Humidifiers are used in air conditioning systems to increase the humidity of the air. There are several types of humidifiers: Adiabatic Humidification Process Adiabatic Humidifier with Recirculation of Spray Water Adiabatic Humidifiers without Recirculation of Spray Water Spray Water with Recirculation and Heating or Cooling Steam humidifiers are also used in air conditioning system. The two basic types are: Direct steam injection Pan steam humidifier