Offgrid Underground Air Conditioning

[TheJoefussGarage]

I'm a HVAC veteran... I like the Pex tubing approach much better overall.. Less digging for each "Tonne" of cooling or heating capacity, use the glycol piped to a discarded A/C evaporator coil, it has its own condensate pan and drain. Use a filter, and no worries about dust, disease or water clogged underground piping... Save the condensate for watering plants, washing or purify it, for drinking, if yer really had core.... A lot more effort overall, though a lot of concerns licked at the same time.

[paulmaxwell]

My wife and I did something similar here in central British Columbia. We buried two 4" PVC pipes six feet deep, side by side and running out seventy feet from the house. Fans pull outside air in, sending some to our bedroom and some to the kitchen. In the winter, minus 30C air is warmed by the earth to plus 10C. In the summer, plus 30CV air is cooled to plus 15C. It works very, very well. If I had to do it again, I'd go a little deeper (maybe 8-10 ft) and make it longer. We do sometimes get a bit of water in the pipes but haven't had any issues. If the run was sloped away from the house and drainage provided right where the pipes turn up to the surface the system would be self-draining. Anyways, six years later, the set-up works quite well.

[davidharris]

Great plan and execution. Couple of cautions. Run a check on radon from the fan area. And remember in humid weather the pipe will literally fill up with condensate and pump humidity into the cabin. Those two factors ruled out a similar system for my house near raleigh, nc but i am able to pipe the cooler air through my ac to reduce costs there. Good luck and keep on innovating.

[chubbyninja]

I've considered that sort of system before. My concern would be condensation in the cooling pipes. It only takes a little water to create a big mold problem. I think it would be a good idea to run a dehumidifier in the house to limit the amount of moisture that gets into the lines. Dehumidified air also feels cooler on the skin because it's easier for evaporation to occur.

Also, if you're cooking or showering in that structure, make sure that humid air is properly vented as immediately and completely as possible so that humid air doesn't get into the lines.

Now that I think about it, I think a better system might be to cycle the same closed-loop of air through the ground with a furnace-style heat-exchanger that you pass the house's internal air over to cool it. This way, no humid air can ever get into your sub-surface lines, and if any condensation occurs on your heat-exchanger, you can just clean off any mold that might occur.

[walkstheman]

So, a consideration to note on the earthships here in New Mexico, the geothermal tubes are open to the outside for a few reasons, one is to prevent too much condensation build up, and the other is to allow a cross breeze to be your main air mover instead of a fan, so you use little to no power at all. Most earthships will have an attatched greenhouse, or at least a roof peak vent. All the hot air in the house will move to the upper most vent in the greenhouse/house and leave, pulling in fresh air through the geothermal tubes, pulling in that cooled (and typically drier) outside air, with no moving parts, although in some cases a fan may be used for extra movement if needed. These are also used for very light heating in the winter, as we have moderate winters, much like Texas. This will still work in this set up, but just as others have said, condensation is worth considering, but most AC systems have to deal with that anyways. These systems work the best in highly insulated buildings with very little temperature fluctuations

[jeffclark]

Gonna be some real nice mold spore distribution once the condensate in the underground pipes gets good and innocuous.

[Bmetamaximus]

Dude! Finally, an off-gridder who made a sensible and cheap solution at last based off geo-thermal cooling! I love it, great detail and explanation. One question though - have you thought about doing any filtering to prevent dust build-up? I get that it's a cabin and you don't expect HEPA air indoors, but don't discount the additional work a dirty fan motor has to do - your power consumption will take a hit.

[cc-tbst]

Just a thought, probably not important but you decide. Blowing warm, humid air into cool underground pipes might cause condensation in the pipes. Condensation may cause mold growth. The air circulating in the pipes and through the potential mold growth may disperse mold spores throughout the structure and into the lungs of anyone breathing the confined air.

I would consider a redesign personally. I would close loop the air in the pipes and install a radiator in the cabin to push the warm air through. Not as effective but maybe safer. Even better would be to replace the air in the pipes with something with better thermal efficiency like water with some antifreeze depending on climate and usage.

Good luck with your decisions.

[timerickson]

If you put the air intake closer to the ceiling you'll find it much more effective and efficient. As level is evacuating near the same temperature air as it's imputing. Heat rises cool air falls
In thinking about it the air output should be head high also that reduces the hot zone by increasing the cooler area. Im impressed because I am guestimating how much site development will cost ie;solar and battery storage. Ill need and a fan is cheaper and easier to run than a ac unit . Could run a fridge on the savings in energy.

[shawnd]

I would only run this in a closed system. You could use an HRV to do this. You'd run the underground loop across one side of the coil and then the interior air across the other. This would massively reduce mold, mildew, radon, etc issues. HRVs can transfer like 50-75% of the heat so it would work super well

[ronniejohnson]

I had an eccentric friend that buried 4” pvc 6 feet deep . He ran it about 75 yards from his home to his creek fed pond. He ran it to the middle of the pond and elbowed it to exit the water in the pond. He ran it to a box with a cheap box fan. The fan was pulling the cooler air into his house. His house was a dome home built in Mantachie, Ms, by Joel Nichols.

[GeckoHiker]

Brilliant design. We do something similar in an earth sheltered home and livestock housing in the Ozarks. It is completely passive, where warm air rises through vents to the outdoors and cooler air is drawn in from sunken pipes. We often have to shut the vents to keep it from getting too cool.

This is based on the vent design of my unairconditioned familly home in Florida. The intake vents were all along the bottom of an outside facing wall, sheltered by foliage. Lots and lots of foliage. The upper vents let warm air escape and drew the cooler air in. If there had been sunken pipes we could have gotten better than the average summer temperature of around 78 degrees indoors when normally it would be nearer to a hundred degrees. It made the northwest facing side of the house much more bearable without HVAC.

Downside in Florida was the wear and tear on the small screens and the humidity and moisure affecting the jalousy mechanism of the vents.

[jamesarthurreed]

That's a great system! I'm glad that you're already aware of the potential for mold growth. One way to mitigate that risk would be to pick up an ozone generator and once a year, sanitize the air in the cabin and pipes. I would remove anything biological from the cabin that you don't want dead (people, pets, plants, etc.), close up the cabin and with the AC blowers running, fill the cabin with ozone. I'd let the ozone generator run for 24 hours, then let the ozone dissipate for three days after, opening the doors on the third. This is how I've removed mold from basements particularly and older structures (especially before upgrading it with a vapor barrier and vinyl siding), and in a system that is likely to produce mold, the ~$750-$1, 000 for the investment in the ozone generator could well save the occupants from a major health hazard in the future. Anyway, I'm enjoying your channel and you've got a new sub!

[cdp]

Just some helpful advice. Insulate your pipes all the way to the ground and also, , run a dehumidifier. These geothermal mass air flow units will start to sweat and cause some bacterias to grow.
Happy off grid

[Last-Varangian]

The Romans had a similar setup only without the electrical part. They built a chimney on the opposite side of the house that was painted black and let thermal conduction move the air for them. Their intake was also open on the far end, so it wasn't a closed loop system as yours is.

[caseystyer]

A squirrel cage fan will be much more efficient BTW. If you keep some cover crop over the piping, you will increase the cooling effect.

[peteaulit]

Glad to read in one the comments that you’re running a dehu. I live in sunny FL and that is the main thing most people don’t understand.
I hope your cheap solution will work for a long time.
This being said, geothermal is ok but can stop working after a while because of ground heat absorption saturation depending on the type of soil so good luck to you.

[garylester]

I was going to do this back in 1982 when I built my dome house, but decided against it because of the worries of radon, humidity, mold, and trapped moisture in the pipes.
I still think it's a great idea if these problems can be addressed.

[InspiredCraftsman]

Cool setup! I'm looking into the efficiency of a recirculating water system going to a radiator with a fan blowing over it. My soil temps are a bit higher here.

[aarondoyle]

Basically what you’ve built here is a very rudimentary heat pump. These are a great idea in certain climates. You can keep your place above freezing with it if it ever gets cold in your area as well. Unfortunately here in Alaska where I live they are problematic because in many areas we have permafrost and the areas we don’t the frost line is so deep in the winter a heat exchange/pump system like this would be a major undertaking using more energy to build than you’d save over several decades. Of course we’d be using it primarily for heat as the days requiring an air conditioner are minimal.