A thermodynamics based analysis of exergy destruction in vapor compression cycle systems

In the last few decades, vapor-compression cycle systems (VCSs) have undergone many advances in actuation, allowing for variable aperture valves, variable speed compressors, and variable speed heat exchanger fans. Numerous efforts have been undertaken to quantify the energy efficiency of these components through the use of exergy analysis. Despite many studies varying across different types of refrigerants, different physical components, and different cooling capacities, there has been no effort made to analyze the exergy destruction caused by combinations of the variable actuators. In order to obtain information regarding the variable actuators, a physics based model of a VCS at the University of Illinois at Urbana-Champaign (UIUC) was created. Additionally, an offline, static exergy destruction minimization technique was developed, which provides predictions of the thermodynamic operating points within the VCS. Using linear quadratic integrator (LQI) controllers, the variable actuator combinations were tested at the predicted operating points for three different cooling capacities to determine the relative exergy destruction in each configuration. The combined variable valve aperture, evaporator fan speed, and condenser fan speed produced the most exergetically favorable configuration, with a 12.8% savings in exergy destruction over the baseline case. Implementation of variable actuators was found to be most beneficial at higher cooling capacities. Actuator combinations with only one variable component showed little benefit over the baseline conditions. The combinations of both heat exchanger fans as variable and the compressor and condenser fan as variable showed significantly worse exergy destruction over the baseline value