An alternate system runs on the fog or fine mist injected into the intake air stream. Although several commercial systems are available, growers can assemble and install their own system using a ruthless 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 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 decrease the effectiveness of the system and result in accelerated deterioration of the pads. The addition of an algaecide to the drinking water supply will help in control.

It is desirable, especially in hard water areas, to add a wetting agent to the drinking water to obtain additional Greenhouse Exhaust Fan uniform wetting of the pads. A commercial material or liquid household detergent at the rate of 2 tablespoons per 100 gallons can 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 water. A flow rate 113 gallon per minute per linear foot of pad system should be provided to make certain 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 coated cellulose are common pad materials that usually have life of 1 to 3 years. Approximately one sq . foot of pad are is necessary for 20 square feet of floor area.