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Earth Tubes: A Natural Way to Air Condition Your Home

There is nothing nicer than coming inside on a hot, muggy summer day to feel the freshness of an air-conditioned home. Traditional air conditioners, however, are one of the most energy-intensive appliances in our homes. Only a couple feet underneath where you are standing, however, the air is always a comfortable 55 degrees Fahrenheit. If only it were possible to get that cool air from underneath your feet into your blistering hot home. Earth tubes offer a natural, ecologically sound air conditioning option to keep your home cool on even the hottest summer days.

How Much Energy Does Your Air Conditioner Consume?

As with a number of aspects of our modern-day industrial civilization, we simply don´t know or understand the ecological costs associated with the comforts we have come to depend on. In many ways, ignorance is bliss and it is comforting to naively believe that a cool home on a hot summer day is a normal part of the landscape.

The distance between consumer, the origins of his or her consumption and the end place of his or her wastes facilitates this obliviousness to the true effects that our industrial lifestyles perpetuate. Unless you live near a coal burning plant in Kentucky or have nuclear waste buried beside the gravesites of your ancestors in Arizona, you probably have little actual connection to how the electricity your home uses is supplied or the end product of that energy.

The cool air that dries the sweat from our foreheads, however, is far from inoffensive. While some small, window-based air conditioners consume up to 500 watts, a large central air conditioning unit that many large homes and almost all businesses have is easily a 3500-watt appliance.

While you can cut back on your ecological footprint by trying to occasionally open windows or turn the thermostat a bit higher, the fact of the matter is that because most modern-day homes are so poorly designed, chances are that your home could resemble a small oven if you try to turn the air conditioner off. In recent years, heat waves have swept across different parts of the world. The summer of 2003 in Europe was one of the hottest summers on record. In Spain alone, over 140 people died as a result of the heat, mostly elderly people who were stuck in homes that heated up like ovens.

If the modern-day housing and construction industries embraced ecological design principles, much of the potentially dangerous heat from the summer sun could be avoided. Passive solar design makes it possible to block the hot sun from the summer months while allowing the winter sun to enter the home and add needed warmth. Unfortunately, the first step of most home construction is to level the site and clear any trees or vegetation that are “in the way.”

The Coolness of Caves

If you have ever spent time exploring a cave, you might have noticed that caves always seem warmer than the outside temperature during the winter and cooler during the summer. The actual temperature of caves depends on the average annual surface temperature of the place where they´re located. Carlsbad Caverns in Texas has an average temperature of 70 degrees while Crystal Cave in Wisconsin averages a much cooler 49-50 degrees. Might it be possible to move that cool air from underneath the soil into your homes to provide an alternative source of cooling air?

What Are Earth Tubes?

Earth tubes, also known as ground coupled heat exchanger systems, aim to take advantage of the cool air beneath your home to keep your house comfortable during even the worst heat waves.

As we mentioned above, the temperature of the ground just a couple of feet beneath our feet is a usually a comfortable temperature anywhere between 50 and 70 degrees Fahrenheit. While some ground coupled heat exchanger systems involve complicated pumping of water throughout the system of tubes, a simple earth tube system simply requires plastic PVC plumbing pipe, and a small fan.

The entrance for the earth tube system is a piece of pipe that sticks up out of the ground somewhere outside your home. A minimum of 100 feet of pipe is buried several feet underground until eventually passing underneath your home foundation and into your home. You can then branch these tubes in several directions so that the tube system exits into different rooms that you want to cool during the summer months.

A blower is situated at the entrance of the earth tube system to move the air through the piped system and into the home. By burying a long portion of plastic tube underneath the ground, the cool temperature of the soil is exchanged with the warmer air that is entering the tube. Over the course of the 100 feet of pipe (or more) the air, through the physics of heat exchange, becomes cooler as the surrounding soil gets minimally cooler. The result is a comfortable flow of cooler air that enters your home without the aid of any sort of chemicals, compressors or fossil fuel dependent central cooling systems.

How to Install a Natural Air Conditioning System in Your Home

The exact specifications for your earth tube air conditioning system will depend on the specific climatic context where you live. If you live in Maine, for example, the average temperature underneath your soil will be much more pleasant than if you live in southern Florida.

As a general rule, the cooler your average annual surface temperature, the less amount of piping you will need. Since the temperatures of the subsoil will be cooler, you will also be able to get away with not burying your piping too deep. In the case of most cool weather climates, a two-foot depth should be more than enough to reach an optimal soil temperature to cool your home.

If you live in warmer climates, it is advisable to bury more pipe (between 150 and 200 feet) and bury it deeper. You may need to invest in a more powerful blower for the longer your piping.

Once you have your pipes buried, it is important to consider exactly where you want the cooler air to enter your home. The south-facing side of your home is where you will receive the most heat from the sunlight, and is a good candidate for at least one exit for your earth tube system.

Using the Earth to Cool Your Home

Why would anyone choose to cool their home with fossil fueled powered air conditioners when an infinite source of cool air is just below their feet? While remodeling an existing home for an earth tube cooling system could be expensive due to the digging and opening holes in your floor and foundation, the savings (both economic and ecological) will last a lifetime.

Tobias Roberts

After working in the development industry for over a decade, Tobias decided it was time to stop advising Central American farmers how to do things if he didn´t have a piece of land to live coherently with what he taught. Together with his family he runs a small agro-forestry farm, tourism cooperative, and natural building collective in the mountains of El Salvador.

26 Comments

    1. That’s right, and the writer could also have found out with a simple WWW search that the average temperature is not 70 but 56 degrees F.

    1. It is necessary to have a pipe with a small outlet pipe for the condensed moisture in the pipe. For this to drain a slope is usually required. My partner Phil Baulch from Python Solar Heating & Low energy Cooling installed a system like this at Mildura Eco-Living centre, several years ago.

      1. I don’t think a drain pipe will suffice to prevent mold. I would use a stronger fan and put HEPA filters at each outlet

    2. If you pass the cooled air through a mass like a rocket stove uses in your house then you get a cooling mass rather than dealing with the mold or radon issues. I read about a design that uses concrete culvert pipe so there is plenty of airflow and it dehumidifies the air in the tube as it leaves water on the surface by condensation and serves as its own drain to the outlet somewhere down hill. This chimney can also be used as a dehydrator which is great for tropical areas. Yes underground it was on a slope to drain and connected up to an even larger mass chimney for heat transfer from the home to the chilled stone. The chimney was dual purpose allowing fire exhaust for cooking, also using the outside air for draft so as not to draw conditioned air from the house.
      .

      1. I really like the idea of having a cooling mass. Perhaps pipes could be run through the floor on their way to the rocket mass bench. The chimney could provide a draw to pull air through rather than having to blow it–the hotter the day, the more the chimney would heat and the greater the draw (perhaps a black metal pipe could sit on top of the chimney to increase the effect).

  1. I remember reading about these many years ago in popular science magazine and if I recall correctly there is a rough calculation for how many square feet your house is to the diameter of the tubes and length of tubes. you wouldn’t buy any chance know where to find that calculation would you?

  2. While an enticing idea, I am leery of the actual results. Tobias- have you actually done this, or know anyone who has? And how were the results? I would think a couple hundred feet of plastic pipe would quickly warm the surrounding soil, ending the cooling effect. Heat transfer through soil takes time, and the number of air exchanges to cool a house is a large number. Also, what happens to all the condensed water inside the pipe? Mold. And if you try to provide a drain, where to drain to? You are already underground. This article is just feel good fluff if it doesn’t address real world practical details.

    1. The writer says “Over the course of the 100 feet of pipe (or more) the air, through the physics of heat exchange, becomes cooler as the surrounding soil gets minimally cooler.”

      This is nonsense, of course. I think “fluff” pretty well describes the article.

    2. I am doubtful the surrounding soil would warm much, since it is constantly being cooled by all the soil below and around itself. The fact that 50 cm down it is so much cooler than the surface indicates how little the heat from the sun and air penetrate the soil in spite of a constant heat difference.

    3. I believe the Earthship type homes use this concept of a pipe from outside being buried in a large mass of earth so that the hot air of the desert is cooled as it exits into the house. The system looked static to me, that is, no far to move the air, just selectively opened windows on the sunny side of the house. And it seems their homes stay a cool 68-70 degrees.

  3. Steve makes a good point. Cooling the incoming air will warm the soil. If the system is designed properly this can be an advantage in a temperate climate. The incoming air can be warmer than the average soil temperature in the winter and cooler in the summer.

    John Haiti wrote a book called Passive Annual Heat Storage (978-061590588-4). In the book he describes a house he built that uses a similar system. His system is driven by convection currents instead of a blower. So, it really does not use any fossil fuels.

    1. I don’t think radon would be a concern, since the air intake is simply outside air–you are passing the air underground, but, at least if the pipe is sealed, you would not be picking up underground gases.

  4. Digging a straight column can be done through hand-powered percussion drilling, and is not that difficult. It helps to have a group of people to work on it, and you can get 100 feet in a few days, then pass the equipment on to another person. The equipment can be hand-made by scrap metal by a blacksmith in non-industrilalized regions. https://www.wellspringafrica.org/drildesc.htm.

  5. This is not as simple as it sounds. First, if the temperature is the same all year round, that means that the earth is acting like a very good heat insulator. If the earth is acting like a good insulator, then it will be heated by the hot air flowing through the pipe. Second, I see the blowers that run forced air heating are about 500 watts. It would take even more to run air through a long 4″ pipe. It would be better to have many shorter pipes in parallel than one long pipe.

  6. When purchasing another ventilation system, think about the span of the room. A unit too little for space should run always yet one too huge will keep running in short cycles, causing additional wear and tear.

  7. Yes Wendy, you generally need to have a uniquely positioned house to enable this to work, as I do, with the house built on the a slope with the garden area at the top – then a condensation drain can run along the side of the house and come out into the garden down the slope. Otherwise, some form of sump and pump is needed.

  8. I see no mention of humidity. I can’t see this kind of system working at all across the southern part of the United States, especially in the high humidity coastal areas. I was in Natural Bridge Caverns near San Marcos, Texas a number of years back. I remember it being cool down in the cave (70 degrees F), but the relative humidity was 99%, so it felt hot. Of course, on the surface, the humidity won’t be that bad, but cooling the air to 70 degrees F without ridding the house of high humidity will lead to uncomfortableness in the house. I purchased a dehumidifier for my house a few years back, but the thing emitted hot air, thus heating up the house. If I had expelled the hot air outside of the home, humid air would have been sucked in in various places to replace it. This system seems suitable only for low humidity areas in the top half of the United States.

  9. I remember in the 1970’s the idea was called Mexican Cool Tubes. I think it was noted in The Whole Earth Catalogue but can”t be sure of this.

    I have heard of treating the inside of the cooling pipes with colloidal silver to minimise bacteria and mould.

    Assuming that there will be some condensation from the warmer moist air nearer the entrance of the pipe where there is a temperature gradient and the condensate flows down an inclined pipe past a point where there is no longer a temperature gradient, would the passage of the air over the condensed water of the same temperature cause it to slowly evaporate again minimising the need for draining the system?
    Perhaps it depends on the length of the tubes. The longer the tube the better chance of the condensate evaporating again.

  10. I am interested in building a Wallipini attached to a small garage (attached to my home) and have been considering some kind of ground coupling heating and cooling for the Wallipini. Could piping ruin under the slab of the garage and into the Wallipini act as a heating mass in winter and cooling mass in summer? My idea is to bring a pipe up to near the peak of the wallipini that could draw the hot air into the earth mass under the slab during the hot months and push cooler air into the wallipini so it wouldn’t get too too hot. In Winter the air flow could be reversed.

    Insulation a few inches under and a foot or two above would help keep the heat in the earth mass under the garage slab.

    Thoughts on whether something like this might work here in Maine?

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