This guide introduces Step Commissioning in Leanheat® Monitor: what a step response test is, what the result tells you, and when to run one. The step by step instructions are in How to run a Step Commissioning test.
What Step Commissioning does
Step Commissioning runs a step response test on one circuit of an ECL controller. Leanheat Monitor changes the flow temperature setpoint of the circuit in three steps, records the measured temperature for the whole test, and draws the two curves on one chart.
The test is a measurement, not a change. Its purpose is to make the behaviour of the control loop visible, so that you can judge whether the circuit is tuned correctly.
What a step response test is
A control loop is judged by how it reacts to a sudden, known change. Step Commissioning applies exactly such a change and records the answer. Every test has four phases, and each of the three steps lasts the same time:
Baseline. The setpoint is held steady, so that the circuit starts from a known state.
Raise. The setpoint is raised by a fixed amount, the step delta. This is the step the circuit has to answer.
Return. The setpoint goes back to the baseline, which gives you a second response to look at.
Restore. The original settings of the controller are written back and the test is finished.
To keep the step clean, the test holds the circuit at a constant reference for the duration of the run, so that nothing else moves the setpoint while the measurement is taken. Everything the test changed is restored when it finishes.
What the result tells you
The result is a chart with two lines: the setpoint the test asked for, and the temperature the circuit actually reached. The shape of the measured line after each step is the answer you are looking for.
A circuit that reaches the new setpoint and stays there is tuned well.
A circuit that overshoots and then swings around the setpoint is reacting too strongly.
A circuit that creeps towards the setpoint and never arrives is reacting too weakly.
The two values behind that behaviour are the PI tuning parameters of the circuit: the proportional band Xp and the integration time Tn. Correct values let the controller follow its setpoint without delay and without oscillation. Step Commissioning reads the Xp and Tn that were active during the run and shows them next to the chart, so that every result is tied to the tuning it was measured with.
The usual way to work is one change at a time: run a test, adjust one parameter, run the test again, and compare the two charts.
When to use it
When you commission a substation. A step response test confirms that the circuit follows its setpoint before you hand the installation over.
When a circuit does not hold its temperature. If a circuit swings or is sluggish and you suspect the tuning, the test shows you whether the loop or something else is the problem.
After you change the tuning. A second test with the same settings gives you a chart you can compare directly with the first one.
As a record. The result can be exported as a PDF, so the measured behaviour of the circuit can be filed with the commissioning documents.
What you need
Step Commissioning appears as its own tab on the device page. The tab is available when all of the following are true:
The device is an ECL controller connected to Leanheat Monitor as an ECL device. The tab is not available for other device types.
Your user role has commissioning rights. Basic users and Read-only users cannot open the tab.
The device also has to be online when the test starts, because Leanheat Monitor reads the controller before the first step.
What happens to the building and the device
A step response test is a real change to a real circuit, so plan for two effects:
The temperature in the building changes. The flow temperature of the circuit is raised by the step delta for one third of the test, and occupants can notice this. Run the test at a time that suits the building.
The device settings are locked while the test runs. The settings panel of the device is read-only until the test finishes, so that nothing interferes with the measurement.
A test takes three times the step time, from a few minutes up to six hours for the longest possible settings. It runs on its own, and you do not need to stay on the page.
How a test is run, from start to finish
Note the current settings of the circuit, so that you can put them back if you have to stop the test early.
Set up the test on the Step Commissioning tab: the circuit, the source, the size of the step and the duration of each step.
Schedule it for a suitable time, or start it immediately.
Let it run. The test steps the setpoint, records the response, and restores the controller when it is done.
Read the chart, and export it as a PDF if you need a record.
Adjust the tuning if the chart calls for it, then run the test again to check the result.
Each of these stages is described in detail, with the exact fields and buttons, in How to run a Step Commissioning test. That article also covers what to do when a test cannot run, and the warning that appears when other functions are controlling the same device.