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An alternate Greenhouse Exhaust Fan system uses a fog or fine mist injected into the intake air stream. Although several commercial systems can be found, growers can assemble and set up their own system utilizing a high pressure piston pump and fog nozzles. The essential components are demonstrated 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 should be 5-10°F apart.

Algae growth in the pads may become a problem that may decrease the effectiveness of the system and lead to 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 uniform wetting of the pads. A commercial material or liquid household detergent at the rate of 2 tablespoons per 100 gallons may be used.

Drinking water for the pads ought to 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 drinking water. A flow rate 113 gallon each and every minute per linear foot of pad program should be provided to ensure adequate wetting.

In the most typical coolant system (fan and pad), the fans draw air through wet pads that expand the length of 1 endwall or sidewall. Aspen and coated cellulose are normal pad materials that usually have life of one to three years. Approximately one sq . foot of pad are is needed for 20 square feet of floor area.