Quiet 12v Galley Blower?

[colemj]

Originally Posted by CarinaPDX

It is quite possible to find, or at least make with a 3D printer, adapters that attach to computer fans and provide a tube for the duct hose to slide over. As I noted before, fans are available in a broad range of capacities. Just going to Frys and buying one is not likely to yield an adequate fan - look around on the internet and order the most powerful one and I think you may find it will serve. Still, probably not the airflow of a bilge blower but not the noise either.

Greg

The airflow isn't that big of a deal in this application. 100-150cfm works fine (at least for us). The problem is maintaining that airflow in a duct/hood installation. I haven't met any computer fans that can do this. They generally are not made for pulling air through a filtered hood via a few feet of duct and pushing it out through another few feet of duct, while maintaining rated flow.

But my experiences have been with Fry's-type consumer stuff. Maybe some other types exists that can do this?

Mark

[KWISPEL]

The inline fans where verry noisy by me but I replace them wit 2 computerfans from 0,56 amp.
You will find this fans in the game computers and they gif a nice breeze.

[Pauls]

As God May posted earlier, fan noise is exponentially related to the fan speed. To get a decent amount of air flow, quietly, by a larger diameter fan, rated at more CFM than you need, and then slow it down by adding enough resistance into the circuit to drop the voltage to create the speed/flow you like. Muffin type fans are available at least up to 6" diameter. McMaster has a large selection, and you'll find them on EBay cheap. The goal is a large fan running as low speed.

[GordMay]

Originally Posted by leftbrainstuff

... You need at least 20+ air changes per hour for kitchen / galley venting. When you do the math on your max fan size you'll be able to determine the min fan speed.

Indeed.
A Kitchen should have an air change every 2 to 4 minutes; which equates to 15 to 30 changes per hour. Leftbrainstuff's 20 changes/hr falls exactly in the middle of this range.

To determine the cfm required to adequately ventilate an area, divide the room volume (in cubic ft.) by the appropriate "Minutes per Air Change" as shown in the chart below.
➥ http://www.greenheck.com/media/artic...airchanges.pdf

[GordMay]

Originally Posted by leftbrainstuff

... You need at least 20+ air changes per hour for kitchen / galley venting. When you do the math on your max fan size you'll be able to determine the min fan speed.

Indeed.
A Kitchen should have an air change every 2 to 4 minutes; which equates to 15 to 30 changes per hour.

To determine the cfm required to adequately ventilate an area, divide the room volume (in cubic ft.) by the appropriate "Minutes per Air Change" as shown in the chart below.
➥ http://www.greenheck.com/media/artic...airchanges.pdf

When calculating the minimum size of a Range Hood, there are three things to consider.

The size of the cooking surface: 100 cfm per linear foot.

The amount of heat produced by the cooking surface: divide the BTU/hour by 100 = cfm.

And the volume of the kitchen, as above.

Choose the largest from these three calculations, and that will be the minimum size hood you need.

[colemj]

OK, I don't think anyone is really paying attention here.

1. I don't know of any reasonable computer fan that can handle this application, but I would like to be shown wrong on this point. Again, it is NOT just a matter of airflow. Yes, there are lots of computer fans with large airflow. All that I have experienced fail almost completely when put in a ducting restriction where they have to pull and push air.

2. This application has nothing at all to do with air-exchanging the entire cabin. We do have hatches, etc. This is only about removing the heat and vapors directly over the stove area.

3. While it would be great to design or choose a range hood specifically for the size and application, the reality is that this is a boat. The hood is already built in, and there is no practical way to go to Home Depot and buy the "correct" one. There is also no space to design a large blower/trap, move it externally, or exhaust it from some other place. We don't need to meet any homeowner's code, and ABYC says nothing about this stuff.

I know that this application is highly unusual in most boats (I'm beginning to think Canibul and us are the only ones), so people may not fully understand the issue.

Mark

[Canibul]

Computer fans just won't cut it. Bascially, they just don't have the horsepower and are designed for clean environments. They're designed to move air over electronic parts. Clean air. The fans are typically installed against a flat sheet of cabinet metal with a round cutout. They typically have NO restriction on the outflow or inflow. None of them have any protection against steam, and the motors are exposed. in their intended application, they don't have to suck hot greasy scalding fumes out of a galley.

What we need is bascially a vaccum cleaner of a blower. Not a gentle breeze.

Calculating the CFM using those formulas in our case would include most of the boat, if we followed that guideline. The galley is down in one hull, but open via the bridgdeck and salon to the other hull. That's not reasonable, to change the air from the entire boat on that schedule. I just did a rough measurement, and the interior of this catamaran open to the galley stove is 6.25 ft high x 15 ft wide by 18 ft. long. That's 1687 cubic feet, To pump the entire air content of the boat out a 4" vent, usingn4 changes per minute would require a 6700 CFM fan.

Do the computer fan guys make such a thing, nice and quiet?

What we need is a fan that can suck maybe 200 cfm through a 4" diameter straw and blow it six feet through another 4" diameter straw, outside the boat and deal with scalding, wet air.

[feesh]

Interesting dilimma. Having played with many many fans over the past 2 years cooling ASIC's interested to see how this is solved. Immeidately what comes to mind is to relocate the fan inline and away and introduce a silencer as below. That or an externally mounted flange type blower outside. I would also look at RV solutions and venting fans. What about simply adding a proper

inline plus silencer



RV and even soffit fan

Amazon.com: Dundas Jafine SEVZW Soffit Exhaust Vents Fits 4-Inch, 5-Inch and 6-Inch Duct: Home Improvement

quick example RV roof fan, if you can find 4 inch to fit your opening or not, if not configure a box over the opening to bridge the diameter difference.

Airxcel | Maxxair | MAXXFAN

Best bet IMO buy or make a hood vent, place it over the stove and cut the fan speed down till it is quiet enough. Lower the hood vent until the combo of speed / silence and / distance is effective and works etc. Doesn't even have to be permanenent.

[IolantheSF]

Noise is from vibration or from the blades. Did you try balancing the new one? Does it vibrate when you hold it in your hand? Do you hear noise from the blades when it runs in your hand? Vibration is frequently from loose bearings. Are yours worn out? If new, and they are plain, put some STP on them for longer life and quieter running. Centrifugals tend to be somewhat quieter than axials (more blades). If you're still buying fans, there are silent ball bearing computer fans which move a lot of air, last a long time, and are cheap.

[CarinaPDX]

The 120mm square fans (typically 25mm thick) commonly found for computers draw about 0.4A@12VDC and move about 80CFM with no resistance (ducting, etc), and about 30dB noise level. If you look you will find 120mm fans, usually 38mm thick, that are rated at 200CFM, drawing 2A@12VDC and making 60dB noise. There are also 120CFM fans for an in-between solution. As I wrote earlier, insist on real bearings, not bushings. Admittedly these will never move as much air as a bilge blower or a real 120V exhaust fan, but neither will they draw as much power or make as much noise.

A couple of posters have recommended putting resistors in series with the fan to slow them down. If so be careful to keep the voltage across the fan above the minimum rated voltage. The right way to do speed control is with PWM (pulse width modulation, essentially varying the ratio of on/off times). Many case fans are available with a PWM controller built in, and a rheostat for adjustment - clearly the best way to go.

[colemj]

Sigh. It is NOT about moving air in free space - it is about application in a duct system. Computer fans pretty much spin in place moving NO air at all in this type of application. They are NOT designed for operating with head pressure or pull resistance. Power really isn't an issue either, since they only operate a few short times each day.

Unless someone can point to a specific computer fan that can work drawing air through ductwork and pushing air out duct work please stop recommending computer fans. I think there is a reason one does not see ANY applications containing ductwork where computer fans are used as an air movement solution.

Mark

[Canibul]

Ditto. I'll consider a computer ( what we used to call muffin) fan when someone tells me they've had one suspended over their propane stove top with two burners going while frying bacon or boiling pasta and it blows all that hot moist greasy fog through six feet of 4" diameter pipe through an outside mushroom vent. If they haven't personally done this, I just am not interested in discussing computer fans. Different application.

When I first posed this question three pages ago I was hoping someone would steer me toward a specific product designed and sold as a quiet galley range exhaust fan It looks like such an animal may not exist in inline fans. I think I will try a squirrel cage fan next, if I can find one with the right footprint.

Thanks for all the input and musings about potential solutions. Always fun to brainstorm. But I'm actually looking for a product.

[Stu Jackson]

Originally Posted by colemj

Sigh. ...............

Unless someone can point to a specific computer fan that can work drawing air through ductwork and pushing air out duct work please stop recommending computer fans. I think there is a reason one does not see ANY applications containing ductwork where computer fans are used as an air movement solution.

Mark,

"Sigh" is right and so are you.

Speaking as an HVAC engineer, please know that PROPELLER fans, which is what these are, are not ABLE to provide flow through restrictions, which is what ductwork is.

That's why you see propeller fans in the sidewalls of automobile garages: no ductwork, they can move a lot of air; add ductwork, they don't work. That's the reason: it's the basic laws of physics and fan performance.

[Canibul]

These guys have some real interesting stuff:

S&P USA - TD-SILENT Series

But looks like they only supply ac powered motors. dang it.

Looked into squirrel cage fans ( which somehow seem appropriate for CF applications) but the dc ones that would fit have a pretty low CFM rating.

[colemj]

Originally Posted by Canibul

Looked into squirrel cage fans ( which somehow seem appropriate for CF applications) but the dc ones that would fit have a pretty low CFM rating.

The Jabsco one on our generator is 150cfm, which is more than our current galley blower. They make a 250cfm model also.

Mark