How Many Misting Fans Do I Need and Where Do I Put Them?
As a reference our 24” Misting Fans moves approximately 7500 cubic feet (230 cubic meters) of air per minute; this number can be greatly increased where positive pressure ventilation techniques can be employed.
Generally speaking, to achieve maximum indoor or protected area misting fan cooling, you will want to transfer the total volume of air in the space being cooled every 1 to 2 minutes. The appropriate transfer time will depend on the space’s insulation, how closed in it is (is it a warehouse or a canopy), prevailing humidity, acceptable humidity increase and the total temperature drop desired.
When cooling indoor areas with misting fans, it is important to remember that you will need to take advantage of any natural flow of air. You can check for existing ventilation by turning on the mist fans without the fan on and watch where the mist goes. You will also need to determine your source of outside air and where your outlet for the air is. Very often the outlet will be a door or a window on the opposite side of the structure from the inlet air.
Factory 50′ (15 m) length x 80′ (25 m) width x 15′ (4.7 m) ceilings
Totally enclosed structure with fairly good insulation
Complete air transfer every 2 minutes
Calculation of Volume
Length x Width x Ceiling Height
50′ x 80′ x 15′ = 60,000 cubic feet
Factory 16 m x 25 m x 4.7 m = 1880 cubic meters (m)
Calculation of Misting Fans Needed=Volume/(Fan VolumexTransfer Time)
60,000 / (7500 cubic feet x 2 minutes) = 4 fans
1880 / (230 cubic meters x 2 minutes) = 4 fans
Four misting fans will completely transfer the air in this structure every two minutes and should effectively cool this factory. The misting fans should be placed in the oscillation mode to spread the mist throughout the factory and should be pointed in a direction that keeps the air flow moving in the desired direction.
Whenever possible use any natural breeze or air flow to your advantage (point the misting fans the same way the air is moving) Use Positive Pressure Ventilation techniques wherever applicable (See discussion of Positive Pressure Ventilation techniques below) In places where it is either impossible or un-economical to cool the whole structure or area with misting fans, set up smaller misting fan cool areas. In most applications, the mist from the misting fan should be directed slightly above head level.
Positive Pressure Ventilation Techniques
The misting fan is placed on the outside of the structure so that the “air cone” completely seals the opening (A). When this seal is achieved, the air pressure is increased equally at all points inside the structure.
When an exhaust opening is created (B), all of the interior air moves in one mass. This results in faster, more efficient ventilation of the entire structure.
In a large space, additional misting fans should be placed within the structure to achieve maximum cooling. By using this technique, it would be possible to use only 3 misting fans, with larger orifice mist nozzles.