One relatively new solution to this problem is to use existing roof exhaust fans that remove ventilation and/or process air from the building. Since this air (and any pollutants) cannot be brought back into the building, valuable heating (or cooling) energy is also being exhausted into the atmosphere.
Mixed-flow impeller roof exhaust systems have begun to offer an alternative to losing this energy via exhaust. Through the use of unique heat recovery modules, this warm (or cool) air is removed prior to its discharge into the atmosphere, and transferred back into the building's intake ventilation system. As an example of its efficacy, consider that for each 1?F of heat added to makeup air, energy costs are reduced about 3% with this method; and it is not unusual to see heating energy cost reductions of 30% or more. Similar savings - although not quite as dramatic - may also be realized for cooling.