Sand battery - thermal mass proto type.

Today I decided to test out making a sand battery. I had this old pot with a hole in the bottom, I then took two cans cut out the bottom on those and put inside the pot over the hole then filled the pot with sand fir the first layer. Second layer I cut down the can a bit so it would fit in the pot and I laid in another layer of sand. For this first go around I had temps at the bottom at 325 degrees and at the top at 165 degrees.... After this I brought is inside put a welding blanket inside the cooler and put the pot inside.... I noticed a large amount of moisture building up inside the cooler, which figures as the sand I used was from outside. I am formulating how I could improve the heating of the sand was a fun experiment.

Damp sand will absorb and transmit heat more readily than it will when dried (vapor/steam migration), so unless you expect to use a water/sand hybrid, you will need to dry it out before making meaningful tests for function.

Glenn Herbert wrote:Damp sand will absorb and transmit heat more readily than it will when dried (vapor/steam migration), so unless you expect to use a water/sand hybrid, you will need to dry it out before making meaningful tests for function.

You are on target.

Other videos I have seen have said the same thing.    

I would expect a few cycles of this should get rid of most of the moisture,   but I do have some sand that i have dried that I could use.

Thank you for your input,     this is the first prototype, and it is teaching me many things  with just building this one.

After I dried 8 quarts of sand I put in a bread machine heating element.     I am getting much higher temps.       Now I am looking to move on to a 100 gal propane cylinder filled with sand.


To heat I use 4 solar panels in series to power the bread machine coil.

Today,  I switched to a Stove burner, put it into the sand, got 500 - 700 deg with the sand.    

I found this video with a sand battery build, I am seriously impressed !

Thank you for sharing that video.  Amazing how much waste heat was reclaimed via that simple system.  Though to be sure, water heaters aren't make like that in my neck of the woods.  

Update:

Waterglass  + Sand =   Chimney


I was thinking the other day how could I make a chimney that would stand up against the 900 + temps I am reaching with the various rocket stoves I have been making. Then it hit me, I could combine water glass with sand and use the same material used for make metal moulds.... First test worked like a champ sand was cured with the co2 created with the burning of wood. So I could stack pots like this for a chimney that should be most durable, and insulated thus creating a much greater draw. I first packed sand into the pan around the PVC, removed the PVC, then I carved out about 1 inch of sand around the tube, then filled that tube with the pvc in the inside with the water glass mixture.

First prototype looks to work great.     I will add more pans.

So I have I have built a solar water heater with pex  as DesertSun02 on youtube has built..      

I have combined this with 4  260 watt solar panels hooked directly to the hot water heating coil ( no battery, no inverter ),   and with my ghetto insulated 55 gal tank filled with 40 gal of water I was able to raise the temp of 40 gal of water to 112 deg F yesterday.       This morning it was at 100 deg F   so that means my ghetto insulation is doing it's job.


Now I can take a very long hot shower all powered by the sun!


Now this was the ground work I needed to lay for my idea.....

My idea is to take  the pex heater and the coil heater and heat the water and using a heat exchange made with pex store this heat in a sand battery.      

My thought is that once charged to say 180 degrees, I can run cold water thru  that heat exchange with the heated sand and get hot water out for showers....       In theory...    Only testing will prove this out.

Mart Hale wrote:So I have I have built a solar water heater with pex  as DesertSun02 on youtube has built..      

I have combined this with 4  260 watt solar panels hooked directly to the hot water heating coil ( no battery, no inverter ),   and with my ghetto insulated 55 gal tank filled with 40 gal of water I was able to raise the temp of 40 gal of water to 112 deg F yesterday.       This morning it was at 100 deg F   so that means my ghetto insulation is doing it's job.


Now I can take a very long hot shower all powered by the sun!


Now this was the ground work I needed to lay for my idea.....

My idea is to take  the pex heater and the coil heater and heat the water and using a heat exchange made with pex store this heat in a sand battery.      

My thought is that once charged to say 180 degrees, I can run cold water thru  that heat exchange with the heated sand and get hot water out for showers....       In theory...    Only testing will prove this out.

So... I have to point out that those 4 250 watt solar panels could raise 10 gallongs on water to 150-170 degrees f in an hour...

David Baillie wrote:

Mart Hale wrote:So I have I have built a solar water heater with pex  as DesertSun02 on youtube has built..      

I have combined this with 4  260 watt solar panels hooked directly to the hot water heating coil ( no battery, no inverter ),   and with my ghetto insulated 55 gal tank filled with 40 gal of water I was able to raise the temp of 40 gal of water to 112 deg F yesterday.       This morning it was at 100 deg F   so that means my ghetto insulation is doing it's job.


Now I can take a very long hot shower all powered by the sun!


Now this was the ground work I needed to lay for my idea.....

My idea is to take  the pex heater and the coil heater and heat the water and using a heat exchange made with pex store this heat in a sand battery.      

My thought is that once charged to say 180 degrees, I can run cold water thru  that heat exchange with the heated sand and get hot water out for showers....       In theory...    Only testing will prove this out.

So... I have to point out that those 4 250 watt solar panels could raise 10 gallongs on water to 150-170 degrees f in an hour...

Yes that sounds reasonable, unless you have a cloudy day.         I  am glad to see temps that are in a good warm shower range,    I am thinking of lowering the water level to see how high a temp I can get at 20 gallons.

Thomas Tipton wrote:Thank you for sharing that video.  Amazing how much waste heat was reclaimed via that simple system.  Though to be sure, water heaters aren't make like that in my neck of the woods.  

Where I live natural gas water heaters have a central chimney with a spiral metal plate that slows the exhaust gasses.
No spiral heat exchanger, but made to transfer heat from exhaust to water.
It just now occurred to me that you could cap that central chimney and add a plunger tube to it.

William.  Could you elaborate a little more on what you would do with said "Plunger Tube" and how that would work in the water heater tank.

I have such a tank plumbed with threaded fittings at the top and bottom of the "Central Chimney" that I intend to use for the solar collector side of a solar thermal hot water heater.  In which case it would radiate the heat into the 50 gallons of domestic water in the outer jacket.  What are you thinking???

I don't think a plunger tube would work in a gas water heater conversion (to RMH power); the central flue is already smallish and trying to fit a plunger as well would choke off airflow too much.  The hot gases would have to go up and back down to reach the plunger inlet. Given surface layer effects, this would allow only a tiny amount of airflow.

If you were thinking of using hot water flowing through the original flue, considering the spiral vanes I think it would work fine to just run it straight (spiraling) through from top to bottom, heating the contained water without mixing it with the solar collector fluid.

In the midst of testing solar water heating I became very impressed with heating the 40 gal of water with 4 solar panels hooked directly to a hot water heater element ( no battery, no inverter ).

I decided to move down to 20 gal of water, and so far this is the climb in temp in F.

Matching resistance in ohms of the coil or getting close makes a HUGE difference in output.

I was able to raise the 40 gal up to over 150 degrees with Solar +  Pex,  but this I believe destroyed my water pump for some reason.

So...    Since the solar water heating is working so well I have moved the tank next to my bathroom window where I will heat the water with solar, then pump this water inside for a LONG LONG shower.......           Science does pay back ;-)

A "plunger tube" is a a flue pipe that is run from the top of a bell, through the interior, to a point near the bottom of the bell.
A bell refers to a enclosed space where hot gasses (usually products of combustion ) are exhausted and allowed to stratify, the coolest gases falling to the bottom , the hottest rising to the top.
In a bell, the plunger tube is one way to allow gasses to escape.
You could also run a flue out of the bottom or side of the bell.
I think a plunger tube will heat up faster, thereby drawing better and it allows a design that doesn't pierce the sides or bottom of the bell.

Glenn, you are absolutely correct, most of the water heaters I have seen use a 4" diameter flue. which would leave very little space for a plunger tube.
That being said, I've only worked with water heaters in the 40-50 gallon range.
I am speculating that the water heaters in the 80-120 gallon range might have substantially bigger flues, allowing space for a plunger tube.
I am also curious as to how a tiny flue might perform inside a 4" diameter space.
EMT conduit could be pressed into service, or chain link fence  top rail.
I have found that my 3(?) gallon TLUD performs quite well when the 6" chimney is necked down to 4".
Inspired by Permaculture Playground  Carbon Conscious Creations I have built even smaller diameter Tluds.
The way a Tlud burns makes me think they can deal with more restriction than rocket stoves:

https://youtube.com/shorts/HDebxvSQlkU?feature=share


Thomas, I 'm not sure I am picturing what you are describing, but from what I'm getting, a plunger tube would not serve your purposes.

Progress so far,

I am now doing test with insulation combined with a sand battery.      I am using a single 260 Watt solar panel hooked to some restive heaters in the sand,  inside 2 HUGE HUGE 4 foot cubed  bags with chopped up styro foam  inside them.

Last night the temp  went from 150 deg F   to 85 deg  F    after 12 hours......            Outside temp was 65 deg,    I believe starting 20 degr  higher should raise the initial temp up each day I have  the sand stored in this much insulation.       I need to  improve this setup so I can have this setup and not need to move it because of rain...


I am starting to see that  this   thermal cooker /  sand cob oven ( in a sense of it's thermal mass )     could ramp up heat over time over a few days building on the heat of the days before...         I want to document  this, but my wifi thermometer  can only go up to 200 deg :(  

But I am glad to be making progress,  I may just put a tarp over the setup and put down cement blocks so I can run this thru rainy days.

And more progress...

In order to have a heat source for my sand battery, I have been perfecting my solar heat collector.

I have taken a design by Desert Sun on youtube with painting pex pipe black with mirrors on the pex,  and using a circulating pump  I have been successful in raising the temp of a 5 gal bucket from 80 deg to 132 in  5 hours time.      This has worked great for me to have a nice hot shower.

The next leg on this journey is to take this heat  and put it in dry sand thermal mass, and then insulate this.     I am curious how long will the heat stay in the sand battery, and what is the right amount of  sand to pex pipe ratio ?

If nothing else I am getting hot showers for the cost of running a pump for 5 hours on a sunny day, the pump pulls 50 watts of power so this is an excellent capture of heat from  80 degrees to 132 in 5 hours for very little electricity.

Free hot showers are wonderful   :-)

I have dried several 5 gal buckets of sand in my rocket oven wet sand is not very good at storing heat.



I now have built a solar hot water heater able to take 5 gal of water at 80 deg to 132 deg in 5 hours.



Now I have put 100 foot of pex into a black container, connected to the solar hot water heater and pump I am now re circulating the solar heated water thru the sand. I hope to use the sand as a battery ( like a hot water heater ) to capture the heat for later use. I have covered the sand with a bag of loose styrofoam, and put some insulation underneath. Finally I can get some data on what this sand battery can do.

Mart Hale wrote:I have dried several 5 gal buckets of sand in my rocket oven wet sand is not very good at storing heat.



I now have built a solar hot water heater able to take 5 gal of water at 80 deg to 132 deg in 5 hours.



Now I have put 100 foot of pex into a black container, connected to the solar hot water heater and pump I am now re circulating the solar heated water thru the sand. I hope to use the sand as a battery ( like a hot water heater ) to capture the heat for later use. I have covered the sand with a bag of loose styrofoam, and put some insulation underneath. Finally I can get some data on what this sand battery can do.

So the math goes roughly like this and pardon my imperial I don't use it much...
1btu per degree F per pound of water 5gallons= approx 40lbs So 40 btu to raise it 1 degree F so 40 btu x 52 degrees = 2080 BTU rise is 5 hours. Translated that is 2080 BTU/3.41 = 610watts of heating  from your solar array... You used 250 watts of electricity for the circulator motor though so net gain is down to 360 watts. Now conclusions are up to you of course.  It does illustrate well why solar thermal kind of went out of fashion once the price of solar electric panels dropped though. Using the 250 watt surplus panel you already have you could have accomplished the same thing in 2.44 hours plus some losses so call it 3 hours even with a 24 volt heating element and a 24 volt relay
cheers,  David

Your math does add up pretty close...    But I am not sure about what you think the inputs are...   nor do you understand the extra losses I have in this system as I gave a very basic overveiw.

The input was 50 watts of power for the pump for 5 hours.  (excluding the solar heater input )           So that would be 250 watt hours of input power, to get 610 watt hours of  heat output.    


What is not included in this equation is the loss I am getting from a 5 gal bucket that is not insulated  at all,  nor is it including that I have a 100 foot of pex  also attached that is not insulated  also adding heat loss.     Once that is in the sand battery and fully insulated it should greatly help this equation.


So, I don't think you are comparing apples to apples...         To be fair, I have not fully documented the full setup.......  so hard to follow what I am doing....   but your math is close.....






>So the math goes roughly like this and pardon my imperial I don't use it much...
>1btu per degree F per pound of water 5gallons= approx 40lbs So 40 btu to raise it 1 degree F so 40 btu x 52 degrees = 2080 BTU rise is 5 hours. Translated that is 2080 >BTU/3.41 = 610watts of heating  from your solar array... You used 250 watts of electricity for the circulator motor though so net gain is down to 360 watts. Now >conclusions >are up to you of course.  It does illustrate well why solar thermal kind of went out of fashion once the price of solar electric panels dropped though. Using >the 250 watt >surplus panel you already have you could have accomplished the same thing in 2.44 hours plus some losses so call it 3 hours even with a 24 volt heating >element and a 24 >volt relay
>cheers,  David

I gave this some more thought.....

There are 200 feet of pex line,   100 feet of pex line holds .9 gal    so I have 1.8  gal of water in the pex line that is also heated.....

So revised figures.

250 watt hours in,    810 watt hours out,    with much loss because no insulation.....

I think I can bring down the 250 watt hours in, by turning on the pump every 10 min, then shutting it off every 10 min....         It would be interesting to see  how this would affect the temp rise....    or do ever 30 min.... off 10 min on.

Mart Hale wrote:I think I can bring down the 250 watt hours in, by turning on the pump every 10 min, then shutting it off every 10 min....         It would be interesting to see  how this would affect the temp rise....    or do ever 30 min.... off 10 min on.

you could do a motor speed controller to cut wattage but maintain some flow. Might be safer.

Setup yesterday:

100 foot of Pex painted black thin plastic coating. mirrors.

100 foot of pex in sand battery     About 4    5-gal buckets of sand.

Reticulation pump    pulling 50 watts.

5 gal bucket  filled with  2 gal of water.


Yesterday this was my setup....         and I reached 137 degree water temp....      

Today I replaced the 5 gal bucket with 1 gal of water inside  a solar vacuum tube  cooker...          So instead of getting neg energy from the un insulated bucket, now I will be getting more heat....    less water in the system now so temps should climb quicker.

This system is not closed so no danger of steam ..... no "BOOM SQUISH"   events planned   ;-)

I am curious to see how changing the bucket to  solar cooker which is vacuum insulated  will work out.....

Today's results...

New Setup:

100 foot of pex painted black thin plastic coating. mirrors.

100 foot of pex in sand battery     About 4    5-gal buckets of sand.

Recirculating pump   pulling 50 watts.

1 gal of water in vacuum tube.

-----------------------------------------------------------------------------

Setup hit a much higher temp -> 167 degrees,   I shut down at 2  PM because there is a storm moving in.

So with less water, I am getting less thermal storage that I can measure....        

I was thinking that I should take a 5 gal bucket  fill with water, take a temp,    then recirculate that water in my sand batter to get an idea of how much heat is stored there.      

I am now wondering what if I tried this with 10 gallons of water instead of 5 gal?     I imagine there is an optimal amount of water that I could harvest the most amount of thermal energy with...

Looking back at the data I collected that last couple of days.

I have a sand battery with 4 - 5    five gal  buckets worth of sand in the battery.

The temps range from 107 deg  to  132 degrees.       This impresses me for the amount of sand that is in the battery, and the length of hours it takes for it to cool down.


I believe this could be made into a solar powered thermal cooker by removing 1/2 of the sand from the battery I would be in the range of cooking food..


If I use this setup as it is,  I could  use this to create ideal temps for making methane,  or make alcohol just by adding or removing sand.       Or   perhaps a germination chamber for getting seeds started  by adding a few more buckets of sand.....


I plan on adding more insulation to the pex lines, and check for where I am getting heat loss in this setup.           A bit more tweaking and i should have a sand battery hot water heater that I can take a hot shower in the morning from the heat stored from the previous day.           The temp ranges I am seeing is encouraging me that I am on the right path.

Now that I have a few days of data, I am now getting a good idea of what the sand battery can do over cloudy days.


Today I am upping the game by putting a hot water heater element in a metal bucket in the sand with ceramic blocks to prevent shorts.      I have hooked up 2   260 watt panels to this heating element and I will watch the temp rise of the sand closely.          I hope to bring the temp up to 170 deg since I am starting at a temp of 100 degree I believe that should be doable.       I now have approx five 5 gal   buckets of sand in the battery.       I am very curious how this will turn out.

Well.. I switched from having hot water heat the sand to just using a hot water heater element in the sand to heat about 5 five gal buckets of sand.....

Well the temp is now staying between 140 to 153 deg F I have not had a clear sunny day yet it has been mostly cloudy days and it is keeping this temp with two used 260 Watt panels in series. ( they normally give 220 watts of power each )

I am amazed that I have that much mass at that heat level with two panels on cloudy days, when I get a sunny day I will then test extracting heat with the pex pipe I have in the sand..... But for it to keep above 140 degree temps for over 24 hours is very very impressive to me on cloudy days...