Heated Infrastructure in the U.S. - Possible?

[BTB]

Heated Infrastructure in the U.S. -- Possible?

Hi all, I am new here, this is my first post. If this is the wrong forum to be posting this in, please point me in the right direction. I have been wondering about this for some time, and I figured that this forum would be a good place to get some valuble opinions. So I ask, could heated infrastructure be successfully implemented in the United States? Please read on:


Each year, the government (mostly state and local I believe) spends huge sums of taxpayer money in order to keep the roads clear of snow and ice during the winter in the northern states in the US. As you know, most road damage occurs as a result of the freezing-thawing process and the spreading of salt/calcium chloride that is commonly used to de-ice infrastructure has been shown to further the deterioration of the road itself. One would think that investing in some type of sustainable-heating technology that could be installed over time would alleviate the need to constantly maintain roads in adverse weather.

Some countries (Reykjavik, Iceland has some, Japan has a few as well) have heated roads or sidewalks but they are usually few and far between. If some type of technology was put in place as new roads are made/ old ones are repaired, wouldn't they eventually pay for themselves by significantly cutting down on maintenance costs while helping to facilitate economic interaction? Think of the benefits that could be had if road conditions were, apart from mere rainy weather, always generally consistent.

Various methods have been suggested in order to heat a road. Some have pointed to the use of standard electronic energy in order to heat a wire "web" within the pavement itself. Others have suggested using geothermal heating to cut around the potentially high energy costs associated with the first approach. A third technique that has been suggested, is to use the sun-attracting tendency of the road itself, which is essentially a large solar panel (think of stepping on a hot road while barefoot in the summer; roads attract a tremendous amount of energy) to somehow create and store solar energy in order to power heated water-circulation network, a system that is currently at use underneath some soccer fields.

So, in your opinion, what would be some of the specifications necessary to successfully and economically heat roads/highways in the Northern States? Do you think that it could actually be done over time? If no, please state why not, and if yes, what method (feel free to suggest others) do you believe would work best?

 

[minger]

I'm not a civil engineer, but one thing that jumps out to me is where you can put pipes or electrical element. From what I recall, the depth of which they actually build roads/highways is fairly impressive, so the depth of which (let's say) the liquid pipes would need to be put might be too deep to really be effective at transferring heat to the surface.

Also, think about maintenance. If at any point one of these pipes breaks, then you have liquid spilling into the streets at a time that it's cold enough for water to freeze. Repairing roads would be more costly as well.

I think this could work for sidewalks or other places where loads are minimal (such as your driveway), but for commercally driven highways and main streets, I think it's out of the question.

 

[Danger]

Where I live, the frost line is 4' down. My concern regarding a heating system for roads is that most of the energy will be expended into the ground rather than the road surface. I suppose that some sort of reflective container could be arranged, but it seems overly complicated.

 

[Mech_Engineer]

This could never be implemented at a national level just based on the huge amount of roads we have. When you look at the cost of implementation, maintinence, and energy costs I'm sure you'll see that paying for snow plows and salt/deicer is cheaper.

It might be possible for small towns to implement this if they really felt like they had money to burn, but the costs would be pretty incredible even for a small area to implement a heating system for the roads. I have seen heated sidewalks in some ski towns, but even those are a bit of a novelty in my opinion.

 

[BTB]

You guys bring up some very good points. Someone on another forum even mentioned the fact that it would be very difficult to protect the heating elements from the pressure applied by a steamroller to lay the pavement itself. This brings me to reconsider one of the alternate methods I listed in my initial post. Most roads are reinforced with rebar laid in a criss-cross pattern as the road is being constructed. This effectively keeps the road together, especially in places succeptible to shifts in the Earth itself or have soft soil or intense summer heat, etc. Assuming that energy costs could be offset by some type of renewable/sustainable source and you only wanted to heat a reasonable length of highway, could the rebar lattice-work that is already within (most) roads be altered in such a way so that it could act in a similar manner to electronic radiant floor heating?

In radiant floor heating, resistance wire lattice-work (usually copper or chromium) is laid underneath a floor and then covered by cement that acts as a "thermal mass," essentially retaining the heat in order to heat the road. Although concrete and pavement are different in many ways, in theory, could pavement (aka highway) take the place of concrete as the thermal mass? Likewise, could the chemical make-up of rebar be altered in a such a way that it could somewhat-efficiently disperse heat throughout the pavement? After all, and please correct me if I'm wrong, the road doesn't have to actually be "warm," just kept at a temperature at which snow will not "stick" (which is generally considered to be right around freezing).

 

[minger]

The total resistance of the wire is directly proportional to the length of it. I would think the amount of voltage required to even push a negligible amount of juice through a highway-wide grid of wire miles and miles long would be astounding.

 

[Mech_Engineer]

Well I've got a good reason why it can't completely replace snow plows: power requirements for a snow storm.

Say for example you have a 1-mile stretch of 2-lane road you want to keep snow free even during a fairly slow snowfall of 1 in/hr (heavier storms can be 6 in/hr). We will say the road is 7.5m (24.6 feet) wide, the snow falling has a density 8% that of water, and the snow falling is excatly 0 degrees C which means we only have to deal with water's enthalpy of fusion.

1 in/hr of snowfall correlates to 311 m^3/hr over a 1-mile stretch of road, or 25,000 kg/hr of snow. If we want all of this snow to melt right away and not accumulate, we need to put enough power through the heating coils to melt the snow as it falls. Given that water's enthalpy of fusion is 333.5 kJ/kg, that equates to a necessary power throughput of 2.3 MW for a single mile of 2-lane highway. Obviously the power requirements are substantial, at about 1.4 kW/m for 1 in/hr snowfall.

So say hypothetically tiny town X wants to completely get rid of their snow plow fleet and replace it with heated roads that are powered by wind turbines. They have a total of 5 miles of road, all 7.5m wide 2-lanes, that they want to be able to handle a maximum of 4 in/hr of snow. That would mean they would need a total power input of 46.1 MW to heat the entire road system during heavy storms (4 in/hr), and 11.5 MW during light storms (1 in/hr).

That sounds like a pretty significant wind farm/battery bank to me, especially for only 5 miles of road. It's obvious how this would scale up for larger areas, and shows why from a power standpoint a heated road infrastructure system just isn't practical.

 

[BTB]

The total resistance of the wire is directly proportional to the length of it. I would think the amount of voltage required to even push a negligible amount of juice through a highway-wide grid of wire miles and miles long would be astounding.

This is very true, and I can't seem to think of any way to overcome it...

Well I've got a good reason why it can't completely replace snow plows: power requirements for a snow storm...

Thanks for putting the problem into more technical terms, that's exactly what I was looking for (although I would've hoped for an opposite end result! :D). I suppose that if that much power could be easily and cheaply generated, then it would probably be put to better use before heating roads. I'm going to send you a PM about a somewhat related issue late tonight that you may be able to shed some light on. I hope you don't mind.

Thanks for the help guys!

 

[Mech_Engineer]

I'm going to send you a PM about a somewhat related issue late tonight that you may be able to shed some light on. I hope you don't mind.

Just make a new thread so everyone can see. I don't answer questions / communicate through PM's.

 

[russ_watters]

...25,000 kg/hr of snow.

Heh - having no idea what your assumptions were, I just calculated it myself and got 24,960. Great minds think alike!

 

[BTB]

Just make a new thread so everyone can see. I don't answer questions / communicate through PM's.

I already sent the PM before I saw your post, so please disregard it. Thanks for the help.

 

[Mech_Engineer]

Heh - having no idea what your assumptions were, I just calculated it myself and got 24,960. Great minds think alike!

Your calculations was closer to mine than you think, I actually rounded up from 24,920 kg/hr