Passive Dew Condensers Made of Plastic

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Passive Dew Condensers made of plastic

Plastindia Foundation has instituted "Plasticon Awards" recognizing innovation & excellence and these awards are

presented to those who have made path-breaking contribution for development of Indian Plastics Industry. The

Awards germinate from a perceived need to honour and recognize excellence of Organizations, Individuals,

Companies and Institutions actively involved in research and development of plastics, and related products and

honour their path-breaking contribution to the overall development of Indian Plastics industry. A write up on the

Innovative Product Award Winner - Indian Institute of Management, Ahmedabad

Passive-dew-condenser is a device designed to extract moisture from humid air without the use of external energy.

Under a clear sky at night , the condenser surface gets cooled simply by radiative exchange with sky, becoming

colder than the dew-point of the surrounding humid air. When that happens some of the vapour contained in the

air condenses on its surface. The condenser surface is set at an angle from the horizontal to permit draining by

gravity. When conditions are favorable condensation could occur over good part of the night yielding significant

amount of water which has been tested and found potable. Water only needs to be filtered and sterilized by UV

light or boiling. Samples of dew water from a part of Kutch are shown in Figure 1.

Figure 1: Dew water from Kothara - Kutch obtained using passive dew

In the interior regions of India, dew occurs only (or mostly) in winter months. In coastal arid regions such as

Kutch in Gujarat, dew occurs over a period of 8 months from October to May. In fact, measurements have

shown that dew occurs more frequently and in larger quantity in summer months compared to others. It also

happens that good quality water is scarce in these regions. Plastics has been successfully used to develop dew

harvest systems for people living in coastal villages of Kutch to enable them to harvest dew and use it as a

supplementary source of water. Suitably designed large cost-effective dew condensers can enable humans too to

extract moisture from air. Plastics appear to be the most promising material to achieve this. Besides the plastics,

metal sheets used for roofing can also be used as condensers.

Development of condensers

The development work was spread over a three year period and has passed through three stages. In the first

stage systematic measurement of daily dew fall was made at Kothara, Kutch over a one year period. In the

second stage test condensers were made and tried for one year. In the third stage pilot scale condensers were

made and tried.

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Test

Test condensers were made using several materials including polyethylene (PE) film, polyethylene mixed with

titanium-oxide and barium-sulfate (PETB) film, fiber reinforced plastic (FRP) sheet and poly-carbonate sheet. The

PETB film was first developed and tried for dew condensation in France by Nilsson, Beysens and others. The film

was made to specifications. Galvanized iron and aluminum sheets were also included in the trials.

Condensers made of plastic

A condenser has three components: a panel, mounting frame and collection accessories. The panel is made of

two sheets bonded together with adhesive. The sheet on top is made of material being tested for its suitability to

construct condensers, indicated above. This sheet is insulated with styrene foam sheet of 25mm thickness on the

underside. Panels are squares of 1x1 m. Panel is mounted on metal frame made of welded angles. The collection

accessories (channel and tube) are also supported on the frame. The panel is mounted with a 30 angle with the

horizontal. Flow is channeled via a flexible rubber tube into a plastic bottle securely placed on the ground.

All the test condensers were installed in a coastal village - Kothara, Kutch - and daily dew condensation was

measured for one whole year. Figure 3 shows the test site at Kothara.


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Measurements showed that PETB film gave the highest yield {Table 1(a)} :

Monthly dew yield from north oriented Test condensers (Kothara-04-05)

Month GI Aluminium PETB

(ml) (ml) (ml)

Oct 1060 1145 2620

Nov 320 260 830

Dec 370 245 345

Jan 195 140 135

Feb 2255 1530 2085

Mar 5285 2950 4920

April 2405 1090 3052

May 1498 435 2055

Total 13388 7795 16042

Table 1(b) : Dew nights from north oriented condensers (Kothara-04-05)

Month GI Aluminium PETB

(No.) (No.) (No.)

Oct 9 8 12

Nov 4 3 5

Dec 3 2 3

Jan 2 1 2

Feb 12 11 12

Mar 28 20 26

April 18 8 12

May 16 5 12

Total 92 58 94

Trials in Kutch confirm the findings of Nilsson and Beysens from France. Metal sheets give lower yields specially

the new commercial aluminium sheets. FRP and polycarbonate also give good yields but being expensive these

are not suited for suited for large practical harvest systems.

Pilot

After analysis of the year-long measurements, PETB was selected to make larger pilot condensers for further trial.

Figure 4 shows the pilot PETB condenser. It consists of two basic modules, each of 9m2 surface area or 3x3 m

in size. The condenser surface is made of PETB sheet of 400 micron thickness. Condenser is insulated in the

same manner as were the smaller ones. The condenser modules are placed on a sand bed that has a slope of

30o from the horizontal.


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Commercial

Two types of models are ready for commercialization. The smaller model is for individual families living in coastal

arid areas. It is called Dew Family-20. The larger model is for communities and for commercial bottling plants. It

is called Dew Community-X.

Dew Family - 20 is sized for an average output of about 20 liters per day during the season. It will be built

using 300 m2 plastic (PETB) film. Total collection of dew water over the season of 8 months would be

approximately 5000 liters. The system will also harvest rain. The systems could be installed at or near the user's

home (Figure 5).

Dew-Community systems will be larger and will serve a community by bottling dew and selling at affordable price

locally. These will be built on 'waste-land' and other locations along the coast.

Dew harvesting be an attractive option in areas where (a) dewfall occurs frequently, in appreciable quantity over a

long season and (b) where there is shortage of potable water.

Figure 5(a) Roof over roof dew harvest system On a tiled roof house - Front view

Figure 5 (b) Roof over roof dew harvest system On a tiled roof house - side view

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Passive Dew Condensers Made of Plastic