NIST APAR26 – Sensor fault/miscalibration: mixed air temp too low (All Occupied Modes)
Applicable Systems
NISTAPAR: APAR26
Primary: AHU, RTU, MUA, ERV
Objective/Method/Outcome
Objective: Indicates mixed air temperature is lower than both the return and outdoor air temperatures. MAT should be between RAT and OAT. This rule applies when the AHU is in any occupied mode.
Method: Calculate the MAT is less than expected given the OAT and RAT values, for more than 8 occupied hours per week.
Outcome: An insight is generated when the MAT is less than expected given the OAT and RAT values, for more than 8 occupied hours per week.
Logic
If (Min(OAT, RAT) - Temperature Threshold < MAT) { return true; }
NIST APAR26 – Sensor fault/miscalibration: mixed air temp too low (All Occupied Modes)
Inputs
AHU_MODE_CTL {ahu, mode} (Real Trend Log)
MAT {sensor, mixed, air, temp} (Real Trend Log)
RAT {sensor, return, air, temp} (Real Trend Log)
OAT {sensor, outside, air, temp} (Real Trend Log)
Parameters
Parameter
Expression Block Series Number
Description
Default Value (Units)
Temperature Threshold
9
This is the minimum temperature difference between OAT and RAT needed to enable the rule.
2 (C)
Acceptable Hours per Week
22
The amount of time that this error is allowable for the unit per week. Anything more than that time is considered a fault.
