Traditional wall-return re-circulation air systems with ceiling-supply and wall-return air grilles are fairly common in non-unidirectional airflow industrial cleanrooms. Such re-circulation systems normally have longer airflow circulation pathways, which inherently induced higher airflow resistance, resulting in higher fan power demand per unit of airflow rate delivered. To overcome the airflow resistance, Fan Filter Units (FFUs) used in the traditional wall-returned re-circulation system are designed to operate with high external pressures, which also induce high negative pressures in supply air plenums (SAP). The negative pressures within SAP can increase the risks of infiltration of outdoor air and contaminants. A longer airflow pathway corresponds to a higher level of negativity of the air pressure inside the supply air plenum, thus inducing higher risks of cross-contamination. To overcome the above-mentioned drawbacks, a new re-circulation system using fan dry coil unit (FDCU) was proposed. This new system exhibits shorter air re-circulation paths while providing effective environmental controls (e.g., removal rate of 0.1 mu m particle and temperature control) for a cleanroom. In this study, experiments were conducted in a full-scale cleanroom to investigate the energy performance of applying the innovative FDCU-return system, compared to a traditional wall-return system. Results showed that the FDCU-return system can increase energy efficiency and reduce the electric energy consumption by more than 4% compared to the wall-return system. (C) 2014 Elsevier B.V. All rights reserved.