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Smart Dew-Point Water Harvester

Harvesting clean drinking water from sunshine.

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750 million people around the world lack access to safe drinking water; approximately one in nine people. One source of clean water is harvesting it directly from the air.

Dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid water at the same rate at which it evaporates. At temperatures below the dew point, water will leave the air. The condensed water is called dew when it forms on a solid surface.

Harvesting water from air is not a new idea however many systems rely on environmental conditions or large amounts of energy. This system uses what is known about dew point water harvesting and tries to optimize the conditions in the most energy "convenient" way. The result is a type of "black-box" solution requiring little or no user involvement to harvest clean drinking water from the air where there isn't any.

Note 9th Feb 2016: Summing up If the humidity is 32°C/80% then 1 litre of water per hour at 200W can be harvested. This project was an experiment to compete in the 2015 Hackerday Prize. As I'd realised through a number of experiments with solar panels, that we generally use solar panels the wrong way round. Most solar installations waste allot of energy they by charging a bank of batteries and then using the power stored in the batteries to do the "useful work". However, if the power application is not running-time dependent then it is far more efficient to do the "useful work" there and then directly from the solar panels. This has a better than 40% improvement in energy efficiency at half the cost. For those wishing to replicate this project, the easiest and cheapest way to do so, is to simply use a commercially available "dehumidifier" and then power it directly using solar panels, using batteries only to safely power down the dehumidifier and monitoring sensors when sunlight is not available. I also found during these experiments, there was no real benefit in delaying water harvesting at another time, this also simplifies the monitoring equipment. As it became clear that the same amount of water could be harvested regardless of time of day if the humidity didn't increase, as the benefits of improved barometric pressure and ambient temperature were negligible.

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Solar is a highly variable power source, so the aim of this project is to effectively use the power at it's maximum availability using the majority of energy captured to cool liquid coolant and store it in an insulated tank. Rather than storing the energy in large expensive batteries. This coolant would then be used at a later time when conditions are closest to dew-point conditions ( possibly late at night ) when it is cooler and the sun isn't shining. The smart controller will then turn on and off a pump to move the liquid coolant into a condenser coil for dew point collection. The controller is called smart as it will require a small embedded computer Raspberry Pi2 and Arduino to log daily barometric pressure, humidity and temperature so it can calculate the best time to run the water harvesting system.

Note: This is a crude prototype made from hacked off-the-shelf parts as a proof of concept. However, it has proven to work even though a crude example to make measurements and identify improvements including:

  • The condenser coil shape and size
  • Coolant used and quantity
  • Coolant storage methods and insulation
  • Vessel construction and insulation
  • Airflow within the vessel
  • Refrigeration systems
  • DC Regulation between Solar Panels to Peltier Cells

The vessel in which the condenser coil in enclosed is designed to both catch dew as it forms on the condenser coil and establish a low air-pressure than that outside the vessel to increase conditions where water will leave the air (dew point). To achieve this, a filter is used on the inlet of the condenser vessel to both create an air pressure differential and to filter dust particles. A fan is used to draw air from the bottom of the vessel down through the filters at the top and over a condenser coil, while maintaining low air-pressure inside the condenser vessel.

If scaled up a conventional refrigeration system could be used with buffering batteries or even direct sunlight on an Absorption refrigerator system could be used, but in smaller units a Peltier Cell seems quite effective at cooling liquids, such as in this concept prototype.

Peltier Coolers are very lightweight and small compared to a conventional refrigeration systems. However they are not very energy efficient. Also the Peltier Cell itself is thermally conductive so when the power is switched off the heat from hot side quickly rush back to the cool side of the cell. Consequently, to improve the efficiency of Peltier Cell it is important to ensure the liquid coolant moves away from the Peltier Cell...

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  • 1 × 25L Conical bottom Polyethylene Tank Electronic Components / Misc. Electronic Components
  • 1 × 22 Litre Insulated Tank
  • 2 × Brushless Submersible Centrifugal waterpumps 12 Volt DC
  • 1 × 120mm 12V Fan
  • 1 × PVC Tubing

View all 26 components

  • Conclusion of Project

    Robert Hart10/04/2015 at 23:02 0 comments

    This was a crude prototype for testing and proof of concept. Which has demonstrated there is significant energy available from a solar panel to cool over 20 litres of liquid well below -4C in less than 6 hours using off-the-shelf peltier coolers. Further that liquids can be stored over 48 hours and used later to dehumidify air when conditions are best and collect water for drinking. Cooling could be significantly improved using a compressor refrigerator unit with better energy efficiency but at a greater cost. Dehumidifying the air could be significantly improved with better vessel and distillation coil design. The system could be scaled up or scaled down. Coolant storage is not required if batteries are used but this also comes at greater cost. The system could be run while the sun shines if sufficient humidity is available and the dehumidifer vessel is appropriately insulated.

  • 27th September - Solar Panel Regulators

    Robert Hart09/27/2015 at 07:36 0 comments

    An off-the-shelf Solar Regulator is primarily designed to put the bulk of power collected from the Solar panel into charging a battery where the load will draw its power. However, in this project I want the bulk energy from the Solar Panel to be used to cool down the coolant. Consequently I have built regulators that take power directly from the solar panel.

    As it's important to keep the heat sink on which the Peltier Cells are mounted close to ambient temperature, to get the best efficiency from the Peltier Cells. I'm using a Boost Buck Up/Down Regulator for the cooling fans this means there will keep running a low sunlight levels. This uses a LM2577 3.5V to 40V to Boost Buck Up/Down Regulated 12V 900ma for cooling fans.

    The Peltier Cells at 12V consum 5.7 - 6amps and so I am using using 2 x LM2678 in parallel which will provide 15-40V to Buck Down Converter Regulator giving a maximum of 12V at 10A for each Peltier Cells.

  • Solar Tests - Saturday 19th September

    Robert Hart09/19/2015 at 08:38 0 comments

    Very good results today more than enough power to run the cooler and charge the battery. Also prepared a video for the 2015 Hackaday Prize Semifinals Video. Particularly good as it is spring and the sun isn't at its seasonal peak clear day 21C max.

    3 hours of sunshine got the tank down to 4C with improved tank insulation and storage capacity this is ample for reproducing dew-point conditions in the condenser.

    In preparation of dew collection I've added an insulating coat for the condenser vessel.

    My son 10yo is a big fan of the project. Also our dog Alfie.


  • 17th September Thursday Evening

    Robert Hart09/17/2015 at 10:54 0 comments

    I'm currently wiring up the new rig and testing cooling systems for a stand alone solar powered test on Saturday as it's expected to be sunny and I want to get some video for my semifinalist entry.

    Cooling system and new storage tank working well 20 Litres of coolant to -1.8C in ~6 hours.

  • Self-contained mobile frame with Solar Pannel

    Robert Hart09/13/2015 at 07:35 0 comments

    This weekend I assembled some framework to support the Solar Panel to make the project completely self-contained. I also took the opportunity to upgrade the coolant insulated storage tank. The manufacturers claim it can keep ice cold for 3 days.

  • Spring Solar Panel - 12th September 2015

    Robert Hart09/11/2015 at 23:21 0 comments

    Most of my experiments to date have been indoors, as I live in the southern hemisphere and it's been winter, and winter in Adelaide it rains most of the time. It's now spring and the sun starts shining again so I can start the solar power side of this project.

    However although it's spring here in Adelaide the weather is at its most variable with beautiful sunny weather one minute, then cloudy and showers the other, this happens multiple times a day. My son Charlie 10yo

    Here is the frame that this will be mounted on, including all the equipment.

  • Solar Panels - 9th September 2015

    Robert Hart09/09/2015 at 03:43 0 comments

    Just picked up 2 new 260W Australian made solar panels directly from the Tindo Solar factory who agree to sell them to me at wholesale for this project.

    Very high quality and very efficient datasheet here: http://www.tindosolar.com.au/product/tindo-karra-260-dc/

  • Movie Madness -6th September 2015

    Robert Hart09/06/2015 at 02:01 0 comments

    I've been trying to put together a video about this project entry. I have a great admiration for people who produce youtube videos some of my favorites include Veritasium, Applied Science and Vsauce. Although I love making things and talking about it I find this part of the competition the hardest part by far. Here is my first draft, still working on the electronics and solar panel side of the project which I will add to the video.

  • 5th September 2015

    Robert Hart09/05/2015 at 10:59 0 comments

    I have order 2 Panels are 260W Vmp is 30.2V and Imp is 8.6A tindo solar who where kind enough to sell these to me at the whole price. I am currntly preparing the Solar Panel Regular, Charger and Mosfet Controllers.

    Paul Schulz has join the team and is currently developing some code to run on an arduino for sensors and control. Its Brain will be a Raspberry pi2.

    // Digital Inputs
    const int ctlCoolerPin        =  2;
    const int ctlCoolerFanPin     =  3;
    const int ctlCoolerPumpPin    =  4;
    const int ctlCondenserFanPin  =  5;
    const int ctlCondenserPumpPin =  6;
    
    // Outputs
    const int outCoolerPin        =  7; 
    const int outCoolerFanPin     =  8;
    const int outCoolerPumpPin    =  9; // PWM 
    const int outCondenserFanPin  = 10; // PWM
    const int outCondenserPumpPin = 11; // PWM   
    const int outStatus1Pin       = 12;
    const int outStatus2Pin       = 13;
    
    // Analog in
    const int analog1Pin = 0;
    const int analog2Pin = 1;
    const int analog3Pin = 2;
    const int analog4Pin = 3;
    const int analog5Pin = 4;
    const int analog6Pin = 5;

  • 28th August 2015

    Robert Hart08/28/2015 at 04:53 0 comments

    I'm currently developing the electronics to control the Dew-Point Water Harvester. An area I have identified when experimenting with the basic prototype is that reducing the temperature of the condenser coil far below the dew-point temperature does not automatically equate into an increased rate of water collection. With the additional temperature monitoring of the condenser and a PWM control to the speed (flow rate) of the submersible pump it would be possible to regulate the temperature at the optimum temperature. This will decrease the rate at which coolant is reheated heated and increase the time available to collect dew, consequently more water.


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Discussions

Michael Delgado wrote 02/09/2017 at 12:26 point

good day sir Robert, I would like to know if your harvested water was drinkable and if it doesn't have any kind of smell. Because we tried to copy your project and used activated charcoal as a filter but our hasvested water has a smell.

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Michael Delgado wrote 09/29/2016 at 09:04 point

Good Day sir, we used a peltier cooler(TEC1-12706) that has a specs of "12V, 6A, 60watts", when we supply a power came from a "12V 20A battery" it doesn't produce the expected coldness that makes the liquid coolant cold enough to produce moisture in a coil. Can you please give us an advice on what should we do or what's wrong with the procedure? Thank you.

  Are you sure? yes | no

Robert Hart wrote 09/29/2016 at 09:20 point

The peltier must be cooled with a large heat sink and fan.

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Michael Delgado wrote 09/29/2016 at 09:48 point

we forgot to say that we already installed a small heat sink on the hot side of peltier cooler,with a fan also.

  Are you sure? yes | no

Robert Hart wrote 09/29/2016 at 09:53 point

needs to be large

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Michael Delgado wrote 09/29/2016 at 09:58 point

Thank you sir. We'll try it as soon as possible.

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Michael Delgado wrote 10/14/2016 at 10:56 point

What is the length of the condenser coil that is required in your project ? 

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williamwzd wrote 08/23/2016 at 16:40 point

So, What  do you think that is the best way to do it? 

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Robert Hart wrote 08/24/2016 at 01:08 point

I would use an off-the-shelf Dehumidifier,  rig it up to filter the water and store in a larger tank. The important lesson I leaned, was to use the solar panels direct power to run the Dehumidifier while the sun shines using regulated power system.  With only a small amount of power used to charge a batteries that can shut down the Dehumidifier safely when the sun light drops below a specific level. A control system could enhance this by controlling shut-down for night or expected weather conditions.

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williamwzd wrote 06/10/2016 at 01:47 point

What is the flow through a coil when going to condense water?

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Robert Hart wrote 06/10/2016 at 21:16 point

about 400L/H , but this really isn't the best way to do it, as it was an experiment, read my notes.

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williamwzd wrote 06/10/2016 at 01:46 point

What is the efficiency of the machine ?

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Janine Lopez wrote 03/01/2016 at 06:07 point
what else sir?

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Janine Lopez wrote 02/27/2016 at 04:33 point

what are the limitation of this project?

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Robert Hart wrote 02/27/2016 at 07:22 point

Low humidity and/or low levels of sun light or if using wind-turbine wind.

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Marcus Szolkowski wrote 02/11/2016 at 02:39 point

As an efficiency improvement, have you thought about passing the air from fan F1 across the peltier hot side?  You have cold dry air exiting the system that could be used to better cool the peltier, reducing it's delta T and increasing it's heat transfer capabilities.

  Are you sure? yes | no

Robert Hart wrote 02/11/2016 at 03:20 point

Absolutely this would be an improvement. But at the time I was focused on cooling and storing the coolant for later use at night when F1 was operational and the Peltier was not.

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williamwzd wrote 02/08/2016 at 15:22 point

What is the reference plates peltier ?

Coil length ?

What is the power consumption in the system?

What is the amount of water generated in 24 hours?

Thanks!

  Are you sure? yes | no

Robert Hart wrote 02/08/2016 at 22:30 point

Hi William,  If humidity 32°C/80% then 1 litre an hour at 200W. However, this project was an experiment for the Hackerday Prize. I had realised through some experiments with solar panels, that we generally use solar panels the wrong way round. Most solar installations waste allot of energy collected to charge a bank of batteries and the power from the batteries is then used to do the work. If the application is not running-time dependent then it is far more efficient to do the work there and then directly from the panels, this has a better than 40% improvement in energy efficiency and half the cost. Anyway, in summary, the easiest and cheapest way to recreate this project is to simply buy a commercially available "dehumidifier" and power it directly using solar panels. As during the experiment, I found there was no real benefit in water harvesting by waiting until nightfall, as the same amount of water could be collected regardless of time of day if the humidity didn't change.

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Janine Lopez wrote 12/06/2015 at 14:02 point

if you don't mind Sir can you help me about some codes of this project? .. thank you in advance

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Robert Hart wrote 12/08/2015 at 09:23 point

Don't have any to share sorry, haven't developed that side yet.

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Janine Lopez wrote 01/18/2016 at 03:34 point

okay Sir Thank you

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Janine Lopez wrote 12/02/2015 at 14:02 point

can I use this idea in my thesis project Sir? if you don't mind  , I loved the idea of this project .

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Robert Hart wrote 12/06/2015 at 04:55 point

sure its an open source project.

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Dylan Bleier wrote 05/06/2015 at 01:08 point

water from the atmosphere should be well-filtered to make it drinkable because it contains aerosols and dissolved gasses.  especially if you are in a place with poor air quality.

  Are you sure? yes | no

Robert Hart wrote 05/06/2015 at 03:59 point

Very good point Dylan.  The design includes a filter for that reason and also to create a pressure differential inside the condenser vessel to facilitate moister leaving the air. Do you have any suggestions on the type of filter would be ? As I haven't focused on that area yet, mainly working on the mechanical aspects?  Cost, availability, durability, maintenance (i.e. can it be cleaned or made using local materials, etc.)   It may need some active ingredient like lime or carbon but this may also absorb moisture reducing condenser efficiency . I assume it needs to absorb heavy metals, hydrocarbons, acids and alkalines but not water.    

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Dylan Bleier wrote 05/06/2015 at 06:38 point

I dk, I think crushed charcoal (with sand and then pebbles on either side) will get most of the crap out.

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murray wrote 04/15/2015 at 14:24 point

Some ideas...

If your coolant is derived from the water you are extracting, then in the condensation tower, rather than run the water through a heat exchanger, just spray it. This will be much cheaper, gives you an enormous contact surface area, creates a nucleus for the water to condense around, and produces a down draft. If you restrict the top of the tower (can be done with the filter), the draft may even be enough to produce the drop in pressure you were looking for (how much drop do you require?), saving you a fan. 

Additionally. in arid areas temperatures often fluctuate wildly, You could simply save the coldness of the night air in say a 1KL tank of water. passing the air over a radiator. Than you dont need to gennerate coldness, you simply store it at night and use is during the day.

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Robert Hart wrote 04/15/2015 at 21:19 point

Hi Murray,  I'm using antifreeze coolant as it has good heat absorption (or in this case negative heat) and storage qualities. Also to save this,  the design should allow for the liquid to run away from ether the condensation coils or the peltier cooler to insulate the liquid when not in use.  The reference to "Smart" in the name was that the controller is programmable, a small profile computer that measures the environment and determines the best times when to cool the liquid and when the best time to harvest water.  The unit might pre-programmed for a specific location/environment or is dynamically linked to the local meteorological information via the internet. It might even double up as a weather station in itself as part of the internet of things :) 

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johnowhitaker wrote 04/11/2015 at 12:47 point

I like this idea, and had thought about doing something similar. Have you considered having it underground to exploit the cooler soil temperature? Also, this allows you to move the air through with some sort of venturi system, saving the power use of a fan.

Also, I have a peltier cooler and while the are very cool (no pun intended) they are not particularly efficient. Have you considered a more conventional cooling system?

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Robert Hart wrote 04/18/2015 at 10:10 point

Hi John, its a project that's been on my mind for some years too and I'm sure many others. It's not a new idea either, as far as removing water from air and there are many examples of completely passive systems too. I'm thinking along the lines of something that is relatively portable like something not unlike the prop in the 2015HackadayPrize video though a little smaller and that can be used in many different environments so there needs to be a few compromises for weight and size.  This is why I mention the term "energy convenient" and yes the peltier is a very inefficient device. But a compressor system is heavy and costly compared to the peltier (Though I might give it go at some stage). I discovered a experimenting with the idea of motorcycle vest to keep cool a few years ago that a peltier can be improved somewhat when used to cool liquids. The important thing to do is that it must be rigged up so that the liquid runs away from the cell when it was off to insulate the liquide from the peltier.  A peltier is quite thermally conductive so when power is off all the heat from the other side quickly rushes back to the cool side.  Also rather than use solar panels to charge a big bank of batteries to run the peltier, use most of the power to cool liquid while the sun shines and then store this in an vacuum insulated container.  Using the liquid at a better time to cool the air down to dew point using a condensation coil (also not a new idea). This would also be more efficient than using a peltier running on batteries which would have less surface area and cost more. Using only a smaller battery to run a small pump and the controller.

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