×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Insulation of Supply duct

Insulation of Supply duct

Insulation of Supply duct

(OP)
Hello,

I am desiging a small office building where an indoor HVAC unit (Heating and Cooling – 6000 cfm) is placed in the Mechanical room. Ceiling space is used as return air plenum.

My questions in this regard are:

Do we require initial insulation (acoustic) of supply duct? I infer that the noise level for indoor units is low and does not need one.

Do we require Thermal insulation? If yes – which is better Rigid insulation or wrapped foil faced (fiber glass) insulation?

Thanks,

Vicsidhu

RE: Insulation of Supply duct

There are a lot of variable with the acoustic insulation question. Firstly, find out fan outlet spectrum from the supplier. Calculate your ductwork attenation according to the ashrae guide for ductwork and fittings. Subtract the attenuation from the spectrum. If the resultant is greater than your required space NC curve then you will need attenuation.

As for the ductwork insulation. If your supply air temperature is going to be less than approx 13 deg Celcius then you will run the risk of condensation forming on the outside of the supply air ductwork. Check your psychrometric charts.

RE: Insulation of Supply duct

The IECC 2000 energy code requires insulated ducts in unconditioned spaces or outside.
I would wrap the supply air ducts to prevent heat loss the the plenum

RE: Insulation of Supply duct

Vicsidu:

be sure to check your applicable, most current codes: Using ceiling plenum for RA is O.K. if the material up there is non-combustible. Otherwise

Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

RE: Insulation of Supply duct

vicsidhu!

If I correctly guessed your location, you need to insulate the supply air ducts(particulary when ceiling plenum is used for RA) to prevent condensation, for condensation may take place even at 16 deg.C

Rigid PUF can be a better option.

Regards,

RE: Insulation of Supply duct

(OP)
Thanx everyone for your comments.

I agree with Vlad3 for acoustic part and Stevenew and Quark for thermal insulation. I had the same reason to insulate the thermal duct - thermal loss and condensation. I am pretty new in design - so was perplexed when conttractor said they never insulate when the ceiling is a return air plenum. Thought of putting in an enquiry at Eng Tips and am glad I did.

Thanx again!!

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources