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ssilcox 
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 Topic: Fan placement in new hood .. ?
Posted: February 06 2004 at 12:41pm |
So I ordered my lights yesterday, and I am building the hood this weekend. I read this article online today:
"Due to the intense heat generated by metal halide systems, fans may also be required to keep the tank from over-heating. Fans are available from electronics suppliers and most aquarium businesses that sell lighting components. However, do not blow cool air directly over the lamps, as bulb cooling will result in inefficient evaporation inside the arc tube and abnormal spectral variations of the bulb will result. It is important to remember that these bulbs are designed to operate at a pre-determined temperature."
So here is my question. I am putting in dual 150W HQI's, and there is going to be a UV filter (tempered glass). Do I install the fans to blow underneath the glass between the glass and tank top? Would it not get pretty toasty between the lights and the glass?
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rfoote
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Posted: February 06 2004 at 12:56pm |
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Shane - I would install the fans within your retrofit, so between the lights and the tempered glass - just my opinion though. That is where the majority of your heat is going to be.
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Carl
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Posted: February 06 2004 at 2:27pm |
Shane, If you decide on going with a fan in your hood I have a new(ish) Ice Cap 4" 2 speed that I used for about a week and don't need now. I can sell it to you for half of what you'd pay locally. Let me know. 458-7908.
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In Syracuse
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Sarnack
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Posted: February 06 2004 at 3:00pm |
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What kind of hood are you building? If it is a traditional wood canopy are you putting HQI pendants in it or just mounting the sockets and reflector directly into the hood?
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ssilcox
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Posted: February 06 2004 at 4:17pm |
Traditional wood canopy and mounting the sockets and reflector directly to the hood. Ryan - that is what I would think also. I just wanted to make sure that was correct. Carl - I'll give you a call.
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jfinch
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Posted: February 06 2004 at 4:53pm |
I have read similar articles... there must be some bit of truth there, no?
I've always put fans in the side of my hood and blown inward directly past the bulbs. I've never done it any other way, so I can't really comment on whether or not it shorten the life or color shifted the bulbs. My reasoning why it might not matter is in a SE bulb, the arc tube is insulated from the fan air by 1/2 to 1 inch of vacuum and the outer bulb. I'm assuming the bulb manufactures evacuate the air between the inner arc tube and the outer bulb before sealing it off (anyone know if this assumtion is true?). If that's the case, the only mode of heat transfer between the outer bulb and inner tube is radiation and may not be enough to effect the burn. But you're using DE bulbs and in that case you have convection working against you. I'd vent the bulb housing, but blow the fans between the water and UV protecting glass. Evaporation is a major source of tank cooling using fans, not just the mechanical removal of hot air.
Just my 2¢
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Sarnack
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Posted: February 06 2004 at 6:07pm |
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I'm with Jon, I would go with between the UV Glass and water... All of the DE pendants I have seen do not have have fans in them.
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ssilcox
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Posted: February 06 2004 at 7:26pm |
Sounds good to me. I was going to go with 1/8" tempered glass - is that going to withstand the temperatures? I like the idea of venting the bulb area.
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jfinch
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Posted: February 06 2004 at 8:20pm |
My opinion is that 1/8" is ok.
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chrisslc
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Posted: February 06 2004 at 8:30pm |
Just an opinion from someone who used to supercharge pc's alot (personal computers not power compacts). I always put inflow and outflow in everything because just blowing air out or in will create a vacuum or pressure, respectivelly, and nullify your air movement. Even with adequate (sp.?) venting using an inflow fan on one side and an outflow on the other will GREATLY improve cooling by moving out the hot air faster. just adding in my little contribution, not even sure it's 2 cents worth but there ya go 
Edited by chrisslc
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Mark Peterson
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Posted: February 07 2004 at 5:30am |
Chrisslc, your method works well for computer cases and homes, but physics doesn't agree with you in the case of aquarium hoods. 
Aquarium hoods are supposed to be fairly open so there is no real pressure build up. It's been my experience that two fans, both blowing in to avoid salt corrosion, will cool almost twice as good because they move twice as much cool air in. The hot air is pushed out all the openings.
Edited by Mark Peterson
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ssilcox
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Posted: February 07 2004 at 2:29pm |
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Hmmm - dont want to start a debate on that but being the computer geek that I am I was planning on the push - pull fan method also. I wonder if I would get less evaporation if I blew air in and then out the back?
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jfinch
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Posted: February 07 2004 at 2:49pm |
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If you have enough vents (my hoods are always open in the back, plenty of vent space) then Mark's right, ime. Blowing in across the water results in better cooling. I think it also results in more "dust" falling into the water which is something I've pondered about. The key might be having enough venting. My current hood (125 gal) has one 6" fan. Originally I had it pulling, it didn't do the job. So I switched it to push and have much better temperature swings.
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ssilcox
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Posted: February 07 2004 at 2:52pm |
Right on. I will have two 4" fans blowing in, between the uv filter and the water.
Great - thanks guys. I'll let you know how it works out.
-Shane
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jfinch
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Posted: February 07 2004 at 3:00pm |
Shane, Try just one fan to see if it will do the job on it's own. One less fan is $25 less bucks and a few dB lower.
BTW, you didn't ask, but Standard Supply has orion (www.orionfans.com) 4" fans for around $25. They're the quietest big air moving fan I've ever not heard. They're the same fan Hamilton uses in their fan kits.
Edited by jfinch
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