CEMP-E
TI 810-11
30 November 1998
(5) Smoke Detectors in the supply air and return air ductwork shall stop the supply fan and
initiate a smoke alarm if smoke is detected at either location. Restarting the supply fan shall require
manual reset at the smoke detector.
(6) The DDC system shall modulate the preheat coil control valve from the signal of a
temperature sensing element and transmitter in the preheat coil discharge to maintain the setpoint as
shown.
(7) During occupied and ventilation delay modes, the DDC system shall compare the signals of
a space temperature sensor / transmitter and space relative humidity sensor / transmitter to operate the
cooling coil valve. Based on the highest signal received, the DDC system shall modulate the valve to
maintain space temperature or space humidity at setpoint. During the unoccupied mode, the cooling coil
control valve shall remain closed.
(8) During the occupied mode, the DDC system shall accept the signals from a space relative
humidity sensor and a duct relative humidity sensor to control the humidifier valve and the cooling coil
valve. The DDC system shall gradually open the cooling coil valve in the event that the space relative
humidity continues to rise after the humidifier valve is closed. The DDC system shall gradually operate
the humidifier valve from the signal of a space relative humidity sensor / transmitter to maintain relative
humidity setpoint. The DDC system shall receive a signal from a relative humidity sensor / transmitter in
the ductwork downstream of the humidifier and shall limit the relative humidity at that point to a high limit
relative humidity setpoint. During unoccupied and ventilation delay modes, the humidifier valve shall
remain closed.
(9) The DDC system shall gradually close the reheat coil valve on a rise in space temperature to
maintain the setpoint.
(10) The DDC system shall accept a signal from a temperature sensing element and transmitter
in the heating supply line, and shall modulate the hydronic system control valve to maintain the setpoint.
26. SINGLE ZONE HVAC CONTROL SYSTEM WITH DIRECT-EXPANSION (DX) COOLING COIL.
a. Description of the HVAC system. This air handling system consists of a supply fan, economizer
dampers, filter, heating coil, and a three stage direct expansion cooling coil. Figures 4-22a through 4-22f
show the control system design for this type of air handling system using a SLDC control panel. Figures
4-22g through 4-22j show the control system design for this type of air handling system using DDC
controls.
Figure 4-22a. Control system schematic for single zone HVAC system with DX coil.
Figure 4-22b. Control system ladder diagram for single zone HVAC system with DX coil.
Figure 4-22c. Control system equipment for single zone HVAC system with DX coil.
Figure 4-22d. Control panel interior door layout for single zone HVAC system with DX coil.
Figure 4-22e. Control panel back panel layout for single zone HVAC system with DX coil.
Figure 4-22f. Control panel terminal block layout for single zone HVAC system with DX coil.
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