An alternate system uses a fog or good mist injected in to the intake air stream. Although a number of commercial systems can be found, growers can assemble and install their own system using a high pressure 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, shiny days. Temperature settings should be 5-10°F apart.
Algae development in the pads may become a problem which will decrease the effectiveness of the system and lead to accelerated deterioration of the pads. The addition of an algaecide to the water supply will help in control.
It is desirable, especially in hard 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 price of 2 tablespoons per 100 gallons may be used.
Water for the pads ought to be clean and low in mineral content to prevent 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 system ought to be provided to make sure adequate wetting.
In the most common coolant system (fan and pad), the fans draw air through wet pads that lengthen the length of 1 endwall or sidewall. Aspen and covered cellulose are normal pad materials that Greenhouse Exhaust Fan always have life of one to 3 years. Approximately one square foot of pad are is necessary for 20 square foot of floor area.