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

  1. #1
    lampost's Avatar
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    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 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?

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  3. #2
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    Another question... flow direction?

    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?

  4. #3
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    I'd say get a fan speed controller and tune it down because 200cfm isn't going to do much at all...
    Take everything said with a grain of salt, nobody knows everything and everybody knows nothing.

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    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.
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    Quote Originally Posted by EvilCartman View Post
    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.
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    Cold air?

    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.

  8. #7
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    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.
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    ^Thanks bro

    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?

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    Quote Originally Posted by lampost View Post
    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.
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    Quote Originally Posted by senorx12562 View Post
    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!

    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.
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    Quote Originally Posted by EvilCartman View Post
    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!

    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.
    Are you talking about the rise in temp of the cooling air, or in the room in general?
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    Quote Originally Posted by senorx12562 View Post
    Are you talking about the rise in temp of the cooling air, or in the room in general?
    Yes, just the lamp cooling air as a separate system. Drawing & exhausting outside of the grow environment.
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    Reading this gives me cause for concern.
    I've got 3 enclosed 400wt hps lamps all being cooled by a 4" ActiveAir doing 165cfm. The glass on the hoods gets too hot to touch if feeling directly under the lamp. They're moderately warm as you span out from center. Is this too hot?

    So is my 165cfm under power for cooling 3 lamps?

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    Quote Originally Posted by RoundEye View Post
    Reading this gives me cause for concern.
    I've got 3 enclosed 400wt hps lamps all being cooled by a 4" ActiveAir doing 165cfm. The glass on the hoods gets too hot to touch if feeling directly under the lamp. They're moderately warm as you span out from center. Is this too hot?

    So is my 165cfm under power for cooling 3 lamps?
    The glass should be hot. Is the space too hot for the plants? You should have the plants about 8-12" from a cooled bank of 400s. You should be fine in the winter at lower cfms.

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    Quote Originally Posted by RoundEye View Post
    I've got 3 enclosed 400wt hps lamps all being cooled by a 4" ActiveAir doing 165cfm. The glass on the hoods gets too hot to touch if feeling directly under the lamp. They're moderately warm as you span out from center. Is this too hot?

    So is my 165cfm under power for cooling 3 lamps?
    If it's working for your space, then I wouldn't worry too much. If the plants are happy, run with it.

    But, IMO that blower is borderline *at best*. Depending on the number of bends and the length and type of ducting, you're moving significantly less than the rated flow. Check the seal of the reflectors, any leaks are reducing useful airflow. The glass should not be "too hot to touch" anywhere.
    I can picture in my mind a world without war, a world without hate. And I can picture us attacking that world, because they'd never expect it
    - Jack Handey

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    Quote Originally Posted by EvilCartman View Post
    Yes, just the lamp cooling air as a separate system. Drawing & exhausting outside of the grow environment.
    Good to know. Thank you.
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    EvilCartman....

    hey cartman, you seen very knowledgeable about HVAC systems and they have been giving me fits the past couple weeks trying to figure my new ventillation system out...

    I am upgrading my medical grow and have some questions on my new design.

    I am planning on having 3 rows with each row having 9 1000w XXXL air cooled reflectors. each row will be 4ft wide and 36ft long. There will be a space of 3ft between each row so that the plants are each to access. I live in the north west USA so during the summers it can get up to 100 and the winters get down below zero at times. I am planning on having the intake for my lights to be pulling air from the crawl space and exhausting it outside or back into the house during the winter to help with heating. I'm sure that pulling air from the crawl space (which is 4ft tall with 1360 square feet) I will need to have an intake fan for the crawl space/basement to help create a positive pressure. I will also be pulling air across the lights compared to pushing it since it is more efficient.

    My Questions:
    How many reflectors can I hook up in a row? I can't imagine I could hook up all 9 in a row with each flowing into each other cause after the 2nd or 3rd light wouldn't the air be so hot it wouldn't be cooling the lights?

    What size fan will I need to use to cool the lights? I've read that I should have around 250-350cfm per light but is that right?

    I know that the 6" hoods allow for more light to be reflected to the plants but the 8" would give me better air flow. so which should i eventually decide on?


    would this work? have my intake be 30x30 box ducting coming from crawl space, then split into 3 14" intake trunks that run the length of my rows. (I will also have to hook up a 6" or 8" to the main intake for my 4 lights in the veg). Each HPS light will have 6" or 8" flex insulated tubing (i could probably do 6" if i'm doing this method) coming from the intake 14" trunk to the HPS light then to the 14" insulated exhaust trunk for each row of lights then at the end of each exhaust row trunk I could have a 14" canfan 1823cfm fan ($520) or 14" vortex fan 2900cfm ($1000). Each insulated exhaust trunk would directly connect after the fan run into a 20x20 insulted box duct that runs into the attic. does this sound like the best way to run the system? i've done by homework but i cant find a ton of information on this topic or maybe i've just been looking in the wrong spot ha!

  19. #18
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    if you really want to get crazy look into this Hydrogen 6 Inch Ice Box Water Cooled Heat Exchanger - Plantlighting Hydroponics

    I have 8- 1000w hps lights connected with 2- 700 cfm fans and one of these every other light tubed back to 2 - 100 gallon reservoirs with a 1 hp chiller. I also run the hydrogen co2 water cooled burner in the same fashion. My room never gets above 85 degrees with everything running at max and no supplemental ac. These things work very well

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