NIST APAR8 – Outdoor air temp too low for Mech. Cooling w/100% OA (Mode 3)

Applicable Systems

  • NISTAPAR: APAR8
  • Primary: AHU, RTU, MUA, ERV

Objective/Method/Outcome

  • Objective: Indicates that the OAT is too low for the AHU to be running in Mode 3 (Mech. Cooling w/100% OA)
  • Method: Check if the OAT is less than the SAT_SP for over 8 occupied hours per week while the unit is in Mode 3
  • Outcome: An insight is generated when the OAT is less than the SAT_SP for over 8 occupied hours per week while the unit is in Mode 3

Logic

If OAT > (SAT - Temperature Rise Over Fan - Temperature Threshold) { return true; }
NIST APAR8 – Outdoor air temp too low for Mech. Cooling w/100% OA (Mode 3)

Inputs

  • SAT_SP {sp, discharge, air, temp} (Real Trend Log)
  • OAT {sensor, outdoor, air, temp} (Real Trend Log)
  • AHU_MODE_CTL {ahu, mode} (Real Trend Log)

Parameters

ParameterExpression Block Series NumberDescriptionDefault Value (Units)
Temperature Threshold74This is the minimum temperature difference between OAT and SAT needed to enable the rule.This value is recommended by NIST.2 (C)
Const – Temperature Rise Over Fan73The estimated air temperature rise over the fan1.1 (C)
Acceptable Hours per Week77The amount of time that this error is allowable for the unit per week. Anything more than that time is considered a fault.8 (h)
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