NIST APAR9 – Outdoor air temp too high for Mechanical Cooling w/100% OA (Mode 3)
Applicable Systems
NISTAPAR: APAR9
Primary: AHU, RTU, MUA, ERV
Objective/Method/Outcome
Objective: Indicates that the OAT is too high for the AHU to be running in Mode 3 (Mech. Cooling w/100% OA).
Method: Check if the OAT is greater than the changeover air temperature for switching from Mode 3 to Mode 4, for over 8 occupied hours per week while the unit is in Mode 3 (Mech. Cooling w/100% OA). That is, the unit is running in Mode 3 when it should be running in Mode 4
Outcome: An insight is generated when the OAT is greater than the changeover air temperature for switching from Mode 3 to Mode 4, for over 8 occupied hours per week.
Logic
If (OAT > Changeover Temp for Switching Between Modes 3&4 + Temperature Threshold) { return true; }
NIST APAR9 – Outdoor air temp too high for Mechanical Cooling w/100% OA (Mode 3)
Inputs
OAT {sensor, outdoor, air, temp} (Real Trend Log)
AHU_MODE_CTL {ahu, mode} (Real Trend Log)
Parameters
Parameter
Expression Block Series Number
Description
Default Value (Units)
Temperature Threshold
74
The acceptable temperature deviation from set point that is considered normal
2 (C)
Const- Changeover Temp for Switching Between Modes 3&4
73
Minimum changeover temperature for switching between Mode 3 and Mode 4
1.1 (C)
Acceptable Hours per Week
77
The amount of time that this error is allowable for the unit per week. Anything more than that time is considered a fault.
