Retro-commissioning a Central Plant Without Taking It Offline

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A regional medical center came to us with a familiar complaint: the chilled water plant was struggling on design days, and the assumption in the building was that it needed another chiller. Capital had already been penciled in for the following fiscal year.

What we found

Before recommending equipment, we pulled a month of trend data off the building automation system and walked the plant. Three things stood out:

• Staging thresholds had drifted. The lead/lag setpoints no longer matched the sequence of operations, so a second machine was starting well before the first reached efficient load.
• Chilled water reset was disabled. It had been turned off during a service call two years earlier and never restored.
• Two control valves were leaking by, which showed up as a persistent low delta-T across the coils.

None of these required new equipment. All three were recoverable through sequencing changes and targeted valve repair.

The result

After correcting the sequences and repairing the valves, the plant carried the design day load on existing machines with margin to spare. The capital request was deferred, and the facility now has a documented sequence of operations that matches what the system actually does.

That is the case for retro-commissioning in a sentence: the cheapest capacity in a building is usually the capacity it already has.