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With the aid of a Directional Borer, install plastic pipes
(arranged in a loop) approximately three yards (ten feet)
below the road which you want de-iced.
Above ground, nearby, install a solar thermal air heater,
and a solar photo-voltaic panel. The PV panel powers a
fan, which moves hot
air from the solar thermal collector
into the buried pipes. A thermostat ensures that the fan
only goes on when the thermal collector is warmer than
the pipes.
The depth of the pipes, and the slow conduction of heat
through the soil, ensures that the heat will reach the
surface roughly six months after it was produced.
The majority of heat will be produced in summer, and will
reach the surface of the road in winter.
Permeable paving is recommended, but not required, so
that meltwater goes into the road, rather than turn into
runoff water, which would simply refreeze as it moved
beyond the heated road area.
[Edited Feb 06 2015]
To avoid losing heat when the solar collector is cold, we use a
differential thermostat, which both shuts off the fan and closes a
valve.
Annualized geo solar
http://en.wikipedia...nnualized_geo_solar
Storing summer heat for winter, for heating buildings [goldbb, Feb 02 2015]
Permeable paving
http://en.wikipedia...ki/Permeable_paving
Concrete, asphalt and pavers, which let water pass through [goldbb, Feb 02 2015]
Pavement snow melting
http://geoheat.oit.edu/pdf/tp108.pdf
[2 fries shy of a happy meal, Feb 03 2015]
Ground Temperatures as a Function of Location, Season, and Depth
http://www.buildits...rthTemperatures.htm
[scad mientist, Feb 09 2015]
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Annotation:
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Brine would be a much better thermal transfer medium, won't freeze
in the winter, is cheap, and relatively non-toxic. |
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A non-return valve would be needed to stop thermo-syphoning when
the collector is colder than the dissipator. |
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I don't think this would work well in a road. Say
you're at a location where the soil normally freezes
to a depth of 6 inches. The fact that there is
enough heat leaving the ground to accomplish a
phase change in the water to that depth tells me
that there won't be enough thermal mass in 10
feet of soil with no phase change to keep that
above freezing. If this is done in a location that
only rarely freezes, it's wasting heat all winter to
account for he few times when it is needed, so I
think you'll do better to find some other use for
the heat from your solar collectors, and just pump
some hot water through pipes close to the surface
if you need to melt the ice off your road. |
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I can see how the concept would work much
better in well insulated houses as described in
your link. |
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They are doing similar things in some countries. [link] |
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/which would simply refreeze as it moved beyond the heated road area. / |
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If the water goes through the road and into the heated area, it will continue down by gravity to a colder area. If it turns to ice and expands you could have things move and break. You might also end up with a bowl of ice filled with water leaving the liquid water no place to go no matter how porous the pavement. |
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This is way over complex. Go 12 ft down and the
temperature is pretty much 10C all year. Install an
antifreeze-filled loop that goes between 12 ft and 6 inches,
let the thermal cycling do the rest for you. Still more
expensive than salt though. |
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[bs0u0155] - you mean a sort of underground lava lamp? - in that case why not make it transparent and stick a light and some blobs of
(very-low-temperature-melting) wax in it? |
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If you're going to go to the trouble of drilling, why not use actual
lava ? |
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[2 fries] The "similar" thing done in other
countries misses the whole simplification in this
idea. The working systems have pipes a couple
inches below the road, store the heat in a
separate geothermal storage system and pump
water (or use other methods) when the road
needs to be heated. This idea attempts to use
the lag from burying the pipes deeper under the
road to automate/simplify that process, but I
doubt it will work as well. |
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[bs0u0155] having a passive geothermal loop might
work in some very mild climates, but I think you'll
want to have a little control rather than being
completely passive. Otherwise, as the
temperature hovers around 1C, you'll be
continually cooling the earth around the loops so
when it does freeze there will be much less
warmth to use. It would be better to save your
geothermal heat until you actually need it. Of
course if you put the pipes deep enough and have
enough of them you could make it work, but I
think it would be more cost effective to add a
little intelligent control to reduce the volume of
earth from which you need to harvest geothermal
heat, and a small circulation pump would
significantly reduce the size/quantity of pipe
required to get the necessary heating. |
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//It would be better to save your geothermal heat until you
actually need it.// |
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Oh, there's plenty of it, and it's gonna radiate away anyway.
We can worry about conserving it when the
1,097,509,500,000,000,000,000 cubic meters of molten
rock and iron starts showing signs of solidifying. |
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Sure there's plenty of heat in the earth, but it
takes time for the heat to move through the
ground. Therefore any one pipe can only access a
finite amount of that heat. Burying pipe is not a
cheap activity. A valve is much cheaper. Hey, I
bet for the cost of all that drilling, digging, or
boring we could devise a passive valve that is
actuated by the surface temperature, so it turns
on when the temperature drops below freezing
and turns back off when it gets to 1 or 2 degrees. |
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I'm not quite as confident about the savings from
installing a pump, but I'd recommend running the
calculations before doing the install... |
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^So, a thermocouple then. |
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8th, The reason for using air instead of a liquid is that
liquids almost inevitably leak... either in or out. If the
liquid leaks out, the system stops working until the liquid
is replaced. If we use air, and groundwater leaks in, an
automatic pump at the lowest point can automatically
remove it. |
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And if one *did* want to use a liquid... salt brine causes
rusting to happen much faster than it otherwise would,
so you'd have to make *everything* rust proof, including
valves, the pump, and the solar collector. Glycol would
be a better option. |
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I agree about something to prevent circulation when the
solar collector is cooler than the buried pipes... It
shouldn't be hard to add a differential thermostat to both
control the fan *and* open/close a valve. |
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scad, by heating the soil below the road all year long, the
frost line will, as a result, be much, much, shallower than
normal, or even nonexistent. |
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popbottle, why would the ground below the buried pipes
be cold enough to freeze? Remember, heat spreads
through dirt omnidirecionally, including downwards. |
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bs0u0155, the soil temperature 12 feet down is not
*magically* 10C all year. It only happens that way
because 10C is the average yearly atmospheric
temperature in your particular climate. Heat is gained
by the soil in summer and lost by the soil in winter. The
average of these gains and losses happens to work out for
10C (for you), but if we start adding or removing heat
artificially, then the soil temperature will change. |
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If one were to create a loop between shallow pipes and
deep ones, and allow it to thermosiphon, then the heat
from the depths would be depleted at a faster-than-
normal rate. Most likely, the deep soil would eventually
be below 0C, and not have enough heat to melt surface
ice. |
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Another problem with shallow pipes is that any time the
road needs to be repaired, the pipes will be disturbed,
and possibly need to be replaced. |
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With *just* deep pipes, they can be thought of as being
independent of the road surface. If you need to do road
repairs, you don't need to worry about the pipes unless
you dig too deep. |
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There was a link, to an idea which has vanished, of a closed loop system using ammonia in pipes looping below the frost line.
The ammonia would become a gas at above freezing temperatures and then condense to a liquid close to the surface keeping pavement permanently snow free. |
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Ok, I found the links on the ideas 'Pumpless Geothermal Cooling' and 'Electric Driveway' but they have disappeared from the net.
Too efficient maybe? No money to be made in a system that doesn't break down... |
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//the soil temperature 12 feet down is not *magically* 10C
all year. It only happens that way because 10C is the
average yearly atmospheric temperature in your particular
climate. Heat is gained by the soil in summer and lost by the
soil in winter.// |
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No. The atmosphere holds very little sway over the ground
temperature at even those depths. And it keeps getting
warmer as you go deeper. |
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// No. The atmosphere holds very little sway over
the ground temperature at even those depths.
And
it keeps getting warmer as you go deeper. // |
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No, earth core temperature has little effect on
ground temperature until you get much deeper
than the average municipal construction project
(unless you're in a volcanically active area with hot
springs or something). |
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About 30 feet down, the temperature is pretty
constant and is approximately equal to the
year long average air temperature. |
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See ground temperature <link>. |
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