A hydrogen heat pump as a bus air conditioner

Abstract

Abstract The waste heat of exhaust gases of a bus is utilized as a high temperature source for a hydrogen heat pump. The thermodynamic cycle of the hydrogen heat pump is presented and the critical step of the cycle is analysed. In this part of the cycle the process is heat transfer limited and can be enhanced by using hydride compacts of increased thermal conductivity. Data comparing the performance of powder hydrides with that of compacts are shown. A model of a hydrogen heat pump aimed to serve as an air conditioner for a bus was designed and built in our laboratory. The ultimate cooling capacity of the model and its current running capacity are discussed. The following aspects of the model are presented: the hydrides utilized (porous metal matrix compacts consisting of MmNi4.15Fe0.85Hx (Mm ≡; misch metal) with an 18 wt.% Al matrix and LaNi4.7Al0.3Hx powder); the function of the air conditioner, the physical structure of the model, the heat exchangers and the heat transfer, air flow and control system; the available input power and temperature, the efficiency, the coefficient of performance, the cycle time, the cooling power capacity, losses and weights; a bus air conditioner prototype.