I'm looking to model a water-side economizer on an air-cooled chiller that is basically a small cooling tower that can be used to "free cool" the CHW supply instead of (or before) chiller does whenever the OA enthalpy is low enough. I am planning to set this up using a heatexchanger:fluidtofluid and coolingtower:variablespeed. Does anyone have experience or advice making this work?

I am working in DesignBuilder v6.1/EnergyPlus 8.9.