Труды Всемирного конгресса Международного общества солнечной энергии - 2007. Том 2
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Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
762
well as the system parameters collector efficiency curve,
UA-values of heat exchangers and storage tank insulation.
However, with an influence on the solar gain of about 1%
per 1% deviation of sensor value, the influence of the
radiation is twice as high as from all the other values.
Furthermore, investigations regarding the accuracy of the
storage tank initialisation proofed that the energy content of
the tank is the main value to be initialised. It was found that
for tank systems consisting of single tanks with a volume of
1500 litre two temperature sensors (one at each top and
bottom) for each tank are sufficient for a high accuracy of
the initialisation. For systems with solar fractions of up to
50%, an uncertainty of less then 0.05
kWh/m was found
for 90% of the diurnal simulations of the respective
reference year.
Two simulations have been carried out to form the
confidence interval, which is necessary for the comparison
of the actual gain with the desired design gain. For the first
simulations, each parameter has been chosen in a way that
the solar gain is minimal. Similar to this, the second
simulation led to a maximum estimation of the solar gain.
Whether a cross over of the two confidential ranges for
measured and modelled solar gains occurs during an
investigated period is determined automatically. In such a
case, the investigated period can be judged as error-free
considering all uncertainties. Even if failed components
cannot be identified directly with this part of the procedure,
significant system failures are detected reliably. The
proposed simulation based monitoring procedure works
even with lower resolution of input values, e.g. 30-minute
mean values. Thus, it was possible to adapt the procedure
to system data gained within Solarthermie 2000. The
principle of the procedure is demonstrated using measured
data for the solar gain of the solar heating system in
Leipzig (Joh.-R.-Becher-Str.), cf. Fig. 5.
The solid line with the rhombus symbol shows measured
values of the diurnal energy gain determined at the solar
heat exchanger. The dotted lines are forming the
confidential range, within the real values should be located.
The solid line with the round symbol shows the simulated
gain. Again, dotted lines are indicating the confidential
range. During the first half of June, measured and expected
values are matching quite well. In the second half of June,
the measured values are significantly lower than the
expected values, however, on some days both confidential
intervals are crossing each other. In the first half of July,
almost every day is classified as a faulty day. On July, 20th,
air was released from the solar circuit, so that afterwards,
the system was operating again without any problems. The
evaluation of a period of some years demonstrated that
uncertainties of the procedure leads to uncertain results on
days with low irradiation and an expected solar gain of less
than
0.5 kWh/m d . In opposite, a good accuracy of the
proposed procedure was detected for days with high
irradiation and thus days contributing significantly to the
solar gain.
Fig. 5: Results of the simulation based monitoring
procedure of a solar heating system in Leipzig.
4. SUMMARY AND CONCLUSIONS
The developed method for long-term monitoring can be
operated during the whole lifetime of large solar heating
systems and is able to detect nearly all faults and is
furthermore able to even identify several faults. This has
been reached by a combination of two control algorithms, a
“stationary” plausibility check of measured data and system
monitoring based on dynamic simulations. The method has
been tested with measured data of 1-min resolution at two
large solar heating systems in Germany. Data measured in
Solarthermie 2000 are only available as 30-min mean
values. Thus, those data could only be used to test the
system monitoring with dynamic simulations. In all
investigated systems, several minor faults have been
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
763
detected, e.g. controller faults, but also severe breakdowns.
It is noticeable that clogging often led to major solar gain
reductions but did not lead to permanent and complete
system failures. Failures, which occur only under certain
operating conditions, are hardly detectable without an
automated function control.
If logging and transmission of the measured data is not
carried out by a PC but by cheap electronic components,
the overall costs of the long-term monitoring are estimated
to be in the range of 250 to 1000 €/a, which has to be
compared to investments for the solar heating system of for
example 100.000 € resulting in energy gains worth about
10.000 €/a. However, the virtual cost for the long-term
monitoring is even lower, since the method may also
contribute to save other costs for traditional monitoring and
maintenance work.
5. NOMENCLATURE
Q
Heat flow W
ρ Density kg/m
3
c
Specific heat capacity Wh/(kgK)
V
Volume flow l/h
t Time s
T Temperature °C
6. ACKNOWLEDGMENTS
The research was supported by the Rudolf-Otto-Meyer
Umweltstiftung. The authors wish to thank Thomas Freitag
and Jens Göring from the TU Chemnitz as well was Lars
Staudacher from the ZAE Bayern for supplying measured
data.
7. REFERENCES
(1) Altgeld, H., Mahler, M., “Funktionskontrolle bei kleinen
thermischen Solaranlagen ohne Wärmemengenmessung,
Final Report”, Testzentrum Saarbrücken (TZSB),
Saarbrücken, 1999.
(2) Beikircher, Th., Benz, N., Gut, M., Kronthaler, P.,
Oberdorf, C., Schölkopf, W., Drück, H., “A short term
test method for large installed solar thermal systems”,
Proc. ISES Solar World Congress, 4.-9.7.1999,
Jerusalem, 1999.
(3) Keilholz, C., “Vom Gutachten zur Absatzsteigerung –
Wie Defizite helfen können!”, Proceedings 15.
Symposium Thermische Solarenergie, 27.-29.4.2005, S.
266-270, Staffelstein, 2005.
(4) Luboschik, U., Schalajda, P., Halagic, N., Heinzelmann,
P. J., Backes, J., “Garantierte Resultate von ther-
mischen Solaranlagen, Final Report” 1997.
(5) Schwenk, C., Kröger-Vodde, A., Schölkopf, W., “Die
Anwendung des ISTT-Verfahrens zur Erkennung von
Anlagenmängeln”, Proceedings 11. Symposium Ther-
mische Solartechnik, Staffelstein, 2001, S.273-279.
(6) Vanoli, K., Francisco, F., “In-Situ Ertragsüberwachung
thermischer Solaranlagen am Beispiel der ISFH-IOC-
Technologie”, Proceedings 11. Symposium Thermische
Solartechnik, Staffelstein, 9.-11.5.2001, S. 273-279,
2001.
(7) Vogelsanger, P., Haller, M., “Kompakte Kombi-
Solarsysteme auf dem Prüfstand unter Einbezug der
Zusatzheizung”, Proceedings 15. Symposium Ther-
mische Solarenergie, 27.-29.4.2005, Staffelstein, S.
39-43, 2005.
(8) Wiese, F., “Langzeitüberwachung großer solarintegrierter
Wärmeversorgungsanlagen”, Dissertation, Universität
Kassel, 2006. PDF in German at www.upress.uni-
kassel.de.
APPLIED RESEARCH OF A MINIATURE SOLAR POWERED ABSORPTION AIR
CONDITIONING SYSTEM
Wentao Xie
Thermal Technology Institute, College of Power and Energy
Engineering, Harbin Engineering University
Harbin 150001, China
SWC2007China@yahoo.com.cn
Huiling Liu
Best Sea Assembly Institute
College of Automation, Harbin Engineering University
Harbin 150001, China
evelyn.lhl@tom.com
Renqiu Jiang
Thermal Technology Institute, College of Power and
Energy Engineering, Harbin Engineering University
Harbin150001, China
ABSTRACT
This paper makes a study of a miniature solar powered air
conditioning system built on shore for the nuclear
submarine. When the nuclear submarine is at anchor in
shore in summer, the nuclear reactor almost stops working,
and the air conditioning system in the nuclear submarine
mostly (or entirely) stops running which results in not
timely eliminating a mass of waste heat, remaining
humidity and both venomous and nocuous gas in closed
cabins of the nuclear submarine, meanwhile the cabin
environment becomes poor which may cause serious
problems. The novel system is used to improve the cabin
environment. Considering the meteorological factor of the
place where the nuclear submarine stops, the system
employs a flat-plate collector array to drive a single-effect
LiBr-H
2
O absorption chiller. The system is provided with a
partitioned hot water storage tank, an auxiliary oil-fired
boiler, a modular air handling unit, a freshwater-seawater
heat exchanger and an automatic control system.
1. INTRODUCTION
The nuclear submarine cabins environment is a closed area
with many people and complicated equipment. It is
increasingly seriously polluted as other natural environment
or artificial environment, where the pollution sources are so
many and the pollutant is complex. According to a media
report, there are tens of hundreds of gas pollutant in the air
of nuclear submarine cabins, while 368 kinds are detected
in China. Because the air quality in nuclear submarine
cabins directly relates to the combat capability of the
nuclear submarine, navies all over the word attach great
importance to it. The control of nuclear cabins environment
is special and significant, which is always the research
priority for a long time.
Currently, the air handling method of Chinese Navy when
the nuclear submarine stops at the shore is still staying in
the pipeline ventilation which has a series of problems such
as big noise, great electric power consumption, ineffective
purification and dehumidification, poor reliability and so
on.
Consequently, adopting what king of method for efficient,
less energy consumption, lower noise and harmless
processing of air in cabins of the nuclear submarine
which stops at the shore is an urgent problem to be
solved. A miniature solar powered air conditioning
system built on the shore, to control the cabins
environment, is designed in light of the local climatic
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
765
conditions in which the nuclear submarine stops.
Comprehensive analysis of heat load and humid load in
the nuclear submarine proves that the system can purify
the air in the cabins effectively, achieve the purpose of
air conditioning and maintain the necessary thermal and
humid criterion the closed cabins need.
2. ANALYSIS OF THERMAL AND HUMID ENVIRON-
MENT OF CLOSED CABINS IN THE NUCLEAR
SUBMARINE
The space environment in closed cabins of the nuclear
submarine is a place with high temperature (the cabin
temperature reaching 40̚50ć), high humidity (partial
relative humidity reaching 80λ), high noise(local reaching
110dB) and high pollution. If living in this condition for a
long time, the health and the working efficiency will be
severely influenced. When the nuclear submarine is at
anchor in shore in summer, the nuclear reactor almost stops
working, and the air conditioning system in the nuclear
submarine mostly (or entirely) stops running because of no
electricity supply, bringing on the problem that it is inferior
to the time to eliminating a mass of waste heat, remaining
humidity and both venomous and nocuous gas in closed
cabins of the nuclear submarine, which causes the bad
cabins environment. It not only brings difficulties to normal
service and maintenance in the submarine, but also makes
each kind of equipment, apparatus and instruments easily
corrupted, shortening the service life of the nuclear
submarine.
3. MINIATURE SOLA R POWERED ABSORPTION AIR
CONDITIONG SYSTEM BUILT ON SHORE
It is particularly an attractive application for solar energy,
because of the near coincidence of peak cooling loads with
the available solar power in summer. Therefore, adopting
solar energy as the main driven energy to power the
absorption refrigeration system using LiBr-H
2
O as the
working pair is a technology that meets the requirements of
energy conservation and environmental protection. It is a
brand-new attempt to control the thermal and humid
environment of cabins in the nuclear submarine anchoring
in shore.
3.1 System Components
The schematic diagram of a miniature solar powered
absorption air conditioning system built on shore is shown
in Fig. 1 which consists of the following sections:
(1) Solar water heating system, including a high efficient
flat-plate collector array, a partitioned hot water storage
tank, an auxiliary oil-fired boiler, a feed circulating pump
and so on; (2) Absorption refrigeration and air conditioning
system, including a hot water LiBr-H
2
O absorption chiller,
a modular air conditioning unit, an expansion water tank, a
freshwater-seawater heat exchanger, a cooling water
circulating pump, a chilled water circulating pump, a
seawater circulating pump and so on; (3) Automatic control
system, including sensors, electric valves, network control
blocks, operating table and so on.
Fresh
air
Nuclear
submarine
G
C
A
E
AH
Fan-coil unit
Sea
water
Heat
exchanger
Collector
Array
Hot water
Storage tank
Chiller
Expansion
water tank
Freshwater-seawater
heat exchanger
Interface
Static
pressure box
Muffler
A-absorber; G-generator; C-condenser; E-evaporator; AH-Auxiliary heater
Fig. 1: Schematic diagram of a miniature solar powered
absorption air conditioning system built on the
shore.
3.2 Control Strategy
To begin with, solar energy is absorbed by the high
efficient flat-plate collector and accumulated in the hot
water storage tank which is partitioned to serve as two
tanks. In the morning, the collector system is connected to
the upper part of the tank. In the afternoon, the whole tank
is used to provide heat energy to the chiller. The heat
gained is supplied to the generator to boil off water vapor
from a solution of LiBr-H
2
O. The water vapor is cooled
down in the condenser and then passed to the evaporator
wherein it again gets evaporated at low pressure, thereby
providing cooling to the chilled water to be cooled,
producing 7ć chilled water. By the chilled water circulating
Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
766
pump, the chilled water exchanges heat with the fresh air
entering the system in the fan-coil unit which includes
filter-mesh, surface-cooler, electrostatic precipitator and fan
and then provides all the cabins of the nuclear submarine
with the processed air.
Meanwhile, the strong solution leaving the generator to the
absorber passes through a heat exchanger in order to
preheat the weak solution entering the generator. In the
absorber, the strong solution absorbs the water vapor
leaving the evaporator. Cooling water from the
freshwater-seawater heat exchanger removes the heat of
mixing and condensation. An auxiliary heat source is
provided, so that the hot water is supplied to the generator
when solar energy is not sufficient to heat the water to the
required temperature level needed by the generator,
guaranteeing the system to be able to operate 24 hours one
day.
Direct air supply system is used for air conditioning system,
namely all the processed air comes from the outside of the
nuclear submarine, which is provided to the inside of the
nuclear submarine after processing and then discharged. So
the air quality in the cabins of the nuclear submarine is
improved effectively and the necessary thermal and humid
criterion (maintaining the cabin temperature 26.7ć,
relative humidity 60λ)in the closed cabins is maintained.
4. THERMODYNAMIC CALCULATION OF THE
SYSTEM
For simplification and precise calculation, some assum-
ptions on the whole system should be made as follows:
(1) There is no heat loss in flat-plat collector, hot water
storage tank, auxiliary oil-fired boiler, absorption chiller,
freshwater-seawater heat exchanger and all the pipelines.
(2) Neglecting the flow loss in the pipelines and the power
loss of water circulating pumps, each flow rate of hot water,
chilled water, cooling water and sea water is steady.
4.1 The Cooling Load of Air Conditioning System
The place where the nuclear submarine stops: Qingdao.
North latitude: 36.04°, East longitude: 120.20°. The outdoor
air conditioning calculation parameters are in Table 1:
TABLE 1: THE OUTDOOR AIR CONDITIONING
CALCULATION PARAMETERS IN QINGDAO
Season
Ventilation
temperature
Dry bulb
temperature
Wet bulb
temperature
Summer 27ć 29ć 26ć
Winter -1ć -9ć
Season
Relative
humidity
Atmospheric
pressure
Summer 85λ 99720Pa
Winter 64λ 100169Pa
According to the above parameters, checking the h-d chart
to get the humidity of the outdoor air and the enthalpy of
the outdoor air are as follows:
20.06 /
dryair
dgkg
w
= , 80.53 /
wdryair
hkJkg= .
Considering the design temperature and relative humidity
of each cabin of the nuclear submarine, the exit state point
of the fan-coil unit is determined: the exit air temperature is
18
L
t = ć, relative humidity is 95
L
ϕ = λ. The humidity at
the exit of the fan-coil unit is:
0.622
Lqb
out
qb
p
d
pp
ϕ
=
−
i
i
(1)
The enthalpy at the exit of the fan-coil unit is:
1.01 (2500 1.84 )
out L L out
ht td=++ (2)
The cooling load of air conditioning system in summer is:
()
Swout
QGhhρ=−
(3)
In the above three formulas,
p - the local atmospheric
pressure;
qb
p
i
- the pressure of saturated water vapor; ρ -
the density of the air;
G - the flow rate of blasting air of air
conditioning system,
10000G = m
3
/h. According to the
above three formulas, the cooling load of air conditioning
system in summer is gained:
106.22kW
S
Q = .
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
767
4.2 Absorption Refrigeration System
Considering all the factors, a single-effect LiBr-H
2
O
absorption chiller is chosen.
The parameters of it are as follows: the nominal cooling
capacity is:
132.56kW ; the entrance temperature and the
exit temperature of the chilled water are: 12ć and 7ć; the
flow rate of the chilled water is:
22.8 m
3
/h; the entrance
temperature and the exit temperature of the cooling water
are: 31ć and 36.5ć; the flow rate of the cooling water is:
51.3m
3
/h; the entrance temperature and the exit temperature
of the hot water are:95ć and 80ć; the flow rate of the hot
water is:10.9m
3
/h.
The heat balance equation of the absorption refrigeration is:
GE CA
QQ QQ+=+ (4)
The heat removed by the cooling water system
CAP
QQ cmt+= Δ
(5)
The COP of cooling is:
/( )
E
GP
COP Q Q W=+ (6)
In the above three formulas,
G
Q - the heat load of generator;
E
Q - the heat load of evaporator,
E
S
QQ= ;
C
Q - the heat load of condenser;
A
Q - the heat load of absorber;
P
c - the specific heat capacity of cooling water;
m - the flow rate of cooling water;
tΔ - the temperature difference of heat transfer;
P
W - the input power to the pump,
1.8kW
P
W = .
According to the above three formulas, the heat load of
generator and COP of cooling are received:
156.67kW
G
Q = , 0.67COP = .
4.3 Solar Water Heating System
4.3.1 Determination of Collector Area
The solar energy source is abundant in Qingdao because the
annual solar radiation in Qingdao is:
2
5016MJ/m , the
average sunlight time is: 2550.7 hours, and the average
annual solar radiation is:
2
13.74MJ/(m d)i , the solar
absorption refrigeration is strongly recommended.
Suppose that the system working from 8:00 a.m. to 17:00
p.m.. The daily average efficiency of the collector
is:
0.5η = , according to the experimental data.
The daily cooling capacity of the air conditioning system:
3600
dS
QQt=⋅⋅
(7)
The daily theoretical heat load of generator:
'
//
GdEG
QQQQ=
(8)
The daily solar radiation:
'/
RG
IQη=
(9)
The collector area:
/
R
FI I= (10)
In the above four formulas,
t - the daily average working hour,
9th= ;
I – the daily average solar radiation per square meter,
13.74MJ/dI = .
According to the above four formulas, the collector are
obtained:
738.88F = m
2
.
4.3.2 Determination of the Volume of the Hot Water
Storage Tank
The hourly flow rate of hot water:
Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement
768
/' '
hP
qQ ctρ=Δ (11)
The effective volume of the hot water storage tank:
e
Vqt= i (12)
In the above two formulas,
h
Q - the hourly heat consumption, 3600
hG
QQ= i ;
'ρ - the density of the water;
'tΔ - the temperature difference of hot water heat transfer,
'45tΔ= ć.
According to the above two formulas, the effective volume
of the hot water storage tank:
26.99m
e
V = , the design
volume is:
30m . The upper part has one-fourth of the
volume of the entire tank (partitioned mode). It is achieved
by placing two baffle plates in the upper position of the
tank, so that the tank is divided into two parts.
4.3.3 Determination of Auxiliary Heat Source Power
In order to guarantee the air conditioning system to be able
to operate 24 hours one day, the auxiliary conventional
energy system is necessary because the operation of the
solar water heating system will be impact by the climatic
conditions inevitably. An auxiliary oil-fired boiler is
adopted and the power is:
160kWN = , considering the
maximum heat load of the system.
5.
AUTOMATIC CONTROL SYSTEM
The characteristic of solar air conditioning system is using
solar energy to replace some conventional energy sources
to achieve the purpose of refrigeration. So the startup of the
solar system, the storage of solar energy and the switch
between solar energy and conventional energy sources are
very important. In addition, for the partitioned hot water
storage tank, using different parts in different
circumstances automatically is the key to success.
Therefore, designing a safe, reliable and functional
automatic system is terribly necessary.
The automatic control system is composed of sensors,
electric valves, network control blocks, operating table and
so on. The basic steps are: firstly, the operating table (as the
primary PC) issued a directive to each block of secondary
PC, and then each block sends a signal to the implementing
machine. Some of the decision order signals are sent by the
primary PC, others by sensors and delivered to each block,
finally feed back to the primary PC.
6. THE ANALYSIS OF RESULTS AND ECONOMIC
COMPARISION
According to the thermal and humid criterion of the
environment in cabins of the nuclear submarine,
maintaining the cabin temperature 26.7ć, relative
humidity 60λ, and the blasting air temperature 20ć, the
theoretical heat elimination capacity and dehumidification
capacity are respective as follows:
()
N
O
QGhhρ=− (13)
()
N
O
WGddρ=− (14)
In the above two formulas,
N
h - the enthalpy of the air after air conditioning,
60.74 kJ/kgh = ;
N
d - the humidity of the air after air conditioning,
13.22 g/kgd = ;
O
h - the enthalpy of the state point of blasting air,
51.68 kJ/kgh = ;
d - the humidity of the state point of blasting air,
12.48 g/kgd = .
According to the above two formulas, the heat elimination
capacity
30.2 kWQ = and the dehumidification capacity
2.47 g/sW = .
It can be seen from the above calculation that the miniature
solar powered air conditioning system built on the shore is
able to meet the requirements of heat elimination and
dehumidification in cabins of the nuclear submarine. So the
internal environment of the cabins can achieve the designed
requirements.
It should be noted that simple solar air conditioning system
is not economical because the investment of the solar
collector system occupies the major part of the total
investment. But the air conditioning system is used for only
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
769
more than half a year, that is the investment is not fully
utilized. If combined with heat supply, providing hot water
of daily life for the buildings on the shore, the same
investment can bring long-term benefit.
Compared with the traditional method (pipeline ventilation)
when the nuclear submarine stops at the shore, the system
makes full use of the natural conditions in Qingdao,
adopting solar energy, a clean energy, to drive absorption
air conditioning system for air purification in closed cabins
of the nuclear submarine, achieving the required value. In
addition, the system does not destroy ozonosphere and does
not cause greenhouse effect, using solar energy as main
heat source to save the electric power, alleviating the
intense complexion of electricity consumption in summer
and playing a positive role in balancing the season
electricity consumption in cities, bring substantial
economic and social benefits.
7. CONCLUSION
Practice proves that the solar air conditioning system using
solar energy and LiBr-H
2
O absorption chiller is successful.
It is not only a new attempt, but a high practical value new
idea which achieves the expected goal in thermal and
humid environment control of cabins in the nuclear
submarine which stops at the shore.
From the above study the following results can be draw:
(1) Adopting miniature solar absorption air conditioning unit,
coupled with auxiliary energy and automatic control system,
the system is able to effectively purify the air in cabins of the
nuclear submarine. The heat elimination capacity is
30.2 kW and the dehumidification capacity is 2.47g/s .
(2) In solar heating system, the hot water storage tank is
partitioned, which is designed for the system to start up
earlier and quickly in the morning, reducing the heat loss
and improving the system efficiency at the same time.
(3) In summer, the greatest demand for cooling occurs
when the solar radiation is most intense, using this system
both saving energy and protecting the environment can
bring considerable economic and social benefits.
Meanwhile, it is safe because of solar energy utilization and
built on the shore, no need for long-distance transportation,
having high reliability and easy operation and maintenance.
(4) The efficiency of usage and economy and be advanced
if the system provides heating in winter and hot water for
daily life.
8. ACKNOWLEDGMENTS
The first author is grateful to the advisor Prof Renqiu Jiang
who died of cancer this March, for his guiding and
financial support. Without his help, nothing can be done in
this field. Prof Renqiu Jiang will be loved and remembered
for ever. Acknowledgements are also to Huiling Liu, a
member of Best Sea Assembly Institute, for reasonable
advice and technical support.
9. REFERENCES
(1) D. Shi, G. H. Su, Z. Li. The Submarine cabin
pollution control and governance technology. Beijing:
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(2) Z. F. Li, K. Sumathy. “Experimental studies on a solar
powered air conditioning system with partitioned hot
water storage tank”, Solar Energy, May 2001, p.
285-296.
(3) Z. H. Xie, Q. Z. Ye, L. G. Chen, J. Li. “Discussion on
new technologies of air cleaning for cabins in
submarine”, Ship Science and Technology, Jun 2005,
Vol. 27, No. 3, p. 16.
(4) J. H. Li, W. B. Ma, Q. Jiang, Z. C. Huang, W. H.
Xia. “A
100kW Solar Air-conditioning System”, Acta
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239-243.
(5) F. Huang, G. H. Yu. “Application of Small Absorption
Refrigeration Unit Using Solar Energy & Gas on Villa”,
Refrigeration Technology, Jan. 2002, p. 21-23.
(6) Z. N. He, F. Liu, Z. Y. Nan, Y. Liu. “Comprehensive
Solar System for Air Conditioning and Heat Supply”,
Jan. 2002, Vol. 32, p. 1-3.
(7) Y. R. Zhao, C. Y. Fan, D. H. Xue, Y. M. Qian. Air
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(8) X. C. Yang. Refrigeration and Air-conditioning Equip-
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(9) Y. J. Luo, Z. N. He, C. G. Wang. Solar Energy Utilizing
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(10) D. Q. Xue. Solar Cooling Technology. Beijing:
Chemical Industry Press; 2006.
(11) R. Z. Wang, Y. J. Dai. Solar Refrigeration. Beijing:
Chemical Industry Press; 2007.
ABSORBER AND REGENERATOR MODELS FOR LIQUID DESICCANT AIR
CONDITIONING SYSTEMS: VALIDATION AND COMPARISON
USING EXPERIMENTAL DATA
M. Krause
Kassel University, Institute of Thermal Engineering
Kurt-Wolters-Str. 3
34109 Kassel, Germany
mikrause@uni-kassel.de
W. Saman, E. Halawa
Sustainable Energy Centre, University of South Australia
Mawson Lakes Campus,
Mawson Lakes, 5095, Australia
wasim.sama@unisa.edu.au
R. Heinzen, U. Jordan, K. Vajen
Kassel University, Institute of Thermal Engineering
Kurt-Wolters-Str. 3
34109 Kassel, Germany
ABSTRACT
Solar assisted air conditioning systems using liquid
desiccants represent a promising option to decrease high
summer energy demand caused by electrically driven vapor
compression machines. The main components of liquid
desiccant systems are absorbers for dehumidifying and
cooling of supply air and regenerators for concentrating the
desiccant. However, high efficient and validated reliable
components are required and the design and operation have
to be adjusted to each respective building design, location,
and user demand. Simulation tools can help to optimize
component and system design. The present paper presents
new developed numerical models for absorbers and
regenerators, as well as experimental data of a regenerator
prototype. The models have been compared with a
finite-difference method model as well as experimental data.
The data are gained from the regenerator prototype
presented and an absorber presented in the literature.
1. INTRODUCTION
1.1 System Approach
The energy demand for air-conditioning to provide
temperature and humidity control has increased
continuously throughout the last decades and is still rising.
This increase is found both, in commercial and residential
buildings and is largely caused by increased thermal loads,
residents’ comfort demands, and architectural trends. Since
by far most of the air-conditioning systems are electrically
driven vapor compression machines, the increase is
responsible for a large rise in electricity demand and
especially high peak loads. The substitution of these
compression machines by thermally driven cooling systems
using renewable energy or waste heat is a promising
alternative. An overview of different technologies for
thermally driven cooling systems can be found in Afonso
(2006). In particular, due to a high correlation between
solar irradiation and cooling demand for most buildings,
the application of solar energy is very attractive.
Considering all the different technologies, the use of liquid
desiccants in an open cycle system is a promising solution
for solar assisted air-conditioning. The main components of
these systems are absorber, regenerator, indirect and/or
direct evaporative cooling units and heat recovery stages
for both, the desiccant solution and the regeneration air. In
the absorber, a hygroscopic solution, e.g. LiCl or CaCl
2
, is
directly brought in contact with fresh air, which it
3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS
771
dehumidifies. While absorbing the moisture, the concentration
of the hygroscopic solution and thus, its capability to absorb
water, decreases. This requires drying of the solution, which
can be done in a regenerator, where solar thermal energy is
used to drive the process. Solution tanks for concentrated and
weak solutions offer the option to operate the system even at
times when no solar radiation is available.
1.2 Theoretical Background
Many investigations worldwide have been dealing with
modeling and testing of absorber and regenerator designs
and performances. For the absorber, mainly two different
designs to provide the heat and mass transfer area have
been investigated so far:
· Packed-bed designs
· Plate heat exchanger designs
For regenerating the desiccant solution, mainly two more
options have been investigated:
· Multistage boilers
· Collector/regenerator designs
Models for packed-bed absorbers and regenerators with
simultaneous heat and mass transfer in an adiabatic process
have been developed amongst others in Chengqin et al.
(2005). Since flat plate absorbers are usually operated with
much lower solution flow rates compared to packed bed
systems, the absorption process needs to be cooled
internally. Thus, a third fluid has to be considered for flat
plate designs. Khan and Sulsona (1998) developed a model
for parallel plates using NTU relations. Mesquita (2006)
developed a model with variable film thickness.
Models for packed-bed or plate regenerator designs are
usually similar to absorber models, however the operating
temperatures are much higher and thus, the driving forces.
Air collector/regenerator models have been developed for
example by Alizadeh and Saman (2002).
1.3 Experimental Background
Many research groups around the world have been carrying
out experimental investigations on liquid desiccant
components and systems, a few system are close to market
introduction or are even commercially available.
Fundamental research on heat and mass transfer in
packed-bed absorbers and regenerators has been carried out
for example by Liu et al. (2006). Gommed and Grossman
(2007) presented experimental data of a whole liquid
desiccant air conditioning system based on packed-beds.
Biel and Röben (2002) developed a compact system,
incorporating absorber, regenerator, heat recovery and
evaporative cooling in one unit. For both systems, pilot
plants are under investigation. Lävemann and Peltzer (2005)
developed water cooled plate absorbers (and water heated
plate regenerators). A second test system is in operation since
2005. Lowenstein et al. (2006) developed a zero-carry over
plate heat exchanger design using extruded plates. In order to
increase the storage capacity of the desiccant solution,
Kessling et al. (1998) are suggesting to operate the system
with a high concentration step between concentrated and
diluted solution. For both designs, a wicking material, e.g.
cotton or fleece, is attached to the plates to ensure an even
distribution of solution on the plates.
1.4 Current Investigations
In order to find suitable designs of absorber and regenerator
components as well as the control scheme, simulation tools
like TRNSYS can be used. Optimizations of a complete
system have been performed in Krause et al. (2006).
In the present paper, experimental and theoretical
investigations on absorbers and regenerators for liquid
desiccant air conditioning systems are presented.
Numerical models have been developed and two
regenerator prototypes have been constructed and
extensively tested. Test results of the second prototype as
well as test results from literature are used to validate the
numerical models.
2. PROTOTYPE DESIGN
Most solar collectors used for domestic hot water and space
heating are water or water/glycol based. If these collectors
should be used for air conditioning, too, a regenerator is
required, which uses hot water for the regeneration process.
Based on previous approaches for water-cooled absorber
constructions from Lävemann and Peltzer (2005), two
regenerator prototypes designed as plate heat and mass