NIST APAR2 – Outdoor air fraction out of acceptable range (Mode 1 – Heating)

Applicable Systems

  • NIST: APAR2
  • Primary: AHU, RTU, MUA, ERV

Objective/Method/Outcome

  • Objective: Indicates that the fraction of outdoor air is too high or too low while the AHU is in Mode 1 (Heating). MAT, RAT, and OAT are used to calculate the fraction of OA entering the building.
  • Method: Check if the the calculated OAF is not within the desired minimum OAF (30%) for more than 12 occupied hours per week.
  • Outcome: An insight is generated when the calculated OAF is not within the desired minimum OAF (30%) for more than 12 occupied hours per week.

Logic

If (MAT - SAT + Temperature Rise Over Fan > Temperature Threshold && HCV > 0% Open) { return true; }
NIST APAR2 – Outdoor air fraction out of acceptable range (Mode 1 – Heating)

Inputs

  • MAD {cmd, mixed, air, damper} (Real Trend Log)
  • MAT {sensor, mixed, air, temp} (Real Trend Log)
  • RAT {sensor, return, air, temp} (Real Trend Log)
  • AHU_MODE_CTL {ahu, mode} (Real Trend Log)
  • OAT {sensor, outside, air, temp} (Binary Trend Log)

Parameters

ParameterExpression Block Series NumberDescriptionDefault Value (Units)
Minimum OAF outside range11The acceptable minimum Outside Air Fraction30 (%)
Flow Error Threshold12The acceptable flow deviation from set point that is considered normal30 (%)
Damper Error Threshold20The movement tolerance of the MAD15 (%)
Min MAD Position19The acceptable minimum of the damper. This is used to define when the damper is open -everything above Min MAD position is considered saturated.20 (%)
Acceptable Hours per Week31The amount of time that this error is allowable for the unit per week. Anything more than that time is considered a fault.12 (h)
Const- Minimum Temperature Difference to Enable31Minimum deltaT between OAT and RAT to enable rule.5.6 (C)
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