Humid air is the costliest to cool because the cooling coil has to wring some of the water from the air before it can lower the temperature of the air. Most air-conditioning systems are a design compromise between a straight cooling system and a dehumidifying one, dealing simultaneously with the sensible and latent loads, respectively.
Another difficulty is that when air is cooled, the humidity increases. Thus the cooling coils dehumidify a little with every air change but must work harder to cool the air the closer the room temperature gets to setpoint. That’s why the last 3 degrees (i.e., 78°F to 75°F) uses about 15 percent of all the cooling energy.
An energy-saving alternative for a residence is to allow the air temperature to rise during the day when no one is at home but to continue running the AC compressor to dehumidify the air volume. It takes less energy to extract water from air at an elevated temperature, so if this is done in the heat of the day, later when it is time to cool the home down; the unit will be cooling dryer air, which it can do more efficiently.
For buildings occupied all day, this same method can be done at night if the building temperature increases substantially. Otherwise, an extra row of cooling coils that can be activated periodically as a dehumidifying feature will boost the ability of the unit to operate efficiently in hot and humid climates.