CEMP-E
TI 811-12
18 August 1998
Table 8-19. Mixed-Air Damper Modulation.
Condition No.
Description
Control
1
OA temperature
Modulate OA, RA, and relief
< SA temperature
dampers to maintain mixed air
< Changeover temperature
temperature at cold deck supply
temperature setpoint minus 2
degrees F.
2
SA temperature
Set OA and relief dampers at
< OA temperature
100% open; RA dampers closed.
< Changeover temperature
3
SA temperature
Set OA and relief dampers at their
< Changeover temperature
minimum positions, and set RA
< OA temperature
damper at its corresponding open
position.
(6) Zone-Damper and Heating Coil Control - All Modes. A space temperature sensor for each
zone will signal the UMCS to modulate the zone-mixing damper and heating coil valve to heat and cool its
respective zone by mixing cold-deck air and bypass-deck air to maintain the zone setpoint. On a rise in
space temperature, the heating coil valve will gradually close, and after a selected dead band the bypass-
deck damper will gradually close, and the cold-deck damper will gradually open in sequence.
(7) Smoke Control. Smoke detectors in the supply-air and return-air ductwork will stop the
supply fan and the return fan and initiate a smoke alarm if smoke is detected at either location. Restarting
the supply fan and the return fan will require manual reset at the smoke detectors.
l. VAV Air Handling System with Hot Water and Chilled Water Coils Sequence of Operation (Figure
(1)
Outside-Air, Return-Air, and Relief-Air Dampers.
(a) Occupied Mode. The minimum outside-air damper will open. The maximum outside-
air, return-air, and relief-air dampers will be modulated under mixed-air temperature and economizer
control.
(b)
Unoccupied Mode. The dampers will return to their normal positions as shown.
(2)
Supply-Fan Control.
(a)
Occupied Mode. The supply fan will start and will operate continuously.
(b) Unoccupied Mode. The supply fan will cycle on and off according to the night setback
schedule setpoint.
(3) Supply-Duct Pressure Control. When the supply fan starts, the UMCS will modulate the fan
inlet vanes from the signal of a static pressure sensor to maintain the setpoint. When the fan is off the
inlet vanes will be closed.
(4) Freeze Protection - All Modes. A low temperature device, located as shown, will stop the
supply fan, cause the outside-air, return-air, and relief-air dampers to return to their normal position, and
will initiate a low-temperature alarm if the temperature drops below the low temperature device's setpoint.
8-8
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