Development of a Novel High Temperature Heat Pump System

The range of possible application of heat pumps in industrial processes is limited due to maximum supply temperatures of about 100 °C. Increasing the supply temperatures will increase the range of application and the efficiency of industrial processes. The main reason for the limited temperatures is the absence of adequate working fluids and corresponding heat pump systems. Legislative authorities restrict the usage of established working fluids. Only working fluids without ozone depletion potential (ODP) and with a low global warming potential (GWP) are future-proof. The aim of this thesis is to develop a novel high temperature heat pump system using future-proof (no ODP, low GWP) and safe (non-flammable, non-toxic) working fluids. An evaluation investigates a large variety of working fluids. Only two working fluids fulfill the evaluation criteria and are selected for the development of the novel system. The selected working fluids have a complex molecular structure and show the phenomenon of a distinct overhanging behavior. This causes condensation during compression, which could damage the compressor of the heat pump. As a consequence, standard heat pump cycles are not suitable anymore. Operation strategies for alternative cycle designs are developed. New terms like the “limiting temperature lift” define, characterize and classify the operation of overhanging working fluids. A new functional model is developed and built up based on the operation strategies. The concept of the functional model is proven by stable operation of the selected working fluids at condensation temperatures up to 140 °C. The experimental results indicate a promising performance of this novel heat pump system with future-proof working fluids.