LPT (Local Public Transport) electric buses: innovative solutions to reduce the energy absorption of auxiliaries

Abstract

The focus of the study is the analysis and sizing of the air conditioning system on board the vehicle which operates in thermal transient for the duration of the typical mission, using “fan coil” type air conditioning devices powered by a hot or cold heat vector fluid loaded into “electro-thermal” charging station and the related ground cogeneration plant (at the BUS terminus). For winter air conditioning, it was assumed that a heat transfer fluid at a temperature of 90 ° C could be stored on board. This value allows the use of water as a heat transfer fluid without pressurizing the systems, minimizing costs and supply problems, and is compatible with the characteristics of ICE cogeneration systems. For summer air conditioning, it was assumed that ice or fluid at a temperature of -20 ° C could be loaded. Also in this case it was decided to operate with a common fluid, such as a solution of water and salt (e.g. calcium chloride CaCl2). A comparative analysis of two solutions was carried out: the first involves the standard solution with BUS air conditioning system with heat pump powered by traction batteries charged by the grid and the second one analyzes the use of a high temperature Fuel Cell in a trigenerative configuration with refrigeration unit absorption fueled by the fumes of the FC. The trigeneration plant produces 100 kW of electricity via SOFC (Solid Oxide Fuel Cell) and, through an exchanger, water at 95 ° C which is stored on board the BUS for winter heating and feeds an absorption refrigeration machine that produces fluid at a temperature of -20 ° C for summer conditioning. For the two solutions, the savings of non-renewable primary energy and the reduction of GHG emissions compared to the standard solution (recharging the electric BUS from the network with on-board air conditioning powered by the traction batteries) are calculated through a WTW analysis. Consumption and emissions of electric powertrains, potentially for consumption and zero emissions, are closely linked to the methods of production and distribution of electricity.