[SeriousNerd]

Thanks a lot for compiling all this info! I haven't digested all of it yet, but as I'm currently designing my Growbox v2 and I am not satisfied with my current ventilation/odor control solution, this will be very handy!

Just two minor remarks:

SP = K1 * (CFM)^2
or
CFM = K2 * SQRT(SP)

and K1 = 1/K2 where K1,K2 are the unique system constants

I think K1 = 1/(K2)^2.

TOTAL PRESSURE = STATIC PRESSURE - VELOCITY PRESSURE

or another way to look at it is

VELOCITY PRESSURE = TOTAL PRESSURE - STATIC PRESSURE

I think TOTAL PRESSURE = STATIC PRESSURE + VELOCITY PRESSURE. Otherwise you can derive TOTAL PRESSURE = STATIC PRESSURE, which seems wrong!

I hope you don't mind my being pedantic!

[uraverage]

i guess i smoked way to much to underastand this......
who besides me is still lost?????

Originally Posted by redgreenry

yeah, I did that on purpose. See ventilation is a very technical and extremely subtle topic. I need to lay a technical foundation down so when people ask questions I have reference material to draw on and to be able to talk in a common "language" which is CFM, Static Pressure etc....

Thats a GREAT strategy! we need more like this... good work and thanks a lot... you are sacrificing for us all

Originally Posted by uraverage

i guess i smoked way to much to underastand this......
who besides me is still lost?????

it must be understood ! ventilation is the "bermuda triangle" of op design...you know you are putting air in there .....but where did it go...and how did it get there...spooky...for the plants HAHEHEHAHEHH..ERRR

[tommyboi_420]

Originally Posted by redgreenry

Ok lads, here's my grow cabinet. It's designed to take 4 x 42W CFL or a 150 HPS with 2 x 42W CFL. Currently I'm vegging seedlings so I put 4 x 13W CFL and move up to 4 x 26W CFL for early veg. The CFL lightbar makes this box very flexible.

The ventilation design uses a single 65CFM AC 80mm fan from RadioShack in the top section. The lights are separated from the grow chamber similar to a ventilated hood or a cooltube. The fan runs at rated flow because I don't block it up too much and have the intakes opened up to twice the exhaust duct size.

The grow chamber has a small scrubber that runs around 10 CFM. It doesn't need a high flowrate, just enough to change the air every few minutes otherwise a wind in the growbox just stresses the plants.


I picked this cabinet up a Crappy Tire for $50. It's 2' wide x 1' deep and 60" tall. There is 40" of growspace inside.



The top section contains the lights which are sealed off from the grow chamber with a sheet of glass. The scrubber is built into the duct grill. There is a passive intake in the floor of the box.




A sheet of glass separates the light section from the grow section.



This is the light section cooling fan. I've lined the fan chamber with this furnace filter material which works good to muffle the fan noise as well as providing a light trap.



The fan behind the furnace filter material.



This is the intake to the light chamber. It's 5" x 5" to match up with the 4" exhaust fan.


Here's a view of the intake 5"x5" and the 4" exhaust fan.



My scrubber is a cold air return filter for a furnace. I take the filter, spray it with rubber adhesive and shake on aquarium carbon. There is a 65CFM 4" AC computer fan mounted on the back of the cabinet.

ive read your whole thread,but i had to come back here and tell you that your grow cab is awesome RED

[tommyboi_420]

Originally Posted by redgreenry

One of the challenges in building a good ventilation system is to get the right amount of airflow. If you're stuck and you need to add or replace a fan, many times it doesn't quite work out.

One of the reasons is that the Air Flow is proportional to the square of the Pressure. Adding a second fan will not double the flow but will increase it by square root of 2, (1.41), or by about 40 percent. To double the Air Flow requires four times the Pressure.

There are two ways to add a second fan and they have completely different effects on the system.

The first way is to add a second fan inline with the first. The fan curve is the single fan curve with the pressure doubled at the same flow rate value.



The second way is to add a parallel fan. This doesn't boost the pressure at all but doubles the air flow at the original fan curve pressure value.



If you like these fans check out the S&P Catalog. The fans have adapters that make it easy to stack and parallel them.

https://www.hvacquick.com/catalog_fil...vl79qmr7oqqii5




System A is very restricted. We can see that the air flow improves quite a bit with series compared to parallel.

System B and C are less restricted and the improvements in air flow are similar between series and paralllel.

System D is an unrestricted system with the parallel fans providing a significant improvement over the series fans.

****************************** ****************************** ****************************** *****

I did a little experiment a while ago with 4 computer fans. I connected them in series and boy did they ever make a good amount of pressure and they were pretty quiet too. Each computer fan can produce 0.2" static pressure. Four in series will produce the same pressure as a Dayton blower at 0.75". The noise of a computer fan is around 20 db with the noise doubling every 6 db so four fans would make about 38 db of noise which is way quieter than some of the noisy blowers that start at 65-70db.

hey RED i allways thought that running fans in series or inline just had one fan pushing and one fan pulling(draging) the lead fan down with no gain in airflow or pressure??...maybe im just not graspin your idea

[Master_Blaster]

Redgreenry--What a great thread--very informative. I use computer fans in my cab and have had ventilation problems from day one. Now I know that it was due to airflow restriction.

Regarding your ventilation setup in your cab, you use rubber adhesive to secure the carbon to the cold air return filter for a furnace. I don't know anything about rubber adhesive. Does this type of adhesive block air or is it somehow gas permeable. Please let us know how this works. Thanks

My scrubber makes use of this VENT GUARD cold air return vent filter. I came across this at a local hardware store. I can buy replaceable filters for it.

All I did was take a can of Elmers Spray adhesive which is just Contact Cement in an aeresol can and gave the filter a light spraying and dumped some aquarium carbon on it. Let it dry and dumped off the loose stuff. I didn't spray very much on just enough to hold a thin layer of carbon.

You can buy something like this in a activated carbon filter by Web at Home Depot for about $15-$20 for your furnace filter. It's for smokers with stinky pets. There isn't much carbon in these filters so I knew I'd do better making my own.

I found that the carbon coating didn't last very long so I took a second filter and coated it and sandwiched 1/4" of carbon between them and taped it up all around the outside edge.

I have a couple of new filters that I can quickly make a standby and it won't be hard to dump out the other filter and replace the carbon.

Here's an easy to build filter that works great.

Originally Posted by Guest

Carbon Air Filter

My air filter uses two Sterilite containers. The small one must fit inside the large one.

The bottom is cut out of the small tub, I left a small rib in the center to support the screening.
Glue the window screen in place with the epoxy.

The lid of the large box is cut so that the small box with fit into it.

Intake holes are cut into the large box and the dryer adapters are fitted onto it. You can just duct tape it to the side if you don't have the adapters. This is probably the first time that duct tape is actually used for it's intended purpose. The flap is removed from the dryer adapter and I use a hack saw to trim off the pipe on one side.

A computer fan and a dryer hose adapter is fitted onto the lid of the small box.

When the filter is all assembled, I take silicone caulking and seal up crack where the small box goes into the large box lid.

My setup uses 1/2 lb of activated charcoal for a filter depth of 1" that I buy at the pet store. The 1" layer is good for the whole grow.

[rune2008]

Great post! Thanks guys!

Originally Posted by SeriousNerd

I hope you don't mind my being pedantic!

Good catch. I did some of this very quickly and was trying to simplify the calculations. I'll go over that one again.

The real point that I'm trying to make is that the Total Pressure is what the fan makes, Static Pressures are losses and the Velocity Pressure makes the air go.

Originally Posted by tommyboi_420

hey RED i allways thought that running fans in series or inline just had one fan pushing and one fan pulling(draging) the lead fan down with no gain in airflow or pressure??...maybe im just not graspin your idea

Two fans in Series increases the Pressure. Two fans in Parallel increases the Flow. The actual increase depends on the fan curve and the system resistance curve. Most guys think doubling up will give double results but becuase the ventilation calculations have squares and square roots in them the results are 1.4 not 2.0 times at best.


Thanks to everyone for dropping by. If anyone has a ventilation problem or a system that needs to be tinkered with don't be afraid to drop by. I've already fixed a couple of guys up already.

[Pimpslapped]

Originally Posted by redgreenry

Two fans in Series increases the Pressure. Two fans in Parallel increases the Flow. The actual increase depends on the fan curve and the system resistance curve. Most guys think doubling up will give double results but becuase the ventilation calculations have squares and square roots in them the results are 1.4 not 2.0 times at best.


Thanks to everyone for dropping by. If anyone has a ventilation problem or a system that needs to be tinkered with don't be afraid to drop by. I've already fixed a couple of guys up already.

I might have a ventilation issue in the near future, but I think I'm getting a bit of a grasp on it.

This won't apply to me, but in regards to the fans being put together in series... would there be any benefit in setting up two or more fans of differing CFM ratios? I happen to have about 20 identical muffin (Computer) fans sitting around, so it's not a problem I'll be dealing with. But given the topic, the idea popped into my head. I'd assume the best way, in that case, to try and calculate would be basing any increase off of the slower/weaker fan.

But, regardless, great thread! I can't get my head around half of it yet, especially the formulas. Mathematics were never my strong suit, but I'm reading this one a couple times. The comparative listing on exhaust vs intake is handy. Saved me from a bit of a blunder there.