30 November 1998
stop both secondary pumps. The auxiliary contacts of the primary pump starter open, de-energizing
relay R-XX-06. The contacts of relay R-XX-06 remove valve VLV-XX-01 from control, and it closes.
(3) Controller TC-XX-01 raises the setpoint of primary hot water supply temperature controller
TC-XX-02 as the outside air temperature falls, and lowers the setpoint as outside air temperature rises.
(4) Temperature transmitter TT-XX-02 signals the primary hot water supply temperature to
temperature controller TC-XX-02. Controller TC-XX-02 maintains its setpoint by varying its signal to
current-to-pneumatic transducer IP-XX-01. The pneumatic signal from IP-XX-01 modulates high-
temperature hot water converter valve VLV-XX-01 to maintain the primary supply water temperature
setpoint of controller TC-XX-02.
(5) Temperature transmitter TT-XX-03 signals the zone space temperature to controller
TC-XX-03. Controller TC-XX-03 maintains its setpoint by varying its current output signal to transducer
IP-XX-02. The pneumatic signal from IP-XX-02 modulates secondary zone control valve VLV-XX-02,
which mixes primary supply water with secondary return water to maintain the zone space temperature
setpoint. The temperature control loop for the other secondary zone functions identically.
(6) Throughout the occupied mode, the contacts of time clock CLK-XX-01 are closed to energize
relays R-XX-01, R-XX-02, and R-XX-03, and to turn on pilot light PL-XX-01. The contacts of relay
R-XX-01 connect temperature setpoint device TSP-XX-01 to allow manual adjustment of the setpoint of
temperature controller TC-XX-03. Relay R-XX-02 provides the same function for TSP-XX-03 in
adjustment of controller TC-XX-04. Relay R-XX-03 closes contacts in the starter control circuits of the
secondary pumps. The secondary system pumps will start whenever the contacts of relay R-XX-03
(occupied) and R-XX-05 (heating) are closed in their respective pump starter circuits.
(7) During the unoccupied mode, the contacts of time clock CLK-XX-01 are open and de-
energize relays R-XX-01, R-XX-02, and R-XX-03, and pilot light PL-XX-01 turns off. The transfer of the
contacts of relay R-XX-01 transfers the temperature setpoint adjustment of TC-XX-03 from TSP-XX-01 to
TSP-XX-02. The transfer of the contacts of relay R-XX-02 transfers TC-XX-04 temperature setpoint
adjustment from TSP-XX-03 to TSP-XX-04. The contacts of relay R-XX-03 open the secondary pump
starter circuits to place the secondary pumps under the respective night thermostats TSL-XX-01 and
TSL-XX-02. When the zone space temperature falls to 13 degrees C (55 degrees F), the zone
secondary pump is energized and remains energized until the temperature rises to 14 degrees C (57
d. Sequence of operation for DDC applications.
(1) The DDC system shall accept a signal from a sunshielded outside air temperature sensing
element and transmitter located as shown. The DDC system shall start and stop the pumps at the
outside air temperatures shown. The DDC system shall reset the hydronic heating supply temperature
setpoint in a linear schedule based on the outside air temperature as shown. The DDC system shall
accept a signal from a temperature sensing element and transmitter located in the hydronic heating
supply line and the DDC system output shall modulate the converter high-temperature hot water control
valve to maintain the reset schedule setpoint in the hydronic heating supply line.
(2) When the system time schedule places the system in the occupied mode, a space
temperature sensing element and transmitter located as shown shall signal the DDC system, which shall