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AHU-FC10 · Air-side AHU · ASHRAE Guideline 36 FC10

Mixed air not tracking outdoor air at 100% OA

With the outdoor-air damper fully open, the mixed-air temperature should equal the outdoor-air temperature — it doesn't.

Diagnostic · data qualityBAS trendsGuideline 36Medium effort

What does AHU-FC10 mean?

With the outdoor-air damper fully open, the mixed-air temperature should equal the outdoor-air temperature — it doesn't.

Why does it matter?

Either the damper isn't actually open (linkage, actuator), return air is leaking through a closed return damper, or a sensor is wrong — any of which quietly defeats the economizer.

What should you do?

Stroke the OA and RA dampers and watch MAT respond; compare OAT and MAT sensors against a reference; check for a stuck return damper.

This is a diagnostic rule: Energy Agent surfaces and ranks it as a data quality problem and claims no dollar savings for it, by design.

How Energy Agent prices a finding

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

What should the economizer be saving?

Estimate the free cooling a working economizer delivers in your climate.

Tampa is 2A; Atlanta 3A; Chicago 5A; Denver 5B; Seattle 4C.
Share of those hours the economizer actually displaces mechanical cooling.
Enter a repair or controls-change cost to see the simple payback.
Avoidable cost per year—Energy —Simple payback Enter a cost to fix to see the payback.

    Cooling capacity, times the hours a year outdoor air can do the job in your climate zone, times an effectiveness factor, priced at your rate. Energy Agent counts the actual hours the coil ran when it did not need to.

    Screening estimate. Energy Agent measures the real fault hours and load from your trends and prices them at your tariff.

    Request a demoSee how Energy Agent prices a finding

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

    More air-side ahu faults

    All 32 air-side ahu rules →

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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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