NIST APAR15 – Outdoor air temp too low for Mechanical Cooling w/min OA (Mode 4)
Applicable Systems
NISTAPAR: APAR15
Primary: AHU, RTU, MUA, ERV
Objective/Method/Outcome
Objective: Indicates that the OAT is too low for the AHU to be running in Mode 4 (Mech. Cooling w/min OA)
Method: Check if the OAT is less than the changeover air temperature for switching from Mode 4 to Mode 3, for over 8 occupied hours per week while the unit is in Mode 4.
Outcome: An insight is generated when the OAT is less than the changeover air temperature for switching from Mode 4 to Mode 3, for over 8 occupied hours per week while the unit is in Mode 4.
Logic
If (Changeover Temp - Temperature Threshold > OAT) { return true; }
NIST APAR15 – Outdoor air temp too low for Mechanical Cooling w/min OA (Mode 4)
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)
Const- Changeover Temp for Switching Between Modes 3&4
73
To change changeover temperature for switching between Mode 3 and Mode 4, edit block 73
17 (C)
Temperature Threshold
74
This is the minimum temperature difference between OAT and Changeover Temperature needed to enable the rule.
2 (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.
