CEMP-E
TI 810-11
30 November 1998
relays R-XX-01 and R-XX-05, energize relay R-XX-03. One pair of normally open contacts of relay R-
XX-03 connect the output of the minimum outside air flow controller FC-XX-02 to current-to-pneumatic
transducer IP-XX-05, allowing modulation of the minimum outside air damper to maintain the flow at
setpoint. The other pair of normally open contacts of relay R-XX-03 connect the output signal of the
mixed air temperature controller TC-XX-01 to current-to-pneumatic transducer IP-XX-01, if the normally
open contacts of relay R-XX-08 are also closed. Economizer EC-XX-01 controls the action of relay
R-XX-08. The economizer receives signals from outside air temperature transmitter TT-XX-02 and from
return air transmitter TT-XX-03. The difference between the return air temperature and the outside air
temperature controls the DEV contacts, and the return air temperature controls the PV contacts. When
both these contacts are closed, relay R-XX-08 is energized and pilot light PL-XX-03 is turned on. When
relays R-XX-03 and R-XX-08 are both energized, the output of mixed air controller TC-XX-01 is received
by current-to-pneumatic transducer IP-XX-01 and the economizer outside air, relief air, and return air
dampers are modulated to maintain the mixed air temperature controller setpoint.
(4) 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. The auxiliary
contacts of the supply fan starter de-energize relay R-XX-05, and the contacts of relay R-XX-05 in the
return fan starter circuit de-energize the return fan. A set of normally open contacts in low temperature
protection thermostat TSL-XX-01 close, energizing relay R-XX-09 and lighting pilot light PL-XX-05. The
contacts of relay R-XX-09 energize relay R-XX-12 and relay R-XX-13. One set of the contacts of relay
R-XX-12 locks in relays R-XX-12 and R-XX-13, and the normally closed contacts of R-XX-12 de-energize
the supply fan. The normally closed contacts of R-XX-13 in the return fan starter circuit de-energize the
return fan. To restart the fans after a low temperature shutdown, both low temperature thermostat
TSL-XX-01 and the control panel must be manually reset. The control panel is reset by momentarily
depressing manual switch HS-XX-03.
(5) When either smoke detector SMK-XX-01 or smoke detector SMK-XX-02 detects the
presence of smoke, its normally closed contacts in the supply fan starter circuit open, de-energizing the
supply fan. Its normally open contacts close, energizing relay R-XX-10 and turning on pilot light
PL-XX-06. The normally open contacts of R-XX-10 close, energizing relays R-XX-12 and R-XX-13. One
set of contacts of relay R-XX-12 locks in relays R-XX-12 and R-XX-13. The other set of contacts of
R-XX-12 de-energizes the supply fan, and the contacts of relay R-XX-13 de-energize the return fan. To
restart the fans after a smoke alarm shutdown, smoke detectors SMK-XX-01 and/or SMK-XX-02 and the
control panel must be manually reset. The control panel is reset by momentarily depressing manual
switch HS-XX-03.
(6) 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 filter pilot light PL-XX-04.
(7) Differential pressure gauge DPI-XX-03 across the outside air filter provides local indication of
filter loading. On a rise in pressure drop across the filter to its setpoint, differential pressure switch
DPS-XX-03 turns on filter pilot light PL-XX-08.
(8) Temperature controller TC-XX-02, with its temperature transmitter TT-XX-04 in the unit
discharge, through the contacts of relay R-XX-06 and current-to-pneumatic transducer IP-XX-02
modulates cooling coil valve VLV-XX-01 to maintain its temperature setpoint. The contacts of relay
R-XX-06 are closed during the ventilation delay and occupied modes, allowing control. The contacts are
open during the unoccupied mode, the cooling coil valve control signal is interrupted, and the valve
remains closed.
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