CEMP-E
TI 810-11
30 November 1998
Figure 4-8d. Control panel interior door layout for single building hydronic heating system with hot water
boiler.
Figure 4-8e. Control panel back panel layout for single building hydronic heating system with hot water
boiler.
Figure 4-8f. Control panel terminal block layout for single building hydronic heating system with hot water
boiler.
Figure 4-8g. DDC control system schematic for single building hydronic heating system with hot water
boiler.
Figure 4-8h. DDC control system ladder diagram for single building hydronic heating system with hot
water boiler.
Figure 4-8i. DDC control system equipment for single building hydronic heating system with hot water
boiler.
Figure 4-8j. DDC control system I/O table and data terminal strip layout for single building hydronic
heating system with hot water boiler.
b. General Sequence of Operation.
(1) The primary pumping system and the boiler operate continuously whenever the outside air
temperature is low enough for the building to require heating. When this occurs, an outside air
temperature controller starts the primary pump, enables the boiler to function under its own control
system to maintain a constant boiler water temperature, and enables the secondary pump to operate.
The outside air temperature controller raises the primary hot water supply temperature as the outside air
temperature falls.
(2) The primary hot water supply temperature controller maintains its setpoint by modulating a
valve to mix hot water from the boiler with return water from the primary pumping system to maintain the
scheduled primary hot water supply temperature.
(3) During the occupied mode, the secondary hot water pumps run whenever the primary hot
water pumps run. Each zone temperature controller modulates its zone control valve to blend primary
hot water supply with secondary hot water return in order to maintain the zone's space temperature
setpoint, which is adjustable by the zone occupant.
(4) During the unoccupied mode, the secondary hot water pumps are cycled by the zone's night
thermostat to maintain the low limit setpoint and to prevent freezing. During this mode, the controller
setpoint is determined by an adjustment within the system's HVAC control panel.
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