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STR06 (Civil/Environmental) (OP)
18 Nov 10 9:14
I currently have a HVAC company designing replacement HVAC units for a number a School gymnasiums. The problem is there is no duct work in the gym space, simple one or two supply and returns often located in close proximity. I am used to seeing a plenum or a grid of supply and returns. My concerns are poor air flow and noise caused by high velocity. Any comments?
WindOption (Mechanical)
18 Nov 10 13:44
How you doing STR06, Could you upload a drawign that we could see?
Ziggypump (Mechanical)
18 Nov 10 14:00
Gymnasiums are different creatures when it comes to heating and cooling.  They're usually so large (tall) that heating is an issue.  Most of the Gyms that I see are open construction to the deck, with no ceiling to allow a plenum, so the ductwork is exposed.  These types of cases it's almost imperative that the return be located low.

Noise may be an issue, just make sure that the ducts are internally lined acoustically, that usually keeps the noise down.  You can always ask to see some acoustic calculations to make sure the duct doesn't get too loud.
AnotherEllis (Mechanical)
19 Nov 10 8:26
Why is the HVAC company doing the design? Do they have a PE on staff?

www.ellisconsultingengineers.com

Drazen (Mechanical)
19 Nov 10 11:03
With supply and return ducts being close, they could eventually use nozzles directed to opposite low end of hall, with exhaust grilles being on top of return duct, but that needs to be carefully designed, otherwise real mess with drafts can occur, causing even mass health problems.

That is woek which should not be done without licensed designer, contractor should not even do replacement if they do not have approach to original design, to be able to responsively confirm that they are replacing equipment with equal components.

If components are not equal, but substitutes, again licnesed designer is needed to confim it.

This is rather serious issue in my opinion. I am surprised that you are not concerned about liability.
MechEngNCPE (Mechanical)
8 Feb 11 12:28
There at least needs to be a supply duct for each rtu, and I would use drum louvers for the high throw you will need to get down to the occupants.  Return duct is optional.
MechEngNCPE (Mechanical)
8 Feb 11 13:51
Ziggy, it is not industry standard to specify lined duct anymore, it tends to break apart after a while and lead to indoor air quality issues.  Lined duct is being phased out as good engineering practice.  It does have its place where it is acoustically needed, however.
TrippL (Mechanical)
8 Feb 11 16:33
Try DuctSox. http://www.ductsox.com/

Looks and works great. Good experience with use in gyms. See pics from website:

http://www.ductsox.com/ductsoxweb/DuctSoxLibrary.nsf/11147315d3f719b886256d1a0070b258/e50fcf48f782456186256c7e0076ae5a!OpenDocument

***Get a licensed PE to design the system and replace the RTU's***
 
MechEngNCPE (Mechanical)
9 Feb 11 10:27
No offense, but don't do a duct sock, go with galvanized sheet metal.  And why would you need to replace the RTU's???  They just need to have supply duct.  Did I miss something?
TrippL (Mechanical)
9 Feb 11 11:06
MechEngNCPE,

The original post stated that they are replacing the Units and that there is concern over the absence of ductwork in the gym spaces.

Also, galvanized sheet metal is obviously the standard. I was suggesting ductsox because they have been used in many gymnasiums with excellent feedback. Why should ductsox not be considered? Do you have information as to any negatives for the use of ductsox? If so, please let me know. Would be much appreciated.

It will of course be up to the owner / school district as to what the final choice of material used so why not have as many options (along with the positives and negatives associated) as possible to propose?  
dbarry14 (Mechanical)
14 Feb 11 11:19
I second the vote for DuctSox.  It looks good (you can get it in just about any color you want).  However not all fabric duct is created equal.  Some of it looks like cheap plastic and sounds horrible.  Use DuctSox Verona or Sedona.  Also give them airflows and lenghts and they will design it for sound and air distribution.
ChasBean1 (Mechanical)
21 Feb 11 23:41
My personal and unbiased opinion, I'd stay away from any fabric ducts. If you don't perfectly maintain filters at the AHU, the fabric becomes your filter. Laundering ductwork is not something I'd want on my PM schedule. I've seen these on a site with well maintained filters turn from a nice off-white to a gray/brown in a few months.

For the STR06 original post, ceiling fans have been popular and effective in these applications. I do agree with posts by others about air throw, low returns, and having a qualified designer.
 
Waramanga (Mechanical)
26 Feb 11 5:38
Do the duct socks do heating??  do they have nozzles or something to project the air into the space or are they more of a displacment system?
A high level return is fine if you have good diffusion and only need heating in the space.
TrippL (Mechanical)
28 Feb 11 10:44
Another plus to having fabric duct is that fabric does not dent or break when kids throw things at them. These are school gymnasiums, that will happen. That in itself would rule out the use of ceiling fans.

Just like anything else, if it is designed and installed properly it works great.  
walkes (Mechanical)
4 Mar 11 10:58
Your HVAC company must be used to doing big box stores and uses the same down and dirty installation for many projects.
cdxx139 (Mechanical)
5 Mar 11 14:51
Thank you Ellis.  Why havent we heard from the OP?

NCPE, what if you use hospital grade liner?  Closed cell vs fiberglass?  I specify hospital grade liner all the time. Especially when the architect is too cheap to pay for an acoustical engineer.

If you use cieling fans (or destratification fans) which I suggest, use cages to protect them.

As Waramanga implied, Duct sox has next to zero throw, so only use them if you can get low returns (which is the optimum design)

 

knowledge is power

MechEngNCPE (Mechanical)
9 Mar 11 10:40
cdxx, you do have a point about the various grades of liners, there are acoustical methods for determining where to install silencers/attenuators.  I choose to specify attenuators where needed, and I do cleanrooms for pharmaceutical manufacturing facility HVAC, where ANY contaminant in the ductwork is a no-no.  

In an office setting, it is my belief that lined duct should not be specified either, due to the fact that the duct may be used for 30 years, and over that period of time, indoor air quality may suffer from particulates being sheared off of the liner.  

Also, when existing lined duct is tapped into, the cutting of the liner causes particulate to become loose in the ductwork.  

Brush up on applying sound attenuators and other such devices and you will eventually become familiar with and anticipate noise and its causes/propogation.

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