[Equest-users] question about inefficiency of duct

[Nick Caton]

Varkie,

 

I've found your website fascinating, personally.  

 

I'm not currently an educator, so perhaps I'm not the intended audience,
but as an MEP designer actively practicing energy modeling in industry
(outside of academia) I've stumbled into and found the BEPAN site to be
very handy multiple times.  Anyone who hasn't perused the site might
want to dig around a bit... there's quite a few tools/spreadsheet
examples provided which I've found interesting-to-useful, though finding
any one thing can be tricky as it's quite a lot of material!

 

I hope the site doesn't go down, or else if it should have to you'll
give us a fair warning to scramble and make copies of useful
references/tools =).  It seems to exist solely as a good-faith
contribution to helping others learn from your past experiences, and for
that I hope you know I for one very much appreciate your efforts!

 

Thanks,

 

~Nick

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Varkie
C Thomas
Sent: Tuesday, March 29, 2011 6:38 PM
To: Paul Diglio
Cc: equest-users at lists.onebuilding.org; xiaoyang shi
Subject: Re: [Equest-users] question about inefficiency of duct

 

See page 14 to 17 "Thermal Analysis"

http://bepan.info/class-notes/e6_-_loads-ducts-pipes 

AES-Ductwork-System-Design
<http://bepan.info/yahoo_site_admin/assets/docs/AES-Ductwork-System-Desi
gn.2134047.pdf> 

When the cooling DT (Room-Suppy Temp) is 20 degs, every degree temp rise
from the cooling coil affects the supply air by 5%.  For a draw-thru
system with a supply static of 8" to 9" the heat gain across the fan,
the temp rise can be significant. The rule of thumb in the old days,
when no one could be bothered doing these calculations manually, the
temp-rise was assumed to be = 0.5 x SP.   

The velocity upstream of the terminal box from the AHU through the
unconditioned shafts of high-rise bldgs is typically about 4,000 fpm
which results in low heat gain due to the high velocity. The terminal
box and the low velocity ductwork is above conditioned space (typically
RA plenum).  If the ductwork is insulated on both sides of the TB, the
rule of thumb for a temp rise through the ducts is about 1 - 2 degs
which requires about a 10% increase in supply air.

Before anyone replies to this message saying that it has wandered off
the point from the issue being discussed,  I will admit the reply is an
excuse to for mentioning the website. I am thinking of closing it down
if there is no interest from others in developing building energy
analysis course material from a full design perspective and not just
using computer program.  The emphasis would be on teaching Energy
Efficient Building Design with project case studies.  It does not quite
fit in with BEMBook The objectives are in the Introduction 
http://bepan.info/introduction

Varkie

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