Part Load Capability of a High Temperature Heat Pump with Reversed Brayton Cycle

Abstract

This paper studies the part load behavior and capability of a high temperature heat pump that operates with the Brayton cycle. A novel concept of a high temperature heat pump which is currently under construction in Cottbus (Germany) is presented. It goes far beyond temperature levels of current high temperature heat pumps and will provide process heat at above 250 °C. The heat pump uses a closed Brayton cycle driven by axial turbomachinery and provides up to 200 kW of thermal energy. The thermal output can be adjusted by variation of compressor shaft speed, use of internal recuperation and additionally by variation of the fluid inventory. The latter allows operation of our prototype within a broad part load range down to 25 % of the nominal power at nearly constant efficiencies and output temperatures. Brayton cycle heat pumps can be adapted to a wide range of industrial processes and enable highly efficient thermal energy storage systems to balance grid fluctuations.