18 August 1998
minimum-flow position to its full-flow position from the signal of a space temperature sensing element and
transmitter. When the space temperature decreases, the damper will gradually close. If the space
temperature continues to drop after the damper has reached its minimum-flow position, the reheat coil
valve will be controlled to maintain the space temperature setpoint.
(9) 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.
n. Single Zone Air Handling System with Hot Water/Chilled Water Coils and Humidification
Outside-Air, Return-Air, and Relief-Air Dampers.
(a) Occupied Mode. The minimum outside air will open. The maximum outside-air, return-
air, and relief-air dampers will be modulated under mixed-air temperature and economizer control.
Unoccupied Mode. The dampers will return to their normal positions as shown.
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
(c) 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 device's setpoint as shown. Return to the normal mode of operation will require manual
reset at the low temperature device. The UMCS panel will indicate an alarm condition when the low
temperature device trips.
Cooling Coil and Heating Coil Control.
(a) Occupied Mode. The control valves will be modulated in sequence by the UMCS from
the signal of the space temperature sensor to maintain its setpoint. On a rise in space temperature, the
UMCS will gradually close the heating-coil valve and after passing through a deadband, the UMCS will
gradually operate the outside-air damper to admit outside-air beyond the minimum quantity. After the
outside air damper is fully open the UMCS will then operate the cooling-coil valve to maintain the setpoint
(b) Unoccupied Mode - The UMCS will close the cooling-coil control valve to the coil and
will open the heating-coil control valve to the coil.
(4) Mixed-Air Temperature Control. When the UMCS places the system in the economizer
operation, it will modulate the dampers from the signal of the space temperature sensor to maintain the
setpoint based on the conditions shown in Table 8-22.
Table 8-22. Mixed-Air Damper Modulation.
Modulate OA and relief dampers
< Changeover temperature
open, and the RA dampers closed
to maintain the space temperature