Tutorial Ventilation 101

[lbezphil2005]

so series or parallel? lol, i have 2 Mechatronics 120x120x38mm High Speed AC Fans 106 cfm each max,my space is 31 inches tall,36 inches wide and 18 inches deep,cfl's totaling 249 watts(4-42's,and 3-27's) i wanna make a scrubber using kitty litter and carbon using my fans to pull the air from my cab thru the scrubber,trying to figure out if i should put the fans side by side or stacked

side by side, let one exhaust the heat from the lights the other can clean the air - plenty of cfms for that small of space

 

[sm0k4]

so series or parallel? lol, i have 2 Mechatronics 120x120x38mm High Speed AC Fans 106 cfm each max,my space is 31 inches tall,36 inches wide and 18 inches deep,cfl's totaling 249 watts(4-42's,and 3-27's) i wanna make a scrubber using kitty litter and carbon using my fans to pull the air from my cab thru the scrubber,trying to figure out if i should put the fans side by side or stacked

I'm not sure about those 120mm fans, but I am scrubbing the air in a PC case with two 80mm fans stacked. One is attached outside the grow room on the metal PC frame under the front panel. The other is in the room with a 1/2" thick carbon pellet filter attached to it.

I could not get temps under control because my single fan couldn't pull through the scrubber. I had to stack two of them to increase water pressure.

Stacking fans increases pressure, CFM stays the same.

Fans next to each other will exhaust more CFM at the same pressure. What you are looking for is a 120mm fan with great h2o pressure rating.

Pic 1 is the outer fan on outside of case.

Pic 2 is inner fan

Pic 3 is the 1/2" thick DIY carbon filter. I took a regular 80mm PC filter you can buy at computer stores and modified it to stuff with carbon inside panty hose.

Pic 4 is overall cab. Its very low profile and still exhausts. Once I flower will be the odor control test. Currently on day 15 or so of veg.

 

[WESTCRAZY1]

I have a quick question regarding exhaust/intake ventilation. Hopefully i can get some answers on here soon as i would like to start piecing up my grow box. My question is will i be better off running a 5" exhaust fan and using a 6x14" passive intake? My original plan was to use a 5" exhaust fan with a 5" intake fan but that will cause negative pressure correct? At the bottom is a rough draft of my grow box. The 5" exhaust fan that i'll be using is a 5" pc fan with a built in carbon scubber. I know this might not be enough to filter the odor out but if this cause a problem later on then i can always switch the 5" pc fan out in favor for a 6" inline fan with a carbon scrubber.

 

[RomulusUSA]

Hi Red,

First, I want to thank you for all the info! I have a far, far better understanding of ventilation now than I did before. Thanks!

I am going to be using a tent that is said to have final floor dimensions of 4.5' x 4.5' x 6.5' which gives us (rounded) 132 cuft and 20 sqft. I am going to be running two fans/air circuits if you will, one with an aircooled 600w HPS and one with a carbon filter, most likely a CAN 33.

My calculations state the following:

Ventilation for Light Cooling
Maximum CFM @ delta T = 10*F = 190
Minimum CFM @ delta T = 30*F = 65

Ventilation for Air Exchange
2 ACPM - 162 CFM
1 ACPM = 132 CFM
1/3 ACPM = 44 CFM
1/5 ACFP = 26 CFM

My first question is, how often does the air need to be exchanged?? Much of what I have read (books + IC) states 2-5x per minute. You state 1/5-1x per minute a number of times.

I like overkill as well as adjustablility, so thus far I have been planning on using a 340CFM Panasonic WhisperLine for the carbon scrubber, and a 240CFM WhisperLine for the light. I am going to put speed controllers (I want to try a dimmer switch first, as those work on lots of things; Then I'll get a "router speed controller" if the dimmer fails me) on both fans, and decide on speed based on measurements of heat and general airflow.

How does my plan sound fan wise?

Also, if you were to link 2 tents together for carbon scrubbing/ventilation, the second of which would have about 33 cuft of airspace, how would you do it? I was thinking a tube from the top of the smaller tent into the bottom of the larger tent, and have it be equal or slightly larger size than that of my other passive intake. 2x4" holes into the #2 tent, 1x6" connecting tube, and 2x4" holes into the larger tent, perhaps.

Any input would rock! Thanks much!

Hey 420 Wookie - that's sounds like a good setup for an apartment. Let's start by figuring out your specs.

Room 3' x 4' x 7'
Area 12 sqft
Volume 144 cuft

Ventilation for Light Cooling
Maximum CFM @ delta T = 10*F = 190
Minimum CFM @ delta T = 30*F = 65

Ventilation for Air Exchange
1 ACPM = 144 CFM
1/3 ACPM = 48 CFM
1/5 ACFP = 29 CFM

Here are the fan ratings for two styles of Soler+Palau fans. The TD mixed vent line are Axial fans to move lot's of air without restriction. The Powervent are centrifigal blowers.

I'm going to propose a few fans and then we'll pick the winner based on final design if it meets spec.

CFM = 190 - This is to ventilate the light and tent without a cool tube.
TD-125 High Speed/ Low Speed - 197/149 CFM
TD-150 High Speed/ Low Speed - 273/193 CFM
Powervent 125x - 206 CFM

CFM = 65 - This is the cool tube spec with 30* F exhaust
120mm Computer Fan - 65 CFM with no scrubber

CFM = 130 - This is the two tents tied together with no scrubber 60*F exhaust
TD-100x High Speed/ Low Speed - 135/100 CFM

The Fan/Scrubber combo for 65 CFM is going to be trickier to fit.

Both the Can 33 and Can 9000 look good. The Can 2600 is too small.

To read the CFM for a fan/filter combo, find the point where the fan curve crosses the filter curve.

PV-100 and CF 33 look like around 60-65 CFM
PV-100x and CF 33 around 90 CFM

PV-100x and CF9000 around 105 CFM
PV-150 and CF9000 around 110 CFM

Looks to me like your best bet is the PV-100x and CF 33 combo for 90 CFM or the PV-100x and CF-9000. Now you can go shopping. If you want to DIY, get the spec's for the filters and make a copy.

We didn't take a look at the Mixed Vent fans with the scrubbers.

The TD-100x is unsuitable.

The TD-150 and CF9000 are a good combo at 90 CFM.

 

[Indian Culture]

Red - Maybe this is offtopic to blueybong's posts, but it is my understanding that the configuration to which you refer [filter-->light-->fan-->exhaust] is problematic insofar as odor control is concerned, and that filter-->fan-->light-->exhaust is preferable for ensuring that no odor can escape.

As it has been explained to me, the reason for this is as follows: after the scrubbed air leaves the filter, it must be sucked through duct, into the light and through more duct before it hits the fan and gets expelled. The suction of the fan will create negative pressure in the ductwork and will draw in dirty cab air through any tiny hole/gap/etc. in the ductwork, light and connections (and we all know that no air cooled light is 100% leak proof). By the time the air gets to the fan to be expelled, you have potentially mixed stinky air with the scrubbed air, and you will exhaust odor.

The better configuration, as it has been explained to me, is to position the fan as close as possible to the filter to minimize the chance of any stink being sucked in and mixed with the scrubbed air. After the fan, everything is being pushed through the ductwork (positive pressure), so any leaks in the duct/light/connections/etc. will simply result in some amount of clean air being vented back into the cab, but the air that is ultimately expelled will only be scrubbed, non-stinky air.

FYI - this is based off lots of research and conversations with experienced growers. I have no practical experience of my own with filtering/cooling/exhausting cabs, so I am genuinely interested in others' thoughts about this advice that I have been given.

Thanks

This is exactly my thoughts on it. Why would you risk stinky air going into your light and being sucked out of the fan without it being filtered?

You can have your filter first, then your fan sucking through the filter and then have it being pushed through the light and out the exhaust, that way no stinky air is leaving without being filtered first.

 

[GDK]

Awesome thread Red et al.
Im running a 10x6x6 room with 3x600w hps in open reflectors, passive intake from outside drawing fresh air pulled in by a 1900 m3/h(1120 cfm) extractor fan. My problem is the large 315mm fan (12,5") is not matching the intake. The fan is not running on max speed, im using a speed controller, but my total intake area is only 220mm (6,8"), which causes alot of pressure and poor cooling. My question is this: Is my only option to add more intake area, or can i add a intake fan to aid the problem. Or am i missing a third, fourth or even fifth solution?

Stay Safe

 

[lokes]

Awesome thread Red et al.
Im running a 10x6x6 room with 3x600w hps in open reflectors, passive intake from outside drawing fresh air pulled in by a 1900 m3/h(1120 cfm) extractor fan. My problem is the large 315mm fan (12,5") is not matching the intake. The fan is not running on max speed, im using a speed controller, but my total intake area is only 220mm (6,8"), which causes alot of pressure and poor cooling. My question is this: Is my only option to add more intake area, or can i add a intake fan to aid the problem. Or am i missing a third, fourth or even fifth solution?

Stay Safe

I've played with this a bit, and I'd say your spot on with adding more intake area.
3x intake to exhaust is what I've read.
My 6in forced intake doesn't keep up with the negative pressure of my 10in and I have heat problems.
I'm trying to move to a sealed room and negate this once and for all.

 

[GDK]

Word Lokes.
I have been contemplating on moving to a aircooled hood setup. I have a smaller fan that would be great for the closed system of lamps, and maybe then the small intake would be enough to support the cooling of the room...well see.

Stay Safe

 

[cr0n]

why is this thread not a sticky? Please mod, sticky this thread!

 

[frozty]

Thanks mate I really needed to step up my efficiency using 3 31cfm fans with no results. Thanks a lot mate this will really help me out.

 

[outinit]

This post has really educated me, thanks for taking the time to explain it all!!!!

 

[guest 77721]

Hey GDK,

It's been a while since I checked my thread so if anyone really needs help please PM me.

GDK - I ran your numbers through my spreadsheet.

1800 watts, 1120 CFM, Room with 36 sqft, 360 cuft

You're set up for 50 w/sqft and 3.1 Air Changes per Minute. Basically you're right on for equipment sizing.

A 12.5" exhaust has 122.7 sq in of area and I usually recommend 2x for a grand total of 245 sq inches or a 16" x 16" hole.

Your 6.8" intake is only 36.3 sq inches which is around 1/4 of what you need to at least match the exhaust duct size.

It's easy to modify a cabinet to add more intakes but much more difficult with a room or basement.
You're going to have to figure out if you can put more ducting in or add an intake fan to solve the problem.
I'd say the intake fan would be the easiest route.

Normally intake fans are discouraged because they pressurize a growbox and release odour into the rest of the house.
You're going to have to size the intake fan to the exhaust fan. That may be a challenge to get a high flow rate fan in a 7" duct.

Awesome thread Red et al.
Im running a 10x6x6 room with 3x600w hps in open reflectors, passive intake from outside drawing fresh air pulled in by a 1900 m3/h(1120 cfm) extractor fan. My problem is the large 315mm fan (12,5") is not matching the intake. The fan is not running on max speed, im using a speed controller, but my total intake area is only 220mm (6,8"), which causes alot of pressure and poor cooling. My question is this: Is my only option to add more intake area, or can i add a intake fan to aid the problem. Or am i missing a third, fourth or even fifth solution?

Stay Safe

 

[guest 77721]

Hi RomulusUSA,

First question:
I have a table of ventilation rates for common applications which are usually 1-5 Minutes per Air Change or 1 to 0.2 Air Changes per Minute. That's like a light draft.

What has happened is people building single pass systems found out that they need 1-5 Air Changes per Minute (Wind Tunnel) to cool a high intensity light.

This puts a great deal of stress on the plants. If you design a system using cool tubes, ventilated tubes with separate cooling and ventilation, then the ventilation rate needed is really low.
That's why I recommend 1-5 Minutes per Air Change.

The 2 stage system is the only design that you can tailor the growspace ventilation.

Hi Red,

First, I want to thank you for all the info! I have a far, far better understanding of ventilation now than I did before. Thanks!

I am going to be using a tent that is said to have final floor dimensions of 4.5' x 4.5' x 6.5' which gives us (rounded) 132 cuft and 20 sqft. I am going to be running two fans/air circuits if you will, one with an aircooled 600w HPS and one with a carbon filter, most likely a CAN 33.

My calculations state the following:

Ventilation for Light Cooling
Maximum CFM @ delta T = 10*F = 190
Minimum CFM @ delta T = 30*F = 65

Ventilation for Air Exchange
2 ACPM - 162 CFM
1 ACPM = 132 CFM
1/3 ACPM = 44 CFM
1/5 ACFP = 26 CFM

My first question is, how often does the air need to be exchanged?? Much of what I have read (books + IC) states 2-5x per minute. You state 1/5-1x per minute a number of times.

I like overkill as well as adjustablility, so thus far I have been planning on using a 340CFM Panasonic WhisperLine for the carbon scrubber, and a 240CFM WhisperLine for the light. I am going to put speed controllers (I want to try a dimmer switch first, as those work on lots of things; Then I'll get a "router speed controller" if the dimmer fails me) on both fans, and decide on speed based on measurements of heat and general airflow.

How does my plan sound fan wise?

Also, if you were to link 2 tents together for carbon scrubbing/ventilation, the second of which would have about 33 cuft of airspace, how would you do it? I was thinking a tube from the top of the smaller tent into the bottom of the larger tent, and have it be equal or slightly larger size than that of my other passive intake. 2x4" holes into the #2 tent, 1x6" connecting tube, and 2x4" holes into the larger tent, perhaps.

Any input would rock! Thanks much!

 

[guest 77721]

Hey WestCrazy1



I'd cut the hole size for the 6" exhaust and then you don't have to worry about it.

I have a quick question regarding exhaust/intake ventilation. Hopefully i can get some answers on here soon as i would like to start piecing up my grow box. My question is will i be better off running a 5" exhaust fan and using a 6x14" passive intake? My original plan was to use a 5" exhaust fan with a 5" intake fan but that will cause negative pressure correct? At the bottom is a rough draft of my grow box. The 5" exhaust fan that i'll be using is a 5" pc fan with a built in carbon scubber. I know this might not be enough to filter the odor out but if this cause a problem later on then i can always switch the 5" pc fan out in favor for a 6" inline fan with a carbon scrubber.

 

[NextUp]

Great thread RED! Thxs




I'm designing the ventilation part of the system now.

My box is going to be 4' x4' 36" high .....sealed........

I'm going to run 2 400watt CMH...

Anyone like to take a crack at it, with the best way to vent the lights?

Thanks

 

[guest 77721]

Thanks for popping by NextUp

There's a method that I like to follow to design a good ventilation system.

Step 1
Determine the growbox dimensions and what lighting intensity in w/sqft.

Step 2
Determine the Base cooling airflow rates and air changes for the particular growbox design

- Simple growbox
- Simple growbox with scrubber
- Cooltube/Vented Hood
- Cooltube/Vented Hood with scrubber
- Two Stage

Step 3
Build


Step 1
4'w x 4'd x 3'h
sqft = 16
cuft = 48
w/sqft = 50

Step 2
Simple Growbox design
CFM = 253 for a temp rise of 10* above ambient
ACPM = 5.27

Great thread RED! Thxs




I'm designing the ventilation part of the system now.

My box is going to be 4' x4' 36" high .....sealed........

I'm going to run 2 400watt CMH...

Anyone like to take a crack at it, with the best way to vent the lights?

Thanks

 

[NextUp]

Thanks for doing that! But Crickets!!!!!



Cfm = the power of the fans i should use, so if i have a room that keeps 70F and if i buy fans that are spec'd @ double your cfm rating, i should see a inside cab temp of 75F?
ACPM? Crickets! hehe!


Thanks for doing that.

Thanks for popping by NextUp

There's a method that I like to follow to design a good ventilation system.

Step 1
Determine the growbox dimensions and what lighting intensity in w/sqft.

Step 2
Determine the Base cooling airflow rates and air changes for the particular growbox design

- Simple growbox
- Simple growbox with scrubber
- Cooltube/Vented Hood
- Cooltube/Vented Hood with scrubber
- Two Stage

Step 3
Build


Step 1
4'w x 4'd x 3'h
sqft = 16
cuft = 48
w/sqft = 50

Step 2
Simple Growbox design
CFM = 253 for a temp rise of 10* above ambient
ACPM = 5.27

 

[Blacksonempire]

Ok, lots of information here on ventilation, duct diameter and fans, but has anyone done any science on the loss of flow from long lengths of ducting??

I am currently building a grow room which will require ducting upto 15metres (about 45ft) for the exhaust from inside the grow room (not the lights) I am wondering if i need to put fans at both ends of the ducting to get maximum cfm etc...

i intend on using pvc pipe as the long length of ducting, this is smooth and does not have any of the corrigations that the 'silver flexible ducting' generaly does abd im sure this will help out in the long run. I will be using 200mm or 8" pvc or can go bigger or smaller if need be..

the reason i am having to run so far is that i will be venting into a large crawl space under my house and also the intake will be coming from the same crawl space, the theory is not to be sucking in the same air that is going out, it should have time to dissipate etc.

any info of personal experinces will be great.

oh and thanks red for all the great info, most of the hard work has been done!

 

[guest 77721]

It's really difficult to predict the losses in ductwork. My approach would be to get your CFM and see if the velocity is within spec's of a duct sizing chart. For the long runs I'd go up by one or two sizes from the chart.

http://www.engineeringtoolbox.com/water-usage-activity-d_1736.html

 

[Blacksonempire]

thanks for the prompt reply Red, great link too i'll be following that chart for sure...