Abstract
Because single-duct air-handling units (SDAHUs) supply the cooling air to all zones with the same temperature, the cooling air is normally reheated to satisfy the heating demand in exterior zones in cold seasons. Supply air temperature reset reduces the reheat load; however, it increases the supply airflow rate to the interior zones, which increases the fan power. Dual-branch air-handling units (DBAHUs) are proposed to mix the return air with the cooling air to simultaneously distribute the warm air to exterior zones and the cold air to interior zones in cold seasons to reduce the reheat load. The purpose of this study is to investigate the energy performance and control of the proposed DBAHUs through simulations. First, the thermodynamic models 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 CO2 concentration and humidity, is simulated and compared among different systems. The simulation results reveal the proposed DBAHU can significantly reduce the AHU energy consumption by 12.3 W/m(2) (1.14 W/ft(2)) in cold seasons and improve the relative humidity up to 6% with controllable indoor air quality with the CO2 concentration less than 1000 ppm in exterior zones.
