Hood ventilation
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Old 06-05-2006, 05:13 PM   #1
peterl
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Hood ventilation


I'm proposing to start up a new tank 54"x22"x18" (350l or 93USgallons).
To light this at 3W/USgall will require about 300W of lights. If I use 8 48"
40W strips this ought to work as far as plant growth is concerned, but
will generate a lot of heat. So I expect to have to install a computer fan
in the hood for ventilation. But if I use MH or Mercury vapour lamps I'm
supposed to have an open top and pendant suspension. I can't see the
difference between ventilating say 3 125W Mercury vapour lamp bulbs
in a hood and 8 40W strips. Apart from the fact that there has to be
a 20cm gap between the water surface and the MH or MV bulbs. Any comments?
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Old 06-05-2006, 05:51 PM   #2
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haildes and merc. vapor arent the most effecent things in the world and ggenerate ALOT of heat outside of light. its just how they are. and yes, there will be a huge differance in heat between 40 watt flour. and hailes.
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Old 06-05-2006, 06:04 PM   #3
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funny, my hqi mh fixture runs cooler than my cf fixture. the heat under the bulb is about the same also (i haven't measured, but my water temp didn't change). the sunpod has an exhaust fan near the ballast and an intake at the other end, sucking air across the reflector and ballast. the air coming out feels like it's around 30-35c (like a computer's psu).

my older mh fixture (classic bulb) runs pretty hot, but it's mostly due to the passive cooling of the canopy and ballast. this thing is a horrible peice of engineering; it lacks proper vents and the there's nothing to remove the ambient heat from the reflector so it just builds and builds; and there isn't enough room to install an exhaust fan.

hqi mh is about the best price/performance ratio you can get.
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Old 06-05-2006, 11:08 PM   #4
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Having the light mounted above the tank doesn't trap hot air above the water. So, the heating of the water will be a lot less, but the heating of the canopy and light itself will still be bad enough that a fan might be necessary. AHS kits run pretty cool, but I still had to install a little fan in my canopy, since all of the heat generated was almost trapped at the water surface. I had lots of ventilating holes in the canopy, but not enough.
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Old 06-06-2006, 03:29 PM   #5
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Concerning the fluorescent bulbs, the cooler you can get them to run (relative to room temp) the more light they will produce. I had trouble trying to run too many 15W T8 tubes over my 15gal tank, they got so hot the water stayed above 80 deg F and the light output was significantly reduced. I solved the problem by using AHSupply compact fluorescent lights with reflectors, and by providing lots of venting at the top of the hood. The tank is now cooler with more wattage due to the convective heat removal out the top (hot air rises). The aluminum reflectors also work well to dissipate the heat to the air. Looking at your hood, determine how much venting would be overkill and then double it. Also, AHSupply kits are expensive but they work really well.
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Old 06-07-2006, 06:32 PM   #6
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Quote:
Originally Posted by Hoppy
AHS kits run pretty cool, but I still had to install a little fan in my canopy, since all of the heat generated was almost trapped at the water surface. I had lots of ventilating holes in the canopy, but not enough.
Glad I read that post. How did you go about adding the little fan? I assume it was just a generic fan used on computers?
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Old 06-07-2006, 07:55 PM   #7
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This is the type of fan I used:http://www.cyberguys.com/templates/s...search=&child=
I used a 40 mm size because of the limited room I had to mount it. I just drilled a hole about the size of the fan in the end of the canopy, used a couple of screws to hold the fan inside, and ran the wires out the back of the canopy down to a little plug-in 12 volt DC, variable voltage power adapter from Radio Shack. I am running it at about 9 volts for a slower speed and less noise.
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Old 06-07-2006, 10:15 PM   #8
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Quote:
Originally Posted by Brex
Concerning the fluorescent bulbs, the cooler you can get them to run (relative to room temp) the more light they will produce. I had trouble trying to run too many 15W T8 tubes over my 15gal tank, they got so hot the water stayed above 80 deg F and the light output was significantly reduced. I solved the problem by using AHSupply compact fluorescent lights with reflectors, and by providing lots of venting at the top of the hood. The tank is now cooler with more wattage due to the convective heat removal out the top (hot air rises). The aluminum reflectors also work well to dissipate the heat to the air. Looking at your hood, determine how much venting would be overkill and then double it.
This isn't quite correct. For your setup, maybe yes. But fyi, T5 bulbs have the highest light output at 35C, and less efficiency at 25C (normal room temp). Wattage doesn't change.

Of course, in a canopy you will always have higher temps anyway.
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Old 06-08-2006, 04:10 PM   #9
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Quote:
Originally Posted by Wasserpest
This isn't quite correct. For your setup, maybe yes. But fyi, T5 bulbs have the highest light output at 35C, and less efficiency at 25C (normal room temp). Wattage doesn't change.
Cool, thanks for that information. I have only had experience with T8 and CF bulbs. I have heard that if you run a fluorescent bulb in too low of an ambient temperature they won't produce the maximum amount of light, is this true? I'm guessing that there is a "sweet spot" temperature for a type of fluorescent bulb, and above and below that the light output starts to diminish?
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Old 06-08-2006, 04:47 PM   #10
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You are correct... For "regular" fluorescents that sweet spot is around 25C (77F), for T5's it would be 35C (95F), running them in cooler or hotter environment will lead to reduced light output.

Running them too hot also results in short life... I managed to burn up a T5 HO due to insufficient ventilation. Adding a tiny little fan like Hoppy linked to fixed that.
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