Why Two Emissions Calculations Produce Different Results

When two emissions calculations in Chateau provide different numbers, it is usually because of updates to the underlying data or your model settings. Since calculations rely on both your inspection records and configured models, even minor tweaks can cause noticeable changes.

Here is a breakdown of the most common reasons for mismatched runs:

Changes to Source Data

Updates to the raw inputs feeding into your emissions calculator will directly impact results.

• Inspections: Adding new inspections, deleting records, correcting ppm readings, or changing the inspection type (like AVO to OGI or Method 21) will shift your emissions estimates.
   
• Treatment of Leaks and Retests: Logging new retests, editing retest dates, or updating a component's deactivated date changes the timeline for when a leak is considered active or closed.
   
• Component Edits: Moving components to a different unit, changing their type, merging them, or adjusting their active status alters how emissions are grouped and calculated.
   
• Stream and Chemical Updates: If stream compositions are not equal to 100%, chemical types are changed, or composition or chemical types are not entered or normalized properly, it will change your outputs significantly, especially on the Emissions by Chemical report.
   
• Physical State Changes: Modifying a component's state (gas/vapor, light liquid, heavy liquid) can move it to a different emission factor group or eliminate its emissions entirely.

Changes to Model Settings and Factors

These changes affect how Chateau interprets your data, even if the raw inputs remain the same.

• Different Calculation Methods: Switching between calculation methods, such as MidPoint or Modified Trapezoid will produce different final numbers.
   
• Emission Model Settings and Credits: Selecting a different factor set, altering reach back or reach forward logic, or applying emission credits differently changes the entire logic of the calculation.
   
• Active Factor Set Edits: Adjusting Average Emission Factors (AEFs), correlation equation coefficients, or default-zero rules will alter emissions for all applicable components.
   
• Analyzer Peg Values: If peg values are set incorrectly or changed for readings that exceed analyzer limits, the resulting emissions will shift correspondingly.
   
• Unit Settings: Comparing runs where one is set to kilograms and the other to pounds will cause obvious discrepancies. Ensure your units are normalized.