This report is explaining the definition of Evaporative Cooling in architecture and how it works.

1. Evaporative Cooling
Khaled Eyad Almusa
013 2 95 2

2. The concept of evaporative cooling came from the sweating
of our bodies!
The rate of evaporative cooling is a function of both
humidity and air movement.
When sweat evaporates from
the skin, a large amount of heat is
required. This heat of vaporization
is drawn from the skin, which is
cooled in the process. The sensible
heat in the skin is turned into the
latent heat of the water vapor.
As water evaporates, the air
next to the skin becomes humid
and eventually even saturated. The
moisture in the air will then inhibit
further evaporation. Thus, either
air motion to remove this moist
air or very dry air is required to
make evaporative cooling efficient.
Evaporative cooling
is something that we have all
experienced. Wearing a damp
tee shirt on a warm but windy
day gives us a chill. The
phenomenon that causes this
is the latent heat of
vaporization.
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3. What does all this mean?ss
At critical temperature points in the diagram
(0 degrees Celsius and 100 degrees Celsius) water needs
to draw in heat energy from the environment to change
phase.
In order to melt or evaporate the water requires
energy from the environment: this is the latent heat of
vaporization.
So Evaporation is rapid
when the humidity is low and
air movement is high.
Evaporation is slow when the
humidity is high and air
movement is low.
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4. The reason we care about this in terms of evaporative
cooling is that the more energy that water draws the more
we can cool the contents of our Evaptainer. By the numbers
this shakes out to 1g of evaporated water reducing the
temperature of 1kg of water by half a degree
However, this assumes 100% efficiency.Celsius.
.
The energy required to free an atom from the liquid is
equivalent to the energy needed to overcome the
surface resistance of the liquid. You may remember from
school that water has relatively high surface tension
from its hydrogen bonds, thus water needs to absorb a
large amount of energy to go through a phase change.
What impacts this rate
of efficiency is ambient
conditions or "Wet Bulb
to Dry Bulb" :
Whatdoes that
mean ? 3

5. The potential for evaporative cooling depends on the
difference in wet bulb and dry bulb temperatures of the air.
Humid air has a high relative humidity, and not as much
capability to evaporate moisture.
As the relative humidity of the air increases, the
performance of the system will decrease, limiting its
application in moist climates.
Evaporative cooling is
most effective in
climates where average
relative humidity is less
than 30%. As humidity
increases, and the cooling
capability declines, the
temperature difference
between the outside and
inside of the chamber
decreases.
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6. To test if evaporative cooling
wet bulbwill be effective, the
temperature can be measured by
on the end ofmoist clothplacing a
and waving itthermometera
through the air. The temperature
read by the thermometer is the
theoretical minimum temperature
that can be achieved through
evaporative cooling.
For a visual representation of this phenomenon we can use
usefulare achartsPsychometric.psychometric charts
bulb temperature given the-tool for predicting a particular wet
outside ambient conditions: pressure, temperature, and
humidity.
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7. Above and beyond Psychometric charts (which only
have 3 variables) anything that increases the rate of
evaporation of a system will make evaporative cooling more
effective.
This includes:
1 Lowering ambient humidity
2 Decreasing atmospheric pressure
3 Increasing ambient temperature
4 Increasing surface area of evaporation
5 Choosing different evaporative media
6 Adding air movement/wind
Using all of these variables we are able to optimize
the cooling effect of our system across the widest
range of applications.
Evaporative cooling is provided by
the evaporation of water:
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8. This system works in dry climates and uses less energy
than conventional cooling but consumes water
A variety of thermal energy storage technologies are
available. Ice storage is commonly used to shift peak electric
loads from daytime to the night. Rather than saving energy
or reducing carbon emissions, the focus of this technology
is to reduce peak summertime electric demand and thereby
reduce peak demand charges.
Depending on the site, ice storage can in some cases reduce
energy and carbon emissions, but in other cases, it will
increase energy use and carbon emissions. The substantial
embodied energy of the storage vessel, which is often
concrete, should be accounted for in the analysis.
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9. Evaporative cooling VS. Traditional cooling
While evaporative cooling is one of the oldest
forms of climate control still found today, evaporative
coolers remain a highly sought-after alternative to
traditional air conditioning. While very effective and
efficient when used properly, these cooling units are
not for use everywhere. Due to the evaporative
process used by these swamp coolers, these cooling
units are best used in hot, dry climates, In these
climates, however, an evaporative cooler can be your
most effective and efficient means of climate control.
There are many different benefits of evaporative
cooling, but to truly understand them, you have to
compare evaporative coolers to more traditional air
conditioners.
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10. There are two types of Evaporative cooling:
Direct Indirect
With direct evaporative
cooling, outside air is blown
through a water-saturated
medium (usually cellulose) and
cooled by evaporation. The
cooled air is circulated by a
blower
Direct evaporative cooling
adds moisture to the air
stream until the air stream is
close to saturation. The dry
bulb temperature is reduced,
while the wet bulb temperature
stays the same.
With indirect evaporative
cooling, a secondary
(scavenger) air stream is
cooled by water. The cooled
secondary air stream goes
through a heat exchanger,
where it cools the primary air
stream. The cooled primary air
stream is circulated by a
blower.
Indirect evaporative cooling
to thedoes not add moisture
primary air stream. Both the
dry bulb and wet bulb
temperatures are reduced.
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11. Direct Evaporative Cooling
When water evaporates in the indoor air, the
temperature drops but the humidity goes up. In
hot and dry climates, the increase in humidity
actually improves comfort. However, direct
evaporative cooling is not appropriate in humid
climates because the cooling effect is low and the
humidity is already too high.
See the Figure below for the kind of climate
that supports direct evaporative cooling:
When water evaporates
in the indoor air, the
temperature drops but
the humidity goes
up.
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12. The most popular form of direct evaporative
with commerciallycooling is accomplished
(swamp coolers).evaporative coolersavailable
Although they look like active mechanical devices
from the outside, they are actually quite simple
and use little energy.
A fan is used to bring
outdoor air into the building
by way of a wet screen.
A modest amount of water is required to keep the
screen wet. To maintain comfort, a high rate of
ventilation is required during the day.
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1

13. Misting the air has become a popular direct
evaporative-cooling strategy in all hot climates
but works best in dry climates. Water under high
pressure is atomized into tiny droplets, which
then readily evaporate to cool the air.
Misting is mainly used to cool outdoor spaces.
Unfortunately, if the area is too sunny or too
windy, the benefit of misting will be minimal.
However the cooling effect can be significant in
sheltered outdoor spaces and greenhouses.
Misting is often used more for the atmosphere
it creates than for its cooling benefits.
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14. Indirect Evaporative Cooling
A critical aspect of evaporative cooling is that the heat of
vaporization must come from what is to be cooled. Thus, spraying a
sunlit roof is not especially good because the heat of the sun will
evaporate most of the water. On the other hand, the heat to
evaporate water at night or from a shaded roof pond comes mainly
from the building itself.
The cooling effect from
evaporation can also be used
to cool the roof of a building,
which then becomes a heat
sink to cool the interior. This
technique is an example of
indirect evaporative cooling,
and its main advantage is
that the indoor air is cooled
without increasing its
humidity.
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15. This figure illustrates the
basic features of roof-pond
cooling. An insulated roof
shades the pond from the sun.
Openings in the roof enable air
currents to pass over the
pond during the summer. As
water evaporates.
The pond will become cooler together with the ceiling
structure, will act as a heat sink for the interior of the building
during the winter, the pond is drained and the roof openings
are closed. The main disadvantage of this system is the cost
of the concrete or metal ceiling and waterproofing.
A clever alternative to the above roof pond is the roof
pond with floating insulation.
At night a pump sprays the water over the top of the
insulation, and it cools by both evaporation and radiation.
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16. Meanwhile, the water together with the roof structure
acts as a heat sink for the interior. Although the cooling
occurs only at night, it is very effective because of the
combined action of evaporation and radiation.
When the sun rises the pump stops and the water remains
under the insulation, where it is protected from the heat of
the day.
A more conventional version of the water spray design is to
store the cooled water in a tank and to precool the floor
slab at night.
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17. Cases for Direct and Indirect
Evaporative coolers
Evaporative coolers are widely used in hot and dry regions.
- Direct evaporative cooler on the roof a house :
- An evaporative cooler, Colorado, used in the drier
parts of the American West provide economical cooling:
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18. - Indirect Evaporative cooling unit:
Indirect evaporative coolers reduce the indoor air
temperature without increasing its humidity.
- Figure for Indirect evaporative cooler:
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19. - Muscatese Evaporative cooling window system:
- Sample of Malqaf using fountain (Hassan Fathy 1986)
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20. Conclusion:
The process of evaporation happens all the time. Our
bodies, for example, perspire in hot weather; through
evaporation the sweat dries and drops our body
temperature.
Whenever dry air passes over water, some of the water
will be absorbed by the air. That's why evaporative cooling
naturally occurs near waterfalls, at rivers, lakes and oceans.
The hotter and drier the air, the more water that can be
absorbed. This happens because the temperature and the
vapor pressure of the water and the air attempt to equalize.
Liquid water molecules become gas in the dry air, a process
that uses energy to change the physical state. Heat moves
from the higher temperature of the air to the lower
temperature of the water. As a result, the air is cooler.
Eventually the air becomes saturated, unable to hold more
water, and evaporation ceases.
We can use evaporative cooling in our design, to raise the
energy efficiency of the building, and reducing the need of
mechanical equipment.
Evaporative cooling can be made by the design wise of
the building or by using evaporative cooling units, even if
these unit are actually mechanical equipment, their embodied
energy is very low in comparison with other equipment.
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21. References
……………………………………………………………………
[1] HEATING, COOLING, LIGHTING, Sustainable Design
Methods for Architects -Norbert Lechner
[2] Green Building Illustrated - Ching, Francis D. K.
[3] “Review Article: Passive Design for Thermal Comfort in
Hot Humid Climates,” Journal of Architectural/Planning
Research and Studies Volume 5
http://www.ap.tu.ac.th/jars/download/jars/v5-1/01 Review
[4] Application of passive cooling systems in the hot and
humid climate: The case study of solar chimney and wetted
roof in Thailand, Building and Environment
http://gse.cat.org.uk/downloads/passive_cooling.pdf
[5] “Experimental Studies on the Roof Pond House under
Tropical Climatic,” 2006.
http://www.en.kku.ac.th/enjournal/th/images/stories/files/pu
blished/33No-5.pdf
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22. Evaporative cooling Report done by Khaled Eyad Nihad Almusa