Actually my idea is based on that... and on a writeup I saw from NY state (I think), where the guy runs his fridge from a cooling coil that freezes a brick of ice in his cool cabinet. I have also seen someone who has done sidewalk clearing using "7" or upside down "L" shaped tubes full of RV antifreeze. The fluid at the top gets cooled by the icy walkway and falls to the bottom of the down tube, while the relatively warm water at the bottom rises and warms the earth. If I put a tank of white plastic pipe (PVC?) at the bottom of the upright, I should be able to store cool in the mass of the ground and concrete. I think I shouldn't need to put an isolating layer like a PAHS because water sinking through should bring the cool down too.... but I only have a little room to work with anyway (5 by 8 feet or so), so it wouldn't hurt to isolate the bottom part and insulate the concrete wall on the outside above the tank while I am at it. Right now that room is only a few degrees less than the "crawl space" beside it.... The inside walls and roof have 4inch foam insulation, but the outside wall are just concrete and while one of them is NE, the other is SE and gets full sun till about 1pm. It is right next to a driveway, so I can't put bushes there to shade it either. I may have to give up the mass on that wall and insulate inside.
PAHS: Passive annual Heat Storage.
This is a continuation of the thread under LED lights.
The quote is from Len using this concept to cool a root cellar and melt the snow on his sidewalk - BRILLIANT concept. Len, I wonder if one can use wax instead of RV anitfreeze. Probably too cold for wax. I don't care for the toxicity (even food grade glycol).
How about borrowing from the solar HW drainback system and just use water that's heated by the sun and then gravity drain it into a reservoir tank to avoid any freezing?
Also, one of solar thermosiphon principles is there's gotta be an 18" height difference to get thermosiphon action to work. I wonder if some solar HW system would work better for keeping winter sidewalks warm... and then use the PAHS principles to preheat the SHW incoming water?
What's the freezing temp of masonry on a clear nite? For SHW collectors it's about 41F.
Len, you have any web links or illustrations on this? I'm a bit confused... wouldn't freezing temps (frozen transfer fluid) stop any kind of thermal transfer - as in delivering something warmer for the top part to heat the sidewalks?
Also - have you ever seen any look-up tables on freezing temperatures for various surfaces in different configurations?
I get the idea that freezing water at +10C is possible at 5000feet above sea level on a flat plain if the water is no more than a few inches deep....
Great explanation on the cartoon dumb bells. You need to have some sort of expansion tank/vent valve to allow for expanding and contracting fluid and air. Setting up a constant, no-maintenance capillary action will require some fine tuning. When are you going to do this?
There's PAHS and there's PAHS... the discerning difference is using soil as a contained + reflected thermal mass and insulating envelope at the same time. There's gotta be a barrier (plastic/fiberlass layer) around and under the house.
What amazes me is that Dr. Hait published this in 1983 (reprinted in 2005). I was turned onto it by a Danish engineer while at Sieben Linden.... long way around. So why haven't these become more common-place? simple: Water leakage.
There's two parts to a PAHS house... the contained thermal storage of the soil, and the long tube air circulation... both of which are totally static.. in that there is no auxiliary energy required... just intelligent design
I gotta disagree Len with a PAHS house not being partially underground... that's the whole idea. To use the thermal properties of the soil's mass and reflect it back into the house... Ok, maybe if you dig under the house initially and put a thermal barrier there - is that what you're implying?
thankyou for starting the new thread
The heat transfer fluid has to be liquid down to below -10C(14F?). In my area I may be able to get away with salt water as I don't think it gets down to -18C air temp and the ground even 4 inches down will be warmer. I don't know if the salt would settle out at all or stratify with fresh(er) water on top. I could make it saltier than seawater of course.
But I don't want to avoid freezing temperatures, I want to use them... The coldest temperatures will do me the most good. Avoiding freezing temperatures in this set up would be like avoiding heat in a solar heater
The first purpose of this set up, is to keep my root cellar cooler, the heating of side walks would be just a bonus... permaculture principle.... try to make any change do more than just one thing (the Len paraphrase). Anyway, the height difference should be around 36 inches, so thermo-siphon should work... and be the least complex. The tube(s) from the lower tank to the top would be straight. I may put a valve in to stop heat penetration in the summer.... but a steel valve would conduct heat just as well as the fluid... hopefully cooling the earth around the lower tank will make up for that.... and the coolest fluid should fall too. I need to find the smallest pipe that will still work to join the two tanks.
Depends on altitude, sky view, cloudiness... maybe latitude too. Even surface colour affects this.
Hi Len: I hope you're still active in this forum. I'm working on a project in the tropics right now (indonesia) where we need to design and build a 'cool room' to store cheese and milk only for just a few days. I'd like to do total passive cooling in a super insulated room (about 4'x8') with earth tubes and then use available river water going through some car radiators to further cool (if needed) the space. I was thinking of your root cellar and sidewalk snow melter in reverse... bringing cold up from below.
Any thoughts? suggestions?
Some questions :
a) What temperature do you envision this cool room being?
b) What is the yearly average temperature at ground level? This is what ground temp will be 20 feet down.
c) what is the temperature of the water from the river?
If a is lower than both b and c.... you need to be looking for other alternatives.
If b is lower than a, then just building the cool room low enough in the earth may be good enough... no insulation under and lots on top.
If c is lower than a but b is higher than a, then the room needs to be insulated all around but may still need more on top.
In any case, shade will help in the form of either a roof or trees. An air space under the roof (the roof being white or at least light colour) so the air can move and not collect heat is recommended (by me )
If your elevation is high enough and your nights get as low as 10C you may be able to use night time radiation to cool a heat transfer fluid. Sort of like a solar water heater but opened only at night with exposure to as much sky as possible. Mirrors can be used to expand sky view if there are trees or building to the side. It is possible to freeze water so use some kind of antifreeze (even salt). I do not know if thermo syphoning will work fast enough or if pumping would help. I would prefer no pump so that if I got up late to close the lid I would not be pumping hot water to my under ground water tank
If this is a pretty dry place, then evaporative cooling may work if all else fails. I am not sure how easy it would be to do with out power but the zeer pot seems to work in some pretty hot places. There are "outback fridges" based on the same principle to look at too. My sense is that scale may improve this technology. That is, bigger is better. A room cooled by this technique may take some time to get cool, but once cool the centre of the room would not need to be cooled just the outside. Adding mass in rocks or water tanks would help too... although they would also make it take even longer to get cool in the first place. The one thing I see is that it will be used to lower the temperature of relatively high mass things like milk and cheese which will start at around 27C (coming out of a cow). The mass in the cool room needs to be higher (10x would be nice). However one works with what they have.
I do wonder why you say that the 20' down temp will be same as the average surface ground temp? I would say that 20' down temp is fairly consistent at 50-60F anywhere in the world? I believe there's some science to back that up.
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