CEMP-E
TI 810-11
30 November 1998
(2) During occupied and ventilation delay modes the supply fan shall operate continuously.
During unoccupied mode the supply fan shall cycle according to the night setback schedule. The fan
shall start and stop at the setpoints as shown.
(3) A differential pressure switch across the filter shall initiate a filter alarm when the pressure
drop across the filter exceeds the setpoint as shown.
(4) A freezestat, located as shown, shall stop the supply fan, cause the outside air, return air,
and relief air dampers to return to their normal position, and shall initiate a low temperature alarm if the
temperature drops below the freezestat's setpoint. Return to the normal mode of operation shall require
manual reset at the freezestat. The DDC panel shall monitor the freezestat through auxiliary contacts
and shall indicate an alarm condition when the freezestat trips.
(5) Smoke Detectors in the supply air and return air ductwork shall stop the supply fan and
initiate a smoke alarm if smoke is detected at either location. Restarting the supply fan shall require
manual reset at the smoke detector.
(6) The DDC system shall accept the signal of an outside air temperature sensing element and
transmitter and the signal of a return air temperature sensing element and transmitter. The DDC system
shall perform switch over between outside air economizer control mode and minimum outside air mode.
Until the outside air temperature rises above the setpoint, the DDC system shall hold the system in the
minimum outside air mode. When the outside air temperature rises above the setpoint, the DDC system
shall place the AHU in the economizer mode or in the minimum outside air mode as determined by a
comparison of the outside air and return air temperatures in accordance with the differential temperature
setpoints as shown. When the outside air temperature is low with respect to the return air temperature,
the AHU shall be in the economizer mode. When the DDC system places the control system in the
minimum outside air mode, the outside air damper shall be open to the minimum outdoor air setting.
When the DDC system places the system in the economizer mode, the dampers shall be modulated to
admit additional outside air to maintain the space temperature setpoint as shown.
(7) The DDC system shall select the heating and cooling modes based on input from a
temperature sensor and transmitter located in the dual-temperature supply. When the dual-temperature
supply temperature is above the setpoint, the DDC panel shall operate the dual-temperature coil valve as
a heating coil valve in sequence with the outside air, return air, and relief air dampers. When the
dual-temperature supply temperature is below the setpoint, the DDC panel shall operate the
dual-temperature coil valve as a cooling coil valve in sequence with the outside air, return air, and relief
air dampers.
(8) When the DDC system is operating the system in heating mode, space temperature shall be
control led as follows.
(a) When the DDC system is in the economizer mode, it shall maintain the setpoint from the
signal of a space temperature sensor and transmitter. On a rise in space temperature, the DDC system
shall first gradually close the coil valve. After passing through a deadband, the DDC system shall then
gradually operate the outside air damper to admit outside air beyond the minimum quantity to maintain
the setpoint as shown.
(b) When the DDC system is in the minimum outside air mode, the outside air damper shall
be open to the minimum outside air setting. On a rise in space temperature, the DDC system shall
gradually close the coil valve to maintain the setpoint as shown.
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