Energy-Saving Performance of VRF Systems with Different Fresh Air Units in Different Climate Regions

To address the issue of poor indoor air quality caused by the lack of fresh air in traditional variable refrigerant flow (VRF) systems, a combination of VRF and fresh air systems is increasingly adopted in practical engineering applications. However, these two systems are often operated independently, which may result in increased energy consumption. To enable coordinated operation, this study proposes a novel integrated VRF–fresh air system that aims to reduce total energy consumption while ensuring adequate indoor air quality. Based on a full operating condition model, this study evaluates the energy performance of the integrated system with different fresh air unit configurations. Results show that during the heating season, heat recovery effectively reduces the heating load on the VRF system, achieving seasonal energy savings ranging from 28.47% to 45.46%, with greater benefits observed in colder regions. In the cooling season, the combination of heat recovery and bypass control can deliver up to 19.98% seasonal energy savings, especially when outdoor air enthalpy lies between the minimum and maximum indoor setpoints. These findings underscore the importance of optimizing the design and control of fresh air units to enhance the overall energy efficiency of integrated systems.