18 August 1998
(b) 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.
j. Dual Duct Air Handling System with Hot Water and Chilled Water Coils Sequence of Operation
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
Unoccupied Mode. The dampers will return to their normal positions as shown.
Supply-Fan and Return-Fan Control.
Occupied Mode. Supply and return fans will start in sequence, and will operate
(b) Unoccupied Mode. Supply and return fans will cycle on and off according to the night
setback control setpoint.
(3) Hot-Deck Heating Coil - All modes. The UMCS will modulate the control valve from the
signal of a temperature-sensor located in the coil discharge air to maintain the setpoint. The UMCS will
reset the hot-deck temperature setpoint with respect to the coldest space zone temperature as directed
by the hot deck-cold deck temperature reset program.
(4) Freeze Protection - All Modes. A low temperature device, located as shown, will stop the
supply and return fans, 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
setpoint. Return to the expected mode of operation will require manual reset at the low temperature
device. The UMCS will indicate an alarm condition when the low temperature device trips.
Cold-Deck Cooling Coil.
(a) Occupied Mode. The control valve will be modulated by the UMCS from the signal of a
temperature-sensor located in the coil discharge air to maintain the setpoint. The UMCS will reset the
cold-deck temperature setpoint with respect to the hottest space zone temperature in a linear schedule as
Unoccupied Mode. The UMCS will close the cooling-coil control valve to the coil.
(6) Mixed-Air Temperature Control. When the UMCS places the system in the economizer
operation, it will modulate the dampers from the signal of a temperature sensor in the mixed-air stream to
maintain the setpoint based on the conditions shown in Table 8-18.
Table 8-18. Mixed-Air Damper Modulation.
Modulate OA, RA, and relief
< SA temperature
dampers to maintain mixed air
< Changeover temperature
temperature at cold deck supply
temperature setpoint minus 2