Practical limitations of steam humidification capacity and energy consumption often preclude the use of economizer cooling cycles for computer room HVAC systems. Also, available packaged systems have inadequate humidification capacity for the large volumes of low-moisture outside air that are necessary during the free cooling cycle.

After examining the most commonly used psychrometric processes, the author introduces one that integrates evaporative cooling with an economizer cycle and variable air volume that may offer some interesting advantages in energy conservation and relaxed vapor barrier requirements for computer rooms.