| Author |
Message |
Jack Gregg (Jackinkc)
Posted From: 72.129.232.62
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 02, 2006 - 1:43 pm: | |
I want to put a massive 110v exhaust fan on the roof of my bus. The 12v fans just don’t do the job. I was thinking of getting a furnace blower squirrel cage and mounting it inside a sheet metal box about the size of a rooftop air conditioner. A square block of foam would be placed in the ceiling hole in the winter for insulation. The roof shroud would be designed to keep out the rain.
The PROBLEM is, I am told that furnace blowers are designed to push air (as opposed to sucking it out of the bus) and actually don’t work for an exhaust application. The Grainger book say the motor will burn out if there is zero static pressure. Does that mean it will not work? If not, is there another common squirrel cage fan type that I should be using? I don’t find any squirrel cage fans in exhaust applications. I prefer a multi-speed fan. The interior of the bus is about 250 cu ft; I am thinking of a fan that pulls about 1000 CFM.
Thanks in advance for any help or advice.
Jack |
Richard Bowyer (Drivingmisslazy)
Posted From: 66.168.162.246
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 02, 2006 - 2:08 pm: | |
I have seen some relatively large exhaust fans used in the marine industry to evacuate the bilge area or other under deck areas. You might want to do some google'ing under marine exhaust fans. Shrouds should also be available.
Richard
(Message edited by drivingmisslazy on July 02, 2006) |
Bob Greenwood
Posted From: 63.232.214.252
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 02, 2006 - 2:08 pm: | |
That's the smalest prevost I ever heard of...most have 2000+ cubic feet.a squirrel fan will work ,what a monster to bump your head on tho.try useing a fan for a radiator,same 12 volt wireing & available at all wrecking yards,almost all cars have them nowadays |
bruce knee (Bruceknee)
Posted From: 12.76.103.74
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 02, 2006 - 2:23 pm: | |
I think you mean square feet. Go to lowes and get an exaust fan for an attic, it already has the mushroom cap attached, about 70 bucks |
Duane Kaler (Duane)
Posted From: 69.19.14.44
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, July 02, 2006 - 5:16 pm: | |
I was thinking off using a high CFM bathroom exaust fan. |
Jack In KC
Posted From: 65.31.215.35
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 03, 2006 - 9:08 am: | |
Thanks for the comments.
Oops, calculation error; the bus is about 2500 cu ft. I will look at the mushroom exhaust fans but I am concerned that it might leak while driving.
I think a squirrel cage fan would be the best if it will work. Does anyone know of a common application were a squirrel cage fan is used as an EXHAUST at 1000-1500 CFM? Also, I want to get it up on the roof for noise reduction
Thanks
Jack |
Greg Peterson
Posted From: 71.228.18.37
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 03, 2006 - 9:39 am: | |
Squirrel cage fans are used many places for venting. Some examples are vent hoods for chemical areas, painting and conformal coating booths. The reason some fans requires some backpressure is to not exceed the HP ratings of the motor. No backpressure and no input vacuum will give you maximum CFM thru the fan and the most HP load on the motor. These two conditions cannot usually be achieved because of the input and output ductwork resistance.
1500 cfm is a lot of airflow. That is what you need for a 3-ton air conditioner. You will need a good size inlet hole to let all that air into your bus or you will create a vacuum in the bus and not really get any air exchange. I do not understand why you want to exchange all the air in the bus in two minutes or less.
Be careful you have enough input to the outside or the vacuum may pull air from places you don’t want ….like the engine compartment along with DD smoke or odors from the holding tanks.
A variable speed fan with a BPM or ECM motor might be your best system. You can set the CFM and the motor and computer will adjust the speed to compensate for the duct restrictions and air temperature. We just finished a 450W control and motor for a dryer and wow does it get your shirts dry fast. |
James Smith (Tomcat)
Posted From: 207.200.116.133
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 03, 2006 - 11:26 am: | |
http://members.aol.com/fantasticvent/110voltfantasticvent.htm
If 110 volt is a requirement, I wonder if this might not be your best option.
Jay
87 SaftLiner |
motorcoach1
Posted From: 66.147.114.58
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 03, 2006 - 3:56 pm: | |
Max air works real well look it up any Rv dealer |
John MC9
Posted From: 66.217.105.67
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 03, 2006 - 4:40 pm: | |
Huh?
"I am told that furnace blowers are designed to push air (as
opposed to sucking it out of the bus) and actually don’t
work for an exhaust application. "
It can't "push air out" if it isn't "sucking air in".... (It's simple fisicks)
I've been using a fairly large 110v furnace blower in the bus
while I've been working on it, and it's been working fine. It
not only keeps a powerful breeze going, it's quieter than any
other fan I've used.
I've had it hanging from the open escape hatch, blowing the
hot air out, and the breeze felt just dandy. Now with the roof
airs in place, I just set the blower on the floor, and let it blow
the air throughout the bus, from front to rear, and out the open
rear windows. (I don't have sufficient AC power to run the
airs, and the genset is yet to be mounted)
It works so good, that I'm considering building it into a
cupboard, and let it blow out the side (or roof) of the bus. |
Jack Gregg (Jackinkc)
Posted From: 72.129.232.62
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 04, 2006 - 2:41 pm: | |
John, I understand that the air coming into the fan equals the air coming out the other side but I have been cautioned by a couple HVAC guys not to run a furnace blower except under load. The Grainger catalog says WARNING: Motor overload will result if blower is operated at static pressure below performance show I thought maybe the fan was designed for optimal operation with the “load” on the pressure side. Also, I know that some other options include radial fans and centrifugal blowers. A belt driven squirrel cage would probably have too high a profile on the roof.
I keep my bus at my office. When time permits, I go out there and putter or relax in the afternoon. I keep the driver’s window open about four inches and leave the max air exhaust fan running all of the time. Right now, the ambient temperature is 84 and the temperature inside the bus is 97.2. The bus is about half in the shade. If I turn on two roof air units the temperature will drop about ten degrees in an hour. If I had a huge blower that could exchange the air about once per minute then I could turn the blower on for 5-10 minutes before starting the air conditioners.
Like John, I think the furnace blower would be quiet & efficient. Roof mounting should be quieter as long as it does not vibrate. Having a multi speed would allow me to use it both to quickly lower the temperature and as a regular exhaust fan. I guess I will consider a roof mount blower like this.
Thanks.
Jack |
John MC9
Posted From: 66.217.105.211
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 04, 2006 - 10:29 pm: | |
That "under load" part is driving me crazy... Are they suggesting
the motor will run too fast without anything to restrict it?
When I did the sides of my bus, it was around 90 outside.
I ran that common furnace blower for 8-12 hours a day for
about a week. No problems at all! It kept the inside of the
bus cool enough to sit or work in... real nice breeze! In fact,
I forgot to unplug the thing, and it ran for70+ hours continuously.
I've continued to use it since then, without one shred of a problem.
Pick up a used one and try it out.. mine is used. The cost
was -0-; the value, priceless.
(those links were dead, btw) |
Ed Roelle (Ed_roelle)
Posted From: 68.42.178.98
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 04, 2006 - 10:48 pm: | |
Squirrel cage fans are designed to "pull" air through a duct. But as we know, they are used otherwise.
I am surprised that you feel a 12 volt fan, like the Fantastic Vent, is insufficent. I have used them extensively and found them to be able to exchange a lot of air - and they are built for roof top installation. We had 3 in our MCI 8 and opened the windows above our beds to get a nice breeze.
Also, if you have a problem with Fantastic Vent fans, they WILL satisfy you. I have found their customer service to be amazing.
Ed Roelle
Flint, MI |
John MC9
Posted From: 66.217.105.211
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 05, 2006 - 12:14 am: | |
Jack -
Those "Fantastic" fans are truly fantastic! The one in our ex-RV
had one, and it cooled the entire 37' motorhome quickly!
They are more expensive than the squirrel cage furnace fans,
but they are 12 volt DC type and can be run with 110v
through a 110vac to 12vdc converter.
There's a ton of options, the choice is yours. |
Richard Bowyer (Drivingmisslazy)
Posted From: 70.105.143.139
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 05, 2006 - 9:05 am: | |
Then get one of the plastic hoods from Camping World and you can leave the fan on and the cover up when it is raining.
Richard |
johnwood
Posted From: 71.142.141.8
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 06, 2006 - 11:56 pm: | |
John MC9;
That "under load" part is driving me crazy... Are they suggesting
the motor will run too fast without anything to restrict it?
The fan motor without static load runs too SLOW as the amount of air it is trying to move is too great. Block off the inlet of a squirrel cage and notice how much faster it will run. If you can get a clamp on ammeter it will really demonstrate the change in current draw.
Jack Gregg;
Give thought to using a vaneaxial fan. Very quiet and moves a lot of air. Also very efficient in use of power. Commonly used for higher end whole house bathroom venting and dryer boosters. Lifebreath makes a goodun with the moniker of Quantum. Goggle it up.
jw |