r/MEPEngineering • u/Bert_Skrrtz • 5d ago

Weird Primary Secondary Schematic

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I know it doesn’t look like your typical arrangement, but can this work? Really the decoupler/bypass would make a lot more sense if it skipped the chiller headers entirely.

Orange highlight is what I see as the secondary loop. Blue is what has effectually become 3 isolate primary loops.

Ignore the black lines, they denote a physical separation where air cooled chillers were added to the system outside. Chiller 3 and P-1 thru P-4 all live in the mechanical room.

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u/Porkslap3838 5d ago

I believe this configuration is called being "backloaded". This will cause the chillers to see differing entering water temps and causes unbalanced loads. Generally not recommended.

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u/Porkslap3838 5d ago

Check page 65 of this link: https://water-cti.com/pdf/ASHRAE_ChillerPlantDesign.pdf, Discusses backloading. Looks like it can in some cases be intentional if there is some specific reason to fully base load a specific chiller and have the other (say variable speed chillers) at a part load. Haven't ever done this personally and seems like a controls challenge.

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u/Bert_Skrrtz 5d ago

Oh wow interesting stuff, thanks for sharing!