Spray booths must ensure an equal volume of air is coming into and out of the booth to achieve a balanced airflow. This is achieved with the use of an intake fan and an exhaust fan. The exhaust fan draws substantial quantities of air out of the booth to ensure the air change rate remains consistent with the quality of the finish required, while air make up is the opposite, this is the mechanical replacement of air that has been exhausted out.
Negative pressure spray booths are a result of more air been removed than air that is put in. This can result in dust, debris and contamination been pulled into the space through cracks, crevasses and pulled up from floors in the case of cross draught booths. To rectify this situation, a supply air system is put into place to replace the air as it is removed. Industrial fans are the mechanical component that ensures air is pulled in and out of the paint booths. Axair customer who are primarily spray booth manufacturers choose the R63 / LRHF impeller due to its lightweight design and the less cumbersome nature of integrating it into their spray booth design unlike traditional twin fans supplied by older competitors. The aluminium impeller of the R63 will also not spark, causing a fire which is important when working with flammable coatings. Blower fans or backward curved centrifugal fans are often designed to work alongside to force air back into the booth.
There’s a delicate balance between supply and exhaust air. Spray booth manufacturers ensure that airflow and pressure are precisely matched by allowing fan experts such as Axair to select the correct fan to achieve the operating duty and required fan performance in line with the size of the room and the required finish. If a door is opened in a spray booth during operation and the airflow is balanced, this will cause dust and debris to be sucked in, as a slight amount of air is let in causing the environment to become a negative pressure space.
A positive pressure environment makes for a cleaner booth, so when a door is opened, the air is pushed out, creating an airflow path that blocks out external dust. debris and contaminants from entering the booth. A positive pressure room is created by having more supply air than is exhausted. This is often supplied by a make up air unit or through supply fans delivering a greater airflow into the booth.
Sizing a fan that is suitable for a spray booth is dependent on the paint booths size. For this you require the width and height of the booth in feet.
Width of booth (ft) x Height of Booth (ft) x 100
This will give the cubic feet per minute. This can quickly be converted to m3/hr to enable us to review our fan selection based on this duty.
Let’s do an example:
Width: 100ft
Height: 100ft
100 x 100 = 1000, 1000 x 100 = 10,000 CFM
CFM – M3/hr is 16,990m3/hr is determine as the air movement requirement in the booth area. This is the size of the fan needed.
It’s simple to tell when airflow is incorrect in a booth, overspray may be hanging around for a little longer than normal, finish quality is reduced and the environment generally appears to take a while to clear. Airflow readings are crucial to determine if the fan is affected, filters may be dirty and need changing or airflow calculations are incorrect. Not having the correct airflow rate also means you may be creating a hazardous environment and violating spray room standards according to OSHA. Learn more about airflow styles and how the use of industrial fans can affect the quality of the finish.
Learn more about positive and negative pressure in medical containment applications.