Advanced modular simulation of open absorption systems

Open-cycle absorption systems present an intriguing alternative to their more common closed-cycle counterparts, and have generated interest over the years, particularly for air conditioning applications powered by low-grade heat. For specific applications involving both cooling and dehumidification, the open-cycle systems often compete quite well in performance, simplicity of operation and cost. The development of working open absorption systems has created the need for effective and reliable simulations. The computer code ABSIM had been developed for simulation of closed-cycle absorption systems in a flexible and modular form, making it possible to investigate various cycle configurations with different working,fluids. The code has been modified and enhanced to enable simulation of open-cycle systems as well. The modular structure of the code is based on unit subroutines containing the governing equations for the system's components. A main program calling these subroutines links the components together according to the cycle diagram. The system of equations for the entire cycle is thus established, and a mathematical solver routine is employed to solve them simultaneously. Property subroutines contained in a separate database serve to provide thermodynamic properties of the working fluids. The paper describes the modifications made in the original ABSIM code to enable simulation of open-cycle systems. The enhanced program has been applied successfully to simulate several open-cycle systems with different working fluids. Simulation results are described for an air dehumidification system and a DER (Dehumidifier-Evaporator-Regenerator) chiller, both powered by low-grade heat.