CEMP-E
TI 810-11
30 November 1998
the AHU shall be in the economizer mode. When the DDC system places the control system in the
minimum outside air mode, the outside air damper shall be open to the minimum outdoor air setting.
When the DDC system places the system in the economizer mode, the dampers shall be modulated to
admit additional outside air to maintain the space temperature setpoint as shown.
(7) Space temperature control shall be maintained as follows.
(a) During unoccupied mode, the dampers shall remain in their normal positions as shown
and the cooling coil valve shall remain closed. The supply fan shall be cycled by the system's night
thermostat and the heating coil valve shall be modulated to maintain the space temperature low limit
setpoint.
(b) During occupied mode, the supply fan shall run continuously and the heating and cooling
coil valves shall be under space temperature control. While the system is in ventilation delay mode, the
dampers shall remain in their normal position unless the system is also calling for economizer operation.
When the DDC system is in economizer mode, on a rise in space temperature, the DDC system shall
first gradually close the heating coil valve. After passing through a deadband, the outside air damper
shall be modulated to admit outside air beyond the minimum quantity and after the outside air damper is
fully open the cooling coil valve shall be modulated to maintain the space temperature setpoint. When
the system is in the minimum outside air mode, the dampers shall remain in the minimum outside air
position and the heating and cooling coil valves shall be modulated in sequence to maintain the space
temperature setpoint.
24. DUAL-TEMPERATURE COIL SINGLE ZONE HVAC CONTROL SYSTEM.
a. Description of the HVAC system. This air handling system consists of a supply fan, economizer
dampers, filter, and dual-temperature coil. Figures 4-20a through 4-20f show the control system design
for this type of air handling system using a SLDC control panel. Figures 4-20g through 4-20j show the
control system design for this type of air handling system using DDC controls.
Figure 4-20a. Control system schematic for single zone HVAC system with dual-temperature coil.
Figure 4-20b. Control system ladder diagram for single zone HVAC system with dual-temperature coil.
Figure 4-20c. Control system equipment for single zone HVAC system with dual-temperature coil.
Figure 4-20d. Control panel interior door layout for single zone HVAC system with dual-temperature coil.
Figure 4-20e. Control panel back panel layout for single zone HVAC system with dual-temperature coil.
Figure 4-20f. Control panel terminal block layout for single zone HVAC system with dual-temperature
coil.
Figure 4-20g. DDC control system schematic for single zone HVAC system with dual-temperature coil.
Figure 4-20h. DDC control system ladder diagram for single zone HVAC system with dual-temperature
coil.
Figure 4-20i. DDC control system equipment for single zone HVAC system with dual-temperature coil.
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