Total Heat Transfer Effectiveness is low

Objective/ Method/Outcome

Objective: Determines if energy recovery equipment’s total heat effectiveness is too low.

Method: Determines the Total Heat Transfer Effectiveness from the defined ASHRAE Effectiveness equation, based on the entering air, return air, and leaving air enthalpy. If the Total Heat Transfer Effectiveness is lower than the Effectiveness Threshold, the hours of faulty operation are calculated. Avoidable Cost and Potential Savings are calculated based on the Electricity Rate and Natural Gas Rate.

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

Description

Reference: ASHRAE Handbook—HVAC Systems and Equipment Chapter26/ASHRAE90.1-6.5.6.1

This rule determines if energy recovery equipment’s total heat effectiveness is too low. The Effectiveness equation is from ASHRAE Handbook—HVAC Systems and Equipment Chapter26. Enthalpy is used for this calculation.

η = [Vs • (x1 – x2)] / [Vmin • (x1 – x3)]

Where:

 η = Sensible effectiveness

 x1 = OA enthalpy (btu/lb.)

 x2 = SA enthalpy (btu/lb.)

 x3 = RA enthalpy (btu/lb.)

 Vs = Supply air volume (cfm)

 Vmin = The lower of the exhaust or supply air volume (cfm)

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

Default Priority

Medium

Diagnosis

1. Outdoor air damper stuck

2. Exhaust air damper stuck

3. Energy recovery equipment is operating at economizer mode

4. Energy recovery equipment requires maintenance

Message

Total Heat Transfer Effectiveness is low.

Rule Template

Insight Type: Energy

Trigger Type: Active High

Notes

1. Expected values for SF/EF rated CFM are “0” If an airflow station is present.

2. Expected values for SF/EF rated CFM are from building documents if airflow station is not present.

3. Only one “Airflow”, [LPS] or [CFM] is needed.

4. The input(s) that is(are) not used should be set to “0”.

5. Expected values for “SF Speed” inputs are “100” if they are constant speed fans or not available.

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

Default Values:

Const. – Weekly Faulty Hours Threshold [hrs]: 4

Const. – Effectiveness Threshold[%]: 50

Const. – Electricity Rate[$/kWh]: 0.1

Const. – Natural Gas Rate [$/mmBTU]: 3 Const. – Weeks of Operation

CTLs:

Total heat transfer effectiveness low – Hours of Faulty Operation (CUSUM)

Total heat transfer effectiveness low – Weekly Hours of Faulty Operation (KPI)

Total heat transfer effectiveness low – Avoidable Cost [$]

Total heat transfer effectiveness low – Potential Savings [$/Year]