Tutorial Ventilation 101

[guest 77721]

I did a little experiment a while ago with a bunch of PC fans. Just bolted a few together and stuck them on my scrubber. You need at least 4 stacked to get the pressure equivalent of a centrifical blower.

If you have a bunch of pc fans and a good PC powersupply, this will work for ya.

iv got what might seem like a weird question. i know that if you put 2 fans side by side that you double the cfm, and if you stack 2 fans you reduce the static presure by half. so my question is what happens if you put 2 stacked fans next to 2 stacked fans? would you end up with twice the cfm with half the static presure? and 1 more question. if you put 3 fans side by side by side would you then triple the cfm? if it does work that way i may try smaller cfm fans. i know it sounds like alot but if it does work that way and i use that setup then you will understand why i want to try this when you see it. peace

 

[MicroDude]

Can I get a little advice on my ventilation? I am building a NGB style cab. I have a S&P TD-100

• Item: Duct Fan
• Type: In-Line, 2 Speed Mixed Flow
• Fits Duct Dia. (In.): 4
• Inlet and Outlet Dia. (In.): 3 7/8
• CFM @ 0.000-In. SP: 101/97
• CFM @ 0.125-In. SP: 85/81
• CFM @ 0.250-In. SP: 57/51
• CFM @ 0.375-In. SP: 19/16
• Max. Inlet Temp. (Deg. F): 104
• Voltage: 115
• Hz: 60
• Phase: 1
• Max. Amps: 0.45
• Max. Wattage: 26/23
• Motor HP: 1/25
• Motor RPM: 2500/2450
• Motor Enclosure: Totally Enclosed
• Bearing Type: Ball
• Housing Dia. (In.): 5 7/16
• Length (In.): 6
• Flange Width (In.): 1
• Speed Control: 1DGV1

Over all my cab is 17"x27"x23" (L, W, H). My flower chamber will get 17"of the width and the other 2 chambers get 9 1/2". Now I know I should have 8" intake for a passive system. But do I need too? Also if I do need the 8", when venting into the other chambers do I still need an 8" opening into each chamber or only the inital?

Hey Red, Can you help this guy out?

 

[disfunktional]

I did a little experiment a while ago with a bunch of PC fans. Just bolted a few together and stuck them on my scrubber. You need at least 4 stacked to get the pressure equivalent of a centrifical blower.

If you have a bunch of pc fans and a good PC powersupply, this will work for ya.

sweet!! so what about the noise levels? wait did you mean 4 stacked on eachother? or 2 side by side stacked? i found some 120v 4 3/4" axial fans would those have more lung power than the PC fans?

 

[CranAppleGemz]

learned alot..nice thread red

 

[Some1uKnoOf]

Has anybody ever done a real analysis on coolTubes? I am looking for how much heat can you move away using a cool tube as a percentage of the total wattage of the light itself.

I suppose it would depend a large amount on how much energy is radiated through the glass of the bulb and coolTube as compared to how much is conducted through the outer envelope of the bulb itself. It would depend on many hidden heating constants and be specific to your individual setup. This means you have to actually measure the heat moved out through the coolTube exhaust and measure the reduction in heat passed through to the growing area.

I've been looking for this info for a while but never seen any experiments or data on it. At some point, more air through the coolTube wouldn't really cool the box any more, it would just make the coolTube exhaust have more volume of air but not any more heat energy. It would be good to determine how big of an air volume (CFM) would be needed to achieve optimal cooling and how much you could reduce the fan power in the main grow box.

The other thing I see in looking at forums is that people are using flexible ducting for coolTube inlet and exhaust. I know it is convenient to use for that purpose, but that stuff is notorious for adding extra pressure loss due to air resistance from all the pleating. It is best to straighten out the flexiduct as much as possible to remove pleats that rob fan power. A bulb in the tube is bad enough, you don't need to lose even more power to inefficient ducting.

 

[guest 77721]

Hey Some1UknowOf,

This set of curves or the forumula CFM =3.16*Watts/(delta T) is really good for sizing your fan to the amount of heat to be taken out of the box.

Using a cooltube or a separated light section, like I use, there is no benefit in cooling the interior of the cooltube within 10*F of ambient. I always recommend sizing your fan off the curve and reducing by 1/3 to let the exhaust run a bit hotter.

You're absolutely right about big losses coming from flexible ducts.

 

[Some1uKnoOf]

This set of curves or the forumula CFM =3.16*Watts/(delta T) is really good for sizing your fan to the amount of heat to be taken out of the box.

redgreen,

I am highly familiar with that graph and the metric version of it. It speaks to what you can accomplish regarding the intake temperature and the output temperature with a given airflow and wattage inside the box. It really doesn't say anything about what temperatures exist at various spots inside the box. The formula also doesn't account for water evaporation inside the box, which can have a powerful effect on cooling. Still, I think it is still the most useful and applicable method that is easy to use.

Using a cooltube or a separated light section, like I use, there is no benefit in cooling the interior of the cooltube within 10*F of ambient. I always recommend sizing your fan off the curve and reducing by 1/3 to let the exhaust run a bit hotter.

I agree that the actual temp inside of the tube does not matter, for the most part. There are some effects related to temperature regarding how much heat bleeds back into the box through the coolTube ducting by conduction through the duct sides and this is related to air temp inside the tube, but this is a second or third order effect and not what I am talking about.

I was asking about looking at what amount of heat is transferred away by the coolTube and how much heat remains in the box for conventional forced air cooling. We know that the coolTube will pull some percentage out of the box but we don't know what is theoretically possible and what is practically possible.

You could use the formula to determine wattage moved by the tube if you knew the temperature rise for the tube and the airflow through it but I don't know of anbody who can measure airflow accurately without some specialized equipment and a desire to use it.

I would really like to hear from anyone that has worked on this, thought about this, or done experiments with heat transfer using coolTubes. If someone has rules of thumb or guidance on how to size fans or tubes to improve heat flow, I would like to hear about it.

 

[BC Chronic]

i have another question for ya Red..Great thread by the way.
I am doing a pc grow.I have 1.44 cubic feet of space.
There is a delta fan rated 151 cfm blowing on the lights.I have 2-40 watt and 2-36 watt cfl's.

1)I want know what sort of exhaust should I have?

Theres are 2 or 3 fans I could use. 1 is an 80mm aluminum cooling fan ( which is 53 cfm) and 1 is a 120mm with 79 cfm.
I've tried via that curve but I just keep getting frustrated trying to figure it out
I was going with 3 fans for intake and 4 for exhaust and the temps were around 80-81 but I don't know if there was a wind tunnel in there either!
One thing I should note.. I really need that 151 cfm fan blowing on my lights don't I? I have a thread going but there was alot of feedback about all the fans I wanted to use so I thought I would come to the expert.
Thanks alot and ANY help would be very much appreciated.

 

[guest 77721]

Hey BC Chronic, thanks for popping by.

for 152 watts, you need 48 CFM so you 80mm aluminum cooling fan is all you need with about a 5" x 5" intake.

I'd be concerned with putting too much light and high airflow on your plants. The idea of running a micro box is to be bare minumum with everything in balance. You could probably run only 2x42 CFL's and still make 50 watts/sqft for flowering.

Have you read any of MrMicro PC box threads? He has a dialed in proven design worth copying.

 

[BC Chronic]

Thanks sooooo much Red!! I realize I went overboard now..Just wanted to do something different but I also want it to work. So I don't need any fan(the 151 cfm) bring air in at all huh...Interesting...I can just use the 5''x5'' intake hole I have for the fan I WAS going to use....I wish I would have popped by much sooner...I'll check out mr.micro's thread for sure
Thanks Red....Wish I had half the ingenuity you have

 

[Some1uKnoOf]

Fan sizing for Metric users

Fan sizing for Metric users

Redgreen,

I went dredging through my archives and found something you might like. I know you have the same chart for "american" fan sizes that use CFM and Fahrenheit. Here is the metric version that uses CMH and Centigrade. I thought it might be useful to complete your collection and our euro-friends might appreciate it.

cheers!

-SomeoneYouKnow

 

[Bacchusbud]

This is a great thread and really should be stickied....

When i read it last night, it answered alot of my questions but i wanted to make sure i was understanding correctly. Please keep in mind that i am a newbie grower and don't have any equipment in hand, (shoot, iam still waitin on my beans), so this is theoretical but i want to do it correctly the first time.

My cabinet is 64"H, 45"W and 15"D. There is a partial shelf about 10" from the top so plant andlight room is really 54". Because of the narrow shape, i want to run 2 250's in a cool tube along with a carbon filter on a separate fan.(Side note: Is this too much light? I can't seem to find anything smaller with isolated ballasts) Now the light is going to be adjustable, with the intake for the cooltube coming from the top and exiting at the top. I assume that i can accordian the tube to take up excess ductwork so it never has to make more than a 90deg bend to the tube and 90deg back upto the exhaust port as i raise and lower the lights. (For stealth purposes, i can't really vent from the sides...the back is ok as well.)

Red, you stated at one point that you needed .3CFM/watt, so that gives me 150CFM, right? But i am certain that Hoosierdaddy stated that he used a duct booster to cool his 400+150w cooltube with no problem. And i may have been high but i thought you mentioned axial fans for cooltubes as well, no? I had originally planned to put a S&P 100CFM fan there, but while noise is least important to me, it is still a consideration....especially if i can get adequate ventilation with less noise.

For the carbon filter, my space is only about 25cub feet, so to change out the air every 5 minutes is only 5cfm. Pulling through a filter will increase teh need of a more powerful fan, but do i really need another big fan(big to me, but seemily S&P's smallest inline) or is there a way to do it smaller?

I apologize to all for the bookishly long post, but i really do appreciate all the help!

 

[disfunktional]

hey Bacchusbud if your wanting a lower wattage light with a remote ballast give this one a look. the same site also has a Galaxy ballast thats a higher quality. guess it all depends on if your on a budget. anyways i hope this helped.

 

[MicroDude]

Ok My calculations were clearly off. This kind of math hurts my head. So let me give a overview of my problem. I hope somebody can help! I have a small cab I built. It has 3 chambers. The flower chamber is (DxWxH) 16x13x22. The utility and mom chambers are 7.5x8x22. I first vented with 2 light traps that caused the flower chamber to hit 111! So I removed the light traps. Now I have no mom chamber. My flower chamber temp is now 90-94 with the lights on and 72 lights off. Room temps are 74-78.

ATM I have 3x42w 2700k and 1x27w 6500k. When the temp hit 111 I had 4x42w 2700k and the light traps. My fan specs look like this...

# Type: In-Line, 2 Speed Mixed Flow
# Fits Duct Dia. (In.): 4
# Inlet and Outlet Dia. (In.): 3 7/8
# CFM @ 0.000-In. SP: 101/97
# CFM @ 0.125-In. SP: 85/81
# CFM @ 0.250-In. SP: 57/51
# CFM @ 0.375-In. SP: 19/16
# Max. Inlet Temp. (Deg. F): 104
# Voltage: 115
# Hz: 60
# Phase: 1
# Max. Amps: 0.45
# Max. Wattage: 26/23
# Motor HP: 1/25
# Motor RPM: 2500/2450
# Motor Enclosure: Totally Enclosed
# Bearing Type: Ball
# Housing Dia. (In.): 5 7/16
# Length (In.): 6
# Flange Width (In.): 1
# Speed Control: 1DGV1

It is hooked straight to the carbon scrubber and then one turn and its exhaust exits. Also my passive vents from outside to inside mother chamber are 3"x5" and 3"x5" into the flower chamber from the mother chamber, and 8x8 from flower chamber to utility chamber. The fan has a 3.75" exhaust.

Did I forget anything? Any idea how I can get the temp down and get my mom chamber running?

 

[guest 77721]

Thanks Some1uKnoOf

I'm sure the Euro's and some of us Canuckians will appreciate the metric conversions. I'll put it on the main page right away.

Hey Baccusbud,

Your calculations are correct and I think you'll make out fine with the 150 CFM on the separated light and a small scrubber.

I've been able to get 10-15 CFM using a computer fan and a small homemade scrubber using two sterlite boxes stacked together. That's all you need for growbox ventilation.

 

[guest 77721]

I can tell by using the formula CFM=3.16*Watts/DeltaT that your box is
running with only 14 CFM with the light traps and about 25 CFM with them removed. Your 168W needs about 50 CFM to give a 10*F rise so you're not halfway there yet.

It looks to me like you have a major restriction, most likely the scrubber and your intakes. The multiple chamber boxes run hot unless the intakes are sized right between the chambers.

I'd advise you to pull the scrubber and see what the temps look like. With that 100 CFM fan, the box should be 5*F above ambient with all 42W bulbs installed.

Work on your intakes until you get the temps down. The 3"x5" are undersized. Open them up to 5" x 5" and you should see a difference.

Ok My calculations were clearly off. This kind of math hurts my head. So let me give a overview of my problem. I hope somebody can help! I have a small cab I built. It has 3 chambers. The flower chamber is (DxWxH) 16x13x22. The utility and mom chambers are 7.5x8x22. I first vented with 2 light traps that caused the flower chamber to hit 111! So I removed the light traps. Now I have no mom chamber. My flower chamber temp is now 90-94 with the lights on and 72 lights off. Room temps are 74-78.

ATM I have 3x42w 2700k and 1x27w 6500k. When the temp hit 111 I had 4x42w 2700k and the light traps. My fan specs look like this...

# Type: In-Line, 2 Speed Mixed Flow
# Fits Duct Dia. (In.): 4
# Inlet and Outlet Dia. (In.): 3 7/8
# CFM @ 0.000-In. SP: 101/97
# CFM @ 0.125-In. SP: 85/81
# CFM @ 0.250-In. SP: 57/51
# CFM @ 0.375-In. SP: 19/16
# Max. Inlet Temp. (Deg. F): 104
# Voltage: 115
# Hz: 60
# Phase: 1
# Max. Amps: 0.45
# Max. Wattage: 26/23
# Motor HP: 1/25
# Motor RPM: 2500/2450
# Motor Enclosure: Totally Enclosed
# Bearing Type: Ball
# Housing Dia. (In.): 5 7/16
# Length (In.): 6
# Flange Width (In.): 1
# Speed Control: 1DGV1

It is hooked straight to the carbon scrubber and then one turn and its exhaust exits. Also my passive vents from outside to inside mother chamber are 3"x5" and 3"x5" into the flower chamber from the mother chamber, and 8x8 from flower chamber to utility chamber. The fan has a 3.75" exhaust.

Did I forget anything? Any idea how I can get the temp down and get my mom chamber running?

 

[Dr. Conjuror]

Bacchusbudm,

I came across this in the 2008 ASHRAE Handbook:
================================
Some general rules in duct design are as follows:
• Keep main ducts as straight as possible.
• Streamline transitions.
• Design elbows with an inside radius of at least one-third the duct
width. If this inside radius is not possible, include turning vanes.
• Seal ducts to limit air leakage.
• Insulate and/or line ducts, where necessary, to conserve energy
and limit noise.
• Locate branch duct takeoffs at least 4 ft downstream from a fan or
transition, if possible.
• Isolate air-moving equipment from the duct using flexible connectors
to isolate noise.
================================

And it seems that I also read that the accordion type duct has a lot more static pressure when it is not fully extended.

Dr. Conjuror

 

[mayorofthdesert]

if anyone has tips for combating noise in my system I'd love a few ideas. I have a multi-room cabinet with 2 cool tubed 150hps & 2 75Wcfls my exhaust is a 4"duct with an eco plus fan into a can type carbon filter. I've got way more airflow than I need with the cooltubes (they're on their own 3" computer style fans. My temps are fine & I could get by with less airflow but am too broke to spend anything on a different fan right now. I do actually have 4 120v 4" computer style fans not doing anything...

Originally the fan & filter were inside the cab but I moved them up into the attic and ran duct down to the cabinet. That helped some, but the vibration was worse, like through the whole house now. I took two pieces of plywood and a bicycle tube up to the attic and made a bike tube sandwich. i set that on the ceiling joists then set the fan on top. That helped also, but not enough. Now it just sounds like I have a fridge up in the attic. I hear that the speed controlers just trade air noise, vibration & efficiency for an increase in motor hum. I guess I'm going to build a box, line it with insulation (or some other cheap noise absorbing material if you have a suggestion) and put the fan and filter in there. Might hang it from the rafters to further isolate vibration. or what about setting the whole mess on a big box of sand? think that would that totally kill remaining vibration?

 

[Dr. Conjuror]

mayorofthdesert - I am not sure if you have looked at the following thread or not, but there are lot of good concepts in it for what you are trying to do. But if you have not already, certainly read all of RedGreenery's thread (the one you are currently in).

DIY Muffler

Sitting on sand will vibrate the sand out from under it. If you wanted to sit it on something, I think thick fiberglass insulation would be better, but I do not know what weights you are talking about.

What kind of ducting are you using? Flexible or rigid? How big is you intake?

From what I have read, I think the humming is not present with all speed controllers.

Dr. Conjuror

 

[Bacchusbud]

Great! Thanks, Red! That makes me feel better. Thank you as well, Dr Conjour. Those are some good tips and i plan to keep the accordianed bit slid onto a piece of rigid duct at a flange attached to the bottom of the shelf...under the fan.

Now i'm off to find out what a "sterlite" box is and how to make a scrubber with it!