Cycle architectures for two-door refrigerators: Performance breakdown

Abstract

In this study, four different refrigeration cycle architectures for two-door applications were evaluated and compared: (i) fan-and-damper single-evaporator cycle, (ii) serial/parallel (hybrid) dual-evaporator architecture, (iii) parallel dual-evaporator architecture, and (iv) two independent single-evaporator cycles. The performance analysis was carried out by means of quasi-steady mathematical models that combine steady-state submodels for the refrigeration loop with transient submodels for the refrigerated compartments. The numerical calculations were conducted in such a way that layers of internal and external irreversibility could be introduced into the analysis, from a fully-reversible Carnot cycle to the cycling behavior imposed by the control logic. The dual-evaporator cycles, which are far more complex than single-evaporator ones, were prototyped and tested in a climate chamber to gather data used to calibrate and validate the mathematical models. A methodology was devised on thermodynamic grounds to allow a fair comparison between the architectures. The system with two independent single-evaporator cycles performed the best, followed by parallel and hybrid dual-evaporator loops, and the single-evaporator fan-and-damper solution. Also, the replacement of isobutane with n-butane in the fresh-food branch of the two independent cycles led to an extra 5% energy consumption reduction under the same conditions, providing better matching of the compressor capacity to the thermal loads.