| Engineering Report |
| Evaluation of Large Radius Dryer Elbow |
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The equivalent length for 45 and 90 degree bends currently
listed in the code are for fittings that have a radius of
4 inches. When a larger radius bend is installed in the dryer
duct, there is less friction loss and hence, less equivalent
length of duct pipe. ASHRAE Fundamentals Handbook has a methodology
for calculating the friction loss in ducts and fittings. This
exception will allow manufacturers to provide a larger radius
bend to reduce the equivalent length of vent pipe for the
system. A 10 inch smooth radius 90 degree bend will only have
an equivalent vent length of 1-1/2 feet. This will allow a
substantial savings in vent length over the standard 4 inch
radius sectioned bend which is 5 feet of equivalent length.
Julius Ballanco, P.E., JB Engineering and Code Consulting,
P.C.
For a graphic overview of how duct run length is affected when comparing the Dryer-Ell to a typical 90 degree sectioned dryer vent elbow, click HERE.
It is a good introduction to the concepts discussed in the following engineering papers.
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Construction Specifications Can Be Found at ARCAT.COM |
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