Take the 2nd Highest Value in Metasys LCT

This is an advance Metasys tutorial. It was done using a Control System object. The programming tools inside this Control System is called the Logic Connector Tool (LCT).

REAL USE SCENARIO

Let’s say you have an Air Handler Unit (AHU) that serves multiple VAV boxes. In this setup, it is very typical to program AHUs with a static pressure setpoint reset. Meaning that the this setpoint will update as needed per VAVs demand. In this case, a process will evaluate the maximum damper position of all the associated VAVs and the one reading the highest, would be the leading VAV.

THE LOGIC IN LCT

I was able to figure out how to pick the second highest value. I did it with 5 VAV damper points, but you can definitely do it with as many points as you need. I’m leaving you a screenshot below of the LCT logic:

If you were to have more than 1 damper at 100% this logic will surprisingly work as well. It will take out of the equation all dampers that are at 100% and will get the next highest value. See screenshot below:

Depending on how many VAVs you have it can take a lot of resources from your supervisory devices (NAEs, SNE, etc) since for each additional VAV you add a couple of logic blocks.

Feel free to give it a try and see how it behaves. Don’t forget to comment!