Dynamic simulation and experimental validation of a high-temperature Brayton heat pump

The decarbonization of industrial process heating will require widespread adoption of high-temperature heat pumps. Brayton cycle heat pumps are capable of providing heat at temperatures that currently cannot be achieved by conventional vapor-compression cycle heat pumps. However, significant challenges remain in adapting these systems to industrial applications, particularly with regard to operational safety, control strategies, and flexibility in response to varying operational conditions. This study presents a dynamic model of a closed-loop Brayton cycle heat pump capable of producing temperatures of 250 degrees C and higher, validated using experimental data. The physics-based model implemented in Modelica captures key thermodynamic processes and system dynamics, including thermal inertia and volume dynamics. An optimization-based method is used to calibrate model parameters, minimizing the error between measured and simulated data. Given the significant impact of the compressor on overall heat pump performance, a novel calibration method is introduced to adjust an existing compressor map using limited measurement data. This approach ensures that the compressor behavior is represented with sufficient accuracy, smoothness, and numerical robustness. The calibrated model achieves mean-normalized root mean squared errors (NRMSE) ranging from 0.12 % to 1.46 % for temperatures, pressures, and mass flow rates. The model is applied to examine the system's start-up and deceleration sequences, offering insights into compressor stability and heat exchanger temperature profiles. These results demonstrate the model's utility for control design, performance evaluation, and stability analysis.