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R.C.Bishop (Chuckllb)
Registered Member
Username: Chuckllb
Post Number: 635
Registered: 7-2006
Posted From: 75.209.141.87
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 20, 2009 - 11:09 pm: | |
What are suggestions, comments, implications of installing "muffin fans" in an A/C ducting system?
I have a Coleman basement unit, (below floor level  ), amidships, 8 inch round, insulated, ducting to floor level (roughly 27"+-), 6"x24"x48" high plenum, from floor up, branched at the top of the plenum to go the length of a steel chase, fore and aft, on one side of the coach. (where the former seat lights were). The "ducting" in the chase is three inch flex.
Problem is, while the cooling is moving the entire distance, it is, at best, "wimpy" up front.
Got to thinking about "moving the air" a bit more and thought of the computer muffin fans placed in the ducting of the chase.
???
Thanx
RCB |
Chuck Newman (Chuck_newman)
Registered Member
Username: Chuck_newman
Post Number: 327
Registered: 1-2005
Posted From: 99.0.41.3
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 2:02 am: | |
R.C.
3" ducting equates to a 76mm fan. A quick check of my catalogs show most in the 20cfm to 60cfm range, one model slightly less than 100cfm.
From my years of cooling electronics enclosures, that will be fine for a not-too-large enclosure with limited equipment in it. For cooling you, it ain't gonna cut it!
There are folks here that know far more about HVAC than I do, but muffin fans were not designed for the air flows I think you will need. |
Laryn Christley (Barn_owl)
Registered Member
Username: Barn_owl
Post Number: 608
Registered: 10-2006
Posted From: 70.110.7.127
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 2:10 am: | |
I think you would find that a fan made specifically to move air in a duct would be quieter and more effective.
A few examples of a simple search:
http://www.hvacquick.com/howto_booster_fans.php?utm_source=google&utm_medium=cpc&utm_term= ductfans&utm_campaign=resgen
http://www.rewci.com/frdseinrelow.html
http://www.espenergy.com/booster_fans.htm |
Jack Conrad (Jackconrad)
Registered Member
Username: Jackconrad
Post Number: 1025
Registered: 12-2000
Posted From: 71.3.157.139
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 7:41 am: | |
3" ducting may be a bit small. When we installed our RVP (Coleman) basement air, I think they called for 48 square inches of duct area. We made all our supply duct 16" x 3" (inside dimension). The vents feed directly off this duct. As we get get further down the duct from the source, we open the vents a little more. This seems to give us even cooling throughout the bus. Return is 54 square inches (18" x 3") Jack |
John MC9 (John_mc9)
Registered Member
Username: John_mc9
Post Number: 871
Registered: 7-2006
Posted From: 74.162.82.222
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 8:07 am: | |
Re:
"while the cooling is moving the entire distance, it is, at best, "wimpy" up front. "
That's a fairly decent description of the average home cooling systems
down here in Florida.
In the double-wide we owned, the ceiling vents closest to the AC unit
were nearly closed, while the ones furthest away were wide open.
In our "new" house, the previous owner said to do the same thing, to
get the air to the back.... We had the 1.5 ton system replaced with a
larger capacity 3 ton, and had return ducts installed in each room.
That made a big difference, but the duct vents closest to the AC unit
still had to be opened less than the ones at the rear. |
John MC9 (John_mc9)
Registered Member
Username: John_mc9
Post Number: 872
Registered: 7-2006
Posted From: 74.162.82.222
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 8:08 am: | |
(you must be typing a lot faster than me, Jack!) |
Bruce Henderson (Oonrahnjay)
Registered Member
Username: Oonrahnjay
Post Number: 395
Registered: 8-2004
Posted From: 70.60.107.86
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 8:49 am: | |
I have only had experience with fans in automotive A/C but we could never get much air movement with a "fan-type" fan. What could be counted on to work was a "squirrel-cage"/centrifugal type blower. According to one of our suppliers, any back-pressure will stall the air movement from a fan-type fan while a centrifugal blower will build air pressure and force the air through.
I don't know if your situation of having air already being pushed down a duct and you're looking for "boost" would be different, but you may want to look for a blower.
On the other hand, there's a reason that air rail sirens from WWII were made like centrifugal blowers -- and that was because they could be counted upon to make noise! (Seriously, modern well-designed centrifugal fans can move a lot of air with very little noise but not every one you'll run across is modern and well-designed.)
Did somebody say something about "doing it your own way" and "compromises"????? |
Nick Badame Refrigeration Co. (Dnick85)
Registered Member
Username: Dnick85
Post Number: 292
Registered: 2-2006
Posted From: 76.124.92.192
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 9:37 am: | |
Hi RCB,
A big mistake folks make when building a duct system, is with the main trunk line.
In any A/C system, if you start with a box at the blower and branch off from there with smaller runs, the system will never be balanced.
The trick to even and good air flow is to have the main trunk line properly sized and as long as possible with branch runs as short as possible. The branch runs should never be taken from the end of a duct either. This will deflate the longest runs resulting in poor air flow at that point.
Hope this helps
Nick- |
R.C.Bishop (Chuckllb)
Registered Member
Username: Chuckllb
Post Number: 636
Registered: 7-2006
Posted From: 75.208.245.81
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 10:33 am: | |
The chase is large enuf, but no good way to insulate the steel; ergo, the 3"inch ducting,which is the largest one can place in the chase. I hadn't considered other types of "blowers" due to size, but perhaps that would be a possibility.
Nick, this plenum stands straight up; I dropped the ducting into the plenum from the top, going about half way down so that the air is not captured at the top, for reason you indicate. Lots of air there.
I may just need to re-think the ducting and let the air expel at the top of the plenum directly into the coach. Without reconstructing a bunch of stuff, there is no way at present to dump the air "forward or rearward"...don't know if I want to do that.
Difficult to build the "perfect" coach, huh?
Thanx for all the response!
RCB |
marvin pack (Gomer)
Registered Member
Username: Gomer
Post Number: 435
Registered: 3-2007
Posted From: 71.55.197.237
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 21, 2009 - 10:53 am: | |
doggone Nick; I was going to say the same thing and you beat me to the punch again. I also done several units and the KEY is the trunk line to have properly sized and then take-offs to the vents with smaller sizes. NICK you are the man of the hour"AGAIN" Thanks for all you input again.
Gomer |