i cant imagine humidity in dc is much different from philly. up here, the engineers are a tad conservative with these systems, so what you see is typically an energy recovery makeup air unit somewhere in the building. this unit utilizes a total energy wheel, cooling coils with traditional chilled water temp supplied, and a reheat coil. two things are typical, first you see more air movement that usual for a given size buiding, and second control of airside is critical to get dewpoint low enough so condensation isnt an issue. water for the chilled beams is typically kept in the sixty degree range to perform mostly sensible cooling. the dehumidification is done in the makeup air unit. on jobs we see, it is usually one time through, and out no return air utillized. they claim tremendous energy efficiency versus traditional systems.