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8" R-8 flexible insulated duct
Last Post 17 Dec 2009 12:59 AM by engineer. 3 Replies. |
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HHH
New Member
Posts:81
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| 15 Dec 2009 08:38 PM |
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8" R-8 flexible insulated duct, 20' long, inside of duct 100*F, outside of duct, 20*F, how much heat loss? 150 CFM. |
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engineer
Veteran Member
Posts:2749
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| 15 Dec 2009 09:58 PM |
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~60 SF, 80 delta T across R-8 = 600 btuh conduction loss. Plus whatever air leaks out of it.
CFM doesn't matter, except that I'm using it to assume that the inside wall of the duct to be at duct air temperature - ignoring film R-value
During the off cycle the section of duct will slowly become filled with 20F air, which will be the first to be pushed into the conditioned space upon unit cycle on. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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HHH
New Member
Posts:81
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| 16 Dec 2009 12:17 AM |
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What is my exiting temperature? |
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engineer
Veteran Member
Posts:2749
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| 17 Dec 2009 12:59 AM |
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I don't have the specific heat of air convenient to hand. My ballpark guess is that it'll lose 3-4 degrees. Much will depend on install details, principally wherever the duct is suspended or passes over a truss chord, compacting the R8 fiberglass down to R2 or so. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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