A fluid delivery device for an electrochemical conversion assembly. In one embodiment, the electrochemical conversion assembly is a fuel cell system. The device includes one or more fluid-manipulating components combined into a housing to minimize weight, size and complexity. In one form, the device may include a compressor, heat exchanger and a water vapor transfer unit, at least the latter two of which are located within a chamber defined by the housing. A controller can be used to monitor and selectively vary the extent to which at least one of these components modifies properties a fluid (such as air) that can be used as a reactant in the electrochemical conversion assembly. In a particular form, the heat exchanger and water vapor transfer unit can cooperate to promote the hydration of the reactant.