Comparative Analysis of Dual-Objective Control Methods for Fan Coil Units Under Different Fresh Air Ratios

Buildings account for nearly half of global energy consumption, with HVAC systems contributing approximately 40%. Fan coil units (FCUs) and fresh-air systems are widely adopted in commercial buildings for their flexibility. However, this system faces numerous critical challenges in tropical maritime climates, including low temperature control accuracy, high energy consumption, and inadequate coordination between thermal comfort and indoor air quality. This study aimed to optimize the indoor thermal environment and reduce HVAC energy consumption. It compared and analyzed the operational performance of traditional PID control and MPC. Additionally, dynamic CO2 concentration modeling was performed to evaluate the impact of different outdoor air strategies on indoor air quality. A building simulation model was developed in TRNSYS 18. Based on the simulation data, a multi-objective model predictive control (MPC) model was created in MATLAB/Simulink. Results indicate that MPC significantly outperforms PID control in both temperature stability and energy efficiency across all outdoor air strategies, with the occupancy-based demand-controlled outdoor air strategy achieving the greatest energy savings (16.89%) while maintaining favorable indoor air quality. This study provides a theoretical foundation and practical control guidelines for the coordinated optimization of fan coil units and outdoor air systems in tropical maritime climates, facilitating the development of energy-efficient and comfortable HVAC solutions for commercial buildings.