A walk-in is an enclosed storage space refrigerated to temperatures “above, and at or below” (depending on whether it is a cooler or freezer) 32°F that can be walked into, and has a total chilled storage area of less than 3,000 square feet. See 42 U.S.C. 6311(20). Each walk-in is comprised of three key types of components: Panels used for the ceiling, walls, and (for freezers) the floor; at least one door; and a refrigeration system. The discussion will focus solely on the mechanics of measuring the relevant values and the downstream calculations needed to rate the efficiency of WICF refrigeration system basic models that are either sold as mixed or matched systems.