Struggling with storage

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Realmaple

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Apr 21, 2014
1
Ontario
I'm not really set up for a large volume of hot water storage right now (maybe someday).

Along the lines of a heated slab, has anyone ever tried heating a stack of concrete blocks?
In the basement, close to an existing overhead cold air return, elevate a 3' x 5' x 10' stack of blocks with a water to air heat exchanger underneath.
The stack would weigh about 15000#. If its temp could be raised by 10deg F for example, it would provide 150,000 btu of storage.
Just not sure at what rate a copper coil gives off heat or at what rate the concrete would absorb it.
(The whole system would not be suitable for DHW, I know).

Just wondered if anyone has tried such a thing?
 
It would work to an extent. You may over heat the house trying to heat the bricks. Then you cant control how fast the heat comes out, may not be enough to do much, or if it's mild out it may come out to fast and over heat the house.
 
If I had a 3'x5'x10' area I would be looking to fill that area with some type of insulated water vessel,not only would it store more heat but would also be more controllable.
 
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I believe the specific heat of blocks is about .2, so the effective heat capacity of the blocks is .2 x 15,000 lbs x 10F. Most things other than water have a specific heat that is low and usually hangs around .2 while water is 1.

If you are going to stack all these blocks, why not build a tank?
 
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How you gone move these heated blocks; 15,000 Lbs of them.
Seems a lot of work each time moving them back to storage, heat them up and move them to the living room.
I think you will be way better of heating and moving water.
 
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tom in maine said:
I believe the specific heat of blocks is about .2, so the effective heat capacity of the blocks is .2 x 15,000 lbs x 10F. Most things other than water have a specific heat that is low and usually hangs around .2 while water is 1.

If you are going to stack all these blocks, why not build a tank?
Click to expand...


^^
This is absolutely correct. You would be able to store only 20% of the heat compared to the same weight of water.
This idea needs to go in the "circular file".

Apply this to the concept of a masonry heater and you have a clue as to their performance also.
 
heaterman said:
^^
This is absolutely correct. You would be able to store only 20% of the heat compared to the same weight of water.
This idea needs to go in the "circular file".

Apply this to the concept of a masonry heater and you have a clue as to their performance also.
Click to expand...
The thing to remember is that many bits of a masonry heater can run up to the thousand degree mark or higher. where your specific heat is low, the delta T is quite large.
they also are small space heaters mostly. a decent size masonry heater holds 50 lbs of wood per load. compare that to the 80-150 lbs that most gasifiers hold for a 3-4 hour burn and you have an idea of the output (or at least the input)
 
Another problem with masonry as a storage medium is that it's slow to absorb heat an also slow to release heat energy which is wasteful in the heating phase and inadequate in the release phase which would require more supplemental heat. Eutectic salts would be out of the question and too expensive with the temperatures you would be working with.
 
The numbers are tough on phase change materials. They do give you amazing storage for the temperature where they change phase, but when compared to water for the whole range of temps that water can cover, it is hard to justify.
We looked into them since some competitors were making big claims. I found that you need to purchase in raw form in huge quantities to get it economically. You then need to interface it with a heat transfer medium like water.
It can be done and is intriguing. The companies we saw were using stainless steel balls filled with pcm's that were floating in water.
The balls were from India. (A joke somewhere in here?!)

After the initial jump in storage capacity from the actual phase change, the specific heat of the material is a fair bit lower than water so the cumulative performance tends to be equal or lower than water, assuming you heat a tank from say, 120-180F and can use those temps.

Not dissing the idea, but be careful to analyze the whole temperature range you need storage for.
I would love to find something that would work reasonably.
 
tom in maine said:
The numbers are tough on phase change materials. They do give you amazing storage for the temperature where they change phase, but when compared to water for the whole range of temps that water can cover, it is hard to justify.
We looked into them since some competitors were making big claims. I found that you need to purchase in raw form in huge quantities to get it economically. You then need to interface it with a heat transfer medium like water.
It can be done and is intriguing. The companies we saw were using stainless steel balls filled with pcm's that were floating in water.
The balls were from India. (A joke somewhere in here?!)

After the initial jump in storage capacity from the actual phase change, the specific heat of the material is a fair bit lower than water so the cumulative performance tends to be equal or lower than water, assuming you heat a tank from say, 120-180F and can use those temps.

Not dissing the idea, but be careful to analyze the whole temperature range you need storage for.
I would love to find something that would work reasonably.
Click to expand...
also hard to beat the price, toxicity of water. .....
 
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