Evaporative cooling using Badgirs

Research Question: How does the volume of water available inside a Badgir (wind tower) affect temperature reduction

due to evaporative cooling?

Introduction

Solar energy and warming up

Temperature

Water Evaporation

Factors affecting rate of evaporation

Entropy

Uncomfortably hot living around the world has led to many

innovative technological solutions to make life more

comfortable for the inhabitants. In the Middle-East, one of

the most successful solutions has been the Badgirs. A Badgir

is a wind-tower consisting of a tower whose top is rising

between 30cm to 5m above the building and its end is

connected to the underground. On the sides of the tower,

there is one vent or more to catch the wind and direct it

inside the building. Inside the tower, there is water in the

form of wet materials attached to the tower lid, a fountain or

a pool of underground water. When the hot wind is directed

inside the tower; it evaporates the water causing a

temperature reduction due to evaporative cooling.

I investigated Badgirs using a model constructed of wood

and adobe. I managed to answer the research question and I

found that as the volume of water available inside the model

increases, the cooling effect increases. Badgirs can naturally

use sun’s energy, wind power and evaporation to air

condition buildings, without producing CO2.

Physics of Badgirs

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Experiment

Making a Model

The model consisted of a tower and a room.

Its inner surface was covered with mud mixed

with horse straw to give it the thermal

properties of a real Badgir. Providing Water

Five cloths equally sized are attached to the

tower lid so that they can hang inside the

tower and provide water for evaporation.

Providing Heat

A room is heated up to 50℃ , and a fan is used

to blow the warm air inside the model. When

the warm winds blow inside the tower, it

evaporates the water in the wet cloths,

resulting in a decrease in temperature.

Hypothesis

During evaporation, water molecules in the

wet cloths take energy from the warm wind to

escape into air, resulting in a decrease in

temperature inside the model.

As the volume of water is increased, the

number of molecules that can absorb heat

from the hot air increases: Thus, the energy

required to evaporate it increases, resulting in

a greater temperature reduction inside the

model.

Results

The results supported my hypothesis. The

scientific explanation of this phenomenon is

that more cloths offer larger surface area for

more water molecules to evaporate. More

evaporation results in more intake of energy,

therefore greater cooling effect will be. Also,

the heat absorption of adobe walls plays a role

in taking in energy and cooling down the

Model.

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