An alternate system runs on the 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 utilizing a ruthless piston pump and fog nozzles. The basic components are shown in Fig. 1. A two-stage system managed by a two- stage thermostat allows more water to be applied on excessively warm, bright days. Temperature settings ought to be 5-10°F apart.
Algae development in the pads can become a problem that may decrease the Greenhouse Auto Vent effectiveness of the system and lead to accelerated deterioration of the pads. The addition of an algaecide to the water supply can help in control.
It is desirable, especially in hard water areas, to add a wetting agent to the drinking water to obtain additional uniform wetting of the pads. A commercial material or liquid household detergent at the price of 2 tablespoons per 100 gallons may 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 per minute per linear foot of pad system should be provided to make sure 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 coated cellulose are common pad materials that always have life of 1 to three years. Approximately one square foot of pad are is needed for 20 square ft of floor area.