Second article in this series. Describes a second type of system that supplies 100% outdoor air, and is projected to save significant energy over standard HVAC. Notes that nearly all schools and large buildings in the US and many other nations operate on the principle that, to control energy costs, building ventilation systems must recycle a majority of indoor air that is already heated or cooled. In the name of energy conservation, many building owners and managers set their ventilation systems to bring in too little outdoor air.