Hi

I'm going to be making a CF for my grow cabinet based on the Raz design except mine needs to be long and thin. I'm thinking of using a piece of 150mm pvc pipe. I have room in my cabinet for it to be upto 600mm long if neccessary.

Is there any way of calculating the volume or weight of granules required based on the fan's m3/hr ? I don't want to make the filter too long and reduce the airflow too much but at the same time, odour removal must be complete.

My cupboard has a volume of 0.25m3 and the fan has a minimum flow rate of 25m3/hr

Any suggestions as to the required length of filter based on these figures please?

Many thanks

A

the longer the filter the more air should flow through it, I got a 5" rvk and a 150mm/5" Phat Filter but it was too small and restricting airflow a hell of a lot, I replaced it for a nice long budget filter and hey presto no massive air flow restiction like before ... so if you worried about air flow make it long as poss.

Hi established

Thanks for the reply but I'm not sure it applies in my case?

If I assume correctly then your filter is the type with a hollow perforated tube surrounded by carbon and another perforated tube outside that. The air goes in/out the hole on the end and percolates through the sides of the filter. In this type of filter then the bigger it is, the more air will flow as you are making the surface area bigger.
My proposed filter is a tube completely full of granules with air going in one end and coming out the other. The longer it is, the more granules the air has to pass through and the larger the resistance. The only way to decrease resistance is to make the tube a bigger diameter or shorter in length.
What I want to know is... for a 150mm diameter tube, how long does it need to be for the carbon inside it to completey absorb any smells without making the airflow resistance too high. With the hollow tube type filters, the air only passes through about 50-60mm of carbon but over a large area.

If I'm wrong about any of his then please correct me.

Many thanks

A

yep - your principles are wrong.

A fan will not suck through a massive wadge of activated carbon granules. you need a large surface area of a thin layer of carbon

B

Cheers for the quick answer blab

Back to the drawing board!

Any ideas to solve my problem? I do need to have the filter as part of the duct system as I need to duct the extract though a vent hole in the cabinet.
Does it matter whether the fan is sucking air through the filter of blowing air through the filter?

Thanks

A

post pics of your grow space and fan setup if poss, then someone can advise a tailor made setup

hey anon i got work but there is a homemade cf on this site. cant rememba where either. id look, but i got wotk right now so if someone could find it for him;)?!?!?! then tht would be sweet.

it looks jus like a CAN CF

DIV

Hi

I've had a bit of a think and come up with the following as a possible design.

It will be an MDF box with an air inlet hole on one side/one end and an air extract hole at the other side/other end. The carbon granule chamber in the centre will be held in place using a suitable mesh either side of it. The empty spaces either side of the carbon will act as plenum chambers. There is obviously a base and a lid which aren't shown on the drawing.

The overall length of this box will be 36", it's height will be approx 8" and there will be enough space for 2.5" to 3" of carbon (is that about right for the carbon layer?) This will give a carbon layer area of 262"sqr (or 1700cm2 )

Am I now on the right lines?

Many thanks

A

Interesting design. However with that kink in it you are going to get a major drop off in suction. Suction really doesn't like to go round corners.

I've just done another sketch in 3D for anyone wondering what it may actually look like.

I know that bends cause airflow restrictions but I have to work in the space available and I think this makes the best of an non-ideal situation?

A

does it need to be an in-line filter?

basically, the more surface area of carbon you have, the easier it is for the fan to pull the air through it, so the bigger the airflow.
your design isnt really making the most of the space it will take up.
but, yes your desin would work fine

the best diy carbon filter design i can find is this one