An alternate system uses a fog or good mist Greenhouse Exhaust Fan injected into the intake air stream. Although a number of commercial systems are available, growers can assemble and install their own system using a high pressure piston pump and fog nozzles. The essential components are shown in Fig. 1. A two-stage system controlled 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 development in the pads may 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 is desirable, especially in hard drinking water areas, to include a wetting agent to the water to obtain more uniform wetting of the pads. A commercial materials or liquid household detergent at the price of 2 tablespoons per 100 gallons may be used.

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 accustomed to recirculate the water. A flow rate 113 gallon each and every minute per linear foot of pad system should be provided to ensure adequate wetting.

In the most common coolant 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 normal pad materials that always have life of one to three years. Approximately one sq . foot of pad are is needed for 20 square foot of floor area.