Improving the motor and fan systems in residential furnaces and heat pumps promises substantial, cost-effective efficiency gains. In the annual fuel utilization efficiency (AFUE) test heating cycle, the difference between an advanced fan/motor system in a well-designed unit and an ordinary one in a typical system is 500–700 kilowatt-hours per year (kWh/yr), more than the 490 kWh/yr electricity use of a typical 2001-compliant refrigerator.
An estimated 90% of residential furnaces and heat pumps sold use multi-speed, permanent split capacitor (PSC) air handler fan motors. Better units use advanced electronically commutated permanent magnet motors (ECPMs), otherwise called DC permanent magnet motors. With this type of motor installed, furnace fans are about 15–30% more efficient at high speeds used in cooling, and at least twice as efficient at lower speeds used in heating than PSC motors. In 2000, 5.7 million furnaces and heat pumps were shipped. If all had air handlers as efficient as ECPM motors, this would yield annual cohort savings of about 3.6 billion kWh/yr in heating mode and 1,800 MW of avoided demand in the cooling season, with customer paybacks of 2 or 3 years at projected technology costs. Changing over the entire equipment stock as existing equipment needs replacement would yield annual savings about 15 times these figures.
In order to grasp the potential energy savings that ECPMs might offer, a comparison of the savings associated with higher gas furnace efficiency is useful. For a typical house, the savings from ECPMs are equivalent to almost 10% of source or site energy, or 3% of the natural gas consumed. Since an incremental change of one unit AFUE (say, from 80% to 81%) only saves about 1% of the site energy used, the advanced fan motors are comparable to any likely change in standards short of a national standard for condensing furnaces. In the heating season, gas furnaces with ECPMs consume slightly higher amounts of gas to compensate for the reduced dissipation of electrical energy. However, overall, a national standard requiring high-efficiency furnace fan motors in new furnaces would result in considerable savings of electricity annually.
To achieve these savings through incentives or standards, either a prescriptive or a performance approach can be used. We recommend a performance criterion in the range of 0.2 watt per cubic feet per minute (cfm) at stipulated static pressure, which would encourage multiple paths to reduce parasitic energy consumption by air handlers.