Mix air damper is open during Integrated cooling mode

Objective/ Method/Outcome

Objective: Determines if the Mixed Air Damper is open while the system is in integrated cooling mode. 

Method: Compares the Mixed Air Damper Position to the defined threshold and determines if mechanical cooling and integrated cooling are active. If the system is in free cooling range, the Mixed Air Damper Position is open, and the Cooling Coil Valve is active, the hours of faulty operation are calculated. Avoidable Cost and Potential Savings are calculated based on the Electricity Rate.

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

Description

Reference: ASHRAE36-5.16.14.2

This rule is applicable for integrate cooling mode, meaning mechanical cooling is dealing with addition cooling load which are not able to be fully covered by outdoor air solely. Generally, Integrate cooling mode happens when OAT is higher than supply air temperature setpoint and lower than return air temperature.  In this mode, RAD shall fully closed and OAD shall fully open. Beyond that, mechanical cooling valve modulates to meet cooling load.

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

Default Priority

Medium

Diagnosis

1. Input sensor(s) faulty or miscalibration. Verify input sensor(s) operation.

2. Review control sequence. Ensure AHU is not in correct mode. Mechanical cooling with min OA is not being used when mechanical cooling with 100% OA should be used (when OAT is lower than changeover set point).

Message

Mix air damper is open in integrate cooling mode.

Rule Template

Insight Type: Fault Detection

Trigger Type: Active High

Notes

1. Expected values for “SF Status” inputs are “0” or “1”.

2. Expected values for “Supply Fan Speed” inputs are “100” if they are constant speed fans or not available.

Default Constants:

Const. – Changeover OAT High Limit [°C]: 13

Const. – Changeover OAT High Limit [°C]: 22

Const. – Mixed Air Damper Threshold [%]: >5%

Const. – Threshold – Weekly Hours of Faulty Operation [Hours]: 8

Const. – AHU Rated CFM: 10000

Const. – Electricity Rate($/kWh): 0.1

Const. – Weeks of Operation: 8

CTLs:

MAD is open in Integrate Cooling Mode – Weekly Hours of Faulty Operation (KPI)

MAD is open in Integrate Cooling Mode – Hours of Faulty Operation (CUSUM)

MAD is open in Integrate Cooling Mode – Avoidable Cost [$]

MAD is open in Integrate Cooling Mode – Potential Savings [$/Year]