The overlap coupled control unit is widely used in hotels, dormitory buildings, hospitals, and office buildings. Energy simulation models are developed to assess changes in energy consumption and humidity levels due to changes in various system parameters. The simulation results show that the energy consumption of the overlap unit is 3 to 5 times higher than the optimal energy consumption. To improve the energy performance, the following measures are recommended: (1) use the variable air volume technique; (2) balance total airflow based on actual peak load; and (3) replace overlap with humidistat. Quick open valves are also found to improve relative humidity control.