Comparing Residential Furnace Blowers for Rating and Installed Performance

The objective of this study was to assess the performance of residential furnace blowers for both heating, cooling and air distribution applications and to compare their performance at DOE/ARI rating conditions (for AFUE and SEER) and at real installed conditions. A testing program was undertaken at two laboratories to compare the performance of furnace blowers over a range of static pressure differences that included standard rating points and measured field test pressures. Three different combinations of blowers and residential furnaces were tested. The laboratory test results for blower power and airflow were combined with DOE2 models of building loads, models of air conditioner performance, standby power, as well as igniter and combustion air blower power to determine potential energy and peak demand impacts. The results show distinct differences between the two types of furnace blower motor technology: Permanent Split Capacitor (PSC) and more efficient Brushless Permanent Magnet (BPM). The high static pressure differences in real installations reduce the advantage that BPMs have at DOE/ARI rating conditions such that for cooling the two motor technologies have essentially the same power consumption although the reduction in airflow for the PSC results in 10% lower air conditioner efficiency. For heating, the advantage of the BPM is approximately halved when changing from standard test conditions to installed conditions, although the BPM has the advantage of maintaining airflow that avoids the safety implications of the PSC's lower airflow. The BPM retains its advantage for multi-speed systems that can operate for significant numbers of hours in low-fire mode. To better reflect blower performance it is recommended that appliance rating test procedures be amended to use realistic system static pressures of between 0.5 and 0.8 in. water (125 and 200 Pa) and that utility rebate programs ensure that rebates are provided for multi-speed systems and/or systems that have a field measured low static pressure difference below 0.5 in. water (125 Pa).