There are significant height differences between outdoor and indoor units in variable refrigerant flow (VRF) systems deployed in high-rise buildings. Moreover

there are many branches in the pipeline structure in such systems

resulting in the performance degradation of indoor units. Simulation software is needed to determine the influence of these factors to improve the capabilities of such VRF indoor units. This study establishes a distributed parameter model for the pipeline and a flow distribution model for the system based on fluid network theory to accurately reflect the flow characteristics of the refrigerant in the pipeline. A multi-zone separation model for the indoor unit heat exchanger and a fast pulse number calculation model for the electronic expansion valve in the indoor unit were also established to quickly reflect the operating status of indoor units. In addition

a hierarchical iterative solution algorithm was developed to improve the calculation speed of the software. These models were validated using existing data. The results showed that the errors for each model were <12%

and the calculation time for the VRF system with a common structure was less than 1 min. Furthermore

the calculated example using the simulation software showed that the indoor unit performance decreased by 2.7%–11.9% when the height difference between the indoor and outdoor units increased by 20 m and 0.4%–9.7% when the number of branches in the pipeline increased by one.