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AIR HANDLING SYSTEM CONTROL APPLICATIONS
SPECIFICATIONS
See FAN SYSTEM START-STOP CONTROL.
Anytime the supply fan runs, the OA, EA, and RA dampers
shall be modulated by an MA PID control loop to satisfy the MA
temperature setpoint down to a minimum ventilation position.
PSYCHROMETRIC ASPECTS
In the following chart it is assumed that:
1. The manual positioning value is set for one-third
minimum OA.
2. RA condition is 24 C DB and 15 C WB.
3. OA condition is 4 C DB and 1.5 C WB.
4. The MA controller is set at 16 C.
5. The desired MA temperature can be maintained until the
OA temperature falls below the temperature at which only
minimum OA is admitted and until the OA is greater
than 16 C.
MA
3
1
OA
4 C DB, 1.5 C WB
The following results are obtained:
Item
No.
Explanation
1
As OA temperature varies between –1.5 C
and 16 C, the MA condition lies on the 16 C
DB line.
2
As OA temperature rises above 16 C DB, 100
percent OA is admitted, and the MA condition
will lie to the right of the 16 C DB line.
3
As OA temperatures fall below –1.5 C DB,
one-third OA (set by the manual positioning
switch) is admitted, and the MA condition
will lie to the left of the 16 C DB line.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
214
17.5 C DB MA
CONTROLLER SETPOINT
RA 24 C DB, 15 C WB
2
C3236
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