Assessment of Energy Consumption and Range in Electric Vehicles with High Efficiency HVAC Systems Based on the Tesla Expander

Battery electric vehicles (BEVs) are considered one of the most promising solution to improve the sustainability of the transportation sector aiming at a progressive reduction of the dependence on fossil fuels and the associated local pollutants and CO2 emissions. Presently, the major technological obstacle to a large scale diffusion of BEVs, is the fairly low range, typically less than 300 km, as compared to classical gasoline and diesel engines. This limit becomes even more critical if the electric vehicle is operated in severe weather conditions, due to the additional energy consumption required by the cabin heating, ventilating, and air-conditioning (HVAC). The adoption of vapor-compression cycle, either in heat pump or refrigerator configuration, represents the state-of-the-art technology for HVAC systems in vehicles. Such devices typically employ an expansion valve to abruptly reduce the pressure causing the flash evaporation of the working fluid. This component, although necessary to provide the cooling effect, is also responsible of a significant exergy loss, which reduces the efficiency of the thermodynamic cycle. In this paper we study the possible benefits in terms of energy saving and consequent increase of the driving range, that can be obtained in electric vehicles that adopt a high efficiency HVAC system, where the Tesla turbine replaces the classical expansion valve in order to recover part of the exergy typically lost by the working fluid in the expansion phase. First, an off-design thermodynamic model was developed to assess the performance of the proposed HVAC system as function of the ambient temperature. Then, the calculated COP curves were implemented in an in-house Matlab code based on Nissan Leaf design data. Simulations are carried out considering various reference driving cycles showing that this solution may result in a potential increase of the electric vehicle range up to 5%.