Correct fan positioning? (with pics)

[Electrobes]

Yo everyone, I have just set up two 92mm fans and a 80mm fan into my canopy... I sodered the fans to a variable adapter (3v-12v). I have an open back canopy (closed on the front and the two sides). I stuck the two 92mm's in the back blowing air out, and the 80mm is above the metal hallide also blowing air out from the canopy. Is this the best positioning of the fans.. or should I change it somehow.. or do I need to add something else? here are the pics...

 

[TheMadNucleus]

Hi Electrotubes,

Canopy looks good - just a few thoughts. Typically exhaust fans don't work so well in open air space. I.e. they are not likely to cause circulation of fresh air over the bulb(s) to keep the canopy cool. The reason being that they will draw air from all sides around them rather than from inside the canopy. It is better to at least partially close the back off and open vents on the opposite site of the canopy in order to create cross ventilation. This is the optimum - that is why on complete units you will notice the fan on one end and a vent on the other. The fan exhausts the hot air and the vent provides a supply of cool air.

Also you could open vents on both sides of the canopy, close off the back, and mount the two fans (exhausting) in the back panel somewhere near the center. This would draw cool in from the sides toward the center of the cabinet and exhaust it out the back.

But if you want to proceed like this for other constraints an important consideration is CFM. Can you tell me the CFM of the Fans you are using? They look pretty small and you might want to consider something a little larger (mostly cuz of the open back).

This following site has a lot of cheap fans but we careful not all are CFM rated

http://www.allelectronics.com/cgi-bin/category.cgi?category=220&item=CF-190&type=store

This thing moves copious amounts of air (300CFM) compare it to the Radio shack:

http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=273-238

The Radioshack fan moves a pretty good volume (85CFM) if you have two.

Tom

 

[fishfreek]

Does that MH bulb over the center brace cast a shadow in the tank?

 

[Electrobes]

Mad nucleus, at full strength they do move quite a bit of air. I guess I could put vents on the sides but how would I close off the back... do I really need to add an entire panel or can I just cover it with something else that hangs or something like that? Whats wierd is that I got conflicting advice aout covering the entire canopy up like that... and that this design was supposed to be most optimal.

FishFreak - Unfortunately yes.. a slight shadow towards the left. Can't think of anything that I can do about it though... any ideas?

 

[fishfreek]

I dont think there is much you can do about the shadow except to get a second MH bulb and set them on either side of the center brace. The shadow each casts woudl be canceled out by the other.

You cant remove the brace with out sacraficing the integrety of the tank.

I would say you dont have to enclose the back entirerly but have it closed off some as the fans are moving a fair amount of air one of the problems with having fans in the back close to the wall is limited airflow. The fans will end up producing a circular current blowing hot air back aganst the wall and then a fair amount of that warmer air will probably find its way back into the canopy from comming off the wall.

 

[TheMadNucleus]

Electrotube,

Yeah - bottomline is if you feel plenty of airflow then you are perhaps ok and do not have to add any backing. Here's a way you can be sure:

Place the hood so that you can get under it (like propped up with two chairs supporting each side). Then turn on the Fans (lights off) and smoke a cigar under there - i.e. hold something near the bulbs that smokes and watch if the fans are drawing any of it and exhausting it out the back.

I'm pretty sure though that the optimum approach is to try to vent the cabinet so that you are drawing fresh air over the bulbs which are generating heat.

Hey Man - looks good, and good luck.

Tom

 

[Electrobes]

Haha electrotube - thats a good idea, I'll try it!

 

[TheMadNucleus]

 

[Centurion]

an easy way to close off the back would be with an acrylic sheet