Radiant Roof snow melt ??

Tim Potter

I saw ME's response on the post about capping the unused port on a wirsbo manifold.

It got me thinking on roof ice dam melting with hot water tubing vs electric heat trace cables.



In the CO Mtns, 1 KWH of elect = 10.2 cents and 1 therm of Nat gas = 8.44 cents. am I reading that correctly, even if you assume 80% eff on the gas, its still 23 times the cost per btu for electric?????



In the mountains we have to run heat trace on the roof OR pay someone to shovel & pickaxe the ice off the roofs.



How would one use hot water in tubes to clear a path for the melt water to run off the roof & down the gutters/downspouts?

PEX is not uv stabilized & I assume would rot quickly in the high UV Colorado sun.

Onyx Tubing run in a zigzag pattern just like the electric cables ??



Seems like a way to save a ton of money, my heat trace runs me about $150.00/mo on electric.



Thoughts?



Thank You:



Tim

SWEI

Energy costs

Your NG might actually be $0.844 per therm?  If so, the difference is more like $31.08 per million BTU on electric versus $10.55 for 80% NG or $8.88 for a 95% mod/con.



http://www.eia.gov/neic/experts/heatcalc.xls is your friend.  Don't forget to net out the fuel costs from the bottom of the bill -- those surcharges and taxes can easily add 15-20% for smaller users.

Tim Potter

Yea, that sounds more like it,

But it is still 3x the cost for electric vs N gas. I did remove all the other charges, so to have a more accurate reflection of the true cost per btu of electric vs NG



Thanks for getting me on the right track<<br />


Tim

hot_rod

longevity

rubber hose with a UV jacket might get you 8-10 years in that climate. Look around at tractors and machinery, backhoes etc, that hydraulic hose lasts in the sun.



It might take some clever clips to keep the snow creep from tearing it off.



Maybe fasten the hose below the roof sheathing, you just need to warm the shingles a bit above freezing to melt. I'll bet this has been tried before.



We did run the rubber hose down drain PVC to keep the snowmelt waters running away from some driveways that we melted.

SWEI

Just like a dry floor system

only upside down.  Retrofit aluminum C-plates to the sheathing from below, then install tubing and insulate.

Mark Eatherton

Extruded plates, YES

In tohelluride, they used extruded aluminum heat transmission plate from the bottom side of the roof. We limited the roof melt surface to 35 degrees to avoid melting the polar ice caps.



And yes Tim, your decimal is off one place. .84/therm versus $2 for electricity. Still a big difference. Might be better off setting a NG powered electric, water cooled generator, using the electricity to power the heat tape and use the thermal energy for DHW preheat or space heating needs.





ME

Gordy

DHW Preheat

Reverse the operation with that setup in the summer and take advantage of the hot roof. May get more than Preheat out of it.



Recoup some of the expended energy cost during the winter to free solar energy in the summer. Roof decks can get to 110-120* in full sun.

Mark Eatherton

I like the way you think Gordy...

I wish this were mandatory for ALL snowmelt surfaces. With an appropriate load, it would be possible to extract heat even from warm summer evening air, even after sunset.



ME

SWEI

Dawn Solar

Used a design just like this.  Not sure if they are still out there selling "dealerships."



As long as your emitter system is low temp, it should work pretty well most of the year.  Would also work well for black body radiation at night.



Can't beat the lack of visual impact.

Gordy

Thermal mass

Of those surfaces can last quite some time after sun set in the summer. I would love to see the performance of Mad Dogs driveway when he gets it operational.

Jack

I once did a pool heating system

with tubing in the concrete pool skirting. Not only heated the pool but allowed the folks to be able to walk on the concrete during the day.



On the ice melt, I used my tankless on my home in MA. We had serious build-up and everyone was losing their downspouts, gutters and associated damage. It took 3 1/2 hrs of hot water, but the roof and gutters looked like a summer day when I was finished. The run-off melted the ice in the driveway. All Good;)