In 1921, Carrier invented the centrifugal chiller which allowed his company to air condition very large spaces. Earlier air conditioners used piston driven compressors to pump refrigerant but Carrier designed a compressor modeled after the centrifugal turning blades of a water pump. This design proved to be safer and much more efficient allowing for larger designs.
In 1922 Willis Carrier made two critical breakthroughs. First he replaced the toxic coolant ammonia with the much safer coolant dielene. Secondly he greatly reduced the size of the units. This led to air conditioning units being installed places like department stores, office buildings, railroad cars and other small buildings.