A Varible air volume system usually consists of a constant blower operation and thermostats controll the vav dampers to open or close depending on temp set point.Some are constant cooling year round and have a means of providing heat at the individual vav boxes so the occupants have a choice of heating or cooling. Or it switch over from constant cooling in summer through chiller to constant heating in winter through a boiler. Also the boxes(vav) are either manufactured as a power open or power closed design and must match what type your controll system utilizes.The vav's can either be powered by electricity or by air(pneumatic)and can be 1 or 2 pipe systems.They either controll an area or can serve individual rooms with own t-stat.So basically you have large volumes of air moving all the time usually in a big loop and the vav boxes feed off this duct to individual vav's to the areas served.So all it has to do is open to condition the space then close when t-stat satisfies. This is a simple overview and im shure I didnt cover everything, but maybe it will give you a start on what you hope to find.