The influence of the overall heat transfer coefficients in the dynamic behavior of a single effect absorption chiller using the pair LiBr/H2O

Absorption systems offer an alternative way to substitute energy economically in mechanical compression systems in the field of refrigeration and air conditioning. The aim of this article is to investigate the transient performance of a single effect absorption chiller using the pair LiBr/H2O when the overall heat transfer coefficients are varied in time by updating the thermo-physical properties and convective coefficients. A thermodynamic model was developed based on conserving mass and energy and considers, so as to determine the overall heat transfer coefficients of the heat exchangers of a chiller and the correlations of the convective coefficients of the processes of refrigeration by absorption (desorption, absorption, condensation and evaporation). This model when tested for real operating conditions and considering the overall coefficients of heat transfer were constant throughout the process showed relative errors were less than 15% in the chilled water circuit and under 2% in cold water. This difference drops significantly when the variable overall coefficients are considered throughout the process, these errors being approximately 5% and 0.3%, there being a percentage fall in all water circuits.