|
Posted by on February 3, 2007, 11:40 am
>Whew got that top post back again. :)
>
>How the heck do you avoid having a system with a TESP of 0.7" or 0.8"
>when a wet coil is 0.3". The high grade media filter is 0.15" or more
>when new. You've got another 0.06" or so in grilles. You're already
>over 0.5" w/o any duct work.
>
>I was at a product meeting the other day and had another contractor
>tell me you have to design the duct to allow for the static the other
>things eat up and still keep the TESP at 0.5" max. Must be that new
>no SP duct. I've been designing around 0.7" with AC and 0.4" w/o.
FWIW, recently I was involved with modifying blueprints submitted by a
mechanical engineer for multiple mechanical systems for a client. The
mechanical engineers design called for .1 static on the main sa & ra
ducts, with a .08 for the branch ducts. Granted, most of the pkg
units are belt drive, but typically .1-.08 are very common duct sizing
numbers.
If you ever get an opportunity to attend a class on Trane's
Residential zoning, by all means attend. Or for that matter any
manufacturers zoning class that incorporates 0-100% modulating
dampers. You'll see designs on the branches around .04-.05.
FWIW, I design between .06-.08 on all branches and .08-.1 on all
plenums & trunks.
Awhile back I had an extremely interesting situation.....an airhandler
running at 20,000 cfm was pumping air into a cleanroom. In the clean
room were 12" HEPA's, and in the air handler were 2" pleats. About
20% fresh air was being pulled in by the air handler.
The supply from a 10 ton hp was ducted to the return plenum on the air
handler. Right next to the supply was the return duct back to the 10
ton hp.
My job was to install another 5 tons into the very same air handler
return plenum. Once I tapped the new ducting into the return plenum,
the static pressure was so great in the 5 ton pkg return compartment
you had to struggle to get the access door back on. Obviously I went
with a 1hp high static blower motor for the new 5 ton unit.
I guess my point is, sometimes you gotta do what you gotta do, even if
its outside your normal comfort curve of experience or training.
>
>My complaint to the rep putting on the meeting was we need better data
>from the manufacturer than what the blower will deliver at 0.5" when
>there's no way we can realistic way to keep under 0.7".
>
>wrote:
>
>>> And then the problem with the pleated 1" filters is the duct system
>>> hasn't been designed for the high resistance of the filter when new
>>> let alone after they've loaded up so the coil freezes or the high
>>> limit on the furnace keeps shutting it down. Damn, Fish, you're still
>>> looking for the high dollar repairs. :)
>>
>> This is so true for the homes built by the low ball contractors. The HO
moves in and decides to get a better
>>filter and for the next 5 or 6 years he is running his unit at a SP of .7 or
.8. Then the problems start to show... :(
>
>And that's if they don't have AC. :)
>
>> Joseph
>>
>> Fixed that top post problem for ya, :)
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap