Hour-by-hour simulation of solar H2OLiBr absorption heat transformers in Athens

Abstract

A method is presented for predicting the performance of solar H₂OLiBr absorption heat transformers, which receive solar heat at an intermediate-temperature level, reject a part of it in the ambient at a low-temperature level and deliver the remaining useful heat at a high-temperature level. Simple relations are derived, which define the exact thermodynamic cycle of heat transformer and allow calculation of characteristic temperatures and heat quantities exchanged in terms of the main parameters of the unit. A correlation linking the heat gain factor to the main parameters is presented, which may be used for calculating the optimum cycle. The procedure developed has been employed for predicting the hour-by-hour performance of solar driven absorption heat transformers in the Athens area along a typical year, using mean climatological conditions obtained by processing of 20 years hourly measurements. The theoretical heat gain factor has been found to be practically constant (≅51%) along the typical year. With usual flat plate collectors, the calculated maximum values of the specific heat gain for January, March, May, July, September and November are 79, 143, 232, 247, 185 and 107 W/m²-collector, respectively, obtained at 13 or 14 h under a maximum temperature of about 100°C.