Reducing Energy Usage for Residential Furnace Blowers: Blade Re-Design and Assessment of the Impact of Flow Non-Uniformity Elimination
Residential furnace blowers are widely used in North America, but they often are designed to be low-cost rather than highly efficient. In this study, analysis of the literature yields an estimated adiabatic efficiency for typical furnace blowers of approximately 48%. The geometry of a typical furnace suggests much of the cause of this low efficiency is due to poor flow uniformity entering the blower. While the specific diameter and specific speed of the blower lie far from the Cordier diagram locus, these parameters cannot be dramatically changed due to space constraints. Thus, this study aims to quantify the efficiency gain associated with improving flow uniformity and reducing inlet losses for a typical furnace blower using computational fluid dynamics (CFD) methods. The approach taken is to examine different rotor blade angles to find a suitable configuration in which the highest efficiency occurs. The efficiency is calculated using the pressure difference across the blower unit and comparing it to the potential pressure rise that could be generated by the total enthalpy difference across the rotor. This yields a more accurate estimate of blower efficiency under the assumption the blading is well-designed, and thus the difference between the efficiency obtained and that estimated from the literature can be attributed to the impact of inflow losses and non-uniformity. We compute the flow field using a 2D CFD simulation of the rotor blades in MISES. The results of the simulations show that the most efficient blade angle that could generate the required pressure rise at the target flow rate is 69.6° and the rotational speed at this configuration is 1011 RPM. It is found that reducing the power coefficient by increasing the flow coefficient, which would guarantee lower power consumption when inlet losses are reduced, only occurs at very low rotational speeds which result in inefficient configurations. In conclusion, opting for the most efficient configuration and eliminating inlet pressure losses leads to a reduction in system operation time that outweighs the impact of the power coefficient increase in terms of overall energy consumption.