Confusion with ASHRAE 55

Previous versions of ASHRAE 55 required a minimum humidity. The latest version referenced by LEED eliminated this requirement. You may still want to consider humidification in very dry climates, especially if you're dealing with a museum, hospital, or data center.

You can start by looking at hourly weather data / ASHRAE design data for your particular location to see whether the outdoor design dewpoint is above or below your interior target dewpoint. In many climate zones, use of a VAV system addresses dehumidification adequately, since air will be dried out to maintain a 55F supply air temerature. In ASHRAE climate zones 1A-4A, I recommend that additional psychrometric analysis at design and part-load conditions be used to determine whether active dehumification is needed - it is usually helpful to include control sequences of operation to describe any actual dehumidification mode. I recommend coordinating with ASHRAE 62.1, which has a description of dehumification analysis, as well as 90.1, which has restrictions on simultaneous heating and cooling, which used to be common for dehumidification.