Air-cooled hood...can you pull too much air through?

[lampost]

I just picked up an enclosed reflector with 6" air-cooling flanges. I just ordered a 6" inline fan that is rated to 200 CFM, but it looks like it only runs at 160 CFM. I don't think that'll be enough for my 1000W HPS.

My other option was a 424 CFM fan!! That air would be fuckin roaring through the hood! If my nerd calcs are right (Q=VA), then the air would theoretically be coming through the hood at 36 ft/s (25mph). That's a pretty heavy gale. Could that be harmful to the electronics in the lighting circuitry? Harmful to the light in any way?

I haven't really seen any guidance on how much air you can pull through these. Does anyone have any personal experience on high flow rates through these? I don't have a carbon filter or anything to really introduce any headloss to reduce air flow (but I'll probably get one once it starts to stink if I have to).

So is this fan overkill? I'd like to get a bit more ventilation without introducing another line so I plan on venting my whole room (130 CF) through my hood. Is this 420 CFM torrent of air going to fuck up my light?

lampost Reviewed by lampost on 12-30-2009. Air-cooled hood...can you pull too much air through? I just picked up an enclosed reflector with 6" air-cooling flanges. I just ordered a 6" inline fan that is rated to 200 CFM, but it looks like it only runs at 160 CFM. I don't think that'll be enough for my 1000W HPS. My other option was a 424 CFM fan!! That air would be fuckin roaring through the hood! If my nerd calcs are right (Q=VA), then the air would theoretically be coming through the hood at 36 ft/s (25mph). That's a pretty heavy gale. Could that be harmful to the electronics Rating: 5

[lampost]

I'm kind of afraid of even some dust just nailing the bulb at that velocity. I guess I can put a furnace filter at my inlet to introduce a bit of headloss for now and keep out any dust that would threaten the light.

That reminds me of another question. Do you want to draw air in a specific direction in these air-cooled hood arrangements. Should the air enter on the light/socket side OR on the other side?

[redtails]

I'd say get a fan speed controller and tune it down because 200cfm isn't going to do much at all...

[EvilCartman]

Agree with Redtails 100%

Even without a speed reduction, the high velocity of the air will do no harm.

At times, I've had to run my 6" wide open...pulls hard enough that I find carbon bits from the filter, on the glass inside the reflector. Unless somebody pours BBs into your intake, the bulb will be fine.

It really doesn't make much difference which direction the air flows through the hood. But, I think most folks have the air entering opposite the bulb, maybe for fear of particulates suspended in the airstream?

It's overkill, right now. But as you mentioned, you may end up with a filter down the road, and the little 200cfm fan will certainly be inadequate.

Also, if venting the entire space through the hood, make sure to pull the air through the hood. If you must push it, double check the seals of the reflector.

[senorx12562]

Agree with Redtails 100%

Even without a speed reduction, the high velocity of the air will do no harm.

At times, I've had to run my 6" wide open...pulls hard enough that I find carbon bits from the filter, on the glass inside the reflector. Unless somebody pours BBs into your intake, the bulb will be fine.

It really doesn't make much difference which direction the air flows through the hood. But, I think most folks have the air entering opposite the bulb, maybe for fear of particulates suspended in the airstream?

It's overkill, right now. But as you mentioned, you may end up with a filter down the road, and the little 200cfm fan will certainly be inadequate.

Also, if venting the entire space through the hood, make sure to pull the air through the hood. If you must push it, double check the seals of the reflector.

I'm pushing about 700 cfm through a 6 inch-flanged reflector with no ill effects so far. I needed the flow as I have three reflectors in series being cooled by this fan, but the airflow into the first one is the same as having just one light. EvilCartman is right about the reflector seals, as mine, which are pretty high dollar reflectors, dump shitloads of air through the space between the lens and the body of the reflector, at least at the first light in the series, where airflow is still high. In my case this is ok, because the system is sealed and draws air from outside the house, so its just more fresh air to circulate around the girls. I'd be wary of putting a fan downstream of your reflector though, as drawing hot air through the fan motor and bearings won't do them any favors when it comes to longevity.

[lampost]

Thanks guys.

One more question. I also have access to outside (garage) air. Would it hurt the light to draw cold air (10-20 degrees F) over it?

I guess I'm going to call and see if I can switch fans last minute.

[senorx12562]

I've been doing that very thing, and I'm not sure how cold the air would have to be for that to be a negative instead of positive. All electrical equipment will perform better longer in cooler conditions. I guess if the cold air lowered the temp in your grow enough it could affect your plants, but it can't be anything but good for the light. Keep in mind that that outside air will be really hot in the summer, which won't provide much cooling, and may exacerbate heat issues. I've got 3200 watts of lighting, so that cold air (which has gotten down below 0 in the last month) only got my flower room temp down to 59. Good luck.

[lampost]

Thanks. I'm only running 1 x 1000W and yeah, sometimes it gets cold!! I see you in the CO forums so I don't think we live in pretty much the same climate!

Man, it seems like the difference in temps would mess with the glass.. you know like if you take glass from boiling water to cold water it shatters? I guess it's different if it's not a sudden transition?

[senorx12562]

Thanks. I'm only running 1 x 1000W and yeah, sometimes it gets cold!! I see you in the CO forums so I don't think we live in pretty much the same climate!

Man, it seems like the difference in temps would mess with the glass.. you know like if you take glass from boiling water to cold water it shatters? I guess it's different if it's not a sudden transition?

Not if it's tempered glass, which I know mine are. Just think about all the kitchenware with which you can go straight from the freezer to the oven.

[EvilCartman]

I'd be wary of putting a fan downstream of your reflector though, as drawing hot air through the fan motor and bearings won't do them any favors when it comes to longevity.

If properly set up, there is no heat issue at all. I think that bit of popular info has its roots in folks who didn't really understand their airflow requirements. With the passage of time it seems as though it has become accepted as a fact.

The air temp rise from a single 1000HPS with good airflow will be on the order of about 4 degrees F. I've set up banks of lights in series of 6 with a single 8" fan, outlet temps were under 100F with an inlet temp of 70-75F. Any diminished longevity is negligible, unless temps get a good bit higher.

The bulb itself is in the neighborhood of 200F, so with inadequate flow things *will* go south quickly! :detective1:

Not jumping on you, Senorx! Just thought I'd throw this out there. I've seen it posted many times and it's really not a problem. HVAC/R for a couple decades taught me a thing or two.