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Re: [APD] Canopy Cooling

I think Dave is on to something.

For a 4" (nominal 4" or 90 mm) tubeaxial fan to move that
much air, it has to spin like a son-of-a-gun -- doesn't
matter who manufactures it. Even for a 4 1/2" (nominal 120
mm), you're talking some serious rpms to move that much air
with that kind and size fan. Forty-seven dB is not a lot of
noise for a fan that size moving that much air. In fact, it
is possibly a very optimistic rating if one assumes that it
is a 1 meter, on axis, ground plane (half space)
measurement. Of course, they might measure under diff

There are high speed models from others in that size and in
that flow rate neighborhood, but they are relatively rare
-- usually, if one needs to move that much air, then,
rather than get that far to the edge edge of performance
for the fan size, it makes more sense to a larger fan or
use multiple slower fans (the first added fan only adds 3
db and the 2nd added fan even fewer -- decibels are that
kind of scale). 

A 6.7" (175 mm) fan can surely deal with that much airflow
and hum along in the 47 db neighborhood. But I'm inclined
to say that, if a 4" fan performs that way, buy all you can
get your hands and expect to make a fortune -- you might
have the exception to the laws of physics or at least a
serious warp in the fabric of space and time? Otoh, perhaps
they only measured sound in a particular bandwidth or from
ten or 15 feet away, or maybe it's not a ground plane
measurement, or who knows . . . ?

Scott H.

--- David Grim <grim1214 at bellsouth_net> wrote:

> >
> > Message: 1
> > Date: Mon, 05 Sep 2005 19:51:04 -0700
> > From: Jerry Baker <jerry at bakerweb_biz>
> > Subject: [APD] Canopy Cooling
> > To: aquatic plants digest <aquatic-plants at actwin_com>
> >
> > I see that the IceCap fans are horribly expensive at
> some $45, and loud
> > at 47.8dBA. I can put together a 35.5dBA fan and a
> 12VDC transformer for
> > about $13. True that the IceCap is variable speed, but
> the whole point
> > of variable speed is to be quiet. When the fan I'm
> talking about is
> > 12dBA less than the IceCap (less than half loud as
> perceived by the
> > ear), I don't see where the IceCap has an advantage. Is
> there something
> > critical I am missing, or is this another case of the
> aquarium hobbyist
> > being gouged?
> >
> > -- 
> > Jerry Baker
> >
> I just did a bit of research on the Web regarding cooling
> fans for
> computers, and the main issue I see with using these is
> the CFM (cubic feet
> per minute) rating. This may be where the advantage of
> the Icecap Fans is
> obvious. I didn't see any 12 VDC computer fans that moved
> more than 30 CFM.
> This may work in a smaller tank setup, but could prove
> problematic for a
> multi Halide or Compact Flourescent setup, which probably
> generates a lot
> more heat than a computer case, just a guess on my part.
> So if you consider the larger 4" Icecap cost at $43
> (www.marinedepot.com)
> and the cost of moving the same amount of air with 3-4
> DIY computer fans,
> the cost difference becomes almost negligible, doesn't
> it?

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