CEMP-E
TI 811-12
18 August 1998
Return to the normal 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.
(5)
Cooling-Deck Coil and Preheat Coil Control.
(a) Occupied Mode. The control valves will be modulated in sequence by the UMCS from
the signal of a temperature-sensor located in the fan discharge- air duct to maintain the setpoint.
(b) Unoccupied Mode. The UMCS will close the cooling-coil control valve to the coil and
will open the preheat-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 8-20.
Table 8-20. 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.
Set OA and relief dampers at
2
SA temperature
100% open; RA dampers closed.
< OA temperature
< Changeover temperature
Set OA and relief dampers at their
3
SA temperature
minimum positions, and set RA
< Changeover temperature
damper at its corresponding open
< OA temperature
position.
(7) Pressure-Independent VAV Terminal Box Control. The control damper in the VAV box will
modulate in response to the signal from a flow-sensing element (at the inlet or discharge of the VAV
terminal box) to the UMCS Unitary Controller. The UMCS will control the VAV box damper from its
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.
(8) Smoke Control. Smoke detectors in the supply-air and return-air ductwork will stop the
supply fan and initiate a smoke alarm if smoke is detected at either location. Restarting the supply fan
will require manual reset at the smoke detectors.
m. VAV Air Handling System with Return Fan and Hot Water/Chilled Water Coils Sequence of
Operation (Figure 8-13 and Table 8-13).
(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.
8-9
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