Question about Carrier Heating & Cooling

# Calculation of CFM discharge from an opening of a duct collar

Dear sir,

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?

Regards
M.A.Shah
09314545556

Posted by on

• weathermaker Jun 20, 2009

I want the formula for calculating the size for air distribution from duct collar.

×

• Level 2:

An expert who has achieved level 2 by getting 100 points

MVP:

An expert that got 5 achievements.

Vice President:

An expert whose answer got voted for 100 times.

Sergeant:

An expert that has over 500 points.

• Expert

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".

Posted on Jun 20, 2009

• Boyet Soriano Jun 22, 2009

I assumed that you have an engineering background. Designing a simple centralized A/C system is a complicated job. Its not simply deviding the the total air volume flow to the number of rooms you want to supply air. You need to know the exact A/C load for each room, the contaminants present, the amount of fresh air to supply to ventilate the rooms, the orientation of the rooms, and you need to have a stong knowledge of air psychrometry. Anyway if you really insist in knowing the equation for air flow in a circular duct, the equation is Q = f x Ai x V, where Q is in CFM, Ai (inside cross sectional area of duct, V is the velocity of air in FPM, and f is the flow factor. In ducts the ideal V is 1700 FPM w/ f = 0.75. For air diffusers V is 400 FPM w/ f = 0.85 to .90. Let me remind you theat the air flow from the outlet of the fan to the farthest air outlet will experience a pressure drop . Your calculations should consider this factor. You may assume an equal pressure drop to each outlet. Goodluck to your design!

×

• Level 1:

An expert who has achieved level 1.

• Contributor

Dear sir please forward to me air conditioning grill cfm formula,
how is measure this calculation .
ashraf15.1979@rediffmail.com
mobile:9095553022
Best Regards
M.Ashraf

Posted on Nov 10, 2011

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017

×

my-video-file.mp4

×

## Related Questions:

### 35,000 cfm = ?pounds trust

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.

Mar 04, 2015 | Cfm Heating & Cooling

### What size coil fits this

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.

Jun 15, 2014 | Comfortmaker G8MXN0701716A 66,000 BTU 80%...

### How do you calculate cfm for a room when sizing a hvac system fr a residential

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 pendletonheatandair@hotmail.com please give me a vote and rating

Sep 22, 2010 | Cfm Heating & Cooling

### How to properly size a duct return in a house

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...

Here is a website that will let you get a free trial duct calc.

http://efficientcomfort.net/Calculators.html

Here is another free duct clac...

Heatman101

Sep 21, 2010 | Coleman Heating & Cooling

### How to calculate cfm of air compressure . we have required one air compressure having 7bar-10 bar pressure how much cfm it will have

If you are still looking for an answer to this question, here is a website that will explain how to calculate CFM of an air compressor...

http://www.ehow.com/how_5001852_calculate-cfm-air-compressor.html

Jun 26, 2010 | Atlas Copco LS 16 Hydraulic Cut-Off Saw...

### I have a Rheem RT-36-ACU-N that acts like it needs a blower motor. Also I am replacing the AC unit this fall with one that has a higher SEER number. Can the motor be replaced with one that will have a...

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

Jun 30, 2009 | Heating & Cooling

### What size duct do I need

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

Aug 02, 2017 | Jenn-Air Ventilation System for Custom...

### What size rangehood is required

Hello, here is the best you can get at the moment without further information about your unit,installation location, etc..

go here:http://www.engineeringtoolbox.com/exhaust-hoods-d_1036.html

there are formulas for calculation hood cfm, and a calculator to input your dimensions that should get you close.

With that said, I would advise that if is that critical, call or contact someone in your area that does this all the time, HVAC companies/installers should be able to do this.

Hope this helped, and thank you.

Feb 04, 2009 | Garland H283 Gas Kitchen Range

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. 65F entering your unit and 93F 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

Aug 09, 2008 | LG BG8000ER Air Conditioner

## Open Questions:

#### Related Topics:

1,514 people viewed this question

Level 3 Expert

Level 3 Expert