Indirect Evaporative Cooling Availability and Thermal ...A cooling water distribution system is also...

International Journal of Engineering & Technology IJET-IJENS Vol:13 No:02 40

I J E N S IJENS 3201 AprilIJENS © -IJET-1818-200231

Indirect Evaporative Cooling Availability and

Thermal Effectiveness Characteristics in Air-Water

Systems of Hot and Dry Climates

Waleed A. Abdel-Fadeel Assistant professor, Faculty of Energy Engineering, Aswan University, Egypt

Tel: +20 1142951507, Fax: +20 97 3481234,

E-mail address: [email protected], P. O.: 81528 Aswan, Egypt.

Abstract-- The success of evaporative cooling technology as a

significant means of a cooling in modern application is the ability to generate cooling water, in an indirect circuit, at a temperature

which closely approaches the ambient adiabatic saturation

(AST). Evaporative cooling, can be used to provide effective

cooling in building by means of contemporary water based

sensible cooling system, such as fan coil systems and ceiling cooling convertors (chilled beams). In this research a diurnal

variation for May, June, and July was measured .A comparison

between measured and calculated cooling water temperatures

result from evaporative cooling was done. Also a comparison

between previous work and present study carried out which gave the same trend. Finally this research quantifies evaporative

cooling availability and thermal effectiveness in depth for

southern Egypt (Aswan city) which has hot and dry climates that

suitable for evaporative cooling. The results of this research confirm a major potential for the generation of cooling water by

evaporative means. Where Cooling water could be generated at

range of (20 – 22) oC during months May, June, and July, and at

range of (15 – 18) oC in March and April months for 87%

availability during these months.

Index Term-- Evaporative cooling ; Cooling tower ; Indirect

evaporative; Hot and dry climate; Availability; Thermal

effectiveness.

NOMENCLATURE

IEC Indirect evaporative cooling

DEC Direct evaporative cooling

Tas Ambient adiabatic saturation temperature (AST) o

C

Tpa primary approach temperature (PAT) oC

Tpr primary loop return temperature oC

Tps primary loop supply temperature oC

Tsa secondary approach temperature (SAT) oC

Tsr secondary loop return temperature oC

Tss secondary loop supply temperature oC

WBT Wet bulb temperature

GREEK LETTERS

ηtp primary thermal effectiveness

ηts secondary thermal effectiveness

SUBSCRIPTS

as adiabatic saturation

pa primary approach

pr primary return

ps primary supply

pa secondary approach

pr secondary return

ss secondary supply

tp thermal primary

ts thermal secondary

1. INTRODUCTION

Today’s high cost of energy together with its

environmental impact are reasons enough to warrant a

reduction in energy consumption in current air conditioning

systems, or those at the design stage. Any study of an air

conditioning system in a building should focus mainly on

thermal comfort, energy saving and environmental protection.

The use of indirect evaporative cooling has a high potential for

meeting air conditioning needs at low energy cost.

Buildings, which have significant latent loads and

which require high rates of air supply for ventilation purposes

are often treated with all air-air conditioning systems, in which

all conditioning equipment is confined to a central location

and from which the treated air supply to the building is

distributed. This system require chilled water at low

temperatures typically 5-8 0C, to produce dehumidification on

the coils. These systems generally rely on vapor compression

refrigeration to generate the required chilled water

temperatures.

Not all buildings, however, need high rates of air

supply for ventilation purposes or have significant latent loads

or require close control of humidity. Such buildings are often

successfully treated with air-water systems in which a smaller

central air system (the primary air) is used to supply

ventilation air and offset latent gains. A cooling water

distribution system is also used (the secondary water) to

supply local sensible cooling equipment in each zone.

The temperatures required for the secondary cooling

water circuit also depend on the system employed. For

example, dry mode fan coil units require a supply at 10-14 oC,

while chilled ceilings require water at 14-18 oC. The sensible

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cooling output of these systems is reduced as the cooling

water temperature rises; however this reduction can be

compensated for, if required, by increasing the area of the heat

transfer surface.

A crucial feature of the feas ibility of the evaporative

cooling in temperate climates is the achievement of a low

temperature difference between the water exiting from the

cooling tower and the ambient WBT (the primary approach

temperature, PAT). This is necessary, in order to ensure a

significant level of cooling water availability, especially in

summer. To separate the tower water circuit from the building

cooling circuit by means of a heat exchanger. Hence, the

crucial design parameter becomes the temperature difference

between the water exiting from the heat exchanger and the

ambient WBT (the secondary approach temperature , SAT ).

B. Costelloe and D. Finn [1, 2, 3] confirm a major

potential for the generation of cooling water by evaporative

means, which can be used to provide effective cooling of deep

plan buildings by means of contemporary water based sensible

cooling systems, such as fan coil, radiant chilled ceiling panels

and chilled beams. Also the thermal effectiveness of water

side, of open indirect evaporative cooling has been presented.

Finally the experimental performance of an open industrial

scale cooling tower, utilizing small approach temperature

difference has examined. The performance and energy

reduction capability of combined system has been evaluated

by Shahram Delfani et al [4] through the cooling season. The

results indicate IEC can reduce cooling load up to 75 %

during cooling season. Ala Hasan [5] presents a method to

produce air at sub-wet bulb temperature by indirect

evaporative cooling without using a vapor compression

machine. Cooling performance of two stage indirect/direct

evaporative cooling system is experimentally investigated by

Ghassem Heidarinejad et al [6] in the various simulated

climatic condition. An experimental system of two stage

evaporative cooling was constructed and tested in Kuwait

environment by Hisham El-Dessouky et al [7]. The system is

formed of an IEC unit followed by DEC unit. Results show

that the efficiency of IEC/DEC varies over a range of 90 -

120%.

An analytical evaluation us ing the field performance

results of 1180 L/s IEC unit and the recorded weather data in

coastal and interior location in Kuwait was presented by G.P.

Maheshwari et al [8]. Several types of materials, namely

metals, fibers, ceramics, zeolite, and carbon was investigated

by X. Zhao et al [9], which have potential to be used as heat

and mass transfer medium in the indirect evaporative system,

and the results show that thermal properties of the materials

have little impact on system heat/mass transfer. A new heat

and mass transfer model based on basic principles has been

developed by J.Fsan et al [10] for thermal calculation of an

indirect evaporative cooler. A simplified model for indirect

cooling towers behavior is presented by Pascal Stabat and

Dominique Marchio [11] the model is devoted to building

simulation tools and fulfills several criteria such as simplicity

of parameterization, accuracy, and possibility to model the

equipment under different operation condition. An analysis

was carried out by Francisco Javier et al [12] for the influence

of factors such as temperature, flow, relative humidity, water

flow rate, etc. on the basic characteristics defined by the

mixed system, heat flow, heat efficiency and COP.

Chilled ceiling panels can operate with a s upply

water temperature as high as 18-20 oC [13]. These elevated

secondary cooling water temperatures raise the possibility of

generating the required cooling in cooling towers. Hence, the

view has developed that tower based evaporative cooling

ought now to be the subject of major review as a practical and

low energy means of cooling modern buildings.

At present, cooling systems generally use

conventional vapor compression refrigeration to generate all

cooling water at temperature suitable for primary air

dehumidification and subsequently raise the water temperature

to the required secondary temperature by means of a mixing

arrangement or a heat exchanger. While water side

evaporative cooling arrangements are occasionally used with

air water systems, particularly in more arid climates, the use of

the technique falls far short of its potential. This is particularly

the case in west Egypt Aswan city of hot and dry climates

where high difference between dry and wet bulb temperature

compared to Egyptian cities as in table I that make it suitable

for evaporative cooling, many opportunities to benefit from

evaporative cooling technique are often overlooked. Also from

previous work carried out on evaporative cooling availability

and effectiveness no author touched this point especially for

hot and dry climate . So our present research was directed to

study indirect evaporative cooling availability and thermal

effectiveness characteristics for hot and dry climates.

2. EXPERIMENTAL TEST RIG

At present, however, there is little in depth research

and analysis of the performance, energy efficiency and year

round availability of this alternative form of cooling,

especially in dry and hot climates at very low approach. To

address these issues, an experimental research program has

been established. So laboratory scale of indirect evaporative

cooling was designed and erected at refrigeration and air

condition laboratory at Aswan faculty of energy engineering

Aswan University. The test rig as in Fig. 1 is consists of an

open counter-flow cooling tower, optimized for close

approach conditions and incorporating a shell and tube heat

exchanger which designed also for close approach conditions

with two shell and two tube pass . The heat exchanger length

of 1 m and a diameter of 0.16 m.. The tower is upset

truncated pyramid in shape as in Figure 1 . Its lower base

dimensions are 82 cm wide and 62 cm deep and its upper base

dimension are 100 cm wide and 80 cm deep and the tower

height is 2 m. The tower has a forced draft fan of a power

0.37 kw and a revolution per minute of 1425. The cooling load

is provided by two electric immersion heaters each of which

1200 w connected parallel to give a load of 1200 W and 2400

W that put in a vertical cylindrical container of 0.5 m length

and 0.32 m diameter. A key issue in this research is the

detailed evaluation of the extent of cooling availability which



can be expected, a range of cooling water supply

temperatures, and thermal effectiveness. The test rig was

instrumented to measure both the water supply and return

temperatures of primary and secondary loops using

thermometer.

3. OPERATING PROCEDURE

1-check the cooling tower water and make sure that it

sufficient for whole operation

2-turn on the cooling tower pump and fans

3-check the boiler water level and adjust the electric heater at

required load Loads (1200w-2400w)

4-turn on the secondary pump and electric heater

5-check air valve of the secondary pump to release vapor from

boiling water to protect pump from failure

6-recording the results from measuring devices and plot

results curves

4. EXPERIMENTAL RESULTS

In this part, the obtained experimental results will be

comprehensively discussed. The results include diurnal

variation, availability of cooling water, and thermal

effectiveness of primary and secondary loops of water side.

4-1 diurnal variations

In this section the results of climate graph through all

year and diurnal variation in conditions during May, June ,

and July will be discuss.

Table II confirms that a PAT of no greater than 2.8 K

is feasible for no load. Also a PAT of no greater than 3.6 K is

feasible for 1200 W load. This research confirms that open

cooling towers in cooperating modern high surface density

packing designs and operating under very close approach

considerations. Also it could be noted from table II that PAT

depends on the ambient AST or WBT. From features of the

test results shown in table II that using PAT of 2K will be

approximated value for most runs .

Figures 2-4 show the diurnal variation in conditions

during May, June, and July month 2010. The figures 2-4 could

be considered to represent a typical design day in Aswan

(Egypt) with a maximum ambient dry bulb temperature

reaching 39 oC and minimum WBT reaching 17.5

oC.

Nevertheless, it was possible under these conditions, to

produce cooling water temperatures of 20 -22 oC, which

could provide or contribute towards building cooling

depending on the thermal conditions considered acceptable. In

figure 2 a primary cooling water temperature of 21oC were

produced in June, while in figure 3 a primary cooling water

temperatures of 20 oC were produced in July a condition

which would suit a dry mode fan coil application. While in

Fig. 4 cooling water temperature of 22 oC were produced in

May.

4-2 Availability analysis

4-2-1 Determination adiabatic saturation temperature

In order to quantify the evaporative cooling

availability which can be expected for any given location it is ,

therefore, necessary to establish the typical yearly record

pattern of the ambient AST. This can be achieved by using,

either a meteorological test reference weather year or

alternatively, where such is available. The method has been

used in this research as it is now readily available in [14]. For

wide range of world wide locations.

The available data based on record of hourly weather

data for 12 typical months. The hourly weather records

typically include data on dry bulb temperature, relative

humidity, wind speed and solar radiation. By using the dry

bulb temperature and relative humidity a new data has been

developed which lists a hourly record of standard

psychometric properties included the WBT a long Aswan city.

4-2-2 Evaporative Cooling Potential

Having established the hourly psychometric data for

the site (Aswan Egypt), the data can now be analyzed to

determine the evaporative cooling potential using the

percentage annual availability of cooling water A where it

could be defined as

A= (1)

where Σ(Htas) is the statistically typical total number of

annual hours, during which, the ambient AST is less than or

equal to (Tpf _ Tpa). Tpf is the primary flow temperature (0C),

Tpa the PAT (K), 8760 the number of hours in a year. In the

first instance the occurrence of the ambient WBT is calculated

and then, using a 2K PAT the potential for cooling water

generation is determined.

Figure 5 shows the percentage occurrence of the

cooling water temperature for Aswan based on the hourly

prediction of the ambient condition. The results show that the

WBT of 13 oC required to supply cooling water at 15

oC (as in

Figure 5) is statistically available for 35% of the year in

Aswan. The annual occurrence is calculated on a 24 h day

basis and is defined as the percentage of the total annual hours

(8760 h) during which a temperature at or below a particular

temperature, occurs.

4-3 Calculation of cooling water temperature through year

2010

In this section a daily cooling water temperature

possible for all year month at Aswan will be calculated based

on [14] and using 2 k PAT, monthly possible average cooling

water temperature , and finally a comparison between

calculated and measured cooling water temperature for some

days will be discuss. Figure 6 shows calculated cooling water

temperature versus days from November to April through

2010 year. It could be seen that cooling water temperature

fluctuating with days for all months, also it could be seen that

the lowest values in temperature are (second half of January

and First half of February). Finally the higher values of

cooling water are through November and December.

Figure 7 shows calculated cooling water temperature

versus days from May to October through 2010 year. It could

be seen that cooling water temperature fluctuating with days

for all months, also it could be seen that the lowest values in



temperature are through May month. Finally the higher values

of cooling water are through July and August.

Figures 8 and 9 show comparison between measured

and possible cooling water temperature versus time for July 5

and May 17. It could be seen that there is a good agreement

between measured and calculated cooling water temperature

for May and July. Also the maximum deviations between

measured and calculated cooling water temperature is less

than 20%.

4-4 Thermal effectiveness

A suitable means of assessing the thermal

performance of the process is the thermal effectiveness ( ηt ).

This is defined as the cooling achieved, expressed as a fraction

of the maximum possible cooling which could have been

achieved in the ambient conditions pertaining . For the

secondary circuit this parameter is defined by equation (1 ) as

in [2]; a similar equation defines the primary circuit. As this

parameter involves both the approach and range condition.

The two key determinants of energy performance, it is also a

suitable parameter from this point of view. In particular the

secondary thermal effectiveness (STE) is an important

parameter as it assesses the performance of the indirect system

as a whole, as distinct from the performance of the tower. It is

also an important indicator of availability of cooling water

generation potential.

The STE can be defined with reference to figure 1 in

terms of the following equation:

ηt = Tsr-Tss / Tsr-Tas = Tsr-Tss / [ (Tsr-Tss) + (Tss-Tas)]

(1)

which can be expressed qualitatively as

secondary range / (secondary range) +(secondary approach)

Tests were conducts to investigate the impact of a

range of operating variables on the thermal effectiveness

achieved. These variables are (time, ambient dry bulb

temperature, and wet bulb temperature ). For testing purposes

the parameter being examined was varied while the other test

rig variables were maintained constant. As there is no control

over the ambient dry bulb temperature and ambient wet bulb

temperature so a large number of tests were conducted and

those tests with different values was selected.

Figure 10 shows secondary effectiveness versus time

in Aswan for June 27 2010. It could be seen that the secondary

effectiveness fluctuating with time. Also the average

secondary effectiveness increase with time up to a certain time

after that it decrease. As this could be attributed to change of

dry bulb temperature with time which affect the cooling water

temperature produced and affect secondary effectiveness as

well

Figure 11 shows comparison between primary and

secondary thermal effectiveness versus ambient dry bulb

temperature. It can be seen that the primary thermal

effectiveness has higher values than secondary thermal

effectiveness. Also it could be seen that both primary and

secondary thermal effectiveness increase with dry bulb

temperature. And this could be attributed to increasing dry

bulb temperature increase the range between dry bulb and wet

bulb which affect secondary effectiveness by increasing it .

Figure 12 shows thermal effectiveness versus wet

bulb temperature through May , June, and July 2010 at

Aswan. It could be seen from the figure that thermal

effectiveness at wet bulb temperature of (18-21 oC) increase

with wet bulb temperature. Also it could be seen that primary

effectiveness has a higher values than that the secondary

effectiveness. And this could be explained as primary

effectiveness is occur as a first exchange between air and

water and occur at relative high temperature. At the opposite

side secondary effectiveness occurs at relative low

temperature and as we know that the efficiency is increase

with temperature. So primary effectiveness is higher than

secondary effectiveness as in figure 12.

4-5 Comparisons with previous work

A comparisons of Measured diurnal variation and annual

availability between reference 1 (a) and present study (b) was

shown in Figures 14-15. It could be seen that the result of

reference 1 and present study has the same trend although the

result different in values according to different conditions

which could be attributed to changed meteorologic condit ions

such as ambient temperature, solar radiation, and wind

velocity where reference 1 carried out at temperate climates

condition where present study carried out at hot and dry

climates. Also comparisons of variation in primary and

secondary approach temperatures and thermal effectiveness

versus wet bulb temperature for both reference 2 and present

study was shown in figures 16-17. It could be seen that the

result of reference 2 and present study has the same trend

although the result different in values according to different

conditions which could be attributed to changed meteorologic

conditions such as ambient temperature, solar radiation, and

wind velocity where reference 2 carried out at temperate

climates condition where present study carried out at hot and

dry climates.

CONCLUSIONS The results of a detailed meteorological analysis of

evaporative cooling availability for south Egypt Aswan city

have been presented and discussed. The results confirm a

major potential for the generation of cooling water, which can

be used to provide effective cooling of modern building by

means of contemporary water based sensible cooling system,

such as fan coils and chilled ceiling panels and beams. While

the technique offers most potential in location as Aswan

where the difference between dry bulb and wet bulb

temperature is the highest over all Egypt. Also this paper

outlines how the thermal effectiveness can be used as a

measure of the degree to which the evaporative cooling

system has succeeded in exploiting the cooling potential of the

ambient air.

The following specific conclusions can be drawn:-

1-Cooling water could be generated at range of (20 – 22) oC

during months May, June, and July, which implies that

buildings, such as educational institutes which are occupied



during these months may be successfully sensibly cooled

through the year.

2- Cooling water could be generated in March and April

month at range of (15 – 18) oC for chilled ceiling panel and

beams for 87% availability during these months.

3-The test results indicate that thermal effectiveness is not

affected by change in load.

4-The results of the tests indicate that both primary and

secondary thermal effectiveness are significantly affected by

both dry and wet bulb temperature.

5- Comparison between previous work and present study

carried out which gave the same trend.

REFERENCES [1] B. Costelloe and D. Finn “Indirect evaporative cooling potential in

air water system in temperate climates” Energy and building, 35 (2003) 573-591

[2] B. Costelloe and D. Finn “Thermal effectiveness characteristics of

low approach indirect evaporative cooling systems in buildings” Energy and building, 39 (2007) 1235-1243

[3] B. Costelloe and D.P. Finn “ Heat transfer correlations for low

approach evaporative cooling systems in buildings” Applied Thermal Engineering 29 2009 105-115

[4] Shahram Delfani, Jafar Esmaeelian, Hadi.P,and Maryam Karami “ Energy saving potential of an indirect evaporative cooler as a pre-

cooling unit for mechanical cooling systems in iran” Energy and buildings 42 2010 2169-2176

[5] Ala Hasan “ Indirect evaporative cooling of air to a sub-wet bulb temperature” Applied Thermal Engineering 30 2010 2460-2468

[6] Ghassem Heidarinejad, Mojtaba Bozorgmehr, Shahram Delfani, and Jafar Esmaeelian “ Experimental investigation of two stage

indirect/direct evaporative cooling system in various climatic conditions” Building and Environment 44 2010 2073-2079

[7] Hisham El-Dessouky, Hisham Ettouney, and Ajeel Al-Zeefari “Performance analysis of two stage evaporative coolers”

Chemical Engineering Journal 102 2004 255-266 [8] G.P. Maheshwari, F.Al-Ragom, and R.K. Suri” Energy saving

potential of an indirect evaporative cooler” Applied Energy 69 2001 69-76

[9] X. Zhao, Shuli Liu, and S.B. Riffat “ Comparative study of heat and mass exchanging materials for indirect evaporative cooling systems” Building and Environment 43 2008 1902 - 1911

[10] J.FSan Jose Alonso, F.J.Rey Martinez, E.Velasco Gomez,

M.A.Alvarez-Gurra Plasencia” Simulation model of an indirect evaporative cooler” Energy and buildings 29 1998 23-27

[11] Pascal Stabat and Dominique Marchio” Simplified model for

indirect contact evaporative cooling tower behaviour” Applied Energy 78 2004 433-451

[12] Francisco Javier, Mario Antonio, Eloy Velasco, Fernando Varela, and Ruth Herrero” Design and experimental study of a mixed

energy recovery system, heat pipes and indirect evaporative equipment for air conditioning” Energy and Buildings 35 2003 1021-1030

[13] J. Fa Cao, A.C. Oliveira, Thermal behavior of closed wet cooling

towers for use with chilled ceilings, Applied Thermal Engineering 20 2000 1225-1236

[14] http://www.wunderground.com\global\EG.html

T ABLE I

AVERAGE EXTERNAL CONDITIONS FOR SOME EGYPTIAN CITIES THROUGH MAY TO JULY 2010

DBT-WBT WBT°C RH% DBT°C CITY

5 21 65 26 ALEXANDRIA

9 20.5 64 29.5 CAIRO

4 21.5 27 25.5 PORT SAID

14.5 72 77 31.5 ASUIT

14.5 19 24 33.5 LOXUR

16.6 18 18 34.6 ASWAN



T ABLE II

SUMMARY OF SOME EXPERIMENTAL TEST RESULTS FROM COOLING

TOWER TEST RIG.(ASWAN) THROUGH MAY TO JULY 2010

Nominal

load

AST oC

Primary

flow

temperature

Secondary

flow

temperature

PAT SAT

No load 18.5 21.3 - 2.8 -

No load 19 20.7 - 1.7 -

No load 20 21.4 - 1.4 -

1200 21 24.6 30.3 3.6 9.3

1200 22.5 23.4 29.5 0.9 7

1200 24.9 25.4 32.9 0.5 7.5

2400 19.5 25.1 37.4 5.6 17.9

T ABLE III ANNUAL AVAILABILITY OF COOLING WATER TEMPERATURE IN ASWAN AT

2 K PAT

Mont

h

Cooling water temperature, oC

4 6 8 1

0

1

2

14 16 18 20 22 24

Jan. 0 3 7

4

5

5

8

7

71

1

71

1

71

1

71

1

71

1

71

1

Feb. 0 2 7

6

3

4

4

8

87 88 84 10

0

10

0

10

0

Mar. 0 1 3 7

1

5

8

27 86 86 10

0

10

0

10

0

Apr. 0 1 1 3 3

1

41 81 71

1

71

1

71

1

71

1

May 0 1 1 1 4 38 82 71

1

71

1

71

1

71

1

Jun. 0 1 1 1 1 1 71 82 71

1

71

1

71

1

Jul. 0 1 1 1 1 1 4 55 22 86 71

1

Aug. 0 1 1 1 1 1 1 74 82 82 71

1

Sept. 0 1 1 1 1 1 2 22 71

1

71

1

71

1

Oct. 0 1 1 1 1 1 73 81 71

1

71

1

71

1

Nov. 0 7 3 7

1

7

6

35 68 83 84 88 71

1

Des. 0 1 1 6 6 72 74 38 26 28 38

Annu

al

0 7 3 7

1

7

6

35 68 83 84 88 71

1

Open counter cooling tower

Primary circuit Tpr Lood

Tss

Fan Tps Secondary

Circuit

Shell & tube Tsr

Heat exchanger

Air Fig. 1 Simplified schematic of indirect evaporative cooling syst em



0

5

10

15

20

25

30

35

40

6 8 10 12 14 16 18

Tem

pe

ratu

re C

o

Time hr

Tps

Tpr

Tss

Tsr

TDB

TWB

Fig. 2. Measured diurnal variation for June 27 2010 in Aswan at constant

1.2 kw load.

0

5

10

15

20

25

30

35

40

45

6 8 10 12 14 16 18

Tem

pe

ratu

re C

o

Time hr

Tps

Tpr

Tss

Tsr

TDBT

Twbt

Fig. 3. Measured diurnal variation for July 3, 2010 in Aswan at constant

2.4 kw load.



0

5

10

15

20

25

30

10 12 14

Tem

pe

ratu

re C

o

Time hr

Fig. 4. Measured primary supply loop temperature for May 18, 2010 in

Aswan at no load.

Fig. 5. Percentage annual occurrence of cooling water temperature in Aswan



Fig. 6. Calculated cooling water temperature for November to April At 2 k PAT in Aswan.

Fig. 7. Calculated cooling water temperature for May to October

At 2 k PAT in Aswan.



Fig. 8. Comparison between measured and calculated cooling water temperature using 2K PAT for July 5, 2010.

Fig. 9. Comparison between measured and calculated cooling water temperature using 2K PAT for May 17, 2010.

Fig. 10. Thermal effectiveness versus time for June 27, 2010.



Fig. 11. Primary and secondary thermal effectiveness versus ambient

dry bulb temperature through (May, June, and July) 2010.

Fig. 12. Primary and secondary thermal effectiveness versus wet bulb temperature through (May, June, and July) 2010.



Fig. 13. Primary and secondary approach temperature versus wet bulb temperature through (May, June, and July) 2010 .

a Measured diurnal variation in conditions for 6 September b Measured diurnal variation for July 3 2010 2000, in Dublin at a constant 20 kW and maximum fan power. in Aswan at 2.4 constant kw load.

Fig. 14. comparison of Measured diurnal variation between reference 1 (a) and present study (b)

a Comparison of annual availability with direct and b Percentage annual occurrence of cooling water temperature in indirect system for Dublin and Milan. Aswan



Fig. 15. comparison of annual availability between reference 1 (a) and present study (b)

a Variation in primary and secondary approach temperature with annual. b Primary and secondary approach temperature range of AST in Dublin (load 20 kW, flow rates: tower water flux 2.9 kg/s m2, versus wet bulb temperature through (May, June, tower air flux 4.0 kg/s m2, secondary water 1.6 kg/s). The mean AST of 10.5 8C and July)2010 is shown with associated 3 K SAT

Fig. 16. comparison of variation in primary and secondary approach temperatures between reference 2 (a) and present study (b)

a Variation in thermal effectiveness with typical annual range of AST in b Primary and secondary thermal effectiveness versus wet Dublin (load 20 kW, flow rates: tower water flux 2.9 kg/s m2, tower air bulb temperature through (May, June, and July) 2010 flux 4.0 kg/s m2, secondary water 1.6 kg/s).

Fig. 17. comparison of thermal effectiveness between reference 2 (a) and present study (b)

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