CEMP-E
TI 810-11
30 November 1998
(1) Timeclock CLK-XX-01 has two independent sets of contacts, which between them determine
the mode of system operation. Five minutes before the scheduled beginning of the occupied mode, the
ventilation delay contacts close, energizing relay R-XX-04 and lighting pilot light PL-XX-02. The normally
closed contacts of relay R-XX-04 open, preventing relay R-XX-03 from being energized. The normally
open contacts of relay R-XX-03 prevent any signal from reaching current-to-pneumatic transducers
IP-XX-01 and IP-XX-04. Thus, the dampers remain in their normal positions, with outside air and relief
air dampers closed and return air damper open.
(2) When the timeclock's occupied contacts close, relays R-XX-01 and R-XX-02 are energized
and pilot light PL-XX-01 is turned on. The contacts of relay R-XX-02 energize the supply fan. The
auxiliary contacts of the supply fan starter energize relay R-XX-05 and relay R-XX-07, and, with the
contacts of relay R-XX-01, energize relay R-XX-06. The contacts of relay R-XX-05 are involved in the
energizing of relay R-XX-03 when the ventilation delay mode of operation is over. The contacts of relay
R-XX-06 enable discharge temperature controller TC-XX-02 to control cooling coil valve VLV-XX-01.
The contacts of relay R-XX-07 enable control of the inlet guide vanes on the supply fan. The outside air
and relief air dampers remain closed and the return air damper remains open.
(3) When the ventilation delay contacts of timeclock CLK-XX-01 open to end the ventilation
delay mode of operation, relay R-XX-04 is de-energized and pilot light PL-XX-01 is turned off. The
normally closed contacts of relay R-XX-04, in series with the now closed but normally open contacts of
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-01 to current-to-pneumatic
transducer IP-XX-04, 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. 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. One set of the
contacts of relay R-XX-12 locks in relay R-XX-12, and another set de-energizes the supply fan. To
restart the fan after a low temperature shutdown, both low temperature thermostat TSL-XX01 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 relay R-XX-12. One set of contacts
of relay R-XX-12 locks in relay R-XX-12. The other set of contacts of relay R-XX-12 de-energizes the
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