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how do I dehumidify off-grid?

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posted 7 months ago

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wasn't sure where to ask this so please let me know if I chose wrong....

I intended to have a semi-climate controlled closet (4x8x6h, ~200ft3) in my barn. I'm on the AL/FL line so it never gets that cold for long and humididty is through the roof, Purpose is multi-fold:

Winter - Not so concerned about humidity but need to keep above freezing

long-term storage of paints and other liquids that should not freeze in the winter

short-term storage of eggs in winter

long term storage of lipo batteries when not in use

keep lipo batteries for solar setup 'warm'

give the barn cat a place to sleep or rare very cold days

Summer Not so concerned about temperature but need to lower humidity

long and short-term storage of humidity sensitive equipment and supplies

Rarely occasionally need to remove everything else and jack temp up above ambient (concerned about humidity but can control that manually)

cure sweet potatoes and other crops w similar needs

allow mushrooms to inoculate substrate

I'm using a tricked out diesel air heater to manage temps in winter and to elevate it when needed but do not have a good solution for lowering humidity in summer as the only power is a small solar setup. Unless I can find a 12v dehumidifier for RV/Boats with low consumption (preliminary searches imply these do not exist), an appliance-like dehumidifier (almost as much power draw as AC) is not an option - any suggestions from someone more clever than me?

Matt McSpadden

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posted 7 months ago

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I don't have a lot of experience off-grid, and I suspect that 200 years ago, people would find a place that was lower humidity rather than trying to make a place that is lower humidity. If that makes sense?

I would suggest sealing the room fairly well to help control the humidity better. Make sure there are no sources of moisture in the room. Perhaps a fan would help? Or perhaps something to absorb moisture like charcoal or rock salt?

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C. Letellier

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posted 7 months ago

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This is the one I have been looking at. A few low power fans and low power pump. Primary is solar thermal energy and the rest looks like it can work. Intend to use soil cooling for the last stage.

Country oriented nerd with primary interests in alternate energy in particular solar. Dabble in gardening, trees, cob, soil building and a host of others.

R Scott

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How airtight vapor tight is it? How often do you open the door?

I have a well sealed storage shed about three times that size, I use a gallon bucket of damp rid (available at Walmart rv section or bigger farm stores) and go through about 4 buckets per year. But I do not open it often when it’s damp.

There are small dehumidifiers that run from usb-c that can be rigged direct to solar, but you can buy a LOT of damp rid for that.

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Anne Miller

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posted 7 months ago

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A product called: Damp Rid

https://permies.com/t/162929/Humid-Pantry-problems#1291304

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Douglas Alpenstock

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posted 7 months ago

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I know RV guys who say Damp Rid works well.

Aside: I know that silica moisture absorbing crystals can be heated to release the moisture and used again. What about Damp Rid?

R Scott

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Douglas Alpenstock wrote:Aside: I know that silica moisture absorbing crystals can be heated to release the moisture and used again. What about Damp Rid?

I don’t think so. It’s mainly calcium chloride, so it can be recycled through compost.

Jackson Bradley

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posted 7 months ago

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I just cycled my 30 pint Hisense dehumidifier and watched the power monitor. At peak, it was using 3.8 amps. The tag says it could use up to 5.5 but that was not the case at the settings I had. It is set at 50% and used in 156 sqft RV interior. I would estimate cycle time per hour at 20 mins on days at 80%-90% and down from there. It was readily available at Lowes and would handle your SQFT just fine

Rv's are not normally sealed or insulated well, including ours. I bet you could get a low cycle time if you seal and insulate well.

Our biggest problem, this time of the year, is the heat the dehumidifier generates through its cycling processes. During winter time, it is a bonus. You mention that heat generated is not and issue so no concern there.

To recap, if you do a poor job on sealing and insulating, have a family of 7 who open and close the doors all the time and have 90% humidity days, you'd be looking at using 30.4 amps per day plus whatever loss you incur through the inverter from DC to AC if your cycle time is 20 mins per hour.

A small system with a 100AH would handle that just fine if charged daily with SLA batteries. Lithium would need charged every 2 or 3 days.

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joe baird

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posted 7 months ago

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thanks all for the feedback and suggestions,,, currently just an osb closet with a loose fitting door, but easy enough to insulate and seall the door.Calcium carbonate (CaCO₃) seems to be < $2 lb in small quantities and is a food additive so I'd assume it is safe... seems my best options are this, or a super efficient window unit (like the little midea) that would run 1-2 hrs per day, only when the sun was shining.

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