An alternate system runs on the fog or great mist injected into the intake air stream. Although several commercial systems are available, growers can assemble and install their own system utilizing a ruthless piston pump and fog nozzles. The essential components are demonstrated in Fig. 1. A two-stage system controlled by a two- stage thermostat allows more water to be employed on excessively warm, bright days. Temperature settings should be 5-10°F apart.

Algae growth in the pads can become a problem which will reduce the 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 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 materials or liquid household detergent at the rate of 2 tablespoons per 100 gallons may be used.

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

In the most Greenhouse Auto Vent common coolant system (fan and pad), the fans draw air through wet pads that expand the length of one endwall or sidewall. Aspen and covered cellulose are common pad materials that always have life of one to 3 years. Approximately one square foot of pad are is needed for 20 square feet of floor area.