Has it ever been tried? Run a metal tube for a hundred feet underground, with low voltage DC fans pushing the air constantly. The intake below the frost line in the basement of a house, the output comes in about ten feet from the in.
I suppose it would be best if the tube ran uphill, so during muggy summer days the condensation created when the hot humid air cools runs downhill. Then the tube runs up after some sort of trap to let the water out, to the top of the house. The cool air runs down. Lather, rinse, repeat. Enough air moves circulates through the system and the structure stays at ground temp. 50-55F.
It seems so simple. has it been done? The geothermal stuff I’ve seen is all about pumps. It would seem to me that some 4 inch diameter cast iron pipe and a few solar powered in-line fans in the pipe might give me some relief on hot summer days. And warm to 50 in winter, reducing work that heaters would have to do.
heating is being done currently, the instal is expensive but pays for itself after a few years.
the idea sounds pretty good. something I have wondered about myself more than once
Yeah, but that’s water. A better conducter and all. But I’m thinking about a cabin. A small well insulated building that could be set to 50-55 degrees with a solar set of fans put into some pipes set below the frost line. All air. No water.
Has anything like that been done?
There is some question in my mind as to whether or not the pipe and the ground in contact with it would actually stay at 50-55F. The system has to put the heat from the house into the ground in order to work. So the question becomes where does that heat go? It has to be conducted away throught the ground surrounding the pipe. In order for the pipe to stay close to the initial temperature the heat must be conducted away as fast as it is put in.
The way I figure it 100’ of 5" cast iron pipe would weigh about 1100 lb. The specific heat of iron is 0.15 so it would take 1100*.15 = 165 Btu to raise the temperature 1[sup]o[/sup] F. A small room air conditioner has a capacity of about 5000 Btu/hr and that might be adequate for a well-insulated cabin. That would raise the temperature of the pipe 30 F in an hour if none of the heat were to be conducted away. I don’t have data on ground conductivity so I have no way of knowing how fast the heat would be removed from the pipe into the ground.
My uncle works in construction and was involved with an elementary school built last year that has water pipes snaking around deep underground to cool the water, after which the cooled water was used to cool/condition building air.
I think such systems drill into aquifers and use the water in what is essentially a deep well to cool the water in the pipes.
Based on data on soil thermal conductivity here, insulation thermal conductivity here and adjusting for differences in units, sand is about 10-15 as good a conductor as expanded polyethylene and about as good a thermal conductor as glass. Saturated sand conducts heat about 3.25 times faster than dry sand.
Air is a dismal source, as it doesn’t retain heat energy well. Air source heat pumps have given way to ground source heat pumps, of which there are two types. One circulates a water/glycol mixture through a series of buried piping and then uses a heat exchanger for energy delivery. Newer are the direct source systems which bury copper lines in a corrosion protective grout within the soil, through which refrigerant runs, thereby negating the need for and inefficiencies of a heat exchanger.
I resurrected the thread because I found data on soil thermal conductivity and did a little electrical analog and I’ll be damned if I’m going to just throw it away without showing it to the OP. I used the conductivity data for dry sand. Damp sand would speed the heat transfer up a little but not much.
The simulation is merely a feasibility study. In fact it doesn’t quite rise to that level, more of afeasibility indicator.
The top graph shows the temperature response of the iron pipe (red curve) which, to this scale is virtually a step input. The blue curve is the soil temperature 6" away from the outside of the pipe and the black curve is the soil temperature 1 ft. away. The input temperature was a step in temperature from 0 F to 90 F at time = 0.
The bottom curve shows the three temperature responses for the first three hours after the input. The pipe reaches final temperature in about 42 minutes. However after 3 hours the soil temperature 6 in. away is only 2.4 F and one foot away only about 0.6 F. These low temperature show that very little heat has been transferred to the soil so the air going through the pipe comes in at 90 F and leaves the pipe at virtually the same temperature because the pipe heats up and stays hot.
Soil is a poor conductor of heat and in fact your assumption that the ground temperature at the depth of your pipe was at 50-55 F irrespective of surface conditions was based on that property of soil.
I resurrected the thread because I’ll be damned if I’m going to just throw it away without recognizing your kick ass answer. Thanks.
It is much simpler than some of the posts have made it seem. All you need is a basement maybe 10 feet deep, depending on local conditions. Have lourved (im sure i spelled that wrong) vents in the floor and in the ceiling. hot air from the house will rise, pulling in cool air from the basement. with proper modifications to allow for the size and layout of the house and replenishing the air in the basement, you’d be surprised how much this can cool.
