Large Heat Storage Container.

This is not nearly enough information for any true analysis, but I can tell you that, after casual reflection, my advice is to use electric heat year round and forget about this folly.

Google, "thermal mass" and figure it out for your self.

You may be right, but others feel sure it is workable. e.g.

http://www.energy-storage.org/energy-storage/storage-techniques/water-tanks.html

I am simple trying to ascertain the best way, if any, to do it.

jt.

I hope I am wrong. It may work, I'm not a thermodynamicist.

Good luck with the project.

http://www.google.co.uk/search?q=underground+insulated+heat+storage+container&sourceid=ie7&rls=com.microsoft:en-gb:IE-SearchBox&ie=&oe=&rlz=1I7DKUK_en-GB&redir_esc=&ei=k-ruS830LYWM0gS2zZTcBw

I beleive use of rocks or large mass of concrete, But rocks are cheaper,

or concrete from demolition sites

if it was me i would surround the rocks with water which could be pumped into a large underground container, the water could be used to transfer the heat from source to storage and also back again, ps add antifreeze it will improve the heat transfer.

Now if you can presurise the underground container that would raise its storage potential.

it may be possible to maintain presure by a pump that monitors the presure.

http://science.jrank.org/pages/983/Boiling-Point.html

http://en.wikipedia.org/wiki/Vapor_pressure

http://www.newton.dep.anl.gov/askasci/chem03/chem03336.htm

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/vappre.html

http://www.docbrown.info/page07/equilibria8.htm

just a thought

your turn to do a bit of research

The problem with this is that 100°F is the highest temperature you can achieve without turning on the axillary heaters.

The other problem is that you can't extract 70°F air from the sink, you'll have to mix the100°F air with cooler air to achieve 70°F air. So, you'll need some sort of variable mixing duct to add cool air. Not insurmountable, but a complication.

My point is that to build such a storage device, given the small temperature differential, would require an investment of far more $ than the electric bill for heat over the life of the system.

this is true the cost of making such a system would possibly pay for the electicity used for your life time unles you cna find a way to build for almost nothing.

Which was why i suggested rocks or used concrete

What volume of concrete, or rock, would it take to store enough heat," (to supply air at 70F(21c) for 200 days into a building of 14,000 cubic feet capacity.)" starting with 100 degree air?

I take a SWAG that at least 10 times the volume of the building would be required for heat sink volume. Not practical.

Cheers.

Thank you for the input. Auxiliary elements may be needed.
I hoped to use a computer controlled fan to vary the air speed.
Drawing clean air from outside, the dwell time (in the converter)
could set the temperature?
The payback time (I think) could be far quicker and more rewarding
than say, pv panels and, off peak electricity could be used, if a
home made wind system proved insufficient.

All ideas are open at the moment.

jt.

Thank you for the helpful reply and links. (most helpful)

I am working my way through them, and it looks very encouraging.

Many thanks,

jt.

When you put numbers to this, they will be amazingly indigestible. Alas.

http://www.google.co.uk/search?q=does+it+pay+to+store+heat+underground&sourceid=ie7&rls=com.microsoft:en-gb:IE-SearchBox&ie=&oe=&rlz=1I7DKUK_en-GB&redir_esc=&ei=nxfvS764HpD20wTZoNHlBw

more links for you to look at

http://en.wikipedia.org/wiki/Seasonal_thermal_store

this is a good one

http://en.wikipedia.org/wiki/Seasonal_thermal_store

A better approach would be to bury some pipes in your land and use a heat recovery system, Much smaller out lay

http://www.google.co.uk/search?q=thermal+heat+pump&sourceid=ie7&rls=com.microsoft:en-gb:IE-SearchBox&ie=&oe=&rlz=1I7DKUK_en-GB&redir_esc=&ei=ehvvS7mUEJj60wTZ2JnkBw

http://www.icsheatpumps.co.uk/residential/products_geo_thermal.php

http://www.geothermalint.co.uk/residential/geothermalbasics.html

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=166

Just to pick some working values, let's assume that the during a cold season of 180 days you would normally use a 100,000 Btu/h furnace averaged at 50% of the time. This equates to 180 x 24 x 100,000 x 0.50 = 216,000,000 Btu of thermal energy storage. Water is the best noneutectic medium you will likely have access to. For the 30° difference (100 v. 70) that's 30 Btu/lb, or 7,200,000 lb of water, or about 115,000 ft³. With this in mind, you can calculate various shapes of the storage.

Thanks for that. I'm too lazy to do the calculations.

My pool is about 3,000 ft³ , so it would take 38 back yard pools to store the energy.

Of course you could always save money by using the Tesla blower for circulation.

Thank you for the calculations. The numbers guessed at (by me)
approx. 500cu.metres - I think yours works out just over 400?

I have plenty of room for this, (and lakes) but discounted the lakes
and swim pool as being far too exposed in winter. (they freeze over)
(Good for skating, lousy as a heat store)

My current thinking is to position it in a glass house. (green house)
it will heat up naturally in summer and could be "blinded" in winter.
All considerations are gratefully received.

Thank you for your help.

jt

Forget who said it but.. If I had eight hours to chop down a tree,
I would spend the first 6 hours sharpening my axe!

Two things:

1. The best material in which to store heat would be one that melts at a temperature somewhere between 70 F and 100 F, such as a wax of some sort (although there are certainly other materials that have that characteristic).

The best way to store heat is by having a material change phase while you store it; that means making a solid melt or a liquid vaporize. The heat absorbed/released (and stored/released) by the material as it changes phase is always much greater than what can be stored as 'sensible' heat (heat that can be sensed by measuring temperature).

Vaporizing the heat-storage material will greatly expand its volume and pressurize your tank, which would have to be sealed; because of that, get something that goes from solid to liquid vice versa, not something that goes from liquid to gas.

Make sure that your tank is vented so that expansion/contraction of the material as it freezes (solidifies) and melts (liquefies) doesn't pressurize or create a vacuum inside your tank.

Using a heat-storage material that will change phase while in use will save your greatly is tank size (a smaller volume will be needed to store a given quantity of heat) and excavation costs.

2. Make sure that your tank's well insulated. I recommend coating it with Nansulate thermal-insulating coating (www.nansulate.com).

Cheers! DZ

First part : good aswer. Check out parrafins. The volume needed is higher but you have the benefit that the output temp is stable.

Purely heat storgage/volume, water is the best option. but also a most problematic: you need a watertight container, also preventing evaporation.

Parrafin can be bought in plastic balls, enabling to fill up a container with them and using air of water as heat transfer medium.

Second part: Nansulate is indeed a very good insulator but way to expensive for the task. I would do it with PUR foam, low density (40 - 60 kg/m³), in situ foaming. This technique enables to create perfect insulation systems, with no cold paths.

The foam is also structural, you can create a reservoir "floating" in the foam.

Make sure that both inner and outer wall are metallic, preventing the cell gass to escape.

I have posted some ideas in this direction some years ago.

One way to calculate the volume is to take the heating bill of your house. when possible. I could do it as I do all my heating in with natural gas. This learned me that I would need 60m³ of water with a dT of 70°C.

Find a way to replenish the heat storage and you will be able to work with a smaller tank. My idea was a small windmill (VAWT 5kW) but I have to admit it is all still theorectical due to practical issues (€) and time restraints.

Gwen - great answer!

I must say that these days I'm looking to Nansulate everything I see because of its ease of application and it's not taking up any space. But where space is no problem, I agree that there are often more economical ways to insulate, everyhting else being equal.

As for combining paraffin with with ... uuuhhh ... I have that knowledge now. I'd always wondered how paraffin-only systems could work since the paraffin, when solidifying, would build up on the heat-transfer surfaces and alter the dynamics. I presume that it still does to some degree but adding water just might improve that.

For my own info: are there ways to get around the solid-buildup on heat- transfer surfaces problem? I tell myself that placing vertically the tubes that carry heat-transfer fluid (whatever it may be) will help the solid slide off to the tank bottom (or top if the storage medium is water since ice is less dense than liquid water), but is there a better way to handle this?

Looking forward to your answer. Cheers!
DZ

P.S. A solar-thermal system would be a good addition to this, too ... even in winter, it would add heat during the daytime to that stored in the tank.

Gentlemen,

It sounds very exciting. I have been down that road a few years ago. There are substances that can use phase change to store a lot of energy but at the end, the volume (mass) required and the insulated container cost much more than the energy I will use to heat and cool my house for many, many years.

I eventually used a geothermal heat-pump with 1Km of pipes buried 2 meter deep. It works very well and cuts my energy consumption by ~50%. Other artificial storage methods would probably use less energy but still need some re-circulation pumps or fans. At the end, a heat pump is much simpler.

It is easier if your weather is milder than in Quebec. You can then use a simpler air to air heat-pump all year long. It uses the atmosphere as the energy storage container!

People can also take advantage of various construction techniques to keep their houses cooler in the summer and warmer in the winter. (This applies to the northern hemispheres. Sorry Australians and other southerners, you have to reverse everything once again...)

A technique that works very well is to plant large leaf trees on the south and west side of the house. You get shade in the summer and sun heat in the winter. It is mostly self maintaining and even provide nice leafs for composting. Free fertilizer. Eventually, cutting some trees limbs will give you fire wood. The trees are also good to keep you mentally and physically healthy. Fruit trees will even feed you!

Nature had it figured out all along!

Have fun!

To overcome the solidification of the parrafin round the heat exchanger tubes they pack the parrafin in balls or plates, using plain water to transfer the heat.

This way the contact surface is improving and the distances in the parrafin is lower, enabling it to give its heat.

It is true that it might look a very expenisve way to heat your house but regulations and fuel costs are changing and not everyone has a garden with trees.

Storing the heat in the ground is also an option, but you will require a heat pump to reach hot water.

Combining the system: a storage container, heat pump, solar collectors and windmill can make you completly independent.

The only but is the price: it must be feasible to do for less than 25 K€ more than a traditional system. otherwise it costs more than a predictable 15 year consumption of a normal system. If you would add the cost of burning fuels to the environment to it.

But someone has to start somewhere, the first car producer was also mad for the rest of the world, a horse is much easier. Why the hell did we need planes? And there was no real commercial need for computers.

When you really have the option to build such a system, I'm willing to help with the calculations and design.

Good luck.

Does not seem workable. The heat loss will be too much. Much better to design an above ground solar air heater with a granite (Or any stone) thermal mass. For the indicated volume and assuming 5 air changes an hour one will need about 100,000 KCal for an ambient at 0 C. This will need a collector area of about 600 sq.mtr. Much more detailing has to be done, in case you want to continue with this option. By the same token, for the suggested under ground storage one will need a far larger storage space, thermal mass, air distribution and collection system and a high power blower, which may negate much of the power savings envisaged. bioramani

Might try just sticking with the electrical heating elements - the rest will not do much. Might consider a solar thermal air heater if you get any sun. No storage used.

If you are serious about heat storage then consider a saline solution as it has a very high heat capacity. It would take a parabolic solar collector to heat the saline solution to keep it liquid. Some research is being done on MOHC (metal organic heat carriers) which increase the heat carrying capacity by a significant margin, but I am unsure of the stage of the research at this point. A prototype system being implemented ( don't ask where it is I don't recall--google it) research is fun and required! It will take you months of data collection even to make a preliminary determination on whether your project is viable or not. There are projects running that use a saline solution as the heat carrier and it is economically at least for that project. That is the solution for the project I am pursuing at the moment. It is unfair to use others to do all of the 'fun' research. If you are going to do this thing then you need to do the 'fun' stuff yourself and then if you run into a technical glitch, this is the place to come.

The concentrating solar method seems to be the only viable concept for storage at this point in time. Even then you will be looking at 24 or 48 hours of storage - not 200 days.

the earth temp. below frost line is always about 55 degrees f. warm in winter, cool in summer. all you need to do is absorb it. radiant heat from mass only heats what is touching it . it is the ultimate storage container. there are ways to use /capture this energy. the best way is to let your home touch this energy, and let the sun shine in, on to mass. and when it doesn't, block the heat loss. The foot print of the home touches this energy 24/7 , but in most cases is overlooked. in the geothermal industry the earth temp. is absorbed using pipes and pumps and fluids and then the central air system can move it. all these things have a price. using passive alternatives is cost effective, but you and your home have to learn to ware your environment. I know that I wandered off subject but oh well, hope this helps you.

I tend to agree with peter7Lq and his websites to various ground source reservoirs of heat are indications that mother nature has already provided the heat reservoir...so why build and artificial one even at higher cost. Ground water will take on the average ambient temperature of a particular area. Where I live it is about 13 degrees C or 55 degrees F. If you can extract 80 BTU per gallon of water that means a well producing 4.1 gpm can support a house with a 20,000 BTU per hour demand. More than enough for most reasonably built and insulated houses.

The heat reservoir can also be found in short depths below ground frost lines and have a proven track record. These shallower systems can be installed in most areas and would work as air conditioners by reversing the process ( only in areas where the ambient temperature is cool enough for air conditioning though).

The areas where space is limited may be the areas you run a vertical systems to take advantage of depth. These systems can use ground water or any suitable transfer media. Do not reinvent mother nature, she has lots of capacity to store solar energy in the ground. Just use the storage she provides.

It's already been said but just to make it clear: water has the highest specific heat capacity per unit volume of any known substance:-

http://en.wikipedia.org/wiki/Heat_capacity#Table_of_specific_heat_capacities

You can only do better with phase change materials.

If you use simple solar panels (water running in blackened tubes) you can attain much higher temperatures than ambient air temperatures. This system even allows you to capture heat from the sun in the middle of winter.

İf you are talking about a geothermal heat pump (GSHP) then why the discussion on generating heat and dumping it in the ground? The storage and heat supply for the system is already in the ground. To do any more is a waste of time and money. Geothermal heat pumps are an excellent choice in a cold climate whereas air source heat pumps (ASHP) are better in milder climates. The better COP of the GSHP can not compete with an ASHP where climates are suitable. The additional cost of the GSHP system is the only negative.

A GSHP lowers the average gound temperature with a few °, worsening the seasonal COP over time. This lower local temp will drain more heat from the surrounding but eventually it will cost you money.

Recharging the soil with heat captured from simple black plastic tubes on your roof will drastically inmprove the soil temperature and thus bring you money.

The same heat collector could be used when the outside is higher in temperature as the soil, thus again improving the seasonal COP. (spring and summer use)

Don't stare blind to a single COP figure, as decent supplier has graphs showing the relation between evaporator and condensor temperatures, if you can shift the evaporator higher for longer periods (eventually preventing it to really drain the heat out of the soil) it will lower the electricity bill.

The loss of temp (or gain) over time is conjecture. İ have seen speculation but no study showing it to be true. İ believe you would have to have one very, very, very large house to have an affect. The graphs you cutely refer to are available for many models on the net - İ probably have 90% downloaded to my PC as İ was studying what type of systems we should be using. Shifting the evap temp higher is hardly a suggestion İ would want to make to a buyer of one of our homes.

It is known that large systems sometimes completely drain the heat from the soil, the ultimate power of the earth is not that high. (in W/m²)

Of coarse when you have flowing ground water the heat will be supplied, and storage is not feasible.

The discussion always remains: is the investment worth the money? and it is in many cases discussable how to calculate it. the result can be tweaked to prove what you want to achieve.

When I did the study to add PV cells to my roof one salesmand came with payback in 6 to 7 years, and enormous gains at the end. I checked his calculations and found that he indexed the cost of electricity with 5% per year, which over 20 years is very expensive electricity. according to his way of calculating it is a must to invest in these systems. When I did the calculus I came to a payback after 11 years. Still positive but an accountant would have hesitated to do the investment.

Agreed about the calculation method - but you still did good with solar - mine would be 20 years plus (plus) - no FİT, no net metering, no subsidies or incentives plus paying duty on the panels and other equipment. You are talking about large GSHP systems draining the heat from the earth - that means far more than one home and still İ have not seen any study on it though they were to do one in Sweden İ believe.

but imagine every house has its own GSHP, then the systems will start to influence.

Water is the only choice for thermal storage. No other medium can hold nearly as much heat.

Calculate how many BTUs you need (1 BTU= 1 LB H2O x 1 degree F) and divide by the delta T (30 degrees in this case). This gives the number of pounds of water you will need.

A home in winter in Sacramento will use a 100K BTU/H heater an average of about 6 hours per day for the winter. 600,000 BTU/ day X 200 days gives 120,000,000 BTUs. Divide by 30 degrees F delta t and you get 4,000,000 pounds of water. Since a cubic foot is about 62 pounds of water, you will need 64,500 cubic feet of water.

If the tank is cylindrical, with a height and diameter the same, the tank will be 42 feet tall and 42 feet in diameter.

You need to insulate the tank, and even then expect 1% daily heat loss. This will increase the tank sze needed by about three times or so, a tank 64 feet high and 64 feet in diameter should do it.

Also, the heat exhaange between water and air may not be perfect, so you may have to move quite a lot of air and hold a little more water.

Oh, and you can't really heat a cold house with 70 degree air.

Thee project may be difficult.

When building my home İ worked this out for the equivalent of a 5 ton heat pump - like you say, it is totally impractical. İf sunlight is available a solar air heater providing heat as available is a valuable resource though.

Depends what you want to do.

Water has only a limited range to store heat and has the bad habit to evaporate, consuming a lot of heat.

In solar applications we tend to choose for molten salt, which is usable up to 600°C.

The Phase change approach has the benefit that you will have a constant temperature heat storage, making it usable in simple domestic applications.

With a water tank system you will always need to regulate the temperature to the level you want it. (or even use heat pumps to cranck it up)

İ don't think traneengineer really meant for someone to use a 20 meter dia and high water tank! Salt that we (?) use for solar energy storage is yet to be tested on an industrial scale and even then the systems presently being constructed hold maybe 6 hours of heat for the system. Heat storage over time (days and months) is impractical - that is the reason it is not done - it is not that no one has thought of it before.

I think he better moves to LA.

old but are you there?

Thanx for these posters, all!

Have found tracking above zone 4 USA, HVAC, GTHP are generally ADDING heat to the ground but that is a technical .0001%.

Wells since 1980 in Cincinnati: still at 18ft: 56f.

In Cleveland 51.9 have yet to see (and I believe there is) even any global warming affect: still 34 years later 51.9 to 1/4 of a tenth of a degree.

in an overheated corporate office center, 52f Earth went from loop temps (nothing running) in three weeks from 103f-96f coming back, then all equipment shut off: to 57f-56f coming back in a 4th week tracking-testing.

I believe in global warming because the polar caps on Mars are melting too, and Jupiter is up in temp since data has been acquired, per NASA. (Cable: Wash Review program 2 years ago)

the Dep Nat Resources has not shifted their lateral lines on the US in 30+ years, for well water temps. Any links to research would be interesting.

Towers in Dayton on over 250 ton chiller to condenser-heat rejected exchanges of heat raising well water re-circulations between 90-ft spaced 2-well open systems, runs similarly since 1980. (too, some 2 or more underground flows are found)

We have approached this problem with our house. This was engineered to utilize ground thermal energy for both summer cooling and winter heating. NOT a geothermal heat pump. For what you are considering it will be important to deal with the heat capacity required and then the thermal insulation required to isolate that thermal mass from the ground temperatures. This is calculable. I have not calculated this. My scientific intuition implies that this may not be economically viable.

We chose some compromises to utilize air/ground thermal heat exchangers that we built and then buried that work very well. These utilize air fans as the means of heat transfer. The big benefit is also in air quality in that in the dead of winter we warm incoming air ground thermally. This oxygenates it and actually improves air quality as leaks are from in the house to the outside. In the summer, incoming air is cooled so that the heat pump burden is minimized. This is not so much about saving energy but the larger issue of maximizing air quality. Our system removes all pollens and other stuff and keeps us fresh air supplied at all times.

1) What is the amount of heat actually stored? 2) When you talk about air quality İ see many more problems generated than solved - mold for one. A rather good filtration system would be required.

We initially did this to save energy. The exchanger is a large plastic piping assembly and we use inlet filters. The air and ground do not touch. Think about how air comes into a house - either through leaks through walls etc and door jambs. Air is always recycled in conventional systems. Introducing a controlled volume of filtered air reverses leaks which are unaccounted air paths. The ground thermal system merely removes the temperature extremes of that air volume in the winter and summer months.

We have been monitoring this very carefully with a computer system measuring inside and outside weather conditions.

Mold spores etc are reduced. An additional benefit is that use of the system has actually reduced the amount of dusting my wife has had to do this last year.

OK - Now İ understand the intent of your system as regards heat - not storage but smoothing out the swings. İ still expect you will see problems over time with mold etc.

Use water and solar panels, this will provide heating even in the middle of winter vastly reducing the storage demand. With underfloor heating the temperature required is much lower and you can bleed in the higher temperature storage water (90degC) to keep the floor at a sensible temperature (25-30degC). That is what I intend to do down here in sunny NZ (where the blood runs to your head cause we're upside down). If the solar panels are optimised for mid winter they are not roasted in summer. I was thinking of mounting them vertically on a north and a west facing wall.