An air cooled chiller is a machine that removes heat from a liquid via a vapor-compression cycle. Air cooled chillers are directly cooled by ambient air being mechanically circulated directly through the machine's condenser coil to expel heat to the atmosphere. The two types of air cooled chillers are scroll compressor air cooled chillers and screw compressor air cooled chillers. Scroll compressors are used for the smaller air cooled chillers, and screw compressors are used for larger air cooled chillers and have a variable speed drive option for increased efficiency.