IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C1 Report, 31 October 2010
2.10.4 Conclusions
Today’s technology for thermally-driven domestic air-conditioning cannot compete with the
cooling capacity of electric-powered air-cooled mechanical compression systems. Solar
cooling systems use renewable energy, with a concomitant savings in fossil fuel. The initial
investment is sizeable, however, while renewable energy is not always able to cover a
building’s total demand and the power consumed by the ancillary equipment is excessive. As
a result, cooling costs are higher than with the conventional system. Nonetheless, inasmuch
as these technologies are environmentally friendly, a research effort should be made to solve
the problems associated with their current state of development. Against this backdrop, the
Subproject SP3, "Sustainable power generation in homes", part of a broader INVISO Project,
proposes to modernize absorption cooling technology as a first move toward the
development of viable solar-powered cooling systems, or systems fired by renewable energy
in general, including waste heat.
The first step was to design and build a new adiabatic absorber that increases the mass
transfer coefficient of falling film absorbers 18-fold and the Warnakulasuriya and Worek
apparatus (an improved version of the Ryan absorber) five-fold. This absorber was then built
into a prototype for an air-cooled, direct-fired, lithium bromide double effect absorption chiller
of 7 kW nominal cooling capacity that has been experimentally proven to be competitive with
the air-cooled mechanical compression chillers used for domestic air-conditioning. A second
prototype was also developed, consisting of a similarly air-cooled, combination single-double
effect chiller. In this prototype the heat from a renewable (solar) source or waste heat is
supplied to the single-effect chiller. When this heat source is depleted, double-effect, fossil
fuel-fired operation is enabled. The high efficiency of this facility reduces cooling costs. The
prototype can also operate simultaneously as a single and double effect chiller, for the two
share essential components such as the absorber, condenser, evaporator, pumps and so on.
The research group presently plans to experiment with this mode of operation. The
experimental results set out above show that lithium bromide solutions are effective in very
high outdoor temperatures, up to 44 ºC, at which temperature they do not crystallize.
The conclusions that can be drawn from these results are:
Air-cooled, natural gas-fired double-effect facilities can compete with electric-powered aircooled
mechanical compression chillers.
Single-double-effect chillers fired by waste heat from trigeneration systems are
competitive with mechanical compression chillers.
Integrated in a solar heating-cooling system, the present single-double effect chiller can
significantly reduce cooling costs and is coming closer to being competitive with electric
chillers.
2.10.5 Future Work
The group’s future research will aim to:
Reduce the cost of collector fields, increasing their performance to reduce the area
needed and raising energy generation.
Reduce the cost of auxiliary equipmentet used by absorption machines.
Increase absorption chiller efficiency.
2.10.6 Acknowledgements
This research was funded by Spain's Ministry of Science and Innovation under the following
projects: DPI 2002-02439; ENE 2005-08255-CO2-01 and the Subprogram SP3 of PSE
INVISO. The authors wish to thank Emilio Martin, R&D Technician, for his enthusiastic
contribution to this study.
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