Author: Akshay Desai (University of Liverpool) - Automotive air-conditioning systems predominantly use the vapour compression cycle (VCC) with R134a as the working fluid. While effective, R134a’s high global warming potential (GWP 1430) has driven interest in natural refrigerants such as ammonia (R717), which has zero ozone depletion potential and negligible GWP. This study investigates R717 as a potential replacement for R134a, focusing on energy performance in different automotive cooling loads.
A steady-state VCC model was developed in Aspen Plus® V14 with components including a compressor, condenser, expansion valve, and evaporator. Thermophysical data were obtained from REFPROP. Climatic conditions for Qatar were used to set operating parameters: evaporator temperatures at 5 °C, 10 °C, and 15 °C, and condenser temperatures from 38 °C to 58 °C. Cooling loads of 3.5 kW, 9.43 kW, and 41.17 kW, representing small cars, minibuses, and train trailer cars, were maintained using Aspen’s design specification method to adjust mass flow rate.
The model was validated against published R134a data, showing strong agreement in coefficient of performance (COP) and compressor work. Parametric analysis revealed that R717 achieved higher COP across most conditions, particularly at higher evaporator and moderate condenser temperatures, due to its higher latent heat of vaporisation and reduced volumetric flow requirement.
These results suggest that R717 could significantly lower the environmental footprint of automotive cooling while sustaining or improving energy performance, though its higher discharge pressures require careful system design.