Modeling Variable Refrigerant Flow (VRF) systems in building applications: A comprehensive review

Variable Refrigerant Flow (VRF) systems have gained recognition for being energy-efficient and adaptable for use in heating, ventilation, and air conditioning (HVAC) applications. This review aims to bridge specific knowledge gaps in modeling VRF systems, particularly focusing on addressing limitations in representing complex control dynamics, calibrating for varying loads, and validating under transient operating conditions, while also exploring their applications in buildings. The review begins by exploring the range of modeling approaches available, such as empirical performance curved-based, detailed component-based, machine-learning-based, and hybrid modeling methods. Special attention is given to modeling tools like EnergyPlus and Modelica, along with crucial factors such as modeling dynamics, heat recovery capabilities, and control features. The review also examines the calibration and validation processes for VRF models, including validation procedures, performance metrics, and data sources. In addition, it synthesizes recent literature spanning from 2000 to 2023 to elucidate various applications of VRF system modeling, such as energy analysis, control strategies, system design, operational optimization, and grid integration. Lastly, the review highlights key areas and future research directions. These include improving dynamic modeling for control, integrating with complementary systems and grid infrastructure, and developing accurate heat recovery models to optimize VRF system performance in buildings.