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Attic fans in series?

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Posted by I can't do that Dave on June 8, 2014, 6:56 pm
 
Hi all,

We have been given two 2200cfm fans (Lakso 20" box) and am thinking of moun
ting them in series and then fitting the assembly to the man-hole opening i
nto the ceiling crawl space. The idea is to use a timer to run them during  
the night when it is cooler outside suck air through the place. They are cl
ose to the same size as the opening into the ceiling so series makes sense.

Does anyone have details on how far apart to mount them for the best effici
ency? I have been testing with a small 12v fan and voltmeter in front of th
em and moving them closer or farther apart. It does not seem to make much d
ifference to the voltage developed by the small wind-driven 12v fan on wher
e they are placed.

With one fan, the voltage generated is pretty stable at 1.47vdc. With them  
in series, it is around 1.98vdc and I can't seem to find any sweet spot.

I have found this graph, which shows almost double output for a large perce
ntage of the flow volume but I am not seeing that.

http://www.greenheck.com/images/articles/fansinseriesgraph.gif  

Thoughts and helpful suggestions?

Thanks

Dave




Posted by clare on June 8, 2014, 7:52 pm
 
On Sun, 8 Jun 2014 11:56:00 -0700 (PDT), "I can't do that Dave"


What is the rationalle for mounting them in series??

Posted by I can't do that Dave on June 9, 2014, 2:53 pm
 On Sunday, June 8, 2014 12:52:49 PM UTC-7, Clare wrote:

Clare, if you look at that link I provided all will be revealed.

Dave



Posted by Jim Wilkins on June 9, 2014, 3:29 pm
 
http://www.greenheck.com/library/articles/42  
You misinterpreted the graph. Two fans increase the pressure capacity  
but not the flow rate. Either way they max out at unrestricted  
Flow. The second graph shows how to increase the flow rate.

-jsw  



Posted by David Lesher on June 10, 2014, 3:15 pm
 

I have seen such on 1-U Dell servers, where you have no room for bigger diameter fans.
But the two fans rotate in opposite directions...


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