In commercial, government and education buildings today, it is standard practice to replace the entire volume of indoor air with outside air every one to two hours to minimize concentrations of unhealthy indoor pollutants. While the process helps dilute these contaminants, the high volume of outdoor air must be heated or cooled to maintain comfortable temperatures and humidity. This represents 30 to 50 percent of the total load on HVAC systems in most climates, resulting in higher equipment costs, and higher ongoing energy costs. Further, “fresh air” is no longer fresh, especially for buildings located near highly-trafficked roads or in busy urban centers. Ventilating these buildings can introduce additional harmful contaminants that are known to cause serious diseases when people are exposed all day long.