Tuning Practice 8 — Temperature — chilled water cooling coil

The job

What you are looking at

Chilled water flows through a cooling coil in a vessel, and a control valve sets how much. Opening the valve lowers the temperature. The heat coming into the vessel is the load.

This is the slowest loop in the set — the vessel has a great deal of thermal mass, and it takes a long time to respond to anything. The measurement reads in degrees Celsius, not percent.

The controller is on factory defaults and the acting direction has not been commissioned.

This is practice, not a test. Nothing on this page is scored and nothing is submitted anywhere. Judge your tuning by the trend in front of you: how quickly the measurement reaches the setpoint, how far past it goes, whether it settles, and how the loop behaves when the load changes. Change something, watch it, change it again.

How to work through it

Steps

Press Start. The loop begins balanced at setpoint, so nothing will move until you disturb it — move the setpoint, or change the load, and watch which way the measurement goes. This loop is slow — raise the simulation speed if you would rather not wait.
Set the acting direction for this loop.
Tune it, and be patient enough to let each change finish before you judge it. Move the setpoint and change the Heat load to test it.
If the temperature is overshooting badly and taking a long time to come back, consider whether you have tuned it as though it were a fast loop.
Before you call it tuned, change the load and confirm the loop brings the measurement back and holds it. A loop that only looks good on a setpoint move is not proven.

This loop is tuned with the proportional and integral terms. The derivative term is fixed at zero here.

Adjustment range available for each tuning term on this exercise
Tuning term	Lowest	Highest
Proportional gain (Kp)	0	22
Integral gain (Ki, 1/s)	0	0.55

These ranges are set for this loop only. Another exercise will have different ones, because a different process needs different numbers.

Simulator

For your own record

Commissioning notes

Nothing here is graded or sent anywhere. Write down what you settled on and why, so you have it to compare against the next exercise.

Which way did this controller have to act, and how did you work that out? What did you leave the tuning set to? Record the numbers themselves, in whichever form the controller was showing them. What did the loop do when you changed the load, and were you satisfied with the recovery?

Your notes stay in this browser, on this computer, and they belong to this exercise alone — each exercise keeps its own set. Open this exercise again on this computer and they will be here waiting for you. They are not sent anywhere and they are not graded, and they will not follow you to another machine, so copy anything you want to keep elsewhere.