Very Basic Offgrid Geothermal Cooling

mjp24coho
mjp24coho Solar Expert Posts: 104 ✭✭✭
in Off Grid Solar & Battery Systems #1
Anyone have experience with offgrid geothermal cooling (the very basic kind)? I saw a show with the following example, and it got me thinking about using it at my offgrid cabin (from their website):

"One plan is to simply lay 4 inch PVC pipe in the ground. One end of the pipe opens up at ground level and has a screen to keep bugs and rodents out. The pipe angles down into the earth to a depth of about 5 or 6 feet. In the middle there should be gravel underneath and drain holes in the pipe to allow condensation to drain out. Angle the pipe back up to the surface right next to your home and bring it inside.

"Use a fan inside the home to pull air through the pipe. Fresh air will come into one end of the pipe and travel along the length of the pipe. The air will be cooled down as it travels. 50 degree F air will enter your home, cooling it."

I have a cabin with a sloped hillside that would be perfect for this set up. I'm always trying to find the best way to efficiently cool the place during a few summer months when I'm there on the weekend (only visit once a month for 3 days). Presumably the only energy draw would be some high efficiency 4" fans (one for each pipe). Not sure how many would be needed to move enough air (1000 sq ft log cabin with a loft). Not sure what kind of fan options there are or their energy draw.

Anyone have any experience or thoughts?
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Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Very Basic Offgrid Geothermal Cooling
    mjp24coho wrote: »
    Anyone have any experience or thoughts?

    Other than YouTube, I have not seen anyone other than the inventor/promotor who reports good results from them. The 4 inch pipe is far too small. There can be problems with moisture and bacterial growth, and the cooling produced is just too small to be worth it. Especially if you use a very long tube or multiple tubes with individual fans.
    SMA SB 3000, old BP panels.
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  • peakbagger
    peakbagger Solar Expert Posts: 341 ✭✭✭
    #3
    Re: Very Basic Offgrid Geothermal Cooling

    If you live in an area with radon, this system is perfect way to bring radon into the house. There were many variations of this design generally including rock storage tried in the late seventies and most were no successful. Proper passive cooling design is generally more effective. If the house is in an area with low relative humidity (dry climates) evaporative cooling (AKA swamp coolers can work) and are not very complicated. Unfortunately if the cabin is in most of the east coast it doesn't work due to high RH.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #4
    Re: Very Basic Offgrid Geothermal Cooling

    As long as all the pipe joints are properly glued, radon shouldn't be a problem, it couldn't get into the pipe. That said, as others have suggested, the actual cooling would be quite limited, and definitely mold etc would soon grow on the inside of the damp / wet inside walls of the pipe, releasing their spores into the air as it passes by on its way into the house.
    A great idea until the unforeseen problems crop up.
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  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    #5
    Re: Very Basic Offgrid Geothermal Cooling
    Anyone have any experience or thoughts?

    I have seen something similar in operation at two of the Earthships near Taos NM (these were at the "Greater World" community, not in the ones in the mountains). In the two I saw, they ran the pipe underneath a large earthen berm that they constructed at the north end of the home.

    It seemed to work well; I visited these one summer and it was certainly cool in the houses. A friend who lives in an Earthship nearby (although not one with this cooling system) also said it was working out for them.

    These systems had no fan. Instead, both of these houses had large greenhouses in front. At the top of the greenhouses they could open a vent window to draw hot air out and produce a slight vacuum inside the house (Earthships are pretty tightly sealed) which then drew the outside air through the cooling pipes.

    Another consideration is that NM is dry in the summer. I'm not sure if it would work so well with moist, humid air.

    Down this page is the layout of one of the Earthships I was in with this system.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Very Basic Offgrid Geothermal Cooling

    Gee, you guys just aren't old enough! Nothing new about this sort of thing. Back in the days before refrigeration is was quite common to build a "cold pantry" along the same lines. Usually it was clay pipe, which created a chimney effect to move air through the underground (and cellar) and up through the pantry and out. The pipe was not an open duct into the house; the cool pipe surface is what cooled the room.

    Keep in mind the room was small; only large enough to be a larder, not a whole house. And "cool" is a relative term. Efficient? Not by today's standards. So technically it works, but how practical is it for cooling a whole house? PVC, by the way, would not be a good choice for this as it has poor heat-transfer qualities.
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  • mjp24coho
    mjp24coho Solar Expert Posts: 104 ✭✭✭
    #7
    Re: Very Basic Offgrid Geothermal Cooling

    Thanks all for the input. I didn't think about the mold potential - that would be a deal breaker for me. Back to the drawing board I guess...
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  • R Whitt
    R Whitt Registered Users Posts: 5 ✭
    #8
    Re: Very Basic Offgrid Geothermal Cooling

    This certainly is not a new concept, 50 years or so ago on a trip with my elementary school class we visited one of Thomas Jefferson's [no relation to George] home . I remember the guide pointing out the "air conditioning system" which consisted of a large tunnell 8 to 10 feet in diameter which ran through a hill and into the house. I don't remember if this was at Monticello or Popular Forrest.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #9
    Re: Very Basic Offgrid Geothermal Cooling
    R Whitt wrote: »
    This certainly is not a new concept, 50 years or so ago on a trip with my elementary school class we visited one of Thomas Jefferson's [no relation to George] home . I remember the guide pointing out the "air conditioning system" which consisted of a large tunnell 8 to 10 feet in diameter which ran through a hill and into the house. I don't remember if this was at Monticello or Popular Forrest.
    He also had a tunnel running under the house, underneath the indoor privy, so that the slaves could empty the waste container without disturbing the household. That was at Monticello.
    SMA SB 3000, old BP panels.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #10
    Re: Very Basic Offgrid Geothermal Cooling

    I think your best bet for your ~15 days a year at the cabin, would be a portable A/C and an inverter-genset to save on fuel. Depending on your elevation you may be able to get by just running it during the day.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Sparkie
    Sparkie Registered Users Posts: 3 ✭
    #11
    Re: Very Basic Offgrid Geothermal Cooling

    I can't personally vouch for this, but this article has a lot of info, highlighting the pitfalls and how to overcome them. It's written by an engineer and seems pretty good at face value
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