Anyone Know How to Size Ductwork for AC/Heating?

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DigitalDon

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I've found several on-line demos for this but they don't really tell me the actual size the ductwork should be. I can supply the parameters if someone knows this stuff.


DD
 
DigitalDon said:
I've found several on-line demos for this but they don't really tell me the actual size the ductwork should be. I can supply the parameters if someone knows this stuff.


DD
how many rooms and how big?
 
Thanks for the reply. See the link below but change the dimensions to the following. The total building is 1200 sqft (30'x40'). It's a metal building with R13, resilient channel and 5/8" sheetrock on all exterior walls. The metal roof has an R11 blanket under it. There are 2 main rooms to be conditioned. The live room is 23 1/2' wide by 28' deep. It has a cathedral (suspended) ceiling that starts on the 23 1/2' walls at 8' and peaks at 13'. If I figured right the square footage is about 658 sq ft and volume is about 6,909 cu ft. I didn't take into account the angled wall of the vocal booth to keep it simple. Oh and the HVAC is no longer in the corner of the live room. It's now over the hallway near the entrance (the air handler is a horizontal draft unit).

The control room is 14 1/2' wide by 22 1/2' deep. It also has a cathedral (suspended) ceiling. The ceiling starts at the near side (door) at about 10', continues up to the peak at 14' then drops down to the opposite wall at 8'. Again, if I figured right the square footage is about 326 sq ft and volume is about 3,589 cu ft. I didn't take into acount again the angled wall of the vocal booth. Oh and I won't be ducting into the vocal booth.

If I figured right the total heated/cooled sq footage is about 984 sq ft with volume of 10,498 cu ft.

The suspended ceiling doesn't have insulation laying on it. The live room has 18'' of clearance above it and the control room has 8" clearance. The plywood floor over the hall extends over the vocal booth and bathroom so I figured wall registers would be required to the control room due to lack of overhead clearance. I assume the ductwork to the live room would be best with supply registers at the far end and a return register closer to the front near the hall door.

Here's the kicker. I got a 3 ton split unit for a great price. The outside unit is 3 ton and the air handler is 3 ton. I know that's overkill for a building this size but I want to make it work. I'm sure the ducts will have to be pretty large to dump that much tonnage. Also, it won't be running during actual recording as I'm sure it'll be a little windy.

Additional info: Location (if you're using software that lists it) is near Albany, Ga for environmentals. There is only one door (metal) and no windows. On the drawing the exterior wall to your left is North. Lights are: Live Room - 4 flourescent fixtures (4 tube 32W) and four sets of track lights (4 x 40W each). Control Room - 1 flourescent fixture (same as above) and 2 sets of track lights (same as above).

Let me know what additional info you need and I'll get it. My son's band is doing a benefit tonight for a cancer patient so I won't be home until about 1:30 AM.

Sorry this got so long.

Here's the link.

http://www.homerecording.com/bbs/showthread.php?threadid=64775

Thanks for the help
DD
 
Looks like I'll have to use the "P" word (pay) to get someone out here to spec the duct work. I guess my windows will have to wait a little while longer. My "budget" is already busted anyhow :eek:

DD
 
Don, the only tidbit of info I can provide off the top of my head, is Everest's comment that air NOISE is roughly proportional to the 4th or 5th POWER of velocity - so, if a normal HVAC system needed ducts that were 1 sq ft, and you increased the size to 2 sq ft, you wouldn't have just half the noise, but MUCH less - all the comments I've seen on studio HVAC relate to larger, slower, softer, more corners in ducts, making EACH run start from the unit and not breaking off at each room, etc - The other notable I remember is that squirrel cages are MUCH quieter than axial fans.

If you already have the unit and it's found to be really overkill, maybe you could swap motor or pulleys to slow it down - that would be the one biggest improvement in noise level you could do.

Also, rubber boots for isolating ductwork from HVAC unit, cushion mounts on fan unit, saw something about specific resonant frequency of motor/fan unit needing specific mount resonance or cushions actually making things LOUDER...

Lining ductwork, particularly at corners, cuts noise - If you have a specific noise frequency, a tuned resonator/plenum chamber, with hangers (like bass traps) inside -

'Bout all I remember, the "bible" is at work again, gotta think seriously about ordering a second copy. Hope this helped some... Steve
 
Don, just a little advice from someone who is married to a construction estimator..... check your local building department for the codes in your area!!!

That work is gonna get real expensive if they come in and find it's not up to code and you have to rip it out and start all over again....
 
Thanks for the info Steve. The fan is a direct drive squirrel cage and has 3 speed settings (set by jumpers). The only problem there is you have to move enough air to unload the system. If you don't move as much as the system (particularly cooling) provides then you stand a chance of freezing up your cooling coils (in the air handler).

I will be using insulated flex duct (not metal) for both supply and return trunks. Probably either 12" or 14". Like you said, better to have the duct work oversize to quite it down some. Registers for supply and return will be 2'x2'.

At this time I don't intend to have the air running during actual recording. That's why the thermostat will be next to my desk.


Tim - I live in a rural area and code is not a problem. Still, everything I've done so far is to code just because it should be. I can sleep easier at night knowing the studio isn't going to burn down or someone get shocked due to faulty electrical.


DD
 
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