IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask C1 Report, 31 October 2010
The performance of an adsorption chiller depends on the operating conditions. High heat
rejection temperatures reduce the COP and power of the machines. Typical COP values are
around 0.6.
As normally there is no pump within the machine, the operation is almost noiseless. It is
possible to modulate the power within a certain range but this affects the COP. Normally
efficiencies are higher under part load operation.
The main advantages are:
• It is a robust technology with no risk of crystallization, no danger of damage due to
temperatures.
• The materials used today (zeolite, silica gel) are environmentally friendly.
• Very low intrinsic electricity consumption due to the lack of a pump. Electricity is only
required for the switching valves and the control unit.
• Very little moving parts with the potential of low maintenance effort and costs.
• High potential of cost reduction in series production due to the small amount of
individual parts.
The main disadvantages are:
• High requirements of vacuum tightness of the container.
• Slightly lower COP than for comparable absorption technology.
• Cyclic temperature variation in the hydraulic circuits requires careful design of the
external hydraulic circuits.
• Commercially available machines are expensive and only few suppliers on the
market.
3.3 State of the art and present R&D topics
The use of adsorption technology for cooling is a new technology compared to absorption
technology. Thus, a lot of R&D is still going on in the field of material research, heat & mass
transfer and component & machine development.
The next paragraphs describe the resent developments in the field of heat & mass transfer,
working pairs, component development and projects involving state of the art chillers. A good
overview of the techniques is also given in “Klimatisierung, Kühlung und Klimaschutz:
Technologien, Wirtschaftlichkeit und C02 -Reduktionspotentiale: Materialsammlung“ [41] in
German language. For a short English review see Wu et al. [41].
3.3.1 Heat & Mass Transfer
A major focus of research in the field of adsorption chillers is on the topic of heat and mass
transfer. Due to the fact that adsorption chillers are periodic working chillers, the COP is
limited by the sensitive heat capacity of the adsorber. Therefore, the scope of the research is
to reduce the weight of the chillers. This will lead to higher COPs. At the same time also the
size of the chillers is in the focus of scientists. There is an urgent need of smaller and lighter
adsorption chillers and therefore to increasing the specific cooling power per volume or
mass. A good overview about the current state of the art in adsorber development can be
found in Schnabel [47]. Research is now going on in the field of foams and sponges for
compact adsorber development in order to increase the fraction of adsorbent coated
surfaces to the required substrate mass; Bonaccorsi [49], Berg [48].
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