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Annualized Geo Humidity? :P passive/low energy dehumidification

 
Brian Shaw
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Wasnt sure what other group to put it in at the moment, feel free to suggest an alternative.


I expect to find alot of interesting topics and discussions here but at the moment when planning out a future off grid low energy home, I keep coming up against one problem I can't figure out how to solve - how to dehumidify the place.

Passive Heating and Cooling, great, but if your indoor humidity is 60-90% your books and furniture are ruined, youre sucking in mold. Humidity becomes more of a problem if the temperature is dropped without any according removal of moisture - like it is in AGS/PAHS. I currently live in minnesota and we can get rainforest-humid in the summer, the dew points can often be over comfortable indoor temperatures meaning it will be 100% humidity plus condensation indoors on every surface using AGS...

Some people don't mind it, for me it's health reasons and concerns about mold and I can't move somewhere dry. This is a future achilles heel where i've figured out good solutions for every future problem except that.


So what suggestions do you have?

I'm trying to figure out a way to do this off grid and low energy, instead of running a genset 24/7 and some huge air conditioners...

I saw something on "Subterrainean Heating and Cooling" involving phase change to heat and cool a greenhouse, which I still dont properly understand, but perhaps that could be adapted to primarily remove moisture instead?

Another option might be rotating wheels of dessicant, i'm told something similar is used for large buildings needing efficient dehumidification which can use waste heat to recharge the dessicant. I'd hope to use solar heat to recharge however, which should leave only the wattage needed for a slow turning wheel and some blowers. However excessively high costs don't really solve it either, if this is something i'm spending five figures for it wont be feasible either. >_< I know dessicant can dry things alot further than phase change even, it's possible some combination would actually work better than just one method, although I don't understand all the math.

I know they use forced ventilation to dry out damp basements but that assumes outdoor humidity is lower - in minnesota forests in summer that sometimes never gets below 90% outdoors. They also ridiculously overcharge for such glorified fans that i've seen.
 
John Elliott
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Welcome to Permies, Brian!

To dehumidify, you need to input energy, so you can't really have a "passive" system in the way you can have passive solar. That said, there is a way to draw water out of room air if hook it up to a cooling loop that is regenerated by solar energy. If you were to construct an Einstein refrigerator and pass room air over it, that is as passive a dehumidification method as I can think of because it has no moving parts. Einstein refrigerators have been manufactured using butane as the working fluid, which means that the cold side is less than 0C and you have the possibility of making ice. If you only want to cool air and/or pull the humidity out of it, you could use a different working fluid where the cold side is 10C and that would fine tune it for this application.

I've thought about this and have a working model half assembled, but it really isn't a hot area of research. There is some interest in using Einstein refrigerators in hot places, like Africa, but as refrigerators, not as air conditioning units. I've tried to keep current on any space cooling applications, but I've learned not to hold my breath for any new projects.
 
Dave Turpin
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Location: Groton, CT
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Hot and humid is possible to dehumidify passively. Use cooling tubes. This has been done on newer Earthship projects. Basically you vent the house through a gravity skylight and draw air through tubes buried fairly deep underground where it is cool. The cooling effect causes condensation in the tubes which drain back outside (the tubes are angled slightly away from the house). This cools and dehumidifies the air.

The difficult problem is dealing with cool, moist air like in the Northwest or Alaska. Sounds like this isn't your case, though.
 
Brian Knight
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Location: Asheville NC
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Personally, I dont think Annualized geo, or PAHS has proven itself beyond theory yet. I also disagree that Earth tubes are a good thing for any climates other than very dry. The problem is that the condensation on the interior walls of the tubes will collect dust, pollen etc and grow mold and mildew. Not exactly the kind of air you want to be breathing.

There are interesting technologies being tinkered with but nothing has proven itself as effective as heat pumps and dehumidifiers. I like to challenge off-gridders on their decision to ignore the benefits of the grid and turning their back on the grid when it comes to the excess energy that is wasted by off-gridders during peak demand hours. I strongly recommend for those looking to go off-grid to do net-zero energy instead. The system will be more affordable, much less maintenance and will benefit your community and environment more.

If the cost of adding grid infrastructure is more than the battery storage system, then its tough to argue against the financials. Then I question the decision to contribute to sprawl and wilderness fragmentation but I know people here dont like to hear any of that business. For strictly financial decisions, be sure to try to include the ongoing battery storage maintenance and replacement which can be considerable over time.

I would have you look into heat pump water heaters which are ridiculously efficient if done right and offer dehumidification benefits. In cold climates like yours however, it probably wouldnt make much sense unless you have lots of passive solar input or heat with wood. Mini-split heat pumps is probably your best option. Extremely efficient heating, cooling and dehumidification even in cold climates. However, without alot of R value to bring down the heating load requirements, you better be prepared to gather, split, and burn a ridiculous amount of wood to keep your un-insulated structure comfortable.
 
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