An alternate system uses a fog or fine mist injected in to the intake air stream. Although a number of commercial systems are available, growers can assemble and install their own system utilizing 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 Greenhouse Exhaust Fan excessively warm, shiny days. Temperature settings ought to be 5-10°F apart.
Algae development in the pads can become a problem that will reduce the effectiveness of the machine and lead to accelerated deterioration of the pads. The addition of an algaecide to the water supply will help in control.
It really is desirable, especially in hard drinking water areas, to include a wetting agent to the water to obtain more uniform wetting of the pads. A 
commercial material or liquid household detergent at the rate of 2 tablespoons per 100 gallons may be used.
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 water. A flow rate 113 gallon per minute per linear foot of pad system should be provided to assure adequate wetting.
In the most typical coolant system (fan and pad), the fans draw air through wet pads that extend the length of one endwall or sidewall. Aspen and coated cellulose are normal pad materials that always have life of 1 to three years. Approximately one sq . foot of pad are is necessary for 20 square foot of floor area.