To Suck or To Blow

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tgriffin

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Please excuse the title, but I figured it would make folks look.

I'm interested in other people's opinions on whether or not it is better and more efficient to have fans suck air out or blow air in a canopy.

Please give me your reasoning behind which one you think is better

Thanks
Tyson
 
I have the blowing out. You can have them sucking in if you like but only if you have a good area for the air to exit
 
BLOW IN!

Suck would make them get salt creep all over.

And the biggest NO NO is having both - it complicated to explain, but as per some aerodynamics laws it would be less efficient that having both suck or blow...
 
Most of my tanks are setup with a fan sucking cold air in and blowing it over the water surface and one fan up high blowing hot air out.
 
I'll try...

Let's say one fan moves 120cfm, that air (unless you have a 100% airtight canopy) is coming from somewhere (or going somewhere), the other fan (moving the same amount of air) is now basically not doing anything since the first fan already moved the 120cfm.
Since these two fans NEVER EVER be absolutely in sync, the one that spins slightly faster is now limited by the other fan spinning slightly slower, the slower fan on the other hand is now being pushed by the bigger fan to spin slightly faster than it would by itself...
So basically energy wasted...
Both pushing OR pulling is maximum efficiency
 
Love the title, hehehe! Just what a Moderator (for a couple more days at least) wants to see!:D
 
LilRobb;594842 wrote: BLOW IN!

Suck would make them get salt creep all over.

And the biggest NO NO is having both - it complicated to explain, but as per some aerodynamics laws it would be less efficient that having both suck or blow...
Click to expand...


I agree with the salt creep, but I think back to if you have a fan sitting in a window in a room in your house and have it blowing out of the house and have another window cracked you will get pretty good airflow through the open window.

On the other hand you won't get much airflow if you have it blowing in and have another window cracked open as well.

The first option (blowing out) seems more efficient. But I don't want everything covered with salt creep!
 
tgriffin;594856 wrote: I agree with the salt creep, but I think back to if you have a fan sitting in a window in a room in your house and have it blowing out of the house and have another window cracked you will get pretty good airflow through the open window.

On the other hand you won't get much airflow if you have it blowing in and have another window cracked open as well.

The first option (blowing out) seems more efficient. But I don't want everything covered with salt creep!
Click to expand...


Sorry,

laws of physics are against you here - in the above scenario the airflow will be exactly the same, no matter which direction the fan works...
 
LilRobb;594853 wrote: I'll try...

Let's say one fan moves 120cfm, that air (unless you have a 100% airtight canopy) is coming from somewhere (or going somewhere), the other fan (moving the same amount of air) is now basically not doing anything since the first fan already moved the 120cfm.
Since these two fans NEVER EVER be absolutely in sync, the one that spins slightly faster is now limited by the other fan spinning slightly slower, the slower fan on the other hand is now being pushed by the bigger fan to spin slightly faster than it would by itself...
So basically energy wasted...
Both pushing OR pulling is maximum efficiency
Click to expand...

This is absolutely correct. Good explanation Robb!

tgriffin;594856 wrote: I agree with the salt creep, but I think back to if you have a fan sitting in a window in a room in your house and have it blowing out of the house and have another window cracked you will get pretty good airflow through the open window.

On the other hand you won't get much airflow if you have it blowing in and have another window cracked open as well.

The first option (blowing out) seems more efficient. But I don't want everything covered with salt creep!
Click to expand...

I understand your thinking, but I'm not sure if the two scenarios are comparable. It may work, but I think you'd have more efficiency with two fans rather than one fan sucking air through small slots on the other side of the canopy. The rest of the canopy would have to be closed, then I don't think one fan would be able to keep up with the heat.

I think you'd be better off having two fans blowing in with an open, or partially open back.
 
Then I do agree with you, this oonly applies to closed or semi-closed vessels...
 
brianjfinn;594861 wrote:

I understand your thinking, but I'm not sure if the two scenarios are comparable. It may work, but I think you'd have more efficiency with two fans rather than one fan sucking air through small slots on the other side of the canopy. The rest of the canopy would have to be closed, then I don't think one fan would be able to keep up with the heat.

I think you'd be better off having two fans blowing in with an open, or partially open back.
Click to expand...

My thinking was two 4 or 5" fans in the top of the canopy (30x30x20) sucking air out. I was going to either have 3 5" holes in the bottom half on the back side of the sealed canopy or have a 2"x25" slot cut on the bottom of the back side.

I was thinking that this way the fans would be on when my MH turned on and then maybe 10-15 mins after and allow for a constant supply of cooler air to help cool the canopy.

Would I be better off with two or three fans blowing in from the bottom of the back canopy wall and have two or three holes in the top of my canopy to allow the hot air to exit?
 
tgriffin;594870 wrote: My thinking was two 4 or 5" fans in the top of the canopy (30x30x20) sucking air out. I was going to either have 3 5" holes in the bottom half on the back side of the sealed canopy or have a 2"x25" slot cut on the bottom of the back side.

I was thinking that this way the fans would be on when my MH turned on and then maybe 10-15 mins after and allow for a constant supply of cooler air to help cool the canopy.

Would I be better off with two or three fans blowing in from the bottom of the back canopy wall and have two or three holes in the top of my canopy to allow the hot air to exit?
Click to expand...

MUCH!
Hot air rises, and with the fans you would just promote this effect even more
 
LilRobb;594872 wrote: MUCH!
Hot air rises, and with the fans you would just promote this effect even more
Click to expand...

So with fans blowing in do you see a salt creep issue?
 
I have two cans pulling air in and Mr. convection takes it out from the holes in the top of the canopy.
 
LilRobb;594842 wrote: BLOW IN!

Suck would make them get salt creep all over.

And the biggest NO NO is having both - it complicated to explain, but as per some aerodynamics laws it would be less efficient that having both suck or blow...
Click to expand...

I have been running my fan for 5 months blowing out and I have 0% salt creep on my fans our outside of the fans where they blow. So im not sure what you mean by this exactly. Obviously a lot of different things is going to come into play as every setup is not identical maybe it has to do with the rate of water evap as my system runs really really cool since its all LED and I run a fan with it.
 
SuperClown;594888 wrote: I have been running my fan for 5 months blowing out and I have 0% salt creep on my fans our outside of the fans where they blow. So im not sure what you mean by this exactly. Obviously a lot of different things is going to come into play as every setup is not identical maybe it has to do with the rate of water evap as my system runs really really cool since its all LED and I run a fan with it.
Click to expand...

Leave everything the same and check it again in two years. If you don't have any salt creep (assuming you aren't regularly cleaning those areas where the air would be blowing) I would be surprised.
 
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