Variable primary is the way to go, IMHO
Are you getting multiple modules short cycling or just one? How far are the AHUs and CRACs?
Originally Posted by PowerPlay
What might help is cranking down the balance valves on the bypass legs of the three port valves so that the sum of the flow through all bypass legs is equal to the flow of one module. Along with that I'd add two position two port valves on each of the evaps and add dP control to the CHW pumps. You gotta do all three. This is actually going to reduce the mass flow rate of water through the chiller plant, but it is likely to increase the mass flow rate per active module. More importantly, it will improve the dT across the active module which may encourage the controller to leave compressors on longer. The controller behavior discussion should go to your ArctiChill rep as I'm just guessing, although I suspect this is part of the reason they suggested variable flow.