There are Three main types Hvac Systems
Equipment and systems generally fall into three main types, all-air, all-water and all-refrigerant, however, in every case, refrigerant is used as the final cooling source or medium.

Most systems these days are also referred to as air cooled, as opposed to water cooled. That is, the final rejection of heat to external atmosphere is via air, using a dry coil and fans. Water-cooled systems use a cooling tower and if this is not properly maintained can lead to problems with legionnella or legionnaires disease.

All-Water systems
Water based systems use a single chiller plant or chiller plus boiler to produce water which is then pumped around a building to, most commonly, fan coil units; a fan blows air over a coil containing the water, which then cools or heats the room air. The heat rejected from the room to the water is then pumped back to the chiller unit where it is rejected by a condenser to external air. The water is then chilled or heated again and pumped back to the room units.

This type of system is generally the most expensive to install and own, and is classed as the least energy efficient in terms of transfer of energy