CEMP-E
TI 810-11
30 November 1998
(9) When the DDC system is operating the system in cooling mode, space temperature shall be
controlled as follows.
(a) When the DDC system is in the economizer mode, it shall maintain the setpoint from the
signal of a space temperature sensor and transmitter. On a rise in space temperature, the DDC system
shall first gradually open the outside air damper to admit outside air beyond the minimum quantity.
When the outside air damper is fully open, on a further rise in space temperature, the DDC system shall
gradually open the coil valve.
(b) When the DDC system is in the minimum outside air mode, the outside air damper shall
be open to the minimum outside air setting. On a rise in space temperature, the DDC system shall
gradually open the coil valve to maintain the setpoint.
25. SINGLE ZONE HVAC CONTROL SYSTEM WITH HUMIDITY CONTROL.
a. Description of the HVAC system. This air handling system consists of a supply fan, filter, preheat
coil, cooling coil, reheat coil, and humidifier. The system also has a steam-to-water heat exchanger and
pump to supply hot water to the preheat and reheat coils. Figures 4-21a through 4-21f show the control
system design for this type of air handling system using a SLDC control panel. Figures 4-21g through
4-21j show the control system design for this type of air handling system using DDC controls.
Figure 4-21a. Control system schematic for single zone HVAC system with humidity control.
Figure 4-21b. Control system ladder diagram for single zone HVAC system with humidity control.
Figure 4-21c. Control system equipment for single zone HVAC system with humidity control.
Figure 4-21d. Control panel interior door layout for single zone HVAC system with humidity control.
Figure 4-21e. Control panel back panel layout for single zone HVAC system with humidity control.
Figure 4-21f. Control panel terminal block layout for single zone HVAC system with humidity control.
Figure 4-21g. DDC control system schematic for single zone HVAC system with humidity control.
Figure 4-21h. DDC control system ladder diagram for single zone HVAC system with humidity control.
Figure 4-21i. DDC control system equipment for single zone HVAC system with humidity control.
Figure 4-21j. DDC control system I/O table and data terminal strip layout for single zone HVAC system
with humidity control.
b. General sequence of operation.
(1) Supply fan off. When the fan is off, the outside air damper and the cooling coil, humidifier
and heat exchanger valves are all closed, and the pump is off. The reheat coil valve remains under
space temperature control.
4-61
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