The AAF-HermanNelson® self-contained unit ventilators with two-stage compressors are ideal for classroom retrofits because they are an affordable alternative to renovations, fit easily into existing ventilator space, offer the ultimate classroom comfort for students and teachers, and meet energy-efficiency requirements, states the company. In addition to air conditioning with electric heat, units are available in both air-source and water-source heat pump configurations. The new two-stage compressor reduces noise in the classroom and provides a more consistent and comfortable room temperature by allowing units to operate efficiently at reduced fan speeds a majority of the time. As a result, the units use less energy, lowering utility costs, and require fewer repairs with a longer part life. The unit ventilator uses non-ozone-depleting R-410A refrigerant.