Applied simulation study of a metal hydride refrigeration system for fuel cell trucks

Abstract

Refrigeration units in semi-trucks or rigged-body trucks have an energy demand of 8.2 - 12.4 MWh/y and emit 524.26 kt CO2e/y in Germany. Electrification with fuel cell systems reduces the CO2 emission, but an increase of efficiency is necessary because of rapidly increasing hydrogen costs. A metal hydride refrigeration system can increase the efficiency. Even though, it was already demonstrated in lab scale with 900 W, this power is not sufficient to support a truck refrigeration system and the power output of the lab system was not controllable. Here we show the design and validation of a MATLAB© Simulink model of this metal hydride refrigeration system and its suitability for high power applications with a scaled-up reactor. It was scaled up to rated power of 5 kW and efficiency improvements with an advanced valve switching as well as a controlled cooling pump were implemented. Two application-relevant use cases with hydrogen mass flows from hydrogen fuel cell truck systems were analyzed. The simulation results of these use cases provide an average cooling power of 4.2 and 6.1 kW. Additionally, the control of the coolant mass flow at different temperature levels, a controlled hydrogen mass flow with a bypass system and an advanced valve switching mechanism increased the system efficiency of the total refrigeration system by 30 % overall.