You may be familiar with a survival procedure taught to travelers to remote areas, where they spread a small sheet of black plastic suspended above the ground. The relatively cool ground beneath it causes the plastic to (often) be cooler than the hot daytime air, and some humidity (moisture) in the air can condense into droplets on that cooler plastic, and then be collected to drink to survive. That very crude method enables capturing a very small amount of the humidity in the air. The system described here is a far more sophisticated and far more effective way of doing that same process.
All atmospheric air contains some moisture, water, which we call humidity. If that air is COOLED, its "RELATIVE" humidity increases, because cooler air cannot contain as much moisture in it. If it is possible to cool it enough, the air gets to 100% relative humidity, and the saturated air starts having tiny droplets of water condense out on cooler surfaces. That water is PERFECTLY PURE water that is called Distilled water.
We have found that for many environments, simply blowing hot daytime air through a COOL underground tube, is able to cool the air enough for the condensation to occur. A Chart below provides the necessary information to know how many gallons of perfectly pure distilled water can be obtained in this way, directly from the atmosphere! (If any local supply of groundwater happens to be available, no matter how contaminated it might be, the performance of this system can even be greatly increased!)
This new system operates in a way that is also somewhat similar to how a solar still works, except that the Sun is not necessary, no sheets of glass are necessary, and not even any source for contaminated water is necessary! Rather than a solar still HEATING water to increase the humidity inside the chamber, so that it will condense on a relatively cooler glass cover panel, this approach uses the fact that deep underground, the soil is naturally cooler than the daytime air temperature.
All of these things occur because warm air can hold more water vapor in it than cooler air can, and that the deep soil is always cooler than the air temperature during hot summer days, and usually during winter days as well.
This amazingly simple and inexpensive system can realistically supply 10 gallons of perfectly pure water every day! There is essentially nothing which can break down, so it should reliably provide water for many, many years.
We are showing the warm daytime air as the red arrow at the right of this drawing, where it goes into and down through an inexpensive PVC 4" plastic sewer pipe arrangement. As tiny droplets of water form on the inner walls of the pipe, gravity causes them to flow downward to collect in the bottom of the Tee shown. A small pipe goes downward from there to a storage tank or simply a kitchen pot. The air continues upward and out, shown now as light blue to indicate that the air has actually also been cooled by the cooler ground, as well as the desired dehumidification that provided the pure water.
We show that the pipe must be at least one meter deep to be in cool soil that is not heated by summer heat. Deeper is ALWAYS better! The length of the underground pipe should be as long as is possible. If only a short pipe is used (say 16 meters or 50 feet) it will work fine for a while, but that deep soil will gradually get heated up by the hot air constantly going through the tube, and the effect gets reduced. Thirty meters or 100 feet should give very reliable water supply for most climates. Longer is ALWAYS better!
If this air can be de-humidified so that it becomes around 20% relative humidity, it would then only contain 0.014 pound of water in it. We would capture the difference, around 0.008 pound of water, as actual water droplets. This does not sound like much, but if we send just 1000 pounds of air through our underground tube, this is 8 pounds of water, or around one gallon.
The same Psychrometric Chart shows that at that temperature and humidity, one pound of air takes up just over 15.0 cubic feet, so we are talking about 15,000 cubic feet of air. If we hope to produce one gallon of this Distilled Water per hour, we then only need to send around 250 cubic feet of air through the tube every minute (15,000/60), a relatively reasonable airflow.
Depending on the local (daytime) temperature and humidity and the deep ground temperature, two gallons of water produced per hour is generally very realistic! Roughly 10 gallons of absolutely pure water to drink and for washing and batheing every day! All from a very simple underground tube!
This system can be installed WITH an underground tank and hand-pump, or WITHOUT that tank and pump, if a pit is provided so that people would climb down a ladder to get a jug of water. (drawings below).
There are actually a variety of ways that this performance can be easily enhanced. All the water that is produced by this system COMES FROM THE AIR. That means that it is absolutely pure water, called Distilled Water. Those accessories simply increase the relative humidity of the air entering the underground tube by evaporating any source of water that might be available, since when that water evaporates from its source, all the contaminants are left and only the pure water evaporates.
We will use the example of where the air temperature is 120ºF (60ºC) and the relative humidity is 30%. (Any other local weather conditions can be similarly analyzed). In the Psychrometric Chart below, this is along the very right edge of this chart, at the bottom right end of the red line. We can see that the air contains about 0.022 pound of water in every pound of air (which the chart also shows takes up a little over 15 cubic feet). THIS is the air that we will have enter the start of the buried tube system. As this air is cooled down by contact with the much cooler (80ºF or 27ºC) walls of the tube, it first cools in a process that is called reversible adiabatic. This means that the Enthalpy of the dry air, the energy content per pound, stays constant during the process. This is represented by our red line toward the left and upward.
We can see that the Relative Humidity percentage keeps rising as the air gets cooled. This is because cool air cannot hold as much moisture as warm air does. This process can continue until the air becomes saturated, or is at what is called the dew-point. Once our air has cooled to around 88ºF (31ºC), it has gotten up to 100% Relative Humidity, meaning that it cannot hold any more water in it than that.
At this point, the process necessarily moves along the green line in our example, downward and to the left, as the air continues to be cooled in the underground tube. This process is where mositure condenses out of the air, in our case, on the walls of the cool underground tube. By the time it has gotten to the end of the tube and the air is then at around 80ºF or 27ºC, the Psychrometric Chart shows us that the air which had contained 0.030 pound of water per pound of air at the start of the green (dehumidification) portion of the process, now contains only 0.0225 pound of water in it. The remainder of that initial humidity has necessarily condensed into (absolutely pure, distilled) water droplets on the inside of the underground tube. For every pound of air that passes through, (0.030 - 0.0225 or) 0.0075 pound of water forms inside the tube.
This basic system does not usually work at night, but generally should work well for at least five hours each day, meaning that more than ten gallons of pure safe water would be available from this extremely simple system each day. (One of the possible accessories, the HG 3a unit, enables this system to work 24 hours every day.)
Air needs to be passing through the system. It should NOT be necessary to have to use any blower, because the entrance to the tube could be provided with a wind-vane type of tail to turn the intake into the wind at all times.
However, if the climate is such that a blower is sometimes necessary, the 12-volt blower from a car heater system could be used, powered from a standard 12-volt battery which is charged by a simple windmill, such as a Savonius rotor made of an old 55-gallon drum.
The system as shown only involves maybe $60 of new 4" (10cm) PVC pipe. It could also be created using surplus large diameter pipe that might be locally found. It CANNOT use CORRUGATED pipe, as the water droplets would then be trapped in many puddles inside the tube. It should NOT be made of any pipe or materials that had earlier been used to carry dangerous chemicals. It should also NOT be made of "ceramic drain tiles", because the many joints between the tile sections are likely to leak and lose the precious water being collected, or allow insects or bacteria inside the pipe.
There are countless ways that this system could be created using only locally available materials. For example, if 4" (10 cm) or 6" (15cm) or larger sections of iron pipe are found, they might either be coupled with standard pipe fittings or there are standard rubber couplings and hose clamps that are inexpensive to join two sections of such pipe.
These arrangements really only produce significant amounts of water when the air temperature is high, in other words on sunny days near the middle of the day. Therefore, if a blower is used, there is no sense in it running except during those few hours during the daytime.
However, even in climates where the natural Relative Humidity is too low for this system to work, there may still be ways to enable it to provide excellent pure water. In the field near the tube's entrance, a large tarp might be spread out on the ground on which saltwater or rainwater other non-potable water might be spread. A second tarp, such as polyethylene, would then be supported several feet above that. The heat of sunlight would heat the upper tarp and cause the contents of the chamber created to get quite hot, probably even hotter than the 120ºF (49ºC) we first assumed. More importantly, any water inside that chamber would get heated, with a lot of it evaporating. This would greatly increase the Relative Humidity inside that chamber, possibly even getting up near 100%. In that case, the water there would evaporate (leaving any salt or other contaminants there on the bottom tarp) to raise the Relative Humidity of the air entering the intake tube. As that much higher humidity air has a lot of its moisture condense inside the tube, the system would provide even larger quantities of absolutely pure distilled water. The additional water production is difficult to predict as it is dependent on many variables, but it can be quite significant.
Off-Grid provisions for safe drinking water.
The Earth's Rotation as a Source for Energy
Waste Nuclear Power For Making Electricity And Heat?
The Physics of Efficiency In Electric Power Plants
Individual Ways of Reducing Your Energy Usage
Methods of Storing Energy for Later
How Much Energy Comes From the Sun? And Why is there Global Warming?
How does the Sun create so much energy?
Inventions Which Might Help Deal With Coming Energy Catastrophes
An Invention to Efficiently Make Electricity from Solar
Enormous Heating of the Atmosphere by the Alaska Pipeline
Air Conditioning without Huge Electric Bills and without Freon
A Method of Storing Summer Heat to (Nearly) Entirely Heat a House all Winter
An Extremely Highly-Efficient (and Fast, 200.0 mph) Transportation System for People and Products
The Sophisticated Woodstove I Invented in 1973
The Physics of Wood as a Heating Fuel
Why is the North Pole Heating Faster than the rest of the Earth?
A Possible way to greatly reduce Aerodynamic Drag of Airplanes
( http://mb-soft.com/public/index.html )
C Johnson, Physicist, Physics Degree from Univ of Chicago