Ice melting system
Ice melting system
(OP)
I am working on a project where there is a water filling station up north. The station is covered by a canopy, but the ambient temperature is about -40C plus some wind speed too. We have to design a heating system to melt the spilled water or rain water on the slab. Apparently we have three options: hydronic slab heating, electrical slab heating and overhead infrared heater. Gas is the cheapest so hydronic seem to have lower operating cost, but the installation cost is much higher; plus we don't know how responsive the system would be. Would we have to keep the system running 24 hours a day to keep the slab above 0C with the thermal mass? If so, we'll end up using more energy and more costly than infrared? How about electrical slab heating, how would that compare??
Which system would you use and why?
Thank you very much.
Which system would you use and why?
Thank you very much.





RE: Ice melting system
While electricity is expensive, hydronic implies a pump somewhere, doesn't it? In order to keep the heating system from dying, it would need to be flowing and/or above freezing whenever the temperature is below freezing.
I'd vote for standard electrical heaters. You need heaters to generate the infrared, so why waste the heat? An embedded heater could be configured to direct all its heat upward, with suitable insulation below the slab.
Presumably, you're doing a control system, so that would monitor the ambient temperature and only activate if below freezing, although, you might need to turn it on at night, even if the temperatures are well above freezing, because of infrared emission into the much colder sky.
TTFN
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RE: Ice melting system
For bulk heating methods, the energy required is independent of method. Electric has the advantage of near 100% efficiency. Hydronic won't be anywhere near that after heat exchanger losses and pumping costs. Electric also has the advantage of being nearly maintenance free.
IR probably won't achieve the same amount of bulk heat into the slab. I would suspect that re-radiation to the canopy and sky combined with convection will whisk heat away faster than conduction within the slab will allow heating of the concrete. However, maybe that's ok for ice melting. I would be worried about thermal gradient and associated stresses.
By the way, how can you have rain with -40C temperatures?
I would focus on preventing spills and dealing with them as needed when the do happen. How about an adsorbent and a heating blanket?
RE: Ice melting system
Convective loss for 10 W/m^2-K convection coefficient is about 500 W/m^2. That's a pretty windy condition; still air would be about 2.5 W/m^2-K
End result is that you'll need about 700 W/m^2 of heating capacity.
TTFN
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RE: Ice melting system
From what we see, infrared will kind of have a double purpose for providing warmth to the users during the filling too. But yeah, there'll be radiation and convective heat loss thru the canopy and the ambient. That's why we're debating all these options...
RE: Ice melting system
If user comfort is a strong desire, it might make more sense to have a slab heater AND a motion-sensing IR heater.
TTFN
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RE: Ice melting system
Now, I think I still have some question about the response time comparing the two. For electric slab heating, you would have to warm up the whole slab and then the heat would slowly act upon the ice. However, for infrared, even though the heat will re-radiate toward the sky and canopy, at least the heat is immediate and it act direct to the ice. Suppose the cost of gas is half of electricity per energy unit, I can have a gas infrared heater twice the size of the electric slab heater. As long as the combined efficiency of infrared heater not less than half of electric, it would still be more advantages (both economical and practical). Is this right??
RE: Ice melting system
The radiant heater under conditions I posited above will lose at least 1.5 kW for every 1 kW emitted. Additionally, IR does not transmit well through fog, rain, or snow.
TTFN
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RE: Ice melting system
RE: Ice melting system
RE: Ice melting system
Let's say, for the sake of argument, that you have a rubber mat, a heater, insulation, then slab. Then, the heating requirement and time shouldn't be that different from the IR heating.
What's the required longevity of the setup?
TTFN
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RE: Ice melting system
RE: Ice melting system
RE: Ice melting system
A cheap pre-eng, or garage package could be cheaper than a condensing boiler and snowmelt system.