Integrated design optimization of a novel electrically-driven helicopter ECS using low-GWP refrigerants as working fluid

Abstract

The Environmental Control System (ECS) is the main utilizer of non-propulsive power among the aircraft subsystems. Onboard helicopters, the ECS is based on the Vapour Compression Cycle (VCC) concept, and the standard refrigerant is R-134a. The objective of this study is to evaluate the impact of replacing the conventional scroll compressor with a high-speed centrifugal compressor operating with a low-GWP refrigerant as the prime mover of the VCC system. The case study is the ECS of a large helicopter and the sizing operating condition is that of the helicopter on the ground on a hot and humid day. The working fluids identified as potential alternatives to R-134a are the haloolefins R-1233zd(E), R-1234ze(Z), R-1224yd(Z) and R-1336mzz(Z). An integrated design optimization method has been employed to simultaneously account for the design of the VCC system, its main components, and the selection of the working fluid. The model of the VCC system has been coded with the acausal Modelica language. The design of the high-speed compressor has been performed with an in-house program validated with experimental data. The objectives of the optimization are the maximization of the Coefficient of Performance (COP) and the minimization of the system weight. The results show that the use of haloolefins in place of R-134a allows the design of lighter and more efficient VCC systems. In particular, the refrigerant R-1234ze(Z) enables the identification of an optimal design point featuring a 12% increase in COP and a 26% reduction in weight.