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Technology Makes Cheap Drinking Water from Air Answered

INTRODUCTION:  

How can we best apply basic technology to help the underprivileged and/or disaster-hit countries like Haiti? Daily hygiene and nourishment are among the top needs for disaster ridden regions!  Simply put, no water means no hygiene. The Romans understood that over two millennia ago and created their complexly beautiful aqueduct networks for handling both fresh and wastewater! Other ingenious water systems like “air wells” have been found in the city of Theodosia (cf: discovered in 1900 by Zibold, see Zibold’s Collectors/Dehumidifiers) dating back to Greco-Roman times during the Byzantine Empire. These were strictly passive systems that naturally dehumidified air, collecting its potable water in underground basins.

All air, even in relatively dry desert regions, will precipitate or release its natural water content (initially in the form of vapor) through condensation when it hits its dew-point temperature and below. That means you “chill” it to an appropriate level that is anywhere from 5F to 50F below its current air temperature, depending upon how much water content (relative humidity) it has locally absorbed. The condensation of the water vapor releases its internal latent heat (reheating the cooled air) which must be constantly dissipated (absorbed by something) in order for water formation to steadily continue. So how do we dissipate this resultant vapor-heat and chill our air without any infrastructure or electricity, in an underprivileged or disaster-ridden region? We simply bury a long cast-iron or any metallic drain-pipe sufficiently underground where the temperature of the earth is naturally held to a constant at around 45F to 55F. That’s our “free” chiller gift from nature. One end of the pipe, Figure-1,  sticks out of the ground to suck-in local outside hot air, and the other end dumps cooled dry air and water into an underground cistern where it gets collected and is piped to the surface to both exhaust the cooled dry air and connect to a water pump. We need a hand operated water pump to lift up the water above ground, and we need an electric fan to constantly pump air through the ground-chilled piping system. We can even force the cooled piped air to exhaust into a tent-like structure where it provides air conditioning as an added bonus, but this adds the penalty of both power and the increased fan size necessary to drive our required airflow further into an enclosure!

While this concept is not “passive” (requiring electricity to work) like those clever Byzantine air-wells, it will produce much more potable water and within a smaller volume than those elegantly passive historic devices. The electricity for our fan power requirements can be produced by any one of four ways using either “active” or “passive” techniques: 1) An active playground or bike-pedaling-person or oxen-driven mechanism-generator, 2) A passive windmill generator, 3) A passive solar energy collection system that directly generates electricity, or 4) A passive thermo-electric system that directly generates electricity using the Peltier effect, operating solely on temperature differences between the cell’s top and bottom surface (we jury-rig the cool pipe and hot ambient air to contact separate sides of the cell).

Depending upon how much water is needed, the required air volume plus pipe length and diameter, together with the fan will be sized accordingly. We can also configure groups of parallel fan-driven air pipes that are radially fed into the cistern. The sizing of this underground network depends upon the ambient air’s local average temperature and relative humidity (how much water gets absorbed into the air) plus buried pipe depth and effective underground temperatures achieved.

The basic concept is one where we “wring” water from air at some given humidity content. The higher its relative humidity the more water is recovered from the air. The air-wringing process simply chills the air as it scrubs along the cooled internal pipe surface until it starts to rain inside the pipe from condensation onto its surface. The condensation is like the dew that forms on car windows, grass or any cooled surface in the early morning, before the sun comes out and evaporates the dew back into the heating air. A further bonus is that our dew-formed water is naturally distilled and very clean. It is potable water ready to drink without the need for additional sterilizing agents. Of course, we must make sure that the interior piping and cistern network is biologically cleansed before burying it underground. The hand pump with its 10 to 15 foot extended piping to reach the underground cistern must also be cleansed.

The beauty of this constantly replenishable water supply is its convenient underground installation anywhere! After the in-ground installation, we have a virtual, partially passive, no moving parts, non-breakdown system containing above ground total access to all moving parts that could breakdown, namely the water pump and electric fan. Also, it is easily maintained, with few moving parts (water hand-pump and electric fan) and basically lacking any technical complexity which makes it ideal for technologically backward regions.

The example below uses a relatively small industrial fan moving air at 1500 CFM (Cubic Feet per Minute) with a DC motor rated at 1kW. This fan together with our underground piping system will conservatively generate 12 GPH (Gallons Per Hour) of potable drinking water without need for any purification chemistry. Based on an average electrical cost of 14-cents per kWh (kilo-Watt hour), the typical commercial distillation of one gallon of drinking water costs roughly 35-cents as compared to our cost of only 1.2-cents. Furthermore, if we decide to go green and use solar energy for generating our water, it would effectively cost us nothing beyond the initial installation!

USING A PSYCHROMETRIC CHART TO SIZE OUR WATER SUPPLY:
The following gets a little technical and is only provided for those die-hards who are truly interested in how the science works. Those non-technically schooled may skip this part and not miss the basic concept.

Figure-2 shows a Psychrometric Chart for air. This chart summarizes some of the basic thermodynamic properties of air throughout its typical range of operating temperature. The chart uses six basic air properties that defines the physical chemistry of water evaporation into air:  (1) the enthalpy or total energy contained within a unit of air which is a combination of its internal and external energy, expressed as the amount of BTU-energy per unit mass of reference dry-air, (2) the specific volume or the ratio of a unit volume of local air to its mass of reference dry-air, (3) the humidity ratio or the amount (mass) of moisture in a local unit of air divided by its reference mass of dry-air, (4) the percent relative humidity per unit of local air, or the mass ratio (expressed in percentage form) of the partial pressure of water vapor in the air-water mixture to the saturated vapor pressure of water at those conditions (the relative humidity depends not only on air temperature but also on the pressure of the system of interest),  (5) the dry-bulb temperature or the locally measured air temperature, and (6) the wet-bulb temperature or saturation temperature which is the local air temperature experienced during constant water evaporation (a wet-bulb thermometer is typically used:   a thermometer that measures resultant temperature while wrapped in a water wet-gauze and spun to generate local air movement and max-evaporation) 

1.0   The Process and A Sample Calculation

Our Psychrometric Chart uses six thermodynamic properties that help to determine the amount of water available for extraction from the local ambient air as a function of its temperature, pressure and relative humidity.  Let’s assume the following local ambient conditions for the region we plan to construct our water system at:  (1) Typical daily air temperature Td = 106F and one atmosphere pressure assumed at sea-level, (2) Relative Humidity, RH = 55%, and (3) Typical underground temperature down at six feet is measured at Tu=55F (at 12ft. it drops to ~45F).

This yields the following calculated results for obtaining a steady-state supply (changes at night) of water to fill the cistern:     

1)      In our example, the “local” air (dry-bulb) temperature is Td=106F, at a relative humidity of RH= 55%.  Fig-2 indicates that the resultant Humidity Ratio is HR= 0.0253 Lbs-water/Lb-Dry-Air (intersection of Td=106F line and RH=55% line, then horizontal to HR value).  We then determine the “gulp” of air volume containing the HR Lbs-water which corresponds to the point of intersection of Td and RH. Interpolating on specific volume “mv” yields mv=14.7 ft3/Lb-Dry-Air (this value sets the optimum unit airflow for our given ambient conditions, and creates a ballpark pipe length to diameter ratio needed later). It represents the basic unit of air volume that will enter our underground pipe per given time, and ultimately defines the size of our fan and piping network. For increased water creation, multiples of this unit volume will scale up the additional amounts of water that can be collected.

2)      As the inlet air cools down to a temperature of Tu=55F, from contact with the relatively cold underground pipe, we follow the constant enthalpy line (red upward left-diagonal) from the intersection of Td and RH to its saturated air temperature condition of Ts= ~88F, which is its dew-point temperature where the corresponding local RH=100%.  At this temperature or under, the air precipitates and releases its moisture content, resulting in water condensation onto the pipe walls.  Since our air will chill to a final pipe temperature of Tu=~55F, we follow the RH=100% saturated curve (green) down to yield an HR=~0.009 Lbs-water/Lb-Dry-Air. This is how much water is left in the air when it gets to 55F.  Therefore for every pound of local outside air that enters the pipe, mw=0.0253 – 0.009 = 0.0163 pounds of absolute pure, distilled potable water precipitates onto the inside pipe wall (per pound of dry air that is cooled and dehydrated) to gravity-flow out the pipe exit and into the cistern.

3)      We now convert pounds of air per unit time into a unitized volumetric airflow that yields gallons of hygienically pure potable water production per unit time. For every Va=100 ft3 of local volumetric air movement per minute (CFM) through the pipe, which translates into ma=Va/mv= 100/14.7 = 6.8 lbs. of dry air per minute or 6.8 * 60 = 408 lbs. per hour (PPH), to yield a water-flow of mwf=ma * mw = 408 * 0.0163 = 6.65 PPH or 6.65/8.345 = 0.8 GPH of water.  An industrial fan rated at 1kW DC will typically move 1500 CFM at a pressure of 8-iwc, to continuously produce 15 * 0.8 = 12 GPH of pristine potable water.

4)      Not shown here are the design details of sizing our pipe, fan and solar collection system for electric power requirements using heat transfer principles coupled with a thermodynamic heat balance, and aerodynamic fan performance assessment. These details help to size the electric power generation requirements plus margin used to properly size a solar collector containing further margins for overcast days. The engineering involved here is straight forward but beyond the scope of the current project.

Discussions

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Kelina
Kelina

3 months ago

Hello, we are trying this in southern Angola where rural folk are hard up for water. We used 10cm PVC pipe x 30 meters 2 meters down at the shallow end and 2 ½ meters depth at the bottom end where the collection bucket is. We painted the tall top end pipe black to heat up and create air flow. The short pipe at the deep/bottom end where the bucket is. Both vertical pipes have mesh to keep out insects and both have a little roof to keep out droppings from birds. We are planning to create more shade for the short, non-black pipe so there is more difference in the temp between the two vertical pipes. No water so far.

Do we really need a fan?
We want something that would be accessible for rural folk. For that reason we did not use galvanized pipes which are prohibitive in cost and would have defeated the purpose of having something that basically any rural family could have. Passive whirlybird ventilators can be found sometimes in the city, though only 30 cm diameter. Maybe another option given we generally have a breeze.
Should we have used a wider diameter pipe?
Should we reserve the tall-black and non-black-short pipes so that the air would be drawn in the reverse direction?
I would really appreciate help. As I am sure you can tell this is not my area of expertise, just really want to see help for the communities in the bush. Manpower to dig is not a problem and the cost of PVC pipe is ok. I really hope it can work. Thanks.

0
RT-101
RT-101

Reply 2 months ago

A. QUICK REPLY:
1. A fan is best way to make lots (GPH - gallons per hour) of water. You need to move 1500 SCFM (standard cubic feet per minute) of air through a 10 inch (25cm) diameter plastic pipe of 150 ft. to make about 12 GPH of water. That much air through 10 inch pipe makes the air velocity at 55 MPH (miles per hour) which is very fast to chill the air down by dumping heat through plastic pipe into colder ground. If you use metal pipe you only need about 100 ft. instead of 150 ft. length.

2. It's very hard to generate free convective air movements without a fan. You need to move lots of moist ambient air over 30 meters and that's hard to do using just free convection. If you want to eliminate fan, you need very large diameter pipes or a cave that allows natural air movements into cave to chill air against cold rocks and get water. My system is not designed for this and trades off large caves with natural convective air movements for 10 inch narrow pipes and a high pressure fan to pump the right amout of air through pipe.

B. DETAILED REPLY
Hi Kalina,
Unfortunately engineering is a very exacting procedure and
to make machinery work properly requires geometries and fan blowers
designed for specific sizing. Without a high power fan capable of moving
about 1500 SCFM of moist air from ambient surroundings through your
pipes, your system simply won't work to produce about 12 GPH of
condensed water for drinking. You can't rely on natural convective air
currents to move that much required moist air through 90 ft (30 meters)
of 4 inch (10 cm) diameter plastic pipe. And even if it's 40 inch (110 cm)
diameter piping, and you probably sized for free convective
air movement, its way too large pipe for the forced convection that uses a
fan and only needs 10 inch diameter pipe. My system design is not based on free convection air movement which
you realized needs large size dimensions to naturally move small
amounts of air. Moving and chilling small amounts of air using natural
convection will only yield droplets and not gallons of water over an
hour's time. And such natural convective systems need very specific
geometry and proper wind conditions that would force air into a cave
opening whose internal cold rock walls are mostly underground and chill the air and create water droplets. This
air would then need some large cave exit flow to keep it's draft moving
in and out while slowly creating water droplets. One can build such air inlet and
exit draft cave structures using huge piles of rocks. But don't confuse
this with my "active" or dynamic fan air design, which uses minimal volume space and no caves,
without cave-stone like structures. They are different entities.

It
takes a very powerful fan using about a 1.25 HP (1000 watt) electric
motor to push 1500 SCFM of airflow through a 10 inch (25 cm) diameter
pipe. That airflow and pipe diameter over a 150 ft length of buried pipe
will yield about 12 GPH of condensed water. Water yields will vary with
ambient relative humidity, pipe length and diameter, and amount of air
pushed through pipe. The longer the pipe used to better chill the moist
air, the more water generated but at the expense of a more powerful fan as greater pipe length means more power needed to push air though.
Metal pipes need shorter lengths than plastic pipes. With less airflow
you get less water. Decreasing the pipe diameter will also reduce
airflow capability, for a given size fan, and reduced water generation. It's all
a technical balancing act that requires either engineering knowhow or
lots of trial and error to get it right.

In technical terms the
fan must be capable of generating 1500 SCFM of air flowing through 150
ft of 10 inch diameter plastic piping. That takes a fan air pressure capability
of about 10 inches of water column (iwc). You need to move your humid
air at speeds of about 55 MPH inside the plastic pipe to chill air down and
get 12 GPH water. Your free convective system is similar to a fan
capable of only 0.05 iwc at a flow of maybe 1 SCFM. Yielding no
condensed water.

Decreasing the pipe diameter causes more
airflow pressure drop and needs an even more powerful motor to get your
1500 SCFM of airflow and yield 12 GPH water. Lesser fans yield lesser
pressure drop and less generated waterflow. Cutting the airflow rate in
half yields half the condensed water and requires a smaller cheaper fan.
Unfortunately, my 1500 SCFM fan with 10 iwc costs about $4000.

Regards
Herman Vogel

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Kelina
Kelina

Reply 2 months ago

Thank you so much for your detailed reply.
Our goal is to have 5 - 10 gallons per 24 hours,
that is, during 8 hours of warm daytime, have ~1 gallon/hour. Even ½ gallon per hour for 8 hours would be a help for those who walk miles for water. Often the water is an open pond, dirty, shared with cattle.

I also saw a site online using a weather vane to direct a swivelling elbow in the direction of the wind for the intake pipe. That is what gave me hope that it would be possible without electrics.

Our PVC pipe, after all, is 15 cm (I am not on site and we had some communication issues).

1. Does it matter which way the air flows, from the higher end to the lower end, or vice versus?

2. The whirlybird ventilator may give us 700-1600 cfm, depending on the wind. If it does result in water condensation, would a 25 cm diameter pipe be better? If I understand your reply, there is no point to going larger than a 25cm diameter? We were concerned about the weight of the 2m of earth on the pipe, or is that not a consideration for 25 cm PVC pipe?
Thank you so much for your help.
Kelina





0
RT-101
RT-101

Reply 2 months ago

Dear Kelina,
GENERAL:
I'm intetested in helping you help others in need for
such fundamental basics as life sustaining clean drinking water. I'm
glad to help you develop a working system to yield about 0.1 GPH water
without electrics. Consider my efforts as pro-bono, meaning I don't want
any payment for my services.

We should exchange our ideas
directly using email (vogelhn@yahoo.com) without Instructables as the
middleman. The process requires that we do some research regarding: a)
what types of Whirlybird exhaust fan hardware is available versus price,
b) an optimum blade size, and c) the suction draft such devices are
capable of in "iwc" (inches of water column). We would probably set it
up to suck moist ambient air through a carefully calculated length of
from 25 to 50 cm diameter PVC pipe. Whirlybird fans need certain minimum
wind speeds to twirl their blades and create suction to pull enough
moist air through the underground pipe and make perhaps 0.1 or more GPH
water which we will calculate exactly.

DIRECT ANSWERS:
1)
Swivel elbows on intake are worthless. Elbows cause extra airflow
pressure drop and reduces not enhances flow through underground piping.

2)
Natural, draft-causing whirly-fans are designed for suction and will be
placed at the exit of our pipe system. They have limited capacity to
suck out the flow through our piping and create sufficient airflow rate
to generate some significant amount of water. Even small amounts of 0.1
GPH water generated steadily is better than nothing. And in principle,
can be run 24 hrs with daytime operation yielding more water.

3)
Flows run from higher to lower pipe end. Lower end contains our cistern
bucket to catch the genetated water. A hand pump will extract this water
from some 15 ft underground.

4) Whirly-fans (WF) quoted as
capable of 700 to 1600 CFM suction airflow as based on external wind
conditions and are not quoted correctly. They assume a suction pipe
length of perhaps no more than 15 ft. Our pipe will need to be much
longer to be able to cool down the moist air and create condensed water.
And our calculated flow capacity will depend upon how long the pipe is
that the airflow must pass through. Longer pipes produce more "pressure
drop" (quoted in iwc) for a given flow and reduces the actual flowrate,
no matter the outside wind speed experienced. We will pick the highest
capable WF pressure drop for the largest flowrate at some given,
site-measured external wind speed of maybe 5 to 10 MPH at a ground level
height of perhaps 10 ft. above ground level. Optimum pipe diameter and
length are calculated based on WF capability of flow versus pressure
drop, and then be factored into calculating what combinations will yield
the highest water production. Our calculations are similar to you
physically testing different combination system designs but without the
hassle of all that testing trouble. And so we will design engineer an
optimum water supply system based on what hardware is available, with
getting it to work using minimal design assembly iterations. I currently
don't yet have what the optimum pipe length, diameter, WF performance
hardware would look like. But the pipe diameter will be somewhere from
25 to 50 cm. The math gets complex as flow, pipe diameter and length, as
well as ambient air moisture content and and pipe buried depth all come
into play mathematically in our analysis.

5) 5 meters of di buried plastic pipe is no problem

Regards
Herman Vogel

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Ctingle30
Ctingle30

1 year ago

Great post and discussion. If one had access to a vast amount of rocks and was able to coil up and burry 1300 feet of 6in flexible drainage pipe inside the pile (a pile 60 feet in diameter and 20 feet high) how powerful of a fan would one need to move the appropriate amount of air through the pipe to get condensation going? I envisioned one end of the pipe coming out of the top of the pile and the other leading to a collection tank buried beneath. I'd obviously need a "T" somewhere near the bottom to connect to the pipe leading out of the side of the pile with the fan on it. Mahalo. Chris

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RT-101
RT-101

Reply 1 year ago

Hi Chris. I can show you how to fish (show math equations on calculating pressure drop and fan size) or just give you the fish (answers), which do you prefer?

Fan pressure needed is based on multiplying a known fan pressure drop (base on flow, pipe-length and diameter) by ratio of new pipe-length to diameter used. Then multiplying that by ratio of new to old flow rate squared. Units don't matter since its a ratio as long as they're consistent ones. Result is a needed fan pressure drop for pipe length, width, and airflow rate. This drop is the fan pressure needed to flow your air.

In my case a 200ft long pipe 0.75ft diameter (9inches) yields about 10iwc (inches water pressure) drop. I'm flowing 1500CFM of air. This yields about 12 GPH of water under conditions I noted in my report. Now a fan this hefty with about 1ft diameter blades will cost ~$2000. Keeping my same geometry pipe, and cutting the air flow rate in half (750CFM) yields ~half the GPH water or 6GPH. And fan air pressure drop lowers to (750/1500)^^2 x 10iwc = 2.5iwc from 10iwc, which is a much cheaper fan power, but only yields 6GPH water generated.

Careful about using corrugated plastic tubing. Corrugations add perhaps another 30% to pressure drop and requires a more powerful fan. Your needed tubing length is based on heat transfer equations relying on air flowrate, tube diameter, underground dirt temperature (Your case pile of rocks), and the inlet air temperature. RH also enters these equations. But don't worry, using some of these basic ratios with some trial and error will get you started on track.

NOTE: Measure your pile of rocks' internal body temperature and compare to 5ft under dirt temperature. Colder is better and needs less airflow and RH to get more drinking water. Old air well structures of rock were cold to touch and usually well hidden in grottos from direct Sun.
Mahalo.

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Ctingle30
Ctingle30

Reply 1 year ago

Thanks RT-101. Was that the fish or the teaching? LOL. Just kidding. I appreciate the feedback. I'd like to share with you some schematics I've worked up and get your thoughts (at some point in the future). Thanks for the assist. Chris

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gamebaivinwin
gamebaivinwin

1 year ago

but you wirite too long :))) i trying to understand anything you said

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RT-101
RT-101

Reply 1 year ago

Sorry about too many details. Needed to get message across. Questions, just ask!

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IzakB1
IzakB1

1 year ago

Did anyone tried this and does it work?

0
RT-101
RT-101

Reply 1 year ago

I was email contacted by some green movement society in Germany who applied this concept and claimed to successfully create water. My friends and I built a small test model in an indoor warehouse. Instead of burying plastic pipes, we submerged them in an above ground swimming pool whose water was chilled to simulate the cooler temperatures existing with underground pipes. We used a cheap fan that couldn't blow enough humid air through our 100 foot 10-inch ID pipe to condense out very much water droplets. We made only a little condensed water in the pipe because of our small amount of pipe airflow created. However, the idea was proven and by math-scaling my results we would generate the GPH shown in my Instructables model.

0
IzakB1
IzakB1

Reply 1 year ago

Morning my friend, thanks for your reply and I appreciate your feedback. Your model is great and got all my brains in a row.
I farm weekends on my farm in the Drakensberg South Africa and do have a water shortage during the winter months. The humidity on the mountain is most of the time 50% plus and the average temperature is 21'C.
I am going to work on your model and will keep you informed.

0
RT-101
RT-101

Reply 1 year ago

Glad to help, keep me informed of your efforts/challenges.
Key Points:


  • 1)Generating
    Large GPH: To generate ~12GPH (gallons
    per hour) of water you need a costly, high performance fan to produce a
    flowrate of 1500CFM at a pressure drop of about 10 iwc (inches of water
    column). The pressure drop is rating is calculated based on flowrate, pipe
    diameter (~10 inches), and pipe length (~ 200 – 250 feet). Generated water is scaled
    by the flowrate, so that same geometry at 750CFM you get ~6GPH. Typically,
    water generating systems use lots of electricity to create only a few gallons
    of water per day and not per hour. Our system efficiency uses the chilling
    temperature of the underground instead of an electric cooler to make the water.
    We are MUCH cheaper with larger water volume production.
  • 2)Windspeed
    VERY IMPORTANT: Your math will find that for the pipe diameter and air flowrate,
    you will get about 55MPH air velocity through the pipe. This means that the
    condensed moving water droplets won’t be able to adhere to pipe walls and will get
    sucked up with the windflow. So to capture these droplets suspended in windflow,
    and to collect them into the cistern, you must have a porous, fiberous splash-surface
    located inside the cistern for the wet wind to splash upon, condense and form the
    water droplets for collection in the cistern. Otherwise, the exhausting wet airflow
    exiting the cistern and dumping into the general ambient will cause local “rainfall”
    to occur. You actually have your own weather machine that locally creates rain
    for your crops! Make sure you have an umbrella!
  • 3)Produce
    Cooler Byproduct: Keeping farm produce
    in a cooled, air conditioned warehouse is another benefit and byproduct of your
    water generating system. Our water generator has the capacity to act as a
    cooler. Remember you’re using underground pipes to chill airflow down by
    perhaps 15 F lower thanambient (deeper
    underground pipes provide more chilling). Since this cooler exhaust air “must”
    be continuously dumped somewhere, why not dump it into a warehouse to get free
    air conditioning and preserve your produce!
0
RT-101
RT-101

Reply 1 year ago

I was email contacted by some green movement society in
Germany who applied this concept and claimed to successfully have created water. My
friends and I built a small test model in an indoor warehouse a few years back to prove a point. Instead of
burying plastic pipes, we submerged them in an above ground swimming pool whose
water was chilled to simulate the cooler temperatures existing with underground
pipes. We used a cheap fan that couldn't blow enough humid air through our 100
foot 10-inch ID pipe to condense out very much water droplets. We made only a
little condensed water in the pipe because of our small quantity of pipe airflow
created. However, the idea was proven and by math-scaling our results we proved we could
generate the GPH shown in my Instructables model.

0
RT-101
RT-101

Reply 1 year ago

I looked at the youtube video link and agree that
it doesn't math out! The rebuttal mentioned it very nicely. The diagram shown
will generate some marginal water, maybe a gallon a day, but such passive
systems are not designed for high capacity throughput, and require multiple
cells for generating reasonable quantities of water. You need a hefty air
moving fan rated at ~1Kw to move at least 1500 CFM (cubic feet per minute) of
moist air to generate sufficient water as reviewed in my report. At that
airflow rate and a pipe diameter of about 10inch, plus 150ft long, you could
generate a hefty water supply of 12 GPH. I've created a design code based on
fundamental heat transfer engineering principles that addresses the necessary
variables needed to create XX GPH of water, but didn't include its design
procedure in this report.


Takes several weeks to dig ~150ft treansh and lay
down 10inch-dia piping, plant a say 50gallon sisterm down about 10ft, and get
an electric fan capable of pushing that much air through ~150 of piping. Such
fans easily cost several thousand.


Good concept, but convective draft of such
chimneys are minor compared to the required ~10iwc draft pressure drop.


Good thinking, but we need about 150ft of 10inch
piping burried about 5ft underground where the soil is cooler.

0
RT-101
RT-101

Reply 1 year ago

I looked at the youtube video link and agree that it doesn't math out! The rebuttal mentioned it very nicely. The diagram shown will generate some marginal water, maybe a gallon a day, but such passive systems are not designed for high capacity throughput, and require multiple cells for generating reasonable quantities of water. You need a hefty air moving fan rated at ~1Kw to move at least 1500 CFM (cubic feet per minute) of moist air to generate sufficient water as reviewed in my report. At that airflow rate and a pipe diameter of about 10inch, plus 150ft long, you could generate a hefty water supply of 12 GPH. I've created a design code based on fundamental heat transfer engineering principles that addresses the necessary variables needed to create XX GPH of water, but didn't include its design procedure in this report.

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MichaelC501
MichaelC501

2 years ago

While more expensive, would copper pipes change the efficiency of the design? If PVC pipe is used, the heat transfer from the soil would be low, and the air passing through the pipe could warm the pipe faster than the soil can cool it.

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MichaelC501
MichaelC501

Reply 2 years ago

Well, I guess I mean the heat transfer from the pipe to the soil, but hopefully you know what I meant. Also, could anything be added inside the pipe to increase the surface area? Normally, when water reaches it's saturation point, it condenses on a surface. Would baffles added inside the pipe allow more water vapor to condense, which could mean a shorter pipe can be used?

0
RT-101
RT-101

Reply 1 year ago

Correct on all counts, except:
1) Yes fins attached outside the pipe will help HT, but costs a lot more.
2) Adding swirlers inside pipe will help efficiency and reduce pipe length, but your cost is the need for a larger pressure drop fan... more cost.

0
RT-101
RT-101

Reply 1 year ago

Yes copper is much better and would improve our 1500CFM airflow design system by reducing the length needed for heat exchange of a 10inch diameter pipe, from a PVC length of 150ft down by more than 50%. BTW: the airflow moves at about 35MPH and won't get heated by friction but rather loose its heat by convection with pipe.

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RT-101
RT-101

Reply 1 year ago

Sorry for delay, switched email address.
But YES you are correct about copper being more conductive and efficient in heat transfer. Result is less pipe length needed to condense water vapor.
New email: vogelhn@yahoo.com

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DragonDon
DragonDon

7 years ago

After reading(err, skimming) info and comments, I think a smaller unit is a better way to go. Multiple cheap units rather than one large one. I understand the scale you are talking but if a simple device would be setup, then it removes a ton of other issues (bugs, rodents...). Using the strips from this kit (http://solarpocketfactory.com/collections/solar-panels/products/solar-pocket-kit) could easily be utilized to power simple devices. (Actually, I did buy the DIY solar kit as suggested from this 'ible https://www.instructables.com/id/Five-minute-solar-phone-charger/ but they don't seem to be available, they were cheap. Someone must have them).

I'm sure there is a simple solution out there. Keep digging!

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RT-101
RT-101

Reply 1 year ago

No argument about size reduction and redundancy to generate our say 12GPH of water.

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DragonDon
DragonDon

Reply 1 year ago

Holy 6 years later Batman! Lol!

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RT-101
RT-101

Reply 1 year ago

Sorry! NEVER meant intentionally. Had lots of personal issues plus changed my email contact, while sadly forgetting to notify Instructables how to get in touch with me.

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charizzardd
charizzardd

7 years ago

Cool idea! I have a couple concerns. The first is what a couple people mentioned, purity. Organics and other contaminants could become an issue.

My bigger concern is actually the thermo of it. At 100 cfm, you guesstimate you can get around .8 gph of water. But that correlates to a little over 5,000 btus/hr of cooling capacity. This may be realistic to achieve. However, looking at a 1500 cfm fan and wanting to remove that much heat (76,000 btus/hr) you will need a very large or long pipe. The heat transfer of that pipe has to be the equivalent of around a 6 ton hvac system. That's big enough for most small commercial buildings/small retail building.

Now I am not saying it can't be done, 100 cfm seems a bit more realistic for a much more passive system easily running off a bike or much smaller blower. Also keep in mind that blower has to be on non stop to be producing water. In my experience the fan ad blower consume more energy than the the compressor/rest of the hvac system. Point being, powering a blower like that may be more burdensome than you think. I'd look into some calculations to see the diameter and length of pipe you need to maintain heat transfer by flow rate. Then figure out the length of pipe that seems to be justifiable. My guess is any thing above 200-300 cfm is going to require significant piping.

Also, heat transfer is better in metal pipes, which would seep into your water and cost more. Many geothermal systems use plastic tubing because its better for corrosion and such but have to use significantly longer pipes since they are basically attempting to transfer heat using a conductor.

Sorry if my math is wrong, but that's my best guess. Good luck with this, it's a pretty cool idea!

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RT-101
RT-101

Reply 1 year ago

1) Purity: Yes purity will become ant issue if water in system stagnates for very long.
2) Heat Transfer: Thermal cooling of air takes high convective airflow and I've calculated that at 1500CFM and a 10inch diameter pipe about 150ft long will take care of that issue.
3) Metal Pipes: Yes metal pipes are more conductive and the math says my 10inch, 150ft PVC pipe length will be cut in ~half.

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bprophetable
bprophetable

4 years ago

You just install this downpipe on a ravine or slope on a hill, sand dune, only needs a 10 degree slope to drain effectively all the time. If you have a building with a basement put the tank in the basement and run the pipe coiled on the walls in the interior of the basement.

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RT-101
RT-101

Reply 1 year ago

Good thinking, but we need about 150ft of 10inch piping burried about 5ft underground where the soil is cooler.

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RT-101
RT-101

Reply 4 years ago

Yes, agreed if you had no power. But with power (solar cells, etc.), I want at least 1500 CFM through a 10-inch plastic pipe (for making 10-12 GPH drinking water) to run moist air at ~45MPH. Under such air speeds you don't even need a sloped pipe. You could use a horizontal pipe and need a water catcher screen at the dump-exit to catch condensed water droplets mixed with and moving with the airflow that will drip into the cistern collector.

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wkg4
wkg4

4 years ago

Could this be combined with a solar chimney at the exit point of the cooled dry air? This would create stack ventilation pulling the air through the system and might support the fan during the day.

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RT-101
RT-101

Reply 1 year ago

Good concept, but convective draft of such chimneys are minor compared to the required ~10iwc draft pressure drop.

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RT-101
RT-101

Reply 4 years ago

Hi wkg4,
Yes it would work, but the resultant updraft would be ~1/10 to 1/100 of what we need to generate 10 to 15 GPH of drinking water at ~10 inches of water column pressure

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616136
616136

2 years ago

How long would it take to replicate or make this water generator.? Its for a project im doing

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RT-101
RT-101

Reply 1 year ago

Takes several weeks to dig ~150ft treansh and lay down 10inch-dia piping, plant a say 50gallon sisterm down about 10ft, and get an electric fan capable of pushing that much air through ~150 of piping. Such fans easily cost several thousand.

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Jayefuu
Jayefuu

8 years ago

I agree with the others. The idea (is it yours?) is interesting. But it's far too long to read without breaking it up with pictures. I've subscribed, I hope you turn some of these into Instructables.

Some thinks to consider:
1) Disaster zones and solar panels.... possible with aid. But the things that will have the most impact should be built easily from materials to hand. This could be built from salvaged guttering and electronics if it wasn't for the solar collector. Which leads to other things that might be on hand.... car batteries? Bikes?

2) In your response to chesterjohn you say you think the one he suggests couldn't make more than a few gallons per day and discount it because it needs electricity. Again... where are you going to get solar panels in an emergency? It would be interesting to see calculations on how much air a human powered bike could move.

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RT-101
RT-101

Reply 8 years ago

Hi. Thanks for your feedback.

1) IDEA: This is only partially my idea, discussions with friends led to this blog.

 2) INSTRUCTABLES: This website is a great idea (wish I thought of it) and I’m an avid fan. But I’ve got the problem of trying to make something that only works on large scale. Small models won’t work well based on doing the math. Making 12 GPH of water or better would need at least a 50-ft metal pipe, at least 8” to 10” inner diameter and buried at least 6-ft underground. That alone is backhoe excavation work using heavy equipment! Then a ~100-lb electric fan motor, etc. My point is it’s silly of me to actually create an Instructable when the process is like building a house? What do you think?

 3) SALVAGED MATERIALS AT HAND: Boy you really got me there! A worthy challenge. I’ll have to talk with my friends to come up with some ideas.

 4) HUMAN POWERED FAN: Great idea! Attach a geared bike-like system to run a fan. Exercise bikes exist that generate electricity, but your suggestion of direct coupling to fan motion is best for efficiency! Stairmasters might work better because you use your weight to create energy. It’s easier, produces more power with greater human endurance than biking: StepPowerOutput (SPO) = Weight x Step Height x Steps Per Second = 150lbs x 0.5 ft x 1.5 SPS = 113 ft-lbs/sec = 0.205 HorsePower = 159 Watts energy for maybe 2 – 3 hour steady clips?

 5) FAN POWER REQUIRED (FPR): The energy required to run our fan varies with the number of blades available. Assuming a 5 bladed system with n=95% air movement efficiency and:  a) volumetric airflow of ma =  1500 CFM, b) a ID = 10-inch diameter pipe, c) L = 50 foot long pipe, and d) fric = pipe friction factor = 0.015:

we have ...

FPR = [(Mass Airflow Kinetic Energy / time) + (Pipe Pressure Drop x Volume Airflow) ] / n 

Where:  
(Mass Airflow Kinetic Energy / time) = ma x (air-density) x (pipe-air-velocity)^2 / 2

 and 
(Pipe Pressure Drop x Volume Airflow) = ma x (air-density) x [fric  x 12 x L / ID x (pipe-air- velocity)^2 / 2
therefore...

FPR = [(83W) plus (72W)] / 0.95 =  163 Watts.

Which says it’s doable with a 150 lb person walking steps!

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Jayefuu
Jayefuu

Reply 8 years ago

I would think a bike would be better over steps.
1) It's easier to translate the motion to the fan
2) If a bike has cups on the pedals you can power on the lifting of the leg as well as the pressing down.

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chesterjohn
chesterjohn

8 years ago

How do you keep cockroaches out of it. One thing you don't want is bugs crawling down there and living. How do you protect it from molds and fungus. these are important as these will affect the quality of water not to mention it sanitary condition.

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RT-101
RT-101

Reply 8 years ago

Bugs and algae growth are definitely issues to contend with. We will need periodic hygiene antibiotics to deal with algae. The only way bugs will get into the sealed underground system is either at the pipe inlet or exit. So mosquito screens will be placed at both points. Thanks.

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chesterjohn
chesterjohn

8 years ago

Go here to learn more on how to make a safe drinking atmospheric water generator in your home.
https://www.instructables.com/id/DIY-Atmospheric-Water-Generator/

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RT-101
RT-101

Reply 8 years ago

Thanks.  A very clever device.

My only concerns are that it needs electricity and probably makes no more than a few gallons of water a day, which is maybe good for one person but not more. Typical Haitian camps housed hundreds to thousands of people, had no electricity, yet each person needed at least one gallon of water per day. Multiply that by hundreds of camps throughout the country and that’s a lot of electricity and water needed?

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RT-101
RT-101

Reply 8 years ago

Agreed!
Remember, those in real need would want even more detail!