Chillers use a refrigeration cycle to cool water to 42-55 F for pumping to chilled water cooling coils. Air is then blown over the chilled water cooling coils to provide cool air to the conditioned space. DX systems also use a refrigeration cycle, but distribute refrigerant directly to DX cooling coils. High-efficiency chillers can produce chilled water using less than 0.60 kW per ton of cooling capacity. A refrigeration system must also reject the heat that it removes using a cooling tower or condenser.
Boilers produce hot water or steam to distribute to heating coils.
Though hot water is the most common fluid, steam is sometimes used because of its high heat per unit volume. Both types of boiler are typically 80-85 percent efficient. Gas is the most common fuel. Pumps circulate chilled water, hot water, and cooling tower water. Centrifugal pumps, driven by electric motors, are most common.