Ventilation for 150w hps

[dec]

Hey!

I'm constructing a small personal grow 2,06x 1,5 x2,26(height) with a vertical 150w in cool tube in the middle for small vertical SOG style.

Because I would like the grow to be almost completly silent I would like to use PC fans, but don't know how hot does a 150w hps get. I was thinking of putting 80mm fan on bottom of cooltube and a 120mm 70 CFM with DIY scrubber as exctractor fan. Intake would be passive.

I do have a S&P 160TD-SILENT but it is still a little too loud and I don't want to waste money to find out if variac would make it silent enough.


Do you think I would be able to control temperatures with PC fans only?
Thank you for your anwser!

 

[The Doktor]

This will be just what the Doktor ordered.

http://www.amazon.com/Panasonic-FV-20NLF1-WhisperLine-In-Line-6-Inch/dp/B000EDUIX2

 

[dec]

This fan would be the best choice but it is too big for my small grow

Hope to get some more advice from people that grow or grew with 150w hps.

 

[The Doktor]

Then I think what you are looking for does not exist for our hobby. Best of luck.

 

[early_bird]

150W with pc fans worked in a homebox xs. Even 250W was possible, but get much warmer.
I tryed this for fun. You can use 2 or more fans, for example one right on the carbon scrubber, few cm exhaust, one more there, so more air is passing throught.

But PC-Fans are not always sooo silent. There are huge differences in pressure a fan can provide and noise. A extreme silent Fan is usally too weak.

 

[r2k]

The amount of fan power depends on the air temperature of your cooling air source and the temperature you want your plants. If you pull air at 40 DegF in, it will cool plenty. If you pull in air at 70 DegF, it will have much less cooling power.

I had a 150 watt HPS box and used two little computer fans to cool it, passive intakes. The fans worked well in the winter when incoming air was about cooler, it was harder to keep temperatures in summer when incoming air was at 70 DegF. The coolTube will help get heat away quicker, so it could work well.

You need to make sure your intake holes are about twice the area of your fan surface. The problem with that is light pours out of the intake holes if you don't have it handled. I never really solved that problem well.

You will also need to control the fan speed if you want to regulate temperature. I built a controller for this but it is really complicated and not easy to duplicate. You need to control the voltage into the fans to control their speed. I would probably just let the coolTube fan run at maximum all the time and just regulate the other fan. The amount of control you have depends on the incoming air temp, since hotter air will require more fan power.

As early bird says above, PC fans are not completely silent. They really drop in noise when you run them slower, but then you lose cooling power.

-r2k

 

[dec]

Hey! Thanks for your anwsers!

Did some tests today. Haven't bought 150w yet so I tried with 250w that I have and temps were 93 F at the top of the cab. Had only 1 fan which was silent but the air moving through the ducting to the filter wasn't. Have to buy insulated ducting and hope it will be more silent. The cabinet is still very raw and not sealed so the fan was pulling air from everywhere not only from intake hole.

Bought Y duct and ordered another same fan so this should give me more CFM. Do you guys think this will work? ( see picture)

So if cabinet got to 93 F @ 250w with 1 fan will I be okay with 150w and 2 fans? ( ambient temps are 69 F)

 

[r2k]

A couple of things.

The cooltube isn't vented to the outside with a duct, it just dumps into the box. You are missing out on all your cooling power from the tube because you vent the tube into the box. With this setup, all the heat is dumped directly into the box and only the orange fan in the top corner is doing any cooling.

Running the box with the door open isn't going to tell you much. It needs to be buttoned up so air flows like it should.

The intake looks like the hole where the cord comes in. Is that the only intake? You have a problem here because the inlet is on the same wall as the fan. Air is lazy and will tend to take the shortest path between intake and outlet. The far side of the box (where your door is) will have a problem with cooling. It would be good to draw air across maximum distance of the box to get best cooling in all corners. If you have an intake on the door then this could help balance out all the flow. YOu can also put a partition across the box at about dirt height to help force the air to around all inside the box.

The temp difference between input and measured value is misleading. You really only care about the heat at the canopy height, not the top of the box. Heat will collect in various places and the box will be hotter in some spots than others. You need to measure the places that matter.

Assuming your values are correct, the temp difference is 24 degF. If your bulb is burning 250 watts, that means you have only about 33 CFM of airflow. That seems pretty weak for a fan of that size. Look up the specs on your fan and compare it 33 CFM, I bet you are missing about half of what the fan is capable of. That could be misleading due to all the other items I mentioned above.

The first thing to do is the easy stuff. Move the temp probe down to canopy height first and do the test again. Make sure the box is sealed up and let it run long enough to stabilize. I think about 30 minutes of bulb running should do it, but just watch the thermometer until it stops moving.

I'm not sure what the Y duct is for. Can you post new pictures of where it is used?

I have used metal duct tape to seal edges and corners. It is really sticky on one side and seals well on any flat surface. It is also light-tight. You can get it at Home Depot or any good home improvement store. Cut the metal tape with scissors or a knife, don't try to tear it from the roll. It is about 3 inches wide. DON'T use typical duct tape, it is shit. Typical duct tape is not light-tight and the stickum dries out with heating from the bulb and peels off over time.

Flexible duct is easy to work with but adds lots of air friction that kills our airflow. If you use it, pull it as tight as possible so the tube is smooth and has no pleats. You will get a bit of pleating as you bend around corners but try to minimize that as much as possible.

-r2k

 

[dec]

I still have to install a duct to the top of the cooltube which will lead hot air directly in to the orange fan ( outtake fan). Making a separate ventilation for cooltube would require more holes, ducting and space and it has to be 100% airtight or I would have smell leaking :/

Yes,that is the only intake. I can't have an intake at the doors as it wouldn't look like an ordinery cabinet anymore. Thinking about putting a duct from intake to the front of the cabinet so the air would be drawn from there.

Thanks for the advice on straightening the ducting and using a metal tape!

As you can see in the picture the Y duct would attach to the outtake hole and I would move the orange fan + another same fan on the end of Y so in theory I would have double outtake fans = more CFM if this works...

What do you think?

Thank you for your reply

 

[r2k]

Hmmm, pushing it all through one hole is going to lose a big chunk of your cooling power. Fans in series like that tend to increase the pressure and push against more duct resistance but it doesn't do more much more air than what one fan can do. It is better to punch a second hole would allow you to have two fans running in parallel and increase the cubic feet per minute, which is what makes the box temperature drop. It's all about how many pounds of air per minute you can move. Moving more weight gives you more cooling.

I'm not sure about the Y duct. It could work for you if the fans are equally matched and running at the same speed. I guess you have to try it and see.

Make sure you have your fans sealed around the edges. You can really kill off your cooling ability by just leaving a few cracks around the edges and let the air seep around from the output back into the box.

I still wonder if your intake is big enough. Passive intakes should be about twice the hole area as your outlet hole. I don't think you have that.

In the end, you need to plug it all together and prove to yourself that it works like you want. If it doesn't work well without plants, it will work even less better if you start filling the box.

What are the stats on your fans? How many CFM will they move? I think the typical fan like that moves about 35 or 40 CFM under the best conditions, and you have to derate them to about 80% (or more) because of air resistance in your application. That is about the right value for what I calculated above and your 250 watt bulb.

If you have the same fan power and intake air temperature in your test above and switch to a 150 watt bulb, I think you would measure about 84 degrees F. That seems higher than what you probably want. It all depends on your exact numbers, but something needs to get better if you want to achieve a goal of something like 80 degrees. You need more like 45 CFM to get 80 degrees. If the intake air temp goes up, you will need to move even more air. Of course, you may be able to adjust your fans and system to get temps down. Do a better test to see if you can get rid of some measurement errors.

-r2k

 

[dec]

Hey!

You were almost right on with your calculations about temperature. I intalled the 150w and test showed 83 degrees F. This would work at the moment with low ambient temperatures( 69,8 ) but would soon become a problem in summer.

My fan is CF-V12HP COUGAR VORTEX = 70.5 CFM but I have it on Rhino filter which is rated for 294 CFM. If I had a carbon filter rated for around 100 CFM would it be less restrictive?

As far as I've been thinking these are the options I have:

1. Leave everything as is it and just use 70w HPS. Yield would probably be alot smaller...

2. Make another hole and have 2 fans in parallel and make bigger intake. By calculations this would be enough airflow for 150w but I would have to have 2 carbon filters and there is only room for one behind the cabinet??

 

[early_bird]

@dec
nice setup, dumping the air from cooltube into box is not bad, it´s better than reflector. A reflector blocks the heat below, the hot air can´t escape to the top and creating hotspots. In your setup nothing holds the hot air back, it can flow smootly to the top of the box, where the exhaust is. So this is much better than a reflector

But use 2 Fans to double cfm is nice bot not the best setup i think (depends of the strenght of your fans). The bottleneck of PC Fans is usally pressure not CFM!
I whould try to use 2 fans in a row. CFM stays the same but pressure doubles ! And this is mostly what you want, more pressure not more CFM, more pressure means more air is sucked throught your carbon filter! The setup has more strenght and power. And you need less space.
But as i said this really depends in detail from the fans you are using and the setup overall, in special pressure loose of carbon filter!
I whould try stacking of fans. Optimal is some tube between the fans not one screwed on the other with just a few cm between, this is not optimal.
With some tape this is easy to try

I used this setup, there came more air out than on my cabinet with an S&P TD-350 Fan (But was not really comparable, because the TD-350 run in low mode with Cool Tube).

 

[dec]

Thank for your reply early_bird.

Just found out no matter how I switch things around I will always have 33 CFM exaust therefore the temp difference will always be the same no matter what.

So in theory: [FONT=Arial, Helvetica, sans-serif]CFM = 3.16*(Total Watts)/deltaT
where deltaT = *F [/FONT]

Right now the temperature difference is 14,2 F. That means I have 33 CFM exaust and cabinet goes from 69,8 F to 86F.

So if I made holes for another exaust and intake I would have around 66 CFM exaust all together. Which means my cabinet would go from 69,8F to 77,8F and the difference would be 8 F. That means I could even have this setup in the summer when temps rise to 75 F in my room.

Just need someone to confirm if this is true and will this work please...?

Spent alot of time trying all different setups with this cab and feel like I'm going crazy, so I don't want to start punching holes, wasting time and still not be able to have a 150w whidout high temps.
Now that I see these theoretical calculations it's logical why there was no way on earth I could drop my temps while having the same CFM on exaust.. stupid me...


[FONT=Arial, Helvetica, sans-serif]
I do have 1 more problem I could use some help with and that is lightproofing the front door of the cabinet... any ideas?[/FONT]


Thank you!

 

[r2k]

I think you are the right track. One thing you should do is listen to your exhaust fan. Take a moment to listen closely to your fan with the door open, and then shut it while you continue to listen. If you hear the fan change pitch when you open and shut the door, it means you have intake restriction. Usually, the pitch will increase in frequency because the fan has less to push against and will spin faster. It would be great if you had an RPM meter to measure the fan speed directly but I doubt you do. Some fans have a third wire that goes high and low each time the fan spins once. If you can watch that output, it gives you a direct measurement of fan speed to know if it is increasing when the door shuts.

Your thought process is correct about adding the same kind of fan in parallel to increase air flow. Double the air flow and you cut the temperature difference in half. It means cutting more holes, but that's the price of progress.

I still wonder if you could vent the bulb more directly into the exhaust fan. Better yet, vent it outside the box and you get your extra fan for the price of one more hole and another intake. Worse case, you cut holes in the box and vent the tube through them and find it doesn't work, so you get the extra fan and put it in the same holes.

The light leaks around your door are familiar. It's tough making a door that is light proof. The trick is having overlapping edges that are light proof. You need black surfaces around the door to minimize reflection. I have used black electrical tape to do this kind of thing, it works reasonably well but not perfect. Line the edge around the door, the wall edges where the door touches, etc. For overlapping edges, think of a shoe box and top, where the edge overlaps the side of the box when you put the top on. Any surface not in the box should be covered with flat black to minimize reflections. You could also get a blanket and drop it over the top of the box to block light. Just don't block any vent holes and make sure the blanket is light proof. I tried using one of those mylar space blankets but it isn't even close to light-proof when you have an HPS bulb behind it. You see right through like an x-ray machine.

-r2k

 

[r2k]

Sorry, I forgot to respond to your question about the filter.

I think changing to a small filter will probably add more resistance, not less. If your fan is 70 CFM and you are seeing 33 CFM effective, it means you have a big air drag. It's probably your filter. Just for kicks, can you try removing the filter to see how much the temp drops?

Since you have the filter and it adds so much resistance, it might be just as beneficial if you add the second fan to pull air through the filter, effectively mounting your fans in series. It would save having to cut a second hole and all the light leaks that means. It is something you might be able to easily try by making an adapter from duct tape.

-r2k

 

[dec]

Okay I am willing to make more holes since in theory that would allow me to have 150w.Right?

'Better yet, vent it outside the box and you get your extra fan for the price of one more hole and another intake. Worse case, you cut holes in the box and vent the tube through them and find it doesn't work, so you get the extra fan and put it in the same holes.'

Thanks for this great advice! That is exactly what I am going to do. First I will make a separate ventilation for cool tube only and that will save me the hassle for another filter.

In theory:
My cabinet with separate cool tube fan needs 24 CFM of cooling for a 20*F temp rise in the exhaust temps with a 1 *F rise in the growbox. 1 Minute between Air Changes requires only 7 CFM through the scrubber.

I have 33 CFM scrubber exaust and I will have atleast that or more( because there will be less restrictions and same fan) through my cool tube. That means I will have absolutly no high temperature problems with my 150w.

Will this really work??

Just asking this because I almost went crazy when I spent 2 days switching things around,trying all possible options only to find out that I simply can't change my temperature because in the end my exaust CFM is still the same.

 

[r2k]

I don't really understand your "in theory" math. The part about 24 CFM=20*F rise makes sense, I don't get the part about 1*F rise in the growth box.

I have never been a big supporter of sizing your fan in air changes per minute. It just can't really find any basis for it, other than it kinda works for small boxes and big lights. I think it was just something that somebody noticed and started talking about years ago. It never seems to really work for people with problems. The formula we use now actually makes sense because it is based on how heat transfer occurs.

The easiest way to cool it off is to move more air through the box. Heat energy is transferred in pounds of air moved. Move more pounds, transfer more heat. Water would work even better, but the plants might not like it much.

I have had a theory for a long time but I don't know how to prove or disprove it. CoolTubes are an interesting thing. To cool the plants you can either move more air per minute, or you could move more heat energy if you could move only the hot air. That's where a CoolTube comes in. Not only do you get the benefit of the air you move through the tube, there is a multiplier effect because the air in the tube is hotter (I hope) than the air in the surrounding air in the box. If you move hotter air, you don't need to move as much air to carry the same amount of heat. Once you let the tube air go back and mix into the box, you have lost the race. You can't unmix the hotter and cooler air. If you keep them separate and vent the tube independently, it should work better than mixing the air and using the same fan power to pull air out of the box with both fans. I can't believe it would be worse performance and I strongly suspect it will be better to vent the tube independently. I just can't tell you better by how much.

I'm not surprised that you can't improve temps by switching things around. Unless you remove some inefficiency, you can only do what your system allows until you increase air, decrease bulb wattage, or decrease incoming air temp. Assuming you don't have air intake constriction, you could reduce the air resistance of your filter (not likely).

The other good news is that you might have one more benefit if you stock up on healthy plants in the box. It turns out the BEST cooling method is evaporation. It is the only way on earth (almost) to produce air that is cooler than ambient. It is certainly the only practical way to remove large amounts of heat energy. Healthy plants are really good at evaporating water, and you want to encourage that. If you can evaporate a gallon per day, it's like taking 100 watts off your light. I'm not saying you can evaporate a gallon per day with 150 watts, but any amount is better than none.

-r2k

 

[early_bird]

Thank for your reply early_bird.

Just found out no matter how I switch things around I will always have 33 CFM exaust therefore the temp difference will always be the same no matter what.

So in theory: [FONT=Arial, Helvetica, sans-serif]CFM = 3.16*(Total Watts)/deltaT
where deltaT = *F [/FONT]

Right now the temperature difference is 14,2 F. That means I have 33 CFM exaust and cabinet goes from 69,8 F to 86F.

So if I made holes for another exaust and intake I would have around 66 CFM exaust all together. Which means my cabinet would go from 69,8F to 77,8F and the difference would be 8 F. That means I could even have this setup in the summer when temps rise to 75 F in my room.

Just need someone to confirm if this is true and will this work please...?

Sorry, i don´t read the whole thread, just wanna drop my opinion ;-)
No, i think your calculation is may wrong, at least you use wrong variables.

Some theory. Let´s say a filter has the ability of x cfm @30 PA (Pascal) pressure. It doesn´t matter how much cfm you fan delivers, 30 or 100.000, your carbon scrubber only can do x at a certain pressure!

Switching 2 fans parallel doubles your cfm NOT the pressure the fans deliver!
Got it ;-) ?

Next step: Find out if you lacks pressure or airflow ? I whould guess pressure, PC-Fans often lacking pressure, thats the common problem of axial fans.

 

[dec]

Wow r2k... Thanks for this great reply!

Haven't had much time to play with my box. Could only manage to do some smaller things and I have yet to make new holes for cooltube cooling.
I placed duct adapters on my cooltube as fan is 5 inch and cool tube is 4 inch. Still have to figure out how to securely place it vertical.

@r2k: The in theory math was copied from https://www.icmag.com/ic/showthread.php?t=112862 ( check Two Stage Cooling part)

@early_bird: I understand and when I tried your advice on doubling fans for scrubber for increased pressure it definetly worked! After I try the separate cooltube ventilation I will listen to the fan that pushes into carbon scrubber and if it will be struggling I will order another one so there will be more pressure and less strain on single fan.

Will update once I have everything set up and tested for temperatures

 

[r2k]

I just looked at that link. There is lots of really good (and I mean, REALLY GOOD) info in it. When it comes to the two stage ventilation, respectfully, I call "handwaving". I didn't say "bullshit", I said "handwaving".

Based on numbers in that link:
He is claiming 7 CFM through the main box area and a 2*F temperature rise. If you do the math, that means you are removing heat at the rate of 4.4 watts from the growing area. That means you are moving (400Watts-4.4Watts)=395.6 watts through the coolTube exhaust. If you are moving 63 CFM through the tube, that means the CoolTube air has a temperature rise of 19.8*F. If you use 42 CFM air the temperature rise would be 29.8*F. So far, the math works out,

--- BUT ---

I don't believe that only 5 watts of energy escapes through the coolTube. That means your lighting efficiency is only about 1.1% (4.4 watts out / 400 watts in x 100%). I think an HPS light is more like 20% or 30% efficient at generating light. Plus, there is the radiant heat that escapes through the coolTube as as infraRed. To make a long story short, I don't believe you can trap 99% of the energy inside the coolTube. It will only pick up heat conducted into the air. Any radiant energy will shine right through the tube and be lost to capture by the tube. In my opinion, I would have to guess that about 100 to 150 watts (only my personal guess) makes it through the coolTube and into the box. I don't think 7 CFM is going to do it.

The mistake made in that thread is that it assumes you can just decide how much heat will go through the tube. Real life doesn't make it that easy. It will be what it is, and I don't know how to analyze it. Everything depends on the capture efficiency of the tube, please how well you can retain that heat as it blows through the ducting and out of the box. There are just too many variables to know how it will work. The only thing I know for sure is that the answer is more than 0% and less than 100%. After that, you just have to build it and find out.

-r2k