Exhuast fan and ducting sizing

What type of room? What are you trying to exaust?

Where are you located? Do you have a mechanical/building code to follow?

Is there provision for make-up air? Or do you want a negative pressure room?

Guest, thank you for your reply,

My is painting material store room in a manufactuere plant which is fully air conditioner (positive pressure),due some painting materials smell want to exhaust out.

Regards

It would be better to contain properly the materials that are causing the smell.

• Are all the lids on?
• What can be done to prevent spillages?
• What operations can be moved into the fresh air?
• What else is causing the smells?
• Etc.

None of these are capital investments. They are basic housekeeping.

Why is the room air-conditioned if it is only a store room? If no-one works in there then could the air-con be turned off?

Hi! hope you have how to size the fan already solved.

Will you send you "smell" out or scrubbe it? You, most probably, don´t want the smell to be transferred from your building to the community. Size of fan be influence by this fact too. vertical arrangement --if no scrubber-- is easy, use a double suction fan, bring downwards your cilindrical duct then divide it into two rectagular legs addressed to a top suction fan. Take care not to load the fan with the duct weight.

Regards & good look, WManso

Volumetric flow rate (m³/min) = (volume of room x required no. of air changes/hr) ÷ 60. Pressure of 14.7 - 15psi is sufficient.

For 35 meter duct, air velocity of 40m/s is good. Duct cross-sectional area = air voulmetric flow rate (m³/sec) ÷ air velocity. From here you can work out the required duct Ø .

on what data are these calculations made ? (40 m/s)

Because the units of Psi and m/s do not match.

Assuming a room height of 2.44m, gives a room volume of 61m^3; and volumetric change of 2 changes/h, produces 122m^3/h, or ~2m^3/min flow. A velocity of 183m/min puts me right in the middle of the chart, at about the 12.7cm (5 inch) dia duct, for a friction loss of 0.16"H20/30m (assuming I did all the metric-to-ft conversions correctly). I wonder if 2 changes/h would be enough to get rid of the smell.

Dear flyinghigh,

Thank you very much of your very clear and good explaination to me.

Please advise what type chart you are usinf to calculate the air velocity ? and how to determine the suction blower pressure ?

Best Regards

Good morning, aikhh. I am using the Friction Loss in air ducts, Fig. 12-4, in "Air Conditioning and Refrigeration", by Jennings and Lewis, reproduced with permission from Heating Ventilating Air Conditioning Guide 1949. It plots cfm, fpm, in. duct diameter, and friction loss in inches H20/100ft.

If my calculations are correct, the blower pressure must be equal to the frictional loss of the entire length of duct, plus equivalent length of fittings, plus frictional loss of any filters or scrubbers, plus a safety factor. Good luck.