THERMOECONOMIC OPTIMIZATION OF VAPOUR ABSORPTION SYSTEMS

Abstract

In recent times, the vapour absorption refrigeration (VAR) systems are regaining importance mainly because; these systems use environment friendly working fluids and are driven by low-grade energy sources. These systems can also be driven by waste heat and renewable energy, like, solar energy. Moreover, these systems are attractive in terms of total energy utilization. The demand for building cooling is a major contributor to the peak demand for electricity during summer peak periods. It will be economical to reduce this peak demand by using heat-operated VAR systems rather than constructing new power plants. However, due to their lower efficiency and higher cost, the VAR systems have been preferred less compared to their vapour compression counterpart. Thus, the VAR systems need effective design and optimization to reduce the product (cooling effect) cost and to raise the exergetic efficiency. In recent years, there has been a growing interest in using the exergy analysis (i.e. Second Law analysis) in analyzing thermal systems, as it provides information about the losses qualitatively as well as quantitatively along with their location. Thermodynamic optimization (based on Second Law of Thermodynamics) shows improvement in thermodynamic performance of a system by improving its exergetic efficiency. This improvement, however, is accompanied by an increase in capital investment of the system. Hence, thermal systems should be optimized from both thermodynamic and economic points of view. In this regard, thermoeconomic optimization is a better tool as it combines the thermodynamic analysis with the economic principles. Since exergy gives a clear picture about the losses of a system, it is rational to use exergy in the thermoeconomics. Here, appropriate costs are assigned to the thermodynamic inefficiencies of the system components through some meaningful fuel-product definitions. The overall objective function for the system is defined as to minimize the sum of fuel cost and investment costs.