Besides energy modeling, you may need to use the exceptional calculation methodology (ECM) when any of the following situations occur: The energy software cannot carry out calculations for a specific systems like natural ventilation or unusual HVAC e

Besides energy modeling, you may need to use the exceptional calculation methodology (ECM) when any of the following situations occur: 

• The energy software cannot carry out calculations for a specific systems like natural ventilation or unusual HVAC equipment.
• Process loads are different in baseline and design cases and can influence total energy cost savings.
• The proposed design can’t demonstrate savings with the modeling protocol and needs additional calculations.