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[spaghettilee]

Within the last year our studio has gone through two different HVAC units and ductwork. The most recent being installed this past week. To our dismay, the new units are louder than the last. We have two American Standard 3-ton units (one for the control room and one for the live room) with attenuaters before each of the rooms. The control room is 2,500 cu ft. and live room is approx. 9000 cu. ft. There is about 50 feet of duct between the rooms and the units. The HVAC company claims the airflow of these units can't be slowed down any more than they already have been. We think the units are too big, though the company won't admit it (especially since they had an overabundance of these units around). I think our biggest problem is that we can't find any information about any SUPER quiet HVAC units. What's the queitest unit available? The HVAC company won't give us any straight answer and there isn't much information on the net.... any help?

[franman]

In our work, there is no magic "quiet" HVAC equipment. Quiet installation are achieved by following a few basic rules:

1. Mount the equipment as distant from the air outlets and rooms as it practicle.
2. Mount the equipment on springs (properly sized!!)
3. Use LINED duct work throughout!! 1" Duct liner minimum...this will help attenuate machine noise as well as cross talk through the duct work.

now the tricky stuff:

4. The duct work must be sized to lower the air velocity to a very slow speed (compared to normal HVAC installations). We use a 400 FPM (Feet Per Minute) max in trunks within 20 feet of the air outlets and like to have it lower down to 300 FPM once you get within 20 ft of the air outlets. This is VERY SLOW compared to what HVAC guys are used to!!! They are used to 1000 FPM and higher installations and slowing the air down AT THE AIR GRILL for comfort (no wind in the rooms!!).. This will not work in studios as the noise is still generated at the air outlets.

5. OVERSIZE All your air grills and plenums at the air outlets and returns.. This will further quiet any air jet noise that is left at the point of air entering (or leaving) the room.

6. Remember how important the Return is!! I've gone into so many studios where you close the door, and the noise at the supply air inlets goes up through the roof... This is because the returns is not large enough or is restricted.. "return air starved".. It messes up the system performance and totally jacks up the noise..

What can you do now??

1. check the way the units are mounted!

2. Make sure your duct work is lined!!

3. Enlarge the last few feet of duct work and/or plenums AND the air grills to lower noise at these critical locations.

Hope you can make an improvement.. but don't go out shopping for a particularly 'quiet unit'... that's the the problem typically..

final caveat: If you've got some crappy really noisy equipment, then obviously that's a problem BUT almost all new commercial equipment is quiet compared to older stuff and totally usable for studio installations...

[lofi]

franman wrote on Mon, 04 June 2007 03:00

2. Make sure your duct work is lined!!

what doest that mean ? any link to some example ?? plzzzz

[gullfo]

duct liner info - check this description out
 http://www.owenscorning.com/comminsul/applications.asp?appli cation=97

http://www.owenscorning.com/comminsul/products.asp?product=2 89&system=81

[lofi]

i c

basicly that means that inner side of duct cannal is covered in rockwool and no srcapes or dents exist.?

i was also wondering does round or rectangle profile of duct canals make any difference ?

of course I think its much easyer to line rectangle ones but...just wondering.

[gullfo]

there's a variety of information to be found on the Internet regarding which type is best - round versus rectangular. i think its more of the care in the design and installation rather than one or the other, but i'm not an HVAC expert.