Building a drying cabinet for my crop, would like to get input on it.

[ellz]

Greetings all. I am making a drying cabinet out of an old wooden cabinet I picked up for next to nothing on craigslist. It's a split door cabinet that is 4x2x6 and the drying area is 2x2x6 (24cu.ft.) I plan on installing a 4 inch duct starter on top, hooking up a run of 4 inch ducting to that with a 190CFM fan pulling the air and a carbon filter cleaning the smell out of the cabinet. I also plan on installing 2 120MM AC powered computer fans for intake air. My biggest question is should I use a fan as well or just let the natural flow of air be my "fan" for drying? Basically I live in a very dry area to start with...relative humidity stays around 20-40% depending on the weather...usually the low end. I plan on leaving some of the fan leaves to help slow the drying process and wanted to know if using a fan would make the buds dry out too fast? The intake fans are both low-speed fans that each produce about 51CFM of airflow (so 102CFM total with both). I have also attached a crude MS Paint drawing of what I am talking about. Thanks for any input.

One other thing about the cabinet...I plan on sanding down the wood on the inside to where it's bare. This should help absorb moisture and keep it in the cabinet I believe. It's also a good way to ensure it's very clean before my plants go inside!

[oldjarhead100]

Great idea eliz I have put a fan blowing into my box before but usually its to keep it from growing mold (at least thats what I think lol). If you live in a dry area you might get away without a fan, I would feel more comfortable with a small fan (like those clip on 6 inch fans) just in case good luck

[JohnC]

My growing cabinet doubles as my drying cabinet once the plant has been cut down. I have a single 120mm PC fan pushing air in at the bottom. At the top is my extraction fan, rated at 75 cfm.

I've done six grows (and drys) in this cabinet and after trial & error found that I DON'T want to use the extraction fan. The fan pulls too much fresh air through the cabinet and my buds would dry too quickly.

What I found works perfectly for me is to have the 120mm fan running, pushing fresh air into the cabinet, but to leave the extraction fan turned off. The PC fan provides enough air movement through the cabinet to allow the buds to dry slowly and evenly.

[ellz]

I wanted to use my cabinet as a drying location but with that bug infestation I had, I am not taking any chances. Also, I anticipate having to cut this crop in stages as there are parts that may need to go a bit longer than others. I replied to DW2 below regarding the fan idea...what do you think about it? Just using one fan bringing air in, and one fan blowing it out? 51CFM in and 51CFM out? Or should I just make them intakes and have a passive exhaust?

[DW2]

Howdy ellz, That looks like a good idea. The four inch fan will move the air too quickly thru Your cabinet, the air will change out approx. 8 times a minuet (7.916667, 190 / 24). To get the moisture to exchange from the bud to the ambient air, the flow needs to be slow to allow the moisture to get into the air. As well, a high velocity can cause some of the terpines to evaporate, a gentle flow will remove the moisture and not degrade the bud's quality. To get an even air flow the intake holes and the exhaust holes should be located as symmetrically as possible, or diffusers (boards with holes or screen wire) above the intake holes (or below the exhaust holes) to 'spread' out the flow evenly thru the buds. The flow of air (as well as water and electricity) follow the path of least resistance.
Good luck with Your cabinet.

[ellz]

One other thought is I can skip using the inline fan and instead use the AC powered computer fan that only moves 51CFM. Instead of installing both as intakes, I could install one as an intake and one as an exhaust. Only thing is the carbon filter...it's rated for 200CFM so would a 51CFM fan be okay with that or would it be too weak to push the air through the charcoal?! I also have a high-speed version of that computer fan that moves double the air so 102CFM.

[DW2]

Whether the computer fans will work with the carbon filter will depend on the pressure that they can create and the resistance (or flow loss) that the filter creates. I doubt that the computer fans have a pressure rating on them and the filter is most likely a maximum air flow thru the filter. The best thing I could suggest is to set up a test, connect one (or both of the fans to the filter (in a 'pull' or exhaust set up) and using something to produce a little smoke (a stick of incense or smoldering cotton cord) turn on the fans and hold the smoke source at the intake end of the filter, if the smoke goes into the open end of the filter, then the fans will work with it. The flow will, most likely be reduced, so the larger fan may be needed. Also I would recommend to use the fans either as pulling (exhaust) on the cabinet or pushing air into the cabinet (with the exhaust setup the preferred method) as that doing both will make it more difficult to make the air flow even throughout the cabinet.

[ellz]

So from what you all have said, it sounds like I may want to drop the exhaust fan altogether and only go with intake fans and a passive exhaust. Basically I would bring more air IN to the cabinet than I would be pushing out, which should help slow the drying. Is that correct or am I backwards?

[JohnC]

What's important is the total volume of air (CFM) moving through your drying cabinet. Whether the air is being pushed through with an intake fan or pulled through using an exhaust fan is irrelevant, IMO.

In simple terms, I like to imagine my air moving through the cabinet at about the same speed snow falls to the ground. Nice and gentle.

[Green75]

Just use brown paper bags.. Works great... And they are cheap

[ellz]

I am thinking I am going to use one 120mm fan for my exhaust and one 120mm fan for my intake. The CFM rating is 51 max but as you add duct or really any area, you add space so if I place the exhaust fan down run of the duct, it should reduce it's effectiveness and cause the intake fan to draw in more than the exhaust can exit. Just my thinking on it. I am NOT going to use the fan I ordered that is 190CFM. Instead, I am going to send that back and keep my ducting and my filter. The good news is I will get some money back on my CC from returning that! The bad news is there is no bad news! LOL.

I have an adapter that will convert the 120mm fan to around a 4" opening. I should be able to put that on and then mount my duct to the bracket and that will allow me to use the bigger fan. Also, by reducing the size, it should block some of the effectiveness of the fan even more so I imagine it will bring the flow down to about what my dry space is. I am rambling now but basically I plan on running a max of 51CFM in and a max of 51CFM out of a 24cu.ft. area.

[oldjarhead100]

Ellz if you are going to put more air in than out you will need to seal your cabinet so no smelly air can escape though corners,door,wood just a thought

[ellz]

OJH100 Do you think the lack of a seal will affect the drying time or is it more of a smell issue only? The reason I ask is that the cabinet is really old and I am not sure I can get a decent seal on the door because of it. However, I am not too concerned about the smell just because it's legal here and there are a ton of grows around here. In fact, every time I drive down the road to go anywhere, I smell that distinct smell all over the place. Originally, I was going to just hang the buds across my garage door brackets and tell the kids to stay out of the garage for a week but I decided to use the cabinet to make it a bit less obvious and in an effort to better control the humidity and temp.

[oldjarhead100]

no the sealing was just a thought to keep smell down, the fan you are running will move 51 cfm if it has a straight run with no restrictions . from your drawing you will have two spots the top 90% turn and the filter . I would go ahead and try it but if it doesn't work so good then you will know what the problem is

[Obi-Wan]

In a low humidity environment I think you would be better off using going the passive intake route, that along with the 120mm fan for exhaust should provide a gentle exchange of air in the cabinet.

[ellz]

Okay everyone....so after testing my low-speed and high-speed fans, I can say that neither is strong enough to push air through the carbon filter. I may scrap the filter altogether and just put a fan in the bottom to exhaust the air. By placing it down low, I assume this will draw warmer, moist air from up top back down over the plants and out of the cabinet. The opposite would be pulling cooler, dryer air from down low, over the plants and then out. That seems as if it would dry them out too fast but the other way might work just fine. I may do like Obi-Wan said and only put a passive intake (basically just a hole with a dust filter) and then have the exhaust pushed by the slower fan. At this point, I may only use the cabinet for the larger buds and hang my mesh drying rack for the smaller popcorn.

Or, I may dry the larger buds in the garage and work on my drying cabinet later since I waited too long to start it. If my garage stays about 40-45% humidity and the temps are between 60-70ºF, that should be decent for drying right?

[Kobayashi]

Could you use a carbon filter from a cooker/stove hood built into a shelf above your hanging buds? You could then put a low speed extractor fan above it to draw the air through it and then out of the cabinet. If you put it on a fan speed controller you could fine tune it to your needs.

[ellz]

That's a good suggestion. Thanks for your input.

[ellz]

Something I drew up...taking into account the overall cabinet size, this may be do-able.

[oldjarhead100]

Ellz that would work much better, if you have the height you could put it vertically with out ducting,just filter and fan, like a chimney,but I think your idea will work great