Pneumatic Control System Example; Start-Stop Control Sequence - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

PNEUMATIC CONTROL FUNDAMENTALS

PNEUMATIC CONTROL SYSTEM EXAMPLE

The following is an example of a typical air handling system
(Fig. 74) with a pneumatic control system. The control system
is presented in the following seven control sequences (Fig. 75
through 79):

— Start-Stop Control Sequence.

— Supply Fan Control Sequence.
— Return Fan Control Sequence.
— Warm-Up/Heating Coil Control Sequence.
— Mixing Damper Control Sequence.
— Discharge Air Temperature Control Sequence.
— Off/Failure Mode Control Sequence.
Controls are based upon the following system information
and control requirements:
System Information:
— VAV air handling system.
— Return fan.
3
— 16.5 m /s.
3
— 1.9 m /s outside air.
3
— 1.4 m /s exhaust air.
— Variable speed drives.
— Hot water coil for morning warm-up and to prevent
discharge air from getting too cold in winter .
— Chilled water coil.
— Fan powered perimeter VAV boxes with hot water reheat.
— Interior VAV boxes.
— Water-side economizer.
— 8:00 A.M. to 5:00 P.M. normal occupancy.
— Some after-hour operation.
GRAVITY
RELIEF
OUTSIDE
AIR
Control Requirements:
— Maintain design outside air airflow during all levels of
— Use normally open two-way valves so system can heat
— Provide exhaust/ventilation during after-hour occupied
— Return fan sized for 16.5 m
START-STOP CONTROL SEQUENCE
to starter-mounted Hand-Off-Automatic Switches.
Electric-Pneumatic Relay 2EP at 0645 by one of the following:
— An Early Start Time Clock 1TC
— A drop in perimeter space temperature to 18 C at Night
— An after-hour occupant setting the Spring-Wound Interval
safety devices including Supply and Return Air Smoke
Detectors; a heating coil, leaving air, Low Temperature
Thermostat; and a supply fan discharge, duct High Static
Pressure Cut-Out.
RETURN FAN
MIXED
AIR
Fig. 74. Typical Air Handling System.
90
supply fan loading during occupied periods.
or cool upon compressed air failure by manually running
pumps and adjusting water temperatures.
periods.
Fans 1M through 3M (Fig. 75) operate automatically subject
The Supply Fan 1M is started and controls are energized by
Thermostat TN
Timer for 0 to 60 minutes.
The Supply Fan 1M operation is subject to manually reset
EXHAUST
RETURN
AIR
SUPPLY FAN
DISCHARGE
AIR
ENGINEERING MANUAL OF AUTOMATIC CONTROL
3
/s.
EAST
ZONE
WEST
ZONE
M10298