During earlier studies, system optimization was based on experience and intuitive analysis because simple yet reliable model of each component was not established. Stoecker claimed that to
increase heat exchanging efficiency so that to achieve higher
Coefficient of Performance (COP), superheat and subcool should
both be minimized [5]. With the introduction of variable speed
drive to the compressor and electronic expansion valve, the energy saving potential of vapor compression cycle (VCC) was further studied, theoretical comparison of various refrigeration capacity control methods in full and part-load conditions shows that both of
them are efficient technique for capacity control [6,7]. Optimization
scheme for whole system based on components' polynomial
models was also investigated, Sanaye et al. assigned cost functions
for components and used Lagrange multipliers method to minimize the objective function [8]. Jensen and Skogestad proposed to add an active charger as complementary variable for manipulation and discussed the selection of the controlled variable to improve the
system efficiency [9e11]. Larsen et al. proposed a gradient method
to find the suboptimal solution for condensing pressure, while keep