An alternate system uses a fog or fine mist injected in to the intake air stream. Although many commercial systems are available, growers can assemble and set up their own system utilizing 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 enables more water to be employed on excessively warm, bright days. Temperature settings should be 5-10°F apart.
Algae development in the pads may Greenhouse Exhaust Fan become a problem that may decrease the effectiveness of the machine and result in accelerated deterioration of the pads. The addition of an algaecide to the drinking water supply will help in control.
It really is desirable, especially in hard water areas, to add a wetting agent to the water to obtain additional uniform wetting of the pads. A commercial materials 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 clogging and coating of the pads. A pump, pipes and gutters are accustomed to recirculate the water. A flow rate 113 gallon per minute per linear foot of pad system ought to be provided to guarantee adequate wetting.
In the most common coolant system (fan and pad), the fans draw air through wet pads that prolong the length of one endwall or sidewall. Aspen and coated cellulose are common pad materials that usually have life of 1 to 3 years. Approximately one square foot of pad are is needed for 20 square feet of floor area.