What type of air system is classified under indirect open spray systems?

Indirect open spray systems are designed to cool or humidify air using the principles of evaporation without directly adding humidity to the air stream that is to be conditioned. Air washers, in particular, fit this classification as they work by passing air through water or over a water surface to gain moisture and also cool the air through the evaporation process.

In air washers, the air is cooled as it moves through the system and comes into contact with water that is either sprayed or splashed within the unit, allowing for efficient heat exchange. This process results in a cooling effect while indirectly maintaining humidity levels in the air.

Other options, while they relate to air systems, do not fit the criteria for indirect open spray systems as precisely. Air conditioning units primarily use refrigerant cycles for cooling instead of evaporation directly from water sources. Evaporative coolers do incorporate a direct evaporation process but are not considered indirect systems. Forced air systems typically rely on blowers to circulate air and do not inherently use the evaporative cooling method described in indirect open spray systems.