Engineering a heated mesh to melt snow - Page 1
Forum section: electronics / beginners

author: tezla
author_rank: Newbie
timestamp: November 08, 2014, 10:02:47 pm
content: Hello Everyone,I not an Electric Engineer (I wish). I have always been interested in Electricity since I was 4 years old. I live in the US, in Chicago to be exact. I hate snow and of course we have to shovel the snow during the winter. I have been wondering how efficient it would be to use a heated mesh to put on the sidewalk to melt the snow instead of having to use of having to shovel it?Any responses would be greatly appreciated.Thank you.

author: Psi
author_rank: Super Contributor
timestamp: November 08, 2014, 10:28:14 pm
content: Producing heat uses A LOT of electricity.So this idea would be quite expensive in terms of running costs.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 08, 2014, 10:50:28 pm
content: Well, it would be 100% efficient, thermally, but that's a rather far cry from what is possible (a heat pump over 300% I would guess) or cheaper alternatives (actually, you know, picking it up and shoving it aside).Thermal deicing is used exclusively where the extreme cost is tolerable and necessary, such as airplane wings. Circuits for those purposes are something like 48V and 300A... for the small ones.Physics:Rule of thumb, 10" of snowfall is 1" of water. So, on your typical Chicagoan winter, expect a few of these during the year.Supposing you're on an average suburban lot, you probably have 50 feet of sidewalks, 3 feet wide (probably being generous), plus a 9 x 25' driveway. Or 375 ft^2. Or for you metric guys following along, say ~40m^2 and 2.5cm water per snowfall. Or for you guys who don't know what snow is... get lost.So, that's around 1 m^3 of water, which weighs around 1 ton(ne). Lifting that to about waist height (whether with a shovel or an average snowblower; a proper two stage blower will achieve more height, though) takes about m*g*h = 1 tonne * 10 m/s^2 * 1m (assuming a crude figure for average waist height, and the heavy gravity typical of a tiring and annoying physical task) = 10kJ. Also, shoving it aside takes some energy, but let's just say it's always leaving the shovel / snowblower at a 45 degree angle so the total energy is 20kJ.Presumably, a 1 HP snowblower (~ 3/4 kJ/s) would be able to finish the job in 27 seconds, though I doubt the mechanical efficiency is nearly good enough for that. Still, doing it in a few minutes seems reasonable, which I guess isn't too bad an estimate; they're limited by walking speed, really.On the other hand, presumably it would be possible for a very athletic shoveler to clear the same in under two minutes, which seems... impressive.As for thermal means, water's heat of fusion is 334 kJ/kg, so melting all that ice entirely to water requires 334 MJ. If supplied by pure electrical energy, it would cost $10. Or with a heat pump of 300% efficiency, $3.The average home can only supply 24kW (a 240V 100A circuit), so it would take at least 4 hours to melt the entirety of the snowfall. That's pretty reasonable, given that it will take about as long to fall in the first place. It's not as reasonable if the air temperature is very cold, like the worst February blizzards can produce. In that case, the heat dissipation of the surface becomes significant, both into the surrounding ground and up into the air. On a cold enough day, you might turn on the "defrosters", and never melt anything at all: a total waste of precious electricity!There's also the matter of where the water goes: can it soak into the ground, or is it going to dam up immediately? Again, this is dependent on air temperature (and for how long). The advantage to salt is, it remains liquid at the temperature it melted at, so it drains easily.It's easy to see the mechanical method has the advantage, and why, in part, it's so useless to use flamethrowers to clear snow (cathartic though it may be).Some more esoteric options:- Seismic transducers. Set up a travelling wave in the ground, so that the snow literally walks itself off your sidewalk. Advantages: cracks, loosens and clears any ice deposits. Disadvantages: earth is a very lossy and dispersive medium, acoustically, so you will require quite a lot of power to actually do this, even in local areas. The vibration will also induce settling, liquefaction (if sufficiently wet), cracking of concrete, subsided foundations, and so on.- Conveyor belts. Cheap to operate: no lifting needed. Expensive to install and maintain. May conflict with local zoning laws.- Electromagnetic kickers: by mounting a plate on top of the sidewalk, you can apply force directly under the snow, enough to bounce it off. Advantages: doesn't (necessarily) crack the sidewalk, moderately efficient. Disadvantages: expensive and noisy; may induce accidental ankle failure in unaware pedestrians.- Nuclear radiation. Advantages: stays warm all year long; zero maintenance. Disadvantages: expensive, probably conflicts with local zoning laws for all points on the Earth's surface.Tim

author: liquibyte
author_rank: Frequent Contributor
timestamp: November 08, 2014, 11:08:37 pm
content: Too complicated Tim.http://www.warmlyyours.com/en-US/snow-melting/heated-driveways

author: miguelvp
author_rank: Super Contributor
timestamp: November 08, 2014, 11:18:36 pm
content: I live in Chicago as well, and even the last winter which was one of the worse of them the snow didn't bother me much.I've heard pickle juice helps melting snow/ice but haven't tried it myself, but if it's as cold as it was last year I think even the pickle juice will freeze

author: Jeroen3
author_rank: Super Contributor
timestamp: November 08, 2014, 11:56:31 pm
content: QuoteOr where there is plenty of energy available. Such as Iceland, with their infinite geothermic energy.

author: AG6QR
author_rank: Frequent Contributor
timestamp: November 09, 2014, 12:00:34 am
content: Melting snow, even at perfect efficiency, requires a LOT of energy. The heat of fusion of water/ice is 80 cal/g. In other words, the heat to turn snow at freezing temperature to water at the same freezing temperature is equal to the heat required to raise that same amount of water at freezing temperature to 80 degrees C. That's 176 Fahrenheit.Just for the sake of back of the envelope comparison, how high could we lift the snow if we used the same amount of energy to move it mechanically instead of to heat it?334 J/g / (9.8 m/s^2) = 334000/9.8 m = 34 kilometersSo we could lift snow 34 kilometers, or 21 miles, straight up vertically, using the same energy it would take to turn it to water at freezing temperature. That's assuming perfect efficiency in both the lifting and the melting, which isn't a very realistic assumption for either process in practice.But that back-of-the envelope calculation shows why we almost always clear roads by using snowplows to move snow a few feet or meters instead of melting the snow.

author: zapta
author_rank: Super Contributor
timestamp: November 09, 2014, 12:58:17 am
content: IIRC Algore has his manison heated driveway. Takes a lot of energy. Try to think of more creative solutions.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 09, 2014, 01:43:22 am
content: Quote from: Jeroen3 on November 08, 2014, 11:56:31 pmGood point.

author: miguelvp
author_rank: Super Contributor
timestamp: November 09, 2014, 02:19:07 am
content: Quote from: T3sl4co1l on November 09, 2014, 01:43:22 amForget deicing, last year it was so cold in Chicago that:QuoteFrom wikipedia's references:http://en.wikipedia.org/wiki/2013%E2%80%9314_North_American_cold_wave

author: Psi
author_rank: Super Contributor
timestamp: November 09, 2014, 04:30:44 am
content: Just have a layer of radioactive material a few mm under the pavement to keep it a few degrees above zeroSomething that emits only alpha particles should get blocked by the pavement.

author: tezla
author_rank: Newbie
timestamp: November 11, 2014, 01:55:53 am
content: I just want to say thank you to everyone who took the time to respond to my dumb idea. Now, I feel confident that it is not doable.Again, Thank you so much everyone.

author: magetoo
author_rank: Frequent Contributor
timestamp: November 11, 2014, 07:07:40 pm
content: Quote from: Jeroen3 on November 08, 2014, 11:56:31 pmMy town uses waste heat from the district heating system (I think that is the term) to keep a football field snow free year round. Hot water goes out to buildings at about 80 degrees, does various useful stuff, and comes back at 10-15 degrees. Too cold to really heat anything up at that point, but still enough to melt snow.Which gives me the idea that maybe solar panels (not talking PV here obviously) could work for this sort of thing. People put them on their rooftops here, at 60 degrees north, so I'd think it wouldn't be that hard to get enough heat to melt snow and ice.But that sounds like a lot of plumbing. Perhaps a bit off topic for an electronics forum. :-)

author: miguelvp
author_rank: Super Contributor
timestamp: November 11, 2014, 07:29:47 pm
content: Quote from: magetoo on November 11, 2014, 07:07:40 pmWill be easier to dig and use the earths temperature to melt the snow, only problem will be that if you use water it will freeze in the surface stopping the convection, but antifreeze might do the trick or some other liquid/gas. Also it probably needs to be 40 to 100 feet deep to get a good heat exchange.

author: wiss
author_rank: Frequent Contributor
timestamp: November 11, 2014, 08:14:54 pm
content: Quote from: magetoo on November 11, 2014, 07:07:40 pmI think those are mostly for hot-water during summer, much easier to heat up to 40-50 degC when it it's 20-30 in the air, compared to -30 in winter...During winter you'll have any heating system fired up anyway, hot-water for "free".

author: magetoo
author_rank: Frequent Contributor
timestamp: November 11, 2014, 08:52:20 pm
content: Quote from: wiss on November 11, 2014, 08:14:54 pmWell, you don't need 40-50 degrees to melt snow. (see previous example)And I'm no expert, but I believe those panels do give a useful contribution even during most of winter; don't know if it is just preheating or anything above that though.

author: wiss
author_rank: Frequent Contributor
timestamp: November 11, 2014, 09:03:56 pm
content: Yea, 20 degC increase would melt snow here most of the year!

author: C
author_rank: Super Contributor
timestamp: November 12, 2014, 07:12:56 am
content: A friend in Maine has had solar hot water panels sense the 70's.Fuel oil or wood is common heat source there. A lot of homes use hot water baseboard heat.The solar system uses Propylene glycol in the outside closed loop with double-wall heat exchanger for safety. It is actually two complete solar systems. One does domestic hot water while the second the home heating.As for a lack of electronics guess again.You have the two solar systems to control. You have the backup fuel oil boiler. The wood fired boiler. The Lady likes her backup Kitchen wood stove to cook on ( it heats water also ). You have to plan on having many cloudy days in a row.Add the ice storms that take out the electric supply for days and you have quite a control problem.Where the melted snow goes would be the big problem. Could also see it making nice ice caves.C

author: mzzj
author_rank: Super Contributor
timestamp: November 12, 2014, 08:08:18 am
content: Quote from: miguelvp on November 11, 2014, 07:29:47 pmEthanol-water mix is pretty standard for underground heat exchangers. But 40 feet deep is nowhere enough. Here solid bedrock is average 6 cel year round and you need 150 meter drill hole in solid bedrock to get 10kw of energy. If you have 50 m of loose soil on top of the bedrock you are looking at a 200m(900feet) drill hole. Not exactly cheap or easy. And that 10kw is enough for tiny area something like 10 square meters , depending where you live.

author: miguelvp
author_rank: Super Contributor
timestamp: November 12, 2014, 08:12:04 am
content: I get that, but even as cold as it was last year we are not in the tundra, if so yeah, dig deeper.