Residential HVAC systems are much smaller and require less energy than commercial systems. Usually, a residential HVAC system is only cooling a house or single-family residence, so the air volume that is being cooled or heated is much lower than in a commercial space.
Commercial buildings have massive amounts of air that need to be cooled or heated efficiently. These require vast, modular rooftop units that can be set up to cool or heat tens of thousands of cubic feet of air.