The Standard 52.1-1992 is the old US - standard for performance testing of HVAC air filters. This standard is however still sometimes quoted and provides three evaluation criteria:
- dust spot efficiency
- dust holding capacity
The 52.1 standard is "replaced" by standard 52.2-1999, that provides more realistic data on filter performance. It provides filter’s initial efficiency as a function of particle size, as well as a numeric value that allows a user or engineer to specify a product's minimum efficiency reporting value (MERV).
Read the Camfil overview, which fully explains the standards and how to use them.
ASHRAE Testing for HVAC Air Filtration