design optimization and installation of the evaporative cooler in the

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 11, November 2012)

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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,

3Assistant Manager, Khan Brothers Shipbuilding Ltd., Dhaka,

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.

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.

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].

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.

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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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.

Figure 2: Experimental setup at Heat Engine Lab, MIST [3]

Figure 3: Cooling Tower schematic diagram. [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].

BBB

ava

x

v

xm

10137.00137.0 (1)

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

(A)Packing-1 (B) Packing-2

(C) Packing-3 (D) Packing-4 (E) Packing-5

Figure 4: Different packing (pad) for test.

E. Assembly of evaporative pad in Angle bar frame

Step-1 step-2



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Step-3 Final assembly of pad-3

Figure 5: Assembly of pad in tower column.

IV. DATA COLLECTION

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.

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.

Figure 6: Experimental setup with air tight heated chamber.

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.

Step -3:

Outlet of the heated chamber was connected with the

damper opening of cooling tower’s base unit through a pipe

cone arrangement.

Figure 7: Sensible heating process.

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 (Mano-

metric deflection)



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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 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).

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 10: approaches for packing-1

Figure 11: Approaches for packing-2



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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.

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.

25

30

35

0 10 20 30

Temp ºC

Time(min)

T(wet bulb in)? T water out ?

T water reserviour ?

Figure 15: Condition of if it is re-circulated (packing-1)




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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

Figure 18۰: Condition of if it is re circulated (packing-4)

Figure 19: Condition of if it is re circulated (packing-5)

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.

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 High Medium Low Low Medium

Sustainability High High Low low Low

Odor No No High No Low

Availability Low High High High High

Pressure drop Low Low High Low 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?



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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

(a) Indoor Unit (b) outdoor unit

Figure 20: Industrial Installation (RFL plastic factory)

As per the experimental result for industrial use at least

50% unit should be installed inside the space (applicable

for all space where room air face high sensible heating).

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).

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. 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 .

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 .

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.

Entha

lpy

- kJ/

kg(a

)

Satu

ratio

n te

mpe

ratu

re -

deg

C

Hum

idity

ratio

- g/

kg(a

)

Pressure: 101325 Pa

Dry bulb temperature - deg C0 10 20 30 40 50

10

20

30

20%

40%

60%

80%

0.80

0.85

0.90 Volum

e - cu.m/kg(a)

0.95

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140150

160

70

80

90

100

110

120

130

140

150

160

10

20

30

A B

P C



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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]).

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.



749

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.

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 .

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.

Acknowledgement

This project is partially funded by University Grant

Commission (UGC), Bangladesh.

REFERENCES

[1] Camargo, J. R. 2008, Evaporative cooling: water for thermal comfort,- An Interdisciplinary Journal of Applied Science, vol. 3, pp.

51-61 .

[2] www.atecdenver.com/glasdek_lit.htm 2010

[3] P.A. Hilton Ltd. "Manual of bench top cooling tower.

[4] "Software Psychrosoft SI units."

[5] www.climatetemp.infoClimate of Bangladesh.

[6] Tassou. 1998, Low energy cooling technologies for buildings. Mech.

Engg. Seminar. London,

[7] Watt, J. R.; Brown, W. K. 1997, Evaporative air conditioning

handbook. 3. ed. Lilburn: The Fairmont Press,. 507 p.

[8] Hasan, A.; Sirén, K. 2003, Performance investigation of plain and finned tube evaporatively cooled heat exchangers. Applied

Thermal Engineering, v. 23, p.325-340,

http://www.atecdenver.com/glasdek_lit.htm%202010

design optimization and installation of the evaporative cooler in the

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