Re: [APD] Cooling fans for hoods...

["S. Hieber" <shieber at yahoo_com>]

Thre's no easy answer to this. Fan output is very
directional and fan intake is not. So it can be easier to
control airflow within the hood if the fan is blowing in.
Otherwise, air might be sucked in from wherever it can get
in closest to the fan. But with careful layout of intakes
and output vents (and avoiding leaks, you can move the air
directionally within the hood with the fan blowing either
way.

But it can make a diff in another way. As a rule, from a
cooling efficiency standpoint, it's more efficient to move
the air over the cooler stuff first and hot stuff last
(temperature differentials and heat transfer and all that)
-- in other words, don't have the the air already hot when
you move it over the cooler parts. 

However, the light output of a fluorescent is determined by
the coolest part of the bulb and a twin tube PC has a hot
ened and cool end. So if you blow over the cool end of PC
first to get the most efficient cooling, you might
"overcool" that end of the bulb. Otoh, blowing over the hot
end first gives the most even bulb temp while moving away
heat and can yield the most energy efficient lighting
although not the most efficient cooling.

So, like most things, you have to pick from among imperfect
choices.

sh 

--- Jerry Baker <jerry at bakerweb_biz> wrote:

> Rory O'Brien wrote:
> > Now, am I better off having the fan(s) oriented to suck
> warm air out of the
> > hood, or blowing cooler air into the hood ?
> 
> I believe if your lights are oriented parallel to the
> front of the tank, 
> placing a single fan blowing in at one end will have
> better results. 
> Such a configuration will create a strong local current
> around the 
> lights. Orienting the fan to blow out will remove the
> same amount of air 
> from the hood, but not from the same places. In other
> words, the air 
> current right around the bulbs would be lower.
> 
> -- 
> Jerry Baker
> _______________________________________________
> Aquatic-Plants mailing list
> Aquatic-Plants at actwin_com
> http://www.actwin.com/mailman/listinfo/aquatic-plants
> 

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