koti

Black 2.0 paint + water exchanger for roof tops.

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Posted (edited)

So say you live in a house in a cold sunny place like deep Russia or Canada or Alaska. Do you think it would make sense from the engineering and cost saving point of view to create a thin, flat water container to place as the house roof top, paint it with Black 2.0 paint which is extremely black so it should absorb a really big amount of heat from the sun which would heat up the water in the roof top container and distribute it through a pipe system into the household? It should be a fairly cheap system, just an aluminium water container, bunch of pipes running into the house and a simple water pump...plus lots of that black 2.0 paint. Anyone know how would this do in real life efficiency wise? Theres a bunch of videos on youtube showing how the paint looks...I thought of this while having a smoke on my balcony barefoot in the mid day full sun - my balcony floor tiles are dark grey color and I had to put some flip flops on as my feet couldn’t stand the heat. Yeah I know, its a simple silly idea and I bet Im not the first one to come up with it. Still I wonder how efficient this kind of system would be? Imagine a how much heat could be generated when putting up a system like that somewhere high in the mountains where the air is thinner. 

Edited by koti

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Hi.

In real life efficiencywise, the contraption has to be shielded from cold wind to diminish heat losses.  In cold climate real world,  should be under a clear film or glass.

In real world, this is much convenient dollarwise than an aluminium container.  Paint the HDPE pipe even blacker if you prefer, but the blacker coating will not be as effective as protecting from wind, which this is not :

image.png.1ae0fa4958350b2160cb4c7756260853.png

And much gentler to any roof by spreading the weight in a large area.  Low profile, and the volume the hose contains can be sustantial on larger pipes..

 

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23 minutes ago, Externet said:

Hi.

In real life efficiencywise, the contraption has to be shielded from cold wind to diminish heat losses.  In cold climate real world,  should be under a clear film or glass.

In real world, this is much convenient dollarwise than an aluminium container.  Paint the HDPE pipe even blacker if you prefer, but the blacker coating will not be as effective as protecting from wind, which this is not :

 

And much gentler to any roof by spreading the weight in a large area.  Low profile, and the volume the hose contains can be sustantial on larger pipes..

 

I was thinking about a container with dimentions like 1000cm x 300cm x 10cm filled with water and painted with pitch black color. Or any other size container but a thin one so the pump could exchange the water (or some other more efficient fluid than water) failry quickly. The wind factor is something unavoidable so there will be heat loss obviously, plus the paint will surely fade out some over time. Is this something someone sells or it doesn't make sense efficiency wise? I would presume that if this was worth the effort someone would sell it since its such a simple idea.

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22 minutes ago, koti said:

I was thinking about a container with dimentions like 1000cm x 300cm x 10cm filled with water and painted with pitch black color. Or any other size container but a thin one so the pump could exchange the water (or some other more efficient fluid than water) failry quickly. The wind factor is something unavoidable so there will be heat loss obviously, plus the paint will surely fade out some over time. Is this something someone sells or it doesn't make sense efficiency wise? I would presume that if this was worth the effort someone would sell it since its such a simple idea.

search for 'rooftop solar water heater'

There are passive and active systems

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I see not much opportunity as business selling the idea as anyone can do the coil for laughable amounts of $ compared t much smaller, probably less efficient and costly 'professional' methods from ripoffers.

This 'sophisticated' much smaller unit adds a second ripoff for installation: ----> https://www.amazon.com/Duda-Solar-Collector-Evacuated-Certified/dp/B00HP846KK?ref_=fsclp_pl_dp_5

The pipe spiral has a shine from its extrusion at fabrication, which sand blasting/sanding can turn to matte to save on fancy paints.  The flow can be in series or parallel to existing water heater with no added pump.  For spas, pools, household usage.

Get a quote for the aluminium container you describe and compare costs.

Includes many unnecesarily elaborated methods with unrealistic massive amounts of copper and soldering :

----> https://duckduckgo.com/?q=pipe+coil+roof+water+heater&t=canonical&ia=images&iax=images

 

 

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You would have to drain the system and 'winterize' it when temperatures get to below freezing, or you'll be testing the waterproofing of your roof shingles.
We don't seem to get much Spring and Fall anymore ( when such a system would be effective ); just freezing Winters that go directly to scorching Summers.

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21 minutes ago, Externet said:

 The pipe spiral has a shine from its extrusion at fabrication, which sand blasting/sanding can turn to matte to save on fancy paints.  

How much will that gain you?   

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Guessing around 2% more heat captured, but sanding mentioned to compare with the intention on applying fancy paint.

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1 hour ago, Externet said:

Guessing around 2% more heat captured, but sanding mentioned to compare with the intention on applying fancy paint.

That's not much, considering the emissivity is low to begin with. Just because the material isn't shiny doesn't mean it's not reflecting a lot of light. It can be that it's just a diffuse reflection.  

Whereas painting it with vantablack makes almost 100% absorptive. Going from perhaps 20% absorption to ~100%

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2 hours ago, koti said:

I was thinking about a container with dimentions like 1000cm x 300cm x 10cm filled with water and painted with pitch black color.

No. It should be long thin black pipe, like Externet showed on the photo. Pipe has larger area than simple box.

Are you sure your numbers? It is 3000 L = 3 tons of water.. That's quite a lot of mass on the roof which was not designed to hold 3 tons...

What will be usage of such amount of water anyway? Single person (full) bath per day is 120 L of water heated to 32-37 C.. 3000 L / 120 L = 25 peoples baths per day. Way too much for single family little house.

 

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Posted (edited)
3 hours ago, MigL said:

You would have to drain the system and 'winterize' it when temperatures get to below freezing, or you'll be testing the waterproofing of your roof shingles.
We don't seem to get much Spring and Fall anymore ( when such a system would be effective ); just freezing Winters that go directly to scorching Summers.

Thats why I anticipated to use some other, more efficient liquid :)

3 hours ago, Externet said:

Guessing around 2% more heat captured, but sanding mentioned to compare with the intention on applying fancy paint.

2% more by sanding down metal compared to pitch black paint? I dont get it.

1 hour ago, Sensei said:

No. It should be long thin black pipe, like Externet showed on the photo. Pipe has larger area than simple box.

Are you sure your numbers? It is 3000 L = 3 tons of water.. That's quite a lot of mass on the roof which was not designed to hold 3 tons...

What will be usage of such amount of water anyway? Single person (full) bath per day is 120 L of water heated to 32-37 C.. 3000 L / 120 L = 25 peoples baths per day. Way too much for single family little house.

 

The „box” I gave dimentions to is a long, thin, flat rooftop container, could wven make it 6cm instead of 10cm but the pump would have to do more work. I agree that a long, spiral shaped hose would do aproximately the same job (despite aluminum being a better heat conductor) but thats not the main issue here.

The reason for so much water in such a big container is to keep you warm inside your house at -45C outside throughout most of the year.

Edited by koti

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6 hours ago, swansont said:

Going from perhaps 20% absorption to ~100%

Given that the stuff is "black" the absorption of light is probably well over 50% so you can't do better than doubling the efficiency (on that score). Using two sets of pipe would get twice the energy.

What's the price of vantablack compared to another hundred yards of pipe??

You need to put a box with double glazing over the pipes to keep them warm.

I gather the usual use of such a system is to pre heat water,  before a more conventional system gets it hot enough to shower with or whatever. You might be able to use it as a source for a heat pump.

In any event, you have a choice of problems, either clean water runs through the pipe in which case it will freeze in winter or you have antifreeze in the pipe and some sort of heat exchanger which adds enormously to the complexity


 

A big advantage to plastic pipe is that it doesn't have any joints to leak. Good luck to anyone constructing a closed box which will hold water for a few years.

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9 minutes ago, John Cuthber said:

...Good luck to anyone constructing a closed box which will hold water for a few years.

I’m decent at welding aluminium but I get the point.

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12 hours ago, koti said:

2% more by sanding down metal compared to pitch black paint? I dont get it.

Sanding black plastic, not metal.

But I think using a pipe that's 2% longer would be easier.

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8 hours ago, John Cuthber said:

Sanding black plastic, not metal.

I missed that we were talking about plastic earlier. I was thinking metal in my post.

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Hi Koti.

This popped up, may be of interest ----> https://www.youtube.com/watch?v=3fnekWvlEp4

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1 hour ago, Externet said:

Hi Koti.

This popped up, may be of interest ----> https://www.youtube.com/watch?v=3fnekWvlEp4

Thats some pretty neat efficiency comparisons. I wonder how much the black 2.0 paint would add, probably a few percent not more. Still a viable idea for house heating...that is if youre willing to use miles of hose :D 

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2 hours ago, koti said:

...if youre willing to use miles of hose :D 

It is all about insulation. For storage of large masses of water, 

On 7/1/2019 at 1:29 PM, koti said:

... to keep you warm inside your house at -45C outside throughout most of the year.

A book I have suggests drums (a couple of dozens of them) to keep the warm water.  Stones could be used too. Circulation pump then would be convenient...

 

 

P1010823.JPG

P1010824.JPG

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12 minutes ago, Externet said:

It is all about insulation. For storage of large masses of water, 

A book I have suggests drums (a couple of dozens of them) to keep the warm water.  Stones could be used too. Circulation pump then would be convenient...

 

 

P1010823.JPG

P1010824.JPG

Yep, storage of gathered heat would be an issue in really cold areas so a circulation pump would probably be a must. Thanks for the book tips.

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