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Simple(ish) solar road deicier

Annualized geo solar road heating
  [vote for,

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.

goldbb, Feb 02 2015

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]


       Brine would be a much better thermal transfer medium, won't freeze in the winter, is cheap, and relatively non-toxic.   

       A non-return valve would be needed to stop thermo-syphoning when the collector is colder than the dissipator.
8th of 7, Feb 02 2015

       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.   

       I can see how the concept would work much better in well insulated houses as described in your link.
scad mientist, Feb 02 2015

       They are doing similar things in some countries. [link]   

       /which would simply refreeze as it moved beyond the heated road area. /   

       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.
popbottle, Feb 03 2015

       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.
bs0u0155, Feb 03 2015

       [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?
hippo, Feb 03 2015

       If you're going to go to the trouble of drilling, why not use actual lava ?
8th of 7, Feb 03 2015

       [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.   

       [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.
scad mientist, Feb 03 2015

       //It would be better to save your geothermal heat until you actually need it.//   

       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.
bs0u0155, Feb 03 2015

       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.   

       I'm not quite as confident about the savings from installing a pump, but I'd recommend running the calculations before doing the install...
scad mientist, Feb 03 2015

       ^So, a thermocouple then.
AusCan531, Feb 03 2015

       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.   

       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.   

       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.   

       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.   

       popbottle, why would the ground below the buried pipes be cold enough to freeze? Remember, heat spreads through dirt omnidirecionally, including downwards.   

       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.   

       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.   

       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.   

       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.
goldbb, Feb 06 2015

       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.

       <later edit>   

       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...

       //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.//   

       No. The atmosphere holds very little sway over the ground temperature at even those depths. And it keeps getting warmer as you go deeper.
bs0u0155, Feb 08 2015

       // No. The atmosphere holds very little sway over the ground temperature at even those depths. And it keeps getting warmer as you go deeper. //   

       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).   

       About 30 feet down, the temperature is pretty constant and is approximately equal to the year long average air temperature.   

       See ground temperature <link>.
scad mientist, Feb 09 2015


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