Does a closet wine cellar need its own cooling unit?
For aging, yes. A closet without cooling tracks house temperature; a cooled, insulated closet holds the steady conditions wine needs.
Where does the cooling unit vent?
Through the wall into a suitable ventilated room, as described in the cooling section above, or through ducts or a split system to a utility space or outdoors. Never into another closet, a laundry room or a garage.
What has to change besides the racking?
The door, the insulation and the vapor control. An insulated exterior-grade door replaces the interior one, walls and ceiling get insulation and a warm-side vapor retarder, and penetrations are sealed.