An alternate system runs on the fog or fine mist injected into the intake air stream. Although several commercial systems can be found, growers can assemble and set up their own system utilizing a ruthless piston pump and fog nozzles. The essential components are shown in Fig. 1. A two-stage system controlled by a two- stage thermostat enables more water to be employed on excessively warm, bright days. Temperature settings should be 5-10°F apart.
Algae development in the pads may become a problem that may reduce the effectiveness of the machine and result in accelerated Greenhouse Auto Vent deterioration of the pads. The addition of an algaecide to the drinking water supply will help in control.
It really is desirable, especially in hard drinking water areas, to add a wetting agent to the water to obtain more uniform wetting of the pads. A commercial material or liquid home detergent at the price of 2 tablespoons per 100 gallons may be used.
Water for the pads ought to be clean and low in mineral content to avoid clogging and coating of the pads. A pump, pipes and gutters are accustomed to recirculate the water. A flow rate 113 gallon per minute per linear foot of pad program should 
be provided to guarantee adequate wetting.
In the most common cooling system (fan and pad), the fans draw air through wet pads that expand the length of one endwall or sidewall. Aspen and covered cellulose are normal pad materials that usually have life of 1 to 3 years. Approximately one sq . foot of pad are is necessary for 20 square ft of floor area.