An alternate system runs on the fog or fine mist 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 basic components are proven 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 Greenhouse Auto Vent should be 5-10°F apart.

Algae growth in the pads may become a problem that will reduce the effectiveness of the system and lead to accelerated deterioration of the pads. The addition of an algaecide to the drinking water supply can help in control.

It really is desirable, especially in hard drinking water areas, to include a wetting agent to the 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 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 per 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 covered 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 foot of floor area.