CEMP-E
TI 811-12
18 August 1998
(a)
Occupied Mode. Supply and return fans will start in sequence, and will operate
continuously.
(b) Unoccupied Mode. Supply and return fans will be cycled 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-sensing element and transmitter 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 signal 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
device 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.
(5)
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 as directed by the hot
deck-cold deck temperature reset program.
(b)
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 8-17.
Table 8-17. 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.
(a) Zone-Damper Control - All Modes. A space temperature sensor for each zone will
signal the UMCS to gradually operate the zone-mixing damper to heat and cool its respective zone by
mixing cold-deck air and hot-deck air to maintain the zone setpoint. On a rise in space temperature, the
hot-deck damper will gradually close, and the cold-deck damper will gradually open.
8-5
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