International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
Design Optimization and Installation of the Evaporative
Cooler in the Perspective of Bangladesh
Md. Almostasim Mahmud 1, Dr. Md. Alamgir Hossain 2, M. A. Muktadir 3
1
Lecturer, 2 Assistant Professor, Department of Mechanical Engineering, MIST, Dhaka-1216,
3
Assistant Manager, Khan Brothers Shipbuilding Ltd., Dhaka,
When the air to be cooled is kept separated from the
evaporation process, and therefore is not humidified while
it is cooled, it is called indirect evaporative cooling (IEC)
[1].
Abstract— This Evaporative cooling is an environmentally
friendly air cooling system that operates using induced
processes of heat and mass transfer, where water and air are
the working fluids. It consists, specifically, in water
evaporation, induced by the passage of an air flow, thus
decreasing the air temperature. In Bangladesh, Evaporative
cooler is already being used in different industries that is
imported from varies countries. But most of the cases these
are not efficient due to installation error & lack of adjustment
with climate change over the year. Initially this paper presents
the construction of an evaporative cooler using a test bench of
cooling tower for the air flow and water supply facility where
local materials were used as evaporative pad. Afterwards; it
presents installation in different situation & adjustment of the
cooling units with the climate. It concludes that under proper
installation, evaporative cooling system is very cost effective &
has a very large potential to propitiate thermal comfort and
can still be used as an alternative to conventional systems in
regions where the design wet bulb temperature is low.
II. METHODOLOGY
Evaporative cooling is a process by which moisture is
added to air in order to reduce air temperature and increase
relative humidity. It occurs when moisture is added to air
that has a relative humidity of less than 100 percent. The
lower the relative humidity, the greater the cooling affect
that is possible when moisture is added. In order to
evaporate water, heat is required. This heat comes from
whatever the water is in contact with as it evaporates. As
heat is removed from an object; the temperature of that
object is decreased, in this case, the air. The efficiency of
any evaporative cooling device is directly related to its
ability to evaporate water (cool) at a given relative
humidity.
Keywords— Evaporative cooling; Air cooling; Climate;
Installation; Thermal comfort.
I. INTRODUCTION
Evaporative cooling is a natural phenomenon. It is just
like that when the wind blows off the sea; it will lead the
evaporation of the water, so the temperature will be lower.
To do so common requirements are: a surface which can
allows the water’s evaporation, a water-supply systems
which can drip the surface wet, and a control means which
can allow the air pass through the surface to make the
effective working of the whole system. In the last 10 years,
evaporative cooling technology for air conditioning
systems has increased as an alternative to the conventional
vapor compression systems. An evaporative cooling system
operates using induced processes of heat and mass transfer,
where water and air are the working fluids. It consists,
specifically, in water evaporation, induced by the passage
of an air flow, thus decreasing the air temperature. When
water evaporates into the air to be cooled, simultaneously
humidifying it, that is called direct evaporative cooling
(DEC) and the thermal process is the adiabatic saturation.
Figure 1: Basic principle of evaporative cooling [2]
III. EXPERIMENTAL PROCEDURE FOR METHODOLOGY
ASSESSMENT
A ‘bench top cooling tower’ has been used to
demonstrate the evaporative cooler unit where evaporative
pads of different material act a packing. Control of water
and air flow is very easy in this setup. Main parts of an
evaporative cooling unit are (a) Fan/blower, (b)
Evaporative pad (c) Water supply system (pump,
distributor, reservoir).
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
Alignment, height, packing material, water flow rate, air
flow rate, water temperature all these parameter has been
investigated for suitable evaporative pad and optimum
design. The Cooling Tower has been designed to give an
appreciation of the construction, design and operational
characteristics of a modern evaporative cooling system.
B. Water Flow Circuit
Water enters the top of the tower and is fed into troughs
from which it flows via notches onto the packing. The
distributors are designed to distribute the water uniformly
over the packing with minimum splashing.
C. Location of the 6 Temperature readings to be taken
when using the system [3]
T1: Dry bulb temperature of air entering base of column
T2: Wet bulb temperature of air entering base of column
T3: Dry bulb temperature of air at exit from column
T4: Wet bulb temperature of air at exit from column
T5: Water temperature on entering column
T6: Water temperature on leaving column
D. Evaporative pad used (packing)
Packing-1: Wet able, laminated plastic plate
Packing-2: PVC doormat
Packing-3: Synthetic fiber (scouring-pad)
Packing-4: Steel wool
Packing-5: Foam
Figure 2: Experimental setup at Heat Engine Lab, MIST [3]
(A)Packing-1
(B) Packing-2
Figure 3: Cooling Tower schematic diagram. [3]
(C) Packing-3
A. Air Flow Circuit
Under the action of the fan, air is driven upward through
the wet packing. It will be seen that the change of dry bulb
temperature is smaller than the change of wet bulb
temperature, and that at air outlet there is little difference
between wet and dry bulb temperatures. This indicates that
the air leaving is almost saturated, i.e. relative humidity 100%. This increase in the moisture content of the air is
due to the conversion of water into steam and the ‘latent
heat’ for this account for most of the cooling effect [3].
m a  0.0137
x
x
 0.0137
1  B vaB
vB
(D) Packing-4
(E) Packing-5
Figure 4: Different packing (pad) for test.
E. Assembly of evaporative pad in Angle bar frame
(1)
Step-1
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step-2
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
Figure 6: Experimental setup with air tight heated chamber.
Step-3
Step -2:
Entering air into the chamber was heated by the hair
dryer continuously, up to 40ºC single hair dryer was used
and above 40ºC two hair dryer were used for continuously.
Final assembly of pad-3
Figure 5: Assembly of pad in tower column.
IV. DATA COLLECTION
Step -3:
Outlet of the heated chamber was connected with the
damper opening of cooling tower’s base unit through a pipe
cone arrangement.
For each packing all the data were collected in two
sessions. In the first session normal ambient air was passed
through the unit to observe the effect in household use as
well as in office use. Because in all these case outside air is
passed through the duct into the room. The temperature
difference between inside and outside air is not so high,
there is a significant difference in RH and both sensible and
latent heat rise simultaneously. During April to May data of
packing 1 and 2 was taken under this session. Data of
packing 3 and 4 under this session was taken from July to
August 2010.
In the second session, ambient air was heated by electric
heater for sensible heating (hair dryer was used for
experiment purpose) and heated air was passed through the
unit to create artificial environment where pace air face
high sensible heating (i.e. in some factories and mills,
described in previous chapter). Data of packing 1,2,3,4
under this session was taken during July to August 2010.
Figure 7: Sensible heating process.
A. Procedure followed for electric heating (second
session)
Step-1:
At first an air tight chamber (figure ۶) was made and then
the entering air was heated by hair dryer (figure 6). Two
hair dryer (HITACHI 700 watt and NOVA 900 watt) were
used for the experiment.
V. EXPERIMENTAL RESULTS AND OBSERVATION
Only for packing 1, 2 water and air flow rate was varied
to investigate effect of crossing fluid flow rate under the
first session (deals with normal ambient air).Note: To avoid
complexity air flow rate is presented in mm H2O (Manometric deflection)
743
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
 For a specific packing there must be a critical air flow
rate for which the effectiveness is maximum (output
air relative humidity approaches towards 100%).
 But if it is required that the output air RH will be
lower then 100% (85-90%) then air flow rate is
maintained below the critical flow rate.
C. Dry bulb temperature of outlet air and outlet water
temperature approaches towards the wet bulb
temperature of entering air and ultimately relative
humidity of outlet air approaches to 100 %
 Figure 10 to figure 14 illustrates that if the inlet air go
through the sensible heating process then its relative
humidity reduces but the outlet air temperature always
follow the wet bulb temperature of inlet air. So, pad
effectiveness will be 100 % if out let air temperature
is equal to the wet bulb temperature of inlet air.
Figure 8: Change in outlet relative humidity with air flow rate at
different water flow rate.
A. From the above shown graph effect of water flow rate
can be summarize as follows
 Up to certain limit with increasing water flow rate
effectiveness of a pad increase (relative humidity
approaches towards 100%).
 After a certain limit effectiveness of a pad decreases
with water flow rate. Because higher water flow rate
reduce the effective exposed surface area of a packing
(figure 9).
Figure 10: approaches for packing-1
Figure 9: Evaporation inside the column.
So there must be a critical water flow rate for which the
pad effectiveness is 100%.
 Maintaining water flow rate under that critical point
relative humidity of output air can be within 85-90%
that is required for household and official use.
 So evaporative unit must not supply air more then that
critical point.
B. From the above shown graph effect of air flow rate can
be summarize as follows
 Normally with increasing air flow rate for specific
pad’s effectiveness decreases (relative humidity of
output air decreases).
Figure 11: Approaches for packing-2
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
Basic concept of evaporation is that, when evaporation
takes place then the fluid (may be air or water) in contact
with this process will lose their temperature up to the wet
bulb temperature of inlet air. This is very interesting that
wet bulb temperature is measured through the process of
evaporation. So the wet bulb temperature is the direct
measure of outlet air temperature that could be possible by
an evaporative cooler. Science both the outlet water and
outlet air come into contact with the evaporation process so
for 100% efficient evaporative cooler outlet air temperature
must be equal to the wet bulb temperature of inlet air. From
the figure 10 to 14 it can be concluded that both the high
temperature & low temperature air can be cooled up to its
wet bulb temperature. When room temperature faces
sensible heating by machine then room temperature
become uncomfortable. In these situation an evaporative
cooler may be the best option to create a thermal
comfortable (more specifically a tolerable) environment.
Figure 12: Approaches for packing-3
D. Water temperature has no significant influence on the
process in case of recirculation system
 Figure 16 to figure 20 illustrates how the reservoir
water temperature follows the wet bulb temperature of
the inlet air.
T(wet bulb in)?
T water reserviour ?
35
T water out ?
C
º
p
m30
e
T
Figure 13: Approaches for packing-4
25
0
10 Time(min) 20
30
Figure 15: Condition of if it is re-circulated (packing-1)
Figure 14: Approaches for packing-5
Figure 16: Condition of if it is re-circulated (packing-2)
745
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
Wet bulb temperature of the inlet air. Even from the
figure 15 to 19 it is clear that temperature of inlet water is
not the dominant factor if normal pipe line water is used.
But excessive hot water must affect the evaporation
process.
E. Selection of pad material
To select a material, odour and sustainability is the primary
concern. But the dominant factor is the effectiveness.
Effectiveness 100% means outlet air Relative Humidity is
approximately 99%.To make the cooling unit it is
necessary to select a material that is cheap & available.
From the observation some qualitative properties of
different evaporative pad are given in the table I.
Figure 17: Condition of if it is re-circulated (packing-3)
As evaporative cooler works on the principle of water
evaporation, then the question will arise what type of water
is more efficient. Normally it seems that cold water will
reduce the outlet air temperature. Yes it will do that but not
that much & not efficiently as well. If water is recirculated
from reservoir then at a time reservoir temperature will
reach to a constant temperature that is almost equal to the
TABLE I
PROPERTIES FOUND OF DIFFERENT PAD (PACKING)
Parameter
Pad-1
Pad-2
Pad-3
Pad-4
Pad-5
Effectiveness
Low
High
High
High
High
Cost
Sustainability
Odor
Availability
Pressure drop
High
High
No
Low
Low
Medium
High
No
High
Low
Low
Low
High
High
High
Low
low
No
High
Low
Medium
Low
Low
High
High
VI. INSTALLATION
In the factories high heat generating machine
(appliances), furnace, electric heater, high capacity light,
steel rerolling mills, plastics industries, ceramic industries,
welding shop, casting shop, boiler, heat treatment unit,
oven etc all these are responsible for sensible heat gain.
These sources increase dry bulb temperature at constant
specific humidity and RH decreases gradually. So ultimate
space condition becomes hot and dry which is the
prerequisite of effective operation of an evaporative
cooling unit.
By using evaporative cooling unit this excessively hot
and dry climate can be controlled. Air leaving the unit may
be cooler and humid, but it is more desirable and/or
tolerable then the hot dry condition.
When working space temperature goes high , Then
it is hardly tolerable . If conventional air condition is
used to cool this space , then large capacity of the AC
unit is required . But comfortable space increases the
effectiveness of the workers
and increases the
economical strength of company. Conventional comfort
air condition is 20-24 °C temperature and RH 50-70 %.
But sometime industrial space temperature rises up to
40°C or more . In this case which one is desirable first? To
make conventional comfort zone or tolerable zone?
Figure 18۰: Condition of if it is re circulated (packing-4)
Figure 19: Condition of if it is re circulated (packing-5)
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
Definitely tolerable zone will get the priority. An
evaporative cooler will create this tolerable zone. Because
to create conventional comfort zone 20 times more
electricity is required that is not economical for
production process and if is not possible to supply
that much electricity demand for a developing country
Then the mixture of this two stream maintains room
condition at point along the path A-C (in the figure point P
is shown as mixture condition). So by proper optimization
of design effect of machinery’s heat can be avoided. But
this effect will not be applicable if the entire unit is
installed in the outside & outdoor relative humidity is high.
VII. APPLICATION OF EVAPORATIVE UNIT OVER THE
YEAR
Evaporative cooler best works when relative humidity of
the inlet air is minimum. Over the year climate of
Bangladesh changes so it is not possible to get equal
effectiveness over the time. So some sort of adjustment like
figure 21 is necessary to create tolerable condition.
(a) Indoor Unit
(b) outdoor unit
A. From March to June
During this period air condition is hot and dry
(Figure 21). So it is the most suitable time to use
evaporative cooling unit in the domestic space
effectively . In case of industrial use during this time
both inside and outside units will work effectively .
: 101325 Pa
14
15
60
0
0
Figure 20: Industrial
Installation
(RFL 1plastic
factory)
1
30
As per the experimental
result for industrial use at least
16
0
12
0
50% unit should
be installed inside the space (applicable
11
15
0
for all space
where room air face high sensible heating).
0
10
0
30
-d
rat
ure
70
80
%
tem
on
%
60
Sa
0
13
0
12
0
11
0
10
0
me
30
.m/k
- cu
%
40
90
80
)
20%
10
g(a
10
0.85
B. From July to August
During this period air condition is hot and wet . So
in case of domestic unit continuous operation of unit
over the day is not effective enough . But when hot
condition is created in the environment then it can be
operated . For instance during depression like situation
is nature and from 12 pm to 7 am it can be operated
effectively. In case of industrial space outside units
will acts like domestic unit but inside units will cool
the air effectively .That’s
why when outside air
condition is wet in nature , Then number of inside
unit in operation must be increased and outside unit in
operation should be decreased . It will reduce the
overall power consumption. To make the balance
over different time period of the air , some standby
unit should be installed both inside and outside of
industrial space .
20
Volu
40
20
0.90
tur
ati
50
B
A
pe
60
Humidity ratio - g/kg(a)
eg
C
kJ
alp
y-
80
0.95
En
th
C
P
14
30
/kg
(a
)
90
0.80
70
10
20
30
40
Dry bulb temperature - deg C
50
Figure 21: Sensible heating processes in psychometric chart. [4]
In figure 21 it is shown that most of the evaporative unit
is placed outside the factory (pipe manufacturing factory of
PRAN-RFL group) & there is a few numbers of units
inside the factory. In figure 21 it is shown that how inside
air face sensible heating during working hour (the sensible
heating process is A-B). The evaporative unit inside the
space will process this heated air along the path B-C. In
this condition if sufficient ventilation fan is used to supply
enough air inside the room then it will supply air at a
condition of a (say for example in graph 30ºC temp & 70%
relative humidity).
C. From September to October
During this period relative humidity decreases with
time(figure 23) that is suitable for effective operation
of evaporative cooling unit . In this case effectiveness
of evaporative unit will be almost similar with May
June operation.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
Then another power consuming element is the
water supply system . If overhead tank of a building
is used as the water reservoir then additional water
reservoir or recirculation pump is not required at all .
In this cases water is not recirculated , rather exit
water from the evaporative pad is drained . But in
other application a reservoir is used and cooling water
is recirculated by a pump which power requirement
is very low. For a small unit, a pump with discharge
of 10 gm/sec is enough which power demand is 30-40
watt hardly .So for a small unit overall power demand
is around 100 to 200 watt . [8]
VIII. CONCLUSION
Summer heat and industrial heat can cause indoor
conditions to become much hotter than desired.
Evaporative cooling is one way to reduce temperatures
inside buildings. As water evaporates, it absorbs energy
from the surrounding environment. A well-maintained
ventilation system with evaporative cooling can reduce
incoming air temperature by 5 to 10°C. Cooler indoor
temperatures can improve the environment for plants and
animals, plus significantly improve working conditions for
employees. Evaporative cooling systems lower air
temperature using mists, sprays, or wetted pads.
Introducing water into ventilation air increases relative
humidity while lowering the air temperature. For
evaporative direct cooling systems a technology is
presented which involves adiabatic humidification and
cooling of air with supplementary heat exchange facilities
to lower final air temperature and try to reduce relative
humidity. The main advantages of the system are:
• Significant reductions in energy consumption
compared to normal air conditioning.
• No refrigerant circuit and no compressor energy
required.
• Low cost, simple units for easy assembly even in
areas with limited industrial facilities.
• Easy installation and service by ventilation personnel.
Modifications of the standard cooling tower have been
presented and it is generally considered that the
performance of cooling tower depends upon the
characteristics of evaporative pad and the circulation of
water. The most cost-effective solution for a particular
installation depends substantially upon the importance of
reducing water consumption and also the performance of
evaporative pad. As the relative humidity in the experiment
is not much satisfactory but it is quite significant for hot air
condition.
Figure 22: Climate graph for Dhaka city, Bangladesh. [5]
D. From November to February
Normally in this time air condition is cold and dry
(figure 22). So for domestic unit are out of operation.
These units must be cleaned and covered with cloth to
prevent dust . In case of industrial unit, still inside
temperature may be high. In this situation both inside
and outside unit will works more effectively.
E. Root cause of load shedding
In perspective of Bangladesh load shedding increases
during hot day . Basically this excessive power
demand raises due to AC unit installed in house ,
office , industry , school , college, University and so on.
For instance when depression (sudden high temperature)
occurs in a certain zone then the dry bulb temperature
goes up to 35 °C relative humidity goes to 60-70 % [6]
. Normally AC unit temperature is set to 27 °C or less. So
to handle this temperature difference (T=34-27 =7 °C)
Power demand rises suddenly and load shedding occurs.
Simply AC unit capacity varies from 3 to 20 KW .
That is equivalent to 300 – 2000 energy saving bulb of
10 watts of 30 -200 low quality electric fan of 100
watts . So in hot day huge power demand raises due to
artificial tempering of air condition [7].
F. How an evaporative cooler can reduce or eliminate
huge power demand in hot day
Main power consuming element of an evaporative
cooling is the blower or fan (30W to 90W) ( [7]).
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)
So, the control of relative humidity and reduce of water
flow can make the whole system rather satisfactory.
Though the power consumption of the system is not so high
if the power consumption can reduce to a moderate level
then it will become serviceable in all sorts of requirements.
Based on these knowledge
a commercial
evaporative cooling unit can be developed that will
reduce excessive power demand , cost of space
cooling, increase productivity of different industry,
increase efficiency of worker. Due to low cost all class
of people will be able to installed evaporative cooler
for their domestic space.
IX. RECOMMENDATION FOR FURTHER WORK
There were three main purpose of this research project.
(a) To study of evaporative cooling principle
(b) To select suitable material that can be used
as evaporative pad and locally available
(c) Performance test of the evaporative cooling unit.
These three objectives have been successfully
completed. But this is not sufficient enough for final
installation and manufacturing . Further study is
required to select best material that is that is
compatible with estimated cost . To do so some objective
must be completed .These are as follows:
(a) To manufacture an independent evaporative
cooling unit without any help of test bench .
(b) To minimize power consumption and cost.
(c) Structural design of the unit for optimum
effectiveness.
(d) To relate cooling load of a space and size
(capacity) of evaporative unit .
(e) Compact design of an evaporative unit.
(f) To develop
most effective water distribution
system and air circulation system .
After completing the objectives mentioned above ,
further research is required on the indirect type
evaporative cooling unit. Because indirect type
evaporative cooler will provide more cold air and
moderate relative humidity (80-85 %) for same degree
of cooling .
Acknowledgement
This project is partially funded by University Grant
Commission (UGC), Bangladesh.
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