Building Controls VI: When to Use Each Response
Gain
Amount of response changes when gain decreases
When a derivative is added
A cost is incurred.
Slow Responding Systems
Best fit for a Proportional Response
How much offset is resonable
Depends on the needs.
Fast response system
Floating Control is the best choice.
Proportional Response has
Good Stability, Reasonable Offset
Higher Strength Loads Require
Proportional System tuning that pushes back harder
Stabilization with too much offset
Requires more work to satisfy requirements
Slow responses are expected when we are controlling the
Temperature and Humidity
Gain is not concerned with setpoint, but with
a constant value reached.
A system is tuned to
best respond to a certain load condition
Setpoint Adjustments are a reason to have
derivatives
Duct temperature and humidity changes are
felt more quickly.
If a system is below setpoint, gain added is
negative
Duct pressure and flow changes
occur even faster.
If a system is above setpoint, gain added is
positive
Integral component gets added to the system the longer
that the system is away from setpoint.
When the gain is changed,
the step for what is up and down changes for every given temperature change
Gain encourages stability
to be more easily reached.
PI gives the ability
to decrease the gain for stability.