Sources for duct insulation savings

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Permalink Reply by Bud Poll on February 9, 2013 at 3:04pm

Hi Craig,
I don't have materials to recommend, but I have considered different insulation values. When ducts are located in unconditioned spaces they first must be air sealed, foil tape of duct mastic or other approved solution. Then consider your climate, heating and or air conditioning. If those ducts are in a high loss/gain area, then consider them as wall area. Would you apply 1/2" of insulation to one of your walls? There is some give and take when deciding how much "R" you need, but in my cold climate, I would want them well insulated.

You can calculate the inside surface area, estimate the run time, and add in the delta T and it will give you the heat transfer. Each installation will be different.

Bud

Bud

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Permalink Reply by Craig Bird on February 9, 2013 at 9:32pm

Thanks Bud, I am good on the application of the job, just interested in the validation of the savings. Supposed I could just run a REM/Rate model for my avg housing stock and vary the insulation level of the ducts.

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Permalink Reply by Norbert Muller on February 14, 2013 at 11:52am

How does Rem handle the ductwork inside the walls? Can you tell the software how many feet of ducts you are insulating?

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Permalink Reply by Bud Poll on February 10, 2013 at 5:03am

Let me know how much REM applies for savings. I run all of my calculations myself for the level of work I perform so have developed methods for getting my predicted loss to match what the customers actual spend. I actually see very few ducts in totally unconditioned spaces.

Bud

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Permalink Reply by Brennan Less on February 14, 2013 at 8:37am

Here's an LBNL research report by Iain Walker, who tested 24 retrofitted duct systems in the Central Valley of CA.  Retrofits increased delivery efficiency by 64-76%, and reduced HVAC system energy by 18%, on average.  This is going from uninsulated to insulated and airtightened systems; not exactly what you're looking for, but probably the best you'll find of actual data.  Energy reductions varied substantially from house to house, and they suggest targeting homes with higher supply-side leakage to outside.  

http://cgec.ucdavis.edu/ACEEE/1994-96/1996/VOL01/147.PDF

Cheers!

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Permalink Reply by Curt Kinder on February 15, 2013 at 5:53am

Heat / cool load calculation software (Manual J) provides ability to run different scenarios for duct insulation levels and duct leakage into unconditioned spaces.

Be careful with two layers of insulation on ducts in humid spaces - could create condensate / mold problems

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Permalink Reply by John Nicholas on February 15, 2013 at 2:33pm

REM allows you to estimate the length of supply and return duct based on the size of the home and # of registers.  I have never done so, but it also allows you to directly enter the length.  On two new Energy Star Homes I measured the actual lengths and was within 1% both times.  A) 4000 sf home B) 1100 sf home.

Depends on where the ducts are located for the savings.  You will get no savings for conditioned space.  Still might be a good idea.  You get most in  a vented attic, some in an enclosed crawl space.  More for supply, less for returns.  Less still for panned body cavities.

Get the ducts out of the attic. Get them out of the crawl space and the unconditioned basement! Seal them up.

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