Snow melt coil design 1

[pbmechtech]

I am trying to design a heating coil for a snowmelt pit in a hockey rink. Using the Zamboni specification, it says that one Zamboni can hold 100 cu.ft. of snow. We have two rinks and the Zamboni will clear each rink once an hour, so that gives me 200 cu. Ft of snow I have to melt every hour.

1 cu. ft. foot of water weighs 62 lbs, so let us say 1 cu. Ft. of compacted dirty snow weighs 50 lbs.

It takes 144 btu to melt one pound of snow @ 32 F to water a @32F

200 cu. Ft of snow X 50 lbs = 10000 lbs of snow that needs to be melted every hour

144 BTU X 10000 lbs of snow =1440 MBH to change the snow to water. Once the snow has turned to water, I would only need 1 btuh per lb of water to heat the water to melt the snow faster?

Am I correct so far?

I need to transfer this amount of heat through a heating coil in the bottom of a pit that is 120 sq. ft. in area and 36” high. (360 cu. Ft)

I want to use ¾” copper to make a coil(s) to place in the bottom of the pit. How do I calculate the length of copper tubing to transfer this much heat?

Thanks

 

[IRstuff]

The density of new snow is typically 1/6th that of liquid water.

Your length of coil is dependent on how hot the heating coil is, or how much heat you can generate per unit length of the coil, and how fast you want to melt the ice. You can take your heat load in BTU and divide by an hr to get an idea of how much power you are looking at; it's HUGE, btw... even after fixing your math error...

TTFN
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[EdStainless]

I see two options.
1. Spray the snow with warm water. As the snow compacts you will get better heat transfer.
You will need drain channels, so maybe a couple of the spray nozzles should be a lot higher flow to keep paths open.
2. Look at the hardware for in-floor heating. They are Al caps that fit over PEX tubing. In this way you get the entire area of the Al heated, a lot more surface.

Even if we say that this is slushy snow, and maybe weighs 25#/cu ft
That is 200 x 25 x 144=720k BTU/hr
Look at commercial boilers such as

http://www.htproducts.com/commercial-eliteft.html

You would still need two of these.
This is why most rinks pile it up and let nature handle the melting.
Have you run the numbers on the amount of natural gas this will take?

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Plymouth Tube

 

[racookpe1978]

The single coil would heat up the snow just above the coil ... and after that melts you'd have a "cave" of packed snow+ice jammed in the hopper above the coil ... but not touching the coil.

rather: Heat two sides (or all four) of the hopper's walls. Set the hopper walls at a strong angle 60-70 degrees (NOT vertical) so the residue slumps down and in but is forced by the slope to keep in touch with the packed snow+ice above. Water of course drains out the bottom.

But why melt it? Dump the stuff out back and save money.

 

[EdStainless]

But if you have no place to melt you can melt it slower.
How many time a day is the ice cleaned?
You don't have to keep up, just make sure that you are ready for the next day.
It still seams like a waste of energy.

Where is the heat dumped from your chillers that freeze the ice?
Perhaps you can use this waste heat to melt the 'snow'.

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P.E. Metallurgy, Plymouth Tube