NIST APAR1 – Supply air temp should be greater than mixed air temp (Mode 1 – Heating)

Applicable Systems

• NISTAPAR: APAR1
• Primary: RTU, MUA, ERV

Objective/Method/Outcome

• Objective: Indicates an inconsistency between the supply and mixed air temperature. Heating the air should result in a supply air temperature that is higher than the sum of the mixed air temperature and the temperature rise across the supply fan. This rule applies when the AHU is in heating mode (Mode 1).

• Method: Check if the SAT is more than 2 degrees below the MAT for over 8 occupied hours per week while the unit is in Mode 1 (Heating).

• Outcome: An insight is generated when the SAT is more than 2 degrees below the MAT for over 8 occupied hours per week while the unit is in Mode 1 (Heating).

Logic

If(MAT - SAT + Temperature Rise Over Fan > Temperature Threshold && HCV > 0% Open) { return true; }

Inputs

• SAT {sensor, discharge, air, temp} (Real Trend Log)
• HCV {cmd, heat, water, valve } (Real Trend Log)
• MAT {sensor, mixed, air, temp} (Real Trend Log)
• AHU_MODE_CTL {ahu, mode} (Binary Trend Log)

Parameters

Parameter	Expression Block Series Number	Description	Default Value (Units)
Temperature Rise Over Fan	64	The acceptable temperature deviation from set point that is considered normal	1.1 (C)
Temperature Threshold	37	The acceptable temperature deviation from set point that is considered normal	2 (C)
HCV Error Threshold	66	The movement tolerance of the HCV. This is used to define when the valve is open -everything above the formula (100 – HCV Error Threshold) is considered saturated.	0 (%)
Acceptable Hours per Week	72	The amount of time that this error is allowable for the unit per week. Anything more than that time is considered a fault.	8 (h)