A chilled water/glycol system contain two primary components: the chiller unit and the air handling unit. This system uses one or more central chiller units as it cools either water or, typically, a glycol-water solution. The glycol-water mixture leaves the chiller unit, and it is pumped through pipes connected to the air handling units. Within the air handling units, the glycol-water solution passes through cooling coils. Air from the room is directed through the coil and becomes conditioned.
Compared to a RTU system, the coil temperature of a chilled water system is controlled by adjusting the temperature of the glycol-water solution feeding the coil. This allows for greater control over the room humidity, as well as greater diversity in the sizing of the unit. These units can better adapt to the conditions in the room and provide better overall temperature and humidity control. However, chilled water systems require piping, control valves, and pumps in addition to the chiller and air handling units. This may create more system maintenance, but these systems can be more energy efficient (which can offset the additional maintenance costs).