j. r. adhikari et al design and analysis of solar...

J. R. Adhikari et al: Design and analysis of solar absorption air cooling system for an office building

Rentech Symposium Compendium, Volume 2, December 2012 22

Design and analysis of solar absorption air cooling system for

an office building Jhalak Raj Adhikari*, Bivek Baral, Ram Lama, Badri Aryal, and Roshan Khadka

Department of Mechanical Engineering, Kathmandu University, Nepal

Abstract- Cooling system, for cooling purpose, is generally felt

essential during the summer days due to large solar radiation. This

causes the greatest need for cooling and at the same time,

maximum possible solar energy is also available.

The paper covers the need and importance of solar based

cooling system that can play a very prominent role in attenuating

energy crisis by the use of solar energy. The study investigated and

evaluated the feasibility of an absorption refrigeration unit on solar

power. The system designed here functions with the principle of

absorption refrigeration cycle having water as a refrigerant and

Lithium Bromide as an absorbent.

The cooling load for the office building is 5 KW. The designed

absorption system has 0.77 average coefficient of thermal

performance (COP). For this design, we also analyze the effect of

COP in the variation of the refrigeration mass flow rate (ṁ) and

generator temperature (Tg). The ultimate goal in the long term

would ideally be to reduce the consumption of electricity used for

refrigeration and air conditioning, hence saving money and

reducing the stress on our electricity generation and distribution

networks.1

Index Terms- Absorbent, coefficient of thermal performance,

consumption of electricity, cooling load, Lithium Bromide,

refrigerant, summer days, water

Symbols, Abbreviations and Subscripts:

∆T Temperature difference ṁ Mass flow rate

∆W Change in humidity NE North East OF Degree Fahrenheit NW North West OC Degree Celsius N North

A Area SC Shading Coefficient

BTU British Thermal Unit SHGF Solar Heat Gain Factor

CLF Cooling Load Factor SW South West

E East Q Heat energy

EES Engineering Equation

Solver

U Overall heat transfer

coefficient

ES East South W Mass flow (kg/s)

CLTD Cooling Load

Temperature difference

x Concentration of lithium

bromide

COP Coefficient of

Performance

Sq. Square

h Enthalpy (kJ/kg) 1, 2, 3 System’s point designation

KJ Kilo Joule a Absorber

KPa Kilo Pascal c Condenser

KW Kilo Watt e Evaporator

KWh Kilo Watt hour g Generator

I. INTRODUCTION

The demands for air cooling system in household,

offices, hotels, laboratories or public buildings are

increasing considerably. Under adequate conditions, solar

and solar-assisted air cooling systems can be reasonable

alternatives to conventional air cooling systems. The use of

energy in the building sector for heating and cooling is

nearly one- third of the total energy consumed in the world

[1]. As there is growing concern in the fossil fuels which is

depleted soon and due to sustainability issue, an alternative

* Corresponding author, [email protected]

source of energy must be found to meet energy supply of

high energy consumption sector. The building is one of the

prominent sectors, which could save tremendous amount of

fossil fuels if renewable energy sources like solar cooling

substrates them. As the solar energy is advantageous from

energy, environment and sustainability point of view, efforts

should focus on to develop an efficient absorption cooling

system. Thermodynamic analysis of the system would

produce scientific results help us to evaluate and optimize

the system.

According to American Society of Heating, Refrigeration

and Air-Conditioning Engineers (ASHRAE) “Air

cooling(conditioning) is the process of treating air so as to

control simultaneously its temperature, humidity, cleanliness

and distribution to meet the requirement of the conditioned

space”. Cooling may be defined as the process of achieving

and maintaining a temperature below that of the

surroundings, the aim being to cool some product or space to

the required temperature.

Air conditioning is one of the most widely researched

applications, resulting from the potential reduction of carbon

emission and the reduction of electricity consumption peaks.

The commonly used refrigeration process today is the

vapor compression system. The basic system consists of an

evaporator, a compressor, a condenser and an expansion

valve. Schematic Diagram of Vapor compression System is

shown in figure 1. The refrigeration effect is obtained in the

cold region as the heat is absorbed by the vaporization of

refrigerant in the evaporator. The refrigerant vapor from the

evaporator is compressed in the compressor to a high

pressure at which its saturation temperature is greater than

the ambient or any other heat sink. Hence when the high

pressure and high temperature refrigerant flows through the

condenser, condensation of the vapor into liquid takes place

by heat rejection to the heat sink. To complete the cycle, the

high pressure liquid is made to flow through an expansion

valve. In the expansion valve, the pressure and the

temperature of the refrigerant are decreasing. This low

pressure and low temperature refrigerant vapor evaporates in

the evaporator taking heat from the cold region. It should be

observed that the system operates on a closed cycle. The

system requires input in the form of mechanical work. It

extracts heat from a cold space and rejects heat to a high

temperature heat sink.

The problems associated with the commercial air cooling

system are high consumption of high grade energy i.e.

electricity and due to releasing of CFCs it doesn’t seem

environment friendly. Our main objective is to design an air

cooling system based on solar absorption refrigeration

principle.



Fig. 1: Schematic diagram of vapor compression system [3]

The working principle of an absorption system is similar

to that of a mechanical compression system with respect to

the key system components evaporator and condenser. A

vaporizing liquid extracts heat at a low temperature (cold

production). The vapor is compressed to a higher pressure

and condensed at higher temperature (heat rejection). The

compression of the vapor is accomplished by means of a

thermally driven ‘compressor’ consisting of the two main

components absorber and generator. Subsequently, the

pressure of the liquid is reduced by expansion through a

throttle valve and the cycle is repeated. Absorption cycles

are based on the fact that boiling point of a mixture is higher

than corresponding boiling point of pure liquid [4].A simple

schematic diagram for absorption system is shown in figure

2. In this figure Qg and Qa represent the heat given in to the

generator and heat release from the absorber.

Fig. 2: Basic vapor absorption system [3]

Lithium bromide is the most common absorbent used in

commercial cooling equipment, with water used as the

refrigerant. Smaller absorption chillers sometimes use water

as the absorbent and ammonia as the refrigerant. The

absorption chillers must operate at very low pressures (about

l/l00th of normal atmospheric pressure) for the water to

vaporize at a cold enough temperature to produce chilled

water. This water vapor is absorbed by the concentrated

lithium bromide solution due to its hygroscopic

characteristics. The heat of vaporization and the heat of

solution are removed using cooling water at this step. The

solution is then pumped to the concentrator at a higher

pressure where heat is applied (using steam or hot water) to

drive off the water and thereby re-concentrate the lithium

bromide. The water driven off by the heat input step is then

condensed collected, and then flashed to the required low

temperature to complete the cycle. Since water is moving

the heat from the evaporator to the condenser, it serves as

the refrigerant in this cycle. There are also absorption

chillers in use that use ammonia as the refrigerant in the

same cycle.

The absorbent is the material that is used to maintain the

concentration difference in the machine. Most commercial

absorption chillers use lithium bromide. Lithium bromide

has a very high affinity for water, is relatively inexpensive

and non-toxic. However, it can be highly corrosive and

disposal is closely controlled. Water of course is extremely

low cost and safety simply isn't an issue.

II. THERMODYNAMIC ANALYSIS

This paper focus on the thermal analysis of the system

and its performance in pre assumed temperature of the

evaporator and condenser. The temperature of the

evaporator and the condenser assumed to be 10oC and 40

oC

respectively. The thermal analysis depends on the basic

governing equation of thermodynamics. Moreover, the

analysis has been based on simulation work on Engineering

Equation Solver (EES). In developing the model the

following basic assumptions have been made.

• There are no kinetic and potential energy effects

and there is no chemical or nuclear reaction.

• All processes are steady state and steady flow.

• The system surrounding is considered as large

thermal reservoir and no influence of local

activity of source or sink.

• The refrigerant-absorbent are considered to be

ideal.

• No pressure changes except through the flow

restrictors and the pump.

• Pump is isentropic.

An absorption air conditioner or refrigerator does not use

an electric compressor to mechanically pressurize the

refrigerant. Instead, the absorption device uses a heat source,

such as natural gas, solar heated water or geothermal heated

water to evaporate the already-pressurized refrigerant from

an absorbent/refrigerant mixture. This takes place in a

device called the vapor generator. Although absorption

coolers require electricity for pumping the refrigerant, the

amount is small compared to that consumed by a compressor

in a conventional electric air conditioner or refrigerator. The

coefficient of performance of this refrigerating machine with

absorption system is defined as follows:

COP = qe /qg (1)

J. R. Adhikari et al

Rentech Symposium Compendium, Volume 2

For the analysis, we will have to establish the mass and

energy balance equations for the various elements of the

refrigerating cycle. The total mass flow rate through the

pump is assumed to be 0.6 kg/s as shown in figure 3.

General mass balance equation in the generator:

w3 + w5 =w2

Mass balance of the refrigerants i.e. water

w5 = w6 = w7

Lithium bromide mass balance

Fig. 3: Schematic diagram absorption system with reference temperature of different components [2]

III. SYSTEM DESCRIPTION

Sunny summer days are beautiful, yet in the office a hot

day can be altogether stressful. Because productivity can

suffer under such conditions, more and more buildings are

being fitted with air-conditioning systems. This is where

solar air conditioning comes in: As the amount of solar air

conditioning consumer is increasing air conditioning

industry with several challenges. Among these are demands

for increased energy efficiency and improved indoor air

quality, growing concern for improved comfort and

environmental control, increased ventilation requirements,

phase-out of chlorofluorocarbons (CFCs), an

demand charges. As a result, new approaches to air

conditioning are being evaluated to resolve these economic,

environmental, and regulatory issues.

Since this study is focused on air cooling system in the

office building operated by the solar absorption system. We

have chosen the staff room nearby bio-gas equipped room as

our basis for calculating load as shown in figure 4. Cooling

load is the rate at which heat must be removed from the

space to maintain room air temperature at a constant val

The different load from the office building are

exfiltration, transmission, internal load, solar and infiltration

as soon figure 5 are consider for cooling load calculation.

For the cooling load calculation different load like

conduction from roof, wall and floor, air exchange from gap,

heat loss from people and heat release from equipment

should be consider as shown in figure 6.


2, December 2012

analysis, we will have to establish the mass and

energy balance equations for the various elements of the

refrigerating cycle. The total mass flow rate through the

pump is assumed to be 0.6 kg/s as shown in figure 3.

nerator:

(2)

Mass balance of the refrigerants i.e. water vapor:

(3)

w3x3= w2x2

Heat added to the generator

qg= w5h5+w3h3 – w2h2

Heat rejected through the absorber

qa = w7h7 + w4h4 - w

Heat rejected through the condenser

qc = w5h5 – w6h6

Heat is to be given in the evaporator; q

from the cooling load calculation.

Schematic diagram absorption system with reference temperature of different components [2]

ESCRIPTION

Sunny summer days are beautiful, yet in the office a hot

productivity can

suffer under such conditions, more and more buildings are

conditioning systems. This is where

solar air conditioning comes in: As the amount of solar air

conditioning consumer is increasing air conditioning

ith several challenges. Among these are demands

for increased energy efficiency and improved indoor air

quality, growing concern for improved comfort and

environmental control, increased ventilation requirements,

out of chlorofluorocarbons (CFCs), and rising peak

demand charges. As a result, new approaches to air

conditioning are being evaluated to resolve these economic,

Since this study is focused on air cooling system in the

r absorption system. We

gas equipped room as

our basis for calculating load as shown in figure 4. Cooling

load is the rate at which heat must be removed from the

space to maintain room air temperature at a constant value.

ffice building are

, solar and infiltration

as soon figure 5 are consider for cooling load calculation.

For the cooling load calculation different load like

nd floor, air exchange from gap,

heat loss from people and heat release from equipment

Fig. 4: Reference office building

Fig. 5: Different losses from the building

and analysis of solar absorption air cooling system for an office building

24

(4)

(5)

Heat rejected through the absorber

w1h1 (6)

Heat rejected through the condenser

(7)

Heat is to be given in the evaporator; qe is calculated

Schematic diagram absorption system with reference temperature of different components [2]

Reference office building

ifferent losses from the building


Rentech Symposium Compendium, Volume

Fig. 6: Terms in cooling load calculation

The cooling load are depends upon the specification of

the office building. The table I shows the dimensions and

direction of the components of the room. The overall heat

transfer coefficient is depends upon the materials of the wall

and the table II shows materials and direction of the roof and

the four walls.

TABLE I

SPECIFICATION OF OFFICE BUILDING

TABLE II

MATERIALS AND DIRECTION OF THE ROOF AND F

The sensible and latent heat gains due to occupants,

lights, appliances etc. within the conditioned space are the

internal heat load and the internal load and their numbers are

shown in Table III.

TABLE III

ITEMS FOR INTERNAL LO


Rentech Symposium Compendium, Volume 2, December 2012

calculation

The cooling load are depends upon the specification of

shows the dimensions and

direction of the components of the room. The overall heat

transfer coefficient is depends upon the materials of the wall

shows materials and direction of the roof and

CE BUILDING

ON OF THE ROOF AND FOUR WALLS

The sensible and latent heat gains due to occupants,

lights, appliances etc. within the conditioned space are the

internal heat load and the internal load and their numbers are

TEMS FOR INTERNAL LOAD

The temperature difference between the ambient and the

room is the major parameter for the cooling load. A man

body feels comfortable thermodynamically when the heat

produced by the metabolism of the human body is equal to

the sum of the heat dissipated to the surrounding

heat stored in human body by raising the temperature of

body tissues [5]. The inside temperature of the room for

human comfort is assumed to be 22

average outdoor temperature are as soon in the table

TABLE

TEMPERATURE FOR

The solar radiation in the building is also depends on the

elevation, latitude and longitude of the building. Elevation

of Dhulikhel from sea level is 5500 ft and latitude and

longitude are 27.42N and 85.19E respectively

IV. MODEL ANALYSIS AND

The overall heat transfer coefficient and other parameter

for the cooling load calculation of the different components

of the building are taken from the ASHRAE Fundamentals

Handbook of HVAC of 1997 edition

1. Cooling Load Calculation

1.1Transmission from Walls, Floor and Roof

Heat gain through walls, floors, ceilings, and doors is

caused by the air temperature difference across such

surfaces and solar gains incident on the surfaces. Cooling

load can be estimated by using following

a) Roof Load

The roof of the building is medium

ASHRAE hand book of HVAC the overall heat transfer of

the roof (Uroof) is 0.23 btu/hr.sq.ft.

roof is 480 sq. ft. The cooling

the room (CLTDroof) is calculated to be 78.8

b) Floor Load

Since the floor of the building is made of up medium

cement. For this specification overall heat transfer (U

the floor is 0.213 btu/hr.sq.ft.

between floor and cooling space is 15

c) Wall Load

The wall of the building is medium face brick with one

side plaster. The overall heat transfer coefficient, area and

CLTD of the four walls are listed in the table 4.

1.2 Transmission from Glass

Glass is the major material of most of the building,

provides the most direct route for entry of the solar radiation.


25

difference between the ambient and the

room is the major parameter for the cooling load. A man

body feels comfortable thermodynamically when the heat

produced by the metabolism of the human body is equal to

the sum of the heat dissipated to the surroundings and the

heat stored in human body by raising the temperature of

body tissues [5]. The inside temperature of the room for

human comfort is assumed to be 22oC.The maximum and

average outdoor temperature are as soon in the table IV.

ABLE IV

EMPERATURE FOR THE BUILDING

The solar radiation in the building is also depends on the

elevation, latitude and longitude of the building. Elevation

of Dhulikhel from sea level is 5500 ft and latitude and

longitude are 27.42N and 85.19E respectively.

NALYSIS AND SIMULATION

The overall heat transfer coefficient and other parameter

for the cooling load calculation of the different components

of the building are taken from the ASHRAE Fundamentals

Handbook of HVAC of 1997 edition.

ion

1.1Transmission from Walls, Floor and Roof

Heat gain through walls, floors, ceilings, and doors is

caused by the air temperature difference across such

surfaces and solar gains incident on the surfaces. Cooling

load can be estimated by using following formula,

Q=U*A*CLTD (8)

The roof of the building is medium colour tin. From the

ASHRAE hand book of HVAC the overall heat transfer of

btu/hr.sq.ft.0F. And the area of the

roof is 480 sq. ft. The cooling load temperature difference of

) is calculated to be 78.80F.

Since the floor of the building is made of up medium

cement. For this specification overall heat transfer (Ufloor) of

btu/hr.sq.ft.0F. The temperature difference

between floor and cooling space is 150F.

The wall of the building is medium face brick with one

side plaster. The overall heat transfer coefficient, area and

CLTD of the four walls are listed in the table 4.

ssion from Glass

Glass is the major material of most of the building,

provides the most direct route for entry of the solar radiation.



There are two types of heat admission into the room i.e.

conduction and solar heat gain. TABLE V

SPECIFICATION OF THE FOUR WALLS

Direction U,btu/hr.sq.ft.0F Area(sq.ft) CLTD.(

0F)

NE 2.61 66 13.7

NW 2.69 200 16.8

SW 2.69 84 19.3

ES 2.69 200 13.7

a) Conduction Heat Gain The conduction from the wall is depends on the overall

heat transfer coefficient, CLTD and area of the glass which

are listed in the table VI. TABLE VI

OVERALL HEAT TRANSFER COEFFICIENT AND CLTD OF THE

WINDOWS

Direction U(btu/hr.sq.ft.oF) Area(sq.ft.) CLTD(0F)

NE 0.0554 16 65.4

WS 0.0554 16 13.7

b) Solar Heat Gain Cooling

The direct heat gain from the glass is the function of the

shading coefficient, solar heat gain factor and Cooling load

factor which are listed in the table VII. TABLE VII

SHADING COEFFICIENT, COOLING LOAD FACTOR AND SOLAR HEAT

GAIN FACTOR

Shading

coefficient(sc)

Area

(sq.ft.)

Cooling

load factor

(clf)

Solar heat gain

factor

(SHGF)[btu/hr.sq

ft]

0.92 16 0.21 51.5

0.92 16 0.28 51.5

1.3 Infiltration and Ventilation

Cubic feet per (cfm) per person are assumed to be for the

office building 15. Both latent and sensible heat must be

count for the infiltration. Because of entry of outside air into

the space influences both the air temperature and humidity

level in the space.

1.4 Internal Loads

The primary sources of internal heat gain are lights,

occupants and equipments operating within the space.

a) Occupants Load

The number of person assumed to be two who are seating

and computer typing. Both sensible and latent heat must be

accounts for cooling load calculation. For this case CLF is

taken to be 0.77.

Sensible and latent head are 255 Btu/Hr per person and

100 Btu/Hr per person respectively.

b) Lighting Loads

The amount of heat gain in the space due to lighting

depends upon the wattage and used hours. There are two

florescent lighting.

c) Appliance

Since in the room there are two personal computer and

one impact printer. The heat gain, used hour and CLF of the

appliance are shown in the table 7.

Total thermal Load is the sum of all above mentioned

load. The total cooling load of this room is listed in the table

8. From this calculation, total thermal load is 17051Btu/hr.

Thus total thermal cooling load in the cycle is calculated to

be 5KW. TABLE VIII

THE HEAT GAIN, USED HOUR AND CLF OF THE APPLIANCE

Applianc

e

Numbe

r

Heat

gain(Btu/hr

)

Use

d

hour

Coolin

g load

factor

(CLF)

Personal

computer 2 432 6 0.72

Impact

printer 1 67 0.5 0.72

TABLE IX

THE HEAT GAIN, USED HOUR AND CLF OF THE APPLIANCE Compone

nts of

room

Equation for heat transfer Q (

Btu/hr)

Q (W)

Roof Q=U*A*CLTD(adj) 3621.0 1061.3

walls Q=U*A*CLTD(adj) 8725.0 2557.2

Glass Q=U*A*CLTD(adj) 70.1 20.5

Solar Q=A*SC*SHGF*CLF 371.5 108.9

Floor Q=U*A*∆T 2210.0 647.7

Internal

light Q=INPUT*CLF 262.6 77.0

People

Q=numb.(Sense

H.G.*LatentH.G.*CLF) 734.4 215.2

Appliance Q=numb.*heat gain*CLF 670.3 196.5

Ventilatio

n and

infiltratio

n

Sensible,Qs=1.1*cfm*∆T,latent

=4840*cfm*∆W 386.1 113.2

Total ∑Q 17051.0 4997.4

2. Absorption System Analysis

The computation of mass flow rate incorporates material

balances using applicable concentrations of LiBr in the

solution. Since saturation condition prevails in the condenser

in the generator and condenser temperature 40 oC fixes the

pressure in condenser (or in generator) 7.38 kPa.From

similar reasoning, the evaporator temperature of 10 oC

establishes the low pressure at 1.23 kPa.The p-x-t diagram

display the state points of the LiBr solution.

From the graph p-x-t diagram

X1=0.5(30oC & 1.23 kPa)

X2=0.664(100oC & 7.38 kPa)

Heat given in the evaporator qe is 5 kW, which is taken

from cooling load calculation.


Rentech Symposium Compendium, Volume

From the h-x-t graph of LiBr – water solutions, enthalpy

at different stand point are

h1 = -168 kJ/kg; h3=-52kJ/kg; h5=

h6=167.5kJ/kg and h7=2520kJ/kg.

From energy and mass balance equation which are given

in the equation (2) to (7):

qc = 5.33 kW

qg = 6.46 kW

qa = 6.04 kW

Hence coefficient of the performance of absorption

system is given by,

COP = qe /qg

= 0.77

Hence, the coefficient of the system is 0.77.

3. Solar panel

The maximum solar radiation for Dhulikhel is 5.5 kWh/

m2/day i.e. 0.81 W/m

2/s. Since from absorption system

analysis, qg was found to be 6.46 kW. The total area of the

panel is calculated to be 8 m2 in the peak load. If the solar

radiation is decreases, there is also cooling load decreases.

Hence the system is balances by itself.

V. SIMULATION AND RESULTS

We use EES for the simulation of this system. The first

of all the governing equation of the absorption system are

coded the equation window (terminology of EES) of this

software. Then for the analysis different parameter such as

mass flow rate, temperature of the generator, heat added to

the generator etc. are varies and the COP of the system is

plotted. The simple architecture of the absorption system is

shown in the figure 7.

This figure 8 shows that, with the increasing value of

heat added to the generator, the COP of the system goes on

decreasing. This shows that the COP of the system has

inverse relation to heat added to the system.


Rentech Symposium Compendium, Volume 2, December 2012

water solutions, enthalpy

52kJ/kg; h5=2676kJ/kg;

From energy and mass balance equation which are given

Hence coefficient of the performance of absorption

Hence, the coefficient of the system is 0.77.

The maximum solar radiation for Dhulikhel is 5.5 kWh/

/s. Since from absorption system

was found to be 6.46 kW. The total area of the

in the peak load. If the solar

radiation is decreases, there is also cooling load decreases.

ESULTS

We use EES for the simulation of this system. The first

of all the governing equation of the absorption system are

coded the equation window (terminology of EES) of this

software. Then for the analysis different parameter such as

e of the generator, heat added to

the generator etc. are varies and the COP of the system is

plotted. The simple architecture of the absorption system is

This figure 8 shows that, with the increasing value of

generator, the COP of the system goes on

decreasing. This shows that the COP of the system has

inverse relation to heat added to the system.

Thus for the fixed evaporator load, there is no

significance of higher heat added to the generator. This

inverse relation in the graph is due to the relation COP = q

/qg . It is obvious that if the generator heat (q

and the evaporator heat (qe) is kept constant, then the value

obtained from the ratio get decrease, i.e. system COP

decreases and vice versa.

Fig. 8: Plot between generator heat and COP

The COP of the system is decrease on increasing

generator heat; it is based on fact that a higher amount of

water was separated from the ammonia

thus more solution had to be circulated so

refrigerant.

Similarly, the COP of the system has inverse relation

with the generator temperature (T

increasing generator temperature the COP gets decrease and

vice versa as shown in figure 9. The generator temperat

increases, which is due to increase of generator heat and

hence COP decreases for fixed cooling load.


27

Thus for the fixed evaporator load, there is no

significance of higher heat added to the generator. This

lation in the graph is due to the relation COP = qe

. It is obvious that if the generator heat (qg) is increased

) is kept constant, then the value

obtained from the ratio get decrease, i.e. system COP

Plot between generator heat and COP

The COP of the system is decrease on increasing

generator heat; it is based on fact that a higher amount of

water was separated from the ammonia-water solution and

thus more solution had to be circulated so as to maintain the

Similarly, the COP of the system has inverse relation

with the generator temperature (Tg). It shows that for

increasing generator temperature the COP gets decrease and

vice versa as shown in figure 9. The generator temperature

increases, which is due to increase of generator heat and

hence COP decreases for fixed cooling load.



Fig. 7: Architecture of absorption system using EES

Fig. 9: Plot between generator temperature (Tg) and COP (at

constant mass flow rate)

Fig. 10: Plot between mass flow rate and evaporator heat and

generator heat

The figure 10 shows that on increasing mass flow rate of

refrigerant and absorbent mixture, the both heat added to

the generator and heat at the evaporator increases. Also, the

distance between two graphs is increases on increasing mass

flow rate of refrigerants. In other words, while increasing

the mass flow rate of the refrigerant the heat taking capacity

of the refrigerant from the conditioned area get increases.

That results the high reduction in temperature of the

conditioned area. However the COP of the system is

decreases due to increasing distance between two lines of qg

and qe. The relation between mass flow rate and COP is

shown in figure 11. On the increasing temperature cooling

effect increases it is because of increasing mass flow rate of

the refrigerants i.e. water vapor.

Fig. 11: Plot between the mass flow rate of refrigerant and the

COP

VI. CONCLUSION

A design and simulation of absorption air cooling system

using solar as source of energy, for an office building was



done and the system performances were analyzed

parametrically by using EES. It appears that best

performance in terms of COP would be obtained when we

work with low generator temperature and low generator

heat.

The cooling load for our system is obtained as 5kw. The

COP of the System is 0.77. Solar collector area to conduct

system is 8 m2. On the increase of mass flow rate of

refrigerant, the overall cooling effect increases, but COP

decreases. This absorption air cooling system is alternative

to conventional vapor compression cycle. Here, Lithium

bromide has been selected as absorbent for cooling purpose

and water as refrigerant.

The ultimate goal in the long term would ideally be to

reduce the consumption of electricity used for refrigeration

and air conditioning.

ACKNOWLEDGEMENT

The author acknowledge to Asst. Prof. Sunil Prasad

Lohani for his invaluable support and continuous

encouragement to conduct this project. They also express

gratitude to Mr. Suman Aryal who has played a pivotal role

to conduct this project, share his precious idea and guide

them. They also voice their appreciation to Mr. Shiva Poudel

for diligent guidance on cooling load calculation. Lastly,

they thank the Mechanical Engineering Department,

Kathmandu University for its support and co-operation.

REFERENCES

[1] Energy conservation in building and community systems (ECBCS).

Viewed 21.11.2012, http://www.ecbcs.org/home.htm.

[2] Refrigeration and Air conditioning, W.F. Stoecker, J.W. Jones, second

edition , p. 337

[3] History of Refrigeration, http://nptel.iitm.ac.in/courses/Webcourse

contents/IIT%20Kharagpur/

Ref%20and%20Air%20Cond/pdf/RAC%20%20Lecture%201.pdf,

viewed on 14th June, 2010.

[4] Henning,Dr Hans-Martin, Air Conditioning with Solar Energy,

Fraunhofer-Institut für Solare Energiesysteme ISE, Freiburg.

SERVITEC; Barcelona, October 3, 2000.

[5] Refrigeration and Air-conditioning, R. k. Rajputh, First Eddition

2004, p.515

BIOGRAPHIES

Jhalak Raj Adhikari has done BE in Mechanical

Engineering from Kathmandu University.

Currently, he is the researcher in Renewable

Nepal project on “High rate anaerobic digester for

biogas production from waste water treatment” at

the department of mechanical engineering,

Kathmandu University.

Dr Bivek Baral has done PhD from the

University of Auckland, New Zealand, Doctor of

Philosophy in Mechanical Engineering. He is

completed Master in Mechanical Engineering

from the University of Tokyo, Japan. Currently,

he is the Assistant Professor at the department of

Mechanical Engineering, Kathmandu University.

Ram Lama has don BE in mechanical

engineering from Kathmandu University. He has

done internship in particle method at ENT,

Kathmandu, Nepal.

Badri Aryal has done BE in mechanical

engineering from Kathmandu University. He is

working in particle method at ENT, Kathmandu,

Nepal.

Roshan Khadka has done BE in mechanical

engineering from Kathmandu University. He

has done internship in sand erosion at TTL,

Kathmandu University.

j. r. adhikari et al design and analysis of solar...

Documents