CEMP-E
TI 810-11
30 November 1998
(3) The hot water supply temperature controller maintains its setpoint by modulating the
converter valve to maintain the scheduled temperature.
(4) When the system is indexed to cooling, the converter valve closes. The pump continues to
run for cooldown and when the return water temperature falls to 29 degrees C (85 degrees F), the
changeover valves transfer the water flow from the converter to the central plant chilled water system.
(5) As long as the heating/cooling switch is indexed to cooling, the pump will be energized
during the occupied mode and de-energized during the unoccupied mode.
c. Detailed sequence of operation.
(1) Manual switch HS-XX-02 provides for indexing the system to the heating or the cooling
mode.
(2) When heating/cooling switch HS-XX-02 is indexed from heating to cooling, relay R-XX-02 is
de-energized, and relay R-XX-05 is energized. Contacts of relay R-XX-05 open, removing control from
the converter valve, which then closes. Through the normally closed contacts of relay R-XX-02 and the
normally open contacts of relay R-XX-06, pump relay R-XX-07 is energized and the pump runs to
distribute the hot water in order to reduce its temperature. When the return water temperature falls to the
setpoint of TSL-XX-01, the solenoid actuated pneumatic valve EP-XX-01 and relay R-XX-06 are
energized, and cooling pilot light PL-XX-03 is turned on. Through EP-XX-01, changeover valves
VLV-XX-02 and VLV-XX-03 stop the flow to and from the converter, and open the system to the central
plant chilled water system. The normally closed contacts of relay R-XX-06 (line 13) open to stop the
pump, but the normally open contacts of that relay (line 12) close. If occupied relay R-XX-01 is
energized, the pump continues to run.
(3) Throughout the cooling mode, pump relay R-XX-07, through the normally closed contacts of
relay R-XX-02 and the normally open contacts of relay R-XX-06, is energized during the occupied mode
and de-energized during the unoccupied mode by the contacts of relay R-XX-01.
(4) When heating/cooling switch HS-XX-02 is indexed from cooling to heating, relays R-XX-05
and R-XX-06 and solenoid actuated pneumatic valve EP-XX-01 are de-energized, cooling pilot light
PL-XX-03 is turned off, and relay R-XX-02 is energized. When EP-XX-01 is de-energized, valves
VLV-XX-02 and VLV-XX-03 open the system to the converter and close it to the central plant chilled
water system.
(5) On a fall in outside air temperature to the setpoint of the PV contacts of controller TC-XX-01,
relay R-XX-04 is energized and heating pilot light PL-XX-02 is turned on. The contacts of relay R-XX-04
(line 11), which are closed throughout the heating mode, energize relay R-XX-07. The contacts of relay
R-XX-07 energize the system pump. Pump starter auxiliary contacts, through the normally closed
contacts of relay R-XX-05 (line 4) energize relay R-XX-03, and the contacts of relay R-XX-03 connect the
output of temperature controller TC-XX-02 to current-to-pneumatic transducer IP-XX-01. The transducer
output modulates hot water converter valve VLV-XX-01. On a rise in outdoor air temperature to 17
degrees C (62 degrees F), the PV contacts of controller TC-XX-01 open, and relay R-XX-04 is de-
energized, de-energizing relay R-XX-07 and stopping the pump. Pump starter auxiliary contacts remove
the converter valve from control, and the converter valve closes.
4-16
Previous Page
