WATER COOLED VAV PACKAGE UNITS ARE NOT THE SAME!
While similar in concept to a Rooftop Unit as its the central Heating, Cooling, Ventilation and humidification/dehumidification source for a building or zone, the similarities end there.
Replacing a RTU many times means simply replace the box on the curb and you are all set. For an indoor unit you must consider the time and effort to pull the old unit out and getting the new unit in. Many times the existing unit was built during the building construction and it will be near impossible to simply “swap boxes”