heat from lights, need assitance

High all.. SWIM has a closet for their grow op. It is about 6 feet long by approx 4 feet wide (grow space).

Using 1 inline fan 600cfm to bring cool air in from outside and 1 600cfm fan to exhaust from room.

SWIM wanted to know why the heat is still as high as 87 in the closet? The duct work is 4" but the inline fans are 8". Reducers are being used beucase of the duct. For the exhaust, the duct is not connected to the light to draw from. Would this be the best bet? Put the duct to draw from the hood through the fan, then exhaust out? Will that help to bring the heat level down? Also using 1- 12" fan to move air and to blow air across the plants.

Any help is appreaciated.

before trying to cool the reflector directly I would use both 600cfm fans as exhaust fans to pull air out of the room. Air will automatically be sucked into the closet at the same rate that it is being pulled out of the room. You don't need a fan to pull air into the room. Just make sure that if you use both openings in the closet for the fans that you have another opening for air to get suck into (this will happen automatically). This way you will be clearing the closet at 1200 cfm instead of 600 cfm, which should help the temp of the closet.

splifman said:

before trying to cool the reflector directly I would use both 600cfm fans as exhaust fans to pull air out of the room. Air will automatically be sucked into the closet at the same rate that it is being pulled out of the room. You don't need a fan to pull air into the room. Just make sure that if you use both openings in the closet for the fans that you have another opening for air to get suck into (this will happen automatically). This way you will be clearing the closet at 1200 cfm instead of 600 cfm, which should help the temp of the closet.

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okay I def. understand what your saying. Let me add a bit more if I could.

Fresh air is being pulled in from outside with one of the fans. The other is exhausting into the attac. How do you put two fans together to pull the air out? I've read you cannot do this. Can you actually put two inline fans together and have them work correctly? Meaning will they really pull the air through? The closet is 99% closed off from the rest of the house.

From what you have said this is what I'm imagining your set up looks like: You have a closet that on one side has duct piping connected to a fan that leads to the outside somehow. On the other side of the closet or on the top of the closet you have another hole with duct pipe running from it to the attic, also connect to a fan.

If this is the case then keep the duct piping to the outside connect, just remove the fan. Create another hole near the other exhaust hole that leads to the attic. Connect the other fan to another piece of duct piping and connect the piping to the second hole. Join the two duct tubes that come from the exhaust holes into one duct tube using a fork adapter (whatever the hell its called) that allows you to transform two tubes into one. then connect the other end to the attic. Or you could just run the second exhaust tube directly to the attic as well, if that is easier for you.

This will pull twice the air out. If you were to put the fans one behind the other, that would not pull out twice the volume of air. The point is to have another exhaust hole in your closet.

^^

you have the closet correct..

thanks for your assitance.. going to try your suggestions

Yes you need to exhaust the heat that is being generated by your light.

by using the ducting reducers, you are seriously hampering the fan's ability to move air, as it is designed for an 8" duct (over 3 times the volume of a 4")

600 cfm should clear the volume of that size room in about 15-30 seconds, depending on height. Forget about inlining two fans or adding another 4" duct. Just use one of the fans properly and you'll be in good stead.

If you are adding a carbon filter to the mix, you may need a tad more flow to maintain a lower temp, but you should be very well off with one 600cfm inline on a single 8" duct. Just make sure to add an intake port that is at least 6" duct or the equivalent size hole. Sometimes having the intake hole smaller has the benefit of added suction and "sucks" light-sealed closet doors shut.

splifman and heady wanted to report back what's happened.. attached a 4" vent hose from the light to the 600cfm that is exhausting outside the closet. After running the light for 2 hours, the top temp reached 80 degrees and held. Over night temp 60.

It seems that things are much better just from venting the light. I'm going to add a glass protector to the hood to protect it from water spray etc. which should bring the heat level down a bit more. Utilizing timers for the intake fan is all I'll need at this point.

thanks for your help

I use one of the cool tubes with the glass and vent holes on either side of the fixture to run air across the light. Totally inclosed. 400 watts of hps in a small storage shead and my temp never gets above 75 degrees. For any one reading this the "Cool Tubes," really work for small spaces with big lights.

^^

I actually thought about getting one of them for my 1000 watt. But I think I got lucky with venting the hood only.

i use 5 lights in 12 x 12

tubs or cylinders are a key to keeping the temp right.

Heady said:

by using the ducting reducers, you are seriously hampering the fan's ability to move air, as it is designed for an 8" duct (over 3 times the volume of a 4")

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Incorrect. As long as the fan is still running, a 4 inch duct will not hinder the fans ability to clear the air from the closet at the same rate as an 8 inch duct. The air will pass faster through the 4 inch duct, in order to keep the mass transfer constant. This is derived from the law of Conservation of Mass: (rTVA)1 = (rTVA)2

r = density
T = temperature
V = velocity
A = area

T and r remain constant, which means velocity and area are inversely proportional.

splifman:

I appreciate your reply. And your math is right on from a volumetric sense. Respectfully, I would disagree with regards to this application. You've ignored fluid dynamics. These aren't straight volumetric measurements anymore.

Here's an experiment (and an exaggeration to display the point):
Take a straw from a mixed drink (about 2mm core diameter)
and a straw from a McDonald's Shake (about 6mm diameter)

Suck as hard as you can on a glass of water for 1 second. Which session results in a fuller mouth?

You don't really need to do the experiment to understand the implications, but air DOES have mass, and this mass turbulates, causing friction. If the surface of the output goes from 8" diameter to 4" diameter in a short space, you bet there's gonna be backwaves from the compression of the material (air) and the turbulence results in geometrically increasing amounts of friction/suction (or back-pressure) as the push/pull pressure goes up.

HVAC is more complex than most people think, mainly because of this very fact.

Much respect.

Guys, guys, you're completely ignoring the effect of air pressure! Of course, depending on altitude.

But no matter the altitude, I'm looking from above you.

okay i've made a few changes.. air temp is still under 78, venting from light hood. the flange from the hood is 4" so nothing I cn do about that.. I use reducers to go from 4" - 6" - 8" (fan) On the exit end of the fan, I have an 8" reducer to 6", then 6" duct to exhaust to the attic. I've left my intake as is, but on a timer to bring in less cool air, but to keep a constant temp of 75 to 78. Humiditiy is in the range of 20 to 25%, I know a little low, but I'm working on this. Since I've made the changes to the air temp over the last few days, my girls are responding nicely to the cool air. All green and looks healthy. Since I've just put all cloans in soil, i'm using 1/4 strength nutes on them for 1 week ( i water 2 cups every two days). Then I'll bring the nutes up to 1/2 staingth for another week, then full strength for the remainder.

I appreaciate all the assistance on this. I've learned a lot about air movement. There's a lot to it, a lot more then I ever thought.

Heady:

With all do respect your experiment makes sense but it serves to compare apples with oranges. In the case of the straws, in each instance you are starting with two completely different mass flow rates.

Here we are talking about a transition from 8' to 4' with a constant force pushing the fluid. My math is also correct with respect to fluid dynamics.



Check out what NASA has to say: Conservation of Mass

I agree that the laminar flow will be disrupted and experience turbulence, however, at these speeds and given the specific disruption (8' to 4') the effect of friction on the flow is somewhat negligible. Basically the difference in how much air will be cleared from the closet is not worth worrying about.

nightfun said:

okay i've made a few changes.. air temp is still under 78, venting from light hood. the flange from the hood is 4" so nothing I cn do about that.. I use reducers to go from 4" - 6" - 8" (fan) On the exit end of the fan, I have an 8" reducer to 6", then 6" duct to exhaust to the attic. I've left my intake as is, but on a timer to bring in less cool air, but to keep a constant temp of 75 to 78. Humiditiy is in the range of 20 to 25%, I know a little low, but I'm working on this. Since I've made the changes to the air temp over the last few days, my girls are responding nicely to the cool air. All green and looks healthy. Since I've just put all cloans in soil, i'm using 1/4 strength nutes on them for 1 week ( i water 2 cups every two days). Then I'll bring the nutes up to 1/2 staingth for another week, then full strength for the remainder.

I appreaciate all the assistance on this. I've learned a lot about air movement. There's a lot to it, a lot more then I ever thought.

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Sounds good. Looks like you have a stable environment now. My room fluctuates between 78 and 82 F and I've had good results so far. Keep us posted and good luck. Feel free to post pics too!

splifman said:

Sounds good. Looks like you have a stable environment now. My room fluctuates between 78 and 82 F and I've had good results so far. Keep us posted and good luck. Feel free to post pics too!

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Yeah it's looking ok. Just still working on the humiditiy factor. Leaving for FLA today, but will post pics soon.

thanks again guys!

forget the math reducing the induction size does hinder the flow.Its a simple fact thos in heating and air conditioning can verify.its like a drain of sorts one has a 8 inch opening with an 8 inch drain pipe andother an 8 inch opening with a 4 inch drain pipe,the simple fact is flow speed will increase but total volume has no choice but to wait inline to even get a chance there for the small outlet will increase in out go speed but diminish th total amout of outlet per measurment.Basically the small duct can allow the max flow the bigger duct can even at the accelorated speed.no matter what math you try to use it just is a reducer is simply that...a reducer.

If splifman were correct, we'd all be able to vent our closets with 1" (or less) ducting. Now that's stealthy!

No offense splif, but you ignored the pressure/backpressure factor, which myself and others mentioned.

This is why industrial/commercial centrifugal fans are given Static Pressure ratings, instead of airflow (CFM) ratings.

NASA. Pffffft! Since when are they experts?