Ever since the adoption of the 2009 International Residential Energy Conservation Code (IECC), duct sealing efforts have been tested using the total leakage or leakage to outdoors methods.  It really is amazing how much duct gains effect the operation of your equipment and the comfort of your customer.  The missing part of "duct testing" appears to be how well the ducts are insulated.  Sure, you are required to use R-8 insulation on supply ductwork when located outside the building envelope, but how do we know it was installed correctly?  We're not required to test like the duct leakage codes, so is a check in the box sufficient?  How about we use some simple math to figure the gains, or lost capacities in cooling, and hold everyone to a standard - check out the equation below.

Sensible Btu/hr = CFM x Delta T x 1.08
   So, based on this math, one can take a few simple temperature measurements and calculate the lost sensible capacities due to duct leakage and insulation.   You should measure the temp of the air entering the return grille and at the unit to figure the return gain in sensible temperature.  I would also recommend averaging the temp readings at the furthest supply register, an average supply register, and a close one to figure the delta T from the air exiting the coil or air handler.  Do the same for an extensive return system.


  When you start measuring, it is very scary what you start to find.  As you can see, like the industry accepted national average, this system is losing 30% of the 3-ton capacity through it's well sealed, but poorly insulated duct system.  Unfortunately, the method is not perfect since a hotter day in the attic could cause greater gains.  But, that would be the time to sell duct sealing and insulation to the homeowner!  Any of you energy auditors out there could probably comment on how much attic ducts effect home infiltration as well.  So, why do we hate R-8 insulation?  Is it really just the hassle of wrapping the equivalent of a blanket around the ducts?  I don't recommend retrofitting a distribution system in an attic in the middle of July, but maybe it makes sense to offer to come back in the Fall?  Please, don't just leave it be!  Doing so makes it hard for this tree hugger to sleep at night!

http://excessair.blogspot.com/2012/06/duct-gains-why-do-we-hate-r-8...

Views: 581

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Comment by Bob Blanchette on June 29, 2012 at 6:44pm

The best bet is to reduce duct surface area if you can't get the ductwork into conditioned space. Have fewer registers and larger ductwork instead of lots of registers with small ductwork. Use truck/branch instead of '"ductopus". Keep runs short as possible. Eliminate runs to small/lightly used spaces. Put registers on sidewalls closer to the air handler, set sidewall registers to blow out into room.

The return isn't as big of an offender as the supply. As long as return is tightly sealed the wetbulb temperature won't change much. Wetbulb determines evaporator load. Then there is doing what you can to reduce attic temps, the best solution is typically large area passive vents. If you can see light coming through while in the attic, it's working...

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Don Fitchett posted a blog post

Small Businesses: Diversify with Infrared Thermography Services, Save Your Business, Save the Country...

HERS should all offer Infrared Thermography Services.It is all ways great advice for small…See More
6 hours ago
Richard Beyer replied to Mike Kandel's discussion Our Homes Suck – And That's Why Our Kids Have Sinus Problems
""There are thousands of potential harmful products that can contribute to existing homes poor…"
7 hours ago
Richard Beyer replied to Mike Kandel's discussion Our Homes Suck – And That's Why Our Kids Have Sinus Problems
"Barbara, We both know a fan switch will only conserve on energy. What is Berkeley devising to clean…"
8 hours ago
Richard Beyer replied to Mike Kandel's discussion Our Homes Suck – And That's Why Our Kids Have Sinus Problems
"Ted no one can help anyone with their head stuck in the sand. All you said is MONEY is your God.…"
8 hours ago
Richard Beyer replied to Richard Beyer's discussion Spontaneous Combustion and Flash Fire regarding Spray Foam Insulation
"Hal, Thank you for laying out those facts. Fire safety is just as important of an issue as energy…"
8 hours ago
Don Fitchett commented on Diane Chojnowski's group Facebook Pages
"I just went through the 1st 2 pages of member's facebook pages liking them. While our training…"
9 hours ago
Don Fitchett joined Diane Chojnowski's group
Thumbnail

Facebook Pages

Does your company or organization have a Facebook Page?This group is for pros who have facebook…See More
10 hours ago
Mike Kandel added 3 discussions to the group Building Performance Institute (BPI)
11 hours ago
Mike Kandel posted discussions
11 hours ago
EnergyLogic Academy updated an event

RESNET Phase 2 Rater Training - Field Training at EnergyLogic Academy - Berthoud CO

September 22, 2014 to September 24, 2014
The EnergyLogic Academy will be hosting the second phase of HERS Rater Training August 4th - 7th,…See More
11 hours ago
Mike Kandel commented on David Byrnes's blog post Strategies To Keep Millennials At Their Peak Performance In A Home Performance Company
"David - I'd like to speak with you about this article. Please email me at mkandel@bpi.org."
11 hours ago
Hal Skinner replied to Richard Beyer's discussion Spontaneous Combustion and Flash Fire regarding Spray Foam Insulation
"This thread has certainly turned into what sounds like  a thread from a fire safety website…"
14 hours ago

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service