I'm in the middle of building a new home, and I have a concrete block foundation for a masonry heater that I would like to fill with sand and use as passive heat storage in winter and passive cooling in the summer.

I plan to build a fake chimney on the side of the masonry heater, and pull air down with a fan from the peak of the ceiling, through the sand and out in the basement.  Return vents with fans will pull push passively cooled basement air back up at either end of a long thin bungalow.  In winter, this should heat up the sand during the day and release it at night.  In the summer, I am preparing to plumb the house water system to run through the same sand, so that all water drawn will circulate 46 degree well water through the sand before going to the rest of the house.  The air then coming down from the peak of the main floor in summer will be cooled by the cool sand. 

I have calculated out the heat storage ability and it seems like it will work, with dehumidification added in, at 1 gallon per minute of flow for 6 hours a day.  ( The house is on an old quarry with a pond on site for discharge.)

My question is, what materials would work best and does anyone know how to calculate if enough heat can transfer into the water on the way by.

Thanks in advance.

STeven Kayser

Oh man, IMHO sand is the wrongest medium for this. You want river-gravel, of about 3/4".

Quantum, why do you say sand is wrong?

- Sand is a poor holder of heat;
- Sand will pack down and be impossible to blow air through;
- When sand gets wet it is impossible to blow air through.

For storing heat from air you want ~3/4" washed river gravel, and for storing heat from hydronic loops you want hard rock crushed to ~1/4" or most efficient, water.

Steven,

I like the idea. I have thought about similar things myself. But, I think Quantum is right.

If you really are thinking about blowing through the sand that is. The sand will pack down with time and the no longer be porous enough. I also have some reservations about humidity and the river rock. This of course depends on the typical levels of humidity where you are building. Where I live the summer humidity levels are way too high IMHO.

On the other hand... If you are piping the air through the sand it might work the way you want. I don't know the math to do the kinds of calculations you need to find the optimal amount of pipe surface area to sand mass. I'm sure there are others on this forum that do. There is also the questions of what material to use for the air ducting/piping. If it was just water then it would be simple, PEX-AL-PEX.

Quantum is also right about water being a much better medium for heat storage. I may not know the math but I have done a lot of reading, and everyone seems to agree that water can hold more than anything else. The only down side seems to be that it also releases it faster than many. I'm looking for ways to integrate to same kinds of systems into my own new home.

I'd have to go back and find my hen scratching that made it clear to myself this is the case. I was considering a rock pile in a bath of water for a heat storage system until I worked out the numbers. Even though rock is much heavier than water, the specific heat, i.e., Btus required to raise one pound of material 1 degree F, is so much less than water that on a volume basis water will hold much more heat. I'm thinking is something like twice as much per cu foot.