Safe Water Supply
Pure Distilled Water for Third World Village Residents
A High-Performance Natural Water Still, but with NO flame or fire!
Here is a very simple, very inexpensive system to provide absolutely
pure water for remote Third World Villages that otherwise do not
have easy sources for safe drinking water. It is essentially a
natural dehumidifier, which causes some of the moisture that
is always in the air as humidity to be condensed out in a cool
underground pipe-tunnel, even in semi-arid regions near deserts.
Ten gallons (40 liters) of absolutely pure distilled water per day is
very realistic for many climates.
First placed on the Internet in March 2008|
- You have noticed that when you have a glass of iced soda, that
often droplets of water form on the OUTSIDE of the glass. There are
people who think that water is seeping through the glass, but that is
not true! What is actually happening is that the cold liquid INSIDE
the glass causes the glass itself to get cold (which you know).
THEN, when WARM room air happens to pass near that cool glass, the
AIR cools down. IF it cools down enough, and if the humidity in the
room is high enough, the air cools to below the Dewpoint.
What that means is that the cooler air cannot then contain as much water
vapor as it normally had, and so droplets of water MUST form on the
cool surface as some of the water condenses.
- This is also
why fog occurs (in that case, the water droplets condense around tiny
specks of dust in the air) or why basement walls are often damp or
why some windows can have water or even ice form on them in winter.
- Sometimes in the morning, you see a whole
yard full of dewdrops on lawn grass. This occurs because the grass had
cooled during the night and normally warm and humid air condenses on
every blade of cooled grass. This is actually sometimes gallons of
very pure (distilled) water as dew, which might seem collectible, but which
will simply naturally evaporate as the grass warms in the morning sun.
The system described here is just an organized way to permit that natural
dew creation, underground where it is cool, and collection,
maximized with modern Engineering techniques.
- These water droplets that form are PERFECTLY PURE water,
also called distilled water. All you would need to do would be
to collect all those droplets! THAT is what this system does, but
on a far more organized basis and far more efficiently.
- By sending normal warm daytime outdoor air through a COOL UNDERGROUND
tube that is deep enough and long enough, some of the humidity in the air
can condense on the tube walls. If that water is then collected,
it is essentially distilled water, very pure! If the tube is slightly
sloped downhill, similar to a house rain gutter, the water droplets run down to a
pot where you can collect the pure water!
- This is a very simple and inexpensive system which virtually
cannot ever break down! Depending on the climate, two gallons to
ten gallons of perfectly pure water is EASILY produced and collected
each day. Some modifications can increase that performance a LOT,
and they are described below. Instructions and a calculator will
even help you predict how much pure water YOU could get each day!
- You have certainly seen water dripping
from window air conditioners. You probably never realized how extremely
PURE that water is! (Although you should not drink it as some air conditioners
have lead solder inside them which is dangerous)
You may also know that central air conditioners condense as much
as 12 quarts (3 gallons) of humidity from the air (per day) in the process
of cooling it. Dehumidifiers do the same thing with the INTENTION
of removing humidity from the air (by cooling the air briefly!)
The water flow through the drain hose of any air conditioner is easily
confirmed and is quite impressive!
- Maybe you think that only an irrelevantly small amount of water
exists as humidity in the air. That is not the case! If the entire
Earth's atmosphere is considered, we know that about
4,000,000,000,000,000 gallons of water is always in it! There are
over 7 billion people now living, but that means that there is enough
humidity in the total atmosphere where around 6,000,000 gallons of
water could theoretically be provided for every single one of us!
And it gets replaced every day as warm ocean waters evaporate over
3/4 of the Earth's surface area!
It is certainly true that over a desert, the humidity is lower, but it is
never zero! The water production of this simple system is much less
in a desert than in a tropical rain forest, but it ALWAYS can work!
- This process of sending air through underground (cool) tubes
has long been the process of our "free air conditioning"
system, but this case is different in that we intentionally
send HUMID outdoor air through the tubes rather than less humid house air.
- A consistent 2 gallons of water per day is usually produced by the
BASIC system, but additional features can easily increase this to
many gallons per day (above 200 gallons per day is fairly easy to accomplish).
- Existing methods of purifying contaminated water (commonly RO
or Reverse Osmosis) are all incredibly
expensive (on the order of a million dollars per installation or more);
they require large and consistent supplies of diesel fuel, to power the
high pressure pumps (as high as 1180 PSI) note 4
which are needed to force the water
through filters which have incredibly small holes in them; those
filters clog up regularly and require Technicians to constantly
be cleaning and repairing them; and all those tons of equipment
can rarely be transported to remote locations to be installed;
in addition, the water that is produced is barely safe to drink,
generally having 500 ppm of contaminants still in it,
where our low-expense system provides virtually PURE water!
- In fact, we have Engineered a larger-scale Municipal system which might
be used in Port-au-Prince, Haiti to
provide 700 gallons or 3,000 gallons of perfectly pure distilled water
there every day, and all for a total cost of roughly $10,000, and it is
installable in possibly a single day. If they chose to install
twenty such systems, they might nearly immediately be able to
supply as much as 60,000 gallons of pure water to combat the
many severe diseases that are spreading due to people having to
use contaminated water. This Municipal system is a Desalinization
variant of this humidity condensation system, and of much larger
scale than this presentation generally discusses. That system
is also suitable for many other places where pure water supplies are
limited and ocean water is available, such as Indonesia, Bangladesh,
India, Egypt or most islands.
This presentation was first placed on the Internet in
You are probably familiar with the fact that during the summer,
concrete basement walls are often damp or even wet. That occurs
because the warm outdoor humid air gets into the basement, and when
it passes near the colder concrete wall or floor, it cools and
loses some of its ability to hold moisture. If the air drops
to a temperature low enough, then some of the moisture has to
condense into water droplets. That is essentially the concept
used here, but this system uses an enclosed chamber to keep
the water purer.
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.|
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 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! (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!)
If you live in a cold climate, and ever wear glasses, you know that
if you have been outdoors where the glass has gotten cold, that when
you enter a warm house, your glasses immediately fog up! What
happens is that the warm humid air of the house cools down when it
gets near anything cold, such as the glass, and that cooler air cannot
contain as much moisture as when it was warmer. If the room is
humid enough and the glass is cool enough, the (local) relative
humidity gets up to 100% and tiny droplets of water condense
out of the air onto the surface of the glasses. (A minute later,
the glasses warm up and this problem ends.) Similarly, if house
windows are single-pane, on cold winter days, room humidity condenses
on the cold window glass and droplets of water form, and can even
freeze into ice!
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 summer 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 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 (40 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.
Basic setup, which can be modified in many ways for locally available
materials and conditions:
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 new 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 the summer air is around 120°F (49°C) temperature, and the outdoor
relative humidity is just 30%, then every pound of that air contains
about 0.022 pound of water in it as water vapor. This is standard
thermodynamics information, as shown in the Psychrometric Chart
presented and discussed below.
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 (4 liters).
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 (4 liters) 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
Depending on the local (daytime) temperature and humidity and the
deep ground temperature, two gallons (8 liters) of water produced per hour
is generally very realistic! This is roughly 10 gallons (40 liters) of
absolutely pure water to drink and for washing and bathing every day! All
from a very simple underground tube!
This system can be installed WITH an underground tank and hand-pump,
for an entire village, or WITHOUT that tank and pump for a single
family (who would place a pot or jug under the water collection
pipe underground) (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.
If this system is used without either of the accessory components,
where the air which enters the tube is directly from the local
atmospheric air, then it is possible that dust or even small sand
grains can be carried in that air, and therefore get inside the
sloping underground tube. So, in certain climates, it is possible that
the resulting water might appear to be slightly cloudy rather than
perfectly clear. These are materials which are NOT dissolved in
the water. They are generally absolutely safe in water, but they
can be removed either by letting the water remain in a container for
some time to let such things settle out, or the water could be poured
through any of many simple filters to remove such materials.
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.
The following section is some technical info that shows how to determine
how much water might be captured from the air in any specific climate.
It is based on a standard Psychrometric Chart.
We will use an example of where the air temperature is 120°F (60°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
End of technical information!
I have come to realize that I may have been optimistic regarding
whether many people could find usefulness in the Psychrometric
Chart above! Therefore, I have created a simplified way of getting
the needed data, without having to understand the Thermodynamics
or Engineering involved! You can use the following automatic
calculator to get the results you need, for any location and
If 500 cubic feet of air pass through the tube in a minute, that is
around 33 pounds of air (the Chart shows us that the air is around
15.1 pound per cubic foot). This means that around 0.25 pound of water
would form inside the tube every minute. This is 15 pounds of water
in an hour, or just over two gallons (8 liters) of pure distilled water
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 (40 liters) 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 very simple system shown and described above should be wonderfully
useful in many places in the world where water supplies are inadequate.
It involves digging a trench to bury the tube, which MUST slope
downward, with the entire tube at least three feet (one meter) deep
and preferably six feet (two meters) deep. The horizontal run of pipe
should be at least 50 feet (16 meters) long, and longer still is
better, to ensure that all the air passing through it is
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.
This basic system can be made on a small scale for an individual family,
where a kitchen pot can be placed under the water collection pipe.
This approach obvious requires a pit and ladder for a family member to
climb down to get the water container once it has filled. A shutoff
valve could be added to allow some amount of water to accumulate
inside the system, to fill the container more quickly.
Plenty of water for eating and drinking and also sufficient for
cleaning food utensils and washing and bathing.
For a Village
On a larger scale for a community, where a larger tank (represented
here by a discarded hot water tank) can be connected to the water
collection pipe so the tank would gradually fill. A different pipe
connection on the water tank could be used to get water from out of the
tank. If people would climb down a ladder, they could use the standard
draincock of the tank to remove water.
If a village was more prosperous,
they could obtain a hand-operated pump, where each family could then
pump a few times to get out the water their family needs for that day,
into a convenient container.
Notice that for each of these, we show simple natural airflow due to
wind, to drive the air through the tube. The intake is able to rotate
with the wind with a tail like a weathervane, so that the intake is
always able to face into the wind. If that does not provide
desirable amounts of water, a funnel might be added to the air intake,
to catch more air and force it through the tube. Finally, a blower from
an automobile heater might be used to actively blow air through the tube.
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.
For Climates Where the Natural Humidity is too Low
There are some climates where the Relative Humidity is normally too
low for this system to work. The Psychrometric Chart above is provided
so that anyone could quickly and easily determine whether it will work
in a specific location and even how much water it should supply.
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 other non-potable water might be spread. A second tarp, such as
polyethylene, would then be supported several
feet above that note 2. 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 120°F
(49°C) 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
In the event that there is minimal sunlight and heat available in
a particular climate, such as on a mountain, the intake air
could be pre-heated by a system such as the HG 3a heating system
(shown here as a green circle at the right)
described in some other pages in this web-site Domain (linked below). It
can provide a consistent 130°F (54°C) to 150°F (66°C) heat source
twenty-four hours a day, and also extremely high relative humidity,
using only dead field grasses and leaves as the
energy source! note 1
Finally, BOTH of these accessories can be added to the basic system.
In this case, this simple device, in combination with the two rather
simple accessories discussed above, can provide
as much as ten gallons (40 liters) of perfectly pure Distilled water every
hour, 24 hours each day, or 250 gallons (1,000 liters) of water that is
pure to a purity even BETTER than when expensive high-tech equipment
Pure Desalinated Seawater Distilled Water for Off-Grid Residents.
Pure Distilled Water for Third World Village Residents.
Pure Desalinated Seawater Distilled Water for Third World Villages.
Pure Distilled Water for Emergencies when Wells are Unusable.
Pure Desalinated Seawater Distilled Water for Off-Grid Residents.
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.
Brief Functioning of the HeatGreen 3a Device
The chemical reaction of Photosynthesis is generally this one:
(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
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 gallons
(1,300 liters) 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!
This presentation was first placed on the Internet in March 2008.
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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago