Will be starting My solar driveway this week

Mad Dog_2

,the technical expertise of my Good Friend Jimmy The Gent Burke of The Comfort Zone, and the labor of Albert the Crazy Columbian Production Mechanic and the World's Greatest Father in Law, Don, we will take this experimental plunge. Mark Hunt has weighed lin. Gleaning what I have from several smart sources and opinions - including SIGGY - and what the paving contractor is comfortable with doing...this is the plan

- Insultarp Want to save time, $, and less excavating costs
Remember this will be a solar driveway NOT snowmelt although I am certain to run it ateleats ONCE during a snowstorm to watch it. Snowmelt is NOT cheap to run and
a luxury in most cases. Also, I think the 2" polystyrerne might slow the transfer of heat from the asphalt down in to the tubing. In my simple mind...heat goes to cold right? heat (asphalt) goes to cold (earth under the subslab) Sounds plausible? By insulating too well I envison a slowing of the transfer rate.

- sub slab 3-4" inches of poured concrete for driveway strength. This is what the paving contractor insists on to guarantee HIS work.

- wire mesh sheets will be kept high in the slab on brick blocks, keeping the tubing JUST under the surface of the
concrete....as close as we can get to the bottom of the
hot asphalt slab which will be 2"s
- slab sensors in both the concrete slab and the asphalt slab
- I will split driveway in the atleast 3-4 sub zones to take compensate for the afternoon gradual shading of the driveway.
- 1/2" wirsbo tubing on 6" centers (wanna grab all the btus I can get....PEX is cheap)

The driveway runs north to south and gets really good sun for most of the day.

I have NO dump zone like a pool, But I will compensate for that by having atleatst 2 large storage tanks to have a large reserve of hot or preheated water for domestic and even radiant. This months weather is an encouraging sign:
Old asphalt gets to 92-95 degrees at the peak of the day and weather drops in to low 40s at night. I could dump that stored water in to my radiant zones at night and keep the Wall hung Mod Con (brand yet to be determined)from firing to warm the slab. ME says Steilbel eltron makes some 120gallon tanks. This is an experiemnt and several people think I'm nuts...I am! But I know instictively that this will work and perhaps be one of the best learning experiences I've ever had. ME will lend me his data logger to track out results. I am VERY excited about this. I am spending some $$$ over and above the driveway, so I am a little nervous about performance, but I am moving ahead. At worst, if I ever sell the house....they have a snowmelt system. Jimmy THe Gent has a solar driveway out there that he said is pulling 130 out of the driveway on a hot day. I welcome all comments, opinions and criticicms. If you see anything I am missing, please let me know. That can be a Wallie learning experience for all. Thanks in Advance

To clarify:

The new driveway will be about 1100 s.f of asphalt
- I will use a gas mod con for
domestic water, radiant in slab for basement, 3 bathrooms
and a dry radiant system for the barn wood floor sleeper system, a medium temp zone for a large ornate CI rad in barn and a hanging modine unit for prefab shop.
I will have at least 2 large storage tanks

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Steamhead (in transit)

Keep us posted

I can see redoing my driveway in the next year or two... much of the old concrete would have to be broken up and replaced anyway, so why not make a collector out of it?

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laurence salvatore_2

We did this in washington depot conn. about 3 years ago. The intent was to heat the swimming pool (apr. 40,000 gallons) We did it just as you have described except we used 1 inch golden jet polybutlyne pipe in a 5000 square foot area. The place is a summer house on a lake for some tony Wall Srteet types. We had it ready for Memorial day weekend and according to the home owner, he switched it on Thusday afternoon and by 2 pm he was having large blocks of ice delivered to help the wind off lake to cool the pool off.

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laurence salvatore_2

that was 2pm friday the next day

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hot_rod

If you need a new driveway

it makes sense.

If not that same money could buy a bunch of solar panels and insulated storage. It would work much more efficient and even provide energy when the driveway is covered in snow

hot rod

ALH_4

Data

I would love to see data from a BTU meter on such a system.

What is the least expensive BTU meter available for an application like this?

Mad Dog_2

Thanks Hot Rod

Believe it or not, My town is not crazy about the look of roof mounted collectors and I would have to go before architectural review board. This is much more palatable. Do you guys see any improvements to the way we do it? Do you agree with my theory that using real good insulation might slow heat transfer from the the asphalt to the tubing or am I splitting hairs? Gramps AKA Mark Eatherton will obe glending me his data logger. We will ALL learn from this. Mad Dog

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kal_2

i would still have water flowing...

through the pex when you pour the asphalt - even though the pex is in the concrete - it's still real close to the hot asphalt and you dont want to chance the pex changing in any way - just my two cents - can't wait to see the hard data - as i am looking at a pool heat application too - there has to be enough btu's to justify the cost

ALH_4

performance

Temperatures would be interesting too, but even a thermometer in the supply pipe, one in the return pipe, and a rotameter on the piping to the driveway would be very intormative. With the rotameter and thermometers, you could calculate instantaneous heat transfer of the "solar panel". With a digital btu meter, you could totalize the btu's transferred.

I think insulation beneath the slab is a very good idea. Heat does flow from hot to cold, but you want it to flow from the hot asphalt to the cold tube, not the cold earth. Insulating beneath the slab would allow the slab to achieve a higher temperature and therefore increase the heat transfer through the tube.

Brian_18

Why asphalt?

I'm a little curious why bother with the asphalt? If you are being forced to lay down concrete, why not just make the entire driveway in concrete? And colorize the concrete, or just give the concrete a coat of blacktop sealer, as you'll most likely do to the asphalt anyway. I know you must have a good reason, maybe I'm just being dense.

Metro Man

colored concrete

I agree with Brian. A dark red or ? colored concrete should provide plenty of heat transference. NREL in colorado has done extensive testing with different colors other than black for heat absorption.

One truck, one time. But sounds like your set on the black top.

Good luck!

Bob Gagnon plumbing and heating

Go for it!

It might not work that good when it is real cold in the winter, but I like the idea of all that thermal mass. Instead of heating your house only when you have enough heat, what about having a seperate, supplemental radiant system, like a couple of walls or ceilings, connected to the driveway. You could use water down to about 80 degrees, at the same time your boiler is running. I think you could collect and use a lot more energy that way.
Thanks, Bob Gagnon

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ALH_4

separate system

I'm not sure a separate system wouldn't reject some of the heat from the boiler to the driveway if that panel was colder than the boiler emitter. The driveway-heated panel could be warmer than the MRT, but cooler than the boiler-fired radiant panel.

Does that make sense or am I imagining things?

hot_rod

Are you sure some evac tubes can't be used SOMEWHERE?

I'm thinking that hot driveway will generate oddles of hot water when you need it least. Like June thru August

So much in fact you may end up spending electrical energy to dump it somewhere. the cost of dumping may outweigh the "free" energy you gain inn the heating season.

And I doubt on a 30 degree, sunny winter day that it would even provide much DHW preheat?

I'd bet an eight tube evac tube collector would out perform that driveway. especially if it gets any wind across it.

But we all do crazy things from time to time.

Check out the solar control from tekmar, Regsol and others. if you have a flow indicator or meter in the loop, they will give you the data (delta t over a given time) to calculate BTU harvest.

Go to either of their website and download the tech sheets to see how this works. Since you need a delta t controller anyways may as well spend a few bucks to get one with an onboard logger.

hot rod

realolman

Would you mind

a short explanation of what you hope / expect to accomplish?

Ron Huber

sorry

you could probably heat a pool in the summer, but any unglazed panel will not give you space heating temps when you need it.

Think about it, winter ambient temps in marginal solar gain, trying to heat a heavy mass and transfer usable btu's to pex.
Do not forget to factor in some wind factor in this equation, moving (cold) air will suck the heat off that surface before it thaws that puppy from the cold dark night before. But hey, if it is just a fun project to play around with, it's like the man said, "It's your money"

[Deleted User]

Allow me...

Now that I've had a chance to see your theory explained, allow me to disagree with you. What you say about heat flowing from hi to low is true. The insulation on the earth side of the solar sandwich has to do with thermal isolation between the mother earth, and the concrete/solar heated sandwich. The insulation won't act like a magnet to draw the heat downward, as it looks in your minds eye. If it were me, I'd put a minimum of 1" XPS insulation below the slab. Actually, if you really want to experiment, use NO insulation in one area, insult arp on another, and real XPS insulation on a third area. Bury a sensor a few inches below each insulation package (ala Eatherton test) and show us what happens.

I'm excited about the potential. To those who are poopooing this idea, why not do it? If we wasteful Americans can make a snowmelt system produce more energy than it uses, it might make it easier for us to justify it use (snowmelt), no?

Mad Dog isn't the first to attemp this idea. He's just the first to attemp to document the crap out of it to prove one way or another the feasibility of doing this.

Me, I'm putting my money on my roof up at the ranch. I'm going to put down Warmboard with 1/2" PEX in it on the roof instead of CDX, and cover it with dark green raised metal roofing. When I'm done heating my DHW, if there is demand for it, I'll divert the free energy to my house. If the house doesn't need it, I'll send it into the ground source loop field. Low grade solar colectors at their finest :-)

On the opposite end of the scale, I get free night time radiant cooling from the roof/Warmboard package during the summer months to keep my ultra efficient dwelling cool, and if I end up with more cooling than I need on the main floow, I can dump it into the extra thick concrete slab in the basement.

During the winter months, I can use my wood burning gasifier boiler to heat the roof, thereby melting the snow, which I can harvest and store for domestic use in a more controled nature than allowing it to accumulate, freeze, and melt randomly.

Thanks for thinking outside the box Matt, and thanks for having the gumption at actually do it instead of just talking about it.

If you can think about, it CAN be done :-)

BTW. the Steibel Eltron tank holds 160 gallons, and has two coils, one low an done high.

http://www.houseneeds.com/shop/solar/stiebelsolarheat/solarindirecttanks.asp

ME

1solarguy

Ron Huber and hot Rod got it right.Unless your driveway is really steep, it is pointed at the sun in the summer only. In the dead of winter the sun is low in the sky. Maybe you could have your driveway tilt up. Then the snow would slide off, and it would "see" more photons.

Bob Gagnon plumbing and heating

separate systems

Andrew, I think if room temp is 70 degrees, the floor radiant is about 80 degree surface temp- with 130 degree boiler water supplying it. And if you harvested solar energy, down to about 80 degrees, and supplied a separate ceiling panel, wouldn't that heat be dropped off in the house? If the air temp is 70 I think anything over that would transfer heat into the house. I think we lose a lot of BTU'S by trying to heat the whole house once in a while, rather than getting part of the heating load much more often. Does that sound right? I appreciate your input.
Thanks, Bob Gagnon

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kal_2

of course evac tubes are better...but..

But you wont get the same sense of satisfaction as you would get from knowing that the sun baking on your blacktop isn’t going to waste – and the evac tubes wont melt your driveway when the “white” hit’s the fan!!!

ALH_4

driveway collector

I was just thinking hypothetically. Let's say there was a radiant ceiling panel driven by the driveway and a radiant floor driven by the boiler. Given that the ceiling panel could be cooler than the floor panel at times, could it pick up radiant energy from the floor and transfer it to the driveway? Maybe I am thinking wrong and it just needs to be warmer than the room. Or maybe it would be better to run radiant walls with the driveway.

In any case, I have a feeling the efficiency of the driveway panel will be very low compared even to an unglazed pool collector. We all know what wind can do to snowmelt. I wonder the magnitude of the effect of wind on a hot driveway in the summer. Also the heat must pass through a lot of boundaries with this system. Through asphalt to the tube to the fluid to the storage tank (hx?) through a hx to the dhw. Each one of those boundaries requires a delta-T. I really don't see this doing much space heating. A swimming pool seems like the best application.

That's the reason I would really like to see a totalizing btu meter on this system. Either it will confirm that this is worthwhile or dispel the myth. A driveway could get quite hot in the summer and still have very little heat transfer capacity. For a few hundred bucks this debate could be ended forever.

Mad Dog_2

I'll be pleased as punch

If I can supplement my radiant in the spring and fall and pick up most of my domestic hw load in the summer. The past few weeks have been very encouraging: The asphalt is reaching 90-95 degrees at peak of day AND temps are going down to low 40s at night - even kicking on the steam system!
Instinctively I know this is going to work AND Jimmy The Gent has a couple out there working well. My key here since I don't have a pool is storage. And, I plan on atleast 2 large tanks. In winter, I don't expect to get anything...if I do, get somethin' that's swell. I will also set the mech room up for an easy switch to snowmelt if I wanna run off a snow storm for kicks as I sip my Bourbon. Also, AT VERY LEAST...If I ever sell the house....ITS GOT SNOWMELT!!!!! Mad Dog

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Mad Dog_2

Funny you say that.....

Going over the pitch for drainage, Steve the contractor shot the transit and we will have decent pitch, so if that helps great! Mad Dog

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Mad Dog_2

The crappy driveway was the last vestige of the old house

In fact, 2 more dumpsters today...that brings the total from 2000 to almost 30!!!!!!!dumpsters...mostly 30 & 40s. Total rehab. Yep HR, I actually do need to do this driveway over and as ME says..."Friends don't let friends pour concrete or tile w/out tubing first." Thanks for the input HR. Mad dog

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Mad Dog_2

Absolutely

I will. Mad Dog

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jp_2

cold summer roof?

mark,

how cold do you expect your roof to get in the summer?

Mad Dog_2

Actually, we have some 2\" polystyrene in the shop

from the last snowmelt job. I will use it up and also do an area with NO insulation and one with insultarp and 3
Eatherton-Mother-Earth-ground sensors. Mad Dog

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Mad Dog_2

I can see dumping that 90 plus solar-gained-water

in to the radiant slabs in the shoulder seasons - like now. Mad Dog

Mad Dog_2

I've just always preferred Asphalt

Perhaps it brings back great memories of an ultra smooth surface to roller skate and play hockey on. My three youngin's deserve a nice driveway to play on (we live on a street where people constanly blow the stop sign and speed thru). I believe it will conduct heat better than even stained concrete...just a hunch, but 39 years of stepping on hot concrete versus hot asphalt tells me that. Mad Dog

Mad Dog!!!!!!!!

A shame not too

fRANK...mAD dOG

Mad Dog!!!!!!!!

VERY ENCOURAGING NEWS

Mad Dog

Mad Dog!!!!!!!!

Thanks ...but Yes I prefer blacktop

in this application. MD

Mad Dog!!!!!!!!

Evac tubes possible....

If ARB approves. Maybe down the line. HR, If I get THAT much excess energy, why not store domestic at higher temps and mix it down? I am planning on atleast 2 large (160 X 2) storage tanks. The driveway will be around 1350 s.f., Mad Dog

[Deleted User]

At night, with a clear sky...

I can pull temperatures below ambient, and that's good enough for me :-) It gets down to around 40 or 50 degrees F at night up there...

ME

realolman

If you had this project done

and complete the way you wanted it, what would you have gotten out of it in the last week? What would you have done with it?

I have a paving crew coming in approx 2 months.

My two bits ... (might be worth even less )... I wouldn't do any portion of it with less than the best insulation under it. I wonder if a heat pump could do anything useful with it.

Kevin_in_Denver_2

asphalt pros and cons

Mad Dog,

The brick "chairs" for the PEX will cause cracks to propagate from them. Whenever you have discontinuities and sharp inside corners, there will be "stress risers" which cause cracks.

Round pavers instead of bricks will help slightly.

But cracks are no problem for you if you have an asphalt topping.

Asphalt won't perform thermally as well as black concrete, however. The reason asphalt always feels hotter in the sun is because it doesn't conduct heat as well as concrete. Think about it for a moment - on a sunny day, 10 am. A dark red concrete sidewalk still feels quite cool because it conducts heat relatively quickly right down to the ground. The asphalt driveway is much warmer because it can't conduct the heat away from the surface layer as quickly. It's not a thermal mass issue, because 3" of concrete is comparable in thermal mass to 3" of asphalt.

But you're right about skateboard performance!

jp_2

nice to see

it will be nice to see some data.

seems you'll have a fair amount of mass that is heating all day, i assume you will have insulation tight to the warmboard underneath.

sound like a prefect situation for an air to air exchanger if the nights are that cool. pull cool air from the north exposure in early evening.

ALH_4

Night sky

Night sky radiation cooling systems are not unheard of in the southwest. I have no first hand experience with them, but from what I understand generally water is sprinkled on the roof at night that is drained back into a storage tank and used for cooling during the day. That way it takes advantage of evaporative cooling as well as night sky radiation.

Using Warmboard in this fashion will be far less efficient than what I described above. The cooling has to pass through the roofing, the Warmboard, the pex, and into the fluid. That's (3) delta-T's that can hardly be afforded where the overall delta-T is already so small. Plus there is no evaporative component.

CC.Rob_4

another vote for concrete

I agree. The thermal conductivity of concrete is up to about twice that of asphalt.

Also, with small kids in the equation I think concrete makes more environmental/health sense as well. If you're committed to putting down 1100 sf of impervious surface (another debate) that will have significant recreational use, then I'd vote for concrete. Asphalt, even though there's certainly a lot of it in this world, is not the greatest thing for people or the environment.

Perhaps more importantly, looking down the road I could see that seal-coating would be needed to maintain the blackness of the surface for solar production, mitigate cracking, etc. Now you're talking nasty stuff loaded with PAHs (polycyclic aromatic hydrocarbons) that are toxic to people (and suspected carcinogens), animals, aquatics, etc. Not what I would give my kids as a summer play surface.

Kids are exposed to enough nasty chemicals in their everyday lives. My preference would be to minimize exposure wherever possible. If you can meet the performance needs of the system with concrete and a more environmentally-friendly colorant, I'd go that route.

For the record, I still skateboard at least once a week so definitely appreciate a fine fresh asphalt surface! But it's not as hard and fast as concrete in warm weather.

Mad Dog_2

Reasons & expectations &^ replies to queries....

#1: Need a new driveway
#2: Just always liked asphalt better
#3: This could also do snowmelt if I chose.....great
selling point on a house (not planning on moving)
#4: I have the greatest reverence for learning and
will learn a TREMENDOUS amount on this project
#5: Have lots of extra pex and materials lying around
the shop...paid for...why not use them up?
#6: Only get one chance to do this before new drive is down
#7: We will ALL Learn from this.
#8: I have the highest regard for Mark's knowledge and
experience...if he thinks it will work, that's good
enough for me.
#9: This is ALL out of MY company's pocket...we are not
getting ANY support or help from ANY manufacturers
NOR ir MarK Eatherton getting anything but
LOTS of questions from me and hopefully some good
real life data. I will try to write this off as
company R &^ D as ME suggested.
#10: I AM trying to do this on as low a budget as possible,
so, I WILL USE up what polystyrene I have, PEX etc.

Worst case: I have a snowmelt system that I turn on for
kicks or clients as we sit in my pub in the
barn sipping Hot Toddies as the snow falls

Moderate success: I picked up ALL my domestic hw ALL summer
and use hot water like its going out
of style. I pick up partial load in
spring and fall.
Best case: I pick up all my dom. hw load in spring, summer
and fall AND supplement my radiant loads in
spring and fall. Happy camper....look like
the solar driveway king of LI (ok I'll share
with Jimmy The Gent). SAVE FUEL!!!
In ALL cases...I and YOU'LL will learn a S---- load here.

To HR's question about high temp stagnation w/out a dump load: That may be true but we see that MOST snowmelt systems are already doing that anyway...is it good ? No, but how bad will it be on the pex? only time will tell. I can't get too concerned with that...I have more faith in PEX
than that. Thanks for all the input HR and all you guys.....This will be a fun journey and I am REALLY excited about it. I didn't get the "Mad DOg" moniker for nuthin'....I can sometimes do WILD things with Very little fear AFTER I think it through....I usually make sound decisions...its only PEX and life is too short....NO GUTS>>>NO SOLAR GLORY. MD

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Mad Dog!!!!!!!!

Appreciate the input Rob, but

I can't envision the kids rolling around the driveway or licking it...if they do..the've got other problems. Look, even concrete could have toxins in it and you would never know. Last, think of all the CRAP the we drive over on a daily basis...PCBS in the road, animal waste, biohazard waste, asbestos. That all comes back to your driveway...concrete or asphalt. Good insight though and I thank you. Mad Dog