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AHU-FC08 · Air-side AHU · ASHRAE Guideline 36 FC08

SAT and MAT not tracking in economizer

In pure economizer mode (no mechanical heating or cooling), SAT should equal MAT plus the fan-heat rise — but it doesn't.

Capacity-basedBAS trendsGuideline 36Medium effort

What does AHU-FC08 mean?

In pure economizer mode (no mechanical heating or cooling), SAT should equal MAT plus the fan-heat rise — but it doesn't.

Why does it matter?

Indicates a leaking coil (chilled water trickling through a closed valve, removing heat from supposedly-untreated air) or a SAT/MAT sensor calibration drift.

What should you do?

Check chilled-water and hot-water valve seat integrity (water-side closed temp test). Verify SAT and MAT sensor calibration against a reference thermometer.

How Energy Agent prices a finding

Written by Pelorus Engineering · Brent Waluzak, P.E. (FL), President, Pelorus EngineeringLast updated

Screening-level estimates; confirm with measurement and verification before capital commitment.

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Send twelve months of interval data and a BAS trend export. Energy Agent returns a ranked list of what is wasting money, what each item is worth per year at your tariff, and what to do about it.

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