Full Description ASHRAE Standard 84 provides rules for the measurement and expression of values characterizing the energy-related performance of air-to-air heat/energy exchangers.The revised 2020 edition of the standard includes the following changes:* Rules are provided for measurement of fixed-bed regenerator performance.* The metric “energy recovery ratio,” first introduced in ASHRAE Standard 90.1-2016, is defined. This metric differs from the fundamental effectiveness equations in that it characterizes only an exchanger\'s ability to reduce the load associated with the supply air at a specified condition.* The standard was revised to comply with ASHRAE’s mandatory language policy.