During the last few years, a new displacement air distribution system with low-velocity air supplied directly to the occupied zone and a displacement flow in the floorto- ceiling direction has been introduced into office buildings in Scandinavian countries. The purpose of this study was to evaluate displacement air distribution systems and compare their performance to the performance of traditional variable- and constant-airflow systems in U.S. office buildings. The loads of a typical large U.S. office building were calculated for four representative U.S. climates (Minneapolis, Seattle, Atlanta, and El Paso) with the DOE-2.1C building simulation program. Hourly loads and hourly weather data were used as inputs for new computer programs that simulated system performance. Energy consumption, air quality, thermal satisfaction, and the cost of the systems were calculated for three building zones (south, north, and core) in each climate. The displacement systems were simulated using results from recent laboratory measurements. The results indicate that displacement systems generally yield superior air quality and thermal comfort compared to conventional systems with air recirculation. The energy consumed by displacement systems with heat recovery or variable-air-volume (VAV) flow control was similar to the energy consumption of conventional air distribution systems operated with recirculation. However, the first cost of displacement systems is substantially higher than the first cost of conventional systems when the maximum cooling load exceeds 13 Btu/ho ft ² (40 W/m²) and cooling panels are required. The energy consumption of the traditional VAV systems was low. However, indoor air quality can deteriorate significantly if the combination of minimum supply airflow and minimum outdoor air entry into the air handler do not bring an adequate amount of outdoor air to each region of the building.