# passive underground ventilation (w/ backup)



## zthaynes (Aug 20, 2017)

Hello all... I am just testing the waters and looking at theories only here. I am considering (within several years) building a small underground shelter that can be used for multiple purposes (storms, power outages in the winter, the apocalypse...) and I am curious if anyone has ever considered using a solar "trombe wall" style system to provide passive ventilation when the sun is out, saving energy, fuel, battery power, etc... (note: even if this would work, I know and accept that it would NOT work for fallout or airborne pathogens / chemicals)

The "THOUGHT" here is that air heated in the solar "thingy" will naturally flow up. Air from the bunker will already be warm due to occupancy underground, also flowing up. Air coming in from under the structure (on a hill maybe) will also be cooler, keeping the temperature of the bunker from being unbearable.

During summer months, when the sun is blocked by clouds the airflow would need a fan to push it most likely... but the OVERALL yearly energy requirements for this would be minimal.

Thoughts?


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## Sentry18 (Aug 5, 2012)

I will let a more knowledgeable forum member chime in on this, but Welcome to PS.


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## tmttactical (Nov 23, 2015)

Warm welcome from the Arizona valley folks. All things are possible most are not viable (cost vs. ROI). To be of any assistance, we would have to have many more details. The number of people x the air exchange rate is just one factor that must be considered. Example: one person in a 100 x 100 foot enclosure may only need one air change per day. 10 people in a 10 x 10 foot space will want 10 changes per hour. Too many unknowns to provide suggestions.


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## zthaynes (Aug 20, 2017)

Thx for the quick reply! 

I had thought about that caribou, but the thought of standing water building up in the "U" underneath (and all of the life ending microbes that come with it) is why I haven't given serious consideration to geothermal before. Given access to the hillside on my property, and making sure all of the piping has a downward slope seems like the way to go.

Also, do you think the piping should be distributed (as in the photo) or should all the intake be on one side and the output on the other?


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## zthaynes (Aug 20, 2017)

Yeah tmtactical... This is in the VERY early stages here... just thinking about possibilities. This just popped into my head a few weeks ago and after searching the web without seeing something like this, I just wondered if my duct-tape and coat-hanger mind was actually on to something.


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## zthaynes (Aug 20, 2017)

Well... The picture in my head shows a 12x30x8 structure (actually 10 feet, but with 4' knee wall and 6' arch... so round up to 8) with a dorm on one end and communal area / food / storage on the other. The thing won't be designed for lots of people for an extended period, but if the Zombie Apocalypse happens who knows. Could sleep up to 10 but supplies (and air) would probably run out quick.

My thought without doing any math was to have 6-4in intake pipes at a 2-3 degree angle feeding into one end of the structure at floor level. The same number of pipes feeding from the opposite ceiling into 3 or more "trombe wall" solar air heaters to aid in convection.

I'm fairly certain that IF I ACTUALLY put 10 people in the thing we would need double the air intake and probably a constant electric fan to move it... but my plan was to have a backup manual pump for cloudy days.

Again... Just in the "I wonder what's possible" phase of this thing. By the time I get to the "you need natural gas and diesel backup power supplies and dig a well and a $10,000 filtration system and a sewage/waste incinerator" stuff I will realize that it can't be done without selling a kidney For right now though...


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## zthaynes (Aug 20, 2017)

Here's kind of what my brain was thinking... With all the stuff it reduces the volume of air... so maybe triple the amount of air?


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## Tirediron (Jul 12, 2010)

as you mentioned simple chimney effect should create circulation, due to differences in temperature, if the intake tubes are sloped and smooth there shouldn't be any build up of much, but built in clean outs would be a good idea
anything that doesn't require outside energy inputs is always a good idea.


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## tmttactical (Nov 23, 2015)

zthaynes said:


> Well... The picture in my head shows a 12x30x8 structure (actually 10 feet, but with 4' knee wall and 6' arch... so round up to 8) with a dorm on one end and communal area / food / storage on the other. The thing won't be designed for lots of people for an extended period, but if the Zombie Apocalypse happens who knows. Could sleep up to 10 but supplies (and air) would probably run out quick.
> 
> My thought without doing any math was to have 6-4in intake pipes at a 2-3 degree angle feeding into one end of the structure at floor level. The same number of pipes feeding from the opposite ceiling into 3 or more "trombe wall" solar air heaters to aid in convection.
> 
> ...


People used to dig out the side of a hill and build their homes (sod houses) and it worked for them. The issue is cost verses sophistication. The more creature comforts and security required, the more organs (kidneys, first born, etc.) you are going to have to sell.


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## LastOutlaw (Jun 1, 2013)

I visited a guy once who was building dome houses out of rebar, chicken wire and cement on the side of a hill then covering them with earth and living in them. As he built more he would connect them with a tunnel and cover it along with the domes. He said his biggest problem was humidity from the human breath. He had to install Air Conditioners to remove moisture from the air.


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## Flight1630 (Jan 4, 2017)

LastOutlaw said:


> I visited a guy once who was building dome houses out of rebar, chicken wire and cement on the side of a hill then covering them with earth and living in them. As he built more he would connect them with a tunnel and cover it along with the domes. He said his biggest problem was humidity from the human breath. He had to install Air Conditioners to remove moisture from the air.


Wouldn't dehumidifier work just as well?


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## Tirediron (Jul 12, 2010)

dehumidifiers are basically air conditioners, that dump their heat into the air that they are cooling, only extracting the moisture, and leaving some residual heat


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## VoorTrekker (Oct 7, 2012)

Everywhere on earth (or the Northern Hemisphere) at five feet below the surface the temperature remains 55 degrees F. Some people are digging a trench 5 feet deep and whatever length and dropping in a type of flexible erosion hose about 4 or 6 inches diameter minimum. 

The part of the hose extending from the trench are wrapped in insulation and installed to the structure. (House, office building, barn, etc.) It has a feed and exhaust port and is not a closed system. Structure ventilation helps with eliminating moisture. 

As for extracting moisture from a shelter or "wine cellar," I agree with the dehumidifier of have the feed lower than the exhaust. Much cheaper system than the solar thing. 

In Africa, the termites dig numerous tunnels about five feet deep and the tunnels lead to a central shaft in the termite mound. The central shaft has ports at each level to feed cooled air and the central shaft also transmits the warmer air to the roof, where baffled or a manifold shaft jettisons the warmer air by convection and "demand flow."


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