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* Garden hose costs $15/50" from [http://www.homegardenandpatio.com/garden/hoses.htm this] source
* Garden hose costs $15/50" from [http://www.homegardenandpatio.com/garden/hoses.htm this] source
* A container should be easily obtainable for free
* A container should be easily obtainable for free
<br>
In total, this project is very inexpensive. For a family sized house, with roof area of 60m<sup>2</sup>, the estimated cost would be approximately $60.


== Case Studies ==
== Case Studies ==

Revision as of 06:44, 16 April 2010

The project recommended here is as economical as possible. There are design features, such as thermally insulating the roof, that would add to the dew yield; however they would be quite costly. Instead, what is considered is an appropriate retrofit for a roof to install a dew collection system. It should be able to provide 2L per dew night from an average family sized roof.

Regional considerations

Currently, dewfall is not recorded by meteriologists. Thus it can be difficult to assess the feasibility dew installations. Refer to Atmospheric water vapor processing (AWVP) for information on dew formation, and a discussion of how to predict the amount of dewfall in a given area. In general, for dew to form on a given night, the following conditions must be met:[1]

  • locations must have low wind speeds of approximately 2-6 m/s.
  • A relative humidity of at least 30%.



More work is needed to help determine a reliable and simple way for a layman to determine the usefulness of dew in a particular area.

Design

The design is similar to that of a rainwater collection system. Gutters feed water into hoses, which run to a collection barrel. The roofing material must be something that will not absorb any water. Ideal materials corregated Galvinized Iron (GI), or plastic. Dew roof diagram.jpg
The steepness of the roof is an important criterion. 30o from the horizontal is optimal.[2] [3] Anything less than 20o forfeits it from consideration. Gutters should be angled downward at approximately 15o to ensure that water flows, and does not stagnate. The collection barrel should have a screen or net over the intake to prevent debree and insects from getting in.

Construction

Dew collection off of a roof in Croatia
  1. Install the rain gutters on the roof at an angle of 15o sloping away from the prevailing wind.
  2. Funnel low end of gutter through hosing
  3. Attach hosing to cointainer

Refer to roof rain collection devices for more detail.

Materials

The required materials for this project are simple, and easily obtainable. Choose alternatives liberally, so long as they do not pose a risk of contaminating the water. Below is a numbered list of the required materials with bulletted alternatives.

  1. Roof gutter, including means of attaching it to the roof
    • Standard vinyl rain collecting gutters will work and should be inexpensive and easily obtainable
    • The gutter material must be hydrophylic. Something like wood would be too absorptive
  2. Hosing
    • Garden hose
    • 1/4" PVC piping
  3. Collection Tank
    • A 10L plastic food safe container

Tools

There are no specialty tools required for this project. Most of the tools needed for the construction of a solar still are common. The tools depend on what materials are being used and the level of complexity of the water collection system.

  • hacksaw
  • measuring tape
  • silicone gun
  • level
  • pliers
  • screwdrivers or hammer (for screw or nail installations)

Skills and Knowledge

For the installation, no special skills or knowledge are required. Currently however, there is no easy way for a layman to determine the usefulness of dew colletion in a particular area. For this task, an engineering background, with knowledge of dew formation, would be required.

Estimated Costs

All prices in CAD $, and are costed based on north american prices.

  • Gutters cost $50 -$100 for 120 feet from sources like this
  • Garden hose costs $15/50" from this source
  • A container should be easily obtainable for free


In total, this project is very inexpensive. For a family sized house, with roof area of 60m2, the estimated cost would be approximately $60.

Case Studies

In [1], they investigated the extent to which existing roofs given the retrofit described above can collect dew water. It was the first study of this nature done in India. The location was Kothara, India ( 23°14N, λ 68°45E, at 21 m a.s.l.), which is typical of rural north-western India.

The most common source of water during the dry season is wells. However, the ground water is being tapped out, receding, and becoming contaminated by salt. Dew is abundant during 8-9 months of the year. The other months are during the monsoon, where cloud cover prohibits dew formation.

Many of the local buildings use corrugated galvanized iron (GI) sheets for roofing. So, they did their testing on such a roof with an 18m2 surface area. There were 74 days during which dew formed, and a total of 113.5L of dew water collected.

References

  1. 1.0 1.1 Sharan, G., 2006, "Dew harvest: to supplement drinking water sources in arid coastal belt of Kutch," Foundation Books, .
  2. Beysens, D., Milimouk, I., Nikolayev, V., 2003, "Using Radiative Cooling to Condense Atmospheric Vapor: A Study to Improve Water Yield," Journal of Hydrology, 276(1-4) pp. 1-11.
  3. Sharan, G., Beysens, D., and Milimouk-Melnytchouk, I., 2007, "A Study of Dew Water Yields on Galvanized Iron Roofs in Kothara (North-West India)," Journal of Arid Environments, 69(2) pp. 259-269.
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