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Old 05-24-14, 04:40 PM   #34
jeff5may
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A new thread recently popped up, introducing a new concept for indirect evaporative cooling and dehumidification of buildings:

http://ecorenovator.org/forum/geothe...25-energy.html

The NREL paper describing the system, named the DEVAP, is here:
http://search.nrel.gov/cs.html?url=h...nrel&n=4&la=en

This thread got me thinking about the solar dehumidifier again. Indoors, a desiccant waterfall or forced air, swamp cooler type unit would dehumidify the air. Outdoors, a solar desalination tower could effectively remove as much water as one needed. Consider this description borrowed from Wikipedia:

In 1993 a desalination plant was invented by Akhtar Iqbal Zuberi in Pakistan. Zuberi’s plant produces 40 liters of water per square meter per day. This is at least ten (10) times more productive than a conventional Horizontal Solar desalination plant. Water desalinated from this plant has 16 parts per million (ppm).[14]

The structure is a raised tower made of cement, with a tank at the top. The whole plant is covered with glass of the same shape, but slightly larger, allowing for a gap between the cement tower and the glass.

The tank is filled with saline water and water from an outside tank, drop by drop water enters the inner tank. The excessive water from the inner tank drips out onto the cement walls of the tower, from top to bottom. By solar radiation, the water on the wet surface and in the tank evaporate and condense on the inner surface of the glass cylinder and flow down onto the collecting drain channel. Meanwhile, the concentrated saline water drains out through a saline drain.

In this process fresh saline water is continuously added to the walls from the top of the tower. After evaporation, the remaining saline water falls down and drains out continuously. The movement of water also increases the energy of molecules and increases the evaporation process. The increase in the tower’s height also increases the production.

This plant’s base is 3.5 by 1.5 feet by 10 foot high, and gives about 12 liters of water per day.Built horizontally, a structured plant receives solar radiation at noon only. But Zuberi’s plant is a vertical tower and receives solar energy from sunrise till sunset. From early morning, it receives perpendicular radiation on one side of the plant. While at noon its top, gets radiation equivalent to the horizontal plant. From noon till sunset, the other side receives maximum radiation. By increasing the height, the tower plant receives more solar energy and the inner temperature increases as height increases. Ultimately this increases the water yield.

A number of experiments have been conducted and a much more productive plant has been developed, with further work continuing.

This project can be implemented anywhere there is ground water, brine or sea water available with suitable sun. During different experiments a plant six (6) 6 feet high can attain a temperature of 60 degrees Celsius, while a plant of ten (10) feet high can reach a temperature of up to 86 degree Celsius.



http://www.energyglobe.info/awards/n...8#.U4FRUnJdV48

In this application, there is no need to save the purified water. Once the evaporation process has occurred, we are done. Therefore, a simple thermostat-controlled venting system could be used to "smokestack" the humid air from the top of the tower. This humid air would be replaced by ambient air at the bottom of the tower. With the original application, the shaded side of the plant would definitely condense more water.

This assumes a tower made of concrete or bricks, but the tower may not need to be constructed as such. For example, a dark colored strip of towels or other wicking material sandwiched between suntuf panels may work well. The structure would need additional support, which may end up costing more than cinder blocks. As long as it got sun on both sides, it would collect the same energy from the sun.

Last edited by jeff5may; 05-24-14 at 09:12 PM..
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