There are a number of methods to humidify air.
The most common method is injecting steam into the air stream. This is done via a steam distributor mounted in the air stream of the unit. The steam distributor is piped to a humidifier. The humidifier can be either electric or natural gas and supplied as part of the unit or supplied by others.
Air atomizing is another method of humidification. This also involves mounting a distributor in the air stream. This distributor has separate water and compressed air lines feeding it. Through a valve arrangement the water and compressed air mix atomizing the water as it enters the air stream.