Thermodynamics-based Optimization and Control of Vapor-compression Cycle Operation: Control Synthesis

This paper considers the implementation of an exergy-based multiple degree of freedom (MDOF) optimization and control methodology for the operation of VCC systems. The optimization problem for the standard VCC is characterized in terms of 4 thermodynamic variables and 1 fluid-dynamic variable. The resulting control problem is then analyzed, and a design variable, Λ, is introduced which allows the user to choose how the optimization variables are projected onto a control space of lower dimension. The potential of this approach to improve operational efficiency, with respect to both first and second law efficiency metrics, is demonstrated on an experimental VCC system through implementation of the proposed optimization using a feedforward plus feedback control architecture. NOMENCLATURE a aperture C cooling capacity h specific enthalpy K flow coefficient, gain matrix ṁ mass flow rate P pressure Q̇ heat transfer rate T temperature Ẇ work transfer rate δ displacement ρ density ω rotational speed X exergy ∗Address all correspondence to this author. Subscript 1,2,3,4 transition points of the VCC (applies to thermodynamic state variables) a air c condenser e evaporator H high-temperature reservoir k compressor L low-temperature reservoir r refrigerant v electronic expansion valve vol volumetric