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