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Supplv Zone 4 (S-4)
The S-4 supply air system is located on the roof of Building 991 and supplies ventilation
for Rooms 101, 132, 134, 135 and 136. The S-4 supply system has been inoperable for the past
five years.
Outside air enters the S-4 plenum through a set of dampers that open when the fan is
started. The air then passes through a stage of fimace filters and to a preheat coil. A controller,
located on the East Dock, will start pump P-4 if the air temperature is less than 55°F and
circulate heating water through a three-way valve and the preheat coils. A pneumatic controller
located in the S-4 cabinet on the west wall of Room 130 will modulate the three-way valve for a
discharge temperature of 55°F. Pump P-7 operates to supply heating water to the preheat coils.
A freezestat is located on the side of the plenum to stop the S-4 fan and shut the outside dampers
if the air discharge from the preheat coils drops below 35°F. If the freezestat engages it must be
reset before the supply fan can be restarted. The supply air then passes through an air
conditioning D/X coil for cooling if need. The air conditioning is controlled by the thermostat in
the warmest zone by opening the liquid line solenoid valve to the D/X coil. The S-4 fan then
discharges to the three zones through a reheat coil for each zone. Heating water to the coil is
controlled by a room thermostat and a pneumatic valve. Reheat pump P-5 operates to supply
heating water to the reheat coil.
Suuplv Zone 5 6-5)
The S-5 supply system is located in Room 402 and supplies the Buildings 996, 997 and
999 (vaults and corridors). The S-5 supply system is inoperable due to need to replace belts.
This system draws outside air through a set of dampers that open when the fan is started.
The air then passes through a stage of Mace filters and then through a heating coil that
operates if the outside air temperature is less than 60°F. A heating water pump (P-5) circulates
heating water through a three-way valve and the coil to control the fan discharge temperature to
60°F. A controller located on the plenum is used to sense the outside air temperature and start
P-5 if the temperature drops below 60°F. Pump P-7 operates to supply heating water to the
preheat coils. The supply fan discharges into the tunnel complex and supplies the rooms of the
vaults. The S-5 system has no cooling or reheat coils.
S-5 is interlocked with the Building 985 exhaust fans such that if the exhaust fans stop,
air supply from S-5 will stop.
Supplv Zone 6 (S-6)
The S-6 supply system has been removed and the area it supplied on the north side of the
building has been connected to Zone 6 and Zone 9 on the S-1 system.
Revision
Building 991 Complex FSAR
Swtcmher 1999 I
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