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Updated list of peer-reviewed articles about #water from air

26/6/2013

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Picture: Computer screen with articles about water-from-air on top of keyboard
I have updated my list of peer-reviewed articles relevant to the topic of water-from-air systems.

A nice thing the articles listed below have in common is that they cited my article from 2001 !

The paper by Blackburn and Peters (2009) is especially interesting. They discovered that a home/office Atmospheric Water Generator in the context of Australia has a greater environmental impact than a bottled water cooler. This provides a challenge to the water-from-air industry—how do we use life cycle analysis to design AWGs having minimal environmental impact?


        Blackburn, N. J. and Peters, G. M. 2009. Atmospheric water generation—an environmentally friendly alternative to bottled water?  Australian Life Cycle Assessment Society (ALCAS) Conference 2009.     

       Habeebullah, B. A. 2010. Performance Analysis of a Combined Heat Pump-Dehumidifying System. JKAU: eng. Scie., 21 (1), 97–114.

        Zimmermann, R., Mantelli, M. B. H., Borges, T. P. F., and Costa, C. A. S. 2010. Viability study of retrieving the evaporated water in a  mechanical draft cross flow cooling tower. 2010 14th International Heat Transfer Conference, ITHC 14 4, 751–760.

        Bergmair, D., Metz, S. J., De Lange, H. C., Van Steenhoven, A. A. 2012. Modeling of a vapor selective membrane unit to increase the energy efficiency of humidity harvesting. Journal of Physics: Conference Series 395 (1), art. no. 012161.

        Alipour, V., Mahvi, A., and Rezaei, L. 2013. Water condensate management of atmosphere humidity in Bandar Abbas, Iran. in Kanarachos, A. and , Mastorakis, N. E. (editors). 2013. Recent Advances in Environmental Science. WSEAS Press, 279–284.

        Khayet, M. 2013. Solar desalination by membrane distillation: Dispersion in energy consumption analysis and water production costs (a review). Desalination 308, 89–101.

        Muñoz-Garcia, M. A., Moreda, G. P., Raga-Arroyo, M. P., 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.

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Cactus spine gives clues to improving efficiency of collecting #water on chilled surfaces

16/1/2013

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Researchers at the Chinese Academy of Sciences and other laboratories in Beijing, China discovered why the spines of the cactus Opuntia microdasys are so efficient at capturing fog droplets:
  • spine tip is has oriented barbs;
  • Conical form of barbs increases water harvesting area;
  • Conical form causes water droplets to flow to spine base; and
  • Spine grooves become less rough near the spine base, setting up a force pushing water towards the base.

Although the research looked at fog droplet capture by the cacti, the findings are applicable to surfaces chilled by mechanical refrigeration (evaporator coils) or by a liquid coolant (chiller coils). If the cacti spine attributes can be mimicked on the coil surfaces, condensate will drain more quickly from the coil.  Rapid draining minimizes the presence of an insulating water film on the chilled surfaces. This promotes additional condensation per unit time which increases liquid water production rate of the water-from-air system (atmospheric water generator).
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Limits to mechanical dehumidification efficiency

28/9/2012

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When designing drinking-water-from-air systems it is useful to know the limits to mechanical dehumidification efficiency. Mechanical dehumidifiers use chilled water coils, direct-expansion refrigerant coils or thermoelectric devices to provide a cooled surface over which flows the air to be dehumidified. Systems are designed usually with defrost controls to avoid frosting of the coil surface. Practically, the minimum temperature for coil operation is about 5 °C. The air leaving a wet coil is saturated so the state of leaving air may be, for example, dry bulb = 5 °C with 100% relative humidity. This combination of temperature and humidity is associated with air having a water vapour density (WVD) of 6.8 grams of water per cubic metre of moist air. The blue curve in the chart below shows how efficiency of water collection varies depending on the water vapour density of the ambient (entering) air.

Let's use an example to explain how the curve was constructed. Ambient air at standard testing conditions of 26.7 °C, 60% relative humidity enters the dehumidifier (atmospheric water generator). At standard atmospheric pressure of one atmosphere (1.013 bar), psychrometric calculations show the ambient air is capable of holding 15.3 grams of water vapour in a moist air volume of one cubic metre. As this unit volume of air flows across the 5 °C chilled surfaces of the coils the mass of condensate collected =  (15.3 g per cubic metre - 6.8 g per cubic metre) x 1 cubic metre = 8.5 g. The table below shows a series of similar calculations encompassing the natural range of water vapour densities in the atmosphere at the Earth's surface (about 4 to 22 g per cubic metre).

Ambient temperature together with the refrigeration capacity of the dehumidifier will determine whether or not a chilled surface temperature of 5 °C can be achieved. Therefore, the chart also has efficiency curves for leaving air at 10 °C and 15 °C. In Belize City air temperature was about 32 °C and the 40 Ton refrigerant capacity machine I was testing for my client had a leaving air temperature (similar to coil temperature) of 16 °C. Efficiency of water production was about 45%, near the limit of what could be expected given the weather conditions and equipment capacity. The atmospheric water generator (about the size of a 20-foot shipping container) was producing drinking water at the rate of about 2500 L/day—its designed capacity.

Note: You may click on the chart and table to enlarge them.
Picture: Chart showing limits to mechanical dehumidification efficiency
Picture: Table showing limits to mechanical dehumidification efficiency
3 Comments

Air Handling Unit Condensate Collection Economics

23/8/2012

2 Comments

 
Is water-from-air regarded as a valuable water resource in the heating, ventilation, and air-conditioning (HVAC) industry? The answer is, "yes", as shown by the article, AHU Condensate Collection Economics: A Study of 47 U.S. Cities, published in the ASHRAE Journal, vol. 54, no. 5, May 2012. AHU is the acronym for the Air Handling Unit in an HVAC system. The authors list of U.S. cities where they recommended condensate collection included: Athens, GA; Charlotte, NC; Dallas, TX; Honolulu, HI;; Knoxville, TN; Memphis, TN; Miami, FL; New Orleans; New York, NY; Oklahoma City, OK; Orlando, FL; San Antonio, TX; San Diego, CA; St Louis, MO; Topeka, KS; and Washington, DC. It is notable that most of these cities, with the exception of Honolulu and San Diego are in the eastern half of the USA.
2 Comments

    Roland Wahlgren

    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.

    Discover previous interesting and informative scientific/technical posts by clicking "<<Previous" at the bottom of each page!

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