Crystallization as a limit to develop solar air-cooled LiBr-H2O absorption systems using low-grade heat

In the present work the use of low-temperature solar heat is studied to produce cooling at 5degreesC, using a double-stage LiBr-H2O air-cooled absorption cycle. A solar plant, consisting of flat plate collectors feeding the generators of the absorption machine, has been modeled. Operating conditions of the double-stage absorption machine, integrated in the solar plant without crystallization problems for condensation temperatures up to 53degreesC, are obtained. Results show that about 80degreesC of generation temperature are required in the absorption machine when condensation temperature reach 50degreesC, obtaining a COP equal to 0.38 in the theoretical cycle. A comparative study respect to single-stage absorption cycles is performed. Efficiency gain of the double-stage solar absorption system, over the single-stage one, will increase with higher condensation temperatures and lower solar radiation values. Single-stage cycles cannot operate for condensation temperatures higher than 40degreesC using heat from flat plate collectors. For higher condensation temperatures (45degreesC) the generation temperatures required (105degreesC) are very high and crystallization occurs. Condensation temperatures able to use in double-stage cycles may be increased until 53degreesC using heat from flat plate collectors without reaching crystallization. (C) 2003 Elsevier B.V. All rights reserved.