Evaporative cooling in India
Practical Action
Depending on the size, it may require a great deal of water. Although the community
has reliable access to water, the quantities needed would require additional trips to
local wells which could be seen as an undue burden.
While the cool chamber was far more suitable to the community than an electric fridge, many
families did not have the space near their home, where meals are prepared, to construct such
an object. Also, the size is too large for one family. Therefore, this option was kept as a
backup in case the Pot-in-Pot did not prove to be successful.
The pot-in-pot
Similar to the cool chamber, the pot-in-pot relies on evaporative cooling to keep fruits and
vegetables fresh for longer periods of time. Instead of a double brick walled structure though,
two earthenware pots are used; one needs to be able to fit within the other. Again, the gap
between the two is filled with river or lake bed sand and must remain moist.
The advantages of the pot-in-pot are:
It is relatively inexpensive.
It can be made from locally available materials.
It can easily fit within a home.
It can be easily made and maintained.
It requires less water than the cool chambers.
The drawbacks are:
Needs to be watered daily.
If it needs to be transported, it can easily break.
Potters may not have large pots readily available, and specially designed pots may be
required.
The pot-in-pot has clear advantages over the other two options: it not only fitted the villagers'
budgets and lifestyles, but it also fitted into their homes.
Implementation
Pilot technology
The pot-in-pot was piloted at the home of a local NGO staff member. All told, the two pots
along with a small lid cost 50 rupees. The head of WORLD Society donated 1 kg of tomatoes
for the trial run. The family was told how to water the sand to preserve the internal
temperature of the device and it was checked everyday for approximately two weeks.
There were initial difficulties in determining how much water to use in the pot-in-pot. The
first two days, the family was not using enough water. The sand was dry to the touch. Starting
the third day, the family started pouring too much water in the sand. The inner pot then
began to absorb some of the water. As a result, the water then lay at the bottom of the inner
pot, creating the possibility that the tomatoes would spoil. The family then used a moderate
amount of water but this produced no change in the excess water used by day four, so Karthik
added a plastic bag to separate the tomatoes from the excess water. It was difficult to
determine the exact amount of the water needed to keep the pot running at the optimum level
because humidity, temperature and other climatic conditions affecting the evaporation rate of
water so demand kept on changing on a daily basis. In the end, it was not able to determine
the exact amount of water needed on a daily basis; instead we relied on the plastic bags to
ensure the produce did not spoil from too much water.
The tomatoes lasted and came out unharmed after a total of seven days from being placed in
the pot. The family then consumed the tomatoes. Initially the family only used the device to
2