Fans, Vents, and CFMs

[milge]

I'm kicking around ideas of different ways to vent a van. This will be a normal sized van, so about 200 cubic feet. It will be used in all climates in the US. I'd be using these vents to cool the van when stationary and to clear out exhaust from propane heating.

How many CFMs are needed total to be safe running a propane burner for heat overnight? At 200 CFM, a normal sized van will clear all of the air in one minute.

The ceiling vent fans are nice and boast 900 CFMs. But they let in light and aren't rainproof. A large consideration needs to be made for sound level. I sleep best in quiet. I usually sleep with ear plugs in when camping, but that would be dangerous while burning propane. I'd like to plumb some pipes from the floor and use computer fans.

What are the best, quietest computer fans for doing this? How many CFMs should I be targeting? Is anyone building any soundproof boxes for fans?

 

[speedhighway46]

Milge:

To me, vent fans are a lot like salted-in-the-shell peanuts, you can't have enough of them!

When I was planning the layout of our 16' Morgan dry van box on our Peterbilt motorhome conversion, I planned on three powered vent fans down the center of the ceiling/roof. I chose Fantastic vent fans, the mid-level model (with thermostat but not self-closing). I've had previous experience with the Fantastic product; they are high quality and last for years. They are somewhat expensive and there are probably cheaper products out there. I went with what I knew. In the five years since they have been installed they have performed flawlessly, as I expected. Go their web site for models and specs.

Because our motorhome has a pretty much flat all aluminum roof, which is uninsulated, means that in the bright sun when the temp outside gets above 85 degrees, the inside of our box starts getting hot. Air movement is required to keep the space as cool as possible. With the three vent fans running on low speed, the temperature is tolerable. Sometimes we use additional oscillating fans within the space to provide air movement pointed right at us. We find all this very tolerable.

I cannot speak objectively as to how many cfm are required to vent a propane heater. I can tell you that with one vent just "cracked" provides enough fresh air to run our Buddy heater all night with no problems in cold weather.

Our fans are very rainproof and on low speed make almost no noise. Make sure you do a good job of caulking when you install the unit and you will not ever have a leaking problem with Fantastic.

Hope this helps.

 

[highdesertranger]

a note about ventilation, if you have a exhaust fan rated at 200 cfm then you must have another opening capable of letting 200 cfm in or you will not get 200 cfm out. highdesertranger

 

[ZoNiE]

I have two Fantastic Vents. They only really work well when you are directly under them, or, if blowing out, you are sitting next to the only open window...

Now I have about 160 Sq ft of space. It may work better in a van.

 

[SternWake]

I use a a lot of computer fans.  


In cold weather my Silverstone FM121( adjustable speed) on low moves about 33CFM(if unrestricted), is very quiet and I can cook inside.

On high it is rated for 110CFM, and is quite loud.  I have a counter rotating Arctic Cool fan rated at 55cfm, inline, feeding the silverstone fan. Inline fans need to be counter rotating. If they both spin in the same direction they both get louder and move less air.  Together they are rated for 170CFM or so.  I've no real idea what they move together through my Mushroom vent, I'll guess 130 to 145cfm, but the AC fan significantly increases airflow when I switch it on, it also lessens the silverstone fan noise when it is at half speed or more.

From a noise perspective, my ceiling exhaust is not very pleasant on high speed.  These fans push air through a mushroom style vent which originally had a 4 inch fan powered by tiny solar panels and had a C type Nicad battery to run it all night long.  I've basically gutted the original motor and use only the mushroom housing.  Very little lights gets through it.  Only if I direct a hose perfectly can water get inside.

Airflow over the Mushroom vent increases airflow through it.  Driving at highway speeds with window open and both fans can be turned off and will spin faster than when they are powered when not moving.

A larger fan can turn slower, move more air and consume less electricity.

I own a silverstone AP182 which is a roughly 7 inch fan.  On low it moves 65cfm for just 0.05 amps, and is practically silent, on high it moves 170cfm consumes 1.3 amps and is fairly loud, but it is not as annoying a high pitch as smaller fans spinning faster.  Its hub gets too hot at full speed when fed battery charging voltages  above 13v though.  I limit it to no more than 11 volts by a $2.50 gizmo.  This does cut the top end speed, but it is so much airflow it is no big deal.

I'd LOVE to have a 7 inch diameter mushroom roof vent and stuff this SS AP182 fan up there as it, at highest speed, is a much more tolerable pitch, and might be able to force air through a restriction better.  But the 2 inline fans together are about 0.55 amps and the AP182 is 1.3 amps at highest speed. However at the lowest speed the SS FM121 draws 0.09 amps for 33cfm and the AP182 moves 64CFM for 0.05amps.

The 120MM size is the most common on computer fans.  They range extremely widely in quality, amp draw for air moved and noise made.

One of the most impressive companies making computer fans is Noctua.  They are not cheap, but they have a 7 year warranty and are among the most efficient fans available.  The Noctua NF-f12 moves 53CFM for just 0.05 amps.  most Fans in this size consume twice that much or more, to move that much air.

If you want fans in your floor, they might have to be constructed  a bit burlier.  Noctua has Industrial versions of their regular lineup that move more air and achieve water and dust prevention ratings:

http://www.amazon.com/Focused-NF-F1...36126&sr=8-2&keywords=Noctua+industrial+120mm

I really like the silverstone fans that have their own built in speed controllers, but most  computer fans will respond favorable to a PWM motor speed controller, or an LED light dimmer such as this.

http://www.amazon.com/s/ref=nb_sb_s...d+controller&sprefix=pwm+motor+speed+,aps,204

I highly recommend being able to control the speed and noise of a fan through a controller.

http://www.amazon.com/LEDwholesaler...qid=1448336444&sr=8-1&keywords=pwm+led+dimmer

There is the possibility the windings in the motor might make a high pitched humming sound when the speed is lowered via PWM. Some list KHZ rates, and the higher the better in this regard, though Fido might still protest.

If one does not want to punch a hole in their roof at all, A bilge blower fan and some tubing can suck warmer air from the ceiling.  The fan itself can be mounted below the vehicle.

But these are pretty loud and definitely need to be tamed down via a speed controller at night.  One could employ various dampening methods to reduce their noise, but it might be rather involved to achieve an acceptable noise level.

http://www.amazon.com/SEAFLO--Line-...id=1448336684&sr=8-2&keywords=4"+bilge+blower

http://www.amazon.com/s/ref=nb_sb_s...lexible+duct&sprefix=4+inch+flexible+,aps,202.

I've not tested all fans with all available speed controllers so I can;t say definitively that it will work to ones satisfaction.  All I can say is speed control is very important to me, and these PWM dimmers'motor speed controllers, allow one to both change noise, airflow, and amp draw.

I have one super powerful 120MM fan, rated at 252CFM and it cannot be slowed enough to be used in my Van by my PWM controllers.  Once reaches a certain speed, it just shuts off.

BUt it would be ideal to have a fan that could move that much air when needed, and also be tamed to whisper quiet too, but I have not found such a product, and am kind of done experimenting at this point as I can turn my Van into a windtunnel and hang out inside in direct sun on hot days, as long as my reflectix is covering the windows.

 

[milge]

Thank you much SternWake, that was exactly the info I needed. I'll have to give it a shot to see what works best. I've seen some ideas online for quieting fans by putting them in boxes with foam.

 

[akrvbob]

Every portable heater will come with a number for it's required square inches of ventilation. To find out what they need you can download their manual as a .pdf and it'll list it right there. I don't believe any of them call for a fan, in fact they need surprisingly little ventilation.

Of course for heat you need all the fans you can get, but it isn't an issue for cold.
Bob

 

[speedhighway46]

Here's a couple of shots of my vent fan installation.

 

[milge]

Every portable heater will come with a number for it's required square inches of ventilation. To find out what they need you can download their manual as a .pdf and it'll list it right there. I don't believe any of them call for a fan, in fact they need surprisingly little ventilation.

Of course for heat you need all the fans you can get, but it isn't an issue for cold.
Bob

Are you talking specifically about catalytic heaters like mr buddy or the olympian wave? What about burning a propane stove? I'd actually be fine with the heat. I thought the fans were necessary for exchanging CO/CO2 with fresh air.

Here's a couple of shots of my vent fan installation.

Looking good!

 

[GypsyDogs]

My brilliant idea for 'stealth' air intake- If you have a van, likely you have a perfect spot for this.  The side door (slider or barn) has a step.. and usually there is little to nothing right behind that step. That vertical wall, usually about 5-7" tall, right where your toe hits when you step up. That is where I will cut a rectangular slot and install a small floor forced-air heater register (with screen added for bugs) and make sure I use one that has the open/close flue thingey (highly technical term, that.. lol)  That way, when I have my draw fans running when it is warm, it pulls the air up from under the van- where there is shade and theoretically cooler air.. and pulls it up through the living area.  Also, it should provide the dogs a cooler spot on the floor to escape heat.  
I plan on using a couple computer fans to draw air out the upper back area.  
Just my $0.02

 

[SternWake]

That is a pretty neat idea for a location of an intake fan.  I was considering cutting a square hole in my third seat swivel base which is sitting on 2 pieces of 3/4" plywood at one point and stuffing a computer fan in there with a tightly sealing lid, but never followed through.

But a Bilge blower fan in the toe step,  on a speed controller with perhaps a filter,  would certainly be easier to install and be more resilient.

Thanks for the idea.

 

[akrvbob]

By portable heater I mean the Mr Buddy heaters and the Olympian. None of them require a fan for ventilation. All they need is a certain number of square inches of ventilation, if memory serves, it's around 20 square inches. Lower your front windows by an inch and that is about all it needs.

Don't bet your life on my memory, get the manual and follow it!!

I use my Coleman 1 burner propane stove for 99% of my heat. I don't give it any extra ventilation at all, but neither my trailer or van are very tight.
Bob

 

[GypsyDogs]

. Welcome