ENGINEERING CMANUAL OF AUTOMATION CONTROL
AIR HANDLING SYSTEM CONTROL APPLICATIONS
214
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 75°F DB and 59.5°F WB.
3. OA condition is 40°F DB and 35°F WB.
4. The MA controller is set at 60°F.
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 60°F.
C2545-1
60°F DB MA
CONTROLLER SETPOINT
RA 75°F DB, 59.5°F WB
MA
OA
40°F DB, 35°F WB
3
2
1
The following results are obtained:
Item
No. Explanation
1As OA temperature varies between 30°F and
60°F, the MA condition lies on the 60°F DB
line.
2As OA temperature rises above 60°F DB, 100
percent OA is admitted, and the MA condition
will lie to the right of the 60°F DB line.
3As OA temperatures fall below 30°F DB, one-
third OA (set by the manual positioning
switch) is admitted, and the MA condition
will lie to the left of the 60°F DB line.
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