Theoretical and experimental analysis of an absorption chiller

Abstract

A theoretical model for the performance of an absorption chiller has been derived using thermodynamic laws. From the model, a non-dimensional temperature ratio, T ∗ , is proposed. It relates to the water temperatures that are supplied to the condenser and the evaporator of an absorption chiller. The analysis shows that when the inlet water temperatures of the heating and cooling sources are held constant, as required by the standard rating and application rating tests, the ratio of the energy input at the generator to the cooling capacity produced or 1/COP is a linear function of a non-dimensional temperature ratio. An experimental investigation was conducted to validate the theoretical model using a single-stage, water-lithium bromide absorption chiller of 2 t rated capacity. The tests were conducted in a water-cooled chiller testing facility, which does not require any external heating or cooling. Instead, it employs a mixing tank that neutralizes the heating effect of the condenser-absorber with that of the cooling effect of the evaporator, and the remaining excess heat is rejected through a cooling tower. The experimental results and the manufacturer's data for the test unit both indicate a linear relationship for the proposed T ∗ parameter. Such a linear characteristic is valid and practical for a wide range of operating conditions. In the range of interest for the temperatures of heat source and cooling water, the cooling capacities obtained from the test unit are consistently lower than the manufacturer's by about 10–25%.