You may be familiar with a survival procedure taught to travelers to remote areas, where they spread a small sheet of 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.
OK. You are skeptical! How can there be much water in the
atmosphere? And, in SOME climates, such as deserts,
that concern is valid.
But look at this graph of the outdoor relative humidity for a location
near Chicago, Illinois, USA. See that the outdoor relative
humidity is amazingly high in nearly all months! In the morning,
it is nearly always at least 80% and in the afternoon when it is usually
lowest, it is still generally over 60%. There is a LOT of water
in the atmosphere as humidity!
In the Summer, it works impressively. In the winter, the moisture is still in the air, but the ground is probably not cold enough to cause it to condense there. So, for a climate like Chicago, only about six to eight months of substantial water production is possible with the basic system. However, the (discussed) addition of a $200 accessory, an HG 3a device can produce even larger quantities of water every day of the year, and THAT is true in ANY climate, even a desert!
Roughly two billion of the six billion people living on Earth now do not have adequate supplies of safe drinking water and water for adequate cleaning and bathing. Many people have to walk hours to obtain small amounts of borderline quality water on which to try to survive. This amazingly simple device can provide PLENTY of water for MOST of those people!
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.
| NOTICE: The system described here is SEALED. The air inside the underground tube and any water in the soil CANNOT mix! This is EXTREMELY important! Otherwise, any sewage in the groundwater or pesticides or industrial contaminants in the soil or the groundwater might be able to seep into the pure distilled water that this system creates. |
There are actually three separate components to this very efficient desal system. Each is simple and inexpensive to create at the location.
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. In this case, we use the very humid air near an ocean as the source of that air, which contains a lot of water vapor in it that had recently evaporated from the ocean.
The other two components of this system are to maximize the relative humidity in the air going into this tube and to heat that air to also increase its ability to contain moisture. A Chart and also an automatic Calculator 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! (Much of the operation of the combination of the three devices is so effective that it is off the right hand side of that Chart!)
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 seawater and some local dead vegetation are the
only necessary materials! The first two components HEAT the air and the
water to increase the amount of water vapor in the air that goes into the
underground tube. This concept uses the fact that deep underground, the
soil is naturally cooler than the daytime air temperature note 3
.
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 cooler than the air temperature during hot summer days, and usually during winter days as well. The fact that it might not be cooler than the nighttime temperature is taken care of by the first device involved, the HG 3a unit.
This amazingly simple and inexpensive system can realistically supply 250 gallons (1,000 liters) 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 three devices from right to left. (1) The (green circle
here) HG 3a unit is normally designed as a heating system, but the exhaust
coming out of it is excellent for this system. The HG 3a unit
actually PRODUCES around SIX POUNDS OF WATER PER HOUR from the very
material of the dead vegetable material put into it. This is due to the
chemical reaction of the decomposition of cellulose and the other
organic materials into carbon dioxide and water vapor, the opposite
of what happened when the plant grew due to
photosynthesis note 1.
The plant material generally also contains some water as well, so the
total amount of water coming out of the HG 3a unit is generally greater
than the 6 pounds per hour. (That alone is around 18 gallons (70 liters) of
perfectly pure distilled water per 24 hours.)
The HG 3a also can send around 90,000 Btu/hr of heat out in those
same exhaust gases, all in the range of 130°F to 150°F (or 54°C to
66°C). (2) This amount of heat is sent into the second component of this
system, a relatively simple "heat bag" over a very shallow
pond of seawater. That rather hot air passing over the seawater causes
some of it to evaporate, which further increases the moisture contained
in the air inside the chamber bag. Since it takes roughly 1000 Btu
to evaporate one pound of water, the 90,000 Btus provided to the
bag by the HG 3a device has the (maximum) capability of evaporating
nearly 90 pounds of water (or about 12 gallons [50 liters]) per hour. This
amount is actually less because some of the heat is lost upward through the
bag, except in the middle of very sunny days in Equatorial locations.
At such times, the evaporation is even greater than this, due to the
added heating due to the Sun's heat. At night the performance is less
due to greater heat losses through the top of the bag. A 30-foot-square
tarp as a water tray, with one-inch deep of seawater, contains
around 600 gallons (2,400 liters) of seawater. A thinner layer of water
would heat up better and faster, and therefore more would evaporate to
provide humidity in the air for the final
device note 2
.
(3) After the air has been heated and humidified by the first two devices, it goes into the third device, the underground tube, where the coolness of the deep soil causes much of the moisture contained in that hot humid air to condense as tiny water droplets on the walls of the buried tube. Those water droplets go downhill and into the collection pipe area and then the collection tank. A conventional hot water tank can usually be considered to be clean of previous chemicals, while a 55-gallon drum might not be. A simple hand-crank pump can raise water for each family that brought a container for it.
The rightmost device, the HG 3a unit is fully described, with all the engineering information included, in Alternative GREEN Furnace with no Fire HeatGreen heating system. That page also includes a Big Bag version that is very crude but very simple and inexpensive
The construction instructions for the HG 3a is provided at HeatGreen heating system HG 3a construction
The information and construction guidelines for the underground device is at Pure Water Supply for Third World Villages
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 0.046 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 46 pounds of water, or around six gallons (25 liters).
The same Psychrometric Chart shows that at that temperature and humidity, one pound of air takes up around 16 cubic feet, so we are talking about 16,000 cubic feet of air. If we hope to produce ten gallons (40 liters) of this Distilled Water per hour, we then only need to send around 450 cubic feet of air through the tube every minute ((16,000 * 10/6)/60), a relatively moderate airflow. (Obviously, additional buried tubes or additional HG 3a devices or larger evaporation pond areas can be arranged for greater water production per day.)
This is roughly 250 gallons (1,000 liters) of absolutely pure water to drink and for washing and bathing every day! All from a rather simple arrangement of three simple and inexpensive devices!
The original ocean seawater is not drinkable due to the high salt content in it. Existing systems which try to desalinate saltwater are incredibly expensive, complex and high-tech. Unfortunately, they generally do not work on seawater because the high salt content quickly clogs up microscopic filters and accumulated salt deposits clog up nearly everything else. This simple system, of the underground tube in combination with the two rather simple accessories, can provide as much as ten gallons (40 liters) of perfectly pure Distilled water every hour, 24 hours each day, or around 250 gallons (1,000 liters) of water that is desalinated to a purity even BETTER than when expensive high-tech equipment is used!
All the water that is produced by this system COMES FROM THE AIR. The seawater or other water is evaporated, which leaves all contaminants behind. The water in that air is then condensed in the underground tube. 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 the seawater which is available, since when that water evaporates from its source, all the contaminants are left and only the pure water evaporates.
Say that the normal tides cause a change of two vertical feet in the level of the ocean, in a constant cycle of around every 13 hours. So imagine arranging for the "shallow water tray" of the middle device in this system to be located around half a foot above the average ocean level. That should cause the incoming tide to overflow the shallow tray with about six inches of water and also the turbulence of many waves, which should have the effect of naturally cleaning all the salt deposits from the previous 10 hours from that tray. After maybe two hours of this effect, the tide goes back out, leaving an entirely new supply of seawater in the tray, ready for the system and sunlight to evaporate it.
This would seem to provide not only an automatic supply of new ocean water in the tray, but also an automatic cleansing of the tray from previous salt deposits.
However, some Third World communities may not want the ocean to be automatically cleaning the evaporation tray! Some communities in India had developed a very profitable business by collecting and selling the sea salts that remain after the water has evaporated. Each Village would have a choice of the convenience of the automatic cleansing or the availability of a new source of a lot of sea salts.
The only other real complication is that the basic system described here is dependent on the heat from sunlight to evaporate the water into becoming humidity, so the basic system can (usually) only operate during daytime hours. The solution to a larger water production and also 24-hour water production is to include the HG 3a unit as a heat (and water) source.
We will use an example of where the air temperature is 120°F (49°C) 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 (70°F or 21°C) 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 88°F (31°C), 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 moisture can condense 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 70°F or 21°C, the Psychrometric Chart shows us that the air which had initially contained 0.022 pound of water per pound of air at the very start of entering the tube, is now fully saturated air which now contains only 0.016 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 entered the tube, (0.022 - 0.016 or) 0.006 pound of water forms inside the tube. If 100 cubic feet of air enters the tube every minute, that is about (100 / 15.3) 6.5 pounds of air every minute or 390 pounds of air every hour. This then means that for this situation, (390 * 0.006) 2.4 pounds of water would condense out every hour, around 0.3 gallon per hour. A realistic two gallons of absolutely pure water every day.
Air needs to be passing through the system. It may NOT be necessary to have to use any blower, because the entrance to the HG 3a unit could be provided with a wind-vane type of tail to turn an intake funnel 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.
Many variants of such equipment exist, with most being versions of either Reverse Osmosis (RO) or Electrodialysis (ED). The main reason they clog up so extremely often is because 1,000 gallons (4,000 liters) of seawater contains about 300 pounds of dissolved salt and other chemical ions. Both RO and ED systems work far better on what is called brackish water, which is far less salty than seawater. ED is not even attempted on seawater any more, after attempts were essentially all failures, and RO is not particularly successful for seawater either.
Distillation is the other common method used for desalinating water. Traditional distillation was considered to be too slow and inefficient, and most recent installations involve variants, such as what is called flash distillation. Due to the large quantities of salts in the seawater, such equipment tends to quickly get encrusted with salt, because such actions increase with temperature and flash distillation uses rather high temperatures. Many modifications have been added to the distillation process to try to deal with such problems, which has made such installations very large and complex and expensive.
The system presented here is a variety of standard distillation, but it does not have such problems. The two tarps (bottom as a tray and top as a heat and humidity cover) are simple to clean of accumulated salt deposits, and there are communities in India that collected such sea salt to be sold for significant profit (as mentioned above). The underground tube never has any contamination or deposits form as the only thing that enters it is air with humidity in it. If the atmosphere in the area is heavily polluted, it is possible that some of that air pollution could get into the tube and therefore into the resulting distilled water. A simple intake filter can be used to keep most dust out of the pipe, and if desired, the resulting water could be poured through a cloth or carbon filter to remove any slight color or taste. That is rarely a problem for Third World countries unless natural dust storms occur. It also is rarely a problem even for any remote location where Americans try to go off-grid.
In general, RO and ED systems are designed to filter out enough salt to lower the seawater's normal concentration of 35,000 ppm (parts per million) of salt down to around 1,000 ppm, which is considered usable for some purposes. If the water is to be potable, it must be lowered even more down to below 500 ppm. In much of the US, the requirement for potable water is to be less than 250 ppm. This represents a reduction of salt content of seawater by a factor of about 140, which is why desalinization of seawater has not become broadly used, with previous approaches. Those methods are good when the source water is BRACKISH, that is, less salty than ocean water is, where that brackish water can be filtered quite successfully.
With any Distillation method, including ours, there is ZERO salt content in the resulting Distilled water! The reason is obvious, that the salt CANNOT be evaporated with the water, and therefore can never even get into the underground tube to get condensed. So Distillation methods result in far purer water than RO or ED can even hope to achieve.
There are many other methods which have been tried, such as freezing seawater. The premise is that fresh water freezes at 32°F or 0°C, where seawater freezes at a temperature that is several degrees lower. So if seawater is cooled to around 30°F, only the fresh water can actually freeze, which should result in pure fresh water. Unfortunately, the reality is that this process results in crystals of salt being trapped within the fresh water ice that results, and so there is still significant salt in the resulting water or ice. It turns out that this process also involves massive usage of electricity for refrigeration, and it has generally been ignored as being too expensive for practical use.
Note that the system we describe in this presentation has a total cost of around $60 for the underground tube part and $200 for the HG 3a device and $40 for the simple tarps or $300 total, and it can provide a consistent 250 gallons (1,000 liters) of pure distilled water per day.
The larger-scale system Engineered for Haiti is estimated to have a cost of $10,000 in providing as much as 3,000 gallons of pure water per day. It is true that around 300 such installations would be needed to provide a million gallons per day, and that would cost a total of around $3 million dollars to install. However the resulting water would be far purer than any water from any RO or ED installation. This is not only far less expensive than the $6 to $8 million of current technologies, but it would provide water at a far greater purity, approaching 0 ppm of dissolved materials rather than the 1000 ppm that is currently accepted.
The actual cost of providing water is higher still, because of the extensive need for (externally provided, fossil fuel, usually diesel oil) power needed for those various systems, as well as for getting supplies of such fuels to remote locations where desalination operations are needed. The fact that highly trained technicians must always be on-site to maintain and repair the equipment adds to the cost of operation.
When these factors are combined with the cost of the initial capital, the interest on those funds, and depreciation of the equipment, the following general guidelines result: (obtained from Handbook for Mechanical Engineers, 1995)
Cost per thousand gallons of water provided
In contrast, modern American Municipal water supplies averaged around $0.15 (in 1995), with an additional $0.20 to $0.40 for distribution costs.
The new system presented here involves no distribution costs, as the water is produced locally for the users. In addition, maintenance and repair are minimal and very simple, where local villagers should generally be able to correct anything that could go wrong, and also clean any of the items that might require such maintenance.
It also involves NO FOSSIL FUELS at all, as it is entirely self-powered by a combination of sunlight and the decomposition of locally available organic materials such as grasses and leaves. A very small amount of other power might be needed for a blower if that is required due to lack of sufficient winds, but a small and crude windmill should be able to provide those minimal requirements.
In contrast, all current desalinization systems which are being generally used require around half a million Btus of energy from fossil fuels to produce one thousand gallons of usable water.
This results in THIS system having essentially no costs for fuel or other power, beyond the hauling and loading of that vegetative matter into the HG 3a device every few days (if the HG 3a is used as part of the system), and essentially no costs for labor or maintenance or repair parts. This results in the cost for the water being primarily in amortizing the cost of the initial materials. As these devices should last for at least ten years without requiring replacement, this suggests that 250 gallons of water per day times 3650 days or around 900,000 gallons of water should be provided by the $300 initial costs. This indicates that the operating costs of this new system (involving an HG 3a) would be around $0.33 per thousand gallons of pure distilled water provided. That is not quite as economical as American Municipal water supplies, but decently close.
The larger-scale system Engineered for Haiti has this amortization cost analysis. Lifetime of the underground iron pipe should be at least 40 years or 14,600 days, where 3,000 gallons of pure water should be provided on each of those days, or a total of 44 million gallons of pure water. If the installed cost is $10,000, then the amortization would be ($10,000 / 44,000) around $0.22 per thousand gallons of delivered pure water.
No other method of desalinating seawater is remotely close!
(It IS true that this system requires a lot of energy, which is required to evaporate the water, which is around 1,000 Btu/pound of water. However, in this system, all that energy is supplied by either or both of the HG 3a system [which captures energy as rotting organic materials naturally decompose] and sunlight. Since that standard-sized HG 3a unit can easily contain 400 pounds of organic matter at a time, that represents around 3.6 million Btus of heat that can be provided into the water heating chamber. The decomposition of the 400 pounds of material itself causes around 240 pounds or 35 gallons (140 liters) of water (vapor) to be added to the air, in addition to the heat being able to evaporate about another 3,500 pounds or 500 gallons (2,000 liters) of water. This is all accomplished with NO fossil fuels at all!)
NOTE: The water that is produced by this system CAN appear slightly cloudy! This can occur if the AIR going through the tube has dust particles in it. For any location where the air might contain a lot of dust or even sand particles, it is a good idea to add a filter over the intake to the underground air tube, and/or pour the resulting water through a cloth or better filter. Extremely tiny particles such as cigarette smoke are so tiny that they are harder to filter out, so an even better filter, such as charcoal, might be desirable.
Pure Desalinated Seawater for Port-au-Prince, Haiti
I Have Engineered a version of this system to provide a great deal of
PURE water, realistically 60,000 gallons per day,
for Port-au-Prince, Haiti, in its hour of need. It is relatively simple
and relatively inexpensive (Realistically $200,000 total
installed cost), and could be installed in a few days.
It is quite large!
This example is specifically Engineered for Haiti, but I will present each step of the Engineering such that any other village or town anywhere on Earth could determine the performance they would obtain.
The underground tube is the primary bought component of the system. It is a 24" diameter iron pipe, welded or otherwise joined to a straight, watertight and airtight length of 200 feet (60 meters). The underground pipe can NOT be corrugated tubing, as that would catch the water and keep it from draining to the collection tank. A backhoe needs to dig a straight trench of at least that 200-foot length, eight feet deep NEAR the ocean, deepening to 10 feet deep at the opposite end. This ensures that the entire pipe will forever be beneath the level of the ocean water. In Haiti, that deep ocean water is always at around 78°F or 25°C. The trench gets deeper so that the 24" pipe slopes downward in that direction. The trench is filled back in after the pipe is laid down in its bottom. Only the two ends are elbowed upward to receive and to discard the air which will be sent through it. A pump can be installed at the lowest point of that pipe to pump the new pure water up into a conventional raised water tank, for standard existing distribution to the community.
The walls of the iron underground pipe will therefore always be at 78°F. Moderate NATURAL wind at 10 mph causes 47 cubic feet of natural air (15 f/s * 3.14 sf) to pass through the 24" diameter pipe every second or 2800 cubic feet per minute. With air that is passing through the 200 foot long pipe at 10 mph (15 f/s), we see that the humid air is inside the cool pipe for around 15 seconds, sufficient so that most of the air will have a chance to pass near the cool walls and have some of its water condense out on the pipe walls.
The next step is to use the automatic calculator above THREE TIMES.
Climate data shows that Port-au-Prince has an AVERAGE relative humidity of 49.2%, ranging from a monthly low of 43% in July to a monthly high of 56% in October. For our first calculation, let us use a summer daytime air temperature of 110°F and humidity of 49.2%. This is for the MINIMAL PERFORMANCE calculation. This is for determining the capability of the system to just condense out natural atmospheric humidity, before we consider adding in water from the oceans. When these numbers are put in the calculator (English units) we find that 0.223 gallon of water is in each 1000 cubic feet of air. We just determined that 2800 cfm of air will go through the tube, which is 168,000 cubic feet per hour. Multiplying these two numbers we find that 37 gallons of NATURAL atmospheric humidity will ENTER the tube every hour.
Now we need to calculate how much humidity will remain in that air after it has passed through the underground tube. At the end of that pipe, the air will be at the deep ground temperature, 78°F, and at 100% humidity. This data shows that 0.181 gallon of water is still in every thousand cubic feet of air. This shows that 30 gallons of humidity will still remain as the air leaves the tube, each hour.
This would result in a DIFFERENCE of 7 gallons per hour, which is the amount of water that would condense out of NATURAL HUMIDITY per hour.
For a municipal water source, this is not enough! Therefore, the ACCESSORY of the "heat bag" or "covered evaporation pond" will be seen as being extremely important for this application. A portion of a seashore is selected such that a shallow pond of ocean water will be left by each high tide (every 13 hours). The pond is shallow enough so that the water in it can heat up quickly. It is COVERED by a cover as simple as a clear polyethylene sheet. The water and air UNDER that cover would heat up much like a closed car does on a hot summer day. At the moment, we do not yet know how LARGE that evaporation pond needs to be, which will be calculated shortly. If we make a good enough cover to achieve the 140°F temperature of the inside of a (black) car interior, and our pond is shallow enough so that the water heats enough to evaporate, we can then provide a source of air for the underground tube which is at 140°F and at least 90% relative humidity. THIS is the third usage of the automatic calculator. We now see that 0.877 gallon of water is in every thousand cubic feet of this air which is going INTO the underground tube, which is 147 gallons of water per hour.
THIS now gives us the actual performance which can be expected. We know that 147 gallons of water is in the air which goes INTO the underground pipe, and we know that 30 gallons of water per hour remains in the air which comes out of that pipe. Therefore, each hour, 117 gallons of water will have to condense out on the walls of the underground pipe.
We can now use this information to determine the smallest size the pond needs to be. We know that the NATURAL air going into the pipe contains 37 gallons of water as humidity each hour. And we have just learned that the coolness of the underground pipe allows 117 gallons of water to condense out and that there is also another 30 gallons of water that remains in the air that leaves the tube. Therefore, 117 + 30 - 37 is 110 gallons of water that our evaporation pond must ADD to the natural humidity, each hour. A gallon of water requires around 8,000 Btus to evaporate it from liquid to gas, and so our pond must ADD around 900,000 Btus of heat to the pond water each hour. Full sunlight commonly contains around 300 Btus/square foot/hour, but the process of absorbing sunlight into seawater is not very efficient. We will assume a VERY conservative 10% efficiency. In other words, every square foot of our pond and cover will be counted on (during sunlight) to provide about 30 Btus/hour. Dividing (900,000 / 30) tells us we should provide a pond of about 30,000 square feet. A square area about 170 feet on a side would provide this. This is about 2/3 acre. Yes, a less conservative estimate about the absorption efficiency of sunlight could allow this to be smaller. For example, if we used BLACK materials either UNDER the pond water or as the covering plastic, maybe we could then assume 80% absorption of the sunlight. In that case, each square foot would absorb 240 Btus/hr and we would only need to have around (900,000 / 240) 4,000 square feet of area, comparable to the size of some large U.S. houses. In any case, it is important to make sure that enough water gets evaporated to provide maximum performance of this system.
This is still a relatively moderate performance, as it does not use any source of heat energy than the few hours of the sun to evaporate any of the seawater. If six good hours of sunlight can be expected, that suggests that this single pipe system should provide 6 * 117 or around 700 gallons of absolutely pure (distilled) water each sunny afternoon.
It is certainly possible to use an HG 3a or other heat source to evaporate seawater under the poly cover during the night, so that the 117 gallons of pure water could then be obtained every hour, which is nearly 3,000 gallons of perfectly pure water every day, nearly all of which would come from seawater that was desalinated by this process.
As this process proceeds, the water in the shallow pond evaporates. If the depth of the pond left by each high tide is planned well, nearly all the water will evaporate during each tidal cycle, which leaves salt deposits there. It is possible that someone might want to collect that sea salt to sell it, but if that is not desired, the next high tide would flood the shallow pond and wash away most of the salt. This system is greatly self-maintaining and self-cleaning.
The cost of buying 200 feet of 24" diameter iron pipe (roughly 6 tons of pipe) and digging the trench to install it should be roughly $5,000 for the pipe and $5,000 for digging the trench, for a total of around $10,000. Such a trench could be dug in a few hours and then filled back in in another few hours, so the entire system could be installed in a single long day! And then, every day after that should have 700 to 3,000 gallons of absolutely pure water available for the community.
Considering the paucity of water that Haiti has received since their earthquake, this seems like it would be welcomed, but this system is so simple and inexpensive that $200,000 could be spent to install twenty such systems, so that 14,000 gallons to 60,000 gallons of perfectly pure water would be available every day.
For ANY installation, there are several ways of increasing the performance, such as by using an electric blower to force air through the pipe faster. That certainly works, but I feel that the cost of the electricity and the new requirements for maintenance might suggest that it might just be simpler, easier and cheaper to just dig another trench and install another pipe. However, it IS true that in relying on NATURAL WIND, there are times when the wind stops, and then briefly, if this system does not have a blower, it might not supply any additional water for a short time. However, traditional methods of using raised water tanks to store water for a few days could eliminate this problem.
(6) H2O + (6) CO2 + sunlight energy gives C6H12O6 + (6) O2.
In words, this says that water from the ground plus carbon dioxide from the air plus the energy from sunlight can produce glucose and free oxygen.
The chemical process of COMPLETE (aerobic) decomposition is exactly the opposite (there are many partial decomposition processes that result in other compounds):
C6H12O6 + (6) O2 gives (6) H2O + (6) CO2 + released energy equal to that absorbed from the sunlight.
In words, this says that glucose combined with oxygen from the air can decompose into water (vapor) and carbon dioxide and a lot of energy, primarily due to the activities of certain types of bacteria which are in soil.
More complex organic molecules such as cellulose are first broken down into glucose to permit this process, gaining some extra energy in the process.
The numbers in parentheses are the number of those molecules which are involved in the reaction. They are important.
In Chemistry, we know that those numbers can be used to describe the number of moles of each compound, so in this case, we have one mole of glucose combines with six moles of oxygen from the air to decompose into six moles of water (vapor) and six moles of carbon dioxide. This tells us the quantities of each which are involved. We need to know the molecular weights of each of the compounds, which are 180, 32 and 18 and 44, respectively. It is then really easy to calculate the WEIGHT of each material involved. 1 * 180 + 6 * 32 gives 6 * 18 + 6 * 44. This is true for any unit of weight/mass: grams, kilograms, ounces, pounds, etc.
We confirm that there is the same amount of mass on both sides, 372 units, which confirms Conservation of Mass. If we use grams, then we now know that 180 grams of glucose will combine with 192 grams of oxygen from the air to create 108 grams of water and 264 grams of carbon dioxide. This natural decomposition occurs worldwide every day, every second.
The important point here is that for every 180 units of weight of glucose that decomposes, there are 108 units of water created. So 180 pounds of glucose will give 108 pounds of water, about 15 gallons (60 liters).
The HG 3a device always has rather high humidity inside it, so when additional water is created like this, it gets carried out and away through the exhaust connection, along with the carbon dioxide (gas) that was also created. In this case, once that hot and humid air gets outside, it cools and most of the moisture in that air condenses into water droplets, which we choose to do inside the cooled underground tube. So, without actually using the large amount of heat that the HG 3a unit produces, if just the exhaust gases are sent into the underground tube, 15 gallons (60 liters) of water will be produced for each 180 pounds of organic material that is allowed to decompose. This is in addition to the moisture in the natural air itself, of the underground tube alone.
Where the underground tube alone can only function during the day, due to the energy of sunlight, when the HG 3a is added, the system can then produce water 24 hours a day. Since the HG 3a can reasonably be expected to decompose about 10 pounds per hour, or 240 pounds per day, this source therefore can provide an additional 20 gallons (80 liters) of absolutely pure distilled water every day. This is true even in an extreme desert climate where the atmospheric humidity is very near zero.
Water Evaporation Bag Functioning
Tarps could be used to enclose any source of water, of any level of
contamination by any chemicals. If this is done without using
an HG 3a unit, then it will be dependent on sunlight to heat up and
evaporate the water, which thereby becomes humidity in air that is
sent into the underground tube to condense as pure water. A moderate
amount of extra water can be provided in this way, but the exact
amount is difficult to calculate since there are many variables that
can affect performance, especially regarding the sunlight.
But if this sort of evaporation chamber is combined with a HG 3a device, then the 90,000 Btus of heat that the HG 3a system can generate can all be made to come out with the exhaust gases, and therefore into the evaporation chamber. The heat of vaporization of water is around 970 Btu per pound, with another 70 Btu/pound or so used in heating the water up. This means that the 90,000 Btu/hr heat output that the HG 3a unit can continuously create can evaporate roughly 90 pounds of water per hour. However, a simple poly tarp cover can allow considerable heat loss at night, so the water evaporation then will be less. During the daytime, the amount of heat lost outward through the tarp may be greater or less than the amount of sunlight heating which comes in through the poly tarp, so the evaporation rate may be less than or greater than the 90 pounds of water per hour. This is roughly 13 gallons (50 liters) per hour or around 320 (1,300 liters) gallons of water evaporated from the chamber per day. Due to the night heat losses and other reasons, a more practical expected amount is around 250 gallons (1,000 liters) of water per day. Included in this is the 20 gallons (80 liters) of water the HG 3a system naturally creates in a full day of operation, so a total of around 250 gallons (1,000 liters) of perfectly pure distilled water is realistic every day. This quantity is relatively independent of local humidity, since most of the heat used is produced by the HG 3a device, although in extremely cold climates, the water production will be less.
Solar Still Operation
The operation of a solar still has many limitations. The tilted
glass cover is usually faced to the south, so early in the morning
or late in the afternoon, the sunlight cannot easily get in to heat
the water because of the angle of the sunlight. The water is not of a
color that is particularly absorbent (technically, high emissivity)
to solar energy. A critical part of a solar still is that the
high humidity air that is produced by the evaporation of some of the
water needs to encounter a COOL or COLD surface, such that the
effects described in this presentation can occur, where the (local)
relative humidity gets up to 100% and therefore water must condense
into droplets. Since the glass cover is the surface in a solar still
which must also represent that cooler surface, it would be great
if it were as cool as possible. However, as the sunlight passes
through the glass on the way in, a little of the heat is absorbed.
Also, the location of the glass exposes it to the outdoor air,
so the glass can never be cooler than the ambient air temperature.
And finally, the glass cover is constantly exposed to the warm or
hot air inside the chamber, so it generally becomes quite a bit
HOTTER than the current ambient air temperature. Per the
Psychrometric Chart, these effects all greatly reduce the amount of
water that can be produced in a solar still. A little water is better
than no water, true, but our approach of having the cool surface
fairly deep UNDERGROUND, that factor alone keeps the condensation
surfaces 20°F or 30°F (10°C or 15°C) or COOLER than the
glass cover of a solar still. The Chart shows the wonderful
advantages of this factor.
Reverse Osmosis Pumps
If the water is merely brackish, salty, the pumps can be in the
250-400 PSI pressure range, still rather high and energy consuming.
When the water is seawater, much more salty, the pumps must be
much stronger to force the water molecules through the very tiny
filters, 800-1180 PSI.
In addition, such equipment can work reasonably reliably with a supply of brackish water, where maintenance can be manageable, but for seawater, RO equipment tends to have those filters clog up almost immediately and constantly. Therefore, there are a number of installations where brackish water is desalinated reasonably successfully, but virtually no successful attempts at desalinating seawater has yet been installed based on RO or the other high-tech micro-filter technologies, like ED. In general, they now know to not even TRY to desalinate seawater!
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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago