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 essential components are shown in Fig. 1. A two-stage system managed by a two- stage thermostat enables more water to be applied on excessively warm, bright days. Temperature settings ought to be 5-10°F apart.
Algae development in the pads can become a problem that will reduce the effectiveness of the machine 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 water areas, to include a wetting agent to the drinking water to obtain additional uniform wetting of the pads. A commercial material or liquid home detergent at the price of 2 tablespoons per 100 gallons may be used.
Water for the pads should be clean and low in mineral content to avoid Greenhouse Auto Vent 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 program should be provided to assure adequate wetting.
In the most common coolant system (fan and pad), the fans draw air through wet pads that lengthen the length of 1 endwall or sidewall. Aspen and covered cellulose are common pad materials that usually have life of one to three years. Approximately 
one square foot of pad are is necessary for 20 square feet of floor area.