Which statement describes the maximum CO2 differential among some space types per ASHRAE standards?

• A. It is defined exactly in the base standard with a fixed ppm differential for all spaces.
• B. Addendum ab to 62.1-2022 provides maximum CO2 differentials for indoor/outdoor air.
• C. CO2 differentials are not considered in ASHRAE 62.1.
• D. There is a universal 500 ppm differential for all spaces.

Answer: (B)

The concept being tested is how CO2 differentials between indoor and outdoor air are treated in ASHRAE 62.1. The base standard does not impose a single fixed CO2 delta for all spaces. Instead, CO2-based ventilation controls (DCV) are addressed, and updates to the standard have introduced specific guidance on maximum indoor-outdoor CO2 differentials for certain space types through addenda.

Therefore, the statement that the maximum CO2 differential is defined for indoor/outdoor air by a specific addendum to the standard is the correct one. This reflects how the guiding limits are not universal in the base document but are provided in subsequent addenda to address practical DCV applications.

The other options aren’t accurate because the base standard doesn’t fix a universal ppm differential, it does consider CO2 in DCV contexts, and there isn’t a single universal 500 ppm limit.