Rooftop units are what are known as package units in the HVAC industry. A package unit is set apart from a split system, which is the common type of air conditioner/heat pump found in houses. A split system has an outdoor cabinet and an indoor cabinet with different sets of components. The outdoor cabinet has a compressor, fan, and a condenser coil; the indoor cabinet has a blower, dampers, air handler, and evaporator coil, and hooks into the ventilation system.
With a rooftop package unit, all the components are housed in one cabinet stored on the top of the building. Both sets of coils, to release and absorb heat, are in the cabinet along with the compressors and the fans. The unit connects directly into the building’s ventilation system to circulate the air.
Rooftop units can be configured either as air conditioners, or as heat pump capable of both heating and cooling. With installation of a humidistat on a rooftop unit, it can also control humidity and permit the ventilation of fresh air into the system; this is a benefit that split systems do not have, and it is a great asset for increasing indoor air quality.