NIST APAR17 – Supply air temp should be less than return air temp (Mode 4 – Mech. Cooling w/min OA)
Applicable Systems
NISTAPAR: APAR17
Primary: AHU, RTU, MUA, ERV
Objective/Method/Outcome
Objective: Indicates that the supply air temperature is greater than the return air temperatures while the unit is in Mode 4 (Mechanical Cooling w/min OA).
Method: Check if the SAT is more than the RAT for over 8 occupied hours per week while the unit is in Mode 4.
Outcome: An insight is generated when the SAT is more than the RAT for over 8 occupied hours per week while the unit is in Mode 4.
Logic
If (SAT > RAT - Temperature rise over fan + Temperature Threshold) { return true; }
NIST APAR17 – Supply air temp should be less than return air temp (Mode 4 – Mech. Cooling w/min OA)
Inputs
SAT {sat, ahu} (Real Trend Log)
RAT {rat, ahu} (Real Trend Log)
AHU_MODE_CTL {ahu, apar mode} (Real Trend Log)
Parameters
Parameter
Expression Block Series Number
Description
Default Value (Units)
Const- Temperature Rise Over Fan
31
The estimated air temperature rise over the fan.
1.1 (C)
Temperature Threshold
30
This is the minimum temperature difference between OAT and RAT needed to enable the rule.
2 (C)
Acceptable Hours per Week
33
The amount of time that this error is allowable for the unit per week. Anything more than that time is considered a fault.
