An alternate system runs on the fog or fine mist injected in to the intake air stream. Although many commercial systems are available, Greenhouse Exhaust Fan growers can assemble and install their own system utilizing a high pressure piston pump and fog nozzles. The essential components are demonstrated in Fig. 1. A two-stage system controlled by a two- stage thermostat allows more water to be applied on excessively warm, shiny days. Temperature settings should be 5-10°F apart.
Algae development in the pads may become a problem that 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 drinking water areas, to include a wetting agent to the drinking water to obtain more uniform wetting of the pads. A commercial materials or liquid home detergent at the price of 2 tablespoons per 100 gallons can be used.
Drinking 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 used to recirculate the drinking water. A flow rate 113 gallon each and every minute per linear foot of pad system should be provided to assure adequate wetting.
In the most common cooling system (fan and pad), the fans draw air through wet pads that extend the length of one endwall or sidewall. Aspen and covered cellulose are normal pad 
materials that always have life of one to three years. Approximately one square foot of pad are is necessary for 20 square feet of floor area.