Canopy fan: suggestion for air flow direction?

reef_doug · #1 04/10/2007, 08:36 PM

Canopy is 72 x 24 x 11 high. Holes are drilled on the ends. No holes on top.

Lighting is:
3 x 250w ROIII DE pendants and 2 x 72" VHO bulbs.

I want to use 4 x Vantec Stealth 120mm x 120mm fans, parallel wiring running on 9v (hopefully).
Fan locations are 2 on the ends and two in the back hanging down, each spaced between the ROIII pendants. Back is open with gutter guard netting.

Flow options:
A) Fans on both ends blow in, and fans in the back blow out
B) Fans on both ends blow out, fans in back blow in
C) 1 Fan on end blows in, other end blows out. What about the back fans?
D) All blowing out
E) All blowing in

thanks

Fish'InMN · #2 04/10/2007, 10:48 PM

Any fan "drawing out" air from above your tank will be more likely to corrode and/or fail than a fan blowing in based on my experience. I would have all four fans blowing in since it will give you the most amount of air movement and the best evaporative cooling. You may even notice a slight improvement in VHO efficiency due to a cooler operating environment, but nothing spectacular...

Excellent choice on the Vantecs, by the way; you will certainly not be disappointed. A temperature-based controller would be a good addition as well, being able to turn on 2 or all of the fans based on how warm your tank is would certainly come in handy. But I can't recommend any products for that task, I haven't decided where to put my money just yet either.

Marty

reef_doug · #3 04/11/2007, 03:03 PM

it sounds like:

E) all fans blowing in.

Any other suggestions?

barbra · #4 04/11/2007, 03:19 PM

Having all the fans blowing in is not the answer IMO. At most you want 2 blowing in and 2 blowing out to keep the air moving. All 4 fans blowing out will work as well.
Since what you are really trying to do is evacuate all the hot air, it doesn't really make sense to have them all blowing in now does it? Corrosion has not been an issue in the several years I have been doing this.

hohmfree · #5 04/11/2007, 03:23 PM

2 in & 2 out

Gools · #6 04/11/2007, 05:01 PM

I'm doing 3 in 1 out

cham · #7 04/11/2007, 05:27 PM

I had one in and one out for awhile, my temps would creep up during the day and cool off quickly after lights out.

On a whim, I changed the one to blowing in so that both are blowing in and my temps stay rock steady at 79*.

I too thought you needed some sucking back out but not at all in my case. I noticed a HUGE difference blowing all of them inwards. I also left a very small gap in the front of my canopy between the glass and wood and every time my fans cut on while I am looking at my tank I get blasted with hot air.

Create a positive air pressure, the air will find ways to get out. Plus you want the air to physically blow across the waters surface. You get better evap, cooling and O2 exchange that way.

IMHO

snulma1 · #8 04/11/2007, 06:58 PM

It also depends on how high your canopy is off of your tank! If it is fairly close, as you blow air in, its gonna blow that heated air onto your tank, which will still raise your tank temp as well. I used to have 1 blowing in and 2 blowing out on my old 55g and I had 2 175's and 3 96w pcs. And corrosion never happened.

AZDesertRat · #9 04/12/2007, 10:01 AM

All blowing in with sufficient escape holes in the top or high up in back. The key is the amount of surface area for hot air to travel out without increasing the air pressure the fans must pump against. Make sure you have more surface area for exits than you do fans blowing in and it will work like a charm.

shiftyfatdwarf · #10 04/12/2007, 10:34 AM

blowing all in doesn't mean that the hot air won't get out. air temp changes.

i would say all in because you are lettin in cool air and cooling the hot air. it does help keep your tank at a steady temp.

Sk8r · #11 04/12/2007, 10:36 AM

My commercially made one uses one in, one out, at opposite ends.

tlharbin · #12 04/12/2007, 11:15 AM

Fan direction depends first on what you are trying to accomplish. Do you want to cool the tank or the lights?

Most commercial light units and canopies blow the air out-- because they are cooling the unit to prevent its failure. Some have one in and one out. I have never heard of this being an efficient design choice. If your canopy has a shield between the lights and the water (and it does not sound like yours does) then blow the air out.

Cooling the tank only works if you blow the air in and let gaps or holes expell the air. This sounds like your goal. The best design (for cooling--not necessarily for light transmission) is to have a shield between the lamps and water surface; have the lights cooled by fans blowing out above the shield; and have the tank cooled by fans blowing in below the shield.

Fish'InMN · #13 04/12/2007, 11:19 AM

Quote:

Originally posted by shiftyfatdwarf
blowing all in doesn't mean that the hot air won't get out. air temp changes.

i would say all in because you are lettin in cool air and cooling the hot air. it does help keep your tank at a steady temp.

Did you mean "blowing all in doesn't mean that the hot air will get out"? (Otherwise your sentence makes no sense to me.) To which I would agree, but as AZDesertRat and tlharbin already mentioned: ensure you have more than adequate room to vent the canopy and you will see the most impact with the least amount of fans.

AZDesertRat · #14 04/12/2007, 11:46 AM

The biggest disadvantage of a one in one out combination is you only have the CFM equivalent of one fan not two. You can put 20 fans in a row but you still are only moving along the same air the first one moved to begin with.
Over the last 17 years I have tried every combination I could think of and always come back to 120mm DC fans blowing in and using a variable voltage power supply to control their speeds.

nick18tjetta · #15 05/05/2007, 11:48 PM

Would it be good to have 2 fans blowing in at the back up the canopy, and then to cut 2 holes, the size of the fans in the top of the canopy to allow air out??? I just got the basic framework of my canopy built, and now I am working on adding the lights/fans/trim.

AZDesertRat · #16 05/06/2007, 10:15 AM

Sure. If you mount the fans close to the ends then put the exit holes nearer the center or vice versa so the air has to travel some distance and not short circuit.

Bebo77 · #17 05/06/2007, 10:28 AM

if i were you i would put 1 fan on each side blowing in and 2 or 3 fans on the top blowing out.

nick18tjetta · #18 05/06/2007, 11:23 AM

Putting fans on the end is out of the questions, it just looks bad. I am pretty sure I am going to put the fans on the back (one far right one far left) and then I am going to put my vent on the top of the canopy, dead center, and right between the Halides. That should give me 200 CFM in and 200 CFM out. I am running the icecap 120mm fans.

Rich_1833 · #19 05/06/2007, 11:24 AM

Well It seems that everyone has there own way. But I think everyone is on same track here. What might work for somebody else might not be the best for you. I think that the canopy fans should be use to remove heat from the lights not the tank per say. I have a negative air pressure system in my canopy meaning, that all 4 fans are blowing out and the air will find its way in throw the smallest of cracks, holes, whatever. As far as cooling the tank I have 2 fans blow across the water in the sump. So the canopy fans remove heat from lights and sump fans remove heat from water. I you do not have a sump then I would cut those holes into the top of the canopy because we all know that hot air rises. I would then have all 4 fans on the sides blowing into the canopy and either but fans blowing out the top or leave them open.