Calculation of CFM discharge from an opening of a duct collar
I would like to know while designing of duct how will i calculate the cfm Airdischarge in units like CFM through a collar opening?
What is the formula for giving the collar size for air discharge.
Lets for Example I have a AHu of Capacity 1200 CFM
I have to distribute the total cfm equally through duct on three seperate room . then what will be the duct collar opening for each room so that each room will get 400 cfm each?
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Re: Calculation of CFM discharge from an opening of a...
There's a thumb rule in A/C air distribution. At 1 TR load, the air supply is about 400 CFM and the ideal diffuser size is 16" x 16" with an effective flow area of about 70%. Branch duct size for this outlet should be around 12" x 12".
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There is no equivilancy between the two...pounds of thrust would be 'foot pounds of torque' and cfm is the amount of air delivery is passing a specific sized opening in cubic feet per minute.
If you are looking at how much pressure is in for instance a residential air conditioning system, they are typically designed for .5"w.c. total system static. Meaning the pressure in the supply air duct plus the negative static added together cannot exceed .5" of water column. Approximately 28" w.c. per pound of pressure and we don't want any more than 1/2 of one inch water columm....
Now if you're talking about turbo-chargers....thats a different story and I haven't a clue.
The 70 stands for 70,000 btu and the 16 stands for 1600 cfm.. Air conditioning requires 400 cfm per ton, so the blower is capable of delivering enough air for a 4 ton a/c unit. However, the blower is is amultispeed and has a 'blower chart' in the manual that will give you an idea of air flow delivered on all 4 (usually) speeds. You wouldn't want to deliver 4 tons of air across a 3 ton coil. That would effect the temperature drop across the coil and also effect humidity removal.
4 tons of a/c is a considerable amount of cooling, so unless you have a large space or extremely high average summertime temps, I would ask a local contractor to do a heat load calculation to properly match a system to your specific needs.
Every area has a 'design temp' around which a system should be designed. Here in the St Louis area, the design temp for the winter is 5 degrees and for the summer its 95 degrees.
70,000 btu in gas equates to 20 kw in electric heat for what its worth.
their is a chart that homedepot use to give in a/c dept may still be their but a 6" run is about 100 cfm this will cover 10x10 1 sq inch is 1 cfm 1 ton is 400 cfm a gas system is 400 per ton and a heat pump is more like 425 but is best to figure the 400 cfm for both say you got 12x10 room that is 120 sq ft so you need around 120 cfm and if the 6" duct is 100% hard pipe with no flex you can get that if you balance your air if more help is needed email email@example.com please give me a vote and rating
Hi, To size that return duct you need to know the cfm of the unit, and size according to that...Ell's and distance also need to be factored in.... Here is a free duct calc. that you can use to help you size you ductwork...
Yes, but why more cfm? you need the proper cfm to match the tonage higher cfm wont accommodate your present blower wheel .have a load calculation done. A reputable contractors will do it for free as long as ya buy from them you will be happier with a prorerly sized unit. Good Luck Tom
there are online formula to calculate what you want
google ---formula to calculate air flow in pipes--
calculation will have to allow for the turbulence and restriction caused by the spiral construction of the tubing and the bends involved so you may have to incorporate several formulas to get the desired result
distance is critical as there are frictional coefficients to be considered as well
I would consider from large shop air circulation systems (as you see in Aldi, woolworths , sears etc ) that a staged diameter difference from motor to exhaust point be considered as that will keep a steady air flow for the length of the tube and a hp rating of 3hp 3 phase as a minimum
Talk with the engineers of shop and factory air conditioner designers and installers to get a close idea to what would be suitable for you
Here are a few ways to calculate your BTU's.
Get ready to use that algebra you thought you'd never use.
1 Ton = 12000 BTU's
400cubic feet per minute (CFM) = 1 Ton on standard ac units (300 is an absolute minnimum)
BTU's air heat = difference in temp. ( ∆T ) x 1.08 x CFM ∆T = BTU's / (1.08 x CFM) i.e. 65◦F entering your unit and 93◦F air leaving on a 12000BTU unit. ∆T = 28 CFM = 400 28 x 1.08 x 400 = 12096BTU's Another way... Electric heat calculations. BTU's = KW (killowatts) x 3413 Watts = Volts x Amps (single Phase) Most Homes)) Watts = Volts x Amps x Phase (this is for three phase units.)three wires and a ground)) 120 volts 30 amps single phase (common) 120 x 30.0 x 1 = 3600 or 3.6KW 3.6 x 3413 = 12286BTU's