Trane CNT-APG002-EN, PID Control - page 41

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Chapter 4 Applications
36 CNT-APG002-EN
Figure 26: Space temperature and calculated discharge-air setpoint
The discharge-air temperature setpoint calculated by the PID loop may
not control the discharge-air temperature depending on other conditions
that have priority, such as high and low setpoint limits. The high limit
controls the discharge-air temperature for much of the time in Figure27
(because the calculated setpoint is too high). Also, Figure 27 shows how
aggressively the PID loop responds to disturbances in space temperature.
Figure 27: Effective d ischarge-air temperature setpoint
Time (minutes)
Temperature (°F)
Space temperature
PID calculated
discharge-air setpoint
Space setpoint
Time (minutes)
Temperature (°F)
Space setpoint
PID calculated
discharge-air setpoint
Space temperature
Effective discharge-air
temperature setpoint