One of the largest HVAC loads in commercial buildings results from the combining of ventilation air with that of heating and cooling air. With the arrival in the North American market of a line of very high-efficiency commercial HRVs and ERVs, it is now possible to radically reduce commercial HVAC system energy use and GHG emissions (including reducing natural gas use for space heating to zero) while significantly improving indoor air quality. If the right systems are chosen, it is also possible to provide the most sophisticated and reliable controls available today for the smallest commercial building spaces as part of the system conversion process. This is possible because these 21st century controls cost about one-tenth as much per square foot as typical direct digital control (DDC) systems while far outperforming them.