Paper No 021 – An overview of hydrogen compressors for heat pump systems -13th IEA Heat Pump Conference, Jeju, Korea
Metal hydrides present an alternative heat pump approach to efficiently achieving extreme temperatures, without high GWP refrigerants. These materials work by complexing with hydrogen in order to generate incredible thermal lifts; an alloy of TiCrMn, complexes hydrogen at 90°C and exhausts at approximately - 60°C, for example. A drawback of this class of materials is that greater temperature lifts require higher pressure hydrogen. This paper analyzes four methods of producing pressurized hydrogen: two electrochemical systems, one system employing metal hydride compression, and one using conventional mechanical compression. Electrochemical compression makes use of ion selective electrolytes that provide pressurized hydrogen when a potential gradient is applied. Metal hydride compressors operate by reversing the principle behind the metal hydride heat exchangers used in these heat pumps – i.e. releasing hydrogen at pressure when the metal hydride is heated. Mechanical compressors use various designs to move a mass of gas and shrink the volume it occupies, thereby compressing the gas. This paper provides operational data for these four different compression strategies. Heat pump cycles employing these systems are analyzed for critical performance parameters.