Storing heat in sand?

[eXodus]

Sand can hold a lot of heat, for sure. But to do a proper job with it, you need a lot of it to make a difference. Back in the 70s and 80's, people were building passive houses with 3-4 feet of sand/gravel, etc as a heat storage medium. That was under their entire house. One of the ideas I always thought was cool was to lay rows of cement blocks on their sides, so air could pass through them like a tunnel, and then use either a small blower, or convection to cause the air to circulate through the structure.

Those are actually pretty easy concepts to increase the thermal mass.

We have been adding below grade insulation for a while in Germany. It's cheap and you get many days or weeks of buffer.

The house I had in Germany - took 4-5 days turning of the heater to cool out. But also the other way, when you are cold and turn the radiant in floor heater up a degree - took 3-4 days to take effect. Not something for people which change there temperature in their homes twice a day.

 

[Guda]

If you want to use hot water in some fashion, I'd look at a solar water panel set up.

David Poz did an experiment where he tested solar heating water vs heating water with the pv system.

The conclusion is, heating water with pv is cheaper. Only situation where those solar hot water heaters are better. Is if you have limited space.

 

[Guda]

Sand can hold a lot of heat, for sure. But to do a proper job with it, you need a lot of it to make a difference. Back in the 70s and 80's, people were building passive houses with 3-4 feet of sand/gravel, etc as a heat storage medium. That was under their entire house. One of the ideas I always thought was cool was to lay rows of cement blocks on their sides, so air could pass through them like a tunnel, and then use either a small blower, or convection to cause the air to circulate through the structure.

Thats pretty awesome

 

[SolarPrep]

Guda: I'd encourage you to look into solar hot water panels. They are actually pretty easy to set up, and they work really well, and last a long time. Water holds a tremendous amount of energy, and you can easily, and cheaply pipe it where you want the heat to end up. (Assuming you do some of the work yourself)

I converted to all radiant heat, and am setting up a bank of them right now. And, a tiny little DC pump I picked up for $10 at a thrift store. I plan to run that off PV & batteries of course!

Good luck with your project.

 

[DerpsyDoodler]

David Poz did an experiment where he tested solar heating water vs heating water with the pv system.

The conclusion is, heating water with pv is cheaper. Only situation where those solar hot water heaters are better. Is if you have limited space.

It's not clear what you're communicating here. It looks like you're saying "solar heating isn't as efficient as solar heating". Can you clarify?

I feel like this should be stated: heating water with the use of electricity is not as efficient as heating it with the sun. Is that what you're trying to communicate? Rather than convert solar to electricity, it is more prudent to have the sun directly heat the water (for the purpose of heating).

 

[Guda]

My biggest failure is communication. So I'll defer to the pro

TBH I want more that 1 water heating solution. Solar heat when I have it. Propane when not enough solar. Storing tank(s). I might do the sand tank for heating. There is that point when there is more power than battery. Pumping hot water up on top of my containers into a sand box will hold the heat for heating. Maybe I;ll do that, not sure

I was using 200gal of water as thermal mass all last winter & it was great. But when it got hot, it held the heat too late so I dumped it. Didn't really want to put it back but the cold is already here.....

This weather is fucking crazy. There, I said it

 

[DerpsyDoodler]

My biggest failure is communication. So I'll defer to the pro

TBH I want more that 1 water heating solution. Solar heat when I have it. Propane when not enough solar. Storing tank(s). I might do the sand tank for heating. There is that point when there is more power than battery. Pumping hot water up on top of my containers into a sand box will hold the heat for heating. Maybe I;ll do that, not sure

I was using 200gal of water as thermal mass all last winter & it was great. But when it got hot, it held the heat too late so I dumped it. Didn't really want to put it back but the cold is already here.....

This weather is fucking crazy. There, I said it

I think the video begs the question "what is his thermal system?" i dont know the guy and have never seen his videos. curious about what a direct comparison of a solar concentrator vs propane heating vs electric heating in different climates and different latitudes would render.

 

[time2roll]

David Poz did an experiment where he tested solar heating water vs heating water with the pv system.

The conclusion is, heating water with pv is cheaper. Only situation where those solar hot water heaters are better. Is if you have limited space.

Did he use resistance heating or a heat pump?

 

[SolarPrep]

I would hesitate to call David Poz a "pro". He is learning along the way, just like everyone else. He does appear to be a professional YouTuber who makes his living off referral fees. His videos where he carries his baby around on his back while he works on devices with lethal voltage, and lets her walk around his shop littered with dangerous tools makes me cringe.

Guda: let me save you a lot of work/time/money/ etc.....hot water can be easily made through the use of solar panels. You can build them yourself if you like, and if you are careful, they will work well and last a long time. There is a forum for that that called Build It Solar. Excellent site. Read on that site for hours, and you will learn a lot. The key to hot water is storage and insulation. If you are willing to do so, build a contained room, insulate the living crap out it, and put your equipment in it. That way, it will only add heat to the structure when you want it to. And that would be done by pumping the water. If you have PV, you should have batteries, and then you can do any of this 24/7. Just as an example, I have personally evaluated things like buying a precast concrete septic tank, and burying it outside my foundation to store large quanities of water. A local company that casts them can even add special coatings to the inside to make them perfectly watertight. They are actually very affordable, and give you a LOT of storage. I was looking at 1500 and 2000 gallon models. My plan was to insulate around the tank on all sides with rigid foam, or have someone come in and spray foam it in place. You can also consider buyilding a tank yourself, and line it with EPDM. There are limitations on that approach, whhich you can learn by doing.the research.

In-floor heat is the most efficient, if you can do it. Underfloor heat panels work great too, but are harder to do, and cost more.

If you really walk a "massive-passive", then take the time to get some help, and figure out what you really need. Don't guess. Get someone to do a heat loss calculation on your structure. If you are yet to build this, then you need to plan it correctly. Personally, if I had the right building site, I would seriously consider building a super low energy loss structure, and put PV on it.

 

[Wellbuilt]

Why not concrete ? I have a insulated slab 1400 sf 4to 41/2” thick there are pex 1/2 radiant pipe running thru it .
I’ve never used the floor heat but the house stays warm just burning my wood stove once in the morning and once at night .
The floor just absorbs the heat from the room and keeps the place warm .
I never burn wood over nite .
The radiant heat tubes work good they make hot water even in the rain in the winter .
I don’t think you need to store hot water

 

[eXodus]

I have a insulated slab 1400 sf 4to 41/2” thick

Interesting cultural difference, calling 4 inch thick concrete a "slab". In Europe that would not be sufficient for a walkway in your yard.
"Slab" begins at 10 inches thick. If you are building in frost zones in Germany we are using slabs of 50-80cm 20-30 inches.

Yes homes are more expensive there.

 

[Guda]

His videos where he carries his baby around on his back while he works on devices with lethal voltage, and lets her walk around his shop littered with dangerous tools makes me cringe.

LOL!

I have personally evaluated things like buying a precast concrete septic tank,

Thats a good idea.

Why not concrete ? I have a insulated slab 1400 sf 4to 41/2” thick there are pex 1/2 radiant pipe running thru it .
I’ve never used the floor heat but the house stays warm just burning my wood stove once in the morning and once at night .
The floor just absorbs the heat from the room and keeps the place warm .

I am. Hope I have the same effect.

in Germany we are using slabs of 50-80cm 20-30 inches.

Ouch

 

[eXodus]

LOL!


Thats a good idea.


Ouch

Different design philosophy.

Residential construction, is meant to hold up for your ancestors. There are many buildings in Europe which are hundreds or thousands of years old. So anticipated lifespan of building is at least 3 digit.

 

[SolarPrep]

eXodus: People here don't value longevity in the same way that people do in Europe and other areas of the world. We have a disposable culture. I've spent a big hunk of my life fixing problems other people created because they didn't want to invest the time or money to do things right the first time. It is so sad. I've traveled around the world for my career, and even 15 -20 years ago saw technology that people here are just starting to think is "new".

Hot water heat is a great example..most people just don't get it. I'm not saying it should be for everyone, but perhaps it would be used more if people looked at the long term cost of ownership. It is a positive sign that at least that is happening with solar.

I'm done with commenting on the topic with Guda; especially after he typed "LOL" to a comment about carrying a baby around on your back while working on dangerous equipment. I don't think it is funny, and it sends a bad message to people who might not think about safety issues.

 

[Guda]

I'm done with commenting on the topic with Guda; especially after he typed "LOL" to a comment about carrying a baby around on your back while working on dangerous equipment. I don't think it is funny, and it sends a bad message to people who might not think about safety issues.

LOL GOOD!. I believe in natural selection. I wish the worlds machines were much much more dangerous. I also think we should speed up in school zones. I personally believe that stupid people breeding is the biggest threat to wonderful peaceful world.

FYI, Laughing at a cringe is the most common response to a cringe.

I truly believe stupid people should not breed & if they do & their kids die. I am not going to feel bad. We are all going to die if stupid people are allowed to continue breeding. So..... Maybe you are not paying attention to global warming. Here let me fill you in. TOO MANY DUMB PEOPLE DOING DUMB THINGS!!!

 

[Guda]

People here don't value longevity in the same way that people do in Europe and other areas of the world. We have a disposable culture. I've spent a big hunk of my life fixing problems other people created because they didn't want to invest the time or money to do things right the first time. It is so sad. I've traveled around the world for my career, and even 15 -20 years ago saw technology that people here are just starting to think is "new".

Thats the garbage system called capitalism. Thats a system setup by & for sociopaths. All the isums are garbage because they were setup by people who know nothing, like lawyers. A new system setup by engineers is the only wat we will survive.

 

[Posplayr]

I think there is more involved that how much heat it will hold .... for instance what is the heat transfer rate as compared to water?

I think specific heat is most relevant. SH of water is 4182 J/Kg DegC
for sand it is 830 J/kg degC

Sand will get much hotter (5X as many delta DegC) containing the same amount of heat which means it will dissipate that heat much faster to the surrounding environment. Heat transfer (loss) is related to the temperature differential so.

 

[eXodus]

Thats the garbage system called capitalism.

capitalism is not the issue, there is capitalism in Europe for a few hundred years. You need a healthy market.

Cultural perception of time.

It's same with solar - People in the US didn't start installing those system got a return on Invest under 5- years. While in Europe people already jumped in at 20 year ROI.

 

[Wellbuilt]

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Interesting cultural difference, calling 4 inch thick concrete a "slab". In Europe that would not be sufficient for a walkway in your yard.
"Slab" begins at 10 inches thick. If you are building in frost zones in Germany we are using slabs of 50-80cm 20-30 inches.

Yes homes are more expensive there.

It’s not a money thing , all our slabs for radiant heat have a minim of 2” foam board on the bottom , and a max of 4” of concrete 4500 psi with glass fiber.
I allso use steel 6x6 wire so I can tie the pex tubing to it .
I use steel tubing chairs to keep the pipe in the top half of the slab .
The reason is a 4” slab with the heat tube 11/2 from the top gives the floor a fast recovery .
You can
I can run the water at 100o and it comes back @ 92o with a 200 foot loop .
My floor has 7 runs at 189 ‘ so it dosent cool much at all .
A 10” slab will not get hot enough to pass heat to the home , you would end up running the water at 120 o +
and that kills the efficiency.

 

[PVorBust]

Sometimes it is important to understand the WHY a phenomenon happens, not just that it does. Especially when applying things to other situations.

If I may, I'll reword that statement.

If you don't understand why a phenomenon happens, you can't (reliably) apply it to other situations.

A second point to remember is that if someone offers an analogy to explain a situation; the analogy doesn't prove the original statement is true and shooting holes in the analogy doesn't prove it isn't.

The analogy is just a tool to save you spending year at uni learning the math