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. Most facilities use packaged air handlers, but built-up air handlers may be found in larger facilities. All air handlers adjust air temperature and humidity and remove dust and other particles from air before distributing it to occupied spaces. This is accomplished through a series of coils, filters, humidifiers, fans, and dampers. Ducts, plenums and shafts distribute air.