Thermal Conductivity and Retention

If you do not intend to save at too high temperatures water with its highest thermal capacity in Joule/Kkg will lead to the lowest volume for same amount of saved energy and thus to the lowest area to be insulated against thermal losses. The depth should be optimized so that the air temperature will have the lowest influence.

The resrvoir should approximate a sphere since this volume has the lowest lateral area.

A Friend of mine put that tubing in his new kitchen floor under the tile and in the bathrooms. He has a tank setting near the exhaust of a 5 hp briggs engine outside in a small building. He replaced the exhaust with a 3/4 piece of pipe. The tubing is run inside 1 in. pvc pipe to the house. He has an anti- freeze mix in the lines and uses a small pump that runs off the 5 hp briggs to move the heated mix. He says it works. He rigged a remote starter in his laundry room for the ejngine.

This in the Mountains of N.C. 70 miles from Ashville near the ski resort.

I intend to collect heat from sol and store under ground to provide both domestic heated water and hot water from my ancient radiators too during winter. I'm hopeful to obtain the material specks and thermal mass requirements to build the unit next year.

I'd prefer to be off-grid...

My house is over 100 years old so trying to use that type in-floor heat would be a bucket I'd rather not open...

Thanks

What about small flat tanks with compartments that would hold heated water but also allow water to flow thru them to other tanks and back to the water heater.

line in ------l / \ / \ / l / \ l--------- line out ----

---------- l_\___/\__/_\_l

Pardon drawn quickly in MS WORD lol

I have experience with micro-encapsulated phase change materials placed into various types of concrete (portland, hydrolytic, Magnesium phosphate, Magnesium Oxychloride, etc.)

look at www.microal.de

These are engineerable to within one degree C and can store heat many, many times more than most any other substance.

sorry--typing in the dark.

it is www.micronal.de

bwire,

I applaud your intentions, but I fear that you will find that it is quite expensive to store heat from a low temperature source like a solar collector. Your most cost effective solution will probably be to store the solar collector heat in a large volume of water. Then extract the heat with a water to air heat pump. If your solar collection could produce temperatures in the 500 + deg. range, then you could possibly use some fairly inexpensive phase-change salts as thermal storage.

LG_DAVE

I'd been toying with designs on this subject and also incorporating water harvesting that was discussed a year or so back.

I've concluded that for the hot water side the use a normal solar panel direct would be more effective.

A further panel would then put heat into an approx 10,000 litre concrete tank in the back garden which would be approx 3m dia x 1.5m deep. (trusting the arith is ok ) - extracting heat with a water to water heat pump for the CH.

(A further tank or concentric container would be needed for the cold water harvest).

I've also looked at designs for daily storage / night retrieval using the thermal capacity of hollow underfloor blocks - but these are essentially for new build, not a 100 yr old.

Hi,

as stated above, water is best,

but if you compare not by weight but by volume then any type of stone is the same and does not need a tight container,

so if you count total price then a pile of sand or medium size stone pebbles is best.

Grain size should be evaluated experimentally, if heated by warm or hot air then it is necessary to get very coarse material (I expect 5 to 15 cm) if heated by warm or hot water I expect 5 to 10mm to be near optimum.

The material itself will give you some heat insulation if enough is piled. There is existing a fired clay - used as substrate in hydro-culturing plants - that has high porosity and is thus a good insulator (if dry).

RHABE

I would like to make a comment with respect to the sizes.

Heat transfer from the fluid to the accumulating stuff at "saving" and from the hot material to the fluid at "recovery" depends on the convection coefficient of the fluid and of course on the thermal difusibility of heat in the "accumulator".

The quantity of accumulated energy is directly related to the accumulator mass for a given temperature.

For the same total mass the contact surface depends on the nominal dimension of parts. The smaller the particles the higher the contact area. Since air has a rather low convection coefficient and water a high one and since the accumulator material has in both cases the same capacity to diffuse heat it seams to me more logical to try to get a quite high product area x convection coefficient which ever the fluid will be, the conclusion would be many small particles for air and bigger components for water.

Hi nick name,

if you consider fastest possible heating up and cooling down than your design rules are the right ones,

but if you have enough time (months) to heat and cool then it is drag and power loss of the moving fluid. (Combined with mass-flow and specific heat).

Can you include this into your calculation? (I did not calculate).

RHABE

I agree with your argument. I considered the day by day variations and the requirement to loose as little as possible from the available energy during fluid recirculation. The management of fluid circulation has any way to be complex in order to avoid losses during night via the heater.

LG is right, I have worked with thermal energy storage and came to the conclusion that it is not usually worth it as there are much better techniques. Here are the results.

The major problem is the temperature difference between the energy source (AC in the summer) and the temperature needed to heat up the house. Your AC might give you a 50C fluid at best. In the winter you need the storage to be at least 25C to give you any heat using natural flow. This 25C of delta T means that you will need at least a 1000 tons of material (rock or water) to store enough heat for the winter. If you use a heat pump, you may extract heat down below freezing. This cuts your storage needs in half. If you use water and go through the freezing phase change, you roughly double your storage capacity (many problems with ice and expansion). You then only need about 250 tons of water or 500 tons of rock. Of course you have to insulate and install heat exchangers etc... Where are you going to store the iceberg?

A phase change material does not really store more heat than freezing water but is a lot more expensive (~1000X).

I have a 24' x 12' pool (27 tons of water) in my basement and it only stores enough heat for a few days.

The only feasible solution (at least without gouv. $) is to use a geothermal heat pump with a few thousands feet's of coils underground in the back yard (5-6 feet's deep). I have this and it works very well. My storage is the earth itself. It is free!. A bonus is that the summer sunshine heats up the earth storage even when the AC doesn't work. The earth is a solar captor / storage. I don't need a container, or insulation. I have access to many thousands of tons of energy storage with only 3000' of plastic pipe.

See extracts from previous posts for more details on my installation.

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The main gain is in reducing consumption.

Air conditioning is a huge consumer of energy that could be used more efficiently:

1-Keep the thermostat at a decent level. 18C or 62F is way too cold. It also promote condensation in the walls and mold growing.

2-Use house insulation to save on cooling needs.

3-Do something useful with the AC heat. See extract from another post below:

I have this air conditioning / heating system at home and it works very well. I installed it myself in 2000 when I built the house. It is a geothermal heat pump similar to an air conditioner.

I used a standard "climate master" heat pump.

1-I added another water coil to dump the heat collected by the AC into my pool. It is a nickel plated coil to protect it from the chlorine. You need an AC tech to do this and it may void the warranty but it is worth it as far as I am concerned. When I need to heat the pool, (or hot water for another application) I switch off the closed loop earth water recirculation pump and open the valve to let the pool water circulate in the supplementary (hot side) coil. I added a contactor to turn on the pool pump when the AC is running. This replace the pool timer as the filter is used about 25-50% of the time.

2-The de-super heater for the hot water is also very good, especially in the summer. Try to get the biggest one possible and consider using a second hot water tank as described in the manual. You will get almost free hot water in the summer.

My total annual energy bill is about $1900 per year including AC and warm pool in the summer. It is much more efficient but it is more complicated than most other heating systems. Are you up to it? By the way, I live in Montreal, Canada.

P.S. I am also surprised that it is not mandatory for central air conditioners to have a water heating connection (de-Superheater). So much energy is lost... It would only cost one or two hundred dollars for the manufacturer to do it.

I am essentially using the earth as a heat well at least that is my intent. I intend to use the same 1000's of feet of tubing used in geothermal collection within the heat storage unit to transfer heat collected from sol and to extract heat for use.

I have a small area of city lot space to use for retention about 20' x 40' and additional to form "L" 20' x 20'.

In addition to solar collection I may also pile a biomass upon the retention field to produce a sustained release during the winter. this could produce methane for fuel too.

A friend of mine is running an experiment in Alaska now on the tundra. He is covering a small section of the ground now where the perma frost has melted to see if the materails that are decaying naturally will give off enough gas that someone could trap it and use it to heat homes.

So that's what is melting the ice cap