Thermodynamic study of absorption cycles using low temperature heat sources

In the present work the use of low temperature heat (between 50 degreesC and 90 degreesC) is studied to drive absorption systems in the meteorological conditions of Madrid, where the ambient temperature ranges from -5 degreesC to 42 degreesC. Double stage and triple stage absorption systems, in two different applications: refrigeration and heat pump cycles, are modelled and simulated, allowing a comparison between the absorbent-refrigerant solutions H2O-NH3, LiNO3-NH3 and NaSCN-NH3. The results obtained for the double stage refrigeration cycle show that the LiNO3-NH3 solution operates with a COP of 0.32, the H2O-NH3 pair with a COP of 0.29 and the NaSCN-NH3 solution with a COP of 0.27, evaporating at -15 degreesC and condensing and absorbing at 40 degreesC. The heat supplied to the generators separates the superheated vapour at 90 degreesC. The results are presented for double and triple stage absorption systems with evaporation temperatures ranging between -40 degreesC and 0 degreesC and condensation temperatures ranging from 15 degreesC to 45 degreesC. The results obtained for the double stage heat pump cycle show that the LiNO3-NH3 solution reaches a COP of 1.32, the NaSCN-NH3 pair a COP of 1.30 and the H2O-NH3 mixture a COP of 1.24, condensing and absorbing at 50 degreesC and evaporating at 0 degreesC. The heat supplied to the generators also separates the superheated vapour at 90 degreesC. For the double and triple stage cycles, the results are presented for evaporation temperatures ranging between 0 degreesC and 15 degreesC.