How to Size a Telescopic Spray Booth: Dimensions, Airflow and Fan Power
Quick answer: Size the internal length, width and height from the largest workpiece plus 1.5-2 m of working space on each side and above; multiply width by height by 0.3 m/s (minimum cross-draft) to get the airflow in m3/s; then select a centrifugal fan that delivers that airflow against the pressure drop of the filter wall, ducting and exhaust treatment. A 20 x 10 x 4 m booth needs about 12 m3/s (43,000 m3/h) at the minimum velocity and is normally fitted with a 75 kW fan rated 54,000-79,400 m3/h to cover filter loading and treatment losses.
Step 1: fix the internal dimensions
Take the longest, widest and tallest part that will be painted in the booth, not the average one. Add 1.5-2 m on each side for the painter and hose, and 1-1.5 m above the part for the spray pattern and lighting. Frames are made in 1 m modules, so round the length up. Check the crane hook height: the booth height plus frame depth must clear the hook when the booth is retracted, and the part on its stands must clear the folded frames.
Step 2: calculate the airflow
Cross-draft booths are ventilated along their length, so the controlling section is width x height. At the minimum 0.3 m/s used in our specifications: a 10 x 4 m section gives 12 m3/s or 43,200 m3/h; a 7 x 4.5 m section gives 9.45 m3/s or 34,000 m3/h; a 5 x 4.1 m section gives 6.15 m3/s or 22,000 m3/h. Heavier solvent use or a stricter workplace exposure limit calls for 0.4-0.5 m/s and proportionally more air.
| Booth L x W x H (m) | Section (m2) | Airflow at 0.3 m/s (m3/h) | Fan fitted | Treatment |
|---|---|---|---|---|
| 20 x 10 x 4 | 40 | 43,200 | 75 kW, 54,000-79,400 m3/h | carbon + UV, 50,000 m3/h |
| 12 x 7 x 4.5 | 31.5 | 34,000 | RCO unit fan 45 kW | RCO, 30,000 m3/h |
| 12 x 5 x 4.1 | 20.5 | 22,100 | shared with second booth | RCO, 30,000-40,000 m3/h |
| 13 x 5 x 3 | 15 | 16,200 | per oil-film unit | oil film + carbon |
Step 3: select the fan
The fan must deliver the airflow at the total pressure drop of the system: labyrinth paper filter (rising from about 40 Pa new to 250 Pa at change-out), glass-fibre bag, carbon beds, UV unit or RCO, ducting at 12 m/s or less and the stack. Centrifugal fans on anti-vibration mounts with star-delta or VFD starting are standard; the VFD lets the plant run at the minimum velocity when the filters are new and raise speed as they load. Fan noise is held to 85 dB(A) or less and booth noise to 80 dB(A) or less.
Step 4: check power and stack
Installed power for a 20 m booth with a 75 kW fan, two 1.5 kW drives, a 30 kW UV unit and 60 explosion-proof 18 W LEDs comes to about 109 kW. The stack height follows the local emission rule; 15 m above ground is the value used in our standard proposals.
Step 5: decide the number of booths
Two booths 30 m apart can share one treatment unit through ducting, as in a plant that runs an 8 m2 and a 20 m2 booth on one RCO. Sharing saves a treatment unit but means both booths draw through the same fan, so the damper settings must be set at commissioning and locked.
FAQ
What velocity should I specify? 0.3 m/s is the minimum in our specifications; 0.4-0.5 m/s for heavy solvent use or where the workplace exposure limit for xylene and toluene must be met with margin.
Can I use a smaller fan and lower velocity to save energy? Below 0.3 m/s overspray drifts back onto the painter and the finish; use a VFD and run at the minimum instead.
How is the filter pressure drop monitored? A differential pressure gauge across the filter wall; filters are changed when it reaches about 250 Pa.
Does booth length change the airflow? No, airflow follows the cross-section; length changes the fabric area, the number of frames and the lighting count.
Where MUSI Technology fits
MUSI sizes the enclosure, fan and treatment from your part drawings and paint consumption, and states the velocity, airflow and noise values in the written specification. Product details, typical sizes and the quotation checklist are on the telescopic mobile spray booth page.
Provided by Lin Cong, Technical Director, MUSI Technology
Send us your part size, throughput and coating type — our engineers reply with a layout and budget within one working day. Contact MUSI Technology or browse our equipment range.
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