Radiant Heat Snow Removal: Relevance To Large-Area and Civic Applications

electrical vs. liquid radiant

You forgot one, for comparison you should have the costs on how it currently being done

phoenix911

Hi, phoenix911!

Good point.

And certainly will be looked at when comparing the relative merits of each. Any thoughts on that topic from yourself? One city in northern Japan is using a combination of heat sources, including I believe geothermal(!), to remove snow.

Mark

±To estimate the realistic of it I think one has first to estimate the energy requirements of such an approach. Some times we have to remember that engineering is not only to dream but also to deal with numbers.

Let us consider a street section 20m wide (it is not a large one) and 1km long.

Area = 20x1000 = 2E4 m²/km

Assume 0.3 m of snow and an ambient temperature of -10C°.

Volume of snow= 6000 m^3/km

Such assumptions are rather low since the problem is set for "cold" areas but we start with something.

Density of snow 110±40 kg/m^3

Mass of snow = (110±40 )x6E3= 4.2E5 to 9E5 kg/km

Latent heat of ice 3.35 E5 J/kg

Energy to melt the snow= 1.41 E11 to 3.01E11 J/km

Assume that this will be spread on 7 days (for an order of magnitude) = 7x24x3600 = 6.05E5 s

Power in kW = Energy (J)/(T(s))/1E3= 233 to498 kW/km

A plus of energy has to be used to maintain the temperature at 0°C. Assuming a free convection of 8W/m^2/°C the amount will be:

8x10x2E4/1E3= 1600 kW/km

In fact it can be higher due to wind.

Is it realistic?

I let you comment.

Have a good day

Nick Name

Hey Mark.........whatsamatter .......wore out your snow shovel?

I know TO hasn't seen any snow in 30 yrs (well, last year was an exception) but really!...ain't the taxes enough already? What with city hall needing a $50 mil retrofit and other necessities council invents.........

Where's Lastman and the army?

I've only seen this done in a few places, and what I gathered was:

1) It costs a LOT up-front.

2) If it ever needs maintenance, God help you.

3) It costs a lot to keep going and isn't really efficient.

And that was for under floors inside buildings. Probably would be even less efficient outdoors. Where I've seen it work outside was where there was a lot of waste heat to be gotten rid of, and it was directed into under-sidewalk tunnels. That must be kind of rare, seems it would catch on if it was a common resource.

Hi, EnviroMan!

Hadn't thought about tunnels under the sidewalks and roads. What kind of radiant heating would make use of them? And what other uses might they have in addition to running pipelines and power/communication lines?

Also, if tunnels were constructed below the sidewalks and roads, what techniques could they employ to get that heat to the road/sidewalk surface from, for example, a tunnel below running up the middle of the road or sidewalk?

How about a pipeline system run from the tunnels containing electrics or forced air heating units?

eg:

Certainly, tunnels would obviate the worry about replacing electrical wiring on the road bed and maintaining a buried system.

Mark

I still wait for your comment.

Where do you expect to get the energy?

Have you seen the huge amount of power required?

If you are not accustomed with kW consider that a 1kW = 1.36 HP and multiply all values with this factor for a more common unit for you.

That in a country where the geothermal energy is available this approach could be a solution it is NO solution where the required energy has to be generated. You suggest solar panels. In the warm part of earth where this "central heating" is not required the maximal power is in the range of 1kW/m^2.

Where the solution would be of interest specific power is less due to the angular effect and as I presume that noticed in winter the sky is not always without clouds. So this solution is also not possible.

As I mentioned in my comment engineering although requiring ingenious solutions is also a technical profession dealing with numbers.

The best idea is not more than a dream if the numbers do not support it.

Hi, nick name!

"Where do you expect to get the energy?"

Good question. And it's part of this blog set, since the "best" form of heating style and energy supply has not yet been suggested. Perhaps you can suggest something. I postulated the solar array to cover a small part of the electrical energy provided should the electrical route be the best one to take. For the rest of that supply, I added in home generation and the grid. But those were only a couple of ideas I am throwing into the discussion.

Writing from an electrical perspective, how might you share those three supply sources (as an example) to minimize overall costs in a resistance-line heating grid? Or otherwise, what would you suggest? How about a dedicated power source?

The main idea is to minimize the costs of running and sustaining such a system. It could very well be that either electrical energy is not the way to go, or if it is, it is done in a different way that doesn't require such an intensive application of resistance wiring.

The idea is that the time has come for this style of snow clearing, since we as a civilization have technical advances that could provide its means. CR4 is blessed with the talent to figure out an answer, perhaps, via this discussion forum. If we can, rest assured that cities all over the world will listen to the ideas we come up with.

Mark

I would suggest you make a comparison between energy for a thermal solution (you have the figures from my comment) and what will be required for the other solutions as used today. Then you will see if it is any possibility to do some thing. many many years ago the person in charge of the technical dept where I worked as a young eng. had same idea and I got the project. He was very enthusiastic till he got the values. He checked them several times to be sure since he assumed first that I made an error and after it -because he was a very good technical man- he recognized that mechanical solutions are more economical even if not satisfactory.

Hi, nick name!

So what "mechanical solutions" did your colleague consider, and were they successfully implemented?

As far as obtaining the 2000 kW power source is concerned, that much power derived from a single source might be more difficult than providing it from hundreds of small sources along the heating lines in the form of household grid-return power, civic-owned power generators (such as a SWERF unit or powering generators using wild methane from dumps, etc.) and solar arrays or the like set up to supply local heating units.

Do you think this might be possible as well?

Mark

Traditional

Hi, nick name!

Would you care to enlarge on that?

Mark

I've not seen electric radiant heating used. In some buildings, I've seen boiler-fed hot water piping laid in the floor. That worked sort of, but prompted my "God help you" comment in case of leaks. In some cities, waste heat from heating buildings goes into tunnels under streets & sidewalks. I don't know if the original plan was melting snow and ice, but it does do so. I have never been in one of those tunnels, but always presumed they were utilidors (utility corridors).

Vent hot subway exhaust in utilidors under sidewalks/roads. That's a reasonable possibility. Though, if anybody has done any work in excavating urban areas, you know that whatever is down there is unknown until you get there. I could easily foresee that with regular city construction, these utilidors would get beaten up and become ineffective.

Electrical/fluid radiant heating seems inherently inefficient for such a large scale. The only reason radian heat is efficient in buildings is because they are heavily insulated.

I heard not too long ago about radiant heating on some sidewalks in Aspen. As comfort comes over cost in a place like that, I could see it actually being implemented there on a small scale.

Can anybody confirm/deny this claim?

We might be able to get some quantitative data from their experience. I don't think that this data would be able to justify such a system, but it could provide proof (aside from what has already been provided here by others) of its un-feasibility, at the least.

I'll be perusing the inter-web for it...

little off topic, some larger manufacturers have radiant heating in the shop floors, shipyards that I know of. It was originally put in for worker comfort, but the worker complain its hard on thier feet. Or maybe I should say, uncomfortable.

have you come up with a ansew to the question. can a street of city street be cleared using radiant. want to experiment? I am a builder / developer in ma getting ready to do a sub-div. goe thermal looks good to me???

Hi, Guest!

The "new" geo-thermal is a heat exchanger dug deeply into the earth with a glycol carrier to transport the temperature differences between surface and depth. In my neighbourhood, builders of new apartment buildings are including them to make the buildings 'greener' in terms of HVAC energy efficiency.

The dificulty with transmitting that heat to the surface has been pointed out by Enviroman (point #2) who indicates that if you have a liquid heating source beneath the road/sidewalk surface (in pipes or hoses, most likely) and it needs repair, you are going to have to destroy it when you dig up the road/sidewalk to get at it.

Apossible solution for this problem is to bury the conduits deep enough into the road bed that it should rarely if ever encounter a destructive encounter.

Mark

Hi, Guest!

While the (above) geo-thermal application saves the costs of burning direct fuel consumption in order to proved a heated sidewalk and road surface, I personally like the prospect of hot forced air travelling through piped corridors below the surface. Possible inexpensive heat sources for that purpose could be generated by methane tank farms driving electrical generating systems (which could independently power your subdivisions and provide an additional source of income); perhaps in the following configuration (see sketch below).

Of course, these would have to be manufactured and installed when services went in to your development(s); but over time, the cost would be offset by not employing snow removal (street repair), and other associated traffic costs.

In addition, the system would make an amazing sales point, allowing you to upscale the market for the homes in the subdivision.

Good luck with it if you and your civil/environmental engineers decide to pursue it in one form or another. Keep me posted. I'm interested in its value from the point of view of a large city.

In the meantime, comments are invited about [whether this is]/[how to make it] efficent.

Mark

If all factors were included yes it would be far more cost effective than conventional methods.

All factors include:

environmental damage by fuel vapors burned or not, chemical run-off including fluids spilled at accident scenes, etc.

Costs associated with property damages and pain or loss of life limb and the loss productivity when conventional methods fail

Freeze thaw damage mitigated and the decrease of maintenance due

Fuel costs of conventional application equipments.

Reduction insurance claims

etc. etc. etc..

I am not as sure as you are about cost effective.

The power required is at least 100 W/m². To avoid risks the convection surface to ground should be at least at -1m. Considering the thermal conductivity of soil (dry 1W/m°K or wet 2W/m°K) and 0.75 W/m°K for asphalt and an air convection coefficient of around 20W/m²°K the gas temperature should be at least 66..70 °C. With an increase of 1°/30m depth the ground should be drilled down to -2000m. Since the heat transport capability of air is low huge air quantities will be needed and require a lot of power to be displaced. Use of water will be more adapted for a higher convection up to 2500 W/m²°K and and a much more important capacity to transport heat but of course other problems as already mentioned will arose. How you turn the problem it is not any more so easy if one goes from qualitative to quantitative. Unfortunately as I wrote engineering is a profession for which numbers have to be used not only ideas.

HI, nick name!

This is really helpful information you are providing, and it does indeed contribute to the 'engineering' (i.e. 'accomplishment') end of the general idea.

I am left with some questions, based on the following:

"With an increase of 1°/30m depth the ground should be drilled down to -2000m"

Conventional applications in the local apartment buildings I mentioned earlier are applying the "new geothermal" at depths of 100m - 200m, and getting enough exposure to a more or less steady 11.5^o - 12^o C at below the frost line (about 1.3m below grade here in Toronto) over that length (X 2, I guess, since the liquid travels both down and up; and, because it is below the lowest floor of the building, never actually gets to 'see' frost) to modify the glycol temps sufficiently for heating and cooling assist per ≈25 apartment units year-round, although I'm not informed as to whether only one of these systems is used or whether for example 2 may be used per building [clarification invited].

-and-

"Since the heat transport capability of air is low huge air quantities will be needed and require a lot of power to be displaced"

This would appear to consider the air as the direct pavement-heating medium. But if the radiant piping were to be composed of a good heat retention/release material as for example cast iron or clay, one might expect the hot air to maintain the temps of the heating units rather than being applied directly to the road/sidewalk surfaces or directly to the soil and hence into the cold air.

Given the concepts, questions, revisions (including tossing around ideas as to whether or how this concept might be accomplished efficiently), and solutions in the form of engineering remain re the numbers:

• At what depth might a forced air radiant heating system have effectiveness, where "effectiveness" is maintaining the pavement at a temp only 1 or 2 degrees above freezing in order to melt the precipitation?
• What temps would have to be maintained in the main heat corridors in order to produce that temp over a 5m corridor and maintain it with an e.g. 120m overall combined length of e.g. ø0.3m radiant pipe distributed within that 5m [to cover all the necessary (e.g. 5m long X 15m wide, including a roadway and two sidewalks) ground surface being serviced by a 5m section] in ground at 0^oC?
• What kinds of electricity consumption would be involved in producing the desired result?
• Since this might be described as a form of conventional 'radiator' system, might hot water or steam be a better heating medium for the radiant piping than forced air?
• Would the "new geothermal" act as a useful adjunct for this type of system, and how? How about the addition of 'in-situ' electricity generation from nearby homes and solar panels to help defray heating costs?

As for the corridors themselves, I suppose that they could serve a dual purpose as transmission line conduits as well (creating an opportunity to partner with or lease to utility companies and thus lower overall costs). So in the case of transmission line maintenance, the pavement-heating fans and heaters would have to be lock-mounted on a vertical pivot for crews to get by, and be locally switch-operated so the conduits could be suitable for temporary human occupation. Access would have to be via airlock manholes.

"engineering is a profession for which numbers have to be used not only ideas."

I agree completely. The entire engineering process would be impossible to accomplish with scientifically unsupported ideas, and less interesting if it were dependent on numbers without concepts to give the numbers life.

The order in which these two essential elements of engineering occurs varies. Sometimes, we determine what needs to be done first, and then generate the numbers afterward to support attempts at solving the initial questions. This approach is also useful for gathering a useful resource to be used in invention and tackling future engineering problems.

In the case of an engineer acquiring the experience to generate the numbers he/she has at hand, someone (usually, but not always also an engineer...take the Sterling engine as an example: the brother who was a clergyman conceived of the idea and the brother who was an engineer designed it) first had to conceptualize the possibilities so the science could be applied. Often, it's a chicken and egg thing, where ideas are tossed around and checked by the science, while numbers and realistic possibilities equally generate the ideas we toss around.

Mark

You'll need maintain the pavement at least 3° - 4° above freezing due wind and or extreme temperature influence.

Hi, bwire!

Good point.

Mark

Hi, bwire!

By "conventional methods", do you refer to standard snow clearing by machine?

Mark

Yup