A comparative study on energy consumption for HVAC systems of high-tech FABs

The unique system dynamics of five different HVAC designs including the RCU (recirculation air unit) system, the MAU (make-up air unit) + RCU system, the MAU + RCU + FCU (fan coil unit) system, the MAU + axial fan system, and the MAU + FFU (fan-filter unit) system for a typical 200 mm DRAM wafer fabrication plant are discussed and compared. The energy performances of the RCU system, the MAU + RCU system, the MAU + RCU + FCU system, and the MAU + axial fan system are 3.8, 1.19, 1.12 and 1.08, respectively, folds that of the most efficient MAU + FFU system. The MAU + axial fan system exhibits slight less efficient in energy performance, compared with the MAU + FFU system. The most influential factor on energy performance between these two systems is the design of the noise abatement system, especially the pressure drop of the silencer, which dominates almost half of the internal static pressure of axial fan. When the static pressure of silencer of the MAU + axial fan system is reduced to 50 Pa, energy consumption of these two systems is comparable. Bypassing a certain portion of FAB return air to mix with make-up air can maximally reduce 50% of energy consumption of the RCU system.