More musings---see previous blog post. This time I was reading a recent issue of Eos (August 2021), published by the American Geophysical Union (AGU). One article (Climate Clues from One of the Rainiest Places on Earth, page 11, by A. J. Wight) contained a wonderful quote. "In the atmosphere, we are all connected," and the [low-level jet stream] "is part of the engine that redistributes the heat from the tropics to higher latitudes." So stated John Mejia, associate professor of climatology at Nevada's Desert Research Institute. The water-from-air industry's main resource is the water vapour in the atmosphere. Water vapour is transported great distances between regions on Earth by the global atmospheric circulation processes. We are all connected in seeking to utilize this water resource residing in our "atmospheric commons". Atmospheric water vapour is, of course, just one part of the water cycle, one of the many essential planetary cycles of natural materials.
Participants at this well-attended webinar had lots of questions---too numerous to answer during the Q & A period at the end of the webinar. So the three panelists were asked to reply to a set of questions---the answers were sent recently to the registered attendees. Here are my answers to the set of eight questions assigned to me. They cover a variety of topics. I hope you find the answers interesting and useful.
Water vapor, the gas phase of water, diffuses along pressure gradients to zones of lower water vapor pressure. If a lot of water vapor was condensed into liquid water in a specific region such as a city, water vapor from outside the region would flow in immediately. No net loss of atmospheric water vapor density would be observed in the city.
Water consumed for domestic water requirements does not exit from the water cycle. Within a day or so the liquid water that is used or temporarily with-held from the water cycle would be returned to the environment by evaporating into atmospheric water vapor.
On a clearly bounded terrestrial surface such as a tropical island, atmospheric water vapor processing systems would increase slightly the annual precipitation. Let us say a large-scale AWG array is installed on an island such as Grand Turk (Turks & Caicos Islands). The island has a surface area of 18 square kilometers (1,800 ha). The AWG array produces water from the air at a rate of 75,335 cubic meters annually. This is equivalent to a rainfall of 7,533 mm over one hectare (10,000 square meters). The average annual precipitation of Grand Turk is 604 mm. This value would be enhanced by [7,533 mm/ha/1,800 ha] = 4 mm (or 0.7% annually, an amount less than the natural variability from year to year. The annual total precipitation in the year 2000, for example, was 704 mm.
To reinforce the fact that long-term human direct impact on atmospheric water is negligible, note that dehumidifiers and air-conditioners dripping condensate have been increasingly used since the 1950s. I used NOAA global specific humidity data (measured in grams of water per kilogram of air) and subtracted the earlier 30-year 1951 to 1980 annual field from the more recent 39-year 1981 to 2019 field. The resulting map showed several pools of higher specific humidity (+2 g/kg). These are likely related to climate change. Drying of about -2 g/kg is noticeable over the Sahara and Gobi deserts---more likely to be related to climate change than use of HVAC equipment. Over most of Earth specific humidity has been remarkably stable (+/-1 g/kg) for the past seven decades. By the way, I posted the map in the Atmoswater Research blog. Indirect environmental impacts are more likely. These will be related to the materials used in manufacturing AWGs, product life cycle aspects, and so on. Also, AWGs will enable humans to expand their footprint which could increase population density in a region, lead to increased sewage and waste disposal challenges, and increase energy use.
These analyses indicate widespread global atmospheric water use will not noticeably affect the world climate.
More conventional sources of water have these electrical energy costs:
- Surface water, public supply: 0.37 kWh/cubic meter (Young, 2014)
- Groundwater, public supply: 0.48 kWh/cubic meter (Young, 2014)
- Tap water, 0.46 kWh/cubic meter (Gleick & Cooley, 2009)
- Municipal water (S California): 3 kWh/cubic meter (Gleick & Cooley, 2009)
- Seawater Desalination (reverse osmosis): 2.5 to 7 kWh/cubic meter (Gleick & Cooley, 2009)
- Seawater Desalination (reverse osmosis): 2 kWh/cubic meter (Elimelech & Phillip, 2011, p. S1)
- Bottled Water: 519 to 945 kWh/cubic meter [Gleick & Cooley, 2009; thermal energy units were converted to electrical energy units (3:1) to derive these values]
It was interesting to discover that AWGs used in tropical climates are competitive with bottled water. Keep in mind the apparently cheaper conventional sources may not even be available in some water scarce regions. The desalination costs do not include the apparently difficult to monetize costs of harming local ecosystems with brine disposal.
Elimelch, M. & Phillip, W. A. (2011) Supporting Online Material for The Future of Seawater Desalination: Energy, Technology, and the Environment. Science 333, 712-717.
Gleick, P. H. & Cooley, H. S. (2009). Energy implications of bottled water. Environ. Res. Lett. 4 (2009) 014009 (6pp).
Young, R. (2014). Watts in a Drop of Water: Savings at the Water-Energy Nexus. An American Council for an Energy-Efficient Economy (ACEEE) White Paper. Retrieved from https://www.aceee.org/sites/default/files/watts-in-drops.pdf
- AWG rated for 5 gal/day: $300/gal (residential quality)
- AWG rated for 10 gal/day: $420/gal (balance of list is commercial/industrial quality)
- AWG rated for 40 gal/day: $178/gal
- AWG rated for 140 gal/day: $121/gal
- AWG rated for 800 gal/day: $98/gal
- AWG rated for 1800 gal/day: $82/gal
The energy cost of water produced by a desiccant AWG was estimated two ways (note that kilowatt is a unit of power---the energy unit is kilowatt x hours, kWh, which is power acting over a period of time):
a. Specifications for a line of industrial rotary desiccant dehumidifiers (using electrical energy) manufactured by Hangzhou Peritech Dehumidifying Equipment Co., Ltd. (http://www.desiccantwheeldehumidifier.com/sale-2082217-industrial-rotary-desiccant-dehumidifier-silica-gel-economical-dehumidifier.html). Their 14.4 L/day model produces water using 2.8 kWh/L (10.6 kWh/US gal or 10,600 kWh per 1000 US gal). Their 1,102 L/day model produces water using 1.3 kWh/L (4.9 kWh/US gal or 4,900 kWh per 1000 US gal).
b. Using information in the SOURCE Global (formerly Zero Mass Water) Patent Application US 2018/0043295 A1. The document includes an example of operation in Amman, Jordan at 14:00 on a July day. Airflow is 90 cfm. Relative humidity is 30%. A solar thermal panel with surface area 1.5 square meters provides 700 W (at 50% efficiency) to heat the desiccant to release captured water at the rate of 0.3 L/h. This information can be interpreted three different ways because international consensus is lacking on comparing different energy sources (e.g., solar thermal versus electricity; read more at the American Physical Society Site https://www.aps.org/policy/reports/popa-reports/energy/units.cfm). We need to make this comparison because the Peritech dehumidifiers and all chilled-coil AWGs are energized by electricity.
i. Thermal energy = electrical energy cost of water = (700 W x 1 h)/0.3 L = 2.33 kWh/L; efficiency of solar thermal assumed to be 100% as per OECD/IEA publication guidelines
ii. Equivalent electrical energy cost = 0.76 kWh/L; efficiency of solar thermal assumed to be 33% as per DOE/EIA (USA) publication guidelines
iii. Equivalent electrical energy cost = 1.17 kWh/L; efficiency of solar thermal assumed to be 50% as stated in the patent application
The range of energy costs for the SOURCE Global patent application example is 2.8 kWh/US gal (2,800 kWh per 1000 US gal) to 8.7 kWh/US gal (8,700 kWh per 1000 US gal).
Has widespread use of dehumidifiers and air-conditioners dripping condensate affected in the long-term the amount and geographical distribution of water vapour in the atmosphere? An analysis using data available from NOAA suggests not. The figure above shows the difference field of specific humidity resulting from subtracting the composite means (Jan to Dec) for the 30 year period 1951 to 1980 from the 39 year period 1981 to 2019, Several pools of higher specific humidity +2 g/kg are noticeable. These are likely related to climate change. Drying of about -2 g/kg is noticeable over the Sahara and Gobi deserts---more likely to be related to climate change than use of HVAC equipment. Overall, specific humidity has been remarkably stable (+/-1 g/kg) over the past seven decades.
Reference: NCEP Reanalysis Derived data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/
Here are some product design notes applicable to atmospheric water generator products. The notes are based on an interview with Mitch Maiman, Intelligent Product Solutions by William G. Wong of Electronic Design magazine (July 26, 2020).
Common design mistakes to avoid
Embrace smart products
This quotation defines the fundamental market for the water-from-air industry.
"The pandemic has exposed huge inequalities in water security, with more than 2 billion people, half of schools, and one-quarter of health-care facilities lacking a basic water or sanitation service."---as stated by 16 co-signatories in Correspondence published in Nature 583, 360 (2020).
But, it is challenging to develop business models to address these markets in which the individual members seldom can afford innovations. Although technical water-from-air advancements remain important to work on, the need for business model inventiveness is likely to be even more necessary.
Journalist Verity Ratcliffe of Bloomberg wrote an interesting article about Zero Mass Water's installation supplying water-from-air to a bottled water plant in Dubai, UAE.
For technical details, see this page: https://www.atmoswater.com/case-studies-zero-mass-water-inc.html
This is an interesting article about the drinking-water-from-air industry. It also includes a section on fog harvesting. Atmoswater Research got a nice mention!
Water-from-air systems often use ultraviolet light means to sanitize the incoming air, the stored water, and the water as it is being dispensed. This 4-page fact sheet, by the nonprofit IUVA, is useful knowledge for the water-from-air industry community as it copes with the COVID-19 pandemic.
Recently, I was invited to discuss some aspects of water-from-air technologies as posts (each about a one minute read) in the GWW Connect Network. I posted the seventh and final article today. Here are links to the posts.
This newly published article, by water industry experts Mary Conley Eggert and Graham Symmonds, is worthwhile reading for current perspectives about the role of water-from-air technologies in drinking water supply infrastructures.
This YouTube video by the Dutch foundation, Happy With Water Foundation, reviews several atmospheric water vapour processing methods and then states that an absorption cooling method using solar energy and vacuum tubes with heat pipes reduces the energy cost of water making it relatively more affordable and practical compared to most other options.
Field trial of the AKVOS water-from-air system in January 2018 on Sal Island, Cabo Verde. The water production module is on the left and the atmospheric water vapour absorption module is on the right. Water vapour in the air is aborbed by liquid glycerol flowing on the white fabric in the metal framework. The hydrated glycerol is transferred to the water production module. Solar heat is used to evaporate water out of the glycerol. The water vapour condenses into liquid water on the bottom inside surface of the module. Photo by Roland Wahlgren.
For some time I have wanted to highlight this interesting water-from-air system. The photo shows a prototype system using glycerol as the liquid desiccant to absorb water vapour from the air on Sal Island in the eastern tropical Atlantic Ocean (17°N, 23°W). The prototype was designed and built by Dr. Pavel Lehky who holds United States Patent 9,200,434 B2 for the system. The field trials were done during Team AKVOS's participation in the Water Abundance XPRIZE competition. I was a member of the team. During a typical night at the site, the absorption module with its 9 square metres of surface area absorbed over 4 L of water. The 0.25 sq. m. production module was able to recover about 0.3 L of this during a typical day. So, one of the lessons from the trial was the water production module area has to be better matched to the capacity of the absorption module. Improving the efficiency of the water production module is also of benefit—this is a focus of ongoing design improvements. Find out more about Stiftung Sanakvo (Team AKVOS) at their website. Sanakvo also has a video on YouTube with an explanation of the system and showing the prototype operating during the field trial.
The University of California, Berkley research group led by Omar M. Yaghi published recently an article in ACS Central Science describing how they built and tested a metal-organic framework water harvester prototype. The system produced fresh water at the rate of 0.7 L/day in the Mojave Desert during a 3-day trial (October 17–20, 2018). During this period the ambient air dew-point was less than 5 °C for 85% of the time.
#WaterfromAir Industry News: Jeff Szur, formerly VP of Drinkable Air, starts The Trident Water Company
You can read the update by Jeff Szur at this link: https://mailchi.mp/5b1d9c7272fb/my-new-venture?fbclid=IwAR3ZLsQGIUKDRT3lPfATLn4ATO2Shjfjs1QKXEus_9L5rZRl2N1cUL0FBt0
Today, I learned about Aalto University's Water Scarcity Atlas from The Water Network. The atlas is a useful and credible resource for learning about various aspects of the water supply challenges facing humanity. For those of us in the water-from-air community it is definitely worth visiting and bookmarking. The atlas is a useful guide to the regions on which to focus water-from-air research and development efforts.The data & code section of the atlas website had a link to the City Water Map Initiative whose data source was
McDonald and others (2014). Water on an urban planet: Urbanization and the reach of urban water infrastructure. Global Environmental Change 27, 96–105.
This paper gives the results of the first global survey of the water sources for the world's largest cities. Table 2 in the paper lists the largest cities enduring water stress. The cities (in order of population) are Tokyo, Delhi, Mexico City, Shanghai, Beijing, Kolkata, Karachi, Los Angeles, Rio de Janeiro, Moscow, Istanbul, Shenzhen, Chongqing, Lima, London (UK), Wuhan, Tianjin, Chennai, Bengaluru, and Hyderabad.
Enjoy watching our 4 minute 40 second video presentation about using mechanical dehumidification technology for obtaining drinking water from the water vapour in the air. To access the video, just click on the image above.
Chemical & Engineering News published an interesting article about drinking-water-from-air technologies which may be accessed at by clicking on the page excerpt image above.
The September 28, 2018 earthquake and tsunami disaster in Palu has caused shortages of clean water (see for example, "Palu earthquake, tsunami victims get clean water support", The Jakarta Post). The Water-from-Air Resource Chart for Palu is a free download.
Moscow and London among the cities that could run out of drinking water? Yes, according to a BBC report in February 2018.
Moscow's drinking water comes mostly from surface water. Industrial pollution affects surface water in Russia.
London has relatively low average annual rainfall feeding the Thames and Lea rivers which supply much of London's drinking water. Capacity limits are being approached and are likely to be exceeded in the next couple of decades.
Although Moscow and London are not ideal sites for a year-round water-from-air resource, there is enough moisture in the air during the summer months to allow machines to operate.
The new Water-from-Air Resource charts for Moscow and London, now available for purchase and download at the Atmoswater Shop, will be of interest to city planners and others concerned about ensuring water security for the people living in these two cities.
Thermoelectric cooling technology has had wide appeal as an alternative to mechanical refrigeration cooling technology for at least twenty years. Thermoelectric systems avoid the use of hazardous, harmful refrigerants and noisy compressors. Low coefficient of performance (COP, in the range of 0.9–1.2) is the main problem preventing widespread use of thermoelectric cooling especially for systems requiring large cooling capacities (Riffat & Ma, 2004). A COP of 1.2151, achieved using a multistage thermoelectric module, was considered "remarkable" by Patel and others (2016) Only smaller capacity niche applications have been commercialized.
There have been several peer-reviewed papers published and patents issued for atmospheric water generators or dehumidifiers using thermoelectric cooling devices which use the Peltier effect. Some information and products have been featured on websites. Each reference below represents a clickable link to more information.
Examples of papers
Atta, R. M. (2011). Solar Water Condensation Using Thermoelectric Coolers. International Journal of Water Resources and Arid Environments, 1(2), 142–145.
Milani, D., Abbas, A., Vassallo, A., Chiesa, M., & Bakri, D. A. (2011). Evaluation of using thermoelectric coolers in a dehumidification system to generate freshwater from ambient air. Chemical Engineering Science 66(12), 2491-2501.
Muñoz-Garcia, M. A., Moreda, G. P., Raga-Arroyo, M. P., and Marin-González, O. (2013). Water harvesting for young trees using Peltier modules powered by photovoltaic solar energy. Computers and Electronics in Agriculture 93, 60–67.
Nandy, A., Saha, S., Ganguly, S. & Chattopadhyay, S. (2014). A Project on Atmospheric Water Generator with the Concept of Peltier Effect. International Journal of Advanced Computer Research, 4, 481–486.
Suryaningsih, S. & Nurhilal, O. (2016). Optimal design of an atmospheric water generator (AWG) based on thermo-electric cooler (TEC) for drought in rural area. AIP Conference Proceedings 1712, 030009 (2016); doi: 10.1063/1.4941874
Davidson, K. B., Asiabanpour, B., & Almusaied, Z. (2017). Applying Biomimetic Principles to Thermoelectric Cooling Devices for Water Collection. Environment and Natural Resources Research 7(3), 27–35.
Examples of Patents
Peeters, J. P. and Berkbigler, L. W. 1997. Electronic household plant watering device. United States Patent 5,634,342. [expired, now in public domain]
Wold, K. F. 1997. Plant watering device and method for promoting plant growth. United States Patent 5,601,236. [expired, now in public domain]
Reidy, J. J. 2008. Thermoelectric, High Efficiency, Water Generating Device. United States Patent 7,337,615.
Waite, R. K. & Neumann, A. (2017). Water production, filtration, and dispensing system. United States Patent 9,731,218 B2.
Examples of Websites
The "instructables" website published the article "How to Make a Dehumidifier (Thermoelectric Cooling) in 2016.
Amazon.com sells several models of "thermoelectric portable compact dehumidifiers".
Patel, J., Patel, M., Patel, J., & Modi, H. (2016) Improvement in the COP of Thermoelectric Cooler. International Journal of Scientific & Technology Research 5(5), 73–76.
Riffat, S. B. & Ma, X. (2004) Improving the coefficient of performance of thermoelectric cooling systems: a review. Int. J. Energy Res. 28: 753-768 (DOI:10.1002/er.991)
The target market for atmospheric water generators, in the broadest sense, are people in locations with perennial water shortages due to population growth, climate change, and lack of enough sustainable surface or groundwater within a radius of 100 km. The reference for these defining conditions is: Lalasz, R. (2011). New Study: Billions of City Dwellers in Water Shortage by 2050; retrieved from https://blog.nature.org/conservancy/2011/03/28/pnas-billions-city-urban-water-shortage-2050-nature-conservancy/. A study led by the Nature Conservancy defined these conditions. At least 23 cities fit these conditions. From north to south they are: Shenyang, Beijing, Tehran, Haifa, Tel Aviv, Jerusalem, Lahore, Delhi, Dubai, Riyadh, Abu Dhabi, Kolkata, Mexico City, Mumbai, Hyderabad, Manila, Chennai, Bengaluru, Caracas, Lagos, Cotonou, Abidjan, and Johannesburg. Some small tropical islands such as Grand Turk, Turks and Caicos Islands and Sal Island, Cabo Verde also fit these defining conditions. Recent reports such as “The 11 cities most likely to run out of drinking water - like Cape Town” by the BBC (http://www.bbc.com/news/world-42982959; 11 February 2018) suggest that we could add other cities to the Nature Conservancy’s list. From the BBC report here are nine more cities to add to the list of those likely to run out of sustainable natural water supplies: Cape Town, São Paulo, Cairo, Jakarta, Moscow, Istanbul, London, Tokyo, and Miami.Water-from-Air Resource Charts are available for all the highlighted locations mentioned in this post—just click on the location name to go to the relevant page in the Atmoswater Shop. By the way, if you like bargains, the charts for the 23 water-scarce cities listed by the Nature Conservancy are all included in the book, Water-from-Air Quick Guide.
I have the privilege of being accepted as one of the presenters during the Technical Sessions at the 23rd Annual Caribbean Water and Wastewater Association (CWWA) Conference and Exhibition scheduled for October 6-10, 2014 at Atlantis Resorts on Paradise Island, Bahamas. Here is the Abstract of my paper:
Regional droughts in the Caribbean are common. Water managers seeking solutions to water scarcity are often unfamiliar with the option of using water-from-air technology. Maps of the specific humidity composite mean for Junes and Decembers during the ten-year period 2004–2013 quantify the water-from-air resource demonstrating it is suitable for operation of water-from-air systems in Caribbean countries. Quantitative investigations by the author found droughts and long-term climate change do not appear to affect the magnitude of the Caribbean region’s water-from-air resource. Case studies include one for a proposed water-from-air commercial greenhouse on Grand Turk. Another case is about the experience of commissioning a 2500 L/d water-from-air machine in Belize City. Lessons learned from the case studies are outlined.
Air masses with relatively high water vapor densities (exceeding 12 grams of moisture per cubic meter of moist air) surround San Francisco / San Jose and Los Angeles / San Diego. 'Good' performance is expected from water-from-air systems (atmospheric water generators) operated in these regions. Over the balance of the state, the water-from-air resource is graded as 'fair'.
This map is from the new Atmoswater Research 45-page publication, Atlas of the Water-from-Air Resource for California.
I have been researching and developing drinking-water-from-air technologies since 1984. As a physical geographer, I strive to contribute an accurate, scientific point-of-view to the field.