Abstract
We have studied the operating performance of a large-scale metal hydride heat pump which utilizes a hydrogen compressor. Generally, the hydriding reaction of hydrogen storage alloy is exothermic, and causes a rise in the alloy's temperature. The dehydriding reaction is endothermic. We developed a new heat pump system that utilizes these exothermic and endothermic reactions. We adopted the 'shell and tube type' heat exchanger, which has middle fin tubes made of copper to enhance heat transfer. In this heat exchanger, there is a metal powder composed of calcium, nickel, misch metal and aluminum, and the heat is transferred through the metal powder and copper fin tubes to the water in the tubes. The hydrogen pressure in the shell is controlled by a hydrogen compressor. In this paper we discuss the relations between heat output, cycle time, hydrogen mass flow and temperature of hot water. We found that normal operation in combination with periodic no-load operation as shown in Fig. 4(b) is optimum, and it maximizes COP of the system. In addition, the design heat output (150000kcal/h) was achieved when COP equaled about 6. This heat output value is the highest in the world for a metal hydride heat pump system using a hydrogen compressor.
