canopy fan placement

[GeoB]

Is it okay to have air blowing close to my halide bulbs? I plan to have 3 250 watt halides and 2 6’ VHOs over my 180. I’m thinking of placing three fans low on the back of the canopy blowing in to the front and locating them so that they blow below each of the halides. The top will have some slots or it may be semi-open for ventilation. Is there a better arrangement?

Is there a rule of thumb for how much CFM you should have blowing in?

[erick]

Well, I have one of my setups where the fan (120v/ac- computer tower fan) blows across the 250w/mh bulb and there is very little temp spike in the 50g tank it rests upon (about 1-2 degree temp change from when light is on/off). In another set up, I have a small (7") house fan the pulls air up and out of a canopy that houses 2-250w/mh lights, which hangs over a 110g tall tank. There is more of a temp rise in this tank though, 2-3 degrees, as the tank is closed and there is little to no evaporation of water, the 50 gal top is halfway open, thus more cooling/evaporation. I prefer to blow across the bulb and water surface, rather than pull air out of the canopy, but this is just how I feel, no scientific evidence other than temp ranges for ea. tank... Hope this helps...Erick....

[alton]

I have 2 on my 200, one on each end. One comes on when the VHO(1x160w)/T5HO's(4x54w) come on and the other when the two 250w MH's come on. Except in the winter like now the only one running is the one running when the MH's come on and my tank stays around 76.

[GeoB]

Thanks for the info! One of the things I was wonder is if there is a problem with air blowing on or near the bulb and I finally found an answer to that from a Reefkeeping article:

"Hello Lights, a popular aquarium lighting company, kindly assisted me and researched the issue of air flow on and around the bulb in the IES Reference Manual. The manual stated, "With HID equipment [such as metal halide], temperature variations have practically no effect on light output." In order to affect the light output the arc tube's temperature would have to be changed, and since the arc tube is running at such high temperatures, any ambient temperature variations are negligible. The bottom line: unless you are blowing a huge fan right on the metal halide bulb, you will not affect its function or damage."

[alton]

We install MH fixtures in coolers and freezers all the time. The only thing is MH electronic ballast do not like to run in temps over 100 degrees. In both mag, and electronic ballast the cooler the better.

[cbianco]

...I prefer to blow across the bulb and water surface, rather than pull air out of the canopy, but this is just how I feel, no scientific evidence other than temp ranges for ea. tank... Hope this helps...Erick....

Originally, my fans were blowing the air out my canopy. While reading "The Reef Aquarium," it was stated that your fans should always blow inwards, not outwards. When I changed the direction on both of my fans, I was afforded a 2-3 degree drop in temperature. I almost couldn't believe it!

Christopher