A thermal network model for hydrocarbon heat pump systems: A coupling analysis of configuration, working condition, and refrigeration distribution

The ambition of zero emission neighborhood has been set out to operate the building components with zero life cycle greenhouse gas emissions. Hydrocarbon heat pumps as the building components with nearly zero greenhouse gas emissions are faced with the problem of simultaneously reducing refrigerant charges and maintaining competitive capacities. These must be resolved by formulating an effective modeling tool for detailed design and optimization. To develop a resistance-capacitance network model, interdisciplinary knowledge (including graph theory, heat and mass transfer, local moving boundary modeling, and algebraic multigrid) is integrated. The model simultaneously considers heat exchanger circuitries with a high detail level and component behaviors at a holistic system level. Based on experimental validation, the model's error is similar to 10%. In an R290 heat pump case study, the coupling mechanism of the system's configuration, working conditions, and refrigerant distribution are analyzed. Results indicate that the refrigerant charge can be reduced by 11.6% at the expense of a 4.2% reduction in the coefficient of performance, by varying the compressor displacement alone. In response to the variation in the system's refrigerant, 46.8%, 7.85%, and 44.2% of the total amount of refrigerants are allocated to the condenser, evaporator, and compressor, respectively. The distribution of the refrigerant quality in the heat exchanger is also visualized to indicate the direction of refrigerant reduction.