Same refrigerants work. Getting a large decrease in temp vs outside is a matter of insulation, air sealing, roof/wall color, and sizing of units/ducts.
One more question- what about commercial spaces where they will have a door open and be flooding the store with ice cold air. It sure feels like more than a 20 degree difference.
It's still just a 20°F difference from the vent that the AC sucks air from to the supply the AC blows out of.
That has (essentially) nothing to with the relationship between the indoor and outdoor temp.
For simplicity, imagine a balmy 110°F outside temp, an 80°F inside temp. That's 30°F from inside to outside [and will feel refreshing], but probably results from a supply temp [the coldest air coming right out of the vent] at 68°F, a return temp [the air being drawn into the AC duct] of 88°F.
The key 20°F delta-T is the measure between the 88°F and the 68°F (both temperatures inside the conditioned [in other words, "indoor"] space). All of the other temperatures can be all over the place. Even if the outside temp was 120°F, provided the unit was sized large enough or the insulation good enough, the indoor air might average 80°F and keep the same 88°F/68°F [20°F delta-T].
As a more extreme example, your freezer probably works on a delta-T of ~10°F. That's the difference between the air going into the evap coil area and the outlet. If your indoor kitchen temperature is 80°F, your freezer still keeps things frozen even though its delta-T is only 10°F. You don't take the 10°F from the 80°F. You take the 10° from the 30-ish°F and get a warm temp of 30°F and a cold temp of 20°F in the freezer.
