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Proceedings of the
International Conference on Mechanical Engineering 2011
(ICME2011) 18-20 December 2011, Dhaka, Bangladesh
ICME11-RE-014
© ICME2011 1 RE-014
1. INTRODUCTION
The increased use of the vapor compressor driven
refrigeration devices made us more dependent on the
primary energy resources. As the primary energy once
used up cannot be used in the same form again, therefore,
it is necessary to reduce the consumption of these
resources and introduce renewable energy for the
sustainable development in the global energy sector.
Furthermore, in the late 1980s, chlorofluorocarbons were
found to be contributing to the destruction of earth’s
protective ozone layer. Therefore, the production of these
chemicals was phased out and the search for a
replacement began. Thermally driven, sorption
technology is one of the possible alternatives. At present,
absorption (liquid vapor) cycle is most promising
technology. Nevertheless, adsorption (solid vapor) cycle
have a distinct advantage over other systems in their
ability to be driven by heat of relatively low,
near-environmental temperatures, so that the heat source,
such that waste heat or solar heat, below 100 C can be
recovered. Kashiwagi et al. [1], in determination of
conservation of heat energy, carried out investigation on
heat driven sorption and refrigeration system.
For the last three decades investigations have been
carried out both mathematically and experimentally
about different features of this system. It is well known
that the performance of adsorption cooling / heating
system is lower than that of other heat driven cooling/
heating systems. Different choices of
adsorbate/adsorbent pairs have been investigated to
study about the optimum driving heat source. Zeolite -
water pair studied by Rothmeyer et al. [2], Tchernev and
Emerson [3] and Guilleminot and Meunier [4]. In these
studies the driving heat source was reported as 200 C. In
the study of Critoph [5] a lower heat source temperature
was observed, i.e. over 150 C with activated carbon –
ammonia pair. The use of driving heat source with
temperatures of less than 100 C was reported in the study
of basic adsorption cycle with silica gel – water pair
investigated by Saha et al. [6] and Chua et al. [7]. Later,
Saha et al. [8,9] and Alam et al.[10] showed that even
less than 70 C heat source can be utilized by employing
the advanced multi-stage cycle.
For the effective utilization of low temperature solar
thermal energy, Sakoda and Suzuki [11] studied the
simultaneous transport of heat and adsorbate in closed
type adsorption cooling system. Li and Wang [12]
investigated the effect of collector parameters on the
performance of solar driven adsorption refrigeration
cycle. Later, Yong and Sumathy [13] applied lumped
parameter model for two bed adsorption refrigeration
cycle with direct coupling of solar collector.
Clausse et al. [14] considered the models of whole
units of a residential air conditioning sytem to investigate
the performances of the system for the climatic condition
of Orly, France. Recently, Alam et al. [15] studied the
silica-gel water adsorption cooling cycle with direct
coupling of solar collector under the climatic condition
of Tokyo.
The article investigates a similar approach for the
climatic condition of Dhaka, located in the northern
hemisphere at
6423
N (latitude), and
3290
E
ABSTRACT
An analytic investigation on the prospect of solar cooling for the climatic condition of Dhaka is presented.
The simulation is done based on the area of the solar radiation collector and cycle time of the adsorption
cooling unit. It is found that 14 CPC collectors each of area 2.42m² is required to run the system with base
run conditions. It is seen that the optimum cycle time need to be adjusted according to the seasonal change
for best possible performance. It is seen that maximum 11 kW (around 3RT) cooling capacity is achievable
during hot and humid seasons with base run condition. Based on this motive mathematical analysis is
revealed for a number of months during the hot season of Dhaka station (Latitude
6423
N, Longitude
3290
E). It may be concluded that better performance is possible by decreasing the number of collectors
and adjusting optimum cycle time.
Keywords: Solar Cooling, Adsorption Cooling, Renewable Energy.
PROSPECT OF SOLAR COOLING BASED ON THE CLIMATIC
CONDITION OF DHAKA
R. A. Rouf1, K. C. A. Alam2, M. A. H. Khan3 and T. Ashrafee1
1School of Engineering and Computer Science, Independent University, Bangladesh, Dhaka, Bangladesh,
2Department of Electronics and Communication Engineering, East-West University, Dhaka, Bangladesh,
3Department of Mathematics, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh.
© ICME2011 RE-014
2
(longitude). In the present study the performance of a two
bed adsorption cooling system which is run by solar
collector, with silica gel-water pair as adsorbent/
adsorbate, is analyzed mathematically for several months
of hot seasons, namely summer and autumn.
2. PRINCIPLE AND OPERATIONAL PROCESS
OF THE SYSTEM
A two- bed conventional adsorption cooling cycle
driven by solar heat has been considered. Silica gel-water
pair as adsorbent/ adsorbate is well examined for
air-conditioning process driven by low temperature(less
than 100
C) heat source. There are four
thermodynamics steps in the cycle, namely, (i)
Pre-cooling (ii) Adsorption/Evaporation (iii) Pre-heating
and (iv) Desorption-condensation process. No heat
recovery or mass recovery process is considered in the
present study. The adsorber (A1/A2) alternatively
connected to the soar collector to heat up the bed during
preheating and desorption-condensation process and to
the cooling tower to cool down the bed during
pre-cooling and adsorption-evaporation process. The
heat transfer fluid from the solar collector goes to the
desorber and returns the collector to gain heat from the
collector. The valve between adsorber and evaporator
and the valve between desorber and condenser are closed
during pre-cooling/pre-heating period. While these are
open during adsorption-evaporation and
desorption-condensation process. The schematic of the
adsorption cooling with solar collector panel is presented
in Figure 1. The characteristics of adsorbent/adsorbate
(silica gel-water) are utilized to produce useful cooling
effect run by solar powered adsorption chiller. The
chilled water delivered from the evaporator cools the
floor of the house.
Fig 1. Schematic of the solar driven adsorption space
cooling system.
2.1 Mathematical Model
It is assumed that the temperature, pressure and
concentration throughout the adsorbent bed are uniform.
Based on these assumptions the energy balance equation
of the adsorbent bed is represented by
( )
++
=++
out,bed
T
in,bed
T
f
C
f
m
bed
T
eva
T
dt
dq
sv
C
s
W
dt
dq
s
WQst
bed
T
sw
qC
s
W
s
C
s
W
pM
C
M
W
dt
d
(1)
)/()
,
(
,f
C
f
m
bed
UAEXP
bed
T
inbed
T
bed
T
outbed
T
(2)
where, equals to zero or one depending whether
adsorbent bed is working as desorber or adsorber.
The energy balance for the condenser is represented
by
( )
++
=+
out,con
T
in,con
T
f
C
con,f
m
bed
T
con
T
dtd
dq
v,r
C
s
W
dtd
dq
con
WL
con
T
r
C
r,con
W
M,con
C
M,con
W
dt
d
(3)
)
,
/()
,
(
,f
C
conf
m
con
UAEXP
con
T
incon
T
con
T
outcon
T
(4)
Energy balance for the evaporator is
( )
++
=+
out,chill
T
in,chill
T
f
C
chill,f
m
con
T
eva
T
dtd
dq
l,r
C
s
W
dta
dq
s
WL
eva
T
ml
C
r,eva
W
M,eva
C
M,eva
W
dt
d
(5)
)
,
/()
,
(
,f
C
chillf
m
eva
UAEXP
eva
T
inchill
T
eva
T
outchill
T
(6)
The mass balance of the refrigerant inside the
evaporator is expressed as
dt
d
dq
dta
dq
s
W
dt
reva
dW ,
(7)
The concentration in bed is
*
dq kasp q q
dt
(8)
where,
.exp .
s a gas
kasp D E R T
2
0
15.
s s p
D D R
,
*.BB
s v s b
q AA P T P T
23
0 1 2 3
AA A AT A T A T
23
0 1 2 3
BB B BT B T B T
The saturation pressure is calculated according to the
Antonie’s equation, as Saha et al [8], where the values of
i
A
’s and
i
B
’s will also be found.
The energy balance for the each collector can be
expressed as:
A1
A2
CPC
Solar
Collector
Qsolar
Condenser
Evaporator
Cooling
tower
Chilled
water
© ICME2011 RE-014
3
( )
out,i,crin,i,crfcr,fi,cri
i,cr
i,CrM TTCmIA
dt
dT
W
+=
(9)
f
crf
icpicp
icrinicricrouticr Cm AU
EXPTTTT
,
,,
,,,,,, )(
(10)
Where, i=1,number of pipe in a collector
The collector efficiency equation is considered to be
same as Alam et al [15].
The cyclic average cooling capacity is calculated by the
equation
, , ,
endofcycletime
chill chill f chill in chill out cycle
beginofcycletime
CACC m C T T dt t
(11)
The cycle
COP
(coefficient of performance) and
solar
COP
in a cycle (
sc
COP
) are calculated respectively
by the equations
, , ,
,,
endofcycletime
chill chill f chill in chill out
beginofcycletime
cycle endofcycletime
f f d in d out
beginofcycletime
m C T T dt
COP
m C T T dt
(12)
,,
.
endofcycletime
chill chill chill in chill out
beginofcycletime
sc endofcycletime
cr
beginofcycletime
m C T T dt
COP
n A Idt
(13)
2.2 Simulation Procedure
Measured monthly maximum radiation data for
Dhaka (Latitude
6423
N, Longitude
3290
E) has been
used. This data is supported by the Renewable Energy
Research Center (RERC), University of Dhaka. Results
are generated based on solar data of Dhaka on a number
of months during the summer and autumn seasons.
Chiller configurations are same as Saha et al [8] and
collector data are same as Alam et al [15]. During hot
seasons in Dhaka, the sunrise time is at 5.5h and sun set
at 18.5h, whereas maximum temperature varies between
30°C to 34ºC and minimum temperature varies between
20°C to 26ºC during this period. The maximum solar
radiation, in the considered period of the year, for Dhaka
station, varies between 980 W/m
2
to 1100 W/m
2
. The
input data are given in Table 1.
Implicit finite difference approximation method is
applied to solve the set of differential Equations. The
water vapor concentration in a bed is represented in Eq. 8.
Where, the concentration q is a nonlinear function of
pressure and temperature. It is almost unfeasible to
divide the concentration in terms of temperature for the
present time and previous time. Hence, to begin with, the
temperature for present step (beginning of the first day)
is based on assumption. The pressure and concentration
is then calculated for the present step based on this
assumption of temperature. Later, gradually the
consequent steps are calculated based on the primary
concentration with the help of the finite difference
approximation. During this process, the newly
calculated temperature is checked with the assumed
temperature if the difference is not less than convergence
criteria, then a new assumption is made. Once the
convergence criteria fulfilled, the process goes for the
next time step. The tolerance for all the convergence
criteria is 10
4
. The program runs for consecutive
several days (as it is set). After a few days the system
appears to its steady state. In this paper all results are
presented for the 3rd day, since the system reached to its
steady state condition from day 3 i.e. all output appeared
to be identical for the consecutive days. The design and
the operating conditions used in the simulation are
illustrated in Alam et al. [15]. The nomenclature is
attached in appendix.
3. RESULT AND DISCUSSION
14 collectors each are of 2.42m2 has been taken into
consideration for the present analysis. The number of
collectors has been decided through the simulation data.
The program is allowed to run with various numbers of
collectors and different cycle time for several months
during hot and summer season. First the driving
temperature level which is reported as below 90 ºC for
silica-gel water pair(Saha et al.[6] and Chua et al.[7]) is
checked, then the performances has been checked. For
the present case 14 collectors is the best option for which
the performances do not affect too much and driving heat
source temperature level can be controlled by adjusting
the cycle time. Figure 2 presents a comparison between
simulated and measured data of radiation for the months
of March and August. It is seen that the model for the
radiation shows a good agreement with measured data
for March. The deviation seen in the model and
Fig 2. Solar radiation data for the months of March and
August.
measured data for August is due to cloud coverage.
Figure 3 illustrates the temperature histories of the
© ICME2011 RE-014
4
collector outlet and bed temperature. It is seen that the
bed temperatures are within the range of the temperature
of driving heat source temperature, that is, below 90 ºC.
It could be also observed that the half cycle time (heating
or cooling) 1000s is required for March while 800s is
required for August to reach the same temperature level.
This is due to the solar radiation as solar radiation of
August is higher than that of March. It can be also
claimed that the number of collector can be reduced by
adjusting the cycle time; however, excessive long or
shorter cycle may affect the performance of the system.
Therefore, it is essential to choose appropriate cycle
time.
Figure 4 shows the performance of the chiller for
different months and their optimum cycle time. It can be
seen that almost same amount of cooling capacities for
different months are achievable with different cycle
times. It is also seen that cyclic average cooling capacity
(
CACC
) of August is slightly higher than that of other
months. This is due to the higher solar radiation in
August. It is also observed that the values of cycle
COP
for different months are also almost same though there
are some little variation in late afternoon. For all cases
cycle COP increases steadily up to late afternoon.
Fig 3. Temperature profile of the heat exchangers for the
months of March and August
The increase of COP at after noon happens due to the
inertia of collector materials. In afternoon, there is less
heat input but due to the inertia of materials, of collector,
there is slow increase of COP. However, it starts
declining suddenly when the radiation is too low to heat
up the heat transfer fluid. A sudden rise of cycle COP is
observed for the month of March at late afternoon. This
happens due to the excessive long cycle time comparing
with low radiation at afternoon. Due to the long cycle
time at afternoon, there were some cooling production at
the beginning of that cycle but there is a very less heat
input in whole cycle time. If one takes variation in cycle
time for the different cycle in the whole day then this
behavior will not be observed. For solar COP almost
same observation was found as for the cycle COP.
Fig 4. Comparative Performances of the
chiller for different months
The maximum 0.34 solar COP is achievable with the
proposed system in the region of Dhaka.
In air conditioning system, CACC and COP are not
the only measurement of performances. If those values
are higher but there is relatively higher temperature
chilled water outlet, then the system may not provide
comfortable temperature to the end user. From this
context, the chilled water outlet temperatures for
different months are presented in Fig.5. It can be seen
that the chilled water outlet temperature varies from 8 ºC
to 12.5 ºC for the month of March and it is from 7.5 ºC to
11.5 ºC for the month of August. It is well known that the
less the fluctuation of chilled water temperature the
better the performance of the system. However, the
chilled water outlet temperature can be controlled by
adjusting the flow rate of chilled water which can be the
future work to analyze.
© ICME2011 RE-014
5
Fig 5. Chilled water outlet temperature for the month
of March and August
4. CONCLUSION
An analytical investigation has been conducted to
examine the prospect of solar driven adsorption
air-condition system in Dhaka. A mathematical model is
employed to investigate the performances of adsorption
cooling system driven by solar collector for the climatic
condition of Dhaka. 14 collectors each of area 2.42 m2
can be installed to get desirable performance of the
adsorption chiller with base run condition. For the two
consecutive hot and humid seasons i.e. summer (which
starts from April) and the autumn (which ends at
September) seasons have been taken into consideration
for the present analysis. It is found that 800s to 1000s
cycle time is required during hot and humid seasons to
get the optimum performance. The chiller is capable of
producing 11 kW (3 RT) cooling during this hot period of
the year. Also it is noticeable that, the increase in the
cycle time increases the temperature of the silica gel bed.
Therefore, it may be concluded that better performance is
possible by decreasing the number of collectors and
adjusting optimum cycle time.
5. REFERENCES
1. Kashiwagi, T., Akisawa, A., yoshida, S., Alam, K.
C. A., Hamamoto, Y., 2002, “Heat Driven Sorption
Refrigerating and Air Conditioning Cycle in Japan”,
Proc. of Int. sorption heat pump conf., September
24-27, Shanghai, China, pp 50- 62.
2. Rothmeyer, M., Maier-Luxhuber, P., Alefeld, G.,
1983, “Design and Performance of Zeolite-Water
Heat Pumps” , Proc. of IIR-XVIth Int. congress of
Refrigeration; Paris, pp 701-706.
3. Tchernev, D. I., Emerson, D. T., 1988, “High
–Efficiency Regenerative Zeolite Heat Pump”,
ASHRAE Trans 94 (2), pp 2024-2032.
4. Guilleminot, J. J., F. Meunier, F., 1981, “Etude
Experimental D’une Glaciere Solaire Utilisant Le
Cycle Zeolithe 13X-eau” , Rev Gen Therm Fr 239,
pp 825-834.
5. Critoph, R. E., “Forced Convection Adsorption
Cycles” , 1998, Appl Thermal Eng 18, pp 799-807.
6. Saha, B. B., Boelman, E. C., Kashiwagi, T.,
“Computer Simulation of a Silica gel-water
Adsorption Refrigeration Cycle – The Influence of
Operating Conditions on Cooling Output and COP” ,
1995, ASHREA Trans Res 101 (2), pp 348-355.
7. Chua, H. T., Ng, K. C., Malek, A., Kashiwagi, T.,
Akisawa, A., Saha, B. B., “Modeling the
Performance of Two-bed, Silica gel-water
Adsorption Chillers” , 1999, Int J. Refrigeration 22,
pp 194-204.
8. Saha, B. B., Boelman, E. C., Kashiwagi, T.,
“Computational Analysis of an Advanced
Adsorption Refrigeration Cycle” , 1995, Energy 20
(10), pp 983-994.
9. Saha, B. B., Alam, K. C. A., Akisawa, A., Kashiwagi,
T., Ng, K. C., Chua, H. T., “Two Stage
Non-regenerative Silica gel-water Adsorption
Refrigeration Cycle” ,2000, Proc. of ASME
Advanced Energy System Division, Orland, pp 65-78.
10. Alam K. C. A., Saha B. B., Akisawa A., Kashiwagi
T., “Influence of Design and Operating Conditions
on the System Performances of a Two-stage
Adsorption Chiller” , 2004, Chemical Eng
Communication, vol 191 (7), pp 981–997.
11. Sakoda, A., Suzuki, M., “Simultaneous Transport Of
Heat And Adsorbate In Closed Type Adsorption
Cooling System Utilizing Solar Heat” , 1986,
Journal of Solar Energy Engineering, vol. 108, pp.
239-245.
12. Li, M., Wang, R. Z., “A Study of the Effects of
Collector and Environment Parameters on the
Performance of a Solar Powered Solid Adsorption
Refrigerator”, 2002, Renewable Energy, vol. 27 (3),
pp. 369-382.
13. Yong, L., Sumathy, K., “Modeling and Simulation of
A Solar Powered Two Bed Adsorption Air
Conditioning System”, 2004, Energy Conversion
and Management, vol. 45 (17), pp. 2761-2775.
14. Clausse, M., Alam, K. C. A., Meunier, F.,
“Residential Air Conditioning And Heating By
Means Of Enhanced Solar Collectors Coupled To An
Adsorption System”, 2008, Solar Energy, vol. 82
(10), pp. 885-892.
15. Alam, K. C. A., Saha, B. B. and Akisawa, A.,
“Adsorption Cooling Driven by Solar Collector: A
© ICME2011 RE-014
6
Case Study for Tokyo Solar Data” 2011, Applied
Thermal Engineering,. (in Press)
7. NOMENCLATURE
Symbol
Meaning
Unit
p
c
specific heat
kgKJ /
I
m
Qst
L
M
q
t
T
U
V
W
solar radiation
mass flowrate
heat of adsorption
latent heat of vaporization
mass
adsorption capacity
time
temperature
heat transfer coefficient
volume flowrate
lumped capacitance
2
/mW
skg/
kgJ/
kgJ/
kg
ac
kgkg/
S
K
KmW 2
/
sm /
3
KJ /
8. SUBSCRIPTS
Symbol
Meaning
a
adsorber
s
amb
cd
CW
d
ev
floor
fresh
HW
Indoor
w
MW
sc
Silica gel
Ambient
Condenser
Chilled water
Desorber
evaporator
floor
fresh air
hot water
indoor
water
cooled water
solar collector
9. MAILING ADDRESS
R. A. Rouf
School of Engineering and Computer Science,
Independent University, Bangladesh, Dhaka, Bangladesh.
E-mail: rifat_rouf@yahoo.com,
