CEMP-E
TI 810-11
30 November 1998
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's high-temperature hot
water control valve to maintain the reset schedule setpoint in the hydronic heating supply line.
(3) When the cooling mode is selected, the converter high-temperature hot water control valve
shall be closed. The DDC system shall accept a signal from a temperature sensing element and
transmitter located in the system return as shown. The DDC system shall continue to operate pump to
circulate water through the system. When the system return water temperature drops below the setpoint
shown, the DDC system shall allow the changeover valves to close to flow through the converter and to
open to the central plant chilled water flow, and place the control of pump under control of the system
time schedule. During the occupied mode, pump shall operate continuously. In the unoccupied mode,
pump shall stop.
16. SINGLE BUILDING DUAL-TEMPERATURE HYDRONIC CONTROL SYSTEM.
a. Description of the hydronic system. This hydronic heating and cooling system consists of a boiler,
chiller, pump and distribution piping. This system varies the hot water flow through the boiler.
Therefore, it can be used only with boilers that are not sensitive to flow variation. A variation of this
system which utilizes constant flow through the boiler is depicted in Chapter 5. Figures 4-12a through 4-
12f show the control system design for this type of hydronic system using a SLDC control panel. Figures
4-12g through 4-12j show the control system design for this type of hydronic system using DDC controls.
Figure 4-12a. Control system schematic for single building dual-temperature hydronic system.
Figure 4-12b. Control system ladder diagram for single building dual-temperature hydronic system.
Figure 4-12c. Control system equipment for single building dual-temperature hydronic system.
Figure 4-12d. Control panel interior door layout for single building dual-temperature hydronic system.
Figure 4-12e. Control panel back panel layout for single building dual-temperature hydronic system.
Figure 4-12f. Control panel terminal block layout for single building dual-temperature hydronic system.
Figure 4-12g. DDC control system schematic for single building dual-temperature hydronic system.
Figure 4-12h. DDC control system ladder diagram for single building dual-temperature hydronic system.
Figure 4-12i. DDC control system equipment for single building dual-temperature hydronic system.
Figure 4-12j. DDC control system I/O table and data terminal strip layout for single building dual-
temperature hydronic system.
b. General sequence of operation.
(1) Heating and cooling modes are manually selected at the control panel. The position of the
dual-temperature changeover valves is manually selected at the control panel.
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