CEMP-E
TI 810-11
30 November 1998
temperature decreases, the damper shall gradually close to the minimum flow position to maintain the
cooling setpoint as shown. When the space temperature calls for heating after the minimum flow
position is reached, control shall then pass through a temperature dead band as shown. When the space
temperature has dropped through the dead band, the duct heater coil shall be gradually controlled to
maintain the heating setpoint as shown.
23. SINGLE ZONE HVAC CONTROL SYSTEM.
a. Description of the HVAC system. The air handling system consists of a supply fan, economizer
dampers, filter, heating coil, and cooling coil. Figures 4-19a through 4-19f show the control system
design for this type of air handling system using a SLDC control panel. Figures 4-19g through 4-19j
show the control system design for this type of air handling system using DDC controls.
Figure 4-19a. Control system schematic for single zone HVAC system.
Figure 4-19b. Control system ladder diagram for single zone HVAC system.
Figure 4-19c. Control system equipment for single zone HVAC system.
Figure 4-19d. Control panel interior door layout for single zone HVAC system.
Figure 4-19e. Control panel back panel layout for single zone HVAC system.
Figure 4-19f. Control panel terminal block layout for single zone HVAC system.
Figure 4-19g. DDC control system schematic for single zone HVAC system.
Figure 4-19h. DDC control system ladder diagram for single zone HVAC system.
Figure 4-19i. DDC control system equipment for single zone HVAC system.
Figure 4-19j. DDC control system I/O table and data terminal strip layout for single zone HVAC system.
b. General sequence of operation.
(1) Supply fan off. When the fan is off, the cooling coil valve and the outside air and relief air
dampers are closed, and the return air damper is open. The heating coil valve remains under space
temperature control.
(2) Supply fan operating. When the fan is on, the control dampers and the cooling coil valve are
operated as required by the system's operational modes. The control dampers are positioned for full
recirculation of air, positioned to introduce minimum outside air, or modulated to maintain space
temperature. The cooling coil valve is either closed, or modulated to maintain space temperature.
(3) Control of supply fan. Unless the fan is stopped as the result of a safety shutdown, it is on or
off as required by the control system mode of operation.
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