The main thrust of this research is to verify the heating energy reduction capacity of an indirect and direct evaporative cooler assisted 100% outdoor air system (IDECOAS) via actual winter operation of the pilot unit installed in a campus building. A conventional variable air volume (VAV) system was also installed for comparison with the proposed system. By measuring variation of air temperature and relative humidity at each measurement location, effectiveness values of the indirect evaporative cooler (IEC) and the sensible heat exchanger (SHE) were monitored. In addition, the influence of balanced and unbalanced flow conditions between the supply air and the exhaust air on the sensible heat exchange effectiveness was also observed. Fan energy and heating coil energy consumptions were also measured by installing a wattmeter at each device. It was concluded that the IDECOAS shows 60-85% operating energy saving over the conventional VAV system. The sensible heat reclaimed from the exhaust air at the IEC and the SHE reduces the heating coil energy consumption significantly in the proposed system. It was also found that the IDECOAS consumes more fan energy than the conventional VAV, but this penalty is offset by the heating energy reduction. (c) 2012 Elsevier B.V. All rights reserved.