Chilled beam systems provide sensible cooling in the occupied space using chilled water flowing through modular beams mounted to a ceiling. Such systems achieve greater energy efficiency than all-air system due to larger thermal energy of the chilled water than air, and thus are well-suited for spaces with relatively large sensible cooling load. This paper presents a numerically based study focusing on the performance of combined passive chilled beam (PCB)-displacement ventilation (DV) systems. Using computational fluid dynamics (CFD) simulation, the amount of sensible cooling by PCB and its impacts on ventilation effectiveness and occupant comfort in a typical office room are investigated. Along with the PCB system, two ventilation systems are compared and analyzed: mixing ventilation (MV), displacement ventilation. Simulations under different load conditions are conducted to study the relationship between cooling effect of different systems and load variation. The study results reveal that the performance can vary significantly with PCB cooling output, but not with the arrangements of heat loads. The results also show that the combined PCB-DV systems can provide relatively good indoor air quality and thermal comfort compared to the combined PCB-MV system. Simulations of spatial distribution of age-of-air (air freshness) suggest that combined PCB-DV systems can achieve high ventilation effectiveness with lower energy consumption.