insulation thickness

[sethuME]

hi everybody,
how will we decide the thickness of insulation material for the ducting
for example- a supply duct of air at 21 deg.celcuis,what will be the thickness of fibreglass insulation whose density is 24kg per cu.m and k-value is 0.033 at 20 deg.c.
please let me know the equation or reference book.

 

[ChrisConley]

I'd recommend Chaper 26 - Insulation for Mechanical Systems of ASHRAE's Fundamentals Handbook.

http://www.ashrae.org

 

[GMcD]

The critical information you need is: What is the ambient air temperature around the duct? How long is the duct? What is the velocity of the air in the duct? What is the thermal performance of the insulation (R=? per inch thickness)?

The insulation thickness "should" be thick enough to prevent excessive heat gain or loss from the supply air inside the duct from the source to the terminal where it is delivered. Short duct run can use thinner insulation and a longer duct run should have thicker insulation, all other things being equal. There may also be local codes that require minimum duct insulation thicknesses for different conditions, which would be your starting point.