Each apartment or office has one or more water-cooled air conditioning units that condition that space and reject the heat into the central Condenser Water (CW). That CW is pumped by large pumps throughout the project in large pipes called risers because they usually are vertical serving A/C units in a “stack”. The CW pumps create the pressure difference that forces the flow from the supply riser through the AC unit condenser to the return riser. That pressure difference between the supply and return risers must be adequate to force enough flow through the AC unit. After returning from the risers, the warm CW flows through a heat exchanger where it transfers that heat to the cooler Cooling Tower Water (CTW). The cooled CW then moves back through the risers to repeat the process over and over again.
Other large pumps move the CTW through the heat exchanger to the Cooling Tower (CT) where the heat is exhausted to the atmosphere through evaporation. The evaporated water is replaced by metered water from the Board of Water Supply. This process continues non-stop 24/7/365. It is a very expensive process as your treasurer will verify.