Supply air temperature is not less than mixed air temperature when mechanical cooling

Objective/ Method/Outcome

Objective: Determines if the Supply Air Temperature is less than Mixed Air Temperature while Cooling Coil active.

Method: Compares the Supply Air Temperature to the Mixed Air Temperature, the defined Temperature Threshold, and the Fan Temperature Gain. If the Supply Air Temperature is greater than the defined range while the Cooling Coil Valve is open, the hours of faulty operation are calculated.

Outcome: This rule generates an insight if the Daily Hours of Faulty Operation exceeds the acceptable daily threshold.

Description

Reference: ASHRAE36-5.16.14.8/NIST APAR1

This rule indicates an inconsistency between the supply and mixed air temperature. Cooling the air should result in a supply air temperature that is lower than the sum of the mixed air temperature and the temperature rise across the supply fan.

This rule is part of the CopperTree Standard rule-set. (Aliased Celsius / Aliased Fahrenheit)

Default Priority

Medium

Diagnosis

1. SAT sensor error

2. MAT sensor error

3. Cooling coil valve stuck closed or actuator failure

4. Fouled or undersized cooling coil

5. CHW temperature too high or CHW unavailable

6. DX cooling unavailable

7. Gas or electric heat stuck on

8. Heating coil valve leaking or stuck open

Message

SAT is above MAT while cooling. This may be indicative that the cooling coil valve is not responding, or the heating coil valve is passing through (leaking).

Rule Template

Insight Type: Fault Detection

Trigger Type: Active High

Notes

Default Constants:

Const. – Acceptable Hours of Fault per Day: 2

Const. – Valve Open Threshold [%]: 2

Const. – Fan Temperature Gain [°]: 1.1°C/2°F

Const. – Temperature Threshold [°]: 2°C/3.6°F

CTLs:

SAT High, Cooling On – Weekly Hours of Faulty Operation (KPI)

SAT High, Cooling On – Hours of Faulty Operation (CUSUM)