An alternate system uses a fog or great mist injected in to the intake air stream. Although many 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 employed on excessively warm, bright days. Temperature settings 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 water supply will help in control.
It is Greenhouse Auto Vent desirable, especially in hard water areas, to include a wetting agent to the drinking 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 can be used.
Water for the pads ought to be clean and lower in mineral content to avoid 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 ought to be provided to ensure adequate wetting.
In the most typical 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 common pad materials that usually have life of one to 3 years. Approximately one square foot of pad are is needed for 20 square feet of floor area.