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AHU-FC11 · Air-side AHU · ASHRAE Guideline 36 FC11

Mechanical cooling with outdoor air cold enough to do the job

The unit is at 100% outdoor air and still running the cooling coil, although the outdoor air alone is colder than the supply setpoint.

Capacity-basedBAS trendsGuideline 36Medium effort

What does AHU-FC11 mean?

The unit is at 100% outdoor air and still running the cooling coil, although the outdoor air alone is colder than the supply setpoint.

Why does it matter?

The economizer should be modulating the damper down instead of paying for chilled water. This is pure waste for as long as it lasts.

What should you do?

Check the economizer changeover and the damper minimum/maximum limits; verify the cooling valve seats; confirm the sequence lets the damper modulate before the coil enables.

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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