Push or Pull? Fan Air Movement through Hoods?

U

unity

Well-Known Member
Muffy said:
Doesn't the back pressure change with the output of the fan? If we are limited to 10,000cfm but we only need 400 then it's nothing to worry about.

Heat will naturally move toward cold but that is passive cooling. On a hot day you would be more comfortable in front of a fan than behind it.
Click to expand...
Cheers Muffy :) You are correct, if we only need 400cfm but get a 800cfm fan for example, then the added back pressure from pushing vs. pulling would not reduce air flow below our required 400cfm. It will however reduce fan efficiency dramatically as well as cause premature failure of the fan due to a high static environment. Furthermore, why pay for a larger fan then you need, be it higher up front costs of the fan or higher energy consumption due to the larger motor, when you could just install it in the most efficient way?!
Your fan, if it is a decent one will have performance data on it, for example:
Fan Tech FKD Series Performance
Fan Model Max Watts Max Amps 0" +++.25"+++ .5"+++ .75"+++ 1.0"+++ 1.25"+++ 1.5"
FKD++ 8"+++ 327++++ 2.99 (1) 836 ++ 761+++ 680++ +595+++ 499+++ 393 ++++286
So this is the performance data for a 8" Fantech inline fan. You can see that as the static increases from 0" to 1.5", the performance (cfm) decreases from 836 cfm at 0" to 286 cfm at 1.5". Note that the watts consumed remain the same under both conditions.
Sound ducting and installation would dictate that the the static pressure, be it forced or induced, should remain as low as possible. Anything above .5" is not installed in an energy efficient way.

Kind

BTW, the only reason you feel better in front of a fan then behind it is that the fan is not in an enclosure i.e. ducts. Was the fan enclosed you would get the same cooling effect behind the fan as you would in front of the fan.
 
M

medz

Member
While on subject, Is it better to run a separate fresh air line to each AC hoods or is it Okay to daisy chain them?

If I daisy chain 1000w to another 1000w, the 2nd light isnt' getting cooled nearly as much.

Also is this damaging to the fan to have this hot air sucking through?
 
Biologically Incorrect

Biologically Incorrect

Active Member
If you have a big enough fan you'll have no problem, but it will have to be a beast :)

Peace out

medz said:
While on subject, Is it better to run a separate fresh air line to each AC hoods or is it Okay to daisy chain them?

If I daisy chain 1000w to another 1000w, the 2nd light isnt' getting cooled nearly as much.

Also is this damaging to the fan to have this hot air sucking through?
Click to expand...
 
Muffy

Muffy

Active Member
unity said:
Cheers Muffy :) You are correct, if we only need 400cfm but get a 800cfm fan for example, then the added back pressure from pushing vs. pulling would not reduce air flow below our required 400cfm. It will however reduce fan efficiency dramatically as well as cause premature failure of the fan due to a high static environment. Furthermore, why pay for a larger fan then you need, be it higher up front costs of the fan or higher energy consumption due to the larger motor, when you could just install it in the most efficient way?!
Your fan, if it is a decent one will have performance data on it, for example:
Fan Tech FKD Series Performance
Fan Model Max Watts Max Amps 0" +++.25"+++ .5"+++ .75"+++ 1.0"+++ 1.25"+++ 1.5"
FKD++ 8"+++ 327++++ 2.99 (1) 836 ++ 761+++ 680++ +595+++ 499+++ 393 ++++286
So this is the performance data for a 8" Fantech inline fan. You can see that as the static increases from 0" to 1.5", the performance (cfm) decreases from 836 cfm at 0" to 286 cfm at 1.5". Note that the watts consumed remain the same under both conditions.
Sound ducting and installation would dictate that the the static pressure, be it forced or induced, should remain as low as possible. Anything above .5" is not installed in an energy efficient way.

Kind

BTW, the only reason you feel better in front of a fan then behind it is that the fan is not in an enclosure i.e. ducts. Was the fan enclosed you would get the same cooling effect behind the fan as you would in front of the fan.
Click to expand...
I was thinking about it like if the duct limits us to 800cfm then we could do whatever we want with a 400cfm fan. :razz: Like I said before the corners are the hottest area of my hood and if I have a fan agitating those corners instead of letting convection do it business then I have a cooler environment for the plants. Be sure I don't run a fan for fan's sake.
 
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