Storing heat in sand?

[toms]

How are you going to make it cheaper than using PV/batteries/diesel generator combination to generate heat as required, or are you thinking very large scale?

 

[svetz]

If you know of any 65° to 75° PCM let me know.

C or F? I'm sure if you looked up some melting points you'd fine a number of things either way.

I'm quite sure it's physically impossible to achieve a heater greater than the source..without more work input, say, from a compressor or something.

+1


The rest are nits... while I'm certain the poster knows some readers might not....

Heat does not rise. This is a myth that comes from the fact that hot air rises.

Hot air doesn't rise either, but if separated from cooler air (e.g., hot air inside a hot-air balloon) then because hot air is is less dense it is buoyant.
Why is hot air less dense than cooler air? Gases follow (roughly) PV = nRT. So, n = PV/RT. If T changed and P and V don't change, then n must change (n is the number of molecules of gas, so as T increases n must decrease for given volume/pressure, so it is less dense).

Water can achieve any temperature...

There are limits even with increasing pressure.
Most gases will disassociate at some point into atoms, become plasma around ~3000 °C at 1 atm.

 

[Supervstech]

Quite right

I should have said, water can achieve any temperature useful for home heat storage...

 

[Guda]

Google: rocket stove mass heater
It may give you some additional ideas.

A thousand years ago in Germania massive stoves were popular. The wood burned hot and fast, heating the mass which released the heat into the room all day.

Yup. Been planing on 1, maybe 2. Plan on running a coil in that also.

Water can achieve any temperature... the thing is, without pressure, higher temp means a change in phase.
Water close to 212F holds a massive quantity of heat before becoming steam. That heat massively transfers into its surroundings when it phases back to water.
Can you design a setup to include low pressure steam?

The phase shift is why I said sand can hold more heat. I just forgot to add the phase shift to the equation. IE, heat sand to 250f in a tank water could only go to 200f ish in.

Water is better if you have the correct tank. The tank needs to deal with low pressure & stand up to the chemicals to preserve the water.

Maybe super insulate a off the shelf hot water tank. 50gal of hot water would be about a days worth. If the goal is 3 days of hot water, have 3-4 of these super insulated tanks.

 

[Guda]

Find product information, documents, videos, and installation assistance for the Rheem Marathon Thermal Storage Tank

Find product information, documents, videos, and installation assistance for the Rheem Marathon Thermal Storage Tank

www.rheem.com

 

[Bob B]

Hot air doesn't rise either, but if separated from cooler air (e.g., hot air inside a hot-air balloon) then because hot air is is less dense it is buoyant.

Sorry .... but I disagree with that ..... Hot air does rise. We depended on that all the time when designing HVAC.
A heat source at the floor placed in front of a cold window as an example. The hot air will rise and create a "curtain" of warm air. That warm air not only supplies heat to the air as it rises and mixes with the colder air, but it will block much of the radiant heat loss from objects in the space ... maybe people ... so the space feels warmer. The effects of radiant heat are very important.

A hot air balloon rises because of the difference in displacement ... much the same as a metal boat floats on water.

 

[Supervstech]

Sorry .... but I disagree with that ..... Hot air does rise. We depended on that all the time when designing HVAC.
A heat source at the floor placed in front of a cold window as an example. The hot air will rise and create a "curtain" of warm air. That warm air not only supplies heat to the air as it rises and mixes with the colder air, but it will block much of the radiant heat loss from objects in the space ... maybe people ... so the space feels warmer. The effects of radiant heat are very important.

A hot air balloon rises because of the difference in displacement ... much the same as a metal boat floats on water.

Actually, hot air does not rise… cold air falls, as it is denser than warmer air, and the cold air pushes up the less dense air.

 

[Bob B]

Actually, hot air does not rise… cold air falls, as it is denser than warmer air, and the cold air pushes up the less dense air.

Whatever the physics of it .... the result is that hot air rises.

 

[DerpsyDoodler]

Sorry .... but I disagree with that ..... Hot air does rise. We depended on that all the time when designing HVAC.
A heat source at the floor placed in front of a cold window as an example. The hot air will rise and create a "curtain" of warm air. That warm air not only supplies heat to the air as it rises and mixes with the colder air, but it will block much of the radiant heat loss from objects in the space ... maybe people ... so the space feels warmer. The effects of radiant heat are very important.

A hot air balloon rises because of the difference in displacement ... much the same as a metal boat floats on water.

Di...didn't yall just say the same thing in different ways? You both agree that hotter air ends up above colder air, right? Toma toe tomot ohhhhhh.

 

[Bob B]

Whatever the physics of it .... the result is that hot air rises.

Actually ... both may be true. The more dense cold air will fall .... and the less dense hot air will rise.

 

[Bob B]

While it's not relevant to this thread ... another interesting tidbit about water.

Cold water is more dense and falls to the bottom of a lake .... this will cause rapid cooling of the water in the fall as temperatures drop. The result is called turnover as the warmer water rises and the cold water falls.

The only reason that a lake doesn't freeze all the way to the bottom is the unique property of water that causes it to become less dense as if freezes. This causes the less dense ice to float on the surface and effectively insulate the water. If the frozen water continued to be less dense, the lake would freeze solid from the bottom up.
Pretty neat property that allows fresh water animals to survive winter ... well I guess salt water too.

 

[Supervstech]

Di...didn't yall just say the same thing in different ways? You both agree that hotter air ends up above colder air, right? Toma toe tomot ohhhhhh.

No, svetz said hot air needs to be separated from cold air like in a balloon to rise, and this is not so. Hot air all by itself will get pushed up on top of colder dense air… no separation needed.
as an HVAC contractor myself, or anyone who has ever had a multi story house can attest… cold air falls down the stairs…

 

[Supervstech]

While it's not relevant to this thread ... another interesting tidbit about water.

Cold water is more dense and falls to the bottom of a lake .... this will cause rapid cooling of the water in the fall as temperatures drop. The result is called turnover as the warmer water rises and the cold water falls.

The only reason that a lake doesn't freeze all the way to the bottom is the unique property of water that causes it to become less dense as if freezes. This causes the less dense ice to float on the surface and effectively insulate the water. If the frozen water continued to be less dense, the lake would freeze solid from the bottom up.
Pretty neat property that allows fresh water animals to survive winter.

True and false… frozen water does become less dense and float, but the reason the lake doesn’t freeze solid isn’t from insulation, it is due to higher pressure water requiring lower temps to change phase. At one atmosphere, ice freezes at 0C, as the depth increases, the phase change point similarly changes, that’s why ice on a lake at 20F will be 1” thick, and ice on a lake at -20F will be a foot thick…
Also, the ground temp is warming the lake water from below.

 

[DerpsyDoodler]

I

No, svetz said hot air needs to be separated from cold air like in a balloon to rise, and this is not so. Hot air all by itself will get pushed up on top of colder dense air… no separation needed.
as an HVAC contractor myself, or anyone who has ever had a multi story house can attest… cold air falls down the stairs…

Oh I don't disagree. However, I wasn't talking about svetz. I was talking about your and Bob's back and forth.

 

[Supervstech]

I

Oh I don't disagree. However, I wasn't talking about svetz. I was talking about your and Bob's back and forth.

Ahh. Then you quoted the wrong passage.
yes, he and I were tomatoe tomatah semantic posting…

 

[Bob B]

True and false… frozen water does become less dense and float, but the reason the lake doesn’t freeze solid isn’t from insulation, it is due to higher pressure water requiring lower temps to change phase. At one atmosphere, ice freezes at 0C, as the depth increases, the phase change point similarly changes, that’s why ice on a lake at 20F will be 1” thick, and ice on a lake at -20F will be a foot thick…
Also, the ground temp is warming the lake water from below.

.... but .... if the colder water continued to fall instead of suddenly reversing it's properties and starting to becoming less dense .... the cold water would continue falling to the bottom and freeze the lake from the bottom up.

 

[Supervstech]

I look at the heat rises misunderstanding and I always think about drinking straws…

odd I know… I am indeed an off thinker.

A drinking straw functions because high pressure air pushed the beverage up the straw. You don’t suck the drink up the straw, you reduce the air pressure inside the straw, and the atmosphere pushes it into your mouth.

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

 

[DerpsyDoodler]

Except

I look at the heat rises misunderstanding and I always think about drinking straws…

odd I know… I am indeed an off thinker.

A drinking straw functions because high pressure air pushed the beverage up the straw. You don’t suck the drink up the straw, you reduce the air pressure inside the straw, and the atmosphere pushes it into your mouth.

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

that's what sucking is/does (how it works). It's called creating a vacuum. It is an unnatural phenomena that would not have occurred had you not taken the necessary action to make it happen.

Though in comparison to conventional vs unconventional current flow, its not exactly a bad thing to think outside the box.

 

[Supervstech]

.... but .... if the colder water continued to fall instead of suddenly reversing it's properties and starting to becoming less dense .... the cold water would continue falling to the bottom and freeze the lake from the bottom up.

Hmmm. I bet it would. Good point.

remember, cold water isn’t a lot denser, just slightly less dense, and the ground below the lake is warming the falling water as well. It is the cold air mass exceeding the water current’s ability to move the heat loss that allows the phase change on the surface.

 

[Bob B]

Snippet from a scientific article.

Same reason Eskimos make an igloo.