Completely electricity-free cooling based on 3,000-year old principles.
How do earth tubes remove condensate?
There are small holes drilled into the bottoms (only) of tubes where the condensation drains into a gravel bed. In some designs non-perforated tubes are sloped away from the house and the condensate may go into a deep gravel pit, cistern for collection, or a drain sump may be used.
What are average soil temperatures year around?
It depends on where you live and what kind of winters and summers you have. Generally speaking, the deeper underground you go, the more stable the temperature. The air moving through the tubes in the earth at deeper depths, will follow those temperatures closely. Ambient temperature below the frost line, at an 8â€™ (2.5 m) depth may drop to 41 degrees F (5oC) in winter, and rise to around 65 F (18oC) in North America. It is not usually logistically or economically feasible to place earth tubes below the 10â€™ (3 m) level.
Can earth tubes be used in a humid climate?
The short answer is yes, although there appears to be some misconceptions floating around the Internet about whether or not earth tubes can work in humid climates. I think the misunderstandings come from poor designs, based on everything I have read.
We visited local homes in Nebraska and copied the designs of their earthtubes, which had been used for five years, and even 10 yearsâ€”the owners said they worked great in that humid climate. We made our own tubes when we built our straw bale house, then finally moved in and used the earthtubes (mid-late â€˜90â€™s). In 1999 we sold the house, and to this day the current owner continues to use the earthtubes and has never had a problem.
In fact, when it is 99% humidity outside and 99 degrees F (37oC), it is a cool and dry 70 degrees F (21oC) inside the houseâ€”a 30-degree (F) difference! So yes, if designed properly, earth tubes can absolutely be used in hot humid climates. If someone is having trouble and it is not a design problem, or user error, and if the heat and humidity levels are extremely high all of the time, then it could probably be remedied by adding extra earth tubes.
How long should earth tubes be?
We were told that, for completely passive earth tubes (no moving parts), 70 feet (21 m) might work okay, that 100â€™ (30 m) is ideal, and that 130â€™ (40 m) is better, but that after that the temperature does not really drop enough to make the extra cost worthwhile. We used 100â€™ tubes and they worked well for us, as did they for other people in our region. How much land do you have? Are you utilizing a fan (if so longer tubes are essential)? Is it much more costly to add a few 10â€™ sections to the tube? If not, consider going up to 130â€™ long, but I personally would not recommend going less than 100â€™ in length unless you simply do not have the room in your yard, in which case you might have to add more tubes to compensate.
These in-ground PVC cooling tubes are also known as air tubes, earth air tubes, a ground-coupled heat exchanger, an earth-air heat exchanger, thermal labyrinth, heat recovery ventilation, geothermal energy tubes, sustainability tubes, or a number of other terms. Earthtubes are an efficient way to cool or help heat your house in winter using natural cooling principles. They require no pumps or fans, and are completely passive (no moving parts).
This also means no electricity bill to â€œrunâ€ them, saving the building costs for the lifetime of the building, which keeps money in your pocket, and keeps your carbon footprint down. This is both natural cooling, and green cooling, simultaneously, and the principles take advantage of what nature already knows how to do.
Running the A/C (air conditioning) unit in a standard electric HVAC-based house can cost up to hundreds of dollars per month, especially in homes that are not insulated well. What a waste of money, yet who wants to deal with the summer heat! Earth tubes are aÂ solution as their payback time is minimal.
Earth tubes work by harnessing what nature provides us naturally, but just utilize simple principles and allow us to cool the ambient air temperature by usually at least 10 or up to 20 degrees Fahrenheit, depending on your homeâ€™s energy efficiency values.
Since they last for the lifetime of the house (some have been going for 25+ years without any problems, and mine were constructed in the late 1990â€™s and are still in use today), andÂ use no electricity, they can replace, or nearly replace any evaporative cooler (swamp cooler or Mastercool) or full size air conditioning unit (or several window air conditioners), depending on the house, location, and efficiency of the home.
History of earthtubes
Earth-air tubes are based on very old technologies from the Middle East, including ancient Persia, with similar designs that the Romans used, etc. Waterways and underground canals or qanats diverted water through a tunnel system that ran underneath buildings.
A vertical shaft was put in the lowest room of the house or building to tap into the tunnel of water, and sometimes a tower or chimney (sometimes a solar chimney) was added to the top of the house. The air would get sucked up out of the underground tunnel channel, up through the rooms in the house, and then escape out of the chimney/tower. The result was a very cool house, and a basement style room that was even quite chilly (similar to a root cellar).
Earth tube style A/C is similar in design and very simple to make, and does not require any underground water source (in fact, it creates its own water, much like a window air conditioning unit does, which drips away into a gravel pit back into the earth), and is not nearly as labor intensive as qanats or yakhchals. However, where you live and what kind of soil you have, how deep your frost line is, what type of weather you have, etc., will determine just how hard (or easy) installing your earthtubes will actually be.
Another consideration is whether you have a house you live in already that you want to add earthtubes to, or if you are planning on building a new house and would like to incorporate these into the infrastructure of the house prior to building. Both or either can be done.
Cheap home air conditioning â€“ how earth tubes work
When 1 or 2 windows ONLY (preferably high windows) is/are opened the hot air rises and escapes out that window(s). This will create a pressure difference inside the building, causing it to suck in air from the tubes. This is the natural process of convection working in your favor and why no pumps or fans or electric motors are needed.
The air going into the tubes from the outside, over 100â€² away from the floor/wall registers, cools off due to the earthâ€™s stable and cooler temperature, causing the water to condense out of the air, bringing the cooler dryer air into the house. It is a natural slow process and moves gently as an air exchange process all day long. Inside the house there will be a 10-20+ degree drop in temperature compared to outside.
You will need about one earth tube per room, although there are methods to split off the tubes in a â€œYâ€ fashion, or even make larger tubes that break off into smaller tubes. There are even ways to make the tubes above ground and covered over with a mound of dirt, and are ideal for underground or earth bermed houses. The earth-air tubes can even be used to create water from thin air, which can be collected for use on plants and more.