AHU Mode of Operation (for use with NIST APAR rule set)

Applicable Systems

  • Primary: AHU, RTU, MUA, ERV

Objective/Method/Outcome

  • Objective: Determines AHU mode of operation.
  • Method: Look at control signal sequencing of HCV, CCV, and MAD systems.
  • Outcome: A calculated Trend Log is created which records AHU modes as follows:
    • Mode 1 (Heating)
    • Mode 2 (Free Cooling)
    • Mode 3 (Mechanical Cooling w/100% OA)
    • Mode 4 (Mechanical Cooling w/min OA)
    • Mode 5 (Undetermined Mode)

Logic

AHU Mode of Operation (for use with NIST APAR rule set)

Inputs

  • HCV {cmd, heat, water, valve}
  • CCV {cmd, cool, water, valve}
  • MAD {cmd, mixed, air, damper}
  • OCC {occupied}

Notes

  • The calculated Trend Log AHU_MODE_CTL can be used as an input to the NIST APAR rule set to enable/disable a rule. This will help prevent nuisance alarms.
  • IMPORTANT: Minimum MAD position is currently set to 20%. This value varies per system, and the parameter should be changed within the logic flow accordingly (edit block 14).
  • Occupancy Trend Log should reflect normal occupied hours and exclude special modes like morning warm-up or night set back.
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