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.
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 23
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.
J. R. Adhikari et al: Design and analysis of solar absorption air cooling system for an office building
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
J. R. Adhikari et al
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
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
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.
and analysis of solar absorption air cooling system for an office building
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.
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 26
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.
J. R. Adhikari et al
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.
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
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.
and analysis of solar absorption air cooling system for an office building
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.
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 28
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
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 29
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.