Question:Refrigeration units are always placed at the tops of fridges. Do you know why?
Because cold air sinks as it is more dense than the surrounding air.
This enables fridges to create a convection current by cooling instead of heating.
The convection current increases the rate of cooling of the air in the fridge.
If the cooler was at the bottom of the fridge the cool air would just stay at the bottom and the warmer air would stay at the top and not be cooled at all.
NB It does not have to be a freezer at the top, in separate fridges and freezers, both will have the cooling element at the top on the back to enable convection.