I think the original idea behind the dumbwaiter was to allow direct delivery from the kitchen to the room(s) or hall(s) along its shaft. This would require a kitchen staff one could call down to for an informal meal or snack. The idea that Ray would be in a pad that is designed to be staffed by servants is outstanding in allowing me to ponder the abuse said staff might endure.
Did he not mention having someone who worked for him at one point? A maid or some such? Maybe I'm misremembering.
Also there's the possibility Ray just climbs into his dumbwaiter to go to the kitchen quickly.