This document summarizes a paper that examines the viability of solar powered air conditioning systems using absorption refrigeration. It describes the principles of absorption refrigeration, which uses a thermal compressor driven by heat rather than electricity. The document outlines a demonstration solar air conditioning system at the University of Wollongong, which uses solar collectors to power a lithium bromide absorption chiller. It also discusses the potential environmental benefits of replacing conventional air conditioning systems, which produce greenhouse gases, with solar powered absorption systems.

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Successful Strategies for Ecologically
Sustainable Development
Assoc. Prof. M Sivakumar
Dr Judy Messer
Futureworld: National Centre for Appropriate Technology (NCAT) Inc

2. PROCEEDINGS OF THE NATIONAL CONFERENCE ON
SUCCESSFUL STRATEGIES FOR ECOLOGICALLY SUSTAINABLE
DEVELOPMENT
WOLLONGONG, NEW SOUTH WALES, AUSTRALIA
S - 7 DECEMBER 1994
PROTECTING THE
FUTURE:
ESD IN ACTION
Edited by: Assoc Prof M Sivakumar
Dr Judy Messer
FUTUREWORLD:
NATIONAL CENTRE FOR APPROPRIATE TECHNOLOGY (NCAT) INC
MAY 1995

3. Solar Powered Air Conditioning -
Is it a Viable Option ?
Paul Cooper and Antonio Chan
Department of Mechanical Engineering,
University of Wollongong, Northfields Ave,
Wollongong, NSW 2522, Australia
ABSTRACT: Air conditioning of offices and homes in Australia consumes a significant
proportion of our national primary energy and is a major source of ozone depleting gases.
Currently conventional air conditioning systems use vapour-compression refrigeration plant
which requires high grade electrical energy for power to cool the air in a building. However,
there are a number of methods by which air conditioning can be powered using renewable
energy sources and solar radiation in particular. This paper examines the viability of air
conditioning systems powered by solar thermal energy with emphasis placed on the lithium-
bromide absorption refrigeration system which uses environmentally benign working fluids
(i.e. water and lithium-bromide salt).
Here the principles of operation of a solar powered absorption system are described and
details are provided of a system currently in place at the University of Wollongong. The
current and future viability of the technology is briefly discussed in terms of both economics
and environmental impact.
1 INTRODUCTION
There is a world wide recognition that global warming and ozone depletion are critical
environmental problems. CFCs (chlorofluorocarbons) are destroying the ozone layer which
protects life on Earth from damage by UV radiation. Both CFCs and carbon dioxide are held
as contributing to global warming and climate change. One major source of emissions of
both these pollutants is air conditioning systems. Conventional air conditioning systems use
vapour compression refrigeration with CFC or HCFC working fluids to cool the air in a
building. The mechanical energy required to drive the compressor is usually gained from
electric motors and this perhaps is not the most appropriate use of our non-renewable primary
energy resources. ·
One potential means of greatly reducing emissions of CFC's and HCFC's is the
replacement of vapour compression air conditioning systems with systems based on the
absorption refrigeration cycle. In the absorption cycle the conventional mechanical
compressor is replaced by a "thermal compressor", thus, only a very small amount of
mechanical energy is required to drive the system, the majority of the driving energy being
provided by heat. The second advantage then of the absorption air conditioning system is that
it can be driven by a solar thermal collection system eliminating the need for production of
carbon dioxide in the course of the air conditioning process.
Solar powered air conditioning has been considered by many researchers and
manufacturers in the past. Close (1978) and Basu and Cogger (1985) have reviewed the
options available In Australia research projects have been carried out various groups
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including those at the Universities of Queensland and of Western Australia (Langridge and
McCorrnick, 1981 ). There are a number of possible ways in which solar energy may be
harnessed to provide air conditioning. Perhaps the simplest method in concept is to driv t:. the
electric motor of a conventional air conditioning system with photovoltaic cells While
perfectly feasible m principle this system would be enormously expensive due to the larse
area of solar cells required to dnve a relatively modest air conditionrng plant. e
A quite different approach is that where the refngeration system is driven by heat
energy rather than electrical energy as in the case of the absorption refrigeration system.
There are many different types of absorption refrigeration systems available. Many have
been around for a long time such as the "kerosene fridge" or the "gas fridge". In air
conditioning systems today the most widely used absorption system is the Lithium Brornide .
Water system. This uses the most benign working media possible i.e. a salt and water!
We will briefly consider firstly how significant the production of CFC's, HCFC's and
electricity consumption from air conditioning systems is at present. Secondly, a
demonstration solar air conditioning plant at the University of Wollongong is described.
Finally, a case study of the economics of solar powered air conditioning of an office building
is considered.
Considerable attention has been given to our use of CFC's since the Montreal Protocol
and efforts have been made to clearly quantify the amount of CFC's and other halocarbons
that are used in various applications. In Australia in 1992 air conditioning and refrigeration
accounted for the use of approximately 5900 tonnes of CFCs; 63% of the total national usage
(IEAust, 1992). Since that time the refrigeration and air conditioning industry has been
moving toward replacement of CFC's with HCFC's and HFC's with much less ozone
damaging potential. However, HCFC's do still have a significant ozone depleting potential
and they will also have to be phased out in the not too distant future. Indeed, some
refrigeration applications such as water chillers for the cooling systems in large commercial
buildings cannot as yet use HFC's. It is estimated that there are approximately 4000 of these
units in high-rise buildings in Australia alone (IEAust, 1992). Much of the CFC emissions
comes from maintenance operations on these systems when refrigerant may escape,
accidentally or otherwise. Commercial absorption refrigeration machines which have been
available for many years have the potential to replace the great majority of these conventional
chillers resulting in reduced ozone depletion.
From the National Energy Survey for 1986-87 (Australian Bureau of Statistics, 1987)
and the report on Australia's Environment (Australian Bureau of Statistics, 1992) it can be
deduced that approximately I0% of electricity consumption by both industry and domestic
users is employed for air conditioning. This suggests that the total electricity usage for air
conditioning throughout Australia is of the order of 40,000 TeraJoules. Thus. a much wider
use of absorption air conditioning systems powered by heat from solar radiation, or other
industrial sources which might otherwise be simply wasted, has the potential to greatly reduce
the amount of carbon dioxide we release to the atmosphere in Australia.
2 ABSORPTION REFRIGERATION
Absorption refrigeration technology has been around for many years and has found
application in the past in many industries, notably for food preservation. However, the
introduction of CFC refrigerants some forty years ago resulted in a great improvement in the
efficiency of vapour compression refrigeration systems. Absorption refrigeration systems
were then displaced by this technology for most applications.
The absorption refngeration system comprises two media, the refngerant and the
absorbent. There are many possible refrigerant-absorbent pairs. The most common
refrigerant-absorbent pair for air conditioning applications is Lithium Bromide (a hygroscopic
salt) and water A schematic of the basic absorption cycle is shown in figure 1. The cycle is
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5. 327
essentially driven by heat energy which is added at high temperature to the generator. In the
solar powered system hot water from the solar collectors is supplied to the generator.
Cooling of the air from the room is effected by passing "chilled water" through the evaporator
coil of the refrigerator to remove heat and then through a fan coil unit. As with any
refrigeration system the energy from the cooled air and from the driving device (in this case
the heat energy from the collectors) must be rejected to the environment through the
condenser.
Cooling Water
Condenser
Separator
Solar Heated
Hot Water
Evaporator
1
Chilled Water
Cooling Water
Generator
Heat Exchanger Absorber
Figure 1. Schematic of the absorption refrigeration system.
The great environmental benefits of the solar powered absorption system are that there
is a negligible energy use above the energy already available from the immediate
environment and that a minimum of environmentally deleterious materials are used.
3 DEMONSTRATION SOLAR POWERED AIR CONDITIONING SYSTEM
A demonstration solar powered absorption air conditioning system has been
constructed at the University of Wollongong. The purpose of this plant is firstly to publicise
the potential benefits of this type of technology and, secondly, to provide a research facility
for improvement in the design and operation of these systems. A schematic of the system is
shown in Figure 2.
Twelve solar flat-plate collectors; each having an absorber area of 2m2, have been
mounted on a laboratory roof. The heart of the system is a commercially manufacture
absorption chiller designed for servicing the requirements of a domestic dwelling. The unit is
a Yazaki WFCC-400S Lithium Bromide (LiBr-H20) hot water powered absorption chiller
with a nominal cooling capacity of 4.7 kW. [This unit was previously used at the Solar
Energy Research Centre at the University of Queensland and was kindly donated to the
present research project in 1990]. A 350 litre hot water storage tank is used to maintain the
temperature of the supply hot water to the chiller.
The system has only recently been installed and final commissioning is currently in
progress. System performance will be monitored using a computer-based data acquisition
system. Performance of the chiller itself has been checked and found to be close to the
original manufacturer's specification. Since the unit had not been operational for some years
this was a great relief as absorption refrigeration systems can be sensitive to inappropriate
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6. 328
handling and shipment. The most important factor m maintainmg the efficienr-, of the
absorption chiller is maintenance of the vacuum in the unit through removal of non-
condensable gases; that can quickly render an absorption refrigeration machine inoperable
The chiller can operate with generator hot water supply temperature..., of between 75°c
to 95c.c. As the unit is principally for demonstration and research purposes the collector
array is somewhat undersized and auxiliary electrical heating is used to boost the ener£v
collected by the solar array. The performance of absorption system is dorrunated by the
operating temperature of generator. The higher the hot water operating temperature the
higher the COP (coefficient of performance) One of the important research activities in the
future will be to opnrruse the control S) stern for cooling water and generator wate-
temperatures and flows.
FEED&.
EXPANSION
TANK
AIR VENTS
SOLAR COLLECTORS
FAN COIL UNIT
AUXILIARY
IJATER HEATER
12 kw'
350L
HOT IJATER
STORAGE TANK
YA ZAKI
ABSORPTION
CHILLER
CODLING
TDIJER
Figure 2. Schematic of demonstration solar powered absorption
air conditioning system at the University of Wollongong
4 ECONOMICS OF SOLAR POWERED ABSORPTION AIR CONDITIONING
OF A COMMERCIAL BUILDING
Deterrrurung whether a new technology will be economically viable is always
difficult task particularly as unit costs are often unrealistically high in the early development
of the technology. From the outset it should be noted that the solar powered absorption air
conditioning system is not presently a viable alternative to the conventional systems when
viewed purely agamst economic criteria. Here we make a very simple estimate of the
economics of installing a solar powered absorption system in a commercial office building
with a water-cooled air conditioning system. It should be noted that this analysis does not
attempt to optimise the configuration of the solar cooling system vis a vis economic viability
but serves to give the reader an indication of the issues involved. The floor area of the office
is ta.ken as 2700m2 Many of the cost estimates of construction, operation and fuel costs for
such a building are taken from the very useful set of data in the Building Energy Manual
(NSW Public Works, 1993)
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The data relating to design conditions, equipment performance, etc are listed in Table
I. The base case of a conventional air conditioning system is taken as a typical water-cooled
air conditioning system with a reciprocating chiller and cooling tower. The solar case
represents a solar powered absorption air conditioning system with flat plate collectors,
absorption chiller, hot water storage tank and auxiliary heater. The additional cost
implications of the absorption system are the cost of the collectors, solar hot water circuit, the
cost of the absorption chiller over and above that of a conventional chiller and the additional
heat rejection capacity of cooling water tower. Currently very few (if any) absorption chillers
are used in commercial buildings in Australia and are only economically viable if a source of
suitable waste heat is available on site from an industrial process. These units must be
imported from overseas and one of the smallest units available (400kW cooling capacity)
costs of the order of $130,000 compared with just $60,000 for a conventional reciprocating
chiller of the same capacity.
Table 1. Estimate of the present economic viability of solar powered absorption air
conditioning based on current fuel and plant costs
Description Conventional Solar system Remarks
system
Office area (m2) 2700 2700
Max. cooling load (kW) 400 400
Chiller Vapour LiBr-water
compression Absorption
Average COP 2.2 0.58
Fuel cost p.a. $ $12,000 Assuming electricity 16¢/kWh
Fuel cost p.a. $ $6,760 Assuming solar fraction of 0.34
(as Bong et al, 1987) gas as
auxiliarv suonlv 1 ¢/MJ
Estimate of total cost of 350,000 Cost estimate provided by
conventional air con. svstem Southern Air Conditioning
Add. cost-solar collectors --- $800 Assume 5m2/kw (similar to
per kW cooling Bong et al, 1987) costs by
Solarhart™
Add. cost of cooling tower --- $56 Double the capacity of cooling
lper kW cooling tower reauired for solar
Total additional cost per kW --- $856
cooling
Add. cost for absorption --- $70,000 Prices by Trane™ Australia Pty
chiller
Tot. Additional cost for solar --- (856*400 + 70,000)
air conditioning $412,400
Simple payback period 412,400/(12,000-6,760)
78 years!
The data in Table 1 clearly indicates that even a crude estimate shows the economic
feasibility of solar powered absorption refrigeration to be very remote given the current
pricing of equipment and fuels. However, this is not to say that this will always be the case in
the future. It may only be a decade or so before the greenhouse effects on climate preclude
the use of fossil fuels in many applications that are accepted now. Unit costs of both solar
components and absorption refrigeration machines could dramatically fall under high volume
manufacturing regimes.
Furthermore, conventional refrigeration machines face an uncertain future as our
understanding of the importance of ozone depletion mechanisms increases and it is possible
that there may have to be a complete shift away from the use of any type of halocarbon
working fluids for refrigeration purposes.
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5 CONCLUSIONS
So 1s solar air conditioning a viable option? Of course the answer depends on the
critena by which one measures viability.
Technically, solar thermal powered absorption air conditioning is a viable technolooy
that has been proven in the past by several researchers using the technology on
demonstration scale.
From the environmental point of view the lithium-bromide absorption solar air
conditiorung system is not only viable but is greatly superior to conventional air conditioning
systems. It not only uses renewable energy as a source of power but employs
environmentally benign working fluids. As with any solar thermal system non-renewable
auxiliary backup energy is used to maximise the economic viability of the system. However,
use of the technology has the potential to substantially reduce greenhouse gas enussions and
to eliminate the release of ozone depleting refrigeration working fluids.
Economically, however, this type of system is currently not viable when compared to
the installation and operating costs of conventional systems. Nonetheless, it is essential that
non-conventional energy systems continue to be developed and demonstrated to ensure that
the community is aware of the non-polluting alternatives that exist and may be yet further
developed in the future.
6 ACKNOWLEDGMENT
The authors wish to thank both the Environmental Research Institute and the
Department of Mechanical Engineering of the University of Wollongong for financial and
technical support of the solar air conditioning project. We would also like to thank the
Department of Mechanical Engineering, University of Queensland for donation of the Yasaki
chiller.
7 REFERENCES
Australian Bureau of Statistics (1987) National energy survey (energy consumption in
industry, Australia) 1986-87.
Basu, R. N. and Cogger, L. L. (1985) Cooling by Solar Energy, Australian Refrigeration Air
Conditioning and Heating, Feb. 1985, pp26-33.
Bong, T. Y., Ng, K. C. and Tay, A. 0. (1987) Performance of a solar-powered air
conditioning system, Solar energy, Vol. 39, pp 173-182.
Close, D. J. (1978) Building Heating and Cooling Systems, Search, V 9, No. 4, pp138-143.
IEAust ( 1992) Mixed response to CFC phaseout, Engineers Australia, Journal of the
Institution ofEngineers Australia, Nov. 1992.
Langridge, D. and McCormick, P. G. (1981) Solar air conditioning using concentrating
collectors, Proc. !SES meeting, Brighton, UK, pp 554-561.
NSW Pubhc Works (1993) Building Energy Manual.
Yazak.i water fired absorption chiller: Technical manual, Yazaki Corporation, 1975.
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Author index
Adorni-Braccessi, G. 449 Izmir, G. 417 Seidlich, B. 357
Alla, P. 249 Snashall, D. 437
Anselme, C. 261 James, K. 437 Sperling, K. 475
Audie, J.M. 261 Jeans, P.E. 23 Swarbrick, G.W. 311
Johnson, M.K. 339 Sweatman, A. 429
Beder, S. 119 Johnston, K. 385
Birkeland, J. 397 Taylor, J. 273
Bishop, R.J. 311 Kanako, M.K. 373 Thomas, C. 175
Katsof, E. 33 Thwaites, R. 221
Caines, G. 383 Keating, P. 3 Trainer, T. 87
Cairnes, L. 165 Turner, A. 93
Caswell,T. 435 Laird, P.G. 449 Turpin, T. 141
Chan, A. 325 Lambropoulos, N. 311
Clarke, B. 311 Lawson, B. 313 Usback, R.G. 339
Clarke, G. 363 Lefevre, F. 261
Cooper, P. 325 Lofthouse, A. 385 van der Broek, B. 311
Craik, W. 127 Loken, S. 43 Verhey, R. 199
Cullen, P. 7 Lovins, A. 45
Wadhwa, L.C. 103
Denlay, J. 303 McCotter, B. 437 Watkinson, P. 221
Deville, A. 141 McDonald, R. 193 Wescott, W. 201
Dunstan, C. 331 McKelvey, M. 243 Whitaker, 0. 381
McLaren,N. 423 White, S. 279
Evans, R. 383 Winterbottom, D. 207
Mandra, V. 261 Woods, P. 113
Falk, J. 13 Mills, T. 391
Ferry,B. 423 Mowbray, P. 461
Figgis, P.J. 231 Munro, D.A. 49
Fritz, S. 251
Fry, T. 403 Newman, P. 59
Galloway, D. 213 Okraglik, H. 77
Gayler, D. 411
Gertsakis, J. 77 Partridge, H. 313
Goldie, J. 153
Greene, D. 159 Radovic, D. 467
Rathur, A.Q. 287
Haggen, K. 311 Reeve, D. 81
Hales, R. 319 Reynolds, C.W. 339
Hall, C. 165 Rismiller, P. 243
Hart, K. 311 Rolls, E. 485
Hindmarsh, M. 257 Rosier, P. 349
Hunt, C. 183 Rudolph, V. 311

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