ANAHEIM, Calif. - Engineers can calmly agree that although residential heating-cooling equipment is reaching higher efficiencies than ever, there is still room for improvement. There is also little dissent regarding the major gains that can be achieved by fixing leaky ductwork. Start talking about motor efficiencies, however, and the gloves start to come off.

Speakers at an ASHRAE symposium, "Factors Influencing the Energy Performance of Forced-Air Systems," looked at the various benefits of permanent-split capacitor (PSC) AC motors vs. brushless DC (BDC) motors in furnaces, and how they can affect the efficiency of the cooling cycle.

The speakers agreed that in variable-speed systems on low speed, some PSC motors "do make DCPM [DC permanent magnet] motors look good."