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The optimum instantaneous driving temperature of a solar cooling facility is determined along a day. The chillers compared use single effect cycles working with NH3/LiNO3, either conventional or hybridised by incorporating a low pressure booster compressor. Their performances are compared with a H2O/LiBr single effect absorption chiller as part of the same solar system. The results of a detailed thermodynamic cycle for the absorption chillers allow synthesizing them in a modified characteristic temperature difference model. The day accumulated solar cold production is determined using this optimum temperature during two sunny days in mid-July and mid-September, located in Madrid, Spain. The work shows the influences of operational variables and a striking result: selection of a time-constant temperature during all the day does not necessarily imply a substantial loss, being the temperature chosen a key parameter. The results indicate that the NH3/LiNO3 option with no boosting offers a smaller production above-zero Celsius degrees temperatures, but does not require higher hot water driving temperatures than H2O/LiBr. The boosted cycle offers superior performance. Some operational details are discussed.
solar cooling; optimum hot water temperature; hybrid cycle; chillers; nh3/lino3; h2o/libr