An alternate system uses a fog or fine mist injected into the 
intake air stream. Although several commercial systems can be found, growers can assemble and install their own system using a high pressure piston pump and fog nozzles. The basic components are demonstrated in Fig. 1. A two-stage system controlled by a two- stage thermostat enables more water to be applied on excessively warm, shiny days. Temperature settings ought to be 5-10°F apart.
Algae development in the pads may Greenhouse Auto Vent become a problem which will decrease the effectiveness of the system and result in accelerated deterioration of the pads. The addition of an algaecide to the water supply can help in control.
It really is desirable, especially in hard 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 rate of 2 tablespoons per 100 gallons can be used.
Water for the pads should be clean and low 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 each and every minute per linear foot of pad program should be provided to guarantee adequate wetting.
In the most typical cooling system (fan and pad), the fans draw air through wet pads that lengthen the length of one endwall or sidewall. Aspen and covered cellulose are common pad materials that always have life of one to three years. Approximately one square foot of pad are is needed for 20 square feet of floor area.