I'm wondering if anyone might have experience in temperature control of cold WFI where there are two heat exchangers in series. One is a chilled water to WFI hx where a modulating chilled water valve is manipulated. The other is a free-cooling WFI to condenser water hx a modulating condenser water valve is manipulated. The current scheme is a split range PID that favors the free cooling first and then chilled water once the free cooling is maxed out.

 

I am not sure if I understand.

I did a chilled vs cool city water dual mixing valve application for a large industrial bakery. The objective was a large tank of X degree water for a batch mix. Repeated many times. Rather than doing a split range PID, I used dual PID outputs (chilled water was more responsive) and used an integral freeze when the tank was done filling.

It took a little time to tweak the settings, but ultimately worked great.