Trim & Respond logic is a sequence used to reset various set-points. Often used in VAV applications to reset static pressure set-points. Can also be used to reset discharge air temperature as well as variable speed pump output. T&R logic is optimal for controlling a single variable that is subject to the requirements of multiple downstream zones
In a VAV application where we are resetting static pressure set-points. T&R will look at the number of requests from zones. Once we pass our threshold of requests from zones, the fan output will slowly ramp up incrementally. Rather than a PID loop where the control signal will ramp up proportionally.
Once our requests falls below the threshold, additional static pressure is no longer needed. So the fan speed will ramp down incrementally until our request threshold is breached again. Trim rate can be increased to rapidly meet the needs of the zones or decreased to increase system stability.
This method allows you to ignore 'rogue zones' by raising the threshold for required requests from zones. This method also will also utilize far less control system network traffic due to the simplicity of the request system as opposed to a PID loop that is constantly polling every point to maintain a damper position. T&R can also factor zone priority by giving critical zones more weight, something a PID loop cannot viably do.