature alarm
if the temperature at any point of the sensing element falls
below the setpoint. Normal operation will occur only after the
freezing condition is corrected and the freezestat is manually
reset.
8.2.6
Operation of Smoke Detectors. Duct type smoke
detectors located in the supply fan discharge air duct and in the
return air duct (as required by NFPA) shall stop the supply fan,
return system components to their fail-safe position, and shall
activate the smoke alarm if either detector senses the presence
of smoke. Normal operation will occur only after the smoke is
cleared and the detector(s) is manually reset.
8.2.7
Operation of Chilled Water Coil Discharge Control. A
dry bulb temperature sensor located in the chilled water coil
discharge air shall, on a rise in temperature, first, gradually
close the preheat coil valve, next, gradually open the outside
air damper from its minimum ventilation air position while
simultaneously gradually close the return air damper (ensure
thorough mixing) and gradually opening the exhaust air damper,
and then gradually open the chilled water coil valve. An outdoor
air dry bulb sensor disables the economizer cycle and maintains
minimum ventilation air when outside air dry bulb temperature
exceeds the changeover point.
8.2.8
Operation of Preheat Coil Control. (Where required by
outdoor design temperatures and ventilation air requirements.)
A dry bulb temperature low limit sensor located in the mixed air
(ensure thorough mixing) shall, on a fall in temperature,
gradually open the preheat coil valve. Primary control shall be
sequenced by the chilled water coil discharge sensor or supply
air sensor.
8.2.9
Operation of Heating Coil Control. A dry bulb
temperature sensor located in the heating coil discharge air
shall, on a rise in dry bulb air temperature, gradually close the
heating coil valve.
8.2.10
Operation of Space Control (Single Zone Unit). A room
type dry bulb temperature sensor located in the most critical
spot shall, on a rise in dry bulb temperature in the space, first
gradually close the heating coil valve, next gradually close the
preheat coil valve, then gradually open the outside air damper
from its minimum ventilation air position while simultaneously
gradually close the return air damper (ensure thorough mixing)
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