CEMP-E
TI 810-11
30 November 1998
shown. The DDC system shall continue to operate the distribution pump to circulate water through the
system with the boiler shut off. When the system supply water temperature drops below the setpoint
shown, the DDC system shall allow the changeover valves to close to flow through the boiler and to open
to flow through the chiller, and shall place the chiller and the distribution pump under control of the
system time schedule. During the occupied mode, the distribution pump shall operate continuously and
the chiller shall be permitted to operate. When the system is in the unoccupied mode, the chiller shall
shut down. The distribution pump shall continue to operate until the expiration of the time delay.
17. HEATING AND VENTILATING CONTROL SYSTEM.
a. Description of the heating and ventilating system. This air handling system consists of a supply
fan, outside air, return air and relief air dampers, a filter, and a heating coil. Figures 4-13a through 4-13f
show the control system design for this type of air handling system using a SLDC control panel. Figures
4-13g through 4-13j show the control system design for this type of air handling system using DDC
controls.
Figure 4-13a. Control system schematic for heating and ventilating system.
Figure 4-13b. Control system ladder diagram for heating and ventilating system.
Figure 4-13c. Control system equipment for heating and ventilating system.
Figure 4-13d. Control panel interior door layout for heating and ventilating system.
Figure 4-13e. Control panel back panel layout for heating and ventilating system.
Figure 4-13f. Control panel terminal block layout for heating and ventilating system.
Figure 4-13g. DDC control system schematic for heating and ventilating system.
Figure 4-13h. DDC control system ladder diagram for heating and ventilating system.
Figure 4-13i. DDC control system equipment for heating and ventilating system.
Figure 4-13j. DDC control system I/O table and data terminal strip layout for heating and ventilating
system.
b. General sequence of operation.
(1) Supply fan off. When the fan is off, the outside air and relief air dampers are closed and the
return air damper is open. The heating coil valve is under the control of the space temperature
controller.
(2) Supply fan operating. When the supply fan is on, the control dampers and the heating coil
valve are operated as required by the system's mode of operation. The control dampers are either
positioned for full recirculation of air, positioned to introduce minimum outside air, or modulated in
sequence with the heating coil to maintain space temperature. The heating coil is modulated by the
space temperature controller.
4-23
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