Question-and-Answer Resource for the Building Energy Modeling Community
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Like @Javed said, LoadProfile:Plant (I/O reference) is what you're looking for. It's a bit weird to setup and manipulate the first time. You'll have to provide two schedules, one for the load itself [W] and another for flow fraction that gets multiplied by the nominal flow rate you enter in it.
It is directly available in the OpenStudio Application. You'll need to set up a single plant loop with a pump, a SPM, your supply equipment (cooling towers) and that load profile object. Aside from that, you need a weather file and a couple of design days unless you hardsize everything. Here's a dummy example:
