Determine if cooling control is ineffective/unresponsive

Applicable Systems

• Primary: AHU, RTU, MUA, ERV

Objective/Method/Outcome

• Objective: Determine if the cooling system is having issues due to possible improper sequencing or equipment failure. Based on NIST APAR 16.

• Method: Check if the SAT is greater than the MAT when the CCV is open during occupied hours.

• Outcome: An insight is generated if the SAT is greater than the MAT while the CCV has been open for more than 12 hours.

Logic

   If(SAT > MAT + Temperature Rise Over Fan + Temperature Threshold) {return true;}

Inputs

• SAT {sensor, discharge, air, temp} (Real Trend Log)
• MAT {sensor, mixed, air, temp} (Real Trend Log)
• CCV {cmd, cool, water, valve} (Real Trend Log)
• Occ {occupied} (Binary Trend Log)

Notes

This rule compensates for the temperature rise across a supply fan between the MAT and SAT sensors. This value varies per system, and the parameter should be changed within the logic flow accordingly. The temperature rise over a fan is currently to 1.1 degrees in accordance with NIST recommendations. The CCV must be over 20% in order for this rule to take effect, as its cooling effects will be insignificant otherwise.

Parameters

Parameter	Expression Block Series Number	Description	Default Value (Units)
Temperature Threshold	77	The acceptable temperature deviation from set point that is considered normal	2 (C)
Temperature Rise Over Fan	76	The temperature increase cause by air passing over a fan. This should be changed based on the site and system.	1.1 (C)
Valve Open	81	The valve position for which the cooling provided by the CC is considered significant.	20 (%)
Acceptable Hours per Week	80	The amount of time that this error is allowable for the unit per week. Anything more than that time is considered a fault.	12 (h)