Snow melt

george_culbertson

Here ya go

1600 square foot driveway.

13 circuits

5/8 Tubing

250 length with 40' leader.

Leader is in 5in Pvc Duct encased in R 8 aluminum bubble wrap.

Asphalt driveway

6 in modified with 2 in foam.board above

5/8 pipe stapled to foam board with 6in OC. 2" screenings above pipe.

3 in asphalt base coat on top.

Return water temp during paving never got hotter than 135 degrees at 3 GPM per Circuit.

Derheatmeister

In our area we would need approx 200.000 BTU/HR for this operation which can be very expensive to operate..😲

If you can now reverse this operation and utilize the Snowmelt as a "Solar Collector" to produce DHW/Supplemental Heat you may be able to offset your Carbon footprint.

george_culbertson

I thought about that during install. With the heat we have been having I tested it and could easily produce 125 degree water at 8 gpm. which is more than enough to run thru the Indirect.

I did leave out that I have my house sidewalk at 32k Btu / hour. And a another sidewalk at 24K and driveway at 160K ..For a total of 216 K… These are worst case scenario numbers

With a 0 degree day, 42 degree slab 10 Mph. I calculated $6 an hour to run for Natural gas and Electric in the Philadelphia area + taxes..

On a 25 degree Air temperature a 38 degree slab temp and a 10 MPH wind. $.54 cents per hour to run with Gas and electric costs + taxes.

hot_rod

The amount of BTU you push into the slab is more about how quickly you want snow to disappear. Can some accumulate, or do you want to melt as quickly as it is falling?

I seen sidewalks work fine with 75 btu/ft. Hospital heli-pads at over 200 btu/ ft.

I would think a driveway to solar DHW would behave like an unglazed pool collector. Great output potential when ambient temperature and load temperature are close.

This graph shows how an unglazed collector can be 80% plus efficient when the water and ambient are equal. 0 on the bottom axis. As ambient drops, performance falls off quickly. The ambient air temperature grabs the energy before you can stuff it into a tank.

If you need to run a large or high head circ to do this the power spent may not equal to amount of solar harvested?

Getting 120F to a tank on a 90F ambient day may not be possible? The idea comes up a lot but I have not seen a system operate or actual collection data. Has anyone? Probably an 80° pre-heat is doable.

I would guess the Germans would be all over this solar driveway collector concept if it penciled out :) Certainly Viessmann engineers have crunched the numbers??

Miles of the highway to Buderus have snowmelt tube. Is it collecting solar thermal in the summer months? For a district heating system/ dhw?

One of the main issues with solar thermal is in the best solar months there is not enough consistent load to make it $$ out. Same with co-gen units. No consistent thermal load, then the numbers won't work.

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GroundUp

I attempted to connect one of my aprons through a HX for DHW in my shop and while it did bring the temp up to some extent on a spicy day, it certainly wouldn't make any volume over about 85* in the best case scenario. Maybe it's just my location but even on a 100* day with full sun, the fluid in the slab never exceeded about 90*. I disconnected it after a month of messing around and just bought a POU unit

hot_rod

It could be molded with FEA, maybe it has been. Probably the reverse of what you see here with bare tube in a slab.

If the tube happens to be at the bottom, as most is, there could be a 10- 15 degree delta from surface to tube, maybe more with a short solar window of 4-6 hours to warm the slab.

So 80- 85° would sound reasonable on a 100° surface temperature day. Then there is the quantity question, as you discovered.

Wind would scrub away some btus just as it does on an uncovered swimming pool.

Ever seen the Viessmann ice storage system? Bury an insulated tank in your back yard. At the end of the heating season you have a block of ice for the cooling season. These are the people that eat, drink, and sleep about thermal energy transfer.

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