"Humidor" with peltier cooling and humidistat

[ruwtz]

I have problems in my dry/cure since it shares the veg room. 75F is too warm, and even at 60-65% humidity things dry out too fast and its costing me dearly on flavor and quality.

I want to build a dedicated dry cabinet with full environmental control: aiming for 60F and 50-55%RH.

Building the cabinet is easy, but i'm putting some thought into the temp and humidity controls.

My first idea is using a peltier element for cooling. Check this on YouTube for folks building mini fridges with them.

Obviously I don't need this much cooling, but i'm thinking a peltier + heatsink + fan, connected to a mini controller or thermostat can bring the interior temp down 10-15F to my desired 60F.

Then I can run a mini dehu like this one inside to get humidity under 60% or better (this is probably just calcium chloride or similar desiccant).

I can run a passive vent on the other side if it helps air cycle, although that could mess with either of the above more than i would like.

A small and indirect desk fan inside would keep air moving.

A few quick ideas here, so why don't you smart folks tell me what you think? Has anyone done or seen anything similar to this before? Any pointers for me to consider before I get going.

Measuring up the space and modeling the cabinet on Sketchup today. I have a harvest in two weeks so I don't have long to finish this.

Thanks all -

 

[ruwtz]

I understand that neither oxygen nor CO2 play a role in the decarboxylation of chlorophyl, and so I don't think the lack of "fresh air" as we like to say would be an issue in the dry process. A more pertinent issue would be mold risk, but I think this can be managed by the dehu and good air circulation, much like a sealed room grow.

Anyone? Thoughts?

Framing up the cabinet on SU right now. A simple 3x3x3ft cube using 1x2 trim lumber, ply sheath and some polyfoam insulation. Will probably put it on casters too for moving.

 

[Shugglet]

This is a pipe dream, go back to the design board.

I dont think peltiers will be an effective solution.

 

[ruwtz]

This is a pipe dream, go back to the design board.

Care to elaborate?

 

[Shugglet]

Care to elaborate?

How big of an array of peltiers do you think youll need to cool down 27 cubic feet by 10 to 15degrees?

Because a single ~60w peltier chip will do literally nothing...

 

[ruwtz]

I haven't worked it out, but my first thought is not so many as to render it a useless idea.

Do you have any idea? Or a way to work it out?

 

[Shugglet]

I haven't worked it out, but my first thought is not so many as to render it a useless idea.

Do you have any idea? Or a way to work it out?

Well, I tried using one to cool down a volume of 4 cubic feet and it didnt do shit. Dont waste your time and money.

If I had to guess, youll probably need over 600watts of terribly inefficient peltiers to achieve your goals...

Youd be further ahead tapping into your existing cooling setup, or just buying the smallest window AC unit you can find and adapting it to work.

 

[Rrog]

Other peltier cooler videos show they work poorly.

 

[Jonstipated]

Maybe you could make it out of a fridge.

 

[ruwtz]

Well, I tried using one to cool down a volume of 4 cubic feet and it didnt do shit. Dont waste your time and money.

If I had to guess, youll probably need over 600watts of terribly inefficient peltiers to achieve your goals...

Youd be further ahead tapping into your existing cooling setup, or just buying the smallest window AC unit you can find and adapting it to work.

Hmm, interesting.

Did you seal and insulate the space? Were you aiming for the same purpose? I'd like to know more.

There's also folks building out small peltier arrays (4-6) on larger heatsinks or avail coils as AC units for cars and even a boat.

Is this really so far fetched??

 

[Shugglet]

Hmm, interesting.

Did you seal and insulate the space? Were you aiming for the same purpose? I'd like to know more.

There's also folks building out small peltier arrays (4-6) on larger heatsinks or avail coils as AC units for cars and even a boat.

Is this really so far fetched??

Well it wasnt very well insulated but it was completely sealed. It was a small grow space (4 cubic feet) that I had planned to cool. Even with nothing else on (lights pumps etc) it failed to reduce temperatures in the box.


Watch this video and tell me what conclusions you come to...

That box is what, roughly 2-3 cubic feet and has roughly 250 watts of peltiers. It seems to get that setup to your desired temp. But your setup has about 10 times the volume of air needed cooling...

 

[ruwtz]

Maybe you could make it out of a fridge.

Yeah I spent a minute thinking on this. A lot of work to modify a fridge, it would have to fit the space perfectly, and then find a way of interrupting the thermostat so its not just cold.

I think i'm better starting from scratch.

Well it wasnt very well insulated but it was completely sealed. It was a small grow space (4 cubic feet) that I had planned to cool. Even with nothing else on (lights pumps etc) it failed to reduce temperatures in the box.


Watch this video and tell me what conclusions you come to...

Actually it was that vid that got me started thinking on peltiers. I know his conclusions aren't great for his purposes.

Its cool to hear that you tried though. Not sure what grows in 4cuft but nothing surprises me these days.

 

[Jonstipated]

Yeah I spent a minute thinking on this. A lot of work to modify a fridge, it would have to fit the space perfectly, and then find a way of interrupting the thermostat so its not just cold.

I think i'm better starting from scratch.

True, maybe a wine cooler would be better.

 

[Shugglet]

Also remember that when the peltier shuts off, the cooling side will equalize temps with the hot side and effectively dump heat into your box.

 

[ruwtz]

Yuk, ok, peltier is dead to me.

Perhaps I will have to consider the fridge conversion after all, and place it outside the grow room. Perhaps it doesn't need much work after all: the fridge can be run on a thermostat controller, and a dehumidifier placed inside also on a controller, exhausting through one wall.

I know people have done similar things to DIY a meat curing charcuterie or a cheese cave.

Could be a simple conversion, what do you lot think?

 

[ruwtz]

True, maybe a wine cooler would be better.

Hmm, i didn't realize some wine coolers are in fact thermoelectric, as explained here.
http://www.newair.com/articles/how-thermoelectric-wine-coolers-work/

Again, they're small spaces, but it is at least doable.

Perhaps pelters aren't a total disaster after all.

Funny, I have a bar-style beverage cooler I need to fix but its compressor style and too small for what I need for the green.

 

[ruwtz]

Here's an example:

https://www.amazon.com/EdgeStar-Stainless-Trimmed-Digital-Controls/dp/B000Y18ZL6

This wine cooler is a little under 12cuft in size, has 4 peltier module/heatsink/fan combos and runs at 210w. Gets down to 50F, with ambient conditions being optimal.

It may not be as simple as to scale this up, but just for giggles lets say I can cover my mega insulated 27cuft space with 8 modules and hit 60-65F.

Thats 420w or 10kwh per day. For me thats about $2 a day, running for one week every month.

@Shugglet raises a good point about residual heat 'back flowing' into the space as the peltier cycles off via the thermostat but if I wire the 12v fan on the hot side to run continuously this ought to be drawn away.

Imma keeping thinking here...

 

[Jonstipated]

Hmm. Maybe make a liquid cooling system, you could buy blocks or bags of ice or freeze your own during the other 3 weeks.

I'd take a large styrofoam cooler and put a smaller one inside with a coil of copper tubing inside it. Connect that with insulated plastic or pvc or whatever tubing to another coil of copper in your cabinet with a fan behind it.

But I worry about condensation on the line in the cabinet. Maybe some sort of aluminum heat sinks or a radiator type thing.

 

[ruwtz]

So I picked up this fridge/freezer for nothing. I'm told the fan freezes up eventually but I reckon thats just a clogged drip line and I can fix it.



It needs a good clean and then i'm gonna have a go at modifying it to a dry cabinet.

Its a double depth unit, 21cuft and appears to have a single evap coil in between the fridge and freezer section. Looks like one of those models that runs the freezer and the fridge simply pulls cool air from this rather than its own separate cooling system.



I would like to knock through this divider between the two spaces but I probably can't move this evaporator which is a bummer. I doubt I can simply bend it upwards and out of the way. Anyone know better than me on that?

I would strip out the shelves, the water filter, the ice maker and the door molding to maximize space.
Running on its highest temp setting today for tests: seems to be holding around 56F and RH15%.

I have some outdoor green that I care nothing for which I can test in here to see how much humidity chopped plants will add.

It would be a simple conversion to add an external thermostat, and either a dehu or humidifier or both, and possibly an intake fan and exhaust if necessary. Not much work and pretty cheap over all for optimized drying environment.

The big bonus is I can have this outside the grow room in the yard and save on space.

Any immediate thoughts?

 

[ruwtz]

Basic checks have gone fine: compressor works, relays are fine, evap and condenser fans run, thermostat is good and the defrost heater and timer also work. This is a decent fridge/freezer.

I've ripped out the ice maker, removed the water lines, gutted the shelving etc.

That evap coil is still in the way. I'm thinking I can bend it up against the back wall as its only on a copper refrigerant line and box it off, then move the fan to point up into the coil. The fan will assist with air circulation.

The front wall of the divider needs to stay for the doors of course. And I think there's a heater bar in there too as it is warm to touch. Will need to work around this, but all being well I will end up with a single space of 21cuft.

I've bought an STC-1000 thermo controller which will bypass the fridge thermostat to manage cooling power. I'm also contemplating wiring the defrost heater into the "heat" relay so it can warm things up if necessary. I will have no need for defrosting as temps will be kept 60-65F and no more freezer function.

I'm logging temp/humidity around the clock, currently averaging 56F and RH12% in the fridge section.

I've also picked up a humidistat controller (similar to the STC-1000 above). It is possible I will need a dehu and humidifier to manage 55%, but I won't know until I load her up with fresh plant material and see what they put off. D

Dehu could be as simple as an exhaust out determined by the controller, but this will be the last thing to figure out.

Perhaps the only other thing to add would be another fan for circulation.

What do you lot think? C'mon brainiacs, where are you?!