30 November 1998
switch MPS-XX-01 or under control of space temperature controller TC-XX-01, whichever signal is
(4) Temperature controller TC-XX-01, with its temperature transmitter in the space served,
through current-to-pneumatic transducer IP-XX-02, modulates heating coil valve VLV-XX-01, and during
the occupied mode after the expiration of the ventilation delay mode, modulates the control dampers in
sequence with the heating coil valve to maintain the temperature controller setpoint.
(5) On a fall in temperature to its setpoint, low temperature protection thermostat TSL-XX-01
opens a set of closed contacts in the supply fan circuit, de-energizing the supply fan. Through its open
contacts, thermostat TSL-XX-01 energizes relay R-XX-05 and lights pilot light PL-XX-04. The contacts of
relay R-XX-05 energize relay R-XX-07. The normally closed contacts of relay R-XX-07 de-energize the
supply fan, the normally open contacts lock in relay R-XX-07. To restart the fan after a low temperature
shutdown, both the low temperature protection thermostat TSL-XX-01 and the control panel must be
reset. The control panel is reset by depressing manual switch HS-XX-02.
(6) Whenever smoke detector SMK-XX-01 or smoke detector SMK-XX-02 detects the presence
of smoke, its normally closed contacts in the supply fan start circuit open, de-energizing the fan. The
normally open contacts close, energizing relay R-XX-06 and lighting pilot light PL-XX-05. Normally open
contacts of relay R-XX-06 close, energizing relay R-XX-07. Normally closed contacts of relay R-XX-07 in
the supply fan start circuit open, and the normally open contacts close to lock in relay R-XX-07. To
restart the fan after a smoke shutdown, smoke detectors SMK-XX-01 and/or SMK-XX-02 and the control
panel must be reset. The control panel is reset by depressing manual switch HS-XX-02.
(7) Differential pressure gauge DPI-XX-01 across the filter provides local indication of filter
loading. On a rise in pressure drop across the filter to its setpoint, differential pressure switch
DPS-XX-01 turns on pilot light PL-XX-03.
(8) At the conclusion of the occupied mode, the occupied contacts of time clock CLK-XX-01
open, and relay R-XX-01 is de-energized. The contacts of relay R-XX-01 open, de-energizing the supply
fan and placing it under the control of the night thermostat TSL-XX-02.
d. Sequence of operation for DDC applications.
(1) Ventilation delay mode timing shall start prior to the occupied mode timing. During
ventilation delay mode, the DDC system shall prevent the outside air damper from opening. At the time
shown, the DDC system shall place the system in the occupied mode. At the expiration of the ventilation
delay mode timing period, the DDC system shall place the outside air, return air, and relief air dampers
under space temperature control. At the time shown, the DDC system shall place the control system in
the unoccupied mode of operation and the dampers shall return to their normal positions.
(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