Insulation of Supply duct 1

[Vicsidhu]

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

 

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.

 

[stevenw]

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

 

[Goorah]

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."

 

[quark]

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,

 

[Vicsidhu]

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!!