Influence of operational modes of the internal heat exchanger in an experimental installation using R-450A and R-513A as replacement alternatives for R-134a

This paper presents a first and second law of thermodynamics study using experimental data from a medium capacity refrigeration system using R-450A, R-513A and R-134a as working fluids and an internal heat exchanger (IHX) operating in three different modes: disabled (Off), activated at 38% thermal effectiveness (Middle), and activated at 78% thermal effectiveness, which is the maximum value by design (ON). When the IHX is in the Middle mode, R-513A showed to be the best option and its coefficient of performance (COP) overcomes that of R-450A and R-134a. On the other hand, for temperatures above of −7.5 °C, both R-450A and R-134a reached the highest COP when the ON and Off modes were set, respectively.Regarding the second law study, for the Off and Middle mode, the largest exergy destruction happens in the compressor for the three refrigerants. The influence of the IHX can be observed directly in the increase of the global exergetic efficiency which passes from being 8.7% in Middle mode to 18.3% for the ON mode. Additionally, a reduction of exergy destruction ratio is seen from the Middle mode, 10.6%–22.2% in the ON mode.