The most common HVAC system used in commercial buildings is a split system. This type of system consists of two components: an outdoor unit and an indoor unit. The outdoor unit contains the compressor, condenser, and expansion valve, while the indoor unit contains the evaporator coil, blower, and air filter. The two units are connected by refrigerant lines, which allow the system to transfer heat from the indoor environment to the outdoor environment. Split systems are popular in commercial buildings because they are energy efficient, reliable, and easy to maintain. Additionally, they can be customized to meet the specific needs of the building.