Innovative Metal Hydride Refrigeration System

Abstract

Multiple unit rolling stock needs extensive energy storages for use cases where no overhead line is available. Moreover, high availability is mandatory for the railway operators, which leads to short refueling or recharging times as a requirement and therefore hydrogen fuel cell powered trains can be a CO2 emission free alternative for diesel trains in the state of the art. Hotel loads, such as the HVAC system, can reduce the autonomous range of such a fuel cell multiple unit train by up to 50 %, which reduces train’s availability. The metal hydride refrigerator uses the pressure energy between pressure tank and fuel cell system to drive a heat pump and therefore provides cooling and heating power. The system absorbs hydrogen in an exothermic reaction and desorbs hydrogen in an endothermic reaction in two alternating batch reactors to provide a continuous hot and cold flow. However, the system’s benefits were only calculated in a passenger car simulation in KULI so far and the advantages in railway use cases are currently unknown. Here we show a first energy reduction potential by using metal hydrides with calculating the annual energy demand according to the EN 50591 and EN 14750 standard with a co-simulation of the existing and validated KULI metal hydride refrigeration model in combination with a generic car body model in the modelica language. The KULI model is first exported in a functional mock up model and fresh air precooling and mixed air precooling are investigated as two integration options. The evaluation shows, that a significant reduction in energy demand of the HVAC system by 9 % can be achieved in climate zone 1. Furthermore, additional improvements in the hydrogen pressure levels and an optimized selection of metal hydrides show efficiency increasing potentials of up to 70 % in specific test cases defined in EN 50591. Reducing energy in fuel cell powered trains reduces the annual energy consumption and affects the hydrogen demand.