This concept was invented and tested in 1977|
Imagine storing about 30 MILLION Btus of summer heat to use for heating a house in winter! Since a medium-sized house near Chicago needs only around 40 million Btus for an entire winter's heating, this would massively reduce heating bills, consumption of oil or gas, pollution and global warming! A slightly larger version could even provide 100%+ of the house's heating needs!
Imagine the SAME house storing around 12 MILLION Btus of late winter cooling to easily provide the 4 MBtu of air conditioning cooling generally used in an entire summer!
Now imagine that this is not very expensive to install (with the house value probably being enormously higher, too!). Unfortunately, this concept is really only best compatible with NEW CONSTRUCTION buildings, and would be far less beneficial in trying to use it for any existing buildings. Amazingly, most ways of installing this system are TOTALLY INVISIBLE after it is installed, and it is compatible with virtually ANY house style or layout!
This is as GREEN as one can get! Simply "shifting" the effects of summer and winter seasonal weather, with NO fossil fuels required at all. Actually, not even any woodstove or methane or any alternative heating fuel is likely even needed!
And there are very simple and crude (thereby inexpensive) methods of "boosting" the performance of this system by collecting a little extra sunlight on any sunny winter days!
This is not even any super-complicated idea! It is essentially storing all that heat or coolness in a VERY highly insulated "room" hidden completely underneath the house. It is actually OBVIOUS! (We just did a lot of Engineering to maximize the performance, so the home occupants would probably never know that a conventional furnace and A/C were not providing their comfort.)
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In the combined heating-cooling concept, a separate source of cooling MAY be needed (depending on the climate. For many climates, the massive storage capability can provide enough house air cooling for an entire summer! OR the huge energy storage capability can be divided into two (or more) sections, where one could have a supply of heat while the other had a supply of coolness, such as for a late Spring day when heat is needed at night and in the morning but cooling may be needed in the afternoon. And for those warmer climates where extra cooling might be needed, our related "Free Air Conditioning" (which is an array of buried, sealed underground air passageways to capture cool from the cool soil deep underground, like in caves) is an excellent choice. In a slightly modified version of this storage, which could then only be used for cooling, the external cooling system may be unnecessary.
This is SERIOUS storage! Our normal intention is to design a storage of at least 30,000,000 Btu of heating capability (a hundred times more than others even dream about!) This system can be Engineered for a wide variety of climates and occupant expectations, but our generic planning is usually to plan for a situation where DURING THE FIRST THREE MONTHS OF WINTER around 10 million of those Btus would get lost through the excellent insulation, which leaves the other 20 million Btus to heat the house! Since decently designed modern houses commonly need around 40 million Btus of actual heating for a whole winter, this approach takes care of HALF OF EVERY YEAR'S HEATING BILLS!
Actually, in most cases, it will work BETTER than that, and handle most or even all of the house's heating needs. We use an extremely conservative approach and generally choose to use very conservative values in our designing, specifically, of being able to get the storage up to just 120°F at the beginning of the winter. (This low storage temperature permits us to store the heat for a LONG time! The far hotter storage temperatures that most solar systems try to use cannot store heat for more than a few days at most, as they lose heat like crazy through the insulation they use.)
Say that our storage is identical but might have a little better insulation and that it is heated to just a little warmer, around 140°F at the beginning of the winter. That is then about 60% extra capacity, meaning nearly the whole winter's heating load could be provided! It is also very easy to make the heat storage chamber a little taller than the eight feet than we describe, to then have even greater heat storage, but we again have tried to stay conservative, and also kept the footprint of the heat storage chamber entirely under the area of the house, and also kept the chamber having just an eight-foot height, such that conventional concrete basement construction procedures could easily be used.
For most climates, cooling is even easier! The system mentioned above commonly can have around 13,000,000 Btus of cooling capability at the start of a summer. A 30,000 Btu/hr central air conditioner needs to run for about 420 hours straight to provide that much cooling. In many climates, a standard house actually uses around 3 or 4 million Btus of cooling during an average summer.
This sub-basement structure would not be used as a room. It would actually be painted with a waterproof sealer, REALLY well insulated on all sides, and then entirely filled back in with relatively standard backfill earth materials, and used as a "heat storage" chamber. A complex arrangement of hollow tubes gets buried in the storage material to provide the necessary methods to get heat into and out of the storage. Once this sub-basement was made and filled in (and then properly compacted), a standard basement floor would be poured on top of it, and the house built normally above it. In other words, the final house would show absolutely no evidence of the sub-basement even existing! The house would be absolutely "normal"! That allows almost infinite flexibility in the architecture and style of the house's design and construction.
The final basement floor WOULD have some ducts sticking up through it at various places, to either send hot air down into the storage or to remove warm air to go to one or more rooms (it can very easily be Zoned so that different parts of the house could be kept at different temperatures). The system is even compatible with hydronic heating/cooling where water piping is used instead of air ducts.
Among many additional options available, INSIDE the 120°F storage material, a relatively small chamber could be built, and well insulated, where that chamber would only lose heat to the 120°F material surrounding it, and so it could be maintained at an even higher temperature. For example, if it were kept at a constant 160°F or 180°F, then water pipes running through that higher temperature material would come out at roughly that higher temperature. This would be for people who did not feel that hot water at 120°F was hot enough!
If the sub-basement was built with a 10-foot height instead of 8-feet, those numbers would be proportionately increased to 31 million Btus and 44 million Btus.
What is the expected house use of cooling? In a climate like Chicago's, there are commonly around 20 days each summer where a central air conditioner is used for the six hours of the afternoon. That's 120 actual hours of air conditioning that is needed in a summer. A modest-sized house such as the above would often have a central air conditioner rated at 30,000 Btu/hr (2.5 tons). Multiplying these numbers gives a full summer's air conditioning usage of around 3.6 million Btus of cooling.
Note that for Cooling Only, no insulation would be needed to be installed inside the walls and floor of the sub-basement chamber. This actually allows the chamber to naturally cool by losing heat into the deep soil directly below it, for even greater capacity.
Since the proposed storage could provide the initial 11.5 million Btus plus constant bonuses due to the floor being cooled by the deep soil under it, ALL of the 3.6 million Btus of cooling needs would easily be taken care of! No other air conditioning system would be needed, ever! The cooling-only version of this storage even constantly and naturally replenishes itself, so its capabilities are actually even greater.
Regarding the heating-cooling version, if the climate is such that additional summer cooling is likely to be required, our related Free Air Conditioning system can simply ahd easily connect into this storage. Not only would this eliminate the annual summer electricity usage for air conditioning (forever!) but it would even eliminate the initial cost of buying and installing the conventional air conditioning system. That's several thousand dollars of initial cost that is eliminated, greatly offsetting the cost of the sub-basement.
In case it is overlooked, a LOT of thermal insulation is involved when you intend to store heat or cool for MONTHS! R-60 would be an absolute minimum, with R-100 more likely for many climates and situations. That is a LOT of foam insulation, and actually represents a major cost in installing this system.
For some climates, it might even be appropriate to pour an additional partition wall to separate the sub-basement into two separate chambers. One would be intended to be used for heating and the other for cooling. On a late May day, heat might be extracted from the one during the night and in the early morning, while coolness could then be extracted in the afternoon! Even better, different rooms of the house could extract heat or coolness per the calls of standard wall thermostats turning on blowers!
Bottom line: ALL air conditioning is taken care of, forever, without the big electricity bills of conventional air conditioning, and without any Freon refrigerants that might be environmentally bad.
If, in the Autumn, either solar heating or any of a variety of other heat sources is used to warm up the storage, then maybe by November 1, the storage could have been gradually gotten up to the desired 120°F. That stored heat could then be used during the winter for heating the house. Certainly, all of November, December and January should be completely provided for. But if February and March heat is also desired, no real problem, just TALLER sub-basement and storage material and THICKER insulation to reduce long-term heat losses. Notice that we say WARM and not HOT!
This is meant as a very "low-tech" system. You have certainly noticed that the interior of a closed car can soon get over 140°F on a sunny summer day. The point is, getting this massive storage up to, say 120°F, over several weeks is quite easy without having to resort to any exotic equipment. Many other heat sources are possible, too, like a woodstove or similar. Even the HG 3a device which we invented to allow cut lawn grass and leaves to naturally decompose, which gives off a LOT of heat, could be used!
When anyone else talks about trying to provide "solar heating" for domestic hot water or for space heating, they always try to store the heat at 200°F or above. Yes, that allows a small volume of storage material to hold a lot of heat, a good thing. However, it causes enormous heat losses through surrounding insulation if the heat is to be stored more than three or four hours! We see great wisdom in minimizing the amount of heat lost through the insulation. With our design storage temperature of only 120°F, our heat loss rate is less than half that of a 200°F storage! This is a central reason why our storage can provide heat for a full house for MONTHS!
Using this very conservative value of 120°F for the top temperature of the storage, let's do the math. If a desired house temperature is the usual 70°F, then the storage would have (120°F - 70°F) * 500,000 or 25 million Btus of heating available for the house at the beginning of the winter.
In Chicago's fairly nasty climate, our modest-sized house, if reasonably well insulated, might have an annual heating load of 40 million Btus. That means that around half of the entire house's winter heating load could easily be provided by our massive storage, without turning on any furnace or using any heating fuel, EVEN IF IT IS ONLY MAXXED AT 120°F! (It actually turns out to be almost exactly half for this example, because several million Btus are lost through the insulation over those months of storage, but much of that is lost UPWARD into the basement floor and therefore the house above it.)
If the storage could be warmed to 140°F, then the benefits would be even better. The storage would then contain around 35 million Btus, representing MOST of the house's heating load for each winter. That means that, for every following winter, only a small portion of the usual heating bills would be necessary! Forever!
If this heat storage capability is intended to be maximized, it is easy to do. If the sub-basement was made 12 feet tall instead of the 8 feet mentioned above, there would be one and one half times as much heat storage capabilities. If the storage began in the Autumn having been heated to 140°F, it's storage of 53 million Btu should easily be able to entirely heat the whole house for the whole winter, never having to turn on a furnace at all!
There is also the option of adding additional insulation around the storage, to reduce even more the amount lost over a period of months. Keep in mind that we estimate losing roughly 10 million Btus over a three month period, and if the insulation was doubled, that loss would only be around 5 million Btus during those three months. For most climates, we do not encourage excessive insulation, to keep expenses down.
To get your lofty thoughts back down to reality: A 2-inch thick layer of blue foam insulation is rated at R-10. It would take TEN such layers stacked up to get R-100 insulation! That's 20 inches thick of foam on all walls and floor and ceiling! The chamber volume has been discussed rather generically here in the calculations, but you can see that this massive amount of insulation would materially reduce the available volume of the storage material. More and more thicker insulation can reduce the millions of Btus of heat loss, but also reduces the total amount of heat stored in the smaller volume of material. For each climate and application, there is generally a best thickness of insulation, which can be determined with rather simple Calculus solutions. And thicker insulation also would permit HOTTER storage (due to slower heat loss) provided that you had some heat source which could provide heat at higher than the Low-Grade heat (120°F or 140°F or so) that we tend to find attractive! There are a zillion options regarding this system! We (or a very talented Engineering Firm) probably need to be involved in maximizing the design of a system for any specific application. We know that people see this as really obvious and apparently simple, and nearly everyone seems to assume that they could build it without any help. Well, sort of! It will certainly WORK no matter how poorly it was Engineered! It's just that our attitude about such things is that IF you are going to go to the trouble to do something like this, you might as well do it right! Which means some calculation and Engineering toward maximizing performance.
Also, please note that the re-sale value of a house that would NEVER have any air conditioning expenses and would have possibly less than half the winter heating expenses, would be VERY high. The additional re-sale value of the house almost certainly would be greater than the cost of installing this system! Also, do you realize how quickly such a house would sell?
Actually, even without much planning at all, you can probably see how this general idea is bound to be helpful, for both heating and cooling of the house. So, really, you would not even need our help at all! But, if you're going to do this, you might as well do a little planning so that it will work really well. You should either do the math yourself or have us do it (or provide the equations) or just over-estimate how much storage material you will need, based on the heat capacity of the material you choose. That is pretty easy to do, and the example of the moderate sized house near Chicago is a good example. In a normal Summer, only around 3.6 million Btus of cooling is likely to actually be needed, but the calculations above show that over 11 million Btus of cooling is available. This "over-design" is a good idea, so that it would always provide excellent cooling, even for a record hot summer. And, as an additional note on the actual air conditioning usage, it is very rare that the compressor in a conventional central A/C runs absolutely constantly for the six hours described. It generally cycles on and off to keep the house temperature at what you set the wall thermostat at. Therefore, the needed amount of cooling is generally even less than the season total 3.6 million Btus stated.
The discussion above should have convinced you that almost any version of this concept will be of benefit, but if you're going to do it, you might as well get maximum benefit from it! The variables that have the greatest effects on performance are three: (1) the insulation R-factor used; (2) the type and condition of the storage medium itself; and (3) the method of efficiently getting heat into and out of the storage. In these areas, we have extensive understanding, and we are confident that we can assure maximum performance of either version of this system for any house and climate.
If you want our help, we have two possible fees that could be charged.
If this is of interest to you, send us an e-mail (below) and we can send you our mailing address.
Unfortunately, there were a number of political complications in India which arose in the Summer of 2008, and those plans got shelved, at least for now. Apparently, there are some leaders there who expect to soon use these methods to entirely heat and cool, either that Airport or some other Airport in India, but apparently such things must wait until politicians resolve differences about other matters first!
The only reason that is mentioned here is that the basic concepts of the Sub-Basement heat storage and the Low-Tech Solar Heat Capture and Collection, are easily scalable for very large applications. It seems likely that some large commercial or industrial building, somewhere in the world, will install this pair of systems, in order (1) to become GREEN; (2) to save really massive amounts of heating and/or cooling utility bills; and (3) to attract media attention for being an socially-responsible company (or country).
C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago