Civil Engineering Handbook

Postretrofit Energy Usage And Electric Demand Calculations

Method #1: Single point with manufacturer's performance data

For each HVAC system:

Annual energy use = (Measured Energy Use) x (Full Load Runtime Hours)

Monthly demand use = (Measured Peak Electric Demand Use for System) x (System on/off Status for Each Month)

For each HVAC system:

Annual energy use = (Measured Energy Use) x (Full Load Runtime Hours)

Monthly demand use = (Measured Peak Electric Demand Use for System) x (System on/off Status for Each Month)

Method #2: Multiple point with manufacturer's performance data

For each HVAC system:

Annual energy use = (Measured Energy Use for Each Operating Point) x (Full Load Runtime Hours for Each Operating Point)

Monthly demand use = (Measured Peak Electric Demand Use for System for Each Operating Point) x (Maximum Operating Point for Each Month)

For each HVAC system:

Annual energy use = (Measured Energy Use for Each Operating Point) x (Full Load Runtime Hours for Each Operating Point)

Monthly demand use = (Measured Peak Electric Demand Use for System for Each Operating Point) x (Maximum Operating Point for Each Month)

Method #3: Multiple point using short-term data and manufacturer's performance data

For each HVAC system:

Annual energy use = (Measured Energy Use for Each Operating Point) x (Full Load Runtime Hours for Each Operating Point)

Monthly demand use = (Measured Peak Electric Demand Use for System for Each Operating Point) x (Maximum Operating Point for Each Month)

For each HVAC system:

Annual energy use = (Measured Energy Use for Each Operating Point) x (Full Load Runtime Hours for Each Operating Point)

Monthly demand use = (Measured Peak Electric Demand Use for System for Each Operating Point) x (Maximum Operating Point for Each Month)

Method #4: Short-term monitoring and calibrated, simplified simulation

For each HVAC system:

Annual energy use = (Simulated Energy Use Using Calibrated Air-side Model) x (Binned Weather Data)

Monthly demand use = (Simulated Peak Electric Demand Use for System) x (Maximum Bin Temperature for Month)

For each HVAC system:

Annual energy use = (Simulated Energy Use Using Calibrated Air-side Model) x (Binned Weather Data)

Monthly demand use = (Simulated Peak Electric Demand Use for System) x (Maximum Bin Temperature for Month)

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