ZVACs require either an accessible door or an access panel. The return air from the room to the unit may enter the enclosed closet through one of four ways - a louvered door, a wall mounted access panel (RAVRG1), a return air grille (RAVRG2) or a field supplied return air grille.
With this RAVRG1, the return air goes through the panel and the filter bracket is mounted behind the grille louvers. It requires a 28" wide x 48" high cutout. It is a warm gray-beige in color and provides a finished look to the room.
If you have door access to the closet in which your unit is installed, this access panel (RAVRG1) is not required, but you will need a return air grille (RAVRG2).