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The performance of the system is governed largely by the temperature
difference between the generator and the condenser and absorber units.  Since
the generator temperatures in solar driven systems are only moderate, it is
important to keep the condensor and absorber temperatures as low as possible.
The LiBr system is preferred over ammonia systems for solar energy appli-
cations because of the lower generator temperatures required.  Permissible
generator temperatures for a water-cooled LiBr system range from 170 deg. F
to 210 deg. F (76 deg. C-99 deg. C) compared to the 205 deg. F to 248 deg. F
(95 deg. C-120 deg. C) temperatures required for a water-cooled ammonia
absorption system.  Most, if not all, of the commercially available
absorption units use LiBr and water as the absorbent-refrigerant fluid pair.
Because the LiBr will crystallize at the higher absorber temperatures
associated with air cooling, these units must be water cooled.  A prototype
ammonia-water unit, amenable to direct air cooling, has been built by
Lawrence Berkeley Laboratories.
A number of equipment requirements and limitations must be considered in the
analysis and design of solar powered absorption systems.  The first
consideration involves the type of collector used.  The temperatures required
by absorption coolers are obtainable with flat plate collectors but at low
collection efficiencies.  Collection efficiency is improved with an increased
number of glazings and with a selective surface, therefore, it may be cost
effective to improve the collector rather than to simply oversize.

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