Some people who apparently have never been in a cool cave or do not understand science or Engineering seem to try to find ways to deny that this system works. Some note my reference to many thousands of installed system where they say I must be lying as they have never heard of anyone using this system. I am actually also somewhat surprised about that, as it is common in human nature to want to brag about having something special! I agree that it seems logical that at least SOME of the owners of these systems seem likely to have called a Reporter to brag about what they had installed. But I have several thoughts about this matter. Once this system is installed, it is all entirely 'invisible' underground! I guess I imagine that a Reporter or Camera Crew would not have much interest in anything which they couldn't show or document any part of it! In addition, the fact that I have always GIVEN this technology away, there is no company which is trying to 'promote' this system in order to SELL products! And maybe some people simply want to 'appreciate' a valuable gift, without creating any publicity over it. I don't really know! In fact, since we NEVER have even ASKED anyone to PROVE that they have installed this system, and we have never even asked WHERE someone claimed to be installing it, I suppose it IS possible that 19,000 people have all lied to me over the past 13 years regarding their intention of installing this system! However, it seems to me rather unlikely that ALL of those thousands of people would have lied to me, since it IS a wonderfully useful air conditioning system! It seems to me that no matter how skeptical one might be, at least a FEW hundred or thousand people would certainly have TRIED to install it over the past 13 years! I suppose that I compound this matter by NEVER having used FaceBook or Twitter or any other social media. Thousands of people have told me that I SHOULD HAVE, in order to 'promote' this system more. But they miss the point of the fact that I have NEVER 'wanted' to crowd anyone to use any of the systems which I describe in web-pages. In my opinion, my job is simply to PRESENT the science and technology, to then LET each reader DECIDE for himself or herself whether they want to actually USE it! It is NOT my function to try to 'push' anyone into doing or not doing anything! So those 'skeptics' are free to NOT use any of the things that my web-pages describe!
So if you or anyone else decides that I chose to WASTE many months of my life to do a lot of Math and Engineering, just to apparently somehow deceive readers for some reason that is beyond me, fine! Clearly I did not do that in order to deceive anyone into paying me money! And as a Theoretical Physicist, I certainly never needed to try to inflate an ego by lying to uneducated people about some very basic Laws of Science!
It has recently occurred to me that there is a description of the
following system which might be more understandable to the public.
You PAID several thousand dollars to buy a central air conditioning
system for your house, which has as its ONLY function to (temporarily)
cool some house air down to nearly exactly 60°F (16°C). Why?
For two reasons! One is to be able to then mix with other house air to
provide air at around 76°F (24°C) which is considered the most
desirable indoor temperature during the summer. The other reason
is because when that air is cooled to that 60°F (16°C), it necessarily
loses some of the humidity, which happens when the 60°F (16°C) air
is SATURATED or AT THE DEW POINT. When that air is warmed back up to
the desired 76°F (24°C), the briefly SATURATED (100% humidity)
air drops to 40%, which is ALSO considered the most comfortable during
After having paid all that money to BUY the A/C equipment, you then spend $1,000 or $2,000 or more each summer to pay for the electricity to run the A/C compressor! Have you yet had to pay to have the central A/C repaired??? Worse, that electricity probably comes from a coal-fired electric power plant (52% of all electricity in the US is created from burning coal.) So you PAID at the start, you pay (a lot) every year to run it, AND you are causing global warming. A pox upon you!
Remember, the SINGLE purpose of all that is to cool some of your house air down to 60°F (16°C).
But now consider this: IF you could simply send your house air DOWN into deep soil, that soil is COOL during the summer! As noted above, the deep soil around Chicago stays at around 52°F (11°C), WAY better than is actually required! NO fossil fuels need to get burned! NO huge summer electric bills! Duh!
You CAN do this crudely, sure. Many people seem to stop reading right here, as they TOTALLY understand everything! But this (long and complete) presentation includes the benefits of several months of advanced Engineering Design, which was done by a Theoretical Nuclear Physicist, to make sure it performs excellently! During the past ten years of offering this system, I have heard several THOUSAND people say that THEY UNDERSTAND but THEY DON'T NEED NO STINKIN' ENGINEERING (well, they didn't actually say that!), and THEY have far better ideas anyway on how to do it! Fine with me, since I an not SELLING anything anyway! Their ideas PROBABLY WORK, but if they would have actually READ this whole thing and tried to use the information, it certainly would have worked FAR BETTER, and they would even have said EXCELLENTLY! But each person has their own choice about doing such things. When people KNOW IT ALL, they also never see any reason to hire a local HVAC Engineer to read this stuff and apply it to their application. Why bother, right?
There IS an extremely crude version of this which COULD be of very limited value IF ONLY ONE SMALL ROOM is to be cooled. Consider finding an old hot water heater tank WHICH DOES NOT HAVE ANY LEAKS! Dig, dig, dig down ten or twelve feet deep and stick the tank down there. Seal off most of the pipes and only connect pipes to the INLET line and OUTLET line. It actually works a little better if it is standing right side up, but laying it down down there is nearly as good. The pipes run to send that (cool) water through a standard car radiator inside your room. A standard car radiator fan AND A SIX VOLT BATTERY is used so the fan runs slowly and quietly. A car water pump can recirculate the water through this SEALED system. This CANNOT cool a very large area or very continuously, but it can be nice for a rather small room. If that 40 gallons of water in the tank down there is at 52°F, that is around 300 pounds of water which could contain a maximum of about 6,000 Btus of cooling (that is 300 pounds times a temp differential of about 20°F). So for two or three hours, you could nicely cool a small room. But after you have heated that water down there to 70°F, it would seem to stop working UNTIL the water in that tank could again cool down. The cool (52°F) soil surrounding the tank will GRADUALLY cool the tank and the water back down (YOU HAVE removed the insulation from around the tank, of course!). But the surface area of a hot water tank is not very large, and so that takes a while! Easily calculated for any climate, any tank, any sized room, etc, but no one seems willing or able to do that math!
A wonderfully air-conditioned doghouse is easy with such a system. Some planning and calculations might find that SEVERAL buried tanks might cool one bedroom or small home office.
While I am on tangential subjects, there is a peculiar situation which is true nearly anywhere on Earth. If you dig or bore MODERATELY deep (like 3 feet or 10 feet) the soil is COOLER than the summer daytime temperature, because it always stays near the ANNUAL AVERAGE. THAT is the basis of this AIR CONDITIONING system (which works great!) The peculiar situation is that IF it were financially practical to bore a foot-diameter borehole maybe 7,000 feet deep, at that depth, the Earth is around 130°F, due to the center of the Earth being heated by radioactive materials. Such a borehole would be ridiculously expensive so it is not practical, but the peculiar situation I note here is that BOTH COOLING an entire house AND HEATING the entire house could be done from geothermal processes! No fossil fuels, and FOREVER heat and cooling, each of which could be controlled by wall thermostats for the comfort that we all now expect!
Imagine if you happened to live directly over Mammoth Cave in Kentucky.
Down below you, on a 95°F (35°C) hot summer day, there was all kinds of 56°F (13°C)
air down in the cave! So imagine that you bored two large holes down from
your house into the ceiling of the cave. (The government would seriously
frown on you doing that to a tourist destination!) You would then be able to
use a standard furnace blower to draw cool air up one, to push it into the house
through your existing heating/air conditioning ducts and registers. The
second duct would be to allow your hot house air to go back down into the
cave to replace the cool air you removed. Presto! You have awesome
air conditioning! Well, that crude approach would have some problems
regarding humidity, because it would not be a SEALED system, and
our Engineered system takes care of that!|
Here is some homework for you! On a hot sunny summer afternoon, take a drive out along a Frontage Road along an Interstate Highway or similar large highway. Make sure it is a day with moderate wind, and that you have chosen to be on the downwind side of the highway! Find a concrete or metal culvert where water is able to pass under the highway, and walk to the end of the culvert. You will feel air coming out of it, and that air will be IMPRESSIVELY COOL! You immediately realize that you could stay there for hours and hours, and cool air would continuously come out your end. You can look THROUGH the culvert and see where the 90°F (32°C) hot summer air was going INTO the culvert, and yet here at your end, it CONSTANTLY comes out wonderfully cooled! Continuously, all day, every hot day! This is a truly impressive experiment to do, and it is immensely convincing regarding the whole point of the system which is described in this presentation!
Well, that general concept will work in many climates, if an "artificial cave" is created deep in the ground near your house. Note that there is nothing complicated or complex about this idea, it is actually really simple, and even obvious! All we did was, in 1979, to apply modern Engineering methods to calculate how to make an "artificial cave" that is most efficient. We also found a way to use really inexpensive materials that are already available in a store near you!
Actually, we even make an improvement over that idea involving a natural cave, because it turns out that a natural cave could foul up the humidity (IRH) in the house. So the system presented here (which is a sealed, RECIRCULATING system where the house air is actually never mixed or exchanged with any other air, essentially duplicating a modern heating or air conditioning system which has air return ducts) is even better than what was just described!
We actually Engineered this system in 1979, as an important part of the NorthWarm 100% solar-heated house system that we designed at that time. As far as we know, NO ONE ELSE working in solar heating has ever (even yet) given any thought to A/C, because they always plan and market such small solar systems that they can only provide a small portion of the house's heat anyway! The few solar systems that actually had significant capability, such as the French Trombe Wall approach of the 1960s and 1970s, caused houses that were absolutely unbearably hot in the summer, far beyond the capability of any A/C to deal with, that actual serious solar space heating was considered impractical. Our NorthWarm 100% solar-heated house is extremely unique in many ways. It not only has the capability of heating many times greater than any other approach being marketed, but it includes THIS "natural and GREEN" system of air conditioning as a central part of the system. Where people who experiment with solar heating seem to be tolerant of overwhelming heat in some rooms during the summer, we consider that to be intolerable. Therefore, we designed many special features in the NorthWarm (Version 1) System, one of which is this A/C sub-system. When California was faced with extreme shortages of electricity (2000), we realized that it was possible for those homeowners to benefit from just the A/C portion of our NorthWarm Solar House system, and as discussed to the right, beginning in November 2000, we chose to provide the information of this and linked presentations to the public.
We happen to feel good about the very idea that a "solar heating system" has such great performance as to even NEED air conditioning! The presentation of the Solar Heated House can better describe why the A/C was even necessary. In the same way the solar heating portion was Engineered to be extremely sophisticated and efficient, we made sure to Engineer this A/C system to be equally as impressive in operation.
Using ONLY locally available materials, it is possible for ANY homeowner to virtually eliminate their electric bills for air conditioning FOREVER! If a million California homeowners would choose to individually save this money, they would collectively reduce the electricity power load on the California power grid by around 5,000 Megawatts! That reduction might even help the electricity suppliers keep up with their demand! A grass-roots solution for a problem that the honchos can't solve!
This is a method for supplying plenty of cooled, de-humidified air for almost any house or many commercial buildings, WITHOUT needing to run an electricity-eating air conditioner compressor! Even better, it is fairly inexpensive to install and unbelievably environmentally friendly! All of the rooms of a house will be EXACTLY as comfortable as if that expensive compressor was running! The temperature, humidity and comfort level can even be regulated by the very same wall thermostat you already have!
A number of museums and other tourist destinations have found an additional benefit, of not having to have a NOISY and UGLY air conditioning compressor next to their building! THIS approach provides identical comfort without those usual disadvantages.
This system is extremely logical and actually very simple. It involves moving the house's air through large tubes (like tunnels) underground. In technical terms, these tubes are "heat exchangers" that use long-proven simple techniques to transfer heat FROM the house air INTO the cool deep soil.
This technology is being GIVEN away, FREE. Beginning in November,
2000, we have tried to get word out to California homeowners that this
option is available to each of them. It is given in the spirit of
one human being helping a neighbor.|
We are just trying to offer assistance for people who seem to be destined for some great adversity. We have heard that in San Diego, electric rates quadrupled in 2000. People who paid out $1000 the previous year for a summer of air conditioning are amazed at their recent bills for this and all following summers! And the electric companies have basically confirmed that blackouts will occur for up to ten years, until they have enough new power plants built.
No incredible breakthrough is presented here. The concepts have been known for many decades. I heard a rumor that even the ancient Romans "air conditioned" a few buildings with this method (but I doubt it!) Our primary contribution is to figure out a system that only costs on the order of one or two thousand dollars and which would probably save the homeowner more than that outlay every single year, forever.
We have a single request. The fact that we are giving away a pretty thorough explanation of this system, does NOT mean that we are also offering unlimited free engineering expertise as well! For unusual houses, or ones in unusual locations, or in especially hot climates, it is sometimes prudent to have individual engineering calculations done, to ensure proper performance. Any local engineer (HVAC, civil, mechanical, chemical, etc) should be able to do the necessary calculations. If they (or you) wish, we can provide all the necessary technical equations (and examples) for such analysis, (the Technical Packet) which anyone that understands algebra should be able to use. Since November 2000, we have required that a person make an anonymous donation of $250 to any Charity, Church, Soup Kitchen, Food Bank, Homeless Shelter, Animal Shelter, etc, and then we have provided the Technical Packet. (We have never required any receipt or proof beyond the person's word.) Details are in a link below. (Well over 9,200 people have done this to request the Technical Packet, so we believe that roughly two million dollars has been anonymously given to such worthy causes. We LIKE that!)
We feel that most houses in most climates do NOT need this extra engineering effort!
The temperature a few feet down in the ground is remarkably constant throughout the day and year. In Chicago, for example, that deep soil remains approximately 52°F (11°C), day and night, summer and winter. In the summer, the hot house air is blown through some underground tubes and that hot house air is cooled by contact with the cool (52°F) (11°C) walls of the underground tubes. It turns out that it is also de-humidified, too! It turns out that IF the soil happens to be at or below 60°F (16°C), when the house air is cooled to that temperature, the relative humidity in the tubes rises to 100% and moisture in the air condenses out on the walls of the tubes. When that 60°F (16°C) air at 100% moisture is again raised to the desired 76°F (24°C) air temperature in the house, the humidity (called IRH) is at the desired 40%. If the soil is cooler than 60°F (16°C) then the air is pushed through faster so the humidity is not lowered too much. If the soil is above 60°F (16°C), a separate dehumidifier is likely to be necessary.
By the time the air has returned to the house, it is then exactly the same as the cooled air that would have come out of a standard central air-conditioner. Air conditioning is accomplished without running an energy-expensive compressor, virtually eliminating air-conditioning expense. In the winter, there is even a bonus effect which can be provided pretty easily! Make-up air for the house, that might sometimes enter the house at -10°F (-23°C), would enter the house at around 52°F (11°C) instead! The heat load of the house can be significantly reduced, minimizing heating bills.
Have you ever been in a cave? Remember how cool it was, even if it was 90°F (32°C) outside? The air inside that cave that you were breathing did not start out in the cave. Some winds had blown air in through some opening somewhere. Hot outside air that had gone into the cave had been cooled by the cool walls down there. That's pretty much what we are doing with this system. You can do this with locally available materials, which should cost on the scale of $500, in just a day or two, which would mostly be digging up and refilling trenches across your yard! If you hire a backhoe or trencher to do that might be another $500. Adding in some other expenses, the whole works might be do-able for well under $2,000. (These estimates depend on house size, climate and other factors, and are suggested as a ball-park estimates.) Simple, easy, fairly inexpensive, perfect!
WHY is a cave cool like that? It is actually very simple and logical. In the summer, you get a lot of natural solar heating and in the winter a lot of natural cooling. For YOUR climate and location, there is some "average annual temperature". THAT is the natural temperature of the deep ground where you are, no matter WHERE you are! As it happens for Chicago, summer temperatures are generally around 72°F (22°C) and winter around 28°F (-2°C) (average day/night), and halfway between those is around 50°F (10°C), which happens to be about the deep soil temperature. It is NOT a coincidence!
Below, we provide a map of the US which shows the measured well water temperatures, which generally accurately reflect this annual average temperature. For other countries in the world, it is easy to get a pretty good idea of this number. Just find the daily average temperatures throughout the year and average them. Here are a few examples:
The European cities shown here would have excellent performance of this system, as their annual average temperatures, and therefore their deep soil temperatures, are in the low 50°sF. The cities that have deep soil temperatures around 80°F would have no way to cool house air down to a desired 76°F! Probably around 85°F is the best they could hope for, if that were acceptable, but in a linked page, we discuss using this system in very hot climates to pre-cool the house air such that a conventional A/C might have to work less to save some money. So this system DOES have some limits! We provide linked pages which present two other variant approaches, one of a vertical system to get the heat exchangers much deeper underground where they will not heat up as much during continuous brutally hot summers. The other is an approach that adds in a crude bellows or air pump to operate similar to how the very first air conditioners and refrigeration worked in the 1840s. This last approach can provide as much air conditioning and de-humidification benefit as anyone could ever want or need, anywhere in Earth.
By being able to entirely and continuously cool a house all summer, without a compressor running, many homes could save $1,000 or more, EVERY summer! This is certainly a great thing for the homeowner, who has to pay the bills, but it can also help many energy-strapped utility companies. If a substantial number of people would install this system, the summer electricity demand could be substantially reduced.
Does it GET any better than this? You SAVE $1,000 (or more) every year for the rest of your life. You have a cooling system that is unbelievably environmentally friendly. AND you're helping the short-sighted electric companies past their crisis. And all this does not even cost an arm and a leg! (Maybe a toe or two! But how often do you ever have to count above eighteen anyway?) There are a lot of variables, like home size, climate, soil type, etc, but a do-it-yourselfer could put the whole system in for under $1,000 for some houses. (Contractors would charge more, but probably still a manageable cost.)
There is a higher class way to calculate this very accurately for
any location and any type of soil and any level of groundwater in it,
mentioned below, which uses the Kelvin Integral to do the calculation.
That method can accurately predict the deep soil temperature at any depth and with any of the variables just mentioned (and more) and it also can predict the effect of you sending large amounts of house heat into that soil from the tubes. A local Engineer should be able to solve the Kelvin Integral for your application, should you feel it critical to know ahead of time. However, in assuming that most people will not do that, I simply OVER-DESIGNED the generic system described below by about a factor of two, for moderate climates. As a science geek, I happen to LIKE the results of the Kelvin Integral as it provides predictions for how the system will work: (a) immediately; (b) after one hour of really hot sun; (c) after an entire day of unbearable heat; (d) after an entire week of such; (e) after an entire month of such; (f) you get the picture! As you and the sun are loading that soil with heat, the heat gradually conducts and convects away (which the Kelvin Integral also accounts for), but the deep soil temperature may rise after extensive heat input, from either or both of the sun and your house. The point is, with SHALLOW tubes, you might get great cooling for a few minutes but then the ground may heat up enough to stop providing any more cooling (until it can dispose of that heat naturally first).
If you followed the information in these few paragraphs, then you now understand WHY we mention using the Vertical-Water-Filled variant in really hot climates. By boring down well beyond 16 feet deep, the temperature down there should be as good as it gets for you, as the Sun cannot cause it to heat for the reasons discussed above. However, the water-filled variants do have an additional complication! I chose the AIR system to base this whole presentation on because there is only a SINGLE heat exchange which has to occur, when your house air wanders by some cool wall surface on its regular trips down there. The water-filled variants all need a SECOND heat exchange, first from the hot house air to the water, and second from the water to the walls of the tubes down there. The reason why this needs to be considered is a little technical! Any heat exchange process REQUIRES a temperature difference to drive it. A GOOD heat exchanger commonly only needs a few degrees difference, but when that has to be done twice, and you're in a climate that is hot to start with, the benefit of the deep wells has to overcome the needed few degrees temp differential before actually doing wonderful things! It probably will, but CALCULATING it is what entire courses of College Thermodynamics are spent on! No innocent bystanders deserves the pain of having to learn thermodynamics, so my generic guidance, of using the standard AIR system if your climate is Temperate, but using the vertical-water-filled variant if your climate is beyond what the air system could deal with. Other than that, find a College student to do some math for you!
The following discussion often refers to LONG-TERM PERFORMANCE as well as SHORT-TERM PERFORMANCE, as both are important for most climates. However, if you are in Alaska, you may not need to worry about long-term cooling, and a single afternoon of A/C may be all you need to have! I designed a GENERIC system below, which should work great for the majority of people. However, if you happen to live on the surface of the Sun, some adjustments will be necessary!
A side note, added Summer 2010: You may have noted that the trapped Chilean miners were inside a mine that was constantly at around 95°F. Is this a problem for this system? No. For nearly everywhere, for the first 400 feet of depth, the temperature gradually COOLS as we have been describing. So as long as you don't dig deeper than 400 feet, the A/C effects will be as described here! However, BELOW 400 feet deep, the soil (actually rock) starts getting hotter, at the rate of around 4°F (2°C) per 300 feet (100 meters). Why is that? Because the center of the Earth contains a lot of radioactive elements which are constantly decaying and therefore giving off heat, and that heat (slowly) makes its way through the 4000 miles (6400 km) radius of the earth up to escape from the surface to outer space. The miners were in that hot mine because they were at 2200 feet (700 meters) deep. Even deeper mines are even hotter. (This will probably NOT appear on Trivial Pursuit or Jeopardy!)
Warning! This presentation is VERY long and sometimes more technical than many people are comfortable with! Sorry about that! But there are some rather stupid ideas sometimes presented that resemble this concept, and we want people to be able to get actual good performance from this system, so we feel the need to try to make sure that people do not confuse this with systems that use tiny buried pipes or coils or such things! So IF you like this concept but cannot swallow all the technical stuff here, there must be some relative or neighbor who loves technical stuff that you can dump this on to see if it can be used by you! That person might even LIKE Psychrometric Charts and such things!
Some Technical StuffThere is a somewhat similar energy source called Geothermal Energy. That is actually different from the energy involved in this device. Geothermal energy taps energy that is coming upwards from the hot center of the Earth. Most geothermal energy applications involved rather deep wells or a location near natural hot springs. This system does not need that energy source. Most of the energy involved in this system is actually solar energy, which had arrived months earlier and became stored in the mass of the earth, just a few feet deep.
Each location on Earth has a certain annual energy input from the Sun and a certain energy loss from radiation (into space), conduction and convection. In the long-term, these two must be identical.
The consequence of this is that Equatorial locations, which receive more solar energy during a year, must necessarily have a higher average ground temperature in order to radiate, conduct and convect that greater amount of incoming heat away. Polar regions have colder earth for the same reason. Very near the surface, the ground temperature is greatly affected by day and night and summer and winter, but even three feet deep, those effects are fairly minimal. If you go down to twelve feet deep, the summer-winter differences are generally under 1°F, and they tend to lag several months behind the seasons.
Here is a map of the US showing average deep soil/well temperatures.
Just find your location. The usual indoor design air temperature for
air conditioning is 76°F, so if the deep soil in your area is under
76°F, this approach can work! This system needs to have several degrees
of temperature differential to drive the heat exchange processes,
with around 5°F usually being sufficient, so a deep soil temperature
of 71°F or lower is best for the best performance.
(Even if it was above, house air could
be substantially cooled, reducing the need for a central air conditioner
to work, STILL saving you a lot of money!)
As cooling or heat is removed from the deep ground in our system (or in a ground-source heat pump), it is gradually replaced primarily by heat conduction from nearby soil, through the soil. It turns out that many soils are pretty lousy at conducting heat in this way, so this replenishment tends to be fairly slow and nearly always represents the limiting factor in the long-term operation of this system. In areas where the soil is saturated with water, some convection can occur, too. Therefore, if the deep soil is moist, this system works tremendously better. Water-source heat pumps nearly totally rely on this convection effect.
Because any substantial volume of earth contains enormous amounts of heat/cool storage but the many soils are so poor at heat conduction, the AREA of the interface (tube wall) between the soil and the tube contents nearly always is the greatest limiting effect on short-term system performance. Ground-source heat pumps generally have very small diameter copper tubing, so the circumference and the outside surface area in direct contact with the soil is very limited. This tends to make ground-source heat pumps to often act like they have depleted the energy source very quickly. Fortunately, they have their compressor that just has to work harder, but can still continue to work during fairly severe depletion. And, in any case, energy from nearby soil replenishes the energy source in just a few hours.
Our approach is to use much larger diameter tubing underground, which greatly increases the contact area between the soil and the tubing surface. This total "area of contact" is one of the most important characteristics to design for in this system! Again, in more technical terms, heat exchange is proportional to the surface area of the heat exchanger. It determines the amount of heat (or coolness) that can be given to the house air that is flowing through the tubes, in other words, the Btu/hr rating of the system (or short-term performance). Even normal ground-source heat pumps would benefit from such a larger surface contact area, but their compressor allows designers to calculate very minimal systems, to keep their digging (and copper tubing) costs at a minimum.
Further, our approach is to divide the underground air passageway into several "parallel" paths, separated from each other by around six horizontal feet. This configuration takes into account the very slow soil heat conductance and yet allows using a FAR larger mass of soil to participate in this system, which determines the long-term performance of the system.
In case you are curious, we chose bundling all the tubes together on the way to the house as the simplest and least expensive way to join the tubes and also make sure they are all watertight. Other, better ways exist, where the bundles are replaced by large ducts, and especially tapered ones, to make sure that the same amount of air goes through each tube. All such ways that we know of are very expensive to do! So even though the bundling approach has some disadvantages, it is reliably sealable to be water-tight/air-tight, fairly simple and easy to install, and fairly inexpensive. For the technical ones out there, yes, we intentionally over-designed the generic system to account for the different amounts of air flowing through the different length tube air paths!
In case you're still skeptical, the "heat exchanger" arrangement we are describing has a coefficient U that is around 8 Btu/hr/square foot/°F difference. If you look at ONE of our nine tubes, its circumference is around one foot and it is 50 feet long, so its area is around 50 square feet. If the house air begins at 90°F and the deep soil temperature is 53°F, there is 37°F difference. Multiplying these (8 * 50 * 37) gives an effective rating of 14,800 Btu/hr. That's ONE of our tubes, and there are nine of them! This suggests that the total system is capable of about 135,000 Btu/hr cooling, around four times as much as the normal house requires! Well, it could (almost) actually do that for a few minutes, but there are a number of factors that would get it down below 100,000 Btu/hr of cooling in under an hour and within a few hours to the 36,000 Btu/hr that we designed our "standard configuration" for.
Many larger houses and hot climates should probably have specific engineering done to determine that that is enough, but this system's million pounds of cool soil would often be sufficient for many houses and climates.
Basically, we are using modern engineering concepts to maximize the effectiveness of a natural phenomenon!
We could describe this in a different way. A 4" diameter tube can realistically carry around 60 to 80 cfm (cubic feet per minute) of air through it. Nine of them in "parallel" can therefore carry around 700 cfm, 12 can carry around 1,000 cfm, and 16 can carry around 1,300 cfm of total airflow. Conventional A/C units generally have greater airflow rates than this, but it is actually because their performance is poorer at slower airflow rates, and the house does not actually need that great an airflow. In fact, that same central A/C/furnace uses far less airflow during heating in the winter! The total airflow rate is mostly related to the comfort level inside the house, regarding how well the cooled (or heated) air is distributed to all rooms and to corners of those rooms.
Here are some recent additional versions of this system.
Virtually all of the heat that replenishes this system (or ground-source or water-source heat pumps, close cousins) originally began as solar energy that heated the surrounding fields, often months before. Virtually no actual "geothermal" heat is involved. However, there is no commonly accepted name for this process and we suspect that it will generally be thought of as geothermal heating/cooling. Oh, well!
Essentially, this is why basements generally stay cool in the summer and why caves remain at very constant temperatures. In case you have any doubts, just find a long underground culvert (like under a highway) or aqueduct or cave and stand near the open end of it. If the wind happens to be blowing in your direction, you will feel a rush of very cool air coming out of it. That air had actually entered the other end at the 90°F of the outdoor air and had been cooled in passing through that tunnel. That is essentially exactly what our sub-system does.
This might lead you to believe that no planning or engineering is actually necessary! Well, technically, you would be right! If you chose to bury a mile-long culvert, it would certainly work excellently! However, most people couldn't afford to do that! They would want the shortest, most compact arrangement possible, both to fit under their yard and to minimize the digging expense.
The example described above will work extremely well for most medium-sized homes in moderate climates. So, no additional engineering is necessary for such applications! But, where soil is extremely dry, or the climate is extremely hot, or the house is especially large, prudent design might involved extra engineering. There is even often an alternative here, too! OK! You make 4' deep trenches and place the ABS-PVC-DWV tubing in the bottom of them. Instead of immediately filling in the entire trenches, for such applications, consider filling in ONE foot deep of fill in the trenches! THEN, get (cheap) 100 foot-long coils of black polyethylene 1/2" water line from the store, and drill LOTS of small holes in it! Make water connections to this set of water pipes, which are now one foot above the much bigger air tubes below. THEN fill in the trenches and re-plant your grass.
Let's say you have a moderate sized house in a moderate climate and you want to have 36,000 Btu/hr of cooling. Again, there are straightforward engineering conversion formulas that indicate that this is equivalent to about 10.5 Kilowatts of actual cooling effect. Our thoughtful government has provided us with a SEER (Seasonal Energy Efficiency Ratio) or COP (Coefficient of performance) for each air conditioning system sold. Let's say for a moment, that yours happens to have a SEER of 10 (about the same as a COP of 3.0). You would just divide the cooling load (36,000) by the SEER (10) to know how much electricity will actually be used (about 3.6 kW) of electricity. If you knew the COP instead, you would divide the cooling effect (10.5 kW) by the COP (3.0), or again, about 3.6 kW of electricity.
Most actual central air conditioners have a lower SEER than 10. Government studies have established that home central air conditioners average using 1.49 kW of electricity for the compressor and another 0.14 kW for fan motors, for each "ton" (12,000 Btu) of rating. Our example 36,000 Btu/hr system (3 tons) would therefore probably use about 4.9 kW of electricity (which calculates to a SEER of about 7.3).
Still with us? Now say you have a REALLY hot day, and the compressor ran virtually continuously for all 24 hours (not particularly good for the compressor!). You would have used up 4.9 * 24 or around 118 kWh of electricity that day. Look at your latest electric bill and it will tell you what each kWh costs you. Recently, electric rates have been going wild in many parts of the country. In an area where such rates are still relatively stable (Chicago), the rate is still only around 10 cents per kWh. This number actually rises to an actual bill rate of around 15 cents per kWh because they add a Monthly Delivery Charge and a variety of taxes onto your monthly bill. One hundred eighteen kWh would therefore cost 118 * 0.10 or about $12. That single very hot day would have cost $12 in air conditioning. This is for a very moderate sized house and air conditioning system and for very reasonable priced electricity. We have shown you this logic here so you could figure these things out for YOUR system using electricity available to YOU.
You can probably now better understand the very large electric bills you receive during the summer. Twelve dollars for a hot day could easily account for $200 per month. Far more, for larger homes and for where electricity is more expensive than ten cents per kilowatt-hour.
The system described here does not involve any compressor! The only electricity necessary is for a fan or blower to push the house air through the underground tunnels! In many cases, this can be accomplished with a fan or blower that only uses 200 watts (0.2 kW) or less of electricity. In terms of SEER, the effective rating would be (36,000/200) around 180! That's nearly TWENTY TIMES as energy efficient as the very BEST heat pump or air conditioning system!
On that example very hot day described above, let's look at the figures. Instead of continuously using up 4.9 kW of electricity, this system only needs 0.2 kW. In 24 hours, that's 4.8 kWh. At the electricity cost mentioned above, that's $0.48 of electricity instead of $12.00! A full month of such heavy cooling would cost around $10 instead of over $200!
There are actually even some possibilities of eliminating the cost of running the fan, too, eliminating even that last $10 of monthly operating expense! However, it is such a minimal remaining expense, it is probably not worth even trying to do that!
This basically states the point of this system (regarding air conditioning). If you have a moderate sized house in a moderate climate and you have moderate electricity costs, you are STILL likely to sometimes save $200 in a single month! In a whole summer, this "eliminating" of the cost of air conditioning the house or building, might easily save you $1,000. Basically, whatever your total electric bills were last summer, inflated for the recent price hikes, THAT'S what you would save! And, that savings would be EVERY year, for the rest of your life! What a deal!
And the coolest (pun intended) part of this is that all of the comfort in the house is PRECISELY identical to that when using conventional air conditioning. The temperature and humidity levels will be identical. Of course, you would not have a noisy condenser unit running outside your house, so if you like that sound, you're outa luck! All this, in a system is about as "natural" as you can get! And bonus $$$ savings in the winter!
If you live in ANY house, and YOU pay the electric bills, you must now see the exquisite logic of this system. It even has a bunch of additional bonus characteristics. For example, there is virtually NO chance of ever being charged for any repairs to the system, because there is virtually nothing that could ever break or fail or leak!
It seems to us that such homeowners will even be doing good things for society and the environment, as well as pocketing an extra $1,000+ each year. Consider California and its amazing energy woes, particularly electricity. Even during the winter, their electric companies and power grid have great difficulties in keeping up with electrical demand. Consider if a million California homeowners decide to save $1,000 each, every summer, with this type of system. They're smiling! LOTS of happy people in California! But consider this! If a million California homeowners are NOT taking 5 kW each from the power grid during the summer, that's a reduction of load on the power grid of FIVE THOUSAND MEGAWATTS! It is unclear if that would "solve" the lack of planning of California's electricity needs, but it would have to help!
Summer Air ConditioningThis underground tube concept is REALLY beneficial during the summer! The deep ground is still around 52°F in Chicago in the summer. Rather than using an electrical air conditioner, which is pretty expensive to operate, why not make BOTH ends of that underground tube come through the basement wall? Then, use the existing air handler or furnace blower to push the house air through this tubing. The hot house air (maybe 80°F or 90°F) that was sent into the tubing would obviously be cooled (and even de-humidified!) while passing through the underground tubing loop and the SAME air would come out the other end of the tube, back into the house at as low as around 52°F. It would quickly and comfortably mix with the existing house air and cool the entire house down, without huge electric bills for operating an air conditioner. (This is again describing the system shown earlier).
Any existing furnace/air conditioning system already has a 'Summer Fan' switch on the wall thermostat. This switch just turns on the blower, without activating the furnace or air-conditioner, and could easily be used to control the airflow through the underground tubes. Alternately, the 'Air Conditioning' switch position on the thermostat could be used. This would then allow the wall thermostat to automatically turn on and off the blower, blowing the house air through the underground tubes as necessary to maintain the desired temperature set on the thermostat! Absolutely automatic! Absolutely identical in usage to traditional air conditioning!
Summer De-HumidificationIt turns out that there are even bonus benefits for summertime use, if the tubes are installed in a certain way. The hot summer house air that is sent into the tubes often has very high relative humidity. Both the heat and the humidity make us uncomfortable in the summer. An air conditioner not only cools air but it removes humidity from it as well. (That's why window air conditioners tend to drip.) (It's also why the walls of caves are usually damp and the air down there seems dank.) In the underground tube, that hot, humid air is cooled down by the cool pipe and soil around it. For complicated physical reasons, the RELATIVE humidity gets higher as the air cools. Soon, some of that humidity can condense out on the walls of the tube. (This occurs at a temperature called the dew-point). If the design and planning of the tube system is good, by the time the air has gotten to the house, it is not only cooler, but it has been de-humidified as well! Both of the functions accomplished by an air conditioner are accomplished in a far more natural way. With FAR less electricity and expense involved!
Interestingly enough, this system usually actually lets you control a comfort parameter that normal air conditioning does not, the Indoor Relative Humidity! Massive government tests have determined that the ideal summer indoor conditions are 76°F dry-bulb temperature (normal temperature) and 40% Indoor Relative Humidity (IRH) (See any ASHRAE Handbook or any psychrometric chart, as below). Store bought air conditioners were designed to accomplish approximately the right IRH as a function of the temperature, so you don't actually have any control.
This system actually does (if you wish it!) Much of the foregoing discussion has mentioned air returning to the house at 52°F in our examples. This system can actually be used in that way, but that is usually not the ideal situation. If the air passing through the tube actually gets down to 52°F, then the great majority of its moisture content would condense out on the walls of the underground tubes. That's a desirable goal, but in this case, we're doing TOO good a job! Once that air comes out into the house and becomes warmed to the 76°F room temperature, it may have too low an IRH for best comfort.
You can use a standard Psychrometric Chart, as below, if you want to plan the humidity. Say you are starting with air that is 85°F and 60% indoor relative humidity (the lower end of the red line in our example). The Psychrometric Chart immediately shows that there is 0.0155 pound of water vapor in every pound of the air. When it is cooled, it is first a reversible adiabatic process, which keeps the Enthalpy, the energy content of the mixture, constant (the red line in our example to the left and upward, along a line of constant Enthalpy) and the actual amount of water vapor does not change, so the movement is to the left on that Chart. As air is cooled, it can hold less water vapor, so the RELATIVE humidity rises. You can see the red line cross the higher relative humidity percentages in the chart. In this case, you can see that by the time the air is cooled to about 74°F, the relative humidity has risen to 100%. Up to now, no de-humidification has occurred. But once the relative humidity has gotten to 100%, further cooling requires that water condense out, in this case, on the walls of our underground tubes. On the Psychrometric Chart, continued cooling follows the 100% humidity line downward and to the left (as the green line in our example). If the air is cooled all the way to available 53°F as in our (Chicago) example, the Chart shows that we would now have 0.009 pounds of water per pound of air. This means that about 0.009 pound of water was removed (during the green line portion). (If the house was 1500 square feet, with 8 foot ceilings, and therefore contained 12,000 cubic feet of air, or around 930 pounds of air, then 930 * 0.009 or about 8 pounds of water was removed, more than a gallon.) When that air becomes heated to the desired room temperature of 76°F, we go isentropically down to the right on the Chart, to find a resulting IRH of about 20%. That is too low for best comfort, and NOT inside the Comfort Zone of the ASHRAE Comfort Chart (a special version of the Psychrometric Chart). Therefore, conventional A/C units (and our recommendation) only cool the air down to around 60°F, as we have shown in our example green line. Then, when that air warms up to the desired 76°F of the house air (as along our blue line), the resulting Relative Humidity is the 40% that the ASHRAE Comfort Chart recommends as most comfortable (in summer).
We (and all conventional A/C systems) have reduced both the air temperature and the Relative Humidity to the desired levels.
So, how would we control the IRH? By controlling how long a time that individual air molecules would be inside the tube system! There are elegant engineering ways of calculating what cfm of blower airflow would provide final airflow temperature, but it is generally easier and more accurate to just measure the (web-bulb) temperature as the air re-enters the house. Or the Psychrometric Chart could be used to determine it. If it is higher or lower, just adjust the air flow cfm through the tube system so that the air returns at that saturation temperature. For locations where the ground temperature is higher than that 60°F, the house humidity level may be higher than desired, and, under some circumstances, a de-humidifier may be necessary in the house.
It might seem that changing the air flow through the tubes, and therefore the temperature that the air returns to the house, would affect the overall system Btu/hr capability. In general, it doesn't. A LOT of air coming back at 60°F has as much cooling effect as a lesser quantity of 52°F air. The actual coolness being delivered is proportional to the PRODUCT of cfm and temperature differential. So, with 80°F air entering the system, either 1000 cfm at 52°F or 1400 cfm at 60°F, would provide the same Btu/hr of cooling. Only the IRH would be different.
In case you are an environmentalist, please note that there is no CFC Freon refrigerants that could affect the ozone layer or otherwise pollute anything. This system represents a version of an elegantly natural, low-tech approach that does the job far better than the high-tech air conditioner does.
Depending on the climate of the house, it might be desirable to arrange this system for primarily or exclusively A/C operation, with little or no concern about winter benefits. In such a situation, there can be additional benefits from looping the tube around so that both ends of it come through the basement walls. Ducts (with dampers) would connect the existing furnace (or air handler) ducts to this path. At whatever point the wall thermostat would call for cooling, that existing blower would turn on and appropriate dampers would move so house air is blown through the underground tubes. This recirculating method has certain advantages, like better control of house humidity, better usage of the available cooling effects (higher net efficiency), and air filtration advantages. A pure recirculating system would have the potential of the super tight house Indoor Air Purity concerns. Probably the ideal solution for a primarily cooling installation would be a primarily recirculating system with a small intake provision for bringing in a little make-up air (for pressurizing the house).
If you already have a full basement, you already have a crude version of this system! You have certainly noticed that such a basement always stays cool in summer (but that it is also often rather humid). The basement floor is actually acting like the walls of the underground tubes we have been describing. House air that flows along that basement floor becomes cool from the coolness of the floor. Just like in the underground tube arrangement, that air also gives up some of its moisture in the process of being cooled, which tends to make basement floors slightly damp and makes the basement sometimes feel humid.
With the underground tubing, the effect of all this is much more prominent, and the moisture that condenses out of the air is collected and removed, very much like a normal air conditioner does.
The basement floor has plenty of "interface area" so short-term performance can be great. If you live in a climate where air conditioning is only needed for a few hours at a time, you could probably get most of the benefits of air-conditioning from just recirculating your upstairs house air through the basement, using the existing house blower/air handler.
If there is NOT thermal insulation under the basement floor, then fairly simple engineering shows the short-term benefit you can get from this cool basement floor. Say the house is 25 feet by 40 feet, so the basement floor is 1,000 square feet. If the ground underneath it is at 52°F and the house air is at 80°F, then the "cooling effect" is seen to be (1,000) * 8 * (80-52) = 224,000 Btu/hr! That would be PLENTY to cool your house, and that's why recirculating the upstairs air through the basement can quickly cool the house. Just sending that air through the basement does not actually send all of that air right along the basement floor, so the "basement effect" winds up to be far less than 224,000 Btu/hr, but can definitely be the 36,000 Btu/hr of cooling that your house actually needs. For the record, if you do NOT cause the house air to blow along the basement floor, and leave it to natural convection, instead of 8 in the formula above, ASHRAE says that it is 2.347; also, the basement air is probably nearer to 65°F instead of 80°F, so the calculation gives around 104,000 Btu/hr of cooling, again, explaining why basements stay cool! (Keep in mind that this approach does NOT remove moisture from the house air, so there is no de-humidifying effect and a separate de-humidifier would be needed).
However, if your air conditioning needs are for more than a few hours at a time, this approach will soon lose its effect. Gradually, the soil underneath the basement floor will warm up. Since it is a finite volume of soil (basically the size of the house), once it has all warmed up, the cooling effect would be greatly reduced, until an extended period of non-use occurred so the soil could again cool back down. Anyone who has tried to cool their house in this way has noticed the reduction in cooling effect over time.
Any Engineer can solve this Integral Kelvin equation to determine this effect. (By the way, this is the scariest of the equations involved! And the Technical information Packet described below includes a table of solutions for this equation for all practical situations.) If a common, fairly dry, Midwestern soil is under the house, and if this example house needed continuous cooling of 36,000 Btu/hr, the solution shows that the soil a foot below the basement floor would have risen in temperature by 24°F after just one week! By then, the floor would have been at 76°F and there would have been no cooling effect at all. Even after just a couple days, the cooling ability would have dropped to about half, because the soil down there would have heated up to around 64°F. With a more moist common Midwest soil down there, the effect is only half as bad, with a decent cooling effect existing beyond a full week.
A simplistic engineering approach could also be used to roughly estimate long-term performance. In VERY approximate terms, the soil temperature one foot down would probably reflect the overall effect on TWO feet deep of soil down there. One thousand square feet, two feet deep is 2,000 cubic feet or about 200,000 pounds of soil. The specific heat of dry soil is around 0.3, so the heat capacity of this mass of soil is around 0.3 * 200,000 or 60,000 Btu/°F. If 60,000 Btus are put into that ground, it would rise an average of 1°F. Since we are talking about putting 36,000 Btu/hr down into that soil, that's 864,000 Btu/day. This implies that the soil would rise in temperature by around 14°F in a 24 hour period of operation, relatively in line with the solution of the more precise Integral Kelvin equation.
These comments are included to emphasize the need for calculating the long-term performance. Even though a basement floor starts out with incredible short-term cooling capability, in just a few days of use, that cooling effect gets depleted. Larger volumes of soil need to be involved when extended periods of cooling as necessary. The network of underground tubes accomplishes this.
Ever since we first started offering this system for free in late 2000, we have also offered a Technical Packet, too. We have always asked people to make a Donation to ANY Charity or Church of their choice, anonymously, Cooling System - Technical Info Fee Arrangement of $250, for a collection of equations, formulas, charts, (pre-calculated solutions of that Integral Kelvin equation!), and a lot of additional guidance regarding designing of the tube sizes, materials, lengths, and a bunch of general suggestions. If you happen to be or to know a Thermodynamics Engineer, he could probably do all of this for you and you wouldn't have to pay anyone anything! The planning involves the size of the house, the climate it is in, its estimated heating/cooling load, the number of members of the family, the size and shape of the yard available, the type of soil, etc., to determine the diameters, configurations, patterns, depths, etc. of the components of this system. Many variables are sometimes involved, including mountains, lakes, forests, and other local conditions.
By the way, we really LIKE the fact that many thousands of people, world-wide, have indicated that they planned to install this system. But just as much, we like the fact that, so far, in mid-2012, over 9,200 people have requested the Technical Packet. Assuming that they each fulfilled their word of Anonymously Donating $250 (US) to some Charity or Church, that means that those people have contributed over a million total dollars, all anonymously, to many different worthy causes! We REALLY like that! Can you imagine a Soup Kitchen or Homeless Shelter or Food Bank that finds an envelope of $250 in their mailbox one day? Does it get any better than that?
Back to the underground tubes system described in this web-page!
Depending on the local cost for usage of a backhoe, or if you happen to love to shovel(!?), the installed cost of this system may be less than a conventional central air conditioning system. Depending on the climate and house size, the necessary pipes could cost around $500. Depending on how much a backhoe or trencher costs in your area, that might also be around $500. This suggests that some installations could realistically be put in for well under $2,000. If you can put in LOTS of narrower tubes, a Ditch Witch Model 1820 trencher can make 4 foot deep trenches for around $220 rental per day. And you essentially eliminate ALL those huge summer air conditioning electric bills! And you get significant energy savings in winter, too! Forever!
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