Coupled control units typically condition a single zone with constant air volume. A thermostat controls the heating valve or cooling valve when the room relative humidity is below the set point. When the room relative humidity is higher than the set point, a humidistat controls the cooling coil to dehumidify air and the thermostat controls the heating coil to maintain room temperature. Theoretical modeling is performed to investigate the energy performance of coupled control units and potential improvement measures. The study shows that the annual thermal energy consumption of the coupled-control units is up to four times higher than the optimal thermal energy consumption. Thermal energy consumption can be reduced by (a) eliminating excessive airflows, (b) minimizing valve leakages, and (c) modulating airflows with a zone sensible load This paper presents the simulation models and results and discusses improvement measures.