Which way to mount a fan.

[Sacohen]

On my new 90 gallon setup I'm going to doing in the next couple of months (hopefully) I'm going to build cabinets over the tank for storage, but the cabinets wlll stop about 2' short of the tank and that will be my canopy with my LED lights underneath the cabinets.

I want to mount some 4" computer fans to help with heat from the lights.

My question is...

Is it better to mount the fans so the are blowing cool air into the canopy or pulling hot air from it?

On the 125 that I had years ago I had one fan on the left side of the canopy pulling in cool air and one fan on the right side exhausting warm air, plus the back was open and that seemed to work pretty well.

Just wanted opinions.

Thanks;

 

[evolved]

One in each direction at opposite ends will be the most efficient.

 

[Sacohen]

That's what I did on my last tank, but this one the right side is going to be up against a wall.

I'm putting it in what would have been a closet, flush with the front of the wall and the right side is going to be about 1-2" away from the wall.

The left side is open and the back will have about a 10" space whee I can squeeze in and clean the back glass or do some things.
Most of the equipment will be underneath in the stand and what isn't will be on the other side of the wall in the garage.

 

[evolved]

Still, one in each direction is the way to go, regardless of where you'll have to put them. Just keep them as far apart as you can.

 

[AZDesertRat]

Two, both blowing cooler dryer air in, with equal sized exit holes either in the roof of the canopy or as high up and as far away as possible. This configuration also takes advantage of natural convection even when the fans are not running if you place the exits on top or high up in back.
One in and one out wastes a fan since it will only have the CFM of one fan, the second only moves what the first feeds it if the canopy is at all sealed. Blowing out soon gums the fans up due to the moisture in the air. I have done many threads on the subject over the last 10 years and my experiences with all the different methods, types and sizes of fans and configurations.

 

[Bad Company]

I used to design cooling systems for electronics on naval vessels. Is your canopy going to come all the way down the tank? If so, you will want the following:

- You want the fans spaced apart as highs possible in the space you want cooled, exhausting hot air. The reason for this is that the hot air will gather at the top of the enclosure.
- You want to be sure that the airflow is as even as possible, eliminating dead areas.
- You want the inlets to have at least as much open total square inches of area as the fans themselves, so as to not choke off airflow. 1.5X even better, diminishing returns after that. Small returns from nicely radiused inlets Xd
- You want the inlets to be pulling as cool of air as possible.
- If you do not have enough airflow, the lights will overheat. Too much, and you will have excess evaporative cooling and water loss. Exhausted air should be just a bit warmer than ambient as a good guide for flow.
- Ideally, the fans would exhaust straight up, and draw from all sides. Another solution would be to have air inlets low on one side and high exhaust on the other.

One pushing and one pulling is only if you expect higher airflow resistance. You'll move more air with two pulling. The key is to pull out the hot air at the top.

Fans blowing in might cause hot spots in low flow areas at the top, but do mean longer life of the fans, and slightly higher airflows (fans are volumetric pumps essentially, and cooler air is denser). Your choice. If I were to use fans to pressurize the canopy, I'd make sure my exhaust holes were high up (maybe even slant the roof towards them), and placed properly to ensure good even flow.

Good luck!

 

[AZDesertRat]

Fans exhausting in an aquarium scenario don't last due to the damp salt air. As he mentioned though the key is to have the exhaust as high as possible but make those the equally sized holes them mount the fans down low so they suck cooler dryer air in which displaces the warmer damp air exhausting out the top.

Having used it this way for 11 years in my current canopy after trying many different configurations and using a digital thermometer to test it all I can say with certainty it works. No hot spots and no dead spots with only two 53 CFM 120 mm fans.

 

[JPG@CFI]

I agree with Bad Company. I have been building and installing reef tanks for over 20 years, and in a 180 gallon, I put 2-3" smart fans and does a great job with LED's. Back in the Halide/VHO era, I would do 2-4" fans. If you push air into the canopy,your asking for contaminants in. Like windex or other cleaning agents, not to mention dust. Just some food for thought.
Here is the last canopy I did for a client. J

The canopy is upside down on my work bench.

 

[TankedNTn]

If your are simply wanting to vent the hot air out then the fans should be at the top pulling the air out..but...you need an opening or openings lower, like in the sides somewhere or the rear for the cooler fresher air to enter the contained space. Other wise the fans will pull moisture out with it and the fans won't last very long and there won't be near enough cooling taking place.

 

[Sacohen]

The way I'm planning to do this I will not be able to have it go out the top.

There will be custom cabinets above the tank, but not right on top of the tank.for storage of supplies and testing kits.

The cabinets will hang from the ceiling, come down about 1.5 to 2' then there sill be some space for my lights under the cabinets, but there will be doors that open upwards to access the top of the tank and the lights.

The tank will be below with the stand below that.
It will kind of be a built in, but I have access to the back from the left side.

 

[mrbee2828]

JPG@CFI how are you powering the fans?

 

[iReef86]

I mounted one of mine on the side blowing across my light bulbs and the other at opposite end aiming up and out!

 

[AZDesertRat]

I power my fans with variable voltage DC power supplies like a phone or video camera charger may use. by varying the DC voltage between say 6v, 7.5v, 9v, 10.5v and 12v I can vary the fan speed according to the cooling needs. The slower they run the quieter they become. If you can't cut holes in the top of the canopy then place them as high as possible in back and near the cenbter of the tank so air has to travel at least half way across the tank before it exits carry heat with it. Based on testing and practical applications with about 30 years in the hobby I still disagree with fans sucking damp hot air out, I was replacing fans annually when I tried that and haven't replaced a single fan in 11 years with my current design. Fan bearings don't like moisture and the blades eventually gum up and quit turning.

 

[JPG@CFI]

JPG@CFI how are you powering the fans?

Mrbee,

If you look close, the power wire is entering the electrical chase. They are 12V powered. J