Because single-duct air-handling units (SDAHUs) supplythe cooling air to all zones with the same temperature, the coolingair is normally reheated to satisfy the heating demand inexterior zones in cold seasons. Supply air temperature resetreduces the reheat load; however, it increases the supply airflowrate to the interior zones, which increases the fan power. Dualbranchair-handling units (DBAHUs) are proposed to mix thereturn air with the cooling air to simultaneously distribute thewarm air to exterior zones and the cold air to interior zones incold seasons to reduce the reheat load. The purpose of this studyis to investigate the energy performance and control of theproposed DBAHUs through simulations. First, the thermodynamicmodels are developed for both SDAHUs and DBAHUs,then the system energy performance, including the fan power,terminal box reheat, and cooling coil load, as well as zone CO2concentration and humidity, is simulated and compared amongdifferent systems. The simulation results reveal the proposedDBAHU can significantly reduce the AHU energy consumptionby 12.3 W/m² (1.14 W/ft²) in cold seasons and improve the relativehumidity up to 6% with controllable indoor air quality withthe CO₂ concentration less than 1000 ppm in exterior zones.